## Responses to Significant Comments on the 2009 Proposed Rule on the Prim ary National Ambient Air Quality Standards

for Nitrogen Dioxide (July 15, 2009; 74 FR 34404)

Docket Number OAR

- 2006

- 0922 U.S. Environmental Protection Agency

January 2010

## Table of Contents

I. Introduction ................................ ................................ ................................ ........................... 1 II. Responses to Significant Comments on the Scientific Evidence and Exposur e/Risk Information ................................ ................................ ................................ ................................ .... 2 A. General comments on the scientific evidence

................................ ................................ .. 2 B. Comments on the epidemiologic evidence

................................ ................................ ....... 2 C. Comments on the controlled human exposure evidence

................................ ................ 10 D. Comments on air quality , exposure, and risk anal yses ................................ .................. 13 III. Responses to Significant Comments on the Adequacy of the Current Standard ......... 35 IV. Comments on A New Short
- Term NO 2 Primary Standard ................................ ............ 37 A. Indicator

................................ ................................ ................................ ......................... 37 B. Averaging time

................................ ................................ ................................ ............... 38 C. Form

................................ ................................ ................................ ............................... 39 D. Approach and level

................................ ................................ ................................ ......... 40 1. Comments on the approach to setting the standard

................................ .................... 40 2. Comments on standard level

................................ ................................ ....................... 45 3. Comments on the annual standard

................................ ................................ .............. 51 V. Technical Issues with Monitoring Requirements ................................ ............................. 53 A. Comments on near

- road monitor siting requirements

................................ .................... 53 B. Comments on area

- wide monitor requirements

................................ ............................. 59 C. Comments on the need for a research monitoring network

................................ ........... 61 D. Justification of meteorological measurements

................................ ............................... 65 E. Monitoring technology

................................ ................................ ................................ ... 65 F. Timing of monitor deploy ment
................................ ................................ .......................... 68 G. Other monitoring issues

................................ ................................ ................................ . 69 VI. Air Quality Index ................................ ................................ ................................ ................ 72 VII. Comments on the Process for Reviewing the NO 2 Primary NAAQS ............................. 74 V III. Interpretation of the Clean Air Act ................................ ................................ ............ 76 IX. Comments on Implementation ................................ ................................ ........................... 78 X. References ................................ ................................ ................................ ............................ 86

## Frequently Cited Documents

The following documents are frequentl y cited throughout EPA = s response to comments, often by means of the short names listed below: Integrated Science Assessment (I SA) : EPA. (2008a). ISA for Oxides of Nitrogen

- Health Criteria. National Center for Environmental Assessment, Research Triangle Park, NC. Available at: http://cfpub.epa.gov/ncea/cfm/recordisplay .cfm?deid=194645. Preamble to the final rule (final notice) : Preamble to the Fi nal Rule on the Review of the Primary National Ambient Air Quality Standards for Nitrogen Dioxide ; to be published in the Federal Register in January or February of 2010

. Proposal notice: Primary National Ambient Air Quality Standard for Nitrogen Dioxide : Proposed Rul e. 74 FR 34404, July

15, 2009

. Risk and Exposure Assessment (REA) : EPA. (2008b). Risk and Exposure Assessment to Support the Review of the NO 2 Primary Nation al Ambient Air Quality Standard . Office of Air Quality Planning and Standards, Re search Triangle Park, NC. Available at: http://www.epa.gov/fedrgstr/EPA

- AIR/2009/July /Day

- 15/a15944.pdf

## Acronym s and Abbreviations

AADT Annual average daily traffic AAM Al liance of Auto Manufacturers AAQM Am bient Air Quality Monitoring AASHTO American Association of State Highway and Transportation Officials ACC American Chemistry Council ACSBPP Annapolis Center for Science

- Based Public Policy AGCA Association General Contractors of America AHR A irways hyperresponsiveness AQRL AirQuality Research and Logistics ALA American Lung Association ANPR Advance Notice Of Proposed Rulemaking API American Petroleum Institute AQI A ir quality index ATS American Thoracic Soci ety CAA Clean Air Act CAAPCOA California Air Pollution Control Officer's Association CAC Clean Air Council CASAC Clean Air Scientific Advisory Committee CBSA C ore -based statistical area CE Consumers Energy CO C arbon monoxide COPA Colorado Petroleum Association CSE Coalition for a Safe Environment Dow Dow Chemical Company EDF Environmental Defense Fund EEI Edison Electric Institute EJ EarthJustice EMA Engine Manufacturers Association EPA U.S. Environmental Protection Agency Exxon ExxonMobil Refining and Supply Company FEM Federal Equivalent Method FEV Forced Expiratory Volume FRM Federal Reference Method GASP Group Against Smog and Pollution HCPHES Harris County Public Health and Environmental ServicesHEI Health Effects Institute

HLI H ealthy Lungs Initiative IADNR Io wa Department of Natural Resources INDEM Indiana Department of Environmental Management INGAA Interstate Natural Gas Association of America IPAMS Independent Petroleum Association of Mountain States ISA Integrated Scien ce Assessment MET Meteorological MODNR Missouri Department of Natural Resources Air Pollution Control Program NAAQS National Ambient Air Quality Standards NACAA National Association of Clean Air Agencies NAM National Association of Manufacturers NCDE NR North Carolina Department of Environment and Natural Resources NESCAUM Northeast States for Coordinated Air Use Management NIOSH National Institute of Occupational Safety and Health NMA National Mining Association NMED New Mexico Environment Department Air Quality Bureau NO 2 Nitrogen Dioxide NO X Nitrogen Oxides NPRA National Petrochemical and Refiners Association NRDC National Resource Defense Council NSR New Source Review NTAA National Tribal Air Association NYDOH New York Department of Heal th NYSDEC New York State Department of Environmental Conservation OIPA Oklahoma Independent Petroleum Association OLM Ozone Limiting Method OSHA Occupational Safety and Health Association PAW Petroleum Association of Wyoming PEL Permissible Exposure Level PM Particulate Matter ppb Parts Per Billion ppbv Parts Per Billion by Volume ppmv Parts Per Million by Volume PSD Prevention of Significant Deterioration PVMRM Plume Volume Molar Ratio Method QC Q uality controlREA Risk and Exposure Assessment

RHAMC Respiratory Health Association of Metropolitan Chicago RIA Regulatory Impact Analysis SCAQMD South Coast Air Quality Management District SDDENR South Dakota Department of Environment and Natural Resources SIL Significant Impact Level SIP Stat e Implementation Plan STEL Short

- T erm Exposure Level TFI The Fertilizer Institute TXCEQ Texas Commission on Environmental Quality UPA Utah Petroleum Association UARG Utility Air Regulatory Group VADOT Virginia Department of Transportation

## I. Intr oduct ion

This document, together with the preamble to the final rule on the review of the primary national ambient air quality standards (NAAQS) for nitrogen dioxide (NO 2 ) , presents the responses of the Environmental Protection Agency (EPA) to the public comme nts received on the 200 9 NO 2 NAAQS proposal notice (7 4 FR 34404 ). All significant issues raised in timely public comments have been addressed. Where comments were submitted after the close of the public comment period, EPA has responded to the extent fea sible

. Due to the number of comments that addressed similar issues, this response

- to
- comments document does not generally cross - reference each response to the commenter(s) who raised the particular issue involved, although commenters are identified in so me cases where they provided particularl y detailed comments that were used 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 ru le or to address comments not discussed in the preamble to the final rule. Although portions of the preamble to the final rule are paraphrased in this document where useful to add clarity to responses, to the extent any ambiguit y is introduced by this par aphrasing, the preamble itself remains the definitive statement of the rationale for the revisions to the standards adopted in the final rule. In man y instances, particular responses presented in this document include cross references to responses on rel ated issues that are located either in the preamble to the NO 2 primary NAAQS final rule, or in this Response to Comments document. In other instances the comment is appropriatel y addressed b y the Agency’s discussion in other parts of the record. All issu es on which the Administrator is taking final action in the NO 2 primary NAAQS final rule are addressed in the NO 2 NAAQS rulemaking record. Accordingl y, this Response to Comments document, together with the preamble to the NO 2 primary NAAQS fi nal rule and the information contained in the Integrated Science Assessment ( IS A ) (EPA, 2008a), the Risk and Exposure Assessment ( REA ) (EPA, 2008b), and the Notice of Proposed Rulemaking should be considered collectively as EPA’s response to all of the significant comments submitted on EPA’s 2009 NO 2 primary NAAQS proposed rule. This document incorporates directl y or b y reference the significant public comments addressed in the preamble to the NO 2 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 following topics are addressed in this document: the scientific evidence and exposure/risk information (section I I); the adequacy of the current NO 2 standard to protect public health (section II I ); revisions to the current standard in terms of indicator (section IV

. A), averaging time (section IV

. B ) , form (section IV .C), and level ( section IV .D ); revisions to the NO 2 monitoring network (section V); the air quality index (VI); the process for reviewing the standard (section VII); interpretation of the Clean Air Act (section VIII ) ; and implementation of the standard (section IX );

.

## II. Responses to Significant Comments on the Scientific Evidence

and Exposur e/Risk Information A. General comments on the scientific evidence (1) Comment: Some commenters (e.g., AAM, ACC) stated that it is not clear what was meant in the I SA by

a “likely causal” relationship, stating that this clas sification is “somewhat ambiguous” and “at odds with” frameworks developed b y IAR C and NAS/I OM (ACC, p. 2) These groups concluded that it would have been preferable not to include this characterization of the evidence in the I SA. Response: EPA’s causa lity framework is not at odds with other frameworks. EPA’s use of a five

- level hierarchy

in the I SA is consistent with EPA’s Guidelines for Carcinogen Risk Assessment (EPA, 2005). Excerpts from those guidelines are included in Annex A (AX1 pp. 1

- 6 to 1

- 9) ; the second of five descriptors is “L ikel y to be Carcinogenic to Humans.” IARC’s classification of carcinogens is also excerpted in Annex A (AX1 pp. 1

- 14 to 1

- 20), and it includes Group 1 (carcinogenic), Group 2A (probabl y carcinogenic), Group 2B (possibl y carcinogenic), Group 3 (not classifiable) and Group 4 (probably not carcinogenic). In contrast with commenters’ assertion that IARC’s s ys tem differs from EPA’s, these five groups and subgroups are clearly analogous to the five tiers in EPA’s framework. C ommenters also refer to the NAS/IOM framework (IOM, 2007) that was used as a resource for EPA’s causal framework and excerpted in Annex A (AX1 pp. 1

- 9 to 1

- 12). The four categories used in that sy stem

– “sufficient”, “equipoise and above”, “below equipoise ” and “against”

– are different from those used in most other classifications. However, the IOM report included detailed discussion of the approach to evaluating evidence from across scientific disciplines that served as an important resource for EPA’s wei ght of evidence determination. In developing its framework drawing causal inferences, EPA carefully considered and drew upon the work of previous assessments to build a framework for determination of causality that is consistent with EPA’s cancer risk asse ssment guidelines as well as those of other expert organizations. The development and implementation of this framework has been lauded by the CASAC in recent ISA reviews such as that in the PM NAAQS review (Samet, 2009a)

. 

