i 

## Responses to Significant Comments on the 2012 Proposed Rule on the National Ambient Air Quality Standards

for Particulate Matter (June 29, 2012 ; 77 FR 38890)

Docket Number EPA-HQ-OAR-2007-0492

U.S. Environmental Protection Agency

December 2012This page left intentionally blank.ii Table of Contents

I. INTRODUCTION

.............................................................................................................................. .............. I-1

II. RESPONSES TO SIGNIFICANT COMM ENTS ON PROPOS ED PRIMARY PM 2.5 STANDARDS ... II-1

A. G ENERAL C OMMENTS ON P ROPOSED P RIMARY PM 2.5 S TANDARDS

............................................................ II

‐ 1

B. S PECIFIC C OMMENTS ON P ROPOSED P RIMARY PM 2.5 S TANDARDS

.............................................................. II

‐ 1

1. Need to Revise Current Standards ............................................................................................................. II-1

2. Indicator

.............................................................................................................................. .................... II-44

3. Averaging Time

.............................................................................................................................. .......... II-46

4. Form

.............................................................................................................................. .......................... II-47

5. Level

.............................................................................................................................. .......................... II-52

C. S PECIFIC C OMMENTS ON THE Q UANTITATIVE H EALTH R ISK A SSESSMENT

............................................... II

‐ 90

D. S PECIFIC C OMMENTS R ELATED TO D ATA H ANDLING (A PPENDIX N)

........................................................ II

‐ 99

1. Identifying PM 2.5 data “appropriate” for NAAQS comparisons ............................................................. II-99

2. Procedures for combining data for design value computations ............................................................ II-100

3. A DDITIONAL PM 2.5 DATA SUBSTITUTION TESTS

...................................................................................... II

‐ 101

4. S EASONAL SAMPLING SPECIAL 98 TH PERCENTILE CONCENTRATION IDENTIFICATION PROCEDURE

........... II

‐ 103

E. S PECIFIC C OMMENTS R ELATED TO THE AQI FOR PM 2.5

.......................................................................... II

‐ 104

III. RESPONSES TO SIGNIFICANT COMMENTS ON PRIMARY PM 10 STANDARD ....................... III-1

F. C OMMENTS FROM G ROUPS S UPPORTING R ETENTION OF THE P RIMARY PM 10 S TANDARD

......................... III

‐ 1

G. C OMMENTS FROM G ROUPS S UPPORTING R EVISION OF THE P RIMARY PM 10 S TANDARD

............................ III

‐ 4

IV. RESPONSES TO SIGNIFICANT COMMENTS ON SECONDARY PM STANDARDS ................. IV-1

A. G ENERAL C OMMENTS ON P ROPOSED S ECONDARY PM S TANDARDS

......................................................... IV

‐ 1

B. S PECIFIC C OMMENTS ON P ROPOSED S ECONDARY PM S TANDARD TO P ROTECT V ISIBILITY

...................... IV

‐ 1

1. Indicator

.............................................................................................................................. ..................... IV-2

2. Averaging Time

.............................................................................................................................. ......... IV-12

3. Form

.............................................................................................................................. ......................... IV-18

4. Level

.............................................................................................................................. ......................... IV-19

5. Specific Comments on Visibility Preference Studies ............................................................................... IV-28

6. Need for a Distinct Secondary Standard ................................................................................................ IV-43

7. Specific Comments on Surrogacy Analysis ............................................................................................. IV-47

8. Legal Issues

.............................................................................................................................. .............. IV-49

9. Other Issues

.............................................................................................................................. .............. IV-56

C. S PECIFIC C OMMENTS ON P ROPOSED S ECONDARY PM S TANDARDS FOR N ON -V ISIBILITY W ELFARE E FFECTS

IV

‐ 59

V. RESPONSES TO SIGNIFICANT COMMENTS ON AMENDMENTS TO AMBIENT MONITORING AND REPORTING REQUIREMENTS ............................................................................................................... V-1

A. C OMMENTS ON G ENERAL I SSUES FOR R EFERENCE

, E QUIVALENT

, OR A PPROVED R EGIONAL M ETHODS

.... V

‐ 1

B. C OMMENTS ON USE OF CSN AND IMPROVE METHODS TO PROVIDE SPECIATION DATA USED IN THE

PROPOSED NEW SECONDARY PM 2.5 VISIBILITY INDEX NAAQS.

.................................................................. V

‐ 3

C. C OMMENTS ON THE T ERMINOLOGY C HANGES

............................................................................................ V

‐ 5

D. C OMMENTS ON R EVOKING U SE OF P OPULATION -O RIENTED AS A C ONDITION FOR C OMPARABILITY OF PM 2.5 M ONITORING S ITES TO THE NAAQS

.......................................................................................................... V

‐ 5

E. C OMMENTS ON A PPLICABILITY OF M ICRO

- AND M IDDLE S CALE M ONITORING S ITES TO THE A NNUAL PM 2.5 NAAQS

............................................................................................................................... ..................... V

‐ 11

F. C OMMENTS ON THE ADDITION OF PM 2.5 MONITORS TO THE NEAR

- ROAD MONITORING STATIONS

. ............ V

‐ 16

G. C OMMENTS ON R EVOKING PM 10-2.5 S PECIATION R EQUIREMENTS AT NC ORE S ITES

.................................. V

‐ 47

H. C OMMENTS ON THE NETWORK DESIGN FOR THE PROPOSED SECONDARY PM 2.5 VISIBILITY INDEX

. ............ V

‐ 47

I. C OMMENTS ON THE USE OF PM 2.5 C ONTINUOUS FEM S AT SLAMS

.......................................................... V

‐ 50

J. C OMMENTS ON W EIGHT OF E VIDENCE A PPROACH IN THE R EVISIONS TO THE Q UALITY A SSURANCE

R EQUIREMENTS FOR SLAMS, SPM S

, AND PSD.

...................................................................................... V

‐ 53iii K. C OMMENTS ON Q UALITY A SSURANCE R EQUIREMENTS FOR THE C HEMICAL S PECIATION N ETWORK

. ...... V

‐ 55

L. C OMMENTS ON W AIVER FOR W IDER S PACING OF C OLLOCATED M ONITORS

............................................ V

‐ 55

M. A DDITIONAL QA R ELATED C OMMENTS NOT S PECIFICALLY R ELATED TO P ROPOSED C HANGES TO A PPENDIX
A

............................................................................................................................... ................................ V

‐ 55

N. C OMMENTS ON P ROBE AND M ONITORING P ATH S ITING C RITERIA

........................................................... V

‐ 56

O. C OMMENTS ON THE A NNUAL M ONITORING N ETWORK P LAN AND P ERIODIC A SSESSMENT

...................... V

‐ 58

P. C OMMENTS ON O PERATING S CHEDULES

................................................................................................... V

‐ 59 Q. C OMMENTS ON D ATA R EPORTING AND C ERTIFICATION FOR CSN AND IMPROVE DATA

........................ V

‐ 60

R. C OMMENTS ON THE R EQUIREMENTS FOR A RCHIVING F ILTERS

................................................................. V

‐ 62

S. F UNDING AND R ESOURCES I SSUES ASSOCIATED WITH A MBIENT A IR M ONITORING R EQUIREMENTS

........ V

‐ 62

VI. RESPONSES TO SIGNIFICANT CO MMENTS ON IM PLEMENTATION ..................................... VI-1

A. S PECIFIC C OMMENTS R ELATED TO D ESIGNATION OF A REAS

..................................................................... VI

‐ 1

B. S PECIFIC C OMMENTS R ELATED TO S ECTION 110( A )(2) I NFRASTRUCTURE SIP R EQUIREMENTS

................ VI

‐ 6

C. S PECIFIC C OMMENTS R ELATED TO I MPLEMENTING THE P ROPOSED R EVISED P RIMARY A NNUAL PM 2.5 NAAQS IN N ONATTAINMENT A REAS

........................................................................................................ VI

‐ 9

D. S PECIFIC C OMMENTS ON P REVENTION OF S IGNIFICANT D ETERIORATION AND N ONATTAINMENT N EW
S OURCE R EVIEW

............................................................................................................................... ....... VI

‐ 11

E. N ONATTAINMENT N EW S OURCE R EVIEW

................................................................................................ VI

‐ 25

F. O THER NSR I MPLEMENTATION C OMMENTS

............................................................................................ VI

‐ 25

G. S PECIFIC C OMMENTS R ELATED TO T RANSPORTATION C ONFORMITY

...................................................... VI

‐ 27

H. S PECIFIC C OMMENTS R ELATED TO E XCEPTIONAL E VENTS

...................................................................... VI

‐ 29

VII. RESPONSES TO SIGNIFICANT COMMENTS ON LEGAL, ADMI NISTRATIVE, PROCEDURAL,

OR MISPLACED COMMENTS ....................................................................................................................... VII-1

A. L EGAL I SSUES

............................................................................................................................... ............ VII

‐ 1

B. A DMINISTRATIVE /P ROCEDURAL I SSUES

................................................................................................... VII

‐ 4

C. M ISPLACED C OMMENTS

........................................................................................................................... VII

‐ 6

REFERENCES

APPENDIX A: Provisional Science Assessmentiv List of Acronyms

The following acronyms have been used for th e sake of brevity in this document:

AAM Alliance of Automobile Manufacturers

AAMMS Ambient Air Monitori ng and Methods Subcommittee

AASHTO American Association of Stat e Highway and Trans portation Officials ACC American Chemistry Council ACS American Cancer Society

AFBF American Farm Bureau Federation

AFPM American Fuel & Petroleum Manufacturers

AHA American Heart Association ALA American Lung Association AMC Appalachian Mountain Club APHEA Air Pollution and Health: A European Approach

APHENA Air Pollution and Health: A Eu ropean and North American Approach

API American Petroleum Institute AQCD Air Quality Criteria Document AQI Air Quality Index AQMD Air Quality Management District AQS Air Quality System ARMs Approved Regional Methods ARS Air Resource Specialists ATS American Thoracic Society

BC British Columbia

CAA Clean Air Act CAPs Concentrated ambient particles CASAC Clean Air Scientific Advisory Committee

CBD Center for Biological Diversity

CBSA Core Based Statistical Area

CDC Centers for Disease Control CF Cystic fibrosis CFR Code of Federal Regulations CHPAC Children’s Health Protection Advisory Committee

CI Confidence intervals

CPC Coarse Particulate Matter Coalition

CPL Candidate Protection Level C-R Concentration-response

CRA Charles River Associates

CSA Combined Statistical Area CSN Chemical Speciation Network

CVD Cardiovascular disease

DC District of Columbia DEC Department of Environmental Conservation DEQ Department of Environmental Quality DOH Department of Healthv DOI U.S. Department of the Interior DPHE Department of Public Health and Environment df Degrees of freedom

dv Deciview DV Design value

EC Elemental carbon ED Emergency department EPA U.S. Environmental Protection Agency

EPRI Electric Power Research Institute FEM Federal Equivalent Method

FEV 1 Forced expiratory volume in one second, volume of air exhaled in first

second of exhalation FR Federal Register

FRM Federal Reference Method GMA Georgia Mining Association IARC International Agency Research on Cancer IMPROVE Interagency Monitoring of Protected Visual Environment

IHD Ischemic heart disease ISA Integrated Science Assessment ISEE International Society fo r Environmental Epidemiology IUGR Intrauterine growth retardation

Km Kilometer

LML Lowest measured level μg Microgram μm micrometer, micron μg/m 3 microgram per cubic meter MCAPS Medicare Air Pollution Study

Mm -1 Inverse megameters, 1/(million meters) MSA Metropolitan Statistical Area NAAQS National ambient air quality standards NACAA National Association of Clean Air Agencies

NAM National Associ ation of Manufacturers

NCBA National Cattle men’s Beef Association NCore National Core Monitoring Network

NEDA/CAP National Environmental Devel opment Association/Clean Air Project

NESCAUM Northeast States C oordinated Air Use Management NMA National Mining Association NMMAPS National Morbidity, Mo rtality, and Air Pollution Study

NO 2 Nitrogen dioxide

NPCA National Parks Conservation Association NSSGA National Stone, Sand, & Gravel Association

NTAA National Tribal Air Association

O 3 Ozone OC Organic carbon OM Organic mass PA Policy Assessmentvi PACF Partial autocorrelation function

PM Particulate matter

PM 2.5 In general terms, particulate matter with an aerodynamic diameter less than or equal to a nominal 2.5 μm; a measurement of fine particles

PM 10 In general terms, particulate matter with an aerodynamic diameter less than or equal to a nominal 10 μm; a measurement of thoracic particles (i.e., that subset of inhalable part icles thought small enough to penetrate beyond the larynx into the thoracic region of the respiratory system

PM 10-2.5 In general terms, particulate matter with an aerodynamic diameter less than or equal to a nominal 10 μm and greater than a nominal 2.5 μm; a measurement of thoracic coarse part icles or the coarse fraction of PM 10 PRB Policy-relevant background PSR Physicians for Social Responsibility QA Quality assurance

RA Risk Assessment REA Risk and Exposure Assessment RH Relative humidity

RR Relative risk RTC Responses to Comments SANDWICH Sulfate, Adjusted Nitrate, De rived Water, Inferred Carbonaceous mass approacH

SD Standard deviation

SES Socioeconomic status

SHS Secondhand smoke SIP State Implementation Plan SLAMS State and local air monitoring stations

SO 2 Sulfur dioxide TCEQ Texas Commission on Environmental Quality TSP Total suspended particulate UARG Utility Air Regulatory Group UFPs Ultrafine particles UFVA Urban Focused Visibility Assessment VAQ Visual air quality

WESTAR Western States Air Resources Council

WHI Women’s Health Initiative WHO World Health Organizationvii Frequently Cited Documents

The following documents are frequently cited throughout the EPA’s response to comments

Integrated Science Assessment (ISA)

Integrated Science Assessment for Particulat e Matter: Final Report. National Center for Environmental Assessment-RTP Division, Office of Research and Development, Research Triangle Park, NC. EPA/ 600/R-08/139F. December 2009. Available: http://www.epa.gov/ttn/naaqs/standards/pm/s_pm_2007_isa.html

.

Risk Assessment (RA)

Quantitative Health Risk Assessment for Particulate Matter – Final Report. Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, NC. EPA-452/R- 10-005. June 2010. Available: http://www.epa.gov/ttn/naaqs/standards/pm/s_pm_2007_risk.html

.

Urban-Focused Visibility Assessment (UFVA)

Particulate Matter Urban-Focu sed Visibility Assessment – Final Report. Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, NC. EPA-452/R-10- 004. July 2010. Available: http://www.epa.gov/ttn/naaqs/standards/pm/s_pm_2007_risk.html

.

Policy Assessment (PA)

Policy Assessment for the Review of the Part iculate Matter National Ambient Air Quality Standards. Office of Air Qual ity Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, NC . EPA 452/R-11-003. April 2011. Available: http://www.epa.gov/ttn/naaqs/standards/pm/s_pm_2007_pa.html

.

Proposal

National Ambient Air Quality Standards for Particulate Matter: Proposed Rule. 77 FR 38890, June 29, 2012

Preamble to the final rule

Preamble to the Final Rule on the Review of the National Ambient Air Quality Standards for Particulate Matter; signed December 14, 2012I-1 I. INTRODUCTION

This document, together with the preamble to the final rule on the review of the national ambient air quality standards (NAAQS) for pa rticulate matter (PM), presents th e responses of the Environmental Protection Agency (EPA) to the more than 230,000 public comments received on the 2012 PM NAAQS proposal notice (77 FR 38890, June 29, 2012). The EPA has addressed all significant issues raised in the public comments.

Due to the large number of comments that addres sed similar issues, as we ll as the volume of the comments received, this response-to-comments docum ent does not generally cross-reference each response to the commenter(s) who raised the pa rticular issue involved, although commenters are identified in some cases where they provided partic ularly detailed comments that were used by the EPA to frame the overall response on an issue.

The responses presented in this document are intended to augment the responses to comments that appear in the preamble to the final rule or to address comments not disc ussed in that preamble. Although portions of the preamble to th e final rule are paraphrased in th is document where useful to add clarity to responses, the pr eamble itself remains the definitive statement of the rationale for the revisions to the standards adopted in the final rule.

In many instances, particular responses presented in this document include cross references to responses on related issues that are located either in the preamble to the PM NAAQS final rule, or in this Response to Comments (RTC) document. All issues on which the Administrator is taking final action in the PM NAAQS final rule are addressed in the PM NAAQS rulemaking record.

Accordingly, this RTC document, together with the preamble to the PM NAAQS final rule and

the information contained in the Integrated Science Assessment (IS A, U.S. EPA, 2009a), Risk and Exposure Assessments (REAs, U.S. EPA, 2010a; U. S. EPA, 2010b) and the Policy Assessment (PA, U.S. EPA, 2011a), should be considered collectivel y as the EPA’s response to all of the significant comments submitted on the EPA’s 2012 PM NAAQS proposed rule. This document incorporates directly or by reference the si gnificant public comments addressed in the preamble to the PM NAAQS final rule as well as other significant public comments that were submitted on the proposed rule.

Consistent with the final decisions presented in the notice of final rulemaking, comments on the primary standards for fine particles and for thoracic coarse particles are addressed separately in this document in sections II and III, respectively. Comme nts on secondary standards for fine and coarse particles are addressed below in section IV. Comments on related monitoring and implementation issues are addressed below in sections V and VI, respec tively. Section VII includes responses to legal, administrative, procedural, or misplaced comments.

In the PM NAAQS proposal, the EPA recognized th at there were a numbe r of new scientific

studies on the health effects of PM that had been published recently and, therefore, were not included in the ISA (77 FR at 383899, June 29, 2012). The EPA co mmitted to conduct a review and assessment of any significant “new” studies, including studies submitted during the public comment period. The purpose of this review was to ensure that the Admi nistrator was fully aware of the new science before making a final decision on whether to revise the cu rrent PM NAAQS. The EPA screened and surveyed the recent literature, including studies submitted during the public comment period, and conducted a provisional assessment that places the results of those st udies of potentially great est policy relevance in the context of the findings of the ISA. This provisional assessment, entitled Provisional Assessment of Recent Studies on Health Effects of Particulate Matter Exposure (US EPA, 2012a), is included asI-2 Appendix A of this document. This RTC document is part of the basis for the EPA’s responses to specific public comments on the “new” science.II-1 II. RESPONSES TO SIGNIFICANT COMMENTS ON PROPOSED PRIMARY PM 2.5 STANDARDS

A. General Comments on Proposed Primary PM 2.5 Standards

A large number of comments on the proposed primary standards for PM 2.5 were very general in nature, basically expressing one of two substantively different views: (1) support for revisions to the primary standards to be more public health-protective or (2) opposition to any

revision of the current PM 2.5 standards. Many of these comment ers simply expressed their views without stating any rationale, while others ga ve general reasons for their views but without

reference to the factual evidence or rationale presented in the pr oposal notice as a basis for the Agency’s proposed decision. The preamble to the fina l rule in its entirety presents the Agency’s response to these very general views.

Specific public comments on a range of i ssues related to the proposed primary PM 2.5 standards are addressed in the preamble to the fina l rule and/or in this document. In particular, significant public comments related to whether or not the current PM 2.5 standards should be

revised are addressed in secti on III.D.2 of the preamble. Sec tions III.E.1, III.E.2, III.E.3, and III.E.4.c of the preamble discuss significant comme nts addressing the four basic elements of the standard: indicator, averaging time, form, and le vel, respectively. Significant comments on the revised Air Quality Index (AQI) for PM 2.5 are discussed in section V of the preamble. Significant comments on the data handling conventions for PM 2.5 are discussed in section VII.A of the preamble. Below, the EPA provides more specific re sponses to the full range of significant issues raised in the public comments on these issues.

B. Specific Comments on Proposed Primary PM 2.5 Standards

A large number of commenters provided more detailed comments regarding the proposal to revise the level and form of the primary annual PM 2.5 standard in conjunction with retaining the current 24-hour standard. Below, the EPA provi des more detailed responses to the full range of significant issues rais ed in these comments.

1. Need to Revise Current Standards

This section responds to more detailed comments that either support or oppose any

revision to the current PM 2.5 primary standards. The responses to these comments are generally

discussed in section III.D.2 of the preamble to the final rule and discussed more fully below. Significant comments on specific long- and short-term exposur e studies that relate to

consideration of the a ppropriate level of the annual and 24-hour PM 2.5 standards are addressed in

sections III.E.4.c.i and III.E.4.c .ii in the preamble to the final rule and discussed more fully below in sections II.B.5.a and II.B.5.b, respec tively. Incorporating responses contained in sections III.E.4.c of the preamble to the final rule, the EPA provides the following responses to specific issues related to the need to revise the fine particle standards

.

a. Support for Revising the Current Standards

Many public commenters assert ed that the current PM 2.5 standards are insufficient toII-2 protect public health with an adequate margin of safety and that revisions to the standards are therefore appropriate wi thin the meaning of section 109 (d) of the Act, indeed necessitated. Among those calling for revisions to the current st andards were the Children’s Health Protection Advisory Committee (CHPAC); major medical a nd public health groups including the American Heart Association (AHA), American Lung Asso ciation (ALA), American Public Health Association (APHA), American Thoracic Soci ety (ATS); the Physicians for Social Responsibility (PSR); the International Societ y for Environmental Epidemiology (ISEE); major environmental groups such as the Clean Air C ouncil, Clean Air Task Force, Earthjustice, Environmental Defense Fund (EDF), National Re sources Defense Council (NRDC), and Sierra Club; many environmental justice organizati ons as well as medical doctors, academic researchers, health professionals, and many private citizens.

All of these medical and public health commenters stated that the current PM 2.5 standards need to be revised, and that even more protect ive standards than those proposed by the EPA are needed to adequately protect public health, particularly for at-risk populations. Many environmental justice organizati ons and individual commenters also expressed such views.

The National Association of Clean Air Agen cies (NACAA), the Northeast States for Coordinated Air Use Management (NESCAUM), and many state and local air agencies and health departments who commented on the PM 2.5 standards supported revi sion of the suite of

current PM 2.5 standards, as did five state attorneys general (Schneiderman et al., 2012) and the National Tribal Air Association (NTAA).

(1) Comment: In general, all of these commenters ag reed on the importance of results from the large body of scientific studies and techni cal analyses presented and discussed in the Integrated Science Assessment (ISA), the Risk Assessment (RA), and the Policy Assessment (PA) and on the need to revise the PM 2.5 standards as articulated in section III.D of the preamble to the proposal. Many of these commenters, however, generally expressed views differing from the EPA’s propos ed judgments about the extent to which

the standards should be revised based on th is evidence, specifically for providing protection for at-risk populations. These comm enters generally conc luded that the body of evidence assessed in the ISA was stronge r and more compelling than in the last review. In addition, these commenters gene rally placed much weight on the Clean Air Scientific Advisory Comm ittee’s (CASAC) interpretati on of the body of available

evidence and CASAC’s recommendation to revise the PM 2.5 standards to provide increased public health protec tion. In arguing for more health protective standards, these commenters expressed the following specific views:

 Multiple, multi-city studies show clear evidence of premature mortality, cardiovascular and respiratory harm, as well as reproductive and developmental

effects at ambient concentra tions “far below the level of the current standard” (ALA, et al., 2012, p. 39). Specific studies cited by commenters included:

o Extended analyses of seminal long-te rm exposure studies - the American Cancer Society (ACS) (Krewski et al., 2009a), Harvard Six Cities (Laden et al., 2006), and Southern California Child ren’s Health (Gauderman et al., 2004) studies.II-3 o Additional long-term exposure studies avai lable in this review, specifically a study of premature mortalit y in older adults (Eft im et al., 2008) and the

Women’s Health Initiati ve (WHI) study of cardiovascular morbidity and mortality effects in women (Miller et al., 2007) providing stronger evidence of mortality and morbidity effects associated with long-term PM 2.5 exposures at lower concentrations than had previously been observed, including studies of effects in at-risk populations.

o A number of short-term PM 2.5 exposure studies providing evidence of mortality and morbidity effects at co ncentrations below the level of the

current 24-hour PM 2.5 standard. Specifically, these commenters made note of multi-city studies of premature mortal ity (Zanobetti and Schwartz, 2009) and increased hospitalizations for cardiovascular and respiratory-related effects in older adults (Bell et al., 2008).

 Single-city short-term PM 2.5 studies “provide valuable information regarding impacts on susceptible populations and on health ri sk in areas with high peak to mean concentration ratios” (ALA, et al., 2012, p. 65).

 Progress has been made in reducing many of the uncertainties identified in the last review, in better understanding mechanisms by which PM 2.5 may be causing the observed health effects, and in improving our understanding of at-risk populations.

 The EPA’s quantitative risk assessment concl uded that the risks estimated to remain

when the current standards are met are la rge and important from a public health perspective and warrant increased protection.

 PM 2.5 -related risks are likely larger than thos e estimated in the RA, in part because the EPA focused on limited study areas and he alth endpoints. Some commenters cited to a recent study based on 2005 air quality da ta. In this study, the EPA staff published estimates that “peg the annual toll from PM 2.5 at 130,000 premature deaths each year” 1 (ALA et al., p. 5). Furthermore, “thi s analysis estimated a staggering 1.1 million life years lost among people over ag e 65, accounting for 7 percent of life years lost in 2005 in this popul ation of elderly Americans. Looking at it another way, this translates into an average shorte ned lifespan of 8.5 months per individual affected. Further, the analysis estimat ed 1,800 deaths among babies and infants attributable to PM air pollution.” Id.

 The EPA’s distributional statistic al analysis of population-le vel data (i.e., health event data and study population data) provide d important information beyond a single statistical metric (e.g., mean) to consider in reaching decisions on the appropriate

annual standard level.

Response: The EPA generally agrees with these commenters’ conclusion regarding the

need to revise the current suite of PM 2.5 standards. The scientific evidence noted by these

1 Fann et al., 2012II-4 commenters was generally the same as that a ssessed in the ISA and the PA, and the EPA agrees that this evidence provides a str ong basis for concluding that the current PM 2.5 standards, taken together, are not requisite to protect public health with an adequate margin of safety, and they need to be revi sed to provide increased protection. For reasons

discussed in section III.E.4.c of the preamble to the final rule and in section II.B.5 below, however, the EPA disagrees with aspects of these commenters’ views on the level of protection that is appropriate.

In addition, with regard to progress made to better understand mechanisms by which

PM 2.5 may be causing the observed health effects and to impr ove our understanding of atrisk populations, the EPA notes that CASAC found that the ISA clearly presented and

discussed the current scientific information re lated to potential mode s of action (Chapter 5) and at-risk populations (Chapter 8) (S amet, 2009e, pp. 7 to 8; Samet, 2009f, pp. 2 and 11 to 12).

(2) Comment: With regard to the scope of the literature reviewed for PM 2.5 -related health effects, some commenters asserted that th e EPA inappropriately narrowed the scope of the review by excluding a number of categories of relevant studies, spec ifically related to studies of diesel pollution and traffic-rela ted pollution (ALA, et al., 2012, p. 17). These commenters argued that, based upon the exclusion of these types of studies, the ISA

“came to the erroneous conclusion that the cau sal relationship between PM and cancer is merely suggestive. This conclusion does not square with the In ternational Agency Research on Cancer (IARC) finding that diesel emissions are a known human carcinogen

nor with the conclusions of the extended an alyses of the [Harvard] Six Cities and ACS cohort studies that report positive and stat istically significant a ssociations between PM 2.5 and lung cancer.” Id.

Response: The EPA disagrees with these commente rs’ views that dies el exhaust studies

were excluded from the ISA and were not considered when making the causality determination for cancer, mutagenicity, and ge notoxicity. As discusse d in section 7.5 of the ISA, diesel exhaust studies were integr ated within the broa der body of scientific evidence that was considered in reaching th e causality determination for these health endpoints. Additionally, as discussed in secti on 1.5.3 of the ISA, the evidence from diesel exhaust studies was also considered as part of the collective evidence evaluated when making determinations for other, noncancer health outcomes (e.g., cardiovascular and respiratory effects). Specifically, when ev aluating this evidence, the ISA focused on understanding the effects of dies el exhaust particles. It is important to recognize that the

ISA focused on diesel exhaust studies that ev aluated exposures that were relevant to ambient concentrations, i.e., “within one or two orders of magnitude of ambient PM concentrations” (U.S. EPA, 2009a, section 1.3). The causal dete rmination for cancer, mutagenicity, and genotoxicity presented in the ISA represents an integration of experimental and observational evidence of exposures to ambient PM concentrations. The EPA fully considered the findings of st udies that assessed these and other health effects associated with exposure to diesel pa rticles in reaching cau sality determinations regarding health outcom es associated with PM 2.5 exposures.II-5 In developing the second draft ISA, the EP A reexamined the controlled human exposure and toxicological studi es of fresh diesel and gasoline exhaust. This information, in addition to other considerations, supported a change in the causal determinations for ultrafine particles. Specifically, in reevaluating the causal determinations for short-term ultrafine particle exposures and cardiovascul ar and respiratory eff ects, the EPA changed the classification from “inadequate” to “suggestive” for both categories of health outcomes (Vandenberg, 2009, p. 3). CASAC agreed with the EPA’s rationale for revising these causal determinations (Samet, 2009f, pp. 2 and 10).

With regard to traffic studies, the EPA disagrees with the commenters’ views that traffic studies that focused on exposur e indicators such as distan ce to roadways should have

been included in the ISA. These studies were excluded from consideration because they

did not measure ambient concentrations of specific air pollutants, including PM 2.5 , but instead were studies evaluating exposure to the undifferentiated “traffic related air pollution” mixture (ALA et al., 2012, p.17) (U .S. EPA, 2009a, section 1.3). As a result,

these studies do not add to the collective body of evidence on the relationship between long- or short-term exposure to ambient concentrations of PM 2.5 and health effects.

(3) Comment : A number of commenters argued that by making the standards more protective, the PM 2.5 NAAQS would be more consistent with other existing standards (e.g., California's annual aver age standard of 12 μg/m 3 ) (CARB, 2012; CA OEHHA, 2012). Some commenters argued that “in the intervening decade since the California standard was established, substantial new info rmation regarding adverse health effects at lower concentrations supports setting a more protective stan dard (ALA et al, 2012, p. 23). Other commenters argued that revising the primary PM 2.5 standards would be more

consistent with the recommendations of th e World Health Organi zation (WHO) and/or Canada (e.g., ALA et al., 2012, pp. 22 and 62; ISEE, 2012, p. 2; MOE-Ontario, 2012, p. 1).

Response: In considering these comments, the EPA notes that the Administrator’s decision on setting an appropriate annual standard level is cons trained by the provision of the CAA that requires that the primary NAAQS be requisite to protec t public health with an adequate margin of safety. This require s that her judgment is to be based on an interpretation of the evidence that neithe r overstates nor understates the strength and limitations of the evidence, or the appropriate inferences to be drawn from the evidence. This is not the same legal framework that governs the standards set by the State of California or Canada or the gui delines established by a worki ng group of scientists within the WHO. For example, the California statute doe s not refer to setting a standard that is ‘‘requisite’’ to protect, as that term is used in the CAA, and California, unlike EPA, may take economic impacts into consideration in se tting air quality standa rds. In addition, as with the WHO guidelines, the standards appear to be more in the nature of goals as compared to binding requirements that must be met.

As discussed in section III.E.4.d of the preambl e for the final rule, the Administrator has considered the epidemiological and other scient ific evidence, estimates of risk reductions associated with just meeting alternative standa rds, air quality analys es, related limitations and uncertainties, the advice of CASAC, a nd the extensive public comments on theII-6 proposal in reaching her conclusions regardi ng final decision on the appropriate primary

annual PM 2.5 standard level, consistent with the requirements of the CAA.

(4) Comment: Some of these commenters also identified “new” studies that were not included in the ISA as providing further support for the need to revise the PM 2.5 standards.

Response: In the proposal, the EPA recognized that there were a number of new scientific

studies on the health effect s of PM that had been published since the mid-2009 cutoff date for inclusion in the ISA (77 FR 38899) . As discussed in section II.B.3 of the preamble to the final rule, the EPA conducte d a provisional assessmen t of “new” science published since the close of the ISA including studies submitted to the EPA during the public comment period. The purpose of the provis ional science assessment was to ensure that the Administrator was fully aware of the “new” science that has developed since 2009 before making final decisions on whethe r to retain or revi se the current PM NAAQS.

Specifically, the EPA screened and surveyed th e recent health literature, including but not limited to studies submitted during the public comment period, and conducted a provisional assessment (U.S. EPA, 2012b) that places the results of those studies of potentially greatest policy relevance in the c ontext of the findings of the ISA (U.S. EPA, 2009a). This provisional assessment, includ ing a summary of the key conclusions is included in Appendix A to this RTC document.

The provisional assessment found that th e “new” studies expand the scientific information considered in the ISA and provi de important insights on the relationship between PM exposure and health effects. The provisional assessment also found that “new” studies generally strengthen the eviden ce that long- and shor t-term exposures to fine particles are associated with a wide range of health effect s (i.e. the strongest causality determination possible under the EPA framework). Although some of the “new” epidemiological studies report e ffects in areas with lower PM 2.5 concentrations than those in earlier studies considered in the ISA, and “new” toxicological and epidemiological

studies continue to link various health effects with a range of fine particle sources and components, the provisional a ssessment found that th e results reported in “new” studies do not materially change any of the broad sc ientific conclusions regarding the health effects of PM exposure made in the ISA.

As further noted in section II.B.3 of the pr eamble to the final rule, as in prior NAAQS reviews, the EPA is basing its decision in this review on st udies and related information included in the ISA, RA, and PA, which ha ve undergone CASAC and public review. The studies assessed in the ISA, and the integrati on of the scientific evidence presented in that document, have undergone extensive critical review by the EPA, CASAC, and the public during the development of the ISA. The rigor of that review makes these studies, and their integrative assessment, the most reliable source of scientific information on which to base decisions on the NAAQS. NAAQS decisions can have profound impacts on public health and welfare, and NAAQS decisi ons are based on studies that have been rigorously assessed in an integrative ma nner not only by the EPA but also by theII-7 statutorily-mandated independent advisory co mmittee, CASAC, and have been subjected as well to the public review that accompanies this proce ss. As described above, the provisional assessment did not a nd could not provide that kind of in-depth critical review.

This decision is consistent with the EPA’ s practice in prior NAAQS reviews. Since the 1970 amendments, the EPA has taken the view that NAAQS decisions are to be based on

scientific studies and related information that ha ve been assessed as a part of the pertinent air quality criteria. See e.g., 36 FR 8186 (April 30, 1971) (the EPA based original NAAQS for six pollutants on scie ntific studies discussed in air quality criteria documents

and limited consideration of comments to thos e concerning validity of scientific basis); 38 FR 25678, 25679 to 25680 (September 14, 1973) (t he EPA revised air quality criteria for sulfur oxides to provide basis for r eevaluation of secondary NAAQS). This longstanding interpretation was strengthened by new legislative requirements enacted in 1977, which added section 109(d)(2) of the CAA concerning CASAC review of air quality criteria. The EPA has consistent ly followed this approach. 52 FR 24634, 24637 (July 1, 1987) (after review by CASAC, the EPA issued a post-proposal addendum to the PM Air Quality Criteria Document (AQCD), to address certain new scientific studies not included in the 1982 AQCD); 61 FR 25566, 25568 (May 22, 1996) (after review by CASAC, the EPA issued a post-proposal supplement to the 1982 AQCD to address

certain new health studies not included in the 1982AQCD or 1986 Addendum). The EPA reaffirmed this approach in its decision not to revise the ozone NAAQS in 1993, as well as in its final decision on the PM NAAQS in the 1997 and 2006 reviews. 58 FR 13008, 13013 - 13014 (March 9, 1993) (ozone revi ew); 62 FR 38652, 38662 (July 18, 1997) and 71 FR 61141, 61148 -61149 (October 17, 2006) (PM reviews) (The EPA conducted a provisional assessment but based the fina l PM decisions on studies and related information included in the air quality crit eria that had been reviewed by CASAC).

As discussed in the EPA's 1993 decision no t to revise the NAAQS for ozone, “new” studies may sometimes be of such significance th at it is appropriate to delay a decision on revision of NAAQS and to supplement the pe rtinent air quality cr iteria so the “new”

studies can be taken into account (58 FR at 13013 to 13014, Ma rch 9, 1993). In this 2012 review of the PM NAAQS, the provisional asse ssment of recent studies concludes that, taken in context, the “new” information and findings do not materially change any of the

broad scientific conclusions re garding the health e ffects of PM exposure made in the ISA (U.S. EPA, 2012b). For this reas on, reopening the air quality crit eria review would not be

warranted even if there were time to do so under the court order governing the schedule for this rulemaking. Accordingly, the EPA is ba sing the final decisions in this review on

the studies and related inform ation included in the PM air quality criteria that have undergone CASAC and public review. The EPA will consider the “new” published studies for purposes of decision making in the next periodic review of the PM NAAQS, which will provide the opportunity to fully assess them through a more rigorous review process involving the EPA, CASAC, and the public.

(5) Comment: Some commenters encouraged the EPA to consider emerging evidence for a broader range of health outcomes. For ex ample, one commenter urged the EPA “to exercise a high level of vigilance in order to identify and act on additional peer-reviewedII-8 studies that may strengt hen a putative link between PM and diabetes and neurodegenerative diseases” (PSR, 2012, p. 7).

Response: The EPA agrees that additional res earch could expand our understanding of a broader range of health outcomes (e.g., centr al nervous system effects) and potential additional at-risk populations (e.g., diabetics). The PA highlighted a number of areas for future health-related research, model developm ent, and data collection activities that could provide important evidence for inform ing future PM NAAQS reviews (U.S. EPA, 2011a, section 2.5). The EPA will consider all policy-relevant studies published in the peer-review literature, including “new” studies published since the close of the ISA in its next PM NAAQS review.

b. Support for Retaining the Current Standards

Another group of commenters opposed revising the current PM 2.5 standards. These views were most extensively presented in comments from the Utility Air Regulatory Group (UARG), representing a group of electric generating comp anies and organizations and several national trade associations; the American Petroleum Ins titute (API) representing more than 500 oil and natural gas companies; the National Associat ion of Manufacturers (NAM), the American Chemistry Council (ACC), the American Fuel & Petroleum Manufacturers (AFPM), the Alliance of Automobile Manufacturers, and other ma nufacturing associations ; the Electric Power Research Institute (EPRI); and the Texas Comm ission on Environmental Quality (Texas CEQ). These commenters generally mentioned many of the same studies that were cited by the commenters who supported revising the standards, as well as ot her studies, but highlighted different aspects of these studi es in reaching substantially di fferent conclusions about their strength and the extent to which progress has been made in reducing uncertainties in the

evidence since the last review. Fu rthermore, they asserted that the evidence that has become

available since the last review does not establish a more certain risk or a risk of effects that are significantly different in character to those that provided a basis for the current standards, nor

does the evidence demonstrate that the risk to public health upon atta inment of the current standards would be greater than was understood when the EPA esta blished the current standards

in 2006.

These commenters generally expressed the vi ew that the current standards provide the requisite degree of public health protection. In supporting their vi ew, these commenters generally argued that the EPA’s conclusions are inconsiste nt with the current st ate of the science and questioned the underlying scientific evidence incl uding the causal determinations reached in the ISA. More specifically, this gr oup of commenters argued that:

 the EPA did not apply its framework for causal determination consistently across

studies or health outcomes and, in the process, the EPA relied on a selective group of long- and short-term exposure studies to reach conclusions regarding causality

 toxicological and controlled human e xposure studies do not provide supportive

evidence that the health eff ects observed in epidemiologi cal studies are biologically plausible

 uncertainties in the underlying health science are as great or greater than in the PM NAAQS review completed in2006II-9  there is no evidence of greater risk since the last review to justify tightening the

current annual PM 2.5 standard

 “new” studies not included in the ISA continue to increa se uncertainty about possible health risks associated with exposure to PM 2.5

These comments and other similar comments are addressed below.

(1) Comment: Multiple commenters asserted that the EPA did not apply its framework for causal determinations consistently acro ss studies or health outcomes (API, 2012, Attachment 1, p. 30). 2 These commenters further cont ended that the EPA relied on a selective group of long- and short-term PM 2.5 exposure studies when making causality determinations in the ISA (ACC, 2012, Att achment A, pp. 1 to 2; API, 2012, pp. 18 to 20; API, 2012, Attachment 1, p. 30; NAM et al., 2012, pp. 22 to 25; Texas CEQ, 2012, pp 2 to 3; UARG, Attachment 1, p. 17 to 23). These allegations incl uded: “che rry-picking studies” and ignoring a number of studies that reported no association with PM 2.5

.

Response: The EPA disagrees with these commen ters’ assertion that the EPA did not consistently apply the causality framewor k. The EPA’s evaluation of the scientific evidence and its application of the causal framework used in the current PM NAAQS review was the subject of exhaustive a nd detailed review by CASAC and the public. Prior to finalizing the ISA, two drafts were released for CASAC and public review to evaluate the scientific integrity of the documents. Evidence related to the substantive issues raised by CASAC and pub lic commenters with regard to the content of the first

and second draft ISAs were discussed at le ngth during these public CASAC meetings and considered in developing the final ISA. CASAC supported the development of the EPA’s causality framework and its use in the current PM NAAQS review and concluded:

The five-level classification of strength of evidence for causal inference has been systematically applied; this approach has provided transparency and a clear

statement of the level of confidence w ith regard to causation, and we recommend its continued use in future Integrated Science Assessments (Samet 2009f, p. 1).

The EPA disagrees with these commenters ’ views on assessing the health effects evidence and on their conclusions regarding th e causality determinations reached in the ISA. The commenters’ specifically focused on counting the number of epidemiological studies that reported results with statistical significance without regard to other considerations that are important in a comprehensive evaluation of the evidence. Specifically, the EPA recognizes the di stinction between evaluation of the relative scientific quality of individual study results , and the evaluation of the pattern of results within the broader body of scientific evidence and considered both in reaching causality determinations and in determining the form and level of the PM 2.5 and PM 10 standards.

The more detailed characterizations of indivi dual studies included an assessment of the

2 The EPA notes that the same concer ns about the causal determinations presented in the ISA were raised in comments to CASAC on the first and second draft ISAs (e.g., UARG, 2009; API, 2009; ACC, 2012, Appendix B). CASAC, therefore, had the op portunity to consider these comments as it reached consensus conclusions that the EPA had consistently and appropriately applied the causality framework, as well as its consensus agreement on the causality determinations themselves.II-10 quality of the study, which was based on specifi c criteria as described in the ISA (U.S. EPA, 2009a, section 1.5.3).

Statistical significance is an indicator of the precision of a stu dy’s results, which is influenced by a variety of factors incl uding, but not limited to, the size of the study, exposure and measurement erro r, and statistical model specifications. Statistical significance is just one of the means of ev aluating the validity of the relationships determined with epidemiological studies. Th e EPA can reasonably look to other indicia of reliability such as the consistency and coherence of a body of studies as well as other confirming data to justify reliance on the results of a body of ep idemiological studies, even if individual studies may lack statistical significance. American Trucking

Association v. EPA , 283 F. 3d 355, 371 (D.C. Cir. 2002). As a result, in developing an integrated assessment of the health effects evidence for PM, the EPA has emphasized the importance of examining the pattern of results across various studies and their coherence and consistency, and has not focused solely on statistical significance as a criterion of study reliability.

It has been clearly articul ated throughout the epidemiological and causal inference literature that it is important not to focus on results of statisti cal tests to the exclusion of other information. For example, Rothman (1998) stated: “Many data analysts appear to remain oblivious to the qualitative nature of significance testing [a nd that]... statistical significance is itself only a dic hotomous indicator. As it has only two values, significant or not significant.” As a result, Rothman r ecommended that P-values be omitted as long as point and interval estimates are available.

The concepts underlying the EPA’s approach to evaluating statis tical associations reported for the health effects on PM 2.5 have been discussed in numerous publications, including a report by the U.S. Surgeon Genera l on the health consequences of smoking (Centers for Disease Control and Preventi on, 2004). This report cautions against overreliance on statistical significance in eval uating the overall evidence for an exposureresponse relationship:

Hill made a point of commenting on the value, or lack thereof, of statistical testing in the

determination of cause: “No formal tests of significance can answer those [causal] questions. Such tests can, and should, remind us of the effects the play of chance can create, and they will instruct us in the likely magnitude of those effects. Beyond that, they contribute nothing to the ‘proof’ of our hypothesis” (Hill 1965, p. 299).

Hill’s warning was in some ways prescient, as the reliance on statistically significant testing as a substitute for judgment in a cau sal inference remains today (Savitz et al., 1994; Holman et al., 2001; Poole 2001). To unde rstand the basis for this warning, it is critical to recognize the difference between inductive inferences about the truth of underlying hypotheses, and deductive statistical calculations that are relevant to those inferences, but that are not inductive statemen ts themselves. The latter include p values, confidence intervals, and hypothesis te sts (Greenland 1998; Goodman 1999). The dominant approach to statistical infere nce today, which employs those statistical measures, obscures this important distinction between deductive and inductive inferencesII-11 (Royall 1997), and has produced the mistaken vi ew that inferences flow directly and inevitably from data. There is no mathematical formula that can tr ansform data into a probabilistic statement about th e truth of an association w ithout introducing some formal quantification of external know ledge, such as in Bayesian approaches to inference (Goodman 1993; Howson and Urbach, 1993) . Significance testing and the complementary estimation of confidence interv als remain useful for characterizing the role of chance in produci ng the association in hand (CDC, 2003, pp. 23 to 24).

Accordingly, the statistical significance of findings from an individual study has played an important role in the EPA’s evaluation of the study’s results and overall the EPA has placed greater emphasis on studies reporting st atistically significant results in making

determinations as to the elements of the standard. In particular, as noted in section III.E.4.b.i of the preamble to the final rule , the EPA identified long- and short-term exposure studies considered “key” multi-city studies for consideration for informing the decisions on the appropriate st andard levels and included th ose studies observing effects for which the evidence supported a causal or likely causal association. Figure 4 in the preamble to the final rule (also Figure 4 in the proposal, 77 FR 38933) represents the subset of multi-city studies included in Figur es 1 through 3 of the preamble to the final rule (also Figures 1 through 3 in the pr oposal, 77 FR 38929 to 38931) that provided evidence of positive and generally statistically si gnificant effects associated in whole, or in part, with more recent air quality data, generally represen ting health effects associated

with lower PM 2.5 concentrations than had previously been considered in the last review. The EPA notes that many of these studies eval uated multiple health endpoints, and not all of the effects evaluated provided evidence of positive and statistically significant effects. For purposes of informing the Administrato r’s decision on the appropriate standard levels, the Agency considers the full body of scientific evidence and focuses on those aspects of the key studies that provided evidence of positive and generally statistically significant effects..

However, in the broader evaluation of the evidence from many epidemiological studies, and subsequently during the process of form ing causality determinations, the EPA has emphasized the pattern of results across epid emiological studies for drawing conclusions on the relationship between PM 2.5 and health outcomes, and whether the effects observed are coherent across the scientific discipline s. Thus, in making causality determinations,

the EPA did not limit its focus or considera tion to just studies that reported positive

associations or where the results were statistically significant.

As discussed in section III.D.2 of the preambl e to the final rule, the EPA notes that the final causality determinations presented in the ISA reflected CASAC’s recommendations on the second draft ISA (Samet, 2009f, pp. 2 to 3). Specifically, CASAC supported the EPA’s changes (in the second versus first draf t ISA) from “likely causal” to “causal” for long-term exposure to PM 2.5 and cardiovascular effects and for cancer and PM 2.5 (from “inadequate” to “suggestive”). Id . Furthermore, CASAC reco mmended “upgrading” the causality classification for PM 2.5 and total mortality to “causal” for both the short- and long-term timeframes. Id. With regard to mortality, the “EPA carefully reevaluated the body of evidence, including the collective ev idence for biological plausibility for mortality effects, and determined that a causa l relationship exists for short- and long-termII-12 exposure to PM 2.5 and mortality, consistent with the CASAC comments” (Jackson, 2012). With respect to ultrafine particles, in developing th e second draft ISA, the EPA reexamined the controlled human exposure and toxicological studies of fresh diesel and gasoline exhaust This information, in addi tion to other consider ations, supported a change in the causal determinations for ultraf ine particles. Specifically, in reevaluating the causal determinations for short-term ultrafine particle exposures and cardiovascular and respiratory effects, the EPA change d the classification from “inadequate” to “suggestive” for both categories of health outcomes (Vandenberg, 2009, p. 3). CASAC agreed with the EPA’s rationale for revisi ng these causal determin ations (Samet, 2009f, p. 10).

(2) Comment: Some commenters asserted that the EP A inappropriately used the Hill criteria by failing to consider the limitations of st udies with weak associations, thereby overstating the consistency of the observed associations (API, 2012, Attachment 1, pp. 30 to 35). Specifically, these commenters argued that risk estimates greater than 3 to 4 reflect strong associations s upportive of a causal link, while smaller risk estimates (i.e., 1.5 to 3) are considered to be weak and requi re other lines of evidence to demonstrate causality. Additionally, these commenters believed that the EPA downplayed null or inconsistent findings in nu merous long-term mortalit y studies with reported PM 2.5 concentrations above and below the leve l of the current annual standard (e.g., Id. ; NAM et al., 2012, p. 9).

Response: As discussed in section 1.5.3 of the ISA, the EPA thoroughly considered the uncertainties and limitations of all studies during its evaluation of the scientific literature (U.S. EPA, 2009a, pp. 1 to 14). This colle ctive body of evidence, including known

uncertainties and limitations of the studies evaluated, were considered by the EPA (and reviewed by the CASAC) duri ng the process of forming cau sality determinations as discussed in Chapters 6 and 7 of the ISA. Fo r example, the EPA concluded that “a causal relationship exists between short-term PM 2.5 exposure and cardiovascular effects”; however, in reaching this conclusion, the Ag ency recognized and considered limitations

of the current evidence that st ill requires furthe r examination (U.S. EPA, 2009a, section 6.2.12.1). Therefore, the commenters have misc haracterized the EPA’s process. The limitations of the studies, and their uncertainti es, were noted and considered by the EPA.

The EPA also disagrees with the commenter s’ assertion that th e magnitude of the association must be large to support a determination of cau sality. As discussed in the ISA, the strength of the observed associati on is an important asp ect to aid in judging causality and “while large effects support causality, modest effects therefore do not preclude it” (U.S. EPA, 2009a , Table 1-2, section 1.5.4). 3 The weight of evidence approach used by the EPA encompasses a multitude of factors of which the magnitude of the association is only one component (U.S . EPA, 2009a, Table 1-3). An evaluation of the association across multiple investigators a nd locations supports th e “reproducibility of findings [which] constitutes one of the str ongest arguments for causality” (U.S. EPA, 2009a, Table 1-2). Even though the risk esti mates for air pollution studies may be

3 For example, environmental tobacco smoke (second-hand smoke) causes lung cancer in humans, even though the magnitude of the association is small (U.S. EPA, 1992).II-13 modest, the associations are consistent acr oss hundreds of studies as demonstrated throughout the ISA (U.S. EPA, 2009a, Figures 2-1, 6-27, and 7-7). Furthermore, the causality determinations rely on different lin es of evidence, by integrating evidence across disciplines, including animal toxicol ogical studies and controlled human exposure

studies.

The EPA recognizes that the popula tion potentially affected by PM 2.5 is considerable, including large subgroups of the U.S. populati on that have been identified as at-risk populations (e.g., children, older adults, pe rsons with underlying cardiovascular or respiratory disease). While in dividual effect estimates from epidemiological studies may be modest in size, the public health impact of the mortality and morbidity associations can be quite large given th at exposure to airborne PM 2.5 is ubiquitous. Indeed, with the large population exposed, exposure to a pollutant causally asso ciated at a population level with mortality and serious illness has signifi cant public health consequences, virtually regardless of the relative risk. Taken together, this information indicates that exposure to

ambient PM 2.5 concentrations has substant ial public health impacts.

Additionally, the EPA disagrees with the commenter that long-term PM 2.5 exposure studies with null or inconsistent findings we re not accurately presented in the ISA. For example, as discussed throughout section 7.6 and depicted in Figures 7-6 and 7-7, the EPA presented the collective evidence from all studies that examined the association between long-term PM 2.5 exposure and mortality. Overall, across these studies there was evidence of consistent positive associations in different cohorts. That evidence in combination with the biological plausibility provided by experimental studies evaluated in sections 7.1 and 7.2 of the ISA supporte d that a causal relationship exists between long-term PM 2.5 exposure and mortality, which is c onsistent with CASAC advice (Samet, 2009f, pp. 2 to 3).

(3) Comment: Some commenters argued that in some cases, the EPA used the same study and the same underlying database to conclude that there was a causal association between mortality and multiple criteria pollutants. These commenters contended, “[i]n doing so, the EPA attributes the cause of the mortality effects observed to whichever criteria pollutant it is reviewing at the time” (API, 2012, pp. 14 to 16).

Response: The EPA strongly disagrees that the Agen cy “attributes the cause of mortality effects observed to whichever criteria polluta nt it is reviewing at the time.” The EPA consistently recognizes that other pollutants ar e also associated with health outcomes, as is reflected in the fact that the EPA has established NAAQS to limit emissions of the particulate criteria pollutants as well as other gase ous criteria pollutants. Epidemiological

studies often examine the association between short- and long-term exposures to multiple air pollutants and mortality within a common dataset in an attempt to identify the air pollutant(s) of the complex mixture most st rongly associated w ith mortality. It is important to recognize that more than one po llutant can have effects on the same system; in fact, it is not reasonable to assume that effects can be at tributed to only one pollutant

and to exclude effects of all other pollutants.

The EPA carefully considers evidence from experimental studies providing informationII-14 on mode(s) of action in evaluati ng the overall weight of the sc ientific evidence to develop causal judgments. In evaluating these studi es, the EPA employs specific study selection criteria to identify those st udies most relevant to the review of the NAAQS. In its assessment of the health evidence regarding PM 2.5 , the EPA has carefully evaluated the potential for confounding, effect measure m odification and the role of PM as a component of a complex mixture of air po llutants (U.S. EPA, 2009a, pp. 1 to 9). The EPA used a rigorous weight of evidence appro ach to inform its causality determinations that evaluated consistency across studies w ithin a discipline, evidence for coherence across disciplines, and biological plausibility. Additionally, during this process, the EPA assessed the limitations of each study in the co ntext of the collective body of evidence. It was the collective evidence, not one individual study that ultimately determined whether a causal relationship exists between PM 2.5 and specific health outcomes.

In the ISA, the combination of epidemiol ogical, toxicological, and controlled human exposure studies formed the basis for the Ag ency concluding that a causal relationship exists between short- or long-term PM 2.5 exposures and total mort ality (U.S. EPA, 2009a, sections 2.3.1.1 and 2.3.1.2). This was the first time that the Agency concluded that a causal relationship exists between short-or long-term exposure to a criteria pollutant and mortality.

Additionally, while the EPA has evaluated th e studies used to inform the causality

determination for PM 2.5 in ISAs for other criteria air pollutants, the Agency has done so in the context of examining the collective body of evidence for each of the respective criteria air pollutants. Therefore, the EP A disagrees with the commenter that the underlying database used in the PM ISA was also used in concluding a causal relationship exists between mortality and othe r criteria pollutants. As discussed in the recently-completed ISAs for nitrogen oxide s, sulfur oxides and carbon monoxide, the

EPA did not conclude that a causal relationshi p exists with mortality and these criteria pollutants due to either short- or long-t erm exposures (U.S. EPA, 2008e, 2008f, 2010k).

(4) Comment: A number of commenters questioned th e underlying scientific basis used in

the ISA to conclude that a causal re lationship exists between long-term PM 2.5 exposure and mortality. Specifically, commenters asserted that evidence from two studies, Janes et al. (2007) and Greven et al. (2011), indicated that the a ssociation between long-term

PM 2.5 exposures and mortality is subject to unmeasured confounding. The commenters

further asserted that these studies theref ore indicated that unmeasured confounding is inherent in all long-ter m exposure studies of mortality (UARG, 2012, pp. 10 to 11, Attachment A, pp. 17 to 23; API, 2012, pp. 13 to 14, Attachment 1, pp. 11 to 14, Attachment 7, pp 3 to 10; ACC, 2012, p. 18 to 21; AFPM, 2012, p. 8; TCEQ, 2012, p. 4; EPRI, 2012, p. 3). In addition, all of the authors of the Janes et al. (2007) and Greven et al. (2011) publications, (i.e., Francesca Dominici, Scott Zeger, Holly Janes, and Sonja Greven) submitted a joint comment to the public docket in order to clarify specific points regarding these two studie s (Dominici et al. 2012).

Response: The EPA evaluated the study by Janes et al. (2007) in the ISA (U.S. EPA, 2009a, p. 7-88) and evaluated the study by Greven et al. (2011) (an extension of the study by Janes et al. (2007) incorpor ating three additional years of data) in the ProvisionalII-15 Science Assessment (U.S. EPA, 2012b). In the EPA’s evaluation of the relationship between long-term exposure to PM 2.5 and mortality, the Janes et al. (2007) study was included in the body of evidence that suppor ted the determination that a causal relationship existed (U.S. EPA, 2009a, secti on 7.6.5.1). For the reasons discussed below, the EPA does not agree with the commenters’ views that these two studies call into question the scientific merit or the consistency of the re sults of long-term exposure studies of mortality that cont ribute to this body of evidence.

Both studies used nationwide Medicare mo rtality data to examine the association between monthly averages of PM 2.5 over the preceding 12 months and monthly mortality

rates in 113 U.S. counties and examined whet her community-specific trends in monthly

PM 2.5 concentrations and mortalit y declined at the same rate as the national rate. The investigators examined this by deco mposing the association between PM 2.5 and mortality into two components: (1) “national” trends , defined as the association between the national average trend in monthly PM 2.5 concentrations averaged over the previous 12 months and the national average trend in mont hly mortality rates a nd (2) “local” trends, defined as county-specific deviations in monthly PM 2.5 concentrations and monthly mortality rates from national trends.

The EPA does not question the results of the national trends analyses conducted by Janes et al. (2007) and Gr even et al. (2011). 4 Both Janes et al. (2007) and Greven et al. (2011) observed positive and statistically significant associations between long-term exposure to

PM 2.5 and mortality in their nati onal analyses. However, Janes et al. (2007) and Greven et al. (2011) eliminated all of the spatial variation in air pollution and mortality in their data set when estimating the national effect, fo cusing instead on both chronic (yearly) and sub-chronic (monthly) temporal differences in the data (Domin ici et al. 2012). Janes et al. (2007) (Table 1) highlighted that over 90 percen t of the variance in th e data set used for the analyses conducted by both Janes et al. (2007) and Greven et al. (2011) was attributable to spatial variability, which th e authors chose to discard. The focus of the analyses by Janes et al. (2007) and Greven et al. (2011) was on two components: (1) a temporal or time component, i.e., the “nati onal” trends analysis, which examined the

association between the nationa l average trend in monthly PM 2.5 concentrations averaged over the previous 12 months and the national average trend in monthly mortality rates and (2) a space-by-time component, i.e., the “local” trends analysis, which examined county-specific deviations in monthly PM 2.5 concentrations and monthly mortality rates from national trends. These two components co mbined comprised less than 10 percent of

the variance in the data set. The auth ors included a focus on the space-by-time component, which represented approximately 5 per cent of the variance in the data set, in an attempt to identify, absent confounding, if PM 2.5 was associated with mortality at this unique exposure window. Thus, the national effects reported in th ese studies are not directly comparable to other cohort studies investigating the relationship between longterm exposure to PM 2.5 and mortality, which make use of spatial variability in air

4 In its evaluation of Janes et al. (2007) in the ISA, the EPA did not identify limitations in the statistical methods

used per se (U.S. EPA, 2009a, p. 7-88) and included the results of the national-scale analyses in that study in the body of evidence that supported the determination that there is a caus al relationship between long-term PM 2.5 exposure and mortality.II-16 pollution and mortality data. 5 Indeed, the study authors noted expressly that “when one

considers that this wealth of [spatial] information is not accounted for in that study, it is not as surprising that we see vast ly different estimates of the PM 2.5 /mortality relationship

than in other studies that do exploit that variability” (Dominici et al. 2012, p. 2).

For the local analyses, both Janes et al. (2007) and Greven et al. (2011) observed associations between exposure to PM 2.5 and mortality that are near the null value, often negative, and not statis tically significant. The fact that the authors did not observe an association in the local analyses is not surp rising. As stated in Ja nes et al. (2007), they were estimating “associations between tem poral changes in exposure and outcomes

within counties relative to the national trend.” However, a limitation of the analysis conducted by Janes et al. ( 2007) [and subsequently by Greven et al. (2011)], and recognized in a commentary by Pope and Burnett (2007), is the use of monthly average
PM 2.5 concentrations to examine associations at the local scale. This is a limitation because such an exposure assignment approach does not provide enough exposure contrast to observe temporal changes in mortality. The ISA (U.S. EPA, 2009a, p. 7-88) recognized comments made by Pope and Bu rnett (2007) that pointed out that the conclusions of Janes et al (2007) “are overstated. . . their anal ysis tells us little or nothing about unmeasured confounding in those and re lated studies because the methodology of Janes et al largely excludes the sources of variability that are exploited in those other studies. By using monthly mortality c ounts and lagged 12-month average pollution concentrations, the authors elim inate the opportunity to explo it short-term or day-to-day variability.”

Furthermore, the EPA disagrees with commenter s that Janes et al. (2007) and Greven et al. (2011) provide evidence that other studies of long-term exposure to PM 2.5 and mortality are affected by unmeasured c onfounding. As noted above, the design of the studies conducted by Janes et al (2007) and Greven et al (2011) are fundamentally different than those used in other studies of long-term exposure to PM 2.5 and mortality, including the ACS cohort and the Harvard Si x Cities study. Studies, such as the ACS and Harvard Six Cities studies, used the spatial vari ation between cities to measure the effect of long-term (annual) exposures to PM 2.5 on mortality risk, and did not conduct any analyses relying on the te mporal variation in PM 2.5 . The opposite is true of the Janes et al. (2007) and Greven et al. (2011) studies whic h first removed the spatial variability in

PM 2.5 and then examined the temporal variati on at both the national and local scale to measure the effects of temporal differences in PM 2.5 on mortality risk. Janes et al. (2007) and Greven et al. (2011) focus on changes in PM 2.5 concentrations over time and

therefore control for confounders would be ba sed on including variab les that vary over time rather than over space. As a result, any evidence of poten tial confounding of the

PM 2.5 -mortality risk relationship derived from Jane s et al. (2007) and Greven et al. (2011)

5 Though not directly comparab le, the effect estimates for mortality reported by Janes et al. (2007) and Greven et al. (2011) were coincidentally similar in magnitude to those pr eviously reported in other long-term cohort studies. It is important to note that previous cohort studies focused on identifying spatial differences in PM 2.5 concentrations between cities, while Janes et al. (2007) and Greven et al . (2011) primarily focused on temporal differences in PM 2.5 concentrations. In fact, Greven et al. (2011) stated, “We do not focus here on a third type [of statistical approach] used in cohort studies, measuring the association between average PM 2.5 levels and average age-adjusted mortality rates across cities (purely spatial or cross-sectional association).”II-17 cannot be extrapolated to dr aw conclusions related to potential spatia l confounding in studies based on the spatial variation in PM 2.5 concentrations.

As detailed in the ISA (U.S. EPA, 2009a, s ection 7.6), and recognized by the authors of Janes et al. (2007) and Greven et al. (2011), the cohort studie s that informed the causality determination for long-term PM 2.5 exposure and mortality “hav e developed approaches to adjust for measured and unmeasured c onfounders” (Dominici et al. 2012). These approaches were specifically designed to adjust for spatial confounding. The hypothesis

that the authors of Janes et al. (2007) and Greven et al. ( 2011) chose to examine was that

differences in the local and national effect s indicate unmeasured temporal confounding in

either the local or national effect estimat e. This hypothesis was specific to these two studies that examined temporal variability in exposure to air pollution and did not include known potential confounders at eith er the national or local sc ale as covariates in the statistical model. The authors acknowledged that the interpretation of either the national

or local estimates needs to occur with an appreciation of the poten tial confounding effects

of national and local scale covariates that were omitted from the model (Dominici et al., 2012). It is important to recognize that becau se Janes et al. (2007) and Greven et al. (2011) focused on variations in PM 2.5 over time and not space, th e results from these two studies do not provide any indication that other studies of long-term exposure to PM 2.5 and mortality exhibit spa tial confounding, or that PM 2.5 does not cause mortality. 6 The authors of Janes et al. (2007) and Greven et al. (2011) recognized “i t is entirely possible that these papers are looking for an associ ation at a timescale for which no association truly exists” (Dominic i et al. 2012, p.3).

Specific comments by UARG (UARG, 2012, Attach ment A, pp. 19 to 23) stated that there are flaws in the criticisms offered by Pope and Burnett (2007) on the paper by Janes et al. (2007). First, the comment ers did not agree with Pope and Burnett (2007) that data used by Janes et al. (2007) was too aggregate (i.e., using deaths and PM 2.5 concentrations averaged over months rather than days does not provide adequate temp oral variability) to

detect short-term variation. The commenters stated that most of the long-term cohort studies of mortality rely on even more aggregate timescales that are multi-year averages.

The EPA agrees that many of the long-term cohort studies rely on timescales that are aggregated beyond monthly averages (as was done by Janes et al., 2007) in multi-city studies where spatial variabil ity in exposure is being exam ined. However, Janes et al. (2007) discounted all of the sp atial variability in their analyses. Thus, the EPA agrees with the criticism by Pope and Burnett (2007) that when looking within a single city or geographic area, as Janes et al. (2007) did in their “local” analysis , there was not enough variability in exposure to aggregate exposure at the monthly level instead of the daily

level.

Second, the commenters took issue with the crit ique by Pope and Burnett (2007) that the use of county-level fixed effects eliminated the source of long-t erm average spatial variability. As stated by the commenters, “To estimate the new model developed by Janes

6 Further, the EPA notes that Janes et al. (2007) and Greven et al. (2011) provide no information relevant to examining confounding in studies of short-term exposure to PM 2.5

.II-18 et al. (2007a), they must use other sources of variation: they must use temporal and spatial-temporal variation” (UARG, 2012, Attachment A, p. 21). While this may be true, as mentioned above, the Medicare mortality dataset used by the authors does not have adequate temporal resolution to look at spatial-temporal vari ation in the “local” analyses conducted by Janes et al (2007) and reanalyzed by Greven et al. (2011). As noted by Janes et al. (2007) (See Table 1), and discussed by Dominci et al. (2012) only 5 percent

of the variance in the data set used in these analyses is attributable to the space by time component. Therefore, although Janes et al. (200 7) and Greven et al. (2011) attempt to use temporal and spatial-temporal variation in the data set to examine associations

between PM 2.5 exposure and mortality as stated by the commenters, there is not enough temporal variability to identify associations using this approach.

Third, the commenters identified the critique by Pope and Burnett (2007) that the analysis by Janes et al. (2007) was limited by the scale of the study (i.e., three years), which did not allow for consideration of longer-term vari ability in mortality and air pollution data. The commenters stated that “[a]ll researcher s are limited by the data available to them, and Janes et al. (2007a) used only three years in their analysis because that is all the data they had available” (UARG, 2012, Attachment A, p. 21). While the EPA acknowledges that the researchers may be limited by the data available to them, scientists must decide

whether those limitations enable them to answ er the scientific question that they are posing. Because the Medicare mortality was aggr egated at the monthly level, it could take decades and decades of data to provide the appropriate exposure contrast to conduct these analyses.

There were also specific comments sugges ting that the study by Gr even et al. (2011)

substantiated the result s of Janes et al. (2007). Specifica lly, the commenters stated that Greven et al. (2011) used “station-level” data instead of county level data, added three additional years of data to the study period, incorporated controls for socio-economic confounders, and investigated trends at the regional level (UARG, 2012, Attachment A, p. 22). While these may be improvements upon th e original study by Janes et al. (2007), Greven et al. (2011), like Janes et al. (2007), eliminated all of the spatial variation in their data set. Therefore, the results in Greven et al. (2011) similar to Janes et al. (2007), are not comparable to, nor would they invalidate, the results of cohort studies investigating the relationship between long-term exposure to PM 2.5 and mortality (Dominici et al. 2012, p. 1.).

One commenter suggested that the epidemio logical results from studies of long-term exposure to PM 2.5 and mortality characterized in the ISA are inconsistent and discordant, indicating significant confounding (API, 2012, Attachment 7, pp. 2 to 10). This commenter pointed to the study by Greven et al. (2011) as an exam ple of a study that avoids such potential confounding. The EP A disagrees with this comment. As demonstrated in the ISA, there is a la rge body of evidence suppor ting the association between long-term exposure to PM 2.5 and mortality that gene rally reports consistent, positive relative risks (U.S. EP A 2009a, Figures 7.6 and 7.7). The EPA does not interpret these results as being “incons istent and discordant”.

This commenter also suggested that the data used by Greven et al. (2011) were “superiorII-19 or comparable to data used in other studies of PM 2.5 and mortality” ((API, 2012, Attachment 7, p. 5). For example, the commenter claimed that Greven et al. (2011) used

data from more locations than other research ers. Specifically, this commenter pointed out that Greven et al. (2011) incl uded data from 814 ZIP code area s while Pope et al. (2009) focused on 211 county units. The EPA acknowledge s that Greven et al. (2011) used a more spatially resolved data set (i.e., ZIP codes instead of countie s), but points out that the study by Greven et al. (2011) includes da ta from just 113 counties, compared to the 211 counties included in Pope et al. (2009). Furthermore, while this enhanced spatial resolution may help to reduce exposure meas urement error, the focus on the study by Greven et al. (2011) was on temporal variabil ity in exposure, and in this case does not provide additional exposure contrast. We c onsequently do not accept the conclusion that the data set in Greven (2011) was su perior to that in other studies.

In addition, the commenter cited the use of monthly average mo rtality data as a strength of the study by Geven et al. (2011), when, in fact, for a study focusing on temporal variability in exposure, daily average mort ality would be preferable. The EPA thus considers the use of monthly-average morta lity data in the study as a limitation, not strength. Finally, the commenter acknowledged that the study by Greven et al. (2011) did not include any individu al-level covariates, but had to rely on county- and month-level information for potential confounders, incl uding smoking whereas other cohort studies have used individual-level data (e.g., th e ACS cohort (Pope et al., 2002)). For these reasons, the EPA disagrees with the commente rs’ views that the study by Greven et al. (2011) is superior to other cohort studies of long-term exposure to PM 2.5 and mortality.

In summary, the EPA does not question the qua ntitative results presen ted by Janes et al. (2007) and Greven et al. (2011); however, th e EPA disagrees that the results of these studies are comparable to the results of other cohort stud ies of long-term exposure to

PM 2.5 and mortality, or that the results presented in these two studies invalidate either the results themselves, or the c onsistency of the results obser ved across other cohort studies of long-term exposure to PM 2.5 and mortality. Janes et al. (20 07) and Greven et al. (2011) chose to eliminate the spatial variability in the air pollution and mo rtality data. Thus, the

results of these studies cannot be directly compared to time- series studies of short-term exposure to PM 2.5 and mortality (which rely on day-to-day changes in PM 2.5 concentrations and mortality) because the au thors only use temporal variability measured on a monthly scale. Nor can the results of th ese studies be directly compared to cohort studies of long-term exposure to PM 2.5 and mortality (which rely on the spatial variability of air pollution concentrations and mortality) because their analyses include a fixed effect for county in the regression mode l which eliminates spa tial variability when estimating the national effect. Additionally, Jane s et al. (2007) and Greven et al. (2011) use a different time scale in their analyses compared to the timescales used in other

cohort studies. Janes et al. (2007) and Greven et al. ( 2011) examined whether an

association exists at a sub-ch ronic (i.e., monthly) time scale. Thus, the results of the study by Janes et al. (2007) are incl uded in the ISA and contributed to the body of evidence for an association between long-term PM 2.5 exposures and mortalit y, but are not directly comparable to other cohort studies that rely on a different timescale and focus on spatial variability.II-20 As demonstrated in the ISA, there is a la rge body of evidence s upporting the association between long-term exposure to PM 2.5 and mortality that gene rally reports consistent

relative risks between 1.0 and 1.5 (U.S. EPA 2009a, Fi gures 7.6 and 7.7). Based on this large body of evidence, the EPA concluded thata causal relationship exists between longterm exposure to PM 2.5 and mortality (U.S. EPA, sect ion 7.6.5.1). The results presented by Janes et al. (2007) and Greven et al. (2011) are not comparab le to the results of these studies of long-term exposure to PM 2.5 and mortality. Therefore, the EPA concludes that these studies do not invalidate the large body of epidemiological ev idence that supports

the EPA’s determination that a causal re lationship exists between long-term PM 2.5 exposure and mortality. 7

(5) Comment: Some commenters questioned the use of epidemiological studies in assessing the adequacy of the current PM NAAQS because “of the untestable assumptions on which much of air pollution epidemiology, along with EPA’s proposed NAAQS revisions, are built” (ACC, 2012, pp. 20 to 21). These commenters made this claim based on a recent publication by Moore et al. (2012), which they asserted demonstrates that “most, if not all, results from epidemiologi c studies of air pollution – requires reliance on untestable and possible invalid a ssumptions, and that the altern ative analyses designed to meet such assumptions can produce different (e.g., null instead of positive) results” (ACC, 2012, p. 20).

Response: The EPA disagrees with the commenters’ views that the results of the recently published Moore et al. (2012) study bring in to question the epidemiological evidence used to inform whether or not the PM NAAQS should be revised. First, the Moore et al. (2012) study focused on evaluating e ffects associated with ozone (O 3 ) exposures, which brings into question its releva nce in the context of considering the available scientific evidence for the PM NAAQS review. This study was not included in the ISA or

considered in the Provisional Science A ssessment as this study did not include

consideration of measured ambient PM 2.5 concentrations. Sec ond, Moore et al. (2012) examined heat as a pote ntial confounder of the O 3 -asthma hospital admission relationship. For PM, temperat ure is also a known potential confounder, but a number of

studies have demonstrated that alternative approaches to controlling for the potential confounding effects of weather do not influen ce PM risk estimates (e.g., Welty and Zeger (2005), as discussed on p. 6-163 and 6-164, U. S. EPA, 2009a). Therefore, the study by Moore et al. (2012) does not info rm the relationship between PM 2.5 exposure and health

effects.

(6) Comment: With regard to toxicological and controlled human exposure studies, some commenters argued that the available evidence does not provide coherence or biological plausibility for health effects observed in epidemiological studies (API, 2012, pp. 21 to 22, Attachment 1, pp. 25 to 29; AAM, 2012, pp. 15 to 16; Texas CEQ, 2012, p. 3). With regard to the issue of mechanisms, thes e commenters noted that although the EPA recognizes that new evidence is now availa ble on potential mechanisms and plausible biological pathways, the evidence provided by toxicological and controlled human

7 We note that the EPA’s conclusion with regard to in terpretation of the results from Janes (2007) and Greven (2012) is supported by the study authors’ conclusion that “[o]ur results do not invalidate previous epidemiologic

studies ” (Dominici (2012) p. 1 (emphasis original)).II-21 exposure studies still does not re solve all questions about how PM 2.5 at ambient concentrations could produce the mortality and morbidity effects observed in epidemiological studies. More specifically, for example, some of these commenters

stated that:

A review of the Integrated Science A ssessment, however, suggests that the experimental evidence is inconsistent and not coherent with findings in epidemiology studies. Specifically, the findings of mild and reve rsible effects in most experimental studies conducted at elev ated exposures are not consistent with

the more serious associations describe d in epidemiology studies (e.g., hospital admissions and mortality). Also, both animal studies and controlled human exposure studies have identified no effect le vels for acute and chronic exposure to

PM and PM constituents at concentrati ons considerably a bove ambient levels. The EPA should consider the experimental findings in light of these higher exposure levels and what the relevance may be for ambient exposures (API, 2012, Attachment 1, p. 25).

Response: The EPA notes that in the review comp leted in 1997, the Agency considered

the lack of demonstrated bi ological mechanisms for the varying effects observed in epidemiological studies to be an important cau tion in its integrated assessment of the health evidence upon which the standards were based (71 FR 61157, October 17, 2006). In the review completed in 2006, the EPA recognized the findings from additional

research that indicated that di fferent health responses were linked with different particle

characteristics and that both individual components and complex particle mixtures appeared to be responsible for many biologi c responses relevant to fine particle

exposures. Id . Since that review, there has been a gr eat deal of research directed toward advancing our understanding of biological m echanisms. While this research has not resolved all questions, and further research is warranted (U.S. EPA, 2011a, section 2.5), it has provided important insights as discussed in section III.B.1 of the proposal (77 FR at 38906 to 38909) and discussed more fully in the ISA (U.S. EPA, 2009a, chapter 5).

As noted in the proposal, toxicological studie s provide evidence to s upport the biological plausibility of cardiovascular and respiratory effects associat ed with long- and short-term

PM 2.5 exposures observed in epidemiologi cal studies (77 FR 38906) and provide supportive mechanistic evidence that the card iovascular morbidity effects observed in long-term exposure epidemiological studies are coherent with studies of cardiovascularrelated mortality (77 FR 38907). The ISA conclu ded that the new evidence available in this review “greatly expands” upon the evidence available in the last review “particularly in providing greater understanding of the underlying mechanisms for PM 2.5 induced cardiovascular and respiratory effects for both short- and long-term exposures” (U.S. EPA, 2009a, p. 2-17). The mechanistic evidence now available, taken together with newly available epidemiological evidence, in creases the Agency’s confidence that a causal relationship exists between lo ng- and short-term exposure to PM 2.5 and cardiovascular effects and mortality. In a ddition, CASAC supporte d the ISA approach and characterization of potential mechanisms or modes of action (Samet, 2009e, pp. 7 to 8; Samet, 2009f, p. 11), as well as the findings of a causal relations hip at the populationII-22 level between exposure to PM 2.5 and mortality and cardiovas cular effects (Samet, 2009f, pp. 2 to 3).

Additionally, the EPA disagrees with commenter s that the mild and reversible effects

observed in controlled human e xposure studies are inconsiste nt with the more serious effects observed in epidemiological studies. Et hical considerations re garding the types of studies that can be performed with human subjects limit the e ffects that can be evaluated to those that are transient, reversible, and of limited short-term consequence. The relatively small number of subjects recruite d for controlled exposur e studies should also be expected to have less variability in health status and risk factors than occurring in the general population. 8 Consequently, the severity of h ealth effects observed in controlled human exposure studies eval uating the effects of PM 2.5 should be expected to be less than observed in epidemiological studies. Nonethel ess, that effects are observed in healthy individuals participating in c ontrolled exposure studies serv es as an indication that PM 2.5 is initiating adverse health re sponses and that more severe responses may reasonably be expected in a more diverse population, speci fically, in at-risk popul ations. Put another way, there are serious public health risks from exposure of large populations of people including those with pre-existing illnesse s, to ambient concentrations of PM 2.5 , but these are not the same as the very small risks that individuals who do not have such conditions face when participating in a controlled human exposure study.

It should also be noted that there is a sma ll body of toxicological evidence demonstrating mortality in rodents exposed to PM 2.5 (e.g., Killingsworth et al. 1997). Overall, it is not surprising that lethality is not induced in mo re toxicological research, as these types of studies do not readily lend themselves to th is endpoint. Epidemiological studies have

observed associations between PM 2.5 and mortality in communities with populations in the range of many thousands to millions of pe ople. Clearly, it is not feasible to expose hundreds (if not thousands) of animals to PM 2.5 (potentially over many years) in a laboratory setting to induce enough lethalities to distinguish between natural deaths and

those attributable to PM 2.5 . Furthermore, the heterogeneous human populations sampled in epidemiological studies are comprised of individuals with differe nt physical, genetic, health, and socioeconomic backgrounds whic h may impact the outcome. However, in toxicological studies, the rodent groups most frequently ev aluated are typically inbred, such that inter-individual variability is minimi zed. Thus, if the rodent strain used is quite robust, PM 2.5 -induced effects may not be observed at low exposure concentrations.

8 For example, the EPA excludes from its controlled human exposure studies involving exposure to PM 2.5 any individual with a significant risk factor for experienci ng adverse effects from such exposure. Thus, the EPA

excludes a priori the following categories of persons: those with a history of angina, cardiac arrhythmias, and ischemic myocardial infarction or coro nary bypass surgery; those with a card iac pacemaker; those with uncontrolled hypertension (greater than 150 systolic and 90 diastolic); those with neurogenetive diseases; those with a history of bleeding diathesis; those taking beta-blockers; those using oral anticoagulants; those who are pregnant, attempting to become pregnant, or breastfeeding; those who have experienced a respiratory infection within four weeks of exposure; those experiencing eye or a bdominal surgery within six weeks of e xposure; those with active allergies; those with a history of chronic illnesse s such as diabetes, cancer, rheumatolo gic diseases, immunodeficiency state, known cardiovascular disease, or chronic respiratory diseases; smokers. The EPA “Application for Independent Review Board Approval of Human Subjects Research: Cardiopulmonary Effects of healthy Older GSTM1 Null and
Sufficient individuals to Concentrated Ambient Air Particles (CAPTAIN),” Nov. 9, 2011, p. 9

.II-23 (7) Comment: A number of commenters disagreed with the EPA’ s evaluation of specific long-term PM 2.5 exposure and mortality studies (e.g., ACC, 2012, pp. 6 to 14; AAM, 2012, pp. 6 to 18) and contended that the EPA’s ev aluation of the scientific evidence fails to accurately reflect the la test scientific knowledge. Common points raised by these commenters were that the results from long- term exposure studies were limited because they: (a) found biologically implausible risk estimates; (b) estimated PM 2.5 concentrations for years in which data were not availa ble; and (c) did not account for exposure

misclassification.

Response: The EPA carefully evaluated “the body of evidence, including the collective evidence for biological plausibility for mortality effects, and determined that a causal relationship exists for ...long-term exposure to PM 2.5 and mortality, consistent with CASAC comments” (Jackson, 2012). This evaluation of the evid ence included review of the potential limitations mentioned by comment ers. Furthermore, CASAC supported the

EPA’s evaluation of the scientific evidence a nd the application of the causal framework in making a causal determination for mortalit y attributed to long-term PM exposures (Samet, 2009f, pp. 2 to 3). Below, the EPA responds to each of the specific limitations noted by commenters:

(a) With respect to biological plausibility, some commenters argued that the estimated

associations between ambient PM and mortality are stronger than those for long-term heavy cigarette smoking, thereby defying biol ogical plausibility (ACC, 2012, pp. 6 to 7). The comparison of smoking and ambient PM-rel ated effect estimates was not considered relevant for the PM NAAQS review and, thus, wa s not considered in the ISA. This issue was not raised during the CASAC and public review of the drafts of the ISA. In order to address the comments submitted, the EPA conduc ted a provisional review of the “new” literature published since the close of the ISA including studies cited by commenters, and

identified several relevant studies that compared and evaluated effect estimates determined for relationships between specifi c health outcomes and ambient particulate matter and active smoking (Pope et al. 2009; Po pe et al. 2011). These authors analyzed

data from the ACS cohort in order to ev aluate the shape of the exposure-response relationship for PM 2.5 and both lung cancer mortality (Pope et al. 2011) and cardiovascular disease (CVD) mortality (Pope et al. 2009; Pope et al. 2011). In these studies, the authors evaluated th ree sources of exposure to PM 2.5 : active smoking, passive smoking, and ambient air pollution.

For lung cancer mortality, the authors obser ved “a monotonic, nearly linear exposure response relationship with fairly constant marginal increases in RR [relative risk] with increasing exposure” across the full range of observed exposures (Pope et al. 2011).

When the authors evaluated CVD morta lity, they observed “an exposure-response relationship that is substantially non-linear, that is, much steeper at the very low levels of exposure compared with higher levels of exposure” (Pope et al. 2011). In fact, the study authors noted that “For lung cancer mortalit y, the RRs steadily increase to nearly 40 at the highest increment of cigarette smoking (>42 cigarettes per day), whereas for CVD mortality, the RRs level off at approxima tely 2.0-2.5” (Pope et al. 2011, Figure 1).II-24Figure 1. Adjusted RRs [with 95% confidence intervals (CIs)] of lung cancer mortality (A) and IHD, cardiovascular, andcardiopulmonary mortality (B) plottedover estimated daily exposure of PM2.5(milligrams) and increments of cigarettesmoking relative to never smokers (cigarettes/day). Diamonds represent comparative mortality risk estimates (with 95% CIs)for PM2.5from air pollution from the comparative studies (Dockery et al. 1993;Laden et al. 2006; Milleret al. 2007; Pope et al.1995, 2002, 2004). Stars represent comparable pooled RR estimates (with 95% CIs) associated with SHS exposure fromcomparative studies (Teo et al. 2006; U.S.Department of Health and Human Services 2006). The dottedlines represent thenonlinear power function fit through theorigin and the estimates(including active smoking, SHS, ambient PM2.5). Estimateddoses from different increments of activesmoking are dramatically largerthan estimated doses from ambient pollution or SHS;therefore, associations at lower exposure levels (due to ambient air pollution and SHS) are shown as insets with a magnifiedscale. Source: Pope et al. 2011.II-25 Because of the much steeper exposure-res ponse relationship for long-term exposure to

PM 2.5 and CVD mortality at low PM 2.5 concentrations, which flattens out at higher PM 2.5 concentrations (i.e., those associated with passive and active cigarette smoking), it is biologically plausible that th e risk estimates for CVD mortality due to exposure to

ambient concentrations of PM 2.5 would be similar to risk estimates for CVD mortality due to active cigarette smoking. These results ar e consistent with th e results observed in epidemiological studies of long-term exposure to PM 2.5 and mortality, and with the conclusions drawn in the ISA. For example, Dockery et al. (1993) found essentially the same risk estimates for CVD mortality associated with both ambient PM 2.5 concentrations and active cigarette smoking in an area with relatively high levels of ambient PM 2.5 concentration. Thus, contrary to views expr essed by commenters, the EPA concludes that the scientific evidence provides biologically pl ausibility for the mortality effects observed in epidemiological studies of ambient PM.

(b) With regard to estimating PM 2.5 exposure for periods when da ta are not available, as discussed in section III.E.4.c.i of the preambl e to the final rule and in section II.B.5.a.i below, both in the last review and the current review, the EPA has assessed studies that used different air quality periods for estimating long-term exposure and tested associations with mortality for the differ ent exposure periods (U.S. EPA, 2004, section 8.2.3.5; U.S. EPA 2009a, section 7.6.4). In th is review, the ISA discussed studies

available since the last revi ew that have assessed the relationship between long-term exposure to PM 2.5 and mortality to explore the issue of the latency period between exposure to PM 2.5 and death (U.S. EPA, 2009a, section 7.6.4).

Notably, in a recent analysis of the extende d Harvard Six Cities Study, Schwartz et al. (2008) used model averaging (i.e., multiple models were averaged and weighted by probability of accuracy) to assess exposure periods prospectively. The exposure periods were estimated across a range of unconstraine d distributed lag models (i.e., same year, one year prior, two years prior to death). In comparing lags, the authors reported that the effects of changes in exposure to PM 2.5 on mortality were strongest within a two-year period prior to death (U.S. EPA, 2009a, p. 7- 92, Figure 7-9). Similarly, a large multi-city study of the elderly found that the mortality risk associated with long-term exposure to

PM 10 reported cumulative effects that extended over the years that deaths were observed in the study population (i.e., the follow-up peri od) and for the three-year period prior to death (Zanobetti et al., 2008).

Further, in a study of two locations that experienced an abrupt decline in PM 2.5 concentrations (i.e., Utah Steel Strike, coal ban in Ireland), Röösli et al. (2005) reported that approximately 75 percent of health benef its were observed in th e first 5 years (U.S. EPA, 2009a, Table 7-9). Schwar tz et al. (2008) and Pue tt et al. (2008) found, in a comparison of exposure periods ranging from 1 month to 48 months prior to death that exposure to PM 10 24 months prior to death exhibite d the strongest a ssociation, and the weakest association was reported for exposure in the time period of 1 month prior to

death.

Collectively, the EPA notes that the availa ble evidence for determining the window over which the mortality effects of long-term PM exposures occur, as discussed above and inII-26 section III.E.4.c.i of the preamble to the fi nal rule and in section II.B.5.a.i below, suggests that a latency period of up to five years would account for the majority of deaths, with the strongest association observe d in the two years prio r to death. Further, the EPA recognizes that there is no discernible population- level threshold below which effects would not occur, such that health effects may occur over the full range of concentrations observed in the epidem iological studies, including the lower concentrations in the latter years. (U.S. EP A, 2009a, section 2.4.2.3). In light of this evidence and these considerations, the EPA concl udes that it is appropriate to consider air quality concentrations that ar e contemporaneous with the coll ection of health event data (i.e., collected over the same time period) as being causally associated with at least some proportion of the deaths assessed in a long-term exposure study.

In addition, the EPA acknowledges that the a ppropriate exposure period for mortality effects observed in long-term exposure studies may extend up to a few years prior to the years in which health event data were collected. Such an extended exposure window would likely more fully capture the PM 2.5 -related deaths in such studies. To explore how much higher the long-term mean PM 2.5 concentrations would lik ely have been had air quality data prior to the fo llow-up years of the studies b een included, the EPA conducted a sensitivity analysis of long-term mean PM 2.5 concentrations (Schmidt, 2012a), particularly, considering studies that only included d eaths from a relatively recent followup period. As examples of such studies, this an alysis considered the Eftim et al. (2008) study of mortality in the ACS site s and the Harvard Six Cities sites, as well as sites in the eastern region in the Zeger et al. (2008) study. Using data from the EPA’s AQS database, the analysis added the two year s of air quality data just pr ior to the follow-up period in each study, which was 2000 to 2002 in Eftim et al. (2008) and 2000 to 2005 in Zeger et al. (2008). The analysis then calcula ted the extended long-term mean PM 2.5 concentration for each study. As discussed in Schmidt (2012a ), in each case the long-term mean PM 2.5 concentration averaged over the extende d exposure period was less than 0.4 μg/m 3 higher than the long-term mean PM 2.5 concentration averaged over the follow-up period. The

EPA finds it reasonable to conclude that such a relatively small difference in long-term

mean PM 2.5 concentrations would likely apply for other long-term exposure studies that used similarly recent follow-up periods as well (e.g., Goss et al., 2004; Lipfert et al., 2006a). Furthermore, the EPA finds that this sensitivity analysis i llustrates that, even when considering a somewhat longer exposur e window, including the years the health event data were collected plus the two previous years, hea lth effects are occurring at

concentrations below the current level of the annual standard (i.e., below 15 μg/m 3 ).

Moreover, as discussed in section III.E.4.c.i of the preamble to the final rule and in section II.5.a.i below, the EPA notes that th e relevant exposure period for the short-term exposure studies is the period contemporaneous with the coll ection of health event data, and that this exposure period is not subject to the uncertainti es related to the long-term exposure studies. This is one of the reasons th at the EPA gave special consideration to the long-term mean concentrations evaluated in key short-term exposure studies in revising

the level of the annual standard.

(c) The EPA has long recognized that expos ure error is an important issue for interpretation of epidemiological studies and that assessment of air pollution exposureII-27 using community average concentrations ma y lead to exposure misclassification or exposure measurement error. To investigate th is issue, several analyses using ACS data focused on neighborhood-to-neighborhood differences in urban air pollu tants (Jerrett et al. 2005; Krewski et al. 2009a) (U.S. EPA, 2009 a, section 7.6.3). These analyses used spatial interpolation and land use regression methods to assign exposure to study subjects living in Los Angeles, CA, resulting in im proved exposure assessment compared to the full cohort of the ACS study. Statistically significant associations between PM 2.5 and mortality from all causes and cardiopulm onary diseases were reported with the magnitude of the relative risk s being greater in the analys es with the improved exposure assessment compared to the relative risks re ported for the full ACS cohort. This provides evidence that reducing exposur e error can result in str onger associations between PM 2.5 and mortality than generally observed in studi es having less well-char acterized exposure.

(8) Comment: Some commenters contended that th e associations observed in long-term exposure studies were due to exposures that occurred many years earlier when PM 2.5 concentrations were much higher and therefor e are “misattributing those risks to more recent, lower PM 2.5 levels” (UARG, Attachment 1, pp. 14 to 15; Southern Company, 2012 p. 2; AAM, 2012, pp. 14 to 15). Additionally , these commenters asserted that mortality due to long-term exposure is the re sult of cumulative expos ure over a lifetime, which led to the development of chronic conditio ns that ultimately c ontributed to death.

Response: As an initial matter, the EPA has rec ognized the challenge in distinguishing

between PM 2.5 -associated effects due to past a nd recent long-term exposures, and in identifying the relevant latency period for l ong-term exposure to PM and resultant health effects (U.S. EPA, 2009a; 77 FR 38941/1). While the EPA acknowledges that there remain important uncer tainties related to characteriz ing the most relevant exposure periods in long-term exposure studies, the EPA notes that there are a number of studies that help inform the Agency’s consideration of this issue.

Both in the last review and the current re view, the EPA has assesse d studies that used different air quality periods for estimating long-term exposure and tested associations with mortality for the different exposure periods (U.S. EPA, 2004, Section 8.2.3.5; U.S. EPA 2009a, section 7.6.4). In this review, the ISA discussed studies available since the

last review that have assessed the rela tionship between long-term exposure to PM 2.5 and mortality in exploring the issue of th e latency period between exposure to PM 2.5 and death (U.S. EPA, 2009a, Section 7.6.4).

Notably, in a recent analyses of the Harvard Six Cities Study, Schwartz et al. (2008) used model averaging (i.e., multiple models were averaged and weighted by probability of accuracy) to assess exposure periods pros pectively (77 FR 38907/1-2). The exposure periods were estimated across a range of uncons trained distributed lag models (i.e., same year, one year prior, two years prior to death). In comparing lags, the author s reported the effects of changes in exposure to PM 2.5 on mortality were strongest within a two year period prior to death (U.S. EPA, 2009a, p. 7- 92, Figure 7-9). Similarly, a large multi-city study of the elderly found that the mortality risk associated with long-term exposure to

PM 10 reported cumulative effects that extended over the years that deaths were observed in the study population (i.e., the follow-up period ) and for the 3-year period prior to deathII-28 (Zanobetti et al., 2008).

Further, in a study of two locations that experienced an abrupt decline in PM 2.5 concentrations (i.e., Utah Steel Strike, coal ban in Ireland), Röösli et al. (2005) reported that approximately 75 percent of health benef its were observed in th e first 5 years (U.S. EPA, 2009a, Table 7-9). Furthermore, Schwar tz et al. (2008) and Puett et al. (2008) found, in a comparison of exposure periods ra nging from 1 month to 48 months prior to death that exposure to PM 10 24 months prior to death exhi bited the strongest association, and the weakest association was reported for exposure in the time period of 1 month prior

to death.

Overall, the EPA notes that the availabl e evidence for determining the window over which the mortality effects of long-term pollution exposures occur suggests that a latency period of up to five years would account for th e majority of deaths, with the strongest association observed in the two years prior to death. Further, the EPA recognizes that

there is no discernible threshol d below which effects would no t occur, such that health effects may occur over the full range of c oncentrations observed in epidemiological studies, including the lower concentr ations in the latter years. In light of this evidence and these considerations, the EPA concludes that it is appropriate to consider air quality concentrations that are contemporaneous with the collection of health event data as evidence to be used in determining ca usality. The EPA acknowledges that exposure windows that extend up to a few years prior to the follow-up period in which health event data were collected would likely more fully capture the PM-related deaths in such

studies.

To explore how much higher the long-term mean PM 2.5 concentrations would likely have been had air quality data pr ior to the follow-up years of the studies been included, the EPA conducted a sensitivity analysis of PM 2.5 concentrations (Schmidt, 2012), particularly, considering studies that only included deaths from a relatively recent followup period. As examples of such studies, this an alysis considered the Eftim et al. (2008) study of mortality in bo th the ACS sites and the Harvard Si x Cities sites, as well as sites in the eastern region in the Zeger et al. (2008) study. Using data from the EPA’s AQS database, the analysis added th e two years of air qua lity data just prior to the follow-up period in each study, which was 2000 to 2002 in Eftim et al. (2008) and 2000 to 2005 in Zeger et al. (2008). The analysis then calculated the extende d long-term mean PM 2.5 concentration for each study. As discussed in Schmidt (2012), in each case the long-term

mean PM 2.5 concentration averaged over the exte nded exposure period was no more than 0.4 μg/m 3 higher than the long-term mean PM 2.5 concentration averaged over the followup period. The EPA finds it reasonable to conclu de that such a relatively small difference in long-term mean PM 2.5 concentrations would likely a pply for other long-term exposure

studies that used similarl y recent follow-up periods as well (e.g., Goss et al., 2004; Lipfert et al., 2006a).

Based on the above considerations, the EPA conc ludes that it is appr opriate to consider the available air quality information from th e long-term exposure studies, while taking into account the uncertainty in the relevant long-term exposure period when weighing the information from the long-term exposure studie s in the context of the broader array ofII-29 epidemiological studies that inform the EPA’ s consideration of th e level of the annual

PM 2.5 standard. Furthermore, as noted in the prea mble and in the response to the previous comment (Comment (7)), the relevant exposure period for the short-term exposure studies is the period contemporaneous with th e collection of health event data, and that this exposure period is not subject to the unc ertainties related to the long-term exposure studies. In this review, the EPA accordingly ga ve special consideration to the long-term mean concentrations evaluated in key short- term studies in revi sing the level of the

annual standard. These comments are addres sed further in section III.E.4.c.i of the preamble to the final rule and in section II.B.5.a.i below.

(9) Comment: Some commenters asserted there were limitations in specific long-term exposure studies of mortality. For example, one group of commenters (NAM et al., 2012, pp. 23 to 24) asserted there were serious w eaknesses in the long- term exposure studies considered by the EPA (e.g., Harvard Six C ities Study, Laden et al., 2006). Specifically,

NAM et al. asserted that the Harvard Six Cities Study did not account for increasing age of the cohort, and that there were discrepa ncies in the results of the study. Another commenter (EPRI, 2012, p. 3) asserted that th e EPA mischaracterized the results of the Veterans Cohort Study (Lip fert et al., 2006).

Response: The EPA disagrees with the commenters ’ assertion that the increasing age of the study subjects from the Harvard Six Cities Study was not accounted for when estimating the association between decreased PM 2.5 concentrations and decreased mortality observed by Laden et al. (2006). Th e average age of the cohort at enrollment was 50 years (range 25 to - 74 years) and th e first follow-up period consisted of the 15 years following enrollment (including 104,243 person-years of follow up and 1,364 deaths). An additional follow-up period (16 to 24 years after enrollment) included an additional 54,735 person-years of follow-up a nd 1,368 deaths. The overall death rate for the first follow-up period was 13.1 deaths pe r 1,000 years of follow-up; it was 25.0 in the second follow-up period “reflecting the aging of this cohort” (Laden et al. 2006, p. 668). To account for this, Laden et al. (2006) contro lled for baseline indivi dual risk factors and potential confounders, including age. The auth ors stratified study s ubjects “by sex and 1- yr age groups, such that each sex/age group had its own baseline hazard.” Id . The authors

found that the associ ations between PM 2.5 and mortality were comparable for both follow-up periods (Laden et al. 2006, p. 669). Additionally, NAM et al. asserted that there were discrepancies in results among th e six cities in the study that lead to considerable uncertainty. The EPA acknowledges that there was variab ility in the results

for the individual cities in the Harvard Six Cities Study (in fact the objective of the study was to look at the variability between cities), but disagr ees that such variability contributes to uncertainty. In fact, variability in the PM 2.5 concentrations among the cities is necessary in long-term cohort studies, such as the Harvard Six Cities Study, which rely on spatial variability for expos ure contrast (see also res ponse to Comment (4), above). Laden et al. (2006) recognized that there is variability in the association between the cities, but noted that “the drop in the adjusted mortality rate was largest in the cities with the largest reductions in PM 2.5 after controlling for such a period effect.” Id.

With regard to the Veteran’s Cohort Study, the EPA acknowledges that the air quality data in Figures 1 and 4 (77 FR 38929) of the proposal were attributed to the wrongII-30 Lipfert et al. study published in 2006. The air quality data reported in Figure 1 of the proposal incorrectly identif ied the long-term mean PM 2.5 concentration for Lipfert et al (2006a – labeled Lipfert et al. (2006) in Figure 1) as 14.3 μg/m 3 , which was instead the long-term mean PM 2.5 concentration reported for Lipfer t et al. (2006b). This mistake was also made in the Figure 2-2 of the ISA (U .S. EPA, 2009a, p. 2-15). The EPA notes that footnote a for Figure 4 of Lipfert et al. ( 2006a) identified that the mortality risks for

PM 2.5 were based on one year of air quality data (1999), al though the study did not report the long-term mean PM 2.5 concentration for that year. Rath er, in Table 1 of Lipfert et al. (2006a), the study authors re ported long-term mean PM 2.5 concentrations of 14.3 μg/m 3
for the years 1989 to 1996 and 14.6 μg/m 3 for the years 1997 to 2001. Based on this information, the EPA concludes that 14.3 μg/m 3 is a reasonable a pproximation for the long-term mean PM 2.5 concentration in Lipfert et al . (2006) even though this value was not specifically repor ted in that study.

The EPA disagrees that the pr oposal mischaracterized the re sults of the Lipfert et al. (2006) study. The effect estimate for Lipfert et al., (2006a) was posit ive and statistically significant in a single pollutant model, and remained positive (though no longer statistically significant) in a two-pollutant m odel that included traffic density, as well as in a three-pollutant model that included traffic density and PM 10-2.5 . The EPA also acknowledges that this effect estimate repres ents an association for which the deaths

occurred before PM 2.5 measurements were collected, but disagrees with comments that it is inappropriate to consider this study as part of the body of evidence that informed the

EPA’s causal determinations. Although the comments are unpersuasive that this study should be invalidated for purposes of a ssessing causality, the EPA notes that consideration of this study play ed no part in actually determ ining any of the elements of

the revised annual PM 2.5 standard.

(10) Comment: Some commenters contended that PM 2.5 risk estimates are highly sensitive to the approach used to control for temporal trends (API, 2012, Attachment 1pp. 11 to 12; AAM, 2012, pp. 6 to 10). Specifically, the resu lts of the Air Pollution and Health: A European and North American Approach (APHENA) study provided evidence of no effect of short-term PM exposure on mortalit y and morbidity because the “overall pattern [of effects] is not what one would expect if PM health effects associations have a real physiological basis” (AAM, 2012, pp. 6 to 10). AAM stated that this conclusion was supported by the lack of consistent statistical ly significant associations across all models examined. Additionally, API contended that the sensitivity of PM 2.5 risk estimates to the selection of degrees of freedom to control fo r temporal trends was further demonstrated in Dominici et al. (2007) and Ostro et al. (2006).

Response: The EPA disagrees with the commenters’ view that the results from Katsouyanni et al. (2009), Domini ci et al. (2007), and Ostro et al. (2006) demonstrate the sensitivity of PM 2.5 risk estimates to the method used to control for temporal trends and bring into question the associ ation between short-term PM 2.5 exposures and mortality and hospital admissions. Additionally, these commente rs have focused solely on the statistical significance of risk estimates a nd not on the pattern of associ ations across studies as is discussed more fully in response to Comment (1) above.II-31 The APHENA study combined data from exis ting multi-city study databases from the U.S. (the National Morbidity, Mortality, and Air Pollution Study [NMMAPS]), Europe (Air Pollution and Health: A European Appr oach [APHEA]), and Canada to “develop more reliable estimates of the potential ac ute effects of air pollution on human health [and] provide a common basis for [the] co mparison of risks ac ross geographic areas” (Katsouyanni et al., 2009). In an attempt to address both of th ese issues the investigators conducted extensive sensitivity analyses to ev aluate the robustness of the results to different model specifications (e.g., penalized splines vs. natural splines) and the extent of smoothing to control for temporal trends. In models where an appropriate number of degrees of freedom (df) to control for tempor al trends were employed risk estimates were robust across the different model specificat ions. The trend analyses consisted of subjecting the models to varying extent of smoothing selected either a priori (i.e., 3 df/year, 8 df/year, and 12 df/year), which was selected through e xploratory analyses using between 2 and 20 df, or by using the abso lute sum of the residuals of the partial autocorrelation function (PACF). Although the investigators did not identify the model they deemed to be the most appropriate fo r comparing the results across study locations, they did specify that “overall effect estimates (i.e., estimates pooled over several cities) tended to stabilize at high degrees of freedom” (Katsouyanni et al., 2009).

The results of the APHENA study are consistent with those reported by both Dominici et al. (2007) and Ostro et al. ( 2006), which as part of their studies conducted sensitivity analyses to examine the influence of increasi ng the degrees of freedom per year to control for temporal trends on the PM 2.5 -mortality association. In both cases the authors found evidence that as the degrees of freedom per y ear increases a point is reached where risk estimates tend to stabilize, which for both of these studies was approximately 7 degrees of freedom or more per year.

It should be noted that even the commenter s acknowledged that “[i]n most cases, the results and conclusions from these updated an alyses were not significantly altered, but effect estimates were lower” (API, 2012, A ttachment 1, p 12). The EPA, therefore, disagrees with the commenters that the lack of consistent statistically significant results across all models supports the lack of an a ssociation between short-term PM exposure on hospital admissions and mortality. The inconsis tency in the results across some of the models (i.e., for APHENA thos e that controlled for temporal trends using 3 df/year or PACF compared to those that employed 8 or 12 df/year, whil e for Dominici et al. (2007) and Ostro et al. (2006) those less than 7 df/yea r) is due to inadequate control for temporal trends. Additionally, the EPA disa grees with these commenters sole reliance on statistical significance when evaluating the results of these studies. As stated in the response to Comment (1) above, focusing solely on statis tically significance is inappropriate when evaluating a body of studies.

(11) Comment: Multiple commenters (ACC, 2012, pp. 14 to 18; AAM, 2012, pp. 6 to 10) questioned the EPA’s interpretation of results from specific short-term PM 2.5 exposure studies that examined associations with mo rbidity and mortality outcomes. Specifically, these commenters questioned: (a) interpretati on of results from copollutant models; (b) lag selection; (c) the derivation of national ri sk estimates from multicity studies; and (d) the ignoring of evidence indi cating a reduction in PM-mor tality risk over time.II-32 Response: Overall, the EPA disagrees with each of the points raised by the commenters and provides detailed res ponses to each below:

(a) Interpretation of results from copollutant models

The commenters questioned the EPA’s interpre tation of results from the copollutants models examined in Burnett et al. (2004) as we ll as all studies that examined copollutants models based on Ito et al. (2007), which stated that the use of multipollutant models “are a cautionary exercise, and throw into que stion the now commonplace practice of using multipollutant models in health effects analysis.” The EPA disagrees with the commenters’ interpretation of the results from Burnett et al. (2004). The main copollutant analyses conducted over the entire study duration used PM 2.5 data that were not collected every day. As a result, when including PM 2.5 in copollutant analyses with other pollutants that are measured on a daily basis, the overa ll sample size is redu ced, which reduces the precision of resulting effect estimates. Bu rnett et al. (2004) performed a sensitivity analysis that further illustrates this point. When limiting the dataset to days in which daily

PM 2.5 concentrations were available, the PM 2.5 association remained robust after adjustment for NO 2 , while the NO 2 association was attenuated. Ov erall, this result brings into question the results from copollutants analyses including PM 2.5 that is collected every third or every sixth day when other pollutants are collected more frequently.

Finally, the EPA disagrees with the commenters’ interpretati on of the quote from Ito et al. (2007) that they relied on to discredit the results from c opollutant analyses. Ito et al. (2007) cautioned against incl uding all pollutants in one model, which, as they demonstrated can result in “the po llutant that varies least like all the rest of the pollutants, and is least affected by concurvity in such a multi-pollutant model” being the pollutant that looks to be causing the effect. The EPA has emphasized evaluation of models including no more than two pollutants becau se models that included multiple pollutants are difficult to interpret due to the potentia l multicollinearity betw een pollutants. (e.g., U.S. EPA, 2004, sections 8.4.3.2 and 8.4.3.3).

(b) Lag selection

With regard to the lags selected in certain mortality studies (i.e., Franklin et al. 2007), commenters questioned the selection of lag days a priori and not through the use of model fit criteria (ACC, 2012, pp. 14 to 18). As demonstrated in the ISA, studies that

examined the association between short-term PM 2.5 exposure and mortality “were consistently observed at lag 1 and lag 0-1, which have been confirmed through extensive analysis of PM 10 -mortality studies” (U.S. EPA, 2009a, p. 6-200). Therefore, the lag days selected by Franklin et al. (2007) a priori (i.e., lag 0-1) were c onsistent with the large body of evidence that has demonstrated asso ciations between short-term PM exposure and mortality.

(c) Derivation of national risk estimates from multicity studies

Some commenters questioned the derivation of national risk estimates from multi-city studies. Specifically, these commenters questioned the approach employed by studyII-33 investigators to calculate a national estimate, claiming that it did not use the entirety of the community-level data (ACC, 2012, pp. 14 to 18). The EPA disagrees with these commenters understanding of the approach used to calculate nationa l risk estimates in multicity studies. Multi-city studies, in fact, do use the entirety of the dataset to calculate national risk estimates. By calculating city-speci fic risk estimates and then utilizing either a meta-regression or a second stage Bayesian Hierarchical model, investigators use the city-specific estimates to calculate the nationa l risk estimate. Investigators of multi-city studies are not excluding any community-level data, but instead are us ing the totality of data to provide information that is needed to calculate a nation al risk estimate.

(d) Ignoring evidence of a reduction in PM-mortality risk over time

Some commenters also questioned the EPA’ s interpretation of evidence indicating a reduction in PM-mortality risk estimates over tim e, and pointed to the results of Dominici et al. (2007) to support their argument (e.g., ACC, 2012, pp. 14 to 18, NAM et al., 2012, p. 9). At first glance, the resu lts of Dominici et al. (2007) would seem to indicate that PM-mortality risk estimates have declined over time due to the observed decline in the slope for all-cause and cardiorespiratory mortality. However, this analysis was motivated by accountability research and instead of measur ing the impact of a s udden change in air quality, this study attempted to measure the im pact of policy interv entions. As such, “a flaw in the use of the time-series study design for this type of analysis is that it adjusts for long-term trends, and, therefore, does not estimate the change in mortality in response to the gradual change in PM 10 ” (U.S. EPA, 2009a, p. 6-163). Therefore, the EPA disagrees with the commenters. Although this analysis may indicate a sli ght reduction in PMmortality risk estimates over time “the analy tic approach used in the study does not allow for a systematic analysis of the effect of air pollution policies on the risk of mortality” (U.S. EPA, 2009a, p. 6-163).

(12) Comment: In asserting that the uncertainties in the underlying health science are as great or greater than in the last review and therefore do not suppor t revision to the standards at this time, multiple commenters (e.g., API, 2012, pp. 1, 17 to 20, and Attachment 1, pp. 9 to 24, Attachment 7, p. 9, Attachment 9; ACC, 2012, pp. 2 to 7, 14 to 18; NAM et al., 2012, pp. 9, 23; AAM, 2012, pp. 5 to 15; AFPM, 2012, p. 3; Southern Company, 2012, pp. 2 to 3; EPRI, 2012, pp. 1 to 4; Texas CEQ, 2012, pp. 1 to 4; AFPM et al., 201, p. 32)

discussed a number of issues relate d to: (a) copollut ant confounding; (b) ecological/contextual confounding; (c) heter ogeneity in risk estimates, (d) exposure measurement error; (e) model specification; (f) the shape of the concentration-response (C-R) function; and (g) unders tanding the relative toxicity of components within the mixture of fine particles.

Response: The EPA believes that the overall uncertainty about possible health risks associated with both long- and short-term PM 2.5 exposure has diminished since the last review. The EPA disagrees with commenters’ views that the remaining uncertainties in the scientific evidence are too gr eat to support revising the current PM 2.5 NAAQS. The EPA has carefully considered the uncertainties highlighted by commenters in its

evaluation of the scientific evidence as discusse d in section III. D.2 of the preamble to the

final rule and below:II-34 (a) Copollutant confounding

Some commenters asserted that the EPA has not adequately interpreted the results from studies that examined the effect of copo llutants on the relationship between long- and

short-term PM 2.5 exposures and mortality and mo rbidity outcomes (e.g., NAM et al., 2012, p. 23, ACC 2012, pp. 14 to 18). These commenters contended that the EPA has inappropriately concluded that PM 2.5 -related mortality and morbidity associations are generally robust to confounding. The commenters stated that stat istically significant

PM 2.5 associations in single-pollutant models in epidemiological studies do not remain statistically significant in copollutant models.

The EPA recognizes where PM 2.5 and other pollutants are hi ghly correlated, it can be difficult to distinguish effects of the various po llutants in copollutant models. The loss of statistical significance or the reduction in the magnitude of the effect estimate when a copollutant model is used may be the resu lt of factors other than confounding. These changes do not prove either the existence or absence of confounding. These impacts must

be evaluated in a broader context that consid ers the entire body of evidence. The broader

examination of this issue in the ISA include d a focus on evaluating the stability of the

size of the effect estimates in epidemiological studies c onducted by a number of research groups using single- and co-pollutant models (U.S. EPA, 2009a, sections 6.2.10.9, 6.3.8.5, and 6.5, Figures 6-5, 6-9, and 6-15). Th is examination found that, for most epidemiological studies, there was little change in effect estimates based on single- and copollutant models, although the ISA r ecognized that in some cases, the PM 2.5 effect estimates were markedly reduced in si ze and lost statistical significance.

In questioning the influence of co-pollutants on associations observed in short-term PM exposure and mortality studies, commenters highlighted the lack of control for copollutants in Dominici et al. (2003, 2007) and Frankl in et al. (2007). The EPA recognized that a limitation of the multi-cit y studies that examined the association

between short-term PM 2.5 exposure and mortality evaluate d in the ISA was the relative lack of copollutant analyses. This lim itation was mentioned when evaluating the collective evidence and forming the causality de termination for mortality. In Chapter 2 of the ISA (U.S. EPA, 2009a, p. 2-11), the EPA stated, “Although recently evaluated U.S.- based multi-city studies did not analyze potential confounding of PM 2.5 risk estimates by gaseous pollutants, evidence from the limited number of single-city studies evaluated in the 2004 PM AQCD (U.S. EPA, 2004) suggest that gaseous copollu tants do not confound

the PM 2.5 -mortality association. This is further supported by studies that examined the

PM 10 -mortality relationship”, which were di scussed in section 6.5.2.1 of the ISA (U.S. EPA, 2009a).

These commenters also questioned the lack of copollutant analyses in long-term exposure and mortality studies. The EPA recognizes that a limited number of studies investigating the association between long-term exposure to PM 2.5 and mortality have included copollutant models. As discussed in the pr evious review, the analysis of multiple pollutants from the ACS cohort observed incr eases in two-pollutant models that incorporated CO, NO 2 , and ozone, and were reduced only for models that incorporated

SO 2 (Krewski et al. 2000). The 2004 AQC D recognized, however, that SO 2 is a precursorII-35 for fine particle sulfates, which complicates the interpretation of copollutant model results. In a follow-up study of the ACS cohort restricted to just Lo s Angeles, CA (Jerrett et al. 2005), the authors observed that O 3 “did not confound the relationship between particles and mortality.” Si milarly, analysis of the AHS MOG cohort (Chen et al. 2005)

found that the association between mo rtality and long-term exposure to PM 2.5 became stronger when O 3 and SO 2 were included in copollutants models, and the association for

PM 2.5 did not change when NO 2 was included in co-pollutants models. The results of these studies provide confidence that more recent reports with updated datasets are showing independent effects of PM 2.5

.

The EPA notes that these public comments do not adequately reflect the complexities inherent in assessing the issue of copolluta nt confounding. As discussed in the proposal (77 FR 38907, 38909, and 38910) and more fully in the ISA (USEPA, 2009a, sections 6.2, 6.3, and 6.5), although copolluta nt models may be useful tools for assessing whether gaseous copollutants may be potential confounde rs, such models alone cannot determine whether copollutants are in fact confounders . The EPA believes that observing robust effect estimates after examination of copollu tant models provides greater confidence in

the observed associations between sh ort- and long-term exposures to PM 2.5 and mortality and morbidity, while recognizing that pot ential confounding by copo llutants remains a very challenging issue to addr ess, even with well-designed studies. Interpre tation of the results of copollutant models is complicat ed by correlations that often exist among air pollutants, by the fact that some pollutants pl ay a role in the atmospheric reactions that form other pollutants such as secondary fine particles, and by the st atistical power of the studies in question inherent in the study methodology. For example, as discussed in response to Comment (12)(a) above, the every- third or sixth-day sampling schedule often employed for PM 2.5 compared to daily measurements of gaseous copollutants drastically reduces the overall sample size to asse ss the effect of copollutants on the PM 2.5 -morbidity or mortality relationship, such that the reduced sample size can lead to less precise effect estimates (e.g., wider confiden ce intervals, as demonstrated in Burnett et al. (2004)).

The EPA recognizes that when PM 2.5 is correlated with gaseous pollutants it can be difficult to identify the effect of individua l pollutants in the ambient mixture (77 FR 38910). However, based on the available evidence, the EPA concludes epidemiological studies continue to suppo rt the conclusion that PM 2.5 associations with mortality and morbidity outcomes are robust to the inclus ion of gaseous copollutants in statistical models. The EPA evaluated the potential confounding effects of gaseous copollutants and, although it is recognized that uncertainti es and limitations still remain, the Agency concluded the collective body of sc ientific evidence is “stronge r and more consistent than in previous reviews providing a strong basi s for decision making in this review" (77 FR 38910/1).