### B. Comments on the epidem iologic evidence (1) Comment: Several industry groups ( e.g., API, AAM, ACC) commented that the epidemiologic studies did not support a causal relationship between NO 2 and health effects due to uncertainties and issues related to model specification. These comment ers state that EPA has ignored or understated issues such as selection of degrees of smoothing appropriate to adjust for weather and time trends and selection of lag period. Response: EPA has not ignored issues related to model specification for epidemio logic studies, such as selection of models and approaches to adjust for meteorological and temporal variables. EPA agrees with commenters that these are important issues. In this and previous NAAQS reviews, EPA has carefull y evaluated such issues, includin gsponsorship of workshops and special anal ys es of epidemiologic data, such as the Health

Effects Institute (HEI) report (2003) cited b y several commenters (e.g., ACC, AAM). As observed in the NOx I SA (p. 3

- 1), extensive discussions of the issues surroundi ng model selection and model specification have been presented in the PM AQCD (EPA, 2004) and the Ozone AQCD (EPA, 2006) and are thus not reiterated at length in this ISA. The NOx ISA makes clear, however, that these issues were were carefull y considered i n selecting studies for inclusion in the I SA and interpreting the results of the body of epidemiologic evidence. Commenters specificall y refer to the Health Effects Institute report on the reanal ys is of a series of time

- series epidemiologic studies to e valuate alternative modeling strategies, and include a brief quote from the Health Review Committee Panel (HEI, 2003): “Neither the appropriate degree of control for time, nor the appropriate specification of the effects of weather, has been determined for time

- series anal ys is.” (ACC, p. 7, quoting HEI, 2003, p. 269). Taken in full context, it can be seen not as condemnation of all epidemiologic time

- series studies but rather as a call for further investigation. The primary conclusion drawn by

the HEI panel was, rather: “The overall impact of revising these studies include: While the number of studies showing an association of PM with mortality was slightly

smaller, the PM association persisted in the majority of studies. In some of the large number of studi es in which the PM association persisted, the estimates of PM effect were substantially smaller. In the few studies in which investigators performed further sensitivity anal ys es, some showed marked sensitivity of the PM effect estimate to the degree of smo othing and/or the specification of weather” (HEI , 2003, p. 269). The results of this extensive set of reanal ys es was thoroughly discussed in the PM AQCD (EPA, 2004, Section 8.4.2). EPA has not ignored or downplay ed these issues, in fact, EPA has scrutinize d epidemiologic studies and has funded independent reanal ys es of epidemiologic studies. EPA observes that the reanal ys es discussed above and cited b y commenters are primarily on PM health effects studies. Few reanal ys es have specificall y focused on NOx; h owever EPA has recognized that model specification issues are generall y similar for both PM and the gaseous criteria air pollutants. EPA agrees that model specification and control of time

- varying factors such as weather, remains important and has consider ed the available evidence in its evaluation of epidemiologic studies. The EPA also agrees with commenters that season

- specific anal ys es have not been widel y used in epidemiologic studies for NOx, 1 however, EPA observes that a number of studies included in the I SA did report results from seasonal models. The EPA disagrees that the available studies can support a conclusion that air pollution effects are consistently and strongl y modified by season. In summary , EPA has not ignored the potential influence of model selection and specification in reviewing epidemiologic studies; rather, EPA has scrutinized such issues in previous assessments as well as the NOx I SA. These issues were full y considered in

1 Itshould be noted that use of smaller data subsets will markedly reduce statistical power to detect associations and also red uce the precision on any

findings when the data are stratified by season.drawing the conclusion that there was a likel y causal relat ionship between short

- term

exposure to NOx and respiratory morbidity

. (2) Comment: AAM challenges IS A conclusions on several health outcome categories on pp. 31

- 44. The commenter contends that “EPA overstates the strength and consistency of epidemiologi cal evidence regarding various potential health effects”

. Response: The EPA disagrees with these commenters approach to assessing health effects evidence as well as their conclusion regarding the lack of a scientific basis to support the continuation of NAAQS to protect against the health effects of NO 2 . The EPA contrasts these commenters’ narrow focus on counting the numbers of epidemiologic studies that report results with statistical significance, without regard to other considerations that are impor tant to consider in a comprehensive appraisal of the evidence , with the approach taken b y EPA in the ISA

. Specificall y , EPA recognize s the distinction between evaluation of the relative scientific quality of individual study

results, and evaluation of the pattern of results in a body of evidence. The EPA has done both. The more detailed characterizations of individual studies include assessment of the quality of the study, based on criteria for assessment of the epidemiologic studies that are described i n Section AX 1.1.2 (pg. 1

- 3) and Figure AX1.1

- 1 (pg. 1

- 2) of the Annexes to the I SA for Oxides of Nitrogen. Statistical significance is an indicator of the precision of a study ’s results, which is influenced by the size of the study , as well as exposure and measurement error, model specifications, and other such factors. In developing an integrated assessment of the health effects evidence for NO 2 , EPA has emphasized the importance of examining the pattern of results across various studies, and not focus ing solel y on statistical significance as a criterion. It is important not to focus on results of statistical tests to the exclusion of other information. As observed b y Rothman (1998): Many data analy sts appear to remain oblivious to the qualitative nature of significance testing. Although calculations based on mountains of valuable quantitative information may go in to it, statistical significance is itself only a dichotomous indicator. As it has only two values, significant or not significant, it cannot convey much useful information....Nevertheless, P

- values still confound effect size with study

size, the two components of estimation that we believe need to be reported separatel y. Therefore, we prefer that P

- values be omitted altogether, provided that point and interval estimates, or some equivalent, are available. (Rothman, 1998, p. 334) The concepts underl yi ng EPA’s approach to integrated assessment of statistical associations reported for the health effects on NO 2 have been discussed in numero us publications, including a recent report b y the U.S. Surgeon General on the health consequences of smoking (Centers for Disease Control and Prevention, 2004). Thisreport also cautions against over

- reliance on statistical significance in evaluating the

overall evidence for an exposure

- response 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 hy pothesis” (Hill 1965, p. 299). Hill’s warning was in some way s prescient, as the reliance on statistically significant testing as a substitute for judgment in a causal inference remains today (Savitz et al., 1994; Holman et al., 2001; Poole 2001). To understand the basis for this warning, it is critical to recognize the difference between inductive inferences about the truth of underlying hy

potheses, and deductive statistical calculations that are relevant to those inferences, but that are not inductive statements themselves. The latter include p values, c onfidence intervals, and hy pothesis tests (Greenland 1998; Goodman 1999). The dominant approach to statistical inference today , which employ s those statistical measures, obscures this important distinction between deductive and inductive inferences (Royal l 1997), and has produced the mistaken view that inferences flow directl y and inevitably from data. There is no mathematic formula that can transform data into a probabilistic statement about the truth of an association without introducing some formal quantification of external knowledge, such as in Bayesian approaches to inference (Goodman 1993; Howson and Urbach 1993). Significance testing and the complementary

estimation of confidence intervals remain useful for characterizing the role of chance in pro ducing the association in hand (CDC, 2003, pp. 23

- 24). Accordingl y, the statistical significance of individual study findings has played an important role in EPA’s evaluation of the study’s results and EPA has placed greater emphasis on studies reporting statistically significant results. However, in the broader evaluation of the evidence from man y epidemiologic studies, EPA has also emphasized the pattern of results for drawing conclusions on the relationship between NO 2 and health outcomes, as well as c onsideration of the integration of epidemiologic evidence with findings from laboratory

studies. The EPA considered the results of studies conducted in many different countries to draw conclusions about the likelihood of a causal relationship between NO 2 and health outcomes. Because EPA places greater weight on US and Canadian studies in determining standard levels, the I SA, REA and proposal notice present graphical results from epidemiologic studies in these two countries, standardized to a common increm ent of NO 2 , and based on similar anal yt ic strategies (i.e. single

- pollutant results). EPA believes that the examination of multipollutant model results and the inherent instability that often occurs in effect estimates for correlated pollutants in such st udies justifies the use of single pollutant model results , in addition to multi

- pollutant model results, for comparing effect estimates for NO 2 and health outcomes.The comparisons across studies in the I SA begins with an evaluation of the overall

patte rn of excess risk results

– whether generall y positive or centered around zero

- the consistency

in size of effect estimates, the precision of the studies evidenced in the width of the confidence intervals, with special attention to comparisons of similar effect categories. Finally , it is important to reiterate that the EPA’s evaluation of the scientific evidence used in the current NO X NAAQS review was the subject of exhaustive and detailed review b y the CASAC and the public. Two drafts of the I SA were released for CASAC and public review at public meetings. Evidence related to the substantive issues raised b y submitted comments were evaluated in the I SA drafts and discussed at length in public CASAC meetings. This process ensured that overemphasis on an y study or group of studies was addressed. Following the final meeting with CASAC on the I SA, the CASAC panel found the coverage of the literature in the I SA to be appropriate. (3) Comment: Several industry groups ( e.g., API, AAM, ACC, ACSBPP , CE, COPA, Dow, EEI , EMA, Exxon, NMA , TFI, UARG ) and an individual (Roger McClellan) commented that , given the presence of numerous copollutants in the air, epidemiologic studies do not support the contention that NO 2 itself is causing health effects. These groups concluded that EPA has overstated the strength and consistency of the epidemiologic evidence. For example, APIcommented that “These [epidemiologic] studies do not provide support for a causal association between short

- term NO 2 exposure and respirato ry effects and, thus, do not provide appropriate support for a 1

- hour daily maximum NO 2 standard.” API also stated that “Most [epidemiologic studies] only report statistically

significant findings in single

- pollutant, but not multi

- pollutant, models, and no statistically significant finding is large, robust, or consistent. ” Several industry commenters (e.g., API, ACC, ACSBPP) further noted that the IS A relies primaril y on single

- pollutant models when interpreting epidemiologic studies, rather than evaluat ing the results with in the context of the full suite of air pollutants. These commenters noted that this can lead to overestimating NO 2 effects and to double or triple counting b y attributing effects to NO 2 in the current review that are attributed to dif

ferent pollutants in other NAAQS reviews. Similar conclusions were also expressed b y other commenters. Response: These comments and EPA’s responses are discussed in section II.E.2.a of the final rule. The Administrator’s consideration of the epidemiolog ic evidence specificall y as it relates to decisions on the adequacy of the current standard, the averaging time of a new short

- term standard, and the level of the short

- term standard are discussed in sections II.E and II.F of the final rule. EPA has not focused solely on the results of single pollutant models, but has also carefully examined the implications on multiple pollutant results. The greatest weight of evidence for multi

- pollutant results has been placed on two

- pollutant models (NO 2 plus one ad ditional pollutant), as the inclusion of each additional pollutant in the model can decrease model stability . This decrease in model stability is often reflected in wider confidence intervals, making it less likely for a statistically

significant result t o beobserved. Thus, when a statistically significant effect estimate observed in a single pollutant model is no longer statistically significant in a copollutant model (even though the magnitude and direction of the effect estimate has not changed substantially), this may be an artifact of model instability

. Results in Figures 3.1

- 5, 3.1

- 7, 3.1

- 10 and 3.1

- 11, indicate that the association of NO 2 with respiratory morbidity

is robust to the addition of copollutants. While some individual studies may report specific findings that are more influenced b y copollutants, Figures 3.1

- 5, 3.1

- 7, 3.1

- 10 and 3.1

- 11 clearl y demonstrate EPA’s conclusion of robustness. The EPA strongl y disagrees that the agency is “ double or triple counting by attributing effects t o NO 2 in the current review that are attributed to different pollutants in other NAAQS reviews ”. The EPA consistently recognizes that other pollutants are also associated with health outcomes, as is reflected in the fact that EPA has established regulatio ns to limit emissions of the particulate criteria pollutants as well as other gaseous criteria pollutants. In its assessment of the health evidence regarding NO 2 , EPA has carefully evaluated the potential for confounding, effect measure modification or other interactions between NO 2 and other criteria pollutants, and concluded that the results attributable to NO 2 are robust. (4) Comment: Some industry groups (e.g., API, Exxon Mobil (Exxon) ) commented that reliance on central monitors in epidemiologic st udies leads to a high degree of exposure misclassification. Specifically , Exxon commented that “there is a lack of correlation between measurements fro m ambient monitors for NO 2 and those from personal monitors for NO 2 . This makes the observational epidem iology data invalid for assessing the connection between exposure and health effects for NO 2 . ” API commented that “All [epidemiologic] studies used measurements from central monitors, which likely led to a high degree of exposure misclassification.” R esponse: As discussed in the I SA (section 5.2.2), EPA agrees that there is variability in the extent to which NO 2 concentrations measured by ambient monitors correlate with personal exposures. However, EPA disagrees with the conclusion of the commenter that “This makes the observational epidemiology data invalid for assessing the connection between exposure and health effects for NO 2 .” Rather, as noted in the conclusions of the ISA (section 5.2.2, p . 5

- 3), “ The errors and uncertainties associated with th e use of ambient NO 2 concentrations as a surrogate for personal exposure to ambient NO 2 generall y tend to reduce rather than increase effect estimates, and therefore are not expected to change the principal conclusions from NO 2 epidemiologic studies.” The refore, EPA continues to judge that it is appropriate to consider the NO 2 epidemiologic evidence in reviewing the NAAQS. (5) Comment: UARG also stated the following with regard to the epidemiologic evidence:

Another compelling source of uncertainty re garding the epidemiologic studies on which EPA relies is the discrepancybetween the levels at which health effects were observed in these studies versus human clinical studies. The epidemiologic studies on which EPA relies in the Proposed Rule report effe cts at NO 2 concentrations much lower than the doses use d in human clinical studies. Response: As discussed in detail in the final notice (sections II.A and II.F.4), controlled human exposure studies reported effects down to the lowest concentration evalu ated; no studies have been conducted at lower concentrations. While these concentrations are higher than the mean concentrations reported in epidemiologic studies, it is important to note that epidemiologic studies conducted in the United States have repo rted associations between ambient NO 2 concentrations measured at area

- wide monitors in the current network and increased respiratory s ymptoms, emergency

department visits, and hospital admissions. Area

- wide monitors in the urban areas in which these epide miologic studies were conducted are not sited in locations where localized peak concentrations are likel y to occur. Thus, they

do not measure the highest ambient NO 2 concentrations across the area. Rather, the area

- wide NO 2 concentrations measured b y the se monitors are used as surrogates for the distribution of ambient NO 2 concentrations across the area, a distribution that includes NO 2 concentrations that are higher than the area

- wid e concentrations measured in study locations. As noted in the I SA (se ction 5.3.2.1 and Figure 2.4

- 13), 1

- hour NO 2 concentrations measured at area

- wide monitors in the United States have been observed in the range of 100 to 200 ppb. In addition, even higher 1

- hour NO 2 concentrations could occur on and/or around major roads, where NO 2 concentrations could be 30

- 100% higher than measured b y existing area

- wide monitors (section II.A.2 of the final notice). Therefore, EPA does not agree that the NO 2 concentrations that occurred in the locations of epidemiologic studies did not include concentrations that overlapped with those reported to cause respiratory

effects in controlled human exposure studies. (6) Comment : AAM contends that “the I SA uses the results of respiratory s ymptom studies to claim coherence with the hospital and ED admission results. However the authors of the Mortimer et al. and Schildcrout et al. multi

- city studies that the Agency relies on do not implicate NO 2 , per se, but summer time air pollution and fine PM, respectively”, and claims that the characteriz ation of the results in studies by Mortimer et al. (2002), and Schildcrout et al. (2006) is not consistent with the authors’ conclusions. Response : The commenter is wrong in the characterization of these studies. They have inaccuratel y characterized the authors’ conclusions from these studies. In fact, Mortimer et al. (2002) concluded that “Nitrogen dioxide, sulphur dioxide, and particles with a 50% cut
- off aerodyn amic diameter of 10 μm were associated with increases in sy mptoms, with nitrogen dioxide exhibiting the strongest influence”. Similarly in the Schildcrout et al. (2006) study , the authors conclude that “Among the pollutants studies, carbon monoxide and nitrogen dioxide appeared to capture the most relevant health information. Sulfur dioxide showed less evidence for a relation with asthma exacerbations unless it wasconsidered in combination with carbon monoxide or nitrogen dioxide. There was no

evidence of a warm

- season effect of ozone or of a year - round effect of PM 10 .” Infact, fine PM (PM 2.5 ) was not even included in the study b y Schildcrout et al. (2006), though the commenter contends that the authors implicate "fine PM" as the agent causing the respiratory

morbidit y. (7) Comment: Several industry groups (e.g., ACC, API , NAM) commented on the reliance on the epidemiologic study by Delfino et al. (2002). Specificall y, a s part of a Request for Correction (RFC) submitted under EPA’s Information Quality Guidelines 2 , NAM stated the following: In the Final REA, EPA relied on a purported as sociation between short

- term NO 2 exposure and asthma from a study that was not properl y reviewed in the Final ISA to support selection of a lower bound for potential short

- term NO 2 standards. This use of a study that has not been full y reviewed b y EPA scie ntists violates EPA Guidelines requiring use of the “best available science.” The study in question did not find any association between asthma sy mptoms and NO 2 exposure after controlling for the effect of particulates. EPA must include a proper review of this study in the Final ISA, and must explain why

it believes the study

would provide any support for selection of a standard for NO 2 . Response: These comments and EPA’s responses are discussed in detail in section II.E.2.a of the final rule. (8) Comment: A s part of that RFC, NAM also stated the following:

EPA assessments of several studies in the Final ISA differ materially

from analy ses of these same studies in EPA documents for prior NAAQS. Differing scientific evaluations by EPA which appear to depend on the regulatory purpose for which data are being evaluated violate EPA Guidelines requiring “objectivity .”

2 NAM submitted a Request for Correction under the Information Quality Act in regards to the ISA for NOx (and seeking conforming changes to the final REA for the primary NO 2 NAAQS). http://www.epa.gov/QUALITY/informationguidelines/documents/09002.pdf. Consistent with EPA's Information Quality Guidelines, EPA responded to this request by deferring to the notice and comment process, despite NAM's failure to submit a comment during the i nitial comment period relating to these documents. http://www.epa.gov/QUALITY/informationguidelines/documents/09002

- response.pdf . EPA has addressed NAM's concerns in the final notice and this RTC. EPA has fully satisfied the requirements of the Information Quality Act, and has acted consistently with EPA's Information Quality Guidelines.EPA must either correct its current analy ses to be consistent with its prior conclusions or explain why it believes those pri or conclusi ons were incorrect. Response: These comments and EPA’s responses are discussed in detail in section II.E.2.a of the final rule.


### C. Comments on the controlled hum an exposure evidence (1) Comment: A number of industry commenters disagreed with EPA’s reliance on a meta
anal ys is of controlled human exposure studies, which was included in the final I SA. API stated that “Evidence from controlled human exposure studies of airway hy perresponsiveness in sensitive individuals does not support the need for a short term standard at the levels on which US EPA is taking comment .” ACC described a number of shortcomings of the ISA meta

- analy sis. These commenters generall y referenced a recentl y published meta

- anal ys is (Goodman et al., 2009) and recommended that EPA rel y on that meta

- anal ys is rather than the anal ys is included in the final ISA. Roger McClellan made similar comments and also referenced a recently published article in support of his views (Hesterberg et al., 2009)

. Response: EPA generall y disagrees with the commenters’ characterization of the “meta

anal ys is” of NO 2 - induced airway responsiveness. Furthermore, EPA has considered the Goodman et al. (2009) study and has provided a detailed response to these comments in section II.E.2.b of the final rule. (2) Comment: NAM provided the following comment as part of their RFC. If EPA elects to retain the meta

- anal ys is in the Final IS A, EPA must correct the Final IS A to resolve inconsistencies between the conclusions in the section on Airway

Hy perresponsive n ess and in the summary chapter. Response: EPA disagrees with this comment and finds there is no inconsistency to be resolved between the discourse presented in the Final I SA Section 3.1.3 (Airway Hy perresponsiveness) and associated text presented in the Final I SA Section 5.3.2.1. (Respiratory

Effects Related to Short

- Term Exposure). The section in Chapter 3 of the Final ISA to which the commenter refers was clearly labeled as a summary of the p revious section. Specifically , s ection 3.1.3.3. was entitled “Summary of Short

- Term Exposure on Airway

Responsiveness.” Summaries are intended to provide brief statement of main points or substance of a matter. However, just as an abstract of a paper, summaries do not present all substantive or pertinent matter cont ained in the larger body of a paper or, in this case, the previous section on airway s responsiveness. Furthermore, in Section 3.1.7 (Summary and Integration

–Respiratory

Health Effects with Short

- term Exposure) it is specifically stated on pg 3

- 42 that, “No nspecific responsiveness was also increased following 30

- min exposures of resting asthmatic subjects to 0.2

- to 0.3

- ppm NO 2 and following 1

- h exposures to 0.1

- ppm NO 2 .” In Section 5.3.2.1 it is stated on pg5

- 10 and 5

- 11 that, “...increases in nonspecific h y perresponsiveness were observed ... between 0.2 and 0.3 ppm NO 2 for 30

- min exposures and at 0.1 ppm NO 2 for 60

- min exposures in asthmatics.” Thus, there is clearl y no merit to the commenters’ assertion of inconsistency

in presentation of levels to which asthmatics experience NO 2 - induced airway hy perresponsiveness between Chapters 3 and 5. ( 3 ) Comment: Some commenters (e.g., API, COPA) concluded that AHR is not an appropriate endpoint to inform decisions on standard level. Because exposure to other agent s in combination with exposure to NO 2 is required to trigger AHR , the commenters said EPA would need to demonstrate the frequency and extent of exposure to these other agents and whether these exposures would occur at sufficient concentrations to actually trigger AHR . And if AHR is occurring subsequent to ambient NO 2 exposure , the commenters argued that the frequency of NO 2 - induced AHR versus background rates of A HR has not been documented; therefore, the significance to public health of a NAAQS based on th is endpoint cannot be determined (COPA, API). Specificall y, APIstated the following: EPA has not documented the frequency of NO 2 - induced AHR, if in fact it is occurring, subsequent to exposure to NO 2 in ambient air. Nor has the Agency

compared the estim ated frequency of AHR induced through combined exposure to ambient NO 2 and provocative agents in the environment to background rates of AHR produced b y other causes. Thus, it is not possible to judge the signficance to public health of a NAAQS based on red ucing the estimated reduction in the incidence or magnitude of AHR, or whether reducing ambient NO 2 will have any measurable impact on the overall in cidence of AHR. Response: EPA disagrees with these commenters’ views on NO 2 - induced airway responsivenes s. EPA believes that its interpretation of airway hy perresponsiveness following short