(b) Ecological/contextual confounding

Some commenters contended that both short- and long-term PM 2.5 exposure studies of mortality did not appropriately control for ecological or contextual confounders (ACC, 2012, p. 3; API, 2012, Attachment 1, p. 14; NAM et al., 2012, p. 23).II-36 In the case of short-term exposure studies, an ecological confounder would need to vary on a day-to-day basis with both air pollution a nd with the specific health outcome being evaluated (e.g., mortality or hospital admissi ons or emergency department visits). The

confounders that fit these criteria for short- term exposure studies ar e related to weather (e.g., temperature, dew point, relative humi dity). The short-term exposure studies, specifically time-series studies, evaluated in the ISA all included weather covariates in their models to account for their potential confounding effects (U.S. EPA, 2009a, Chapter 6).

With regard to long-term exposure studies, a number of multilevel cohort studies (Naess et al. 2007; Jerrett et al. 2003; Jerrett et al. 2005) have ev aluated individual-level and contextual, or ecologic-level va riables as potential confounders. As reported in Jerrett et al. (2005), “Contextual effects occur when i ndividual differences in health outcomes are associated with the grouped variables that represent the social, economic, and environmental settings where the individuals live, work, or spend time (e.g., poverty or crime rate in a neighborhood). These contextu al effects often operate independently from (or interactively with ) the individual-level variables such as smoking.” These studies

found that the inclusion of cont extual variables tended to at tenuate the risk estimates for the association between long-term exposure to PM 2.5 and mortality, but that an independent effect of PM 2.5 on mortality remains. For exam ple, Jerrett et al. (2005) found

that for PM 2.5 (controlling for age, sex, and race), the relative ri sk was 1.24 (95% CI 1.11, 1.37) for a 10 μg/m 3 exposure contrast. In a parsimoni ous model that controlled for 44

different individual covariates and ecological confounder variab les that both reduced the pollution coefficient and had associations w ith mortality, the rela tive risk was 1.11 (95% CI 0.99, 1.25) for the same exposure contrast. Th e EPA believes that the results of these studies provide confidence that more recent reports with updated datasets are showing independent effects of PM 2.5

.

Additionally, commenters contended that non -traditional confounders have not been accounted for in epidemiological studies of short- and long-term exposure to air pollution, which could confound the associa tions observed (API, 2012, Attachment 1, p. 14). These confounders include physical and ps ychological population stress factors. The EPA disagrees with these commenters because : (1) there is very limited evidence of stress affecting the air pollution-health e ffect relationship upon which to base the commenters assertion; (2) in order for stress to be a true confounder it would need to vary temporally (for short-term exposure studies ) and spatially (for long-term exposure studies) with both air pollution c oncentrations and the health e ffect of interest, which has not been demonstrated; and (3) rather than st ress acting as a true confounder, more than likely stress is on the causal pathway to the hea lth effects that have been observed to be associated with air pollution. The EPA acknowle dges that stress may contribute bias to epidemiological studies; however, stress more than likely would influence the magnitude of individual effect estimates in a single-c ity or multi-city study and not the trends of positive associations observed across studies conducted in multiple locations.

(c) Heterogeneity in risk estimates

Some commenters argued that the heterogeneity in risk estimates observed in multi-cityII-37 epidemiological studies and the lack of statistical significance in many regional or seasonal estimates highlights a potential bi as associated with combined multi-city epidemiological study results (e.g., API, 2012, Attachment 1, pp. 15 to 19). Additionally,

these commenters contended that the wide range of individual city results in these multicity studies, specifically NMMAPS, demonstrat ed a biologically im plausible wide range of associations (e.g, AAM, 2012, pp. 6 to 10) . One commenter asserted, “there is overwhelming epidemiologic evidence, dating back to 2000, which shows clear and large geographic variation in PM 2.5 mortality risk across the United States. The PM 2.5 mortality risk is much stronger in the eastern portion of the US than in the western portion of the

U.S. and there is no PM 2.5 mortality risk in Californ ia” (Enstrom, 2012, p. 1). Other commenters further argued that more refine d intra-urban exposure estimates conducted for two of the largest cities included in the ACS study, Los Angeles and New York City, based on land-use regression models and/or kreiging methods (Krewski et al., 2009a) “underscore the importance of considering city-specific health estimates, which may account for heterogeneity in PM 2.5 concentrations or other differences among cities, rather than relying on pooled nationwide results from multi-city studies” (API, 2012, Attachment 1, p. 17).

With respect to understanding th e nature and magnitude of PM 2.5 -related risks, the EPA agrees that epidemiological st udies evaluating health effect s associated with long- and

short-term PM 2.5 exposures have reported heterogene ity in responses between cities and effect estimates across geographic regions of the U.S. (U.S. EPA, 2009a, sections 6.2.12.1, 6.3.8.1, 6.5.2, and 7.6.1; U.S. EPA, 2011a, p. 2-25). For example, when focusing on short-term PM 2.5 exposure, the ISA found that multi-city studies that examined associations with mortality and cardiovascular and respiratory hospital admissions and emergency department visits de monstrated greater ca rdiovascular effects in the eastern versus the western U.S. (Domin ici, et al., 2006a; Bell et al., 2008; Franklin et al. (2007, 2008)). However, the rationale that heterogeneity in risk estimates presents a potential bias as posed by the commenters is simplistic and does not account for a

number of factors that have been shown to influence city-specific risk estimates in epidemiologic studies. As discussed in th e ISA, the EPA recogni zes that there are compositional differences in PM 2.5 across the country and that the county-level air quality data used in epidemiological studies may re sult in exposure error, which could in part account for variability in city-specific risk estimates (U.S. EPA, 2009a, section 2.3.2).

There are a limited number of studies that evaluated regional heterogeneity in the association between long-term exposure to PM 2.5 and mortality. Krewski et al. (2009a) conducted subset analyses of the ACS cohort in Los Angeles, CA and New York City, NY, and observed a relative risk in Los Angele s that was greater in magnitude than what was observed in the full ACS cohort, while the relative risk in New York City was less

than what was observed in the full ACS cohort. These observations are likely due to the greater spatial heterogeneity in PM 2.5 concentrations observed in Los Angeles, and the overall spatial homogeneity of PM 2.5 concentrations in New York City.

In another retrospectiv e cohort, Zeger et al. (2008) obser ved associations between longterm exposure to PM 2.5 and mortality for the eastern a nd central ZIP codes that were similar to those reported in the ACS and Harvard Six Cities studies, though noII-38 association was observed in the western region. The lack of the association in the western region is “largely because the Los Angeles basin counties (California) have higher PM levels than other West Coast urban centers, but not higher adjusted mortality rates” (Zeger et al. 2008). The ISA also evaluate d studies that provided some evidence for

seasonal differences in PM 2.5 risk estimates, specifically in the northeast. The ISA found evidence indicating that individuals may be at greater risk of dying from higher exposures to PM 2.5 in the warmer months, a nd at greater risk of PM 2.5 associated hospitalization for cardiovascular and respirat ory diseases during colder months of the year. The limited influence of seasonality on PM risk estimates in other regions of the U.S. may be due to a number of factors including varying PM composition by season, exposure misclassification due to regional tendencies to sp end more or less time outdoors and air conditioning usage, and the prevalence of infectious diseases during the winter months (U.S. EPA, 2009a, p. 3-182).

Overall, the EPA recognizes that uncertainties still remain re garding various factors that contribute to heterogeneity observed in epidemiological studies (77 FR 38909/3). Nonetheless, the EPA recognizes that this hete rogeneity could be attr ibuted, at least in part, to differences in PM 2.5 composition across the U.S ., as well as to exposure differences that vary regionally such as personal activity patter ns, microenvironmental characteristics, and the spatial variability of PM 2.5 concentrations in urban areas (U.S. EPA, 2009a, section 2.3.2; 77 FR 38910).

As recognized in the PA, the current epidemio logical evidence and the limited amount of city-specific speciated PM 2.5 data does not allow conclusions to be drawn that specifically

differentiate effects of PM in differe nt locations (U.S. EPA, 2011a, p. 2-25). Furthermore, as discussed in section III.E.1 of the preamble to the final rule, the ISA concluded, “that many constituents of PM 2.5 can be linked with multiple health effects, and the evidence is not yet sufficient to allo w differentiation of those constituents or sources that are more closely related to sp ecific health outcomes” (U.S. EPA, 2009a, p. 2- 17). CASAC thoroughly reviewed the EPA’s pr esentation of the sc ientific evidence indicating heterogeneity in PM 2.5 effect estimates in epidemiological studies and

concurred with the overall conclu sions presented in the ISA.

(d) Exposure measurement error

Industry commenters argued th at the EPA did not adequa tely consider exposure measurement error, which they asserted is an important source of bias in epidemiological

studies that can bias effect estimates in either direc tion (e.g., API, 2012, Attachment 1, pp. 19 to 20).

The EPA agrees that exposure measurement error is an important source of uncertainty, and that the variability in risk estimates obser ved in multi-city studies could be attributed, in part, to exposure error due to measuremen t-related issues (77 FR 38910). However, the Agency disagrees with the commenters’ asse rtion that exposure measurement error was not adequately considered by EPA in this review. The ISA included an extensive

discussion that addresses issues of e xposure measurement error (U.S. EPA, 2009a, sections 2.3.2 and 3.8.6). Exposure measuremen t error may lead to bias in effectII-39 estimates in epidemiological studies. A number of studies evaluated in the last review (U.S. EPA, 2004, section 8.4.5) and in the cu rrent review (U.S. EPA, 2009a, section 3.8.6) have discussed the direction and magn itude of bias resulting from specified patterns of exposure measurement error (Arm strong 1998; Thomas et al. 1993; Carroll et al. 1995) and have generally concluded “classi cal” (i.e., random, within-person) exposure

measurement error can bias effect estimates to wards the null. Therefore, consistent with conclusions reached in the last review, the ISA concluded “in most circumstances, exposure error tends to bias a health effect estimate downward ” (U.S. EPA, 2009a, sections 2.3.2 and 3.8.6). Thus, the EPA has both considered and accounted for the possibility of exposure measurement error, and the possible bias would make it more difficult to detect true associations, not less difficult.

Additionally a commenter specifically questio ned the influence of exposure measurement error on the results from epidemiological analyses by referenci ng a study conducted by Sarnat et al. (2009) (API , 2012, Attachment 1, p. 19). Th is commenter stated:

Sarnat et al . (2009) found that personal exposures to sulfate (a major component

of PM 2.5 in certain parts of the country), av eraged over time, varied by individual, city and season, and this vari ability can lead to CRFs that do not represent the true relationship between exposure and outcome. These factors may bias the results of an epidemiology analysis in either direct ion and are particular ly relevant for longterm studies (for which these f actors likely vary over time).

The EPA disagrees with the interpretation of Sarnat et al. (200 9) by the commenter. Sarnat et al. (2009) describe s variability in the use of home ventilation (i.e., air conditioning) as a key factor contributing to bo th the bias and the variability in personal exposure. Air conditioning usage varies by in dividuals and between cities. Use of air conditioning results in the intr oduction of less outdoor air to the indoors, resulting in the central-site monitoring value overestimating ex posure. In an epidemiological analysis,

this condition causes the effect estimate to be biased towards the null, with some variability. Given the limiting condition that the maximum indoor concentration of ambient PM is that of the outdoors, the exposur e error would not be expected to bias the effect estimate away from the null. Moreover, Sarnat et al. (2009) di d not assert that the bias can go in either direction.

(e) Model specification

Commenters contended that th e EPA did not account for th e fact that “selecting an appropriate statistical model for epidemiol ogic studies of air po llution involves several choices that involve much ambiguity, scant biological evidence, and a profound impact on analytic results, given that many estimat ed associations are weak” (ACC, 2012, p. 5) For short-term exposure studies, the EPA rec ognizes, as summarized in the HEI review panel commentary that selecting a level of control to adjust for time-varying factors, such as temperature, in time-series epidemiologi c studies involves a tr ade-off (HEI, 2003). For example, if the model does not sufficiently ad just for the relationship between the health outcome and temperature, some effects of te mperature could be falsely ascribed to the pollution variable. Conversely, if an overly aggressive approa ch is used to control forII-40 temperature, the result would possibly undere stimate the pollution-related effect and compromise the ability to detect a small but true pollution effect (U.S. EPA, 2004, p. 8- 236; HEI, 2003, p. 266). The selection of approach es to address such variables depends in part on prior knowledge and judgments made by the investigators, for example, about weather patterns in the study area and expect ed relationships between weather and other time-varying factors and health outcomes considered in th e study. As demonstrated in section 6.5 of the ISA, the EPA thoroughly considered each of these issues and the overall effect of different model specifica tions on the association between short-term

PM 2.5 exposure and mortality. Regardless of the model employed, consistent positive

associations were observed across studies th at controlled for the potential confounding effects of time and weather using different approaches (e.g., U.S. EPA 2009a, Figure 6- 27, with additional details found in Appendix E, section E.3, Table E-16,). The EPA also considered the influence of model specifi cation in the examination of long-term PM 2.5 exposure studies. For example, in section 7.6, Figures 7-6 and 7-7, the ISA summarized

the collective evidence that evaluate d the association between long-term PM 2.5 exposure and mortality. Regardless of the model used, these studies collectively found evidence of consistent positive associations between long-term PM 2.5 exposure and mortality.

The EPA, therefore, disagrees with comm enters that model specification was not considered when evaluating the epidemio logic evidence used to form causality determinations. The EPA specifically points out that the process of assessing the scientific quality and relevan ce of epidemiologic studies includes examining “important methodological issues (e.g., lag or time pe riod between exposure and effects, model specifications, thresholds, mortality displacement) related to interpretation of the health evidence (U.S. EPA, 2009a, p. 1-9).” Consis tent with the conclusions of the 2004 PM AQCD, the EPA recognizes that there is still no clear consensus at this time as to what constitutes appropriate contro l of weather and temporal tr ends in short-term exposure studies, and that no single statis tical modeling approach is lik ely to be most appropriate in all cases (U.S. EPA, 2004, p. 8-238). Howe ver, the EPA believes that the available evidence interpreted in light of these rema ining uncertainties does provide increased

confidence relative to the last review in the reported associations between short- and long-term PM 2.5 exposures and mortality and morbidit y effects, alone and in combination with other pollutants.

(f) Shape of the concentrati on-response relationship

With regard to the C-R relationship, comme nters questioned the interpretation of the shape of the C-R relationship, specifically st ating that multiple studies have demonstrated

that there is a threshold in the PM-health e ffect relationship and th at the log-linear model is not biologically plausi ble (API, 2012 pp. 17 to 20; API, 2012, Attachment 9; ACC, 2012, Appendix A, pp. 7 to 8). The EPA disagree s with this asserti on due to the number

of studies evaluated in the ISA that conti nue to demonstrate a no- threshold log-linear model most adequately represen ts the PM concentration-resp onse relationship (U.S. EPA, 2009a, section 2.4.3). While recognizing that uncer tainties remain, the EPA believes that our understanding of this issu e for both long-and short- term exposure studies has

advanced since the last review. As discu ssed in the ISA, both long- and short-term exposure studies have employed a variety of statistical appr oaches to examine the shapeII-41 of the concentration-respons e function and whether a thre shold exists. While the EPA recognizes that there likely are individua l biologic thresholds for specific health responses, the ISA concluded the overall evid ence from existing epidemiological studies does not support the existence of thresholds at the population le vel, for effects associated with either long- or short-term PM exposures within the ranges of air quality observed in these studies (U.S. EPA, 2009a, section 2.4.3). While epidemiological analyses have not identified a population threshold in the range of air quality concentr ations evaluated in these studies, the EPA recognizes that it is possible that such thresholds exist towards the lower end of these ranges (or below these ra nges). This would be a concentration far

lower than the level of the re vised annual standard. The ISA c oncluded that this evidence collectively supported the conc lusion that a no-threshold, log-linear model is most appropriate (U.S. EPA, 2009a, sec tions 6.2.10.10, 6.5.2.7, and 7.6.4). CASAC likewise advised that “[a]lthough there is increasing uncerta inty at lower levels, there is no evidence of a threshold (Samet, 2010d, p. ii).

The EPA recognizes that some short-term e xposure studies have examined the PM C-R relationship in individual cities or on a city-to-city basis and observed heterogeneity in the shape of the C-R curve across cities. As discussed in (b) above, these findings are a source of uncertainty that the EPA agrees re quires further investigation. Nonetheless, the

ISA concluded that “the studi es evaluated further support th e use of a no-threshold, loglinear model, but additional issu es such as the influence of heterogeneity in estimates

between cities and the e ffects of seasonal and regional differences in PM on the concentration-response-relations hip still require further inve stigation” (U.S. EPA, 2009a, p. 2-25).

(g) Relative toxicity of components

Some commenters highlighted uncertainties in understand ing the role of individual constituents within the mix of fine partic les. These commenters asserted that a massbased standard may not be appropriate due to the growing body of evidence indicating

that certain PM 2.5 components may be more closely related to specific health outcomes (e.g., elemental carbon (EC) and orga nic carbon (OC)) (EPRI, 2012, p. 2).

With regard to questions about the role of i ndividual constituents within the mix of fine particles, as a general matte r, the EPA recognizes that a lthough new research directed toward this question has been conducted si nce the last review, important questions remain and the issue remains an importan t element in the Agency’s ongoing research program. At the time of the last review, the Agency determined that it was appropriate to continue to control fine part icles as a group, as opposed to singling out any particular component or class of fine particle s (71 FR 61162 to 61164, October 17, 2006). This distinction was based largely on epidemiological evidence of health effects using various indicators of fine particles in a large number of areas that had signi ficant contributions of differing components or sources of fine pa rticles, together with some limited experimental studies that provided some evid ence suggestive of health effects associated with high concentrations of numero us fine particle components.

In this review, as discussed in the proposal (77 FR 38922 to 38923) and in section III.E.1II-42 preamble to the final rule, while most epidemio logical studies continue to be indexed by

PM 2.5 mass, several recent epid emiological studies included in the ISA have used PM 2.5 speciation data to evaluate hea lth effects associated with fine particle exposures. In the ISA, the EPA thoroughly evaluated the scientif ic evidence that examined the effect of

different PM 2.5 components and sources on a variet y of health outcomes (U.S. EPA, 2009a, section 6.6) and observed that the availa ble information continues to suggest that many different chemical components of fine pa rticles and a variety of different types of source categories are all associated with, and probably contribute to, effects associated

with PM 2.5 . The ISA concluded that the current body of scientific evidence indicated that “many constituents of PM can be linked with differing health effects and the evidence is not yet sufficient to allow differentiation of t hose constituents or sources that are more closely related to specific health out comes” (U.S. EPA, 2009a, p. 2-26 and 6-212). Furthermore, the PA concluded that the eviden ce is not sufficient to support eliminating any component or group of components associ ated with any specific source categories from the mix of fine par ticles included in the PM 2.5 indicator (U.S. EPA, 2009a, p. 2-56). CASAC agreed that it was reasonable to retain PM 2.5 as an indicator for fine particles in this review as “[t]here was insufficient peer-reviewed literature to support any other indicator at this time” (Samet, 2010c, p. 12).

This information is relevant to the Agency’s decision to retain PM 2.5 as the indicator for fine particles as discussed in section III.E.1 of the preamble for the final rule. The EPA also believes that it is relevant to the Agen cy’s conclusion as to whether revision of the suite of primary PM 2.5 standards is appropriate. While there remain uncertainties about

the role and relative toxicity of various components of fine PM, the current evidence continues to support the view that fine pa rticles should be addressed as a group for purposes of public health protection and that “many constituents of PM can be linked with differencing health effects and the evidence is not yet sufficient to allow

differentiation of those constituents or source s that are more closely related to specific health outcomes” such that it is inappr opriate to remove any constituent of PM 2.5 from the standard (U.S. EPA, 2009a, 2- 17; U.S. EPA, 2011a, p. 2-25).

In summary, in considering the above issu es related to uncerta inties in the underlying health science, on balance, the EPA believes that the available evidence interpreted in light of these remaining uncertainties does pr ovide increased confidence relative to the last review in the reported associa tions between long- and short- term PM 2.5 exposures and mortality and morbidity effects, alone a nd in combination with other pollutants, and supports stronger inferences as to the causal nature of th e associations. The EPA also believes that this increased confidence, wh en taken in context of the entire body of available health effects evidence and in lig ht of the evidence from epidemiological

studies of associations observed in areas meeting the current primary PM 2.5 standards, specifically in areas meeting the current primary annual PM 2.5 standard, adds support to

its conclusion that the current suite of PM 2.5 standards needs to be revised to provide increased public health protection from exposure to all types of PM 2.5

.

(13) Comment : In asserting that there is no evidence of greater risk since the 2006 review to justify lowering the current annual PM 2.5 standard, some commenters argued that, “if the current primary PM 2.5 annual standard of 15 μg/m 3 was considered to be adequatelyII-43 protective of public health in 2006, given rela tive risk estimates that EPA was using at that time, then that standard would surely still be adequately pr otective of the public

health if relative risk estimates remain at the same level (or lower)” (UARG, 2012, Attachment 1, p. 24). These commenters compared risk coefficients used for mortality in

the EPA’s risk assessment done in the last revi ew with those from the Agency’s core risk assessment done as part of this review, and th ey concluded that “the entire range of the core relative risk for long-term mortality is lower now than it was in the prior review” (UARG, 2012, Attachment 1, p. 24). These commen ters used this conclusion as the basis

for a claim that there is no reas on to revise the current annual PM 2.5 standard.

Response: The EPA believes that this claim is fundamentally flawed. In comparing the

scientific understand ing of the risk presented by exposure to PM 2.5 between the last and current reviews, one must examine not only th e quantitative estimate of risk from those exposures (e.g., the numbers of premature d eaths or increased hospital admissions at various concentrations), but al so the degree of confidence that the Agency has that the observed health effects are causally linked to PM 2.5 exposure at those concentrations. As

documented in the ISA and in the recommenda tions and conclusions of CASAC, the EPA recognizes significant advances in our unde rstanding of the he alth effects of PM 2.5 , based on evidence that is stronger than in the last review. As a result of these advances, the

EPA is now more certain that fine particles, alone or in combination with other pollutants, present a significant risk to pub lic health at concentr ations allowed by the current primary PM 2.5 standards. From this more comprehensive perspective, since the risks presented by PM 2.5 are more certain, similar or ev en somewhat lower relative risk

estimates would not be a basis to concl ude that no revision to the suite of PM 2.5 standards is “requisite” to protect public health with an adequate margin of safety. The comment also ignores that the relative risk estima te is only one factor considered by the Administrator. Most obviously, it ignores th at epidemiological studies since the last

review indicate associations between PM 2.5 and mortality and morbidity in areas meeting

the current annual standard.

In any case, the commenters’ reliance on the flawed 2006 review is badly misplaced. As discussed in section III.A.2 of the preamble to the final rule, the D.C. Circuit remanded

Administrator Johnson’s 2006 decision to retain the primary annual PM 2.5 standard because the Agency failed to adequately explain why the annual standard provided the requisite protection from both short- and long-term exposure to fine particles including protection for at-risk populations. The EPA, in fact, knows of no legitimate explanation. The 2006 standard was also at sharp odds w ith CASAC advice and recommendations as to the requisite level of protection (Henderson, 2006a,b). The judgment of the thenAdministrator that the 2006 primary annual PM 2.5 standard was requisite to protect public health with an adequate margin of safety is thus not precedential a nd is an inappropriate benchmark for the comparison drawn in the comments.

(14) Comment: One group of commenters who argued that a revised annual standard was not necessary to protect the public health asserted that the propo sed standard was “far more stringent that the standards in other industrialized count ries” (NAM et al., 2012, p.5). These commenters cited to standards set by the European Union a nd Japan Ministry of

the Environment . Id.II-44 Response: In considering these comments, as discussed in Comment (3) in section II.B.1.a above, the EPA notes that the Admini strator’s decision on setting an appropriate annual standard level is constrained by the pr ovision of the CAA that requires that the primary NAAQS be requisite to protect public he alth with an adequate margin of safety. This requires that her judgment is to be ba sed on an interpretati on of the evidence that neither overstates nor understates the streng th and limitations of the evidence, or the appropriate inferences to be drawn from the evidence. This is not the same legal framework that governs the standards se t by the European Union or Japan.

As discussed in section III.E.4.d of the preambl e for the final rule, the Administrator has considered the epidemiological and other scient ific evidence, estimates of risk reductions associated with just meeting alternative standa rds, air quality analys es, related limitations and uncertainties, the advice of CASAC, a nd the extensive public comments on the proposal in reaching her conclusions regardi ng final decision on the appropriate primary

PM 2.5 standard levels, consistent with the requirements of the CAA.

(15) Comment : Some of these commenters also identifi ed “new” as well as older studies that had been included in prior reviews as provi ding additional evidence that the causality determinations presented in the ISA did not consider the totality of the scientific literature, further s upporting their view that revision of the PM 2.5 NAAQS is inappropriate.

Response: As discussed in section II.B.3 of the pr eamble to the final rule and in section II.B.1.a above, the EPA notes that, as in pa st NAAQS reviews, the Agency is basing the

final decisions in this review on the studies and related information included in the PM ISA that have undergone CASA C and public review, and will consider newly published studies for purposes of decision making in th e next PM NAAQS review. Nonetheless, in provisionally evaluating commenters’ argumen ts, the EPA notes that its provisional

assessment of “new” science found that such studies did not materially change the conclusions reached in the ISA (U.S. EPA, 2012b).

2. Indicator

The EPA received comparatively few public co mments on issues related to the indicator for fine particles. No public comments were s ubmitted regarding the use of a different size cut for fine particles. Public comments from all ma jor public and private sector groups received on the proposal were generally in favor of the EPA’s proposal to retain PM 2.5 as the indicator for fine particles. In addition to the responses contai ned in section III.E.1 of the preamble to the final rule, the EPA provides the following responses to sp ecific issues related to the indicator for fine particles.

(1) Comment: Some commenters emphasized the need to conduct additional research to more fully understand the effect of specific PM 2.5 components and/or sources on public health. These commenters expressed views about the importance of evaluating health

effect associations with vari ous fine particle components and types of source categories as a basis for focusing ongoing and future research to reduce uncertainties in this area and for considering whether alternat ive indicator(s) may be appropria te to consider in futureII-45 PM NAAQS reviews for standards intended to pr otect against the array of health effects

that have been associated with fine particles as indexed by PM 2.5 . For example, the PSR encouraged more research and monitoring related to PM 2.5 components and noted the importance of components associated with coal combustion (PSR, 2012, pp. 5 to 6). EPRI asserted that “new” studies support fo cusing on elemental carbon (EC) and organic carbon (OC) and encouraged the EPA to seri ously consider the mass-based approach (EPRI, 2012, p. 2). Likewise, Georgia Mini ng Association (GMA) supported additional monitoring and research efforts related to PM 2.5 composition and specifically encouraged the evaluation of using particle number (e .g., particle count) (GMA, 2012, pp. 2 to 3). ALA et al. argued that causal conclusions of an European expert elicitation workshop (Knol et al., 2009) are stronger than the causa l determinations reached in the ISA for ultrafine particles. These commenters suggest ed that “action is needed to establish ambient air quality standards fo r ultrafines in the next revi ew cycle” (ALA et al., 2012, p. 21). One group of commenter st ated “Further delay in moving the process forward of acquiring the necessary data and beginning the long process of establishing and implementing a standard for ultrafine particle s/nano particles repres ents an unacceptable

health risk to the nation” (Sammons, et al., 2012, p. 6).

Response: The Administrator agrees with these comm enters that the results of additional research and monitoring efforts will be help ful for informing future PM NAAQS reviews. Section 2.5 of the PA highlighted areas fo r future health-related research, model development, and data collection activities and recognized that “these efforts, if undertaken, could provide im portant evidence for information future PM NAAQS reviews, and, in particular, consideration of possible alternative indicators, averaging times, and/or levels” (U.S. EPA, 2011a, p. 2-106). The EPA recognizes that information from such studies could also help inform th e development of strate gies that emphasize control of specific types of emission sources so as to address particles of greatest concern to public health.

These views are consistent with comments offered by CASAC. In general, “CASAC urges the Agency to reinvigorate research that might lead to new indicators that my be more directly linked to the health ad welfare effects associated with ambient

concentrations of PM. CASAC also suggests the ongoing collection of more comprehensive PM monitoring data, including expanding the range of sizes to provide information in the ultrafine particle ra nge, and adding measurements of numbers, chemistry, species, and related emissions ch aracteristics of part icles” (Samet, 2010d, p. iii). More specifically, CASAC asserted that “PM 2.5 has been a useful surrogate index since it was adopted in the 1997 PM NAA QS promulgation, but may become an increasingly inadequate inde x of health risk as the ma ss concentration limits are

reduced...While research evidence on PM and he alth has evolved, we urge the Agency to undertake additional efforts to leverage the ga ins made thus far. Now is the time to look ahead to future review cycles and reinvi gorate support for the development of evidence that might lead to newer indicators that may correlate better with the health effects

associated with ambient air concentrations of particulate matter (PM) and for more comprehensive PM monitoring data, including expanding the range of sizes, and adding measurements of numbers, chemistry, species , and related emissions characteristics of particles. There is an inherent feedback in the cycle from research to policy formulationII-46 whereby researchers use the monitoring data that are gathered primarily for regulatory purposes with available indicators, and, in tu rn, expand the scientific basis for regulation. If EPA initiates efforts with air pollution re search and monitoring communities now to create a more robust monitoring platform for research, the Agency will be better positioned to make an evidence-based transition to the ‘next generation’ of indicators of PM-related health risks” (Samet, 2010c, p. 2).

See also response to Comment (12)(g) in section II.B.1.b above.

3. Averaging Time

The EPA received few comments on the issue of averaging time for the PM 2.5 primary standards. One specific significan t comment is addressed below.

(1) Comment: As discussed in section III.E.2 of the preamble to the final rule, the EPA received no significant comments on the approp riateness of either the 24-hour or annual averaging times for the PM 2.5 primary standards. However, one group representing several States (i.e., NESCAUM, 2012) sugge sted consideration of a rolling 24-hour average, rather than a midnight-to-midni ght 24-hour average, for the 24-hour PM 2.5 standard. In justifying this recommendati on, NESCAUM noted that using a rolling 24- hour average, rather than the current midnight-to-midnight average, “would be particularly helpful in providi ng better public health protecti on in areas where there is the potential for seasonal overnight PM 2.5 events (e.g., from woodsmoke).”

Response: The EPA agrees with NESCAUM that it is appropriate in this review to increase public health protection against exposures to PM 2.5 . As discussed in the preamble to the final rule (sect ion III.E.4.c.ii), the Administ rator has judged it appropriate to achieve such an increase in public health protection by lowering th e level of the annual

PM 2.5 standard and retaini ng the current 24-hour PM 2.5 standard. These judgments reflect in large part the Administrato r’s consideration of ambient PM 2.5 concentrations in the locations where long-term and short-term PM 2.5 health studies have been conducted. The

PM 2.5 concentrations reported in these study locations are based on midnight-to-midnight sampling.

Altering the sampling time period for the 24-hour PM 2.5 standard, as suggested by these commenters, would alter the PM 2.5 concentrations reported and, thus, would alter the degree of health protection provided by the 24- hour standard. As di scussed in section II.A of the preamble to the final rule, the CAA charges the Administrator with setting NAAQS that are “requisite” (i.e., neither mo re nor less stringent than necessary) to protect public health with an adequate margin of safety. In setting such standards, the Administrator must weigh the available scie ntific evidence and information, including

associated uncertainties and limitations. In reaching her proposed decisions on the PM 2.5 standards that would provid e “requisite” protection, th e Administrator carefully

considered the available scie ntific evidence and risk info rmation, making public health policy judgments that, in her view, neither overstated nor understa ted the strengths and

limitations of that evidence and informa tion. Commenters have not provided new information or analyses to support the appropr iateness of the changes in public healthII-47 protection that could result fr om their recommended alterations in the sampling time period.

4. Form

The EPA received a number of public comments on the appropriate forms for the PM 2.5 standards, primarily related to the spatial averaging provisions within the form of the annual standard. Few public commenters commented specifically on the form of the 24-hour standard. None of the public commenters raised objections to continuing the use of a concentration-based

form for the 24-hour standard.

Incorporating responses contai ned in sections III.E.3.a a nd III.E.3.b of the preamble to the final rule, the EPA provides the following res ponses to specific comments related to the form of (a) the annual PM 2.5 standard and (b) the 24-hour PM 2.5 standard.

a. Annual Standard

(1) Comment: Of the commenters noted in section III. D.2 of the preamble to the final rule

and in section II.B.1.a above who supported a more stringent annual PM 2.5 standard,

those who commented on the form of the annual PM 2.5 standard supported the EPA’s proposal to eliminate the spat ial averaging provisions. Thes e commenters contended that the EPA’s analyses of the potential impacts of spatial averaging, discussed in section III.E.3.a of the preamble to the final rule, dem onstrated that the current form results in uneven public health protection leading to disproportionate impacts on at-risk populations. Specifically, the ALA and ot her environmental and public health

commenters contended that “s patial averaging allows expos ure of people to unhealthy levels of pollution at specific locales even within an area meeting the standard” (ALA et al., 2012, p. 23). These commenters particul arly focused on the importance for lowincome and minority populations of eliminati ng the spatial averagi ng provisions. They concluded that spatial averaging “is an environmental justice concern because poor people are more likely to live near roads, de pots, factories, ports, and other pollution

sources.” Id. p. 24. ALA et al. further asserted th at “in order for EPA to meet its Environmental Justice and Clean Air Act requ irements dictating that all Americans be protected from environmental health concer ns, spatial averaging must be removed” Id . p. 25.

Other commenters (e.g., AAM, 2012; Dow, 2012) also supported the elimination of spatial averaging in order to “avoid pote ntial disproportionate impacts on at-risk populations” and to maximize “the benefits to public health of reducing the annual PM 2.5 standard.” However, these groups expressed concern that the elimination of spatial averaging, in combination with the requirement for near road monitors (as discussed in section VIII.B.3.b.i of the propos al), would effectively and in appropriately increase the stringency of the annual PM 2.5 standard.

This concern was also shared by other commen ters who disagreed with the elimination of spatial averaging. For example, the Cla ss of ’85 RRG emphasized concerns about increasing the stringency of the standard while providing few health benefits if spatialII-48 averaging is eliminated, particularly in co mbination with the requi rement for near-road

monitors. These commenters contended that “[b]ecause EPA proposes to use the readings from the highest single worst case monitor (r ather than the average of all community area monitors), and since roadway monitoring locatio ns will likely be worst case monitors, the proposed NAAQS will become more st ringent without targeting the PM 2.5 species most harmful to human health” (Class of ’85 RRG , 2012, p. 6). Other comm enters argued that “unless the Agency adjusts the level of the NAAQS to account for the difference in concentrations at the community-based monito rs used to set the standard and those at near-roach monitors, use of the latter to judge compliance with the NAAQS would be unreasonable” (API, 2012, p. 58).

Several commenters also maintained that be cause spatial averaging is consistent with how air quality data are cons idered in the underlying epidemiological studies, such averaging should not be eliminated. Speci fically, commenters including NAM et al., AFPM, API, and ACC pointed out that PM 2.5 epidemiological studies use spatially averaged multi-monitor concentrations, rather than the single highest monitor, when evaluating health effects. Therefore, these commenters contended that allowing spatial averaging would make the PM 2.5 standard more consistent with the approaches used in the epidemiological studies upon which the standard is based. One commenter argued that averaging measurements across multiple m onitors in an area “would almost certainly

also have included monitors in areas in which minorities and low-income individuals reside. Therefore, their poten tially higher exposures would have been addressed in the epidemiological studies” (API, 2012, pp. 24 to 25) . Thus, this commenter asserted that elimination of spatial averaging is not warranted.

In addition, some commenters contended th at the EPA failed to consider whether modifying, rather than eliminating, the constr aints on spatial averaging would have been sufficient to protect public health. If so, th ese commenters argued that “elimination of spatial averaging would go beyond what is requ isite to protect the public health” (NAM et al., 2012, p. 20).

Response: In considering the public comments on th e form of the annual standard, the EPA recognizes a number of commenters agreed with the basis for the EPA’s proposal to eliminate spatial averaging. Wh ile other commenters expressed disagreement or concern with the proposed decision to eliminate th e spatial averaging provisions, the Agency

notes that these commenters did not challe nge the analyses or considerations that provided the fundamental basis for the Ad ministrator’s proposed decision. These unchallenged analyses indicate that public health would not be protected with an adequate margin of safety in all locations, as required by law, if disproportionately higher exposure concentrations in at -risk populations such as lo w income communities as well as minority communities were averaged together with lower concentrations measured at other sites in a large urba n area. Moreover, the Agen cy’s concern over possible disproportionate PM 2.5 -related health impacts in at-risk populations extends to populations living near im portant sources of PM 2.5 in the ambient air, including the large populations that live near major roadways.

Rather than addressing these analyses speci fically, these commenters generally raisedII-49 concerns that eliminating the option for sp atial averaging would increase the stringency of the standard, especially in light of additional monitoring sites in near-road

environments as discussed in section VIII. B.3.b.1 of the preamble for the final rule.

The EPA does not agree with the comment th at siting some monitors in near roadway environments makes the standard more stringe nt or impermissibly more stringent. As

discussed in section VIII.B.3.b.i of the preamble to the final ru le, a significant fraction of the population lives in proximity to major road s, and these exposures occur in locations that represent ambient air. Monitoring in su ch areas does not make the standard more stringent than warranted, but rather affo rds the intended protection to the exposed populations, among them at-risk populations, ex posed to fine particles in these areas. Thus, in cases where monitors in near roadway environments are deemed to be representative of area-wide air quality they would be compared to the annual standard (as discussed more fully in section VIII of the preamble to the final rule). The 24-hour and annual NAAQS are designed to protect the public with an adequate margin of safety, and this siting provision is fully consistent with providing the protection the standard is designed to provide and does not make the standard more stringent or more stringent than

necessary.

Monitors that are representative of area-wide air quality may be compared to the annual standard. This is consistent with the use of monitoring data in the epidemiological studies that provide the primary basis for determin ing the level of the annual standard. In addition, the EPA notes that the annual standard is designed to protec t against both longand short-term exposures through controlling the broad distribution of air quality across

an area over time. 9 It is fully consistent with the pr otection the standard is designed to provide for near road monitors to be compared to the annua l standard if the monitor is representative of area-wide air quality. This does not make the standard either more stringent or impermissi bly more stringent.

The EPA notes that CASAC agreed that it was “reasonable” for the EPA to eliminate the spatial averaging provisions (Samet, 2010d, p. 2) . Further, in CASAC’s comments on the first draft PA, it noted, “Given mounting evid ence showing that persons with lower SES levels are a susceptible group for PM-related health risks, CASAC recommends that the provisions that allow for spatial averaging acro ss monitors be eliminated for the reasons cited in the (first draft) Policy Assessment” (Samet, 2010c, p. 13). In its review of the second draft PA, CASAC recognized that “although much of the epidemiological research has been conducted using comm unity-wide averages, several key studies reference the nearest measurement site, so th at some risk estimates are not necessarily biased by the averaging process. Further, the number of such studies is likely to expand in the future” (Samet, 2010d, pp. 1 to 2).

In considering CASAC advice and public comme nts, the EPA notes that the stringency or level of protection provided by each NAAQS is not based solely on the form of the standard; rather, the four elements of the st andard that together serve to define each

9 This is in contrast to the 24-hour standard which is designed to provide supplemental protection, addressing peak exposures that might not otherwise be addressed by the annual standard. Consistent with this, monitors are not required to be representative of area-wide air quality to be compared to the 24-hour standard.II-50 standard (i.e., indicator, aver aging time, form, and level) mu st be considered collectively in evaluating the protection afforded by each standard, including the protection afforded to at-risk populations. Theref ore, the EPA considers it appropriate to discuss these comments collectively with other issues related to the appropriate level for the annual

standard as discussed in section III.E.4.c-d of the preamble and in section II.B.5.c below.

The EPA notes further that this issue is simila r to the issue of whether to base compliance

with the standard on use of a maximum monitor or composite monitors. As explained in responses addressing that para llel issue, the EPA’s analys is of nationwide air quality patterns indicates that in many instances there is no difference at all, or minor difference,

between maximum monitor results and thos e from composite monitors (Frank, 2012a.). Further, there were only a few other ar eas in which the maximum monitor mean concentration was appreciably higher than th e composite monitor mean concentration, such as areas in which some monitors may be separately impacted by local sources. There were only 10 such areas in the count ry in which the maximum monitor mean concentration was between 2 to 6 μg/m 3 higher than the composite monitor concentration (Frank, 2012a, Table 4) Thus, the EPA does not ag ree that there is a si gnificant difference between composite monitor mean PM 2.5 concentrations and maximum monitor mean

PM 2.5 concentrations in the large majority of areas across the country such that implementation of the standard on a maximum monitor basis, or without the option of spatial averaging, provides more protection than is requisite due to some inconsistency with key underlying epidemiologic studies.

Based on the analyses done to inform consider ation of the form of the standard (Schmidt, 2011, Analysis A), as well as the nationwid e analysis of composite and maximum monitor values just discussed, the EPA concludes that spatial averaging (or a composite monitor approach) does not provide a margin of safety for the at-ris k populations that live around the monitor measuring the highest concen tration, such as in those few areas in

which the maximum monitor concentration is appreciably higher than the composite monitor concentration. Thus, the comment that eliminating spatial averaging makes the standard more stringent misstates the issu e. The proper question is what level of protection is requisite with an adequate margin of safet y. If the standard needs to be made more stringent to provide such protection, th en such stringency is not only permissible but required (or “appropriate ” in the words of section 109 (d)). Diluti ng the needed protection by averaging monitoring results can demonstrably result in potentially disproportionate impacts on at-r isk populations and so would fail to carry out the core statutory requirement to provide requisite protection to public health with an adequate margin of safety. 10

(2) Comment: One commenter argued that the rational e to support elimination of spatial averaging to potentially avoi d disproportionate impacts on at -risk populations is flawed because the “evidence for grea ter susceptibility from PM e xposures in these populations

10 As noted in section II.A of the preamble to the final rule , the legislative history of section 109 indicates that a primary standard is to be set at “the maximum permissible ambient air level . . . which will protect the health of any [sensitive] group of the population,” and that for this pu rpose “reference should be made to a representative sample of persons comprising the sensitive group rather than to a single person in such a group.” S. Rep. No. 91-1196, 91st Cong., 2d Sess. 10 (1970).II-51 is weak” (API, 2012, Attachment 1, pp. ES-2). Fu rthermore, this commenter asserted that the “evidence presented in the ISA and su mmarized in the PA and Proposed Rule in support of increased susceptib ility to PM among children, older adults, those with preexisting heart and lung diseases , and those of lower SES is limited and inconsistent. This

evidence does not add to th e understanding or iden tification of sus ceptible populations, and it should not be used to support changes to the form of the annual PM 2.5 standard” (API, 2012, Attachment 1, p. 47).

Response: The EPA strongly disagrees with the commenter’s conclusion regarding the evidence for populations at increased risk for PM-related health effects. Chapter 8 of the ISA discusses the available evidence rega rding at-risk populati ons, and why children, older adults, those with pre-ex isting heat and lung diseases , and those of lower SES are legitimately regarded as at-risk. For example, “[o]lder adults represent a potentially susceptible population due to the higher prev alence of pre-existing cardiovascular and respiratory diseases found in this age range compared to younger age groups.” (U.S. EPA, 2009 a, p. 8-3). Results of epidemiologi cal and toxicological studies support this conclusion, and indicate as we ll increased susceptibility of older adults to all-cause mortality from short-term exposure, and increas ed susceptibility to respiratory morbidity and mortality. Id. at pp. 8-4 to 5. Children have generally been considered more susceptible to PM exposure due to factors such as more time sp ent outdoors, greater activity levels, exposures resulting in highe r doses per body weight and long surface area, and the possibility of irreversible eff ects on the developing respiratory system. Id. p. 8-5.

Two drafts of the ISA drawing these conclusions with regard to at-r isk populations were reviewed by CASAC and by th e public, and these same comments were before CASAC as part of that public comment pro cess. CASAC found the “organization and presentation” of the eviden ce for at-risk populations pres ented in the ISA to be “complete, clear, and well-organized” (Sam et, 2009f, p. 12). Furthermore, CASAC found that the “data presented fully justifies consid eration of lower socioeconomic status (SES) people as a susceptible group” (Samet, 2010c. p. 11). Indeed, as noted above, one of the reasons CASAC supported eliminating spatial averaging from the form of the annual standard was due to the “mounting evidence sh owing that persons with lower SES levels are a susceptible group for PM-related health risks” (Samet, 2010c, p. 13).

(3) Comment: Some commenters asserted that elimination of spatial averaging from the form

of the annual standard “does not excuse EPA’ s obligation under the CAA to set standards that explicitly incorporate a margin of safety” (ALA et al., 2012, p. 25).

Response: The EPA agrees with the commenters that setting a standard that provides protection with an adequate margin of safety is not limited to considering the protection afforded by the form of the standard alone. As noted in section III.E.3.i of the preamble to the final rule, the EPA notes that the stri ngency or level of protection provided by each NAAQS is not based solely on the form of the standard, rather, the four elements of the of the standard that together serve to define each standard (i.e., indicator, averaging time, form, and level) must be considered collec tively in evaluating the protection afforded by

each standard. As discussed in section III.E .4, the EPA Administrator’s conclusions on the appropriate indicator, averaging time, fo rm, and level are considered together inII-52 reaching her final decision on the appropriate annual standard that will provide requisite public health protection with an adequate margin of safety.

b. 24-Hour Standard

(1) Comment: Many of the individuals and groups w ho supported a more stringent 24-hour

PM 2.5 standard noted in section II I.D.2 of the preamble to th e final rule and in section II.B.1.a above, however, recommended a more restrictive concentration-based percentile form, specifically a 99 th percentile form. The limited number of these commenters who provided a specific rationale for this recomm endation generally expressed their concern

that the 98 th percentile form could allow too many days where concentrations exceeded the level of the standard, and thus fail to adequately protect pub lic health. Other public commenters representing state and local ai r agencies and industry groups generally supported retaining the current 98 th percentile form. In most cases, these groups expressed the overall view th at the current 24-hour PM 2.5 standard, including the form of the current standard, should be retained.

Response: The EPA notes that the viewpoints repres ented in this review are similar to

comments submitted in the last review and through various NAAQS reviews. The EPA recognizes that the selection of the appropr iate form includes maintaining adequate protection against peak 24-hour values while also providing a stab le target for risk management programs, which serves to provi de for the most effective public health protection in the long run. 11

As discussed in section III.E.3.b of the preambl e to the final rule, th e PA considered air quality data reported in 2000 to 2008 to upda te our understanding of the ratio between peak-to-mean PM 2.5 concentrations. This analysis provided evidence that the 98 th
percentile value was a more stable metric than the 99 th percentile (U.S. EPA, 2011a, Figure 2-2, p. 2-62).. In retaining the 98 th percentile form, the Administrator focused on the relative stability of the 98 th percentile form as a basis for her decision, while recognizing that the degree of public health pr otection likely to be afforded by a standard

is a result of the combination of the form and level of the standard.

5. Level

A large number of comments on the proposed levels for the primary PM 2.5 standards basically expressed one of two substantively diffe rent views. As explained in section III.D.2 of the preamble to the final rule and in secti ons II.A and II.B.1 above, one group of commenters generally opposed any change to the current primary PM 2.5 standards and more specifically disagreed with the basis for the EPA’s proposal to revise the annual st andard level. Another group of commenters supported revising the current suite of primary PM 2.5 standards to provide increased public health protection. Some comment ers in this second group argued that both the

11 As noted in section III.E.3.b of the preamble to the final rule, it is legitimate for the EPA to consider promotion of overall effectiveness of risk management programs design ed to attain the NAAQS, including their overall stability, in setting a standard that is requisite to protect the public health. The context for the court’s discussion in ATA III is identical to that here; whether to adopt a 98 th percentile form for a 24-hour standard intended to provide supplemental protection for a generally controlling annual standard.II-53 annual and 24-hour standard levels should be lowered while other commenters in this group agreed with the EPA’s proposal to retain the level of the 24-hour standard in conjunction with revising the level of the annual standard.

Many of these commenters simply expressed their views without stating any rationale, while others gave general reason s for their views but without refe rence to the factual evidence or rationale presented in the propos al notice as a basis for the Agency’s proposed decision regarding the levels of the primary PM 2.5 standards. A number of commenters, including many environmental and public health organizations as well as state and local air agencies and health departments and tribes, who suppor ted the revising the standard levels generally placed great weight on the recommendations of CASAC. Sections III.D.2 and III. E.4.c of the preamble to the final rule present the Agency’s response to these very general views. In addition to the discussion contained in those sections, th e EPA provides the following respons es to specific issues related to the levels for the primary PM 2.5 standards. This includes comments on the general approach used by the EPA to translate the available scient ific information into standard levels and how specific PM 2.5 exposure studies should be considered as a basis for the standard levels.

a. Annual Standard

i. Support for Retaining the Current Level

The group of commenters opposed to any cha nge to the current suite of primary PM 2.5 standards generally raised ques tions regarding the underlying scie ntific evidence, including the causal determinations reached in the ISA, and fo cused strongly on the uncertainties they saw in

the scientific evidence as a basis for their c onclusion that no changes to the current standard levels were warranted. In commenting on the proposed standard levels, these commenters typically relied on the arguments summarized and a ddressed in section III.D.2 of the preamble to

the final rule and in section II.B.1.b above as to why they believed it was inappropriate for the EPA to make any revisions to the suite of primary PM 2.5 standards. That is, th ey asserted that the EPA’s causal determinations were not adequa tely supported by the underlying scientific information; the biological plausibility of health effects observed in epidemiological studies has

not been demonstrated in cont rolled human exposure and toxicolo gical studies; uncertainties in the underlying health science are as great or greater than in 2006; there is no evidence of greater risk since the last review to just ify tightening the current annual PM 2.5 standard; and “new” studies not included in the Integrated Science A ssessment continue to in crease uncertainty about possible health risks associated with exposure to PM 2.5

.

With regard to the level of the annual standa rd, these commenters strongly disagreed with the Agency’s proposed decision to revise th e level to within a range of 12 to 13 μg/m 3 and argued that the current standard level of 15 μg/m 3 should be retained. For example, UARG, API, and other commenters in this group raised a numbe r of issues that they asserted called into question the EPA’s interpretation of the epidemiological evidence to support revising the annual

standard level. These commenters raised specific questions relate d to the general approach used by the EPA to translate the air quality and ot her information from specific epidemiological

studies into standard levels whic h are discussed in section III.E.4.c.i of the preamble to the final rule, including:II-54  the EPA’s approach for using composite mon itor air quality distri butions reported in epidemiological studies to select a standard level that would be compared to measurements at the monitor recording the highest value in an ar ea to determine compliance with the standard;

 the appropriate exposure period for effects observed in long-term exposure mortality studies;

and

 the use of the EPA’s analysis of distributions of underlying population-le vel data (i.e., health event and study population data) for those ep idemiological studies for which such

information was available.

These commenters also raised questions rega rding the EPA’s consideration of specific

scientific evidence as a basis for se tting a standard level, including:

 evidence of respiratory morbidity effect s in long-term exposure studies and

 more limited evidence of health effects whic h have been categori zed in the ISA as suggestive of a causal relationship (i.e., develo pmental and reproductive outcomes)

These comments and other comments are discussed below.

(1) Comment: Some commenters in this group argued that one reas on why they believe there is no basis for setting a standard level below 15 μg/m 3 is that the air quality metric from epidemiological studies that the EPA relied on in the proposal is not the same metric that will be compared to the level of the standard to determine compliance with the standard. That is, commenters noted that the long-term mean PM 2.5 concentrations that the EPA considered, shown in Figure 4 of th e preamble to the final rule, are composite monitor mean concentrations (i.e., concentrations av eraged across multiple monitors within areas with more than one monitor), whereas the PM 2.5 concentrations that will be compared to

the level of the standard are maximum monitor concentrations (i.e., the concentration measured by the monitor within an area re porting the highest c oncentration). This comment was presented most specifi cally in UARG’s comments (UARG, 2012, Attachment 1, pp. 2 to 6), which raised tw o overarching issues as discussed below.

First, the commenter noted that the EPA’s approach of considering composite monitor

mean PM 2.5 concentrations in selecting a sta ndard level, and then comparing the

maximum monitor mean PM 2.5 concentration in each area to the standard level when the standard is implemented, was characterized in the proposal as inherently having the potential to build in a margin of safety (UARG, 2012, Attachment 1, p. 4, citing 77 FR 38905). The commenter asserted that the Admi nistrator is ignori ng this distinction between composite and maximum monitor concen trations, and that this approach creates an unwarranted case for lowering the standard level, since in the commenter’s view, it would result in a margin of safety that w ould be arbitrary, not based on evidence, and unquantified (UARG, 2012, Attachment 1, p. 4). In support of this view, the commenter asserted that there is a significant diffe rence between composite monitor mean PM 2.5 concentrations and maximum monitor mean PM 2.5 concentrations. The commenter

asserted that the maximum monitor value wi ll always be higher than the composite monitor value (except in areas that contain only a single monitor), such that when an areaII-55 just attains the NAAQS, that area’s composite monitor long-term mean PM 2.5 concentration will be lower than the level of the standard (UARG, 2012, Attachment 1, p. 3).

Second, the commenter asserted that a more “reasoned and consistent approach would be to decide on a mean composite monitor PM 2.5 level that should be achieved and then identify the maximum monitor level that w ould result in that composite value” (UARG, 2012, Attachment 1, p. 4). The commenter conduc ted an analysis of maximum monitor versus composite monitor annual mean PM 2.5 concentrations using monitoring data 12
from 2006 to 2008 and presented results averag ed across areas with in two groups (i.e., those with design values 13 above the current standard leve l and those with design values just below the current standard level) to i llustrate their suggested alternative approach. The commenter interpreted this analysis as showing that the composite monitor long-term

mean PM 2.5 concentrations from the subset of the epidemiological studies shown in Figure 4 (of the preamble to the final rule) that the commenter considered to be an appropriate focus for this analysis would be achieved across the U.S. if the current annual NAAQS of 15 μg/m 3 is retained and attained. The commenter considered the subset of epidemiological studies that included only l ong-term exposures studies of effects for which the evidence is categorized as causal or likely causal, but di d not consider shortterm exposure studies. On this basis, the co mmenter asserted that attaining the current

annual PM 2.5 standard would result in composite m onitor long-term mean concentrations in all areas that would be generally within or below the range of the composite monitor long-term mean concentrations from such st udies and, as a result, there is no reason to

lower the level of th e current annual NAAQS.

Response: In considering the first issue related to the EPA’s approach, the EPA notes that in proposing to revise both the form and le vel of the annual standa rd, the Administrator clearly took into account the distinction between the compos ite monitor long-term mean

PM 2.5 concentrations from the epidemiological st udies, considered as a basis for selecting an annual standard level, and ma ximum monitor long-term mean PM 2.5 concentrations. In deciding to focus on the composite monitor lo ng-term mean concentrations in selecting the standard level, and on the maximum monito r concentrations in se lecting the form of the standard (i.e., consistent with proposing to eliminate the option for spatial averaging

across monitors within an area when implementing the standard 14 ), the Administrator reasonably considered the distinction betw een these metrics in a manner that was

consistent with advice from CASAC (Samet et al., 2010d, pp. 2 to 3).

As noted in section III.A.3 of the preamble to the final rule, the EPA recognizes that a statistical metric (e.g., th e mean of a distribution) based on maximum monitor concentrations may be identical to or a bove the same statistical metric based on composite monitor concentrations. More specif ically, many areas have only one monitor,

12 The commenter indicated that this analysis was based on monitoring data for every core based statistical area (CBSA) in the EPA’s Air Qua lity System (AQS) database.

13 The design value is the air quality statistic that is compared to the level of the NAAQS to determine the attainment
status of a given area

. 14 As discussed in section III.E.3.a of the preamble to the final rule and in response to comment (1) in section

II.B.4.a above.II-56 in which case the composite and maximum monitor concentrations are identical. Based on the most recent data from the EPA’s AQS from 2009 to 2011 in the 331 CBSAs in

which valid PM 2.5 data are available, as discussed in Frank (2012a, Table 5), there were 208 such areas (with design values ranging up to about 15 μg/m 3 ). Frank (2012a) also observed that other areas have multiple monitors with composite and maximum monitor

mean PM 2.5 concentrations that were the same or relatively close, with 57 areas in which the maximum monitor mean concentration was no more than 0.5 μg/m 3 higher than the composite monitor mean concentration and 56 areas in which the difference was between 0.6 and 2 μg/m 3 . Further, there were only a few other areas in which the maximum monitor mean concentration was appreciably higher than the composite monitor mean concentration, such as areas in which some m onitors may be separate ly impacted by local sources. There were only 10 such areas in the country in which the maximum monitor mean concentration was between 2 to 6 μg/m 3 higher than the composite monitor concentration (Frank, 2012a, Table 4). 15 Thus, the EPA does not agree that there is a significant difference between composite monitor mean PM 2.5 concentrations and

maximum monitor mean PM 2.5 concentrations in the large majority of areas across the

country.

In proposing to revise the form of the annual PM 2.5 standard, as discussed in section III.E.3.a of the preamble to the final rule , the EPA noted that when an annual PM 2.5 standard was first set in 1997, the form of th e standard included th e option for averaging across measurements at appropriate monitoring sites within an area, generally consistent with the composite monitor approach used in epidemiological studies, with some constraints intended to ensure that spatial av eraging would not result in inequities in the level of protection for communities within larg e metropolitan areas. In the last review the EPA tightened the constraints on spatial averaging, and in this review has eliminated the option altogether, on the basis of analyses in each review that showed that such constraints may be inadequate to avoid subs tantially greater expos ures for people living

in locations around the monito rs recording the highest PM 2.5 concentrations in some areas, potentially resu lting in disproportionate impact s on at-risk populations such as persons with lower SES levels. In light of these analyses, and consistent with the

Administrator’s decision to revise the form of the annual PM 2.5 standard by eliminating the option for spatial averaging, the EPA con tinues to conclude that a standard level based on consideration of long-term mean c oncentrations from composite monitors, and applied at each monitor within an area in cluding the monitor measuring the highest concentration, is the appropriate approach to use in setting a standard that will protect public health, including the he alth of at-risk populations, w ith an adequate margin of safety, as required by the CAA.

The EPA acknowledges that at proposal, the Ag ency characterized the approach of using

maximum monitor concentrations to determ ine compliance with the standard, while selecting the standard level based on consider ation of composite m onitor concentrations, as one that inherently had the potential to build in a margin of safety (77 FR 38905), and

15 The average difference between the maximum and composite design value among the 123 CBSAs with two or more monitors is 0.8 μg/m 3 and the median difference is 0.6 μg/m 3 . The 25 th and 75 th percentiles are 0.3 and 1.0 μg/m 3 , respectively (Frank, 2012a, p. 4).II-57 CASAC reiterated that view in suppor ting the EPA’s approach (Samet, 2010d, p. 3). Nonetheless, in light of the analysis discussed above, the EPA more specifically recognizes that this approach does not build in any margin of safety in the large number

of areas across the coun try with only one monitor. Furthe r, based on the analyses done to

inform consideration of the form of the standard (Schmidt, 2011, Analysis A), the EPA concludes that this approach does not provide a margin of safety for the at-risk populations that live around the monitor measur ing the highest concentration, such as in

those few areas in which the maximum monito r concentration is appreciably higher than the composite monitor concentration. Rather, this approach properly treats those at-risk populations the same way it does the broader pop ulations that live in areas with only one monitor, by providing the same degree of protection for t hose at-risk populations that would otherwise be disproportionately impacted as it does for the broader populations in other areas. Moreover, while the EPA recognize s that this approach can result in some additional margin of safety for the subset of areas with multiple monitors in which at-risk populations may not be disproportionately represented in areas around the maximum monitor, which may be the case in areas w ith relatively small differences between the maximum and composite monitor concentrations , the EPA notes that this margin would be relatively small in such areas.

Based on the above considerations, the EPA does not agree that the Agency’s approach of using maximum monitor concentrations to determine compliance with the standard, while selecting the standard level base d on consideration of composite monitor concentrations, creates an unwarranted case for lowering the standard level based on a margin of safety that would be arbitrary, not based on evidence, or lacking quantification. The EPA recognizes that setting a standard to protect public health, including the health of at-risk populations, with an adequate margin of safety, depends upon selecting a standard level sufficiently below where th e EPA has found the strongest evidence of health effects so as to provide such prot ection, and that the EPA’ s approach regarding consideration of composite a nd maximum monitor concentra tions is intended to, and does, serve to address this requirement as part of and not separate from the selection of an appropriate standard level and form based on the health effects evidence.

In considering the second issue related to the commenter’s suggested alternative approach, the EPA strongly disagrees with th e commenter’s view th at a more “reasoned and consistent approach would be to decide on a mean composite monitor PM 2.5 level

that should be achieved and th en identify the maximum monitor level that would result in that composite value” (UARG, 2012, Attachme nt 1, p. 4). As discussed above, the EPA notes that for areas with only one monitor, or with multiple monitors that measure concentrations that are very close in magn itude, the maximum monitor level that would limit the composite monitor PM 2.5 level to be no greater than the level that should be achieved to protect public health with an ade quate margin of safety, would essentially be the same as that composite monitor level. Fu rther, as discussed above, even for areas in

which the maximum monitor concentration is appreciably higher than other monitor concentrations within the same area, public health would not be protected with an adequate margin of safety if the disp roportionately higher exposures of at-risk, susceptible populations around the monitor meas uring the highest concentration were in essence averaged away with m easurements from monitors in other locations within largeII-58 urban areas. Further, the commenter’s sugge sted approach would be based on annual average PM 2.5 concentrations that have been meas ured over some past time period. Such an approach would reflect the air quality th at existed in the past, but it would not necessarily provide appropriate constraints on the range of c oncentrations that would be allowed by such a standard in the future, when relationships between maximum and composite monitor concentrations in areas acr oss the country may be different. For these reasons, the EPA fundamentally rejects the commenter’s suggested approach because it results in a standard that demonstrably would not protect public health, including providing protection for at-risk populations, with an adequate margin of safety in areas across the country.

More specifically, in further considering the commenter’s analysis of design values based on maximum versus composite monitor annual mean PM 2.5 concentrations using monitoring data from 2006 to 2008 which they assert supports retaining the current standard level of 15 μg/m 3 , the EPA finds flaws with the numerical results and the scope of the analysis, as well as flaws in the comment er’s translation of the analysis results into the basis for selecting an annual standard level.

In considering the commenter’s analysis, the EPA notes that the analysis compared maximum versus composite monitor annual mean PM 2.5 concentrations, averaged over 3 years, for two groups of areas: (1) areas with design values th at exceed the current annual standard level (i.e., greater than 15.0 μg/m 3 ) and (2) areas with design values that are just attaining the current annual sta ndard (i.e., between 14.5 and 15.0 μg/m 3 ). 16 The commenter indicated that they used the full body of PM 2.5 monitoring data from the EPA’s AQS database (UARG, 2012, Attachment 1, p. 4). In attempting to reproduce the commenter’s results, the EPA repeated the ca lculations using only va lid air quality data (i.e., data that meet data completeness and m onitor siting criteria) from the AQS database for the same time period (Frank, 2012a). 17 Based on this corrected analysis, the EPA finds that the composite monitor concentratio ns averaged across the areas within each group are somewhat higher than those calcu lated by the commenter, and the average differences between the maximum and compos ite monitor concentrations are somewhat smaller (Frank, 2012a, Table 3). 18 Notably, the difference between the maximum and composite monitor average concentrations for the second group of areas is substantially

16 For the first group of areas (which in cluded 33 areas), this analysis calcu lated an average across the areas of

maximum monitor annual mean PM 2.5 concentrations, averaged over 3 years, of 17.2 μg/m 3 compared to an average of composite monitor concentrations of 14.3 μg/m 3 . For the second group of areas (which included 11 areas), this analysis calculated an average across th e areas of maximum monitor annual m ean concentrations, averaged over 3 years, of 14.8 μg/m 3 compared to an average of composite monitor concentrations of 13.6 μg/m 3 (UARG, 2012, Attachment 1, Table 1).

17 The EPA notes that the Frank (2012a) analysis is similar to an earlier EPA staff anal ysis (Hassett-Sipple et al., 2010), which used air quality data from the EPA’s AQS database to compare maximum versus composite monitor long-term mean PM 2.5 concentrations across the study areas in six selected multi-city epidemiological studies.

18 The EPA’s analysis was intended to repeat the commenter’s analysis, but using only valid air quality data (from 2006 to 2008). For the first group of areas (which included 21 areas with valid data), the EPA’s analysis calculated an average across the areas of maximum monitor annual mean concentrations, averaged of 3 years, of 16.8 μg/m 3
compared to an average of composite monitor concentrations of 14.8 μg/m 3 . For the second group of areas (which included 10 areas with valid data), the EPA’s analysis cal culated an average across the areas of maximum monitor annual mean concentrations, aver aged over 3 years, of 14.8 μg/m 3 compared to an average of composite monitor concentrations of 14.2 μg/m 3 (Frank, 2012a, Table 3).II-59 reduced in the corrected analysis, such that the difference (averaged across the 10 areas

with valid data in the second group) is approximately 0.5 μg/m 3 , not 1.2 μg/m 3 as in the commenter’s analysis. In addition, the comm enter’s analysis comp ared the average of the composite monitors to the average of the maximum monitors for each subset of areas. This comparison of averages ac ross all the areas in each subs et masks the fact that the large majority of areas across the country ha ve only one monitor, with the composite

monitor and maximum monitor values the sa me for such areas, and many other areas

have a maximum monitor value that is cl ose to the composite monitor value. As discussed above, these circumst ances have a major impact on the protection that would be achieved by the approach suggested by the commenter.

With regard to the scope of the commenter’ s analysis, the EPA finds that by limiting the scope to a small subset of areas with design values above or just below the current annual standard level of 15 μg/m 3 , the analysis ignores the larg e number of areas across the country with lower design values that ar e relevant to consider in light of the epidemiological evidence of serious health effects at concentrations lower than 15 μg/m 3

, well below the level of the current standard.

In translating its analys is results into the basis for select ing an annual standard level, the commenter’s translation is prem ised on the view that the “nat ural focal point” for setting

an annual PM 2.5 standard level should be somewhere within the range of the long-term

mean PM 2.5 concentrations from the subset of ep idemiological studies that included only long-term exposure studies of effects for which the evidence is categorized as causal or likely causal, but not for effects categorized as suggestive of causal ity, nor did it include short-term exposure studies (which are include d in Figure 4 of the preamble to the final rule). Ignoring effects for whic h evidence of causality is sugg estive is not consistent with setting a standard that would provide sufficien t protection from the serious health effects reported even in the limited subset of studi es considered by the commenter, much less protecting public health with an adequate margin of safety. Moreover, as discussed below, the EPA does not agree with the commenter’s view as to the appropriate focal point for selecting the level of an annual PM 2.5 standard, or with the limited set of studies considered by the commenter as a basis for selecting the level of the annual PM 2.5 standard.

Regarding an appropriate focal point for sele cting the level of th e annual standard, as discussed in the proposal and as advi sed by CASAC, the EPA has focused on PM 2.5 concentrations somewhat below the lowest long-term mean concentrations from each of the key studies of both long- and short-term exposures of effects fo r which the evidence is causal or likely causal, as considered by the EPA (i.e., the first two sets of studies shown in Figure 4 of the preamble to the fina l rule and in the pr oposal, 77 FR 38933). If the level of the annual standard was set just somewhere within the range of the long-term mean concentrations from the various long-te rm exposure studies, then one or more of the studies would have a long-term mean con centration below the se lected level of the standard. Absent some reason to ignore or discount these studies, which the commenter does not provide (and of which the EPA is unawa re), setting such a standard would allow that level of air quality, wh ere the evidence of health e ffects is strongest, and its

associated risk of PM 2.5 -related mortality and/or morbidity effects to continue. SelectingII-60 such a standard level could not be considered sufficient to protect the public health with an adequate margin of safety.

Further, focusing on just the long-term mean PM 2.5 concentrations in the key epidemiological studies – even the lowest l ong-term mean concentration from the set of key studies -- is not appropriate. Concentr ations at and around the long-term mean concentrations represent the part of the ai r quality distribution wh ere the data in any given study are most concentrated and, thus, where the confidence in the magnitude and significance of an association in such study is strongest. Ho wever, the evidence of an

association with adverse health effects in the studies is not limited to the PM 2.5 concentrations just at and around the long-term mean, but rather extends more broadly to a lower part of the distribution, recognizing that no discernible popul ation-level threshold for any such effects can be identified ba sed on the available evidence. This broader region of the distribution of PM 2.5 concentrations should be considered to the extent relevant information is available, recogni zing that the degree of confidence in the

association identified in a st udy would become lower as one moves below concentrations at and around the long-term mean concentr ation in any given study. The commenter’s approach ignores this f undamental consideration.

Regarding the set of studies that is appropriate to inform the selection of the level of the

annual PM 2.5 standard, the EPA finds that limiting consideration only to the long-term

exposure studies, as this commenter suggests, would be tantamount to ignoring the shortterm exposure studies, 19 which provide some of the str ongest evidence from the entire body of epidemiological studies. Thus, selec ting an annual standard level using the limited set of studies suggested by the comm enter would fail to provide a degree of protection that would be suffici ent to protect public health with an adequate margin of safety.

For all the reasons discussed above, the EPA finds the commenter’s concerns with the EPA’s approach to considering composite and maximum monitor PM 2.5 concentrations in selecting the level of the annual PM 2.5 standard to be without merit. Further, the EPA finds no support in the commenter’s analysis for their suggested alternative approach.

(2) Comment: With respect to the appropriate exposure period for mortality effects observed in long-term exposure studies, some commenter s in this group generally expressed views

consistent with comments from UARG that argued that these studies “are most likely detecting health risk from earlier, higher PM 2.5 levels and misattri buting those risks to

19 The commenter suggests that the EPA should not place significant reliance on the long-term mean concentrations from short-term exposure studies because “]the short

‐ term studies did not use the annual average of PM 2.5 to develop their associations; they used the daily 24

‐ hour averages of PM 2.5 . Thus, short

‐ term studies do not provide a natural indicator for the appropriate level of an annual standard....” (UARG, 2012, Attachment 1, p. 3). The EPA finds this argument unpersuasive. Quite simply, effects were observed in these studies with an air quality distribution that can meaningfully be characterized by these long-term mean c oncentrations. Indeed, in remanding the 2006 standard, the D.C. Circuit discussed at length the interrelationship of the long- and short-term standards and studies, and remanded the 2006 standard to the EPA, in part, because the EPA had either ignored these relationships or had failed to provide an adequate explanation for disregarding them. American Farm Bureau Federation v. EPA. 559 F. 3d at

522-24.II-61 more recent, lower PM 2.5 levels” (UARG, 2012, Attachment 1, p 7). Further, this

commenter asserted that “there is no knowledge or evidence indicating whether premature deaths are the result of PM 2.5 exposures in the most recent year; or due to physical damages incurred from PM 2.5 exposures much earlier in life (with the impact on lifespan only emerging later in life ); or due to total accumulated PM 2.5 exposure over many years.” Id . In addition, the commenter asserted that the long-term exposure studies of mortality are central to the EPA’s basis for proposing to set a lower annual standard level, since most of the estimated bene fits associated with a lower annual PM 2.5 standard are based on reductions in mortality related to long-term exposures to PM 2.5

.

Response: As an initial matter, the EPA has rec ognized the challenge in distinguishing

between PM 2.5 -associated effects due to past a nd recent long-term exposures, and in identifying the relevant latency period for l ong-term exposure to PM and resultant health effects (U.S. EPA, 2009a, section 7.6.4; 77 FR 38941/1). While the EPA has acknowledged that there remain important uncertainties relate d to characterizing the most relevant exposure periods in long-term expos ure studies, the asserti on that there is “no knowledge or evidence” that helps to inform th is issue is not correct, as discussed below.

Both in the last review and in the current review, the EPA has assessed studies that used different air quality periods for estimating long-term exposure and tested associations with mortality for the different exposure periods (U.S. EPA, 2004, section 8.2.3.5; U.S. EPA 2009a, section 7.6.4). In this review, the ISA discu ssed studies available since the

last review that have assessed the rela tionship between long-term exposure to PM 2.5 and mortality to explore the issue of the latency period between exposure to PM 2.5 and death (U.S. EPA, 2009a, section 7.6.4).

Notably, in a recent analysis of the extende d Harvard Six Cities Study, Schwartz et al. (2008) used model averaging (i.e., multiple models were averaged and weighted by probability of accuracy) to assess exposure periods prospectively (77 FR 38907/1-2). The exposure periods were estimated across a range of unconstrained dist ributed lag models (i.e., same year, one year prior, two years pr ior to death). In comp aring lags, the authors reported that the effects of changes in exposure to PM 2.5 on mortality were strongest within a 2-year period prior to death (U.S. EPA, 2009a, p. 7-92, Figure 7-9). Similarly, a large multi-city study of the elderly found thatthe mortality risk associated with longterm exposure to PM 10 reported cumulative effects that extended over the years that

deaths were observed in the study population (i.e., the follow-up period) and for the 3- year period prior to death (Zanobetti et al., 2008).

Further, in a study of two locations that experienced an abrupt decline in PM 2.5 concentrations (i.e., Utah Steel Strike, coal ban in Ireland), Röösli et al. (2005) reported that approximately 75 percent of health benef its were observed in th e first 5 years (U.S. EPA, 2009a, Table 7-9). Schwar tz et al. (2008) and Pue tt et al. (2008) found, in a comparison of exposure periods ranging from 1 month to 48 months prior to death, that exposure to PM 10 24 months prior to death exhibite d the strongest a ssociation, and the weakest association was reported for exposure in the time period of 1 month prior to

death.II-62 Overall, the EPA notes that the available ev idence for determining the exposure period that is causally related to the mortality effects of long-term PM 2.5 exposures, as discussed above, cannot specifically disentangle the e ffects observed in long-term exposure studies associated with more recent air quality meas urements from effects that may have been associated with earlier, and most likely higher, PM 2.5 exposures. While the evidence suggests that a latency period of up to five years would account for the majority of deaths, it does not provide a basis for concluding that it is solely recent PM 2.5 concentrations that account for the mortality risk observed in such studies. Nonetheless, the more recent air quality data does well at explaining the rela tionships observed between long-term exposures to PM 2.5 and mortality, with th e strongest association observed in the two years prior to death. Fu rther, the EPA recognizes that there is no discernible population-level thre shold below which effects would not occur, such that it

is reasonable to consider that health effects may occur over the full range of concentrations observed in the epidem iological studies, including the lower concentrations in the latter years. In light of this evidence and these considerations, the EPA concludes that it is appr opriate to consider air qual ity concentrations that are generally contemporaneous with the collection of health event data (i.e., collected over the same time period) as being causally associ ated with at least some proportion of the deaths assessed in a long-term exposure study. This would include long-term mean PM 2.5 concentrations from most of the key long-term exposure studie s of effects with causal or likely causal evidence shown in Figure 4 of the preamble to the final rule, which reported long-term mean PM 2.5 concentrations ranging from 13.6 μg/m 3 to 14.3 μg/m 3 . These

studies include studies of mort ality by Eftim et al. (2008), wh ich separately analyzed the ACS and Harvard Six City sites, Zeger et al. ( 2008), and Lipfert et al. (2006a), as well as studies of morbidity endpoints by Goss et al. (2004), McConnell et al. (2003) and Gauderman et al. (2004), and Dockery et al. (1996) and Razienne et al. (1996). The EPA acknowledges that uncertainty in the relevant exposure peri od is most notable in two other long-term exposure studies of mortalit y. The Miller et al. (2007) reported a longterm mean PM 2.5 concentration for a 1-year exposure period that post-dated the follow-up period in which health event data were collect ed by two years. Also, the Krewski et al. (2009a) study reported a long-term mean PM 2.5 concentration for an exposure period that included only the last two years of th e 18-year follow-up period. Based on these considerations, the EPA does not now consid er it appropriate to put weight on the reported long-term mean concentrations fr om these two studies for the purpose of translating the information from the long-term mortality studies into a basis for selecting

the level of the annual PM 2.5 standard. 20

In addition, the EPA acknowledges that exposur e periods that extend at least a couple years prior to the follow-up period in which h ealth event data were collected would likely more fully capture the PM-related deaths in such studies. To explore how much higher the long-term mean PM 2.5 concentrations would likely ha ve been had air quality data prior to the follow-up years of the studies b een included, the EPA c onducted a sensitivity analysis of long-term mean PM 2.5 concentrations (Schmi dt, 2012a) particularly

20 Nonetheless, the EPA notes that the Krewski et al. (2 009) and Miller et al. (2007) studies provide strong evidence of mortality and cardiovascular-related effects associated with long-term PM 2.5 exposures to inform causality determinations reached in the ISA (U.S. EPA, 2009a, sections 7.2.11 and 7.6).II-63 considering studies that only included deaths from a relatively recent follow-up period. As examples of such studies, this analysis considered the Eftim et al. (2008) study of mortality in the ACS sites and the Harvard Six Cities sites, as well as sites in the eastern region in the Zeger et al. ( 2008) study. Using data from the EPA’s AQS database, the analysis added the two years of air quality da ta just prior to the follow-up period in each study, which was 2000 to 2002 in Eftim et al. (2008) and 2000 to 2005 in Zeger et al. (2008). The analysis then calculate d the extended long-term mean PM 2.5 concentration for each study. As discussed in Schmidt (2012a ), in each case the long-term mean PM 2.5 concentration averaged over the extende d exposure period was no more than 0.4 μg/m 3
higher than the long-term mean PM 2.5 concentration averaged over the follow-up period.

The EPA finds it reasonable to conclude that such a relatively small difference in longterm mean PM 2.5 concentrations would likely apply for other long-term exposure studies that used similarly recent follow-up periods as well (e.g., Goss et al., 2004; Lipfert et al., 2006).

Based on the above considerations, the EPA conc ludes that it is appr opriate to consider the available air quality information from th e long-term exposure studies, while taking

into account the uncertainties in the relevant long-term exposure periods in weighing the information from these studies. The EPA recogni zes that considering such information in selecting an appropriate annual standard level has the potential to build in some margin of safety. The EPA further concl udes that it is appropriate to consider the air quality information from the set of long-term exposur e studies discussed above in the context of the broader array of epidemiological studies that inform the EPA’s consideration of the

level of the annual PM 2.5 standard.

The EPA also notes that while the long- term exposure studie s are an important component of the epidemiological evidence th at informs the Agency ’s consideration of the level of the annual standard, they do not provide the only rele vant information, nor are they the set of studies for wh ich the relevant long-term mean PM 2.5 concentrations are the lowest. As discussed in the proposal, the EPA also considers the long-term mean

PM 2.5 concentrations from the short-term mort ality and morbidity studies as providing important information in considering the le vel of the annual standard. As discussed above, a large proportion of the aggregate ri sk associated with short-term exposures results from the large number of days duri ng which the 24-hour average concentrations are in the low- to mid-range of the concentrations observed in the studies. Thus, setting the level of the annual standard based on long- term mean concentrations, as well as the

distribution of concentrations below the mea n, in the short-term e xposure studies is the most effective and efficient way to reduce total PM 2.5 -related risk from the broad array of mortality and morbidity effects asso ciated with short-term exposures.

Further, the EPA notes that the relevant exposure period for the short-term exposure studies is the period contemporaneous with th e collection of health event data, and that this exposure period is not subject to the uncertainties discussed above related to the long-term exposure studies. Recogni zing that the long-term mean PM 2.5 concentrations from several of the multi-city short-term exposure studies shown in Figure 4 of the preamble to the final rule ar e below the long-term mean PM 2.5 concentrations from theII-64 long-term exposure studies (with the exception of Miller et al., 2007). 21 It is reasonable that in selecting the level of the annual standard primary consideration should be given to

the information from this set of short-term exposure studies. There is no reasonable basis to discount the long-term mean concentrations of the shor t-term exposure studies for purposes of setting the level of the annual standard. Thus, th e commenter is incorrect in asserting that the long-term exposure studies , not the short-term exposure studies, would

be central in the Administrator’s decisi on on the level of the annual standard. The standard is ultimately intended to protect not just against the single type of effect that contributes the most to quantitative estimates of risk to public hea lth, but rather to the broad array of effects, incl uding mortality and morbidity effects from long- and shortterm exposures across the range of at-risk populations impacted by PM 2.5 -related effects.

(3) Comment : With regard to the EPA’s analysis of distributions ofunderlying populationlevel data (i.e., health event and study populat ion data) and correspond ing air quality data from each study area in certain key multi-city epidemiologi cal studies (Rajan et al., 2011), some commenters in this group raised a nu mber of issues related to this analysis (e.g., McClellan, 2012; API, 2012, Attachment 1, pp. 5 to 6). Some commenters noted

the limited number of studies for which h ealth event and study population data were available, and questioned whether these di stributions would apply to other studies. Commenters expressed concerns that this an alysis had not been formally reviewed by CASAC and was not published in the peer-rev iew literature. One commenter asserted that the data sets the EPA used in the distributional analysis were “not available to other scientists for critical independent analys is and interpretation” (McClellan, 2012, p. 2). Based on such concerns, some commenters asse rted that the EPA should not consider this

information as a basis for se lecting a standard level.

Response: As an initial matter, as discussed in section III.E.4.b of the preamble to the final rule and in previous responses in this document, the EPA agrees with CASAC’s advice that it is appropria te to consider additiona l data beyond the mean PM 2.5 concentrations in key multi-city studies to help inform selection of the level of the annual

PM 2.5 standard. As both the EPA and CASAC rec ognize, in the absence of a discernible threshold, health effects may occur over the full range of concentrations observed in the epidemiological studies. Nonetheless, the EPA recognizes that confidence in the magnitude and significance of an association is highest at and ar ound the long-term mean

PM 2.5 concentrations reported in the studies and the degree of confidence becomes lower at lower concentrations within any gi ven study. Following CASAC’s advice (Samet, 2010d, p.2), the EPA used additional population-leve l and air quality data made available by study authors to conduct an analysis of the distributions of such data, to help inform

consideration of how the de gree of confidence in the ma gnitude and significance of

observed associations varies acro ss the range of long-term mean PM 2.5 concentrations in study areas within key multi-city epidemiol ogical studies. In the EPA’s view, such consideration is important in selecting a level for an annua l standard that will protect public health with an adequate margin of safety.

21 As noted in sections III.E.4.c.i and III.E.4.d of the preamble to the final rule, the EPA is not placing weight on the reported long-term mean concentrations from the Miller et al. (2007) study for the purpose of translating the information from the long-term mortality studies into a basis for selecting the level of the annual PM 2.5 standard.II-65 With regard to the number of multi-city studies for which an analysis of the distributions of population-level data acr oss the study areas and the corresponding annual mean PM 2.5 concentrations was done, the EPA noted at propo sal that data for such an analysis were made available from study authors for four studies, including two long-term exposure

studies and two short- term exposure studies. 22 The EPA recognized that access to health

event data can be restricted due to confidentia lity issues, such that it is not reasonable to expect that such information could be made available from all studies. In considering the information from these four studies, the EPA has further taken into consideration uncertainties discussed in response to the above comment related to the appropriate exposure period for long-term exposure studies. Based on these consid erations, as noted above, the EPA concludes that such uncertainties are an important fact or in evaluating the usefulness of the air quality information from the two long-term exposure studies in this analysis (Krewski et al., 2009a; Miller et al., 2007) and that it would not be appropriate to place weight on the distributional analysis of he alth event and air quality data from these two studies specifically for the purpose of tr anslating the information from the long-term mortality studies into a basis for selecting the level of the annual PM 2.5 standard. Such

uncertainties are not relevant to the short-term exposure studies, and thus, the Agency focuses on the two short-term exposure studie s in this analysis (Bell et al., 2008; Zanobetti and Schwartz, (2009).

In focusing on these two short-term exposure studies, the EPA first notes that these studies are key multi-city studies that re ported positive and statistically significant associations between mortality and cardi ovascular-related hospital admissions across a large number of areas throughout the U.S. ( 112 U.S. cities in Zanobetti and Schwartz, 2009; 202 U.S. counties in Bell et al., 2008) us ing relatively recent air quality and health event data (i.e., 1999 through 2005 in both studie s). The EPA considers these two studies to comprise a modest but important data set to use for this distributional analysis in this review to help inform consideration of how much below the long-term mean PM 2.5 concentrations in key multi-city long- a nd short-term exposure studies the annual PM 2.5 standard level should be set. While th e EPA acknowledges that having such data

available from more studies would have been useful, the Agency finds the information

from this limited set of studies to be usef ul for consideration in selecting an annual standard level, consistent with CASAC advice to consider such information.

The results of this distributional analysis are shown in Figure 5 below (adapted from Figure 3 in Rajan et al., 2011). For each study, this figure shows the cumulative frequency of the number of health events in each study area and the corresponding longterm mean PM 2.5 concentrations in each area. Consistent with CASAC advice (Samet, 2010d, p.2), such an analysis helps to inform the EPA’s understandi ng of the long-term

mean PM 2.5 concentrations that were most influe ntial in generating the health effect estimates in individual studies. In par ticular, the EPA recognizes that there is significantly greater confidence in the magnitude and significance of observed associations in that part of the air quality distribution correspondi ng to where the bulk of

22 Health event data and study population data were availabl e from two short-term exposure studies (Bell et al. 2008; Zanobetti and Schwartz, 2009) and one long-term exposure st udy (Krewski et al., 2009). Only study population data were available from another long-term exposure study (Miller et al., 2007).II-66 the health events evaluated in each study have been observed. With regard to the part of

the distribution in which confidence in the magnitude and signifi cance of associations observed may become appreciably lower, the EPA considers PM 2.5 concentrations

between the 25 th and 10 th percentiles of the distribution of health events in these studies to be a reasonable range for providing a gene ral frame of reference for that part of the distribution in which confidence in the magnit ude and significance of the association may be appreciably lower than confidence at and around the long-ter m mean concentration. As highlighted in Figure 5, the long-term mean PM 2.5 concentrations corresponding with study areas contributing to the 25 th and 10 th percentiles of the dist ribution of deaths and cardiovascular-related hospitaliz ations in the two short-term exposure studies were 12.5 μg/m 3 and 10.3 μg/m 3 , respectively, for Zanobetti and Schwartz (2009), and 11.5 μg/m 3
and 9.8 μg/m 3 , respectively, for Bell et al. (2008 ). The EPA also recognizes, however,

that there is no clear divi ding line or single percentile within a given distribution (including both above and below the 25 th percentile) provided by the scientific evidence that is most appropriate or ‘c orrect’ to use to characterize where the degree of confidence

in the associations warrants setting the annual standard leve l. The decision as to the appropriate standard level belo w the long-term mean concentra tions of the key studies is largely a public health policy judgment to be made by the Administrator, taking into

account all of the evidence and its related uncer tainties, as discussed in section III.E.4.d of the preamble to the final rule.

In response to concerns that this analysis was not reviewed by CASAC nor published in the peer-reviewed literature, the EPA notes th at this analysis was conducted to directly respond to advice from CASAC, as discussed in section III.E.4.b.1 of the preamble to theII-67 final rule, in conjunction with their review of the PA. The EPA notes that the same type of distributional analysis was presented in the second draft PA based on air quality data, as well as on population-weighted air quality data, rather than on h ealth event or study population data. In consideri ng that distributional inform ation, CASAC urged that the EPA redo the analysis using health event or study population data, which is exactly what the EPA did and presented in the final PA. The EPA provided CASAC with the final PA

and communicated how the final staff conclusi ons reflected consideration of its advice

and that those staff conclusions were based in part on the sp ecific distributional analysis that CASAC had urged the EPA to conduct (Wegman, 2011, Attachment p. 2). CASAC did not choose to provide any additional comments or advice after receiving the final PA. The EPA considers this distributional analysis to be the product of the peer review conducted by CASAC of the PA, and thus does not agree with commenters’ characterization that the analysis lacked appropriate peer review. The EPA’s final analysis was based on the comments provi ded by CASAC, the peer review committee established pursuant to the CAA, on the draft analysis, such th at the final analysis stems directly from CASAC’s advice and th e EPA’s response to its comments.

With regard to the availabili ty of the underlying data sets , the EPA disagrees with the

commenters’ assertion that these data are not publically available. As noted in the EPA staff technical memorandum, the underlying data sets provided by study authors are available in the rulemaking docke t (Rajan et al., 2011, pp. 2 to 3).

Based on the above considerations, the EPA con tinues to conclude th at its analysis of distributions of health event and air quality data from two key multi-city epidemiological studies provides important information relate d to understanding the associations between health events observed in each city (e.g., d eaths, hospitalizations) and the corresponding long-term mean PM 2.5 concentrations observed in the studies. While recognizing that this is a relatively modest data set, the EPA fu rther concludes that such information can appropriately help to inform the selection of the level of an annua l standard that will protect public health with an adequate margin of safety from these types of health effects which are causally related to long- and short-term exposures to PM 2.5

.

(4) Comment : Some commenters in this group assert ed there were limitations in the longterm exposure studies of morbidity, including studies evaluating respiratory effects in children. For example, one commenter ( UARG, 2012, p. 12, Attachment 1, pp. 14 to 16)

asserted there were serious limitations in th e long-term exposure studies of respiratory morbidity in each of the st udies considered by the EPA (including McConnell et al., 2003; Gauderman et al., 2004; Dockery et al., 1996; Raizenne et al ., 1996; and Goss et al., 2004) and argued that this evidence pr ovides only a “weak a ssociation” with PM 2.5 exposures. This commenter asserted that many of these long-term exposure studies evaluating respiratory effects we re considered at the time the EPA reaffirmed the current annual standard level of 15 μg/m 3 in 2006, that the Administra tor in the last review determined that the information they provided “was too limited to serve as the basis for setting a level of a national standard,” and th at they should be given little weight in setting the level of the annual standard in this re view (UARG, 2012, Attachment 1, p. 14).II-68 More specifically, this co mmenter asserted that the McConnell et al. (2003) and Gauderman et al. (2004) studies reported mixed results for associations with PM 2.5 and stronger associations with NO 2 (API, 2012, Attachment 1, pp. 14 to 15). Similarly, this commenter argued that the Dock ery et al. (1996) and Raizen ne et al. (1996) studies showed stronger associations with acidity than with fine particles (measured as PM 2.1 ).

Id. pp. 15 to 16. With regard to the cystic fi brosis study, this comme nter noted that the association between pulmona ry exacerbations and PM 2.5 in this study was no longer statistically significant when the model ad justed for each individual’s baseline lung function. The commenters referred to the data on lung function as an “important explanatory variable,” and s uggested that the EPA should re ly on results from the model

that included individual baseli ne lung function information. Id . p. 16.

Response: For the reasons discussed in section III .E.4.c.i of the preamble for the final rule, the response in section II.B.1.b above, and the further response below, the EPA disagrees with the commenters’ interpretation of these studies.

As an initial matter, the EPA notes that th ree of these studies (McConnell et al., 2003; Dockery et al., 1996; Raizenne et al., 1996) as well as the initial studies from the Southern California Children’s Health Study (P eters et al., 1999; McConnell et al., 1999’ Gauderman et al., 2000, 2002; Avol et al., 2001) were discussed and considered in the 2004 Air Quality Criteria Document (U.S. EPA, 2004) and, thus, cons idered within the air quality criteria suppo rting the EPA’s final decisions in the review completed in 2006. Two additional studies (Gauderman et al., 2004; Goss et al., 2004) were discussed and considered in the provisional science asse ssment conducted for the last review (U.S. EPA, 2006a). All of these studies were consid ered in the ISA that informs the current review (U.S. EPA, 2009a).

With regard to the Southern California Children’s Health Study, extended analyses considered in the ISA provided evidence that clinically important deficits in lung

function 23 associated with long-term exposure to PM 2.5 persist into early adulthood (U.S. EPA, 2009a, p. 7-27; Gauderman et al., 2004). These effects remained positive in copollutant models. 24 Additional analyses of the Southern California Children’s Health Study cohort reported an associ ation between long-term PM 2.5 exposure and bronchitic symptoms (U.S. EPA, 2009a, p. 7-23 to 7-24; McConnell et al., 2003, long-term mean concentration of 13.8 μg/m 3 ) that remained positive in co-pollutant models, with the

PM 2.5 effect estimates increasing in magnitude in some models and decreasing in others, and a strong modifying effect of PM 2.5 on the association between lung function and asthma incidence (U.S. EPA, 2009a, 7-24; Is lam et al., 2007). The outcomes observed in the more recent reports from the Southern California Children’s Health Study, including

23 Clinical significance was defined as an FEV 1 below 80 percent of the predicted value, a criterion commonly used in clinical settings to identify persons at increased risk for adverse respiratory conditions (U.S. EPA, 2009a, p. 7-29 to 7-30). The primary NAAQS for sulfur dioxide (SO 2 ) also included this interpretation for FEV 1 (75 FR 35525, June 22, 2010).

24 Gauderman et al. (2004) clearly stat ed throughout their analysis that NO 2 was one component of a highly

correlated mixture that contains PM 2.5 . Gauderman et al. (2004) did not present the results from copollutants models but stated “two-pollutant models for any pair of pollutants did not provide a significantly better fit to the data than the corresponding single-pollutant models.”II-69 evaluation of a broader range of endpoints a nd longer follow-up period s, were larger in magnitude and more precise than reported in the initial version of the study. Supporting these results were new longitudinal cohort studies conducted by other researchers in varying locations using different methods (U.S. EPA, 2009a, section 7.3.9.1). The EPA, therefore, disagrees with the commenters th at the studies by McC onnell et al. (2003) and Gauderman et al. (2004) are flawed and should not be used in the PM NAAQS review

process.

The 24-City study 25 by Dockery et al. (1996) (long-t erm mean concentration of 14.5 μg/m 3 ) was considered in the current as well as two previous reviews (U.S. EPA, 2009a; U.S. EPA, 2004; U.S. EPA, 1996). This study observed that PM, specifically “particle strong acidity” and sulfate particles (indicators of fine particles), were associated with reports of bronchitis in the pr evious year. Similarly, the ma gnitude of the associations

between bronchitis and PM 10 and PM 2.1 were similar to those for acidic aerosols and sulfate particles, though the c onfidence intervals for the PM 10 and PM 2.1 associations were slightly wider and the associations were not statistically signi ficant. Acid aerosols, sulfate, and fine particles are formed in secondary reactions of the emissions from incomplete combustion and these pollutant s have similar regional and temporal distributions. As noted by the study authors, “the strong corre lations of several pollutants in this study, especially particle st rong acidity with sulfate (r=0.90) and PM 2.1 (r=0.82), make it difficult to distingui sh the agent of in terest” (Dockery et al., 1996, p. 505). Overall, Dockery et al. (1996) (and, simila rly, Raizenne et al., 1996) observed similar associations between respiratory health effects and acid aerosols, sulfate, PM 10 and PM 2.1 concentrations. The commenters noted that th e associations with particle acidity were

sensitive to the inclusion of the six Canadi an sites. The EPA notes that none of these

Canadian cities were in the “s ulfate belt” where particle st rong acidity was highest. Thus, the change in the effect estimate when the si x Canadian cities were excluded from the analysis is likely due to the lower prevalen ce of bronchitis and the lower concentrations of acid aerosols in these cities, and not due to some difference in susceptibility to bronchitis between the U.S. and Canadian popula tions that is not due to air pollution, as suggested by the commenters (UARG, 2012, Attach ment 1, p. 15). In fact, contrary to the statements made by the commenters, the au thors did not observe any subgroups that appeared to be markedly more susc eptible to the risk of bronchitis.

The Goss et al. (2004) study considered a U.S. cohort of cystic fibrosis patients and provided evidence of association between long-term PM 2.5 exposures and exacerbations of respiratory symptoms resu lting in hospital admissions or use of home intravenous antibiotics (U.S. EPA, 2009a, p. 7-25; l ong-term mean concentration of 13.7 μg/m 3 ). The

commenters noted that the association between pulmonary exacerbations and PM 2.5 in this study was no longer statistically signi ficant when the model adjusted for each individual’s baseline lung function. The commenters referred to the data on lung function as an “important explanatory variable,” and suggested that the EPA should rely on results

from the model that included individual baseline lung function information. The EPA

25 The 24-City study conducted by Dockery et al. (1996) included 18 sites in the U.S. and 6 sites in Canada. The Raizenne et al. (1996) study considered 22 of these 24 study areas. Athens, OH and South Brunswick, NJ were not included in this study.II-70 disagrees with the commenters’ interpretati on of this study. The Agency concludes it is unlikely that lung function is a potential conf ounder or an important explanatory variable in this study. In fact, the au thors noted that “it is more likely that lung function decline may be intimately associated with chronic expo sure to air pollutants and may be part of the causal pathway in worsening prognosis in CF [cystic fibrosis]; in support of this explanation, we found both cr oss-sectional and longitudinal strong inverse relationships

between FEV 1 and PM levels” (Goss et al., 2004, p. 819). The EPA notes that adjusting for a variable that is on the causal pathway can lead to overadjustment bias, which is likely to attenuate the association (Schiste rman et al. 2009); this is likely what was observed by the authors. Thus, the EPA continue s to believe it is appropriate to focus on the results reported in Goss et al. (2004) that did not in clude individual baseline lung

function in the model.

In addition, the EPA disagrees with comme nters’ reliance solely on statistical significance when interpreting the study results from indivi dual study results and the

collective evidence across studies. As discussed in section III.D.2 of the preamble to the final rule and in the response in secti on II.B.1.b above, statisti cal significance of individual study findings has played an impor tant role in the EPA’s evaluation of the study’s results and the EPA has placed greate r emphasis on studies re porting statistically significant results. However, in the broa der evaluation of the evidence from many epidemiological studies, and subsequently during the process of forming causality determinations in the Integrated Science A ssessment by integrating evidence from across epidemiological, controlled human exposure, and toxicological studies, the EPA has emphasized the pattern of results across epidemiological studies and whether the effects

observed were coherent across the scientific disciplines for drawing conclusions on the relationship between PM 2.5 and different health outcomes. The EPA notes further that the

D.C. Circuit has held that the EPA can look to other indicia of reliability such as the consistency and coherence of a body of studies as well as other confirming data to justify reliance on the results of a body of epidemiol ogical studies, even if individual studies may lack statistical significance. American Trucking Association v. EPA , 283 F. 3d at 371 (in the context of discussing whether study results were confounded by co-pollutants).

As noted in section III.B.1.a of the proposal , with regard to resp iratory effects, the Integrated Science Assessment concluded that extended analyses of studies available in the last review as well as new epidemiologi cal studies conducted in the U.S. and abroad provided stronger evidence of re spiratory-related morbidity associated with long-term

PM 2.5 exposure (77 FR 38918). The strongest ev idence for respiratory-related effects available in this review was from epidemiol ogical studies that evaluated decrements in lung function growth in children and incr eased respiratory symptoms and disease incidence in adults (U.S. EPA, 2009a, sections 2.3.1.2, 7.3.1.1, and 7.3.2.1).

In considering the collective evidence from epidemiological, toxicological, and controlled human exposure studies, includi ng the studies discussed above, the EPA recognizes that the Integrated Science Assessm ent concluded that a causal relationship is likely to exist between long-term PM 2.5 exposures and respiratory effects (U.S. EPA, 2009a, p. 2-12, pp. 7-42 to 7-43). CASAC concurre d with this causal ity determination (Samet, 2009f, p.9).II-71 The commenter’s assertion that the EPA should adhere to its assessment of these studies as it did in the review completed in 2006 is significantly mistak en. Most obviously, the

EPA’s final decision in the last review was he ld to be deficient by the D.C. Circuit in remanding the 2006 primary annual PM 2.5 standard. As discussed in section III.A.2 of the preamble to the final rule, the D.C. Circuit sp ecifically held that the EPA did not provide a reasonable explanation of why certain morbidity studies, including an earlier study

from the Southern California Children’s H ealth Study (Gauderman et al., 2000, long-term

mean PM 2.5 concentration approximately 15 μg/m 3 ) and the 24-Cities Study (Raizenne et al., 1996, long-term mean concentrations approximately 14.5 μg/m 3 ) did not warrant a more stringent annual PM 2.5 standard when the long-term mean PM 2.5 concentrations reported in those studies were at or lower than the level of the annual standard. American

Farm Bureau Federation v. EPA . 559 F. 3d at 525. Indeed, the court found that, viewed together, the Gauderman et al. (2000) and Raizenne et al., (19 96) studies “are related and together indicate a significant publ ic health risk...On this recor d, therefore, it appears the EPA too hastily discounted the Gauderman and 24-Cities studies as lacking in significance.” Id.

In this review, the EPA recognizes a signi ficant amount of evid ence beyond these two studies that expands our unders tanding of respiratory effect s associated with long-term

PM 2.5 exposures. This body of scie ntific evidence includes an extended and new analyses

from the Southern California Children’s H ealth Study (Gauderman et al., 2004; Islam et al., 2007; Stanojevic et al., 2008) as well as ad ditional studies that examined these health effects (Kim et al., 2004; Goss et al., 2004). Thus , even more so than in the last review,

the evidence indicates a “si gnificant public health risk” to children from long-term PM 2.5 exposures at concentrations below the level of the current annual standard. A standard that does not reflect appropriate consideration of this eviden ce would not be requisite to protect public health with an adequate margin of safety.

(5) Comment : With regard to the use of studies of health effects for which the EPA finds the evidence to be “suggestive” of a causal relationship, some commenters argued that such studies “do not merit any we ight in the setting of the annual NAAQS” (e.g., UARG, 2012, Appendix 1, p. 3). One commenter asserted that the proposed us e of evidence that is only suggestive of a causal relationship to support revisi on to the primary annual PM 2.5 standard is inconsistent with the EPA use of such evidence to retain the primary 24-hour

PM 10 standard and “represents a significant de parture from the Agency’s precedent and is not justified” (AFPM, 2012, p. 2).

Response: The EPA disagrees with the commenter’s view that studies of health effects for which the evidence is suggestive of a causa l relationship, rather th an studies of health effects for which the evidence supports a ca usal or likely causal relationship, merit no weight at all in setting th e NAAQS. To place no weight at all on such evidence would in

essence treat such evidence as though it had been categorized as “not likely to be a causal relationship.” To do so would ignore the impor tant distinctions in the nature of the evidence supporting these different causality de terminations in the ISA. It would also ignore the CAA requirement that primary sta ndards are to be set to provide protection with an adequate margin of safety, includi ng providing protection for at-risk populations. Thus, ignoring this information in making de cisions on the appropriate standard levelII-72 would not be appropriate. 26 Nonetheless, in considering studies of health effects for which the evidence is suggestive of a causal relationship, the EPA does believe that it is appropriate to place less weight on such studies than on studies of health effects for

which there is evidence of a causa l or likely causal relationship.

The EPA also disagrees with the commenters’ assertion that the EPA’s bases for final decision on the primary PM 2.5 and PM 10 standards are inconsistent. As discussed in sections III.E.4.d and IV. G of the preamble to the final rule, in each case the EPA has

considered the relevant available scientific evidence and the uncertainties and limitations

associated with that evidence to reach fi nal decisions on the appropriate primary PM 2.5 and PM 10 standards.

(6) Comment: Some commenters questio ned the long-term mean PM 2.5 concentration reported in the final PA and used in Figure 4 of the proposal for th e Miller et al. (2007) study (e.g., API, 2012, Attachment 1, p. 8; UARG, 2012, Attachment 1, pp. 2 to 3, fn 3, p. 12).

Response: The EPA recognizes that the study aut hors originally reported a long-term

mean PM 2.5 concentration of 13.5 μg/m 3 (Miller et al., 2007, Table 2). This concentration was presented in the ISA (US EPA, 2009a) a nd discussed in the second draft PA (US EPA, 2010f). In response to a request from the EPA for additional information on the air quality data used in selected epidemiologi cal studies (Hassett-Si pple and Stanek, 2009), study investigators provided updated air quali ty data for the study period. The updated long-term mean PM 2.5 concentration provided by the study authors was 12.9 μ g/m 3
(personal communication from Cynthia Curl, 2009; Stanek et al., 2010). The final PA noted that this updated long-term mean c oncentration matched the composite monitor approach annual mean calculated by the EPA (Hassett-Sipple et al., 2010, Attachment A, p. 6) for the year of air quality data (i .e., 2000) considered by the study investigators (U.S. EPA, 2011a, p. 2-32, fn 24). The EPA staf f concluded it was mo st appropriate to include the updated air quality data in the final PA ( Id .). Thus, the long-term mean PM 2.5 concentration for Miller et al . (2007) discussed in the proposal and presented in Figures 1 and 4 of the proposal was reported as 12.9 μ g/m 3 . The PA noted that in comparison to other long-term exposure studies, the Miller et al. ( 2007) study was more limited in that it was based on only one year of air quality data (U.S. EPA, 2011a, p. 2-82). The proposal further noted that the air quality data consider ed were extrapolated from that one single year of air quality data (2000) to the whole study, and that the air quality data post-dated the years of health events consider ed (i.e., 1994 to 1998) (77 FR 38918, fn 62).

For the reasons discussed in section III.E.4.c.i of the preamble to the final rule, the EPA does not now consider it appropriate to put weight on the reported long-term mean concentration from the Miller et al. (2007) st udy (either the original value reported in the published study nor the updated value provided by the study authors) for the purpose of

26 As discussed in section II.A of the preamble to the fina l rule, the requirement that primary standards provide an adequate margin of safety was intended to address uncertainties associated with inconclusive scientific and technical information available at the time of standard setting. It was also intended to provide a reasonable degree of protection against hazards that research has not yet identif ied. This certainly encompa sses consideration of effects for which there is evidence suggestive of a causal relationship.II-73 translating the epidemiological information from the long-term e xposure studies into a basis for selecting the level of the annual PM 2.5 standard. Nonetheless, the EPA notes that the Miller et al. (2007) study pr ovides strong evidence of car diovascular-related effects associated with long-term PM 2.5 exposures to inform causality determinations reached in the ISA (U.S. EPA, 2009a, sections 7.2.11 and 7.6).

(7) Comment: Some commenters who supported retain ing current annual standard level argued there is no basis for the EPA to select a level lower than 13 μg/m 3 (e.g., NAM et al., 2012, pp. 26 to 27; Class of ’85, 2012, p. 2; Dow, 2012, pp 1 to 3).

Response: The EPA disagrees with the commenters’ vi ews that there is no basis to select a level below 13 μg/m 3 . As discussed in section III.E.4.d of the preamble for the final rule, in light of the entire body of scientific evidence and te chnical analyses considered, the EPA Administrator judges that an annual standard level set above 12 would not be sufficient to protect public health with an ad equate margin of safety from the serious

health effects associated w ith long- and short-term PM 2.5 exposures.

(8) Comment : In raising objections to th e requirement for near-road PM 2.5 monitoring, one industry group (AFPM, 2012) compared the consideration of PM gradients around roadways in the current review to the consideration of NO 2 gradients discussed in the most recent revision of the primary NO 2 NAAQS (75 FR 6474, February 9, 2010). Specifically, in discussing the EPA’ s decision to set a new 1-hour NO 2 standard at a level of 100 parts per billion, these commenters stated the following:

In taking this action, EPA noted that NO 2 concentrations could be expected to vary, and therefore, the differences between near-roadw ay monitors and area-wide concentrations that had been used to measure compliance with the pre-existing NO 2 annual standard

could result in a variable level of the standard ( i.e ., between 50 ppb and 75 ppb based on whether concentrations near roadways were 100% or 30% higher than at other monitors). Yet, in this proposed rule, EPA does not offe r any comparable analysis with respect to the relative stringency of a PM 2.5 annual or 24-hour NAAQS as implemented through a

network of new roadside monitors.

Response: As explained in section III.E.4.c.i of the preamble to the final rule and in response to Comment (1) above, it is appropriate to compare the PM 2.5 concentrations

from a maximum area-wide monito r to the level of the annual PM 2.5 standard. Consequently, the approach adopted in this rulemaking for the PM 2.5 standard is

consistent with the ultimate th rust of the approach in the NO 2 NAAQS: providing a level of protection in an area with a maximum monitor afford s requisite protection across the entire area. However, given differences in th e bodies of available scientific evidence for

NO 2 and PM 2.5 , it is appropriate that the EPA employe d different types of analyses in the

two reviews to achieve this ulti mate result. In the case of NO 2 , the scientific evidence that

formed the basis for the final decision on th e level of the revised standard included both epidemiological studies, reporting associations between respiratory endpoints and areawide NO 2 concentrations, and controlled human exposure studies, reporting respiratory effects following short-term exposures to NO 2 concentrations at or above 100 ppb. In considering this evidence, the Administrator set a new 1-hour standard with a level ofII-74 100 ppb.

In setting this new standard, information on the NO 2 gradients around roadways was used

to consider the relations hips between area-wide NO 2 concentrations and potential exposure concentrations. Specifically, because the revised NO 2 standard was intended to

reflect the maximum allowable NO 2 concentration in an area, the Administrator

concluded that this standard would limit exposures to NO 2 concentrations reported in controlled human exposure studies to result in respiratory effects. In reaching this conclusion, the Administrator noted that the highest NO 2 exposure concentrations in urban areas could occur around major roadways. In addition, given the available evidence

for NO 2 concentration gradients around roadways , she concluded that the new standard

would maintain area-wide NO 2 concentrations (away from major roads) well below those in locations where key U.S. epidemiologica l studies had reported associations with adverse respiratory effects (75 FR 6501, February 9, 2010).

In the current review of the PM NAAQS the scientific evidence forming the basis for

final decisions on the PM 2.5 standards includes epidem iological studies reporting

associations between area-wide PM 2.5 concentrations and a number of adverse health outcomes (i.e., including mortality and a va riety of cardiovascul ar and respiratory effects). While controlled hu man exposure studies of PM 2.5 provide coherence and biological plausibility for the effects observe d in epidemiological studies, because of the exposure concentrations and dur ations evaluated they do not provide an appropriate basis

to inform decisions on the levels of the 24- hour or annual standards. In light of this

fundamental difference in the bodi es of evidence available for NO 2 and PM 2.5 , the approach to considering NO 2 roadway concentration gradient s adopted in the most recent review of the primary NO 2 NAAQS would not similarly inform the Administrator’s decisions in the current review of the PM NAAQS. 27 Therefore, the same approach would

not be warranted in the two reviews.

(9) Comment: One group of commenters asserted that “the supplemental 24-hour standard adds to the margin of safety that protect s children and other sensitive subpopulations” (NAM et al., 2012, p. 9). These commenters ar gued that when the 24-hour standard is “controlling” the long-term mean PM 2.5 concentrations were reduced well below the existing or proposed annual standard level. Thus, these commenters expressed the view that “the existing annual st andard, when considered along- side the 24-hour standard, is not only requisite to protect the public healt h, but also ensures an adequate margin of safety for sensitive subpopulations” Id.

Response: The EPA agrees with the first point raised by the commenters; that is, the 24-hour standard provides supplemental prot ection beyond the protec tion provided by the annual standard. The EPA recognizes that th e protection afforded by the two standards working together meets the CAA requirement to set primary sta ndards that provide

27 See also comments of UARG at 55 n. 73 drawing this same distinction (“The fact that the level of the PM 2.5 NAAQS is derived solely from epidemiological studies distinguishes it from the NO 2 NAAQS for which, as EPA notes, 77 Fed. Reg. at 39010/2-3, it r ecently adopted near-road m onitoring requirements. That standard was based, in significant part, on controlled human exposure studies in which actual NO 2 exposures were measured that could reasonably be compared to concentrations measured near roads. 75 Fed. Reg. at 6500/1-01/2.”).II-75 requisite public health protection with an ad equate margin of safety, including providing protection for at-risk populations.

With regard to the second point raised by these commenters, the EPA disagrees with the

commenters’ view that if the 24-hour standa rd is “controlling,” the long-term mean PM 2.5 concentrations would be reduced well belo w the existing or proposed annual standard level. This comment would only be true if the 24-hour sta ndard level was substantially lowered. As illustrated in Figure 2-10 of th e PA, based on 2007 to 2009 air quality data, many counties across the country woul d likely meet the current 24-hour PM 2.5 standard of 35 μg/m 3 but not the current or alternative an nual standard, i.e., the lower right quadrant of the figure characte rizing counties where the annu al standard would be the controlling standard (U.S . EPA, 2011a, p. 2-90).

Furthermore, the EPA recognized in the sec tion III.A.3 of the pr oposal that there are various ways to combine the annual and 24- hour standards to achieve an appropriate degree of protection. The extent to which th ese two standards are interrelated in any given area depends in large part on the relative levels of the standards, the peak-to mean ratios that characterize air quality patterns in an area, and whether changes in air quality designed to meet a given suite of standards are likely to be of a more regional or more localized nature (77 FR 38902), While the EPA recognized that changes designed to meet a 24-hour standard would result not only in fewer and lower peak 24-hour concentrations (especially when coupled with a high percentile-based form, such as the 98 th percentile)

but also in lower annual mean concentrati ons, the EPA also noted that changes in PM 2.5 air quality designed to meet an annual standard would lik ely result not only in lower annual average PM 2.5 concentrations but also in fewer and lower peak 24-hour PM 2.5 concentrations. As discussed in section III.E .4.d of the preamble to the final rule, based on the evidence and quantitative risk assessment, the EPA concludes that it is appropriate to setting an annual standard that is gene rally controlling, which will lower the broad distribution of 24-hour average concentrations in a area as well as the annual average concentration, so as to provide protec tion from both long- and short-term PM 2.5 exposures, with the 24-hour standard providing supplemental protection. The EPA concludes this approach will reduce aggregate risks associated with both long- and shortterm exposures more consistently than a generally controlling 24-hour standard and is the most effective and efficient way to reduce total PM 2.5 -related population risk and so provide appropriate protection.

(10) Comment: One commenter argued that “data from the available epidemiological studies suggest that effects of chroni c PM exposure are reversible an d that even small reductions

in PM levels decrease cardi ovascular mortality within a time frame as short as a few years (Dow, 2012, pp. 2 to 3).

Response: The EPA disagrees that all effects of chronic PM exposure are reversible. The

ISA concluded that there is a causa l relationship between long-term PM 2.5 exposure and mortality (U.S. EPA, 2009a, sections 2.3.1 a nd 7.6), obviously an irreversible effect. Furthermore, with regard to morbidity e ffects, extended analyses of the Southern California Children’s Health Study provide eviden ce that clinically im portant deficits inII-76 lung function associated with chil dren’s long-term exposure to PM 2.5 persisted into early adulthood (77 FR 38907; U.S. EPA, 2009a , p. 7-27; Gauderman et al., 2004).

The EPA agrees with the commenter’s asser tion that improvements in community health related to reducing PM 2.5 concentrations do not require a long latency period. As noted in the proposal (77 FR 38907), the strength of th e causal relationship between long-term

PM 2.5 exposure and mortality also builds upon new studies providing evidence of improvement in community health following redu ctions in ambient fine particles. Pope et al. (2009) documented the population health be nefits of reducing am bient air pollution by correlating past reductions in ambient PM 2.5 concentrations with increased life expectancy. These investigators reported that reductions in ambient fine particles during

the 1980s and 1990s account for as much as 15 percent of the overall improvement in life expectancy in 51 U.S. metropolitan areas, with the fine particle reductions reported to be

associated with an estimated increase in m ean life expectancy of approximately 5 to 9 months (U.S. EPA, 2009a, p. 7–95; Pope et al., 2009). An extended analysis of the Harvard Six Cities study found that as cities cleaned up their air, locations with the largest reductions in PM 2.5 saw the largest improvements in reduced mortality rates,

while those with the smallest decreases in PM 2.5 concentrations saw the smallest improvements (Laden et al., 2006). Another ex tended follow-up to the Harvard Six Cities study investigated the delay be tween changes in ambient PM 2.5 concentrations and changes in mortality (Schwartz et al., 2008) a nd reported that the effects of changes in

PM 2.5 were seen within the 2 years prior to death (U.S. EPA, 2009a, p. 7–92; Figure 7–9). Looking more broadly across studies, the IS A concluded, “Generally, these results indicate a developing coherence of the air po llution mortality literat ure, suggesting that the health benefits form reducing air pollu tion do not require a long latency period and would be expected within a few years of intervention” (U.S. EPA, 2009a, p. 7-95).

(11) Comment: One commenter recognized the need to protect human health and supported the EPA’s effort to set a primary annual PM 2.5 standard that protects human health with an adequate margin, as required by the CAA. However, this commenter asserted that the “EPA should consider the impact of using b ackground levels in establishing the standard.

If the annual PM standard is set close to or below background level, it would be impossible for nonattainment ares to attain the standard (AASHTO, 2012, p.2). This

commenter recommended that “the standard be set at a level that is realistic and

attainable since the standard will lose its meaning as background le vels are approached.”

Id.

Response: The EPA notes that the PM 2.5 standard levels established in the final rule (i.e., an annual standard level of 12 μg/m 3 and a 24-hour standard level of 35 μg/m 3 ) are well above the policy-relevant bac kground concentrations considered in the ISA (U.S. EPA, 2009a, sections 3.6, 3.7 and 3.9.1.7). Therefore, the concern raised by the commenter remains simply an academic one.

(12) Comment: Some of these commenters also identified “new” studies as providing additional evidence to support th eir views that the annual sta ndard level does not need to

be revised.II-77 Response: As discussed in section II.B.3 of the pr eamble to the final rule and in section II.B.1.a above, the EPA notes that, as in pa st NAAQS reviews, the Agency is basing the

final decisions in this review on the studies and related information included in the PM ISA that have undergone CASA C and public review, and will consider newly published studies for purposes of decision making in th e next PM NAAQS review. Nonetheless, in provisionally evaluating commenters’ argumen ts, the EPA notes that its provisional

assessment of “new” science found that such studies did not materially change the conclusions reached in the ISA (U.S. EPA, 2012b).

ii. Support for Revising the Current Level

A second group of commenters supporte d revising the suite of primary PM 2.5 standards to provide increased public health protection. Th ese commenters found the available scientific information and technical analyses to be stronge r and more compelling than in the last review. These commenters generally placed substantia l weight on CASAC advi ce and on the EPA staff analyses presented in the fina l PA. While generally supporting th e EPA’s proposal to lower the level of the annual standard, many commenters in this group disagreed that a level within the EPA’s proposed range (i.e., 12 to 13 μg/m 3 ) was adequately protectiv e and supported a level of 11 μg/m 3 or below.

In general, these commenters expressed the view that given the strength of the available scientific evidence, the serious nature of the health effects associated with PM 2.5 exposures, the large size of the at-risk populations, the risk s associated with l ong- and short-term PM 2.5 exposures, and the important uncertainties inhere ntly present in the evidence, the EPA should follow a highly precautionary policy response by selecting an annual standard level that incorporates a large margin of safety.

More specifically, these commenters offered a range of comments related to the general approach used by the EPA to select standard leve ls, including: (1) the EPA’s approach for setting a generally controlling annual st andard; (2) the importa nce of the greatly expanded and stronger overall scientific data base; (3 ) consideration of the distributional statisti cal analysis conducted by the EPA and other approaches for translati ng the air quality information from specific epidemiological studies into standard le vels; and (4) the significance of the PM 2.5 -related public health impacts, especially potential impact s on at-risk populations, including children, in reaching judgments on setting standards that provide protection with an adequate margin of safety. These comments are discussed in turn below.

(1) Comment: Some of these commenters disagreed w ith the EPA’s approach for setting a “generally controlling” annua l standard in conjunction wi th a 24-hour standard providing supplemental protection particularly for ar eas with high peak-to-mean ratios. These commenters argued this approach would lead to “regional ine quities” as demonstrated in the EPA’s analyses contained in Appendix C of the PA (ALA et al., pp. 26 to 27). Specifically, these commenters argued:

There is no basis in the CAA for such a determination. The CAA requires only that the NAAQS achieve public health prot ection with an adequate margin of safety. It is well-documented that both long- and short-term exposures to PM 2.5II-78 have serious and sometimes irreversible health impacts. There is no health protection reason to argue that one standard should be “controlling” as a matter of policy without regard to the health conse quences of such a policy. To adopt such a policy ignores the obligation to provid e equal protection under the law to all

Americans because it would result in une ven protection from air pollution in different localities and regions of the country (ALA et al., 2012, p. 26).

Response: The EPA believes these commenters misunderstood the basis for the EPA’s policy goal of setting a “genera lly controlling” annual standa rd. This approach relates exclusively to setting standards that will provide requisite protection against effects associated with both long- and short-term PM 2.5 exposures. It does so by lowering the overall air quality distributions across an area, recognizing that changes in PM 2.5 air quality designed to meet an annual standard would likely result not only in lower annual

mean PM 2.5 concentrations but also in fewer and lower peak 24-hour PM 2.5 concentrations. As discussed in section III.A.3 in the proposal and in the preamble to the final rule, the EPA recognizes that there are various ways to combine the two primary

PM 2.5 standards to achieve an appropriat e degree of public health protection. Furthermore, the extent to which these two standards are interrelat ed in any given area depends in large part on the rela tive levels of the standards, the peak-to-mean ratios that characterize air quality patterns in an area, and whether ch anges in air quality designed to meet a given suite of standards are likely to be of a more regional or more localized

nature.

In focusing on an approach of setting a ge nerally controlling annual standard, the EPA’s intent is in fact to avoid the potential “regio nal inequities” that are of concern to these commenters. The EPA judges that the most appr opriate way to set standards that provide more consistent public health protection is by using the approach of setting a generally controlling annual standard. Th is judgment builds upon information presented in the PA as discussed in section III.A.3 of the preamble to the final rule. More specifically, the PA recognized that the short-term exposure studie s primarily evaluated daily variations in health effects with monitor(s) that measured the variation in daily PM 2.5 concentrations over the course of several y ears. The strength of the a ssociations observed in these epidemiological studies was demonstrably in the numerous “typical” days within the air quality distribution, not in the p eak days (U.S. EPA, 2011a, p. 2-9). In addition, the quantitative risk assessments conducted for th is and previous reviews demonstrated the same point: that is, much, if not most, of th e aggregate risk associated with short-term

PM 2.5 exposures results from the large number of days during which the 24-hour average concentrations are in the low-to mid-range, below the peak 24-hour concentrations (U.S. EPA, 2011a, section 2.2.2; U.S. EPA, 2010a, section 3.1.2.2). In addition, there was no evidence suggesting that risks associated with long-term e xposures were likely to be disproportionately driven by peak 24-hour concentrations. 28 See also American Trucking

Association v. EPA , 283 F. 3d at 373 (rejecting arguments to lower the level of the daily

PM 2.5 standard when there is persuasive eviden ce that the main risk from exposure comes

28 In confirmation, a number of studies have presented analyses excluding higher PM concentration days and reported a limited effect on the magnitude of the effect estimates or statistical significance of the association (e.g., Dominici, 2006b; Schwartz et al., 1996; Pope and Dockery, 1992).II-79 from the entire air quality distribution ra ther than from peak days, and the annual

standard will lower that distribution).

For these reasons, the PA concluded that st rategies that focused primarily on reducing peak days were less likely to achieve reductions in the PM 2.5 concentrations that were most strongly associated with the observed he alth effects. Furthermore, the PA concluded that an approach that focused on reducing peak exposures would most likely result in more uneven public health protection across the U.S. by either providing inadequate protection in some areas or overprotecting in other areas (U.S. EPA, 2011a, p. 2-9; U.S. EPA, 2010a, section 5.2.3). This is because reductions based on control of peak days are less likely to control the bulk of the air qua lity distribution. As noted above, this would create the very inequity of resu lts the commenters seek to avoid.

As a result, the EPA believes an approach that focuses on a generally controlling annual standard would likely reduce a ggregate risks associated with both long- and short-term exposures more consistently than a generally controlling 24-hour sta ndard and, therefore,

would be the most effective and efficient way to reduce total PM 2-5 -related population risk. The CASAC agreed with this approach an d considered it was “appropriate to return to the strategy used in 1997 that consider s the annual and the short-term standards together, with the annual standa rd as the controlling standard , and the short-term standard supplementing the protection afforded by the annual standard” (Samet, 2010d, p. 1). The EPA thus disagrees with the comments that this approach will result in the concerns raised by the commenters; rather the EPA c oncludes that this approach will help to

address these concerns.

(2) Comment: Many of these commenters asserted th at the currently available scientific information is greatly expanded and stronger compared to the last review. Some of these commenters highlighted the availability of multiple, multi-city long- and short-term exposure studies providing “repeated, consis tent evidence of eff ects below the current annual standard level” (ALA et al., 2012, pp. 39 to 49) and, more specifically, “significant evidence of harm with strong confidence well below EPA’s proposed annual standard range of 12-13 μg/m 3 ” (AHA et al., 2012, pp. 10 to 12).

Response: The EPA recognizes that in setting st andards that are requisite to protect public health with an adequate margin of safety, the Administrator must weigh the various types of available scientific info rmation in reaching public health policy judgments that neither overstate nor understa te the strength and limitations of this information or the appropriate inferences to be drawn from the available science.

In general, the EPA agrees with these commenters’ views that the currently available

scientific evidence is stronger “because of its breadth a nd the substantiati on of previously observed health effects” (77 FR 38906/2) a nd provides “greater confidence in the reported associations than in the last revi ew” (77 FR 38940/1). The EPA also agrees with the commenters’ position that it is appropriate to consider the regions within the broader air quality distributions where we have th e strongest confidence in the associations reported in epidemiological studies in setti ng the level of the annual standard. However, as discussed in section III.E.4.d of the pr eamble to the final rule, in weighing the available evidence and technical analyses, as well as the associated uncertainties andII-80 limitations in that information, the EPA disa grees with the commenters’ views regarding

the extent to which the available scientific information provides support for considering an annual standard level below the proposed range (i.e., below 12 to 13 μg/m 3 ). In particular, the EPA disagrees with the de gree to which these commenters place more weight on the relatively more uncertain ev idence that is suggestive of a causal relationship (e.g., low birth weight). Cons istent with CASAC advice (Samet, 2010d, p. 1), the Agency concludes it is appropriate and reasonable to place the greatest emphasis

on health effects for which the ISA conclude d there is evidence of a causal or likely causal relationship and to place less weight on the health effects that provide evidence that is only suggestive of a causal relationship.

(3) Comment : With regard to using the air quality information from epidemiological studies to inform decisions on standard levels, comm enters in this group generally supported the EPA’s efforts to explore diffe rent statistical metrics from epidemiological studies to

inform the Administrator’s decisions. Th ese commenters argued that by considering different analytic measures -- either concen trations one standard deviation below the long-term means reported in the epidemiological studies or the EPA’s distributional statistical analysis of population-level data that extends th e approach used in previous PM NAAQS reviews to consider information beyond a single statistical metric -- “the annual standard must be significantly lower than EPA has proposed” (ALA et al., 2012, pp. 50 to 61). Furthermore, with rega rd to characterizing the PM 2.5 air quality at which associations have been observed, some of these co mmenters highlighted CASAC’s recommendation that “[f]urther consideration s hould be given to using the 10 th percentile as a level for assessing various scenarios of levels for the PM NAAQS” (Samet, 2010c, p. 11) (ALA et al., 2012, p. 55). Other commenters urged that the EPA extend the distributional analysis to include additional studies. For example, CHPAC urged the EPA to also conduct distributional analysis for childr en’s health studies to better inform standards that would protect both children and adults from a dverse health outcomes (CHPAC, 2012, p. 3).

Response: The EPA agrees with these commenters’ views that it is appropriate to take

into account different statistical metrics fr om epidemiological studies to inform the decisions on standard levels that are appropriate to consider in setting a standard that will protect public health with an adequate margin of safety. In the development of the PA, the EPA staff explored various approaches for using information from epidemiological studies in setting the standards. The general approach used in the final PA, discussed in sections III.A.3 and III.E.4.a of the preamble to the final rule, refl ects consideration of CASAC advice (Samet, 2010c,d) and public comments on multiple drafts of the PA.

With regard to using the distributional statis tical analysis to char acterize the confidence in the associations, the EPA emphasizes that there is no clear di viding line provided by the scientific evidence, and that choo sing how far below the long-term mean concentrations from the epidemiological studies is appropriate to id entify a sta ndard level that will provide protection for the public health with an adequate margin of safety is largely a public health policy judgment. In this review, the EPA considers the region from approximately the 25 th to 10 th percentiles to be a reas onable range for providing a general frame of reference as to the part of the distribution over which our confidence in the magnitude and significance of the associat ions observed in epidemiological studies isII-81 appreciably lower. Based on these consider ations, the EPA concludes that it is not appropriate to place as much confidence in the magnitude and significance of the associations over the lower per centiles of the distributions in each study as at and around the long-term mean concentrations. Thus, th e EPA disagrees with the commenters’ views that this analysis compels placing more em phasis on the lower part of this range in selecting a level for an annual standard that will protect public health with an adequate margin of safety. The EPA recognizes that this information comes primarily from two short-term exposure studies, a relatively modest data set. In light of the limited nature of this information, and in recognition of more general uncertainties inherent in the epidemiological evidence, the Administrator deems it reasonable not to place more emphasis on concentrations in the lower part of this range, as discussed in section III.E.4.d of the preamble to the final rule.

With regard to the scope of the distributi onal statistical analysis, the EPA requested additional population-level data from the study authors for a group of six multi-city studies for which previous air quality analys es had been conducted (H assett-Sipple et al., 2010; Schmidt et al., 2010, Analysis 2). Thes e six studies were or iginally selected because they considered multiple locations representing varying geographic regions across multiple years. Thus, these studies prov ided evidence on the influence of different particle mixtures on health effects as sociated with long- and short-term PM 2.5 exposures. In addition, these multi-city studies considered relatively more recent health events and air quality conditions (1999 to 2005). As disc ussed in section III.E.4.b.i of the preamble to the final rule, the EPA received and analy zed population-level data for four of the six studies (Rajan et al., 2011). Three of these f our studies (Krewski et al., 2009a; Bell et al., 2008; Zanobetti and Schwartz, 2009) served as the basis for the C-R functions used to develop the core risk estima tes (U.S. EPA, 2010a, section 3.3.3). While the EPA agrees

that it would be useful to have such data fr om more studies, the Ag ency believes that the additional data that was requested and r eceived from study authors provide useful information to help inform the Administrator’s selection of the annual standard level.

(4) Comment: Many commenters in this group highlighted PM 2.5 -related impacts on at-risk populations, including potential impacts on children, older adults , persons with preexisting heart and lung disease, and low-income populations, to support their views that the annual standard should be revised to a level of 11 μg/m 3 or lower (e.g., CHPAC, 2012; AHA et al., 2012; ALA, 2012, pp. 29 to 38; Rom et al., 2012; Air Alliance Houston, et al., 2012, p. 1; PSR, pp. 2 and 4). These commenters urged the EPA to adopt a policy approach that placed less weight on the remaining uncertainties and limitations in the evidence and placed more emphasis on ma rgin of safety cons iderations, including providing protection against effects for which th ere is more limited scientific evidence. For example, CHPAC urged the EPA “to pla ce the same weight on studies examining impacts on children’s health as that of adu lt studies. ... The fact that there may be stronger evidence from adult studies does not m ean that standards based on adult studies will be protective for children and conseque ntly will meet the standard requisite to protect public health with an adequate margin of safety” (CHPAC, 2012 p. 3). Furthermore, with regard to the EPA’s a pproach for weighing uncertainties, some of these commenters stated that “we find no ju stification in the pr eamble for an annual standard level as high as 13 μg/m 3 , other than the vague asse rtion that uncertaintiesII-82 increase at lower concentrations. Further, th e final proposal completely failed to address the Policy Assessment recommendations that if 13 μg/m 3 was proposed, the 24-hour standard should be strengthened as well” (ALA et al., p. 7).

Response: The EPA has carefully evaluated and cons idered evidence of effects in at-risk populations. With regard to effects classified as having evidence of a causal or likely causal relationship with long- or short-term PM 2.5 exposures (i.e., premature mortality, cardiovascular effects, and respiratory effect s), the Agency takes not e that it considered the full range of studies evaluating these eff ects, including studies of at-risk populations, to inform its review of the primary PM 2.5 standards. Specific multi-city studies summarized in Figures 1, 2, and 3 in the preamb le for the final rule highlight evidence of effects observed in two different lifestages – children and older adults – that have been identified as at-risk populations. Thus, the EPA places as much we ight on studies that explored effects in children for which the evid ence is causal or likely causal in nature as on studies of such effects in adults, incl uding older adults. As discussed above in responses to commenters supporting the retention of the curren t standards, in setting the standard, the EPA has fo cused on considering PM 2.5 concentrations somewhat below the lowest long-term mean concentrations from each of the key studies of both long- and short-term exposures of effects for which th e evidence supports a ca usal or likely causal relationship (i.e., the first two sets of studies shown in Figur e 4 of the preamble to the final rule). The EPA has thus considered the available evidence of effects in children as well as other at-risk populations, given that those commenters urging the EPA to discount or disregard those studies pr ovided no legitimate reason to do so. With respect to the

EPA’s consideration of more limited studies providing evidence suggestive of a causal relationship (e.g., developmenta l and reproductive effects), as noted above in responding to comments from the first group of commenter s, the Agency is placing some weight on this body of evidence in setting standards th at provide protection for at-risk populations,. However, the Agency does not agree that the same weight must be placed on this information as on the body of scientific in formation for which there is evidence of a causal or likely causal relationship. To do so here would ignore the difference in the breadth and strength of the evidence suppor ting the different causality determinations

reached in the ISA.

With regard to weighing the uncertainties and limitations remaining in the evidence and technical analyses, as discusse d in section II.A of the preamble to the final rule, the EPA recognizes that in setting a primary NAAQS th at provides an adequate margin of safety,

the Administrator must consider a number of factors including the na ture and severity of the health effects involved, the size of sens itive population(s) at risk, and the kind and degree of the uncertainties that remain. As discussed in section III.E.4.d of the preamble to the final rule, the Agency agrees with these commenters that, in weighing the available evidence and technical analyses including th e uncertainties and limitations in this scientific information, there is no legitim ate justification for setting a primary PM 2.5 annual standard level as high as 13 μg/m 3 (in conjunction with retaining the 24-hour standard at the current level).

(5) Comment: Some commenters urged the EPA “to sele ct a standard based on science, not politics” (ALA et al., 2012, p. 6). More sp ecficially, these comment ers asserted “lastII-83 minute changes to the proposed level (f ollowing interagency review) were not accompanied by substantive changes in the te xt to the proposal. In fact, we find no justification in the preamble for an annual standard as high as 13 μg/m 3 , other than the vague assertion that uncertain ties increase at lower concentrations. Further the final proposal completely failed to address the Po licy Assessment recommendations that if 13 μg/m 3 was proposed, then the 24-hour standard should be strengthened as well. The apparent last minute and unsupported insertion of a less protective annu al standard to the proposal appears to be political interference, not scientific consider ation” (ALA et al., 2012, p. 7).

Response: As stated in the previous response, th e EPA agrees that the evidence in the record of this review does not support an annual standard at the level of 13 μg/m 3 (unless

the 24-hour standard level was to be lowered substantially).

(6) Comment: Some commenters argued that the EP A “committed a serious procedural error in not explicitly soliciting comment on retaining the current [annual] PM 2.5 NAAQS” (API, 2012, p. 9).

Response: The commenter suggested (without provi ding any specific argument) that the EPA somehow prejudged the outcome of th e rulemaking , or otherwise committed procedural error, by not proposi ng to retain the 2006 NAAQS. Th is is incorrect. First, the EPA provided far more process through this review than the amount required by law. Commenters had multiple opportunities to re view and comment on all of the critical documents underlying the review (notably the IS A, the RA, and the PA), as well as on all of the critical scientific and policy issues , assumptions, and factual data informing the review as discussed in the proposal (77 FR 38890). Given that th e basic question being addressed throughout this proceeding is whether or not it is appropria te to revise the 2006 standard (CAA section 109 (d)), that issue was necessarily before the public for comment (as evidenced by all the comment s urging retention of the st andard, among other indicia of proper notice). Nor does the EPA’s proposal indicate a pre-judgmen t of the outcome of the review. Rather, the proposal reflected the EPA’s consideration of the body of scientific data and analysis comprising the record for this review.

The EPA strongly disagrees that the currently available scientific ev idence and technical information supports consideration for reta ining the annual standard level at 15 μg/m 3

. and consequently did not propose to do so. As discussed in section III.D.3. of the preamble for the final rule, having carefully considered CASAC advice and the public comments on the proposal as discussed in section III.D.2 preamble to the final rule and in section II.B.1 above, the EPA believes the f undamental scientific conclusions on the

effects of PM 2.5 reached in the ISA, and discusse d in the PA, are valid. The Agency

believes that since the last review the overa ll uncertainty about the public health risks associated with both long- and short-term exposure to PM 2.5 has been diminished to an important degree. The remaining uncertainties in the available evidence do not diminish confidence in the associations between expos ure to fine particles and mortality and serious morbidity effects. Based on the Agency ’s increased confidence in the association between exposure to PM 2.5 and serious public health effect s, combined with evidence of such an association in areas that would meet the current standards , the AdministratorII-84 agrees with CASAC that revision of the current suite of PM 2.5 standards to provide increased public health prot ection is necessary. Based on th ese considerations discussed in section III.D.3 of the preamble to the fina l rule, the Administrator concludes that the current suite of primary PM 2.5 standards is not sufficient, and thus not requisite, to protect public health with an adequate margin of sa fety, and that revision is needed to increase public health protection. Furthermore, as di scussed in section III.E.4.e of the proposal, the Administrator provisionally concluded th at the available scientific information supported consideration of an annual standard level no higher that 13 μg/m 3 . In considering public comments on the proposal as discussed in sections III.E.4.c.i and III.E.4.d of the preamble for the final rule and above, the Agency concludes there is no scientific basis for considering retaini ng the annual standard level at 15 μg/m 3 (absent a substantially lower level of the daily standard).

(7) Comment: Some of these commenters also identified “new” studies as providing additional evidence to support their views that the annual st andard level needs to be

lowered.

Response: As discussed in section II.B.3 of the pr eamble to the final rule and in section II.B.1.a above, the EPA notes that, as in pa st NAAQS reviews, the Agency is basing the

final decisions in this review on the studies and related information included in the PM ISA that have undergone CASA C and public review, and will consider newly published studies for purposes of decision making in th e next PM NAAQS review. Nonetheless, in provisionally evaluating commenters’ argumen ts, the EPA notes that its provisional

assessment of “new” science found that such studies did not materially change the conclusions reached in the ISA (U.S. EPA, 2012b).

b. 24-Hour Standard

With respect to the level of the 24-hour standard, the EPA received comments on the proposal from two distinct gr oups of commenters. One group that included virtually all commenters representing industry associations, businesses, and many States agreed with the Agency’s proposed decision to retain the level of the 24-hour PM 2.5 standard. The other group of commenters included many medical groups, numerous physicians and academic researchers, many public health organizations, so me State and local agencies, five state attorneys general, and a large number of individual commenters. Thes e commenters disagreed with the Agency’s proposed decision and argued that EPA should lower the level of the 24-hour standard to 30 or 25 μg/m 3 . Comments from these groups on the level of the 24-hour PM 2.5 standard are addressed in section III.E.4.c.ii in the preamble for the final rule and below.

i. Support for Retaining the Current Level

Of the public commenters who addr essed the level of the 24-hour PM 2.5 standard, all industry commenters and most St ate and local commenters suppor ted the proposed decision to

retain the current level of 35  g/m 3 . In many cases, these groups agreed with the rationale supporting the Administrator’s proposed d ecision to retain the current 24-hour PM 2.5 standard, including her emphasis on the annual standard as the generally controlling standard with the 24- hour standard providing supplementa ry protection, and her conclusion that multi-city, short-termII-85 exposure studies provide the str ongest data set for informing decisions on the appropriate 24- hour standard level. Many of th ese commenters agreed with the Administrator’s view that the single-city, short-term studies provided a much more limited da ta set (e.g., lim ited statistical power, limited exposure data) and more equivocal results (e.g., mixed resu lts within the same study area), making them an unsuitable basis for setting the level of the 24-hour standard.

(1) Comment: While these commenters agreed with the EPA’s proposed decision to retain

the current 24-hour PM 2.5 standard, some did not agree with the EPA’s approach to considering the evidence from short-term multi-city studies. For example, a commenter representing UARG point ed out that the 98 th percentile concentrations reported in the proposal for multi-city studies reflect the averages of 98 th percentile conc entrations across the cities included in those studies (UARG, 2012; Attachment 1; p. 25). This commenter contended that such averaged 98 th percentile PM 2.5 concentrations do not provide information that can appropriately inform a decision on the adequacy of the public health protection provided by the current or alternative 24-hour standards.

Response: While the EPA agrees that there is uncer tainty in linking effects reported in multi-city studies to specific air quality concentrations (U.S . EPA, 2011a, section 2.3.4.1), the EPA disagrees with th is commenter’s view that such uncertainty precludes the use of averaged 98 th percentile PM 2.5 concentrations to inform a decision on the appropriateness of the protection provided by the 24-hour PM 2.5 standard. In particular, the EPA notes that averaged 98 th percentile concentrations do provide information on the extent to which study cities co ntributing to reported associations would likely have met

or violated the current 24-hour PM 2.5 standard during the study period. As evidence of this, the EPA notes the three multi-city studies specifically highlighted by this commenter as having averaged 98 th percentile 24-hour PM 2.5 concentrations below 35  g/m 3
(Dominici et al., 2006a; Bell et al., 2008; Zanobetti and Schwartz, 2009). Based on the

98 th percentiles of 24-hour PM 2.5 concentrations in the individual cities evaluated in these studies, the EPA notes that the majority of these study cities would likely have met the current standard during the study periods (Hassett-Sipple et al., 2010). Therefore, regardless of whether the averaged 98 th percentile concentrations or the 98 th percentile concentrations in each city are considered, th ese studies provide evidence for associations

between short-term PM 2.5 and mortality or morbidity across a large number of U.S. cities, the majority of which would likel y have met the current 24-hour PM 2.5 standard during study periods. In their review of the PA, CASAC endorsed the conclusions drawn from analyses of averaged 98 th percentile 24-hour PM 2.5 concentrations (Samet, 2010d) and the EPA continues to conclude that this type of information can appropriately inform the

Administrator’s decision on the current 24-hour PM 2.5 standard. 29

(2) Comment: One commenter questioned whether th e 24-hour standard would offer any additional protection beyond the protecti on provided by the annual standard. This

29 This is not to say that the EPA’s decision on whether to revise the 24-hour PM 2.5 standard should be based on or only be informed by considerations of whether studies repo rted associations with mortality or morbidity in areas with averaged 98 th percentile PM 2.5 concentrations less than 35 mg/m 3 . As discussed in section III.E.4.d of the preamble to the final rule, in reaching a decision in the final notice on the most appropriate approach to strengthen

the suite of PM 2.5 standards, the Administrator considers the degree of public health protection provided by the combination of the annual and 24-hour standards together.II-86 commenter argued that EPA has not provided any evidence that the 24-hour standard is necessary to protect public hea lth and asserted that the EPA should better explain why the existing 24-hour standard is not more stri ngent than necessary (API, 2012, p. 9). More specifically, based on statements in the PA ( quoting “there is no evidence suggesting that risks associated with long-term exposures are likely to be disproportionately driven by peak 24-hour concentrations” and citing to several studies that evaluated the effect on the magnitude and statistical significan ce of the association between PM 2.5 health impacts with and without high PM concentrations days , finding very little difference, U.S. EPA, 2011a, p. 2-9), this commenter asserted “If the annual standard is protective of effects from both short- and long-term exposures, a nd no additional effects are observed with peak events, this indicates that there is likely no additional benefit to having the 24-hour standard. Retaining the 24-hour standard, th erefore, would be an additional level of protection, or ‘margin of safety’” (API, 2012, Attachment 1, p.2).

Response: The EPA disagrees with the commenter’s contention that evidence has not been provided to support the appropriateness of the retaining the current 24-hour standard in conjunction with revising the annual sta ndard. The EPA has carefully considered the degree of public health protecti on provided by the annual and 24-hour PM 2.5 standards working together. As highlighted by commenter s and as discussed in section III.E.4.d of the preamble to the final rule, based on the evidence and quantitative risk assessment, the EPA concludes that it is appropr iate to set an annual sta ndard with a level of 12 μg/m 3 to provide protection from bot h long- and short-term PM 2.5 exposures. In conjunction with the revised annual standard, the EPA concludes it is also appropriate to retain the current

24-hour standard in order to provide supplemental protection in areas with high peak-tomean ratios of PM 2.5 concentrations, possibly associat ed with strong lo cal or seasonal sources, and against PM 2.5 -related effects that may be asso ciated with shor ter-than daily exposure periods.

As discussed in more detail in section III. E.4.a of the preamble to the final rule, in reaching this conclusion the EPA notes that multi-city studies provide clear evidence for positive and statistically significant associations with short-term PM 2.5 concentrations in locations with averaged (i.e., averaged across study cities) 98 th percentile 24-hour concentrations from 45.8 to 34.2 μg/m 3 (Burnett et al., 2004; Zanobetti and Schwartz, 2009; Bell et al., 2008; Dominici et al., 2006a, Burnett and Go ldberg, 2003; Franklin et al., 2008). In many locations , the revised annual PM 2.5 standard is expected to protect against the effects reported in these studies. However, some areas of the United States, particularly in the nort hwest, could experience 98 th percentile 24-hour PM 2.5 concentrations above 35 mg/m 3 while annual PM 2.5 concentrations remain below 12

 g/m 3 (U.S. EPA, 2011, Figure 2-10). In such loca tions, the current 24-hour standard is necessary to provide protection against effects that have been associ ated with short-term

PM 2.5 exposures. Without the 24-hour standard in place, short-term PM 2.5 concentrations

in some locations could be allowed to exceed th ose that have clearly been associated with mortality and morbidity. Therefore, the EPA disagrees with commenters who call into question support for the conclusion that th e 24-hour standard provides appropriate supplementary protection against effects that have been associated with fine particle

exposures.II-87 ii. Support for Revising the Current Level

Another group of commenters ar gued that the 24-hour standard level should be lowered. Many of these commenters supported setting the level of the 24-hour PM 2.5 standard at either 25

or 30  g/m 3

.

(1) Comment: In support of their position, the ALA et al., AHA et al., five state Attorneys General, and a number of additional groups pointed to 98 th percentile PM 2.5 concentrations in locations of multi-city and single-city epidemiological studies. For example, the ALA and others pointed to mu lti-city studies by Domi nici et al. (2006a), Zanobetti and Schwartz (2009), Burnett et al. (2 000), and Bell et al. (2008) as providing evidence for associations with mortality and morbidity in study locations with averaged (i.e., averaged across cities) 98 th percentile 24-hour PM 2.5 concentrations below 35

 g/m 3 . These commenters also pointed to severa l single-city and pane l studies reporting

associations between short-term PM 2.5 and mortality or morbidity in locations with relatively low 24-hour PM 2.5 concentrations. Because some of these multi- and single-city studies have reported associations with health effects in locations with 98 th percentile

PM 2.5 concentrations below 35  g/m 3 , commenters maintained that the current 24-hour

PM 2.5 standard (i.e., with its level of 35  g/m 3 ) does not provide an appropriate degree of protection in all areas.

In further support of their posit ion that the level of the current 24-hour standard should be lowered, these commenters pointed out the vari ability across the U.S. in ratios of 24-hour

to annual PM 2.5 concentrations. They noted that so me locations, includ ing parts of the northwestern U.S., experience relatively low annual PM 2.5 concentrations but can experience relatively high 24-hour concentrations at certain times of the year. In order to provide protection against effects associated with short-term PM 2.5 exposures, especially in locations with high rati os of 24-hour to annual PM 2.5 concentrations, these commenters advocated setting a lower leve l for the 24-hour standard.

Response: The EPA agrees with these commenters that it is appropriate to maintain a

24-hour PM 2.5 standard in order to supplement the protection provided by the revised annual standard, particularly in locations with relatively high ratios of 24-hour to annual

PM 2.5 concentrations. However, in highlighting 98 th percentile PM 2.5 concentrations in study locations without also considering the impact of a revised annual standard on shortterm concentrations, these commenters ignore the fact that many areas would be expected to experience decreasing short- and long-term PM 2.5 concentrations in response to a

revised annual standard. See American Trucking Association v. EPA , 283 F. 3d at 373 (rejecting argument to lower the level of the 24-hour PM 2.5 standard since the argument

had failed to account for the redu ctions in the entire air qual ity distribution resulting from the implementation of the annual standard).

In considering the specific multi-city studies highlighted by public commenters who advocated a more stringent 24- hour standard, the EPA notes that such studies have reported consistently positive and statistically significant associations with short-term

PM 2.5 exposures in locati ons with averaged 98 th percentile PM 2.5 concentrations ranging from 45.8 to 34.2 μg/m 3 and long-term mean PM 2.5 concentrations ranging from 13.4 toII-88 12.8 (Burnett and Goldberg, 2003; Burnett et al ., 2004; Dominici et al ., 2006a; Bell et al., 2008; Franklin et al., 2008; Zanobetti and Schwartz, 2009). 30 The EPA notes that to the extent air quality distributions are reduced to meet the curr ent 24-hour standa rd with its

level of 35  g/m 3 and/or the revised annual st andard with its level of 12  g/m 3 , additional protection would be anticipated against the eff ects reported in these short-term, multi-city studies. Put another way, to attain an annua l standard with a leve l below the long-term

means in the locations of these short-term st udies (as EPA is adopti ng in the final rule), the overall air quality distributions in the ma jority of study cities will necessarily be reduced, resulting in lower daily PM 2.5 ambient concentrations. We therefore expect that

the revised annual standa rd will result in 98 th percentile PM 2.5 concentrations in these

cities that are lower than those measured in the studies, and that the overall distributions

of PM 2.5 concentrations will be lower than those reported to be associated with health effects. Thus, even for effects reported in multi-city studies with averaged 98 th percentile concentrations below 35 μg/m 3 , additional protection from the risks associated with short-term exposures is anticipated from the revised annual standard, without revising the 24-hour standard, because long-term average PM 2.5 concentrations in multi-city study

locations were above the level of the revised annual standard (i.e., 12 μg/m 3 ). 31 As discussed above, reducing the a nnual standard is the most efficient way to reduce the risks from short-term exposures identified in these studies, as the bulk of the risk comes from the large number of days across the bulk of the air quality distribution, not the relatively small number of days with peak concentrations. See American Trucking

Association , 283 F. 3d at 372 (endor sing this reasoning).

In considering the single-cit y studies highlighted by public commenters who advocated a more stringent 24-hour standa rd, the EPA first notes that , overall, these single-city studies reported mixed results. Specifica lly, some studies reported positive and statistically significant associations with PM 2.5 , some studies reported positive but nonsignificant associations, and se veral studies reported negativ e associations or a mix of positive and negative associations with PM 2.5 . In light of these in consistent results, the proposal noted that the overall body of evid ence from single-city studies is mixed, particularly in locations with 98 th percentiles of 24-hour concentrations below 35 μg/m 3

. Therefore, although some single-city studies reported effects at appreciably lower PM 2.5 concentrations than short-term multi-city studies, the uncertainties and limitations

30 Commenters also highlighted associations with short-term PM 2.5 concentrations reported in sub-analyses restricted to days with 24-hour concentrations at or below 35 g/m 3 (Dominici, 2006b). These sub-analyses were not included in the original publication by Dominici et al. (2006 a). Authors provided results of sub-analyses for the Administrator’s consideration in a letter to the docket following publication of the proposed rule in January 2006 (personal communication with Dr. Francesca Dominici, 2006b). As noted in section III.A.3 of the preamble to the final rule and to the proposal, these sub-analyses are part of the basis for the conclusion that there is no evidence suggesting that risks associated with long-term exposures are likely to be disproportionately driven by peak 24-hour concentrations. Because the sub-analyses did not present long-term average PM 2.5 concentrations, it is not clear whether they reflected PM 2.5 air quality that would have been allowed by the revised annual PM 2.5 standard being

established in this notice.

31 It is also the case that additional prot ection is anticipated in locations with 98 th percentile 24-hour PM 2.5 concentrations above 35 μg/m 3 , even if long-term concentrations are below 12 μg/m 3 . As noted in the proposal (77 FR 38938) and in the PA (U.S. EPA, 2011, Figure 2-10), as well as by a number of the commenters (e.g., ALA et al., 2012, p. 26), parts of the northwestern U.S. are more likely than other parts of the country to violate the 24-hour

standard and meet the re vised annual standard.II-89 associated with the single-city studies were noted to be greate r. In light of these greater uncertainties and limitations, the Administrato r concluded in the proposal that she had less confidence in using these studies as a basi s for setting the level of the standard (77 FR 38943).

Given the considerations and conclusions not ed above, in the proposal the Administrator concluded that the short-term multi-city studi es provide the strongest evidence to inform

decisions on the level of the 24-hour standard. Further, she viewed si ngle-city, short-term exposure studies as a much more limited da ta set providing mixed results, and she had less confidence in using these studies as a basi s for setting the level of a 24-hour standard (77 FR 38942). In highlighting specific single-c ity studies, public health, environmental, and State and local commenters appear to ha ve selectively focused on studies reporting

associations with PM 2.5 and to have overlooked studies that reported more equivocal results (e.g., Ostro et al., 2003; Rabinov itch et al., 2004; Slau ghter et al., 2005; Villeneuve et al., 2006) (U.S. EPA, 2011, Figur e 2-9). As such, these commenters have not presented new information that causes the EPA to reconsider its decision to emphasize multi-city studies over single-city studies when identifying the appropriate

level of the 24-hour PM 2.5 standard.

In further considering the si ngle-city studies highlighted by public commenters, the EPA

notes that some commenters advocati ng for a lower level for the 24-hour PM 2.5 standard

also discussed short-term studies that have been published since the close of the ISA. These recent studies were conducted in single ci ties or in small panels of volunteers. As in prior NAAQS reviews and as discussed in mo re detail in section II.B.3 of the preamble

to the final rule and in sec tion II.B.1.a above, the EPA is basing its decisions in this

review on studies and related information asse ssed in the ISA. The studies assessed in the ISA, and the conclusions based on those st udies, have undergone extensive critical review by the EPA, CASAC, and the public. Th e rigor of that revi ew makes the studies assessed in the ISA, and the conclusions based on those studies, the most reliable source

of scientific information on which to base decisions on the NAAQS.

(2) Comment: Some public health, medical, and envir onmental commenters also criticized the EPA’s interpretation of PM 2.5 risk results. These commenters presented risk estimates

for combinations of annual and 24-hour standa rds using more recent air quality data than that used in the EPA’s RA (U.S. EPA, 2010a ). Based on these additional risk analyses,

the ALA and other commenters contended that public health benefits could continue to

increase as annual and 24-hour st andard levels decrease below 13  g/m 3 and 35  g/m 3

, respectively.

Response: The EPA agrees with these commenters that important public health benefits are expected as a result of revising the level of the annual standard to 12  g/m 3 , as is
done in the final rule, rather than 13  g/m 3 . The Agency also acknowledges that

estimated PM 2.5 -associated health risks continue to decrease with annual standard levels

below 12  g/m 3 and/or with 24-hour standard levels below 35  g/m 3 . However, the EPA disagrees with the commenters’ views regard ing the extent to which risk estimates support setting standard levels below 12 μg/m 3 (annual standard) and 35  g/m 3 (24-hourII-90 standard). 32

The CAA charges the Administrator with se tting NAAQS that are “requisite” (i.e., neither more nor less stringent than necessary) to protect public health with an adequate margin of safety. In setting such standard s the Administrator must weigh the available

scientific evidence and inform ation, including associated unc ertainties and limitations. As described above, in reaching he r proposed decisions on the PM 2.5 standards that would provide “requisite” protecti on, the Administrator carefully considered the available

scientific evidence and risk information, making public health policy judgments that, in her view, neither overstated nor understated the strengths and limitations of that evidence and information. In contrast, as discussed more fully above, public health, medical, and

environmental commenters who recommended levels below 35  g/m 3 for the 24-hour

PM 2.5 standard have not provided new informa tion or analyses to suggest that such standard levels are appropriat e, given the uncertainties and limitations in the available health evidence, particularly uncertainties in studies conducted in locations with 98 th

percentile 24-hour PM 2.5 concentrations below 35  g/m 3 and long-term average

concentrations below 12  g/m 3

.

C. Specific Comments on the Quantita tive Health Risk Assessment

This section responds to more detailed comme nts regarding the quant itative health risk

assessment conducted for PM 2.5 (RA, US EPA, 2010a).

.

(1) Comment: Some commenters argued that the qua ntitative health risk assessment

conducted for PM 2.5 was too limited since it “focused on only 15 urban study areas to represent the continental U.S. and only examin ed a fraction of the available combinations of annual and daily standards” (ALA et al., 2012, p. 73). These commenters noted that the RA indicated the qua ntitative risk analyses likely underestimated PM 2.5 -related mortality (U.S. EPA, 2010a, p. 5-16) and argue d that “the measurements of risk should be treated conservatively” (ALA, et al., 2012, p. 73). These commenters also noted that significant additional risk reduction is associated with combinations of annual and 24-

hour standards lower than those considered by the EPA (ALA et al., 2012, pp. 73 to76).

Response: The RA used a case study approach wherei n distinct sets of risk estimates were generated for each of 15 urban study areas. The case study approach was selected in order to make use of site-specific data in modeling PM 2.5 -related risk, th ereby generating risk estimates with higher ove rall confidence. Furthermore, the case study approach was intended to provide coverage for the range of PM-related health effects likely to be experienced by urban residents across the U. S. and was not intended to provide a comprehensive picture of total risk for the U.S. population.

With regard to the scope of the quantitative ri sk analysis, as stated in the proposal, “The selection of urban study areas was based on a number of criteria including: (1) consideration of urban study areas evaluated in the last PM risk assessment; (2) consideration of locations evaluated in key epidemiological studies; (3) preference for

32 This section focuses on the 24-hour standard. Section III. E.4.c.i of the preamble to the final rule and section

II.B.5.a.i above also discuss these commenters’ re commendations within the context of the annual PM 2.5 standard.II-91 locations with relatively elev ated annual and/or 24-hour PM 2.5 monitored concentrations; and (4) preference for includi ng locations from different regions across the country, reflecting potential differences in PM 2.5 sources, composition, and potentially other factors which might impact PM 2.5 -related risk” (77 FR 38912; see also U.S. EPA, 2010a, section 3.3.2). Based on the results of severa l analyses examining the representativeness of these 15 urban study areas in the broade r national context (U.S. EPA, 2010a, section 4.4), the RA concluded that these study areas were generally repr esentative of urban areas in the U.S. likely to expe rience relatively elevated levels of risk related to ambient

PM 2.5 exposure with the potential for better ch aracterization at the higher end of that distribution (U.S. EPA, 2011a, p. 2–42; U.S. EPA, 2010a, section 4.4, Figure 4–17). The CASAC's in their letter response on the 1s t draft RA supported the choice of cities stating that, "The Risk Assessment understa ndably focuses on risk in the urban study areas, where the population is concentrated; and there appears to be an appropriate selection of cities, using defined criteria ." (Samet 2010a, p. 10).

With respect to the selection of various co mbinations of altern ative annual and 24-hour standard levels modeled in the RA, as noted in section 2.3.4.2 of the PA, the quantitative risk assessment initially included analyses of alternative annual standard levels of 14, 13,

and 12 μ g/m 3 paired with either the current 24-hour standard level of 35 μ g/m 3 or with

alternative 24-hour standard levels of 30 and 25 μ g/m 3 . The specific combinations of

alternative standard levels assessed in th e quantitative risk assessment included: (a)

alternative suites of standa rds focusing on alternative a nnual standard levels in conjunction with the current 24-hour standard including combinations denoted by 14/35, 13/25, and 12/35and (b) alternative suites of standards reflecting combinations of

alternative annual and 24-hour standard le vels including combinations denoted by 13/30

and 12/25. This set of alternative annual and 24- hour standard levels was chosen prior to completion of the first draft RA (U.S. EP A, 2009e) and reflected consideration for evidence related to potential PM 2.5 -related health effects as pr esented in the second draft ISA (U.S. EPA, 2009b). The range of alternative standard levels discussed in the PA (i.e., annual standard levels within a range of 13 to 11 μ g/m 3 and 24-hour standard levels within a range of 35 to 30 μ g/m 3 ), reflected consideration of evidence as presented in the final ISA and consequently differed somewhat fr om the set of alternative standard levels originally selected for m odeling in the quantitative ri sk assessment. In addition, subsequent to the release of the second draft RA (U.S. EPA, 2010d), the Agency expanded the range of alterna tive annual standard levels ev aluated in the final RA to

include an alternative annua l standard level of 10 μ g/m 3 and developed risk estimates for

two additional combinations of alterna tive standards – 10/35 and 10/25 (U.S. EPA, 2010a, Appendix J).

While the EPA agrees with the commenters that the combinations of alternative standard levels modeled in the RA were only a “fractio n” of possible combina tions that one might model, the EPA selection of alternative sta ndard levels to model followed a deliberative and transparent process. Modificat ions in the alternative standa rd levels considered in the

first and second draft RAs and the final RA re flected changes made in the ISA, RA, and PA based on CASAC and public comments on multiple draft assessment documents and the EPA’s staff’s expert judgment regardi ng the confidence associated with modeling

different combinations of alternative standard levels. The EPA believes that theII-92 uncertainties associated with the risk es timates increase when simulating increasingly

lower alternative standard levels. For exam ple, in simulating an alternative annual

standard level of 10 μ g/m 3 , the Agency noted increased uncer tainty associated with risk estimates generated for this lower alternativ e standard level and for, that reason, these risk estimates were deemphasized in the final RA (U.S. EPA, 2010a, Appendix J). The EPA’s decision to limit the range of alte rnative standard levels considered to

combinations with increased confidence is consistent with advi ce provided by CASAC. More specifically, CASAC recommended that the “...EPA develop and apply specific criteria for determining the lower-bound exposur e concentrations to be considered in the risk assessment. Mounting uncertainty at lower concentrations would be one such

reasonable basis. Other relevant considerati ons include the range of concentrations at which the epidemiological studies have been ca rried out and the need for consideration of the degree of protection afforded to suscep tible populations unde r various scenarios” (Samet 2010a, p. 2). The EPA read ily acknowledges that additional risk reductions would be expected as one simulates progressively lower alternative standard levels as suggested by the commenters. However, the Agency also recognizes that the uncertainties associated with these lower alternative standard levels would also be increased resulting

in more uncertain basis for inform ing the Agency’s decisionmaking.

With regard to the comment that the RA lik ely underestimates risk and that for this reason, the risk estimates should be treated conservatively by the EPA when considering them in the context of the PM NAAQS re view, the EPA generally agrees with the

commenters’ views. As noted in the proposal, the RA concl uded, “it is unlikely that the estimated risks are over-stated, particularly for premature mo rtality related to long-term

PM 2.5 exposures” (77 FR 38917/2). When m odel uncertainty associated with specification of the effect estimates for long-term exposure-related mortality was considered, the RA noted the potential that th e risk estimates may have been under-stated (U.S. EPA, 2010a. section 4.3.2). This point is clearly made in the RA as noted above

and is further reiterated wh en summarizing the risk estimat es in the PA (U.S. EPA, 2011a, section 2.2.2, p. 2-40). In addition, the EPA recognizes that the RA estimated risks for selective health outcomes (i.e., mortality, cardiovascular- and respiratory-related hospital admissions, asthma-related emergency department visits). As summarized in section III.B of the preamble to the final rule and discussed in more detail in section III.B.1 of the proposal and s ection 2.2.1 of the PA, the Agency recognizes that the currently available scientific information includes evidence for a broader range of health endpoints and at-risk populati ons beyond those considered in the quantitative risk assessment (U.S. EPA, 2011a, p. 2-47). Thus , for the reasons discussed above, the EPA agrees with the comment that the risk es timates are most likely underestimated and should be treated conservatively.

(2) Comment: Some public health, medical, and envir onmental commenters also criticized the EPA’s interpretation of the PM 2.5 risk results. These commenters summarized an expanded analysis of alternative PM 2.5 standard levels (McCubbi n, 2011) that they argued documented the need for more protective standards (ALA et al., 2012, p. 73; PSR, 2012, p.5; CLF, 2012, p.3). Specifically, they asse rted that the McCubbin et al. (2011) demonstrated that (a) the EPA evaluated compliance with the PM 2.5 standard for each year separately, while the McCubbin analys is used an innovative approach thatII-93 considered three years in evaluating complia nce , and (b) risks can be generated using more recent air quality data than that used in the EPA’s RA (U.S. EPA, 2010a) (Id.; ALA et al., 2012, pp. 73.

Response: The commenters’ assertion that th e EPA evaluated compliance with each simulation year separately is incorrect. In the RA, the EPA considered three years of monitoring data in constructing the design valu es for each monitor within an urban study area. The design values were used as the basi s for establishing the magnitude of rollback

to simulate both the current and alternative st andards. While the rollback of each monitor (or of the composite monitor depending on the adjustment method) was completed separately for each simulation year, the desi gn values themselves were based on three years of data (U.S. EPA, 2010a, section 3.2.3).

The commenters stated that the alternativ e risk assessment (McCubbin, 2011) included

more recent ambient PM 2.5 data than the RA. The EPA ag rees with this comment. The McCubbin (2011) analysis used air quality data from 2007 to 2009. The RA, completed in 2010 considered air quality data from 2005 to 2007. The EPA observes that the RA

utilized the most recent PM 2.5 monitoring data available at the time of the analysis. It is always the case with regulatory risk assessmen ts that they reflect the use of input data available at the time of their completion and th at often, portions of th at input data could be updated if the RA is repeated at a future point in time.

(3) Comment: One group of commenters asserted that there was no evidence for a threshold, which, in the commenters’ views, argued agains t constraining simulation of risk to only extend down to the lowest measured level (LML ) as was done in the RA (ALA et al., 2012, pp., 76 to 77).

Response: The Agency agrees that there is no evid ence for a threshold for effects related to endpoints modeled in the RA, as supporte d by conclusions reached in the ISA (U.S. EPA, 2009a, section 2.4.3). However, applicatio n of the LML in the RA does not reflect modeling of a threshold for long-term expos ure-related mortality. Rather it reflects consideration for where we have greater overall confidence in the risk estimates generated within the range of ambient PM 2.5 data reflected in the epidemiological study underlying the effect estimates used in modeli ng risk. Specifically, as discussed in section 5.1.6 of the RA, the EPA has relatively hi gh confidence when we estimate risks

associated with PM 2.5 concentrations within one standa rd deviation (SD) of the mean

PM 2.5 concentrations reported in the epid emiological study unde rlying the effect estimates used to develop the C-R functions used in the risk asse ssment. However, as simulated annual average PM 2.5 concentrations extend below this range, our confidence in the risk estimates decreases, with our confidence being significantly reduced when composite monitor annual average values reach or extend below the LML associated with the epidemiological study. Conse quently, application of the LM L allows us to focus risk on that portion of the PM range where we have relatively higher confidence and is not meant to imply that there is no risk below the LML (U.S. EPA, 2010a, section 4.3.1.2).

(4) Comment : Some commenters cited to the results of an expert elicitati on sponsored by the EPA providing “credence” to the EPA’s use of both the Laden et al. (2006) and KrewskiII-94 et al. (2009a) studies in the RA (ALA et al., 2012, p. 20).

Response : With regard to Laden et al. (2006), th e RA stated, "The Laden et al. (2006) study (which focused on the Harvard Six Cities dataset) was not selected because it used visibility data to estimate ambient PM 2.5 levels." (U.S. EPA, 2010a, p. 3-38). In addition, the EPA recognizes that the Laden et al., 2006 study utilized data from six urban study areas, only one of which (St. Louis) was refl ected in the set of urban study areas modeled in the RA. By contrast, the Krewski et al. (2009a) study included a substantially larger number of urban study areas (116 including all study areas m odeled in the RA). That

means that the effect estimates based on Kr ewski et al. (2009a) are likely to be more representative of the set of urban study areas modeled in the RA than are effect estimates based on Laden et al. (2006). While the smaller number of cities reflected in Laden et al. (2006) may not compromise the study in terms of informing consideration for uncertainty related to specification of effect estimates (as reflected in the Expert Elicitation referenced by the commenter, Roman et al., 2008.), the smaller number of cities in the Laden et al., (2006) study can substantially increase uncertainty associated with using that study’s effect estimates in risk assessm ents when those assessments focus on cities not reflected in the Laden et al., 2006 study, as noted here. The EPA did include Laden et al., (2006)-based mortality estimates as part of the national scale anal ysis in order to look at uncertainty related to model specification in modeling national-sc ale risk (U.S. EPA, 2010a, Appendix G). In that case, matching urba n study areas was not as critical since a single national-level effect estimate was used to generate a national-sc ale estimate of risk.

(1) Comment : Some commenters argued that th e RA is “compromised by the EPA’s willingness to overlook a large amount of un certainty in the epidemiologic studies on

which it relied in the ISA and on which it based the QHRA [Quantitative Health Risk Assessment]. Because it is based on a series of critical assumptions , and the uncertainty associated with those assumptions is not fully quantified, the QHRA cannot serve the functions for which it is intended: to quantif y the risk to public health remaining at the

level of the current standard or at the alternative levels” c onsidered in the proposal (API, 2012, p. 23, Attachment 1, p. 36). These commente rs argued that the “RA results do not warrant being used as evidence for long-te rm PM health risks below current PM standards, and they should not be used to guide decisions regarding the PM standards” (API, 2012, Attachment 1, p. 36). In asserting th at the uncertainties in the quantitative risk assessment have not been appropriatel y considered and, thus, this assessment does not support revision to the sta ndards at this time, the comm enters raised a number of

detailed technical comments related to key modeling elemen ts of the RA including: (a) the use of a no-threshold, l og-linear model to support estim ating risk down to LML and policy relevant background (PRB); (b) uncer tainty related to model specification (selection of C-R functions), (c) failure to su fficiently consider sources of heterogeneity impacting risk estimates; (d) treatment of m easurement error and potential direction of associated bias in the effect estimates; and (e ) representation of the confidence associated

with the risk assessment results.

Response: In presenting response to these comment s, the EPA first addresses each of the detailed technical comments. Then, the EPA a ddresses the broader criticism made by this commenter that asserted the Agency ove rlooked important sour ces of uncertaintyII-95 associated with the risk assessment, ther eby compromising the ability of the risk assessment to be used to support the PM NAAQS review.

(a) Modeling risk dow n to LML and PRB

The commenter disagreed with the EPA’s us e of a no-threshold, log-linear model to support modeling risk down to either the LML or PRB, depending on the health endpoint (API, 2012, Attachment 1, p. 36).

Comments related to the shape of the C-R relationship, specifically issues related to

whether there is a threshold in the PM 2.5 -health effect relations hip are addressed in section II. B.1.b, Comment (12)(f) above. Based on the ISA conclusion, and CASAC’s consensus recommendation, that the overall evidence from existing epidemiological studies does not support the existence of th resholds at the population level for effects associated with either long- or short-term PM 2.5 exposures within the ranges of air quality observed in these studies (U.S. EPA, 2009a, section 2.4.3; Samet 2010d, p. ii), risk estimates were generated without considera tion for a threshold. However, in order to focus the risk assessment on a range of PM wh ere there is greater ove rall confidence (i.e., the range of ambient PM concentrations reflected in the epid emiological study(s) underlying the effect estimates used in the risk assessment), the EPA modeled risk for long-term exposure-related mortality down to the lowest measured level (LML) associated with the Krewski et al., 2009a st udy which provided effect estimates for this endpoint. Short-term exposure-related morbid ity and mortality endpoints were modeled

down to P RB since the 24-hour PM metrics re flected in those epid emiological studies typically have LML values below PRB (U.S. EPA, 2010a, section 3.1.1). The RA included a sensitivity analysis for long-term mortality comp aring modeling of risk down

to LML with risk modeled down to PRB. No t surprisingly, this sensitivity analysis showed that modeling risk down to PRB resu lted in notably greater estimates for total risk (U.S. EPA, 2010a, section 4.3.1.1). Th e CASAC also supported this approach, stating that “[t]here was support [from CASA C members] for modeling risk for long-term

PM 2.5 exposures to the lowest measured level (LML). For short-term risk estimates, the EPA’s approach is appropriate, since as th e document points out, the LMLs (which are daily) are below the PRB” (Samet, 2009c, p.2).

(b) Uncertainty related to model spec ification (selection of C-R functions)

One commenter argued that the EPA only c onsidered a small fraction of overall uncertainty in the epidemiological studies and C-R functions from those studies, specifically reflected in the considering the c onfidence intervals (CIs) associated with the effect estimates (API, 2012, Attachment 1, p. 36). This commenter asserted that

consideration of C-R function CI’s does not capture significant model uncertainty. Specifically, this commenter pointed to variation in the risk estimates resulting from consideration of different C-R functions in the RA sensitivity analysis. This commenter used these arguments to support its views that the analysis results were not "robust" to model specification as stated by the EPA (A PI, 2012, Attachment 1, p. 39). They also

asserted that the EPA communicated with the study authors associated with Krewski et al., 2009a and that, while these authors sugge sted that the EPA use a random effectsII-96 model, the EPA elected to use the fi xed-effects Cox model instead (API, 2012, Attachment 1, p. 38).

Finally, the commenter asserted that the EPA did not consider multi-pollutant models in the RA and relied only on single-pollutant models (particularly for LT mortality) (API, 2012, Attachment 1, p. 36). This commenter point ed out that an earlie r study (Krewski et al., 2000) provided evidence of copollutant effects (API, 2012, Attachment 1, p. 38) and the commenter recognized that the EPA a ddressed the issue of copollutants in a sensitivity analysis. However, the commen ter asserted that the EPA discounted its sensitivity analysis of copollutants because control for SO 2 may capture a portion of the

PM 2.5 effect. The commenter agreed that this may be true for some regions of the country, but not for regions where SO 2 is not a major portion of PM 2.5 . The commenter concluded by observing that si ngle- pollutant models may ove r-estimate risk by including the impacts of other copollutants in the PM 2.5 signal.

The EPA disagrees that the RA did not consider the full range of uncertainty associated with the C-R functions and only considered un certainty captured by CIs (i.e., statistical fit). As noted by the commenter, the EPA includ ed a sensitivity analysis in the RA which specifically examined the issue of model uncer tainty by considering a range of different C-R function model specifications (U.S. EPA, 2010a, section 4.3.2). The results of that sensitivity analysis suggested that, in the case of long-term exposure-related mortality,

consideration of model uncertain ty could result in risk estimat es that are from 2-3 times higher than risk estimates generate d for the core analysis. As discussed in section 5.1.5 of the RA, because the Krewski et al. (2009a) study does not provide coverage for lower

SES individuals who were identif ied in the ISA as an at-ris k population, there is a likely

low-bias in the effect estimates associated with this study (with the results of the sensitivity analysis supporting this observa tion). Therefore, while the EPA agrees that model uncertainty does impact th e core risk estimates, in contrast to the commenters’ views, the Agency believes the direction of the bias in the Krewski et al. (2009a) models is likely downwards which means that it is unlikely that the EPA ha s over-estimated risk using those models. This was an important observation when discussing the overall

confidence in the risk estimates within the policy context and was highlighted in the PA (U.S. EPA, 2011a, section 2.2.2).

Regarding the Krewski et al., 2009a study auth ors’ advice to the EPA on model selection related to long-term exposur e-related mortality, the EPA recognizes that in their communication, the study authors stated that they had “refrained from expressing a preference among the results for their use in quantit ative risk assessmen t,” preferring to “explore several plausible statis tical models that we have fit to the available data.” (Krewski, 2009b). The EPA considered this input along with the authors’

recommendation that a random effects mode l be used. In addition, the EPA staff considered the results of an analysis pres ented in the study examining the importance of exposure time windows in derivi ng C-R functions. This analysis suggested that models developed using both exposure time windows considered in the analysis (1979-1983 and 1999-2000) were equally effective at repr esenting the relationship between PM 2.5 exposure and long-term exposure-related mo rtality (U.S. EPA, 2010a, section 3.3.3) . Therefore, the EPA concluded th at C-R functions used in the core analysis should includeII-97 functions fitted to both exposure time windows. However, the study does not provide random effects models with ecological cova riates for both exposur e time windows (this form of model is only provide d with a fit to th e latter exposure window). Therefore, for the core analysis, the EPA reasonably decide d to use the Cox proportional hazard model, since effect estimates for both exposure time windows were provided for this model. However, had random effects models been provided for the separate exposure windows,

then those would have been considered for the core analysis. It is important to note that

the EPA did include the random effects refere nced by the Krewski et al. (2009a) authors as part of the sensi tivity analysis complete d for the risk assessment, and, as noted above, this sensitivity analysis suggested greater risk than estimated in the EPA’s core analysis.

The issue of copollutant confounding was a ddressed previously in section II.B.1.b, Comment (12)(a) and points made in that re sponse are applicable here. With specific regard to the risk assessme nt, the EPA also notes that the Krewsi et al. (2009a) study was selected by the EPA as the basis for the co re set of risk estimates over other studies, including those using multi-pollutant models, because it has a number of advantages (e.g., extended air quality analysis which incr eases the power of the study and allows the study authors to examine the important i ssue of exposure time windows, rigorous examination of a range of model forms and e ffect estimates, coverage for a range of ecological variables, relatively large overall dataset with over 1.2 million individuals and 156 MSAs) (U.S. EPA, 2010a, section 3.3.3). While the Krewski et al. (2009a) analysis did not provide copollutants models, give n the overall conclusion regarding the robustness of single-pollutant models (as noted in the comment-response referenced above - see section II.B.1.b, comment 13.a ), The EPA concluded that these other strengths of the study design argued for the use of this study as the basis for the core set of risk estimates for long-term exposure-rela ted mortality. In their comments on the first draft RA, CASAC supported the use of the Kr ewski et al. (2009a) study as the basis for modeling long-term exposure-related mortal ity, although they requested that the EPA provide an expanded discussion of our rationale for focusing on this study (Samet 2009c). The EPA provided that expanded discussion in the final RA (U.S. EPA, 2010a, section 3.3.3), which was also reviewed by CASAC.

(c) Failure to sufficiently consider sources of heterogeneity impacti ng risk estimates.

The commenter makes several points regard ing heterogeneity including: (a) Bayes shrunken estimates for ST mortality are likely to mask some of the heterogeneity and can result in overly tight SDs for those effect estimates (API, 2012 Attachment 1, p. 38), (b) seasonality has been shown to impact both l ong-term and short-term exposure related risk and this source of heterogene ity is not captured in the RA (API, 2012, Attachment 1, p. 40, 41), (c) regional effect estimates for ST morbidity (as used by the EPA) only capture a portion of variability in the response a nd do not fully capture spatial and seasonal heterogeneity (API, 2012, Attachment 1, p. 40), and (d) long-term mortality risk

estimates are based on nationwide CRFs that do not reflect heteroge neity across regions (API, 2012, Attachment 1, p. 42).

Regarding the use of Bayes shrunken estimates ; rather than masking heterogeneity, the use of Bayes shrunken estimates has the adva ntage of correcting fo r uncertainty-inducedII-98 heterogeneity. Specifically, city-specific e ffect estimates are shrunken towards the

national effect estimates based on consideration of variance in those city-specific effect estimates. In those cases where a city-speci fic effect estimate ha s a relatively large confidence interval (reflecting uncertainty in sp ecification of that e ffect estimates and not necessarily true heterogeneity), then that effect estimate will be shrunken towards the national mean, in order to incorporate info rmation from the higher confidence national effect estimate. By using city-specific Ba yes shrunken estimates, instead of a single national-level effect estimate, the EPA did re flect consideration for heterogeneity in the

PM 2.5 effect across cities in modeling s hort-term exposure-related mortality.

The EPA addressed comments regarding potenti al heterogeneity in effect estimates related to seasonality in a previous commen t (section II.B.1.b, comment 13c). There the EPA notes that the importance of seasonality as a factor influencing effect estimates varies regionally across the country, but doe s not have a systematic impact on those estimates, reflecting the complexity of this issue. The EPA also points out that for this reason heterogeneity related to seasonality is an area that could be nefit from additional

research.

In response to the comment regarding use of regional effect estimates in modeling ST morbidity, the EPA notes that Table 3-6 of the RA (U.S. EPA, 2010a) addresses qualitative uncertainty associated with the use of regional effect estimates in modeling this category of endpoints (specifically, use of the Bell et al. (2008) study for cardiovascular and respiratory hospital admi ssions). In Table 3-6, the EPA acknowledges that these regional effect estim ates are in some cases non-sta tistically significant, but also notes that this study benefits from larger sa mple sizes compared to city-specific models. In addition, the EPA reiterates that a lack of statistical si gnificance does not demonstrate

a lack of causal association be tween exposure and response. See, e.g. section II.B.5. a. i. Comment (4).

The comment regarding regionality and th e modeling of long-term exposure-related mortality has been addressed in a previ ous comment (see section II.B.1.b, Comment 12.c). As noted there, the PA recognizes th at the current epidemiological evidence and the limited amount of city-specific speciated PM 2.5 data does not allow conclusions to be drawn that specifically differentiate effects of PM in different locations (U.S. EPA, 2011a, p. 2-25).

(d) Treatment of measurement error and pot ential direction of associated bias

The commenters argued that uncertainty relate d to variation in PM and its components (measurement error) has a greater impact on risk estimates than the EPA acknowledges. They argue that measurement error can infl uence results in either direction and not mainly lower as asserted by the EPA. (API, 2012, Attachment 1, p. 42).

The EPA disagrees with the commenter that measurement error has not been adequately

considered in the RA. This issue was a ddressed in an earlier comment response (see section II.B.1.b, Comment 12.d). In that earlier response, the EPA also notes that the ISA concluded “in most circumstances, exposure erro r tends to bias a h ealth effect estimateII-99 downward ” (U.S. EPA, 2009a, sections 2.3.2 and 3.8.6). Thus, the EPA has both considered and accounted for the possibility of exposure measurement error, including possible bias associated with measurement error which can make it more difficult to

detect true associations.

(e) Stratification of risk assessments to consider different regions of confidence

Commenters asserted that the EPA did not st ratify risk estimates to consider those estimates above and below various levels of interest (e.g., LML with estimates falling below the LML having lower confiden ce). (API, 2012 Attachment 1, p. 42).

The EPA disagrees with the comment that th e EPA did not stratify risk estimates to

consider estimates above and below various levels of interest (e.g., LML, PRB etc). In Figures 2-11 and 2-12 in the PA (U.S. EPA, 2011a), the EPA presents percentile risk reductions for long-term and short-term exposure-related mortality, respectively, including stratification of those risk reductions into regions of varying confidence. In the case of long-term exposure-rela ted mortality, these regions include differentiation based on risk estimates falling above and below the LML referenced by the commenter.

D. Specific Comments Related to Data Handling (Appendix N)

The EPA is revising the PM 2.5 NAAQS data handling rules codified in 40 CFR Part 50, appendix N. The EPA is modifying appe ndix N to conform to the revised PM 2.5 standards; most notably, the EPA is amending the appendix N pr ocedures by removing the option for spatial averaging. In addition to making changes to a ppendix N that correspond to the changes in the annual standard form and the revised primary annua l standard level, the EPA is also finalizing additional proposed revisions to the appendix in order to codify existi ng practices currently included in guidance documents or implemented as the EPA standard operating procedures; better align appendix N language and requi rements with proposed changes in PM 2.5 ambient monitoring and reporting requireme nts; provide greater clarit y and transparency in the provisions; and enhance c onsistency with data handling protocol s utilized for other pollutants.

The EPA received a few substantive comments related to data handling for the primary

PM 2.5 NAAQS. Most comments corresponded to sp ecific revisions to appendix N, some addressed issues on which the EPA explicitly so licited feedback at proposal. All substantive

comments are addressed below. Comments are grouped into four issue categories regarding the EPA final decision to: (1) codify proposed changes for identifying PM 2.5 data “appropriate” for NAAQS comparisons; (2) codify proposed modificat ions to the procedures for combining data for design value computations; (3) incorporate additional PM 2.5 data substitution tests; and (4) eliminate the special seasonal sampling 98 th percentile concentration id entification procedure, as proposed.

1. Identifying PM 2.5 data “appropriate” for NAAQS comparisons

This topic concerns “equivalency” issues a ssociated with measurements from certain

continuous PM 2.5 Federal Equivalent Method (FEM) m onitors for the calculation of PM 2.5 design

values. As discussed in section VII.A.3 of the preamble to the final rule, “With regards to

clarification of which mon itoring data are appropriate for comparison to the PM 2.5 NAAQS, theII-100 EPA proposal acknowledged important data qua lity concerns associated with the PM 2.5 measurements collected by continuous PM 2.5 FEMs and referenced a subsequent preamble proposal section that discussed the issue in more depth and put forward a solution to mitigate the data quality concerns.”

(1) Comment : The EPA received numerous comments e xpressing concerns regarding the use of measurement data provide d by certain continuous PM 2.5 FEMs for NAAQS comparisons.

Response : As explained in section VIII of the preamble to the final rule, the EPA is revising the monitoring regulations in c onjunction with the revisions to the PM 2.5 standards to include language allowi ng monitoring agencies to identify PM 2.5 FEMs that are not providing data suffici ently comparable to the PM 2.5 Federal Reference Method (FRM) and, with the EPA approval, to allow su ch data to be excl uded from comparisons

with the PM 2.5 NAAQS. The EPA is modifying Sec tions 1 and 2 of appendix N to comport with these revisions.

2. Procedures for combining data for design value computations

This topic concerns the pr ocedures for combining monitored data from collocated instruments into a single “combined site” data record. The EPA proposed a minor modification to these procedures for the unique situation in which a m onitoring agency identifies a PM 2.5 FRM (that operates on a non-daily sc hedule) as the site’s primary monitor instead of a collocated

continuous PM 2.5 FEM instrument (that provides a meas ured value for every day). This minor modification, which affects few sites, and the impetus for making it are described in detail in section VII.A.3 of the proposal (77 FR 39001). No significant comments were received on the proposed minor modification noted a bove, and thus, for the reasons stated in the preamble to the proposed rule, it was included in the revised appendix N.

In the same section of the proposal that de scribed the minor modification (VII.A.3), the EPA explicitly solicited comment on the more general issue of whether “non-primary” (i.e., collocated) FEM data should ever be combined w ith the primary data as part of the comparison to the NAAQS for PM 2.5 . Numerous comments were received regarding that issue. Most substantive comments noted that due to comparab ility issues between certain FEMs and FRMs, it was not always prudent to combine the two data types for NAAQS comparison purposes (or

even to use an FEM sited without a collocated FR M with that intention). These particular types of comments are addressed above (in the first comment response), as we ll as in expanded detail

in section V below..

One commenter questioned a different as pect of the issue of FEM and FRM comparability and combination of the two data types. This comment, described below, questioned why the EPA had implemented different daily data completeness criteria for the two types of data.

(1) Comment : The EPA received a comment questioning the differences in the data handling

rules for continuous and filter-based data. Specifically, the commenter questioned why continuous (FEM) data required 75 percent co mpleteness (i.e., 18 or more hours) for aII-101 valid daily average, while filter-based (F RM) measurements required 23 to 25 hours (95 percent to 105 percent) for a valid daily value. The commenter suggested that the EPA define consistent data handling proce dures for continuous and filter-based PM 2.5 (and

PM 10 data).

Response : The EPA did not specifically propose, nor did we seek comment on this issue and we are not reopening or otherwise reconsidering the matter in this rulemaking. Nonetheless, the EPA notes that the rules for meeting a valid sample with an FRM, which have been in place since 1997, are based in part on the desire to obtain valid measurements of 24-hour periods, with some flexibility provided if a sample runs less

than the minimum number of hours for a va lid sample (i.e., a minimum 23 hours). The Agency also notes that continuous PM 2.5 methods, which typically report concentrations on an hourly basis and include additional diagnostic data which support data validity judgments, provide a basis for determining data completeness and validity hour by hour

in a manner that is not feasible for 24-hour, filter-based methods.

3. Additional PM 2.5 data substitution tests

With regard to assessments of data comple teness, the EPA proposed two additional data

substitution tests 33 in appendix N for validating annual and 24-hour PM 2.5 design values otherwise deemed incomplete (via the 75 per cent and 11 creditable sample minimum quarterly data completeness requirements). The EPA proposed to add these tests in or der to codify existing practices currently included in guidance docum ents (U.S. EPA, 1999) and implemented as the EPA standard operating procedur es. Further, the EPA sought to make the data handling procedures for PM 2.5 more consistent with the procedur es used for other NAAQS. While the

need for data substitution will lessen as more continuous PM 2.5 monitors continue to be deployed

in PM 2.5 networks, the EPA believes that these subs titution procedures are important to ensure that available data, if incomple te, can be confidently used to make comparisons to the NAAQS. As noted in the EPA proposal, data substitution test s are diagnostic in nature (i.e., they are only

used in an illustrative manner to show that the determination of NAAQS status based on incomplete data is reasonable).

Previously, section 4.1(c) of appendix N speci fied only one data substitution test for validating an otherwise incomplete design value. Th at diagnostic test only applied to the primary and secondary annual PM 2.5 standard, and only applied in inst ances of a violation. This data

substitution test is referred to as the “minimum quarte rly value” test and is used to determine if the NAAQS is not met (i.e., is violated). The EP A proposed two additional data substitution tests to allow comparisons to the primar y and secondary annual and 24-hour PM 2.5 standards to determine whether the NAAQS are met. One of these proposed tests uses collocated PM 10 data to fill in “slightly incomplete” 34 data records, and the other uses quarter-specific maximum values to fill in “slightly incomplete” data records. Th ese two data substitution tests are referred to as

the “collocated PM 10 test” and the “maximum quarterly valu e test,” respectively. Both tests are designed to confirm that the PM 2.5 design value is less than the level of the NAAQS.

33 Data substitution tests are supplemental data complete ness assessments that use estimates of 24-hour average concentrations to fill in for missing data (i.e., “data substitution”).

34 Slightly incomplete is defined as less than 75 percent but at least 50 percent quarterly data capture.II-102 As codified in section 4 of the revised a ppendix N, data are substituted for missing data to produce a “test design value” wh ich is compared to the level of the NAAQS. If the test design value passes the diagnost ic test, the “incomplete” design value (without the data substitutions) is then considered a valid design value. If an “incomplete” design value does not pass any stipulated data substitution test, then the original design value is still considered incomplete (and not valid for NAAQS comparisons).

The EPA received several comments on the proposed addition of the two data

substitution tests to determine that the NAAQS were met. The majority of comments generally supported the addition of data substitution test s. However, two commenters questioned the general philosophy of all appendix N data substitu tion tests (i.e., the exis ting “over NAAQS” test and the two proposed “under NAAQS” tests) by s uggesting that there were more appropriate techniques for filling in for missi ng data that would resu lt in better estimates of true design value level. Another commenter questioned, and ar gued against, the use of collocated PM 10 data in

PM 2.5 data substitution tests.

(1) Comment : One commenter questioned, and argued against, the use of collocated PM 10 data in PM 2.5 data substitution tests.

Response : At the time of proposal, the EPA believed that PM 10 data would be appropriate

for a PM 2.5 data substitution test. However, afte r consideration of public comments and additional air quality analyses, the EPA has decided that substitution of PM 10 data is largely redundant with the maximum quarterly value test and, thus, as discussed in section VII.A.4 of the preamble to the final rule, the EPA decided to not include the PM 10 substitution test in appendix N.

More specifically, the EPA analyzed the most recent three years of PM 2.5 and PM 10 data (2009 to 2011) and assessed th e separate benefit of the PM 10 substitution routine compared to the maximum quarterly value te st (Schmidt, 2012b). In this assessment of

2009 to 2011 PM 2.5 design values which did not meet the nominal data completeness requirements, the EPA found that collocated PM 10 test was almost entirely redundant and infrequently utilized after use of the maximum quarterly value test. For the annual PM 2.5 NAAQS, the maximum quarter value test in 100 cases resulted in a test design value (TDV

max ) less than or equal to 12.0 μg/m 3 . There were only two additional cases (i.e., 2 percent) when TDV

max was greater than 12.0 μg/m 3 but the TDV associated with the

collocated PM 10 test was less than 12.0 μ g/m 3 . Similarly for the 24-hour NAAQS, the maximum quarter value test in 116 cases resulted in a test design value (TDV

max ) less than or equal to 35 μg/m 3 and again only 2 additional site s (less than 2 percent) passed

the collocated PM 10 test but not the maximum quarte rly value test. Furthermore, the maximum quarterly value tests allowed th e annual and 24-hour design value to be validated approximately 5 times more ofte n than through the use of the collocated PM 10 test. Accordingly, the EPA has decide d to not include the collocated PM 10 data substitution tests in appendix N, and th ereby further simplify the data handling procedures for making comparisons to the annual and 24-hour PM 2.5 NAAQS. Furthermore, the two tests that are now codifi ed in the revised appendix N (the retained minimum quarterly value test and the added ma ximum quarterly value test) are consistent with the data substitution tests recently codified for lead, SO 2 , and NO 2

.II-103 (2) Comment : Some commenters questioned the gene ral philosophy of all appendix N data substitution tests (i.e., the existing “minimum quarterly value” test and the two proposed tests) and suggested that there were more a ppropriate techniques for filling in for missing

data that would result in better estimates of true design value levels. Their suggestions

included the use of collocated PM 2.5 concentrations producedby non-reference or nonequivalent monitors and use of data provided by nearby monitors.

Response : While acknowledging that other techniques to acc ount for missing data may exist, the EPA believes that the data substitu tion tests provided in th e finalized appendix N are all appropriate for this purpose, simple to understa nd and implement, and have

been tested over time as the standard operating procedures for making NAAQS compliance assessments. The EPA is finalizing very conservative approaches to data

substitution consistent with the intended purpose of verifying that the NAAQS standards are either met or not met. Finally, the EPA poi nts out that the test design values derived from the data substitution tests are diagnostic in nature; that is; they are only used in an illustrative manner to show that the NAAQS status based on incomplete data is reasonable. The test design values are not used as the best estimators of the design value concentrations (i.e., not used as quantitative replacements for actual design values). 35 While the EPA does not agree with the commenter that information from nearby

monitors or other sources of information would be appropriate for making comparisons with the NAAQS, the use of supplemental information can be used for other purposes, such as to assist with the implementation of the NAAQS.

4. Seasonal sampling special 98 th percentile concentration identification procedure

As stated in section VII.A.4 of the preamble of the final ru le, “With regard to identifying

annual 98 th percentile concentrations for comparison to the primary and secondary 24-hour PM 2.5 standards, the EPA suggested in the proposal to simplify the pro cedures used with an approved seasonal sampling schedule. Specifically, the EPA proposed to eliminate the use of a special formula for calculating annual 98 th percentile concentrations with a seasonal sampling schedule and thereby proposed to use only one method for calculating annual 98 th percentile concentrations for all sites (77 FR 39002).”

The proposal explained that with an appr oved seasonal sampling schedule, a site is typically required to sample dur ing periods of the year when the highest concentrations are expected to occur, but less fre quently during periods of the year when lower concentrations are expected to occur (77 FR 39002). This type of sampling schedule generally leads to an unbalanced data record; that is, a data record with proportiona lly more ambient measurements (with respect to the total number of days in the sampling period) in the “high” season and proportionally fewer ambient measurements in the “low” season.

In the proposal, the EPA noted that th ere were, at that time, very few PM 2.5 FRM monitors that actually operated on an approved seasonal sampling schedule (only 15 sites out of

35 Appendix N states that when the data substitution tests are satisfied, then the NAAQS design values derived from reported PM 2.5 data which otherwise would be considered to be incomplete shall be considered valid for comparisons to the PM 2.5 NAAQS.II-104 approximately 1,000 total sites in 2010) and that al most half of those sites had a collocated PM 2.5 FEM monitor (77 FR 39002). The proposal stated that for the 3-year period 2008 to 2010, the

annual 98 th percentile concentrations cal culated with the special formula at those 15 sites were approximately five percent lower than if the re gular procedure was use d. Updating these results to 2009 to 2011, the EPA shows that among 919 sites there were only 12 (1.3 percent) that still operated on an approved seasonal sampling schedul e as of the end of 2011; five of the 12 seasonal sampling sites had a coll ocated continuous FEM monitor; and for the 12 sites, the 2011

annual 98 th percentile concentrations calculated with the seasonal sampling formula were 1.7 μg/m 3 (4.5 percent) lower on average than if the st andard data handling procedures were used. The corresponding median values were 0.1 μg/m 3 (0.8 percent) lower. Both statistics show that the change in design values using the seasona l sampling formula was very small (Schmidt, 2012c).

The EPA only received a few substantive comments on the Agency’s proposed elimination of the special “seasonal sampling” 98 th percentile concentration identification procedure. All commenters voiced some measur e of support for the elimination of the special formula. No commenter explicitly opposed th e elimination of the formula, however, one commenter suggested that the EPA compare results from the special formula (for the sites that currently use it) to co rresponding results from the “regular” formula to understand the extent, if any, the new method introduces bias in the PM 2.5 design value.

(1) Comment : The EPA should compare the seasonal formula with the simplified “regular” formula to understand the extent, if any, to which the new method introduces bias in the

PM 2.5 design value at those sites that are currently using it.

Response : In section VII.A.4 of the preamble to the fi nal rule, the EPA presents the potential bias between the ‘regular approach’ and the ‘special formula’ for use with a seasonal sampling schedule for estimating calculating annual 98 th percentile concentrations for the primary 24-hour

PM 2.5 standard for the 12 sites that operated an approved s easonal sampling schedule in 2011. For these locations, the annual 98 th percentile concentrations in 2011 calculated with the special formula were 1.9 μg/m 3 (5.3 percent) lower on av erage than if the regu lar procedure was used; the 2009 to 2011 design values were 1.8 μg/m 3 (5.4 percent) lower on average than if the regular procedure was used. Moreover, there are no inst ances in the 2009 to 2011 timeframe (i.e., 0 out of 12 monitoring sites) in which the seasona l-formula 24-hour design value meets the NAAQS but the corresponding regular-formula de sign value does not meet the NAAQS

E. Specific Comments Related to the AQI for PM 2.5

The final rule for PM revises 40 CFR 58.50 Index Reporting, and Appendix G to 40 CFR 58.50, with respect to specifying population of a me tropolitan statistical area for purposes of index reporting, and specific breakp oints for the AQI sub-index for PM 2.5 . Incorporating responses contained in secti on V of the preamble to the fi nal rule, the EPA provides the following responses to specific comments related to the AQI sub-index for PM 2.5

.

(1) Comment: With respect to an AQI value of 100, wh ich is the basis for advisories to individuals in sensitive groups, in the proposal the EPA described two general approaches that could be used to select the associated PM 2.5 level. By far the mostII-105 common approach, which has been used with all of the other sub-indices , is to set an AQI

value of 100 at the same level as the shor t-term standard. In the proposal, the EPA recognized that some state and local air quality agencies have expressed a strong preference that the Agency set an AQI value of 100 equal to any short-term standard (77 FR 38964). These agencies typically expressed the view that this linkage is useful for the purpose of communicating with the public a bout the standard, as well as providing consistent messages about the health impacts associated with daily air quality. The EPA proposed to use this approach to set the AQI value of 100 at 35 μg/m 3 , 24-hour average, consistent with the proposed decisi on to retain the current 24-hour PM 2.5 standard ( Id. ).

An alternative approach discussed in the pr oposal (77 FR 38964), was to directly evaluate

the health effects evidence to select the level for an AQI value of 100. This was the approach used in the 1999 rulemaking to se t the AQI value of 100 at a level of 40 μg/m 3

, 24-hour average, when the 24-hour standard level was 65 μg/m 3 . This alternative approach was used in the case of the PM 2.5 sub-index, because the annual and 24-hour

PM 2.5 standards set in 1997 were designed to work together, and the intended degree of health protection against short-term risks wa s not defined by the 24-hour standard alone, but rather by the combination of the two standards working in concert. Indeed, at that time, the 24-hour standard was set to provide supplemental protect ion relative to the principal protection provided by the annual st andard. In the proposal , the EPA solicited comment on this alternative approach in recognition that, as proposed, the 24-hour PM 2.5 standard is intended to continue to provi de supplemental protection against effects associated with short-term exposures of PM 2.5 by working in conjunction with the annual standard to reduce 24-hour exposures to PM 2.5 . The EPA recognized that in the past, some state and local air quality agencies ha ve expressed support for this alternative approach. Using this alternative approach coul d have resulted in cons ideration of a lower level for an AQI value of 100, based on th e discussion of the health information pertaining to the level of the 24-hour standard in section II I.E.4 of the proposal. The EPA encouraged state and local air quality agenci es to comment on both the approach and the level at which to set an AQI value of 100 together with any supporting rationale.

Of the state or local agencies, or their organizations (e.g., NACAA), that commented on the proposed changes to the AQI, only one organization, NESCAUM, expressed some support for this approach. In its comments , NESCAUM expressed support for a 24-hour standard set at 30 μg/m 3 , 24 hour average. NESCAUM also expressed the view that EPA should carefully consider how to set the br eakpoint for an AQI value of 100. NESCAUM expressed the view that if the EPA were to keep the 24-hour PM 2.5 standard at 35 ug/m 3

, the annual standard would be controlling, and a 24-hour br eakpoint at that level (35 ug/m 3 ) would not be very effective for th e purposes of public health messaging. However, other agencies, such as the Ge orgia DNR and Indiana DEM, expressed the view that linkage between the short-term standard and the AQI of 100 is useful for the purpose of communicating with the public a bout the standard as well as providing consistent messages about the health impact s associated with the daily air quality.

A comment signed by five physicians (Sammons et al., 2012, p.2) expressed the view that based on the body of evidence of morbidity eff ects, if the current 24-hour standard isII-106 retained, then the calculati on of the AQI should be adjusted so that AQI value of 100

occurs at a PM 2.5 concentration less than or equal to 30 μg/m 3

.

Response: Based on these comments, the EPA sees no basis for deviating from the approach it proposed. Thus, as discussed in se ction V of the preamble to the final rule, the EPA is taking final action to set an AQI value of 100 at 35 μg/m 3 , 24-hour average,

consistent with the fina l decision on the 24-hour PM 2.5 standard level as summarized in section III.F of the preamble to the final rule.

(2) Comment: One set of commenters (e.g., API a nd UARG), expressed the view that changes to the AQI are not appropriate (API, 2012, pp. 45 to 46; UARG, 2012, pp. 42 to 43). They noted that air quality is getting bett er, and in fact is be tter than when EPA established the AQI. These commenters stated that the proposed ch anges to the annual standard and the AQI would mean that the public would hear less often that air quality is good, and thereby would receive apparently inco nsistent or misleading messages that air quality is worse.

Response: The AQI has been revised several times in conjunction with revisions to the standards. State and local air quality agen cies and organizations are proficient at communicating with the public a bout the reasons for changes to the AQI. Therefore, the EPA strongly disagrees with these commenters that the public will rece ive inconsistent or misleading messages. Recognizing the importa nce of the AQI as a communication tool that allows the public to take exposure re duction measures when air quality may pose health risks, the EPA agrees with state a nd local air quality agencies and organizations that favored revising the AQI at the same time as the primary standard. Indeed, failure to conform the AQI to the NAAQS could be a derogation of EPA’s duty to utilize “a uniform air quality index” to communicate in formation to the public, and to “provid[e] for ... reporting of air quality based upon such uniform air quality index”. CAA section 319 (a)(1) and (3).

(3) Comment : A few state and local air quality agencies and organizations (e.g., Pennsylvania DEP, South Coast AQMD, and NACAA) recommended against using nearroadway PM 2.5 monitors for AQI reporting. In support of this comment, they expressed the following views: (1) that near-roadway monitors are sour ce-oriented; (2) that nearroadway monitors represent micro-scale conditions; and (3) the agencies do not have experience using such monitors for AQI re porting. Additionally, one state agency, the New York DEC/DOH, commented that such reporting may be possible in the future with experience.

Response: The EPA disagrees with these comments . These monitors will be located at existing near-road stations that have been sited in locations that meet the EPA’s definition of ambient air and also comply w ith applicable 40 CFR part 58 monitoring requirements for operating networks to meet multiple objectives including providing air quality data to the public in a timely manner. As discussed in sect ion VIII.B.3.b.i of the preamble to the final rule, the EPA believes th at these monitors will be representative of

area-wide PM 2.5 concentrations indicative of ma ny such locations throughout a metropolitan area given the ubiquitous nature of roadway emissions in major urban areas.II-107 Although the stations may be representative of somewhat elevated concentrations, they are appropriate for characterizing exposure in typical portions of major urban areas as they provide information about PM 2.5 concentrations in areas where millions of people work, live and go to school. Accordingly, the EPA believes that such data from these near-road monitors are appropriate to use for reporting daily air quality information to the public through the AQI. The EPA is committed to helping air agencies develop appropriate ways to make use of the PM 2.5 measurements from these near-roadway monitors for AQI reporting purposes.III-1 III. RESPONSES TO SIGNIFICANT COMMENTS ON PRIMARY PM 10 STANDARD
Section IV.F of the preamble to the final rule discusses a number of significant public comments on the primary PM 10 standard. This section incorpor ates that discussion from the preamble, as well as discussion of add itional public comments on the primary PM 10 standard.

F. Comments from Groups Supporting Retention of the Primary PM 10 Standard

(1) Comment: Although industry commenters generally agreed with the Administrator’s proposed decision to retain the current primary PM 10 standard, some also contended that the current standard is “excessively pr ecautionary” (NMA and NCBA, 2012, p. 4) and a few expressed support for a less stringent standa rd for coarse particles that are comprised largely of crustal material. For example, the Coarse Particulate Matter Coalition (CPMC) (2012) and several other indus try commenters recommended that the final decision allow application of a 98 th percentile form for the current st andard (i.e. with its level of 150 ug/m 3 ) in cases where coarse particles consist primarily of crustal material. Such an approach would allow more yearly exceedance s of the existing standard level than are allowed with the current one-expected-ex ceedance form. These industry commenters

contended that a 98 th percentile form applied in th is way would provide appropriate regulatory relief for areas where the evidence for coarse particle-related health effects is relatively uncertain.

Response: In reaching her conclusion that the current primary PM 10 standard is requisite to protect public health with an adequate margin of safety, the Administrator considered the degree of public health protection provide d by the current standard as a whole, including all elements of that standard (i.e ., indicator, averaging time, form, level). As discussed above and in the following section, this conclusion reflect s the Administrator’s judgments that (1) the current standard appropriately provides some measure of protection against exposures to all thoracic coarse particles, regardless of their location, source of origin, or composition and (2) the cu rrent standard appropriately allows lower

ambient concentrations of PM 10-2.5 in urban areas, where the evidence is strongest that thoracic coarse particles are linked to mort ality and morbidity, and higher concentrations in non-urban areas, where the public h ealth concerns ar e less certain.

Because the considerations that led to thes e judgments, and to the conclusion that the current primary PM 10 standard is requisite to protect public health, took into account the degree of public health protection provided by the standard as a whole, it would not be appropriate to consider revisi ng one element of the standard (e.g., the form, as suggested by commenters in this case) wit hout considering the extent to which the other elements of

the standard should also be revised. The change in form requested by industry commenters, without also lowering the level of the standard, woul d markedly reduce theIII-2 public health protection provided against exposures to thoracic coarse particles. 36
However, industry commenters have not presen ted new evidence or analyses to support their conclusion that an appropr iate degree of public health protection could be achieved by allowing the use of an alternative form (i.e., 98 th percentile) for some coarse particles, while retaining the other elements of the current standard. Nor have these commenters presented new evidence or analyses challe nging the basis for the conclusion in the proposal that the varying amounts of coarse particles allowed in urban versus non-urban

areas under the current 24-hour PM 10 standard, based on the varying levels of PM 2.5 present, appropriately reflect the differences in the strength of evid ence regarding coarse particle effects in urban and non-urban areas. In light of th is, EPA does not believe that a reduction in public health protection, such as that requested by industry commenters, is

warranted.

In further considering these comments, it is to be remembered that epidemiologic studies have not demonstrated that coarse partic les of non-urban origin do not cause health effects, and commenters have not provided a dditional evidence on this point. While there are fewer studies of non-urban coarse particle s than of urban coarse particles, several studies have reported positive and statistically significant associations between coarse particles of crustal, non-urban origin and mortality or morb idity (Ostro et al., 2003; Bell et al., 2008; Chan et al., 2008; Middleton et al., 2008; Perez et al., 2008). These studies formed part of the basis for the PM Inte grated Science Assessment conclusion that “recent studies have suggested that PM (both PM 2.5 and PM 10-2.5 ) from crustal, soil or

road dust sources or PM tracers linked to thes e sources are associated with cardiovascular effects” (U.S. EPA, 2009a, p. 2-26). More over, crustal coarse particles may be

contaminated with toxic trace elements a nd other components from previously deposited fine PM from ubiquitous sources such as m obile source engine exhaust, as well as by

toxic metals from smelters or other industrial activities, animal waste, or pesticides (U.S. EPA, 2004, p. 8-344). In the proposal, the Admi nistrator acknowledged the potential for this type of contamination to increase the toxi city of coarse particle s of crustal, non-urban origin (77 FR 38960; see also 71 FR 61190).

In suggesting a change in the form of the current standard, industry commenters also did

not address the manifold difficulties noted above , and in the last review, associated with developing an indicator that could relia bly identify ambient mixes dominated by particular types of sources of coarse part icles. See above and 71 FR 61193. Yet such an

36 Based on regression analyses presented in th e PA (U.S. EPA, 2011a, Figures 3-7 and 3-8),

PM 10 one-expected-exceedance concentration-eq uivalent design values were between approximately 175 and 300  g/m 3 at monitoring locations recording 3-year averages of 98 th

percentile 24-hour PM 10 concentrations around 150  g/m 3 (i.e., the level of the current standard). This suggests that, dependi ng on the location, a 24-hour PM 10 standard with a 98 th percentile form in conjunction with the current level (i.e ., as recommended by thes e commenters) could be “generally equivalent” to a 24-hour PM 10 standard with a one-expected-exceedance form and a level as high as approximately 300  g/m 3 . Based on this analysis, a 24-hour PM 10 standard with

a 98 th percentile form and a level of 150  g/m 3 would be markedly less h ealth protective than the

current standard.III-3 indicator would be a prerequi site of the type of standa rd these commenters request.

For all of the reasons discussed above, the EPA does not agree with industry commenters who recommended allowing the application of a 98 th percentile form for the current standard in cases where coarse particles consist primarily of crustal material.

(2) Comment: Some industry commenters contended th at the uncertainti es and limitations that precluded a quantitative risk as sessment also preclude revising the PM 10 standard.

Response: Although the EPA agrees that there are important uncertainties and limitations in the extent to which the quantitat ive relationships between ambient PM 10-2.5 and health

outcomes can be characterized in risk mode ls, the Agency does not agree that such limitations alone preclude the option of revisi ng a NAAQS. As noted above, the lack of a quantitative PM 10-2.5 risk assessment in the current revi ew adds uncertainty to conclusions

about the extent to which revision of the current PM 10 standard would be expected to improve the protection of public health, be yond the protection provided by the current standard. However, the EPA does not agree th at such uncertainties necessarily preclude revision of a NAAQS. Indeed, with respect to th oracic coarse particles, the D.C. Circuit noted that “[a]lthough the evidence of danger from coarse PM is, as the EPA recognizes, ‘inconclusive’, the agency need not wait fo r conclusive findings before regulating a pollutant it reasonably believes may pose a signif icant risk to public health.” 559 F. 3d at 533. Thus, the Administrator’s conclusion that the current 24-hour PM 10 standard provides requisite protection of public health relies on her consid eration of the broad body of evidence, rather than solely on the unc ertainties that led to the decision not to conduct a quantitative assessment of PM 10-2.5 health risks.

(3) Comment: Some industry commenters argued that the EPA did not adequately consider exposure measurement error, which they assert ed is an important source of bias in epidemiological studies that can bias effect estimates in ei ther direction (e.g., NMA and NCBA, 2012).

The EPA has recognized that exposure meas urement error is an important source of uncertainty, and that the variability in risk estimates observed in multi-city studies could be attributed, in part, to exposure error due to measurement-related issues (77 FR 38910). However, the Agency disagrees with th e commenters’ assertion that exposure measurement error was not adequately consider ed in this review. The Integrated Science

Assessment included an extensive discussi on that addresses issues of exposure measurement error (U.S. EPA, 2009a, sect ions 2.3.2 and 3.8.6). Exposure measurement error may lead to bias in effect estimates in epidemiological studies. A number of studies evaluated in the last review (U.S. EPA, 2004, section 8.4.5) and in the current review (U.S. EPA, 2009a, section 3.8.6) have discusse d the direction and magnitude of bias resulting from specified patterns of e xposure measurement error (Armstrong 1998; Thomas et al. 1993; Carroll et al. 1995) and have generally concl uded “classical” (i.e., random, within-person) exposure measurement e rror can bias effect estimates towards the null. Therefore, consistent with conclusions reached in the last re view, the Integrated

Science Assessment concluded “in most circum stances, exposure error tends to bias a health effect estimate downward” (U.S. EP A, 2009a, sections 2.3.2 and 3.8.6). Thus, theIII-4 EPA has both considered and accounted for the possibility of exposure measurement error, and the possible bias would make it more difficult to detect tr ue associations, not

less difficult.

(4) Comment: The CPMC (2012) commented that EPA should retain the current PM 10 standard. In support of their comments , the CPMC submitted analyses of PM 10 air quality characterizing the potential im plications of a revised PM 10 standard. Many of these analyses were originally submitted to EPA in July 2011. The CPMC analyses were also cited by other industry commenters (e.g., NMA and NCBA, 2012) who supported the proposed decision to re tain the current PM 10 standard.

Response: As discussed above and in the preamble , the Administrator’s decision to retain

the current PM 10 standard is consistent with the overall position expressed by the CPMC and by other industry groups. However, the EP A does not agree with all aspects of the analyses supporting this CPMC position. The EPA has previously responded to these analyses in a letter to the CPMC (Wayland, 2011).

G. Comments from Groups Supporting Revision of the Primary PM 10 Standard

(1) Comment: Commenters representing a number of environmental groups and medical organizations disagreed with the Administrator’s proposal to retain the current primary PM 10 standard. These commenters generally requested that the EPA revise the PM 10 standard to increase public health protection, consistent with the recommendations from CASAC.

Response: As discussed above and in the proposal, in reaching provisional conclusions in the proposal regarding the current standard, the Administrator carefully considered CASAC’s advice and recommendations. She specifically noted that in making its recommendation

on the current PM 10 standard, CASAC did not discuss its approach to considering the important uncertainties and limitations in th e health evidence, a nd did not discuss how

these uncertainties and limitations were reflected in its recommendations. Such

uncertainties and limitations contributed to the conclusions in the Integrated Science

Assessment that the PM 10-2.5 evidence is only suggestive of a causal relationship, a conclusion that CASAC endorsed (Samet, 2009e,f). These commenters also did not address the important uncertainties in the ep idemiologic studies on which their comments are based. Given the importance of thes e uncertainties and limitations to the interpretation of the evidence, as reflected in the weight of evidence conclusions in the Integrated Science Assessment and as discusse d in the proposal, the Administrator judges that it is appropriate to consider and account for them when drawing conclusions about the implications of individual PM 10-2.5 health studies for the current standard. Commenters have not provided new informati on that would change the Administrator’s

views on the evidence and uncertainties.

(2) Comment: In recommending that the PM 10 standard be revised, some commenters supported their conclusions by refere ncing studies that evaluated PM 10 , rather than

PM 10-2.5 . These commenters contended that “[t]he most relevant studies to the setting of

a PM 10 standard are the thousands of studies that have reported adverse effects associated

with PM 10 pollution” (ALA et al., 2012).III-5 Response: As discussed in the Policy Assessment, the proposal, and the preamble to the final rule, since the establishment of the primary PM 2.5 standards, the purpose of the primary PM 10 standard has been to protect agai nst health effects associated with exposures to PM 10-2.5 . PM 10 is the indicator, not the target pollutant. With regard to the appropriateness of considering PM 10 health studies for the purpose of reaching

conclusions on a standard meant to protect against exposures to PM 10-2.5 , the proposal

noted that PM 10 includes both fine and coarse particles, even in locations with the highest

concentrations of PM 10-2.5 . Therefore, the extent to which PM 10 effect estimates reflect

associations with PM 10-2.5 versus PM 2.5 can be highly uncertain and it is often unclear

how PM 10 health studies should be interpreted when considering a standard meant to protect against exposures to PM 10-2.5 . Given this uncertainty a nd the availability of a

number of PM 10-2.5 health studies in this review, the Integrated Science Assessment

considered PM 10-2.5 studies, but not PM 10 studies, when drawing weight-of-evidence conclusions regarding the coarse fraction. 37 In light of the uncertainty in ascribing PM 10 - related health effects to the co arse or fine fractions, indicatin g that the best evidence for effects associated with exposures to PM 10-2.5 comes from studies evaluating PM 10-2.5 itself, and given CASAC’s support for the appr oach adopted in the Integrated Science Assessment, which draws weight -of-evidence conclusions for PM 2.5 and PM 10-2.5 but not

for PM 10 (Samet, 2009f), the EPA continues to concl ude that it is appropriate to focus on

PM 10-2.5 health studies when considering the de gree of public health protection provided by the current primary PM 10 standard, a standard inte nded exclusively to provide protection against exposures to PM 10-2.5

.

(3) Comment: Two State commenters (New York DOH/ DEC, 2012) expressed the view that

the PM 10 standard should be tightened if the level of the PM 2.5 standard is tightened.

These commenters contended that “In order to maintain adequate protection against exposure to coarse particle s in urban settings, the PM 10 standard would need to be lowered to ensure that coarse pa rticle levels do not rise as PM 2.5 levels decline.”

Response: While it is possible that the relationships between PM 2.5 and PM 10-2.5 concentrations and/or composition will change in some locations in the future, it is not possible at this time to precisely predict the natu re of such potential future changes, or to account for them in the standard. For example, changes in ambient PM 2.5 concentrations could alter not only the allowable coarse particle concentrations under the PM 10 standard in some locations, but also the extent to wh ich thoracic coarse part icles are contaminated with specific fine particle components (section IV.G of final rule). Alterations in coarse particle composition could impact the toxic ity of ambient thoraci c coarse particles, potentially altering the health effects that result follo wing coarse particle exposures and/or altering the coarse particle exposur e concentrations resu lting in such health

37 Although EPA relied in the 1997 review on evidence from PM 10 studies, EPA did so out of necessity (i.e., there were as ye t no reliable studies measuring PM 10-2.5 ). In the 2006 review, EPA placed primary reliance on epidemiologi c studies measuring or estimating PM 10-2.5 , although there were comparatively few such studi es. In this review, a larger body of PM 10-2.5 studies are available. EPA regards these studies as the evid ence to be given principa l weight in reviewing the adequacy of the PM 10 standard.III-6 effects. Based on the available health eviden ce, it is unclear the extent to which such future potential changes in PM concentrati ons and/or composition could support revisions to the PM NAAQS.

Future scientific studies will evaluate PM 10-2.5 health effects as fine particle

concentrations and/or coarse particle composition change . The issue of whether the existing PM 10 standard remains requisite to protect public health with an adequate margin of safety will need to be revisited in future reviews of the PM NAAQS, in light of new evidence and air quality information refl ecting any future changes in particle

concentrations a nd/or composition.

(4) Comment: Some environmental and public health groups disagreed with the weight-ofevidence conclusions for coarse particles. Sp ecifically, the ALA et al. (2012) contended

that “EPA should re-evaluate th is conclusion and consider se parately a classification of

PM 10 effects on mortality as likely causal, in light of evidence.”

Response: As discussed in the preamble to th e final rule (section IV.F), the EPA disagrees with these commenters regarding the extent to which it is appropriate to rely on

PM 10 studies when considering a standard m eant to protect the public health against exposures to PM 10-2.5 . In addition, the EPA disagrees th at it is appropr iate to draw separate weight-of-evidence conclusions for PM 10 . When this issue was presented to CASAC during the development of the Integrated Science Assessment, they made the following recommendation (Samet, 2009e, p. 3):

Revisions are needed to remove the impression that PM 10 is a separate pollutant from PM 2.5 and PM 10-2.5 . The [draft] ISA handles PM 10 , PM 2.5 , and PM 10-2.5 , as if they were separate en tities, even though the latter two are components of PM 10 . The CASAC cautions against this approach and

notes that PM 10 is a mixture that contains varying proportions of particles in the smaller and larger size ranges.

In light of this advice, the final Integrat ed Science Assessment did not draw separate weight-of-evidence conclusions for PM 10 . Public commenters have not presented new information that would justify going agains t CASAC’s recommendation on this issue.

(5) Comment: Environmental and public health groups also commented on the appropriateness of setting st andards based on evidence that has been judged to be “suggestive of a causal relations hip,” as is the case for PM 10-2.5 . Specifically, the ALA et al. (ALA et al., 2012) stated that “EPA must set standards that protect against effects that are deemed suggestive by the evidence.”

Response: The EPA agrees with these commenters that the available evidence supports the appropriateness of se tting a standard to protect public health against exposures to all thoracic coarse particles. However, although the commenters are correct that EPA may establish standards to guard against threats which are unc ertain, or even which research has not yet identified, it is also the case that EPA may eval uate the strength of the evidence, and a standard may legitimately be more or less stringent in order to reflect the strength of that evidence.III-7 Therefore, in deciding whether it is appropriate to revise the PM 10 standard, it is reasonable for

EPA to account for the uncertainties inherent in the evidence, which underlie the determination that the evidence is “suggestiv e of a causal relationship.” As discussed extensively in the preamble to the final rule (sect ion IV.G), the Administrator concludes that the current PM 10 standard is requisite to protect public health with an adequate ma rgin of safety against effects associated with exposures to thoracic coarse particles.

.IV-1 IV. RESPONSES TO SIGNIFICANT COMMENTS ON SECONDARY PM

STANDARDS

A. General Comments on Proposed Secondary PM Standards

A number of comments on the proposed seconda ry standards for PM were general in nature, basically expressing one of three views: (1) support for setting a distinct secondary standard to protect from visibi lity impairment; (2) opposition to setting a dis tinct secondary standard to protect from visi bility impairment; or (3) s upport for revising the secondary standards to be equivalent in a ll respects to the proposed primary standards, including the revised primary annual standard. Many of these commen ters simply expressed their views without stating any rationale, while others gave general reasons for their views but without reference to the factual evidence or rationale presented in the proposal notice as a basis for the Agency’s proposed decision. In general, the large majority of comments focused on the proposal to set a distinct standard to protect against visibility impairment. Relatively fe w commenters addressed the proposal to retain the existing secondary st andards for non-visibil ity welfare effects.

The preamble to the final rule presents the Agency’s full response to these views, expressly identifying: (1) the strengths and lim itations of the scientific evidence regarding PMrelated visibility impair ment; (2) the need for and appropria teness of a secondary standard to protect from visibility impairme nt; (3) the appropriate indicator, averaging time, form and level for a standard designed to protec t against PM-related visibility impairment; (4) the scientific evidence regarding non-visibility we lfare effects and the appropriate standards to protect against those effects; and 5) the a dvice of CASAC regarding the secondary standard for PM. See sections VI.A, VI.B, and VI.C of the preamble to the final rule for a discussion of these topics.

B. Specific Comments on Proposed Secondary PM Standard to Protect Visibility

A large number of commenters provided more detailed comments regarding the proposal to set a distinct secondary standard for protec tion from visibility impairment. Many of these comments addressed specific elements of the proposed distinct secondary PM 2.5 standard, including indicator, averaging time, form, and le vel. Other comments focu sed on the strength of currently available evidence—particularly the visi bility preference studies—as a basis for setting a distinct secondary standard. In addition, some commenters questioned whether a distinct secondary standard was needed in light of the protection already afforded by the existing secondary standards for PM, while others raised le gal issues or other challenges, such as issues related to the Regional Haze Program, data hand ling, or monitoring. Responses to key issues raised on these topics are generally summarized in section VI.C.1 of the preamble. Below, the EPA provides more detailed responses to the full range of significant issues raised in these

comments.

It is important to note that because the Administrator’s final decision regarding the secondary PM standards differs from what was proposed, a number of issues raised by commenters are now moot. Specifically, since the Ad ministrator is retaining the current suite of secondary PM standards generally, while revi sing only the form of the secondary annual PM 2.5 standard to remove the option for spatial averagin g consistent with this change to the primary

annual PM 2.5 standard, and is not establishing a distin ct secondary standard for protection fromIV-2 visibility impairment, concerns expressed by co mmenters about various aspects of the proposal, such as the overlap with the Regional Haze Program, the data handling requirements, and monitoring requirements, are no longer per tinent. Though the EPA has summarized many of these issues below, it does not re spond to them in detail since th ey pertained to specific aspects of the proposal that were not adopted in the final rule.

1. Indicator

In the current review of the secondary PM 2.5 standards, the EPA considered what type of indicator it would be appropriate to adopt for a distinct secondar y standard designed to protect from visibility impairment. While agreeing with CASAC that a directly measured PM light extinction indicator would provide the most direct link between PM in the ambient air and PMrelated light extinction, the Admini strator concluded this was not an appropriate option in this

review due to technical lim itations, and instead proposed to adopt a new calculated PM 2.5 light extinction indicator, similar to that used in the Regional Haze Program (i.e., using an IMPROVE algorithm as translated into the deciview scale). This kind of indicator, referred to as a PM 2.5 visibility index, would directly incorp orate the effects of differences in PM 2.5 composition and relative humidity on visibility.

A large number of public comments on the secondary PM standards addressed the suitability of utilizing a calculated light extinction indi cator for the distinct secondary standard as proposed. Some commenters supported the prop osal to adopt a calcu lated light extinction indicator, while others advocated relying on di rect measurements instead. Commenters from both groups expressed concern over specific elements of the proposed calculated PM 2.5 visibility index. In particular, commenters expressed differing views on which IMPROVE algorithm should be utilized; whether it is appropriate to ex clude coarse particles fr om the indicator; and whether the proposed protocols for incor porating data on relative humidity and PM 2.5 species are appropriate. In addition, some commenters expressed concern about the omission of other contributors to visibility impairment from the visibility index. The EPA has addressed these comments in section VI.C.1.b of the proposal, a nd provides additional de tails in response to specific issues, below.

a. Comments Supporting Directly Meas ured Light Extinction Indicator

(1) Comment: The majority of commenters noted the uncertainties associated with relying on a calculated indicator and argued that it was inappropriate to rely on a calculated light

extinction indicator rather than direct measurements. A number of these commenters advocated postponing setting a distinct second ary standard until an approach based on direct light extinction measurements can be adopted.

Response: The EPA generally agrees with commenter s that an indicator based on directly measured light extinction would provide the most direct link between PM in the ambient air and PM-related light extin ction. However, as noted at the time of proposal and in accordance with the advice of CASAC, the EP A has concluded that this is not an appropriate option in this revi ew because a suitable specification of currently available equipment or performance-based verification procedures could not be developed in the

time frame of this review.IV-3 In evaluating whether direct measurement of light extinction was appr opriate to consider in the context of this PM review, the EPA produced a White Paper on Particulate Matter (PM) Light Extinction Measurements (U.S . EPA, 2010g) and solicited comment on the White Paper from the Ambient Air Mon itoring and Methods Subcommittee (AAMMS)

of CASAC. In its review of the White Paper (Russell and Samet, 2010a), the CASAC AAMMS commented on the capabilities of currently available instruments, and expressed optimism regarding the near-term de velopment of even better instruments for such measurement than are now commercially available. The CASAC AAMMS advised against choosing any currently available commer cial instrument as the basis for an FRM, or even selecting a general measurement appr oach as an FRM, because to do so could discourage development of other potentially superior approaches. Instead, the CASAC AAMMS recommended that EPA develop performa nce-based approval criteria for direct measurement methods in order to put all approa ches on a level playing field. Such criteria would necessarily include procedures and pass/ fail requirements for demonstrating that the performance criteria have been met, both in the laboratory and dur ing field tests. At the present time of this review, the EPA ha s not undertaken to develop and test such performance-based approval criteria. The EPA an ticipates that if an effort were begun it would take at least several years before such criteria would be ready for proposed regulatory use as an FRM.

Since the available evidence demonstrates that a strong correspondence exists between

calculated PM 2.5 light extinction and PM-related visi bility impairment, the EPA does not believe it would be appropriate to postpone se tting a distinct seconda ry standard until an approach based on direct light extinction measurements coul d be adopted. Furthermore,

the EPA notes CASAC’s conclusion that the proposed calculated PM 2.5 light extinction indicator based on the original IMPROVE algorithm “appears to be a reasonable approach for estimating hourly light extinc tion” (Samet, 2010d, p. 11) and “its reliance on procedures that have already been impl emented in the CSN and routinely collected

continuous PM 2.5 data suggest that it could be imple mented much sooner than a directly measured indicator” (Samet, 2010d, p. iii).

(2) Comment: Some commenters argue d that the proposed calculated light extinction

indictor is ill suited for a br ight line standard because the method uses average humidity and a reconstructed visibility measurement calculated from PM 2.5 speciation filter analysis, rather than measuring what is actually observed by individuals.

Response: The available evidence demonstrates that a strong correspondence exists

between calculated PM 2.5 light extinction and PM-related vi sibility impairment. Thus, the

EPA concludes that in the absence of relia ble direct measurements of visibility impairment in urban areas, it is appropria te to rely on a calcu lated light-extinction

indicator. The EPA notes that CASAC c oncluded that relyi ng on a calculated PM 2.5 light

extinction indicator based on PM 2.5 chemical speciation and relative humidity data represented a reasonable approach. The input s that are necessary include measurements that are available through existing monitori ng networks and established protocols.

(3) Comment: Many commenters stated that relying on direct light extinction measurements

would enable a standard to be based on a s horter averaging time, either 1-hour or sub-IV-4 daily (4 to 6 hours), consistent with the mo re instantaneous nature of perceptions of visual air quality and the advi ce of CASAC in this review.

Response: The EPA agrees with commenters that there would be a number of advantages to direct measurements of light extinction for use in a secondary standard relative to

estimates of PM 2.5 light extinction calculated using PM 2.5 mass and speciation data. These include greater accuracy of di rect measurements with shorter averaging times and overall greater simplicity when compared to the need for measurements of multiple parameters to calculate PM light extinction. However, as noted above, the EPA has concluded, in accordance with the advice of CASAC, that di rect measurement is not an appropriate option in this review because a suitable spec ification of currently available equipment or performance-based verification procedures coul d not be developed in the time frame of this review. Furthermore, the availabl e evidence demonstrates that a strong correspondence exists between calculated PM 2.5 light extinction a nd PM-related visibility impairment. Thus, the EPA concludes that in the absence of reliable direct measurements of visibility impairment in urban areas, it is appropriate to rely on a calculated lightextinction indicator.

(4) Comment: Numerous commenters supported devel oping a pilot study to field test and

evaluate direct measurement instrumenta tion in several areas around the country, as recommended by CASAC AAMMS. These comm enters recommended collocating pilot

direct measurement instruments with othe r existing monitors and cameras such as CAMNET, the National Weather Service’s Automated Surface Observing System monitors, and continuous PM 2.5 and filter-based PM 2.5 speciation monitors. Such a pilot field-study program using candidate instru ments would allow for near real-time measurements of light extinction and w ould enable comparisons between existing monitors and alternative approaches.

Response: The EPA agrees with these commenters that, resources permitting, it would be

useful to establish such a pilot program to inform future reviews of the PM NAAQS. However, in the current review, the Agency continues to agree with CASAC that relying

on a calculated PM 2.5 light extinction indicator based on PM 2.5 chemical speciation and relative humidity data represents a reasonable approach at this time. The inputs that are necessary include measurements that are av ailable through existing monitoring networks and established protocols.

b. Comments Supporting Calculated Light Extinc tion Indicator

(1) Comment: Recognizing the limitations on applyi ng direct measurements at present, commenters supporting the proposal to set a distinct standa rd argued that relying on “calculated light extinction is a reasonable fi rst approach” (DOI, p. 2). These commenters pointed to the advice of CASA C, which had acknowledged that it was not possible for the EPA to develop an FRM for direct measuremen t of light extinction within the time frame

of this review and had conclude d that relying on a calculated PM 2.5 light extinction indicator represented a reasonable approach that could be implemented sooner than a directly measured indicator. These commente rs generally supported the proposal to adopt

a calculated PM 2.5 light extinction indicator, at least as an interim approach.IV-5 Response: The EPA agrees with commenters who stated that relying on calculated PM 2.5 light extinction would be a reasonable appro ach at this time. The EPA notes that this

conclusion is consistent with the advice of CASAC, which advised the EPA not to choose any currently available commercial instrument , or even a general measurement approach for direct light extinction measurement at this time because to do so could discourage development of other potentially superior a pproaches. Given the limitations in current direct measurement options, the EPA continues to conclude that it is appropriate to rely

on a calculated PM 2.5 light extinction approach for purposes of a PM 2.5 visibility index at

this time.

c. Comments on Specific Aspects of Ca lculated Light Extinction Indicator

(1) Comment: A number of commenters expressed concern over the proposal to use the original IMPROVE algorithm as the basis for the calculated light ex tinction indicator. These commenters noted that the original IMPROVE algorithm has been shown to have

consistent biases at both lo w and high levels of light ex tinction. In particular, these commenters expressed concern with the algo rithm’s bias at higher levels of light extinction, which they pointed out were the conditions that might be encountered on hazier days in urban areas. In general, these commenters endorsed using the revised IMPROVE algorithm as a basis for a calcu lated light extinction indicator.

Response: The EPA agrees that the revised algo rithm was developed to correct known

biases in the estimated extinction in remote areas under the original IMPROVE algorithm under very low and very high light extinction conditions, with further modifications and

additions to better account for differences in particle composition and aging in remote areas. However, the EPA does not believe that these same modificat ions and additions would necessarily be appropriate for calcu lating light extinction in urban areas. In general, the EPA considers the original al gorithm to be suitab le for purposes of calculating urban light-extincti on, although the Agency believes some adjustments to this algorithm may be appropriate fo r urban environments, as discussed in the preamble to the

final rule.

There are several reasons why the EPA cons iders the original IMPROVE algorithm better

suited to urban environments than the revised algorithm. First, the EPA considers that the multiplier of 1.8 used to convert OC to OM in the revised IMPROVE algorithm is too high for urban environments. This is discusse d further in response to specific comments on the OC multiplier, below. Second, the EPA does not believe that it would be appropriate to include a term for hygroscopic sea salt for urba n light extinction. Unlike in some remote coastal locations, sea salt is not major contributor to light extinction in urban areas. Pitchford (2010) esti mated that in most instances, the contribution of sea salt

to PM 2.5 light extinction is well below 5% for PM 2.5 light extinction greater than 24 dv. Moreover, urban sources of salt include sandi ng of roads during the winter and those reentrained particles are mostly in the coarse size range.