- term exposure to NO 2 is appropriate and supported b y the available scientific information. Human clinical studies provided evidence for airway hy perresponsiveness, i.e., a heightened bronchoconstrictive response to a challenge agent, following short

- term exposure to NO 2 (see sections 3.1.3 and 3.1.7 of Final ISA). Since these experimental human stud ies evaluated the airway responsiveness to challenge agents following expo sure to both NO 2 and clean air as a control, they allowed determination of the independent contribution of NO 2 on airway responsiveness. An evaluation of all other agents or factors that might affect airway responsiveness, as suggested b y the commenters, w ould not better define the independent effect of NO 2 on airway responsiveness. Table 3.1

- 3 in the Final I SA specifically provided the fraction (or frequency) of NO 2 - exposed asthmatics experiencing non

- specific airway hy perresponsiveness. The I SA concluded that “[t]ransient increases in airway responsiveness following NO 2 exposure have the potential to increase s ymptoms and worsen asthma control” (ISA, section 5.4). Given this, combined with the large size of the asthmatic population in the U.S., the REA c oncluded that it is appropriate to consider NO 2 - induced airway

hy perresponsiveness in characterizing NO 2 - associated health risks(REA, section 10.3.2). CASAC endorsed this conclusion in their letters to the

Administrator on the final REA and on the propos al (Samet, 2008b; Samet, 2009 b ). ( 4 ) Comment: Comment: API expressed the concern that EPA is not using a standard approach to establishing NAAQS. As an example they note that, while EPA has characterized Forced Expiratory Volume (FEV) decrements in the past as adverse health effects, the NO 2 Gradient meta

- anal ys is (Goodman et al, (2009) showed decrements in FEV of onl y 1.6 percent. In revising the ozone NAAQS, a decrement of 3 percent was characterized b y EPA as “relativel y small” and seemingl y not adv erse. Response: EPA disagrees with the commenters’ interpretation of NO 2 - induced changes in airway responsiveness and their approach taken to discern the magnitude of this response. Due to differences in study protocols in the NO 2 - airway response literature (I SA, section 3.1.3), EPA judged it appropriate in the I SA meta

- anal ys is to assess only the fraction of asthmatics experiencing increased or decreased airway responsiveness following NO 2 exposure. Examples of differences in the study protocols include the NO 2 exposure method (i.e., mouthpiece versus chamber), subject activity level (viz., rest versus exercise) during NO 2 exposure, choice of airway challenge agent, and phy siological endpoint used to quantify airway responses. Therefore, EPA judged it in appropriate in the ISA meta

- anal ys is to try to assess the magnitude of the NO 2 - induced change in airway

responsiveness. EPA further notes that Goodman et al. (2009) also recognized heterogeneity among studies as a limitation in their anal ys es. EPA furth er disagrees with the commenter’s comparison and interpretation of the effect of ozone on FEV 1 versus the effect of NO 2 on airway responsiveness to challenge which was subsequentl y assessed by FEV 1 in some studies and by other ph ys iological endpoints such as specific airway

resistance in other studies. Ozone itself causes transient decrements in FEV 1 , whereas, NO 2 does not. Rather, in individuals with asthma, NO 2 - induces an increase in the responsiveness of the airway s to subsequent challenge. FEV 1 is only one of several phy siological endpoints used to discern that a change in airway responsiveness has occurred. Based on studies that evaluated these different endpoints , the I SA concluded that “[t]ransient increases in airway responsiveness following NO 2 exp osure have the potential to increase s ymptoms and worsen asthma control” (I SA, section 5.4). Given this, combined with the large size of the asthmatic population in the U.S., the REA concluded that it is appropriate to consider NO 2 - induced airway hy perres ponsiveness in characterizing NO 2 - associated health risks (REA, section 10.3.2). CASAC endorsed this conclusion in their letters to the Administrator on the final REA and on the proposal (Samet, 2008b; Samet, 2009 b ). Insummary , ozone causes transient changes in FEV 1 , whereas, NO 2 causes transient changes in airway responsiveness

. These are different health endpoints and EPA disagrees with the commenter’s comparison and interpretation. ( 5 ) Comment: AAM concludes that “[r] eliance on the Orehek et al. 19 76 study in an unpublished meta

- anal ys is to claim an effect at 0.10 ppm is scientifically unsound.”Response: Orehek et al. (1976) was peer

- reviewed and published in a scientific journal.

EPA specificall y recognized criticism of the statistical approa ch used b y Orehek in section 15.3.1 of the 1993 NOx CD. However, the statistical significance of findings presented b y Orehek et al. (1976) were not material to inclusion of data into the meta

anal ys is provided in the 1993 NOx CD or the Final I SA. EPA reje cts the assertion that inclusion of the Orehek et al. (1976) study in its meta

- analy sis was scientifically unsound. EPA further notes that the Orehek et al. (1976) study data were also included in the anal ys is by

Goodman et al. (2009). ( 6 ) Comment: AAM a lso concludes that “[t] he effects of NO 2 from controlled studies have not changed materially

since the last review.” Given this, they question EPA’s conclusion that exposure to NO 2 concentrations at or above 100 ppb could increas e airway responsiveness in asthmatics. Response: As shown in Table 15

- 10 of the 1993 NOx CD, data from four studies at 100 ppb and a study at 140 ppb were anal yz ed as a group and showed increased airway responsiveness in 65% of resting asthmatics (p < 0.01). As shown in Table 3.1

- 3 of the Final ISA, even when this analy sis is limited to three studies of changes in nonspecific airway responsiveness following exposure to 0.1 ppm NO 2 , 66% of resting asthmatics (p ≤ 0.05) experienced an increase in airway responsiveness. Therefore, as discussed in section II.E.2.b of the final rule, EPA concludes that scientific evidence reviewed in both the 1993 NOx CD and Final I SA support that expos ure of asthmatic individuals to levels of 0.1 ppm NO 2 and greater results in an increase in their airway responsiveness. In addition, since the 1993 NOx CD, there is a substantial new body of epidemiological evidence showing that short

- term NO 2 exposure i s associated with a broad range of respiratory

morbidit y effects (Final I SA, Section 3.1). This new epidemiological evidence is consistent with and supported b y controlled human exposure studies showing effects of NO 2 on airway

responsiveness. ( 7 ) Commen t: AAM concluded that, because clinical studies of NO 2 - induced airway hy perresponsiveness have not reported increased respiratory s ymptoms or medicine use in exposed subjects, the NO 2 effect on airway responsiveness is not adverse. Response: The inte nt of the clinical studies to which the commenter refers was to evaluate the effect of NO 2 exposure on airway responsiveness, not to evaluate the effect of airway hy perresponsiveness on respiratory s ymptoms or medicine use. EPA disagrees with the commenter s’ characterization of these studies. 

### D. Comments on air quality, e xposure , and risk a nalyses (1) Comment: Several commenters discussed the analy ses of NO 2 - associated exposures and health risks presented in the REA. As in past reviews (EPA 2005 a , 2007 a , 20 07 b ), EPA has estimated allowable risks associated with the current standard and potential alternative standards to inform judgments on the public health risks that could exist under different standard options. A few industry commenters ( e.g., API, NMA , UARG ) concluded that the Administrator should consider modeled exposures and risks associatedwith actual NO 2 air quality rather than with NO 2 concentrations adjusted to simulate just meeting the current annual standard or potential alternative 1

- hour stand ards . These commenters noted that such simulations require large adjustments to air quality and are highl y uncertain and that NAAQS are intended to address actual, rather than highl y improbable, risks to health.
Response: These comments and EPA res ponses are discussed in detail in section II.E.2.c of the final rule. (2) Comment: API/AECOM (December 1, 2008 memo) specifically commented on the EPA approach used to assess air quality that would just meet the current and alternative standards. The three major comments were focused results in the EPA memo by Rizzo (2008) that investigated trends in NO 2 air quality concentrations over time. The commenters charged that (1) the high concentration to low concentration air quality comparisons are not line ar and not proportional, (2) even with “a good fit to the data, the peak

- to
- mean ratio depends on the extremes of the distribution”, and added that the good statistical fits Rizzo (2008) provided are the result of the “middle percentile values, e.g., from 10% to 90%”, and (3) the ambient concentration adjustment “does not consider the atmospheric chemistry

that is involved in the formation of NO 2 from NO X emissions”.
Response : The current and alternative standard air quality scenarios are h ypothetical sc enarios, with the adjustments to the ambient concentrations determined by an anal ys is of the historical trends in air quality data at each monitor. EPA noted in the REA (section 7.4.5) that “there is uncertainty in adjusting concentrations” considering un certaint y in “future source emission scenarios and how these would relate to observed trends in current and historical air quality .” However, given the demonstrated strong relationship of these concentrations over time by Rizzo (2008), EPA believed a prop ortional approach would best represent the modeled air quality scenarios. EPA agrees that demonstration of a linear relationship between the high and low concentration years is not the same as a proportional relationship. EPA acknowledged the presence of features that deviate from proportionality

in the air quality

comparisons (i.e., presence of positive and negative regression intercepts, curvilinear relationships) as potentially contributing to uncertainty in the estimated concentrations used in the alt ernative air quality standard scenarios (REA page 131). The Rizzo (2008) analy sis of air quality concentration trends not only provided graphical comparisons and general goodness of fit statistics but also provided statistics on the individual points that deviated significantly from linearity for up to three high

- ye ar to low

- ye ar comparisons per monitor. “Studentized residuals were computed and compared to a students t distribution at a significance level of 10%” (Rizzo (2008) page 5). The identif ied points are provided in a series of tables for each ambient monitor in the six cities anal yz ed (Tables 1 to 6). On average, 71 percent of the points that significantly deviated from linearity

occurred at the absolute extreme ends of the air quality dis tribution (i.e. the minimum (0) and maximum (100 th ) percentile values). Whenconsidering deviations that occurred at the upper percentiles (i.e., ≥95 th percentile), 3 an

even greater percentage (74%) occurred at the absolute maximum value. This indicates that the linear relationship extends well beyond the 90 th percentile value for the majority of the comparisons; that is on average, the upper bound of the linear range extends through the 99 th percentile of the distribution. EPA acknowledged that, given the scenario modeled and the deviations from proportionality , the selected approach may contribute to both over and under

- prediction in ambient co ncentrations (Table 7

- 31, REA). As far as the impact of deviations from proportionality , Rizzo (2008) added that “[i]n the majority of the monitor cases, the y intercept of the best fit line is positive” and that this “indicates a larger decline between h igh and low ye ar concentrations in the upper end of the distribution than in the lower percentiles”. Further Rizzo (2008) stated “[m]ost although not all of the 98 th and higher percentile points that deviate from their best fit lines do fall below the lin e”, meaning “that percentile point has declined even more strongl y than the middle of the distribution”. For these cases (where a positive intercept exists and upper percentile points are below the linear regression line), when adjusting concentrations up wards based on the annual average concentration, the adjusted upper percentile concentrations would be lower than that observed during a comparable high concentration ye ar. Most of the alternative standard scenarios required an upward adjustment (see comm ent below). Therefore, it is possible that most of the extreme upper percentile concentrations used in the alternative standard scenarios were under

- estimated using the proportional adjustment approach rather than over

- estimated. At the limited number of monitor

- ye ars noted b y Rizzo (2008) where a negative regression intercept was present and upper percentile points are above the linear regression line, it is possible that the extreme upper percentile concentrations used in the alternative standard scenarios were over

- estimated. EPA agrees with the commenter that the primary transformation reaction for NO 2 is through reaction with atmospheric oxidants, primarily ozone. However, this transformation reaction and the potential amount of ozone needed for th e reaction to occur is not needed to address the h ypothetical alternative air quality scenarios . One focus of the NAAQS review is to determine the level of the pollutant that is protective of public health. In this instance, the integrated review plan po ses a series of questions relevant to the NO X review including “Do exposure estimates suggest that exposures of concern for NO X - induced health effects will occur with current ambient levels of NO 2 or with levels that just meet current, or potential alternative, standards?” (US EPA, 2007a). As stated, the objective is to determine what level of NO 2 is considered protective against health effects associated with NO 2 exposures, not what level of NO 2 is plausible under certain atmospheric conditions. It can a lso be stated that future strategies that control ambient ozone concentrations such that the ozone NAAQS would be met are to protect against the health effects associated with ambient ozone (and other atmospheric oxidants ozone is serving as a surrogate fo r), not ambient NO 2 .