Third, the EPA does not consider the revi sed algorithm’s differentiation between different size modes of sulfate, nitrate, a nd organic mass appropriate for urban areas. Like in remote areas, small and large size modes of sulfate, nitrate and organic mass wouldIV-6 exist in the urban environmen t. However, the apportionment of the total fine particle

concentration of each of the three PM 2.5 components into the concentrations of the small and large size fractions in urban areas would likely need a different approach than that

used for remote areas. This is because of th e closer proximity of urban sources to their emissions. This is a particular concern not only for organic mass, which as explained previously has a large contribution from n earby urban emission sources, but also for

PM 2.5 nitrate whose concentrations are also higher in urban areas compared to the surrounding regions. Thus, a higher portion of th e total urban concentration may be in the small mode compared to remote areas a nd thus a different apportionment algorithm

would be needed.

Finally, the EPA does not consider it necessa ry to employ site-specific Rayleigh light scattering terms in place of a universal Ra yleigh light scattering value for purposes of calculating light extinction in urban areas for purposes of cal culating the 90th percentile values. The site-specific Rayleigh value is most important to accurately estimate extinction in remote areas, particularly for th e average of the 20% best visibility days, an essential metric for the regional haze program . In most other instances, the Raleigh light scattering term has relatively little impact. For example, P itchford (2010) estimated that the difference between the approach em ployed by the EPA in the UFVA and Policy Assessment to define the 20 to 30 dv range of candidate protec tion levels and an approach utilizing site-specific Rayleigh li ght scattering terms was less than 0.1 dv for light extinction around 30 dv.

For all of these reasons, the EPA consider s the original IMPROVE algorithm better suited to the task of calculating urban li ght extinction than the revised IMPROVE algorithm. However, the EPA does consider it ap propriate to make certain adjustments to the original algorithm for purposes of calcu lating urban light extinction. As discussed below, the EPA believes it is appropriate to use a 1.6 multiplier to convert OC to OM in urban areas, and to exclude the term for co arse particles from the IMPROVE equation.

(2) Comment: Some commenters supported use of the revised IMPROVE algorithm. These commenters noted that the revised equation has been through a peer review which

confirmed that it is based on the best scie nce and corrects the biases inherent in the original algorithm. Commenters also noted th at this revised algorithm has been widely incorporated into Regional Haze plans, and urged the EPA to use this same equation in the visibility index for the sake of consistency: “EPA approved this approach for regional haze and does not dispute its greater accurac y. Therefore, a national secondary ambient air quality standard based on crit eria that accurately reflect the latest scientific knowledge logically should not revert to the original IMPROVE algorithm” (Oklahoma DEQ, p. 2). Other states agreed, arguing that “Utilizing alternate forms of the equation will lead to inconsistency in how agencies and regulated sources evaluate visi bility impacts and add an additional layer to source, SIP, and Re gional Haze analysis” (Arizona DEQ, p. 3). These states urged the EPA to adopt the revised improve algorithm to maintain consistency between programs.

Response: The EPA agrees with commenters that the revised algorithm represents the best science for estimating visibility impairment from aerosol components in remoteIV-7 areas. The EPA does not agree that this approa ch is necessarily a better approach for estimating visibility impairment in urban areas. Considering the nature of urban PM composition, EPA concludes that it is appr opriate to use the original IMPROVE algorithm (with the adjustments discussed in response to the prev ious comment, above) to relate urban PM to light extinction in urban areas.

The revised algorithm was designed to separa tely account for extinc tion and water uptake from freshly emitted versus aged aerosols and also to account for hygroscopic sea salt which was not considered in the original algorithm. The new formula includes an adjustment for the calculation of OM as 1.8*OC to account for the more aged and oxygenated organic aerosol that is found in remote areas which may also result from

different emission sources.

The EPA does not believe that these same m odifications and additions would necessarily be appropriate for calculating light extinction in urban areas . The composition of, and the mix of emission sources contributing to, PM 2.5 in urban areas is different than in remote areas. Thus, the urban PM 2.5 would have different light extinction properties. In particular, urban organic mass results from local and regi onal sources and thus has a different ratio of fresh to aged emissions and a different mass to organic carbon ratio than rural areas. The approach used by the revise d algorithm to partition OM into small and large particles may not be appropriate for the urban mixture where a higher percentage of smaller particles are likely from the freshe r nearby urban emissions. In addition, the 1.8 OC to OM multiplier in the revised improve algorithm is likely too high for urban OC.

The revised algorithm was developed for use in remote areas and was evaluated with concurrently available light sca ttering measurements at 21 remote locations. The revised algorithm is largely untested in urban areas and in fact, the PM 2.5 portion of the algorithm may overestimate urban extinction because of the contributions from organic mass. For all of these reasons, the EPA has concluded th at it would not be appropriate to use the revised IMPROVE algorithm for purposes of calcu lating light extinction in urban areas.

(3) Comment: Some commenters noted that both the original and the revised IMPROVE algorithms were designed in support of th e Regional Haze Program which is focused on largely rural Class I areas, and that neither algorithm is necessarily suitable for urban areas. Noting that the EPA has not thoroughl y evaluated the applic ability of either IMPROVE algorithm in urban areas, these co mmenters urged additi onal research to evaluate the suitability of either algorithm (or an alternative appr oach) in urban areas.

Response: EPA agrees with commenters that neither the original nor the revised IMPROVE algorithms have been evaluated in urban areas. Based on the advice of CASAC (Samet, 2010b), EPA concluded that it was unnecessary to develop a new urbanoptimized algorithm to assess the relationship between urban PM to PM light extinction.

(4) Comment: Some commenters stated that they believed the 1.4 multiplier used to convert organic carbon (OC) to organic mass (OM) in the original IMPROVE algorithm was too low, and that it would be more appropriate to use a higher multiplier, such as the 1.8 multiplier that has been adopted as pa rt of the revised IMPROVE algorithm.IV-8 Response: The EPA is aware that there has been considerable debate within the research community about the appropriate multiplier to use to best represent urban environments. In general, the EPA agrees with commenters that a multiplier of 1.4 is likely too low, and that a somewhat higher value would be appropr iate. However, the EPA also believes that it would be inappropriate to use a multiplier as high as 1.8 to convert OC to OM in urban areas. As noted by commenters, the organic ma ss contribution to visibility impairment can be large, and generally OM is signifi cantly larger in urban areas compared to surrounding rural areas. Because a large porti on of the organic component of urban PM results from nearby emissions sources, the total OM mass is generally closer to the

measured OC from which it is derived. This means it is appropriate to use a smaller multiplier to convert OC to OM in urban areas as compared to the value of 1.8 used in the revised algorithm, which is tailored to remote areas. The CASAC noted that urban OM

includes fresh emissions and the EPA conclude d in the Visibility Assessment that “the original version is cons idered more representative of ur ban situations when emissions are still fresh rather than aged as at remo te IMPROVE sites” (U.S. EPA, 2010b, p. 3-19). Although the revised algorithm represents the best science of estimating extinction in

remote areas with its aged aerosol, the commen ters did not address how the EPA should modify the revised algorithm to best repres ent the more complex and different urban aerosol, particularly for OM.

As discussed in Appendix F of the Policy Assessment (U.S. EPA, 2011a), the EPA used the SANDWICH mass closure approach (Fra nk, 2006) in the Urban Focused Visibility Assessment (U.S. EPA, 2010b) for purposes of calculating maximum daylight hourly

PM 2.5 light extinction and evaluated which mu ltiplier would produce 24-hour results most similar to the SANDWICH approach using 24-hour PM 2.5 organic carbon derived from the new Chemical Speciation Network (CSN) carbon monitoring protocol established in 2007. Analyses presented in Appendix F of the Policy Assessment indicate that a multiplier of 1.6 is most appropriate for purposes of comparing the hourly PM 2.5 light

extinction with calculated 24-hour extinction (see Appendix F, section F.6 for a full explanation). The EPA also considers this higher multiplier to be a better approach for urban CSN monitoring sites wh ere the new measurements of organic carbon tend to be lower than those produced by the older NIOS H-type monitoring protocol (Malm, 2011). A multiplier of 1.6 is now used to calculate OM from OC measurements at CSN sites.

In light of all of these considerations, in particular the analyses the EPA conducted for Appendix F of the Policy Assessment and the f act that the monitoring method for organic carbon has recently changed in the CSN networ k, the EPA judges that a multiplier of 1.6 for urban areas would be most appropr iate for purposes of calculating PM 2.5 light extinction in urban areas. The implications of th is shift to a 1.6 multiplier for OC in urban areas for decisions about averaging time, level, and need for a distin ct secondary standard are discussed in the preamble to the final ru le in sections VI.C.1.c, VI.C.1.e, and VI.C.1.f, respectively.

(5) Comment: A number of commenters argued that exclusion of coarse PM from the calculated light extinction indicator was in appropriate. These commenters noted that coarse particulate matter is an important c ontributor to visibility impairment in many areas, particularly in the western U.S., and that the levels of “acceptable” visual airIV-9 quality derived from the visibility preference studies reflected total light extinction due to the full mix of particles (including coarse PM) in ambient air.

Response: The EPA does not agree with commenters who suggested that coarse particles

should be included in the calcu lated light extinction indicato r. As noted in the proposal,

PM 2.5 is the component of PM responsible for mo st of the visibility impairment in most urban areas. Currently availa ble data suggest that PM 10-2.5 is a minor contributor to visibility impairment most of the time, although at some locations (U.S. EPA, 2010b, Figure 3-13 for Phoenix) PM 10-2.5 can be a major contributor to urban visibility effects.

While it is reasonable to assume that other ur ban areas in the desert southwestern region of the country may have conditions similar to the conditions shown for Phoenix, in fact

few urban areas conduct continuous PM 10-2.5 monitoring. This significantly increases the difficulty of assessing the role of coarse pa rticles in urban visibility impairment. For example, among the 15 urban areas assessed in this review, only four areas had

collocated continuous PM 10 data allowing calculation of hourly PM 10-2.5 data for 2005 to 2007. In addition, PM 10-2.5 is generally less homogenous in urban areas than PM 2.5 in that coarse particle concentrations exhibit greater temporal variability and a steeper gradient across urban areas than fine particles (U .S. EPA, 2009a, p. 3-72). This makes it more challenging to select sites that would adequa tely represent urban visibility conditions. Thus, while it would be possible to include a PM 10-2.5 light extinction term in a calculated light extinction indicator, as was done in the Visibility Asse ssment, there is insufficient information available at this time to assess the impact and effectiveness of such a refinement in providing public welfare protect ion in areas across the country (U.S. EPA, 2011a, pp. 4-41 to 4-42).

In addition, the EPA notes CASAC’s advice th at it would be appropriate to focus on

PM 2.5 light extinction for purposes of setting a standard to protect visibility. In its comments on the EPA’s White Paper on Part iculate Matter (PM) Light Extinction Measurements (U.S. EPA, 2010g), the Ambient Air Monitoring and Methods Subcommittee (AAMMS) of CASAC made the recommendation that consideration of

direct measurement should be limited to PM 2.5 light extinction as this can be accomplished by a number of commercially available instruments and because PM 2.5 is generally responsible for most of the PM vi sibility impairment in urban areas. The

CASAC AAMMS indicated that it is technically more challenging at this time to accurately measure the PM 10-2.5 component of light extin ction (Russell and Samet, 2010a).

In light of the limited role of PM 10-2.5 in light extinction in most urban areas, and the greater uncertainty and variabil ity involved in the role of co arse particle in visibility impairment, the EPA has concluded that it is not appropriate to set a standard based on a calculated light extinction indica tor that includes coarse particles at this time, and that it would be appropriate to base a calculated indicator on PM 2.5 light extinction.

(6) Comment: Some commenters objecting to the excl usion of coarse particles from the proposed light extinction indicator argued that the EPA had not provided “compelling reasons” for not including coarse particles. For example, North Carolina DENR stated while the coarse particle fr action might contribute only a small amount toward visibilityIV-10 impairment, it should still be included because “nothing presented in the proposed rule would support not including the coarse particle fraction. Wher e coarse particle data are not available, the EPA should develop a method to estimate the coarse particle fraction for use in the equation” (p. 4). However, other commenters, agreed with the EPA’s proposal to exclude coarse pa rticles from the calculated light extinction indicator.

Response: As noted above, in light of the limited role of PM 10-2.5 in light extinction in most urban areas, and the greate r uncertainty and vari ability involved in th e role of coarse particle in visibility impairme nt, the EPA continues to concl ude that it is not appropriate

to set a standard based on a calculated light extinction indicator that includes coarse particles at this time, and the calc ulated indicator should be based on PM 2.5 light

extinction. The EPA notes that this conclu sion was supported by the advice of CASAC.

(7) Comment: A few commenters noted that due to the exclusion of coarse particles, a “deciview” calculated for purposes of the proposed PM 2.5 visibility index is inconsistent with the unit as conventionally defined under the Regional Haze Program.

Response: A deciview is a unit of measure of vi sibility derived from calculated light extinction measurements. A one dv change is approximately a 10% change in the aerosol based extinction. As used by EPA in the PM 2.5 visibility index, however, a one dv change is approximately a 10% change in the PM 2.5 aerosol based extinction coefficient. Typically, coarse particles contribute a very sm all amount of the total light extinction and resulting deciviews. For example, when the PM 2.5 aerosol components result in 30 dv of light extinction, even an additional 10 μg/m 3 (the median value for the U.S., see Schmidt et al., 2010b) of coarse particles would only in crease the visibility index by 0.2 dv. Thus,

the EPA concludes that the exclusion of coar se particles does not have a substantial impact on visibility index values in urban areas and that it is a ppropriate to exclude coarse particles from the indicato r for the reasons discussed above.

(8) Comment: Some commenters questioned why the EPA was proposing to rely on monthly average relative humidity [f(RH)] values when hourly humidity data are widely available, particularly in urban areas. One commente r argued that the EPA’s proposed approach involves “guessing relative humidity” rather th an relying on accurate , readily available measurements (Oklahoma DEQ, p. 1). The commenter stated that since relative humidity is highly variable and weather dependent, th e proposed approach “effectively undermines the capacity of the prescribed monitori ng regime to identify periods when PM 2.5 adversely affects visibility.” Other commenters supported this view, noting that relative humidity can vary substantially even within a 24-hour period, and th at light extinction can be very sensitive to these changes. These commenters recommended that hourly or daily humidity measurements should be utilized in place of the proposed monthly average f(RH) values.

Response: The EPA disagrees that concurrent (h ourly) humidity measurements should be used. The use of longer-term averages for each monitoring site adequately captures the seasonal variability of relative humidity and its effects of visibility impairment, and this approach focuses more on the underlying aeroso l contributions to visibility impairment and less on the day-to-day variations in humid ity. This provides a more stable indicatorIV-11 for comparison to the NAAQS and one that is more directly rela ted to the underlying

emissions that contribute to visibility impairment. More over, the EPA disagrees with commenters that using monthl y average relative humidity undermines the proposed monitoring regime, noting that the Agency’s conclusion that a 24-hour averaging time would be appropriate for a visibility index st andard diminishes the importance of having hourly humidity data. Longer-term average humid ity data are better matched to 24-hour averaging times, which effectively smooth out the influence of peak hourly values regardless of whether hourly data are availabl e. Therefore, the EPA continues to believe that it is appropriate to use f(RH) valu es for purposes of calculating a 24-hour PM 2.5 visibility index. Moreover, the EPA disagr ees that this approach involves “guessing relative humidity” since the f(RH) values are based on 10 years of climatological data for

each location.

(9) Comment: Some commenters reco mmended that the EPA should utilize a 90 percent relative humidity screen rather than 95 percen t cap for purposes of eliminating periods in which visibility impairment is due to rain or fog. These commenters claimed that under a 95 percent cap, both the average f(RH) values and the PM 2.5 visibility index values could be inflated in locations frequently affected by fog and/or precipitation. These commenters preferred the approach of ex cluding hours with relative humidity above 90 percent on the grounds that this approach would elimin ate foggy/rainy hours irrespective of the frequency of occurrence.

Response: The EPA believes that relying on monthly average relative humidity values based on 10 years of climatologi cal data would appr opriately reduce the effect of fog and precipitation. Although the approach of usi ng a 95 percent humidity cap, as in the Regional Haze Program, includes some hours with relative humidity between 90-95 percent, the general approach of using a longer-term average for each monitoring site effectively eliminates the effect of very hi gh humidity conditions on visibility at those locations. In essence, the adoption of mont hly average f(RH) values mitigates (i.e., smoothes out) the peak humidity values, and capping remaining hours at 95 percent relative humidity further reduces the influence of fog or precipitation events (even if those conditions occur frequently). Therefore, the EPA disagrees with commenters that it would be more appropriate to use a 90 percent relative humidity screen.

(10) Comment: One commenter stated that utilizing only one sampling point for purposes of calculating the light extinction indicator woul d not be appropriate because it would not represent visibility across the airshed. The co mmenter stated that the unit of deciviews as used in the Regional Haze Program was “prima rily developed for areas with a long site path to encompass a large sample size” (Clark County, Nevada, Department of Air Quality, p. 2). The commenter urged the EPA to consider requiring the use of additional sampling points for purposes of calcula ting light extinction in urban areas.

Response: EPA agrees that PM 2.5 is more spatially homogeneous in remote areas than in urban areas. For this reason, the visibility impairment estimated from aerosol

concentrations at individual urban locations may not be re presentative of a nearby long urban site path. Thus urban vi sibility measured at the maximum concentration location in an urban area, especially at locations with a small scale of spatial representativeness forIV-12 one or more PM chemical components could provide even more protection against visibility impairment than the location which is more typica l of urban-wide PM 2.5 concentrations.

(11) Comment: A number of commenters criticized ot her specific aspects of the proposed visibility index, especially with regard to the inclusion, exclusion, or construction of specific terms in the IMPROVE equation. In many instances, these commenters argued that the proposed indicator was inappropria te for specific local environments due to unique or atypical conditions influencing aero sol composition or relative humidity. These commenters generally stated that it was ina ppropriate to adopt a single indicator for application nationwide, or that some ch ange in the indicator was necessary to

accommodate local conditions. Some comment ers offered specific recommendations about ways to improve the proposed calculated PM 2.5 light extinction indicator to account for specific, local influences or to accom modate other perceived weaknesses of the proposed indicator, such as those discussed above. Other commenters urged the EPA to

conduct more research on the factors in fluencing light extin ction in specific environments, and to consider developing a re vised indicator in conj unction with a pilot monitoring program. Some of these commenter s stated that the proposed standard was simply too complicated, and failed to capture the full suite of n ecessary components.

Response: The EPA disagrees with these commenters , noting that the proposed calculated light extinction indicator is e xpressly designed to account for differences in humidity and

PM 2.5 composition among various regions. Furt hermore, the EPA notes that both the original and revised IMPROVE algorithms ar e routinely used to calculate PM-related light extinction on a 24-hour basis in Fede ral Class I areas under the Regional Haze Program, despite variability in aerosol co mposition and humidity among these locations. Therefore, the EPA continues to conclude th at a similar approach is appropriate for a standard to protect against PM 2.5 -related visibility impairment. However, as discussed in section VI.C.1.e of the preamble to the fina l rule and section IV.B.4, below, regarding comments on level, the EPA agrees with co mmenters who emphasize the high degree of variability in visibility cond itions and the potential variabil ity in visibility preferences across different parts of th e country. In light of the associated uncertainty, the Administrator has judged it appropriate to esta blish a target level of protection at the upper end of the range of levels considered ( 30 dv), recognizing that no one level will be "correct" for every area in the country. The EPA considers that a standard set at this level appropriately accommodates the variability am ong local environments and the resulting uncertainty that concerns these commenters. In addition, the EPA notes that in light of the Agency’s decision not to esta blish a distinct s econdary standard for protection from visibility impairment at this time, these concerns are generally moot at this time.

2. Averaging Time

a. Comments Supporting 24-H our Averaging Time

(1) Comment: Among commenters supporting the proposed distinct secondary standard for protection from visibility impairment, many commenters recognized the limitations on monitoring methods and currently available data that led to the EPA’s proposal to adopt aIV-13 standard based on a 24-hour averaging tim e. Most of these commenters acknowledged

that the lack of relia ble hourly speciation data means th at a 24-hour averaging time is the only workable approach for a standard based on calculated light extinction. Commenters advocating a distinct secondary standard th erefore generally suppor ted the proposal to adopt a 24-hour averaging time, at least as an interim approach until a directly measured light extinction indicator coul d be adopted in the future.

Response: As discussed in section VI.C.1.c of th e preamble, the EPA agrees with these commenters that a 24-hour averaging time woul d be the most appropriate for purposes of a distinct secondary standard based on a calculated light ex tinction indicator.

(2) Comment: A few industry commenters argued that si nce a visibility index standard would

be based on data from the IMPROVE and CSN monitors, which operate on a 24-hour basis with 1-in-3 (or 1-in-6) day sampling, “it is imperative that EPA retain a 24-hour averaging time if a secondary visibility sta ndard is promulgated” (API, Attachment 3, p. 9).

Response: As discussed in section VI.C.1.c of th e preamble, the EPA agrees with these commenters that a 24-hour averaging time woul d be the most appropriate for purposes of

a standard based on a calculat ed light extinction indicator.

(3) Comment: A number of commenters supported a 24-hour averaging time due to the

limitations that would be associated with us ing a shorter (sub-daily) averaging time. For example, New York DOH/DEC agreed with th e EPA that it would not be appropriate to

utilize the PM 2.5 FEM monitors for purposes of calcul ating a short-term light extinction value at this time. Arizona DEQ stated that it “does not support a sub-daily visibility standard with the proposed monitoring method. This approach would necessarily rely on temporal distribution estimates derived from nearby or on-site hourly PM measurements and extrapolation of 24-hour composite speci ated samples. ADEQ believes this method would prove to be overly complex with seasona l variation of species and too inconsistent to utilize for a NAAQS secondary standard” (A rizona DEQ, p. 3; see also Minnesota, NY).

Response: As discussed in section VI.C.1.c of th e preamble, the EPA agrees with these commenters that a 24-hour averaging time woul d be the most appropriate for purposes of

a standard based on a calculat ed light extinction indicator.

b. Comments Supporting Sub-daily (1-, 4-, or 6-hour) Averaging Time

(1) Comment: A number of commenters expressed th e view that an hourly or sub-daily averaging time would be the most appropria te approach, as supported by CASAC and the EPA’s staff analyses in this review. These comments also generally stressed the desirability of adopting a directly measured light extinction indi cator that could be measured on an hourly or sub-daily time scal e. Some commenters noted that a standard based on a 4-6 hour averaging time would bette r capture peak daily light extinction while allowing stable signal quality; others urged the EPA to a dopt a 1-hour averaging time in conjunction with dir ect measurements.IV-14 Response: In response to comments supporting a 1-hour or sub-daily (4- to 6- hour) averaging time in conjunction with a direct light extincti on measurements, the EPA notes that, as discussed above in the response to comments on indicator, the Agency has concluded that a directly measured light extin ction indicator is not an appropriate option in this review, independent of the deci sion on averaging time. Having reached the

conclusion that a calculated PM 2.5 light extinction indicator would be most appropriate, the EPA next considered what averaging tim e would be most desirable for such an indicator. As noted in the proposal, the EPA has recognized that hourly or sub-daily (4- to 6-hour) averaging times, within daylight hours and excluding hours with high relative humidity, are more directly related than a 24- hour averaging time to the short-term nature of the perception of PM-related visibility im pairment and the relevant exposure periods for segments of the viewing public. Thus, the Agency agrees with commenters’ general point that, as a starting premise, a sub- daily averaging time would generally be preferable.

However, as discussed in section VI.B.1.c of the preamble to the final rule, important data quality uncertainties have recently been identified in association with currently

available instruments that would be used to provide the hourly PM 2.5 mass measurements that would be needed in conjunction with an averaging time shorter than 24 hours. As a result, at this time the Agency has strong technical reservations about a secondary

standard that would be defined in terms of a sub-daily averaging time. The data quality issues which have been identified, including sh ort-term variability in hourly data from currently available continuous monitoring met hods, effectively precl ude adoption of a 1- hour averaging time in this review, given th e sensitivity of a 1-hour averaging time to these data quality limitations. Even with regard to multi-hour averaging times, the EPA

continues to conclude that the data quality concerns pr eclude adoption of a sub-daily averaging time.

(2) Comment: Commenters pointed to significant limita tions associated with using a 24-hour averaging time, including the uncertainties in translating hourly or sub-daily visibility index values into 24-hour equi valent values. Some commenters criticized the analysis presented in the Policy Assessment compar ing the 24-hour calculated light extinction values to the maximum daylight 4-hour calculated light extin ction values. These commenters stated that the scatter plots and regressions presented in the Policy

Assessment indicate there is c onsiderable variation in the 24 -hour vs. 4-hour relationship, and interpreted this to mean that 24-hour lig ht extinction values ar e a poor surrogate for 4-hour values. For example, one consultant cited by several industry commenters noted

that the correlation coefficient between the 24-hour and 4-hour values was as low as r 2 = 0.42 in Houston, and stated that the EPA was be ing overly “optimistic” in concluding that city-specific and pooled r 2 values in the range of 0.6 to 0.8 showed good correlation (UARG, Attachment 2, p. 27).

Response: Analyses conducted for the Policy Assessment indicate that PM 2.5 light extinction calculated on a 24-hour average ba sis would be a reasona ble and appropriate surrogate for PM 2.5 light extinction calculated on a 4-hour basis. The scatter plots comparing 24-hour and 4-hour calculated PM 2.5 light extinction in the Policy Assessment (U.S. EPA, 2011a, Figures G-4 and G-5) do sh ow some scatter around the regression lineIV-15 for each city. This was to be expected, si nce the calculated 4-hour light extinction includes day-specific and hour-specific influenc es that are not captured by the simpler 24-hour approach. Overall, however, in the EP A’s view, both the city-specific and pooled 15-city 24-hour vs. 4-hour comparisons show strong correlation between the two averaging times. Moreover, th e 90th percentile de sign values calculated for 4-hour vs. 24-hour light extinction are much more clos ely correlated than are the values for individual days in particular urban areas calculated usi ng these two approaches. Thus, while the EPA agrees with commenters who pointed out the relatively low correlation

between 4- and 24-hour values in cities such as Houston, the Agency points out that the correlations of 90th percentile values are much higher, particularly when one considers the average values across urban areas. In ge neral, the 90th percent ile values line up better

and demonstrate closer to a one-to-one relationship.

The EPA has conducted a reanalysis (Frank et al., 2012b) of the re lationships between estimated 24-hour and 4-hour visibility impa irment based on the variety of metrics discussed in Appendix G of the Policy Assessm ent that further supports this finding. The reanalysis more appropriately considered th e uncertainty of the cal culated 4-hour values. It also considered the effect of changing th e OC to OM multiplier used in urban areas from 1.4 to 1.6. The revised analysis shows that the 24-hour values are generally closer to the 4-hour values than originally estima ted, particularly with regard to the 90 th percentile values or the average of the 15 city-specific values.

Since conclusions in the proposal about the relationship between 4-hour and 24-hour values were drawn not just on the basis of th e city specific results but also on the more robust 90th percentile values, the EPA disagr ees with commenters who state that the Agency was overly optimistic in considering 24-hour values an appropriate surrogate for 4-hour values. Also, it is a ppropriate to focus on the 90th percentile design value comparison since the design values would determ ine attainment status and the degree of improvement in air quality that could be expect ed in areas instituting controls to meet the standard. Therefore, the EPA does not agree with commenter s who state that a 24-hour averaging time cannot serve as an appropriate surrogate for s ub-daily periods of visibility impairment. On the contrary, the EPA continues to conclude, on the basis of this analysis,

that PM 2.5 light extinction calcula ted on a 24-hour basis is a reasonable and appropriate surrogate for sub-daily PM 2.5 light extinction calcul ated on a 4-hour basis.

(3) Comment: Some commenters emphasized the poor fit of a 24-hour averaging time with the near instantaneous judgment s about visibility impairment reflected in the visibility preference studies. Some of these commenter s objected to a 24-hour averaging time as unsupported by the record in this review: “Becau se the science the Administrator relies on for the other elements of the proposed vi sibility standard is tied to short-term exposures to visibility impair ment, the EPA has no basis for promulgating a standard that uses a 24-hour averaging time” (API, p. 43). These commenters claimed that while the EPA may not have the information or infrastruc ture in place to allow the Agency to set a

standard based on a 1-hour or other sub-da ily averaging time, this does not justify moving to a 24-hour averaging time.

Response: The EPA has recognized that hourly or sub-daily (4- to 6-hour) averagingIV-16 times, within daylight hours and excluding hours with high relative humidity, are more directly related than a 24-hour averaging time to the short-te rm nature of the perception of PM-related visibility impairment and the re levant exposure periods for segments of the viewing public. However, as discussed in sec tion VI.B.1.c of the preamble to the final rule, important data quality uncertainties have recently been identified in association with currently available instru ments that would be used to provide the hourly PM 2.5 mass measurements that would be needed in conj unction with an averag ing time shorter than 24 hours. As a result, the EPA determined it w ould not be appropriate at this time to adopt a standard defined in term s of a sub-daily averaging time.

Instead, the EPA considered using PM 2.5 light extinction calculat ed on a 24-hour basis to reduce the various data quality c oncerns on relying on continuous PM 2.5 monitoring data. However, the Policy Assessment recognized that 24 hours is far longer than the hourly or multi-hour time periods that might reasonably characterize the visibility effects experienced by various segments of the population, including both those who do and do not have access to visibility conditions often or continuously throughout the day. Thus,

the EPA stated in section VI.D.2.ii of th e proposal that consideration of a 24-hour averaging time would depend upon the extent to which PM-related light extinction calculated on a 24-hour average basis w ould be a reasonable and appropriate surrogate for PM-related light extinction calculated on a sub-daily basis. Analyses conducted for the Policy Assessment did indicate that PM 2.5 light extinction calculated on a 24-hour average basis would be a reasonabl e and appropriate surrogate for PM 2.5 light extinction calculated on a 4-hour basis, supporting th e EPA’s decision to consider this longer averaging time appropriate.

(4) Comment: Some commenters expressed concer n over potential bias and greater uncertainty introduced by the inclusion of nighttime hours, noting that because relative humidity tends to be higher at night, inclusion of these hour s could cause areas to “record NAAQS exceedances that have no corresponding visibility impairment value” (UARG, p. 36).

Response: The Policy Assessment recognized that since a 24-hour averaging time combines daytime and nighttime periods, the public preference studies do not directly provide a basis for identifying an appropria te level of protecti on, in terms of 24-hour average light extinction, based on judgment s of acceptable daytime visual air quality

obtained in those studies. The EPA’s consider ation of a 24-hour averaging time therefore also depended upon developing an approach to translate the candidate levels of protection derived from the public preference studies, wh ich the Policy Assessment interpreted on an hourly or multi-hourly basis, to a candidate level of prot ection defined in terms of a 24-hour average calculated light extinction. The EPA’s analyses comparing 24-hour and 4-hour averaging times showed good correla tion between 24-hour and 4-hour average

PM 2.5 light extinction, as discussed further in section IV.2.e regarding comments on level, below, and in section VI.C.1.e of the pream ble. This supported the Agency’s conclusion

that PM 2.5 light extinction calcula ted on a 24-hour average basi s would be a reasonable and appropriate surrogate for PM 2.5 light extinction calcula ted on a 4-hour basis.

(5) Comment: Commenters also noted that there is greater hourly variation in PMIV-17 concentrations and resulting vi sibility conditions in urban ar eas than in Class I areas; thus, while the Regional Haze Program us es 24-hour IMPROVE data, the commenters stated that a shorter averaging time is needed for an urban-focused PM 2.5 standard to protect visibility.

Response: As discussed in section VI.B.1.c of th e preamble to the final rule, the EPA has recognized that hourly or sub-daily (4- to 6-hou r) averaging times, w ithin daylight hours and excluding hours with high relative humidity, are more directly related than a 24-hour averaging time to the short-term nature of the perception of PM-related visibility impairment and the relevant exposure periods for segments of the viewing public. However, analyses of air quality in 15 ur ban areas conducted for the Policy Assessment

indicated that PM 2.5 light extinction calculated on a 24-hour average basis would be a reasonable and appropria te surrogate for PM 2.5 light extinction calculated on a 4-hour basis. Thus, the EPA concludes that a 24-hour averaging time would be appropriate for a

standard based on a calculate d light extinction indicator.

(6) Comment: Some commenters expresse d concern with the proposal to calculate the visibility index over 24-hours, noting that this would intr oduce additional uncertainty in the light extinction calculations: “The NCDA Q understands the Administrator's dilemma with the uncertainty that can be introduced using instrumentation that people do not have confidence in, namely some of the recently approved Federal Equivalent Methods (FEMs). At the same time the NCDAQ currently uses continuous m onitors that are not Federal Reference Methods (FRMs) or FE Ms to comply with meeting air quality reporting requirements. The data from these mo nitors are adjusted seasonally using an equation derived at each specific location so that they match the FRM data. Is the uncertainty that would occur using continuous particle monitors adjusted to match the FRM really greater than the uncertainty that occurs from using 24 hour speciation data?” (NC DENR, p. 4-5).

Response: PM 2.5 FEMs are designed and tested by manufacturers and approved by EPA according to their ability to reproduce 24-hr mass based PM 2.5 concentrations as measured by the PM 2.5 FRM. When these continuous measurements are used as part of the air quality index to publicly report PM 2.5 concentrations, they are adjusted by State and local air pollution agencies to better pr edict 24-hour values. Such adjustments are sometimes performed on a seasonal basis. However, the PM 2.5 FEM is not necessarily designed nor is it tested to produce precise 1-hr values. In fact, some of the potential uncertainty in 1-hour values is removed th rough the process of averaging multiple hours. Moreover, the composition of PM 2.5 can change from hour to hour and the estimated extinction depends on the change in compos ition as well as the change in hourly PM 2.5 mass concentration. However, hourly speci ation and optical measurements which separately estimate the extinction contri butions from scattering and absorbing PM 2.5 aerosols are not widely deployed in urban mon itoring networks. Therefore, as part of the urban visibility assessment, EPA estimate d the change in composition using modeling data to help estimate the change in extinc tion resulting from the di fferent scattering and absorbing components of PM 2.5 . For those complex calculations, the EPA also assumed that the composition did not change from da y to day. Although precise measurements of hourly PM 2.5 would be helpful, EPA does not believe that they are available. Also, use ofIV-18 existing hourly PM 2.5 measurements in combination with all of the other stated factors introduced significant uncertainty into this anal ysis in the urban visibility assessment. For these reasons, EPA has more confidence in th e visibility impairment derived from 24-hr speciation measurements than from the 1-hr PM 2.5 mass concentrations produced by

PM 2.5 FEMs combined with assumed hour to hour changes in PM 2.5 composition.

3. Form

a. Comments on 90 th Percentile

(1) Comment: One commenter stated that it was ina ppropriate to use a 90th percentile form, noting that this would result in the exclusi on of a minimum of 36 days of data annually. The commenter expressed particular concern th at this proposed approach, in combination with a 24-hour standard based on an unadj usted CPL, would not capture the worst visibility impairment and that this would unde rmine “the intent of setting a meaningful secondary visibility standa rd” (AMC, et al., p. 2).

Response: The EPA disagrees that a 90 th percentile form would exclude too many days to offer meaningful protection agai nst visibility impairment. Th e EPA notes that there is a significant lack of information on, and a high degree of uncertainty regarding, the impact on public welfare of the number of days with visibility impairment over the course of a year. For example, the visibility preference studies used to derive the range of CPLs

considered in this review offered no inform ation regarding the frequency of time that visibility levels should be below those values. Based on this limitation, the EPA concluded in the Policy Assessment that it would not be appropriate to consider eliminating all exposures above the level of the standard and that it was reasonable to consider allowing some number of days w ith reduced visibility. Recognizing that the Regional Haze Program focuses attention on the 20 percent worst visibility days (i.e., those at or above the 80th pe rcentile of visibility impair ment), the EPA continues to believe, as noted in the proposal, that a per centile well above the 80th percentile would be appropriate to increase the likelihood that all days in this range would be improved by control strategies intended to help areas attain the st andard. Focusing on the 90th percentile, which represents the median of the distribution of the 20 percent worst visibility days, could be reasona bly expected to lead to impr ovements in visual air quality on the 20 percent most impaired days. Thus, the EPA has made a reasoned judgment based on a full consideration of the upper end of the distribution of visibility impairment conditions, in light of the significant uncer tainty discussed above and continues to conclude that it is appropriat e to focus on the 90th percentil e of visibility impairment

values.

(2) Comment: Another commenter argued that the EP A had provided no scientific basis for why the 90th percentile form was suitable, and claimed that the Agency was making “a somewhat arbitrary judgment that people’s welfare would be affected only if adverse urban visibility were to occur more than 10 percent of the time” (A PI, Attachment 2, p. 4).IV-19 Response: EPA notes that there is a significant lack of information on, and a high degree of uncertainty regarding, the impact on public welfare of the number of days with visibility impairment over the course of a year. For example, the visibility preference studies used to derive the range of CPLs considered in this review offered no information regarding the frequency of time that visibility levels should be below those values. Based on this limitation, the EPA concluded in the Policy Assessment that it would not be appropriate to consider elimin ating all exposures above the level of the standard and that it was reasonable to consider allowing some number of days with reduced visibility. Recognizing that the Regional Haze Program focuses attention on the 20 percent worst visibility days (i.e., those at or above the 80th percentile of visibility impairment), the EPA continues to believe, as noted in the propos al, that a percentile well above the 80th percentile would be appropriate to increase the likelihood that all days in this range would be improved by control strategies inte nded to help areas attain the standard. Focusing on the 90th percentile, which represents the median of the distribution of the 20 percent worst visibility days, could be reason ably expected to lead to improvements in visual air quality on the 20 per cent most impaired days. Thus , the EPA did not arbitrarily pick the 90 th percentile, but has made a reasoned judgment based on a full consideration of the upper end of the distribution of visibi lity impairment conditions, in light of the significant uncertainty as discu ssed above, and continue s to conclude that it is appropriate to focus on the 90th percentile of visibility impairment values.

b. Comments on 3-year Average

(1) Comment: A few commenters argued that averag ing over only 3 years would not provide a stable assessment of visual air quality in the West because this time period is insufficient to properly account for western drought and fi re cycles. These commenters pointed to the approach in the Regional Haze Program of averaging visibility impairment over 5 years, and noted that even within this longer time period data can be significantly influenced by high emissions during significant fire years.

Response: The EPA disagrees that it would be appr opriate to average the 90th percentile values over periods longer than 3 years. Th e EPA recognizes that a multi-year percentile form offers greater stability to the air quality management process by reducing the possibility that statistically unus ual indicator values will lead to transient violations of the standard. Utilizing a 3-year average form provi des stability from the occasional effects of inter-annual meteorological variab ility that can result in un usually high pollution levels for a particular year. The Agency has adopt ed this approach in other NAAQS, including

the current 24-hour PM 2.5 NAAQS, which has a 98th percentile form averaged over 3 years. However, adopting a multi-year aver aging period longer than 3 years would increase even more the number of days with visibility impairment above the target level of protection and would therefor e reduce the protectiveness of the standard. Based on this the EPA does not believe it would be appropriate to average 90th perc entile values over a period as long as five years.

4. Level

The EPA received relatively few comments e ndorsing a specific level for a distinctIV-20 secondary standard to address visibility impairment. In ge neral, commenters who opposed setting a distinct secondary standa rd at this time did not address the question of what level would be appropriate if the EPA were to set a distin ct secondary standard to address visibility impairment; similarly, commenters who supported a dopting a distinct seconda ry standard at this time generally did not recommend a specific leve l. However, a few commenters did provide comments in support of a specific level or range of levels, with some commenters advocating standards at the upper end of the range of proposed levels (i .e., 30 dv), while others supported levels below the lower end of the proposed rang e (i.e., below 28 dv). These comments reflected

consideration of the resu lts of the public prefer ence studies as well as an alyses conducted in the Visibility Assessment and the Policy Assessment. Comments addressing the appropriateness of specific levels are discussed in this section. In addition, the EPA received a large number of comments addressing the information available from the public preference studies with regard to the acceptability of various leve ls of visual air quality. These comments, which are discussed in section IV.5, below, address the EPA’s use of visi bility preference studies as the basis for the selection of a range of a ppropriate levels for the Ad ministrator to consider.

a. Comments Supporting a Level of 30 dv or higher

(1) Comment: Several industry commenters submitted an analysis which they argued indicated that the proposed le vel of 28 or 30 dv did not refl ect the substantial difference in visibility preferences between the East and the West reflected in the preference studies (UARG, Attachment 2, p. 11), and that it did not reflect the full range of preferences (i.e., potential 50 percent acceptability levels) likel y to exist nationwide (UARG, Attachment 2, p. 19). These commenters further objected to the EPA’s proposal for a level of 28 or 30 dv on the grounds that the EPA had inaccurate ly adjusted 4-hour values into 24-hour values. Based on the analysis, the commenters c oncluded that “a range of adjusted values

from 28 to 32 dv is needed” to account for th e majority of the spread between the 4-hour vs. 24-hour equivalent valu es at the upper end of the distribution of values.

Response: While acknowledging the uncer tainties and limitations associated with the visibility preference studies as discussed a bove, the EPA continues to conclude, as did CASAC, that the preference studies are approp riate to use as the basis for selecting a target level of protection fr om visibility impairment. However, the EPA agrees with commenters who emphasize the high degree of va riability in visibili ty conditions and the potential variability in visibi lity preferences across differe nt parts of the country. As discussed in the preamble, the information suppor ts the view that variability in the results of the studies is likely based on variability in the content of the view at issue in the study, as compared to variability in people’s pr eferences. In addition, the EPA has concluded that in light of the significan t uncertainties, it is appropria te to place less weight on the results of western visibility pr eference studies and that th e CPL value (30 dv) that is based on the eastern preference study results is likely to be more re presentative of urban

areas that do not have associat ed mountains or other valued objects visible in the distant background. In light of the associated un certainty, as noted in the proposal, the Administrator judged it appropriate to establish a target level of protection equivalent to the upper end of the rang e of Candidate Protection Levels (CPLs) identified in the Policy Assessment and generally supported by CASAC. Thus, the EPA considered the issues raised by commenters, and the EPA proposed to set a 24-hour visibil ity index standardIV-21 that would provide protection equivalent to the protection afforded by a 4-hour standard set at a level of 30 dv. In light of the co mments received on the proposal, in particular comments emphasizing the uncertainty and va riability in the results of the public preference studies, the EPA con tinues to conclude that this approach is warranted, and that it is appropriate to set a target level of protection equivalent to the protection that would be afforded by a 4-hour, 30 dv visibility index standard.

In adjusting 4-hour values fo r purposes of defining an a ppropriate level for a 24-hour standard, the EPA noted that there were mu ltiple approaches for estimating generally equivalent levels on a city-spe cific or national basis, and th at both of the two preferred approaches identified in the Policy Assessm ent generated a range of city-specific estimates of generally equivalent 24-hour leve ls that encompassed the range of levels considered appropriate for 4-hour CPLs, in cluding the CPL of 30 dv at the upper end of that range. This led to the conclusion that it would be appropriate to use an unadjusted 4- hour CPL for purposes of establishing a target level of protection fo r a 24-hour standard. The EPA disagrees with comment ers who argued that the EPA’ s approach for translating 4-hour CPLs into equivalent 24-hour values was inappropriate. The EPA has conducted a reanalysis (Frank et al., 2012b) of the relationships between estimated 24-hour and 4- hour visibility impairment base d on the variety of metrics di scussed in Appendix G of the Policy Assessment. The reanalysis has more a ppropriately considered the uncertainty of the calculated 4-hour values. The revised analys is shows that, for all cases considered, the 24-hour equivalent level is even closer to the 4-hour values than originally estimated, demonstrating that the EPA’s approach to tran slating of 4-hour CPLs into equivalent 24- hour values was appropriate.

(2) Comment: A number of commenters questioned wh ether the proposed range of levels was appropriate. One industry commenter cl aimed that the EPA had not explicitly justified why a standard with in the proposed range was re quisite, stating that “EPA makes no attempt to explain how the proposed le vel of the standard is neither lower nor higher than necessary to protect public welfare” (NSSG A, p. 15). Noting perceived problems with the proposed range of levels, a few commenters noted that if the EPA were to set a distinct secondary standard, the le vel should be set no lower than 30 dv, “to account for inconsistent value judgments, a great deal of spatial and temporal variability, and a very high level of uncertainty” (TX CEQ, p. 7).

Response: While acknowledging the uncer tainties and limitations associated with the visibility preference studies as discussed a bove, the EPA continues to conclude, as did CASAC, that the preference studies are approp riate to use as the basis for selecting a target level of protection from visibility impairment. After considering the alternative levels proposed for a 24-hour standard, either 28 dv or 30 dv, the EPA has concluded that the current substantial degrees of variability and uncertain ty inherent in the public preference studies should be re flected in a higher target pr otection level than would be appropriate if the underlying information were more consistent and certain. In addition, the EPA has concluded that in light of the si gnificant uncertainties, it is appropriate to place less weight on the results of western visi bility preference studies and that the CPL value (30 dv) that is based on the eastern pr eference study results is likely to be more representative of urban areas that do not have associated mountains or other valuedIV-22 objects visible in the distant background. In light of all the information available in this review, therefore, the Administrator has concluded that the protection provided by a

standard defined in terms of a PM 2.5 visibility index (based on speciated PM 2.5 mass concentrations and relative humidity data to calculate PM 2.5 light extinction), a 24-hour averaging time, and a 90th perc entile form, averaged over 3 y ears, set at a level of 30 dv, would be requisite to protect public welf are with regard to visual air quality.

(3) Comment: Many commenters also expressed concern over what they perceived to be the high degree of uncertainty asso ciated with the proposed dist inct secondary standard for visibility. For example, Nevada DEP stated “the EPA’s own anal ysis regarding the secondary visibility standard highlights several ar eas of high uncertainty, which preclude a reasonable conclusion that the proposed visibi lity rule is sufficient, but not overly so, to protect public welfare. Therefore, it is inappr opriate to pursue a fatally flawed standard” (p. 9).

Response: While acknowledging the uncer tainties and limitations associated with the information available in this review, the EPA continues to conclude, as did CASAC, that this information provides a sufficient basis fo r selecting a target le vel of protection for visibility in this review. Thus the EPA disa grees with commenters who stated that the uncertainties were so great as to preclude es tablishing a standard at this time. Rather, the

EPA has concluded that the current substant ial degrees of variab ility and uncertainty should be reflected in a higher target protection level than would be appropriate if the underlying information were more consiste nt and certain. In considering the two alternative levels (28 or 30 dv) proposed for a distinct secondary standard to protect visibility, therefore, th e EPA has elected to set a target le vel of protection at the higher of the two levels proposed (30 dv).

(4) Comment: The states of Arizona and Colorado submitted comments arguing that the visibility preference studie s conducted in Phoenix and Denver, respectively, were designed to address a specific lo cal problem and that the results of these studies were not an appropriate basis for selec ting the level of a national standard. For example, Arizona DEQ noted:

The cited studies were conducted consider ing total light extinction; including extinction resulting from particulate ma tter and Rayleigh scattering. Visibility impairment due to coarse particulate ma tter can be an important contributor in Arizona, specifically in the Phoenix ar ea where ongoing measurements have been made. Therefore, ADEQ believes that th e proposed levels of the secondary visibility standard ar e inconsistent with applicable urban studies. (Arizona DEQ, p. 2)

Similarly, the Colorado Department of Public Health and the Environment noted that the Denver visibility standard was designed to a ddress “brown clouds”, i.e., strong inversions that occur in the Denver metropolitan area, and that this standard “is based on a specific

view of Denver” associated w ith particular sight paths and direct measurement methods.

The commenter stated that this standard “is applicable only to this location,” and that these limitations make it potentially unsuitabl e for application as “a national secondaryIV-23 standard, particularly a proposed standard that does not use a direct measurement method” (Colorado DPHE, p. 2).

Response: In the preamble to the final rule, the EPA noted several reasons for caution in interpreting the results of th e Denver and Phoenix preference studies. Noting both that the scenic vistas available on a daily basis in many urban areas across the country generally

do not have the inherent visu al interest or the distance between viewer and object of greatest intrinsic value as in the Denver a nd Phoenix preference st udies, and the caution expressed by Colorado and Arizona about us ing the results of the Denver and Phoenix preference studies, which were aimed at addre ssing specific local visibility problems, to inform the choice of level for a national standard, the EPA concluded that it is appropriate, especially in light of the significant uncertainties , to place less weight on the western preference results. The EPA conclude d that the high CPL value (30 dv) that is based on the eastern preference results is likely to be more representative of urban areas

that do not have associated mountains or ot her valued objects vi sible in the distant background. These areas would include the mi ddle of the country and many areas in the eastern U.S., as well as some western ar eas. In reaching this conclusion, the EPA recognized that no one level would be "corre ct" for every urban area in the country, and that the development of local programs, such as those in Denver and Phoenix, can continue to be an effective and appropriate approach to provide additional protection, beyond that afforded by a national standard, for unique scenic res ources in and around certain urban areas that are particularly hi ghly valued by people living in those areas.

In regard to the commenter’s concern about contributions from coarse particles and Rayleigh scattering, the EPA furt her notes that participants in the Phoenix and other

studies were not asked to break out their preferences based on how much of the haze was caused by contributions from co arse particles, Rayleigh scat tering or fine particles. Instead, Phoenix study participants were simply asked to identify le vels of visual air quality that they would consider “unreas onable or objectionable,” no matter what the source. Based on this information, Phoenix was able to come up with a target level of VAQ, even though pollutant mixes vary temporally and spatially, even within the Phoenix urban area. Since the goal of the secondary PM 2.5 NAAQS is to provide a uniform national level of public welfare protection from PM 2.5 related visibility impairment, the form of the EPA’s proposed secondary standard was selected to allow

each area to achieve that level of protection in a way that ad dresses its own unique mix of contributing pollutants. Therefore, the EPA disagrees with the commenter that it is inappropriate to use the resu lts of the Phoenix study to inform a range of candidate protection levels for consideration by the Administrator in selecting a national level of visibility protection. Instead, the EPA believe the Phoenix results form an important data point that shed light on public preferences for visibility in western areas with urban

scenes that include distant mountains.

b. Comments Supporting a Level below 30 dv

(1) Comment: Some commenters stated that the prop osed range of levels from 28-30 dv was insufficiently protective based on a 24-hour averaging time, and recommended a lower level for the visibility inde x standard. These commenters expressed the view that theIV-24 proposed levels of 28 or 30 dv represented ne ither adequate surroga tes for equivalent 4- hour values, as the EPA claimed, nor sufficien tly protective levels based on recent air quality data. Several commenter s stated that the EPA’s own analyses suggested that a

standard set at a level of 28 or 30 dv was insufficiently protective based on a 24-hour averaging time. One commenter emphasized th at the Policy Assessment had indicated a level between 25-28 dv was appropriate for a st andard calculated on a 24-hour average, and encouraged the EPA to adopt a standard level of 25 dv.

Response: The EPA disagrees with commenters w ho argue that the currently available evidence is sufficient to justify establishing a ta rget level of protection at 25 dv or below. The EPA recognizes that 25 dv represents the middle of the range of 50 percent acceptability levels from the 4 cities studied, and represents the 50 percent acceptability level from the Phoenix study, which the Agency has acknowledged as the best of the four studies in terms of having the least noise in the preference study results and the most representative selection of participants. The EPA also notes the caveats discussed in the proposal regarding whether it w ould be appropriate to interp ret results from the western studies as generally representa tive of a broader range of s cenic vistas in urban areas across the country. The Policy Assessment noted significant differences in the

characteristics of the urban scenes used in each study, with western urban visibility preference study scenes includ ing mountains in the backgr ound and objects at greater distances, while scenes in the eastern study did not. Since ob jects at a greater distance have a greater sensitivity to perceived visi bility changes as light extinction changes compared to otherwise similar scenes with obj ects at a shorter range , this likely explains part of the difference between the results of the eastern study and results of the western

studies.

In the proposal, the EPA noted that the scen ic vistas available on a daily basis in many urban areas across the country ge nerally do not have the inhere nt visual interest or the

distance between viewer and object of greatest intrinsic value as in the Denver and Phoenix preference studies. Also, the Agen cy takes note of the caution expressed by Colorado and Arizona about using the resu lts of the Denver and Phoenix preference studies, which were aimed at addressing specific local visibility problems, to inform the

choice of level for a national standard. Theref ore, the Agency considers it reasonable to conclude, especially in light of the significant uncertainties, that it is appropriate to place less weight on the western preference results an d that the high CPL value (30 dv) that is based on the eastern preference results is likely to be more representative of urban areas

that do not have associated mountains or ot her valued objects vi sible in the distant background. These areas would include the mi ddle of the country and many areas in the eastern U.S., as well as some western areas. As a result, the EPA concludes that it is more appropriate to establish a targ et level of protection at the upper end of the range of 24- hour CPLs considered, recognizing that no one level will be "corr ect" for every urban area in the country.

(2) Comment: Several environmental groups provide d comments stating that a 24-hour average would underestimate a 4-hour value by 13-42 percent and certain areas of the country—particularly the Northeast—would be affected disproportionately. These commenters suggested that a 24-hour PM 2.5 visibility index standa rd should be set at aIV-25 level of 18.6-20 dv.

Response: The EPA disagrees with these commen ters that the EPA’s approach for translating 4-hour CPLs into equivalent 24- hour values was inappropriate. The EPA has conducted a reanalysis (Frank et al., 2012b) of the relations hips between estimated 24- hour and 4-hour visibility impairment base d on the variety of me trics discussed in Appendix G of the Policy Assessment. The rean alysis has more appropriately considered the uncertainty of the calculated 24-hour and 4-hour values. The an alysis in Appendix G of the Policy Assessment used the 4-hour light extinction value treate d as the independent (x-axis) variable in an ordi nary least squares regression. Th e EPA now concludes that this regression approach was not the most appropr iate approach because that variable has error and in fact may be more uncertain th an the calculated 24- hour extinction values. The Frank et al. (2012b) reanalysis uses an or thogonal regression instead of ordinary least squares regression and results in slopes cl oser to the 1:1 line for all the results, particularly for Dallas, TX. Furthermore, c onsistent with the EPA’s conclusion that a higher multiplier for converting OC to OM would be appropriate (see section VI.C.1.b.ii above), the reanalysis substitutes a 1.6 mu ltiplier for converting OC to OM in the

calculation of 24-hour values instead of the value of 1.4 that was used in calculating 24- hour values for Appendix G. The higher multiplier is more consistent with the SANDWICH approach used to calculate the 4-hour values found in Appendix G. See Frank et al. (2012b) for a more detailed explanation.

The revised analysis shows that the 24-hour e quivalent level is gene rally closer to the 4- hour value at the upper end of the range of CPLs than originally estimated, as can be seen in the results for Approaches B, C, and D presented in Frank et al., 2012b. 38 For example, the reanalysis indicates that Approach B (annual 90 th percentile design values regression) yields an adjusted 24-hour CPL of 29 dv as generally being equivale nt to a 4-hour CPL of 30 dv. In contrast, in Appendix G of the Poli cy Assessment, a 24-hour adjusted CPL of 28 dv was estimated to be equivalent to a 4-hour value of 30 dv under Approach B. Similarly, Approach C (all-days city-specific regression) yields a 24-hour equivalent CPL of 29 dv averaged across cities and a range of city-specific values from 25-36 dv in the reanalysis, whereas in Appendix G of the Policy Assessment, under Approach C, a 24- hour adjusted CPL of 27 dv was estimated to be equivalent to a 4-hour CPL of 30 dv when averaged across cities, and city-specific values were estimated to range from 24-30 dv. In the reanalysis, Approach D (all days pooled regression) gene rated results of 28 dv for the 24-hour CPL equivalent to a 4-hour va lue of 30 dv as compared to a value of 27 dv in the original analysis described in Appendix G.

As can be seen in the tables presented in Frank et al. (2012b), not only are the 90 th
percentile and pooled average values closer to the 4-hour CPL of 30 dv in the reanalysis, the range of city-specific results shows a wider spread that clearly encompasses the unadjusted 4-hour value of 30 dv near the mi dpoint of the city-specific range. This provides support for concluding that the EPA’ s approach to translating of 4-hour CPLs into equivalent 24-hour values was appropr iate, and that it is appropriate to use

38 Approach E as presented in the Policy Assessment is ba sed on the median values fo r each city; these results are not affected by the regression analys es. Therefore, Approach E was not incl uded in the reanalysis, and the results remain unchanged from those reported in the correct ed Table G-6 as reported in Frank, et al., 2012b.IV-26 unadjusted 4-hour values for purposes of sel ecting a level for a st andard based on a 24- hour averaging time.

(3) Comment: The Department of the Interior pointed to recent air quality data indicating that visibility on the 20% worst days in se veral large metropolitan areas, including Birmingham, Fresno, New York City, Phoe nix, and Washington, DC was below 29 dv. While noting that these calculations were based on IMPROVE calculations which include contributions from coarse PM mass, DOI expr essed the view that th e proposed level of 28 to 30 dv would not provide adequate visibili ty protection compared to the current 24-

hour PM 2.5 standard of 35 μg/m 3 and recommended that the standard be set at a level of

25 dv consistent with the results of th e Phoenix visibility preference study.

Response: The EPA notes that the purpose of esta blishing NAAQS is to ensure adequate protection of public welfare from a nationa l perspective, not to mandate continuous improvements in areas that may already be rela tively clean. In fact, the evidence from the IMPROVE program cited by commenters indicati ng that many urban areas have total 24- hour PM-related light extincti on below 29 dv on the 20 percen t worst visibility days suggests that many areas have relatively good vi sual air quality already. Furthermore, the development of local programs, such as thos e in Denver and Phoenix, can continue to be an effective and appropriate approach to provide additional protection, beyond that afforded by a national standard, for unique s cenic resources in and around certain urban areas that are particularly highly va lued by people living in those areas.

(4) Comment: One group of commenters suggested that a 24-hour PM 2.5 Visibility Index

standard of 28-30 dv would be equivalent to higher 4-hour values than suggested by the EPA in Appendix G of the Policy Assessment, and that individual areas such as Dallas, TX would have equivalent 4-hour values as much as 9 dv higher . They asserted that further insight into the differences in prot ectiveness of an unadjus ted 24-hour standard could be found by examining Table G-5 in A ppendix G of the Policy Assessment, which indicates that only 1 of 15 cities would exceed a 24-hour, 3-year 90 th percentile standard

at 30 dv . but that 5 of the cities would exceed 30 dv if light extinction were based on daily maximum daylight li ght extinction measured ove r 4 hours. (AMC, et al.)

Response: The EPA disagrees with these commenters that 24-hour light extinction in the range of 28-30 dv would be equivalent to 4-hou r values as high as those presented by the

commenters. The EPA has conducted a r eanalysis (Frank et al., 2012b) of the relationships between estimated 24-hour and 4- hour visibility impairment based on the variety of metrics discussed in Appendix G of the Policy Assessment. The reanalysis has more appropriately considered the uncerta inty of the calculated 24-hour and 4-hour values. The analysis in Appendix G of th e Policy Assessment used the 4-hour light

extinction value treated as the independent (x-axis) variable in an ordinary least squares regression. The EPA now concl udes that this regression a pproach was not the most appropriate approach because th at variable has error and in fact may be more uncertain

than the calculated 24-hour extinction values. The Frank et al. (2012b) reanalysis uses an orthogonal regression instead of ordinary leas t squares regression a nd results in slopes closer to the 1:1 line for all the results, particularly for Dallas, TX. Furthermore,

consistent with the EPA’s conclusion that a higher multiplier for converting OC to OMIV-27 would be appropriate (see section VI.C.1.b.ii above), the reanalysis substitutes a 1.6 multiplier for converting OC to OM in the ca lculation of 24-hour values instead of the value of 1.4 that was used in calculating 24-hour values for Appendix G. The higher multiplier is more consistent with the SANDW ICH approach used to calculate the 4-hour values found in Appendix G. See Frank et al . (2012b) for a more detailed explanation.

Table 4 of the revised analysis shows that at the upper end of the range of levels considered (i.e., 30 dv) the 24-hour equivalent le vel for each city is generally closer to the 4-hour value of 30 dv. Moreover, the EPA notes that with OLS regression, the same regression equation (Y = b 0 + b 1 X) should not be reversed—i .e. the same equation should

no t be used to estimate X from Y (Frank et al. 2012b). Thus the pr edicted 4-hour values constructed by the commenters are flawed b ecause they used the regression equations presented by EPA in Appendix G of the Policy Assessment.

(5) Comment: One group of commenters suggested th at, on the basis of estimated 4-hour average visibility data presented by EPA in Appendix H of the Policy Assessment, shifting to a 24-hour averaging time for a standard set a level of 28 dv would substantially reduce the protectiveness of the st andard. The commenters claimed that this reduction in protection would pa rticularly affect the Northeast, where 50% fewer counties would exceed a design value of 28 deciviews ba sed on a 24-hour average as compared to a 4 hour daily maximum approach. According to the commenters, this indicates that a 24- hour standard in the range of 28-30 deciviews would be weak er than a 4-hour standard

set at the same level and that certain areas of the country would be affected disproportionately. (AMC, et al.)

Response: The EPA notes that the illustrative 4- hour and 24-hr results presented in Tables H-1 and H-2 of the Policy Assessmen t were based on a two different methods.

The 4-hr results were based on a met hod which used 2007-2009 monthly average speciation measurements in combination with hourly PM 2.5 data, used a 1.6 multiplier to estimate organic mass from PM 2.5 OC and only included counties with at least 2500 hours

of PM 2.5 data. The 24-hr results were based on the method described in Appendix G which used daily speciation measurements and a 1.4 multiplier to estimate organic mass

from PM 2.5 OC. A different data selection criteri on was used for these 24-hr speciation

measurement data. Thus the number of in cluded counties is different, and more importantly, the presented illustrative data are not directly comparable.

Although the 24-hr results presente d in Table H-2, as well as th e 4-hr results presented in Table H-1, suggest that several Northeastern counties would exceed a visibility standard of 28-30 dv (even though they do not exceed the existing suite of secondary PM 2.5 standards, 15 ug/m3 annual and 35 ug/m3 24-hour), that comparison was based on 2007- 2009 data. Since that time, the composition of PM 2.5 has significantly changed in the

eastern U.S. due to massive reductions in SO 2 emissions and concomitant changes in

PM 2.5 sulfate. As shown in Kelly 2012a and Ke lly 2012b, all of the No rtheastern counties would meet a 30 dv visibility index NAAQS, using 2008-10 data and using 2009-2011

data.IV-28 5. Specific Comments on Visibility Preference Studies

The evidence relied upon by the Administrato r in determining an appropriate degree of public welfare protection from visibility impair ment is predominately derived from a small number of urban-focused visibility prefer ence studies. As a result, many comments were received on the adequacy and appropriateness of this limited dataset serving as a basis for the Administrator’s judgments regarding what is requisite national protection for visibility impairment. Both CASAC and the EPA staff, as well as a few commenters, concluded that while limited, these studies did form a sufficient ba sis on which the Administrator could make a decision. A majority of commenters, however, expr essed the view that th e existing preference studies provide an insufficient basis for selecti on by the Administrator of an appropriate level of public welfare visibility protection for a national standard. These commenters highlighted a

number of limitations and uncertainties associated with these studies as support for this view. Many of the important and fundamental comments are also discussed in the final rule, with further details provided below. As in the final rule, this section orga nizes and discusses the preference study comments under four broad topic areas, including: (a) limitations and uncertainties associated with the visibility pr eference studies; (b) preference study methods and design; (c) use of preference study results for de termining adversity; (d) the appropriateness of using regionally varying preferen ce study results to select a single level for a national standard.

a. Comments on Preference Study Limitations and Uncertainties

A large and diverse number of limitations and un certainties associated with the visibility preference studies has been identified and discusse d in the public comments. Many of these same

limitations and uncertainties were also identifi ed and discussed by the EPA in the various documents developed throughout this review su ch as the Integrated Science Assessment, Visibility Assessment, and Policy Assessment, as well as in the proposed rule (see section VI.b.2 beginning at 77 FR 38973, 38990) and in th e final rule (section VI.C.1.e.i).

(1) Comment: Most commenters expressed concern ove r the small number of preference

studies that are available in this review. In particular some note that these preference studies cover just four loca tions, only three of which occur in the U.S., that the two studies conducted in Washington, DC were pilot studies, not full preference studies, and/or that three of the pr eference studies were conducted in the West, while only one was conducted in the East, thus providing only limited geographic coverage. Typically

these same commenters also noted the small nu mber of survey participants, which totaled 852 across the four urban areas, which they assert are too few and unrepresentative nationally. These commenters thus concluded that there is insuffi cient information, both geographically and demographically, upon which to select a national level of a visibility index for purposes of vi sibility protection.

Response: The EPA notes that it is well aware of the limited nature of the information, which it has described in great detail in the Integrated Science Assessment, Visibility Assessment, and Policy Assessment, as well as in section VI.B.2 of the proposed rule (i.e., beginning at 77 FR 38973, 38990). The EPA further notes however that limited information does not preclude the Administ rator from making judgments based on the best available science, taki ng into account the existing un certainties and limitationsIV-29 associated with that available science. Thus , in reaching judgments based on the science, the Administrator appropriately weighs the associated uncertainties. The CASAC supported this view and concluded that the available information provided a sufficient

basis on which the Administrator could form a judgment about requisite PM-related public welfare visibility protection. Specifica lly, CASAC stated “[t]he 20-30 deciview range of levels chosen by EPA staff as ‘C andidate Protection Le vels’ is adequately supported by the evidence presented” (Samet, 2010b, p. iii). As discussed in the proposed rule (77 FR 38990), the Administrator recogn ized and explicitly took into account the

uncertainties and limitations in the science in determining an appropriate degree of protection when she proposed a level at the upper end of the recommended range.

(2) Comment: Some commenters also made the point that the EPA relied on much of this

same evidence to reach the conclusion in 2006 that the information was too limited to

allow selection of a national sta ndard. For example, API stated:

[T]he bulk of the VAQ preference studies we re available during the previous PM NAAQS review and were considered by the Agency in its establishment of the 2006 PM secondary NAAQS.... The Proposed Rule does not mention this fact and does not explain why many of thes e same studies now compel EPA to propose this new secondary NAAQS....The Pr oposed Rule notes in passing that, since the last review of the PM NAAQS , ‘limited information that has become available regarding the characterization of public preferences in urban areas has provided some new perspectives on the usefulness of this information in informing the selection of target levels of urban visibility protection.’ 77 Fed. Reg. at 38969/2. It is a serious oversight that the Proposed Rule makes no attempt to explain what that information is or how it affects the inte rpretation of the VAQ preference studies. This ‘limited informa tion’ is an apparent reference to information provided by Dr. Anne Smith. (API, p. 37)

Response: The EPA disagrees with these commente rs. First, the EPA disagrees that it failed to distinguish between studies that we re available in the previous review (see discussion in section VI.A.1 of the proposal wh ich specifically identif ies the studies from Denver, Phoenix and British Columbia (77 FR 38967/2) as being considered in the last review). The EPA further disagrees with the im plication that it is being circumspect about identifying the “limited information that has become available regarding the characterization of public prefer ences in urban areas.” Beginn ing in section VI.A.3 of the proposed rule (77 FR 38969), the EPA wa s clear about what information, both preexisting and new, it relied upon in this revi ew to inform its vi ews and provide the basis for its proposal. In sect ion VI.B.2 of the proposed rule , the EPA elaborates on the specific tools, methods and data which are cons idered in relation to the public preference studies, including the new information available since the last review.

In addition to the substantial PM urban air qu ality information and analyses new to this review, there are three other so urces of information that have specifically “provided some new perspectives on the usefulness of” the pr eference studies “in informing the selection of target levels of urban vi sibility protection”(77 FR 38969) , They include: (1) results from additional urban visibility preference study experiments conducted for Washington,IV-30 DC by Smith and Howell (2009) which added to the preference data fo r that location, and shed light on the role of location in preference responses ( 77 FR 38974, 38976); (2) a review and reanalysis (Stratus Consulting, 2009) of the urban visibility public preference studies from the four urban areas, including the newly available Smith and Howell (2009) experiments which examined the similarities and differences between the studies and evaluated the potential significance of thos e differences on the study results (77 FR 38893, 389975-76); and (3) additional analyses, including most importantly a logit analysis (Deck and Lawson, 2010, as discusse d in Chapter 2 and Appendix J of the Visibility Assessment), which was requested and reviewed by CASAC, which showed that each city’s responses represented unique and statistically different curves (77 FR 38975-76).

Taken together, these sources contribut ed to the EPA’s cu rrent knowledge and understanding of each survey study’s results, the appropriateness of comparing each study’s results to the others, and the key uncer tainties relevant to data interpretation. In addition, in the last review the decision to not adopt a distinct s econdary standard was remanded as contrary to law and failing to provide a reasoned explanation for the decision. As such it is not appropriate for purposes of comparison with the Administrator's judgment and reasoning in this review.

(3) Comment: Other commenters stated support for usi ng the preference studies, concluding they provide an adequate basis, in spite of their limited nature. In particular, AMC et al.

state:

We believe that these studies provide sufficient results to inform setting a national visibility standard. While the number of studies is small, they do incorporate spatial variation and, in the case of Denver and Phoenix, varied populations.... EPA should have confidence, rather than unc ertainty, in the fact that these studies used different methods and respondents a nd yield a range of 20 – 24 dv, with one outlier of 29. (pp. 6-7)

Response: The EPA agrees that these studies provi de a sufficient basis to inform the Administrator’s judgments regarding an appr opriate level of prot ection from PM-related visibility impairment but sh e recognized that these studi es, which are the only studies before her, are a limited source of information (see also response to (1) above). However, the EPA does not agree that the Washington, D. C. results represent an outlier, and thus the EPA believes these results are appropriate ly included in the range identified for the

Administrator to consider.

(4) Comment: A number of other tec hnical features of the st udies were identified by commenters which they assert limit the useful ness of these studies in representing real

world urban views and in elic iting appropriate preferences for urban visibility. For example, some commenters state that the a ssumption of light extinction at 550 nm is unsupported, technically flawed and invalid for a number of reasons, including that it does not account for the mix of pollutants, wh ich varies substantially within and between urban areas, or how changes in th at mix affect light extinction at different wavelengths of light, and it misses the role of sky discoloration from NO 2 and carbonaceous particlesIV-31 (i.e., Brown Cloud phenomenon) which can be significant in urban areas and influence human perception of urban visibility impair ment. Other commenters note that pollutant

concentrations in urban areas are not uniform in all directio ns over the length of a line of sight and that visibility depends upon the site -path integrated concen tration of fine PM. Studies which used photographic data capture th e integrated site path. They further state that momentary glances at 2-dimentional pi ctures cannot represen t the actual way that visibility is perc eived outdoors.

Response: First, the EPA disagrees that its choice of measuring light extinction at 550 nm wavelength is ‘unsupported, technically flaw ed and invalid’. The EPA’s Integrated

Science Assessment makes clear that 550 nm re presents the “most sensitive portion of the spectrum for human vision” and has thus trad itionally “been used to characterize light extinction and its components” (U.S. EPA, 200 9a, p. 9-2). The ISA fu rther states that “the convention for visibility monitoring purposes is to make measurement at or near 550 nm, which is the wavelength of maximum ey e response” (U.S. EPA, 2009a, p. 9-8). The EPA therefore concludes that it remains logica l to select a wavelength of light that is

most relevant to human observers when evaluating impacts to the public welfare. Regarding the comment that 550 nm misses the impacts of NO 2 on sky discoloration, the EPA notes that this PM NAAQS review is in tended to only address visibility impairment caused by particles present in th e ambient air. Thus, while it is true that sky discoloration

from NO 2 results from its ability to absorb mo re light in the short wavelength blue portion of the spectrum giving a yellow or brown appearance to the pollution layer or plume, improvement in the Brown Cloud Phenomenon is not the goal of this NAAQS review and would be expected to occu r only indirectly from a secondary PM 2.5 NAAQS for visibility in as much as PM 2.5 controls also reduced co-emitted NO 2 . The EPA further notes, however, that not ev ery urban or other area su ffers from the Brown Cloud Phenomenon. At background concentrations NO 2 absorption is generally less than five percent of the light scattering by clean air (Rayleigh scatteri ng), making it imperceptible” (U.S. EPA, 2009a, p. 9-5) Regarding the comme nt that measuring light extinction using 550 nm “does not account for the mix of polluta nts, which varies substantially within and between urban areas”, the EPA disagrees, not ing that the IMPROVE algorithm used to calculate light extinction was designed to specifically take into account the variability in the mix of pollutants from place to place and to measure the “photopic-weighted absorption efficiency at the 550 nm wavelengt h” in its calculations of PM-related light extinction. Thus, given the above, the EPA belie ves it is still appropr iate to use the 550 nm wavelength in order to measure the maximum impact of ambient PM on light extinction that is percepti ble to the human observer.

Second, with respect to the ot her technical issues raised above, the EPA agrees that photographic and WinHaze images cannot duplicate the outdoor, three dimensional viewing environment. This limitation of th e preference study design does introduce some degree of uncertainty into th e results. However, the EPA does not believe that this uncertainty significantly limits the usefulness of the results. Peopl e take pictures of aesthetically pleasing vi stas so that they can look at them repeatedly, even though they are not exact replicas of thei r initial outdoor viewing experi ence. This shows that they appreciate the photographic view of the scene, commensurate w ith their appreciation with the scene itself. Thus, the EPA believes photos or digital images can be useful surrogatesIV-32 for the purpose of eliciting public preferen ces. Regarding the commenters other concern that pollutant concentrations in urban areas are not uniform in all directions over the length of a line of sight and that visib ility depends upon the site-path integrated concentration of fine PM, the EPA notes that both the photos used in two of the preference study areas (Denver and British Co lumbia) and the WinHaze images used in two others (Phoenix and Washingt on, DC) depict visibility im pairment over an integrated sight path. The difference between the two me thods is that a photo can capture the nonuniformity across the sight path while th e WinHaze views present a uniform haze integrated across the sight path. Photos of the Denver scene therefore would also have included any layered haze known as the brown cl oud that was present at the time that fell within the integrated site path. Despite these variables, the ordering of the results of these studies appear to be explai nable based predominantly on sc ene characteristics – i.e. people found impairment of the views with the most sensitive scene characteristics (Denver and Phoenix) more unacceptable at lo wer deciview values than those with less sensitive scenes (British Columbia and Washington, DC) regardless of the image depiction methods used. Thus, the EPA conc ludes that the concerns over study methods and designs identified by co mmenters are not substantial, and that the preference study results are still sufficiently informative to allow selection of candidate protection levels.

b. Comments on Preference Study Methods and Design

(1) Comment: Many commenters asserted that the me thodologies used in the preference studies are fundamentally flawed. Most of th ese same commenters also pointed to an assessment of the preference study met hodology conducted by Smith and Howell (2009) of Charles River Associates (CRA) as the basis for their views. These commenters

criticized the EPA for not acknowledging that (in their view) the Smith and Howell results undermined the validity of the ear lier preference studies. For example:

Smith and Howell (2009) show that VAQ preference study outcomes are malleable and depend entirely on the design of the study. Accordingly, such studies do not identify any meaningful threshold of acceptable visibility conditions. Despite Smith and Howell’s conc lusions, EPA continues to assert that the VAQ preference studies can be used to identify minimally acceptable visibility conditions even though the Ag ency has never provided any valid

scientific basis for disco unting the Smith and Howell ( 2009) results. (API, p. 38)

Well-controlled preference studies disc ussed by Anne Smith of Charles River

Associates at the March 2010 CASAC meeti ng demonstrated that the judgment of panel members was affected by the orde r in which photographs were presented and tendency to identify the middle of the range of visibility degredation as a threshold of acceptability. This points to a potential flaw in these studies and that artifacts caused by these tendencies ma y have influenced study results. Dismissing these inherent flaws in the ex isting preference studies and then using these studies to set a secondary NAAQS is arbitrary and capricious. (API, attachment 14, p. 12)

EPA also fails to acknowledge that the onl y study conducted since the last reviewIV-33 rebuts the validity of the VAQ preference studies previously conducted. (UARG, Attachment 2. p. 28)

Response: As noted above, the EPA is aware of the issues raised regarding the

uncertainties and limitations associated w ith the preference studies, including those associated with study methods and design and specifically solicited comment on how

these uncertainties and limitations should be considered (see 77 FR 38990). However, as is explained in the following discussion, the EP A disagrees that the analysis by Smith and Howell (2009) supports the commenters’ conclusion that the preference study methodologies and design were fundamentally flawed, however the EPA notes that their experiments do identify areas wh ere additional research would be useful to further inform our limited understanding of pub lic preferences in urban ar eas. Though still limited, the EPA views the Smith and Howell (2009) expe riments as increasing the EPA’s knowledge and understanding of the findings of the 2001 Washington, DC focus group pilot study (Abt, 2001) in several important ways. Smith and Howell (2009) c onducted a series of three sets of experiments based on the 2001 Washington, DC, focus group pilot study. The first set of experiments (Test 1) was designed to re plicate the 2001 focus group to explore whether the 2001 study findings could be reproduced. Tests 2 and 3 varied the range and distribution of visi bility conditions to examine whether such changes would affect the results. As explained below, the EP A asserts that some as pects of the approach used by Smith and Howell (2009) in Tests 2 and 3 are flawed.

It is important to note as an initial matter, that while Smith and Howell (2009) claims to have replicated the Abt 2001 protocol, there were three distinct differences in the methods used by Smith and Howell (2009) and the methods used in the Washington, DC 2001 pilot study. First, the images of alternative levels of visibility degradation in Washington, DC were prepared and presente d differently. While both studies used the same original photograph of Washington, DC , the 2001 images showing different levels of visibility degredation were prepared by John Molenar of Ai r Resource Specialists, Inc. (ARS) using the mainframe computer version of WinHaze available at that time. The 2009 Smith and Howell experiments, on the other hand, used images prepared in a more simple manner using the MS-Windows © -based version of WinHaze (Ver. 2.9.0) available by that time from ARS.

Second, the 2001 pilot study used high quality photographic transparencies (“color slides”) prepared by ARS, which were presented on a large format, high quality projection screen. The entire group of particip ants was seated at the viewing angle and distance from the projection screen in a dark ened room to provide the optimal viewing conditions recommended by John Molenar. The 2009 study used images presented to individuals on a large desktop computer monitor.

Third, the method used to recruit par ticipants differed between the 2001 and 2009 studies. While a group of only 9 people can neve r be a statistically valid representative set of any population, the 2001 focus group partic ipants were recruite d by a professional focus group facilitation firm to reflect aspe cts of the demographic distribution of the Washington, DC metropolitan area adult population. The recruitment screening method was designed to obtain 9 adults resembling major aspects of the demographic gender,IV-34 age, residence and income distribution of th e Washington, DC area. At least two of the 2001 participants were in each of the follo wing groups: a) Income: at least two people with household incomes under $25k, two with incomes between $25k and $60k, and two with incomes above $60k; b) Age: at least two between the ages 18 and 25, two between 26 and 55, and two over 56; c) Race/Ethnicity : at least two African Americans and two Hispanics; d) Residence location: at l east two living in each of Washington, DC, Maryland and Virginia. In contrast, the Smith and Howell (2009) study did not use a structured recruitments process. Due to the schedule of the Smith and Howell (2009) study, all study participants were employees of CRA, Inc. (where both Smith and Howell are also employed). One variant of Test 1 wa s conducted with participants who work at the CRA Washington, DC office (and who pres umably live in the Washington, DC area).

The other variant of Test 1 was conducted with participants from the CRA Houston office (and likely live in the Houston area). The same set of images of Washington, DC was shown to both the CRA Washingt on and Houston participants.

In spite of these differences in study methods, the Test 1 results (Smith and Howell, 2009, p.11) found a “...remarkable degree of repl ication, given the differences in the samples, and the relatively small sample size of the Abt pilot (nine people).” Furthermore, the preferences for Washi ngton, DC visibility provided by the Houston participants were effectively the same as both the preferences of the CRA Washington office participants and the Abt 2001 participants.

The EPA identified a number of important implications from the similarity between the Test 1 (2009) and 2001 study results.

1. The change in the presentation methods (i .e., from slide projection to computer monitor, and mainframe WinHaze images versus the simpler Windows WinHaze method) shows no evidence of impa cting reported preferences.

2. The replicability of the 50% acceptable cr iteria results supports a hypothesis that the 2001 results, although based on a small sample of 9, were consistent with the preferences from a larger sample of the general Washington, DC population.

3. The similarity of the Test 1 Houston result s to both the Test 1 Washington results and the 2001 Washington study suggest th at an individual’ s preferences for visibility in one location (i.e., Washi ngton, DC) may not depend on whether they

live in that location or in another.

As a result of the similarity between the re sults of these two DC studies and the above implications, the EPA concluded that the Test 1 experiment could legitimately be combined with the 2001 study to effectively more than triple the responses to the original Washington, DC urban visibility prefer ence study, thus increasing the available information from 9 (in the 2001 study) to 31 (with the addition of both the Washington, DC and Houston CRA participants). Smith and Howell’s Test 1 thus instigated a shift in the EPA’s thinking regarding the usefulness of the available Washington, DC preference study data.IV-35 The Smith and Howell (2009) Tests 2 and 3 also provided important in formation relevant to understanding the results of visibility prefer ence studies. In Test 2 and 3 the range and distribution of visibility conditions shown to participants were substantially different than the range and distribution s hown in Test 1 and the 2001 Washington, DC study. Test 2 removed from the range of Test 1 slides those that showed th e 11 worst visibility conditions (all images above 27.1 dv). Test 3 ch anged the visibility conditions presented in two ways: first, the number of clean or cleaner images were reduced substantially, dropping all images in the lower third of th e distribution, and addi ng two new images of substantially worse visibility (42 and 45 dv), wh ich were substantially above the previous worst scene shown (38.3 dv).

Smith and Howell (2009) found that changing the range of visi bility images shown has a pronounced impact on the resulting 50% acceptabili ty level. They concluded that this is an indication that preferences obtained usi ng the general PS method are not stable, and

therefore not an accurate re presentation of the populations pre-existing (or “true”) preferences for visibility.

While the Smith and Howell (2009) results sugges t such a hypothesis, the Test 2 and Test 3 results also are consistent with a very diffe rent effect in visibility preference survey results. The range of visibility conditi ons shown in Test 1 and the original 2001 Washington, DC study were selected by EPA to present a good re presentation of the distribution of visibility c onditions expected to occur in Washington, DC with thencurrent EPA air quality regulations. In other wo rds, the original rang e and distribution of visibility conditions shown to the participants were near to current conditions, and reflected the “policy relevant ” range of expected conditions . This fundamental approach was used in all the existing studies (i.e. Denver, Phoenix, and British Columbia); the range of visibility conditions reflects current real world conditions. While the participants were not informed that the images they were being shown were esse ntially then-current conditions, the range of images would have b een consistent with the participants own experiences.

When the range of images presented was subs tantially different, as in Tests 2 and 3, the participants would very likely recognize that the conditions did not depi ct the real range of conditions. This creates a disconnect between the participants’ own experiences and expectations and the hypothetical scenario be ing presented to them through the use of the altered ranges. This creates a form of the well known “scenario rej ection bias” that has been observed in many types of stated pref erence studies. Current methods of stated preference research on a range of environmental issues find it is very important to present

as realistic and believable a de scription as possible of the real world conditions matching to participants’ pers onal experience and knowledge in orde r to produce robust, stable and reproducible results. The effect Smith and Ho well (2009) see in thei r Test 2 and Test 3 methods are likely to be due to just such a scenario rejecti on biasing influence.

Thus, on the basis of the above discussion, the EPA disagrees that the findings of Tests 2 and 3 in Smith and Howell (2009) make the case that the methodology used in the preference studies is fundamentally flawed and therefore disagr ees with commenter

views that the EPA’s use of these studies is somehow inappropriate, scientificallyIV-36 unsound, or arbitrary and capricious.

(2) Comment: Many commenters also asserted that pr eference study partic ipants were not given guidance on how to interpret the concept of “acceptable urban visibility”. This lack of guidance was considered a detriment by co mmenters because in their view it renders the responses subjective.

Response: EPA notes that while the overall method used in all the pr eference studies is consistent (based on the met hod and elicitation protocol de veloped by Ely et al., 1991 in the Denver study), each study developed a spec ific protocol (including the specific language on both background information and the wording of the key questions) for conducting that study’s survey. The Denver a nd Phoenix studies each gave the survey participants specific guidance on interpreting “acceptability”.

The Denver study framed the question in the expl icit context of setting an urban visibility standard for Denver, and instructed the particip ants that they were being asked to identify the VAQ that in their opinion should violate an urban visibility standard, and that “...standard violations should be VAQ that is unreasonable/objectionable, and unacceptable visually. Participants were asked to discern ‘how much haze was too much’,

not to indicate standard violations base d on whether haze was detectable unless any amount of haze was more than they c ould accept” (Ely et al., 2001, p. 6-7).

The Phoenix study instructions to participan ts defined acceptable (or unacceptable) as “Consider ‘unacceptable’ as vi sual air quality that is unreasonable or objectionable visibility. Please do not mark a slide ‘unaccep table’ just because you can see some haze, unless you believe that any amount of h aze is more than you would tolerate.”

The British Columbia study (Pryor et al., 1996) followed the survey protocol in the Denver survey closely, and gave similar guidan ce to the participan ts on the meaning of “acceptability” in a standard setting context.

The Washington, DC (2001) study was a focus gr oup designed to investigate a series of

issues involved with conducti ng group interview type surv eys about preferences for urban visibility. A key feature of the 2001 focu s group script was to de liberately not give the participants guidance on how to interp ret “acceptable” or “unacceptable” before rating the series of Winhaze images. After the series questions involving rating the images, the focus group moderator lead a discussion about how the participants interpreted the term “acceptable”, and what i ssues and information they considered in forming their responses. The 2009 series of Wa shington, DC urban visibility preference experiments followed a similar procedure, although apparently conducted a more abbreviated focus group follow-on discussion.

Thus, the EPA believes that study participants were given sufficient direction and context so that they could understand the nature of the questions being posed and were all on equal footing in developing subjective judgments regarding “acceptable” and “unacceptable” visual air quality. Since the goa l of these studies was to elicit personal preferences, which by very nature are subjec tive, the EPA does not view the subjectivityIV-37 of the responses as a weakness of the study design or protocols.

c. Comments on Preference Study Results and Adversity

A number of comments were received re garding the EPA’s use of preference study

results to make the determination that adverse PM 2.5 -related visibility effects on the public welfare are occurring. Some of these comment ers questioned whether the EPA had made the case that unacceptable levels of visual air quality based on preference study results alone can be equated with an adverse public welfare effect. Other commenters questioned the EPA’s selection of the 50% acceptability criterion as the appr opriate benchmark for determining adversity.

(1) Comment: Several commenters asserted that the EPA had not made a sufficient case for the occurrence of adverse public welfare effect s in association with ambient levels of

PM 2.5 :

Thus, EPA seemingly was building the f oundation for a determination of what

constitutes an adverse eff ect on visibility in the c ontext of public welfare. However ... EPA subsequently veered toward an oversimplified focus on public acceptance of visibility conditions.... EPA’s discussion of visibility in the Policy Assessment and its proposed rule in th e Federal Register focuses entirely on “acceptable” and “unacceptable” visual ai r quality and make no mention of an

“adverse effect” in the context of visi bility. EPA’s reliance on only 3 urban preference studies represents a paucity of data and a wholesale abandonment of any effort to seek a scientifically m easurable adverse effect. (Kennecott Utah Copper LLC, p. 26)

These commenters suggested that unless preference study information is linked to personal comfort and well-being or other associated welfare effects, it cannot form the basis of a determination of adversity.

Response : The EPA first notes that the definition of effects on welfare included in section 302(h) of the CAA identifies both visibility and the broader category of effects on personal comfort and well-being as effects on welfare. In set ting a secondary standard to address visibility impairment, the EPA considers the effect on the public from impairment of visibility as a separate and di stinct welfare effect in its own right. The EPA is not required to translate this into terms of personal comfort and well-being, as visibility impairment is designated explicitly by Congres s as an effect on welfare. While there may be a large degree of overlap among these di fferent welfare effects, the EPA properly focuses on evaluating all of the information before the Agency on the effect visibility impairment has on the public, whether or not this impairment would also be categorized as having an adverse effect on personal comfor t and well-being. It is in the context of all

of this information that the EPA makes th e judgment as to the appropriate degree of protection from known and anticipated advers e effects on the public from visibility impairment. The EPA recognizes that there is uncertainty about the de gree of adversity to the public welfare associated with PM-re lated visibility impairment. However a secondary standard is designed to provide protection from "known or anticipated" adverse effects, and a bright line determination of adversity is not required in judging theIV-38 requisite degree of protecti on under section 109(b)(2). Furt hermore, the EPA disagrees

that it has abandoned its consid eration of visibility-related impacts on the welfare effect of personal comfort and well-being, as is made clear in the following quote:

Research has demonstrated that people are em otionally affected by low visual air quality, that perception of pollution is correlated with stress, annoyance, and symptoms of depression, and that visual air quality is deeply intertwine d with a ‘‘sense of place,’’ affecting people’s sense of the desirabili ty of a neighborhood (U.S. EPA, 2009a, section 9.2.4). Though it is not known to what extent these emotional effects are linked to different periods of exposure to poor visual air quality, providing additional protection against short-term exposures to levels of visu al air quality considered unacceptable by subjects in the context of the preference st udies would be expected to provide some degree of protection against th e risk of loss in the public ’s ‘‘sense of well-being.’’ (77 FR 38973/1, emphasis added)

The approach taken to address such qualitati ve, but policy-relevant, information in this review is the same as in other NAAQS re views. The review is initiated with a comprehensive assessment of all possible public health and welfare effects associated with PM in the Integrated Science Assessment. Then policy-relevant effects for which there is sufficient quantitative information to allow a determination of the change in risks associated with incremental changes in air quality are assessed (in this review, in the Visibility Assessment) and used to provide a quantitative basis to inform the selection of an appropriate range of levels for further c onsideration in the Policy Assessment. In the Policy Assessment, the EPA considers all important policy-relevant evidence and information, both quantitative and qualitativ e, in making recommendations regarding the range of policy options appropriate for the Admi nistrator to consider. It is in the context

of all of this information that the Admini strator makes her final judgment as to the appropriate degree of protect ion from known and anticipat ed adverse effects on the public from visibility impairment..

(2) Comment: Another issue raised in the commen ts regarding adversity is the EPA’s decision to use the 50 percent acceptability criterion from th e public preference studies in determining candidate protection levels of vi sibility impairment for the selection of a national level of visibility protection. For example, AMC et al. recommended “a 75% acceptability criterion as a target that is in line with protecting the broader public from the negative effects of visibility impairment” (AMC, et al., p. 9).

Response: In the Visibility Assessment, the EPA noted that the use of the 50 percent acceptance level for urban visibility was first presented in Ely et al. (1991) (U.S. EPA, 2010b, p. 2-5). Ely discussed the use of the 50 percent acceptabili ty criterion as a reasonable basis for setting a standard to protect visibility in urban areas.

The standard was determined based on a 50% acceptability criterion, that is, the

standard was set at the level of extincti on that would divide the slides into two groups: those judged acceptable and those judged unacceptable by a majority of the people in the study. The criterion is pol itically reasonable because it defines the point where a majority of the study participants begin to judge slides asIV-39 representing unacceptable visibility. It is also consistent with psychological scaling theory which indicates that a “t rue score” exceeds a standard when more than 50% of the “observed scores” exceed that standard. (Ely et al., 1991, p. 11)

As Ely described, the 50 percent acceptab ility criterion and the preference study conducted by Ely were used as the basis for setting the level of the Denver Visibility

Standard in 1990. That same cr iterion was judged appropriate and selected for use in the Phoenix preference study (BBC re search, 2003) and was also used as the basis for setting the level of the Phoenix Visibility Standa rd in 2003. Most rece ntly, the 50 percent acceptability criterion has been recommende d by the British Columbia Visibility Coordinating Committee as the basis for the visibility sta ndard currently under consideration by British Columbia, Cana da. Furthermore, CASAC supported this approach, while recognizing the uncertainty associated with this issue. Specifically, CASAC agreed that “the 50th percentile for the acceptability criteria is logical, given the

noted similarities in met hodologies employed in the 4 study areas. ... In terms of choosing a specific percentile from the prefer ence studies, we note that there may not be a “preferred” one, but in a ssessing preference studies to propose a PM secondary NAAQS, the 50th percentile is sufficient, as it is the basis for existi ng visibility indexes used in the Denver/Colorado Front Range and Phoenix metropolitan areas” (Samet, 2009c, pp. 8-9). Therefore, after considering the information that served as the original

basis for its selection as desc ribed in Ely et al., 1991, and gi ven its acceptance and use in existing visibility programs, th e EPA continues to conclude, c onsistent with the advice of CASAC, that it is reasonable to use the 50 percent acceptability criterion in determining target levels of protection fr om visibility impairment.

d. Comments on Using Preference Studies as Basis for Nationally Uniform Standard

A number of commenters raised concerns rega rding the bases for and implications of the differences observed in the pref erence study results, concluding that these results were due to regionally varying factors a nd thus could not be used to set a national standard.

(1) Comment: Some commenters asserted that be cause the confidence intervals around the four 50 percent acceptability levels do not overl ap at all, and because there are variations in preference study designs and inherent diffe rences in the visual setting among cities and panels, the four preference curves and thei r associated 50 percent dv values are cityspecific and statistically diffe rent. The commenters conclude d, therefore, that it was inappropriate to aggregate the 50 th percentile dv values from multiple studies and that they should instead be evaluated individuall y. Similarly, other commenters expressed the related view that the preferen ce study results cannot be used to set a national standard for visibility impairment because the results show that visibility preferences vary regionally and/or locally for a variety of reasons. For example:

The ‘one-size-fits-all’ approach...is not viable because it does not account for regional and city-specific fact ors that have been made ev ident in the disparity of preference study data.... It is well known, for example, that the leve l of light extinction to which people in different areas of the country are accustomed, as well as the urban setting, are the primar y factors that affect a person’s visualIV-40 perception of an urban vista. Thus, the degree to which extinction threshold can

be related to human welfare is inevitabl y regionally-dependent. (API, Attachment 2, p. 4)

[T]he proposed method falls short because it is not temporally or geographically representative enough to have any meani ng.... The uncertainty evidenced in these studies and the non-uniformity between the western and eastern vistas makes it impossible at this time to set an accep table light extinction value that would appropriately address visibility conc erns in non-Class I areas. (New York DOH/DEC, pp. 5-6)

These commenters suggest that the basis for the differences in pr eference study results include regionally varying preferences for accep table visual air quality and/or regionally varying factors, such as relative humidity and other differences between Eastern and

Western areas. These commenters asserted that it would be more appropriate to develop distinct visibility standards at the state or local level, since it is not possible to select a single level for a national stan dard to protect visibility across the United States that provides the appropriate degree of protection in locations with distinct characteristics, including areas which lack “important visibil ity vistas” that might not need standards at all, since flat areas without significant te rrain have a limited maximum visual range. (NEDA/CAP, p. 3)

Response: The EPA agrees that the preference curves and the 50 percent dv levels are separate and distinct data points representi ng four different VAQ pr eference curves for four unique urban scenes. However, the EPA does not consider the fact that the four curves are distinct as a weakness of the appr oach or a reason that the results cannot be compared. In addition, the EPA does not agree th at the study results necessarily support a conclusion that preferences are regionally depe ndent. In particular, the EPA notes that the results of Smith and Howell (2009) which s how that participan ts in Houston and Washington, DC did not have significantly different views on acceptable air quality in Washington, DC, provide limited support for the conclusion that people’s preferences differ less because of where they live and more because of the scene they are viewing.

The existing literature indicat es that people’s preferences for VAQ depend in large part

on the characteristics and sensitiv ity of the scene being viewed. The EPA also

understands that there is a wide variety or range of urban s cenes within the United States.

These sensitive urban scenes include those with natural vistas such as the Rocky

Mountains in Colorado as well as those with iconic man-made urban structures like the Washington Monument. The EPA believes that the scenes presented in the four urban areas include important types of sensitive valued urban scenes and therefore, when considered together, can inform the selec tion of acceptable urban VAQ at the national scale, taking into account the variation across the country evidenced in the studies.

In response to the comments that there are factors that vary regionally that are important to take into account when setting a national standard for visibility protection, the EPA agrees, and notes that it ha s clearly taken these into acc ount. Section VI.A of the preamble to the final rule re garding the history of the secondary PM NAAQS reviewIV-41 discusses the evolution of th e EPA’s understanding regarding the regional differences in PM concentrations, relative humidity and other factors. As a result, the current review has gone to great lengths to addre ss these factors, leading to the EPA’s proposal to use the IMPROVE algorithm to calculate light extinction in order to take into account the varying effects of relative humidity and sp eciated PM. While this approach does not

result in a uniform level of ambient PM 2.5 , it does ensure a nationally uniform level of visibility protection. The EPA refers the reader to other sections of the final rule, including sections VI.B.1.a, VI.B.1.c, VI.C .1.b and VI.C.1.f, and other sections of the Response to Comments document for a more de tailed response as to how it is taking

these variables into account.

(2) Comment: The Arizona DEQ stated that it was ina ppropriate to use the Phoenix study for purposes of establishing a leve l for a national standard:

The proposed secondary visibility standa rd does not integrate our measurement method or mirror our index scale, essen tially making the program incomparable with the proposed standard. Four urban visibility studies were cited in the proposed rule as a consideration in de veloping the level of the secondary PM 2.5 standard. The recommended level for the proposed standard, 28 or 30 deciviews, and corresponding calculation method exclude s extinction by coarse particulate matter and Rayleigh scattering. The cited studies were conducted considering total light extinction; including extincti on resulting from particulate matter and Rayleigh scattering. Visibility impairment due to coarse particulate matter can be an important contributor in Arizona, sp ecifically in the Phoenix area where ongoing measurements have been made. Therefore, ADEQ believes that the proposed levels of the secondary visibi lity standard are inconsistent with applicable urban studies. (Arizona DEQ, p. 2)

Response: The EPA understands that each of th e four preference study areas has a different mix of pollutants and that across th e studies a variety of methods for measuring and linking ambient PM concentrations to im ages (either photos or WinHaze) of differing haze levels at a given urban scene were em ployed. However, as discussed above section IV.B.5.a, the EPA conducted a detailed assessment (77 FR 38893, 77 FR 38974-75) of

the differences and similarities that existed be tween the four studies and concluded that it was still appropriate to compare them and consider their results together. The CASAC also reached the same conclusion (Samet, 2010b, iii). In regard to the commenter’s concern about contributions from coarse pa rticles and Rayleigh, the EPA further notes that participants in the P hoenix and other studies were not asked to break out their preferences based on how much of the haze was caused by contributions from coarse particles, Rayleigh scattering or fine particles. Instead, as discussed above in section IV.B.5.b, Phoenix study participants were simply asked to iden tify levels of visual air quality that they would consider “unreasonable or objectionable”, no matter what the source. Based on this information, Phoenix was able to come up with a target level of VAQ, even though pollutant mixes vary temporally and spatially, even within the Phoenix urban area. Since the goal of the secondary PM 2.5 NAAQS is to provide a uniform national level of public welfare protection from PM 2.5 related visibility impairment, the form of the EPA’s proposed secondary standard was selected to allowIV-42 each area to achieve that level of protection in a way that ad dresses its own unique mix of contributing pollutants. Therefore, the EPA disagrees with the commenter that it is inappropriate to use the resu lts of the Phoenix study to inform a range of candidate protection levels for consideration by the Administrator in selecting a national level of visibility protection. Instead, the EPA believe the Phoenix results form an important data point that shed light on public preferences for visibility in western areas with urban

scenes that include distant mountains.

(3) Comment: Similar to comment (2) above, Colora do DPHE expressed concern with the EPA’s use of the Denver study results in a natio nal context. In particular the commenter

states:

The proposed secondary visibility standa rd relies in part on the Denver urban visibility standard as su pporting justification for es tablishing a new secondary standard. However, the Denver visibility standard was originally developed in 1989 in response to a bipartisan directive fr om the legislature to meet a statutory deadline of January 1990 for a standard based solely on aesthetics. The Denver visibility standard, set at about 20 de civiews (32 miles or 0.076/km), was based on a survey of 214 Denver ci tizens that evaluated 25 slid es of the ‘Brown Cloud’, a publically understood name for the strong inversions that occur in the Denver metropolitan area. These slides were specifically referenced to data obtained using a transmissometer. Thus, this standa rd is based on a specific view of Denver and specific transmissometer location and path and is applicable only to this

location. This constitutes a limitation with its applicability to a national secondary standard, particularly a proposed standard that does not use a direct measurement method. ... Visibility from year to year is highly variable.... [A]dditional studies are necessary to establish a secondary NAA QS standard, or what might ultimately become multiple standards, across the United States” (Colorado DPHE, p. 2-3).

Response: The Colorado comment raises some of the same concerns as the Arizona

comment and the EPA refers the reader to its response to comment (2) above. In addition, this commenter states that the visibility sta ndard is “based solely on aesthetics”. This is not a significant difference with the proposed secondary visibility PM NAAQS. While qualitative information was also available regarding personal comfort and well being, the proposed range of levels considered by the Administrator was derived from the quantitative information regarding public pr eferences for the aesthetic quality of the urban view. This commenter also points out that the slides presented to the study participants included images of the Brown Cloud that occurs under conditions of a strong

inversion. The EPA notes that while this c ondition does not happen everywhere, there are other urban areas that experience it and theref ore preference information that takes such a phenomenon into account provides useful info rmation for the Administrator to consider.

The commenter further notes that “this stan dard is based on a specific view of Denver and specific transmissometer location and path an d is applicable only to this location.” In spite of this, however, the EPA observes that Denver still went ah ead and established a standard that applies to the entire metr opolitan area, even tho ugh there are many other views and paths that could be evaluated. Li kewise, the EPA believes it is possible to

select a national level of visi bility protection based on a vari ety of disparate data pointsIV-43 for urban visibility preferences, because wh en taken together, they provide useful information regarding the range of scene and si te characteristics that can influence public perception of acceptable VAQ. While the EPA ag rees that additional studies would be helpful and provide more useful data points to consider, it does not agree that they are necessary to establish a secondary standard.

6. Need for a Distinct Secondary Standard

a. Comments Supporting a Distin ct Secondary Standard

(1) Comment: Some tribal commenters who supported th e proposal to set a distinct standard to protect visibility expre ssed concern about the urban fo cus of the proposed secondary standard for visibility, and ur ged the EPA to focus on visibili ty protection in rural areas as well. Specifically, they urged the EPA to conduct additional preference studies in rural areas, and to expand monitoring in Tribal regions to obtain more information on visibility impairment in rural locations.

Response: The EPA agrees with these commenters that it is impor tant to provide protection against PM-related visibility impairment in both urban and rural areas, and that it would helpful to have additional preference study data from more locations, including rural locations. However, with regard to the commenters’ assertion that the proposed secondary standard for visibility would ne glect rural areas, the EPA disagrees. The EPA has considered both urban and rural areas, a nd has focused on urban-related visibility impairment for a reason. CAA section 109( b) requires the Agency to establish national standards to protect the public welfare, which means that the NAAQS are designed to protect against adverse impacts in both urban and rural areas. In the ca se of visibility, the EPA has also recognized that the Regional Haze Program under sections 169A and 169B of the CAA specifically targets visibility pr otection in Federal Class I areas, most of which are in remote (rural) areas. The goal of the Regional Haze Program is to address all man-made impairment of visibility, and the program specifically targets the widespread, regionally uniform type of haze caused by a multitude of sources. Over time, the Regional Haze Program will provide a level of pr otection of visual air quality in Class I areas that extends far beyond the level of pr otection envisioned for a secondary NAAQS under section 109(b). The EPA notes that any national ambient air quality standard for visibility would be designed to work in conjunction with the Regional Haze Program as a means of achieving appropriate levels of protection against PM-related visibility impairment in all areas of the country, in cluding urban, non-urban, and Federal Class I areas. While the Regional Haze Program is fo cused on improving visibility in Federal Class I areas and a secondary visibility i ndex NAAQS would focus on protecting visual air quality principally in urban areas, bot h programs could be e xpected to provide benefits in surrounding areas. Thus , in considering a distinct st andard to protect visibility impairment under the NAAQS program, the EP A focused particular attention on areas not already covered by the Regional Haze Pr ogram. This led to a focus on urban air quality as a means of ensuring adequate protec tion of visibility in a ll locations (i.e. as a supplement to the protection already a fforded by the Regional Haze Program).IV-44 b. Comments Opposing a Distin ct Secondary Standard

(1) Comment: A number of commenters opposed setting a distinct secondary standard to protect visibility on the grounds that existi ng regulatory mechanisms are adequate to protect urban visibility. A ccording to these commenters, the combination of urbanoriented PM control programs and long-term regional haze strategi es will effectively protect visibility and urban vi sibility will improve over time without a separate visibility NAAQS. These commenters urged the EPA to wait for implementation of the Regional Haze Program to achieve visibility improveme nts and then re-assess whether a secondary standard for visibility is warranted.

Response: While the EPA has determined that a distinct secondary standard to protect against visibility impairment is not needed at this time, this decision was based on the degree of protection afforded by the existing secondary PM 2.5 standards, particularly the secondary 24-hour PM 2.5 standard of 35 μg/m 3 . The Regional Haze Program has more ambitious goals to be implemented over a long er time period (i.e., to eliminate all manmade impairment in visibility by 2064), a nd is focused primarily on remote (Federal Class I) areas. Therefore, it would not be appr opriate to rely solely on that program to protect visibility in all areas across th e country as required by C AA section 109(b) or to wait for the Regional Haze Program to be impl emented before evaluating what additional protection might be needed for non-Federa l Class I areas. The EPA continues to emphasize that the secondary PM NAAQS is designed to work in concert with the Regional Haze Program to afford the requisite de gree of visibility protection in all areas.

(2) Comment: Some commenters urged the EPA to delay setting a distinct secondary standard for visibility pending the establishm ent of a pilot program to gather additional data. For example, NY State Departments of Health and Environmental Conservation stated that while they support the promul gation of a secondary standard to protect visibility, they “have serious concerns w ith the proposed method as it fails to be temporally and geographically representati ve of real-world visibility. EPA should establish a pilot measurement development pr ogram to identify methods that would more accurately measure and report real-time visib ility conditions to the public” (New York DOH/DEC, p. 2).

Response: While acknowledging the uncer tainties and limitations associated with the information available in this review, the EPA continues to conclude, as did CASAC, that this information provides a sufficient basis fo r selecting a target le vel of protection for visibility in this review. Thus, the EPA disagrees with these commenters that the uncertainties are so significant as to precl ude establishing a standard at this time.

(3) Comment: Numerous commenters questioned whethe r a distinct secondary standard for visibility is necessary in li ght of the EPA’s own analysis as presented in Kelly et al. (2012a) which indicated that a 24-hour mass-based PM 2.5 standard of 35 μg/m 3 would protect against visibility impacts exceeding the range of levels considered in the proposal (28-30 dv). Many commenters pointe d to this analysis in support of their argument that a visibility index standard in the range proposed (28-30 dv) would provide no additional protection beyond that afforded by the existing secondary 24-hour PM 2.5 NAAQS, andIV-45 therefore no distinct secondary standard to protect visibility was necessary. These

commenters advocated retain ing the current 24-hour PM 2.5 mass-based standard to protect against visibility effects. “Since the 24-hour PM 2.5 standard already protects the

welfare the 24-hour PM 2.5 visibility standard is designed to protect, the new standard is duplicative and unnecessary” (South Dakota DE NR, p. 2). Michigan DEQ agreed, stating it believed “that the visibility index is an unnecessary standard and that the 24-hour

PM 2.5 standard should be used as a surrogate fo r evaluating visibility” (Michigan DEQ, p. 2).

Response: The EPA agrees with commenters that Kelly et al . (2012a) indicates that the existing 24-hour PM 2.5 standard provides at least the target level of protection for visual air quality defined by a visibility index se t at 30 dv, averaged over 24-hours, with a 90 th
percentile, 3-year average form, which the EP A judges appropriate. While the Kelly et al. (2012a) analysis was conducte d in support of proposed im plementation requirements for a distinct secondary standard (specifically, the modeling de monstrations that would be required under the PSD program), the second pron g of the analysis suggested that the 24-

hour PM 2.5 standard of 35 μg/m 3 would be controlling relative to a standard based on a visibility index set at 30 dv. Kelly et al. (2012a) concluded that the “overall, design values based on 2008-2010 data suggest th at counties that attain 24-hour PM 2.5 NAAQS level of 35 μg/m 3 would attain the proposed secondary PM 2.5 visibility index NAAQS level of 30 dv” (pp. 17-18).

Importantly, the analysis performed by Kelly et al. (2012a) provi des an area-by-area comparison of the relative de gree of protectiven ess of the existing secondary 24-hour

PM 2.5 standard and the proposed distinct standard for visibility. This analysis confirms that for each area examined, it is high ly likely that a standard of 35 μg/m 3 would provide as much or greater protecti on than a standard based on a visibility index set at 30 dv. Based on 2008-2010 data, it appears that there are no areas that would have exceeded a 30 dv, 24-hour visibility index standard that would not also have exceeded a 24-hour

PM 2.5 standard of 35 μg/m 3 . Stated another way, all ar eas that met the 24-hour PM 2.5 standard of 35 μg/m 3 would have had visual air quality at least as good as 30 dv (24-hour average, based on 90th percentile form averag ed over 3 years). The Kelly analysis also shows that for some areas, particularly in the West, areas that would have met a 24-hour

PM 2.5 standard of 35 μg/m 3 would have had visual air quality better than 30 dv for the

PM 2.5 visibility index standard, a nd that at sites that violat ed both the 24-hour level and the secondary visibility index 30 dv level, th e visibility index level of 30 dv would likely

be attained if PM 2.5 concentrations were reduced such that the 24-hour PM 2.5 level of 35 μg/m 3 was attained.

Moreover, the EPA has conducted a reanalysis (Kelly et al., 2012b) that confirms the results of the original Kelly et al. (2012a) memo. This reanal ysis updates the area-by-area analysis in Kelly et al. (2012a) in three respects. Firs t, noting that the or iginal Kelly et al. (2012a) analysis used a 1.4 multiplier to convert OC to OM at those monitors not using the new CSN monitoring protocol, the EPA reca lculated the visibility index design values for 2008-2010 using a higher multiplier for converting OC to OM at monitors not already using the new CSN monitoring protocol SANDWICH appro ach, consistent with the Agency’s view that it is more appropriate to use a multiplier of 1.6 at such monitors asIV-46 compared to 1.4, as described in section VI.C.1.a .ii of the preamble to the final rule and discussed in response to comments on i ndicator in section IV.B.1, above. The recomputed visibility design index valu es for 2008-2010 show the same overall relationship to 24-hour PM 2.5 design values as presented in Kelly et al., 2012a.

Second, the EPA repeated the calculations comp aring visibility index design values with

24-hour PM 2.5 design values using 2009-2011 data, th e most recent three years of air quality information currently available. Third, the EPA modified the area-by-area evaluation to ensure consistency with the da ta completeness criteria of 40 CFR part 50, Appendix N, including the removal of data approved by EPA as exceptional events, for

the current 24–hour PM 2.5 standard and the proposed visibility index standard.

The results of this reanalysis, as presented in Kelly et al. (2012b), show a similar pattern to that described in the original Kelly memo. Specifically, the analysis indicates that there were no areas with visibility impairment a bove 30 dv that did not also exceed the secondary 24-hour PM 2.5 standard of 35 μg/m 3 . The updated memo concludes that the

results for 2009-2011 corroborat e the findings for 2008-2010.

Based on these analyses (Kelly et al., 2012a; 2012b), the EPA concluded with a high degree of confidence that having ai r quality that meets the 24-hour PM 2.5 standard of 35 μg/m 3 would be sufficient to ensure areas would not exceed 30 dv.

However, the EPA also recognizes that it is important to evaluate whether such a standard would be over-protective (i.e. more stringent than necessary to protect public welfare). The analyses presented in Kelly et al. (2012a; 2012b) indicat es that the 24-hour

PM 2.5 standard of 35 μg/m 3 would achieve more than the target level of protection of visual air quality (30 dv) in some areas. That is, when meeting a mass-based standard of 35 μg/m 3 , some areas would have levels of PM-re lated visibility impairment far below 30 dv. Thus, when considered by itself and without consideration of th e secondary standards adopted for purposes of non-visibili ty welfare effects, the 24-hour PM 2.5 standard of 35 μg/m 3 would be over-protective of visibility in some areas. Ho wever, it is important to note that as long as the current secondary 24-hour PM 2.5 standard of 35 μg/m 3 remains in effect, this overprotection for visibility w ould occur, regardless of whether a distinct secondary standard based on a visibility index set at 30 dv were adopted. These issues are discussed more fully in section VI.D of th e preamble which outlines the Administrator’s final conclusions on the secondary PM standards.

(4) Comment: A number of commenters noted that the proposed secondary standard for visibility would not offer si gnificant additional protection beyond the primary standard and yet would place an additional burden on states charged with monitoring and complying with the standard. These comment ers objected to the additional resource burden associated with implementing a standa rd which had, in their view, no practical

effect: “If the 24-hour PM 2.5 mass standard has the same eff ect as the visibility standard, crafting complex regulations to implemen t another standard seems redundant” (South Carolina DHEC, p. 3). Other commenters agreed: “A PM 2.5 -related Visibility Index appears redundant since the benefits achiev ed from the current primary and secondary

annual and 24-hour PM 2.5 standards already provide re ductions that would improveIV-47 visibility. Establishing a new PM 2.5 secondary standard for visibility would be an additional complication and burde n to the states that is not warranted” (Indiana DEM, p. 5). Similarly, Florida DEP argued that “While urban visibility is i ndeed a welfare issue, the standard as proposed would require unwa rranted resource effort s to verify, validate and calculate the visibility parameters, comp lete the designation process, and revise the State Implementation Plan (SIP). These effort s would be fruitless in 49 states where the standard is either currently met or will be met without additional regulation. It is inappropriate to promulgate a national standard to affect the air qua lity in three counties of one state (i.e., Californ ia)” (Florida DEP, p. 1).

Response: The EPA disagrees with commenters who stated that implementation concerns, in particular the additional res ource burden associated with implementing a distinct secondary standard, s hould alter the Agency’s decisi on making with regard to a standard to protect visibili ty. The EPA may not take the costs of implementation into account in setting or revising the NAAQS. The EP A’s decision not to establish a distinct secondary standard to protect against PM-relate d visibility impairment is based entirely on the degree of protection that would be affo rded by such a standard if adopted with the indicator, averaging time, form and level j udged appropriate by the Administrator, as compared to the degree of protection afforded by the existing secondary 24-hour PM 2.5 standard.

7. Specific Comments on Surrogacy Analysis

(1) Comment: Several commenters submitted additional analyses supporting their position that a 35 μg/m 3 24-hour PM 2.5 standard would provide at l east equivalent protection to a distinct 24-hour visibility standard within the range of levels proposed (API, Attachment 2, p. 8 and Attachment 3, p. 1).

Response: The EPA agrees with commenters that Kelly et al . (2012a) indicates that the existing 24-hour PM 2.5 standard provides at least an equivalent measure of protection a distinct 24-hour visibility index set at 30 dv with a 90 th percentile, 3-year average form, which the EPA judges appropriate. Importantly, the analysis performed by Kelly et al. (2012a) provides an area-by-area comparison of the relative degree of protectiveness of the existing secondary 24-hour PM 2.5 standard and the propose d distinct standard for visibility. The Kelly analysis also confirms that for each area examined, it is highly likely that a standard of 35 μg/m 3 would provide as much or grea ter protection than a standard based on a visibility index set at 30 dv. The EPA acknowledges that the conclusions from the additional analyses submitted by the commenters are supportive of the Agency’s

decisions to retain the current suite of secondary PM standards and to not establish a distinct secondary standard fo r protection from visibility impairment. However, the EPA did not rely upon these additional analyses from the commenters to inform its decisions. Rather, the agency based its conclusions on the analysis performed by Kelly et al. (2012a).

(2) Comment: Three environmental commenters (Appalachian Mountain Club, National Parks Conservation Association, and Earthj ustice) made several comments that questioned the technical analysis of the Kelly et al. memo (2012a) that provided theIV-48 justification of the surrog acy policy, specifically the ar ea by area evaluation where EPA compares the design values of various areas to see if areas that attain the mass-based standard are also likely to attain the dis tinct secondary standard to protect against visibility impairment. These commenters clai med that “the analysis actually reaffirms

that the mass-based standard is not a r easonable predictor, but EPA sweeps these concerns away with generalized and conclu sory claims. Figure 6 in the memo by Kelly, et al., shows again that the correlation between meeting the 24-hour mass standard and meeting the visibility standard varies significantly from region to region.” The commenters also stated that “Even more importa nt than the fact that there is no regional consistency in the correlation be tween the mass and visibility standards is the fact that any linear relationship does not exte nd to zero.” (AMC, et al., p. 11)

Response: As shown in Figure 6 of Kelly, et al. (2012a), the differences in 24-hr PM 2.5 and visibility index design valu es across different regions of the country do not detract from the EPA’s analysis as the commenters s uggest. While distinct regions of the country have distinct relationships between the 24-hr PM 2.5 design value and the secondary visibility index design value, th e relationship in all regions is such that an area that meets the secondary 24-hr PM 2.5 standard would also attain the proposed visibility index standard level of 30 dv, and all areas excep t the Industrial Midwes t would attain the proposed level of 28 dv. It is also not possi ble to examine the relationship for design

values near zero since such levels do not o ccur in the ambient atmosphere. However, this situation does not limit our analysis which focuses on the potential impact of sources on design values under realistic atmospheric conditions.

(3) Comment: These environmental commenters claim that the plot in Figure 6 of Kelly, et al. (2012a) “suggests that an area can be closer to a violation of the visibility standard

even when further from a violation of the ma ss standard. This is demonstrated by the fact that it is more likely to find an area viola ting a visibility standa rd of 28 dv and still meeting the mass-based standard of 35 μ g/m 3 than the other way around (i.e., violating the mass standard but meeting the visibi lity standard).” (A MC, et al., p. 11)

Response: The EPA does not believe that compari ng the closeness of the site-specific design values to each standard level is a valid way to examine the relationships between design values. Instead, the trend in the data shown in Figure 6 of Kelly et al. (2012a) from the lowest design values to the highest design values should be considered for each region since that trend is th e best guide to the likely re lationship between ambient mass concentrations and visibility index values in these regions. Trends in Figure 6 indicate that design values in each region would follow a path where exceedance of the 30 dv visibility index level would not o ccur without the secondary 24-hr PM 2.5 standard level of

35 μ g/m 3 also being exceeded. Moreover, the co mmenters are inappropriately comparing design values across different regions in the statement about areas being more likely to violate a visibility index level of 28 dv while meeting the secondary 24-hr PM 2.5 standard

level of 35 μ g/m 3 than the other way around.

(4) Comment: These commenters took issue with th e EPA’s suggestion that the regional

differences will be minimized over time because federal control measures will reduce sulfate levels in the Midwest. The commenters argued that the EPA had made anIV-49 unreasonable claim that in a few years the corr elation between attaining the two standards would get “better” so it is acceptable to allow the surrogacy approach now. The

commenters further stated that the EPA doe s not provide details on the time horizon or magnitude of such improvement. As a resu lt, the commenters conc luded that unless and until there is a change in this correlation, there is not reas onable basis for allowing the proposed surrogacy approach.

Response: The discussion of federal control me asures was not related to minimizing regional differences between 24-hr PM 2.5 design values and visibility index design values. Instead, the control measures were me ntioned to indicate that the few observed

cases in the Industrial Midwes t where the proposed visibil ity index level of 28 dv is exceeded in current air quality data while the 24-hr standard level is attained would be less likely to occur in the future due to ongoi ng control programs. Howe ver, the results of the analysis of 2008-2010 data presented in Kelly et al. 2012a (and the results of the reanalysis using updated 2009-2011 air quality data presented in Kelly et al. 2012b) indicate that, in all regions of th e U.S., an area that met the 24-hr PM 2.5 standard would also have attained the proposed visibility index standard le vel of 30 dv and thus support the use of the surrogacy approach.

(5) Comment: The commenters also added a footnot e stating that “As with other EPA regulatory decisions that have relied on EPA’s Cross-State Air Pollution Rule, the D.C.

Circuit’s recent vacature of the rule undermines EPA’s argument. See EMA Homer City Generation v, EPA, 2012 WL 3570721, (D.C. Cir. Aug. 21, 2012). Unless and until the court’s vacature is reversed, EPA has no basis for claiming that the rule will change the current mix of air pollutants.” (AMC, et al., p. 11)

Response: The EPA’s analysis and discussion as presented in Kelly et al. (2012a) does not rely on the Cross-State Air Pollution Ru le, nor are the conclusions drawn by the EPA with regard to the results presented in this analysis dependent on implementation of the

Cross-State Air Pollution Rule.

8. Legal Issues

Some commenters argued that the entire approach proposed by the EPA is inconsistent with the requirements of CAA section 109(b). They pointed to a number of different aspects of the proposal which in their view made it inco mpatible with the CAA. For example, UARG

stated:

In the past, EPA has always used a measure of PM mass as the indicator for both primary and secondary PM NAAQS. Such a standard is, as a general matter, consistent with the directive in the CAA that the NAAQS “specify a level of air quality” and targets for control the listed criteria air pollutant. CAA § 109(b)(2). The standard contained in EPA’s proposed rule does neither of these things. Instead, it woul d (1) regulate relative humidity, which is not a criteria pollutant; (2) fail to “specify a le vel of air quality” as required by section 109(b)(2) of the CAA; a nd (3) result in a standard necessitating nationally variable PM concentrations inst ead of a standard establishing a nationally uniform, minimally acceptable PM c oncentration. (UARG, p. 22-23)IV-50 Other commenters raised similar or related issues, arguing that the EPA improperly set a visibility standard, and not a PM 2.5 standard, and that NAAQS can onl y be set in terms of a level or concentration of the air pollu tant. Commenters also argued that an endangerment finding and air quality criteria w ould be needed before the EPA c ould set a standard based on PM components. Each of these comments is discussed below.

As a general matter, it should be noted that the EPA disagrees with the points raised by these commenters. While the EPA is not adopting the proposed secondary standard, this decision is not based on concern over the EPA’s authority to adopt a secondary standard such as the one proposed.

(1) Comment: Some commenters argued that the proposed standard is unlawful because it is

“not a PM 2.5 standard at all, but rather a visibility standard, and visibility is neither an air pollutant nor a criteria pollutant fo r which a NAAQS may be promulgated” (NMA/NCBA, p. 21). According to these co mmenters, the CAA requires that NAAQS be

established as limits on the concentration of an air pollutant in ambient air, not limits on the “identifiable effects” caused by that ai r pollutant. These commenters claimed that reduced visibility due to light extinction is not an air polluta nt but instead is an effect, noting that “the Act’s definition of ‘air pollu tant’ speaks in terms of specific substances or matter in the ambient air” (National St one Sand and Gravel Association, p. 8). The commenters pointed to the use of the term “air pollutant” in sec tions 109(a)(1)(A) and (b)(2) as support for their argument, as these provisions refer to sett ing standards for the “air pollutant” to address the effects associated with the presence of the air pollutant in the ambient air. They likewise pointed to sec tion 108(a)(2)’s reference to the presence of the air pollutant in the ambient air. Since reduced visibility is not an air pollutant, they argue the EPA cannot set a NAAQS that is a stan dard for visibility. They argue that the proposed secondary standard it is not a PM 2.5 standard as it does not limit the

concentration of PM 2.5 or any other fraction of particul ate matter in the ambient air and therefore is not an “ambient air qua lity standard” for any pollutant.

Response: The EPA disagrees with these commente rs. The proposed distinct secondary

standard was a standard for PM 2.5 , and was not a “visibility standard.” The proposed secondary standard was based on the mass concentration of PM 2.5 in the ambient air. The

standard was defined in terms of calculated PM 2.5 light extinction, which is based on the

measurement of the mass concentration of ambient PM 2.5 over a 24-hour period. Under the proposed approach, the measured mass c oncentration would be adjusted based on information on the speciated mass components of the PM 2.5 and the relative humidity, resulting in a calculated visibi lity index. The level of the visibility index, combined with the form of the standard and averaging time, would identify whethe r a level of ambient

mass concentration of PM 2.5 achieved the standard or not. Given any specific mass

concentration of ambient PM 2.5 , combined with informati on on speciation and relative humidity, it could be determ ined whether the specific mass concentration of ambient

PM 2.5 achieved the NAAQS. Hence, the proposed secondary NAAQS clearly specified acceptable levels of ambient mass concentration of PM 2.5

.

The combination of indicator, averaging time, form, and level of the proposed NAAQS is designed to provide the appropriate degree of protection from visibility impairmentIV-51 caused by ambient levels of PM 2.5 . It does this by calcula ting the light extinction

associated with ambient concentrations of PM 2.5 and specifying the level of acceptable

PM 2.5 mass concentration in terms of this calc ulation. However this does not change the fact that the standard is for the air pollutant PM 2.5 , and defines acceptable ambient levels of this air pollutant. It does not transform the standard into a “visibility standard” and not

a standard for PM 2.5

.

(2) Comment: One commenter argued that the EPA is re quired to “specify a level of air quality” under section 109(b)(2), which Congr ess intended as an acceptable concentration level of the air pollutant in the ambient ai r, noting that specif ication of acceptable visibility conditions is not the same as an acceptable air pollution concentration level. Citing American Farm Bureau v. EPA, 559 F .3d at 516, one commenter claimed that the court had affirmed that “the NAAQS—whet her primary or secondary—is a mass-based standard” (Nevada DEP, p. 5). Commenters also refer to the legisl ative history of the 1970 amendments, referring to NAAQS as setting the “maximum permissible ambient air level” for an air pollutant. The commenters ar gue that the proposed secondary standard is improper because it would not limit the concentration of PM 2.5 or any fraction of PM in ambient air, but would improperly se t a limit on visibility effects.

Response: The EPA disagrees with these commen ters. The text of sections 108 and 109 does not support the limited in terpretation commenters suggest . Instead, these provisions provide the EPA with significant discretion in determining the metric for air quality that is appropriate to achieve th e required degree of protect ion of public welfare. The commenters’ interpretation would improperl y limit this discreti on, interfering with achieving the goals of section 109(b).

The term “concentration” typically means so me measure of relative content, including relative measures such as mass per unit of volume or parts per million. The EPA has often used such metrics to define the NAAQS, largely because the scie ntific evidence of health or welfare effects supporting the NAAQS typically use such metrics in air pollution studies. For example, the current secondary standards for PM are defined in

terms of the concentration of PM 2.5 and PM 10 in the ambient air, measured as the dried mass of the particulate matter per unit of ai r. However section 109(b) does not require that a NAAQS be defined this way.

Sections 109(a) and (b) both use the general term “air quality” when discussing the EPA’s obligation to set NAAQS. The NAAQS ar e clearly national ambient “air quality” standards under section 109(b), which speci fies that the primary NAAQS “shall be ambient air quality standards” and the sec ondary NAAQS “shall speci fy a level of air quality.” Both the primary and secondary NAAQS are to be based on the “air quality criteria,” which are to accurately reflect the latest scientific knowledge on the effects on public health and welfare asso ciated with “the presence of such air pollutant in the ambient air, in varying quan tities.” Section 109(b ), 108(a)(2). Congress spoke in broad terms, tasking the EPA with assessing the latest scientific knowledge about the public

health and welfare associated with the presence of the po llutant in the air, without limiting this to consideration of only those effects associated with one or more measures of concentration of the air po llutant. Congress referred to a ny and all effects associatedIV-52 with the presence of the pollutant in the ambien t air, not just the e ffects associated with the concentration of the polluta nt in the ambient air. Based on this knowledge, the EPA is required to set standards for the quality of th e air that will provide the appropriate degree of protection from these health and welfare effects, withou t limitation on how to measure or define air quality. While concentration in the air has typically be en an appropriate way to set a standard to achieve these requirement s, the more general terms used in section 108(a) and 109(b) do not limit the EPA to using concentration as the only way to measure air quality for purposes of setting a NAAQS. Th e EPA is charged with setting air quality standards, and has the discreti on under section 109(b) to c hoose the metric for defining air quality that is appropria te to address the health or welfare effect at issue.

Congress did refer to “concentration” in ce rtain situations. In section 109(c) Congress required the EPA to set a primary NAAQS for NO 2 concentration over 3 hours. This addressed Congress’ concern ove r whether the then current NO 2 standard, which used concentration as a metric, provided adequate protection. Congress also called on CASAC

to advise the Administrator on the relative contribution to “air po llution concentrations” of natural and anthropogenic sources, under section 109(d)(2)(C )(iii). This information is in addition to the advice CASAC is required to provide concerning appropriate revisions to the “air quality criteria” and to the NAA QS under section 109( d)(2)(B). While these provisions refer to ambient concentrations of pollutants, this reflects the EPA’s standard practice to date in setting NAAQS, and none of them change or limit the range of discretion provided under section 109(b) in se tting NAAQS. They do not change the fact that the EPA is to set “air quality” standard s, and is not limited to “air concentration” standards. The reference in the legislative history to a maximum permissible ambient air level for the pollutant also does not limit the EP A to a level of air pollutant concentration, as compared to a different metric for specifyi ng the level of air quality, if that is judged to be appropriate.

(3) Comment: Some commenters argued that the pr oposed standard improperly regulates relative humidity because it is included in th e calculation to determine the value of the visibility index. According to these commenters, the CAA allows the EPA to control criteria air pollutants through the NAAQS progr am, but not other various substances. The commenters stated that the EPA recognized this in the last review, treating humidity as a confounding factor and consideri ng addressing it by measuring PM 2.5 mass-based concentration over the midday hours, when humi dity would have the least effect. This would target the effects caused by PM, and not by humidity. Referring to American Farm Bureau v. EPA, 559 F.3d 512, 528 (D.C.Cir. 2009) and 77 Fed. Reg. at 38979 n.153. UARG contested the proposed calculated visibi lity index as it does not approach relative humidity as a confounding factor but instead “em braces it and treats it as if it were a PM effect” (UARG, p. 24).

Response: Contrary to the claims of these commenters, the use of calculated PM 2.5 light extinction does not regulate relative humidity. The proposed secondary standard would define acceptable levels of ambient PM 2.5 , not acceptable levels of relative humidity. In addition, section 108 explicitly requires that the air quality criteria include information on the atmospheric conditions that can alter the effects of the air pollutant on public health or welfare, and relative humidity certainl y has this kind of impact. Section 109(b)IV-53 requires that the standard be based on the air quality crite ria, indicating that this

information can and should be taken into account in setting th e standard. Including relative humidity as an adjustment factor in the calculation of PM 2.5 light extinction is a reasonable and straightforward way to use the scientific information in the air quality criteria in establishing a sta ndard to provide protection fr om visibility impairment.

The EPA disagrees with commenters that the EP A’s treatment of humidity in this review is inconsistent with its handling of this issue in the previous review. In the last review, the

EPA considered a distinct PM 2.5 mass-based secondary standar d. In that context, limiting

the measurement of PM 2.5 mass concentration to the mid-day hours when relative humidity had the least impact would prom ote the correlation between measured PM 2.5 mass concentration and light extinction, which would promote achievement of a relatively consistent degree of visibility protection across the country. However in this rulemaking the proposed calculated PM 2.5 light extinction standard achieves a consistent degree of visibility protection by directly accounting for humidity, in a scientifically defensible manner. The goal has not changed – achieving the desire d degree of protection across the country. What has ch anged is that calculated PM 2.5 light extinction is a more direct and scientifically appropria te way to achieve that result.

Finally, it should be made clear that wa ter is not a separate compound from PM 2.5 that confounds the impact PM 2.5 has on light extinction. As de scribed in the Integrated Science Assessment, “PM is the generic term for a broad class of chemically and physically diverse substances that exist as di screte particles (liqui d droplets or solids) over a wide range of sizes” (U.S. EPA, 2009a , p. 1-4). “Particles composed of water soluble inorganic salts (i.e., ammoniated sulfate, ammonium nitrate, sodium chloride, etc.) are hygroscopic in that they absorb water as a function of relative humidity to form a liquid solution droplet. Aside from the chemical consequences of this water growth, the droplets become larger when relative humidity increases, resulting in increased light scattering. Hence, the same PM dry con centration produces more haze” (U.S. EPA, 2009a, p. 9-6). Thus water is not a compound that is separate and apart from the particle that acts as an extraneous confounding factor. The effect of relative humidity occurs after the water becomes part of the particle. Certain water soluble salts absorb water and the resulting particle is larger in size and scatte rs more light, increasing the visibility impact of the particle. But the particle is still a PM 2.5 particle. The fact that the PM NAAQS traditionally uses a measurement of the dried mass of the particles as the metric for the standard does not change the fact that the particles in th e air include li quid droplets and particles that have increased in size because of absorption of water. These ambient PM 2.5 particles are what are in the air and impacti ng visibility, not just the dried mass of PM 2.5 that is measured in the laboratory and is currently used as the indicator for the PM NAAQS. Thus, the commenters improperly claime d that the proposed secondary standard regulates water or rela tive humidity, and not PM 2.5 , when in fact the proposed secondary

standard accounts in a scientific ma nner for the fact that some PM 2.5 particles are larger in size and have a greater impact on light exti nction when the relative humidity increases.

(4) Comment: The commenters also stated that the use of a calculated visibility index, and

the failure to exclude the effects of humidity, would result in acceptable PM concentrations that vary across the nati on. These commenters claimed that such aIV-54 standard is inconsistent with the requiremen ts of the CAA because the proposed approach fails to establish a nationally uniform PM concentration standard. For example, API argued that the proposed visibility index appr oach is “essentially sp ecifying levels—not a level—of air quality” (API, p. 29). UARG agree d, and stated that the Act “requires that criteria pollutant concentrations throughout the nation reach, at th e least, a single, specified ambient concentration level” ( UARG, p. 25, emphasis in original). The commenters argue that a PM 2.5 visibility index standard cannot provide equal protection nationwide due to geographic variation in key f actors such as relative humidity that affect level of particles allowed in different areas. The commente rs noted that establishing a single national level for the PM 2.5 visibility index would n ecessarily result in unequal acceptable PM 2.5 levels in different areas of th e country, with lowest allowable PM 2.5 levels in urban areas in the Southeast and highest allowable levels in the arid West. UARG recognized that under section 108 the ai r quality criteria are to “address those variable factors (including atmospheric conditions) which of themselves or in combination with other factors may alter the effects on public health or welfare of such air pollutant,” but stated th at while section 108 “allows” th is, it has no bearing on this issue. Instead, the commenter stated that the EPA may take such information into account in setting a permissible con centration of the pollutant th at is uniform and national (UARG, p. 25).

Response: The EPA disagrees with commenters th at section 109(b) requires that the NAAQS set a single, specified ambient concen tration that is nati onally uniform across the country. As discussed above, the text of se ction 109(b) does not specify this limitation of a single national acceptable concentration. Instead the secondary NAAQS is to specify a level of air quality that achieves the a ppropriate degree of protection. The proposed secondary standard would do just that – specif y a level of air quality, defined in terms of

calculated PM 2.5 light extinction, that w ould achieve the desired degree of protection. The fact that this results in varying allowable levels of PM 2.5 mass concentrations is not

inconsistent with the Act. The D.C. Circuit recently approved such a result. In the last

review of the PM 10 primary NAAQS, the court approve d the EPA’s choice of an indicator that was designed to allow varyi ng levels of acceptable coarse PM. The court

stated that:

The industry petitioners ne xt argue that the 150 μg/m 3 standard for PM 10 will result in arbitrarily varying levels of coarse PM, and that the agency should instead have used a

PM 10-2.5 indicator. The EPA does not dispute that using the PM 10 indicator will result in coarse PM levels that vary within the limit of 150 μg/m 3 . As the EPA explains: “Because

the PM 10 indicator includes both coarse PM (PM 10-2.5 ) and fine PM (PM 2.5 ), the

concentration of PM 10-2.5 allowed by a PM 10 standard set at a singl e level declines as the

concentration of PM 2.5 increases. Thus, the level of co arse particles allowed varies depending on the level of fine particles present.” Id. at 61,195.

Although the EPA acknowledges that a PM 10 indicator will result in varying coarse PM levels, it does not agree that the variance will be arbitrary. The EPA agrees with the industry petitioners that prot ection from coarse particles s hould be targeted at urban areas, where coarse particles have been show n to pose the greatest danger. Id. at 61,194. But the agency argues that ta rgeting of urban areas is effectively accomplished by usingIV-55 an indicator that permits the varying levels that the industry petiti oners challenge. ... Id. at 61,195-96 (citations omitted). In other words: “The varying levels of coarse particles allowed by a PM 10 indicator will therefore target pr otection in urban and industrial areas

where the evidence of adverse he alth effects associated with exposure to coarse particles is strongest.” Id.

The EPA also offers a further rationale for tying the stringency of coarse PM regulation

to increases in the level of PM 2.5 . ... EPA argues that it is “logical to allow lower levels of coarse particles when fine particle concentrations ar e high. . . . [I]nclusion of PM 2.5 in

the PM 10 indicator for purposes of coarse particle protection would appropriately reflect

the contribution that contaminants emitted in fine particle form can make to the overall health risk posed by co arse particles.” Id.

In sum, we find that the EPA has provided a reasonable explanation for its decision[ ] ... to utilize a standard that allows targeted variance in coarse PM levels in an inverse relationship to the amount of fine PM in the air. American Farm Bureau v. EPA, 559 F.3d 512, 534-5 (D.C.Cir. 2009).

A similar result applies here. Under the proposed secondary standard there would be a single level of air quality specified for th e NAAQS. The standard would apply across the nation; it would not be a regi onal standard. The proposed st andard would be the same standard everywhere—the acceptable level of mass concentration of PM 2.5 would be defined the same way across the nation, us ing the same method of calculating the

allowable concentration of PM 2.5 . The same degree of protection from visibility impairment would apply across the count ry. While the allowable amount of PM 2.5 could vary, this would be a reasoned way to achie ve the desired degree of protection from visibility impairment. The requirements of section 109(b) would be satisfied.

(5) Comment: Some commenters opposed to the proposed distinct secondary standard argued

that in order to base a standard on measured levels of several speciated substances, the EPA must first make an endangerment finding and issue air quality criteria for each of the speciated substances incl uded in the calculation of PM 2.5 light extinction. According to these commenters, “EPA cannot use NAAQS to indirectly regulate multiple substances which are not criteria pollutants under the gu ise of establishing a visibility standard” (NMA/NCBA, p. 21). Noting that air quality crite ria for particulate matter were issued in 1969, NMA/NCBA argued that the 1969 Criteria Document “did not establish air quality

criteria for individual constituents that occu r in particle form, instead it established criteria for particulate matter as a whole” (p. 27 ). In light of the fact that criteria have never been issued for “individual speciate d components of particulate matter,” these commenters argued, “if EPA wishes to promulgate a rule such as its secondary visibility NAAQS, it first must make a finding that the speciated components listed in Appendix N endanger public health or welfare and then issu e an air quality criteria document for those components” (NMA/NCBA, p. 29). According to these commenters, the approach the EPA adopted in promulgating a NAAQS for lead supports this view:

When EPA promulgated a NAAQS for lead, an individual substa nce in particle form, it did not assert that an endangerment finding or criteria document for leadIV-56 was unnecessary because lead was already covered by the PM Criteria Document. Instead, EPA complied with the Section 108 and 109 NAAQS prerequisites for lead, just as it must do fo r Appendix N substances if it intends to promulgate a NAAQS for those substances. ... [In 1976], EPA listed lead as an air pollutant that adversely affected public health or welfare, issued an air quality criteria document for lead, and promulgated a NAAQS for lead. 43 Fed. Reg. 46246 (Oct. 5, 1976). (NMA/NCBA, p. 29)

Response: The EPA strongly disagrees with comment ers the Agency would need to issue a separate endangerment finding and establish ai r quality criteria for each of the speciated

substances included in the calculation of PM 2.5 light extinction prior to setting a distinct secondary standard based on a PM 2.5 visibility index, as prop osed. The proposed standard

would set an allowable limit on ambient concentrations of PM 2.5 . Information on both the speciated components of PM 2.5 and the relative humidity aff ect how much light extinction

is associated with a ny specific level of PM 2.5 , but the standard would be for PM 2.5 . The

D.C. Circuit has made it clear that PM 2.5 , just like PM 10 and TSP before that, is an appropriate subset of PM for the EPA to focus on in setting the NAAQS based on the

scientific evidence before the EPA. This fo cus of the NAAQS does not make the subset a new pollutant that requires listing and ne w air quality criteria under section 108 before setting a NAAQS. American Trucking A ssociation et al. v. EPA, 175 F.3d 1027, 1055 (D.C.Cir. 1999). Commenters’ inte rpretation would apply to PM 2.5 as well as to components of PM 2.5 , and is inconsistent with the AT A decision. In addition, it is clear that the current air quality criteria do address the scient ific basis for calculating PM 2.5 light extinction as the EPA proposed (U.S. EPA, 2009a, pp. 9-5 to 9-8).

(6) Comment: UARG argued that the EPA has in the past recognized that the secondary NAAQS is an inappropriate vehicle for regul ating PM-related visibi lity, referring to 62 Fed. Reg. at 38680, including fn 49. UARG claimed the same situation continues, and the EPA has not provided a valid basi s for changing this conclusion.

Response: UARG mischaracterized the EPA’s past decision-making. In past reviews the

EPA has been clear that the EPA should take into account the existence of the visibility program under section 169A, the regional ha ze program, when considering a secondary NAAQS and should not treat the secondary NAAQS as the sole mechanism to address visibility impairment across the country. That is the approach the EPA has taken in this and prior reviews. See 77 FR at 38990.

9. Other Issues

(1) Comment: A large number of commenters expr essed confusion and concern over differences between the proposed visibil ity index standard and the Regional Haze Program. This included commenters who supporte d setting a distinct secondary standard to protect visibility as well as those opposed to setting such a standard. Many of these comments focused on concerns relating to im plementation challenges that might be caused by overlap between the programs. These concerns included:

 Visibility impairment would be assessed differently under the two approaches due to differences in the way light extinction is calculated, including different IMPROVEIV-57 equations and differences in the inclusi on and weighting of specific species and components. This would mean having two di fferent regimes for managing visibility impairment in the exact same location.

 Since data from the IMPROVE monitori ng network would inform nonattainment designations, as well as an area’s obligati ons under the Regional Haze Program, there

could be considerable confusion over how to draw nonattainment boundaries and what requirements would affect la rge sources in rural areas.

 There would be a large resource burden a ssociated with maintaining two different programs aimed at protecting visibili ty in the same geographic area.

Response: Though the EPA’s decision not to estab lish a distinct secondary standard for protection from visibility impairment at this time renders these comments moot, the EPA disagrees with commenters in principle th at implementing two programs for visibility protection simultaneously would be overly burde nsome. Since the same data can be used to calculate both visibility impairment under the Regional Haze approach and the proposed visibility index, the additional calc ulation burden for stat e and local agencies would be light. Also, to the extent that ther e is any difference in terms of the emissions control obligations the two different programs would impos e upon state and local areas, this is likely appropriate give n the extent and nature of vi sibility impairment in those areas. The EPA notes that in general, there is likely to be substantial overlap in the control strategies a state or local area would pursue under either program.

(2) Comment: Noting concerns about overlap with the Regional Haze Program, some commenters argued that a visibility NAAQS should not apply to rural areas. The Department of the Interior re quested that the EPA clearly de fine the geographic area to which the visibility index standard would be applicable, and suggest ed that Class I and Class II areas should generally be excluded from the standard.

Response: The EPA disagrees with these commente rs that it would be appropriate to exclude some areas from coverage under a secondary NAAQS to prot ect visibility. CAA section 109(b) requires the Agency to establish national standards to protect the public welfare, and that the specific requirements laid out in the proposal for the distinct secondary standard would ensure that the pr otection it afforded would be appropriately targeted toward urban areas so that it coul d work in conjunction with—not be in conflict with—the Regional Haze Program under sec tions 169A and 169B of the CAA. While it is true that the Regional Haze Program unde r sections 169A and 169B of the CAA also targets visibility protection (focusing on Fede ral Class I areas), the EPA notes that areas affected by both programs would find substan tial complementarities among the controls necessary to meet the requirements associated with each program.

Comment: A number of commenters questioned the need for a distinct secondary standard to protect visibilit y, arguing that the existing primary PM standards combined with the Regional Haze Program ensured adequate protection of visibility, even in urban

areas.

Response: The EPA notes that the objectives of the Regional Haze program are distinctIV-58 from the objectives of the proposed seconda ry standard. While the Regional Haze program is designed to eliminate man-made im pairment of visibility in Federal Class I areas over the course of several decades, a distinct secondary standard for PM-related visibility impairment would be focused on providing a nationally applicable level of protection for all areas, partic ularly urban areas which do not receive targeted protection under the Regional Haze Program. Moreover, th e metric used to assess visibility impairment differs between the two programs precisely because each program is aimed at a different aspect of the problem. Recogni zing the importance of fresh emissions for urban visibility, the Visibility Assessment fo cused on visibility impairment as measured by the original IMPROVE equation because “the original version is considered more representative of urban situati ons when emissions are still fresh rather than aged as at remote IMPROVE sites” (U.S. EPA, 2010b, p. 3-19). The Regional Haze Program, on the other hand, has shifted to a revised IM PROVE algorithm more suited to remote

locations. While this difference is discussed in more detail with regard to comments on indicator, above, and in section VI.C.1.b of th e preamble, the result is that each program would appropriately measure those aspects of visibility impairment most closely related to the problem the program is trying to prevent.

Thus, the EPA disagrees with commenters who st ated that a distinct standard to address visibility impairment as proposed would i nherently conflict w ith the Regional Haze Program or that it would be appropriate to draw geographical dis tinctions that would explicitly exclude some areas (e.g., Class I areas) from the NAAQS. The EPA notes that the CAA requires that NAAQS be national in scope, and that the specific requirements laid out in the proposal for the distinct secondary standa rd would ensure that the protection it afforded would be appropriately targeted toward urban areas so that it could work in conjunction with—not be in conf lict with—the Regional Haze Program under

sections 169A and 169B of the CAA.

(3) Comment: The EPA received numerous comments on data handling related to the proposed secondary standard for PM-rela ted visibility impairment, including minimum number of PM-component measurement days, treatment of missing data, rounding or truncation prot ocols and assignment of relative humidity weighting factors to

monitored locations.

Response: In light of the Agency’s decision not to establish a distinct secondary standard to address visibility impairment at this time, these concerns are moot.

(4) Comment: The EPA received numerous comments on monitoring related to the proposed secondary standard for PM-related visibility impairment, including the use of IMPROVE and CSN methods, the designation of these me thods as Federal Reference or Federal Equivalent Methods (FRM/FEM), preference of alternative methods such as a direct measurement of light extinction, network de sign, data reporting, data validation, and reporting requirements for IMPROVE and CSN data.

Response: For the reasons stated in section VI of the preamble to the final rule, EPA is not establishing a di stinct secondary PM 2.5 NAAQS. Consequently, th e final rule does not include requirements for monitoring to suppor t such a standard and these concerns areIV-59 moot.

C. Specific Comments on Proposed Secondary PM Standards for Non-Visibility

Welfare Effects

Relatively few commenters addressed the pr oposal to retain the existing suite of secondary PM standards to address non-visibility welfare effects. Those who did comment either raised concerns on the proposal to retain the current secondary annual standard, or raised concerns about whether the existing secondary standards offered suffici ent protection against impacts on climate.

(1) Comment: Some commenters opposed the proposal to retain the current secondary annual

PM 2.5 standard of 15 μg/m 3 in light of the proposal to revise the primary annual PM 2.5 standard to a level between 12-13 μg/m 3 . Expressing concern over the implications of this decision for the air quality planning ob ligations of states, these commenters argued that the EPA should revise the secondary PM 2.5 standards to be equivalent in all respects to the primary PM 2.5 standards. For example, the Amer ican Association of State Highway and Transportation Officials (AASHTO) supported “retaining secondary standards that are consistent with the primary standards in order to reduce the complexity of the transportation and air quality planning processe s, as well as the transportation conformity process” (AASHTO, p. 3). Thus , if the EPA were to adopt a lower level for the primary

annual PM 2.5 standard, the commenters recommended that the EPA adopt this same lower level for the primary secondary PM 2.5 standard as well.

Response: As discussed in sections VI.B.2 a nd VI.C.2 of the preamble on non-visibility welfare effects, the EPA lacks an appropriate scientific basis for revising the level of the secondary annual PM 2.5 standard. There is an absence of information that would support any different secondary standards for PM at this time. Comments related to the implementation challenges associated with di stinct primary and s econdary standards are

not relevant to the Administrator’s final deci sions regarding what st andards are requisite to protect the public welfare. Therefore, the EPA continues to conclude that it would be appropriate to retain the curre nt suite of secondary PM sta ndards to address non-visibility welfare effects, as proposed.

(2) Comment: With regard to the impacts of partic ulate matter on climate, one commenter

cited a number of recent studies that consid ered mobile source bl ack carbon emissions and associated climate impacts, and urged the EPA to protect the public welfare by setting “higher standards fo r gasoline quality” (Urban Air Initiative, p. 4). This commenter did not advocate specific secondary NAAQS to address climate impacts of

PM.

Response: The commenters concerns are not rele vant to this rulemaking, which is limited to determining the s econdary NAAQS for PM under se ction 109(b) of the Act.

(3) Comment: The Center for Biological Di versity urged the EPA to “set a separate limit for

black carbon within the overall PM 2.5 standard” to ensure that public welfare is fully protected “from the serious climate impact s of black carbon” (C enter for BiologicalIV-60 Diversity, p. 2). This commenter argued th at “[p]recaution is required for secondary NAAQS,” citing American Trucking Associ ations, Inc. v. EPA, 283 F.3d 355, 369 (D.C. Cir. 2002):

[N]othing in the Clean Air Act requires EPA to wait until it has perfect information before adopting a protect ive secondary NAAQS. Rather, the Act mandates promulgation of secondary standa rds requisite to pr otect public welfare from any “anticipated adverse effects a ssociated with” regulated pollutants, 42 U.S.C. § 7409(b)(2) (emphasis added), sugge sting that EPA must act as soon as it has enough information (even if crude) to “anticipate[]” such effects[.]

The commenter stressed the growing scientif ic evidence regarding the impacts of black carbon on climate, and argued that the EPA’s pr oposal ignores important research studies published within the last five years which provide improved estimates of the radiative forcing associated with black carbon, and the effects of bl ack carbon on snow and ice, the Arctic climate, water availability and clim ate “tipping points.” The commenter also noted that reductions in cooling aeros ol species, particularly sulf ate, due to pollution control programs are leading to an “unmasking” of the true extent of warming due to the accumulation of greenhouse gases in the atmos phere. The commenter argued that this unmasking effect can be offset by ensu ring “that sufficient black carbon reductions accompany reductions in overall aerosol pollu tion” (Center for Biological Diversity, p. 10).

Response: The EPA agrees with the commenters’ assertion that the scientific information about the impacts of aerosol species on climate is developing rapidly, and that understanding of the magnitude of aerosol effects on climate and the contribution of individual aerosol components to those eff ects has improved substantially over the past decade. The EPA also agrees that certain sp ecies, in particular black carbon, play a significant role in multiple aspects of climate. The Policy Assessment recognized that “Aerosols can impact glaciers, snowpack, regional water supplies, precipitation and climate patterns,” and may contribute to th e melting of ice and snow, a decrease in surface albedo, and climate impacts in the Arct ic and other locations (U.S. EPA, 2011a, p. 5-9). The contribution of black carbon to thes e effects is discussed in detail in the EPA’s recent Report to Congress on Black Carbon (U.S. EPA, 2012c). In particular, black carbon plays an important role in heating the lower atmosphere by absorbing incoming solar radiation and outgoing terrestr ial radiation, i.e. vi a “direct” radiative forcing.

However, the EPA disagrees that there is suffi cient information available at this time to establish a NAAQS to protect against the clim ate impacts associated with current ambient

concentrations of black carbon or other PM constituents. While the Integrated Science

Assessment concluded that “a causal relati onship exists between PM and effects on climate, including both direct effects on radiativ e forcing and indirect effects that involve cloud feedbacks that influence precipitation formation and cloud lifetime” (U.S. EPA, 2009a, section 9.3.10), it also identified substan tial remaining uncertainties with regard to

the contribution of individual ae rosol species to these climate effects. The contribution of individual aerosol components to total aerosol direct radiative forci ng is more uncertainIV-61 than the global average (U.S. EPA, 2009a, section 9.3.6.6), and the indirect effects of aerosols and aerosol components remain highly uncertain, in particular with regard to their complex interactions with clouds.

The EPA notes the substantial remaining uncer tainties and gaps w ith regard to the climate impacts of PM components, in cluding black carbon. These include the

uncertainties associated with the spatial and temporal he terogeneity of PM components that contribute to climate forcing; the un certainties associated with measurement of aerosol components; the inadequate cons ideration of aerosol impacts in climate modeling; and the currently insufficient data on local and regional microclimate variations and the heterogene ity of cloud formations. As a result, the EPA continues to

conclude that it is not currentl y feasible to conduct a quantita tive analysis for the purpose of informing revisions of the current seconda ry PM standards based on climate, and that

there is insufficient information at this time to base a national ambient standard on climate impacts associated with current ambi ent concentrations of PM or any of its

constituents.

(4) Comment: The Center for Biological Di versity also argued that the EPA did not consider the negative impacts of clim ate change on public health adequately in the proposal.

Response: Given the large remaining uncertainti es about the impact of aerosols on climate, there is even greater uncertainty with regard to how aerosol-induced climate change will affect public healt h. At this time, it is not possible to estimate the extent to which aerosols in general, let alone partic ular aerosol components, contribute to the

occurrence or exacerbation of adverse health outcomes due to climate change. The EPA therefore disagrees with the Center for Biol ogical Diversity’s clai m that the EPA should pursue black carbon reductions for purposes of reducing the impacts of climate change on public health.

(5) Comment: The Center for Biological Di versity stated that the EPA had an obligation to address the impacts of black carbon in the PM NAAQS, despite the remaining uncertainties. The commenter pointed to th e U.S. EPA’s report to Congress on Black Carbon (U.S. EPA, 2012X), stating that the “report shows that EPA is aware of the climate science and public health information that point to the importance of addressing black carbon pollution. EPA must use this info rmation in its relevant decisionmaking” (p. 13).

Response: As noted above, the EPA disagrees th at there is sufficient information available at this time to establish a NAAQ S to protect against the climate impacts

associated with current ambient concentrations of black carbon or other PM constituents. While the Integrated Science Assessment c oncluded that “a causal relationship exists between PM and effects on climate, including bo th direct effects on radiative forcing and

indirect effects that involv e cloud feedbacks that influen ce precipitation formation and cloud lifetime” (U.S. EPA, 2009a, section 9.3.10) , it also identified su bstantial remaining uncertainties with regard to the contribution of individual aerosol sp ecies to these climate

effects. The contribution of individual aerosol components to total aeros ol direct radiative forcing is more uncertain than the globa l average (U.S. EPA, 2009a, section 9.3.6.6), andIV-62 the indirect effects of aerosols and aero sol components remain highly uncertain, in particular with regard to their complex in teractions with clouds. The EPA’s Report to Congress on Black Carbon provides an exte nsive discussion of these uncertainties.

(6) Comment: The Center for Biological Diversity challenged the uncertainties cited by EPA with regard to the climate impacts of aerosol s generally, arguing that they “do not apply to the regulation of black car bon” (p. 14). Specifically, the co mmenter stated that “there are significant anthropogenic s ources of black carbon that cont ribute a large proportion of total black carbon emissions”; that “there is enough information related to black carbon’s impact to know that global temperatures wi ll rise due to black carbon emissions”; that spatial and temporal heterogeneity in black carbon emissions do not matter for estimating likely climate effects; that “[b]lack car bon’s negative climate impacts do not depend upon

details of cloud interactions w ith aerosols”; and that the EPA does not need to be able to quantify the health or climate benefits precise ly to know that it is appropriate to control black carbon as a specific component of PM under the CAA (Center for Biological Diversity, pp. 14-15).

Response: The EPA disagrees with the commenter’s assertion that the uncertainties about

the role of aerosols in climate do not a pply to black carbon. The Integrated Science Assessment identified substantial remaining un certainties with regard to the contribution of individual aerosol species to climate eff ects. The contribution of individual aerosol components to total aerosol di rect radiative forcing is mo re uncertain than the global average (U.S. EPA, 2009a, section 9.3.6.6), a nd the indirect effects of aerosols and aerosol components remain highly uncertain, in particular with regard to their complex interactions with clouds. Thus, the uncerta inty about black carbon’s effects remains significant, just as for other aerosol species.

The EPA disagrees that “black carbon’s negative climate impacts do not depend upon

details of cloud interactions with aerosols” and that the uncertaint ies associated with climate impacts of aerosols generally do not apply to black carbon. In fact, the EPA has pointed to cloud interactions as the area of greatest uncertainty w ith regard to black carbon: recognizing that black ca rbon affects cloud reflectiv ity (albedo), lifetime, and stability as well as precipita tion, the Report to Congress on Bl ack Carbon noted that “few quantitative estimates of these effects are ava ilable, and significant uncertainty remains. Due to all of the remaining gaps in sc ientific knowledge, it is difficult to place quantitative bounds on the forcing attributable to [black carbon] impacts on clouds at present” (U.S. EPA, 2012c, p. 4). The Report acknowledged that “most estimates of the forcing from aerosol indirect effects are based on all aero sol species (e.g. total PM) and are not estimated for individual species (e .g., BC alone)” (U.S. EPA, 2012c, p. 40). The Report concluded that it remain s unclear the extent to which black carbon contributes to

the overall aerosol indirect eff ect, and did not assign any centr al estimate or even a range of possible values to the role of black carbon in th e overall aerosol indi rect effect. With regard to black carbon’s net contribution to climate, ther efore, the Report concluded:

The direct and snow/ice albedo effects of BC are widely understood to lead to climate warming. However, the globally av eraged net climate effect of BC also

includes the effects associated with cloud interactions, which are not wellIV-63 quantified and may cause either warmi ng or cooling. Therefore, though most estimates indicate that BC has a net warming influence, a net cooling effect

cannot be ruled out. It is also important to note that the net radiative effect of all aerosols combined (including sulfates, nitrates, BC and OC) is widely understood to be negative (cooling) on a global average basis. (U.S. EPA, 2012c, p. 3)

The Report to Congress on Black Carbon also stressed the importance of considering coemitted PM species, such as SO 2 and NOx, in evaluating the benefits of black carbon mitigation options. Noting that many of these co-emitted particles and gases have a cooling influence on climate, the Report noted the difficulty of estimating the net effect of various mitigation measures on net radiative forcing or other climate variables. The EPA concluded that the location and timing of emissions reductions would be critically important for achieving climate benefits, a nd that “more research is needed on the

benefits of individual control measures in specific locati ons to support policy decisions made at the national level” (U.S. EPA, 2012c, p. 140). Thus, the EPA disagrees with the Center for Biological Diversity’ s claim that spatial and temp oral heterogeneity in black carbon emissions do not matter for estimating lik ely climate effects, and continues to believe that being able to quantify the clim ate impacts of various aerosol species, alone and in combination, is essential for inform ing any possible revisi ons to the current secondary PM standards based on climate.

(7) Comment: The commenter noted that the United St ates participates in a number of

international forums that ha ve recognized the need to take action on black carbon, and argued that the U.S. has “an obligation under the Gothenburg Protocol to address black carbon pollution” (Center for Bi ological Diversity, p. 13).

Response : In May, new provisions pertaining to particulate matter were added to the Gothenburg Protocol under the Conventi on on Long-Range Transboundary Air Pollution. Amongst other things, these provisions encourag e parties to develop national inventories and projections for black carbon, and to “give priority” to black carbon when implementing measures to control PM. However, the EPA notes that the U.S. has not yet

ratified the PM amendments to the Goth enburg Protocol, and furthermore, these amendments do not require action specifi cally to reduce black carbon, but rather encourage countries to take such actions volun tarily within the context of their broader PM reduction strategies. Thus the EPA disagrees with the commenter that the U.S. has an “obligation” to reduce black carbon under the Gothenburg Protocol, or that it has “agree[d] to choose mitigation options for pa rticulate matter that focus on black carbon reductions” under the Protocol (Cente r for Biological Diversity, p. 13).

(8) Comment: The Center for Biological Di versity concluded that the current size-based PM mass standard “is insufficient to fully protec t health and welfare,” and that the EPA was obligated to establish a specific limit on black carbon as a component of PM. The commenter argued that “Black carbon must be regulated separately and in addition to

PM 2.5 because absent separate standards sulfates and nitrates may be more likely to be mitigated than the black carbon component of PM” (Center for Biological Diversity, p. 17). To support this point, the commenter cite d the conclusion in the Policy Assessment

that:IV-64 The current standards that are defined in terms of aggregate size mass cannot be expected to appropriately target cont rols on components of fine and coarse particles that are related to climate forc ing effects. Thus, the current mass-based

PM 2.5 and PM 10 secondary standards are not an a ppropriate or effective means of focusing protection against PM-associated climate effects due to these differences in components. (U.S. EPA, 2011a, p. 5-11).

The commenter also noted that existing regul ations on diesel engines, which are the largest source of black car bon in the United States, do not affect existing engines and vehicles, and stated that “T he NAAQS program is one of the few opportunities to reduce black carbon from existing engines, industr ial and biofuel sources within the United States and rapidly reduce emissions from this pollutant” (Center for Biological Diversity, p. 18).

Response: While the EPA agrees with the commenter that a large percentage of black carbon emissions come from anthropogenic s ources, including diesel engines and vehicles, the EPA notes that existing regula tions on mobile diesel engines are already reducing these emissions substantia lly. Between 1990 and 2005, new engine requirements resulted in a 32 percent reduction in black carb on emissions from mobile sources, and a further 86 percent reduction fr om 2005 levels is projected to occur by 2030 as vehicles and engines meeting existing regul ations are phased into the fleet (U.S. EPA, 2012c, p. 175). Long-term historic data indicate that there has been a dramatic overall decline in black carbon emissions over the past century, due to changes in fuel use, more efficient combustion practices, and implementation of PM controls.

Therefore, the EPA disagrees with the Cent er for Biological Dive rsity’s claim that a distinct black carbon NAAQS is necessary to achieve reductions in black carbon emissions. Clearly, U.S. emissions of black ca rbon are already dec lining substantially, suggesting that the existing mass-based PM st andards, though not ta rgeting black carbon specifically, have been effective in achi eving black carbon emissi ons reductions in practice. As acknowledged in the Report to Congress on Black Carbon, “While [black carbon] is not the direct target of existing programs, it has been reduced through controls aimed at reducing ambient PM 2.5 concentrations and/or dire ct particle emissions” (U.S. EPA, 2012c, p. 161). The EPA has acknowledged the need to encourage PM mitigation strategies that focus on reducing directly emitted PM 2.5 for purposes of reducing black carbon, and this is reflected in its genera l support for the revised language in the Gothenburg Protocol, as discussed above.V-1 V. RESPONSES TO SIGNIFICANT COMMENTS ON AMENDMENTS TO AMBIENT

MONITORING AND REPORT ING REQUIREMENTS

A. Comments on General Issues for Reference , Equivalent, or Approved Regional

Methods

(1) Comment: One commenter supported the proposed administrative change to 40 CFR Part 53.9 – Conditions of Designation.

Response : The comment in support of the proposal is acknowledged and EPA is adopting the proposed approached in the final rule.

(2) Comment: One commenter stated that the approach of requiring PM 2.5 FEMs to meet the data objectives necessary for method designation fo r a period of at least one year will not be effective since the data objectives used in the FEM evaluation protocols do not match the required routine operating schedules for monitoring agencies. The FRMs used by monitoring agencies are operated from midni ght to midnight while the vendors used midmorning to mid-morning for the FEM evaluation protocols. This diffe rence creates a bias because the routine midnight-to-midnight agen cy samples will retain a smaller portion of volatile PM than the vendor-operated FRMs. The vendors also were required to operate and average the results from triplicate FR Ms and triplicate candidate FEMs. These averaged results are more stable and cons istent than individua l FRM and FEM data.

Response: The EPA’s intention in making this ad ministrative change to 40 CFR Part 53.9 – Conditions of Designation is to link this long-standing requirement to the appropriate performance criteria as is done for all othe r Federal equivalent methods. The EPA agrees that there are differences in the way the te sting and routine operation of these methods are conducted. However, despite these differenc es, and as explained in the preamble to the final rule, a number of PM 2.5 continuous FEMs monitors are achieving acceptable data comparability. To the extent that this change encourages a closer relationship between instrument companies and monitoring agencies, especially during the first 12 months of operation, EPA believes such a relati onship will lead to mutual responsibility in striving to meet the appr opriate performance criteria. Also, EPA did not propose any changes to the testing criteria.

(3) Comment: One commenter stated that the monitoring methods proposed to support the proposed new secondary PM 2.5 visibility index NAAQS do not address an estimate of

measurement accuracy.

Response: For the reasons stated in section VI of the preamble to the final rule, EPA is not adopting the proposed secondary PM 2.5 visibility index NAAQS. Consequently, the final monitoring rule does not include re quirements on the use of CSN or IMPROVE

measurements.

(4) Comment: A few commenters stated that the EPA does not adequately recognize the potential for intrusion of coarse particle mass into fine particle measurements. The commenters noted that the potential for coarse pa rticle intrusion is significant in the arid West, where PM concentrations of crustal or igin may account for an appreciable portionV-2 of the total ambient mass concentration.

Response: The Agency has long recognized that am bient fine and coarse modes vary appreciably with regard to origin, partic le size, chemical co mposition, and potential

adverse health effects associated with their exposure. As discussed in the Air Quality Criteria for Particulate Matter (October 2004) , intermodal minimums between fine and coarse particle ambient size distribution modes typically range between 1 and 3 μm. Based on recommendations by both Agency sta ff and the CASAC, 2.5 μm was selected as the most appropriate size indicator in th is intermodal size range when setting the fine particle standard for the 1997 PM NAAQS. Th e decision regarding whether to maintain

the 2.5 um size cut for ambient PM 2.5 samplers was also considered during the review of the 2006 PM NAAQS, and it has again been considered during this review (see discussion at Section III.E.1 in the preamble to this final rule). In each instance, selection

of PM 2.5 as the most appropriate indicator of fine particle exposure has been overwhelmingly supported by subsequent Agency reviews, CASAC peer-reviews, and Integrated Science Assessments.

When selecting the most appropr iate size indicator for the fine particle standard within the 1 and 3 μm size range, the Agency recogn ized that there is no unambiguous definition of a size cut that would provide for complete separation of overlapping fine and coarse ambient particle modes under all circumstances . While there is generally very little particle mass in the intermodal size range in most monitoring situations, the fine mode can extend up to and above 2.5 μm in situations of high ambient relative humidity. Conversely, the coarse mode can extend dow n to approximately 1 micrometer in situations characterized by hi gh coarse mode concentrations in conjunction with high wind speeds. Ultimately, the selection of PM 2.5 as the most appropriate size indicator for assessing exposure to fine particles ha s been based on ensuring that ambient measurements completely captured the aerosol component of greatest health concern. As a result, it was deemed by the Agency and CA SAC to be more important to collect fine particles more completely under all sampli ng conditions than to exclude coarse-mode particles which may inadvertently intrude into fine particle measur ements. In addition, there is currently insufficient epidemiological and toxicological evidence to conclude that crustal particulate matter is totally benign with respect to potential a dverse health effects associated with its exposure.

The EPA notes that in order to provide a distinct measurement separation between particles above and below 2.5 μm aer odynamic diameter, the FRM for the PM 2.5 NAAQS employs use of a single-stage inertial separa tor which provides very sharp fractionation characteristics. The FRM’s development a nd subsequent promulgation of equivalent method specifications includes provisions to en sure that the fractionation characteristics

of PM 2.5 NAAQS monitors do not appr eciably degrade as a functi on of aerosol loading. In conjunction with the inherent ly very sharp fractionation characteristics of the inertial separator itself, these provisions are designed to ensure that the intrusion of ambient coarse particles into fine particle measuremen ts does not significantly positively bias fine particle concentrations in the presence of high concentrations of ambient crustal

components.V-3 B. Comments on use of CSN and IMPROVE method s to provide speciation data used in the proposed new secondary PM 2.5 visibility index NAAQS.

(1) Comment: One commenter was supportive of us ing the IMPROVE monitors in urban

areas.

Response: For the reasons stated in section VI of the preamble to the final rule, EPA is not adopting the proposed secondary PM 2.5 visibility index NAAQS. Consequently, the final monitoring rule does not include re quirements on the use of CSN or IMPROVE

measurements.

(2) Comment: Regarding the use of IMPROVE and CS N samplers for use in the visibility index, several commenters do not support th e use of methods that have not been designated as FEM or FRM in comparison to th e NAAQS as this is inconsistent with all other NAAQS.

Response: For the reasons stated in section VI of the preamble to the final rule, EPA is not adopting the proposed secondary PM 2.5 visibility index NAAQS. Consequently, the final monitoring rule does not include re quirements on the use of CSN or IMPROVE

measurements.

(3) Comment: Several commenters preferred a direct measurement of light extinction. For example, use of optical instrumentation such as nephelometers and aethalometers.

Response: For the reasons stated in section VI of the preamble to the final rule, the EPA is not adopting the proposed secondary PM 2.5 visibility index NAA QS. Consequently, the final monitoring rule does not include requirements on the use methods to support

such a standard.

(4) Comment: One commenter recommended that EPA needs to begin the process of developing a Federal Reference Method that directly measures light-extinction.

Response: The EPA can consider the developmen t of a light extinction method for an FRM as part of an overall strategy on me thods development; however, even if the EPA decides to pursue such a direct measurement method as an FRM, which would have to be considered with other method development pr iorities, the timing of developing such a method is expected to take several years to complete the needed laboratory and field studies prior to a future proposal.

(5) Comment: Several commenters recommend the EP A develop a pilot urban visibility network program that would field test and eval uate the most promising methods of direct measurement under varying field conditions.

Response: The EPA can consider such a pilot prog ram; however, since a pilot program is inherently not a national deployment, there is no need to direct any requirements for such a program in the final rule.V-4 (6) Comment: One commenter stated that the EPA should establish a pilot measurement program to identify methods that would more accurately measure and report real-time visibility conditions to the public.

Response: he EPA can consider such a pilot pr ogram; however, since a pilot program is inherently not a national deployment, there is no need to direct any requirements for such a program in the final rule.

(7) Comment: Several commenters stated that th e IMPROVE monitoring network is not suitable for supporting a visibility standard that is intended to be primarily a program for

urban areas.

Response: For the reasons stated in section VI of the preamble to the final rule, the EPA is not adopting the proposed secondary PM 2.5 visibility index NAA QS. Consequently, the final rule does not include requirements for monitoring sites to support such a standard.

(8) Comment: One commenter asked for clarification on how total PM 2.5 mass concentrations from IMPROVE and CSN samplers might be used for comparison to the primary PM 2.5 NAAQS.

Response: It was never the EPA’s intention that the PM 2.5 mass concentrations from IMPROVE and CSN samplers would be used for comparison to the primary PM 2.5 NAAQS. Had we finalized use of the IMPR OVE and CSN samplers for use with the proposed PM 2.5 visibility index NAAQS, which as described in section VI of the preamble to the final rule, we are not doing, we would have clarifie d this issue in the preamble.

(9) Comment: One commenter stated that in additi on to reconstructing visibility from speciated PM 2.5 , states should also have the ability to use direct measurements located at airports (AWOS/ASOS), or from nephalometer, telephotometers, and/or

transmissometers.

Response: For the reasons stated in section VI of the preamble to the final rule, the EPA is not adopting the proposed secondary PM 2.5 visibility index NAAQS . Consequently, the final rule does not include requirements for monitoring sites to support such a standard.

(10) Comment: One commenter stated that they do not believe that at this time the PM2.5

continuous FEMs can be utilized for the purpose of calculating a short-term light extinction value for comparison to a standard.

Response: The EPA would have only needed the PM 2.5 continuous FEMs for use in a short-term light extinction calcula tion had it finalized a secondary PM 2.5 visibility index NAAQS with a sub-daily averaging time. For the reasons stated in section VI of the preamble to the final rule, the EPA is not adopting the proposed secondary PM 2.5 visibility index NAAQS, nor is the short-term secondary PM 2.5 visibility index NAAQS it took comment on being finalized; conseque ntly, the final rule does not include requirements for monitoring methods to support such a standard.V-5 C. Comments on the Terminology Changes

(1) Comment: One commenter supports removing of the term ‘community-oriented’ and ‘community monitoring zone’.

Response: The comment in support of the proposal is acknowledged and EPA is adopting the proposed approach in the final rule.

D. Comments on Revoking Use of Population-Or iented as a Condition for Comparability

of PM 2.5 Monitoring Sites to the NAAQS

(1) Comment: One commenter supports revoking the term “population-oriented” so that data comparable to the PM 2.5 NAAQS are consistent with other NAAQS.

Response: The comment in support of the proposal is acknowledged and EPA is adopting the proposed approach in the final rule.

(2) Comment: One commenter stated that they ar e concerned that revoking the populationoriented requirement may result in monitori ng at locations that ar e not appropriate for comparison with either the annual standard or the 24-hour standard.

Response: The EPA believes that for PM, as with a ll other criteria pollutants, all sites that

meet the definition of ambient air are appropriate for comparison to the NAAQS. However, the EPA provides additional criteri a described in §58.30 on those sites that may be eligible only for comparison to the annual PM 2.5 NAAQS. Although the EPA is removing from this provision the requirement that sites be “populat ion-oriented” to be compared to the annual PM 2.5 NAAQS, all monitoring sites must still be repr esentative of area-wide locations to make this comparison. Thus, these sites will represent locations where there is population exposure. Theref ore, the EPA disagrees that revoking the requirement for sites to be population oriented may result in monitoring at locations that are not appropriate for comparis on with either the annual or 24-hour standards. oreover,

this amendment will not alter the current PM 2.5 monitoring network, si nce (based on data in the Air Quality System (AQS) database) there are no current PM 2.5 monitoring sites that have affirmatively been categorized as “non population oriented” using the current regulations.

(3) Comment: One commenter stated that EPA’s defin ition of ambient air is specified in 40 CFR 50.1—‘‘Ambient air means that portion of th e atmosphere, external to buildings, to which the general public has access. ’’ While this is an appropriate definition of ambient air, monitoring for compliance with any given air quality standard should be carried out at locations where there are people actual ly exposed for time periods that correspond approximately to the averaging time of th at NAAQS. Thus, for comparison with the

annual PM 2.5 standard, the population-oriented defi nition is appropriate since it involves

locations where a substantial number of people spend a significant fraction of the day. Without a requirement to site monitors in this manner, monitoring from locations that have little or no population exposure coul d be used for comparison with the PM 2.5V-6 NAAQS. For example, in the proposal the Agency indicates:

Area-wide means all monitors sited at neighborhood, urban, and regional scales, as well as those monitors sited at either micro- or mi ddle-scale that are representative of ma ny such locations in the same CBSA.

The key issue with this appro ach is that there may be many similar micro-scale locations in a metropolitan area but none of them may have actual human exposures relevant to the averaging time of the NAAQS.

The proposed rule indicated:

In reviewing the impact that this propos ed change might have on the nation’s PM 2.5 monitoring network, the EPA notes that there are no remaining sites operating affirmatively as ‘‘non-p opulation-oriented.’’

While this may be true, the proposed rule al so requires the additi on of a substantial number of near-road monitoring sites the locat ion of which is sti ll to be decided. The Agency provides no examples of cases where th e current definitions ha ve resulted in any ambiguity with regard to monitoring locations. Therefore, the commenter does not support the EPA proposal to re voke the requirement that PM 2.5 monitoring sites be ‘‘population-oriented’’ for comparison to the NAAQS.

Response: The EPA believes that the location of any site meeting the definition of ambient air, which represents a location wh ere the public is (or may be) exposed, will represent current or potential population e xposure and is an acceptable location for comparison to PM 2.5 NAAQS, as is the case with all other criteria pollutants. Additionally, for compar ison to the annual PM 2.5 NAAQS, monitoring s ites are also to represent area-wide air quality; therefore, even if a monitor was located in a location at a small scale where no one was actually exposed on a given day, there is still the potential for someone to be exposed there and that s ite is intended to represent many such other locations in the same area, where the public is (or may be) exposed. For example, undeveloped or lightly utilized areas thatborder industrial so urces or exist along roadways may at one time have little or no population exposure, however, if subsequent housing, commercial, or recreational devel opment occurs than population exposure will occur. Basing monitoring decisions on the ambi ent air definition provid es states with the flexibility to place monitors in these areas befo re as well as after such development. With regard to the comment that “....monitoring for compliance with any given air quality

standard should be carried out at locations where there are people actually exposed for time periods that correspond a pproximately to the averagi ng time of that NAAQS”, the EPA notes that no such requirements exist in the monitoring regulations. While the consideration of NAAQS averagi ng time may be one factor on which to base the siting of monitors, monitoring agencies need flexibil ity in designing their networks to ensure characterization of locations to which the gene ral public has access as well as to support the specific objectives described in Appe ndix D of Part 58, section 1.1. Regarding the commenter’s point that we have not provided any “...examples of cases where the current definitions have resulted in any ambi guity with regard to monitoring locations”,V-7 the EPA points out that such cases do exis t, including the use by stakeholders of dispersion modeling to support NAAQS a ttainment planning, associated SIP development, and the calculation of transpor tation conformity budgets, and that these examples typically apply as often to locati ons that are unmonitored as well as locations

that are monitored. The EPA contends that the monitoring rules need to be clear as to the requirements to monitor and that the removal of the “population orie nted” phrase that has only applied to PM 2.5 sites will provide needed clarity for monitoring agencies that plan and operate ambient networks as well as t hose stakeholders that base implementation strategies, in part, on PM 2.5 monitoring requirements.

(4) Comment: One commenter stated that the EPA proposes to revoke the Part 58 requirement that placement of PM 2.5 monitor placements be “population oriented,” because the Agency argues that this require ment is “inconsistent” with the regulatory

definition of “ambient air” at 40 CFR 50.1.10 Id. 39011. The commenter believes this change of historical practice is unreasonable, particularly since the agency has trumpeted that the value of the propos ed rulemaking is for promulgation of a suite of urban PM 2.5 NAAQS. First, we submit that the EPA conflate d the issue of the defi nition of “ambient air” with the placement of monitors. The defi nition of “ambient air” is relevant to placement of stationary source monitors and compliance, not to the placement of roadside monitors. Further the definition of “ambie nt air” is quite flexible as evidenced by 30 years of NSR determinations. Second, what th e EPA seems to desire is the ability to reorient the placement of monitors from urba n areas to: (1) roads where they can “piggy back” on the recently installed NO 2 NAAQS monitors; and (2) establish a new monitoring network in rural ar eas; and (3) to potential hotsp ots in rural areas caused by energy exploration. These plans, discusse d at length in the proposed notice of rulemaking, certainly do not jive with the objec tive of this rulemaking – a suite of urban

PM 2.5 NAAQS to compliment the regional haze re gulations already in place. For this reason, the proposed changes to Part 58 and the change of the focus of the existing focus of the Part 58 monitoring requirements from “population centers” to rural areas is not supportable at all based on the record of decision and we oppose it on that grounds.

Response: The EPA disagrees with several of th e commenter’s assertions. First, EPA disagrees that revoking the requirement for monitors to be “population-oriented’ is unreasonable. As explained in the preamble, the NAAQS provide protection for the public health and welfare in areas where the public can be exposed (n ecessarily including rural and urban areas). For all other criteria pollutants, monitoring requirements allow the comparability of monitors in any location representative of ambient air to the NAAQS

without further restriction. In the case of PM 2.5 however, the historic rules contained an additional restriction requiring monitors to be in population orient ed locations to be comparable to the PM 2.5 NAAQS. The term “populati on oriented” has lacked a quantitative definition (e.g., the in terpretation of “substa ntial numbers” used as part of the part 58.1 definition of “Population-Oriented Mo nitoring”), therefore monitoring agencies and those stakeholders who based implementa tion strategies and decisions on monitoring regulations have been uncertain about what locations are or are not appropriate for PM 2.5 monitoring. The EPA believes that the c ontinued use of the population oriented restriction on NAAQS comparability represents an unwise limitation on the flexibility ofV-8 monitoring agencies to revise their PM 2.5 networks to account for anticipated changes in demographics or development as well as a cont radiction with the inhe rent applicability of the NAAQS in ambient air locations where th e public has access (e.g., in any location outside the perimeter of a indus trial facility). C onsistent with the long-standing practice of monitoring agencies in locating ambi ent monitors, we also note that, based on supporting data in the AQS, all currently existing PM 2.5 monitors are located in areas that are representative of populati on exposures. There are no PM 2.5 monitors currently operating as “non-population oriented”. The EPA does not believe that removing the restriction for monitors to be population orie nted will result in monitors that are not representative of population exposures. Regard ing the comment that “the definition of ambient air is relevant to placement of stati onary source monitors and compliance, not to the placement of road-side monitors”, the EPA disagrees that “ambient air” is not relevant to road-side monitors. The EPA poi nts out that a significant fraction of the population lives, works, plays, and goes to school near major roads and that these exposures occur in locations that represent ambient air. As noted in the preamble, one referenced study (http://www.census.gov/housin g/ahs/data/ahs2009.html) identified that 45 million Americans live within 300 feet of a major roadway or other major mobile source. The survey provides an estimate of the county’s numerous housing units in the U.S. that are located with 300 feet of a highway with four or more lane s, or a railroad, or an airport.

Regarding the comment “what EPA seems to desire is the ability to reorient the placement of monitors from urban areas to: (1 ) roads where they can “piggy back” on the recently installed NO 2 NAAQS monitors; and (2) establis h a new monitoring network in rural areas; and (3) to potential hotspots in rural areas caused by en ergy exploration”, we point out that the requirement is to site PM 2.5 near-road monitors in urban areas with populations of 1 millions persons or more; ther efore, these monitoring locations are still representative of those urban areas and the populations that live, work, play, and go to school near these major roads. Regarding th e comment that the EPA is to “establish a new monitoring network in rural areas” the EP A disagrees as we di d not propose, nor are we finalizing any changes to monitoring re quirements in rural areas. Regarding the comment to reorient the placement of monitors from urban areas to “potential hotspots in rural areas caused by energy exploration”, we again note that there was no such proposal nor are we finalizing any such language. The commenter’s obscure reference to Regional Haze suggests the commenter was referring to the proposed secondary standard for visibility, which the EPA is not adopting in the final rule.

(5) Comment: One commenter stated that removing th e requirement for population oriented combined with other proposed monitoring chan ges creates a situation where any monitor, anywhere, measuring only very localized air qu ality of a small areas, could be compared to the NAAQS.

Response: As explained in the preamble, the NAAQS provide protection for the public health and welfare in areas where the public can be exposed. Fo r all other criteria pollutants, monitoring requirements allow the comparability of monitors in any location representative of ambient ai r to the NAAQS without furthe r restriction, even if such locations characterize very localiz ed air quality. In the case of PM 2.5 however, theV-9 additional restriction of requiri ng monitors to be in populatio n oriented locations to be NAAQS comparable has existed. The term “population oriented” has lacked a quantitative definition (e.g., the in terpretation of “substa ntial numbers” used as part of the part 58.1 definition of “Population-Oriented Mo nitoring”), therefore monitoring agencies and those stakeholders who based implementa tion strategies and decisions on monitoring regulations have been uncertain about what locations are or are not appropriate for PM 2.5 monitoring for purposes of NAAQS comparab ility. The EPA believes that the continued use of the population oriented restriction on NAAQS comparability represents an unwise limitation on the flexibility of monitoring agencies to revise their PM 2.5 networks to account for anticipated changes in demogr aphics or development as well as a

contradiction with th e inherent applicabil ity of the NAAQS in ambient air locations where the public has access (e .g., in any location out side the perimeter of a industrial facility). Moreover, all PM 2.5 monitoring sites must still be representative of area-wide locations to make the comparison to the a nnual NAAQS. Thus, these sites still represent locations where there is populat ion exposure. Consistent with the long-standing practice of monitoring agencies in locating ambient monitors, we also note that all currently existing PM 2.5 monitors are located in areas th at are representative of population exposures based on supporting data in the AQS. There are no PM 2.5 monitors currently operating as “non-population oriented” and th e EPA does not believe that removing the restriction for monitor to be population orient ed will result in monitors that are not representative of population exposures.

(6) Comment: One commenter (EEI) stated that purportedly to address “ambiguity,” the EPA is proposing to remove ex isting requirements regarding PM 2.5 NAAQS that require monitors to be “population-oriented.” The EPA additionally claims it must now align a 15-year old regulatory require ment (for population-orientati on) with an even older regulatory definition of ambien t air. The EPA offers no an alytical support or logical rationale for this proposal and the EPA s hould not finalize the proposed changes. The EPA states that eliminating the requiremen t does not change the requirements for the design of PM 2.5 networks. But this perspective ignor es other changes that the EPA is proposing to make with regard to PM 2.5 monitoring. As referenced above, the EPA is proposing to allow monitors that measure air qua lity representative of very small areas to be compared to the NAAQS. By additionally pr oposing to eliminate the requirement that such monitors be population-oriented, th e EPA is not conforming its monitoring requirements to the definition of “ambient air” (which includes the specification that such

air be that to which the general public has access). Instead, removing any requirement for population orientation combined with other proposed monitoring changes results in the prospect that any monitor, anywhere, measuring any very localized air quality of any size could be comparable to the NAAQS, and possi bly drive the characte rization of the air quality status of a much broader geographic area. This is inconsistent both with the

definition of ambient air and with the CAA’ s requirement that NAAQS be protective of “public health.” On a fundamental level, it appears fully consistent with the primary NAAQS process contained in CAA sections 107-109 and completely logical to maintain a population-orientation as a criterion for monitors for primary, health-based NAAQS. This is certainly the perspec tive that EPA adopted from the very first staff paper for the

PM 2.5 NAAQS in 1997. As noted at that time, “a ll concentration-res ponse functions used in these analyses are based on findings from human epidemiological studies, which relyV-10 on fixed-site, population-oriented, ambient monito rs as a surrogate fo r actual integrated PM exposures. Measurements of daily variations of ambient PM concentrations . . . have a plausible linkage to the daily variations of exposure from ambient sources for the populations represented by ambient monitoring stations. . .” These conditions have not changed in the years since 1997 and thus s upport retention of the current requirement.

Response: The EPA’s disagrees with a number of the commenter’s statements. With regard to the comment that “EPA is not c onforming its monitoring requirements to the definition of ambient air (which includes the sp ecification that such air be that to which the general public has access) ”, we note that the NAAQS provide protection for the public health and welfare in areas where the public can be exposed. For all other criteria pollutants, monitoring requirements allow the comparability of monitors in any location representative of ambient air to the NAAQS without fu rther restriction. The EPA

believes that the continued use of th e population oriented restriction on PM 2.5 NAAQS comparability represents an unwise limitation on the flexibility of monitoring agencies to

revise their PM 2.5 networks to account for anticipated changes in demographics or development as well as a clear contradicti on with the inherent applicability of the NAAQS in ambient air locations where th e public has access (e.g., in any location outside the perimeter of a indus trial facility). Moreover, a ll monitoring sites must still be representative of area-wide locations to be used for comparison with the annual PM 2.5 NAAQS. Thus, these sites still represent loca tions where there is population exposure. This change thus, results in monitoring requi rements that are completely consistent both with the definition of ambient air and with the CAA’s requirement that NAAQS be protective of “public health.” From an opera tional standpoint, we have noted that from a sample of over 900 operating monitoring stat ions in the country, and none of the currently operated monitors have been dete rmined to not be “population-oriented” based on data in AQS, therefore the practical im plications of this revision on the operating monitoring network are inconsequential.

With regard to the comment that “As noted at that time, “*all concentration-response functions used in these analyses are ba sed on findings from human epidemiological studies, which rely on fixed-site, population-or iented, ambient monitors as a surrogate for actual integrated PM exposures. Measurements of daily variations of ambient PM concentrations . . . have a pl ausible linkage to the daily variations of exposure from ambient sources for the populat ions represented by ambient monitoring stations. . .” These conditions have not changed in the ye ars since 1997 and thus support retention of the current requirement”. The commenter cites language from the EPA’s initial promulgation of the “population oriented” provision (40 CFR Part 58 App. D section 2.8.1.2.3 (1997)), and suggests that a “population oriented” provision is required to be

consistent with the form of the annual st andard and the epidemiologic information on which the standard is based. However, as explained in section III.E.4 to the preamble to the final rule, it is appropriate in this revi ew to eliminate the spatial averaging option

from the form of the annual standard , and appropriate to compare the PM 2.5 concentrations from a maximum monitor to the level of the PM 2.5 standard. Consequently, the commenter’s premise th at the “population oriented” phrase is necessary to be consistent with the form and general structure of the annual PM 2.5 NAAQS is misplaced.V-11 The requirement that a near-road monitor re present area-wide air quality (as defined) assures that the commenter’s example of “any monitor, anywhere, measuring very localized air quality” being used for comparison with the annual PM 2.5 NAAQS will not occur. This is because area-wide air quali ty is representative of those population exposures where large numbers of people li ve, work, play, and go to school. Moreover, the commenter’s concern that air quality measur ed at a micro-scale (or other small- scale) could characterize air quality in a much broa der area is not appropria tely raised here.

Issues as to attainment or non-attainment area boundaries are determined as part of the section 107 designation process.

(7) Comment: Commenters (ALA et al., 2012) stat ed, “We especially welcome EPA’s proposal to abandon and revoke re gulatory language in Part 58 that effectively prevented the implementation of the PM 2.5 NAAQS to protect populations exposed to incremental concentrations near transpor tation facilities. These include the current prohibitions against comparison of micro- and middle-sc ale monitors with the annual NAAQS, and the requirement that only “population-oriented ” monitors be compared with the 24-hour NAAQS. For the reasons discussed below, we believe these policies impose limitations on the applicability of the NAAQS that are inco nsistent with the text, purpose and intent of the Clean Air Act, and must be revoked.

Response: As noted in the preamble and elsewher e in this RTC, we are finalizing the removal of the population-oriented language from the applicable PM 2.5 monitoring regulatory text.

(8) Comment: One commenter (AASHTO, 2012) stated that “CASAC strongly recommends that key population-oriented monitors be main tained, particularly those that have been used in past health-focused and accountability studies.” It was also stated that “AASHTO is concerned that this pr oposal will deemphasize th e need for area-wide and neighborhood scale PM 2.5 monitors in these areas.”

Response: The EPA notes that the removal of th e population oriented language from the applicable PM 2.5 regulatory text in no way affects the current or future distribution of

PM 2.5 monitors in terms of the objectives of supporting population exposure. From a sample of over 900 operating monitoring stati ons in the country, none of the currently operated monitors have been determined to not be “population-oriented” based on data in AQS. As noted in the preamble, neighbor hood scale monitoring sites remain the

backbone of the PM 2.5 monitoring network and the EPA an ticipates they will continue to represent over two th irds of the operating network follo wing the deployment of the nearroad monitors. Maintaining the area-wide and largely ne ighborhood scale design value sites is critical to the long-standing goal of using data to support a variety of monitoring objectives.

E. Comments on Applicability of Micro- and Middl e Scale Monitoring Sites to the Annual

PM 2.5 NAAQSV-12 (1) Comment: One commenter stated that the EPA s hould remove the restriction that the

annual PM 2.5 standard applies only at “area-wide ” sites. The proposed rule requires agencies to exclude sites that are relativ ely unique middle scale or micro-scale from comparison to the annual NAAQS. This constr uction is problematic and will be difficult for agencies to implement.

Response: The requirement that monitors repr esent area-wide air quality to be comparable to the annual PM 2.5 NAAQS is longstanding and the EPA did not propose to

eliminate it or solicit comment on that issu e. While the EPA understands that there may be some challenges in determining the diffe rences between micro-scale and middle scale sites that meet the definition of “area-wide”, such challenges have always been in place since the requirements fo r comparability to the PM 2.5 NAAQS were first promulgated in 1997. The EPA will work with monitoring ag encies through the annual network plan approval process to address such issues.

(2) Comment: Several commenters suggested that th e EPA should revise the network design requirement to reflect the importance of area- wide representative da ta to meet national and state monitoring objectives and remove th e presumption that micro- and middle-scale sites are representative of many such locations.

Response: The EPA fully supports, and is mainta ining, the network design criteria focusing on “area-wide” represen tative data. Current regulat ory language in section 58.30 addressed the NAAQS applicabil ity issue that where micro- and middle-scale sites are representative of many such locations throughout an area, they likewise represent “areawide” air quality. Similarly, regulatory langua ge in Appendix D, section 4.7.1(b) states that (for PM 2.5 ), “The required monitoring stations or sites must be sited to represent area-wide air quality.” The fi nal rule provides that the ai r agency recommend whether the

site is or is not “area-wi de” in the Annual Monitoring Network Plan. Such a recommendation is still subject to ap proval by the Regional Administrator.

(3) Comment: One commenter stated that EPA should e xplicitly state that near-road data are considered unique unless otherwise sp ecified by the Regional Administrator.

Response: EPA has clarified language to note that we do not presume that any near-road monitoring site will be considered unique or not unique; rather it provides that the air agency recommend the status of such site s in the Annual Monitoring Network Plan. Such a recommendation is still subject to ap proval by the Regional Administrator. We disagree that all near-road locations are unique, as these sites can reflect many such locations throughout a metropolit an area. In the preamble, EPA provided examples of

near-road sites that could be considered uni que; these included sites located in proximity to a unique source like a tunnel entrance, near by major point source, or other relatively unique microscale hot spot. EPA expects th at near-road stations placed in other representative locations will reflect area-wide air quality.V-13 (4) Comment: One commenter stated that changing the scale of monitoring site locations that can provide data for use in NAAQS attainment determinations has implications that impact monitoring objectives.

Response: The EPA disagrees that changing the s cale of monitoring site locations that can provide data for use in NAAQS attainment determinations is problematic or has negative implications for monito ring objectives. Locations th at are at micro- and middlescale have always been used for compar ison to the 24-hour NAAQS, and where these locations represent many such locations in the same area, they have always been appropriate to be compared to the annual NAAQS. As stated in the preamble to the final rule, EPA believes that multiple objectives can be supported with the addition of the near-road monitoring stations, so while EP A agrees there are implications, on balance EPA believes the changes will result in a better network.

(5) Comment: One commenter stated that the alte rnative proposal under consideration, permitting micro- and middle-scale sites to be classified as area-wide, would diminish our ability to track future public heal th progress at the neighborhood scale.

Response: EPA disagrees that allowi ng micro- and middle-scale s ites to be classified as area-wide, diminishes the ability to track future public health progress at the neighborhood scale. Individual sites will be st ill be labeled with a given spatial scale (e.g., neighborhood scale) allowing stakeholders to understand the nature and general representativeness of a given site. However, to ensure neighborhood scale sites remain an important part of the PM2.5 network, EPA ha s addressed this issue in the final rule by clarifying language in Appendix D, secti on 4.7.1(b)(1) to state that “At least one monitoring station is to be sited at neighborhood or larger scale in an area of expected

maximum concentration.”

(6) Comment: Several commenters recommend a positive determination that a PM 2.5 monitor represents area-wide air quality, and t hus eligible for comparison to the PM 2.5 NAAQS, which should be proposed in Annual Network Plan submittals, with subsequent concurrence and approval by the Regional Admini strator. Representation of area-wide air quality should not be “presumed” as proposed in section 58.30(a)(2).

Response: The EPA has clarified language to note that we do not presume that any site will be considered unique or not unique; rath er it provides that the air agency recommend

the status of such sites in the Annual Monitoring Networ k Plan. Such a recommendation is still subject to approval by the Regional Administrator. Sites that are approved per section 58.30 as representing area-wide conditio ns will be eligible for comparison to the

PM 2.5 annual NAAQS.

(7) Comment: One commenter (AFPM) stated that cont rary to the EPA’s assertions in the proposed rule, the proposed changes to allow micro- and middle-scale monitors to be compared to the NAAQS and the revoking of the “population-oriented” condition for monitoring locations (discussed below) do not promote consistency with EPA’s existing regulatory definition for “ambient air.” As noted by EPA, the regulatory definition ofV-14 “ambient air” specifically references the porti on of outside air to which the general public has access. In implementing this regulatory definition, EPA has exempted areas where a source owns or controls the property involved and where public access has been precluded. The Agency has consistently reli ed on documents describing the definition of ambient air with regard to not including ar eas “to which public access is precluded by a fence or other physical barrier.” Thus, EPA has never interpreted am bient air to be “any potential location” outside of a build ing and proposing to allow “any” PM 2.5 monitor to be compared to the NAAQS is clearly and dir ectly inconsistent with this long-standing regulatory interpretation. Rather than prom ote consistency, the change would have the opposite effect given the expansive interpretatio n of “any” within the CAA. Therefore,

EPA should retain the current re quirements restricting the us e of micro- and middle-scale monitors and additionally consid er revising the regulations to remove the ability of a Regional Administrator to determine monitor comparability. These changes would better promote the goal of national uniformity by ma king it clear that monitors would not be subject to highly localized condi tions (perhaps measuring high ly transient air quality in areas measuring no more than a few square meters) or subject to the individual (and perhaps inconsistent) preferences of different Regional Administrators

Response : With regard to the comment that th e proposed change to allow micro- and middle-scale monitors to be compared to the NAAQS does not promote consistency with the EPA’s existing regulatory definition for “am bient air”, the EPA di sagrees. Micro- and middle-scale are already comparable to the NAAQS for all other pollutants, and even for

PM 2.5 , all operating micro- and middle scale site s are comparable to at least the 24-hour NAAQS. The EPA believes that its long-standing definition of ambient air is well suited to provide for the consistency needed in en suring monitors are appropriately sited for comparison to the NAAQS. The EPA disagrees that this change would lead to an expansive interpretation for “any” within th e CAA, rather as we have stated, it will promote consistency across all pollutants in determining their applicability to the NAAQS. Moreover, all PM 2.5 monitoring sites must also be representative of area-wide locations to make the comparison to the a nnual NAAQS. Thus, these sites will represent locations where there is populat ion exposure. Consistent with the long-standing practice of monitoring agencies in locating ambient monitors, we also note that all currently existing PM 2.5 monitors are located in areas th at are representative of population exposures based on supporting data in the AQS.

The EPA does not believe it is necessar y to remove the ability of Regional Administrators to determine monitor comp arability. The EPA Regional Offices are the

most familiar with their individual State netw orks and possible changes to them. We do not believe that removing the Regional Ad ministrator from the process of approving

micro- or middle-scale si tes from comparison to the annual NAAQS, will promote consistency. Rather we believe that inform ation provided by monitoring agencies in their annual monitoring network plans will be sufficient to consistently apply recommendations and support determinations by the EPA Regional Administrator as to

whether micro- or middle-scale sites are to be considered” area-wide. With regard to the comment “that monitors may be establishe d in areas subject to highly localized conditions (perhaps measuring highly transi ent air quality in areas measuring no moreV-15 than a few square meters)”, EPA believes th is to be an unreali stic observation for PM 2.5 based on the secondary nature of fine part icle formation that provides for a more homogenous concentration distribution as compared with pollutants dominated by primary emissions such as CO or PM 10

.

(8) Comment: One commenter (EEI, 2012) stated th at EPA is proposing to change the current presumption that micro- and middle- scale monitors are unique and therefore are only comparable to the annual PM 2.5 NAAQS if approved by an EPA Regional

Administrator. EPA claims that its intent in amending the current regu lations is solely for consistency and predictability in the interp retation of monitoring requirements. Micro scale monitors are defined as applying to “c oncentrations in air volumes associated with air dimensions ranging from several meters up to about 100 meters” (emphasis added). Middle scale monitors are defined as “typical of areas up to several city blocks in size with dimensions ranging from about 100 meters to 0.5 kilometers” (emphasis added). When these vague regulatory definitions ar e combined with EPA’s proposal to allow “any” micro- or middle-scale monitor to be comparable to the NAAQS, the result is a “standardless” standard. Under the EPA’s pr oposed rule, the placemen t of a monitor may literally occur anywhere and hence the regulatio ns provide for an arbitrary and capricious designation of nonattainment areas. The EPA provi des no analytical support in the record for this fundamental change in position. In pl ace of current restrict ions, the EPA states

that “ any potential location for a PM 2.5 monitoring site would be eligible for comparison to the annual NAAQS.” Rather than promot e consistency, the change would have the opposite effect given the expansive interpre tation of “any” within the CAA. The EPA should retain the current requirement and c onsider revising the current regulations to remove the ability of a Regional Administ rator to determine monitor comparability. These changes would better promote the goa l of national uniform ity by making it clear that monitors would not be subject to highl y localized conditions (perhaps down to the transient air quality in an area measuring no mo re than a few meters wide) or subject to the preferences on an indivi dual Regional Administrator.

Response : The EPA disagrees with the commenter for several reasons. The EPA asserts that it has always been true that the placement of a monitor may potentially occur anywhere. However, the EPA’s long-standing practice does not allow a monitor to be compared to a NAAQS unless it represents ambi ent air. Even under current rules, when a monitor is placed in an environment that repres ents ambient air, regardless of the scale of representation or whether it represents area-w ide air quality it is eligible for comparison

to the 24-hour PM 2.5 NAAQS. When a monitor – at any sc ale – represents area-wide air quality it is also eligible for comparison to the annual NAAQ S. None of these criteria have changed, other than sa ying “area-wide” instead of “community-wide”, which terms are synonymous. With regard to the comme nt that “Under EPA’s proposed rule, the placement of a monitor may literally occur anywhere and hence the regulations provide for an arbitrary and capricious designation of nonattainment areas”, the EPA notes that such issues can appropriately be handled with the designations proce ss, when states have the opportunity to address the interpretation of ambient air data and make

recommendations on the size of the nonattainme nt areas based on their interpretation of ambient monitoring data.V-16 (9) Comment: Commenters (ALA et al., 2012) stat ed, “We especially welcome EPA’s proposal to abandon and revoke re gulatory language in Part 58 that effectively prevented the implementation of the PM 2.5 NAAQS to protect populations exposed to incremental concentrations near transpor tation facilities. These include the current prohibitions against comparison of micro- and middle-sc ale monitors with the annual NAAQS, and the requirement that only “population-oriented ” monitors be compared with the 24-hour NAAQS. For the reasons discussed below, we believe these policies impose limitations on the applicability of the NAAQS that are inco nsistent with the text, purpose and intent of the Clean Air Act, and must be revoked.

Response : The EPA disagrees that a prohibition has existed against the comparison of

micro- and middle-scale monitors with the annual NAAQS. Current regulatory language in section 58.30 addresses the NAAQS applicab ility issue that wher e micro- and middlescale sites are representative of many such locations throughout an area, they likewise represent “area-wide” air quality and are e ligible for comparison to the annual NAAQS. This flexibility and inclusion in the annual monitoring network plan process has been a long-standing practice that is not changed in this rulemaking. The EPA also disagrees that monitors placed near transportation faciliti es would ever have been discounted in a manner suggested by the commenters. As long as such monitors were located in ambient air, they would have been comparable to the 24-hour NAAQS. Any such monitors that were approved as area-wide monitors would also have been comparable to the annual NAAQS.

(10) Comment: One commenter (CLF) stated that th ey support EPA’s plans to allow air quality measured at micro- and middle-scale s ites near roadways to be compared to the

annual standard.

Response : EPA notes that current regulatory language in section 58.30 addresses the NAAQS applicability issue that where micro- and middle-scale sites are representative of many such locations throughout an area, they likewise represent “area-wide” air quality and are eligible for comparison to the annua l NAAQS. This eligibility for comparison to the annual NAAQS has been a long-standing pr actice that is not changed in this rulemaking.

F. Comments on the addition of PM 2.5 monitors to the near-road monitoring stations.

(1) Comment: One commenter strenuously objected to the PM 2.5 roadway network concept. The concerns expressed included access, safe ty, and other logistic al problems involving roadside monitoring.

Response: As stated in section VIII of the final rule, the addition of PM 2.5 monitors to the near-road environment is part of a multipollu tant design at monitoring stations that are already required and being implem ented as part of the required NO 2 monitoring network. The issues referenced by the commenter ha ve already been addr essed in a Technical

Assistance Document that ha s been provided to monitori ng agencies. Therefore, EPA anticipates any issues on siti ng of the stations will already be resolved by the time theV-17 PM 2.5 monitors are required to be operating. To the extent that si gnificant problems do arise with siting a near-road PM 2.5 monitor, EPA has existing authority to address such situations on a case-by-case basis, or coul d undertake changes to the rule as necessary.

(2) Comment: One commenter stated that a near-road monitor may result in it being the controlling monitor for an area, where the components of PM 2.5 have not been fully identified, and that this is a national issue where more research is needed.

Response: As stated in section VIII of the final rule, the addition of PM 2.5 monitors to the near-road environment is to support a number of monitoring objectives. Specifically on the use of data for comparison to the PM 2.5 NAAQS, the EPA points out that people spend a substantial amount of time in thes e environments, resulting in a significant potential for exposure to pollutants. Th e agency believes near-road monitoring is important to ensure that public health is protected with anadequate margin of safety. EPA agrees that more information is needed on the components of PM 2.5 near roads, and supports the use of supplemental measuremen ts (e,g., aethalometers for black carbon) to contribute to this body of information.

(3) Comment: One commenter stated that they would support PM 2.5 near-roadway monitors

if these monitors were used for research data collection purposes a nd not as a controlling

monitor.

Response: As stated in section VIII of the final rule, the addition of PM 2.5 monitors to the near-road environment is to support a number of monitoring objectives. Specifically on the use of data for comparison to the PM 2.5 NAAQS, the EPA points out that these monitors will be sited at existing near-road stations. Accordingly, data from these nearroad monitors will be compared to the PM 2.5 24-hour NAAQS and where determined to be an area-wide monitoring location they will also be compared to PM 2.5 annual NAAQS. The comparison of these sites to the PM 2.5 NAAQS is appropriate as these sites will represent ambient air. The EPA also agrees that more information is needed on many aspects of PM 2.5 levels near roads, an d supports the use of supplemental measurements (e,g., aethalometers for black carb on, ultrafine particle s) to contribute to research on this topic.

(4) Comment: Several commenters stated that while the requirement for near-road PM 2.5 monitoring can be met by collocation at a near-road NO 2 station, the requirement could also be met by locating a PM 2.5 monitor at a different near-road location where PM 2.5 concentrations are expected to be high.

Response: The EPA discusses this issue in sec tion VIII.B.3.b.i of the preamble to the

final rule. The EPA concludes that there are su fficient existing authorities to address this issue on a case-by-case basis if necessary, e.g., where a near-road site is not area-wide, and that no additional regulat ory language is needed.V-18 (5) Comment: One commenter stated that if additional measurements at near-road monitoring

stations are believed to offer increased know ledge of the near-road environment, EPA should implement a national level program to address the data need.

Response: The EPA can consider such a program in future planning. In at least one example, EPA’s Office of Research and Development is partnering with a state monitoring agency to support th e deployment of additional m onitors at a required nearroad station.

(6) Comment: Several commenters recommended the near-road PM 2.5 network should be smaller and more specifically designed to cap ture the data needed to characterize the near-source exposures and correla te them to key source variable s that extrapolate to other

locations.

Response: The EPA considered comments on the size of the network in finalizing the requirements for the final rule. Rationale fo r the size of the netw ork is explained in section VIII.B.3.b.i of the preamble to the final rule. As noted in the previous response, the EPA continues to pursue additional information on near-road environments.

(7) Comment: Several commenters recommended that the expected maximum concentration

PM 2.5 monitoring sites be neighborhood scale an d that the maximum concentration site not be subject to relocati on on a year-to-year basis.

Response: The EPA agrees with the commenters and has adjusted the requirements accordingly. See section VIII.B.3.b.i of the prea mble to the final rule for a more detailed explanation of this issue. Sp ecifically, EPA has addressed this issue in the final rule by clarifying language in Appendix D, secti on 4.7.1(b)(1) to state that “At least one monitoring station is to be sited at neighborhood or larger scale in an area of expected

maximum concentration.”

(8) Comment: Several commenters recommended that we can improve the efficiency and

effectiveness of the PM 2.5 network and reduce implementa tion costs by a combination of phasing, timing, and focusing the scope of the near road monitoring portion of the network by: refocusing the near-road network to provide better characterization of mobile

source emissions at a more limited number of sites including the correlation of emissions to key variables such as traffic, volume, fleet composition, and prev ailing winds; initiate deployment of the near-road network in MSAs with populations greater than 2.5 million; and commence deployment of near-road PM 2.5 monitors one year af ter implementation of

near road NO 2 monitors.

Response: These issues are addressed in section VIII.B.3.b.i of the preamble to the final

rule.

(9) Comment: One commenter stated that they und erstand the need to develop better characterization of near-road exposures to PM 2.5

.V-19 Response: The comment in support of the proposal is acknowledged.

(10) Comment: One commenter stated that for those CBSAs with just one required monitor, that monitor should be at a neighborhood scale.

Response: The EPA agrees with the commenter s and has adjusted the requirements accordingly. See section VIII.B.3.b.i of the prea mble to the final rule for a more detailed explanation of this issue. Specifically, the EPA has addressed this issue in the final rule by clarifying language in Appendix D, secti on 4.7.1(b)(1) to state that “At least one monitoring station is to be sited at neighborhood or larger scale in an area of expected

maximum concentration.”

(11) Comment: One commenter stated the monitoring ne tworks resources should be used to support a developed NAAQS, not to support expl oratory research. Until such time the EPA can clarify the connection between n ear-roadway emissions concentrations and population exposure, we believe that participation in this research should be voluntary rather than mandated by code.

Response: As explained in the preamble to th e final rule, the EPA points out that a significant fraction of the population lives, work s, plays, and goes to school near major roads and that these exposures occur in locati ons that represent ambient air for which the agency has a responsibility to ensure the public is protected with an adequate margin of safety, including through the requirement fo r a minimum number of ambient monitors for the NAAQS. Indeed, one study identified that 45 million Americans live within 300 feet of a highway with four or more lanes, a rail road, or an airport, and given the relative ubiquity of roads, EPA anticipates that thos e are predominantly near-road exposures. See study of the American Housing Survey, which is available on the web at: http://www.census.gov/housing/ahs/data/ahs2009.html

.

(12) Comment: Two commenters stated that any near -roadway monitor should be classified as representative of micro-scale conditions and thus exempt from comparison to the NAAQS.

Response: There is no exemption from comparabil ity to the NAAQS based solely on the scale of representation. Th ere are requirements for comp arability to the annual PM 2.5 NAAQS based on whether a site is approved in an annual monitoring network plan as

area-wide or not. Near road monitors will be evaluated by monitoring agencies and the EPA to determine whether they meet the criteria to be classi fied as “area-wide” or not. However, all sites representative of ambien t air are at a minimum compared to the 24-

hour PM 2.5 NAAQS. Where an existing near-road site is not classified as area-wide for

PM 2.5 , EPA will work with monitoring agencies to determine whether it is appropriate to locate the monitor at a different location, such as a near-road site that is area-wide for

PM 2.5

.

(13) Comment: One commenter stated that agencies need the maximum amount of time possible to comply with the new near-road monitoring requirements; however, they doV-20 believe they can comply with the proposed requirement for PM 2.5 monitors at near-road stations by January 1, 2015.

Response: As explained in secti on VIII.B.3.b.i of the preamble to the final rule, the EPA is finalizing a phased in approach for deployment of the required near-road PM 2.5 monitors.

(14) Comment: One commenter supports the proposal to allow research at selected near-road monitoring stations, so long as this remains voluntary.

Response: The comment in support of the propos al is acknowledged and the EPA is adopting the proposed appro ach in the final rule.

(15) Comment: One commenter stated with regard to the EPA’s proposal to relocate PM 2.5 monitors to meet the near-roadway environment, the EPA rarely allows a state to simply shut down a monitoring station and relocate it. Also, that the assumption that states will

have extra PM 2.5 monitors to relocate to near-roadway sites is simply untenable and

unrealistic.

Response: The EPA appreciates the concern regard ing the challenges of relocating a site, including getting approval from EPA Regi onal Offices. As explained in section VIII.B.3.b.i of the preamble to the final rule, the EPA will work with monitoring agencies in the phased implementation to address whic h monitors will be most appropriate for relocating. Also, as explaine d in the preamble, the EPA is aware that every existing

PM 2.5 monitor has value to someone or some data user and that relocating these sites will result in the loss of that data; however, the EPA maintains that on ba lance, the siting of

the monitors in the near-road environmen t will provide for a better overall network design to address a number of monitoring objectives.

(16) Comment: The EPA has not provided any information showing the near-roadway data would have any meaning with respect to measurement of population exposures. The proposed near-road monitoring network is more appropriately addressed in a research

venue until such time that the EPA can ad equately demonstrate that near-roadway

environment has a direct nexus to a population exposure.

Response: As explained in section VIII.B.3.(b) i of the preamble to the final rule and in response to Comment (11) above, people spend a substantial amount of time in proximity to major roadways and EPA believes near-roa d monitoring is important to ensure that public health is protected with an adequate margin of safety.

(17) Comment: The PM near-road monitors appear to be an EPA-mandated, state-operated research project. These monitors do not captu re broadly representativ e ambient air, thus they are likely to provide a comparison to th e NAAQS not foreseen by the Clean Air Act.

Response: As explained in, section VIII of th e preamble to the final rule and this response to comments, there are large numbers of people (in the tens of millions) thatV-21 live, work, play, and go to school in close in proximity to major roadways. These exposures occur in locations that represen t ambient air for whic h the agency has a responsibility to ensure the public is protec ted with an adequate margin of safety. Comparison of monitoring results from su ch areas to the NAAQS is therefore appropriate. The EPA disagrees th at the data produced from PM 2.5 near-road monitors compared to the NAAQS will result in some thing unforeseen by the Clean Air Act.

(18) Comment: One commenter disagrees with the placement of (PM 2.5 ) monitors used to represent long-term public exposure at ne ar-road sites because the data are not representative enough to compare to a national standard.

Response: The EPA disagrees that the near-road PM 2.5 data are not representative enough to compare to a national standard. The purpose of a national ambient air quality

standard is not to achieve an average ambient air quality, w ith some areas above or below the standard, but to establish a level of air quality that all areas achieve. Likewise the purpose of a monitoring network design plan, given necessarily limited resources, is generally to locate monitors in areas that pos e a risk of exceeding the standard, subject to decisions about the appropriate spatial scal e or, as here, area-wide monitoring. If the comment is suggesting that the data shoul d not be comparable to the annual NAAQS

even where there is an “area-wide” monito r, the EPA rejects that argument for the reasons explained elsewhere in this docum ent and the preamble. Moreover, if the premise of the comment is that more polluted populated areas are by definition unrepresentative, the EPA rejects that premise, and further rejects th e comment that siting some monitors in near roadway environmen ts makes the standard more stringent or impermissibly more stringent. As discussed in section VIII.B.3.b.i of the preamble to the final rule, a significant fracti on of the population lives in pr oximity to major roads, and these exposures occur in locations that repres ent ambient air. Monito ring in such areas does not make the standard more stringent th an warranted, but rather affords the intended protection to the exposed popul ations, among them at-risk po pulations, exposed to fine particles in these areas. Thus, in cases where monitors in near roadway environments are deemed to be representative of area-wide air quality they would be compared to the annual standard. The 24-hour and annual NAAQS ar e designed to protect the public with an adequate margin of safety, and this siti ng provision is fully c onsistent with providing the protection the standard is designed to provide and does not make the standard more stringent or more stringe nt than necessary.

Monitors that are representative of area-wide air quality may be compared to the annual standard. This is consistent with the use of monitoring data in the epidemiological studies that provide the primary basis for determin ing the level of the annual standard. In addition, the EPA notes that the annual standard is designed to protec t against both longand short-term exposures through controlling the broad distribution of air quality across

an area over time. 39 It is fully consistent with the pr otection the standard is designed to provide for near road monitors to be compared to the annua l standard if the monitor is

39 This is in contrast to the 24-hour standard which is designed to provide supplemental protection, addressing peak exposures that might not otherwise be addressed by the annual standard. Consistent with this, monitors are not required to be representative of area-wide air quality to be compared to the 24-hour standard.V-22 representative of area-wide air quality. This does not make the standard either more stringent or impermissibly more stringent. Furthermore, as the agency explained in the

discussion of the form of the annual standa rd, higher measuring monitors are often located in areas where there are higher num bers of at-risk populations. These areas require requisite protection with an adequate margin of safety, and placing monitors in such areas and comparing results from such monitors to the PM 2.5 NAAQS is part of that process of affording requisite protection with an adequate margin of safety.

(19) Comment: A single monitoring station near a heavily travelled roadway is not adequate to describe the gradient of PM components with increasi ng distance from the roadway.

Response: The EPA is not attempting to addres s the question of PM components in the near-road environment, other than as e xplained in the proposal, those monitoring agencies that voluntarily deploy additional instrumentation in the near-road environment. Additionally, the EPA is not attempting to desc ribe the gradient with a single monitoring station. As described in the preamble to the fi nal rule, the network de sign is intended to provide for representative near-road monito ring stations that are collocated with NO 2 and CO. Thus, while a gradient of the PM 2.5 concentrations from representative near-road stations to neighborhood scale stations ma y be possible, if such neighborhood scale monitoring sites are located in the same general vicinity, it is not the EPA’s goal to have these gradients determined for every area.

(20) Comment: One commenter states that near-road monitoring sites should be considered micro-scale sites due to the lack of experi ence with these monito ring sites, data, and experimental nature of near-road monitoring. Only when we have a better understanding of their relationship to p opulation exposure should these sites be considered for comparison to the NAAQS.

Response: The relative experience of monitoring has nothing to do with the scale of representation of a monitoring station or its applicability to the NAAQS. Rather the variability of that data at the location wher e it is monitored compar ed to the variability of that pollutant in the su rrounding area is what defines it s scale of representation. As explained in the section VIII of the preamble to the final rule and in earlier responses in this document, there are large numbers of people (in the tens of millions) that live, work, play, and go to school in close proxi mity to major roadways. These exposures occur in locations that represent ambient ai r and the EPA believes near road monitoring is important to ensure the public is protect ed with an adequate margin of safety.

(21) Comment: The continued collection of data fr om the neighborhood scale monitors is absolutely necessary because they represent typical worst-case air quality for each Core

Based Statistical Area.

Response: The EPA generally agrees with th e need for continued collection of neighborhood scale data. This comment is addressed in more detail in section VIII.B.3.b.i of the preamble to the final rule for a more detailed explanation of this issue. Specifically, EPA has addressed this issue in the final rule by cl arifying language inV-23 Appendix D, section 4.7.1(b)(1) to state that “At least one monitoring station is to be

sited at neighborhood or larger scale in an area of expected maximum concentration.”

(22) Comment: One commenter disagreed with the pr oposal to add a near-road component to the compliance monitoring network. The micro- scale nature of these sites precludes the data from being used for all of the monito ring objectives except source characterization.

Response: The EPA notes that near-road monitors must represent “area-wide” air quality to be comparable to the annual NAAQS, and that we have a process for determining whether sites at smaller scales (i.e., micro- or middle-scale) represent “area-wide” air quality. The EPA disagrees with the commenter that the micro-scale nature of the nearroad sites precludes their use for a ll monitoring objectiv es, except source
characterization. These sites in combination with the ne ighborhood scale sites in the same CBSA will support a number of monito ring objectives as explained in section VIII.B.3.b.i of the preambl e to the final rule.

(23) Comment: One commenter stated that the pr oposal would remove the population exposure objective from sites used in NAA QS determinations and permit micro- and

middle-scale sites to be classified as area- wide. Micro- and middl e-scale data are not applicable for CBSA-wide exposures and can’t be used for many of the monitoring objectives including health st udies, pollution trends analys is, or State Implementation Plan (SIP) development and control strategy development where necessary.

Response: As explained in the preamble, the PM 2.5 monitors at near-road monitoring stations will in fact support a number of monitoring objectives, including all of the monitoring objectives, where necessary, that the commenter lists (i.e., health studies, pollution trends analysis, or State Implemen tation Plan (SIP) development and control strategy development where necessary) in th e comment. The EPA disagrees that we are removing population exposure from sites used in NAAQS determinations. The near-road monitoring stations, when determined to be representative of many such locations throughout an area, are considered to repres ent “area-wide’ air quality and as such are representative of those populat ion exposures where large numbers of people live, work, play, and go to school.

(24) Comment: One commenter states that the inclusion of PM 2.5 measurements near roadways is consistent with CASAC’s reco mmendations to develop the near roadway network with a multipollutant focus and to include PM 2.5 on the list of pollutants that

should be measured.

Response: The comment in support of the propos al is acknowledged and the EPA is adopting the proposed appro ach in the final rule.

(25) Comment: Several comments stated that the deployment of new near-roadway monitoring should not come at the expense of existing PM 2.5 network objectives, including neighborhood scale popu lation exposure, AQI reporting, environmental justice, transport, and background.V-24 Response: As explained in the preamb le to the final rule, the PM 2.5 monitors at near-road monitoring stations will support a number of monitoring objectives, including several of the monitoring objectives that the commenter lis ts in the comment. Also, as explained in the preamble, the EPA is aware that every existing PM 2.5 monitor has value to someone or some data user and that relocating these sites will result in the loss of that data; however, the EPA maintains that on balance, th e siting of the monito rs in the near-road environment will provide for a better overa ll network design to address monitoring objectives.

(26) Comment: One commenter stated that for CBSAs with populations greater than 1 million, the proposed rule would require that one si te be collocated with a near roadway NO 2 site, which has no corresponding requiremen t to be an area-wide monitor.

Response: The assignment of whether a monitor repr esents area-wide ai r quality is by a combination of the pollutant a nd the location of the station an d not just the location of the station itself. The EPA anticipates that PM 2.5 monitoring located at near-road monitoring stations will often be representative of ar ea-wide air quality, and will consider requests for limited deviations from the requirements of Appendix D, as necessary and appropriate, where an existing near-road site is not classified as “area-wide” for PM 2.5

. Also, although the EPA does not require the NO 2 near-road sites to be area wide, we do explain the in the Near-road NO 2 Monitoring Technical Assistance Document (TAD) that higher weight should be placed on sites that are most influenced by typical roadway activity rather than those that are heavily influenced by unique sources or features.

(27) Comment: One commenter stated that they und erstand and agree with the objective to maximize resources by collocating near road monitors, as well as the desire for comprehensive, multi-pollutant data a single location.

Response: The comment in support of the propos al is acknowledged and the EPA is adopting the proposed appro ach in the final rule.

(28) Comment: One commenter provided recommenda tions on new language for cases where

a third PM 2.5 SLAMS monitor is required in a CB SA. The recommendation stated “For areas with additional required SLAMS, a monitor should be installed to provide additional information necessary for one of the following objectives: source characterization, health studies, selection of c ontrol strategies or SIP implementation”.

Response: The EPA believes the existing langua ge is sufficient to encompass the

recommendations in the comment.

(29) Comment: One commenter stated that the proposed near-roadway monitoring to measure particulate matter from transportation sources is only warranted with a species-based

standard. The commenters also states that many recognized medical experts have long believed that transportation related PM 2.5 is a major contributor to human health impacts. So from that standpoint, th e EPA’s proposal to add PM 2.5 ambient air monitor to roadwayV-25 locations might be a positive step , but onl y if the agency is proposing a speciated PM 2.5 standard.

Response: The EPA has addressed the issue of co nsidering a species based standard in section III.E.1 of the preamble to the fina l rule. As stated there, the Administrator concluded, consistent with CASAC advice, that the currently available scientific information did not provide a sufficient basi s for either targeting or eliminating any individual component or group of component s associated with any source categories from the mix of fine par ticles included in the PM 2.5 mass-based indicator. Consequently, although EPA agrees with the comment that adding PM 2.5 monitoring roadway is a positive step, and accordingly has finalized a requirement for monitoring for PM 2.5 mass at a modest number of locations, the EPA disagrees that a consequence of such a monitoring approach must be a speciat ed indicator for the standard.

(30) Comment: One commenter provided a detailed follow-up comment on the EPAs proposal to revise the form of the annual PM 2.5 standard to base the standard on the highest community-oriented monitor in an ar ea and to eliminate sp atial averaging. The commenter stated that, according to the EP A, for an area with multiple monitors, the appropriate reporting monitor with the hi ghest design value would determine the

attainment status for that area. The commenter does not support this approach as it is not consistent with monitoring results from health study analyses. Furthermore, the commenter is very skeptical of this appro ach given the EPA’s intent to locate more monitors along roadways in major urban ar eas without the requisite knowledge of what

the PM 2.5 readings might be from these monitors.

Response: The EPA has addressed the issue of e liminating spatial averaging in section III.E.3.a of the preamble to the final rule. Re garding the comment that this approach is

not consistent with th e monitoring results from health study analyses, the EPA considered

this issue in the form of the standard which is also describe d in section III.E.3.a of the preamble to the final rule. As explained in se ction II.E.c.i.1 of the preamble to the final rule, it is appropriate to compare the PM 2.5 concentrations from a maximum area-wide

monitor to the level of the annual PM 2.5 standard. Regarding the commenter’s statement on having the requisite knowledge of what the PM 2.5 readings might be from these monitors, the EPA has consider ed the available information 40 and the need to protect the public health with an adequate margin of sa fety in deciding to move forward with this requirement.

(31) Comment: One commenter stated the net effect of relocating the 52 monitors (the

monitors to be located in the near-road envi ronment) will be to overestimate the ambient

air concentration of PM 2.5 . These roadside monitors would be measuring PM 2.5 in a worst

case scenario that would not be representative of ambient air.

Response: The EPA does not believe it will overes timate ambient air concentrations of

PM 2.5 in the near road environment for the follo wing reasons. First, when monitoring is

40 In the preamble to the final rule we cite multiple studie s (Ntziachristos et al., 2007; Ross et al., 2007; Yanosky et al., 2009; Zwack et al., 2011) that are relevant to informing what the PM 2.5 readings may be.V-26 performed, it is an actual measurement and does not constitute an estimate of conditions present at that location. Second, the EPA in almost all cases purposely requires air agencies to site ambient air monitoring in areas that represent maximum concentrations, particularly to meet objectives such as a ssessing NAAQS compliance. EPA does this to focus monitoring resources where they are mo st worthwhile to assess compliance with the NAAQS and protection of public health a nd welfare. For example, our monitoring requirements are typically stated to site monitors “in area of expected maximum concentration”. This is described repeated ly throughout Appendix D to Part 58. Third, EPA’s long-standing practice is to locate monitors that meet the definition of ambient air. In the final rule EPA is requiring PM 2.5 sites in near-road environments to be collocated

with NO 2 . EPA notes that near-road monitors that are not “area-wide” will not be eligible for comparison to the annual NAAQS, but EPA believes that monitors comparable to the NAAQS will be representati ve of ambient air and representative of actual exposures in the near-road environment.

(32) Comment: One commenter stated that the EPA needs to consider modifications to the monitoring system for PM 2.5 emissions beyond the roadside monitors before implementing any revisions to the PM 2.5 standard and making nonattainment designations. The existing PM 2.5 monitoring network is not su fficient to predict ambient air concentrations reliably for all facility locations. For example, many monitors are located in areas expected to yield the highest PM 2.5 emissions. This high sampling bias is not representative of the true ambient air concentrations and will result in an unrealistically high number of nonattainment area s. For example, the ambient air levels for one foundry located in a rural setting are determined from a PM 2.5 emissions monitor

that is located in a more urban area locat ed 60 miles away. Consequently, the foundry may be subject unnecessarily to restrictions on modernization and expansion based on a nonattainment designation from biased and unrepresentative PM 2.5 emissions monitoring

data.

Response: The network design criteria fo r ambient air monitoring of PM 2.5 does not specifically require source oriented monitori ng stations; rather the network design is primarily focusing on characterizing area-wid e air quality which represent many such locations within urban areas. The EPA purposel y requires monitoring sites in the area of expected maximum concentration where it also represents area-wide air quality. The EPA does not believe it is necessary to address source oriented monitoring for facilities, for which there are no specific requirements, prior to implementing PM 2.5 monitoring in near-road environments. Any such discussion wo uld necessarily be premature, absent the specific facts and regulatory context. Th e EPA notes that areas are designated

nonattainment based on a determination that the area either violates or contributes to a violation of the NAAQS, and States are onl y required to implement those control measures that will attain the NAAQS as expe ditiously as practicable. Issues as to the proper extent of the nonattainment area or co ntrol strategy may be considered as those issues arise, but EPA does not believe that avoiding a determ ination of nonattainment is a reason to change the monitoring network design requirements.V-27 We note further, however, that the final rule expressly provides that PM 2.5 measurement data from monitors that are not representa tive of area-wide air qua lity but rather of relatively unique micro-scale, or localized hotspot, or relativ ely unique middle-scale impact sites are not eligible for comparison to the annual PM 2.5 NAAQS. The rule gives the specific example of “a micro- or middle-scale PM 2.5 monitoring site ... adjacent to a unique dominating local PM 2.5 source” being eligible only for comparison to the 24-hour

PM 2.5 NAAQS. Additionally, the majority of the PM 2.5 monitoring network consists of monitors that represent nei ghborhood scale or areas up to several kilometers across. Accordingly, the EPA believes that the revised PM 2.5 network will continue to appropriately characterize concentrati ons in a wide variety of settings.

(33) Comment: Several commenters summarized a seri es of concerns regarding the EPA’s proposal to end spatial averaging, to establis h a new requirement for roadside monitoring, allow comparison of micro- and middle-scale monitors to the PM 2.5 NAAQS and revoke the long-standing requirement that PM 2.5 monitors used for comparison to the 24-Hour

PM 2.5 NAAQS be “population-oriented”. The co mmenters generally object to these changes and request that EPA not act to finali ze any of the new requirements. One of the rationales provided was that EPA has not pr ovided sufficient rationale in the proposed rule for the changes, and the combined effect of all the changes would be to substantially revise the stringency of either the existing PM NAAQS (if retained) or any newly revised NAAQS.

Response: These comments are addressed in section III and section VIII of the preamble

to the final rule.

(34) Comment: One commenter stated that although th e EPA indicates that the new near-road micro-scale monitoring for PM 2.5 promotes efficiency, the EPA has apparently not considered in any substantial fa shion the differences between NO 2 and PM 2.5 formation in such an environment. Instead, the EPA’s ro adside monitoring plan is inherently and irretrievably arbitrary: The EPA essentially admits that the only reason that PM 2.5 monitors will be placed in such locations is that the EPA previously required such a new monitoring network for an en tirely different pollutant.

Response: EPA disagrees that it has not cons idered the differences between NO 2 and

PM 2.5 . As stated in section VIII.B.3.b.i of the preamble, the EPA is requiring the addition

of PM 2.5 monitors at near-road stations to support a number of monitoring objectives. Therefore, we reject the comment th at the only reason we are placing PM 2.5 monitors in near-road environments is that we already have a monitoring network there for another pollutant (i.e., NO 2 ). Regarding the comment that we ha ve apparently not considered, in any substantial fashion, the difference between NO 2 and PM 2.5 formation in such an environment, the EPA believes that the characterization of representative maximum

PM 2.5 concentrations due to on-road mobile sources and the a ppropriate location of such

PM 2.5 monitors will be the same approximate loca tions that are the focus of the near-road

NO 2 network. This is due to the fact that PM 2.5 , like NO X, is disproportionately influenced by heavy duty (HD) vehicles wh ich are predominantly diesel fueled, when compared to light duty (LD) vehicles whic h are primarily gasoline fueled. Specifically,V-28 for both PM 2.5 and NOx, HD vehicles emit more of these two pollutants and their precursors on a per vehicle basis than LD ve hicles. The EPA recognized this fact in the

near-road NO 2 network by requiring stat es to consider the fleet mix of candidate road segments where near-road monitoring mi ght occur. In the design of the NO 2 near-road

network where the PM 2.5 monitors will be installed, states were instructed to place a higher priority on those highly trafficked road s which have more dies el fueled vehicles using a metric called the fleet equi valent average annual daily traffic. 41 As such, the Agency believes it is appropriate that required near-road PM 2.5 monitors would be located

with near-road NO 2 monitors as they are similarly influenced not only by fleet mix but also by total traffic count, congestion pattern s, roadway design, terr ain, and meteorology. In addition, as discussed in section VIII of th e preamble, where an air agency believes a different location is a more appr opriate site for a near-road PM 2.5 monitor, the EPA can use its discretion in approving a deviation from the PM 2.5 monitoring requirements under existing authority in the network design crite ria. A deviation woul d be appropriate for consideration where, for example, a state provides quantitative evidence demonstrating that peak ambient PM 2.5 concentrations would occur in a near-road location which meets siting criteria but is not a near-road NO 2 monitoring site. Such deviations may be approved by the Regional Administrator as described in section 4.7.1 of Appendix D to part 58.

(35) Comment: One commenter stated that in the fi nal rule for the NO2 NAAQS, the near road monitoring requirement was justified by the EPA explicitly on the basis of the averaging time and level of the standard (e .g., the EPA finalized a new 1-hour standard at a level of 100 parts per billi on (“ppb”)). In taking this action, the EPA noted that NO 2 concentrations could be expect ed to vary, and therefore, the differences between nearroadway monitors and area-wide concentra tions that had been used to measure compliance with the pre-existing NO 2 annual standard could resu lt in a variable level of the standard (i.e., between 50 ppb and 75 ppb based on whether concentrations near roadways were 100% or 30% higher than at ot her monitors). Yet, in this proposed rule, the EPA does not offer any comparable analysis with respect to the relative stringency of

a PM 2.5 annual or 24-hour NAAQS as implemen ted through a network of new roadside

monitors.

This lack of information is even more notab le since the EPA is proposing that the probe and siting criteria for near-road PM 2.5 monitoring follow the same probe and siting

criteria for the NO 2 near-roadway monitoring sites. Thes e criteria require monitors “as near as practicable” to the out side nearest edge of traffic lanes, but no greater than 50 meters from the edge of a road. AFPM pr ovided comments to the EPA in 2009 regarding the severe limitations and qualifications that ar e associated with such monitors. To briefly

reiterate and as reflected in the NO 2 NAAQS ISA and REA, such monitors suffer from issues involving accuracy and the relationshi p between area-wide monitoring data and roadside emissions is highly va riable. In addition, there is increased potential for errors associated with monitor placement.