3 There were no upper percentile values les s than the 95 th percentile determined as statistically significant.(3) Comment : Comments from the American Chemistry Council (ACC; May 30, 2008 memo) were also directed towards anal ys es of the current and alternative air quality scenarios, however these commenters primaril y questioned the relations hip between anal ys es conducted b y M cCurdy (1994) used in the prior 1995 NAAQS review and the current anal ys es. These commenters suggest that conclusions drawn during this current NAAQS review regarding the relationship between concentrations and benchmark exceedances differ from conclusions drawn in the previous NAAQS review. The commenters also charge that “for each monitor in the city , EPA determined the annual average concentration and scaled all hourl y concentrations by the ratio of the current standard (53 ppb) and the annual average concentration.” A series of comments were received in three technical memos dated b y the ACC on May 30, 2008 (regarding the 1 st draft REA), September 26, 2008 (regarding the 2 nd draft REA without chapter 8), October 22, 2008 (regarding the 2 nd draft REA chapter 8), and summarized in their September 14, 2009 memo. Response : The conclusions drawn in the current NAAQS review regarding the relationship between annual average NO 2 concentrations and frequency of 1

- hour benchm ark exceedances are not necessarily contrary to conclusions made in the prior NO 2 primary

NAAQS review, as the ACC suggests. In fact, section A

- 6 of Appendix A (US EPA, 2008 c ) documents the investigation of both linear and non

- linear relationships between number of benchmark level exceedances and the annual average NO 2 concentrations using recent ambient monitoring data (i.e., years 1995

- 2006). As described in the Scope and Methods Plan (US EPA, 2007), EPA planned to perform a similar non

- linear regressio n modeling approach first described b y M cCurdy (1994). The non - linear regression approach used b y M cCurdy (1994) to support the previous 1995 NAAQS review was developed to estimate the number of exceedances associated with varying annual average concentrations, including the current standard of 0.053 ppm. As part of the current review, EPA expanded the regression approach used by McCurdy (1994) and evaluated four different regression models (either using normal or Poisson distributions by

linear and expon ential links) and using either all data combined or data stratified by

location (see Appendix A

- 6, US EPA, 2008 c ). The current regression anal ys is included construction of a model similar to that used by McCurdy

(1994) (i.e., a normal distribution, an exp onential link, and stratified by location). The performance of all regression models constructed was evaluated using R

- square and log

- likelihood statistics. While a model employing a Poisson distribution and using an exponential link function demonstrate d the best performance of the models currentl y investigated (i.e., it was still a non

- linear relationship though different from that derived b y M cCurdy (1994)), the overall predictive capabilities of such a regression approach was generall y poor, particularl y for evaluating annual average NO 2 concentrations just meeting the current standard. For many locations, there were extremely wide 95% prediction intervals estimated using the regression models, a direct result of data limitations (i.e., there were very few exceedances of benchmark concentrations > 150 ppb using recent ambient concentrations and most locations had annual average NO 2 concentrations well below the current standard). These results presented in the REA are entirely consistentwith the stat ement made in the 1995 staff paper that was cited b y the ACC as a different

conclusion: However, because all areas of the country reporting NO 2 air quality data are attaining the existing standard and because of the nonlinear relationship of 1

- hour peaks and annual averages, it is not possible to estimate with any degree of confidence what the frequency and magnitude of 1

- hour peaks would be if the standard was selected from the upper end of the suggested range. Based on the performance results of the regression anal ys es (and documented in Appendix A

- 6), an alternative approach was selected to evaluate the number of benchmark exceedances associated with annual average and other time

- averaged NO 2 concentrations. Rather than using a regression model constru cted from the as is air quality to extrapolate to ambient levels approaching the current or alternative standards, EPA adjusted the ambient NO 2 concentrations such that they simulate levels of NO 2 that just meet a standard. These adjusted ambient data “allow comparisons of the level of public health protection that could be associated with just meeting the current and potential alternative standards ” (REA, page 59). A proportional approach was used to adjust the as is air quality to simulate air quality just meeting the current and alternative standards (see REA section 6.3.1 and Appendix A

- 7). Because all locations currently have ambient NO 2 concentrations below the current standard, an approach was needed to, at a minimum, adjust concentrations upwards to reflect concentrations that just meet the current annual average standard in the location. The approach also needed to be appropriate for adjusting air quality that just meets several potential alternative standards, standards of varying form (98 th an d 99 th percentile), concentration level (50, 100, 150, 200 ppb), and averaging time (1

- hour). A proportional adjustment approach was selected b y EPA and justified by the results of two anal ys es: the evaluation of the stability in hourl y and annual average concentration variability

over the span of the data used in the analy sis (Appendix A

- 7) and the comparisons of concentration distributions of historical and recent air quality (Rizzo, 2008). While annual and hourly NO 2 concentrations have steadil y declin ed over time, the concentration variability in each of these measures has generall y remained constant over the same time period (Figure A

- 100). Concentration trends within monitoring sites in six cities were evaluated to determine how the distribution of air quality changed with time at each monitor. In comparing high concentration (historical air quality) to low concentration years (recent air quality) at the same ambient monitor, the majority of monitors demonstrated features of proportionality , that is the proportional change in concentration at each percentile of the air quality distribution was similar. The results of both of these anal ys es indicated that a proportional approach can be used to adjust ambient concentrations (upwards or downwards) in r epresenting alternative air quality conditions. Ambient measurements at a single monitor were used within each of the 17 named locations and with the two aggregate locations to estimate the specific adjustment factorsneeded to simulate air quality just meeting the current and alternative standards. This single design monitor in each location was selected by having the highest annual average NO 2 concentration or the highest 98 th or 99 th 1

- hour daily maximum NO 2 concentration to estimate the respective a djustment factors. Because the concentration adjustment was considered proportional, all 1

- hour concentrations were multiplied by the same specific factor developed for each air quality scenario and in each location. The adjustment factors developed from the single monitor in each location was applied to concentrations at all monitors within each location, such that only one monitor had concentrations that just met the current or alternative standard (i.e., the design monitor), while all other monitors in that location had ambient concentrations below that of the current or alternative standards (page 61, REA). Following the proportional adjustment of ambient NO 2 concentrations (as well as when using the as is air quality), the number of exceedances of ea ch benchmark were counted. This approach does not assume there is a linear relationship between the annual average NO 2 concentration and the number of benchmark exceedances. The commenter is confusing the proportional approach used to adjust the ambient concentrations (where comparisons of high concentration with low concentrations demonstrate features of proportionality

– see Rizzo, 2008) with the regression models that related the number of exceedances with the annual average concentrations (which is no t linear, as demonstrated by the conclusions in the prior 1995 review, is discussed above, and is documented in REA Appendix A

- 6). The two approaches are not comparable in this regard, though the objective of each anal ys is is the same; to estimate of the number of 1

- hour benchmark exceedances when considering alternative air quality

scenarios. There is uncertainty associated with such a concentration adjustment and has been qualitatively

described in REA section 7.4.5. However, EPA notes that there is li kel y less uncertainty in the approach and results generated when using adjusted concentrations that are closest to existing as is air quality . For most locations, this was the either a 98 th or 99 th percentile alternative standard at a 1

- hour daily maximum concentration of 50 ppb (see Table A

- 107). 4 On average, to have air quality just meet the alternative 1

- hour dail y maximum standard level of 50 ppb, the minimum concentration adjustment was less than 10% and ranged from a low of zero percent (i.e., the as is air quality for a given location had either the 98 th or 99 th 1

- daily maximum equal to 50 ppb) to only as high as 28 percent. To simulate just meeting the 50 ppb level of either the 98 th or 99 th percentile 1

- hour daily

maximum standard, a downward adj ustment of air quality was applied in most locations and year - group of data considered. 5 To just meet the 100 ppb level (either form of the 1

- hour daily

maximum standard), all locations required an upward adjustment. At this 100 ppb level, the 99 th perce ntile daily maximum standard required the lowest concentration adjustment at all locations; on average, the upward concentration adjustment was 70% (min 1%, max 131%). Taken together, this means that most

4 Only L os Angeles (2001

- 2003), Other CMSA/MSA (2001

- 2003), and Provo (2004

- 2006) had as is air quality

more similar with a 1

- hour 99 th percentile 100 ppb standard level out of a total of 38 location/year - group combinations. 5 When considering the two forms (98 th and 99 th ), the 19 locations, and two year

- groups (2001

- 2003 and 2004

- 2006), 61/76=80% needed a downward adjustment to meet the 50 ppb level.locations have as is concentrations within the ran ge of the two alternative standard levels

of 50 to 100 ppb and within the range of the newly proposed standard. As the data for simulating just meeting these standard levels required the least concentration adjustment, there is less of an impact of the un certainty associated with the air quality adjustment procedure on the estimated number of daily benchmark exceedances associated with these air qualit y scenarios. ( 4 ) Comment: AAM (September 14, 2009 memo) claimed that the approaches used in the REA to characterize health risks from ambient NO 2 lead to significant overestimation of actual risk

. Specifically , they argued that the first approach ( comparing monitoring data with potential health benchmarks) is known to overestimate the distribution of actual human exposures because monitored concentrations do not necessaril y equal human exposures. Response: EPA believes that the ambient air quality has been appropriatel y characterized in chapter 7 of the REA. The REA also provides ample context for how th e ambient air quality data can serve as a useful indicator of human exposure (sections 2.3.2, 6.1, 9.6, and 10.3.2). EPA recognizes that population personal exposure is not directly equivalent to ambient air quality

measurements however there is no justif ication for discounting the ambient monitoring data simply because they

are perceived by

AAM to “overestimate personal exposures.” The data represent actual measurements of NO 2 levels that a population may

be exposed to, provided the population encounters the given concentration in both space and time. EPA notes that the available evidence indicates that at

- risk populations can be exposed to ambient NO 2 concentrations greater than that represented b y an ambient monitor. EPA has clearly

stated in the REA and NPRM that the current ambient monitoring network does not have a sufficient number or appropriate siting of monitors to reflect NO 2 conce ntrations occurring on or near major roads in most, if not all, urban areas of the U.S. The existing monitoring ne twork is not designed to capture the spatial gradient in NO 2 concentrations surrounding roadway s in an y location, which is why modeling approaches were selected b y EPA staff to estimate on

- and near

- road NO 2 concentrations. ( 5 ) Comment: AAM (September 14 , 2009 memo) comment ed that “there are no reliable data indicating either on