41 See the Near-road NO 2 Monitoring Technical Assistance Document at: http://www.epa.gov/ttn/amtic/f iles/nearroad/NearRoadTAD.pdfV-29 Response: As explained in section III.E.c.i.1 of the preamble to the final rule, it is appropriate to compare the PM 2.5 concentrations from a maximum area-wide monitor to

the level of the annual PM 2.5 standard. Consequently, the approach adopted in this rulemaking for the PM 2.5 standard is consistent with the u ltimate thrust of the approach in

the NO 2 NAAQS: providing a level of protection in an area with a maximum monitor affords requisite protection across the entire area. However, given differences in the

bodies of available scie ntific evidence for NO 2 and PM 2.5 , it is appropriate that EPA employed different types of analys es in the two reviews to achie ve this ultimate result. In

the case of NO 2 the scientific evidence that formed the basis for the final decision on the level of the revised standard included both ep idemiological studies, reporting associations between respiratory end points and area-wide NO 2 concentrations, and controlled human exposure studies, reporting respiratory e ffects following short-term exposures to NO 2 concentrations at or above 100 ppb. In consider ing this evidence, th e Administrator set a new 1-hour standard with a level of 100 ppb.

In setting this new standard, information on the NO 2 gradients around roadways was used

to consider the relations hips between area-wide NO 2 concentrations and potential exposure concentrations. Specifically, because the revised NO 2 standard was intended to

reflect the maximum allowable NO 2 concentration in an area, the Administrator

concluded that this standard would limit exposures to NO 2 concentrations reported in controlled human exposure studies to result in respiratory effects. In reaching this conclusion, the Administrator noted that the highest NO 2 exposure concentrations in urban areas could occur around major roadways. In addition, given the available evidence

for NO 2 concentration gradients around roadways , she concluded that the new standard

would maintain area-wide NO 2 concentrations (away from major roads) well below those in locations where key U.S. epidemiologica l studies had reported associations with adverse respiratory effects (75 FR 6501).

In the current review of the PM NAAQS the scientific evidence forming the basis for

final decisions on the PM 2.5 standards includes epidem iological studies reporting

associations between area-wide PM 2.5 concentrations and a number of adverse health outcomes (i.e., including mortality and a va riety of cardiovascul ar and respiratory effects). While controlled hu man exposure studies of PM 2.5 provide coherence and biological plausibility for the effects observe d in epidemiological studies, because of the exposure concentrations and dur ations evaluated they do not provide an appropriate basis

to inform decisions on the levels of the 24- hour or annual standards. In light of this

fundamental difference in the bodi es of evidence available for NO 2 and PM 2.5 , the approach to considering NO 2 roadway concentration gradient s adopted in the most recent review of the primary NO 2 NAAQS would not similarly inform the Administrator’s decisions in the current review of the PM NAAQS. 42 Therefore, the same approach

would not be warranted in the two reviews.

42 See also comments of UARG at 55 n. 73 drawing this same distinction (“The fact that the level of the PM 2.5 NAAQS is derived solely from epidemiological studies distinguishes it from the NO 2 NAAQS for which, as the EPA notes, 77 Fed. Reg. at 39010/2-3, it recently adopted near-road monitoring requirements. That standard was based, in significant part, on controlled human exposure studies in which actual NO 2 exposures were measured thatV-30 The EPA’s discusses the specifics of siting within the near-road environment in section VIII.B.5.a of the preamble to the final rule.

(36) Comment: One commenter stated that the EPA pr ovides little if any technical support for this proposal. Two documents are mentioned in the preamble: the “Near-road Monitoring Pilot Studies Objectives and Approach” and the “Review of the Near-Road Document – Outline.” But these documents either do not specifically address near-road PM 2.5 monitors or merely mention the issues involved with identifying monitor locations. Therefore, the EPA’s proposed monitoring plan is wholly unsupported in the preamble and the docket for this rulemaking.

Response: The EPA believes that the documents cited in combination with the rationale in the preamble do support the decision to add PM 2.5 near-roadway monitoring. While these documents were created prior to the proposal to add PM 2.5 monitors to near-road environments, for reasons already explained above in this respons e to comment section,

we believe there are a number of reasons that support siting PM 2.5 and NO 2 monitors at the same near-road monitoring station, related both to technical issues such as vehicle mix as well as support for monitoring objectives.

(37) Comment: One commenter stated that compounding the issue of near road monitoring is EPA’s proposal to change the current regulatory presump tion that micro- and middlescale monitors are not co mparable to the annual PM 2.5 NAAQS (unless specifically approved for such use by an EPA Regional Admi nistrator) and to additionally strike other existing regulatory language that limits th e use of such monito rs. EPA should abandon these proposals. Instead, the EPA should cons ider removing the cu rrent role of the Regional Administrator in order to promot e national consistency in NAAQS monitoring and to specifically disallow utilization of microscale monitors except for special purpose monitoring and for the purpose of conducting research.

Under current regulations, micro scale monitors are defined as applying to

“concentrations in air volumes associated with air dimensions ranging from several meters up to about 100 meters.” Thus, such monitors may comply with regulatory requirements yet be placed in varying locations , including at sites wh ich are very close to emissions which could heavily influence m onitoring results. The scale of “several meters” effectively provides no restriction at all on where monitors could be placed. When combined with EPA representati on that “any potential location for a PM 2.5 monitoring site . . . would be eligible for comparison to th e annual NAAQS”, the result is

that nonattainment areas could be consider ed to exist literally anywhere, including extremely small areas within a urban (or rural) area and/or where public access is prohibited.

Contrary to the EPA’s assertions in the pr oposed rule, the proposed changes to allow

micro- and middle-scale monitors to be co mpared to the NAAQS and the revoking of the

could reasonably be compared to concentrations measur ed near roads. 75 Fed. Reg. at 6500/1-01/2.”).V-31 “population-oriented” condition for monito ring locations (discussed below) do not promote consistency with the EPA’s existing re gulatory definition for “ambient air.” As noted by the EPA, the regulatory definition of “ambient air” specifically references the portion of outside air to which the genera l public has access. In implementing this regulatory definition, the EPA has exempted ar eas where a source owns or controls the property involved and where public access has been precluded. The Agency has consistently relied on documents describing th e definition of ambient air with regard to not including areas “to which public access is precluded by a fence or other physical barrier.” Thus, EPA has never interpreted ambient air to be “any potential location” outside of a building and proposing to allow “any” PM 2.5 monitor to be compared to the NAAQS is clearly and directly inconsiste nt with this long- standing regulatory interpretation. It is also contrary to origin al distinctions Congre ss made between ambient air and other air quality issues. In the 1970 Clean Air Act, Congress distinguished

between ambient air issues where emissions emanated from diverse stationary and moving sources, and other pollution agents that were “generally c onfined, at least for detection purposes, to the area of the emission source.”

Finally, as noted above with reference to roadside monitoring, the EPA provides no documentation for this proposal in the preamble or, as of this date, the docket. Rather than promote consistency, the change would have the opposite effect given the expansive interpretation of “any” within the CAA. Th erefore, the EPA should retain the current requirements restricting the use of micro- and middle-scale monitors and additionally consider revising the regulati ons to remove the ability of a Regional Administrator to determine monitor comparability. These ch anges would better promote the goal of national uniformity by making it clear that monitors would not be subject to highly localized conditions (perhaps measuring highly transient air quality in areas measuring no more than a few square meters) or subject to the individual (and perhaps inconsistent) preferences of different Regional Administrators.

Response: The EPA utilizes the Regional Admini strators in the approval of annual monitoring network plans and in many other areas applicable to network design and probe and siting criteria. We be lieve that the annual monito ring network plans, which are described in §58.10, provide an appropriate place for monito ring agencies to describe their networks, since the public has an opport unity to provide input on plans where there are changes. The EPA Regional Offices are th e most familiar with their individual State networks and possible changes to them and there is routine coordination across the EPA Regional Offices on technical and policy issues. Therefore, we do not believe that removing the Regional Administrator from th e process of approving micro- or middlescale sites from comparison to the annua l NAAQS, will promote consistency.

Regarding the comment, “Thus, EPA has ne ver interpreted ambi ent air to be “any potential location” outside of a build ing and proposing to allow “any” PM 2.5 monitor to be compared to the NAAQS is clearly and dir ectly inconsistent with this long-standing regulatory interpretation”. The EPA disagrees that we are intending ambient air to be “any potential location outside of a building” . We will continue to use our long standing definition of “ambient air” which is speci fied in 40 CFR 50.1 – our definition is: –V-32 “Ambient air means that portion of the atmosphere, external to buildings, to which the general public has access”. If a monitori ng station does not meet this definition, monitoring results from the station could not be compared to the PM 2.5 NAAQS. Consequently, the rule does not au thorize comparison with the annual PM 2.5 NAAQS with monitoring data from sites to which the public lacks access. Moreover, the final rule provides that to be compared to the annual PM 2.5 NAAQS, measurement data must come from monitors that are representative of area-wide air quality. Section 58.1. Area-wide “means all monitors sited at neighborhood, urba n, and regional scales, as well as those

monitors sited at either micro- or middle- scale that are representative of many such

locations in the same CBSA.” Id. So in addition to represen ting areas in which there is public exposure, sites must be representative of many similar locations in an area for comparison with the annual PM 2.5 NAAQS.

(38) Comment: One commenter stated that the proposed near-roadway monitoring to measure particulate matter from transportation sources is only warranted with a species-based

standard. The commenters also states that many recognized medical experts have long believed that transportation related PM 2.5 is a major contributor to human health impacts. So from that standpoint, th e EPA’s proposal to add PM 2.5 ambient air monitor to roadway locations might be a positive step , but onl y if the agency is proposing a speciated PM 2.5 standard.

Response: The EPA has addressed the issue of co nsidering a species based standard in section 3E.1 of the preamb le to the final rule.

(39) Comment: One commenter provide a detailed follow-up comment on the EPA’s proposal

to revise the form of the annual PM 2.5 standard to base the standard on the highest community-oriented monitor in an area a nd to eliminate spatial averaging. The commenter stated that, according to the EP A, for an area with multiple monitors, the appropriate reporting monitor with the hi ghest design value would determine the

attainment status for that area. The commenter does not support this approach as it is not consistent with monitoring results from health study analyses. Furthermore, the commenter is very skeptical of this appro ach given the EPA’s intent to locate more monitors along roadways in major urban ar eas without the requisite knowledge of what

the PM 2.5 readings might be from these monitors.

Response: The EPA has addressed the issue of eliminating spatial averaging in the preamble to the final rule. Regarding the co mmenter’s statement on having the requisite knowledge of what the PM 2.5 readings might be from thes e monitors, EPA believes it has

sufficient information to move forward with this requirement. In the preamble to the final rule we cite multiple studies (Ntzi achristos et al., 2007; Ross et al., 2007; Yanosky et al., 2008; Zwack et al., 2011) that ar e relevant to informing what the PM 2.5 readings may be.

(40) Comment: One commenter stated that the EP A is proposing to remove existing requirements regarding PM 2.5 NAAQS that require monitors to be “population-oriented” but provides exceedingly thin and conflicting rationale for the proposed change. On oneV-33 hand, the EPA proposes to eliminate this requirement since it claims it will have no impact. In the same breath, however, the EP A provides a justification for the proposal based on ambiguity in “applying modeling ac ross an area.” The illogic of these two statements is apparent. If a provision has no impact, it can hardly create ambiguity.

Outside of this observation, AFPM believes th at population-oriented requirements fulfill an important purpose in the implementation of NAAQS. Indeed, such requirements are aligned with the focus of primary NAAQS as standards intended to protect public health. Maintaining this current re gulatory requirement is al so consistent with the epidemiological data upon which the 1997 PM 2.5 NAAQS was established and on which this proposed rule still relies. Epidemiological studies, at their h eart, are designed to probe relationships between human exposures an d varying levels of an air pollutant. Such studies explicitly rely on exis ting air quality data in order to assess long-term and shortterm associations, and this relationship has b een noted since the ini tial staff review of

scientific information that was used to fi nalize a fine particul ate standard. The EPA should recognize this associati on and abandon its proposal to revoke this long-standing – and logical – requirement.

Response: In section VIII.B.2 of the preamble to the final rule and in this Response to Comments, the EPA explains that removi ng “population-oriented” does not have a practical impact on siting of monitors, but eliminates ambiguity and confusion that has arisen in other, related NAAQS-regulatory contexts, such as dispersion modeling for attainment planning and SIP development.

The EPA believes that the location of any si te meeting the definition of ambient air, which represents a location where the public is (or may be) exposed, will represent current or potential population exposure and is an acceptable location for comparison to

PM 2.5 NAAQS, as is the case with all other criteria pollutants. Additionally, for comparison to the annual PM 2.5 NAAQS, monitoring sites are al so to represent area-wide air quality; therefore, even if a monitor was located in a location at a small scale where no one was actually exposed on a given day, and this site was determined to be an area-wide site, there is still the potential for someone to be exposed th ere and that site is intended to represent many such other locations in the same area, where the public is (or may be) exposed.

On the comment of maintaining this current regulatory requirement for consistency with the epidemiological data upon which the 1997 PM 2.5 NAAQS was established and on which this proposed rule still relies, as expl ained in section II.E.c.i.1 of the preamble to the final rule, it is appropriate to compare the PM 2.5 concentrations from a maximum

area-wide monitor to th e level of the annual PM 2.5. Moreover, EPA anticipates that monitoring agencies will continue to site monitors that represent population exposure, particularly in light of the requirement to site monitors in ambient air, and the “areawide” requirement for comparabil ity to the annual NAAQS. EP A also points out that it is maintaining the overwhelming majority of the network at existing locat ions and that this

data will continue to be av ailable to support epidemiologi cal studies for comparison to the NAAQS and other objectives. The additi on of near-road PM2.5 monitoring data willV-34 add value to the ambient air network as it will provide for data in near-road environments where millions of people are exposed 43 and for which we have very little data.

(41) Comment: One commenter stated that they ha ve no problem with monitoring anywhere in the near-road environment for research pu rposes, but they are concerned that any PM 2.5 monitoring that is to be used to compare w ith the annual standard for attainment purposes must be population-oriented.

Response: This comment is addressed in the preamble to the final rule. As discussed there and elsewhere in this Response to Comments, a significant fraction of the population lives in proximity to major roads, and these exposures occur in locations that represent ambient air. Monitoring in such areas does not make the standard more stringent than warranted, but rather affo rds the intended protection to the exposed populations, among them at-risk populations, ex posed to fine particles in these areas. Thus, in cases where monitors in near roadway environments are deemed to be representative of area-wide air quality they would be compared to the annual standard. However, the EPA has limited the comparability of monitors that are not “area-wide” for purposes of comparison with the annual PM 2.5 NAAQS.

(42) Comment: One commenter stated several issues with the way the EPA proposes to implement the near-road requirement. The commenter is concerned that the elimination of spatial averaging and the definition of population-oriented when combined with the requirement to co-locate PM 2.5 monitors with near-road NO2 and CO monitors will result

in collection of data in locations that are representative of no-one ’s annual average or 24- hour average PM 2.5 exposure. This could result in a ma jor tightening of the standard, with significant unintended consequences for i ndustry and economic development. Entire metropolitan areas could be placed in non-at tainment based on measurements made where no-one is actually exposed.

The commenter is concerned that the decision to co-locate with NO 2 monitors was based

on convenience and the intent of the NO 2 near-road monitoring is to find the highest

micro-scale concentrations within a few meters of the most heavily travelled segments of the most heavily travelled expr essways, a unique situation.

The proposed rule defends the decision to piggy-back the PM monitoring with the planned NO 2 monitoring because considerable th ought and review has gone into that network design. However, the final guidelin es for monitor placement do not require population exposure at the monitoring site. Th e final Technical Assistance Document notes “It is important to recall that the objective is to monitor in locations that are as near as practicable to roads where peak, ground-le vel NO2 concentrations are expected to

occur.” Once candidate sites are identified ba sed on traffic counts a nd other factors, the potential for population exposure can be considered as noted in the TAD. However, the

43 One study identified that 45 million Americans live within 300 feet of a major roadway or other source of mobile emissions. The commenters’ information is based on the American Housing Survey, which is available on the web

at: http://www.census.gov/housing/ahs/data/ahs2009.html . The survey provides an estim ate of the county’s housing units in the U.S. that are located with 300 feet of a highwa y with four or more lanes, or a railroad, or an airport.V-35 discussion of population exposure su ggests that it is near-by p opulation rather than actual population exposure at the monitoring site that is the relevant consideration. Once a site has been selected and approved, the TAD indicates that the info rmation for the site in the EPA’s Air Quality System identify the site as “source-oriented” and include the horizontal distance from the probe to the near est edge of the target road. The TAD also discusses the fact that the probe may be lo cated in the right-of-way (ROW) of a limited access expressway. Thus, the location of NO 2 and any co-located PM 2.5 monitors will be source-oriented and not populati on-oriented. This would be a major change from prior practice and is not justified. N ear-road monitor results should not be used to compare to

the annual or 24-hour PM 2.5 standard unless it can be s hown that it is from a populationoriented site consistent with the defin ition in 40 CFR 58.1. Although the EPA proposes to allow the Regional Administrator to give a waiver for “unique” micro-scale sites, the Agency should not allow consideration of s ource-oriented sites in the first place.

Response: The commenter raises several points to address, a number of which are discussed in the preamble to the final rule in section III.E.3.a on the form of the annual

PM 2.5 NAAQS or in section VIII.B.3.b.i on the a ddition of a near-road component to the

PM 2.5 monitoring network. For example, section III.E.c.i.1 of the preamble to the final rule explains why it is appropriate to compare the PM 2.5 concentrations from a maximum

area-wide monitor to th e level of the annual PM 2.5

.

The comment suggests that the decision to co-locate with NO 2 monitors was based on

convenience. The EPA does believe that ther e are some benefits to local monitoring agencies in reduced resource needs from siting the PM 2.5 monitors in the near-road environment with other measurements; how ever, the most important reason we are requiring these monitors be located at multi- pollutant near-road station is to support multiple monitoring objectives. As stated in section VIII.B.3.b.i of the preamble: “a number of key monitoring objectives will be supported, including collection of NAAQS comparable data in the near-road environm ent, support for long-term health studies investigating adverse effects on people, prov iding a better unders tanding of pollutant gradients impacting neighborhoods that parallel major roads, availability of data to validate performance of models simulating n ear-road dispersion, char acterization of areas with potentially elevated concentr ations and/or poor air quality

, implementation of a multi-pollutant paradigm as stated in the NO 2 NAAQS proposed rule (74 FR 34442, July 15, 2009), and monitoring goals consistent with existing objectives noted in the specific design criteria for PM 2.5 described in appendix D, 4.7.1(b) to 40 CFR part 58”.

The comment further suggests that the intent of the NO 2 near-road monitoring is to find the highest micro-scale concentrations within a few meters of the most heavily travelled segments of the most heavily travelled e xpressways, a unique situation, and that the monitors “will be source-oriented and not population-oriented. This would be a major change from prior practice and is not justif ied.” The EPA notes that the substantive

criteria for which monitors are el igible to be compared to the PM 2.5 NAAQS monitors are not changing-- near road monitors have always been eligible for comparison to the 24 hour standard, and will continue to be eligible for comparison to the annual standard only if they are found to be “area-wide” (i.e., to represent many such locations in the area).V-36 The EPA disagrees that siting monitors in the area of expected maximum concentration is a unique situation. Such cases of seeking the highest concentrations of a pollutant have been a long-standing goal in the network design of every criteria pollu tant as described in appendix D to Part 58 in order to provide th e greatest degree of protection for public health and welfare without requiring an overly burdensome m onitoring network. The EPA maintains that the near-road environments are locations where there is a significant potential for populat ion exposure to PM 2.5 and it is important to locate monitors to measure that exposure. To the extent th ese sites are “unique” they would not be comparable to the annual PM 2.5 NAAQS.

Regarding the comment that the near-road moni tor results should not be used to compare

to the annual or 24-hour PM 2.5 standard unless it can be shown that it is from a population-oriented site consistent with the definition in 40 CFR 58.1. For the reasons explained in section VIII.B.2.a of the preambl e to the final rule, the EPA will no longer be using “population-oriented” as a condition for comparability to the PM 2.5 NAAQS. The EPA disagrees that we shoul d not allow consideration of source-oriented sites in the first place. There is no exemption from the NAAQS for violations caused by sources. Indeed, for some NAAQS, such as Pb, most of the monitoring network may be sourceoriented but that does not mean that the da ta is not comparable to the NAAQS. Moreover, source oriented and population-or iented are not mutually exclus ive. So there is no basis, even if we were keeping a requirement for population oriented (which we are not), to exclude source oriented sites. However, the EPA is requiring that all monitors must be at least “area-wide” to be comp ared to the annual NAAQS.

(43) Comment: One commenter is also concerned thatEPA is overestimating the gradients in

PM 2.5 near the road. The four references pr ovided in the proposed rule do not make a

sufficient case to add near-road PM 2.5 monitoring. The Zwack et al. (2011) study involves the impact in street canyons in mid-town Manhattan and concludes that PM 2.5 is elevated by from 5 to 8 % over background. Although the Zwack et al. study is useful, it does not apply to the multi-lane expressway case that is at issue in the proposed rule. The Ross et al. (2007) and Yanosky et al. (2008) references are to st udies that used land-use regression to estimate PM 2.5 exposures and do not include any data on actual roadway impacts. The Ntziachristos et al. (2007) study evaluated the composition near the road

with a site 1 mile downwind and did not ev aluate the gradient near the roadway. In contrast to these studies, Karner et al. (2010) synthesi zed the results of 41 studies evaluating the shape and rate of decay curves of pollutants near roadways. The review

included 16 studies with PM 2.5 measured at various distances from the roadway. Karner et al. report, in contrast with other pollutants, PM 2.5 shows little or no gradient with

distance from the road. Since the Karner et al . review analyzed real-world data from a variety of roadway situations, the commenter urges the Agency to re-visit its concern

over PM 2.5 gradients near roadways and the need for near-road monitoring. Karner et al. show that near-road exposures to PM 2.5 are not substantially elevated compared to community-wide exposures.

Response: The EPA has reviewed the Karner paper and believes that the results presented

are consistent with the results from Zwac k, which support our position that there areV-37 gradients in near-road environments. The EPA also believes the other papers cited in the preamble (Ross, Yanosky, and Ntziachristos) ar e useful to support its position that there

are elevated levels of PM 2.5 in near-road environments. The information presented in

Karner states that PM 2.5 concentration levels in near -road environments have a 22% decrease between the edge-of-road concentr ation and the farthest downwind measured value, which was identified at a distance of 986 meters. Therefore, the EPA disagrees with the commenters point that current info rmation establishes there are little or no gradients with distance from road. The EPA maintains its position that these gradients

exist and there is a need for near-road monito ring for the reasons explained in the section VIII.B.3.b.i of the preamble to the final rule. However, the EPA agrees that there are

uncertainties over the extent of the gradient and it may be mode st. To the extent there is a smaller than expected gradient, the info rmation will still be useful to support monitoring objectives, and the f ears of several commenters that near road monitoring is unrepresentative of wider air quality will be dispelled.

(44) Comment: One commenter stated that along with th e small gradient near roadways, there is also evidence that drivers and passe ngers in vehicles experience lower PM 2.5 exposures due to deposition losses in the vehicle air hand ling system. For example, Riedeker et al., 200359 report in-vehicle PM 2.5 was 24% lower than ambient and roadside levels, in a study of the occupational exposure of North Ca rolina State troopers during their normal work shifts, probably due to de position associated with the re circulating air. Similarly, Rodes et al., 199860 in a study of thirty-two, 2-hour commuting trips in Los Angeles and Sacramento, CA in the fall of 1997 reporte d that particle concentrations were significantly higher outside the vehicles than inside, with inside levels often less than roadside levels, presumably due to losses in th e vehicles ventilation system. Thus, there is

also evidence that in-v ehicle exposures to PM 2.5 are not elevated compared to community-wide exposures.

Response: As stated in the secti on VIII.B.3.1 of the preamble to the final rule, we are requiring PM 2.5 monitors in the near-road environmen t to support a number of objectives. However, we did not state that we are at tempting to characterize the actual on-road concentrations; rather, we are attempting to understand, among other objectives, the health impacts of near-road PM 2.5 exposures. Therefore, wh ile the on-road exposure is

still a relevant consid eration, since these are locations where the public is exposed, it was not the sole basis for the proposed network design requirements for PM 2.5 monitors in near-road environments, and the possibility that there is a gradient of exposure for people inside moving cars as compared to outside, while useful to understand, is not a reason to forego near road monitoring. Therefore, we ma intain our position that there are gradients

in the near-road environment and that we have a responsibility to monitor the exposure of the public in these areas.

(45) Comment: One commenter stated that basing attainment designations on each area's single worst-case monitor, instead of using th e current practice of area-wide averaging produces non-representative sampling result s. Compounding this proposed approach is EPA's intent to require placement of monitors near heavily traveled roadways. These twoV-38 elements of the proposed monitoring sche me will significantly and improperly skew results in many areas.

Response: The first part of this comment has to do with EPA’s decision to revoke spatial averaging and use the highest-reading area-wid e monitor in each area for purposes of comparing to the annual NAAQS. This commen t is addressed in the section III.E.3.a of the preamble to final rule, but EPA notes br iefly that no area is currently using spatial averaging. The second part of the comment connects the requirement to place monitors near-heavily travelled roads with the commenters point on producing non-representative sampling results. The EPA disagrees w ith the commenters point on producing nonrepresentative sampling results. The EPA’s network design requirements for PM2.5 include a provision to lo cate sites at area-wide locations, t hus these locations are in fact representative of many such lo cations throughout the same area. In addition, as discussed elsewhere, EPA believe that monitors should generally be located in areas of expected

maximum concentration so th at the NAAQS can be attain ed and provide requisite protection throughout the country.

(46) Comment: Several commenters stated that EPA ha d not demonstrated the need to add a requirement for near-road monitoring of PM 2.5 . The primary purpose of these monitor appears to be research.

Response: The EPA addressed the objectives of the near-road PM 2.5 monitors in section VIII of the preamble to the final rule. The EPA believes these objectives provide sufficient rationale to add the requirement for the near-road PM 2.5 monitors. The EPA agrees that one of the purposes for thes e monitors is research; however, the EPA disagrees that this is the primary purpose.

(47) Comment: One commenter (for API) stated that placing PM 2.5 monitors near roadways rather than at population-or iented locations will like ly measure locally unique concentrations of primary particulate associat ed directly with diesel exhaust, tire and brake wear and roadway dust. These observa tions will likely have limited geographical representativeness, and should be interpreted with caution. M onitors should not be moved near roadways if these measurements do not represent the broader area.

Response: The EPA notes that near road monitors will be characterized by monitoring agencies, subject to Regional Administrator ap proval, as to whether they are “area-wide” (i.e., whether they represent many such locati ons within an area). To the extent that concentrations of primary particulate are captured during th e monitoring of PM 2.5 in any

near-road environment that is determined to be an area-wide location, such monitoring is representative of many lo cations throughout the area a nd therefore is not unique.

(48) Comment: One commenter stated that they view near-road or source-oriented monitoring as failing to represent populati on exposures (unless people are sitting in lawn chairs by roads for extended periods of time) or visibi lity concerns under the proposed primary and secondary PM 2.5 NAAQS. The newly installed NO 2 monitoring network is devised to

address NO 2 emission from mobile sources and addr ess curbside health concerns sinceV-39 NO 2 is radicalized quickly in the atmosphere. The height and distance of such stations from roads, seems particularly unsuited for PM 2.5 formation in urban areas, although we fully appreciate why the EPA w ould like to take advantage of these stations because of the cost of a new monitoring network. We th ink the EPA should re-examine these plans. Instead, the EPA should utili ze existing monitors for thes e purposes, and importantly, that will require much more extensive changes to Part 58 regulations that exceed the proposed changes in this rulemaking. Among th ese are changes that allow for existing

monitors to be relocated.

Response: Regarding the comment that views near-road or source-oriented monitoring as failing to represent population exposures, the EPA disagrees. As explained in section VIII.B.3.b.i of the preamble to the final rule and this response to comments, there are large numbers of people (in the tens of millions ) that live, work, play, and go to school in close in proximity to major roadways. These exposures occur in locat ions that represent ambient air for which the agency has a respons ibility to ensure the public is protected with an adequate margin of safety. Comparis on of monitoring results from such areas to the NAAQS is therefore appropriate.

The height and distance of the PM 2.5 monitors is addressed in section VIII.B.5.a, while the rationale of why PM 2.5 is collocated with NO 2 at near-roadway station is addressed in VIII.B.3.b.i. As we explain in the preamble, we believe that the characterization of representative maximum PM 2.5 concentrations due to on-road mobile sources with PM 2.5 monitors will be at the same approximate lo cations that are the focus of the near-road

NO 2 network. This is due to the fact that PM 2.5 , like NO X, is disproportionately influenced by heavy duty (HD) vehicles wh ich are predominantly diesel fueled, when compared to light duty (LD) vehicles which are primarily gasoline fueled. Specifically,

for both PM 2.5 and NOx, HD vehicles emit more of these two pollutants and their precursors on a per vehicle basis than LD vehi cles. The EPA recognize d this fact in the

near-road NO 2 network by requiring stat es to consider the fleet mix of candidate road segments where near-road monitoring mi ght occur. In the design of the NO 2 near-road

network where the PM 2.5 monitors will be installed, states were instructed to place a higher priority on those highly trafficked road s which have more dies el fueled vehicles using a metric called the fleet equivalent average annual daily traffic. As such, the Agency believes it is appropriate that required near-road PM 2.5 monitors would be located

with near-road NO 2 monitors as they are similarly influenced not only by fleet mix but also by total traffic count, congestion pattern s, roadway design, te rrain, and meteorology. As discussed in section VIII of the preamble, if States can demonstrate that a different monitor location is more appropriate, e.g., thr ough a quantitative demonstration that peak

ambient PM 2.5 concentrations would occur in a n ear-road location which meets siting

criteria but is not a near-road NO 2 monitoring site, then the EPA Regional Administrator may use its existing discretion to approve a deviation from the PM 2.5 monitoring requirements.

(49) Comment: One commenter (H&W) stated they believe an emphasis on near-road

monitors could skew monitored PM 2.5 emissions results away from a representative dataset compatible with measuring NAAQS attainment. NAAQS have traditionallyV-40 assessed air quality health impacts across general areas. The EPA admits near-road

monitors will result in an unde fined "bump" in monitored PM 2.5

. See 77 Fed Reg. at 39007. In this way, requiring n ear-road monitors may morph what are now area-wide air quality assessments into a hot-spot analysis predicated solely on, in EPA's terminology, "bump" PM 2.5 levels. The proposed PM Rule's near -road monitor requirements should not have the normative effect of forcing vast geographic swaths to lower emissions simply because of limited non-representative monito ring data. Instead, EPA should eschew plans that will undermine the representative quality of air quality monitoring data and require

broad PM 2.5 emissions reductions in order to achie ve attainment at discrete locations where no population is likely to be exposed for the averaging periods (24-hour and annual) of the NAAQS. For this reason, the commenter urges the EPA to reexamine the proposed PM Rule's near-road monitoring requirements.

Response: As discussed elsewhere, the EPA gene rally tries to place NAAQS monitors in areas of expected maximum concentration, in order to make the most efficient use of limited monitoring resources while protecting pub lic health and welfare. As explained in, section VIII.B.3.b.i of the preamble to the fina l rule and this response to comments, there are large numbers of people (in the tens of millions) that live, work, play, and go to school in close in proximity to major roadwa ys and the EPA believes it is important to monitor their exposure to PM 2.5 in the near-road environment. EPA notes that the criteria for which monitors are comparable to th e NAAQS are not substantively changing, as monitors will still be required to be “are a-wide” to be comparab le to the NAAQS and

EPA does not believe that removal of th e “population oriented” requirement will substantively affect which monitors are compar able (particularly in light of the area-wide requirement).

To the extent the commenter is concerned a bout the “effect of forcing vast geographic swaths to lower emissions simply because of limited non-representative monitoring data,” the EPA notes that issues as to th e proper extent of the nonattainment area or control strategy may be considered as those i ssues arise, but the agency does not agree that avoiding a determination of nonattain ment is a reason to change the monitoring network design requirements.

(50) Comment: One commenter stated that the EPA propos e s to determine compliance with the proposed PM 2.5 standard based solely on measurements acquired from PM 2.5 monitors that are placed in close proximity to major roads in each air quality area

. Importantl y, data f rom other e x isting PM 2.5 monitors will not be used to calcu l ate the spatial average for the air quality area

. This method of compliance demonstration will bias the results

toward non-attainment sinc e " near road " monitors will likely r e cord higher PM 2 .5 readings than other monitor s

. For example

, assume that the EPA revises the PM 2 .5 standard from 15 μg/m 3 to 12.8 μg/m 3 and that the concentration of PM 2.5 based on the average of existing community monitors for the air quali ty area is 12.5 μg/m 3 . It would appear that the area is in attainment. However

, if the averaged data from the existing network of community-based mon itors is ignored and, instead, a single "near road"

monitor - due to its location - records PM 2.5 at a level that is as little as 5 percent higher

than the network monitors ' spatial average, the air quality area is classified as non-V-41 attainment with the revised ( hypothetical) standard of 12.8 μg/m 3 (i.e., 12.5 μg/m 3 x 105% = 13.1 μg/m 3 ). The Clean Air Act requires that PM 2 .5 sources within nonattainment areas either install additi onal control technologies or restrict growth in order to remedy the non-attainment condition. Non-attainment designation will have a direct economic impact on the vitality if not the viability of business located in or around the non-attainment area. By instituting a techni cally flawed policy of using only near-road

monitors to determine attainment status for an air region, the EPA is unnecessarily increasing the cost of doing business by crea ting an artificial air quality concern.

Response: The EPA disagrees that it will solely us e near-road monitors to determine the

attainment status for an area. The EPA’ s network design criteria include multiple requirements for PM 2.5 monitors, including a requirement to monitor in an area-wide location of expected maximum concentration. All eligible monitors in accordance with Appendix N to Part 50 and Part 58 will be used in comparison to the NAAQS. The EPA disagrees that the addition of PM 2.5 monitors will bias the re sults toward non-attainment since "near road" monitors will likely record higher PM 2.5 readings than other monitors.

The addition of the near-road monitors will lead to an appropriate level of protection, with an adequate margin of safety, for thos e populations that live, work, play, and go to school near major roadways. The rationale for the appropriate le vel and form of the

PM 2.5 NAAQS, including a discussion on elimina ting spatial averaging is described in section III.E.3 and section III.E.4 of the pream ble to the final rule. While the EPA does not dispute the calculations provided in the example of the comment, the EPA points out that this example fails to r ecognize constraints on the use of spatial averaging from the 2006 NAAQS that are intended to ensure that spatial averaging does not adversely affect disadvantaged populations. In the 2006 PM NAAQS final rule, the EPA tightened the criteria for use of spatial averaging to provide increased protection for vulnerable populations exposed to PM 2.5 . This change was based in part on an analysis of the potential for disproportionate impacts on poten tially at-risk populations, which found that the highest concentrations in an area tend to be measured at monito rs located in areas where the surrounding population is more likel y to have lower education and income levels and higher percentages of minority populations (71 FR 61166/2, October 17, 2006; U.S. EPA, 2005, section 5.3.6.1). Since t hose changes, no area has used spatial averaging, and no other NAAQS uses spatial averaging.

(51) Comment: One commenter stated that EPA should not finalize the proposed changes to

PM 2.5 monitoring, which would substantially increase the stri ngency of the PM 2.5 Primary NAAQS, even absent the propos ed tightening of the level of the annual standard.

Response: As described in section III.E.3.a of the preamble to the final rule, EPA took

the addition of near-road mon itoring into consideration in setting the form of the NAAQS. The EPA disagrees that the proposed changes to PM 2.5 monitoring would substantially increase the stringency of the PM 2.5 Primary NAAQS. A significant fraction of the population lives in proximity to major roads. These exposures occur in locations that represent ambient air for which the agency has a responsibility to ensure the public is protected with an adequate margin of safet y. Ignoring monitoring results from such areas (or not monitoring at all) w ould abdicate this responsibilit y. Put another way, monitoringV-42 in such areas does not make the standard strict er, but rather affords requisite protection to the populations, among them at-risk populations, exposed to fine particulate in these areas. Thus, the EPA has made a determina tion to protect all area-wide locations, including those locations with populations living near major roads that are representative of many such locations throughout an area. As discussed above, the EPA concludes that the requirement to locate monitors to repr esent ambient air, along with other siting requirements, will ensure that monitors represent PM 2.5 concentrations in areas of potential public exposure.

(52) Comment: One commenter stated that the EPA is proposing to require that 52 near-road

PM 2.5 monitors be placed in locations around the country, collocated with NO 2 monitors. The EPA states that placing PM 2.5 monitors in such locations will be the “most efficient and beneficial approach” to deploying this network. Given that the EPA performed no analysis of the differences be tween near-road monitoring for NO 2 and PM 2.5 , this requirement is arbitrary and capricious to the extent that it would form the basis for any designation of PM 2.5 nonattainment areas. While there may indeed be economies in placing such monitors at existi ng sites, any monitor so co-loc ated is not rationally related to or comparable to the NAAQS . Further, as discussed later, it appears that the proposed roadside monitors would increase the stringen cy of the standard a nd lead to designation

of additional nonattainment areas.

Response: The EPA disagrees that the requirement to establish and use data from PM 2.5 monitors in near-road environments for th e NAAQS is arbitrary and capricious. As explained in the section VIII.B .3.b.i of the preamble to the fi nal rule, there are gradients in near-roadway PM 2.5 that are most likely to be associ ated with heavily travelled roads (particularly those with signi ficant heavy-duty diesel activit y, which is also associated

with increased NO 2 concentrations), and that the larg est numbers of impacted populations are located in the largest CBSAs in the count ry (Ntziachristos et al., 2007; Ross et al., 2007; Yanosky et al., 2008; Zwack et al., 2011 ). There are a number of reasons identified in the preamble and this Re sponse to Comments that support siting PM 2.5 and

NO2 monitors at the same n ear-road monitoring station, rela ted both to technical issues such as vehicle mix as well as support for m onitoring objectives. Fu rther, a significant fraction of the population lives in proximity to major roads 44 . These exposures occur in locations that represent ambient air for which the agency has determined is important to monitor to protect public heal th and welfare. As discussed elsewhere, the EPA disagrees that monitoring in these areas increases the stringency of the standard, or that the possibility of additional nonatta inment areas is a reason not to monitor in these areas.

(53) Comment: One commenter provided comments on the EPA’s use of two documents as supportive of the new near-road monitoring requirement, i.e., the “Near-road Monitoring Pilot Studies Objectives and Approach” and the “Review of the Near-Road Document – Outline.” These documents are wholly inadeq uate to support the proposed monitoring

44 One study identified that 45 million Americans live within 300 feet of a major roadway or other source of mobile

emissions. The commenters information is based on the Amer ican Housing Survey, which is available on the web at: http://www.census.gov/housing/ahs/data/ahs2009.html . The survey provides an estim ate of the county’s housing units in the U.S. that are located with 300 feet of a highwa y with four or more lanes, or a railroad, or an airport.V-43 requirements. The first document does not specifically a ddress near-road PM 2.5 monitors, but is centered on newly promulgated NO 2 NAAQS; the second document is a 1-page

outline which addresses the identification of locations and parameters for maximum concentrations of several pollutants, not the establishment of monitoring requirements themselves. Instead, the entire basi s of the EPA’s proposed near-road PM 2.5 monitoring network appears to be a suggestion by CASAC that such measurements might be useful.

This is an insufficient informational basis and justification for rulemaking.

Response: With regard to the documents cited a nd their applicability to support the nearroad requirement, the EPA is not exclusiv ely relying on these documents to support its position to add PM 2.5 monitors to the near road envi ronment, rather these documents provide useful technical information that can be gleaned as monitoring agencies consider

the addition of PM 2.5 to the near-road stations. We also explain in preamble section

VIII.B.3.b.i of the final rule that the char acterization of representative maximum PM 2.5 concentrations due to on-road mobile sources and the appropriate location of such PM 2.5 monitors will be the same approximate loca tions that are the focus of the near-road NO 2 network. This is due to the fact that PM 2.5 , like NO X, is disproportionately influenced by heavy duty (HD) vehicles which are predominan tly diesel fueled, when compared to light duty (LD) vehicles which are primarily ga soline fueled. Specifically, for both PM 2.5 and NOx, HD vehicles emit more of these two po llutants and their precu rsors on a per vehicle

basis than LD vehicles. The EPA rec ognized this fact in the near-road NO 2 network by requiring states to consider the fleet mix of candidate road segments where near-road monitoring might occur. In the design of the NO 2 near-road network where the PM 2.5 monitors will be installed, states were instru cted to place a higher priority on those highly

trafficked roads which have more diesel fuel ed vehicles using a metric called the fleet equivalent average annual daily traffic. 45 As such, the Agency believes it is appropriate that required near-road PM 2.5 monitors would be located with near-road NO 2 monitors as they are similarly influenced not only by fl eet mix but also by total traffic count, congestion patterns, roadway design, terrain, and meteorology.

The EPA disagrees with the statement that the entire basis of the EPA’s proposed nearroad PM 2.5 monitoring network appears to be a suggestion by CASAC that such measurements might be useful and that this is an insufficient informational basis and justification for rulemaking. While the EP A did consider CASAC’s advice, it also

considered a number of other factors such as explained in section VIII.B.3.b.i of the preamble to the final rule. For example, th e EPA also considered the significant fraction of the population that lives in proximity to major roads. These exposures occur in locations that represent ambien t air for which the agency ha s a responsibility to ensure the public is protected with an adequate margin of safety.

(54) Comment: Several commenters (AEP) stated that EPA has not demonstrated the need to add a requirement for near-road monitoring of PM 2.5

.

45 See the Near-road NO 2 Monitoring Technical Assistance Document at: http://www.epa.gov/ttn/amtic/file s/nearroad/NearRoadTAD.pdfV-44 Response: The EPA believes that for the reasons stat ed in section VIII of the preamble to the final rule, there are sufficient reasons to add a requirement for near-road monitoring

of PM 2.5

.

(55) Comment: One commenter (AGC) stated that they oppose EPA’s addition of near-road monitoring as it would measure mobile-source emissions instead of ambient air quality.

Response: Any monitoring station sited in an area representing ambient air is by definition measuring ambient air. Since PM 2.5 monitors are to be sited at near-road monitoring stations that are in the ambient air, they are measuring ambient air quality.

(56) Comment: One commenter (AGC) stated monitori ng sites should reflect ambient air conditions to which a significant portion of th e public is exposed – not conditions specific to one location. Emissions are naturally going to be higher in some area of a county and

lower in others.

Response: As explained in section VIII.B.3.b.i, a significant fraction of the population lives in proximity to major roads. These exposures occur in locations that represent ambient air which the agency has determined is important to monitor because of the potential for population exposure to pollu tants at levels exceeding the NAAQS. Although it may be true that emissions will ofte n be higher in one area than another, the EPA generally sites monitors in areas of e xpected maximum concentrations to protect public health and welfare. The EPA notes, howev er that for the reasons explained in the preamble, monitors must be at least “are a-wide” to be comparable to the annual PM 2.5 NAAQS.

(57) Comment: One comment letter representing 48 or ganizations provided strong support for

the addition of the near road monitors. The comment letter stated that monitors with the highest measured concentrations of fine particulate matter tend to be located in areas where the population is more likely to be lo wer-income, have lower education levels, and minority. Furthermore, lower socioeconomic po pulations may be more vulnerable to fine particulate matter because of proximity to roadways and industry, higher rates of preexisting diseases, less access to health care, and nutritional deficiencies. At the same time, rural areas are at high risk because of significant gaps in air monitoring. Further,

numerous scientific studies have now identified increased health risks in association with traffic-generated air pollution, including fine particulate matter. With more than 45 million Americans living less than 300 feet from a highway, there is growing concern about the health impacts of living near heavily traveled roads. One of the most significant aspects of the EPA proposal relates to the proposed extension of the fine particle monitoring network to the near road environm ent. Motor vehicle traffic is a major and undisputed source of emissions of ultrafine, fine and coarse particles. In order to protect all citizens’ right to a safe and healthy air s upply, as mandated by the Clean Air Act, it is imperative that our nation’s air pollution air quality monitoring network require measurement of particulate concentrations ne ar highways and other significant sources of particulate pollution. This protection is long ove rdue and it is critical that that theseV-45 monitored concentrations, or the modeled equi valent, be considered in the designation of nonattainment areas and the development of associated air pollution control programs.

Response: The comment in support of requiring the addition of PM 2.5 monitors to the near-road environment is acknowledged.

(58) Comment: One comment letter representing fi ve organizations stated that they welcome and support EPA’s proposal to monitor the concentrations of PM 2.5 that occur in near-road communities where millions of Americans are exposed to emissions from major highways, truck terminals and facilities that attract concentrations of motor vehicles. This NAAQS proposal seeks to begin for the first time the implementation of the PM 2.5 NAAQS within the zone where emissions of fine particles from existing transportation facilities that attract large concentrations of mobile sources adversely affect concentrations of PM 2.5

.

Response: The comment in support of requiring the addition of PM 2.5 monitors to the near-road environment is acknowledged.

(59) Comment: One commenter stated they were pleased to see that the Agency plans to increase near-roadway monitoring to provide new information on population exposures to

mobile sources of PM.

Response: The comment in support of requiring the addition of PM 2.5 monitors to the near-road environment is acknowledged.

(60) Comment: One comment letter representing 48 organizations (different than the commenters cited above) stated that they support the addition of PM 2.5 roadway monitors, (as) an efficient implementation process specif ically for communities that are already in non-attainment and significant environmental ju stice considerations, as well as consider

in this and future assessments the research studies that describe the disproportionate health impacts on low income, communities of color.

The letter also stated that they applaud the EPA for realizing the importance monitoring for co-pollutants, as well proposing additional PM 2.5 monitors near highways, traffic corridors, especially near re sidential areas. Additional mon itoring will provide a better opportunity for us to understand the health imp acts of exposures, especially in core based statistical areas with one million persons or greater. With approximately 45% of the urban population living near major roads, and ethnic minorities and lower-income populations being more likely to live near sources of PM 2.5 , adding to the current national monitoring network will help researchers to be tter understand the exposure variation near roadways and other hotspots wher e exposure dispar ities exist.

The comment letter also recommends that if at all possible, adding PM 10-2.5 monitors to this network would be extremely helpful, since there are limited PM 10 data in the near road environment. As noted by the CASAC a nd others, there is an obvious data gap to support future regulatory revi ews and better und erstand how PM 10 emissions are contributing to the existing public health bu rden. The comment letter states that theyV-46 support the addition of PM 2.5 near-road monitors to the existing network, and, where possible, adding in PM 10-2.5 monitors.

Response: The comment in support of requiring the siting of PM 2.5 monitors in the nearroad environment is acknowledged.

With regard to the recommendation to add PM 10-2.5 measurements to the roadway environment, where possible, as explained in section VIII.B.3.b.i of the preamble to the proposal, the EPA supports the measurement of other pollutants in the near-road

environment. Such additional measurement ar e not required, but encouraged to support enhancing knowledge of exposures in the near-road environment.

(61) Comment: One commenter offered some support for the addition of PM 2.5 monitors to the near-road environments stating that they agree with the EPA that “...such near-road sites could provide valuable understanding of emissions “such as BC, ultrafine particles, and particle size distribution.”” However, the commenter also expressed concern as they state that “Once again, the EPA unfortunately displays its misgui ded bias prioritizing diesel over gasoline emissions. “The EPA be lieves that there are gradients in nearroadway PM 2.5 that are most likely to be associated with heavily travelled roads, particularly those with significant heavy duty diesel activity.” The commenter later goes on to state that they are “...confident th at these monitors will provide further reinforcement for what is already known about particle-borne toxics in our largest cities.”

Response: The commenter appears to be generally supportive of pursuing

characterization of the near-road environmen t; however, they have a specific concern regarding our placement of monitors in that we incorpor ate diesel as a factor in the identification of the road segment to use, which is tied siting of NO 2 monitors.

We do believe that the characteriza tion of representative maximum PM 2.5 concentrations

due to on-road mobile sources and the appropriate location of such PM 2.5 monitors will be the same approximate locations that are the focus of the near-road NO 2 network. This

is due to the fact that PM 2.5 , like NO X, is disproportionately influenced by heavy duty (HD) vehicles which are predominantly diesel fueled, when compared to light duty (LD) vehicles which are primarily gasoli ne fueled. Specifically, for both PM 2.5 and NOx, HD vehicles emit more of these two pollutants a nd their precursors on a pe r vehicle basis than LD vehicles. The EPA recognized this fact in the near-road NO 2 network by requiring

states to consider the fleet mix of candida te road segments where near-road monitoring might occur. In the design of the NO 2 near-road network where the PM 2.5 monitors will be installed, states were instructed to place a higher priority on those highly trafficked

roads which have more diesel fueled vehicles using a metric called the fleet equivalent average annual daily traffic. As such, the Ag ency believes it is a ppropriate that required

near-road PM 2.5 monitors would be located with near-road NO 2 monitors as they are similarly influenced not only by fleet mix but also by total traffic count, congestion patterns, roadway design, te rrain, and meteorology.V-47 G. Comments on Revoking PM 10-2.5 Speciation Requirements at NCore Sites

(1) Comment: Several commenters support re voking the requirements for PM 10-2.5 speciation

at NCore stations.

Response: The comment in support of the proposal is acknowledged and EPA is adopting the proposed approached in the final rule.

(2) Comment: One commenter stated that with rega rd to the EPA’s proposal to revoke the requirement for PM 10-2.5 speciation monitoring as part of the current suite of NCore monitoring requirements, that dropping this requirement may seem reasonable from a compliance perspective, it is problematic from the research perspective and needlessly delays improved understanding gained fr om the speciated data collected.

Response: This comment is addressed in section VIII.B.3.c of the preamble to the final

rule.

(3) Comment: One comment letter representing five organizations stated that they strongly oppose EPA’s proposal to rescind the speciation requirements for PM 10 monitoring. They find no legal, practical, or scientific justification for eliminating requirements for better characterization of coarse particle concentrations.

Response: This comment is addressed in section VIII.B.3.c of the preamble to the final

rule.

H. Comments on the network design for the proposed secondary PM 2.5 visibility index.

(1) Comment: One commenter stated that the scope of the speciation monitors should be limited to “urban areas” only and should not include IMPROVE monitoring sites, which are already evaluated as part of the Regional Haze program.

Response: For the reasons stated in section VI of the preamble to the final rule, EPA is not adopting the proposed secondary PM 2.5 visibility index NAAQS. Consequently, the final rule does not include requirements on the use of CSN or IMPROVE stations.

(2) Comment: One commenter recommends that the EPA clarify that PM 2.5 chemical species measurements be only required in urban area s, primarily utilizing the CSN network. Also, to the extent that an individual monitoring agency may not have appropriate CSN measurements, and wishes to use IMPROV E instead, the agency should have that flexibility.

Response: For the reasons stated in section VI of the preamble to the final rule, EPA is not adopting the proposed secondary PM 2.5 visibility index NAAQS. Consequently, the final rule does not include requirements on the use of CSN or IMPROVE stations.V-48 (3) Comment: Two commenters stated that use of data from IMPROVE sites could be problematic as those sites are not always operated by state, loca l, or tribal air monitoring agencies. One of these commenters would pr efer to only use data that they collect, analyze, quality assure, report, and certify.

Response: For the reasons stated in section VI of the preamble to the final rule, EPA is not adopting the proposed secondary PM 2.5 visibility index NAAQS. Consequently, the final rule does not include requirements on the use of CSN or IMPROVE stations.

(4) Comment: One commenter stated that with regard to using deciviews th at this metric was primarily developed for areas with a long site path to encompass a large sample size. The approach used for the proposed visibility st andard is only one sampling point, which may not be representative for estimating visibility of an entire airshed. Additional sampling points should be considered.

Response: For the reasons stated in section VI of the preamble to the final rule, the EPA is not adopting the proposed secondary PM 2.5 visibility index NAA QS. Consequently, the final rule does not include requiremen ts for monitoring sites to support such a

standard.

(5) Comment: One commenter stated the many of the urban speciation sites were originally

located close to industrial facili ties to ascertain their unique characteristics and influence upon air quality. These sites represent impacts in only a very small urban area and thus do not necessarily represent areas large enough to comprise “vistas”.

Response: For the reasons stated in section VI of the preamble to the final rule, the EPA is not adopting the proposed secondary PM 2.5 visibility index NAA QS. Consequently, the final rule does not include requiremen ts for monitoring sites to support such a

standard.

(6) Comment: One commenter supported the mini mum network design where only certain cities over 1 million in population would be re quired to have CSN stations to support the proposed visibility index. Th e commenter stated that they agree with the EPA’s approach in not having every city in the state over 1 million in population have to perform CSN measurements as their own analyses shows th at their two major cities, which have longstanding CSN stations (Raleigh a nd Charlotte, NC), both have deciview calculations that

are the same at 24 deciviews as cal culated by the EPA for years 2008 – 2010.

Response: For the reasons stated in section VI of the preamble to the final rule, the EPA is not adopting the proposed secondary PM 2.5 visibility index NAA QS. Consequently, the final rule does not include requiremen ts for monitoring sites to support such a

standard.

(7) Comment: One commenter identified that thei r monitoring program had two speciation

sites in urban areas that ar e not near the population thre shold proposed for the urban visibility standard (i.e., CBSAs greater than 1,000,000 in population).V-49 Response: For the reasons stated in section VI of the preamble to the final rule, the EPA is not adopting the proposed secondary PM 2.5 visibility index NAA QS. Consequently, the final rule does not include requiremen ts for monitoring sites to support such a standard. However, to clarify, the pr oposed network requirements for CSN (or IMPROVE) were intended as minimum networ k requirements and not as criteria for comparability to the NAAQS.

(8) Comment: One commenter stated that the EPA’ s proposal of the visibility standard

indicates that both urban and rural monitors are subject to the visibility standard; however, the commenter believes that rura l monitoring should be excluded for use in determining attainment of the visibility index NAAQS.

Response: For the reasons stated in section VI of the preamble to the final rule, the EPA is not adopting the proposed secondary PM 2.5 visibility index NAA QS. Consequently, the final rule does not include requirements for monitoring sites to support such a standard.

(9) Comment: One commenter stated lacking any empi rical support for its intended use of the existing monitoring network, if the EPA finalizes a secondary PM 2.5 visibility NAAQS, the EPA should at minimum adopt th e approach it took in 1997 when it first

established a PM 2.5 standard. In specific, President Clinton directed the EPA to only address decisions regarding attainment a nd nonattainment areas when a well designed

PM 2.5 monitoring network was in place. Th e 1997 NAAQS implementation strategy stated that, “[b]ecause the EPA is establishi ng standards for a new indicator for PM (i.e.,

PM 2.5 ) it is critical to develop the best in formation possible before attainment and nonattainment designation decisions ar e made.”47 The policy directed that “unclassifiable” designations be issued until there was a r obust network specifically designed to address th e new PM indicator.

Response: For the reasons stated in section VI of the preamble to the final rule, EPA is not adopting the proposed secondary PM 2.5 visibility index NAAQS. Consequently, the final monitoring rule does not include re quirements on the use of CSN or IMPROVE

measurements.

(10) Comment: One commenter (NEDA/CAP) stated EPA’s proposal for the secondary visibility standard is technically flawed. EPA addre ssed visibility at a single point

measurement rather than an in tegrated sight path average PM 2.5 concentration.

Response: For the reasons stated in section VI of the preamble to the final rule, EPA is not adopting the proposed secondary PM 2.5 visibility index NAAQS. Consequently, the final monitoring rule does not include re quirements on the use of CSN or IMPROVE measurements, or their siting to support such a standard.V-50 I. Comments on the use of PM 2.5 Continuous FEMs at SLAMS

(1) Comment: Several commenters were supportive of the proposal allowing identification of

PM 2.5 continuous FEMs that should not be used for comparison to the PM 2.5 NAAQS through an evaluation in the a nnual monitoring network plan.

Response: The comment in support of the propos al is acknowledged and the EPA is adopting the proposed appro ach in the final rule.

(2) Comment: One of the commenters supportive of the proposal allowing identification of

PM 2.5 continuous FEMs that should not be used for comparison to the PM 2.5 NAAQS stated that such an approach would encour age continued use and improvements of these

methods.

Response: The comment in support of the propos al is acknowledged and the EPA is adopting the proposed approach ed in the final rule.

(3) Comment: Of the many commenters that were supportive of the proposal allowing

identification of PM 2.5 continuous FEMs that should not be used for comparison to the

PM 2.5 NAAQS through an evaluation in the annu al monitoring network plan, several of

these commenters also recommended that mon itoring agencies be al lowed to identify and

recommend exclusion of FEM continuous data both prospectively and retrospectively.

Response: The EPA has addressed this issue in se ction VIII.B.3.ii of the preamble of the

final rule.

(4) Comment: One commenter did not support the pr oposal to allow data comparability

assessments between continuous FEMs and FRM monitors that are not located at the

same site.

Response: The EPA’s intention in allowing th e grouping of sites for purposes of allowing identification of PM 2.5 continuous FEMs that should not be used for comparison

to the PM 2.5 NAAQS through an evaluation in the a nnual monitoring network plan is to provide for flexibility so that monitoring agencies do not have to collocate every PM 2.5 continuous FEM with an FRM to assess that FEM’s suitability for NAAQS use. The EPA wishes to recognize the reality that not every continuous FEM is collocated with an FRM. However the final approach does not in any wa y restrict collocating sites. Each agency

can decide for itself if it chooses to collocate more than the minimally required number of

sites.

(5) Comment: One commenter stated that reasonable minimum requirements for demonstration and assessment of FEM performa nce must be clearly stated, not only in a preamble, and consistently applied across all regions. As described in the preamble, the determination, demonstration, and decisions in volved in the assessment of non-equivalent FEM data could easily become a significant burden for monitoring organizations that have relied on the equivalency designati on to design and implement a monitoringV-51 strategy. The EPA must develop a more represen tative and reliable protocol to designate approved monitoring methods.

Response: In the preamble section VIII to the final rule, the EPA provides some additional information for monitoring agencies on how to address this issue. The EPA shares the concern on assessments becoming a significant burden to monitoring agencies

and will work to minimize this burden wherever possible. EPA also points out that such an assessment is not required; however, the EPA has developed an automated tool to assist monitoring agencies when performing assessments. See: http://www.epa.gov/airquality /airdata/ad_rep_frmvfem.html

.

(6) Comment: One commenter stated that th e recent availabili ty of the “PM 2.5 Continuous Monitor Comparability Assessment” web-based tool is a valuable addition, and provides States with a uniform approach to FEM data quality assessment.

Response: The comment in support of this tool is acknowledged.

(7) Comment: One commenter stated that due to lack of experience, data, and the experimental nature of n ear-roadway monitoring, PM 2.5 FEMs should not be used for determining compliance with the NAAQS.

Response: As explained in the preamble to the proposal, the EPA has conducted an assessment of the comparability of PM 2.5 FEMs and found that in many cases the data are meeting the performance criteria used to approve theses methods when compared to collocated FRMs. Since the monitoring agencies are achieving the desired comparability with these continuous FEMs – at least in some cases, the EPA is supportive of their continued use, including for comparison to the NAAQS. The EPA has provided a process for identifying data from continuous FEMS th at is not suitable for comparison to the NAAQS, and will continue to consider issues related to the performance of the

continuous FEMs in the future.

(8) Comment: One commenter does not support the use of PM 2.5 continuous FEMs for comparison to the NAAQS at near-roadway sites until problems with FEMs have been adequately addressed.

Response: As explained in the preamble to the proposal, the EPA has conducted an assessment of the comparability of PM 2.5 FEMs and found that in many cases the data are meeting the performance criteria used to approve these methods when compared to collocated FRMs. Since the monitoring agencies are achieving the desired comparability with these continuous FEMs, the EPA is supporti ve of their continued use, including for comparison to the NAAQS. However, as explaine d in the preamble, there is a process for identifying data from continuous FEMs not su itable for comparison to the NAAQS, and it remains the monitoring agencies choice to us e a FRM, filter-based FEM, or continuous FEM at near-road monitoring stations or ot her SLAMS. So even if the commenter disagrees with the EPA’s position, it can still choose the method that they are mostV-52 comfortable with so long as it is an approved FEM; FRM; or ARM, if one of those

methods were to become av ailable at a later time.

(9) Comment: One commenter stated that the EP A should develop sample language for inclusion in individual agencies’ PM 2.5 Quality Assurance Project Plans (QAPPs) regarding criteria for FEM data exclusion.

Response: The EPA intends to work with monitoring agency stakeholder groups to develop such language. The sample langua ge may be documented in one or more locations; for example, a location such as the Quality Assurance Handbook for Air Pollution Measurement Systems – Volume II, EPA-454/B-08-003, December 2008.

(10) Comment: Several commenters stated that the EPA should provide an acceptable range for each instrument parameter (for the con tinuous FEMs) that is associated with the

ambient concentration data. Over the last several years, the EPA has provided minimal guidance on how to determine when the FEM in struments are satisfactorily performing.

Response: The EPA will work with monitoring agencies and instrument companies on updating the acceptable ranges for instrument parame ters so that they can be incorporated in monitoring agency SOPs and quality assu rance projects plans, where applicable. The EPA has developed draft SOPs for three of the more commonly used continuous FEMs. These SOPs were developed in cooperation w ith several monitoring agencies and they

are available on the web at: http://www.epa.gov/ttn/amtic/contmont.html . The EPA anticipates it will update these SOPs to accomm odate the latest information on acceptable ranges for each instrument parameter.

(11) Comment: One commenter stated that PM 2.5 monitoring methods are widely believed to be suspect. The EPA should revisit the adequ acy of those methodologies before reducing

the PM 2.5 standard. EPA's supporting materials for the FRM for PM 2.5 monitoring set forth in Appendix L to 40 CFR Part 50 indica te that reductions in the standard could exacerbate the limitations of the method, i.e. limiting the method's effectiveness in defining meaningful differences in PM 2.5 concentrations. The commenter understands that ongoing implementation of FEM monito ring (alternative methodologies) indicates inconsistent degrees to whic h a given equivalent method is comparable to the FRM, varying from site-to-site. The inconsistencie s may suggest that the "equivalent" methods are producing more accurate data than the FR M. Further, the EPA research as to the reliability and accuracy of the FRM for PM 2.5 is necessary before reducing the standard.

Response: As stated in the preamble to the fina l rule, the EPA believes that progress is being made to implement well performing PM 2.5 continuous FEMs across the nation. However, in recognition that some monitori ng agencies are not achieving the expected data comparability, and as explained in section VIII of the final rule, the EPA has finalized a process by which monitoring agencies can identify and exclude PM 2.5 continuous FEM data, where comp arability results are not me t, from comparison to the NAAQS. The EPA believes that the combina tion of using the FRMs, filter-based FEMs, and well performing continuous FEMs across the network provides more than a sufficientV-53 number of monitoring options to support the revised PM 2.5 standard. As stated in the preamble, the EPA intends to continue worki ng with monitoring agen cies and instrument manufacturers to document best practices on these methods to improve the comparability and consistency of resulting data, wherever possible.

(12) Comment: One commenter stated that until it is demonstrated that virtually all of the

continuous FEMs reliab ly replicate FRM PM 2.5 concentrations throughout the U.S. and all times of the year, the FEMs should not be used to provide primary data for comparison to NAAQS unless a state provides evidence of the equivalence of FEMs in comparison with the FRM for a specific area.

Response: As described in section VIII of the preamble to the final rule, the EPA finalized an approach to allow monitoring agenci es to specify their intention to use or not

use data from continuous PM 2.5 FEMs that are eligible for comparison to the NAAQS as part of their annual monitoring network plan due to the applicable EPA Regional Office by July 1 each year. The EPA believes this provision ensures monitoring agencies will only use PM 2.5 continuous FEM data where an appropr iate level of comparability with collocated FRMs has been determined. First, despite some differences between the instrument company field testing of the c ontinuous FEMs with collocated FRMs and the monitoring agency operation of these methods (e.g., averaging of three FRMs and three

candidate continuous FEMs in th e instrument company tests; operation of the FRMs from morning to morning periods, rather than midni ght to midnight as is the case in routine monitoring programs) these methods were appr oved as they met performance criteria in each of the field locations where they were tested. These field tests included multiple locations around the country with specifi cations on winter and summer seasons, depending on location. Second, as stated in the preamble there are likely multiple reasons why some of the PM 2.5 continuous FEMs are not meeting the expected performance criteria. Some of these reasons such as differences in installation, operator training, and development and use of Standard Operating Procedures (SOPs) are likely to affect data comparability on an agency by agen cy basis. Therefore, the EPA believes this approach appropriately allows a method work ing in one or more monitoring programs with acceptable comparability to be used in comparison to the NAAQS.

J. Comments on Weight of Evidence Approach in the Revisions to the Quality Assurance Requirements for SLAMS, SPMs, and PSD.

(1) Comment : The large majority of comments were in favor of the weight of evidence approach for determining whether the quality of data is appropriate for regulatory decision-making purposes. Some that supported the approach also provided a word of

caution that there needs to be a minimum se t of requirements for data collection and reporting in order for data to be used fo r attainment/non-attainment decisions.

Response : The EPA agrees with the commenter’s poi nt that data should be subject to a minimum set of requirements for data coll ection, reporting, and quality. While the EPA considers the Appendix A requirements the min imum for reporting, it is not the only data that the EPA and the monitoring organizations use to judge quality. Therefore if an Appendix A requirement for some reason is not complete it should not be the sole reasonV-54 to declare the data invalid or unusable. The comment in support of the proposal is acknowledged and the EPA is adopting the proposed approached in the final rule.

(2) Comment : One commenter felt that the paragraph, as written, unde rmines the importance of the quality control/quality assurance system dictated in Part 58 and also said that while a common sense approach to the assessment of quality data is important, minimum requirements are necessary to ensure scientif ically-defensible data is being used in decision making

. Response: The EPA agrees with the commenter’s poi nt that data should be subject to a minimum set of requirements for data collectio n, reporting, and quality. In developing the weight of evidence approach EPA is not at tempting to diminish the requirements of Appendix A but rather ensuring that other elem ents of a quality system that monitoring organizations implement and are documented in their QAPP can also be used when judging whether data are valid for a particular monitoring objective. After considering the support for this change, EPA will adopt the prop osed weight of evidence approach in the

final rule.

(3) Comment: One commenter who felt that the appro ach may be appropriate suggested that the language of the proposal was vague and may weaken the ability of air monitoring agencies to validate their own data and inst ead allows EPA to make decisions regarding data validity.

Response : The EPA agrees that the monitoring or ganizations know more about their data and that these organizations are responsible for certifying the data as valid. In the majority of cases when the quality of ambi ent air data is called into question, the EPA Regions and monitoring organizations work together and reach consensus on data usability. However, since the EPA is res ponsible for making fina l NAAQS decisions, in rare cases it may ultimately have to ma ke a validity decision that the monitoring organization may not agree with. After consid ering the support for this change, the EPA will adopt the proposed weight of ev idence approach in the final rule.

(4) Comment: A few commenters, although supporting the weight of evidence approach, also commented that Appendix A minimum requi rements should not only apply to all air quality data collected by state, local, and tribal agencies, but also to “secondary” data collected by other monitoring efforts.

Response: The EPA believes that the term secondary data is used to represent information that may have been originally intended for one monito ring objective but is now being used for a “secondary” objective. The EPA assumes this term is used to either represent the Chemical Speciation and IMPROVE Network data being used in the light extinction calculation for the proposed sec ondary visibility inde x NAAQS standard, or for criteria pollutant data collected by enti ties other than the state, local or tribal monitoring organizations. The EPA agrees with the comments that the Appendix A requirements must apply to the CSN and IMPROVE data and included the term “PM 2.5 CSN” to refer to both networks. Based on the assessment of the CSN and IMPROVE data against the PM 2.5 DQOs (10% precision and + 10% bias) it appeared that the PM 2.5 DQOs were being met under the current CSN and IMPROVE quality systems (QAPPs andV-55 SOPs). However, since the EPA is not adopting the proposed secondary PM 2.5 visibility index NAAQS, the EPA will not include thes e QA requirements into Appendix A since the networks will not produce da ta related to NAAQS decisions.

K. Comments on Quality Assurance Requirements for the Chemical Speciation Network.

There were no comments on the proposed addition of collocation and flow rate requirements in Appendix A for the chemical speci ation network (CSN). However, since for the reasons stated in section VI of the preamble to the final rule, the EPA is not adopting the proposed secondary PM 2.5 visibility index NAAQS, we will not include any PM 2.5 secondary standard QA requirements related to the Chem ical Speciation Networ k or IMPROVE Network into Appendix A.

L. Comments on Waiver for Wider Spac ing of Collocated Monitors

(1) Comment: All comments received supported the proposed requirement allowing up to 10 meter horizontal spacing for sites at a nei ghborhood or larger scal e of representation. During stakeholder presentations of the propos al, the EPA received verbal comments that monitoring organizations were also having difficulties meeting the 1 meter vertical limit

since PM 2.5 FEMs are often housed in shelters with inlets extending th rough shelter roofs while the collocated FRM monitors are placed outside usually on low platforms.

Response: The comments in support of the pr oposal are acknowledged and the EPA is adopting the proposed approach in the final rule. Based on discussion with EPA’s Office of Research and Development, the agency will amend the Appendix A requirements to allow for a 1-3 meter vertical spacin g which may be approved by the Regional Administrator for sites at a neighborhood or la rger scale of repres entation. In addition, the language will be amended to allow for waiver approvals during annual network plan approval processes.

M. Additional QA Related Comments not Specifi cally Related to Proposed Changes to Appendix A

(1) Comment: The EPA received a comment that anot her part of the rule appeared to encourage the use of collocated FEM samplers in an official reporting capacity where they have been held back or used sparingly up to now due to concerns regarding operational confidence. The commenter was suggesting this reference was intended to allow primary FRM monitors to be colloca ted with FEM monitors for QA purposes which would require a regulatory cha nge to the current QA requirements.

Response: The verbiage described by the commenter referred to allowing FEM

collocated data from a site that has an FR M as the primary monitor to replace the FRM data (if a scheduled sample was invalidated or not collected) or augm ent data (filling in for unscheduled samples). The FRMs collocated with continuous FEMs in this context were not meant to count towards meeting the QA collocation require ments and EPA does not intend to change the current PM 2.5 QA collocation requirements.V-56 (2) Comment: A commenter had concerns that th e reporting of IMPROVE data for comparison to a secondary PM 2.5 visibility index standard could prove problematic as those sites are not always operate d by state, local, or tribal air monitoring agencies. They felt that the regulation should outline some da ta quality and certifi cation responsibilities to the appropriate state, local, or tribal air monitoring agencies.

Response: The EPA acknowledges this comment; howev er, since the EPA is not adopting the proposed secondary PM 2.5 visibility index NAAQS, the EPA will not include any

PM 2.5 secondary standard QA requirements rela ted to the Chemical Speciation Network or IMPROVE Network into Appendix A.

(3) Comment: Commenters recommended that the EP A develop explicit guidance regarding the methodology and criteria for assessing valid ity of air quality data from secondary

sources. Such data evaluations should be in cluded as part of the five year Network

Assessment.

Response: The EPA acknowledges this comment. However, since the EPA is not adopting the proposed secondary PM 2.5 visibility index NAAQS, the EPA will not include any PM 2.5 secondary standard QA requirements related to the Chemical Speciation Network or IMPROVE Network into Appendix A.

(4) Comment: Commenter felt that EPA should clarify the use of the term "PM 2.5 CSN" in 40 CFR part 58 Appendix A. "CSN" is used several times throughout the proposal to denote a network separate from the IMPROVE network. The definition in Appendix A should clearly state if it includes IMPROVE monitors

.

Response: The EPA acknowledges this comment. However, since the EPA is not adopting the proposed secondary PM 2.5 visibility index NAAQS, the EPA will not include any PM 2.5 secondary standard QA requirements related to the Chemical Speciation Network or IMPROVE Network into Appendix A since the networks will not produce data related to NAAQS decisions.

N. Comments on Probe and Monitori ng Path Siting Criteria

(1) Comment: One commenter supports making the A ppendix E siting criteria for near-road

PM 2.5 monitoring the same as the Appendix E siti ng criteria for near road monitoring of nitrogen dioxide and carbon monoxide.

Response: The comment in support of the propos al is acknowledged and the EPA is generally adopting this approach, except as ex plained in the preamble to the final rule, we are also including a provision for separation distances from horizontal and vertical distances that is consistent with the existing PM criteria (i.e., greater than 2 meters). For gas monitoring the separation distances from hor izontal and vertical distances is greater

than 1 meter.V-57 (2) Comment: Two commenters support the proposal to extend the existing probe and monitoring path siting criter ia described in Appendix E to 40 CFR Part 58 for PM2.5

FRMs and FEMs to the CSN and IMPROVE measurements.

Response: For the reasons stated in section VI of the preamble to the final rule, the EPA is not adopting the proposed secondary PM 2.5 visibility index NAA QS. Consequently, the final rule does not include requir ements on the use of CSN or IMPROVE

measurements.

(3) Comment: One commenter suggested allowing th e same 10 meter collocation waiver provision proposed for the PM 2.5 NAAQS to also apply to CSN monitors.

Response: For the reasons stated in section VI of the preamble to the final rule, the EPA is not adopting the proposed secondary PM 2.5 visibility index NAA QS. Consequently, the final rule does not include requir ements on the use of CSN or IMPROVE

measurements.

(4) Comment: The PM 2.5 monitor should have the same height and distance from the road requirements as NO 2 , but the distance to the nearest ve rtical wall or obstruction should be increased to match the requirements for curren t micro- and middle-scal e installations. It

is not advisable to install a PM 2.5 monitor adjacent to a wall or other obstruction that would disrupt the normal upwind-to- downwind flow across the roadway.

Response: As explained in the preamble to th e final rule, the EPA did not propose to change the existing requirements regarding placement near walls or obstructions. As such, even though a PM 2.5 monitor may be collocated with an NO 2 monitor at a near-road location, the individual siting requirement s regarding placement near walls or obstructions for each pollutant still apply.

(5) Comment: One commenter stated that the re quired near-road measurements of PM 2.5 must be suitably distant from traffic so as not to be influenced by tr affic wake effects that make the measurements unrepresentative of ambient air. For at-grade roadways, the turbulent wakes caused by traffic and wind bl owing across a busy road result in eddies that disturb the air flow and trap pollutants. This phenomenon, similar in some respects to building-wake cavity effects, causes recircul ation and high concentrations can occur if emissions are trapped within this zone. P opulation exposure near roadways generally

occurs outside of this zone. If a monitor were to be placed in this recirculation zone, it could misrepresent concentra tions in ambient air by for ar eas not immediately close to roadways. The general rule of thumb is that this turbulent zone c ould extend 5 to 10 times the vehicle height from the road, which for a box trailer would correspond to about 15 to 30 m. For an elevated roadway or complex interchange with comp lex structures, the required offset distance could be greater.

Response: The EPA is finalizing its pr oposal on the siting of the PM 2.5 monitors in the near-road environment, which is the same as the NO 2 siting, which states to be as near as practicable to the road but no more than 50 meters away. While EPA is finalizing theseV-58 siting criteria, it did consider the optimum distance that sites should be located at in the

Near-Road NO 2 Monitoring Technical Assistance Document (TAD) EPA-454/B-12-002, June 2012. In this document, we recommend that the ideal distance is within 20 meters the road. In providing this addi tional guidance we cite Baldauf et al. (2009) in the TAD,

which notes that a distance of 10 to20 meters should be considered for near-roadway monitoring. The referenced pape r states that this is partly to avoid being in the wake zone as described by the commenter. Now th at we are finalizing requirements for siting

of PM 2.5 monitors in the near-road environment and we want these measurements to be

collocated with the near –road NO 2 monitors, it is appropriate to use the same additional guidance from the Near-Road NO 2 Monitoring TAD when considering the optimum

location of the monitor for PM 2.5 . Therefore, and as stated in the TAD, the EPA strongly encourages state and local agencies to place near-road NO2 monitor probes, and now

PM 2.5 inlets within 20 meters from target road segments whenever possible. To avoid being in the wake zone as de scribed by Baldauf et al. (2009) , monitoring agencies should also consider, but are not required, to site in lets at least 10 meters from the road, if possible. While the commenter’s distance is a little different as its based on an example of a box trailer (15 to 30 mete rs), we believe this approach adequately addresses this issue, taking into consideration the need to address other issues related to monitoring objectives for near road sites.

O. Comments on the Annual Monitoring Ne twork Plan and Periodic Assessment

(1) Comment: One commenter requested that the EPA clarify the requirements for assessments and identify differences between the network assessments and the network plan requirements.

Response: The requirements for annual monitoring network plans and five year assessments are detailed in §58.10. Essentially, a five year assessment is intended to be a comprehensive assessment while an annual mon itoring network plan is intended to be the year to year changes that are being implemented as a result of that comprehensive assessment as well as any other changes that are needed.

(2) Comment: One commenter recommends that an ev aluation of the requirements for the Five Year Monitoring Network Assessment should be reevaluated in light of the frequency with which NAAQS standards are revised. The commenter recommends that this evaluation be conducted by one or more of the National Associ ation of Clean Air Agencies (NACAA)/EPA stakeholder groups.

Response: The comment in support of a reevaluation of the requirements for the Five Year Monitoring Network Assessment, c onducted by one or more of the National Association of Clean Air Agencies ( NACAA)/EPA stakeholde r groups is noted.

(3) Comment: One commenter stated that the tools av ailable (for the five year assessments) are inadequate for the objective assessment needed for urbanized areas, and assessment of inter- and intrastate scales needed by m onitoring agencies. Also, that the monitoringV-59 and supporting data does not, and typically will not, have the spatial resolution to allow adequate network assessment at the most useful scales, the urban area, or MSA.

Response: This comment is addressed in sectio n VIII.B.6.a of the preamble to the final

rule.

(4) Comment: One commenter stated that EPA must take the experience gained by the states and local monitoring organizations in the development of these first assessment documents to immediately start development of new and refined tool s and state-specific data hinted at in the Monitoring Assessmen t Guidance. Many monitoring organizations could greatly benefit from accessible tools that can be used to refine and improve MSA and state scale monitoring networks.

Response: This comment is addressed in sectio n VIII.B.6.a of the preamble to the final

rule.

(5) Comment: One commenter strongly recommended that EPA provide guidance to States at least one year prio r to the due dates for the 5-year assessments.

Response: As stated in section V III.B.6.a of the preamble to the final rule, the EPA will work with States to support tools and guidance on the five year assessments.

(6) Comment: One commenter stated that any requirements for the State agencies should be met with commensurate requirements for the EPA Region to review and respond to the

assessment.

Response: The 5- year network assessments are required to be submitted along with annual monitoring network plans during the years when the assessments are due (e.g., 2010, 2015, etc.). During the initial asse ssment conducted in 2010, many EPA regions did include the network assessment as part of the overall dialogue with the submitting agency. The EPA will consider ways to improve the process and the text of part 58 in a possible future rule making on monitoring.

(7) Comment: One commenter stated that it would be more efficient to make a periodic monitoring network assessment an activity c onducted by regional planning organizations (RPOs) with commensurate funding going to th e RPO as LADCO did for Region V states

for the 2010 assessment.

Response: The coordination of fi ve-year assessments by or through a regional planning organization is an appropriate way to perform these required assessments.

P. Comments on Operating Schedules

(1) Comment: One commenter stated that they generally agree that every day sampling is appropriate for sites whose design values ar e within 5% of the NAAQS. However, for sites with design values great er than 5% above the NAAQS, reduced sampling frequencyV-60 should be allowed only if the si tes has a collocated continuous PM 2.5 monitor that is suitable for Air Quality Inde x (AQI) reporting required by 40 CFR Part 58, Appendix G.

Response: The comment in support of the proposal is acknowledged and EPA is adopting the proposed approached in the final rule. Regarding the recommendation on sites with design values greater than 5% above th e NAAQS, where reduced sampling frequency should be allowed only if the si te has a collocated continuous PM 2.5 monitor that is suitable for AQI reporting required by 40 CF R Part 58, Appendix G, the EPA believes the existing monitoring rules are alre ady largely supportive of operating PM 2.5 continuous methods at SLAMS. For example, at le ast one-half (round-up) the minimum required sites according to Table D-5 of appe ndix D to part 58 are to have a PM 2.5 continuous monitor operating at the sites. This requirement ensures th at there is at least one PM 2.5 continuous monitor operating in each CBSA required to monitor for PM 2.5

.

(2) Comment: One commenter supports that it is re asonable for each agency to determine the applicability of the requirement for daily sampling once a y ear when updating the annual monitoring network plan.

Response: The comment in support of the propos al is acknowledged and the EPA is adopting the proposed approached in the final rule.

(3) Comment: One commenter recommended retaining the current sample frequencies for

PM measurements.

Response: The EPA believes the proposed ch anges will provide flexibility and predictability regarding how sample frequenc y changes are addressed, which will be of benefit to monitoring agencies as they operate their PM 2.5 monitoring programs. Accordingly, the EPA is finalizing the change s to the sample frequency requirements for

PM 2.5 as proposed.

Q. Comments on Data Reporting and Cert ification for CSN and IMPROVE data

(1) Comment: One commenter identified that an ap propriate and efficient approach for implementing the visibility standard woul d be to require urban areas with only

IMPROVE monitors to add one CSN monitor to the urban area and align NAAQS and CSN data reporting and certifi cation requirements to meet the May 1 data certification

deadline cited in 40 CFR 58.15.

Response: For the reasons stated in section VI of the preamble to the final rule, the EPA is not adopting the proposed secondary PM 2.5 visibility index NAA QS. Consequently, the final rule does not include requir ements on the use of CSN or IMPROVE

measurements.

(2) Comment: One commenter recommended that the EPA work with the IMPROVE program to reduce the lead time for data s ubmittal and certification in the EPA’s AirV-61 Quality System (AQS) and align the IMPROVE quality assurance protocol with the CSN

and SLAMS networks.

Response: For the reasons stated in section VI of the preamble to the final rule, the EPA is not adopting the proposed secondary PM 2.5 visibility index NAA QS. Consequently, the final rule does not include requir ements on the use of CSN or IMPROVE

measurements.

(3) Comment: One commenter recommended that data from IMPROVE be submitted to AQS no more than 6 months after they are collected.

Response: For the reasons stated in section VI of the preamble to the final rule, the EPA is not adopting the proposed secondary PM 2.5 visibility index NAA QS. Consequently, the final rule does not include requir ements on the use of CSN or IMPROVE

measurements.

(4) Comment: One commenter recommended that data from IMPROVE and CSN be placed on a separate certification sche dule where data for an entire year is certified by August 1 of the following year.

Response: For the reasons stated in section VI of the preamble to the final rule, the EPA is not adopting the proposed secondary PM 2.5 visibility index NAA QS. Consequently, the final rule does not include requir ements on the use of CSN or IMPROVE

measurements.

(5) Comment: One commenter stated that the proposed delay in data certification could pose problems with the states’ ability to meet mandated due dates to provide technical justification for excluding da ta due to exceptional events.

Response: For the reasons stated in section VI of the preamble to the final rule, the EPA is not adopting the proposed secondary PM 2.5 visibility index NAA QS. Consequently, the final rule does not include requir ements on the use of CSN or IMPROVE measurements or changes to the data certification of this data.

(6) Comment: One commenter stated the certification da ta should be extended to six months from the end of the quarter in which the data were collected to provi de sufficient time for lead, CSN and IMPROVE data certification.

Response: For the reasons st ated in section VI of the preamble to the final rule, the EPA is not adopting the proposed secondary PM 2.5 visibility index NAAQS. Consequently, the final rule does not incl ude requirements on the use of CSN or IMPROVE measurements or changes to th e data certification of this data.V-62 R. Comments on the Requirements for Archiving Filters

(1) Comment: Several commenters support the pro posal to extend the filter archival requirements from one to five years, w ith cold storage during the first year.

Response: The comments in support of the propos al are acknowledged and the EPA is adopting the proposed approached in the final rule.

(2) Comment: One commenter suggested that the EP A study the effectiveness of long term cold storage looking specifically at repeat ability of gravimetric measurements.

Response: Such studies already exist. Also, th e EPA has existing guidance on the storage of filters and may, at its discretion, update that guidance in light of the changes to filter storage requirements.

(3) Comment: One commenter stated that they do not have the space to store four years of samples in either cold or ambient storage and believes this proposed requirement would be burdensome even if the samples dot not need to be stored cold.

Response: This comment is addressed in section VIII of the preamble of the final rule.

(4) Comment: One commenter questioned the value of filter retention beyond one year if they are not refrigerated. Critical information may be lost once filters go to room temperature. Perhaps 2-year cold storag e retention with a 5-year total is more appropriate.

Response: The EPA believes, that at a minimum, analyses for elements can be conducted very successfully for several years after samp le collection and that these analyses can be performed with filters that have either have or have not been refrigerated. Other analyses, such as for nitrate and sulfate ions, provide better results when refrigerated and their long term usefulness is not expected to be as good compar ed to elemental analysis.

S. Funding and Resources Issues associated wi th Ambient Air Monitoring Requirements

The EPA received numerous comments on funding and resources associated with the implementation and operation of ambient air m onitors that are described in the proposed amendments to the ambient monitoring requirement s. We understand that monitoring agencies desire full funding when revisions to monito ring requirements require the purchase of new equipment and installation of new sites, relocation of existing mon itors, and increase burdens for staff and operational budgets. The EPA understands these concerns. The EPA has historically funded part of the cost to State, local, and Tribal governments of installation and operation of monitors to meet Federal monitoring requireme nts. Sections 103 and 105 of the CAA allow the EPA to provide grant funding for programs for preventing and controlling air pollution and for some research and development efforts respec tively. However, the CAA requirements from

which this final rule derives ar e not contingent on the EPA provi ding funding to States to assist in meeting those requirements. Accordingly, th e comments regarding funding are not directlyV-63 relevant to the content of this final rule. Neve rtheless, the EPA recognize s that resources always have been and will remain a practical consider ation for establishing and operating monitoring programs. The EPA will continue to work with St ates in this regard, in particular as the EPA determines how to allocate enacted funding amo ng States and among types of monitoring so as to achieve the best possibl e environmental outcomes.

(1) Comment: One commenter representing many air agen cies across the country stated that

the monitoring requirements must be fully funde d, including staffing as well as operation and maintenance costs. New monitoring ma ndates must be supported by appropriate increases in federal funding. State and local ag encies need additional, adequate federal funding in order to move forward with new monitoring requirements and continue to operate and maintain existing monitoring networ ks, which are crucial to the protection of public health and the environment. Impl ementing a multipollutant near roadway monitoring network requires th e purchase of new equipment a nd installation of new sites, relocation of monitors, and additional staff, operation and maintenance costs, and must be fully funded under Clean Air Act section 103.

Response: Information on how the EPA addresses funding for monitoring is described

above.

(2) Comment: One commenter representing a number of ai r agencies stated that the EPA is proposing new requirements for ambient ai r monitoring. The commenter believes the costs of these requirements have been signifi cantly underestimated, in large part because of the proposed network design and underlying assumptions for the near

‐ road monitors. The commenter offer specific comments on th e proposal that they believe will both

reduce the costs and enhance the effectivene ss of the network; we urge the EPA to incorporate these changes. Even with the ch anges, however, we believe there will be substantial monitoring costs, both for installation and ongoing operation/maintenance of the stations, as well as in data handling a nd network review. The commenter stated that

their members do not have the financial reso urces to absorb these new costs and they believe the EPA must provide full funding for any new monitoring requirements that are

established.

Response: The EPA believes that there will be minimal cost in relocating PM 2.5 monitors required to be implemented according to the schedule described in section VIII of the preamble to the final rule. The EPA cons idered the commenter’s suggestions on the proposal that they believe will both reduce th e costs and enhance the effectiveness of the network and, as described in Section VIII.B .3.b.i of the preamble to the final rule, the EPA is providing for a phased deployment of the near-road monitors. Regarding the

comment that there will be substantial monitoring costs, the EPA believes these costs should not be new costs since we are empha sizing moving monitors, rather than adding

new ones.

(3) Comment: One commenter representing several State air agencies stated that while their States are not opposed to adding PM 2.5 monitoring to the near -road network, as the EPA proposes, there is no funding fo r this new network objective.V-64 Response: As described in Section V III.B.3.b.i of the preamble to the final rule, the EPA noted that a number of air agencies stated concerns that the near-road monitors are challenging to site and that there is additio nal cost in operating these monitors, the EPA maintains that the major challenges in siting would already be accomplished by implementing the required NO 2 monitoring stations in near -road environments since the EPA fully expects that the PM 2.5 monitors will be placed at the NO 2 near roadway

stations and has revised the PM 2.5 monitoring requirements consistent with that expectation. The EPA also point s out that the requirements for the minimum number of

PM 2.5 monitors is unchanged and that in most cases the addition of near-road PM 2.5 monitors can be accomplished by relocating an existing monitor, with no net increase in monitors. Thus, while we are re quiring a new component of the PM 2.5 monitoring network, the overall size of the network is e xpected to remain about the same, and we expect that air agencies can meet this re quirement by relocating existing lower-priority

monitors. Additional information on how monitoring is funded is described above.

(4) Comment: One commenter stated that they co ntinue to stress that monitoring requirements must be fully funded, incl uding staffing as well as operation and maintenance costs. New monitoring mandates mu st be supported by increases in federal funding necessary to establish this new or expanded network based on revisions to the federal air quality standards. State agencies need additional, adequate federal funding in order to move forward with new monitoring requirements and continue to operate and maintain existing monitoring networks, whic h are crucial to the protection of public health and the environment. Implementing a new, multi-pollutant near roadway monitoring network requires th e purchase of new equipment a nd installation of new sites, and additional staff and opera tion and maintenance costs at a time when state agencies are already struggling with budget and sta ffing shortfalls. New federal funding is necessary in order to impl ement these new requirements, and should be provided under

Section 103 of the Clean Air Act (Act), rather than Section 105 of the Act which requires a state match for federal funding.

Response: Information on how the EPA addresses funding for monitoring is described

above.

(5) Comment: One commenter stated that the addition or relocation of monitors can increase staffing, operation and maintenance costs for st ates and local agencies. U.S. EPA must support new monitoring mandates by providing a ppropriate increases in federal funding to ensure states and local agencies can m ove forward with new monitoring requirements and continue to operate and maintain existi ng monitoring networks, which are crucial to the protection of public hea lth and the environment.

Response: Information on how the EPA addresses funding for monitoring is described

above.

(6) Comment: One commenter stated that it is also important to note that the relocation of existing monitors will result in additional costs to states and these costs must be fully funded. For those agencies that may not be ab le to relocate existing monitors – becauseV-65 they are needed to provide neighborhood scale data for a CBSA, for attainment planning or model confirmation, to address specific community-based air qua lity concerns, or because they are part of ongoing research efforts – full funding for the purchase, installation, and operatio n and maintenance of an additi onal monitor must be provided. We believe EPA has significan tly underestimated the initi al cost of the proposed monitoring requirements, as well as the costs of ongoing network operation.

Response: Information on how the EPA addresses funding for monitoring is described above. The EPA disagrees we have significantly underestimated the initial cost of the proposed monitoring requirements, as well as the costs of ongoing ne twork operation, but even if the costs were somewhat higher, the EPA would still judge the monitoring requirements as necessary and appropriate unde r the Clean Air Act. As explained in Section VIII.B.3.b.i of the preamble to the fina l rule, the EPA noted that a number of air agencies stated concerns that the near-road m onitors are challenging to site and that there is additional cost in oper ating these monitors, the EP A maintains that the major challenges in siting would already be accomplished by implementing the required NO 2 monitoring stations in near-road environmen ts since the EPA fully expects that the PM 2.5 monitors will be placed at the NO 2 near roadway stations and has revised the PM 2.5 monitoring requirements consiste nt with that expectation. Th e EPA also points out that the requirements for the minimum number of PM 2.5 monitors is unchanged and that in

most cases the addition of near-road PM 2.5 monitors can be accomplished by relocating an existing monitor, with no net increase in monitors. Thus, while we are requiring a new component of the PM 2.5 monitoring network, the overall si ze of the network is expected to remain about the same, and we expect that air agencies can meet this requirement by relocating existing lower-priority monitors, wh ich generally requires fewer resources than operating new monitors. Additional inform ation on how monitoring is funded is

described above.

(7) Comment: One commenter requests that the EPA pr ovide states with additional funding necessary to implement the revised PM 2.5 standards, including additional ambient air monitoring equipment.

Response: Information on how the EPA addresses funding for monitoring is

described above.

(8) Comment: One commenter stated that if the EPA is going to require PM 2.5 monitoring at the near-road sites, additional funding must be provided. The EPA assumes that states can relocate existing monitors and thus incur no additional costs. This typically will not

be the case as the PM 2.5 monitors decommissioned proba bly will not be in the same

locales where near-road monito ring is being conducted. Theref ore, it cannot be assumed that current staffing levels are adequate for the near-road PM 2.5 monitoring. Second, if a decision is made by a monitoring agency to shift from the FRM to other particulate monitoring methodologies, such as the FEM or aethalometry as allowed in the proposed rule, additional funding for new monitors will be needed. Third, the placement of

additional monitors at some near-road sites may require that more safety barriers orV-66 mitigation measures be installed. Hence, moving monitors cannot be assumed to be a

zero-sum game.

Response: Information on how the EPA addresses funding for monitoring is described above. With regard to the comment that a decommissioned monitor may not be in the

same locale as where the near-road monito ring is being conducte d, the EPA points out that there will already be other measurements at the near-road stations and therefore the

addition of PM 2.5 to this station will result in some efficiency for the operator responsible

for the near-road station. In most cases th e EPA expects that the relocation of a monitor

will be from within the same CBSA. If there are cases where this cannot be accomplished and there are r easons why the relocated PM 2.5 monitors cannot be supported, the EPA will work with agencies on a case by case basis to addresses such

issues.

(9) Comment: One commenter stated that they co ntinue to stress that all monitoring requirements must be fully funded, incl uding staffing as well as operation and maintenance costs. Relocation of existing monito rs does result in addi tional costs to state and local agencies, as it requires the use of additional staff time and resources. New monitoring mandates must be supported by ap propriate increases in federal funding. The commenter stated they need additional f unding in order to move forward with new monitoring requirements and continue to operate and maintain existing monitoring networks, which are crucial to the protection of public health and the environment. New federal funding is needed to implement these new requirements, and should be provided under Clean Air Act § 103.

Response: Information on how the EPA addresses funding for monitoring is described above. With regard to the comment that” Re location of existing monitors does result in additional costs to state and local agencies”; the EPA believes that such costs will be minimal, or at least will be the most cost-effective means of providing necessary monitoring, and can be managed within the tim eframe of the requirement to implement

the near-road monitors described in section VIIIB.3.b.i of the preamble to the final rule.

(10) Comment: One commenter stated that they do not support an expanded network to monitor specifically for a sec ondary visibility standard. St ates do not have the resources to add additional monitors for a secondary standard

.

Response: As described in Section VI of the pr eamble to the final rule, the EPA is not finalizing a secondary NAAQS us ing a visibility index and th erefore is not finalizing the monitoring changes that would have been necessary to support it.

(11) Comment: One commenter stated that they suppor t the integration of multi-pollutant monitoring at NO 2 near-road monitoring stations so long as federal funding is provided for the deployment of the monitors.

Response: Information on how the EPA addresses funding for monitoring is described

above.V-67 (12) Comment: One commenter stated that the U.S. EPA needs to provide funding for all new required monitors, including capital costs a nd operations and maintenance costs. State and local agencies are facing an extraordinar y shortage of resources . The commenter also stated that they are committed to protecting ai r quality and public health but we must also be careful stewards of the public's money. In the current economic environment, state and local agencies are unable to develop the addi tional resources needed to meet the proposed new monitoring requirements. The regulation shoul d be written so that new monitoring is not required unless the U.S. EPA has the ability to f und the initiative.

Response: Information on how the EPA addresses funding for monitoring is

described above.

(13) Comment: One commenter stated that they do not have a PM 2.5 monitor available for relocation to a near-road site. Therefore, th ey will have to purchase a new FEM for this monitoring at a cost of $25,000 to $30,000. In circ umstances such as this, the EPA must provide full funding for the purchase, insta llation, and operation a nd maintenance of a

new PM 2.5 monitor for the required roadway location.

Response: Information on how the EPA addresses funding for monitoring is described

above.

(14) Comment: One commenter stated that the U.S. EPA must provide supplemental funding that does not require matching to sup port purchasing, instal ling, operating, and maintaining additional fine particulate matter (PM 2.5 ) monitors at near-road monitoring sites as currently proposed. If an existing m onitor is relocated to a near-roadway site, supplemental funding should be made availabl e to support the breakdown, relocation, and

installation of the monitor.

Response: Information on how the EPA addresses funding for monitoring is described

above.

(15) Comment: One commenter stated that the regul ation should be written so that new monitoring is not required unl ess the U.S. EPA has the abili ty to fund the initiative.

Response: Information on how the EPA addresses funding for monitoring is described

above.

(16) Comment: In providing comments on the proposal to require near-roadway monitors,

one commenter stated that most of these laud atory objectives are not directly tied to the implementation of the new or proposed PM 2.5 NAAQS, but instead involve support for research. At a time when budgets for NAA QS-compliance monitoring are seriously limited, it does not make sense to devote those limited funds to monitoring for research

purposes.

Response: As stated in section VIII.B.3.b.i , the EPA believes the addition of PM 2.5 monitors to the near-road environment w ill support a number of objectives and isV-68 important for the protection of public hea lth. Information on how the EPA addresses funding for monitoring is described above.

(17) Comment: Multiple commenters stated that the EPA has not demonstrated the need to add a requirement for near-road monitoring of PM 2.5 . The primary purpose of these monitors appears to be research. At a tim e when state monitoring budgets are reportedly inadequate to provide monitors to ascertain compliance with the 1-hour SO 2 NAAQS that the EPA adopted in 2010, funding shoul d not be diverted to fund new PM 2.5 monitoring

sites.

Response: As stated in section VIII.B.3.b.i , the EPA believes the addition of PM 2.5 monitors to the near-road environment w ill support a number of objectives and is important for the protection of public hea lth. Information on how the EPA addresses funding for monitoring is described above.VI-1 VI. RESPONSES TO SIGNIFICANT CO MMENTS ON IMPLEMENTATION

The EPA received comments on a range of implementation topics discussed in section IX of the proposal, including init ial area designations, section 11 0(a)(2) infrastructure State Implementation Plan (SIP) requirements, nonatta inment area SIPs, New Source Review (NSR) and Prevention of Significant Deterioration (PSD ) program requirements (including the specific proposed changes to the PSD regulations to prov ide a transition into meeting new requirements associated with the revised PM NAAQS), a nd the transportation conformity program. Our responses to specific comments rele vant to this final rule are pr esented below. Because the EPA is not finalizing a new secondary PM 2.5 NAAQS in this rulemaking, we are not addressing comments related to implementation of a distinct new secondary PM 2.5 NAAQS.

A. Specific Comments Related to Designation of Areas

This section responds to comments supporti ng and opposing the proposed schedules for initial area designations, recomm ending classification schemes, a nd discussing various technical and policy aspects of the area designations proc ess. The responses to some of these comments

are also discussed in section IX .A of the preamble to the fina l rule. The EPA received numerous comments on these issues from states, state orga nizations, local air pollu tion control agencies, regional organizations, industry, en vironmental organizations, and health-related organizations.

(1) Comment: Most commenters expressed support for a standard 2-year schedule for initial area designations for the primary annual PM 2.5 NAAQS.

Response: Under section 107(d)(1) of th e CAA, the EPA is required to designate areas no later than 2 years following promulgation of a new or revised NAAQS, or by December 2014 based on promulgating the PM NAAQS on December 14, 2012. Also under the schedule in section 107(d)(1 ) and confirmed in the fi nal PM NAAQS action, state Governors and tribes, if they choose, are required to submit their initial designation recommendations for the revised primary annual PM 2.5 NAAQS to the EPA no later than 1 year following promulgation of the re vised NAAQS (i.e., by December 13, 2013). If the EPA intends to make any modifications to a state’s or tribe’s recommendations, including modifications to area boundaries, the EPA is required to notify the state or tribe no later than 120 days prior to finalizing the designation; this would be no later than August 14, 2014. States and tribes will then ha ve an opportunity to demonstrate why the EPA's intended modification is inappropriate before the EPA makes the final designation decisions by December 12, 2014.

(2) Comment: Several commenters encouraged the EPA either to consider additional time (up to 1 year) for initial area designations (or not to designate areas) associated with the proposed secondary PM visibility index standa rd due to the lag in obtaining data from speciation monitoring networks, the variability in monitore d relative humidity data, and the “unique” nature of the proposed secondary standard. Another commenter suggested that, rather than waiting for data from newl y established monitors, designations for the secondary standard should be made based on the existing PM 2.5 monitoring network.VI-2 Response: For the reasons stated in section VI.D.2 of the preamble to the final rule, the

Administrator has decided not to establish th e proposed distinct secondary standard to address visibility impairment. Therefore, the EPA will not promulgate initial area designations for a secondary PM visibility index standard.

(3) Comment: Several commenters asked the EPA to clarify whether data from the proposed new near-road monitors will be used, if available, for initial area designations. Others expressed concern that data from violating near-road monitors not be used when designating areas as these monitors are not representative of surrounding communities and should not drive the designations process for an entire urban area. Many of these same commenters asked the EPA to clarify how near-road data might be used in future designations processes.

Response: The EPA does not believe that data from the new near-road monitors will be available for the EPA to consider within the timeframe for initial area designations provided by the CAA. Section 107(d)(1) of th e CAA requires the EPA to designate areas no later than 2 years following promulga tion of a new or revised NAAQS, or by December 2014. (The CAA provides the Agen cy an additional third year from promulgation should there be insufficient information on which to make compliance

determinations. 46 ) For initial area designations for the primary annual PM 2.5 NAAQS, the EPA relies exclusively on monitoring da ta to identify areas to be designated

nonattainment due to violations of the standa rds and then uses monitoring data and other information to identify areas contributing to violations in those areas. See Catawba County v. EPA , 571 F.3d 12-13 (D.C. Cir. 2009). As indicated in the preamble to both the proposed and final PM NAAQS, the initial set of near-road PM 2.5 monitors will be fully deployed by January 2015 with the requisite 3 years of air quality data available in

2018. 47 The EPA intends to proceed with initial area designations for the revised primary

annual PM 2.5 NAAQS using 3 years of consecutive ai r quality data from the existing,

area-wide FRM/FEM/ARM PM 2.5 monitoring sites to complete designations by

December 2014. 48 Consistent with previous area designations processes used in informing boundary decisions, the EPA would then analyze a variety of area-specific

46 While the EPA intends to make every effort to designate areas for the primary annual PM 2.5 NAAQS on a 2-year schedule, the EPA recognizes that new information may later arise that justifies the need for additional time, up to 1 additional year is available based on insufficiency of data , to complete the process. Any subsequent change to the designations schedule would be announced.

47 The remainder of the near-road monitors in CBSAs with populations between 1 million but less than 2.5 million will be deployed by January 1, 2017.

48 The EPA notes that once the EPA has promulgated initial designations for a new or revised NAAQS, section 107(d)(3) of the Clean Air Act provides a separate process for redesignating areas based upon subsequent air quality-related considerations. We believe that this proce ss is the appropriate process for addressing monitoring

information that was not available in sufficient time to be considered during the designation process. As noted by the

Court in Catawba v. EPA , 571 F.3d 52, “Congress imposed deadlines on EPA and thus clearly envisioned an end to the designation process.” It is important that states can rely on the completed designations and to move forward with
the associated required implementation planning

.VI-3 information 49 in determining which nearby areas contribute to a violation.

Although we do not anticipate that data from the new near-road monitors will be available for initial designations, the EPA would consider near-road data meeting the EPA’s completeness, quality assurance, and NAAQS comparability criteria in future designations processes (e.g., a de signations process associated with a future revision to the NAAQS) or in potential re designation processes under section 107(d)(3). The EPA

believes that data from all near-road site s are comparable to the primary 24-hour PM 2.5 NAAQS and that data from near-road sites approved as area-wide sites would be comparable to the annual PM 2.5 standard. As explained in sections III.E.3.a and VIII.B.3.b.i of the final rule preamble, a si gnificant fraction of the nation’s population lives near major roads. The EPA has a res ponsibility to protect air quality and public

health in all locations that meet EPA’s defi nition of ambient air, including those areas with populations living near ma jor roads. As noted in the previously mentioned preamble sections, air agencies and the EPA will use the annual monitoring network plan described in 40 CFR 58.10 to identify and approve sites that are suitable a nd sites that are not suitable for comparison to the annual PM 2.5 NAAQS.

(4) Comment: One commenter suggested that the EPA conduct dispersion modeling around transportation facilities in acco rdance with the EPA’s transportation conformity hotspot modeling guidance and use concentrations to determine attainment status for the designations process. This same comm enter also supported using modeling for unmonitored areas, e.g., communities near roadways.

Response: As previously indicated, for the primary annual PM 2.5 NAAQS, the EPA relies on monitoring data to identify ar eas to be designated nonattain ment due to violations of

the standards and does not intend to c onduct or use dispersion modeling around transportation facilities or in unmonitored areas to determine whether an area is violating the standard for purposes of establishing nona ttainment areas, as this is not required by

the statute. See Catawba County v. EPA , 571 F.3d 12-13 (D.C. Cir. 2009). The EPA

intends to address the factor analysis and boundary setti ng process in the designation guidance to the states and tribes, expected to be available shortly after promulgation of the PM NAAQS.

(5) Comment: Several commenters emphasized the need for the EPA to provide timely guidance and technical information for ar ea designations. Commenters similarly encouraged the EPA to consult with pot entially affected areas during the area designations process.

Response: As discussed in the preamble, the EPA intends to provide designation guidance and technical information shor tly after the NAAQS are promulgated. In

49 The EPA has used area-specific informati on to support boundary determinations by evaluating factors such as air quality data, emissions and emissions-related data, meteor ology, geography/topography, and existing jurisdictional boundaries. This may include, as appropriate, inform ation from non-FRM/FEM/ARM monitors and air quality modeling, where available, to help define an appropriate boundary for areas contributing to FRM/FEM/ARM-based

monitored violations.VI-4 addition, the EPA plans to offer assistance to states and tribes throughout the designations process on technical and policy issues.

(6) Comment: One commenter suggested that the EPA use the designation categories outlined in the Clean Air Act (i.e., nonattainment, attainment, or unclassifiable) as opposed to the EPA’s practice of using “unc lassifiable/attainme nt” when designating areas that meet the NAAQS. The commenter not ed that the “unclassifiable/attainment” designation is unclear to the public. Another commenter presented an additional designation category approach and asked the EP A to consider using “unclassifiable” or “transitional” when designating nonattainment areas that the EPA projects could reach attainment within 5 to 10 years based on federal measures. The commenter notes that with this approach the “EPA could take the pragmatic step of avoiding the imposition of costly and unnecessary stat ionary source controls while assuring continued progress toward meeting the tighter standard. Such a designation would r ecognize the strong role

of [sic] federal measures provide in helping areas to attain the standard and would set the precedent of avoiding unnecessary an d redundant costs where feasible.”

Response: As previously discussed, the EPA inte nds to provide designation guidance and technical information shortly after the NAAQ S are promulgated. The EPA expects this guidance to include the intended designation categories for area designations for the revised primary annual PM 2.5 NAAQS.

(7) Comment: Several commenters supported the EPA’s proposed approach to use 3 consecutive years of monitored ambient air qua lity data to determine violations of the standard rather than modeling for initial area designations. One commenter urged the EPA to determine and clearly define the “contribution” to nonattainment.

Response: As indicated in both the proposed and final PM NAAQS actions, the EPA intends to proceed with initial area desi gnations for the revised primary annual PM 2.5 NAAQS using 3 years of consecutive air qu ality data from the existing, area-wide

FRM/FEM/ARM PM 2.5 monitoring sites to complete designations by December 2014. Consistent with previous area designati ons processes used in informing boundary decisions, the EPA would then use area-specif ic factor analyses in determining which nearby areas contribute to a violation. These supporting analyses may include information from non-FRM/FEM/ARM monitors and air quality modeling, where available, to help define an appropr iate boundary for areas contributing to

FRM/FEM/ARM-based monitored violations. Shortly after the NAAQS are promulgated, the EPA intends to further clarify in designa tions guidance and tec hnical information the use of monitoring data, factor analyses, and “contribution.”

(8) Comment: Several commenters submitted remarks related to establishing boundaries for

PM nonattainment areas. A few commenters asse rted that a Metropoli tan Statistical Area (MSA), either a Core-Based Statistical Area (CBSA) or Combin ed Statistical Area (CSA), is too large an area to use in establishing presumptive boundaries for nonattainment areas and prefer st arting at the county boundary.VI-5 Response: The EPA did not address the issue of appropriate boundaries for nonattainment areas in the PM NAAQS rule. The EPA will evaluate nonattainment area boundary

recommendations from states and tribes a nd assess appropriate ar ea boundaries during the designations process. Under the CAA, th e EPA must designate as nonattainment any area that is violating the NAA QS or that is contributi ng to a nearby violation.

(9) Comment: Multiple commenters noted that the regulatory burden associated with the EPA’s process of designating nonattainment areas will cause affected areas economic

harm.

Response: The EPA’s Regulatory Impact Analysis (RIA) provides illustrative estimates of the potential costs and health and welfare benefits of attaining several alternative PM 2.5 standards based on one possible set of selected control strategies for reducing direct PM and PM precursor emissions.

As previously discussed, the EPA intends to provide designation guidance and technical information shortly after the NAAQS are pr omulgated. Additionally, the EPA will be developing a PM NAAQS implementation rule , which the EPA intends to finalize around the time the initial area designations deci sions are promulgated in December 2014. This implementation rule will address the c ontrol obligations for areas designated

nonattainment and strive to id entify, with appropriate stakeh older input, approaches that provide flexibility and opportunity for effici ency to the extent such approaches are consistent with the CAA and will not jeopard ize expeditious attain ment of the public health and welfare goals of the CAA. Fina lly, to the extent the CAA does not mandate specific control measures, states may consid er economic concerns in development of their SIPs to address air quality.

(10) Comment: One commenter noted that “[i]n pr eparing new designations, EPA must consider needed redesignations under the 24-hour standard, even if EP A decides to retain the current standard unchanged. To ignore evid ence of violations of the 24-hour standard would be arbitrary and capricious and contra ry to the health pr otection goals of the statute. Designations must be accurate to avoid irrational outcomes, for example, around the proper permitting program for new and mo dified sources. EPA reasonably proposes to apply the nonattainment permitting programs in areas violating either the 24-hour or annual primary standards, but this approach, if the 24-hour designations are not revisited, would not guard against the situation where an area is designated attainment for both the annual and 24-hour standard even though it is violating the 24-hour standard. This would

create the untenable situation wherein new sources in the area, governed by the PSD program, would be required to show that they will not cause or c ontribute to a violation of a NAAQS that the area is in fact already violating. New 2009-2011 data... identify

areas that don’t attain current standard yet are officially in attainment.”

Response: Section 107(d)(1) of the CAA requires the EPA to designate areas no later than 2 years following promulgation of a new or revised NAAQS. In the EPA’s final rule, the EPA revised the primary annual PM 2.5 standard, strengthening it from 15 μ g/m 3

to 12 μ g/m 3 ; retained the existing 24-hour PM 2.5 standard at 35 μ g/m 3 ; retained theVI-6 existing 24-hour PM 10 (coarse particle) standard at 150 μ g/m 3 ; and retained the current suite of secondary PM standards. Under se ction 107(d)(1), the EPA is required to designate areas only for the revised primary annual PM 2.5 standard. The CAA does not require the EPA to designate areas when it reta ins a standard in every aspect (level, form, averaging time and indicator). Therefore, th e EPA does not intend to designate areas for

the retained standards when we designate areas for the revised primary annual PM 2.5 standard. Section 107(d)(3) of the CAA pr ovides a separate process for redesignating areas and provides the EPA with discretion regarding timing for designations/redesignations under section 107(d )(3). The EPA will work with states to

achieve attainment in the most effective ma nner, whether this is accomplished through section 107(d)(3) or other approaches.

B. Specific Comments Related to Section 110( a)(2) Infrastructu re SIP Requirements

In the proposal, the EPA invited preliminar y comment on all aspects of infrastructure SIPs for the Agency to consider in developing futu re guidance. As stated in section IX.B of the preamble to the final rule, the EPA is curren tly developing a guidance document on CAA section 110 infrastructure SIP requirements that will addr ess most infrastructure SIP elements and will aim to help states develop SIP submissi ons for all NAAQS, including the revised PM 2.5 NAAQS, and the EPA is considering comments received as it develops this guidance. The EPA also may issue supplemental infrastructure SI P guidance specific to the revised PM 2.5 NAAQS in the

future if needed.

In addition to seeking comment on all aspe cts of infrastructure SIPs, the EPA sought comment specifically on the timing of infrastructure SIP submittals, particularly in light of the proposed new secondary standard. The EPA received comments both recommending and opposing granting states additional time to submit SIPs for any revised secondary standard, but because the Agency is not revising the secondary NAAQS in this rule, the issue of whether or

not to allow states extra time to submit infras tructure SIPs for the secondary NAAQS is now

moot.

(1) Comment: Some commenters emphas ized the need for infrastructure guidance no later than one year after promulgation of the revi sed standards. The commenters also stated that the EPA's infrastructure guidance s hould include detailed gui dance on how states should address the interstate transport oblig ations in CAA section 110(a)(2)(D), arguing that the guidance for the 2006 PM NAAQS indicated that tec hnical analysis would be required, but it did not specify how the anal ysis should be conducted or how the EPA would evaluate the analysis. The commenters noted that the issue is further complicated by the status of the Clean Air Interstate Ru le (CAIR) and the Cross State Air Pollution Rule (CSAPR or the “Transport Rule”).

A few commenters argued that the EPA should not issue guidance on CAA section 110 infrastructure SIP requirements for a revised PM 2.5 NAAQS, claiming that the requirements are already stated in th e CAA and that EPA guidance would be “inappropriately prescriptive.” One of these commenters felt “the EPA should not attempt to supplant the states’ and di stricts’ discretion in applyi ng the basic infrastructureVI-7 requirements. If the EPA determines in the fu ture that nonattainment areas cannot attain because of emissions outside of the area in qu estion, out of State, or outside the United States, then the EPA can employ any of its statutory powers to a ddress the situation.”

Response: The EPA believes that issuing non-bindi ng infrastructure SIP guidance is appropriate and that it is bene ficial to states by helping them to develop plans in a nationally consistent manner. The EPA also understands commenters’ concerns about the need for timely guidance and intends to issu e, in the very near future, a guidance

document on section 110 infrastructure SIP re quirements, which will aim to help states develop SIP submissions for a ll NAAQS, including the revised PM 2.5 NAAQS. We

intend to address most infrastructure SIP requirements in this guidance including the interstate transport requirements containe d in CAA sections 110(a)(2)(D)(i)(II) and 110(a)(2)(D)(ii). In addition, the EPA may issue supplemental infrastructure SIP guidance specific to the revised PM 2.5 NAAQS if needed.

The EPA does not intend to address in the upcoming infrastructure SIP guidance document the interstate transport requirements contained in CAA section 110(a)(2)(D)(i)(I) – i.e., the requirements related to em issions from one State that significantly contribute to nonatta inment or interfere with ma intenance of the NAAQS in another state. The U.S. Court of Appeals for the D.C. Circuit recently issued an opinion in EME Homer City Generation v. EPA , 696 F.3d 7 (D.C. Cir.) that is relevant to this provision. Among other things the court conclude d that “a SIP cannot be deemed to lack a required submission or be deemed defici ent for failing to implement the good neighbor obligation [its obligatio n under 110(a)(2)(D)i)(I) 50 ] until after EPA has defined the State's good neighbor obligation." EME Homer City Generation v. EPA , 696 F.3d 7, 31 (D.C. Cir 2012). This decision is not yet final as the mandate in EME Homer has not been issued and the EPA has petitioned for rehearing en banc in that case. In the meantime, the EPA intends to act in accordance with the holdings in the EME Homer opinion. Unless

the EME Homer decision is altered, states will no t be required to submit SIP revisions addressing the requirements in CAA secti on 110(a)(2)(D)(i)(I) until the EPA further defines state obligations pur suant to that section.

(2) Comment: Some commenters stated that the EPA should allo w states the full 3-year statutory time period for submitting primar y NAAQS infrastructure SIPs. Another commenter argued that the submittal deadline for section 110(a)(2)(D) SIPs for interstate transport should not be governed by the 3-ye ar submission deadline for infrastructure

SIPs.

Response : As noted in section IX.B of the pr eamble to the final rule, while the CAA

allows the EPA to set a shorter time than 3 years from the date of promulgation of a NAAQS for submission of infrastructure SIPs , the EPA does not currently intend to do so. With respect to the second comment, the EPA is without authority to alter, in this rule, the SIP submission deadline established in the statute. The EPA has historically interpreted section 110(a)(1) of the CAA as establishing the required submittal date for

50 The Court refers to section 110(a)(2)(D)(i)(I) as the “good neighbor provision" and obligations under that provision as a state's “good neighbor obligation." EME Homer City , 696 F.3d at 13.VI-8 110(a)(2)(D) interstate tran sport SIPs, including the provisions in section 110(a)(2)(D)(i)(I) regarding signi ficant contribution to nonatta inment and interference with maintenance. However, as noted above, the D.C. Circuit's recent opinion in EME

Homer , 696 F.3d at 31, concluded that a SIP can not be deemed to lack a required submission under section 110(a)(2)(D)(i)(I) unt il after the EPA has defined the state's good neighbor obligation. Although th is decision is not yet fi nal as the mandate in EME

Homer has not been issued and the EPA has petitioned for rehearing en banc in that case, in the meantime EPA intends to act in accordance with the holdings in the EME Homer opinion. Nothing in the EME Homer opinion, however, affects the state’s obligation to submit SIPs addressing the requirements of CAA sections 110( a)(2)(D)(i)(II) and 110(a)(2)(D)(ii) by the d eadline established in CAA section 110(a)(1).

(3) Comment: Some commenters suggested that th e EPA should not require anything more

than a "traditional infrastructure SIP" to satisfy CAA section 110 requirements for the

PM 2.5 NAAQS, stating that "the EP A has indicated that it will call for only the traditional elements of infrastructure SIPs and will not purport to require specific emission control strategies as part of infrastructure SIPs."

Response: The EPA agrees with these commente rs and does not intend to require in

PM 2.5 infrastructure SIP submittals any specific emission control strategies for the purpose of attaining the standard. Such strate gies will be required in nonattainment area plans.

(4) Comment: One commenter supported the EPA’s approach to allow states to make a

certification that their current infrastructure SIPs are sufficient to implement the revised NAAQS. Another group of commen ters cautioned that a str eamlined certification option "may not be available to Stat es that last updated their infr astructure SIPs before the applicability of requirement s governing condensable particulate emissions and PSD permitting elements specific to PM 2.5 ," and further stated that the EPA should identify in any future guidance changes in requirements that have become effective since the last

round of infrastructure SIPs.

Response: The EPA notes that states may be able to certify that for selected infrastructure SIP elements, existing state regulations are su fficient for meeting the new infrastructure SIP obligations associated with the revised PM 2.5 NAAQS. A SIP submittal in the form of a certification should provide citations to the relevant provision already approved by the EPA that meet the particular infrastructu re SIP element requirements, but it would not have to include a paper copy of those provi sions. Like any other SIP submittal, such a

certification should be made and submitted to the EPA only after the state has provided reasonable notice and opportunity for public hearing, as required in CAA section 110.

The EPA agrees that for infrastructure SIPs to be approvable for the revised PM 2.5 NAAQS, SIP submissions need to address all infrastructure-related requirements that have become applicable since the PM 2.5 NAAQS were revised in 2006. The EPA’s forthcoming guidance on infrastructure SIPs for all NAAQS, including the revised PM 2.5 NAAQS, will include discussion of these requirements.VI-9 C. Specific Comments Related to Implementing the Proposed Revised Primary Annual

PM 2.5 NAAQS in Nonattainment Areas

As explained in section IX of the preambles to the proposed and final rules, the EPA will be undertaking a separate effort to develop and finalize an implementation rule for the revised

PM 2.5 NAAQS through a formal notice-and-comment ru lemaking process. To help inform that effort, in the PM NAAQS proposal we sought preliminary input from stakeholders on implementation issues to update or address in a future implementation rule proposal. The EPA received a number of comments related to a variety of implementation issues either specifically raised in the proposal or in addi tion to those raised in the prop osal. Topics raised by commenters included, but were not limited to, mon itoring requirements, treatment of PM 2.5 precursors, requirements for Reasonable Further Progre ss (RFP) and Reasonable Available Control Technology/Reasonable Available Control Measures (RACT/RACM), and NAAQS implementation burden. We are not taking any fina l actions with regard to these or other implementation issues in this final rule.

We will provide a separate comment period for the submission of comments on the futureimplementation rule proposal. At that time, parties who submitted preliminary implementationrelated comments as part of this rulemaking (t o revise the PM NAAQS) may choose to resubmit their comments for formal consideration as part of the PM 2.5 NAAQS implementation rulemaking. Comments received on the PM NAAQS pr oposed rule will not be considered to be comments “submitted in advance” on any future implementation rule proposal.

1. Transition Period

The EPA sought preliminary comment in the proposal on the poten tial concept of a transition period during which any changes in monitoring requirements would not affect attainment plans and maintenance plans for the 1997 and 2006 PM 2.5 NAAQS. The EPA received comments in support of and in opposition to such a concept.

(1) Comment: In support of a transition period for 1997 and 2006 PM 2.5 SIPs, one commenter argued that attainment demonstra tions and redesignation requests for existing standards should not be impacted by the re vised standards and requirements. Other commenters specified that th e EPA should provide a 3-year transition period for updating attainment plans or maintenance plans for the 1997 and 2006 PM 2.5 NAAQS as they may relate to any new monitoring requirements. A nother commenter stated that EPA will need to address outstanding "transi tion period" issues resulting from changes in the monitoring regulations, especially with respect to the e ffect of this informa tion on designations and the collection of pre-and post-construction m onitoring for projects. The same commenter

noted that states should not be obligated to change their SIPs as part of the transition to

the revised standards in the absence of a SIP call.

In objecting to the concept of a transition period described in th e proposal, a group of commenters argued that the EP A cannot ignore valid data if it raises questions about assumptions or conclusions of SIPs for the 1997 or 2006 PM 2.5 standards. The commenters insisted that the CAA “places upon EPA an affirmative duty to ensure thatVI-10 SIP revisions will not interfere with any app licable requirement concerning attainment,”

and that the “EPA should be clear that agencies must c onsider available data and determine, on a case-by-case basis, whether it is relevant and significant to the planning decision being made.”

Response: As explained in section IX.C of the preamble to the final rule, in consideration of comments received and upon further analys is of the potential effect of monitoring requirement changes, we believe that it will not be necessary to provide for a transition period in any future implementation rule be cause the changes in monitoring requirements included in this final PM NAAQS rule would not automatically affe ct attainment plans and maintenance plans for the 1997 or 2006 PM 2.5 NAAQS. Specifically, there are currently approximately ten PM 2.5 air quality monitors that have been identified as not comparable to the annual standard as part of the annual state mon itoring plan revision process. If a state chooses to re vise the status of one of thes e monitors in order to make it comparable to the annual standard because it is determined to be representative of many other similar locations, it would propose a change in status for that monitor in the next

revision of the state PM 2.5 monitoring plan (state revisions are due in June of each year).

The EPA would then review and take acti on on the state's proposed change. The EPA believes that the monitoring plan revision proc ess provides adequate procedural steps for identifying which monitors are to be comparable to the annual PM 2.5 standard. For this reason, we believe that there is no need to incl ude any "transition peri od" in a future rule.

2. Timing and Development Process for Implementation Rule and Tools

The EPA received several comments that raised concerns about the timing of an implementation rule or guidance and compliance tools for the revised PM2.5 NAAQS, as well as about the development process for an implementation rule. While many of these comments were not relevant to the PM NAAQS review itself, we addressed some of these comments in section IX.C of the preamble to the final rule, where we reiterated our intentions to develop a separate implementation rule through a formal notice-and-comment rulemaking process.

(1) Comment: Several commenters communicated a need for the EPA to issue an implementation rule, either in proposed or final form, simultaneous with the final PM NAAQS rule. Some of these commenters insisted that implementation requirements should be specified at the time a NAAQS is promulgated, while othe rs stated that the EPA should issue the implementation gui dance prior to making the new NAAQS

effective and no later than the date the ar eas are initially desi gnated. Several state commenters noted that a lack of timely impl ementation guidance can prevent them from meeting their own state obliga tions. Another commenter aske d for the EPA to commit to firm deadlines rather than target dates for the proposed and finalized implementation rule and revised monitoring regulations. The comme nter was specifically concerned about timely guidance for reasonably available control technology (RACT) and reasonably available control measures (RACM) and infras tructure guidance to align with the timing of states’ SIP development process.

Response: As noted in the preamble to the final rule, the EPA acknowledges states’ needVI-11 for timely guidance on how to implement the revised NAAQS. However, due to the number of unique and complex issues a ssociated with the PM NAAQS proposal and uncertainty about the outcome of the final NAA QS, at this time the EPA is not able to propose an implementation rule or finalize any aspect of the implementation program beyond a limited set of PSD permitting issu es. The EPA intends to address state implementation planning issues and require ments through a formal notice-and-comment rulemaking process and to finalize a PM2.5 NAAQS implementation rule around the time the initial area designations pr ocess is finalized. We believe this schedule for proposing and finalizing such a rule is timely. With respect to infrastructure guidance, the EPA intends to issue, in the very near future, a guidance document on section 110 infrastructure SIP requirements, which will aim to help states develop SIP submissions for all NAAQS, including the revised PM 2.5 NAAQS.

(2) Comment: Several commenters stated that it is critical that the EPA not promulgate NAAQS prior to the development of tools and techniques suitable for states and regulated entities to use for implementation.

Response: The EPA notes that fine particle stan dards have been implemented by states and regulated entities for a number of years already and there are a number of technical tools in place already to facilitate the implementation of a newly revised PM 2.5 standard. These tools (such as air quality models, em ission factors, and emission inventories) continue to be updated and refined over time.

(3) Comment: A few commenters urged the EPA to c onsult with stakeholders, particularly with states and local agencies, prior to deve loping any rules or gui dance for the revised NAAQS and throughout the process.

Response: As stated in the preamble to the final rule , the EPA agrees that it is beneficial to engage with air agencies early in the rule development process. We have initiated such discussions to help inform the developm ent of an upcoming proposed implementation rule, and expect to have additi onal such discussions during 2013.

D. Specific Comments on Prevention of Sign ificant Deterioration and Nonattainment

New Source Review

This section responds to comments recei ved on the PSD and Nonattainment NSR (NNSR) programs and potential impacts associat ed with the revised PM NAAQS. Several of

these comments are addressed in detail in section IX.D of the preamble to the final rule, and in those cases, the reader is referred to the appropr iate subsection(s) of the preamble for the EPA’s responses. Responses to comments not specifically a ddressed in the preamble to the final rule are provided below.

As a general matter, we note that, with the exception of the PSD grandfathering provisions, the EPA is not taking final action to address NSR implemen tation in this NAAQS package. Nevertheless, we did receive severa l comments raising NSR implementation issues, some of which argued that particular issues may be of greater con cern under the revisedVI-12 NAAQS. Some comments further suggested changes to NSR policy or rules—beyond the grandfathering provision—to allevi ate these concerns. This secti on provides responses to those issues by describing, as appropr iate, current and future EPA efforts to facilitate NSR implementation for the PM 2.5 NAAQS. The responses generall y indicate that the EPA is committed to working with air agencies and other stakeholders to address these issues in the appropriate forum (which could include rulemaking, guidance, or case-by-case determinations). Thus, again with the excepti on of grandfathering, our respons es here do not reflect final decisions by the agency on these issues but inst ead are provided for informational purposes only. In addition, we note that while the particular implementation issues ra ised or the burden

associated with them will receive further consid eration by the Agency as noted above, they are

not relevant to the decisions made on revisions to the NAAQS, including es tablishing the level of

the standard.

1. Prevention of Significant Deterioration

a. Transition Provision (Grandfathering)

(1) Comment:

 The majority of commenters, including all industry and state agency representatives, supported the EPA’s proposed grandfathe ring provision based on the purpose and rationale described in the preamble to th e proposal. These commenters agreed that grandfathering certain pending PSD permit appl ications was reasonable to balance the CAA objectives to protect the NAAQS on one hand, and to avoid delays in processing PSD permit application on the ot her. They also agreed grandfathering provides a reasonable transi tion into the PSD requirements associated with the revised NAAQS. Industry commenters also indicated that such a provision was important to economic growth and recovery, and was consistent with the purposes of the PSD program, i.e., to ensure that economic growth will occur in a manner consistent with preservation of air qualit y. Several state commenters pointed out that finalizing the revised PM 2.5 NAAQS without a grandfatheri ng provision would result in a significant additional resource burden on both permit applicants and air agencies, which would have to reopen pending permit a pplications that have reached advanced stages in processing to addr ess the revised standard. The commenters further noted that there would likely be little if any environmental benefit afforded by such a process. One state agency commenter perfor med a preliminary review of recent PSD permitting actions and determined that in all cases, the proposed primary annual

PM 2.5 standard would not have led to tighter permit restrictions or reduced emissions, and that a re-noticing of the preliminar y permit decisions would accomplish nothing more than to change the margins of comp liance. In other word s, re-noticing would have led to project dela ys with no reduction in PM 2.5 impacts.

 Four environmental group commenters (one representing a coalition of a health advocacy group and several environmental groups) opposed the proposed grandfathering provision based either on concerns about further delay in implementation of the revised PM NAAQS or on a position that the proposed grandfathering provision exceeds the EPA’s statutory authority and is unlawful. Commenters challenging EPA’s legal authority to implement the proposedVI-13 grandfathering provision cont ended that CAA sections 165 and 301 do not confer any authority on the EPA to grandfather PSD permit applications. The commenters asserted that CAA section 165(a) for ecloses the EPA’s proposed approach, specifically citing CAA section 165(a)(3)( B) which provides that no major emitting facility “may be constructed” unless the f acility’s owner or op erator demonstrates emissions from the facility will not cause or contribute to the violation of “any . . . national ambient air quality standard in any air quality control region.” These commenters further claimed that because Congress limited the applicability of the new PSD requirements in several ways, includ ing specific grandfat hering relief for

sources constructed before the enactment of the 1977 Amendments to the CAA, the

EPA is not authorized to waive otherwise applicable statutory requirements (citing

Andrus v. Glover Constr. Co. , 446 U.S 608, 116-17 (1980)). A subset of these same commenters also stated that the EPA’s pr oposed grandfathering approach undermines the policy choices made by Congress in a dopting the PSD program that 1) it is preferable to prevent air pollution from b ecoming a problem in the first place, and 2)

controls should be installed when new sour ces are being constructed rather than as retrofits on existing sources.

One commenter asserted that there is no conflict between CAA sections 165(a) and 165(c) as the EPA had implied; therefore, there is no need for the EPA to invoke the regulatory authority of CAA section 301. Th is commenter also concluded that the EPA’s rationale of balancing of economic growth and the protection of air quality pursuant to CAA section 160(3) was unlawful, and that the EPA had not adequately explained the considerations it sought to balance and how the proposal would achieve its goals. The same commenter questioned the EPA’s authority to leverage principles of equity and fairness in proposing the gr andfathering provision. The commenter also objected to the EPA’s rationale for choosing th e public notice date of a draft permit as the milestone triggering the grandfathering provision, sta ting that the approach was contrary to statute because it would deprive interested persons of their statutory right to comment on elements of the app lication related to the current NAAQS.

 Regarding the need for a sunset clause fo r the grandfathering provision, the majority of commenters supported, as proposed, not including such a clause, and no commenters specifically recommended that a sunset clause be established. Commenters pointed out that permit appli cants and reviewing authorities already have strong incentives to issue final perm its in a timely manner following the public notice stage, and that a sunset clause w ould not add any meaningful incentive to expedite the permitting process, rather potentially causing additional delays. One commenter stated that permitting authorities have ample discretion, which they routinely use, to refuse to issue a draft permit if additional information is requested during a comment period or the agency its elf wants additional information following publication of a draft permit or prelimin ary determination. The same commenter indicated that permitting authorities also have sufficient discretion to reopen permit proceedings if they consider informa tion in an application to be stale.VI-14  Several of the commenters supporting th e proposed grandfathering provision in general recommended that the EPA establish the grandfathering mile stone as the date that a complete permit application is subm itted (or that a submitted permit application is deemed complete by the reviewing agen cy) rather than the publication date of public notice for a draft pe rmit or preliminary determination as proposed. These commenters pointed out the sign ificant level of effort, resources and time involved in preparing all of the information necessary for a complete permit application, including a BACT analysis, air quality analysis, additi onal impacts analyses, and a Class I area impact analysis. They claimed that it would be unfair to establish a grandfathering milestone past the complete application date because the processes and timeframes involved in generating the dr aft permit or preliminary determination materials and publishing the publ ic notice are largely out of the control of the permit applicant and vary from agency to agen cy. They further stated that requiring reevaluation of a proposed project to a ssess impacts with resp ect to the revised NAAQS after a permit application has been deemed complete would result in significant additional cost and delay. Several such commenters cited prior EPA grandfathering provisions th at relied upon that milest one, including the 1987 PM 10 NAAQS (52 FR 24672, July 1, 1987) and the 1988 NO 2 increments (53 FR 40656, October 17, 1998), and contended that the EPA had not justified the use of an alternative date for purposes of the proposed revisions to the PM 2.5 NAAQS. Some

state commenters also indicated that th e proposed draft permit public notice date

milestone could result in additional resource burden on the agency to expedite completion of draft permit packages a nd process public notices. Other state commenters supported the EPA’s proposed draf t permit or preliminary determination public notice date as the appropriate gra ndfathering eligibility milestone, indicating that this approach would provide stat es and industry certainty on the NAAQS demonstration required during the PM 2.5 NAAQS transition period.

 A few industry commenters suggested, as an alternative to the proposed approach, that the EPA should effectively grandf ather PSD permit actions from meeting requirements associated with the revise d PM NAAQS by extending the effective date of the NAAQS by one year.

Response: The EPA has provided detailed respon ses to these comments in section IX.D.1.a.ii of the final rule preamble.

(2) Comment : One local government and one industry commenter suggested that the EPA should extend grandfathering to non-PSD permits, e.g., minor source permits and synthetic minor permits.

Response : The commenters did not demonstrate the need for grandfathering of minor NSR permits nor did they provide any other supporting rationale fo r such grandfathering. The EPA did not propose, and is not finalizi ng, any grandfathering pr ovisions for minor NSR permit applications.VI-15 (3) Comment : One state agency commenter suggested that the grandfathe ring provision be

consistent with the EGU GHG NSPS rule.

Response : The proposed EGU GHG NSPS (“Standa rds of Performance for Greenhouse Gas Emissions for New Stationary Sources: Electric Utility Generating Units,” 77 FR 22392, April 13, 2012) proposed requirements for any electricity generating unit (EGU)

that meets the definition of an “affected facility.” Under CAA section 111(a)(2), any source that is covered by a proposed NSPS and that commences construction after the date of the proposal must meet the require ments of the NSPS that EPA finalizes. However, in this proposal, EPA made clear that certain types of sources would not be

treated as “affected f acilit[ies],” including “transitional sources.” A “transitional source” was defined as, in general, an EGU that had received a complete PSD permit prior to April 13, 2012, and that commences construc tion within 12 months after the April 13, 2012, date of the proposal. Therefore, under th is proposal, a source th at qualifies as a “transitional source” would not be subject to the requirements of the NSPS when the rule is finalized. Although the comment is not spec ific, apparently it is this “transitional source” provision that the comment considers to be the grandfathering provision.

As stated in Section IX.D.1.a.i of the pream ble to the final rule, longstanding EPA policy interprets the CAA and EP A regulations at 40 CFR 52.21(k)(1) and 51.166(k)(1) to generally require that PSD pe rmit applications include a de monstration that new major stationary sources and major modifications will not cause or contribute to a violation of any NAAQS that is in effect as of the date the PSD permit is issu ed (Page, 2010a; Seitz, 1997). Accordingly, a source that has received a final PSD permit prior to the effective date of the final NAAQS would not be require d to meet any new requirements associated

with the revised standards regardless of the scope of the grandfathering provision finalized in this rule. In this sense, this longstanding EPA policy already is consistent with the proposed “transitional source” provision because under the latter, sources with PSD permits prior to the date of proposal (and that commence construction within one year after proposal) would not be subject to the final NSPS requirements. Accordingly, there is no need to make the grandfathering pr ovision in this rule consistent with the “transitional source” provision in the proposed E GU GHG NSPS.

b. Surrogacy Approach for Proposed Se condary Visibility Index NAAQS

The EPA received a large number of comme nts on the proposed implementation of a surrogacy approach for addressing PSD requireme nts associated with the proposed distinct secondary visibility index NAAQS. As described in section VI of the final rule, the EPA is not finalizing a distinct seco ndary visibility index standard at this time and therefore the proposed surrogacy approach for implementing such a standard under the PSD program is unnecessary. Accordingly, the EPA is not responding to co mments on the proposed surrogacy approach for the proposed secondary visibility index NAAQ S here. Comments received on the proposed surrogacy approach and associated technical me morandum that are relevant to the EPA’s final

decision not to establish a distin ct secondary visibility NAAQS at this time are addressed in section VI.D.2 of the final rule preamble and sect ion IV of this response to comments document.VI-16 c. Modeling Tools and Guidance Applicable to the Revised Primary Annual PM 2.5 NAAQS

(1) Comment: Several industry commenters identifi ed a generally common suite of issues and limitations associated with currently available modeling tools and guidance for performing required PSD air quality impact analyses for PM 2.5 (i.e., the requirement that PSD permit applicants demonstrate that source emissions will not cause or contribute to a

violation of the PM 2.5 NAAQS). These commenters stated that the current regulatory air quality model, AERMOD, is unable to predic t the impact of a single source on ambient

PM 2.5 concentrations, incl uding secondary particle formation from PM 2.5 precursors. They further stated that the EPA has yet to provide adequate guidance on how applicants are to address the PSD air quality dem onstration requirements for the current PM 2.5 NAAQS. Many of these commenters also cont ended that current modeling tools and guidance result in over-predic tions and/or overly conservativ e estimates of impacts, and that this, in combination with lower NAAQS levels, would result in project delays and adverse impacts on the economy. Commenters speaking to the same issue referred to a

“narrow window” for source-related impacts under the proposed revised PM 2.5 NAAQS. Many of these commenters indicated that the EPA should resolve the identified PM 2.5 modeling issues prior to finalizing the PM 2.5 NAAQS, and do so through notice-andcomment rulemaking. One industry commenter stated the EPA should not require point source modeling of PM 2.5 until the Agency has an effec tive modeling tool available.

Response: To address PSD air quality demons tration requirements for current PM 2.5 NAAQS, EPA issued, on March 23, 2010, a guidance memorandum entitled “Model Procedures for Demonstrating Compliance with PM 2.5 NAAQS” (Page, 2010b) that recommended certain interim procedures to address compliance with the PM 2.5 NAAQS and acknowledged that there are technical comp lications associated with the ability of existing models to estimate the impacts of secondarily formed PM 2.5 in the atmosphere resulting from emissions of PM 2.5 precursors. The EPA is currently preparing draft PM 2.5 permit modeling guidance that recommends appropriate technical approaches for conducting a PM 2.5 NAAQS compliance demonstration that includes the use of the AERMOD modeling system to account for impacts of directly emitted PM 2.5 and a more adequate accounting for contributions fr om secondary formation of ambient PM 2.5 concentrations resulting from a proposed new or modified source’s pr ecursor emissions.

This draft PM 2.5 permit modeling guidance is nece ssary to inform case-by-case determination of appropriate methods as sources should now conduct a PM 2.5 -based analysis under NSR and PSD to de monstrate compliance with the PM 2.5 NAAQS rather than relying upon a PM 10 -based analysis in accordance with past EPA guidance. (76 FR 28646, 28648, 28659 (May 18, 2011); Page, 2010b). The EPA expects that technical issues related to the PSD compliance de monstration will be resolved during the consultation process with the EPA’s regional offices pursuant to section 5.2.2.1.c so that the most appropriate analytical techniques can be used on a ca se-by-case basis to address the impacts of individua l sources on secondary PM 2.5 formation.

The EPA has provided presentati ons regarding the dr aft guidance at the 10th Conference on Air Quality Models in March 2012 and at the Regional/State/Local Modelers Workshop in May 2012 which are available at:VI-17 http://www.epa.gov/ttn/scram/conferenceindex. htm. The EPA intends to provide this draft guidance for public review and comment soon after final rule signature, no later than end of calendar year, with the intent of issuing fina l guidance in Spring 2013. This guidance extends the guidance from the prev ious March 23, 2010 memo and takes into account specific recommendations from the NACAA PM 2.5 Modeling Implementation Workgroup, public comments received from the 10 th Modeling Conference, and our caseby-case involvement with recent applicant-submitted PM 2.5 compliance demonstrations.

(2) Comment: One industry trade association comm enter provided detailed comments on implementation issues for PM 2.5 modeling including a revi ew of existing models, including AERMOD and CALPUF F, and pointed out specific characteristics and

limitations associated with those models. In summary, the commenter stated that there

was a critical need for EPA modeli ng tools to evaluate secondary PM 2.5 impacts, and that the EPA should develop a research plan, in cluding funding requirements, for addressing model development. The commenter also st ated that the “EPA cannot proceed with modeling implementation of the PM 2.5 NAAQS until field studies with speciated PM 2.5 observations focused upon a single source are av ailable and used in evaluation of new

state-of-the-science models.”

Response: The EPA acknowledges the need to conduct a thorough review and evaluation of existing and developing mode ls and modeling techniques to address the complexities of accounting for PM 2.5 impacts from single sources. As part of the 10 th Modeling Conference in March 2012, the EPA dedicated a session to this issue of emerging models and techniques with detailed presentations on the current state of the science which

included model evaluations with available field study data (see presentations at http://www.epa.gov/ttn/scram/10thmodconfpres.htm ). The EPA sponsored a similar

session at the 11 th Annual CMAS Conference in October 2012 where additional model developments and evaluations were presen ted (See presentations from afternoon of

October 16 th at: http://www.cmascenter.org/conference/2012/agenda.cfm ). The EPA will continue engaging with the modeling community on the evaluation of current models and modeling techniques as part of its commitment to engage in rulemaking to update Appendix W and, as appropriate, incorporate new analytical techni ques or models for secondary PM 2.5 impacts from single sources.

In terms of current complia nce demonstrations under PM 2.5 NAAQS, as noted in the previous comment response, the EPA is preparing draft PM 2.5 permit modeling guidance that will provide recommendations on appropria te technical approaches for conducting a

PM 2.5 NAAQS compliance demonstration for a pr oposed new major stationary source or major modifications. This draft PM 2.5 permit modeling guidance is necessary to inform case-by-case determination of appropriate methods as sources should now conduct a

PM 2.5 -based analysis under NSR and PSD to demonstrate compliance with the PM 2.5 NAAQS rather than relying upon a PM10-based analysis in accordance with past EPA guidance. (76 FR 28646, 28648, 28659 (May 18, 2011); Page, 2010b). The EPA expects

that technical issues related to the PSD co mpliance demonstration will be resolved during the consultation proces s with the EPA’s regional offices pursuant to section 5.2.2.1.c so that the most appropriate anal ytical techniques can be used on a case-by-case basis toVI-18 address the impacts of indivi dual sources on secondary PM 2.5 formation.

(3) Comment: One industry commenter made several sp ecific suggestions to improve model accuracy. The commenter suggested that mode l inputs should be adjusted by: 1) not assuming simultaneous maximum allowable emissions when a reasonable worst case actual emissions scenario is available, and 2) eliminating the inputs for non-stack sources (e.g., haul roads, pits, roof monitors) until adequa te studies of source-sp ecific test data is

conducted to establish a discount factor to offset over-predicti on bias in the model results. The commenter suggested that model outpu ts should be refined by 1) eliminating downwash assumptions during low wind speed ev ents that are contrary to the observed plume rise under these meteorological condi tions, and 2) foregoing the modeling of secondary formation of PM 2.5 until there is a clear unders tanding of when and where it will affect ambient air quality. The comm enter also stated that the EPA should “encourage the use of available monitored da ta to ’ground truth’ the air model results and, where appropriate, use the monitor data to establish calibration factors for adjusting

the model results.”

Response: The EPA will be addressing the commente r suggestions as part of its response

to comments from the at the 10th Conference on Air Quality Models and, as appropriate, will consider updates to current mode ling requirements for PSD compliance demonstrations as part of future rulemaking to revise EPA’s Guideline on Air Quality

Models (published as Appendix W of 40 CFR Part 51).

(4) Comment : One industry coalition commenter sugge sted that the EPA’s pending revised

PM 2.5 modeling guidance be co-proposed as a dr aft for public comment with the final PM NAAQS rulemaking. This commenter also sugg ested that until the new guidance can be finalized, the final rule should indicate that “the 2010 Guidan ce be used judiciously for general directions and that air quality pl anning and permitting authorities can deviate from the 2010 guidance based on their professional judgment.”. The commenter requested that the EPA remind air agencies in the final PM NAAQS rulemaking that “Section 10 of Appendix W allows for the place ment of post-construction monitors in lieu of modeling to collect emissions info rmation where modeling suggests future nonattainment issues, particularly in vi ew of the inadequacy of current PM 2.5 modeling techniques and the stringency of the current and the proposed new PM 2.5 NAAQS.”

Response: As noted in previous comment response, the EPA is currently preparing draft

PM 2.5 permit modeling guidance that recommends appropriate technical approaches for conducting a PM 2.5 NAAQS compliance demonstration. This draft PM 2.5 permit modeling guidance is necessary to inform case-by-case de termination of appropriate

methods as sources should now conduct a PM 2.5 -based analysis under NSR and PSD to demonstrate compliance with the PM 2.5 NAAQS rather than relying upon a PM 10 -based analysis in accordance with past EP A guidance. (76 FR 28646, 28648, 28659 (May 18, 2011); Page, 2010b). The EPA expects that t echnical issues re lated to the PSD compliance demonstration will be resolved during the consultation process with the EPA’s regional offices pursuant to sec tion 5.2.2.1.c so that the most appropriate analytical techniques can be used on a cas e-by-case basis to address the impacts ofVI-19 individual sources on secondary PM 2.5 formation.

EPA will continue to remind air agencies of th e applicability of Section 10 of Appendix W that allows for monitoring in lieu of modeling to demonstrate compliance under PSD

for those situations where it has been dete rmined in consultation with the appropriate reviewing authority that the modeling techniques are not a ppropriate for use. It is important to note that the commenter mischaracterizes this guidance as “placement of post-construction monitors” conceivably in the case of a new source, but the applicability of Section 10 is only in the case of an ex isting source, where monitoring data could be used in a NAAQS assessment following the recommendations in that guidance.

(5) Comment: One state agency commenter raised a concern that the EPA appeared to be planning to make substantive changes to the PSD modeling requirements through guidance instead of through rulemaking, w ithout the opportunity for public comment.

The commenter further stated that any substantive changes to PM 2.5 modeling, including any substantive changes to how secondary formation of PM 2.5 is handled for PSD purposes, should be done thor ough public notice and comment rulemaking (referring to 40 CFR 52.21, 51.166 and Appendix W).

Response : The EPA is currently preparing draft PM 2.5 permit modeling guidance that recommends appropriate technical approaches for conducting a PM 2.5 NAAQS compliance demonstration that includes th e use of the AERMOD modeling system to account for impacts of directly emitted PM 2.5 and a more adequate accounting for contributions from secondary formation of ambient PM 2.5 concentrations resulting from a proposed new or modified source’s precursor emissions. This draft PM 2.5 permit modeling guidance is necessary to inform case-by-case de termination of appropriate

methods as sources should now conduct a PM 2.5 -based analysis under NSR and PSD to demonstrate compliance with the PM 2.5 NAAQS rather than relying upon a PM 10 -based analysis in accordance with past EP A guidance. (76 FR 28646, 28648, 28659 (May 18, 2011); Page, 2010b). The EPA expects that t echnical issues re lated to the PSD compliance demonstration will be resolved during the consultation process with the EPA’s regional offices pursuant to sec tion 5.2.2.1.c so that the most appropriate analytical techniques can be used on a cas e-by-case basis to address the impacts of individual sources on secondary PM 2.5 formation. This guidan ce extends the previous March 23, 2010, memo and takes into account specific recommendations from the

NACAA PM 2.5 Modeling Implementation Workgroup, public comments received from

the 10 th Modeling Conference, and our case-by-cas e involvement with recent applicant

submitted PM 2.5 compliance demonstrations. The EPA intends to provide this draft guidance for public review and comment soon af ter final rule signatu re, no later than the end of calendar year 2012, w ith the intent of issuing final guidance in Spring 2013.

(6) Comment: Three industry commenters, in support of their position that current PM models over-predict impacts, cited the adoption of section 234 of the CAA and the EPA’s recognition of these concerns in communications with Wyoming in which the EPA

allowed some areas to demonstrate PM 10 NAAQS compliance by us of extensive monitoring rather than inaccu rate fugitive dust models (c iting Proposed Approval ofVI-20 Wyoming SIP, 57 FR 38641, 38646-48, August 26, 1992). These commenters also stated that modeling tools and guidance should be de veloped through an ope n process with peer review opportunities to improve the data relied upon in re gulatory decisions. Two of these commenters encouraged the EPA adopti ng modeling changes consistent with the NMA’s comments regarding the 10th M odeling conference (NMA, 2012). One state agency commenter indicated that the agency did not require short-term fugitive PM modeling, and that that a pproach was affirmed in Sierra Club v. Wyo. Dept. of Envl. Quality, 2011 WY42, 251 P.3d 310 (Wyo. 2011) . The same commenter referenced that the AERMOD Implementation Guide acknowledges that the model has shortcomings and may overestimate area source concentrations.

Response: The EPA will be addressing the commen ters’ suggestions as part of its response to comments from the 10th Conf erence on Air Quality Models and, as appropriate, will consider updates to current modeling requirements for PSD compliance demonstrations as part of future rulemaking to revise the EPA’s Guideline on Air Quality

Models (published as Appendix W of 40 CFR Part 51).

(7) Comment: One industry coalition commenter iden tified that current modeling tools are not appropriate to address fugitive PM emissi ons, and that industry has already provided the EPA with a short-term fix to this probl em called an “emissions pre-processing step.” As described, the pre-processing step reduces emission factors for fugitive emissions sources to account for inadequacies in the model. The commenter stated that EPA is already using a pre-processing step in regi onal modeling, and recommended that the EPA extend the approach to point-source modeli ng, indicating that this approach would improve PM modeling and reduce some implementation burden. The commenter also

stated that it would be will ing to “bring resources to the table to help EPA find a longterm solution and verify that solutions effectiveness.”

Response: The EPA will be addressing the commen ters’ suggestions as part of its response to comments from the 10th Conf erence on Air Quality Models and, as appropriate, will consider updates to current modeling requirements for PSD compliance demonstrations as part of future rulemaking to revise the EPA’s Guideline on Air Quality

Models (published as Appendix W of 40 CFR Part 51).

d. PSD Screening Tools: Significant Emissi ons Rates, Significant Impact Levels, and Significant Monitoring Concentration

(1) Comment: The EPA received several comments from industry and state agencies regarding the existing PSD scr eening tools and the potential need to adjust associated values based on the revised primary annual PM 2.5 NAAQS. The majority of these commenters supported retaining the ex isting SERs, SILs and SMC for PM 2.5 (and PM 2.5 precursors in the case of the SERs), indicat ing that there was no compelling technical reason for revision based on the proposed revision to the primary PM 2.5 NAAQS. One industry commenter indicated that there mi ght be a need to revise the annual PM 2.5 SILs based on the approach used in establishing th e current value. However, this commenter and others recommended that any revisi ons to the PSD screening levels for PM 2.5 beVI-21 accomplished through a separate notice-and-comment rulemaking. Several state commenters that supported retention of the current PM 2.5 SILs also urged the EPA to provide guidance on the use of those existing SILs.

Response : As described in section IX.D.1.c of the final rule preamble, the EPA did not propose to make and is not finalizi ng any changes to the existing PM 2.5 SERs, SILs and SMC as part of the final rule. The EPA inte nds to consider the need for any future changes to these values in light of today’s revision of the primary annual PM 2.5 NAAQS and considering public comments received. The EPA will address any changes to the

PM 2.5 SERs, SILs and SMC in a subsequent PSD implementation rulemaking if deemed necessary or appropriate. The EPA will determine the need for, and develop such rulemaking expeditiously, and any such forthcoming rulemaking will provide an additional opportunity for public comment on specific proposed revisions to the PSD screening tool values for PM 2.5 . Until any rulemaking to amend existing regulations is completed, permitting decisions should continue to be based on the SERs for PM 2.5 (and its precursors) and the SILs and SMC for PM 2.5 in existing regulations.

(2) Comment : One set of collaborative comments fr om health and environmental advocacy groups stated that the EPA’s proposal to l eave in place the PSD screening tools adopted with the previous PM NAAQS had no rationa l basis and was cont rary to statutory requirements. Referring the SILs and SMCs, these commenters contended that the EPA has no legal authority to create such de minimis exemptions in the PSD program and that even if EPA could adopt such exemptions, to leave in place exemptions based on PM NAAQS promulgated at higher levels has no technical basi s. The commenters further

stated that the EPA has offered no evidence th at sources with imp acts below the proposed

SILs or SMCs will never cause or contribute to violations of NAAQS or increments, or that the gain from regulating such sources would be trivial, and that the EPA’s proposal to leave the preexisting exemptions in plac e is unreasonable given that the analysis supporting those exemptions was tied to a sp ecific standards that EPA has now found inadequate to protect public health and welfare. Further, the commenters contended that a single national number that defines “trivial ” impact for all attainment areas is fundamentally flawed, given that even a very small impact can be of great significance in an area that is very close to exceedin g an increment or a NAAQS. Finally, these

commenters stated that the EPA must reas sess its SERs, because the SERs cannot be disconnected from the level of the NAAQS an d the EPA must provide a rational basis for concluding that the existing SERs continue to be appropriate. One additional set of

collaborative comments from academic resear chers also supported reconsideration, and possible lowering of the PSD screening levels, citing, in the context of the SERs, the fact

that there is no safe threshold a nd a linear dose response curve for PM 2.5 . These same

commuters recommended that the EPA consider screening levels for other indicators, including ultra fine and nano PM and that those indicators be established based on particle number instead of mass to account for surface area and volume.

Response: As described in section IX.D.1.c of the final rule preamble and in the response to comment VI.C.1.d. (1) above, the EPA did not propose to make and is not finalizing any changes to the existing PM 2.5 SERs, SILs and SMC as part of the final rule. The EPAVI-22 intends to consider the need for any future changes to these values in light of today’s revision of the primary annual PM 2.5 NAAQS and considering public comments received. The EPA will address any changes to the PM 2.5 SERs, SILs and SMC in a subsequent PSD implementation rulemaking if deemed necessary or appropriate. The EPA will determine the need for, and develop such rulemaking expeditiously, and any such forthcoming rulemaking will provide an a dditional opportunity for public comment on specific proposed revisions to the PSD screening tool values for PM 2.5

.

The commenters’ claims that the de minimis nature of the SILs and SMCs are

unsubstantiated and that the EPA has no statut ory authority to establish SILs and SMC

for PM 2.5 are the subject of current litigation in Sierra Club v. EPA , No. 10-1413 (D.C. Cir. filed Dec. 17, 2010). The EPA’s argument in support of the existing PSD screening tools is contained in a brief filed in that case, which is included in the docket for the final

rule. Id. , Brief of Respondent at 26-56 (June 26, 2012).

e. PSD Increments

(1) Comment: The EPA received few comments on whether there was any need or justification to revise the existing PSD increments for PM 2.5 . Industry and state agency commenters generally supported retaining the existing increments. One industry commenter indicated that there may be a need to reevaluate the annual PM 2.5 increment. Commenters again recommended that any revisions to the PSD increments for PM 2.5 be accomplished through a separate notice-and-comment rulemaking.

Response: As described in section IX.D.1.d of the final rule preamble, the EPA did not propose to make and is not finalizing any changes to the existing PSD increments for

PM 2.5 as part of the final rule. The EPA will consider whether it is appropriate to propose any revised PSD increments for PM 2.5 in the future. Any such forthcoming rulemaking will provide an additional opportunity for pub lic comment on specific proposed revisions

to the PSD increments for PM 2.5 . Until any rulemaking to amend existing regulations is completed, permitting decisions should continue to be based on the PSD increments for

PM 2.5 in existing regulations.

f. Other PSD Transition Issues

(1) Comment: Several industry commenters expressed concern that a permitting problem would result from the fact that, upon promulgation of the revised PM 2.5 NAAQS, ambient air quality monitoring data woul d show that for some areas, PM 2.5 concentrations exceed the revised NAAQS, although those areas w ould not be formally designated as “nonattainment” until a later date pursuant to the designations process provided by the

CAA. The commenters noted that sources lo cating in such areas would be required to obtain a PSD permit in order to construct or modify, but could not do so because the requirement that the new or modified source must demonstrate that it will not cause or contribute to a NAAQS violati on, even though the area would t echnically already be in

nonattainment. The commenters further noted th at once the nonattainme nt designation is made, section 173 of the CAA provides a nonattainment area permit program that specifies conditions under which a permit will be issued, including obtaining offsettingVI-23 reductions in emissions rather than demonstr ating through modeling or other analysis that

the source will not cause or contribute to a violation of the NAAQS as required in PSD. Thus, the commenters urged the EPA to offer an interim approach that would avoid the imposition of an effective construction ban on such areas until such time as the nonattainment area designations and the nona ttainment NSR offset requirements are in place instead of the PSD requirements. Some of the commenters specifically requested that the EPA provide either a surrogacy a pproach based on showing compliance with the pre-existing annual PM 2.5 NAAQS or a PSD offset approa ch to avoid a construction

moratorium in such areas.

Response: The EPA has provided a detailed resp onse to these comments in section IX.D.1.e of the final rule preamble.

(2) Comment: One state agency commenter objected to the EPA’s policy that the state must implement a permitting requirement that has not yet been adopted into the SIP, stating

that the EPA should not burden SIP-approved states with the requirement to immediately develop permitting procedures to demons trate compliance with a new NAAQS. The commenter recommended that the EPA promulga te in rule a phase-i n period that would require the demonstration after implemen tation guidance and tools (including singlesource models) are available.

Response: As stated in section IX.D.1.a.i of th e preamble to the final rule, longstanding EPA policy interprets the CAA and EP A regulations at 40 CFR 52.21(k)(1) and 51.166(k)(1) to generally require that PSD pe rmit applications include a demonstration that new major stationary sources and major modifications will not cau se or contribute to a violation of any NAAQS that is in effect as of the date th e PSD permit is issued (Page, 2010a; Seitz, 1997). As described in section IX.D .1.a.iii of the preamble to the final rule, the EPA is finalizing a grandfathering pr ovision under the PSD regulations that is designed to help provide a workable tr ansition to implementing the revised PM 2.5 NAAQS under the PSD permitting program. The CAA does not authorize the type of additional phase-in period recommended by th e commenter. Furthermore, the commenter did not provide any substantive supporting ba sis for the need for such a phase-in period. The final rule establishes a revised level of the primary annual PM 2.5 NAAQS. Permitting procedures and tools should already be in place for the previously existing primary

annual PM 2.5 NAAQS, and these same procedures and tools are applicable to the revised standard. Response to comments on modeling to ols and guidance are provided in section

VI.C.1.c of this document.

(3) Comment : One industry coalition commenter, in support of a general comment that NSR

solutions are needed to resolve the di fficulty in obtaining NSR permits for PM 2.5 emissions, provided some specific suggesti ons. They suggested that the EPA should explore the voluntary use of PM 2.5 “offsets” as an alternative to air quality demonstration requirements under the current regulations. Th ey asked that the EPA explore whether

offsets can be utilized in attainment or uncla ssified areas to reduce the burden of ambient air impact analyses. They also requested th at the EPA “address the ability for source operators in attainment areas to buy NO X or SO 2 credits from cap-and-trade participantsVI-24 in affected states/regions in addition to traditional offsets representing sources that are

deactivated at the time a new ‘source’ star ts up.” They suggested another potential mechanism which was to “‘tier’ requiremen ts post construction to levels of actual emissions from a new project.” Finally, the co mmenter requested that the EPA “affirm in the final rulemaking the use of the existing provisions in Appendix W and Section 10 for the use of ‘post-construction’ monitoring where models may predict certain future air quality impacts from a project.”

Response : The commenter presented several altern ative means of addressing the alleged problem of obtaining a PSD permit where a source’s modeled impact would show the

source would cause or contribu te to a violation of the PM 2.5 NAAQS. With regard to the

commenter’s recommendation that the EPA explore the voluntary use of PM 2.5 offsets as an alternative to an air quality demonstrati on under the current PSD regulations, we point the commenter to our response to comment f.1, above, which is contained in section IX.D.1.e of the final rule preamble. In brief, we believe that the o ffsets option is already available to proposed new major stationary sources and major modifications whose

emissions are shown to cause or co ntribute to violation of any NAAQS.

The commenter’s second recommended alte rnative is to allow a source to “buy NO X or SO 2 credits from cap and trade participants in affected states/regions.” The EPA places

the same criteria on offsets obtained for PSD purposes as are required under the Act for nonattainment areas. Accordingly, any emissions reduction, in order to be creditable as an emissions offset, must be surplus, perm anent, quantifiable and federally enforceable. To the extent that credits purchased from a cap and trade participant meet the required creditability criteria, then we believe they may be considered for use as emissions offsets ( see, e.g. , Rothblatt, 2007). An additional consideration that will need to be made with regard to any credit used for PSD offsetting purposes is the lo cation of the offset relative to the proposed emissions increase. That is, an appropriate emissions offset must be

shown to affect the same area as the ne w emissions so as to provide effective compensation for the adverse impact of the new emissions. See 40 CFR 51.165(b)(3) (“sufficient emissions reductions to, at a minimum, compensa te for its adverse ambient impact where the source would otherwise cau se or contribute to a violation of any [NAAQS]”).

Thirdly, the commenter recommended that th e EPA “tier requirements post construction to levels of actual emissions from a new proj ect.” Unfortunately, it is not clear what the commenter meant by “tiering” the requireme nts, or how using the project’s postconstruction actual emissions would address a potential NAAQS violation. Thus, we are unable to respond to this partic ular comment as presented.

Finally, the commenter recomme nded that the EPA use the existing provisions in section 10 of Appendix W (Guideline on Air Qua lity Models) to allow post-construction monitoring “where models may predict certain fu ture air quality impacts from a project.” As indicated in the response to comment c .4 of this section, the EPA will continue to remind air agencies of the applicability of Section 10 of Appendix W that allows for monitoring in lieu of mode ling to demonstrate complia nce under PSD for existingVI-25 sources in situations where it has been dete rmined in consultation with the appropriate reviewing authority that the modeling t echniques are not appropriate for use.

(4) Comment : One industry trade association commente r, stated that EPA should prepare for NSR/PSD implementation to avoid a practical “permitting moratorium” in areas where existing air quality is such that PSD air quality analyses must be performed to demonstrate compliance with the NAAQS, but cannot in practice because current air quality is: (1) currently monitored at a leve l greater the new NAAQS level before model results are considered; or (2) currently mon itored at a level in the range of 10-12 μg/m 3
(or 13 μg/m 3 ) and would have such a small margin available that a major source or major modification could not practically model a sma ll enough impact attribut able to the source that, when added to the background, coul d demonstrate compliance with the NAAQS. The commenter stated that in many areas , based on the EPA’s 2009-2011 Design Values, modeling of new source growth can be anticipated to be very challenging.

Response: As we indicated in the responses above (f.1 and f.3), we believe that adequate policy exists to enable states to issue permits to proposed new and modified sources that model violations of the NAAQS, as l ong as those sources provide sufficient compensation for their modeled adverse impact s. Accordingly, it is not appropriate to conclude that sources proposing to constr uct or modify in areas already showing

exceedances of the annual PM 2.5 NAAQS or experiencing leve ls near the NAAQS face an automatic “permitting moratorium.”

E. Nonattainment New Source Review

(1) Comment: Several industry commenters recommended that the EPA establish a grandfathering provision for NNSR as was pr oposed under the PSD program. A subset of these commenters recommended that grandfathe ring be accomplished by establishing an effective date for designations 1 year after initial publica tion in the Federal Register.

Response: The EPA has provided detailed response s to these comments in section IX.D.2 of the final rule preamble.

(2) Comment: A few industry and state agency commen ters addressed the issue of potential dual review (applying NNSR and PSD simultaneously) based on distinct designations for separate averaging times of the PM 2.5 NAAQS. These commenters generally agreed with

the EPA’s conclusion that it was reas onable to apply only the NNSR permitting requirements to such si tuations and not PSD.

Response: The EPA has provided detailed response s to these comments in section IX.D.2 of the final rule preamble.

F. Other NSR Implementation Comments

(1) Comment: One industry coalition commenter and one industry trade association

commenter identified issues related to in-stack PM 2.5 test methods. These commenters

stated that available test methods for PM 2.5 from wet stacks overestimate emissions and therefore will subject more sources to NSR/ PSD. One of the commenters indicated that the EPA had committed to study this issue further when it finalized revisions toVI-26 Reference Method 202 for condensable partic ulate, and the other that API and the National Council for Air and Stream Improveme nt, Inc. (NCASI) are working with the EPA to develop a validation test plan for ca ndidate methods, but that this process will

take time.

Response: The EPA recognizes the need to de velop a method which quantifies PM 2.5 emissions in a wet stack environment. Sin ce the proposal of Method 201A, the EPA has been engaged in the development of this capability. In addition, the EPA has been following the efforts of a contractor retained by API to develop this capability but with a somewhat different approach. While these effo rts are promising, the EPA is several years from having a validated test method which all stakeholders are confident is reliable and capable of being performed by mo st stack test consultants.

(2) Comment : One industry association and one stat e agency commented on the lack of accurate emissions information and technical guidance concerning PM 2.5 . The industry

association commenter cited de ficiencies in EPA’s AP-42, in cluding the fact that most emission factors are for total PM, the limited da ta on particle size dist ribution, the lack of data on condensable PM, and the low quality rating of available em ission factors. The state agency commenter stated that the lack of reliable emission factors and data on the condensable portion of PM 2.5 makes it difficult for air agenci es and/or sources to fairly and effectively implement the standards, and that this would be exacerbated by lowering

the standards.

Response: The EPA recognizes that many of the emi ssions factors in AP-42 are outdated and/or deficient for many source categories. Th is situation has arisen due to the inability to obtain and process source test information in an efficient and cost effective way to develop new and revised emissions factors. As a result the EPA is updating the way that stack test reports are documented and proce ssed to develop emissions factors. In 2004, the EPA developed the Electronic Reporting Tool (ERT) for documenting stack tests. The ERT revises the paper method of documenti ng the requisite information so that the remainder of the emissions factor developm ent does not require the level of resources required with paper test repor ts. Since the development of the ERT, the EPA has required

sources to use this tool to report the results of stack test data required for regulatory development efforts. In addition, the EPA ha s promulgated several rules for specific source categories that require sources to s ubmit stack test reports t using the ERT. On January 1, 2012, the EPA activated the Central Data Exchange (CDX) portal for submitting stack test reports. The EPA will be developing a data system to replace the existing WebFIRE which will use test data submitted with the ERT through the CDX to update existing emissions factors or to develop new emissions f actors. To the extent that

sources submit their stack test data to the EPA with the ERT, updated emissions factors will be made available for use by regulated sources’ air agencies.

(3) Comment : One industry coalition commenter sugge sted that a transi tion period may be needed for pre- and post-construction monitoring of PM 2.5 under the PSD program to address changes in the monitoring regulations.VI-27 Response : The EPA does not anticipate that the changes to the monitoring regulations contained in the final NAAQS rule would affect pre- or post-construction monitoring under the PSD program that may be in progr ess or pending at the time the changes become effective. Therefore, the EPA does not believe that a regul atory transition period is necessary. In the unlikely event that case- specific PSD pre- a nd/or post-construction monitoring may be affected by the monitoring regulation changes contained in the final rule, the EPA and permitting authorities may ha ve the discretion to mitigate such impacts by providing a transition period or mechanis m tailored to the specific permit action to avoid unreasonable delays and additional burden.

G. Specific Comments Related to Transportation Conformity

(1) Comment: One commenter was pleased to see th at, if the proposed changes to the PM 2.5 monitoring regulations concerning replacing th e term “community oriented” with “areawide” and revoking the requirement that mon itoring sites be population oriented are finalized, the EPA would update its guidance on conducting quantitative PM 2.5 hot-spot analyses for transportation conformity purpos es. The commenter stated that to avoid confusion the guidance will need to be revised expeditiously.

Response: The changes to the monitoring regula tions are designed to align different elements of those regulations for consiste ncy. The EPA intends to quickly revise its guidance entitled, “Transportation Conformity Guid ance for Quantitative Hot-spot Analyses in PM 2.5 and PM10 Nonattainment and Maintenance Areas” 51 to address these revisions to the monitoring regulations . The preamble to the final PM NAAQS rule

describes how the EPA intends to address the overall transition from the current monitoring regulations to the revised m onitoring regulations. The EPA intends the current PM Hot-spot Guidance to conti nue to apply to any quantitative PM 2.5 hot-spot analysis that was begun before the effective date of today’s revisi ons to the monitoring regulations. Revised guidance woul d apply to any quantitative PM 2.5 hot-spot analysis begun after the effective date of the revise d monitoring regulations. Nonattainment and maintenance areas are encouraged to use th eir interagency consu ltation processes to determine whether an analysis for a given proj ect was started before the effective date of the revised monitoring regulations.

(2) Comment: Two commenters raised issues rela ted to having one or more separate secondary NAAQS for PM 2.5 making transportation and air quality planning and transportation conformity more complex a nd costly by requiring that conformity be demonstrated by comparing future emissions to multiple sets of PM 2.5 motor vehicle emissions budgets. The commenters were also c oncerned that the EPA will not be able to completely revoke the 1997 annual PM 2.5 NAAQS as has been the practice as the ozone NAAQS has been revised meaning that areas will have to conti nue to demonstrate conformity to the 1997 annual PM 2.5 NAAQS. One commenter notes that revoking the previous less stringent NAAQ S conserves resources because the areas no longer have to demonstrate conformity for the ear lier NAAQS after it is revoked.

51 Hereafter, referred to as “PM Ho t-spot Guidance” in this document

. EPA420

­ B

­ 10

­ 040, December 2010. U.S.

EPA (2010j). See www.epa.gov/otaq/stateresources/ transconf/policy .htm#project.VI-28 Response: As discussed in the final rule th e EPA retained the 1997 annual secondary

PM 2.5 NAAQS of 15.0 ug/m 3 , and did not finalize the proposed visibility-related standard because we determined that retaining the current 24-hour PM 2.5 NAAQS provides visibility protection equivale nt to the proposed visibility -related secondary NAAQS. The EPA will work with areas through the conformi ty rule’s interagency consultation process to determine efficient ways to fulfill conformity requirements for each of the PM 2.5 NAAQS that apply in each area in order to minimize the impact on the area’s resources. The comment on revocation is beyond the scope of the current final rule. The potential

revocation of the 1997 annual PM 2.5 NAAQS will be addressed in the planned implementation rule for the 2012 annual PM 2.5 NAAQS.

(3) Comment: In order to reduce the possibility of diverting transpor tation funds from addressing regional air quality which benefits the population of the entire nonattainment area to addressing near road or hot-spot pr oblems, the EPA should work closely with transportation professionals wh en developing implementation policies for these types of

issues.

Response: The EPA will work with a wide range of stakeholders as it develops SIP requirements for implementing the PM 2.5 NAAQS through a future rulemaking.

(4) Comment: Given the potential implications for tr ansportation planning and transportation projects the EPA should c onsult with transportation agencies on changes to implementation and designation requirements , transportation conformity requirements including hot-spot re quirements, and monitoring requirements.

Response: The EPA will work with a wide range of stakeholders as it develops SIP requirements for implementing the PM 2.5 NAAQS in a future rulemaking. The EPA will also update existing transporta tion conformity or issue new guidance as needed, as the Agency has historically done for conf ormity transitions to new NAAQS.

(5) Comment: Adding additional requirements on top of requirements that have not yet been fully implemented could result in transporta tion projects that had been in compliance with the Clean Air Act being determined to be out of compliance which would expose them to litigation.

Response: It is not clear what the commenter is referring to, since the comment provides no information regarding which specific “additi onal requirements” it is referring to, or how transportation projects could be determin ed to be out of compliance with the CAA. Therefore, we are unable to re spond to this comment.

(6) Comment: The commenter seeks assurance that PM 2.5 nonattainment areas will be eligible to receive Conges tion Mitigation and Air Quality Improvement (CMAQ) funds even though they will not be classified.

Response: PM 2.5 nonattainment and maintenance areas are eligible to receive CMAQVI-29 funds from the Federal Highway Administra tion. On July 6, 2012, the President signed the Moving Ahead for Progress in the 21 st Century Act (MAP-21) into law. MAP-21 authorizes transportation funding through the en d of federal fiscal year 2014 and amends the federal transportation law. Under MAP-21, a State with PM 2.5 areas must use a portion of its funds to address PM 2.5 -related emissions in such areas; eligible projects to mitigate PM 2.5 include diesel retrofits. MAP-21 also retains the directi on to states and metropolitan planning organizations to give priority to funding projects in PM 2.5 nonattainment or maintenance areas that are proven to reduce PM 2.5 , including diesel

retrofits.

H. Specific Comments Related to Exceptional Events

Comments related to exceptional events fo cused on the schedule for data flagging and documentation submittal for the primary standard and the schedule for data flagging and documentation submittal for the secondary standard to address the “unique” components of the secondary standard. Each of thes e is addressed below. The respons es to these comments are also

discussed in section VII.B of the preamble to the final rule.

(1) Comment: The majority of commenters supported the schedule by which agencies must flag ambient air data that they believe ha ve been affected by exceptional events, submit initial descriptions of those events, and submit detailed justification to support the

exclusion of those data from EPA-monitori ng-based determinations of nonattainment with the primary annual PM 2.5 NAAQS. A few commenters suggested schedule extensions for one of two reasons: the pot ential resource burden associated with preparing and submitting multiple wildfire exceptional event demonstrations for events in the unusually active wildfire years of 2010 to 2012 and data reporting lags and “unique” monitoring elements associated with the secondary standard.

Response: The EPA is finalizing the exceptional ev ents schedule as proposed and as supported by multiple commenters. For air qua lity data collected in 2010 and 2011, the EPA is extending to July 1, 2013, the otherwise applicable generic deadlines of July 1, 2011 and July 1, 2012, respectively, for flagging da ta and providing an initial description of an event (40 CFR 50.14(c)(2)(iii)). The EP A is retaining the existing generic deadline in the Exceptional Events Rule of July 1, 2013, for flagging data and providing an initial description of events occurring in 2012. Si milarly, the EPA is revising to December 12, 2013, the deadline for submitting documentation to support exceptional events occurring in 2010 through 2012 and potentially influenci ng compliance with the revised primary

annual PM 2.5 NAAQS. If an air agency intends th e EPA to consider in the revised primary annual PM 2.5 designations decisions whether PM 2.5 data collected during 2013 influence compliance with the primary annual PM 2.5 NAAQS, then the air agency must flag these data by the generic Exceptional Event Rule deadline of July 1, 2014. The EPA is finalizing August 1, 2014, as the deadline for submitting documentation to justify

PM 2.5 -related exceptional events occurring in 2013 and potentially influencing compliance with the revised primary annual PM 2.5 NAAQS. The EPA believes these

revisions/extensions will provide adequate time for air agencies to review potential PM 2.5 exceptional events influencing complianc e with the revised primary annual PM 2.5VI-30 NAAQS, to notify the EPA by flagging the re levant data and providing an initial description in AQS, and to submit documen tation to support claims for exceptional

events. These schedule revisions will also a llow the EPA to fully consider and act on the submitted information during the initial area designations process for the revised primary

annual PM 2.5 NAAQS.

The EPA acknowledges commenter concerns th at numerous wildfires occurred between 2010 and 2012 and that air agencies may dete rmine that these wildfires influenced ambient air quality concentra tions potentially affecting compliance with the revised primary annual PM 2.5 NAAQS. The EPA further acknowledges that air agencies may submit detailed exceptional events documentation associated with multiple wildfires. Although some commenters noted that 1 year to provide documentati on of these potential exceptional events may not be sufficient, the EPA believes that the promulgated schedules provide sufficient time for air agen cies to submit information related to the annual standard and for the EPA to fully consider and act on the submitted information during the initial area designations process. The EPA recently released draft exceptional events guidance that clarifies key provis ions of the 2007 Excep tional Events Rule, provides examples of best practices, and streamlines the documentation development process. The guidance provides approaches that are broadly applicable to all event/pollutant combinations and would appl y to many PM events, including wildfire/PM combinations. Additionally, the EPA has posted several concurred upon wildfire/PM exceptional event demonstration packages on its website at http://www.epa.gov/ttn/analysis/exevents.htm . Considered together, the EPA believes this guidance will help air agencies submit information in a timely manner. 52 The EPA notes that under the promulga ted schedule, except for even ts that occur in December 2012, air agencies will have more than 1 year to provide documentation for these potential events. The EPA intends to work w ith potentially affected areas to identify, screen and prioritize events potentially infl uencing compliance with the primary annual

PM 2.5 NAAQS and associated area designations.

For the reasons stated in section VI.D.2 of the preamble to the final rule, the

Administrator has decided not to establish th e proposed distinct secondary standard to address visibility impairment. Therefore, the EPA will not promulgate initial area designations for a secondary PM visibility index standard and, as a result, has not promulgated exceptional event schedule revi sions for events that might influence compliance with the secondary standard.

(2) Comment: Several commenters asked that the EPA clarify the preamble language and the associated promulgated exceptional events schedule to specifically identify the NAAQS to which the exceptional even t schedule revisions apply.

Response: In response to comment, the EPA clarif ied that the preamble language and the associated promulgated exceptional events sc hedules apply only to the NAAQS that the

52 U.S. EPA (2012e). Draft Guidance to Implem ent Requirements for the Treatment of Air Quality Monitoring Data Influenced by Exceptional Events, U.S. Environmental Protection Agency. June 2012. Available: http:// www.epa.gov/ttn/analysi s/exevents.htm.VI-31 EPA is newly promulgating or revising in this action, that is, the revised primary annual

PM 2.5 NAAQS. The promulgated exceptional event sc hedule revisions do not apply to the retained PM standards (i.e., seconda ry PM standards, primary 24-hour PM 10 , primary 24-

hour PM 2.5 ). Further, the revised/extended excep tional event schedules apply only to those data the EPA will use to establish initial area designations for the revised primary

annual PM 2.5 NAAQS.VII-1 VII. RESPONSES TO SIGNIFICANT COMMENTS ON LEGAL, ADMINISTRATIVE, PROCEDURAL, OR MISPLACED COMMENTS

A number of comments were received that addressed a wide range of issues including legal, administrative, and procedural issues . Many legal issues are addressed generally throughout the preamble to the fina l rule. Specific lega l issues are more fully addressed in section VII.A as well as in the previous RTC s ections above. Comments re lated to the Statutory and Executive Orders are addressed generally in s ection X of the preamble to the final rule and discussed more fully in section VII.B below. In addition, a number of comments were submitted related to issues that are not germane to the review of the NAAQS. Such comments have been categorized as “misplaced” comments and are discussed in section VII.C below.

A. Legal Issues

A number of commenters submitted comments addressing specific legal issues. These issues are generally discussed throughout the prea mble to the final rule and more specifically below. A number of legal issues specifically addressing comments related to the secondary

standards are addressed in secti on VI.C.1.g of the preamble to the fi nal rule and in section IV.B.8

above.

(1) Comment: One commenter asserted that the EPA has failed to “review and consider the

latest science in an unbiase d, factual manner...raising the pot ential that its decision to propose a lower standard violates the Clean Air Act” (ACC, 2012, p.2). This commenter further argued that the proposal “presents inadequa te justification for revising the level and form of the primary annual PM 2.5 standard and the EPA ha s “failed to address the

2009 D.C. Circuit remand” Id.

Response: The EPA strongly disagrees with this comment. The final decisions discussed in the preamble to the final rule reflect deci sions based on air quality criteria representing “”the latest scientific knowledge” within th e meaning of section 108 (a) (2) of the Act. The CASAC reviewed this enormous body of ma terial and found it a sufficient basis for agency action with respect to review of th e PM standards, including the primary fine particle standards. Moreover, the EPA is addressing the remand of the 2006 standards by the D.C. Circuit by revising the prim ary and secondary standards for PM 2.5 in a manner consistent with the court’s opinion and mandate.

(2) Comment: A group of commenters argued that th e “EPA’s failure to seek comment on the existing primary annual standard inappr opriately prejudges the outcome, leads to inherently biased rulemaking and is contrary to law” (e.g., NAM, 2012, p. 6).

Response: The commenter suggests that the EPA somehow prejudged the outcome of the rulemaking , or otherwise committed procedur al error, by not proposing to retain the 2006 NAAQS. This is in error. First, the EPA provided far more process through this review than the amount required by law. Commenters had multiple opportunities to review and comment on multiple drafts of a ll of the critical documents underlying the review (notably the ISA, the REAs, and the PA), as well as on all of the critical scientific and policy issues, assumptions, and factual da ta informing the review. Given that theVII-2 basic question being addressed throughout th is proceeding is whether or not it is appropriate to revise the 2006 standard (CAA section 109 (d)), that issue was necessarily before the public for comment (as evidenced by all the comments urging retention of the standard, among other indicia of proper notice). Nor does th e EPA’s proposal indicate a pre-judgment of the outcome of the review . Rather, the proposal reflected the EPA’s consideration of the body of scie ntific data and analysis co mprising the record for this

review.

The EPA strongly disagrees that the currently available scientific ev idence and technical information supports consideration for reta ining the annual standard level at 15 μg/m 3 and consequently did not propose to do so (jus t as the EPA did not propose to make the standard less stringent). As discussed in se ction III.D.3. of the pream ble for the final rule, having carefully considered CASAC advice and the public comments on the proposal as discussed in section III.D.2 of the preamble to the final rule and in section II.B.1 above,

the EPA believes the fundamental scientific conclusions on the effects of PM 2.5 reached in the ISA, and discussed in the PA, are vali d. The Agency believes that since the last review the overall uncertainty about the public health risks associatedwith both long- and short-term exposure to PM 2.5 has been diminished to an important degree. The remaining

uncertainties in the available evidence do not diminish confidence in the associations between exposure to fine part icles and mortality and serious morbidity effects. Based on the Agency’s increased confidence in the association between exposure to PM 2.5 and serious public health effects, combined with ev idence of such an association in areas that

would meet the current standard s , the Administrator agrees with CASAC that revision of

the current suite of PM 2.5 standards to provide increased public health protection is necessary. Based on these considerations as discussed in section III.D.3 of the preamble to the final rule, the Administrator concl udes that the current suite of primary PM 2.5 standards is not sufficient, and thus not requ isite, to protect pub lic health with an adequate margin of safety, and that revi sion is needed to in crease public health protection. Furthermore, as discussed in section III.E.4.e of the proposal, the Administrator provisionally conc luded that the available scie ntific information supported

consideration of an annual standa rd level no higher that 13 μg/m 3 . In considering public comments on the proposal as discussed in sections III.E.4.c.i and III.E.4.d of the preamble for the final rule and in section II .B.5.a above, the Agency concludes there is no scientific basis for considering retaini ng the annual standard level at 15 μg/m 3 (absent a drastically lower level of the 24-hour standa rd). These conclusions represent reasoned consideration of the body of evidence comp rising the record for this proceeding, not impermissible bias.

(3) Comment: One group of commenters argued that the EPA is not bound by the CASAC recommended range or any other CA SAC recommendations (e.g., NAM, 2012, p. 10).

Response: The EPA agrees that the Agency is not bound by the CASAC recommended range or any other CASAC reco mmendations, however, the Agency believes it needs to give careful consideration to CASAC’s advice and reco mmendations, and has done so here. The EPA is also clearly required to explain the reasons for any significant differences in approach. CAA section 307 (d) (3). The EPA’s deviation from CASAC advice and recommendations, and its failure to adequately explain those deviations, wasVII-3 one of the reasons for the remand of the 2006 primary annual PM 2.5 standard. See American Farm Bureau Federation v. EPA, 559 F. 3d at 521.

The EPA has carefully considered CASAC’s advice and recommendations in this review, understanding that CASAC’s views are not binding on the agency. Under sections 108 and 109 of the CAA, the Administrator is re quired to make decisi ons in reviewing the NAAQS using her own “judgment” in determining what standard is “req uisite” in light of all of the evidence, and is not required to accept or follow CASAC’s recommendations on what revisions are appropriate. The merits of the Administrato r’s decision is not determined solely based on whether she did or did not agree with CASAC, but based on a

review of the record as a w hole, including any explanation the Administrator provides for accepting or rejecting a recommendation fr om CASAC. The EPA has provided such explanations here as discussed in the preamble to the final rule, both where the

Administrator’s actions are c onsistent with CASAC’s advice (e.g., final decisions on the primary PM 2.5 standards) and where in her judgmen t a different course of action than recommended by CASAC was appropriate (e.g., final decision on the primary PM 10 standard).

(4) Comment: A group of commenters argued that “issu ing a revised lower PM NAAQS that is both complicated and legally infirm will pr oduce regulatory delay and uncertainty that

could result in adverse rather than beneficial health im pacts (NAM, 2012, p. 26). These commenters further noted the delay in th e EPA’s response to the 2009 remand of the 2006 PM NAAQS and argued that “issuing a final ru le that promotes regulatory and legal uncertainty may delay or even foreclose investments that could reduce overall PM emissions from the manufacturing sector.” Id.

Response: The EPA does not believe the revised sta ndards are legally infirm. Moreover, the remand of the 2006 primary annual standard for PM 2.5 was due to the EPA’s inability to adequately explain why that standard was not more stringent, not less stringent as this commenter would prefer.

(5) Comment : Many commenters asserted that the sta ndards must protect at-risk populations – children, older adults, persons with pre-existing heart and respiratory disease, and persons with an adequate margin of safe ty (e.g., CHPAC, 2012; ALA et al., 2012, pp. 29 to 38).

Response: The EPA agrees with this comment and has carefully considered effects on atrisk populations in considering whether and how to revise the PM 2.5 NAAQS. As noted in section II.A of the preamble to the final rule, the CAA requires the EPA Administrator to establish primary standards that provide an adequate margin of safety. The legislative history of section 109 of the C AA indicates that a primary stan dard is to be set at “the maximum permissible ambient air level . . . which will protect the health of any [sensitive] group of the population,” and that fo r this purpose “reference should be made to a representative sample of persons comp rising the sensitive group rather than to a single person in such a group.” S. Rep. No. 91-1196, 91st Cong., 2d Sess. 10 (1970). The CAA does not require the Administrator to establish a primary NAAQS at a zero-risk level or at background concentration levels, see Lead Industries v. EPA , 647 F.2d at 1156VII-4 n.51, but rather at a level that reduces risk suffi ciently so as to protec t public health with an adequate margin of safety. In the Ad ministrator’s judgment, the final decisions articulated in the final rule represent prim ary PM standards that are sufficient but not more protective than necessa ry to protect the public hea lth, including at-risk populations, with an adequate margin of safety from effects associated with PM exposures.

(6) Comment : Some commenters argued that the EPA must adopt a precautionary approach to the standard setting, and set standards in a manner that deals w ith uncertainty not by ignoring effects but rath er by protecting against adverse he alth effects (e.g., ALA et al., 2012, pp. 9 to 10). In support of this argument, these commenters specifically cited Ethyl Corp v. EPA, 541 F. 2d at 15, H. Rep No. 294, 95 th Cong, 1 st Sess. At 49 to 51 (1977) (explaining amendments designed inter alia “[t]o emphasize the preventive or precautionary nature of the act, i.e., to a ssure that regulatory action can effectively prevent harm before it occurs”), and American Trucking Association v. EPA , 283 F. 3d at 355, 369 (“the Act requires EPA to promulgate protective primary NAAQS even where... the pollutant’s risks cannot be quantifie d or ‘precisely identif ied as to nature or degree’”).

Response: The EPA agrees generally with this co mment, but notes further that a general invocation of precautionary principles doe s not determine where in the range of

reasonable values the EPA could establish the level of a standard. Section III.E.4.d to the preamble to the final rule explains in detail why it is appropriate to revise the annual standard level to 12.0 μg/m 3 in conjunction with retaining the 24-hour standard level at 35 μg/m 3 . The EPA notes further that this choice is consistent with case law in the D.C. Circuit (not cited by the comment er) that the Administrator is to carefully examine all of

the relevant studies in the reco rd, but need not base the level of the standard on either the highest or lowest value in these studies. Ra ther, an informed judgment is called for. API

v. EPA , 665 F. 2d at 1187; NRDC v. EPA , 902 F. 2d 962, 970. Section III.E.4.d to the preamble to the final rule states the basis fo r the Administrator’s ex ercise of informed judgment here in setting the levels of the primary annual and 24-hour PM 2.5 standards.

B. Administrative/Procedural Issues

Several comments addressed administrative and pr ocedural issues related ot he review of the PM NAAQS. These comments are addressed below.

(1) Comment: Several commenters argued that the tim eline for issuing the final rule will likely mean that the EPA will not have tim e to adequately review and respond to comments filed on the proposal (ACC, 2012, p. 2, NAM, 2012, pp. 5 and 15 to 17; Dow, 2012, p. 1; US. Chamber of Commerce, 2012. pp. 2 to 5).

Response: Although the EPA sought to justify a longer schedule in the scheduling litigation leading up to the District Court is suing a preliminary injunction and lodging the governing consent decree, the EPA believes th at it has adequately considered and responded to all of the substantive public co mments. The EPA also notes that it provided multiple opportunities to review and comment on all of the critical documents underlying the review (notably multiple drafts of the ISA, the RA, the UFVA, and the PA), as wellVII-5 as on all of the critical sc ientific and policy issues, a ssumptions, and factual data informing the review. In addition to afford ing multiple opportunities for public comment, review of those comments gave the EPA opportunity to consider commenters’ views throughout the process of reviewing the sta ndards. Consequently, the EPA was already informed of many of the key points raised in the comments to the proposal in advance of the proposal. The EPA notes further that th e time between propos al and final rule, although relatively brief, is not significantly di fferent from that of other NAAQS reviews, including the 2006 PM NAAQS (proposed in January 2006 and signed in September 2006 – eight months versus six months here).

(2) Comment: Further, some of these commenters as serted that in following the current schedule for completing the final rule (i.e ., signature by December 14, 2012), the Agency will not have the results of the EPA Inspector General’s investigation of CASAC’s role in reviewing the EPA”s PM NAAQS recommendations to inform its final decisions (NAM, 2012, pp. 5 and 17 to 18).

Response: As stated in an earlier response in th is RTC section, the decision on whether to revise a NAAQS is the EPA’s alone. By statut e, that decision is informed by CASAC’s advice and recommendations, but not determined by it. Moreover, the EPA is fully capable of assessing the scientific meri t of CASAC’s advice and recommendations.

Review of the EPA’s decision rests on the ad ministrative record, not on some possibly forthcoming report by a non-scientific entity not involved in the review proceeding

. Thus,

EPA does not see that this comment has merit.

(3) Comment: One commenter asserted “it is farcical that EPA claims the proposed rule does not have Tribal implications as specifie d by Executive Order (EO) 13175” (NTAA, 2012, p. 4). Further this commenter argued th at the EPA did not conduct meaningful

consultation with Tribes in accordance with EO 13175. Id.

Response: The EPA disagrees with this comment. As summarized in section X.F of the preamble to the final rule, this rule concerns the establishment of national standards to

address the health and welfar e effects of particulate matte r. Historically, the EPA’s definition of “tribal implications” has been li mited to situations in which it can be shown that a rule has impacts on the tribes’ ability to govern or implications for tribal sovereignty. Based on this historic defi nition, this action does not have Tribal implications, as specified in Executive Order 13175 (65 FR 67249, November 9, 2000),

i.e. because it does not have a substantial direct effect on one or more Indian tribes, since tribes are not obligat ed to adopt or implement any NAAQS. Nevertheless, the Agency was aware that many tribes would be interest in this rule and we undertook a number of

outreach activities to inform tribes about the PM NAAQS review and offered two

consultations with tribes.

Although Executive Order 13175 does not appl y to this rule, the EPA undertook a consultation process including: prior to pr oposal on March 29,2012 we sent letters to tribal leadership inviting consultation on the rule and then sent a second round of letters offering consultation after the proposal was is sued on June 29, 2012. No tribe requested a

formal consultation with the EPA. We conducte d outreach and information calls to tribalVII-6 environmental staff on May 9, 2012; June 15, 2012; and August 1, 2012. The EPA also participated on the National Tribal Air Association (NTAA) call on June 28, 2012.

As a result, we received comments from th e NTAA, the Southern Ute Mountain Ute Tribe, and the Navajo Nation EPA. In genera l, these tribal organi zations were supportive of the EPA’s proposal.

C. Misplaced Comments

Some comments received on the proposed PM NAAQS addressed issues that are not

relevant for consideration in the review of the NAAQS. Thes e comments and other “misplaced comments are discussed more fully below.

(1) Comment : One group of commenters argued that the EPA should ensure that its final rule “does not impose unnecessary costs on th e regulated community” (NAM, 2012, p. 29).

Another commenter asserted th at the EPA should consider th e broader regulatory burden that is being imposed through application of multiple PM standa rds which collectively serve to address many of the same health effects – in addition implementing revised primary NO 2 and SO 2 standards (AFPM, 2012, p. 23).

Response: The EPA strongly disagrees with this comment. As discussed in section II.A of the preamble to the final rule, in setting NAAQS, the EPA may not consider the costs of implementing the standards. See generally, Whitman v. American Trucking

Associations , 531 U.S. 457, 465-472, 475-76 (2001). Likewise, “[a]ttainability and technological feasibility are not relevant considerations in the promulgation of national ambient air quality standards.” American Petroleum Institute v. Costle , 665 F. 2d at 1185.

(2) Comment: Some commenters provided comments related to the EPA’s Regulatory Impact Analysis (RIA) for the propo sal which was issued in June 2012.

Response: As discussed in section II.A of the preamble to the final rule, because the costs of implementation cannot be considered in setting or revising the NAAQS, the results of

the RIA were not considered in the EPA’s decisions on the PM standards. Comments on the RIA for the proposal were considered, as appropriate, in deve loping the RIA for the

final rule.

(3) Comment: The EPA received several comments crit ical of the development process and timing of a revised PM NAAQS implementatio n rule. One commenter stated that the EPA should not finalize the proposed revisi ons without consider ing and responding to comments regarding implementation issues, par ticularly with respect to the secondary

standard. Another commenter stated that the EP A needs to be clear what issues are going to be final in this (PM NAAQS) rulemaking versus a future implementation rulemaking. Another commenter interpreted EPA's request for comment on the NAAQS as purposefully seeking more information about how to implement the standard, which they claimed was problematic due to limited implementation guidance or rulemaking to comment on prior to finalization of the NAAQS.

Response : These comments reflect a possible mi sunderstanding of the scope of the PMVII-7 NAAQS rulemaking with respect to implementati on issues. As explained in Section IX of the preamble to the final rule, the EPA will be undertaking a separate effort to develop an implementation rule for the revised NAAQ S through a formal notice-and-comment rulemaking, which we intend to finalize ar ound the time the initial area designations process is completed. The EPA will seek input from a wide range of stakeholders and the public throughout the implemen tation rulemaking process. To the extent the EPA sought comment on any state implementation planni ng issues as part of the PM NAAQS proposal, the Agency stated th at we would take under cons ideration comments received as we developed a separate future implemen tation rule proposal. (Note, however, that certain PSD issues are specifically addressed in the final PM NAAQS rulemaking; issues related to implementing a secondary standard are not relevant as the Agency is not finalizing the proposed secondary standard relating to visibili ty in this final rule.)

We will provide a separate comment period for the submission of comments on any future implementation rule proposal. At th at time, parties who submitted preliminary implementation-related comments as part of this rulemaking (to revise the PM NAAQS) may choose to resubmit their comments for consideration as part of the PM 2.5 NAAQS implementation rulemaking. Comments receiv ed on the PM NAAQS proposed rule will not be considered to be comments “submitted in advance” on any future implementation rule proposal.

(4) Comment: One commenter suggested that the EPA should, through the appropriations process, request adequate funds for air ag encies to implement any revised or new NAAQS.

Response : This comment is on EPA’s budget reques t and is not relevant to the PM NAAQS rulemaking.

(5) Comment: The commenter asserts that comply ing with transpor tation conformity requirements will delay transportation projects that are intended to address traffic congestion.

Response: This comment is outside the scope of this rulemaking. In addition, we do not

understand the basis of the commenter’s cl aim that complying with transportation conformity requirements results in the dela y of projects designed to address traffic congestion. Areas are successfully implementi ng conformity requirements for the current suite of transportation–related NAAQS (ozone, PM 2.5 , PM 10 , carbon monoxide and nitrogen dioxide) including meeting relevant deadlines. All areas that were designated

nonattainment for the 1997 and 2006 PM 2.5 NAAQS successfully complied with the requirement to demonstrate conformity within one-year of the effective date of their nonattainment designation. The conformity rule also exempts certain congestion-related projects from conformity requirements, includi ng traffic signal sync hronization projects (40 CFR 93.128) and certain intersection a nd interchange projects (40 CFR 93.127). If the commenter is concerned that project-lev el conformity requirements could delay congestion relief projects, the commenter should be aware that a hot-s pot analysis is only required if the project is determined through interagency consultation to be a project of air quality concern.VII-8 (6) Comment: One commenter opines that the transpor tation conformity pr ocess needs to be examined. The commenter supplies examples of several concerns that they have with transportation conformity implementation. Th e other commenter opines that due to transportation conformity requirements tran sportation projects can only proceed in nonattainment and maintenance areas if they do not result in incr eased emissions.

Response: These comments address requirements of the existing conformity rule and are not relevant to the PM NAAQS rulemaking.R-1 References

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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EPA/600/R

- 12/056 F



# Provisional Assessment of Recent

Studies on Health Effects of

Particulate Matter Exposure

National Center for Environmental Assessment RTP Division

Office of Research and Development

U.S. Environmental Protection Agency

Research Triangle Park, NC 27711ii 

### DISCLAIMER

This document has been reviewed in accordance with U.S. Environmental Protection Agency
policy and approved for publication. Mention of trade names or commercial products does not

constitute endorsement or recommendation for use.iii 

## Table of Contents

List of Tables

................................ ................................ ................................ ................................ ............... iv

List of Figures

................................ ................................ ................................ ................................ ............... v

Authors, Contribut ors, Reviewers

................................ ................................ ................................ ................ vi

Executive Summary

................................ ................................ ................................ ................................ ... viii

1. INTRODUCTION AND METHODOLOGY

................................ ................................ ....................... 1

2. OVERVIEW OF RECENT HEALTH STUDIES RESULTS

................................ .............................. 2

2.1. Epidemiologic Studies of Long

- Term Exposure

................................ ................................ ........... 3

2.1.1. Mortality

................................ ................................ ................................ ............................... 4

2.1.2. Morbidity

– Cardiovascular Effects

................................ ................................ .................... 12

2.1.3. Morbidity

– Respiratory Effects

................................ ................................ ......................... 14

2.1.4. Morbidity

– Reproductive and Developmental Effects

................................ ....................... 16

2.2. Epidemiologic Studies of Short

- Term Exposure

................................ ................................ ........ 16

2.2.1. Mortality

................................ ................................ ................................ ............................. 17

2.2.2. Morbidity

................................ ................................ ................................ ............................ 21

2.3. Health Effects Related to Sources or Components of PM

................................ .......................... 30

2.3.1. Epidemiologic Studies Using Source Apportionment

................................ ........................ 30

2.3.2. Epidemiologic Studies on Effects of Fin e PM Components and Sources

.......................... 31

2.3.3. Toxicology Studies

– Source Apportionment and Fine PM Components

.......................... 35

3. SUMMARY AND CONCLUSIONS

................................ ................................ ................................ . 40

AP PENDIX A. Studies Included in the PM Provisional Science Assessment

................................ ........... 42

References ...................................................................................................... ........ 57iv 

## List of Tables

Table 2.1

. Causal Determinations for Short

- and Long

- Term Exposure to PM 2.5

................................ ......... 3

Table 2.2

. Association between mortality outcomes and PM 2.5 components using a 30

- km buffer

(n=43,220) (adapted from Ostro et al. (2011))

................................ ................................ ............................ 34

Table 2.3

. CAPs Sources and Associated Endpoints

................................ ................................ ................. 36

Table A.1. Characterization of Studies of Long

- term Exposure to PM2.5 and Mortality

......................... 42

Table A.2. Characterization of Studies of Long

- term Exposure to PM10

- 2.5 and Mortality

.................... 43

Table A.3. Characterization of Studies of Long

- term Exposure to PM2.5 and Cardiovascular Effects

.... 44

Table A.4. Characterization of Studies of Long

- term Exposure to PM2.5 and Respiratory Effects

.......... 45

Table A.5. Characterization of Studies of Long

- term Exposure to PM2.5 and Reproductive and

Developmental Effects

................................ ................................ ................................ ................................ 47

Table A.6. Characterization of U.S. and Canadian Studies of Short

- Term Exposure to PM2.5 and

Mortality

................................ ................................ ................................ ................................ .................... 49

Table A.7. Characterization of U.S. and Canadian Studies of Short

- Term Exposure to PM2.5 and

Respiratory Hospital Admissions and Emergency Department Visits

................................ ........................ 50

Table A.8. Characterization of U.S. and Canadian Studies of Short

- Term Exposure to PM10

- 2.5 and

Respiratory Hospital Admissions and Emergency Department Visits

................................ ........................ 53

Table A.9. Characterization of U.S. and Canadian Studies of Short

- Term Exposure to PM2.5 and

Cardiovascular Hospital Admissions and Emergency Department Visits

................................ .................. 53

Table A.10

. Characterization of U.S. and Canadian Studies of Short

- Term Exposure to PM2.5 and

Out of Hospital Cardiac Arrests

................................ ................................ ................................ .................. 56

Table A.11. Characterization of U.S. and Canadian Studies of Short

- Term Exposure to PM2.5 and

Time of Stroke Symptom Onset

................................ ................................ ................................ ................. 56v 

## List of Figures

Figure 2.1

. All

- cause mortality risk estimates, long

- term exposure to PM 2.5 in recent cohort studies.

....... 6
Figure 2.2

. Cardiovascular mortality risk estimates, long

- term exposure to PM 2.5 in recent cohort

studies

................................ ................................ ................................ ................................ ........................... 7
Figure 2.3

. Respiratory mortality risk estimates, long

- term exposure to PM 2.5 in recent cohort

studies..

................................ ................................ ................................ ................................ ......................... 8
Figure 2.4

. Percent increase in non

- accidental and cause

- specific mortality for a 10 μg/m3 increase in

24

- h average PM 2.5 concentrations in single

- pollutant models from U.S. and Canadian studies

............... 20
Figure 2.5

. % Increase in respiratory

- related hospital admissions and ED visits for a 10 μg/m 3

increase in 24

- h average PM 2.5 concentrations in single

- pollutant models from U.S. and Canadian

studies

................................ ................................ ................................ ................................ ......................... 25
Figure 2.6

. Percent increase in cardiovascular

- related hospital admissions and ED visits for a 10
μg/m 3 increase in 24

- h average PM 2.5 concentrations in single

- pollutant models from U.S. and

Canadian studies.

................................ ................................ ................................ ................................ ........ 29vi 

## Authors, Contributors, Reviewers

Executive Direction

Dr. John Vandenberg (Director)

– National Center for Environmental Assessment

- RTP Division,

U.S. Environmental Protection Agency, Research Triangle Park, NC

Ms. Debra Walsh (Deputy Director)

– National Center for Environmental Assessment

- RTP

Division, U.S. Environmental Protection Agency, Research Triangle Park, NC

Dr. Mary Ross (Branch Chief)

– National Center for Environmental Asse ssment, U.S.

Environmental Protection Agency, Research Triangle Park, NC

Principal Authors

Mr. Jason Sacks (Team Lead)

– National Center for Environmental Assessment, U.S.

Environmental Protection Agency, Research Triangle Park, NC

Dr. Ellen Kirrane

– National Center for Environmental Assessment, U.S. Environmental

Protection Agency, Research Triangle Park, NC

Dr. Thomas Luben

– National Center for Environmental Assessment, U.S. Environmental

Protection Agency, Research Triangle Park, NC

Dr. Elizabeth Oesterling Owens

– National Center for Environmental Assessment, U.S.

Environmental Protection Agency, Research Triangle Park, NC

C ontributors

Ms. Laura Datko

- Williams

– Oak Ridge Institute for Science and Education Research Fellow,

National Center for Environmental Assessment, U.S. Environmental Protection Agency,

Research Triangle Park, NC

Reviewers

Dr. Dan Costa

, Air, Climate, and Energy Research Program, Office of Research and
Development, U.S. Environmental Protection Agency, Research Triangle Park, NC

Dr. Aimen Farraj

, National Health and Environmental Effects Research Laboratory, U.S.

Environmental Protection Agency, Research Triangle Park, NC

Dr. Ian Gilmour

, National Health and Environmental Effects Research Laboratory, U.S.

Environmental Protection Agency, Research Triangle Park, NC

Ms. Beth Hassett

- Sipple, Office of Air Quality Planning and Standards, U.S. Environmental

Protection Agency, Research Triangle Park, NC.vii Dr. Karen Martin, Office of Air Quality Planning and Standards, U.S. Environmental Protection
Agency, Research Triangle Park, NC.

Dr. Lucas Neas

, National Health and Environmental Effects Research Laboratory, U.S.

Environmental Protection Agency, Research Triangle Park, NC

Mr. Steven Silverman, Office of General Council, U.S. Environmental Protection Agency,
Washington, D.C.

Dr. Lindsay Wichers Stanek

, National Exposure Research Laboratory, U.S. Environmental

Protection Agency, Research Triangle Park, NCv iii 

## Executive Summary

In the proposed rule on the National Ambient Air Quality Standards for particulate matter
(PM), EPA committed to conduct a review and assessment of the numerous studies relevant to assessing the health effects of PM that were published too recently to be included in the 2009

PM Integrated Science Assessment (ISA). This report presents the findings of EPA’s survey and
provisional assessment of such studies. EPA has screened and surveyed the recent literature and
developed a provisional assessment that places those studies of potentially greatest relevance to

the current PM NAAQS review in the context of the findings of the 2009 PM ISA. The focus is

on: (a) epidemiologic studies that used PM 2.5 (i.e., fine PM) or PM 10

- 2.5 (i.e., coarse PM) and were

conducted in the U.S. or Canada, and (b) toxicolog ical or epidemiologic studies that compared

effects of PM from different sources, PM components, or size fractions. T he provisional

assessment is not intended to critically review individual studies or integrate the scientific
findings to draw causal conclusions as is done for an ISA.

This survey and assessment finds that that the new studies expand the scientific

information and provide important insights on the relationships between PM exposure and health

effects of PM. H owever, the new information and findings do not materially change any of the

broad scientific conclusions regarding the health effects of PM exposure made in the 2009 PM

ISA. In brief, this report finds the following:

• Recent epidemiologic studies, most of which are extensions of earlier work, continue to

support the conclusions of the 2009 PM ISA for long

- term exposure to PM 2.5 and
mortality, cardiovascular effects, respiratory effects, and reproductive and
developmental effects

. Notably, updated findings from the Harvard Six Cities and

American Cancer Society cohorts continue to observe an association between long

- term

PM 2.5 exposure and mortality, which supports the findings from previous studies

conducted in these cohorts. Additionally, a new Canadian multicity study observed

associations with mortality at long

- term mean PM 2.5 concentrations below those reported

in the PM ISA. Recent cause

- specific mortality studies also provide more evidence for

cardiovascular mortality associations, especially in women, and additional evidence for
respiratory mortality including lung cancer. Studies of cardiovascular effects provide

evidence of myocardial infarction, hypertension, diabetes, and stroke, especially among

women, which is consistent with the conclusions of the 2009 PM ISA. Recent studies

continue to demonstrate associations with respiratory morbidity including respiratory

symptoms and hospital admissions, as well as incident asthma a mong children.
Reproductive and developmental effects studies continue to provide evidence for

associations between long

- term exposure to PM 2.5 and reduced birth weight.

• Recent epidemiologic studies have also continued to report associations between short

term exposure to PM 2.5 and mortality and morbidity health endpoints, which further

support the causality determinations presented in the 2009 PM ISA. These include multi

-ix and single

- city analyses that demonstrate consistent positive associations across all
respiratory and cardiovascular hospital admissions and emergency department visits as

well as cause

- specific outcomes, particularly asthma. Although limited to single

- city

studies, recent studies continue to demonstrate associations between short

- term fine PM

exposures and nonaccidental and cardiovascular mortality. Additionally, new evidence

for stroke which focuses on assigning exposure from the time of stroke onset, instead of

entry to the hospital, provides new information regarding an uncertainty recognized in

the PM ISA.

• New toxicological and epidemiologic studies have continued to link health outcomes

with a range of PM 2.5 sources and components. Several new epidemiologic analyses

continue to demonstrate health effects attributed to multiple sources and PM components including combustion activities (e.g., motor vehicle emissions, coal combustion, oil
burning, power plants, and wood smoke/vegetative burning), crustal sources, and
secondary sulfate

. Toxicolog ical studies examined various source categories and found

that no source consistently showed the strongest association with cardiovascular health

effects. Additionally, an examination of a number of PM 2.5 components found

associations with various components and both cardiovascular and respiratory endpoints.

• Only a few recent epidemiologic studies have examined health effects of short

- and

long

- term exposures to coarse particles (PM 10

- 2.5 )

. A short

- term exposure and
respiratory emergency department visits ( ED ) visits study found a positive and
significant association with pediatric asthma ED visits in Atlanta, GA. One long

- term

exposure and mortality study did not find any evidence of an association with all

- cause mortality though there was a positive but not statistically significant association with

coronary heart disease ( CHD ) mortality.1 1. I NTRODUCTION AND M ETHODOLOGY

EPA is currently in the final stages of the review of the N ational A mbient A ir Q uality S tandards

(NAAQS) for particulate matter (PM). As described in more detail in the Federal Register Notice

of EPA’s proposed rule on the PM NAAQS (7 7 FR 38890 ), EPA has prepared the Integrated

Science Assessment for Particulate Matter (hereafter 200 9 PM ISA ) which reviewed,

summarized, and integrated the latest scientific knowledge useful in indicating the kind and

extent of all identifiable effects on public health or welfare that may be expected from the

presence of PM in the ambient air in varying quantities, as required by section 108 of the Clean

Air Act (CAA) ( U.S. EPA, 2009 )

. As noted in the PM proposal, 1 EPA is aware that numerous

studies potentially relevant to assessing the health effects of ambient PM have been published
recently that were not included in the 200 9 PM ISA ( U.S. EPA, 2009 )

. The proposal notice also

indicates the Agency’s intent to conduct a review and assessment of these new studies before a

final decision is made on the PM NAAQS. The purpose of this report is to present the findings of

EPA’s survey and provisional assessment of potentially relevant recent studies on the health

effects of PM exposure. This provisional assessment will inform a decision by the EPA

Administrator to proceed with final rulemaking or to revise the ISA to include the new studies

.

T his provisional assessment is focused on those studies most important to the major conclusions
presented in the 2009 PM ISA and most relevant to the considerations of the current review of

the PM NAAQS

. EPA

, therefore, identified potentially relevant studies by applying the
following selection criteria to those studies published through August 2012 : ( 1 ) epidemiologic

studies that used PM 2.5 (i.e., fine PM) or PM 10

- 2.5 (i.e., coarse PM) and were conducted in the U.S.

or Canada

, and ( 2 ) toxicolog ical or epidemiologic studies that compared effects of PM from

different sources, PM components, or size fractions

. In addition, we considered studies identified
by public comments submitted to the docket of the proposed rule. Studies that met these criteria

were evaluated by EPA staff and their key findings were summarize d. T his preliminary

assessment was then developed to place those new studies of potentially greatest relevance in the

context of the findings of the 200 9 PM ISA including a judgment as to whether the new studies
materially change the major conclusions of the 2009 PM ISA

. T he provisional assessment presented here does not attempt to critically review individual studies or to provide the kind of

full integration found in a typical ISA

.

The literature search and submissions from public commenters found that more than 1,500

studies have been published since the ISA closed on the health effects of particulate matter.

1 As stated in the PM NAAQS proposal: “ The EPA is aware that a number of new sc ientific studies on the health

effects o f PM have been published since the mid

- 200 9 cutoff date for inclusion in the Int egrated Science

Assessment. As in the last PM NAAQS review, the EPA intends t o conduct a provisional review and ass essment of any significant new studies pu blished since the close of the Integrated Science Assessment, including studies that may be submitted durin g the public comment period on this proposed rule in or der to ensure that, befor e making a final decision, the Administr ator is fully aware of the ne w science that has developed since 2009. In this p rovisional assessment, the EPA will exam ine these new studies in light of the literature evaluated in the Integ rated Science

Assessment. This provis ional assessment and a summary of the key conclusions will be placed in the rulemaking

docket. ” (77 FR 38899)2 Application of the selection criteria resulted in a list of over 100 studies that are summarized in

the main body of this report. Additional details of the air quality distributions observed in these

studies can be found in the annex to this report. The most significant studies are discussed in the

assessment, and where feasible, quantitative results are compared to those from the 200 9 PM

ISA

. A comprehensive list of s tudies identified as being potentially relevant through the survey

effort

, including those studies not discussed in detail in this report can be found here:
http://hero.epa.gov/pm

. S tudies not discussed in detail include controlled human exposure studies, and toxicological studies that examined health effects attributed to specific PM size

fractions, as well as studies that focused on ultrafine particles

.

The overview in the main body of this report is organized into three main sections:

(1) epidemiologic studies on effects associated with long

- term exposure to PM, focusing on

U.S. and Canadian studies with measurements of PM 2.5 or PM 10

- 2.5 ; (2) epidemiologic studies on

effects associated with short

- term PM exposure
, again focusing on U.S. and Canadian studies

with measurements of PM 2.5 or PM 10

- 2.5 ; and (3) toxicolog ical and epidemiologic studies that

have evaluated health effects with exposure to PM components and PM from different sources.

This last section includes results of studies that assessed the effects of a range of PM sources or
components

, including those using source apportionment methods or comparing effects for

numerous PM components, and not on studies of individual components

. Most studies have

focused on components or sources of PM 2.5 , but information related to sources of PM 10

- 2.5 was

also included to the extent available. Unless otherwise noted, the majority of new studies

included in this assessment did not examine the robustness of single

- pollutant results in
copollutants models.

2. OVERVIEW OF RECENT HEALTH STUDIES RESULTS

As stated in the 2009 PM ISA

, EPA integrated the scientific evidence from toxicological,

controlled human exposure, and epidemiologic studies in combination with evidence from
atmospheric chemistry and exposure assessment studies and developed causal determinations for

health outcomes categories (e.g., respiratory effects, cardiovascular effects, mortality, etc.) for

different exposure durations (i.e., short

- or long

- term) and PM size fractions. Causal judgments

drawn for short

- and long

- term exposure to PM 2.5 and short

- term exposure to PM 10

- 2.5 are

included in Table 2.1.3 Table 2

. 1

. Causal Determinations for Short

- and Long

- Term Exposure to PM 2.5

Long

- term Exposure to PM 2.5

Size Fraction Outcome Causality Determination

PM 2.5 Cardiovascular Effects Causal

Respiratory Effects Likely to be causal

Mortality Causal

Reproductive and Developmental Suggestive

Cancer, Mutagenicity, and Genotoxicity Suggestive

Short

- term Exposure to PM 2.5

Size Fraction Outcome Causality Determination

PM 2.5 Cardiovascular Effects Causal

Respiratory Effects Likely to be causal

Mortality Causal

Short

- term Exposure to PM 10

- 2.5

Size Fraction Outcome Causality Determination

PM 10

- 2.5 Cardiovascular Effects Suggestive

Respiratory Effects Suggestive

Mortality Suggestive

The following sections of this document summarize the scientific evidence published since the
completion of the 2009 PM ISA for each of the health outcome categorie s presented in Table 2.1

.

2.1. Epidemiologic Studies of Long

- Term Exposure

The majority of the epidemiologic evidence evaluated in the 2009 PM ISA ( U.S. EPA, 2009 )

focused on health effects of PM 2.5 exposure, with very limited evidence for health effects of
long

- term exposure to PM 10

- 2.5

. These studies demonstrated consistent positive associations

between long

- term PM 2.5 exposures and a variety of health effects (Chapter 7

, ( U.S. EPA, 2009 ) ).

Sections 2.1.1

- 2.1. 4 highlight results from epidemiologic studies of mortality

, cardiovascular

effects, respiratory effects, and reproductive and developmental effects, respectively, published

since the completion of the 2009 PM ISA ( U.S. EPA, 2009 ) because these wer e the health

outcomes specifically taken into consideration in developing the proposed rule (77 FR 38890)

. Tables A

. 1 through A

. 5 (Appendix A) summarize the recent epidemiologic studies that evaluated4 relationships between health effects and long

- term exposure to PM 2.5 and PM 10

- 2.5

. The

discussions below emphasize results of studies conducted in the U.S. and Canada.

2.1.1. Mortality

Long

- term exposure to PM 2.5

Summary of 2009 PM ISA Conclusions

The 2009 PM ISA synthesized the epidemiologic literature characterizing the association

between long

- term exposure to PM 2.5 and increased risk of mortality and concluded that “ a

causal relationship exists between long

- term exposure to PM 2.5 and mortality ” (See Section 7.6

of the 2009 PM ISA)

. Long

- term m ean 2 PM 2.5 concentrations ranged from 13.2 to 32 .0 μg/m 3

during the study periods in the areas in which these studies

, comprising the entire body of

evidence reviewed in the 2009 ISA, were conducted. When evaluating cause

- specific mortality,

the strongest evidence contributing to this causal determination was observed for associations

between PM 2.5 and cardiovascular mortality

. Positive associations were also reported between

PM 2.5 and lung cancer mortality

. Both the Harvard Six Cities ( Laden et al., 2006 ; Dockery et al.,

1993 ) and the American Cancer Society (ACS) ( Kr ewski, 2009 ; Pope III et al., 2004 ; Pope et al.,

2002 ) studies continued to provide strong evidence for the associations between long

- term

exposure to PM 2.5 and cardiopulmonary disease (CPD) and ischemic heart disease (IHD)
mortality

. Additional evidence from a study that used the Women’s Health Initiative ( WHI )

cohort ( M iller et al., 2007 ) found a particularly strong association between long

- term exposure to

PM 2.5 and cardiovascular disease (CVD) mortality in post

- menopausal women

.

Recent Mortality Studies

Since the completion of the 2009 PM ISA ( U.S. EPA, 2009 )

, a number of studies have been
published that examine d the association between long

- term exposure to PM 2.5 and all

- cause mortality (See Figure 2.1 ) and cause

- specific mortality (See Figure s 2.2 and 2.3 ), including
updated results for both the Harvard Six Cities an d ACS cohorts

. Lepeule et al. ( 2012 ) extended

the analysis of the Harvard Six Cities cohort using 11 additional years of follow

- up and PM 2.5 monitoring data and explored a variety of issues that might affect the size and timing of the
mortality effect

. Generally, the authors observed results similar to those reported by Laden et al.

( 2006 ) for all

- cause and cardiovascular mortality, though the central estimate was slightly

diminished and had slightly narrower confidence intervals ( all

- cause mortality: RR = 1.14 [95%

CI: 1.07, 1.22] 3 for Lepeule et al. ( 2012 ) versus RR = 1.16 [95% CI: 1.07, 1.26] for Laden et al.

( 2006 ) ; cardiovascular mortality: RR = 1.26 [95% CI: 1.14, 1.40] for Lepeule et al. ( 2012 ) versus

RR = 1.28 [95% CI: 1.13, 1.44] for Laden et al. ( 2006 )

. The authors applied both spline and linear

2 For long

- term exposure studies, the long

- term mean PM 2.5 concentration refers to the average PM 2.5 concentrations reported across the entire study duration, which could equate to the monthly or annual PM 2.5 concentration averaged

over many years.

3 All effect estimates for associations between long

- term exposure to PM 2.5 and mortality are presented for a 10

μ g/m 3 increase in PM 2.5 concentration.5 models to investigate the concentration

- response relationship, and observed that for all

- cause mortality, the model fit was better without the spline, indicating a no threshold, linear
relationship with PM 2.5 down to the lowest observed concentration (i.e., 8 μg/m 3 )

. Jerrett et al.

( 2009a ) reanalyzed data from the ACS cohort, including data from 86 metropolitan statistical

areas (MSAs) across the U.S with monitoring data for PM 2.5

. The authors observed an

association between PM 2.5 and all

- cause mortality in single pollutant models (RR 1.048 [95% CI:

1.024, 1.071]) that increased in magnitude in a copollutant model adjusting for ozone ( O 3 )

concentration (RR 1.080 [95% CI: 1.048, 1.113])

. The associations were stronger when limited

to mortality due to cardiovascular disease (CPD mortality: RR 1.129 [95% CI: 1.094, 1.071];

CVD mortality: RR 1.150 [95% CI: 1.111, 1.191]; IHD mortality: RR 1.211 [95% CI: 1.156,

1.268]); these associations also became stronger in copollutant models adjusting for O 3 concentration

. No statistically significant association was observed between PM 2.5 and
respiratory mortality in this re

- analysis of the ACS cohort

. In another analysis among the AC S

cohort, McKean

- Cowdin et al. ( 2009 ) examined the association between long

- term exposure to

PM 2.5 and brain cancer mortality

. The authors observed no associations with brain cancer mortality.6 Figure 2

. 1

. All

- cause mortality risk estimates, long

- term exposure to PM 2.5 in recent cohort studies

. R ed text and triangles represent

new studies published since the completion of the 2009 PM ISA

. Study

McDonnell et al. (2000)

Enstrom (2005)

Jerrett et al. (2005)

Krewski et al. (2009)

Puett et al. (2011)

Ostro et al. (2009)

Laden et al. (2006)
Lepeule et al. (2012)
Lipsett et al. (2011)

Jerrett et al. (2009)
Lipfert et al. (2006)

Eftim et al. (2008)

Hart et al. (2010)

Krewski et al. (2009)

Goss et al. (2004)

Puett et al. (2009)
Zeger et al. (2008)

Krewski et al. (2009)

Crouse et al. (2012) Cohort

AHSMOG

CA Cancer Prevention

ACS

- LA
ACS Reanalysis II

- LA

Health Prof

CA Teachers

Harvard 6

- Cities

Harvard 6

- Cities

CA Teachers

ACS

Veterans Cohort

Medicare Cohort

US Trucking
ACS Reanalysis II
U.S. Cystic Fibrosis

Nurses Health

MCAPS

ACS Reanalysis II

- NYC

Canadian National Years

1973

- 1977

1973

- 1982

1983

- 2002

1973

- 2002

1982

- 2000

1982

- 2000

1986

- 2002

2002

- 2007

1974

- 1998

1974

- 2009

1999

- 2005

1982

- 2000

1989

- 1996

1997

- 2001

2000

- 2002

1985

- 2000

1982

- 2000

1999

- 2000

1992

- 2002

2000

- 2005

1982

- 2000

1991

- 2001 Mean

32

23.4

---

--- 21

21

17.8

17

16.4

15.9

15.6

14.3

14.3

14.3

13.6

14.1

14.1

14.0

13.7

13.9

13.2

--- 9.4

8.9

8.7 Notes

Males

Men

Women

Women

ACS Sites

6

- Cities sites

Men

Women

65+, Eastern

65

- 74, Eastern

75

- 84, Eastern

85+, Eastern

65+, Central

65

- 74, Central

75

- 84, Central

85+, Central

65+, Western

65

- 74, Western

75

- 84, Western

85+, Western

11 cities; remote sensing
11 cities; monitoring data
Nationwide; remote sensing ► All Cause

0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6

Effect Estimate7 Figure 2

. 2

. Cardiovascular mortality risk estimates, long

- term exposure to PM 2.5 in recent cohort studies

. R ed text and triangles

represent new studies published since the completion of the 2009 PM IS A. * As discussed in Federal Register Notice of EPA’s proposed rule on the PM NAAQS (77 FR at 38929 and 38934 n. 82 ). CV = cardiovascular disease, CHD = coronary heart disease,

IHD = ischemic heart disease, CPD = cardiopulmonary disease. Study

Pope et al. (2004)
Laden et al. (2006) Lepeule et al. (2012) Lipsett et al. (2011)
Jerrett et al. (2009)

Hart et al. (2010)
Miller et al. (2007)
Crouse et al. (2012)

Chen et al. (2005)

Puett et al. (2011)
Puett et al. (2009)
Gan et al. (2011)

Jerrett et al. (2005)
Krewski et al. (2009) Pope et al. (2004)
Ostro et al. (2009) Lipsett et al. (2011)
Jerrett et al. (2009)

Hart et al. (2010)
Krewski et al. (2009)

Crouse et al. (2012)

McDonnell et al. (2000)
Jerrett et al. (2005)
Krewski et al. (2009)

Ostro et al. (2009)
Jerrett et al. (2009)
Krewski et al. (2009) Cause

CV

CHD

IHD

CPD Cohort

ACS

Harvard 6

- Cities

Harvard 6

- Cities

CA Teachers

ACS US Trucking

WHI

Canadian National

AHSMOG

Health Prof

Nurses Health
Vancouver, BC

ACS

- LA ACS Reanalysis II

ACS

CA Teachers

CA Teachers

ACS US Trucking ACS Reanalysis II

Canadian National

AHSMOG

ACS

- LA ACS Reanalysis II

CA Teachers

ACS ACS Reanalysis II Years

1982

- 2000

1974

- 1998

1974

- 2009

1999

- 2005

1982

- 2000

1985

- 2000

1994

- 1998

1991

- 2001

1973

- 1998

1986

- 2002

1992

- 2002

1999

- 2002

1982

- 2000

1982

- 2000

1982

- 2000

2002

- 2007

1995

- 2005

1982

- 2000

1985

- 2000

1982

- 2000

1991

- 2001

1973

- 1977

1982

- 2000

1982

- 2000

2002

- 2007

1982

- 2000

1982

- 2000 Mean

17.1

16

15.9

15.6

14.3

14.1
13.5 (12.9) *

8.7

29

17.8

13.9

4.08

21

21

17.1

17

15.6

14.3

14.1

14.02

--- 8.7

32

21

21

17

14.3

14.02

--- Notes

Women

Men

Females

Females

Males

Men

Women

Women

Women

Men

Nationwide

NYC

Males

Women

Nationwide

NYC ►

►

0.5 1 1.5 2 2.5

Effect Estimate8 Figure 2

. 3

. Respiratory mortality risk estimates, long

- term exposure to PM 2.5 in recent cohort studies

. R ed text and triangles represent

new studies published since the completion of the 2009 PM ISA. 

### Respiratory

Lung Cancer Study

Laden et al. (2006)

Lipsett et al. (2011)

Jerret et al. (2009)

Hart et al. (2010)

McDonnell et al. (2000)

Jerrett et al. (2005)

Krewski et al. (2009)

Laden et al. (2006)

Lipsett et al. (2011)

Lepeule et al. (2012)

Hart et al. (2010)

Krewski et al. (2009)

Krewski et al. (2009) Cohort

Harvard 6

- Cities

CA Teachers

ACS

US Trucking

AHSMOG

ACS

- LA

ACS Reanalysis II

Harvard 6

- Cities

CA Teachers

Harvard 6

- Cities

US Trucking

ACS Reanalysis II

ACS Reanalysis II Years

1974

- 1998

1999

- 2005

1982

- 2000

1985

- 2010

1973

- 1977

1982

- 2000

1982

- 2000

1974

- 1998

1999

- 2005

1974

- 2009

1985

- 2000

1982

- 2000

1982

- 2000 Mean

16

15.6

14.3

14.1

32

21

21

16

15.6

15.9

14.1

14.02

--- Notes

Women

Men

Males

LA

Women

Men

Nationwide

NYC

0.5 1 1.5 2 2.5


### Effect Estimate9 In an update to a study by Janes et al. ( 2007 )

, Greven et al. ( 2011 ) used data from a nationwide

Medicare mortality cohort to develop a statistical approach for estimating the associations

between monthly mean PM 2.5 concentrations averaged over the preceding 12 months and
monthly mortality rates among subjects living within ZIP code s with a geographic centroid

within a six mile radius of one of 814 monitoring stations from 2000 to 2006

. The study authors
decomposed the association between PM 2.5 and mortality into two components: (1) the

association between the “national” trend in the monthly PM 2.5 concentrations averaged over the
previous 12 months and the national average trend in monthly mortality rates (purely temporal

association); and (2) the association between the “local” trend in the deviation in the
community

- specific trend from the national average trend of monthly averages of PM 2.5 and the

deviation of the community

- specific tren ds from the national average trend of mortality rates
(residual spatio

- temporal association). Th e authors posit that this second component provide s

evidence as to whether locations having steeper declines in PM 2.5 also have steeper declines in
mortality r elative to the national trend. The authors conclude that differences in effect estimates

at these two spatiotemporal scales raise concerns about confounding bias in these analyses, with

the association for the national trend more likely to be confounded tha n the as sociation for the

local trend. The authors observed no evidence for a “local” effect, but did observe evidence for a

“national” effect. Similar to the study by Janes et al. ( 2007 )

, Greven et al. ( 2011 ) eliminate all of

the spatial variation in air pollution and mortality in their data set when estimating the “national”

effect, focusing instead on sub

- chronic (monthly) temporal differences in the data. As noted by

the authors, this eliminates 90% of the variance in the data set used for these analyses that is

attributable to spatial variability ( Janes et al. ( 2007 )

, Table 1)

. Only 5% of the variance in the

data set used in these analyses is attributable to the space by time component, which was the

focus of the papers by Janes et al. ( 2007 ) and Greven et al. ( 2011 )

. Thus, while the results of the

papers themselves provide evidence for an association between exposure to PM 2.5 and mortality,

it is not possible to directly compare the results of these studies to the results of other cohort

studies investigating the relationship between long

- term exposure to PM 2.5 and mortality, which

make use of spatial variability in air pollution and mortality data. As noted by Pope and Burnett

( 2007 ) and highlighted in the 2009 PM ISA (Section 7.6.1, ( U.S. EPA, 2009 ) )

, the conclusions of

Janes et al. ( 2007 ) “ largely excludes the sources of variability that are exploited in those other

[cohort] studies.” These comments are also applicable to the study by Greven et al. ( 2011 )

.

Crouse et al. ( 2012 ) conducted a nationwide study of the relationship between long

- term

exposure and PM 2.5 in Canada and provide new evidence for a positive association at relatively

low concentrations of PM 2.5

. The authors investigated the association between long

- term

exposure to ambient PM 2.5 and non

- accidental mortality

. The level of ambient PM 2.5 to which the
study population was exposed was estimated from satellite observations and assigned to the

cohort of 2.1 million Canadian adults that completed detailed census data in 1991

. The study

included deaths between 1991 and 2001

. The authors observed a hazard ratio (HR) of 1.15 (95%

CI: 1.13, 1.16) for non

- accidental mortality

. Using spatial random

- effects models, the HR was slightly diminished (1.10 [95% CI: 1.05, 1.15])

. The strongest association was observed for10 deaths due to ischemic heart disease (HR: 1.31 [95% CI: 1.27, 1.35])

. Using spatial random

effects models did not substantially change the association ( HR: 1.30 [95% CI: 1.18, 1.43])

. The

associations between PM 2.5 and deaths due to CVD and circulatory diseases were similar in
magnitude to that observed for non

- accidental mortality

. There was a weaker association with
mortality due to cerebrovascular disease (CBD) (HR: 1.04 [95%CI; 0.99, 1.10]). Sensitivity
analyses including 11 Canadian cities with ground

- based PM 2.5 measurements produced similar

associations to those observed in the full cohort that utilized satellite observations to estimate

PM 2.5 exposure (See Figure 2.1)

.

A number of studies have looked at the association between long

- term exposure to ambient

PM 2.5 and all

- cause mortality among different occu pational cohorts

. Hart et al. ( 2010 ) examined

the association between residential exposure to PM 2.5 and mortality among men in the U.S.
trucking industry

. The authors observed a 10% (95% CI: 2.5

, 18) increase in all

- cause mortality

. This association was stronger when the cohort was restricted to truck drivers that maintained

local routes, and long haul drivers were excluded (15% increase [95% CI: 5.0, 26.6] for all

- cause mortality; 59.7% increase [95% CI: 18.7, 114.9%] for respiratory mortality )

. The associations for

other causes of death (i.e., lung cancer, CVD, IHD, chronic obstructive pulmonary disease

[COPD]) were generally positive, but were not statistically significant. Puett et al. ( 2009 )

examined the relationship of long

- term PM 2.5 exposures with all

- cause mortality among women

from the Nurses’ Health Study

. The authors found an increased risk of all

- cause mortality (HR

1.26 [95% CI: 1.02

, 1.54]) and coronary heart disease ( CHD ) mortality (HR 2.02, 95% CI: 1.07

, 3.78) associated with long

- term exposure to PM 2.5

. More recently, Puett et al. ( 2011 ) used the

same spatiotemporal exposure estimation models to characterize the association between long

term exposure to PM 2.5 and mortality among male subjects in the Health Professionals Follow

- up Study

. In this cohort, long

- term exposure to PM 2.5 was not associated with all

- cause or CHD
mortality

. Ostro et al. ( 2010 ) examined the association between long

- term exposures to PM 2.5 and

all

- cause
, CPD, IHD and pulmonary disease mortality among the subjects from the California

Teachers Study

. No associations were observed between all

- cause mortality and PM 2.5

. There

was a positive association between long

- term exposure to PM 2.5 and CPD mortality (HR: 1.19

[95% CI: 1.05, 1.37]) and IHD mortality (HR: 1.56 [95% CI: 1.24, 1.94]). In a f ollow

- up study,
Lipsett et al. ( 2011 ) examined the associations between long

- term exposure to PM 2.5 and all

cause and cause

- specific mortality among the subjects in the California Teachers Study

. The

authors did not observe an association between long

- term exposure to PM 2.5 and all

- cause mortality in this cohort

, but observed an association with IHD mortality (HR 1.20 [95% CI: 1.02,

1.41])

. They also observed positive associations for respiratory mortality and CBD mortality,
though these associations were not statistically significant.