- road or near

- road exposure in recent ye ars that exceed the 0.20 or 0.30 benchmarks” and referenced several studies to support their claim

. Response : EPA notes first that the ben chmark values have an averaging time of 1

- hour. None of the studies cited by the AAM reported 1

- hour NO 2 concentrations. For example, AAM cites Beckerman et al. (2008) and Singer et al. (2004), which were both studies where weekly average concentrations were measured. A paper by Roorda

- Knape et al. (1998) is also mentioned, where two
- week average concentrations were measured. Given the expected diurnal and day

- of

- week variation of NO 2 concentrations (see ISA, section2.4.4) it is not a surprise that th e average concentrations reported in these studies do not

approach a peak 1

- hour NO 2 concentration at or above 200 ppb. There were onl y two studies cited by AAM that measured NO 2 concentrations inside vehicles: a study b y Westerdahl et al. (2005) condu cted in L os Angeles, CA and one by Riediker et al. (2003) conducted in Raleigh, NC. EPA notes that the researchers in the Los Angeles study

did measure NO 2 concentrations across a two

- hour averaging period, which is the closest an y measurement study came to a 1

- hour averaging period. However, based on the study design, the primary

purpose of the study

is to collect data more relevant for PM exposure than for NO 2 exposure. T he time

- of

- ye ar the data were collected may

not correspond to when NO 2 concentrati ons are highest. The NO x ISA reported that “ in L os Angeles and Riverside, CA, monthly maxima tend to occur from autumn through earl y winter, with minima occurring from spring through early summer”. EPA notes that the Westerdahl et al. (2005) measured NO 2 on February 14 th and 20 th and April 7 th and 16 th (see Table 2 of Westerdahl et al

. , 2005). In addition, the study drive times when measurements were collected did not necessarily correspond to when NO 2 peak concentrations are expected to occur. Accordi ng to the NO x IS A, “NO 2 ty pically exhibits daily

maxima during the morning rush hours ”. Drive times selected for evaluation in the Westerdahl et al. (2005) study were as follows: 2

- 6PM, 11AM

- 1PM, 9AM

- 12PM, and 11AM

- 2PM, times

- of

- day that do not correspond to the morning rush hours. In the second study cited by AAM that reported NO 2 concentrations on

- roads and inside vehicles, Riediker et al (2003) reported that sample averaging times were about 9

- hours in duration and all occurred “during late

- shift patrols (3 p.m. to midnight)”. As discussed above b y EPA, these collection times are not consistent with the averaging time of interest (i.e., 1

- hour) or the time

- of

- day when maximum concentrations are expected to occur (i.e., morning rush hours). Second, the monitoring events in the Riediker et al. (2003) study

did not alway s occur on - or near major roadway s. Often times the automobile was parked in a lot, potentially further limiting the measurement of any maximum NO 2 concentrations. Riediker et al. (200 3) states “[o]n average, troopers spent 35% of their shift away

from the car, either in the office, in jail, in hospitals, for dinner”, etc. The authors of the study also note that “pollutant concentrations in the occupied cars were significantly

higher c ompared to the parked cars (Mann

- Whitney U

- test)” (Riediker et al., 2003). In their comments, AAM stated that the maximum concentration of 0.548 ppm reported b y Riedeker et al. (2003) was “flawed” and “invalid”. N owhere in the Riediker et al. (2003) pape r was it stated that the 9

- hour average NO 2 measurement was flawed or invalid, only

mentioned as an “outlier”. Thus, this maximum reported NO 2 concentration remains a valid measurement. In further review of this paper, EPA notes also that the reported maximum 8

- hour average roadside NO 2 concentration did in fact exceed 200 ppb (212.1 ppb; see Table 1 of Riedeker et al. (2003)), contradicting the above AAM comment. Given the diurnal profile of NO 2 , this suggests that on this day there was likel y more than one hour where roadside concentrations exceeded 200 ppb. ( 6 ) Comment: AAM (September 14, 2009 memo) commented that the distribution of ratios used to represent the relationship between on

- road and ambient concentrations in the airquality characterizat ion (chapter 7 of the REA) resulted in overestimates of on

- road NO 2 concentrations. AAM refer to a statement made by Westerdahl et al. (2005) regarding the relationship between on

- road and ambient concentrations that “roadway concentrations of [CO and] NO 2 were usually no more than about twice the ambient concentrations”. They further comment that higher ratios developed using lower background concentrations will not be appropriate in urban situations having a high background and will “substantially over - estimate the on

- road increment”.
Response: EPA note s that this statement made by Westerdahl et al. (2005) supports an upper bound for the ratio between on

- road and away from road concentrations of at least two. In other words, on

- road NO 2 concentrations may be at least 100% higher than away from road concentrations. This percent difference is consistent with statements made in the REA about the on

- road concentrations that “simulated on

- road annual average NO 2 concentrations are, on average, 80% higher than the respective ambient levels at distances ≥100 m from a road” (section 7.3.2, page 97) and statements made in the ISA regarding the relationship between the two concentrations (section 2.5.4, page 2

- 36). In addition, the use of “usually” b y Westerdah l et al. (2005) in their description indicates that most of the time the ratio was a factor of two or less , but also suggests that there were some instances that the factor difference was greater than two. This statement also supports the ratios EPA used to adjust ambient NO 2 concentrations in estimating on

- road concentrations. Table 7

- 10 (REA) indicates that most of the ratios (64% and 79%, for the summer and not summer ratios, respectively) used by EPA in estimating on

- road NO 2 concentrations were less than a factor of two. 6 EPA also note that in addition to the several papers EPA used to develop the on

- road ratios used in Chapter 7 of the REA, an average factor of two enhancement on

- or near roads concentrations is also reported by Beckerman et al. (20 08) using the normalized NO 2 concentrations provided in that study (see Figure 4 of Beckerman et al., 2008). EPA believes that the ratio approach developed from measurement data available in near

road studies and used to simulate the on

- road NO 2 concentrations in the REA chapter 7 was reasonable. EPA acknowledged in the REA that there is uncertainty in the estimated on - road NO 2 concentrations, particularl y when using ambient monitoring concentrations that may have been influenced by non - road sources (e.g. , section 7.4.6 REA, page 135). We agree with AAM that this particular uncertainty in the approach used to simulate on

road concentrations would tend to lead to overestimation of on

- road NO 2 concentrations. However, EPA note s that there are other sources of uncertainty indentified in the approach used that could also contribute to underestimation of on

- road concentrations. Localized areas such as those within urban street can yons, tunnels, and major intersections may

have instances where on

- road NO 2 conc entrations are greater than a factor of two times the ambient monitor concentration. For example, Vardoulakis et al. (2004) reported mean NO 2 concentrations at a major intersection were about 2.1 times greater than on

- road NO 2 concentrations measured a fe w hundred meters distance away

.

6 Note that to generate the ratio, the m factor has a value of 1 added to it. See REA equation (7

- 2).The I SA (section 2.5.4) reported that NO X concentrations can be 7 times greater at a

tunnel exit when compared with NO X concentrations measured at the tunnel entrance
. Note that the maximum ratio used to simulate on

- road c oncentrations in the air quality characterization was 3.7 (REA, Table 7

- 10). In addition, EPA also acknowledged that there could be uncertainty in the application of ratios developed from rural locations to urban locations (see REA page 137). However, gi ven the limited information on the characterization of the study areas used to develop the data, the limited number of studies containing relevant data, and that there was no apparent difference observed in the distribution of developed ratios when conside ring the study locations as having a rural or urban designation, EPA elected to stratify and appl y the ratios based on observed seasonal differences in the distributions. ( 7 ) Comment: AAM commented (September 14, 2009 memo) that AERMOD was developed and tested primarily for stationary

source applications. AAM reference d a recent EPA review of 21 air

- qualit y modeling tools that simulate line

- ty pe sources to use in near roadway s applications ( EPA/600/R

- 09/001) including an evaluation of AERMOD and several other roadway dispersion models. AAM states th at this “EPA review indicates that AERMOD has not been compared rigorousl y for line source applications and that it contains a very simplistic algorithm for line sources.” Response: First , the highway s in At lanta were simulated not as line sources, but as a set of area sources, a common use of this regulatory model. Second, the referenced EPA review (US EPA, 2008) explicitly cites numerous comparisons of AERMOD in various configurations to the performance of some of the other available models, with AERMOD consistently providing reasonable concentration predictions. For example, “ AERMOD was evaluated with respect to other models such as ADMS

- Roads, ISCST3, and CTDMPLUS. When considering onl y the highest pred icted and observed concentrations, it was found that I SCST3 overpredicts by a factor of seven, on average, whereas ADMS

- Roads and AERMOD underpredicted, on average, by about 20%. It also was determined that ADMS

- Roads performance is slightly better than A ERMOD (Hanna et al., 1999). In complex terrain, AERMOD consistently produced lower regulatory design concentrations than IS CST3, not an unexpected result because IS CST3 uses algorithms from a screening model (COMPLEX1) in its calculations. In comparisons with CTDMPLUS and observed data, AERMOD consistently

performed better than CTDMPLUS, a model approved b y EPA for regulatory

applications in complex terrain. The model has not been compared rigorousl y for line

- source applications. Because AERMOD is used m ost commonly for dispersion anal ys es of stationary

point sources, area sources, and volume sources, there is n o accommodation for different roadway geometries (e.g., bridges and deep roadway cuts). ” Although AERMOD does not currentl y accommodate complex roadway geometries, enhanced turbulence, plume rise, and other characteristics of near road dispersion can be accounted for b y selection of appropriate input parameters, such as initial sigma

- y, initial sigma

- z, and emission release heights (each of which are documented in the REA).Furthermore, according to Appendix W (70 FR 68218), “ AERMOD is a best state

- of

- the

practice Gaussian plume dispersion model whose formulation is based on planetary boundary layer principles ” and is the current preferred model f or near - field and urban

scale air dispersion modeling applications. While Appendix W lists CALINE

- 3 as the preferred model for roadway s , this model is not generall y applicable for modeling long periods in very

large, complex modeling domains such as that considered here. In fact, CALINE

- 3 and CAL3QHCR rely on older dispersion algorithms from ISCST2 (Bailey , 2009), further justifying the use of AERMOD rather than CALINE

- 3 or CAL3QHCR. We note also that currently available versions of the MOVES emissions model will predict NO X emissions 30

- 50 percent higher than the MOBILE model used in the present anal ys is (Beardsley , 2009), suggesting that the newer emissions model would have predicted even higher NO X concentrations and therefore higher NO 2 concentrati ons. Moreover, following analy sis of this dispersion model review report (US EPA, 2008) by Is akov (2009), AERMOD was chosen as the best platform for further model development to address roadway

scenarios . Given the diversity of source emissions, complex ity of the scenario to be modeled in an urban environment, and requisite spatial and temporal resolution for detailed analy ses used in estimating exposures, AERMOD was also judged here to be the most appropriate model for this application. ( 8 ) Comment: AA M (September 14, 2009 memo) believe s that the second approach used to characterize health risk ( estimating risk based on detailed exposure modeling ) , for a variet y of reasons, overestimate s the risk from NO 2 . One reason identified by AAM was that since AE RMOD is not a photochemical model, it does not include the key reactions converting NO to NO 2 in urban areas. In particular, concern was expressed by the commenter regarding EPA assumptions made for the photochemical conversion rate as an air pacel moves downwind, and questioning whether peak NO 2 concentrations are likely to occur on or next to the roadway

. API/AECOM (September 14, 2009 memo) had similar comments regarding the OLM and PVMRM methods used by AERMOD, that is “[b] oth methods are simple and co nservative because they assume that only

nitric oxide titration by

ozone (Equation 2) governs NO 2 formation and that all of the ambient ozone can be consumed ”. L ater they commented “ consideration should be given to using a model platform that includes plume transport time so that if time dependant chemical reactions are needed, they can be included as a function of transport time ”. Response: As discussed in the REA, the AERMOD model was selected to provide the high spatial resolution required for this e xposure assessment. Although the chemical parameterizations of the AERMOD model are far less detailed than the chemistry algorithms in photochemical models, in the near field, no photochemical model would have provided the necessary spatial resolution for this study . Furthermore, most photochemical models are optimized for predictions of O 3 , and may not provide adequate performance in predicting NO 2 , even at the coarser spatial scales at which they areapplied. Given these considerations, AERMOD was jud ged to be the most appropriate

model for this application. EPA recognize s that numerous photochemical reactions take place in the troposphere that influence the relative concentrations of NO and NO 2 from NO X emissions. The complex reactions can be commo nly summarized as: VOC + NO X + h   O 3 + PAN + HNO 3 ... + Particles, etc. (1) (Finlay son - Pitts and Pitts, 1999). However, to a first order, the characterization of the ratio of concentration of NO to NO 2 can be represented by the photostationary

state equation: 

##   ] [ ] [

4 2 3 3 NO k NO j O  ( 2) where j 3 results from the following NO 2 + h   NO + O (3) and k4 from the following O 3 + NO  NO 2 + O 2 . (4) (e.g., Atkinson et al., 1988). This describes a photostationary state where NO and O 3 cannot coexist in significant concentrations and the concentration of NO 2 is proportional to the concentration of O 3 . The commenter(s) stated that the mechanisms in AERMOD do not appropriately parameterize the role of organics in the processing of NO to NO 2 via equation (2). However, although NO is conve rted to NO 2 in a reaction sequence initiated by the hydrox ylradical in an attack on organic compounds and involving numerous free radicals, much of the OH and HO 2 radicals involved are themselves created by photo

reactions involving O 3 . Thus, to the firs t approximation, equation (2) is a reasonable approximation of the balance of NO 2 and NO X , particularl y during the daytime when NO 2 concentrations are highest. While the OLM/ARM workgroup (1998) noted that “oxidation by ozone is ty

picall y the main reacti on for NO 2 formation ”, and that “ the reaction rate is essentially instantaneous” , they

also noted that “ the total amount of NO 2 conversion is limited by how quickly

the plume entrains surrounding air”. Therefore, the OLM algorithms may somewhat overstate the on

- road and near

- road NO 2 concentrations (all other factors being equal) b y not accounting for the possibility of limited entrainment of O 3 - laden air in locations with limited mixing, such as street can yons. However, given the rapid formation of NO 2 i n the presence of ozone, we feel that incorporating transport time intoa model formulation would be unlikely to substantially

affect model predictions in this application. T he location of the peak NO 2 concentration in this study were derived from objec tive modeling predictions, not a priori assumptions. OLM’s characterization of NO 2 /NO X ratios as a function of downwind distance is documented in a series of sensitivity tests by MACTEC (2004). The concentration of NO 2 is a function of both the photostat ionary balance of equation (2) within the plume and the decreasing concentrations of the dispersing plume. Despite certain limitations in the OLM approach identified above, the model predictions show good agreement with measured values off the roadway . And as discussed below, the onroad model predictions compare favorabl y with reported measurement values at other locations. ( 9 ) Comment: API/AECOM comment ed that “th ere are man y other sources of NO that are already competing for ambient ozone ”... “unless the ambient monitor is located in an area similar to the source, it is unrealistic to assume that all of the monitored ozone is available to convert NO to NO 2 ” at the source location. Response: We agree that the modeling methodologies could be strengthene d by enhanced resolution of O 3 concentrations. However, the scale over which the reactions occur is critical. Monitors should represent the average concentrations to which the plumes are exposed in traveling from a source to the receptor, not the O 3 conc entrations immediately

adjacent to source , where the noted titration will reduce the O 3 concentrations below that available elsewhere in the domain. The exception would be where the receptor is immediately adjacent to the source, e.g., the on

- road and ne ar - road microenvironments. In these cases, the OLM algorithms may somewhat overstate the on

- road and near

- road NO 2 concentrations (all other factors being equal) b y not accounting for the possibility of limited entrainment of O 3 - laden air in locations with limited mixing, such as street can yons. However, for this study the overall model performance appears to be reasonable, both when compared to literature values and when compared to regional observations (see comments responses 8 through 10 below). ( 10 ) Comment: AAM (September 14, 2009 memo) comment ed that, “In addition to mis

characterizing the spatial distribution of NO 2 , AERMOD mis

- characterizes the temporal distribution, as shown in Figure 8

- 7 of the REA where the modeled peak NO 2 from the morning r ush hour occurs about three hours earlier than the peak in the monitored concentrations in Atlanta. ” They further comment “m aximum concentrations occur under conditions of minimum dispersion where the impact of turbulence and heat generated b y traffic wil l be greatest. Since the EPA review acknowledges that AERMOD has not been rigorousl y evaluated for line source applications and the algorithm issimplistic compared to other line source models that account for turbulence and other

traffic effects in greate r detail, its predictions of maximum roadway impacts are suspect. ” API/AECOM had similar comments on the diurnal concentration profile stating
“ AERMOD is somewhat successful in simulating the afternoon dip in NO 2 concentrations associated with increased atmospheric ventilation, but the model substantially

overestimates (with about 50% to 70% over prediction) and prematurel y times the earl y morning and evening peaks. The overestimates are probably associated with an overestimation of ambient ozone and the overly conservative treatment of atmospheric reactions that limit peak NO 2 concentrations. ” Response: The discrepancy between modeled and observed peak concentration when considering the diurnal profile is less likely due to the model parameterizations employed than to limitations in the underlying hourly vehicle activity

data from TDM modeling outputs. The activity

data were based on TDM modeling outputs from the regional planning organization and considered the best available information, although som ewhat limited in specification of the temporal profile. Furthermore, the OLM mechanism should not be related to any morning overpredictions since the ambient ozone concentrations are generally low at that time. The uncertainty regarding this input varia ble and magnitude of impact on estimated concentrations was acknowledged by EPA in section 8.12.1.4 of the REA. We agree that with equivalent emissions, maximum concentrations will occur under conditions of minimal dispersion, such as low wind speeds and mixing heights. During these times, ty

pically early morning, effects of vehicle induced turbulence could be significant. However, in the present study, over - predictions occur primarily during the afternoon traffic peak, when ambient turbulence should dom inate any traffic induced values and ambient temperatures are high, minimizing buoyancy effects. Thus any

model over - predictions at these times are less likel y to be due to the parameterized traffic impacts on dispersion. As discussed above, the cited EP A review notes that AERMOD is commonly used for area source applications, which was the way roadway links were characterized for this study ; and input parameters were selected to account for roadway effects. ( 11 ) Comment: AAM (September 14, 2009 memo) c ommented that the data in the “ REA shows in Figures 8

- 6 and 8

- 7 that the AERMOD

- estimated concentrations substantially overestimate measured NO 2 concentrations in Atlanta particularl y at the upper percentiles of the distribution. Figure 8

- 8 also indicates that AERMOD overestimates the maximum on - road concentrations compared to the ratio method used in Chapter 7, which as shown above, itself overestimates maximum on

- road exposures .” A few other commenters made similar comments. For example, ACSBPP and API concluded that AERMOD may overestimate NO 2 concentrations, particularly in the upper percentiles of the distribution. These commenters generall y concluded that, b yrelying on the AERMOD dispersion model, EPA may be overestimating the risk s from current ambient concentrations and the contribution s to risk from on

- roadway and near

roadway exposures . Response: Figure 8

- 8 compares on

- road to no n - road receptor concentration ratios generated by using the concentrations estimated b y AERMOD with concentration ratios generated using the measurement data extracted from the extant literature (i.e., the empirical method

)

. This figure does not compare on

- road concentration predictions. Figure 8

- 8 shows that AERMOD generally predicts both higher and lower (i.e., mo re variable) concentration ratios than the empirical method. The accuracy of neither method could be demonstrated with direct observations, due to the lack of available on

- ro ad , or even near - road, measurement data in the modeling domain. But as noted in the REA, given the greater number of receptors modeled b y AERMOD, the AERMOD approach may better represent the variability in NO 2 concentration ratios than the empirical method. Table 8

- 7 presents a comparison of on

- road NO 2 concentration predictions bet ween the two methods. The comparison suggests that the AERMOD on

- road concentration predictions are higher than those of the empirical method by about 10 to 15 ppb at each percentile level. EPA note s however that the accuracy of neither method could be de monstrated with direct observations, due to the lack of available on

- road measurement data in the modeling domain. Figures 8

- 6 and 8

- 7 show that in the off

- road environment, the high end of the concentration distribution is overestimated at the exact location of one monitor (ID 130890002), but shows very good agreement at the exact locations of the other two (IDs 130893001 and 131210048). For example, Table B

- 37, which presents the data used to construct Figure 8

- 6, shows that for the latter two monitors, the discrepancies between the AERMOD predictions and the measured values for percentiles 90 through 99 is less than 10 ppb. In addition, discrepancies between observed and predicted concentrations are even less when the envelope of all receptors within 4 km of the monitoring location is considered. (1 2 ) Comment: AAM (September 14, 2009 memo) comment that “measured concentrations in on - road and near

- road studies documented in the ISA and summarized in the previous section demonstrate that there are no valid measurements of NO 2 exposures as high as the upper percentiles of exposure predicted by AERMOD. The REA refers to the 0.548 ppm maximum NO 2 concentration in Riedecker et al. ( 2003 ) to support the upper end of the AERMOD predictions, but, as Riedecke r et al. admits, it is not a valid measurement. There is additional evidence in the literature that microscale monitoring will not identify unmonitored “hot spots” of exposure to motor vehicle pollutants. The South Coast Air Quality Management District h as carried out two studies that compared motor vehicle air toxic exposures at microscale sites in Los Angeles suspected of being unmonitored “hot spots” with exposures at current monitoring sites. Inboth cases, the exposures at the anticipated hot spots were similar to the exposures at the fixed neighborhood

- scale monitoring sites.”Response: As noted above, when comparing predicted concentrations, either from

AERMOD or the empirical method, to any measurement data, it is important to consider difference s in averaging times. For example, Riediker et al. (2003) measured NO 2 inside N orth Carolina Highway

Patrol cars on dut y in Raleigh and determined mean concentrations of about 42 ppb with a range of 2

– 548 ppb for measurements of varying durations, with an average sampling duration of about 9 hours. As described above, the authors did not state the maximum concentration of 548 ppb was “invalid” but as an outlier. According to Riediker et. al. (2003), invalid measurements resulting from “laboratory

or handling problems were excluded from the anal ys is.” Note that the roadside measurements from the same study have a mean concentration of about 50 ppb with a range of 13

– 212 ppb (about an 8 hour averaging time). The present study in Atlanta estimated hourly

average on - road concentrations of 43 ± 25 ppb (mean and standard deviation) and a maximum value of 556 ppb (REA Table 8