In a single

- city study conducted in Toronto, Ontario, Canada, Jerrett et al ( 2009b ) examined the

association between long

- term exposure to PM 2.5 and all

- cause mortality among subjects from a respiratory clinic

. The authors observed positive, though not statistically significant associations

with all

- cause, circulatory or respiratory mortality

. A limited number of deaths in the cohort and

low variability in PM 2.5 concentrations (limiting the exposure contrast) led the authors to11 conclude that “no definitive conclusions [could] be drawn about these associations with PM 2.5 ”

. In a single

- city study conducted in Vancouver, British Columbia, Cana da, Gan et al. ( 2011 )

conducted a population

- based cohort study to evaluate the association between traffic

- related
pollutants and risk of mortality due to CHD

. Land

- use regression models were used to estimate

exposure over a 5 year period (1994

- 1998) and the cohort was followed up for 4 years (1999

- 2002). Exposure to PM 2.5 was weakly associated with CHD mortality.

Recent studies that examined the association between long

- term PM 2.5 exposure and mortality

further support the conclusions of the 2009 PM ISA. The strongest evidence for mortality was

from the Harvard Six Cities ( Laden et al., 2006 ; Dockery et al., 1993 ) and American Cancer
Society cohorts ( Krewski, 2009 ; Pope III et al., 2004 ; Pope et al., 2002 )

, which was supported by

a number of other cohort studies. Updated results from the Harvard Six Cities ( Lepeule et al.,

2012 ) and American Cancer Society ( Jerrett et al., 2009a ) cohorts support the findings of the

2009 PM ISA, while a new Canadian multicity study ( Crouse et al., 2012 ) observed associations

below those reported in the PM ISA (i.e., < 10 μg/m 3 ). In the 2009 PM ISA, for cause

- specific
mortality, the strongest evidence was for cardiovascular

- related mortality, particularly among
post

- menopausal women ( Miller et al., 2007 )

. Respiratory

- related mortality was also observed,
particularly for lung cancer mortality ( Naess et al., 2007 )

. Recent studies provide more evidence

for strong associations with cardiovascular

- related mortality among women ( Lipsett et al., 2011 ; Puett et al., 2009 ) and additional evidence for respiratory mortality including lung cancer mortality ( Lepeule et al., 2012 )

.
Long

- term exposure to PM 10

- 2.5

Summary of 2009 PM ISA Conclusions

The 2009 PM ISA synthesized the epidemiologic literature characterizing the association

between long

- term exposure to PM 10

- 2.5 and increased risk of mortality and concluded that the

evidence was too limited to adequately characterize the associations for PM 10

- 2.5

. The findings

from the AHSMOG ( Chen et al., 2005 ) and Veterans ( Lipfert et al., 2006 ) cohort studies
provided limited evidence for associations between long

- term ex posure to PM 10

- 2.5 and mortality

in areas with mean concentrations in the range of 16 to 25 μg/m 3

. Overall, the evidence was

determined to be inadequate to determine if a causal relationship exists between long

- term

exposure to PM 10

- 2.5 and mortality (See Section 7.6 of the 2009 PM ISA)

. Recent studies
published since the completion of the 2009 PM ISA are characterized in Table A

. 1

.

Recent Mortality Studies

Since the completion of the 2009 PM ISA, Puett et al

. ( 2009 ) examined the relationship of long

term exposure to PM 10

- 2.5 with all

- cause and CHD mortality among women from the Nurses’

Health Study

. The authors did not find an association between PM 10

- 2.5 and the risk of all

- cause

m ortality (HR 1.03 [95% CI: 0.89, 1.18]). The association between PM 10

- 2.5 and CHD mortality

was positive, but not statistically significant (HR: 1.14 [95% CI: 0.73, 1.77] ). More recently,

Puett et al. ( 2011 ) used the same spatiotemporal exposure estimation models to characterize the12 association between PM 10

- 2.5 and mortality among male subjects in the Health Professionals

Follow

- up Study

. In this cohort, long

- term exposure to PM 10

- 2.5 was not associated with all

- cause

or CHD mortality.

In summary, two new studies ( Puett et al., 2011 ; Puett et al., 2009 ) evaluated the association

between long

- term exposure to PM 10

- 2.5 and mortality

. The long

- term mean PM 10

- 2.5 concentrations reported in these studies were lower than those reported in the 2009 PM ISA (7.7

and 10.1 μ g/m 3

, respectively). These studies do not provide any additional evidence for an

association between long

- term exposure to PM 10

- 2.5 and mortality that would be sufficient to materially change conclusions made in the 2009 PM ISA

.

2.1.2. Morbidity

– Cardiovascular Effects

Summary of 2009 PM ISA Conclusions

The 2009 PM ISA concluded that “the evidence from epidemiologic and toxicological studies is

sufficient to conclude that a causal relationship exists between long

- term exposures to PM 2.5 and

cardiovascular effects.” The strongest evidence was provided by large, multicity, U.S.

- based

studies of cardiovascular mortality (See Section 7.2.10 of the 2009 PM ISA) with supporting

evidence from a U.S.

- based epidemiologic study (Miller et al. ( 2007 ) ) that reported associations

between PM 2.5 and incident stroke and myocardial infarction ( MI ) among post

- menopausal

women at mean PM 2.5 concentrations of 13.5 μg/m 3

. 4

Recent Cardiovascular Morbidity Studies

Several new studies of long

- term exposure to PM 2.5 and cardiovascular disease were conducted

since the completion of the 2009 PM ISA

. In a study of male subjects enrolled in the Health

Professionals Foll ow

- Up Study, Puett et al. ( 2011 ) used spatiotemporal models to estimate

exposure to PM 2.5 by combining data from available air monitoring networks with geographic

information system ( GIS ) derived variables such as distance to roadway and elevation. The

authors reported no association between long

- term PM 2.5 and total CVD or ischemic stroke;

however, in fully adjusted models (i.e. adjusted for covariates including body mass index ( BMI )

, hypertension, hypercholesterolemia, diabetes, family history of MI, smoking physical activity,

diet) elevated HRs for non

- fatal MI and hemorrhagic stroke were observed (HR: 1. 1 6 [ 95% CI:

0. 81

, 1. 64 ] and 1. 69 [ 95%CI: 0. 59

, 3

. 71 ] ) 5

. Associations of PM 2.5 with all

- cause mortality and

fatal CHD were not observed in this all male cohort. A cross

- sectional study of male and female
patients attending a pulmonary clinic after reporting respiratory complaints reported no

associations of long

- term PM 2.5 exposure with prevalent IHD, although an association with
nitrogen dioxide ( NO 2 ) was reported ( Beckerman et al., 2012 )

. Interactions among exposures,

risk factors and potential confounders were tested and no statistically significant effect modifiers

4 Listed as 12.9 μg/m 3 for the reasons stated in Federal Register Notice of EPA’s proposed rule on the PM NAAQS (77 FR 38 934 n. 82 ).

5 All effect estimates for associations between long

- term exposure to PM 2.5 and cardiovascular morbidity are presented for a 10 μ g/m 3 increase in PM 2.5 concentration.13 were identified. A study using satellite derived aerosol optical depth (AOD) measurements to predict PM 2.5 concentrations, reported a 3.12% (95% CI: 0.30

, 4.29) increase in cardiovascular
hospital admission among older adults for an increase in long

- term PM 2.5 exposure ( Kloog et al.,

2012a )

. A similar increase in risk was reported for stroke hospital admissions (3.49 [95% CI:

0.09

, 5.18]).

The stronger evidence linking long

- term PM 2.5 exposure with cardiovascular disease was
apparent in studies of women as originally demonstrated in the 2009 PM ISA

. In a study of

female teachers residing in C alifornia, Lipsett et al. ( 2011 ) used concentration data from 1999

- 2000 and applied inverse distance weighted interpolation techniques to develop monthly PM 2.5 concentration surfaces from ambient monitor data. This study reported an increased risk for

incident stroke (HR: 1.15 95% CI 1.00

- 1.33), which was highest among post

- menopausal

women, but no association between PM 2.5 and incident MI (HR: 0.99 95% CI 0.84

- 1.15). This
study supports the findings of Miller et al. ( 2007 ) linking incident stroke to long

- term PM 2.5

exposure among post

- menopausal women ; however, they also reported an association with

incident MI. Coogan et al. ( 2012 ) followed African American women who ranged in age from 21

to 69 years at enrollment in the Black Women’s Health Study for 10 years to investigate incident
hypertension and diabetes in association with long

- term exposure to PM 2.5

. PM 2.5 concentrations

were spatially interpolated using monitoring data from state and local stations in the Los Angeles

basin for the year 2000. This study reported an increased risk of incident hypertension (IRR: 1.48

95%CI: 0.95

- 2.31)

. This risk was attenuated

, but remained positive in a copollutant model
containing NO 2 (IRR: 1.32 95%CI: 0.84

- 2.05).

Several studies have been published from the Multi

- Ethnic Study of Atherosclerosis (MESA)

that was designed to inform on mechanistic pathways by which PM 2.5 exposure may act on the

cardiovascular system

. L ong

- term PM 2.5 exposure was associated with increased prevalent QT
prolongation (OR: 1.6 95% CI: 1.2

- 2.2) and intraventricular conduction delay (OR: 1.7 95% C I

1.0

- 2.6) ( Van Hee et al., 2011 )

. In addition, both long

- and short

- term PM 2.5 exposure was

associated with a narrowing of retinal vessel diameter ( Adar et al., 2010 )

. R eductions in flow

mediated dilation have been observed in association with short

- term exposures to PM 2.5 (S ee

Section 6.2.4 of the PM ISA) ; however, O’Neill et al. ( 2011 ) found no association of long

- term

PM 2.5 exposure with chronic arterial stiffness

. Generally, the results of recent studies are consistent with the evidence for an association

between long

- term exposure to PM 2.5 and cardiovascular morbidity characterized in the 2009 PM

ISA

. F indings on incident stroke reported by Miller et al ( 2007 ) in a co hort of post

- menopausal

women are supported by a new study of female teachers ( Lipsett et al., 2011 )

, while a recent study of black women reports an association between PM 2.5 and incident hypertension ( Coogan

et al., 2012 ) at long

- term mean PM 2.5 concentrations ranging from 15.6

– 21.5 μg/m 3 ( Table

A .3)

.14 2.1.3. Morbidity

– Respiratory Effects

Summary of 2009 PM ISA Conclusions

The epidemiologic evidence reviewed in the 2009 PM ISA demonstrated associations between
long

- term exposure to PM 2.5 and decrements in lung function growth, increased respiratory

symptoms, and asthma development in study locations with mean PM 2.5 concentrations ranging

from 13.8 to 30 μg/m 3 during the study periods (See Sections 7.3.1.1 and 7.3.2.1 of the 2009 PM

ISA )

. These studies contributed to a body of evidence that was sufficient to conclude that “ a

causal relationship is likely to exist between long

- term exposures to PM 2.5 and respiratory

effects. ”

Recent Respiratory Morbi dity Studies

Since the completion of the 2009 PM ISA, a number of studies have been published that examine

the association between long

- term exposure to PM 2.5 and respiratory outcomes ( Table A

. 4 )

. These recent studies are consistent with the associations observed for respiratory outcomes reported in the 2009 PM ISA and provide additional evidence for associations between long

- term

exposure to PM 2.5 and respiratory symptoms and asthma development

. For example, in a recent prospective community i ntervention study in Libby, MT ( Noonan et al., 2012 ) ambient PM 2.5 concentrations decreased by 26.7% over four winters following the replacement of over 1

, 100

wood stoves in the community with new lower emission wood stoves or other heating sources

. This decrease in PM 2.5 concentrations was associated with decreases in reported wheeze and
respiratory infections (including colds, bronchitis, influenza and throat infection) among school

children

. These results suggest that beneficial health impacts are associated with decreases in

ambient PM 2.5 concentrations

.

A number of other studies evaluated the association between long

- term exposure to PM 2.5 and
respiratory symptoms

. Several nationwide U.S. studies that used data from the National Health

Interview Survey reported associations between long

- term exposure to PM 2.5 and respiratory

symptoms among children ( including respiratory allergy/hay fever ( Parker et al., 2009 )

, and
respiratory allergy and frequent ear infections ( Bhattacharyya and Shapiro, 2010 ) and adults
(including asthma among African

- Americans ( Nachman and Parker, 2012 ) ; sinusitis ( Nachman

and Parker, 2012 ; Bhattacharyya, 2009 ) ; and hay fever ( Bhattacharyya, 2009 )

. Meng et al.

( 2010 ) examined long

- term exposure to PM 2.5 in the San Joaquin Valley of California and
weekly asthma symptoms among participants with physician

- diagnosed asthma

. They observed

associations between annual average concentrations of PM 2.5 and frequent asthma symptoms

. In

a study conducted in New York City, Patel et al. ( 2009 ) examined long

- term exposure to PM 2.5 and respiratory symptoms in children through 24 months of age

. Long

- term exposure to PM 2.5

was not associated with wheeze or cough in this study, though several PM 2.5 constituents were

associated with wheeze and/or cough (see Section 2.4.2 for results on PM 2.5 constituents).

A substantial body of evidence exists that has evaluated short

- term exposure to PM 2.5 and

emergency department visits and hospitalizations for respiratory causes (See Section 2.2.2.1)

.15 Several recent studies have evaluated the association between long

- term exposure to PM 2.5 and
respiratory hospitalizations

. Karr et al. ( 2009a ; 2009b ) examined exposure to PM 2.5 averaged

over an infant’s lifetime ( 0

- 12 months ) and did not observe an association between PM 2.5 and

bronchiolitis hospitalizations in the Pu get Sound Region of Washington ( Karr et al., 2009a ) or in

the Georgia Air Bas in of British Columbia, Canada ( Karr et al., 2009b )

. Kloog et al. ( 2012a )
investigated hospital admissions for all respiratory causes among residents of New England 65

years of age and older

. The authors observed a 4.22% (95% CI 1.06, 4.75) 6 increase in
respiratory hospital admissions associated with long

- term PM 2.5 concentratio ns

. Similarly,

Neupane et al. ( 2010 ) restricted their analyses of pneumonia hospitalizations to those 65 years of

age and older and found that long

- term exposure to PM 2.5 was associated with hospitalization for
community

- acquired pneumonia (OR 13.64, 95% CI : 1.79, 101.01)

. Meng et al. ( 2010 )

examined long

- term exposure to PM 2.5 in the San Joaquin Valley of California and asthma

related emergency department visits or hospitalizations (analyzed together) among participants

with physician

- diagnosed asthma

. They observed associations between annual average

concentrations of PM 2.5 and emergency department visits and hospitalizations.

The 2009 PM ISA identified a number of prospective cohort studies that provided evidence of an

association between long

- term exposure to PM 2.5 and the development of asthma

. Recent studies

contribute to this weight of evidence, reporting results that are consistent with those summarized

in the 2009 PM ISA

. Akinbami et al. ( 2010 ) conducted a nationwide U.S. study with data on

children (ages 3

- 17 years) from the National Health Interview Survey and observed a positive

association between county

- wide annual average PM 2.5 concentration and current asthma (OR

1.43, 95% CI: 0.98, 2.10 comparing highest quartile of exposure to lowest) and/or a recent

asthma attack (OR 1.30, 95% CI: 0.89, 1.90 comparing highest quartile of exposure to lowest)

. Two studies examining the relationship between long

- term exposure to PM 2.5 and incident

asthma were conducted in British Colu mbia, Canada

. Carlsten et al. ( 2011 ) evaluated birth year

exposure to PM 2.5 and physician

- diagnosed asthma at age 7 and observed an association with an

increased risk of incident as thma

. Similarly, Clark et al. ( 2010 ) assigned exposure based on

average PM 2.5 concentration during the first week of life and the association with incident asthma

between ages 3 and 4

. The authors did not observe an association between PM 2.5 and inc ident

asthma

. McConnell et al

. ( 2010 ) characterized the relationship between childhood incident

asthma and long

- term exposure to PM 2.5 among the Southern California Children’s Health Study
participants

. In this cohort, asthma

- free kindergarten and first

- grade children were followed up

for three years and the authors observed a positive association (HR 1.34, 95% CI: 0.95, 1.90),
though this association was diminished when the authors adjusted for traffic related pollution

concentrations measured near the child’s home and school.

In summary, the results of recent studies generally continue to demonstrate an association

between long

- term exposure to PM 2.5 and respiratory morbidity. Recent e pidemiologic studies

6 All effect estimates for associations between long

- term exposure to PM 2.5 and respiratory morbidity are presented

for a 10 μ g/m 3 increase in PM 2.5 concentration.16 reported associations with respiratory symptoms and respiratory hospitalizations. New f indings

on incident asthma among children are consistently positive, though not statistically significant.

These recent studies demonstrate associations at long

- term mean PM 2.5 concentrations ranging

from 9.7 to 27 μg/m 3 ( Table A. 4)

.

2.1.4. Morbidity

– Reproductive and Developmental Effects

Summary of 2009 PM ISA Conclusions

The 2009 PM ISA synthesized the epidemiologic literature characterizing the association

between long

- term exposure to PM 2.5 and increased risk of reproductive and developmental

effects and concluded that the evidence was suggestive of a causal relationship between long

term exposure to PM 2.5 and reproductive and developmental outcomes (See Section 7.4 of the

2009 PM ISA)

. The strongest evidence was for reduced birth weight and infant mortality,
especially due to respiratory causes during the post

- neonatal period

. The mean PM 2.5 concentrations during the study periods ranged from 5.3

– 27.4 μg/m 3

, with effects becoming

more precise and consistently positive in locations with mean PM 2.5 concentrations of 15 μg/m 3

and above

. The epidemiologic literature did not consistently report associations between long

term exposure to PM 2.5 and preterm birth, growth restriction, birth defects or decreased sperm quality

.

Recent Reproductive and Developmental Outcome Studies

Since the completion of the 2009 PM ISA, a number of studies have been published that examine

the association between long

- term exposure to PM 2.5 and reproductive and developmental

outcomes ( Table A. 5 )

. These recent studies are consistent with the associations observed for
reproductive and developmental outcomes reported in the 2009 PM ISA

, within similar

concentrations ( long

- term mean PM 2.5 concentrations ranging from 11.0

– 19.8 μg/m 3 ), and
provide additional evidence for associations between long

- term exposure to PM 2.5 and reduced

birth weight ( Ghosh et al., 2012 ; Kloog et al., 2012b ; Kumar, 2012 ; Darrow et al., 2011b ; Bell et

al., 2010 ; Morello

- Frosch et al., 2010 ; Salihu et al., In Press )

. Recent evidence remains

inconsistent for the association between exposure to PM 2.5 and preterm birth, with some studies
providi ng evidence for an association ( Chang et al., 2012b ; Wu et al., 2009 )

, while others did not
( Rudra et al., 2011 ; Darrow et al., 2009 )

.

2.2. Epidemiologic Studies of Short

- Term Exposure

The 200 9 PM ISA included the results of many new epidemiologic studies reporting associations

between short

- term exposure to PM and a range of health outcomes. The epidemiologic evidence

evaluated in the ISA contributed to the determination that there is sufficient evidence to conclude

that “a causal relationship exists” between short

- term PM 2.5 exposure and cardiovascular effects

and mortality, and a “likely to be causal relationship exists” between short

- term PM 2.5 exposure

and respiratory effects (Chapter 2, 2009 PM ISA )

. Additionally, the epidemiologic evidence17 contributed to a “suggestive” causal determination for short

- term PM 10

- 2.5 exposure and

cardiovascular and respiratory effects, and mortality (Chapter 2, 2009 PM ISA).

Sections 2.2.1 and 2.2.2 highlight results from recent epidemiologic studies. Tables A. 6 through

A

. 11 (Appendix A) summarize results of recent epidemiologic studies that evaluated
relationships between health effects and short

- term exposure to PM 2.5 and PM 10

- 2.5

.

The 200 9 PM ISA included a particular focus on results of multicity studies due to their

evaluation of a wide range of PM exposures and large numbers of observations, which lead to generally more precise effects estimates than most smaller scale studies of single cities. The
multicity studies also allowed investigation of homogeneity or heterogeneity of PM health
relationships, evaluation of confounding by co

- pollutants across communities with different air
pollution mixtures, and assessment of potential effect modifiers. Since the completion of the

2009 PM ISA, n umerous multicity analyses have been published that evaluate morbidity

outcomes

.

2.2.1. Mortality

Summary of 2009 PM ISA Conclusions

Overall, in the evaluation of m ulti

- and single

- city studies in the 2009 PM ISA and in the 2004

PM Air Quality Criteria Document ( AQCD ) ( U.S. EPA, 2004 ) consistent positive associations

were observed at mean 24

- h average 7 PM 2.5 concentrations above 12.8 μg/m 3

. This collective

evidence contributed to the conclusion that “a causal relationship exists between short

- term

PM 2.5 exposure and mortali t y.” Building on the evidence presented in the 2004 PM AQCD ( U.S.

EPA, 2004 )

, multi

- and single

- city studies evaluated in the 2009 PM ISA reported consistent
positive associations between short

- term PM 10

- 2.5 exposure and mortality (Section 6.5.2.3, 2009

PM ISA ).

Recent Mortality Studies

Several recent studies evaluated the effects of short

- term exposure to PM 2.5 on mortality in single
city analyses

. No new multi

- city studies have been published. Additionally, n o new studies have

been published that examined associations between short

- term PM 10

- 2.5 exposure and mortality in

the U.S. or Canada.

N ew studies have continued to report associations between PM 2.5 and mortality that are

consistent with the conclusions of the 2009 PM ISA as shown in Figure 2.4. T wo of these studies

were conducted in New York City. Ito et al. ( 2011a ) examined the relationship between short

term exposure to PM 2.5 and PM components and cardiovascular disease (CVD) mortality for the
population ≥ 40 years old in New York City for the years 2000

- 2006. PM 2.5 was associated with

CVD mortality at lag 1 in the all

- year and cold season (October

- March) analyses, but the

strongest association with CVD mortality was observed during the warm season (April

-

7 For short

- term exposure studies the mean 24

- h avg PM 2.5 concentration refers to the mean of all daily 24

- h avg PM2.5 concentrations over the course of the study duration.18 September) at lag 0 and 1

. Also in Ne w York City, Chang et al. ( 2012a ) used a novel approach to

examine the relationship between short

- term exposure to PM 2.5 concentrations and
cardiorespiratory mortality

. The authors used a spat io

- temporal deterministic model that was

bias

- corrected with monitoring data to predict daily PM 2.5 concentrations. The authors developed

a statistical model to consider personal exposure to PM 2.5 from outdoor sources to improve

exposure assessment. Using data from 2001

- 2005, positive associations were observed for those

greater than 65 years old

. The model that accounted for personal exposure found a higher risk of
mortality (2.32% [95% CI: 0.68, 3.94] at lag 1) 8 compared to a model that used only PM 2.5 concentrations (1.13% [95% CI: 0.27, 2.00]) suggesting that risk estimates derived using ambient

concentrations as a proxy for exposure are biased towards the null

.

Additional single

- city analyses were conducted in Seattle, Detroit, and Atlanta

. Zhou et al.

( 2011 ) conducted a study using daily PM 2.5 data collected in Seattle and Detroit to examine the

effect of short

- term PM 2.5 exposure on all

- cause, cardiovascular, and respiratory mortality for the

years 2002

- 2004. In a distributed lag model of 0

- 2 days, a strong association was observed

between PM 2.5 and all

- cause and cardiovascular mortality, with some evidence of an association

with respiratory mortality in Detroit during the warm season (April

- September) (quantitative

results not presented)

. There was no evidence of an association with PM 2.5 and any mortality

outcome in Seattle in the warm season. In the cold season (October

- March)

, the strongest

associations were for all

- cause and cardiovascular mortality in Seattle, while there was no

evidence of an association between PM 2.5 and any mortality outcome in Detroit. Interestingly the
magnitude of the cardiovascular mortality association in Seattle in the cold season is larger than

that in Detroit in the warm season even though mean PM 2.5 concentrations are lower, 11.4 μg/m 3

and 14.9 μg/m 3

, respectively. Klemm et al. ( 2011 ) conducted an extended analysis of two previously published studies ( Klemm et al., 2004 ; Klemm and Mason, 2000 ) that examined the

effect of air pollution on mortality in Atlanta, GA. This analysis included an additional 7.5 years

of data and expanded the study location to include two additional counties. Focusing on deaths in

individuals 65 years of age and older, the authors found a positive association between short

term PM 2.5 exposure and nonaccidental (0.78% [95% CI:

- 0.43, 2.0]; lag 0

- 1 for a 10 μg/m 3

increase in 24

- h avg PM 2.5 concentrations) and cardiovascular mortality (0.83% [95% CI:

- 1.1,

2.8]), but no evidence of an association with respiratory mortality (

- 0.86% [95% CI:

- 4.4, 2.8]).

In summary, m ulti

- and single

- city studies evaluated in the 2009 PM ISA provided evidence of

consistent positive associations between short

- term PM 2.5 exposure and nonaccidental,

cardiovascular, and respiratory mortality. Relatively few mortality studies have been published

in the U.S. and Canada since the completion of the 2009 PM ISA and they are limited to single

city studies. T hese studies continue to demonstrate evidence of positive associations between

short

- term PM 2.5 exposures and mortality in the same range of concentrations as those studies

8 All effect estimates for associations between short

- term exposure to PM 2.5 and mortality are presented for a 10

μ g/m 3 increase in PM 2.5 concentration.19 included in the 2009 PM ISA (i.e., mean 24

- h avg concentrations of 12.8 μg/m 3 and above in the

multi

- city studies ).20 Figure 2

. 4

. Percent i ncrease in non

- accidental and cause

- specific mortality for a 10 μg/m3 increase in 24

- h average PM 2.5 concentrations in single

- pollutant models from U.S. and Canadian studies. R ed text and triangles represent recent studies published

since the completion of the 2009 PM ISA. Results presented from single

- pollutant models for purposes of comparing results across studies that included different mixes of copollutants

.

Study

Tsai et al. (2000)

Moolgavkar (2003) Ostro et al. (2006) Klemm et al. (2004) Ito (2003) Klemm et al. (2011) Franklin et al. (2007) Franklin et al. (2008) Klemm and Mason (2003) Fairley (2003) Burnett and Goldberg (2003) Zanobetti and Schwartz (2009) Burnett et al. (2004) Slaughter et al. (2005) Villeneuve et al. (2003) Chock et al. (2000)

Dominici et al. (2007a)

Tsai et al. (2000)

Dominici et al. (2007) Chang et al. (2012)

Ostro et al. (1995) Moolgavkar (2003) Ostro et al. (2006) Ostro et al. (2007) Ito (2003) Lipfert et al. (2000) Klemm et al. (2011) Holloman et al. (2004) Franklin et al. (2007) Franklin et al. (2008) Klemm and Mason (2003) Ito et al. (2011) Zanobetti and Schwartz (2009) Mar et al. (2003) Fairley (2003) Wilson et al. (2007) Villeneuve et al. (2003)

Ostro et al. (1995) Moolgavkar (2003) Ostro et al. (2006) Ito (2003) Klemm et al. (2011) Franklin et al. (2007) Franklin et al. (2008) Klemm and Mason (2003) Zanobetti and Schwartz (2009) Fairley (2003) Villeneuve et al. (2003) Nonaccidental

Cardio

- respiratory

Cardiovascular

Respiratory Location

Newark, NJ Camden, NJ Elizabeth, NJ Los Angeles, CA 9 California counties Atlanta, GA Detroit, MI Atlanta, GA 27 U.S. cities 25 U.S. cities 6 U.S. Cities Santa Clara County, CA

8 Canadian Cities

112 U.S. cities 12 Canadian cities

Spokane, WA Vancouver, CAN Pittsburgh, PA Pittsburgh, PA 100 U.S. cities

Newark, NJ Camden, NJ Elizabeth, NJ 100 U.S. cities New York, NY

Southern California Los Angeles, CA 9 California counties 9 California counties Detroit, MI Philadelphia, PA

Atlanta, GA 7 NC counties 27 U.S. cities 25 U.S. cities 6 U.S. Cities New York, NY 112 U.S. cities Phoenix, AZ Santa Clara County, CA Phoenix, AZ Vancouver, CAN

Southern California Los Angeles, CA 9 California counties Detroit, MI Atlanta, GA 27 U.S. cities 25 U.S. cities 6 U.S. Cities 112 U.S. cities Santa Clara County, CA

Vancouver, CAN Age

All All All All All 65+ All 65+ All All All All All All All All 65+ < 75 75+ All

All All All All 65+

All All All All All All 65+ > 16 All All All 40+ All All All > 25 65+

All All All All 65+ All All All All All 65+ Lag

0 0 0 1 0

- 1 0

- 1 3 0

- 1 1 0

- 1 0

- 1 0 1 0

- 1 1 1 0 0 0 1

0 0 0 1 1

0 1 0

- 1 3 1 1 0

- 1 0 1 0

- 1 0

- 1 1 0

- 1 1 0 0

- 5 0

0 1 0

- 1 0 0

- 1 0

- 1 1

- 2 0

- 1 0

- 1 0 0 ► ► ◄ Mean

42.1 39.9 37.1 22.0* 19.9 19.6 18.0 17.0 15.6 14.8 14.7 13.6 13.3 13.2 12.8 10.8 7.9

---

---

---

42.1 39.9 37.1

--- 13.3

- 17.5

32.5 22.0* 19.9 18.4 18.0 17.3 17.0 ~15.6 15.6 14.8 14.7 14.4 13.2 13.0 13.0 13.0 7.9

32.5 22.0* 19.9 18.0 17.0 15.6 14.8 14.7 13.2 13.0 7.9 98 th

---

---

---

---

---

---

--- 45.8 43.0

--- 59.0 38.9 34.3 38.0 29.6

---

---

---

---

---

---

---

---

---

---

---

---

---

---

---

---

--- 45.8 43.0

---

--- 34.3

--- 25

- 88 31.6

---

---

---

---

---

--- 45.8 43.0

--- 34.3

---

--- | | |

- 5.0

- 3.0

- 1.0 1.0 3.0 5.0 7.0 9.0 11.0 13.0 15.0

% Increase21 2.2.2. Morbidity

2.2.2.1. Associations b etween Short

- Term Exposures to PM and Respiratory

Morbidity

Summary of 2009 PM ISA Conclusions

The association between short

- term PM 2.5 exposure and respiratory

- related emergency department (ED) visits, hospital admissions, and physician visits was evaluated in Section 6.3.8

of the 2009 PM ISA ( U.S. EPA, 2009 )

. The numerous multi

- and single

- city studies evaluated
reported consistent positive associations with respiratory ED visits and hospital admissions for

COPD

, asthma, and respiratory infection in study areas with mean 24

- h average PM 2.5 concentrations ranging from 6.1

– 22 μg/m 3

. However, associations for asthma were imprecise

and not consistently positive when limiting analyses to children. The evidence from respiratory

related emergency department (ED) visits, hospital admissions, and physician visits studies

contributed to the conclusion that a “causal relationship is likely to exist between short

- term

exposures to PM 2.5 and respiratory effects.”

Additional epidemiologic studies evaluated in the 2009 PM ISA examined associations between

short

- term PM 10

- 2.5 exposure and respiratory hospital admissions and ED visits. This limited

number of studies demonstrated consistent positive associations with respiratory

- related hospital

admissions and ED visits with the strongest evidence in children. The evidence from these

studies in combination with the evidence from toxicological and controlled human exposure

studies led to the conclusion that the collective evidence across disciplines “is suggestive of a

causal relationship between short

- term exposures to PM 10

- 2.5 and respiratory effects.”

Recent Respiratory Hospital Admission Studies

Within this section

, respiratory

- related hospital admissions and ED visit studies are discussed
separately. This is because ED visits for respiratory

- related outcomes often represent less

serious, but more common health effects. Additionally, only a small percentage of respiratory

related ED visits result in a hospi tal admission. Therefore

, it is important to discuss the evidence

for each respiratory

- related health outcome separately.

Respiratory

- r elated Hospital Admissions

A number of studies published since the completion of the 2009 PM ISA conducted mu lti city or

multi

- location analyses to examine the association between short

- term PM 2.5 exposures and
respiratory hospital admissions. Figure 2.5 summarizes the evidence from single

- pollutant

models from studies evaluated in the 2009 PM ISA as well as recent studies published since its
completion. Bell et al. ( 2012 ) represented a consolidated and more detailed account of a number

of previous publications, of which most were discussed in the 2009 PM ISA ( Bell et al., 2009a ; Bell et al., 2009b ; Bell et al., 2008 ; Bell et al., 2007 )

. In an all

- year analysis of 187 U.S. counties,

short

- term exposure to PM 2.5 was positively associated with respiratory hospital admissions in

individuals 65 years of age and older across lags of 0 to 2 days, with the strongest association at22 lag 2 (0.41% [95% CI: 0.09, 0.74]) 9

. In seasonal analyses, the association at lag 2 was consistently positive across seasons, but the strongest association was at lag 0 (1.05% [95% CI:

0.29, 1.82]) in the winter season with the largest magnitude of an effect in the Northeast region.

Of note the Northeast region comprised 53% of all counties included in the analysis. In a n

additional analysis using this data ( Bell et al., 2009a )

, there was no evidence of a reduction in the

association between PM 2.5 and respiratory hospital admissions when accounting for air
conditioning use

. In a multi

- city study conducted in the New England region o f the U.S., Kloog

et al. ( 2012a ) examined associations between short

- term PM 2.5 exposure and respiratory hospital

admissions in individuals 65 years of age and older. To estimate exposure the authors developed

a novel prediction model that combined land use regression with physical measurements from

satellite aerosol optical depth. T he authors observed a 0.70% (95% CI: 0.35, 1.05) increase in
respiratory hospital admissions for lags days 0

- 1

. The results obtained using the novel approach
presented (i.e., 0.70% increase in respiratory hospital admissions) were consistent with the

percent increase in respiratory hospital admissions observed in a traditional time

- series analysis

(i.e., 1.51%).

In addition to the multicity studies presented above, a few single city studies were conducted in

the U.S. that examined asthma and acute bronchitis. Silverman and Ito ( 2010 ) conducted a study

to evaluate the effect of short

- term PM 2.5 and O 3 exposure on asthma hospital admissions, both
general and those that required a stay in the intensive care unit (ICU) in New York City.
Analyses focused on four age groups (i.e., <6, 6

- 18, 19

- 49, and 50+) and were limited to the

warm season (April

- August). Positive associations were observed for each age group and for all

ages combined when considering general asthma hospital admissions, with the strongest

association for the age group 6

- 18 (15.5% [95% CI: 9.1, 22.0] at lag 0

- 1). When limiting the
analysis to ICU asthma admissions, again the strongest association was for the age group 6

- 18

(21.1% [95% CI: 8.3, 35.5]). The observed associations remained robust in copollutant models

with O 3

. The authors also examined the shape of the concentration

- response ( C

- R ) relationship
using linear, smooth functions, which allowed for a possible nonlinear relationship. This analysis

found evidence that the linear fit is a reasonable approximation of the relationship between short

term PM 2.5 concentrations and asthma hospital admissions. Grineski et al. ( 2011 ) primarily

focused on examining the effect of dust and low wind events on asthma and acute bronchitis
hospital admissions in El Paso, TX; however, since daily PM 2.5 data were available the authors

also examined associations between short

- term PM 2.5 exposures and each respiratory health

effect. T he authors found that PM 2.5 was positively

, but weakly associated with asthma

(OR=1.02 [95% CI: 0.96, 1.09]) and acute bronchitis (OR=1.01 [95% CI: 0.92, 1.12]) hospital

admissions.

9 All effect estimates for associations between short

- term exposure to PM 2.5 and morbidity are presented for a 10

μ g/m 3 increase in PM 2.5 concentration.23 Recent Respiratory

- related ED Visits Studies

Of the recent studies identified that focused on short

- term exposures to PM 2.5 and respiratory

related ED visits the majority consisted of single

- city studies. However, a couple large

, multi

city stud ies w ere conducted in the U.S

. and Canada

. Zanobetti et al. ( 2009 ) examined the

association between short

- term PM 2.5 exposure and respiratory ED visits in individuals 65 years

of age and older in 26 U.S. communities. In an all

- year analysis, PM 2.5 was strongly associated

with respiratory ED visits (2.1 [95% CI: 1.2, 3.0] at lag 0

- 1), while in seasonal analyses positive

associations were observed across seasons with the strongest association in the spring (4.3%

[95% CI: 2.2, 6.5]). Stieb at al. ( 2009 ) conducted a study in 7 Canadian cities to examine the

effect of air pollution on ED visits for multiple respiratory

- re lated health outcomes including

asthma, COPD, and respiratory infection. The authors found no evidence of an association

between short

- term PM 2.5 exposure and COPD ED visits at any of the single

- day lags examined.

In all

- year analyses, positive associations were observed for asthma with the magnitude of the

association decreas ing as lag day increased (i.e., the strongest association was observed at lag 0,

2.1% [95% CI:

- 3.0, 7.5]). However, in a warm season analysis (April

- September), the
magnitude of the association between PM 2.5 and asthma was nearly 4 times higher (9.3% [95%

CI: 6.3, 12.5]).

A couple of single city studies were also conducted that examined all respiratory

, multiple
respiratory effects, or asthma ED visits

. Darrow et al. ( 2011a ) examine d the association between

short

- term air pollution exposure and respiratory ED visits in Atlanta using various exposure

metrics (i.e., 1

- h max, 24

- h avg, Commute (0700

- 1000, 1600

- 1900 hours), Day

- time (0800

- 1900
hours), and Night

- time (2400

- 0600 hours). PM 2.5 (lag 1) was positively associated with
respiratory ED visits across exposure metrics, with the magnitude ranging from 0.2% to 0.4%

. Kim et al. ( 2011 ) examined the associations between short

- term PM 2.5 exposure and hospital

admissions in Denver, CO. The authors found no evidence of an association with all respiratory

(

- 0.44% [95% CI:

- 5.6, 5.4]), COPD or pneumonia hospital admissions (quantitative results only
presented for all respiratory). However, there was evidence of a delayed effect of PM 2.5 on

asthma hospital admissions with effects not occurring until approximately lag day 4.

A number of studies focused on ED visits and hospital admissions for asthma. Strickland et al.

( 2010 ) conducted an analysis in Atlanta using the same air quality data as Darrow et al. ( 2011a )

to examine the association between air pollution and pediatric (ages 5

- 17) asthma ED visits.

PM 2.5 was strongly associated with pediatric asthma ED visits in both all

- year (2.2% [95% CI:

0.2, 4.2] at lag 0

- 2) and warm season (4.7% [95% CI: 1.7, 7.6]) analyses. The magnitude of the

association was robust to the inclusion of O 3 in the model. An examination of the C

- R
relationship through a quintile analysis and a loess C

- R analysis using lag 0

- 2 day PM 2.5 concentrations found evidence of increased risk of pediatric asthma ED visits down to relatively

low ambient concentrations (i.e., mean 24

- h avg concentrations < 14 μg/m 3 )

. In Tacoma, WA,

Mar et al. ( 2010 ) also examine d the association between short

- term PM 2.5 exposure and asthma

ED visit s

. Individual lag days of 0 to 5 days were examined with the strongest association24 occurring at lag 2 (5.7% [95% CI : 1.4, 10.1])

. Li et al. ( 2011 ) examined the C

- R relationship

between short

- term PM 2.5 exposures and asthma ED visits in children 2 to 18 years of age in

Detroit. Associations were examined in both a time

- series and time

- stratified case

- crossover study design assuming: (1) no deviation from linearity and (2) a change in linearity at 12 μg/m 3

. In the analyses assuming linearity, similar effect estimates were observed in both models for a 0

- 4 day lag, (time series: RR=1.03 [95% CI: 1.00, 1.07]; case

- crossover: OR=1.04 [95% CI: 1.01,

1.07]). In the models assuming a deviation from linearity at 12 μg/m 3

, the authors reported
slightly larger effect estimates

, compared to the linear model, for asthma ED visits in the time

series (RR=1.07 [95% CI: 1.03, 1.11]; lag 0

- 4) and case

- crossover analyses (OR=1.06 [95% CI:

1.03, 1.09]; lag 0

- 4), respectively

. Glad et al. ( 2012 ) conducted a study in Pittsburgh, PA that

found PM 2.5 to be positively associated with asthma ED visits in analyses of all ages and ages 18

to 64 for single lag days and the average of 0

- 5 days (i.e., all ages: OR=1.04 [95% CI: 0.98, 1.10]

and 18 to 64: OR=1.053 [95% CI: 0.99, 1.12] at lag 0

- 5). Additionally, when stratifying by race

there was some evidence for larger effects in African Americans compared to Caucasian

Americans.25 Figure 2

. 5

. Percent ( % ) Increase in respiratory

- related hospital admissions and ED visits for a 10 μg/m 3 increase in 24

- h average
PM 2.5 concentrations in single

- pollutant models from U.S. and Canadian studies. R ed text and triangles represent recent studies published since the completion of the 2009 PM ISA. * ED visit studies. ** Median concentration.

Study

Ostro et al. (2009) Peel et al. (2005) Tolbert et al. (2007) Darrow et al. (2011)* Zanobetti et al. (2009) Bell et al. (2008) Slaughter et al. (2005) Kloog et al. (2012) Kim et al. (2012) Fung et al. (2006) Chen et al. (2005)

Peel et al. (2005)* Ito et al. (2007)* Sheppard et al. (2003) Strickland et al. (2010)* NYS DOH (2006)* NYS DOH (2006)* Li et al. (2011)* Glad et al. (2012)* Silverman and Ito (2010) Grineski et al. (2011) Mar et al. (2010)* Slaughter et al. (2005)* Stieb et al. (2009)* Chimonas & Gessner (2006)

Grineski et al. (2011)

Peel et al. (2005)*

Lin et al. (2005) Dominici et al. (2006)

Stieb et al. (2009)* Chimonas & Gessner (2006) Location

6 CA Counties

Atlanta, GA Atlanta, GA Atlanta, GA

26 U.S. communities

202 U.S. counties Spokane New England
Denver, CO

Vancouver

Vancouver

Atlanta, GA New York, NY Seattle, WA Atlanta, GA
Bronx, NY Manhattan, NY

Detroit, MI Pittsburgh, PA New York, NY

El Paso, TX
Tacoma, WA Spokane, WA

7 Canadian cities Anchorage, AK

El Paso, TX

Atlanta, GA

Ontario, CAN 204 U.S. counties

7 Canadian cities Anchorage, AK Age

0

- 19

All

All

All

65+

65+

All

65+

All

65+

65+

All

All

All

5

- 17

All

All

2

- 18

All

All

1+

All

All

All

0

- 19

1+

All

< 15 65+

All

0

- 19 Lag

3

0

- 2

0

- 2

1

0

- 1

2

1

0

- 1

0

- 14 DL

0

- 2

0

- 2

0

- 2

0

- 1

0

0

- 2

0

- 4

0

- 4

0

- 4

0

- 5

0

- 1

0

- 3

2

1

0

0

0

- 3

0

- 3

0

- 3 2

0

0 ► ◄

◄ All Respiratory

Asthma

Bronchitis

Respiratory Infection Mean

19.4

19.2

17.1

16.0

15.3

12.9

10.8

9.6

8.0

7.7

7.7

19.2

--- 16.7

16.4

15.0

15.0

15.0

13.3

13.0**

12.8

12.3

10.8

6.7

- 9.8

6.1

12.8

19.2

9.6 13.3

6.7

- 9.8

6.1 98 th

---

---

---

---

--- 34.2

29.6

---

---

---

---

---

--- 46.6

---

---

---

---

---

---

---

--- 29.6

---

---

---

---

--- 34.8

---

---

- 15.0

- 10.0

- 5.0 0.0 5.0 10.0 15.0 20.0

% Increase26 The 2009 PM I SA evaluated a number of multi

- and single

- city studies that found consistent
positive associations with all and cause

- specific respiratory hospital admissions and ED visits,
specifically COPD and respiratory infections in study areas with mean 24

- h PM 2.5 concentrations
ranging from 6.1

– 22.0 μg/m 3

. Additionally, there was evidence for asthma hospital admissions

and ED visits, but the effects were not consistent in children. Recent multi

- and single

- city

studies have continued to demonstrate consistent positive associations for all respiratory

- related
hospital admissions and ED visits, and provide additional evidence for increases in asthma
hospital admissions and ED visits. The associations observed in the new studies occur in

locations with mean concentrations similar (i.e., mean 24

- h avg concentrations ranging from 6.7

– 16.4 μg/m 3 ) to those studies included in the 2009 PM ISA.

The 2009 PM ISA also found evidence that associations between short

- term PM 10

- 2.5 exposures

and respiratory

- related hospital admissions and ED visits were strongest among children. A

recent study by Strickland et al. ( 2010 ) that examined the association between short

- term PM 10

-

2.5 exposure and pediatric asthma ED visits in Atlanta, GA further supports this conclusion.

Positive associations were observed in both all

- year (5.8% [95% CI: 1.9, 9.9] at lag 0

- 2) and

seasonal analyses, with the strongest association in the cold season (7.0% [95% CI: 1.7, 12.7]).

An examination of the C

- R relationship in both quintile and smooth estimates of the

concentration

- response provided evidence of associations at relatively low ambient

concentrations for all pollutants, including PM 10

- 2.5 (i.e., mean 24

- h avg concentrations < ~12
μg/m 3 )..

2.2.2.2. Associations b etween Short

- Term Exposures to PM and

Cardiovascular Morbidity

Summary of 2009 PM ISA Conclusions

The associations between short

- term PM 2.5 exposure and cardiovascular

- related hospital

admissions and ED visits was evaluated in Section 6.2.10 of the 2009 PM ISA ( U.S. EPA, 2009 )

. Epidemiologic studies that examined the effect of PM 2.5 on cardiovascular ED visits and hospital

admissions reported consistent positive associations (predominantly for IHD and congestive

heart failure [CHF]) in study areas with mean 24

- h average concentrations ranging from 7.0

– 18
μg/m 3

. This evidence contributed to the conclusion that “a causal relationship exists between

short

- term PM 2.5 exposure and cardiovascular effects.”

Epidemiologic studies of the association of short

- term PM 10

- 2.5 exposure with cardiovascular
hospital admissions and ED visits were also evaluated in the 2009 PM ISA, and the evidence

from these studies contributed to the conclusion that the evidence “is suggestive of a causal
relationship between short

- term exposures to PM 10

- 2.5 and cardiovascular effects.

Recent Cardiovascular

- related Hospital Admissions/ED Visits Studies

Recent multi

- city and multi

- location studies, as well as single

- city studies, add to the collective
body of evidence that examined associations between short

- term PM 2.5 exposure and

cardiovascular

- related hospital admissions and ED visits evaluated in the 2009 PM ISA. Figure27 2.6 summarizes the results from single

- pollutant models from studies evaluated in the 2009 PM

ISA as well as recent studies published since its completion. No new studies have been published

that examined the association between short

- term PM 10

- 2.5 exposure and cardiovascular hospital

admissions or ED visits in the U.S. or Canada.

In a recent Health Effects Institute ( HEI ) report, Bell et al. ( 2012 ) compiled findings from

several multicity analyses of Medicare data (older adults, ≥ 65 years of age) for 204 counties

across the U.S. (some analyses included fewer counties)

. Although additional detail is provided

in the HEI report, these analyses were largely included in the 2009 PM ISA ( Bell et al., 2008 ; Dominici et al., 2006 )

. In an analysis using the same data, Bell et al. ( Bell et al., 2009a ) found a

h igher prevalence of central air conditioning was associated with a decrease in the risk of PM 2.5 - associated hospitalization for cardiovascular disease.

Recent studies are consistent with the evidence assessed in the 2009 PM ISA. In a time

- series
analysis of Medicare records for older adults ≥65 years of age in 26 US communities for 2 000

- 2003, Zanobetti et al. ( 2009 ) reported increases in hospital admissions for all CVD (1.89%

95%CI: 1.34 to 2.45), MI (2.25% 95%CI: 1.10 to 3.42) and CHF (1.85% 95%CI: 1.19 to 2.51;
lag 0

- 1)

. Although the largest excess risks were observed in the spring, statistically significant

excess risks were also observed in the winter

. In a time

- series analysis of hospital admissions in

seven Canadian cities, a 17% (95%CI: 0 to 37%) increase in hospital admissions for heart failure

was observed at lag 0 ( Stieb et al., 2009 )

. Weak, nons ignificant associations were observed

between PM 2.5 and d ysrhythmia and MI hospitalizations.

In a study of emergency hospitalizations among New York City residents ≥ 40 years of age, Ito

et al. ( 2011a ) reported an excess risk of 1.0% (95% CI: 0.40, 1.6

, lag 0). The excess risk was
stronger in the cold season (1.1% [95% CI 0.2 to 2.0]). These results were not sensitive to the

choice of method used to control temperature

. Using a subset of these emergency hospitaliz ation

data, Mathes et al. ( 2011 ) defined two cardiovascular syndromes from a database containing text descriptions of the chief complaint reported by the patient upon admission to the hospital. This
study reported that PM 2.5 was associated with both cardiac and more general cardiovascular
syndromes. In case

- crossover analysis of cardiovascular disease admissions across New York

state from 2001 to 2005, Haley et al. ( 2009 ) found a 3.9% increase in heart failure admissions

per 10 μg/m 3 increase in PM 2.5 (lag 0

- 2)

. A case

- crossover study of atrial fibrillation
hospitalizations between 1993 and 2008 in Utah (Wasatch Front) reported consistent ly positive

, but non

- significant, associations across all lags examined in the study (lag 0 through 21 day
moving average) (quantitative results not provided) ( Bunch et al., 2011 )

. Finally, a 1 .03% (95%

CI: 0.69, 1.34) increase in cardiovascular admissions was reported in a time

- series study of
hospitalizations across New England among older adults (65 years) with predicted PM2.5

concentrations using satellit e

- derived AOD measurements ( Kloog et al., 2012b )

.28 Acute Stroke

Wellenius et al. ( 2012 ) examined the association of PM 2.5 with neurologist

- confirmed ischemic

stroke in predominately white female patients admitted to the Beth Israel Deaconess Medical

Center (BIDMC) in Boston from 1999 to 2008. T ime of stroke symp tom onset (exact or estimated) was available for most patients included in the study. The OR of stroke onset was

1.30 (95% CI: 1.08 to 1.58) per 10 μg/m 3 increase in PM 2.5 in the previous 24 hours. Authors

report a 34% (95% CI: 13 to 58) higher risk of ischemic stroke during the previous 24 hours in

an analysis comparing moderate PM 2.5 exposure (≥15 μg/m 3 ) to good (<15 μg/m 3 ) exposure, as

defined by EPA’s Air Quality Index (AQI)

. These results were confirmed in an additional
analysis conducted by Mostofsky et al. ( 20 12 ) using a subset of the data (i.e., 2003

- 2008) used
by Wellenius et al. ( 2012 )

. Mostofsky et al. ( 2012 ) found a 22.7% (95% CI: 3.1, 47.0) increase in

ischemic stroke onset for an increase in PM 2.5 over the previous 24 hours.

Out of Hospital Cardiac Arrests

The small number of studies of out

- of

- hospital cardiac arrest included in the 2009 PM ISA
reported mixed results. A recent time series analysis of cardiac arrests in New York City reported

an increased risk of 1.06 (95%CI 1.02, 1.10, lag 0

- 1) per 10 μg/m3 increase in PM 2.5 ( Silverman

et al., 2010 )

. Case cross

- over analysis of the same data produced a result that was similar in
magnitude but did not reach statistical significance. The association with cardiac arrest was
stronger in the warm season (1.09 95% CI: 1.03

- 1.15) compared to the cold season (1.01 95% CI

0.95 to 1.07).

I n summary, the 2009 PM ISA found consistent positive associations between short

- term PM 2.5

exposures and all and cause

- specific cardiovascular hospital admissions and ED visits,
specifically IHD and CHF in study areas with mean 24

- h PM 2.5 concentrations ranging from 7.0

– 18 .0 μg/m 3

. New multi

- and single

- city studies further support associations with all

cardiovascular hospital admissions and ED visits at mean 24

- h PM 2.5 concentrations ranging

from 6.7

– 15.3 μg/m 3

. Additional support for associations between short

- term PM 2.5 exposures

and cardiovascular effects comes from a new study of stroke onset (Wellenius et al. ( 2012 ) )

.29 Figure 2

. 6

. Percent increase in cardiovascular

- related hospital admissions and ED visits for a 10 μg/m 3 increase in 24

- h average PM 2.5 concentrations in single

- pollutant models from U.S. and Canadian studies. R ed text and triangles represent recent studies published

since the completion of the 2009 PM ISA. * ED visit studies. ** Median concentration. a = study only presented mean age of participants.

Study

Metzger et al. (2004)
Tolbert et al. (2007)
Zanobetti et al. (2009)*
Ito et al. (2011)
Bell et al. (2008) Slaughter et al. (2005) Kloog et al. (2012)
Kim et al. (2012)

Burnett et al. (1999)
Ito (2003) Metzger et al. (2004)
Dominici et al. (2006) Pope et al. (2006)

Zanobetti et al. (2009)*
Sullivan et al. (2005)
Peters et al. (2001)
Zanobetti & Schwartz (2005)
Stieb et al. (2009)*

Burnett et al. (1999)
Ito (2003) Metzger et al. (2004)* Symons et al. (2006)
Zanobetti et al. (2009)*
Dominici et al. (2006) Haley et al. (2009) Pope et al. (2008)
Stieb et al. (2009)*

Metzger et al. (2004)*
Dominici et al. (2006) Kloog et al. (2012)

Szyszkowicz et al. (2012)* All CVD

IHD

MI

CHF

CBVD

Hypertension Location

Atlanta, GA
Atlanta, GA

26 U.S. Communities

New York, NY

202 U.S. Counties

Spokane, WA New England
Denver, CO

Toronto, CAN
Detroit, MI
Atlanta, GA

204 U.S. Counties Utah Valley, UT

26 U.S. Communities

King County, WA

Boston, MA
Boston, MA

7 Canadian cities

Toronto, CAN
Detroit, MI
Atlanta, GA
Baltimore, MD

26 U.S. Communities

204 U.S. Counties

New York State

Utah

7 Canadian cities

Atlanta, GA

204 U.S. Counties

New England

Edmonton, CAN Age

All

All

65+

40+

65+

All

65+

All

All

65+

All

65+

All

65+

21

- 98

61.6a

65+

All

All

65+

All

All

65+

65+

All

All

All

All

65+

65+

All Lag

0

- 2

0

- 2

0

- 1

0

0

1

0

- 1

0

- 2 DL

0

- 1

1

0

- 3

0

- 2 DL

0

0

- 1

24 h

24 h

0

0

0

- 2

1

0

- 2

2

0

- 1

0

0

- 2

0

- 13 DL

0

0

- 2

0

0

- 1

0

- 3 ◄

◄ ► Mean

17.8

17.1

15.3

14.4

12.9

10.8

9.6

8.0

18.0

18.0

17.8

13.3

10.1

- 11.3

15.3

12.8

12.1

11.1**

6.7

- 9.8

18.0

18.0

17.8

16.0

15.3

13.3

11.1

- 15.5

10.8

6.7

- 9.8

17.8

13.3

9.6

8.5 98 th

---

---

---

--- 34.2

29.6

---

---

---

---

--- 34.8

---

---

--- 28.2

---

---

---

---

---

---

--- 34.8

--- 44.5

---

--- 34.8

---

---

- 4.0

- 2.0 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 16.0 18.0 20.0 22.0 24.0 26.0 28.0 30.0 32.0

% Increase30 2.3. Health Effects Related to Sources or Components of PM

Summary of 2009 PM ISA Conclusions

The 2009 PM ISA evaluated epidemiologic, toxicological, and controlled human exposure

studies that examined health effects associated with ambient PM components and sources. These

studies used a variety of quantitative methods and examined a broad set of PM component s (Section 6.6)

, and found evidence of health effects from sources and components associated with

a number of combustion activities (e.g., motor vehicle emissions, coal combustion, oil burning,

power plants, and wood smoke/vegetative burning), crustal sources, and secondary sulfate. As a result, the ISA concluded that “ the evidence is not yet sufficient to allow differentiation of those

component s or sources that are more closely related to specific health outcomes.” These

conclusions are consistent with those presented in the 2004 PM AQCD where the studies

evaluated found evidence of health effects attributed to a number of source types, including

motor vehicle emissions, coal combustion, oil burning, and vegetative burning.

Recent Studies of Health Effects Related to Sources or Components of PM

Recent studies have continued to examine whether specific PM component s or sources are more closely related to specific health outcomes

. For the purposes of this provisional assessment of

new literature published since the release of the 2009 PM ISA, emphasis has been placed on

studies that investigated the health effects related to PM sources or comparisons of various PM

components. To highlight the scientific content of the recent literature while focusing on key PM
study categories, this section focuses on results of studies that evaluated the effects of a range of

sources or components. Thus, the discussion includes: (1) recent epidemiologic studies using

source apportionment; (2) epidemiologic evidence on effects with PM components; and (3)

results of new toxicolog ical studies using source apportionment with exposures to concentrated

ambient particles (CAPs) to provide insight into potential effects related to PM from different

sources, and comparative toxicology studies using fine PM c omponents

. In addition, numerous epidemiologic and/or toxicology studies have reported effects of several ultrafine PM as

discussed in the 2009 PM ISA. Specific findings for ultrafine PM are not discussed in detail;

instead, the available new studies ar e included in the reference list : http://hero.epa.gov/pm

.

2.3.1. Epidemiologic Studies Using Source Apportionment

Lall et al. ( 2011 ) examined the association between source

- specific daily PM 2.5 mass and

component data and hospital admissions in New York City for the years 2001

- 2002. The use of
daily data allowed for the examination of both single

- day lags and a distributed lag. Source
categories identified through positive matrix factorization included long

- range transported

sulfates, traffic, residual oil, steel metal works dust, and soil

. In single

- day lag models, total
respiratory hospital admissions were positively associated with residual oil at lag 2, but the

strongest associations were with steel metal works dust at lag 0 and 3. For cardiovascular
hospital admissions the strongest association s w ere observed with traffic at lag 0 and residual oil

at lag 3. When examining associations between cause

- specific cardiovascular and the traffic31 source category, the strongest associations were observed at lag 0 for total cardiovascular, heart

failure, and stroke. For associations between cause

- specific respiratory hospital admissions and

the steel source category, pneumonia was associated with steel metal works dust at lag 3, while

asthma was observed to have the largest magnitude of an association across all lags. The

distributed lag model demonstrated a stronger association between traffic and cardiovascular
hospital admissions and steel metal works dust and respiratory hospital admissions than the
single

- day lag models, indicating that single

- day lags may underestimate the magnitude of

associations. Finally, a sensitivity analysis using key tracers of each source (i.e., elemental

carbon for traffic and manganese for steel metal works) found similar patterns of associations as

the source

- specific analyses.

2.3.2. Epidemiologic Studies on Effects of Fine PM Components and Sources

In addition to examining the association between short

- term PM 2.5 exposures and mortality or hospital admissions and ED visits a number of studies also attempted to identify if an individual

PM component or group of PM components could explain the observed association. The
following section describes the results from these studies some of which have been

aforementioned

.

Short

- term exposure to PM 2.5 components and sources and m ortality

In addition to examining the association between short

- term exposure to PM 2.5 and mortality, a

few single

- city studies also examined the effect of individual PM 2.5 components on mortality. Ito

et al. ( 2011a ) focused on key PM components (i.e., elemental carbon [ EC ]

, organic carbon [ OC ]

, sulfate [ SO 4 ]

, nickel [ Ni ]

, vanadium [ V ]

, zinc [ Zn ]

, silicon [ Si ]

, selenium [ Se ]

, sodium [ Na ]

, and

bromine [ Br ] ) identified in previous source apportionment studies conducted in NYC. In all

- year analyses, the strongest associations were observed at lag 1 for EC, OC, SO 4 , Si, Se, and Br. In

the warm season, strong associations were observed for secondary aerosols including OC and

SO 4 , Se, which is associated with transported coal emissions, EC, and Br. In the cold season, the

components associated with residual oil burning, Ni, V, and Zn, all showed a similar pattern of

associations, with the strongest effects at lag 3. Overall, the components representing regional

transport showed a seasonal pattern of associations similar to those found with PM 2.5 mass, while

associations were found throughout the year with EC and NO 2

.

Zhou et al. ( 2011 ) examined the association between PM components with all

- cause, cardiovascular, and respiratory mortality in seasonal analyses in Seattle and Detroit

. The

components selected for analysis represent the major emissions sources of the two cities: soil

( aluminium [ Al ] and Si), smelter effluents ( iron [ Fe ] and Zn), residual oil burning (Ni and V),

coal burning ( sulfur [ S ] ), traffic (EC), sea salt (Na), and wood burning ( potassium [ K ] ). Daily

component data was available in both cities, which allowed for the examination of a 0

- 2 day

distributed lag

. In Detroit, S was associated with all

- cause and cardiovascular mortality and S

and Ni were moderately associated with respiratory mortality in the warm season. No

components were positively associated with any mortality outcome in the cold season in Detroit.32 In Seattle, in the warm season no component was significantly associat ed with any mortality

outcome, but Fe, K, and EC were positively associated with respiratory mortality. In the cold

season, Al, K, Si, Zn, and EC were strongly associated with all

- cause mortality, with the same
components, minus Al, strongly associated with cardiovascular mortality. No components were

associated with respiratory m ortality in Seattle in the cold season. Overall, in Detroit the

components associated with mortality are indicative of coal burning while in Seattle the

components associated with mortality represent cold

- season traffic and combustion sources, such

as residual oil and wood burning.

In the study conducted by Klemm et al. ( 2011 ) in Atlanta, daily concentrations of the PM

components EC, OC, nitrate [ NO 3 ]

, and SO 4 were also available for the entire study duration.

The authors found that EC, OC, and NO 3 were positively associated with nonaccidental mortality

at lag 0

- 1 in individuals 65 years of age and older, with the strongest association for NO 3

. In
analyses of cause

- specific mortality, a similar pattern of associations was observed for

cardiovascular and respiratory mortality. SO 4 was not found to be associated with any of the
mortality outcomes examined.

Respiratory

- related Hospital Admissions and ED Visits

Recent multicity studies were identified that examined the effect of PM components on the
relationship between short

- term PM exposure and respiratory

- related ED visits and hospital

admissions. Zanobetti et al. ( 2009 ) conducted a second

- stage analysis, using the same methodology as Franklin et al. ( 2008 ) (2009 PM ISA; p. 6

- 193

- 195) and examined whether

season and community

- specific long

- term mean seasonal concentration ratios of PM components

to PM 2.5 total mass modified the association between short

- term PM 2.5 concentrations and
respiratory ED visits. Of the components examined only Na + and Ni were found to modify the

association between PM 2.5 and respiratory ED visits

. Using a different approac h

, Levy et al.

( 2012 ) attempted to identify if some PM components are more toxic than others by focusing on

the four components that dominate PM 2.5 mass and are highly correlated with PM 2.5 (i.e., EC,

OC, SO 4 , and NO 3 ). In a time

- series analysis using Medicare data from 119 U.S. counties the

authors examined the association between each component and respiratory hospital admissions

across the U.S. and regionally (i.e., East and West). Of the components examined, only EC and

OC were positively associated with respiratory hospital admissions.

A few single

- city studies were also identified that examined associations between respiratory

related ED visits and hospital admissions and individual PM components. Strickland et al. ( 2010 )

focused on the PM components SO 4 , EC, OC, and water

- soluble metals. For each component positive associations were observed with pediatric asthma ED visits in all

- year analyses. The

strongest associations were observed in the warm season with the magnitude being similar across
components. In addition, analyses including copollutant adjustment were conducted using warm

season data. Risk estimates for PM 2.5 , EC, and SO 4 were attenuated, but remained positive when
including O 3 in the model. In LOESS C

- R analyses, there was evidence of a positive C

- R
relationship for each component. Kim et al. ( 2011 ) examined the lag structure of associations33 between the PM components EC, OC, SO 4 , and NO 3 and respiratory hospital admissions. The

authors focused on these components because they comprise the majority of PM 2.5 mass in

Denver. Consistent with the PM 2.5 results, there was no evidence of an association with COPD or pneumonia and any of the components. For both all respiratory and asthma hospital admissions

there was evidence of greater effects with EC and OC compared to SO 4 and NO 3 , and additional

evidence for delayed effects occurring 2 to 5 days after exposure.

Cardiovascular

- related Hospital Admissions and ED Visits

The 2009 PM ISA included multicity analyses of the effect of PM 2.5 components on

cardiovascular hospital admissions that reported associations between oil combustion and traffic

related PM 2.5 and CVD hospitalizations

.

Two recent studies investigated the association of PM 2.5 components with cardiovascular
hospital admissions. Using Medicare data from 26 US communities, Zanobetti et al. ( 2009 )

examined the modification of the associations of PM 2.5 with CVD, MI and CHF hospital

admissions by season

- and community

- specific PM 2.5 composition. Authors estimated the

relative contribution of specific components (EC, OC, SO 4 , NO 3 , Na, Ni, V, Zn, Si, Se, Br) by
computing concentration ratios (i.e. component species as a proportion of PM 2.5 mass). In the

second stage of a hierarchical model, season

- and community

- specific estimates of the

association between PM 2.5 and CVD hospitalizations were regressed on the concentration ratios.

The association of PM 2.5 with all CVD hospitalizations was significantly modified when the
proportion of Br, Na +

, Ni, V and Al in PM 2.5 was high. The association of PM 2.5 with all MI
hospitalizations was significantly modified when the proportion of arsenic [ As ]

, chromium [ Cr ]

,
manganese [ Mn ]

, OC, Ni, K and Na + was high. Additional increases in CVD hospitalizations per interquartile range (IQR) increase in the proportion of the component ranged from 0.53% to

0.9% (larger, less precise increases were reported for MI)

. None of the components significantly

modified the association of PM 2.5 with CHF admissions (i. e. p

- value > 0.05). Ito et al. ( 2011b )

conducted a time series analysis of the lag structure and seasonal patterns in the association

between emergency hospitalization for CVD and PM 2.5 chemical components. Same day

concentration of most components examined was associated with CVD hospitalizations (EC,

OC, SO 4 , NO 3 , Na, Ni, V, Zn, Se, and Br)

. The association and lag structure of EC with CVD
hospitalization was constant across season; associations of OC, SO 4 , Ni, Zn, Si, Se and Br with

CVD hospitalizations were strongest in the cold season

.

An additional study ( Mostofsky et al., 2012 ) examined different approaches to modeling the

association between PM components and health outcomes using ischemic stroke onset as an example. The authors used three different models that included parameters for the following: (1)

component concentration, (2) component concentration adjusted for total PM 2.5 mass, which

accounts for total PM 2.5 mass, and (3) component residuals, which eliminates confounding by

total PM 2.5 mass. In model 1

, positive associations were observed for a number of components including Al, cal cium [Ca], Br, lead [Pb], Se, titanium [Ti]

, and Fe with the strongest

associations for V, S, Ni, and black carbon [ BC ]

. Models 2 and 3 resulted in relatively few34 components with positive associations, but the pattern of associations across pollutants was

consistent between the two models with the strongest associations for V, Ni, and BC.

Long

- term exposure to PM 2.5 components and mortality

Ostro et al. ( 2010 ) also examined the association between long

- term exposures to PM 2.5 components (i.e., EC, OC, SO 4 , NO 3 , Fe, K, Si, Zn) and all

- cause mortality among the subjects

from the California Teachers Study

. No associations were observed between all

- cause mortality

and any PM 2.5 component. In analyses of cause

- sp ecific mortality, Ostro et al. ( 2010 ) observed

an association between long

- term exposure to several PM 2.5 components and mortality from

CPD, IHD and pulmonary disease

. The authors observed positive associations of CPD and IHD
mortality with each of the measured components, and between pulmonary mortality and SO 4 and

NO 3

. Of the components analyzed, there were positive associations with nitrate, sulfate and

silicon for CPD mortality and all of the components were associated with mortality from IHD

(See Table 2.2 )

.

Table 2

. 2

. Association between mortality outcomes and PM 2.5 components using a 30

- km buffer (n=43,220) (adapted from Ostro et al. ( 2011 ) )

Component (IQR, μg/m 3 ) All

- Cause* CPD* IHD* Pulmonary*

EC (0.65) 1.02 (0.93, 1.12) 1.07 (0.94, 1.22) 1.46 (1.17, 1.83) 0.88 (0.68, 1.15)

OC (0.84) 1.00 (0.95, 1.04) 1.04 (0.98, 1.11) 1.13 (1.01, 1.25) 0.95 (0.84, 1.06)

SO 4 (2.2) 1.06 (0.97, 1.16) 1.14 (1.01, 1.29) 1.48 (1.20, 1.82) 1.04 (0.82, 1.31)

NO 3 (3.2) 1.03 (0.98, 1.09) 1.11 (1.03, 1.19) 1.27 (1.12, 1.43) 1.04 (0.90, 1.20)

Fe (0.13) 1.01 (0.93, 1.11) 1.05 (0.93, 1.19) 1.39 (1.13, 1.72) 0.88 (0.69, 1.13)

K (0.07) 1.01 (0.94, 1.08) 1.06 (0.97, 1.17) 1.27 (1.07, 1.49) 0.90 (0.74, 1.09)

Si (0.03) 1.02 (0.99, 1.06) 1.05 (1.00, 1.10) 1.11 (1.02, 1.20) 0.98 (0.89, 1.08)

Zn (0.01) 1.03 (0.96, 1.11) 1.09 (0.98, 1.20) 1.33 (1.12, 1.58) 0.97 (0.79, 1.18)

*Hazard ratio and 95% confidence interval for an increase in PM 2.5 components equal to the interquartile range (IQR)

Long

- term exposure to PM 2.5 components and sources and morbidity

In a study conducted in New York City, Patel et al. ( 2009 ) examined long

- term exposure to

PM 2.5 components (Ni, V, Zn, EC) and respiratory symptoms in children through 24 months of

age

. Positive associations were observed between Ni and wheeze, but not cough

. No other

associations were observed between the other metals or EC and either wheeze or cough

. PM 2.5

mass w as not associated with wheeze and/or cough (see Section 2.1.3 for results on PM 2.5 mass ).

Several recent studies have examined the association between exposure to PM 2.5 components and

sources and birth outcomes, including birth weight and preterm birth

. Studies examining birth
weight and PM 2.5 components and sources found the strongest associati ons with metals/oil

combustion ( Bell et al., 2012 ; Darrow et al., 2011b ; Bell et al., 2010 ) and elemental35 carbon/motor vehicles ( Wilhelm et al., 2012 ; Darr ow et al., 2011b ; Bell et al., 2010 )

. Similarly,

when evaluating PM 2.5 components and preterm birth, the associations with metals, EC

, OC and

ammon ium nitrate were strongest ( Wilhelm et al., 2011 ; Darrow et al., 2009 )

. Several PM 2.5

sources were associated with preterm birth, including biom ass burning and diesel traffic

( Wilhelm et al., 2011 )

.

2.3.3. Toxicology Studies

– Source Apportionment and Fine PM Components

The 2009 PM ISA examined health effects associated with exposure to ambient PM components

and sources in animals. In vivo and in vitro studies reported a variety of sources and components

were linked with cardiopulmonary effects; however, there was insufficient evidence overall to

determine which sources or components were most closely related to the observed effects. Since

the completion of the 2009 PM ISA, a small number of animal toxicology studies have continued

to assess the role of PM sources and components on effects observed after exposure to PM 2.5

.

2.3.3.1. Toxicology Studies Comparing Ambient Fine PM Sources and

Components

Toxicology studies employing CAPs offer a relevant surrogate for atmospheric PM. Table 2.3

shows the endpoints that were associated with various source categories from rodents exposed to

CAPs from four locations. These three studies compare electrocardiogram ( ECG ) responses during CAPs inhalation to PM 2.5 components associated with source factors ( Kamal et al., 2011 ; Rohr et al., 2011 ; Chen et al., 2010 )

.

Chen et al. ( 2010 ) compared subchronic CAPs inhalation exposures from two locations in New

York, Sterling Forest (SF; undeveloped woodland park) and Manhattan in male hyperlipidemic

mice

. Using Manhattan CAPs ( mean CAPs concentration

, 122.9 ± 81.1 μg/m 3 )

, heart rate ( HR )

decreased with increased current day CAPs mass at all lags and several measures of heart rate variability ( HRV ) increased with increased CAPs mass (i.e., standard deviation of the normal

- to

normal intervals, SDNN; root mean square of the standard deviation of the normal

- to

- normal

intervals

, r MSSD; and frequency domain indices, high

- frequency

, HF, low

- frequency

, LF, and

LF/HF ratio)

. Using SF CAPs ( mean CAPs concentration

, 133.3 ± 110.5 μg/m 3 )

, CAPs mass was positively associated with HR, whereas HRV decreased with increased CAPs

. Using Manhattan

CAPs

, ECG changes were associated with components related to residual oil combustion > long

range transport > traffic > iron/steel > incineration > soil. Using SF CAPs

, ECG changes were

associated with long

- range transport > Ni refinery > soil > residual oil combustion/traffic. Chen

et al. ( 2010 ) also performed single

- element analysis and note that EC did not account for the

acute ECG changes associated with PM 2.5 and that Ni may have an effect in Manhattan but not

SF.

Rohr et al. ( 2011 ) reported altered ECG responses in spontaneously hypertensive rats following

CAPs inhalation exposures from Detroit, Michigan over 13 consecutive days in both the summer

and winter. Source factors were identified using positive matrix factorization. In summer ( time
weighted average CAPs concentration

, 518 μg/m 3 )

, decreased HRV (SDNN) was associated with36 cement/lime, iron/steel, and gasoline/diesel factors, and less so with sludge incineration. In

winter ( time weighted average CAPs concentration

, 357 μg/m 3 ) ; decreased HR was associated

with sludge incineration, cement/lime, and coal/secondary sulfate factors.

Kamal et al. ( 2011 ) also identified source factors (via positive matrix factorization) associated

with ECG alterations in hypertensive rats exposed for 13 days to CAPs (from Steubenville, OH ;

mean CAPs concentration 406 ± 266 μg/m 3 ). S tatistically s ignificant associations were found

between acute cardiac responses and PM components linked with incineration, metal processing,

mobile sources, and iron/steel production. The strength of the association with each source was dependent upon wind direction; however, incineration was consistently found to be associated

with changes in HR and HRV. Several individual CAPs components were also associated with

cardiovascular responses, S, SO 2 , Pb, and oxides of nitrogen ( NO

x )

.

Table 2

. 3

. CAPs Sources and Associated Endpoints

Source Category Elemental Loading Endpoint

Affected Location Exposure

Duration References

Metal processing V, Cr, Ti, Mo, La, Ce ↑ HR

↓ SDNN Steubenville, OH 13 days (s) Kamal et al. ( 2011 )

Incineration
(including sludge) Zn, Cd ↓ HR

↓ SDNN Steubenville, OH 13 days (s) Kamal et al. ( 201 1 )

Zn, Ba, Mn, Sr, Sb ↓ HR (w)

↓ SDNN (s) Detroit, MI 13 days (s & w) Rohr et al. ( 2011 )

Zn, Pb, Cu,

Fe ECG alterations Manhattan, NY 6 months Chen et al. ( 2010 )

Pb Pb, Cu ↓ HR Detroit, MI 13 days (s & w) Rohr et al. ( 2011 )

Iron/Steel manufacturing Fe, Mn, Cu, EC, Pb ↓ HR

↑ rMSSD Steubenville, OH 13 days (s) Kamal et al. ( 2011 )

Mn, Fe ECG alterations Manhattan, NY 6 months Chen et al. ( 2010 )

Fe, Mn, Cu ↑ rMSSD (w)

↓ SDNN (s) Detroit, MI 13 days (s & w) Rohr et al. ( 2011 )

Mobile/Traffic Fe, Sb, As, K, CO ↓ SDNN

↑ rMSSD Steubenville, OH 13 days (s) Kamal et al. ( 2011 )

Fe, Ti, Zn ↓ SDNN (s)

↑ rMSSD (w) Detroit, MI 13 days (s & w) Rohr et al. ( 2011 )

EC, NO 2 , Si, Fe, Cu ECG alterations Manhattan, NY 6 months Chen et al. ( 2010 )

Coal and Secondary
Sulfate S, Se, Al, V,

P ↓ HR

↑ rMSSD Steubenville, OH 13 days (s) Kamal et al. ( 2011 )

S, Se ↓ HR (w)

↑ rMSSD (w) Detroit, MI 13 days (s & w) Rohr et al. ( 2011 )

Oil refinery La, Ce ↑ HR (w) Detroit, MI 13 days (s & w) Rohr et al. ( 2011 )

Cement/lime processing Ca, Sr, Mg ↓ HR (w)

↓ SDNN (s) Detroit, MI 13 days (s & w) Rohr et al. ( 2011 )37 Source Category Elemental Loading Endpoint

Affected Location Exposure

Duration References

Residual oil

combustion V, Ni, EC,

Fe ECG alterations Manhattan, NY 6 months Chen et al. ( 2010 )

Ni

- refinery Cr, Ni ECG alterations Sterling Forest,

NY 6 months Chen et al. ( 2010 )

Soil Al, Si, Ca,

Fe ECG alterations Sterling Forest,

NY

Manhattan, NY 6 months Chen et al. ( 2010 )

Long range transport S, Se, Br ECG alterations Sterling Forest,

NY

Manhattan, NY 6 months Chen et al. ( 2010 )

(w) winter season, (s) summer season, HR: heart rate, SDNN: standard deviation of the normal

- to

- normal intervals, rMSSD: root mean square of the standard deviation of the normal

- to

- normal intervals, Mo: molybdenum, La: lanthanum, Ce: cerium, Cd: cadmium, Ba: barium, Sr: str ontium, Sb: antimony, Cu: copper, CO: carbon monoxide, P: phosphorus

Other studies have used regression and correlation approaches to estimate the relationship

between various PM components and sources with health effects. Happo et al. ( 2010b )
intratracheally instilled mice (10 mg/kg) with size

- segregated ambient PM samples collected in

six European cities over various seasons: Duisberg autumn, Prague winter, Amsterdam winter,

Helsinki spring, Barcelona spring, Athens summer. PM exposure (PM 10

- 2.5 and PM 2.5

- 0.2 )

increased bronc h oalveolar lavage fluid ( BALF ) total cell number and BALF protein

concentration. No formal source apportionment was conducted, but o xidized organic compounds
(e.g., dicarboxylic acids)

, transition metals (e.g., Fe and Cr), and source tracers for fuel oil

combustion ( i.e., Ni and V) were the most strongly correlated components of PM 2.5

- 0.2 contributing to the inflammatory response (i.e., BALF total cell number)

. These studies

measured response to PM 10

- 2.5 and PM 2.5

- 0.2 PM samples, and generally report stronger inflammatory responses (e.g., BALF cytokines, cell number, and total protein) after exposure to

coarse PM compared to fine. Source tracers for soil (K +

, magnesium [ Mg 2+ ], Cu, manganese [ Mn ]

, Fe) and sea spray (Na +

, chlorine [ Cl - ], and NO 3 - ) found in PM 10

- 2.5 were the most strongly

correlated with inflammatory response.

A few studies discuss how seasonal variation in PM components may affect PM

- induced health

effects. Happo et al. ( 2010a ) intratracheally instilled mice (10 mg/kg) with size

- fractionated

ambient PM collected in Helsinki in the winter, spring, summer, and autumn. PM collected in the
spring produced the highest relative inflammatory activity (i.e., total cell number, total protein,

tissue necrosis factor alpha [ TNF

- α ]

, interleukin

- 6 [ IL

- 6 ]

, and keratinocyte

- derived chemokine in

BALF) when dose was adjusted to the PM per cubic meter of urban air, whereas the PM

collected in the autumn produced the highest inflammation per equal mass do s e

. This difference

was influenced by a greater PM mass concentration in urban air in the springtime. The overall
inflammatory activity of PM decreased with particle size, such that PM 10

- 2.5 and PM 2.5

- 1 had a higher potency than PM 1

- 0.2 and PM 0.2

. Components of road dust (Ca 2+

, Fe, Mn, and Al) and

trace metals (presumed to be the result of non

- exhaust PM from traffic; Cu, Chromium [ Cr ]

, cobalt [ Co ] ) were consistently correlated with BALF inflammatory response in PM 2.5

- 1

. Resuspension of road dust was also strongly correlated with inflammatory responses to PM 10

- 2.5

.38 Farina et al. ( 2011 ) treated mice (100 μg, intratracheal aerosolization) with size

- fractionated

ambient PM collected from Milano, Italy in summer and winter. A stronger inflammatory
activity was generally observed after administration of summer PM 10 and PM 2.5 than winter PM

. PM 10 exposure resulted in a higher TNF

- α concentration (in BALF) compared to PM 2.5 , and this

was attributed to the greater endotoxin concentration and bacteria content of PM 10

.

Additional studies assess ed the differential responses of PM collected at different distances from

a highway. Cho et al. ( 2009 ) found similar composition in size

- fractionated ambient PM

collected near (20 m) and far (275 m) from a road in Raleigh, NC ; however, PM collected near

road was enriched with metals and a greater concentration of endotoxin

. Coarse PM samples

, but

not fine PM samples, produced pulmonary inflammation (i.e., BALF

, macrophage inflammatory
protein 2 [ MIP

- 2 ]

, TNF

- α, IL

- 6) in exposed mice (25 and 100 μg) irrespective of distance

collected from the road. Zhang et al. ( 2011 ) reported greater increase s in protein and lactate
dehydrogenase [ LDH ] in BALF after instillation (7.5 mg/kg) of PM 2.5 collected near traffic
compared to far from traffic in Beijing, China. Chemical analysis of the near

- traffic PM revealed
higher concentrations of polycyclic aromatic hydrocarbons [ PAHs ] and heavy metal elements

( arsenic [ As ]

, Cd, Zn, S)

, but no statistical correlations were computed between these

components and the health effects observed

.

A number of studies have attempted to disentangle the role of PM and gaseous components in

the health effects associated with ambient air pollution exposure by removing PM from the

mixture using a high efficiency particle filter

. A few recent studies report cardiovascular,
respiratory, and reproductive effects after exposure to unfiltered (the whole mixture)

, but not

filtered Sao Paulo urban air (20 m from road) ( Pires et al., 2011 ; Matsumoto et al., 2010 ; Akinaga e t al., 2009 )

. These studies suggest that PM but not the gase ous components of the

urban air play a role in these responses.

2.3.3.2. Toxicology Studies Comparing Source

- Derived PM and Components

A number of studies attempt ed to characterize effects from ambient PM sources by exposing

animals in the laboratory to PM derived from potential ambient sources (e.g., coal combustion

, diesel )

.

A series of studies evaluated the health effects resulting from various coal

- fired power plant

emissions scenarios ( Diaz et al., 2011 ; Godleski et al., 2011a ; Godleski et al., 2011c ; Godleski et

al., 2011b ; Lemos et al., 2011 ; Wellenius et al., 2011 )

. Stac k emissions were collected from three

coal

- fired power plants and various atmospheric transformations (e.g., oxidation, reaction with α

pinene, neutralization) were simulated to investigate the toxicity of primary and photochemically
aged ( secondary ) particles. Particle mass concentrations varied from 43.8 to 257.1 μg/m 3 ( Kang

et al., 2011 )

. Rats were exposed to these simulated emissions scenarios for 6 hours and

demonstrated ( 1) increased BAL F total cells, macrophages, and neutrophils ( Godleski et al.,

2011a ) ; ( 2 ) moderately i ncreased heart and lung reactive oxygen species (measured by in vivo

chemilumi n escence) ( Lemos et al., 2011 )

, 3 ) i ncreased premature ventricular beat frequency

, but39 no change in heart rate, HRV, or ECG intervals ( Wellenius et al., 2011 ) ; and 4 ) breathing pattern changes ( Diaz et al., 2011 )

. Overall, specific PM components did not predict respiratory or

cardiovascular effects observed after PM exposure as well as simulated atmospheric

transformation scenarios.

Additionally, a few studies assessed respiratory, cardiovascular, and systemic effects following

exposure to filtered and unfiltered simulated downwind coal combustion emissions ( Barrett et

al., 2011 ; Mauderly et al., 2011 )

. Barrett et al. ( 2011 ) reported different respiratory effects after

exposure to filtered and unfiltered emissions. Mauderly et al. ( 2011 ) found 17 out of 270 species

gender

- time

- outcome comparisons were affected by whole emissions and that PM participated in
only 3 responses (liver weight, serum K +

, and MIP

- 2). The authors concluded that PM

contributed to a few of the effects but that the pollutants responsible for the effects observed

were not able to be identified.

Studies have also evaluated the role of PM in engine emissions on the progression of health

effects

. Tzamkiozis et al. ( 2010 ) instilled mice with PM collected from a gasoline Euro 3 car, a

diesel Euro 2 car, and a diesel Euro 4 car (with a diesel particle filter). Significant pulmonary

inflammation (i.e., BALF polymorphonuclear leukocytes ( PMN ) number) and injury (i.e., BALF
protein concentration) occurred 24 hours after treatment. The strongest associations with these

effects were observed for the PM components, P, Mn, Fe, Pb, reactive oxygen species ( ROS )

, benz( a )anthracene, chrysene, and medium and heavy PAHs. A strong association was also

observed between pulmonary injury and S.

A number of studies evaluated the impact of inhaled diesel exhaust on the cardiovascular system

with and without filtration ( Gordon et al., 2012 ; Lamb et al., 2012 ; Seilkop et al., 2012 ; Campen

et al., 2010 )

. Different cardiovascul ar effects were reported after filtration of diesel exhaust by

Gordon et al. ( 2012 ) and Lamb et al. ( 2012 )

. Campen et al. ( 2010 ) found that filtration of PM

from diesel exhaust did not alter the vascular responses observed. Seilkop et al. ( 2012 ) ranked

components of diesel or gasoline exhaust, wood smoke, or simulated “downwind” coal emissions
by their ability to induce pro

- atherosclerotic responses in the aorta of mice that inhaled these
pollutant mixtures 6 hours/day for 50 days. Filtration of PM did not have a large effect on the

responses measured. Gases (i.e., SO 2 , ammonia ( NH 3 ), NO 2 , CO) ) were found to be most highly
predictive of the response indicators. These studies using filtration of PM from whole mixtures did not consistently identify whether PM or gases from whole air pollution mixtures led to the cardiovascular,
respiratory, or reproductive effects observed.

Summary

The few epidemiologic studies that have been conducted since the completion of the 2009 PM

ISA continue to report health effects with a number of sources and components. Toxicological

studies have attempted to identify whether particular sources or components are responsible for

the health effects observed by comparing the health effects, primarily cardiopulmonary effects,

observed in response to exposures to ambient fine PM sources and components and source

derived PM and components. However, the toxicology studies did not find consistent evidence40 that one source or component is most closely related to a specific health effect. Collectively these

studies continue to report that a variety of sources and components are linked with
cardiopulmonary effects and mortality; however, there is still insufficient evidence to determine

which sources or components are most closely related to the observed effects.

3. SUMMARY AND CONCLUSIONS

The new studies published since the completion of the 2009 PM ISA provide additional evidence
indicating a relationship between exposure to ambient PM and health effects. The new studies
provide important insights on the health effects of PM exposure, with the results continuing to

support a relationship between PM exposure and health effects at ambient concentrations similar

or lower than those observed in previous studies. Overall : (a) the new studies generally
strengthen the evidence that acute and chronic exposures to fine PM ; (b) although limited in

number, coarse PM studies provide evidence of an association with short

- exposures and pediatric

asthma ED visits, but no association between long

- term exposure and mortality ; ( c ) some of the

new epidemiologic studies report effects in areas with long

- term mean or mean 24

- h avg PM 2.5 concentrations lower than that reported in the 2009 PM ISA ; and ( d ) new toxicology and
epidemiologic studies continue to link various health outcomes with a range of fine PM sources

and components. In conclusion, the results of the new studies identified and described in this
provisional assessment does not materially change any of the broad scientific conclusions
regarding the health effects of PM exposure made in the 2009 PM ISA

.

In summary, this provisional assessment found:

Long

- term PM Exposure

• Mortality : Generally, the results of recent studies are consistent with the evidence for an

association between long

- term exposure to PM 2.5 and mortality (i.e., all

- cause and

cardiovascular) within the range of long

- term mean PM 2.5 concentrations characterized in the

2009 PM ISA (i.e., 13.2

– 32.0 μg/m 3 )

, with one new Canadian multi

- city study showing

associations at concentrations below 10 μg/m 3

. New studies provide additional evidence for
respiratory mortality, including lung cancer. T wo recent studies that examined associations

between long

- term PM 10

- 2.5 exposure and mortality do not observe an association in either

men or women.

• Cardiovascular morbidity: Recent studies continue to demonstrate the strongest

cardiovascular effects in women, specifically for stroke, incident MI, and incident
hypertension at long

- term mean PM 2.5 concentrations ranging from 9.7

– 21.5 μg/m 3

.

• Respiratory morbidity: R ecent studies provide additional evidence for respiratory

symptoms and incident asthma, as well as respiratory hospitalizations at long

- term mean

PM 2.5 concentrations ranging from 9.7

– 27.0 μg/m 3

, which is consistent with the conclusions

of the 2009 PM ISA.41 • Reproductive and Developmental Outcomes: Recent studies continue to provide evidence

for developmental outcomes, specifically reductions in birth weight

, at long

- term mean PM 2.5 concentrations ranging from 11.0

– 19.8 μg/m 3

, which further support the conclusions of the

2009 PM ISA

.

Short

- Term PM Exposure

• Mortality: The limited number of mortality studies conducted in the U.S. and Canada

further support the conclusions of the 2009 PM ISA and continue to demonstrate associations

between short

- term PM 2.5 exposure and mortality at mean 24

- h average concentrations

greater than 12.8 μg/m 3

. Since the completion of the 2009 PM ISA no new studies have been

conducted that examined associations between short

- term exposure to PM 10

- 2.5 and mortality.

• Respiratory hospital admissions/ED visits : New m ulti

- city and single

- city studies

demonstrate consistent positive associations for all respiratory

- related hospital

admi ssions/ ED visits, and provide additional evidence for increase s in asthma hospital

admissions/ ED visits in areas with mean 24

- h average PM 2.5 concentrations ranging from 6.7

– 22.0 μg/m 3

, which further supports the conclusions of the 2009 PM ISA

. O ne new study

was identified that examined the association between short

- term PM 10

- 2.5 exposure and
respiratory

- related ED visits

, and provided evidence of increases in pediatric asthma ED

visits.

• C ardio vascular hospital admissions/ED visits: New studies focusing primarily on all

cardiovascular hospital admissions/ED visits continue to demonstrate consistent positive

associations in areas with mean 24

- h average PM 2.5 concentrations ranging from 6.7

– 15.3
μg/m 3

. Additionally, there is new evidence for potential associations with hypertension ED

visits, and a new study demonstrating an association with stroke onset.

Health Effects Related to Sources or Components of PM

• Consistent with those studies evaluated in the 2009 PM ISA, new studies continue to

demonstrate cardiovascular and mortality effects with sources and components related to a

number of combustion activities (e.g., motor vehicle emissions, coal combustion, oil burning,

power plants, and wood smoke/vegetative burning)

, crustal sources, and secondary sulfate

. Additional new studies also add to the limited number of studies that have examined

associations between sources and components and respiratory and birth outcome effects, as

well as, long

- term exposure and mortality. Overall, new studies support the conclusions of

the 2009 PM ISA that many PM components can be linked with differing health effects and

the evidence is not yet sufficient to allow differentiation of those components or sources that

are more closely related to specific health outcomes.42 APPENDIX A. Studies Included in the PM Provisional Science Assessment

Table A. 1

. Characterization of Studies of Long

- term Exposure to PM 2.5 and Mortality

Author Years

of Study Location Outcome Population Size

Fraction Long

- term
Mean
Concen

tration (μg/m 3 ) Upper

Percentile
Concen

trations (μg/m 3 )

Crouse

et al. ( 2012 ) 1991

- 2001 Canada (nationwide ) All

- Cause, CVD, IHD Mortality Nonimmigrant
Canadian

adults PM 2.5 8.7 Max: 19.2

Gan et
al. ( 2011 ) AQ:

1994

- 1 998;

Death

s: 1999

- 2002 Vancouver,
BC
Canada CHD Mortality Adults (45

- 85)

without known
CHD at
baseline PM 2.5 4.08 Max: 10.24

Greven

et al. ( 2011 ) 2000

- 2006 U.S. (nationwide ) All

- Cause Medicare recipients (65+ yrs) PM 2.5 13.0 75 th : 14.7

Hart et
al. ( 2010 ) AQ:

2000

Death

s: 1985

- 2000 U.S. (nation

wide) All

- Cause, Lung Cancer,
CVD Disease, IHD, Respiratory Disease,
COPD Mortality Adult males

from 4 U.S. trucking companies PM 2.5 14.1 NR

Jerrett

et al. ( 2009b ) 1992

- 2002 Toronto,
Canada All

- Cause, Circulatory Mortality Adults from respiratory

clinic PM 2.5 8.71 75 th : 8.83

Jerrett

et al. ( 2009a ) AQ:

1999

- 2000

Death

s: 1982

- 2000 U.S. (nation

wide; 86 MSAs) All

- Cause, Cardiopulmona

ry, CVD, IHD, Respiratory Adults

PM 2.5 14.3 NR

Lepeule

et al. ( 2012 ) 1974

- 2009 U.S (6

cities in

East and Midwest) All Cause, CVD

and Lung
Cancer Mortality Adults

PM 2.5 15.9 (six

cities combined);

means for

individual

cities ranged

from 11.4

- 23.6 NR

Lipsett

et al. ( 2011 ) AQ:

1999

- 2005;

Death

s: 1995

- 2005 California All

- Cause, CVD, Respiratory, Lung Cancer, IHD, CB D Adults (Female teachers)

PM 2.5 15.64 Max: 28.3543 Author Years

of Study Location Outcome Population Size

Fraction Long

- term
Mean
Concen

tration (μg/m 3 ) Upper

Percentile
Concen

trations (μg/m 3 )

McKean

- Cowden

et al. ( 2009 ) AQ:

1979

- 1983;

1999

- 2000;

Death

s: 1982

- 2000 U.S. (nation

wide) Brain Cancer Mortality Adults

PM 2.5 1979

- 1983:

21.1

1999

- 2000:

14.0

Avg: 17.7 Max:

1979

- 1983:

30.0

1999

- 2000:

22.2

Avg: 23.6

Ostro et
al. ( 2010 ) AQ:

2002

- 2007 California All

- Cause, CPD, IHD Mortality Adults

(Female teachers) PM 2.5 and

componen
ts (EC, OC, SO 4 , NO 3 , Fe, K, Si, Zn) 17.0 Max: 34.7

Puett et
al. ( 2009 ) 1992

- 2002 U.S. (Eas t
and Midwest) All Cause and
CHD Mortality Adults (Femal e Nurses) PM 2.5 13.9 75 th: 15.6

Max: 27.6

Puett et
al. ( 2011 ) 1986

- 2002 U.S. (East

and Midwest) All Cause and
CHD Mortality Adults (Male

Health Professionals) PM 2.5 17.8 (at baseline) NR

CVD: Cardiovascular Disease, CHD: Coronary Heart Disease; IHD: Ischemic Heart Disease; COPD: Chronic Obstructive Pulmonary Disease; CBD: Cerebrovascular Disease; NR: Not reported

Table A. 2

. Characterization of Studies of Long

- term Exposure to PM 10

- 2.5 and Mortality

Author Years

of Study Location Outcome Population Size

Fraction Long

- term Mean
Concentration (μg/m 3 ) Upper Percentile
Concentrations (μg/m 3 )

Puett et
al. ( 2009 ) 1992

- 2002 U.S. (East

and Midwest) All

- Cause

and CHD Mortality Adults (Female Nurses) PM 10

- 2.5 7.7 75 th: 9.2

Max: 26.9

Puett et
al. ( 2011 ) 1986

- 2002 U.S. (East

and Midwest) All

- Cause

and CHD Mortality Adults (Male

Health Professionals) PM 10

- 2.5 10.1 (at baseline) NR

CHD: Coronary Heart Disease; NR: Not reported44 Table A. 3. Characterization of Studies of Long

- term Exposure to PM 2.5 and Cardiovascular

Effects

Author Study

Years Location Outcome Population Size

Fraction Long

- term
Mean
Concen

tration (μg/m 3 ) Upper

Percentile
Concen

trations (μg/m 3 )

Puett et al. ( 2011 ) 1989

- 2003 North

east and Midwest,
U.S.* All

- cause Mortality,

Nonfatal MI,
fatal CHD,

and Hemorrhagic

and Ischemic
Stroke Health
Professionals

Follow

- Up Study

men, 40

- 75

yrs of age PM 2.5 , PM 10

- 2.5 Predicted

PM 2.5 = 17.8

± 3.4

Predicted

PM 10

- 2.5 = 10.1 ± 3.3 Interquartile

range (IQR):

PM 2.5 : 4.3

PM 10

- 2.5 : 4.3

Lipsett et
al. ( 2011 ) 1995

- 2000 California All Cause Mortality,
CVD mortality, IHD mortality,

cerebro

vascular

disease mortality, MI incidence,

stroke

incidence California

Teachers Study

N=124,614

women, 20

- >80 yrs 15.64 Max: 28.35

Coogan et
al. ( 2012 ) 1995

- 2005 Los Angeles,
CA Hypertension

and Diabetes

Mellitus (incidence) Black

Women’s

Health Study

N=4204 (hypertension)

N

- 3236 (diabetes)

disease free

at baseline PM 2.5 20.7 75 th : 21.6

Beckerman

et al. ( 2012 ) 1992

- 1999 Toronto,
Ontario IHD (prevalence) N=2360 pulmonary

clinic patients PM 2.5 50th percentile:

8.71 75th: 8.83

Adar et al. ( 2010 ) 2002

- 2003 6 US
Cities** Retinal

Microvasculat

ure MESA, N=4,607

46

- 87 years

, no clinical

cardiovascular

disease at
baseline PM 2.5 16 (±3) 75th: 17.2 personal PM prediction; 17.2; nearest
monitor PM

17.3

Max: personal

PM prediction

26.3; nearest
monitor PM

25.445 Author Study

Years Location Outcome Population Size

Fraction Long

- term
Mean
Concen

tration (μg/m 3 ) Upper

Percentile
Concen

trations (μg/m 3 )

O'Neill et
al

. ( 2011 ) 2000

- 2002 6 US
Cites** Arterial
Stiffness MESA

N=3,996

men and

women, 44

- 84

yrs PM 2.5 Imputed 20 yr
avg: 21.47 ± 5.00

16.80 ± 3.90 (2005)

Van Hee et
al. ( 2011 ) Jul

2000

- Aug

2002 6 US
Cites** Ventricular
Conduction

and Repolarization

Abnormalities MESA

N=4,783

45 to 84 yrs PM 2.5

Kloog et al. ( 2012a ) 2000

- 2006 New England Hospital

Admissions ≥65 years PM 2.5 (predicted) 9.65 17.79

Table A .4. Characterization of Studies of Long

- term Exposure to PM 2.5 and Respiratory Effects

Author Years

of Study Location Outcome Population Size

Fraction Long

- term
Mean
Concen

tration (μg/m 3 ) Upper

Percentile
Concen

trations (μg/m 3 )

Noonan et al. ( 2012 ) 2003

- 2009 Libby, MT Respiratory
infections (including bronchitis) PM 2.5 19.0

- 27.0 NR

Bhattacharyya ( 2009 ) 1997

- 2006 US (Nation

wide) Hay Fever and
Sinusitis National

Health

Interview Survey respondents PM 2.5 13.4

- 11.6 NR

Bhattacharyya

and Shapiro ( 2010 ) 1997

- 2006 US (Nation

wide) Ear Infections National

Health

Interview Survey respondents PM 2.5 13.4

- 11.6 NR

Patel et al. ( 2009 ) 1998

- 2006 NYC, NY Wheeze and Cough Participants in
Columbia
Center for
Children’s

Environmental

Health birth

cohort PM 2.5 13.0 Max: 38.446 Author Years

of Study Location Outcome Population Size

Fraction Long

- term
Mean
Concen

tration (μg/m 3 ) Upper

Percentile
Concen

trations (μg/m 3 )

Parker et al. ( 2009 ) 1999

- 2005 US (Nation

wide) Respiratory Allergies Children (ages 3

- 17) in

National

Health

Interview Survey PM 2.5 13.1 75 th : 15.2

Nachman and

Parker ( 2012 ) 2002

- 2005 US (Nation

wide) Asthma, sinusitis,

chronic

bronchitis National

Health

Interview Survey respondents PM 2.5 12.1 75 th : 14.4

Max: 27.5

Karr et al. ( 2009a ) 1997

- 2003 Puget
Sound Region,

WA Bronchiolitis hospital

admission Washington
State Birth

Events Registry

Database PM 2.5 12.0 75 th : 14.0

Max: 36.9

Karr et al. ( 2009b ) 1999

- 2003 Georgia Air

Basin of BC,
Canada Inpatient or outpatient

bronciolitis Infants born

between

1999

- 2002 PM 2.5 5.8 Max: 12.0

Kloog et al. ( 2012a ) 2000

- 2006 New England Respiratory hospital

admission R esidents ≥65

ye a rs PM 2.5 9.7 75 th : 10.1

Max: 17.8

Neupane et al. ( 2010 ) 2003

- 2005 Hamilton, ON,
Canada Pneumonia hospital

admissions Residents ≥65

ye a rs PM 2.5 10.7 75 th : 113

95 th : 12.4

Max: 13.0

Meng et al. ( 2010 ) 2000

- 2001 San Joaquin Valley, CA Asthma Symptons;

Asthma ED

visits or hospitalizations San Joaquin Valley

residents participating

in 2001
California

Health

Interview Survey) PM 2.5 21.4 75 th : 23.5

Akinbami et al. ( 2010 ) 2001

- 2004 US ( Nation

wide ) Asthma prevalence Children (ages 3

- 17) in

National

Health

Interview Survey PM 2.5 13.3 75 th : 15.7

Carlsten et al. ( 2011 ) 1995

- 2003 Vancouver, BC,
Canada Incident

Asthma Birth cohort

born in 1995 PM 2.5 5.6 NR47 Author Years

of Study Location Outcome Population Size

Fraction Long

- term
Mean
Concen

tration (μg/m 3 ) Upper

Percentile
Concen

trations (μg/m 3 )

Clark et al. ( 2010 ) 1999

- 200 4 South

western BC,
Canada Incident

Asthma Children born

in 1999 and

2000 and

followed up to

3

- 4 yrs PM 2.5 5.6 75 th : 6.1

McConnell et
al. ( 2010 ) 2002

- 2006 Southern
California Incident

Asthma Kindergarten

and First grade children

in Southern
California
Children’s

Health Study PM 2.5 13.9 Max: 17.4

Table A. 5

. Characterization of Studies of Long

- term Exposure to PM 2.5 and Reproductive and
Developmental Effects

Author Years

of Study Location Outcome Population Size

Fraction Long

- term
Mean
Concentration (μg/m 3 ) Upper

Percentile
Concentrations (μg/m 3 )

Lee et al. ( 2011 ) 1997

- 2001 PA C

- reactive protein Healthy

women PM 2.5 16.4 75 th : 18.7

95 th : 26.2

100 th : 40.8

Legro et
al. ( 2010 ) 2000

- 2007 Northeastern
US In Vitro

Fertilization ( IVF )

success Women undergoing

IVF PM 2.5 14.0

- 14.5 NR

Vinikoor

Imler et
al. ( 2012 ) 2000

- 2003 NC Gestational Hypertension All births in
NC PM 2.5 14.5 75 th : 15.7

Rich et
al. ( 2009 ) 1999

- 2003 NJ Fetal Growth All births in

NJ PM 2.5 13.8 NR

Chang et
al. ( 2012b ) 2001

- 2005 NC Pre

- term
birth ( PTB ) All births in
NC PM 2.5 13.0

- 15.3 NR

Darrow

et al. ( 2009 ) 1994

- 2004 Atlanta, GA PTB All births in

Atlanta (5 counties) PM 2.5 16.5 Max: 34.1

Rudra et
al. ( 2011 ) 1996

- 2006 Western WA PTB Healthy

Women PM 2.5 10.0 75 th : 12.7

100 th : 17.2

Wilhelm

et al. ( 2011 ) 2004

- 2006 Los Angeles,
CA PTB All births in

LA county PM 2.5 18.0 NR48 Author Years

of Study Location Outcome Population Size

Fraction Long

- term
Mean
Concentration (μg/m 3 ) Upper

Percentile
Concentrations (μg/m 3 )

Marshall

et al. ( 2010 ) 1998

- 2003 NJ Birth Defects (Oral Clef ts) All births in

NJ PM 2.5 13.4 NR

Bell et al. ( 2012 ) 2000

- 2004 CT and MA birth weight ( BW ) All births

from 5
counties PM 2.5 14.0 75 th : 16.0

Bell et al. ( 2010 ) 2000

- 2004 CT and MA BW All births

from 5
counties PM 2.5 14.0 NR

Darrow

et al. ( 2011b ) 1994

- 2004 Atlanta, GA BW All births in

Atlanta (5 counties) PM 2.5 16.5 NR

Ghosh et
al. ( 2012 ) 1995

- 2006 Los Angeles,
CA BW All births in

LA county PM 2.5 19.8 NR

Kloog et
al. ( 2012b ) 2000

- 2008 MA BW, PTB All births in

MA PM 2.5 9.6 75 th : 11.6

Kumar ( 2012 ) 2000

- 2004 Chicago, IL BW All births

from Chicago
MSA PM 2.5 18.0 NR

Morello

Frosch et
al. ( 2010 ) 1996

- 2006 CA BW All births in
CA PM 2.5 16.7 75 th : 21.0

Salihu et
al. ( In

Press ) 2000

- 2007 Tampa, FL BW, PTB Women participating

in Health
Start Project PM 2.5 11.0 Max: 23.2

Wilhelm

et al. ( 2012 ) 2004

- 2006 Los Angeles,
CA BW All births in

LA county PM 2.5 17.9 NR

Faiz et
al. ( 2012 ) 1998

- 2004 NJ Stillbirth All births in

NJ PM 2.5 14.0 NR49 Table A .6. Characterization of U.S. and Canadian Studies of Short

- Term Exposure to PM 2.5 and
Mortality

Author Years Location Mortality Population Size

Fraction Mean 24

- h avg Concentration (μg/m3) Upper

Percentile
Concentrations (μg/m 3 )

Ito et al. ( 2011a ) 2000

- 2006 New York, NY Cardiovascular ≥ 40 PM 2.5 , PM components (EC, OC,
SO 4 , Ni, V, Zn, Si, Se, Na, Br, NO 3 ) PM 2.5

All

- Year: 14.4

Warm (April

September):

14.8

Cold (October

March): 14.1 NR

Zhou et
al. ( 2011 ) 2000

- 2004 Detroit,

MI

Seattle,

WA Non

- accidental, Cardiovascular, Respiratory All PM 2.5 , PM components (Al, Fe, K, Na, Ni, S, Si, V, Zn, EC) Detroit

All

- Year (Median): 13.2

Warm (April

September) (Mean):15.3

Cold (October

March) (Mean):

14.9

Seattle

All

- Year (Median): 7.9

Warm (April

September) (Mean): 8.0

Cold (October

March) (Mean):

11.4 Detroit

Max: 65.8

Seattle

Max: 41.3

Chang

et al. ( 2012a ) 2001

- 2005 New York, NY Cardiovascular,

Respiratory ≥ 65 PM 2.5 Spring (March

May): 14.3

Summer (June

August): 17.5

Fall (September

November):

13.3

Winter (December

F ebruary): 15.4 NR

Klemm

et al. ( 2011 ) 1998

- 2007 Atlanta,
GA (4 counties) Non

- accidental,

Cardiovascular,

Respiratory ≥ 65 PM 2.5 , PM components (EC, OC,
NO 3 , SO 4 ) 17.0 75 th : 21.6

Max: 72.950 Table A. 7. Characterization of U.S. and Canadian Studies of Short

- Term Exposure to PM 2.5 and
Respiratory Hospital Admissions and Emergency Department V isits

Author Years Location Hospital
Admission/

ED Visit Popul

ation Size

Fraction Mean 24

- h

avg Concen

tration

(μg/m 3 ) Upper

Percentile
Concen

trations (μg/m 3 )

Bell et al. ( 2012 ) 2000

- 2005 187 U.S.

counties Hospital

admissions:

All respiratory ≥ 65

PM 2.5 , PM components All

- Year: 14.0

Summer: 16.2

Winter: 13.9 Max:

All Year: 26.0

Summer: 28.5

Winter: 32.8

Zanobetti

et al. ( 2009 ) 2000

- 2003 26 U.S.

communities ED Visits:

All respiratory ≥ 65 PM 2.5 , PM components (As, Al, Br, Cr, Fe, Pb, Mn, Ni, K, Si, V, Zn, NO3, SO4, NH4, Na +

, EC, OC) 15.3 PM 2.5 Max Spring: 24 (Riverside, CA)

PM 2.5 Max

Winter: 29.9 (Fresno, CA)

Stieb et
al. ( 2009 ) 1992

- 2003 7 Canadian

cities ED Visits:

Asthma

COPD

Respiratory

Infection All

PM 2.5 Montreal (1/97

- 12/02):

8.6

Ottawa (4/92

-

12/00): 6.7

Edmonton (4/92

- 3/02):

8.5

Halifax (1/99

-

12/02): 9.8

Toronto (4/99

-

6/03): 9.1

Vancouver (1/99

- 2/03):

6.8 75 th :

Montreal: 10.9

Ottawa: 8.7

Edmonton: 10.9

Halifax: 11.3

Toronto: 11.9

Vancouver: 8.5

Levy et
al. ( 2012 ) 2000

- 2008 119 U.S.

counties Hospital

Admissions:

All respiratory ≥ 65 PM components

(EC, OC, SO4, NO3) --- ---51 Darrow et

al. ( 2011a ) 1993

- 2004 (PM 2.5 collecte
d from
8/1/98

- 12/31/0 4) Atlanta, GA ED Visits:

All respiratory All

PM 2.5 1

- h max: 29

24

- h avg: 16

Commute: 17

Day

- time: 15

Night

- time: 17 1

- h max:

75 th : 36

Max: 188

24

- h avg:

75 th : 21

Max: 72

Commute:

75 th : 21

Max: 76

Day

- time:

75 th : 19

Max: 71

Night

- time:

75 th : 14

Max: 88

Strickland

et al. ( 2010 ) 1993

- 2004

(PM 2.5 collecte

d from
8/1/98

- 12/31/0 4) Atlanta, GA ED Visits:

Asthma 5

- 17

PM 2.5 , PM components

(SO 4 , EC, OC, water

soluble metals) PM 2.5

All

- Year: 16.4

Warm (May

October): 18.4

Cold (November

April): 14.3

PM 10

- 2.5

All

- Year: 9.0

Warm: 9.7

Cold: 8.3 NR

Kim et al. ( 2011 ) 2003

- 2007 Denver, CO Hospital

Admissions:

All respiratory

COPD

Asthma

Pneumonia All

PM 2.5 , PM components

(EC, OC,
SO 4 , NO 3 ) 8.0 59.4

Mar et al. ( 2010 ) 1998

- 2002 Tacoma, WA ED Visits:

Asthma All PM 2.5 12.3 NR

Kloog et

al. ( 20 12a ) 2000

- 2006 New England Hospital

Admissions:

All respiratory ≥ 65

PM 2.5 9.6 Max: 72.6

Li et al. ( 2011 ) 2004

- 2006 Detroit, MI ED Visits:

Asthma 2

- 18 PM 2.5 15.0 75 th : 18.5

Max: 69.0

Glad et

al. ( 2012 ) 2002

- 2005 Pittsburgh,

PA ED Visits:

Asthma All PM 2.5 13.3 Max: 55.052 Grineski

et al. ( 2011 ) 2000

- 2003 El Paso, TX Hosp ital

Admissions:

Asthma

Acute

bronchitis ≥ 1

PM 2.5 12.8 75 th : 15.6

95 th : 26.6

Max: 119.153 Table A. 8. Characterization of U.S. and Canadian Studies of Short

- Term Exposure to PM 10

- 2.5 and Respiratory Hospital Admissions

and Emergency Department Visits

Table A. 9. Characterization of U.S. and Canadian Studies of Short

- Term Exposure to PM 2.5 and Cardiovascular Hospital Admissions

and Emergency Department Visits

Author Study

Years Location Outcome Population Size Fraction Mean 24

- h avg Concentration

(μg/m 3 ) Upper Percentile

Concentrations (μg/m 3 )

Zanobetti et al. ( 2009 ) 2000

- 2003 USA (26 communities) ED Visits:

MI, CHF Older

adults ≥ 65

yrs PM 2.5

PM 2.5 components: As, Al, Br, Cr,
Fe, Pb, Mn, Ni,

K, Si, V, Zn, NO3, SO4,
NH4, Na +

, EC,

OC 15.3 PM 2.5 Max Spring: 24 (Riverside, CA)

PM 2.5 Max Winter: 29.9 (Fresno, CA)

Stieb et al. ( 2009 ) 1990’s

- early

2000’s (depending

on city) Candada (7 Cities) ED Visits:Angina/MI,

Heart Failure, Dysrhythmia PM 2.5 City

- specific means (range):

6.7

- 9.8 City Specific 75 th

Percentiles:

8.5

- 11.9 Author Years Location Hospital
Admissions/

ED Visit Population Size

Fraction Mean 24

- h avg Concentration

(μg/m 3 ) Upper Percentile
Concentrations (μg/m 3 )

Strickland et al. ( 2010 ) 1993

- 2004

(PM 2.5 collected from
8/1/98

- 12/31/04) Atlanta,
GA ED Visits:

Asthma 5

- 17 PM 10

- 2.5 PM 10

- 2.5

All

- Year: 9.0

Warm: 9.7

Cold: 8.3 NR54 Author Study

Years Location Outcome Population Size Fraction Mean 24

- h avg Concentration

(μg/m 3 ) Upper Percentile

Concentrations (μg/m 3 )

Ito et al. ( 2011a ) 2000

- 2006 New York,

NY ED Visits: CVD ≥40 yrs

PM 2.5

PM 2.5 components:

EC

, OC

, SO4

, NO3

, Na+

, Ni

, V

, Zn

, Si

, Se

, Br All year/Warm/Cold :

14.44/14.79/ 14.09

1.13/ 1.03/1.24

4.3/4.51/4.08

4.14/ 4.81/3.42

2.12/1.52/ 2.78

0.14/ 0.14/ 0.15

0.0171/0.0111/ 0.0236

0.0066/ 0.0054/0.0080

0.0300/ 0.0216/ 0.0389

0.0769/ 0.0886/ 0.0643

0.0013/0.0011/ 0.0015

0.0036/0.0031/0.0040 Not presented

(Note: SD provided so

we could compute)

Mathes et al. ( 2011 ) 2000

- 2002 New York,

NY ED Visits: CVD ≥40 yrs PM 2.5 --- ---

Szyszkowicz

et al. ( 2012 ) Apr 1992

- Mar 2002 Canada (Edmonton) ED Visits: Hypertension N=5,365 PM 2.5 8.5 75 th percentile: 10.9

Max: 1.3.1

Haley et al. ( 2009 ) 2001

- 2005 New York

State ED Visits Discharges

from all

NYS hospitals PM 2.5 NR NR

Bunch et al. ( 2011 ) 1993

- 1998 Wasatch
Front, Utah Hospital

Admissions All PM 2.5 City specific means (range):

9.3

- 11.1 City specific max:

9.3

- 11.1

Kloog et al. ( 2012a ) New England Hospital

Admissions ≥65 PM 2.5 (predicted) 9.6 72.5955 Author Study

Years Location Outcome Population Size Fraction Mean 24

- h avg Concentration

(μg/m 3 ) Upper Percentile

Concentrations (μg/m 3 )

Kim et al. ( 2011 ) 2003

- 2007 Denver Hospital

Admissions All PM 2.5

EC

OC

Sulfate

Nitrate 7.98

0.47

3.09

1.08

1.03 59.41

3.02

10.28

14.32

19.7256 Table A. 10. Characterization of U.S. and Canadian Studies of Short

- Term Exposure to PM 2.5 and Out of Hospital Cardiac Arrests

Author Study

Years Location Outcome Population Size

Fraction Mean 24

- h

avg Concentration (μg/m 3 ) Upper Percentile
Concentrations (μg/m 3 )

Silverman

et al. ( 2010 ) 2002

- 2006 USA (New

York City) Out

- of

hospital

cardiac

arrests N=8,216

<40 to ≥ 70

yrs PM 2.5 Median:

A ll year = 12 Apr

- Sept = 12
Oct

- Mar = 12 Upper (95%):

A ll year = 30 Apr

- Sept = 31
Oct

- Mar = 28

Table A. 11. Characterization of U.S. and Canadian Studies of Short

- Term Exposure to PM 2.5 and Time of Stroke Symptom Onset

Author Study

Years Location Outcome Population Size

Fraction Mean 24

- h

avg Concentration (μg/m 3 ) Upper Percentile
Concentrations (μg/m 3 )

Wellenius

et al. ( 2012 ) 1999

- 2008 Boston,

MA Time of Symptom
Onset (Ischemic Stroke) Patients

admitted to
BIDMC PM 2.5 NR NR

BIDMC= Beth Israel Deaconess Medical Center57 

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