- 7). Even without considering study

differences (e.g., averaging times, times

- of

- ye ar, times

- of

- day included), the mean and maximum A ERMOD on

- road concentration predictions are comparable with the mean and maximum measured roadside concentrations reported b y Riediker et al (2003). In another study CARB (2003) measured NO 2 concentrations inside school buses on urban and suburban/rural routes in L os Angeles with average commute time of approximately

85 minutes and found c ommute average concentrations of about 70 ppb (urban; range 34

– 120 ppb) and 45 ppb (Rural/suburban; range 23

– 68 ppb) . The mean and standard deviation of the on

- road concentrations from the Atlanta exposure assessment are also consistent with this measurement study

. EPA disagrees with the commenters about the relevance of the MATES studies (II and III) referred to by

the commenter to the exposure assessment presented in the REA. First, the MATES studies were designed estimate risk associated with longer

- term exposures to air toxics, not short

- term 1

- hour exposures to nitrogen dioxide. In fact, NO 2 was not measured in either of these studies. The ambient monitoring w as conducted in neighborhoods potentially downwind of important emissions sources; no measurements were made on

- roadway s. Comparisons were made between concentrations measured at neighborhood microscale monitors to fixed site monitors located several mile s away . The studies do not compare on

- road, near

- road, and away from road concentrations along a specific transect line. The study monitoring objectives were to not only assess potential mobile source influence to neighborhood air quality , but also consi dered influence from other localized sources. For example, in the MATESII study (SCAQMD, 2000) only 3 of 14 microscale monitoring sites used for their “hot

- spot” anal ys is were selected “because of influence and proximity to major mobile sources. Conclusi ons reported b y SCAQMD (2000) are consistent with the AAM comments in that “the monitoring at each of the 14 microscale sites did not register significantly higher levels of an y toxic air contaminants.” SCAQMD also added that “it cannot be concluded that ‘ hot spots ’ do not exist at other locations.” The latter statement is made because of extreme limitations noted in the microscale monitoring program and to caution readersagainst drawing particular conclusions based on the data. SCAQMD notes that “the

i ntent to investigate a number of different sites, with available resources, limited the power of the microscale study to detect localized disparities in air toxic levels. The microscale study should therefore be regarded as more of a “pilot study” than as a study to definitively

address possible differences in community air pollutant exposures within the South Coast Air Basin. These factors should be taken into consideration to avoid possible over

- interpretation of the results.” EPA note s that in the summary statements made for one of the microscale monitors placed to capture potential mobile source influences, “measured concentrations indicate more on

- road activity at Montclair than at Fontana” (SCAQMD, 2000). The MATESIII study does not refer to the mo nitoring of “hot spots” at all. The selection of monitoring sites “ was done to ensure sufficient resolution to monitor representative concentrations of varying land use ty pes and characterize spatial gradients in the Basin” (SCAQMD, 2008). The authors al so note “[a]s in MATES II, due to the limited number of mobile monitoring platforms, each microscale site study lasted for a shorter duration than the overall study for approximately two to several months.” This suggests the same caution should be applied regarding the over

- interpretation of the results as recommended for the MATESII study. It was not apparent to EPA how man y of the five microscale sites used in this study

were placed in areas expected to receive significant mobile source influence, howev er SCAQMD found statistically significantl y higher concentrations of mobile

- source related pollutants at two of their microscale monitors compared with corresponding measurements at paired fixed site monitors. For example, 24

- hour average concentrations o f benzene, ethylbenzene, toluene, and xylene were 5 to 6 times as higher at the Santa Ana site than at the Anaheim site (SCAQMD 2008, page 5

- 8). The other three microscale monitors may have been sited to capture localized emissions other than mobile sourc es, given high concentrations noted for hexavalent chromium, 1,3

- butadiene, and manganese composition in PM 10 . While limited in direct relevance to the REA, in general, the overall trend in both MATES studies support the importance of mobile source influe nce to ambient concentrations. (1 3 ) Comment: AAM (September 14, 2009 memo) commented on the approach used to estimate in

- vehicle and near

- road concentrations used to estimate exposures. Specificall y they state that based on the AERMOD on

- road to non

- road receptor concentrations,
“ multiplicative factors from 1 to as high as 10 to 30 inappropriatel y were being used to estimate near

- road exposures from the estimates of ambient concentrations. ” The commenter argued that “multiplicative factors as high as 30 are clearl y suspect compared to the data in the literature on in

- vehicle NO 2 exposures” They also question the use of the same APEX proximity factor for both in

- vehicle and near

- road microenvironments given the sharp reduction in NO 2 concentrations with distance from a roadway

. Response: EPA compared the on

- road/non

- road ratio distributions derived from the AERMOD hourly

receptor concentrations with those of the ratios derived from on

road/near

- road measurement study data (REA Figure 8

- 8, Appendix B T able B

- 39). For this comparison, the AERMOD concentrations were first time

- averaged across seven day s to approximate the time

- averaging of the literature

- derived measurement data (i.e.,most of these observations were time

- averaged over 7 to 14 day s). Th e seasonal patterns

of the ratios was consistent (summer ratios > not summer ratios), though the AERMOD generated ratios exhibited greater variability and had consistently higher values at the upper percentiles of the distribution. The maximum ratio for the not

- summer season based on the empirical data was equal to the value of the 76 th percentile AERMOD derived ratio. The maximum ratio for the summer season based on the empirical data was equal to the value of the 85 th percentile AERMOD derived ratio. Note that the AERMOD ratios were generated using concentrations from 5,570 on

- road receptors simulated in the modeling domain and the corresponding nearest non

- road receptor at a distance ≥ 100 meters from the road. Given the greater diversity of the AERMOD modeled receptor locations compared with the literature derived data (a total of 11 studies using 36 roadway

sites), we expected there would be greater variabili ty and hence a greater range of ratios in the AERMOD derived ratios. The ratios used for the APEX modeling were calculated using the AERMOD predicted hourly concentrations. Ratios having a 1

- hour averaging time are most appropriate for this APEX applicat ion since the PROX factor is applied to a 1

- hour ambient concentration. EPA expected that there would be greater variability in the 1

- hour ratios, likely generating a distribution of PROX factors having a greater range of values than observed with the lon ger averaging time. EPA notes that there are no data reported in the extant literature that have on

- road/non

- road concentrations or ratios of 1

- hour averaging time. In addition to the seasonal influences observed (summer/not

- summer), EPA also stratified the ratios b y the time

- of

- day based on analy sis of this as a potential influential factor. Three time ranges were selected to further stratify the ratios. Lognormal distributions were then fit to each of the six stratifications, with lower and upper boun ds of the distributions approximated by using the 5 th and 95 th percentiles (Appendix B Table B

- 42). In probabilistic exposure analy ses, setting bounds on a fitted distribution is a commonly

used method to control against exceptional or potentially unreali stic values. Note in REA Table 7

- 34, the minimum and maximum observed on

- road ratios were at the 2.3

- 7.8 th and 94.4

- 97.8 th percentiles, respectively of a lognormal fitted distribution, supporting the selection of the 5 th and 95 th percentiles as reasonable lower and upper bounds. In evaluating the ratio distributions, clearly the daytime (6AM

- 7PM) ratio distributions are distinct and higher than the nightime ratio distributions (7PM

- 6AM), confirming that stratification by

at least two time

- of

- day ranges wa s appropriate. Again, seasonal differences were consistent with that of the ratios derived from the empirical data, confirming that seasonal stratification was appropriate. EPA acknowledges that it is possible that there are other potential influential f actors that could be considered in further stratifying and applying the PROX factors, but given the limited time and resources allocated to perform the assessment, additional analy ses were not performed. When considering (1) the absence of observed on

- roa d concentrations of 1

- hour averaging times, (2) having no on

- road concentration measurements within the modeling domain, (3) the reasonable agreement in the AERMOD concentration predictions with available measurement data, and (4) the reasonable agreement in the AERMOD on

- roadconcentration predictions with simulated on

- road concentrations using the empirical

ratios, EPA believes that the PROX factor distributions generated are an adequate representation of the relationship between on

- road and non

- road conc entrations, even with upper bounds of the distributions that extend to values of 9 to 30. Again, EPA is not aware of an y 1

- hour measurement data derived from a study conducted in a similar urban environment across an entire year that could confirm or refute the level of the upper bound used for each of the ratio distributions. EPA used the same on

- road PROX factor distributions to calculate the near

- road microenvironmental concentrations. The near

- road microenvironment generall y refers to locations in cl ose proximity to vehicle emissions such as sidewalks, bus stops, and parking garages, where concentrations would likely be similar to those on roadway s. Not accounting for decay

/dispersion of the on

- road concentration with such short distances from a roadway

was considered by EPA as an appropriate assumption. EPA notes that the maximum concentration does not alway s occur on the roadway , it can occur at a distance from the road (e.g., Beckerman et al., 2008). Therefore, there may be instances where the ne ar - road concentrations are either greater than or less than that observed on the road. In the absence of robust measurement data to inform the development of a potential adjustment factor to approximate on

- road exposure concentrations that deviate above o r below nearby

on - road concentrations, EPA assumed a relationship of unity

. EPA recognizes that when using these ratio distributions to estimate in

- vehicle or near

road exposures, there may be instances where these ratios are unsuitably applied to an expo sure event, given other potential influential factors mentioned above that are not considered in the exposure calculation. This is an important uncertainty that could contribute to both over

- and under

- estimates in exposure concentrations. We acknowledge d that accurately modeling the upper percentiles of the distribution is of concern given that the exposure metric of interest is exposures above selected benchmark levels. EPA qualitatively summarized the overall impact of these and other input data uncertainties in the REA (section 10.3.2.1) indicating that there is the “possibility that we are over - predicting upper percentile NO 2 exposures” and therefore over

- predicting the number of day s with exceedances, particularl y the highest benchmark levels. G ive n the duration of the exposure assessment (i.e., an entire year), this uncertaint y is likely to have a greater impact on the number of day s per year an individual was estimated to experience an exposure above a benchmark rather than the estimated number/percent of persons exposed above a particular benchmark level, though the magnitude of which remains uncertain for either exposure metric. (1 4 ) Comment: AAM (September 14, 2009 memo) commented that a study by Chock (1977) “d emonstrated that the turbulence and heat generated by the traffic had a significant effect on the on

- road and near

- road wind and concentration fields ”. They further add “[t]hese effects limit concentrations that can build up on and near roadways under adverse ambient meteorology and are not included in AERMOD. ” Response: We agree that road

- induced turbulence and buoyancy effects will dominate in the earl y morning hours where stability is likely high and mixing heights andtemperatures are low. In these cases, the local mechanical turb ulence will overwhelm the

ambient turbulence and lead to the effects explicitly designed to be sampled by Chock. As noted above, on

- road vehicle induced turbulence and plume rise were addressed in the selection of input parameters for initial horizontal and vertical dispersion and emission release heights for on

- road, as documented in the REA (section 8.4.3.3). Additionally , to mitigate morning over

- predictions, the mechanical mixing height was raised in cases where AERMOD

- defined mixing heights were jud ged to be unreasonabl y low, as discussed in the REA. (1 5 ) Comment : API/AECOM (September 14, 2009 memo) commented on the importance of developing a database that “provides information on NO 2 to NOx emission ratios ” suggesting that “ the estimation of the NO 2 to NO X ratio is critical in modeling peak hourly NO 2 concentrations

. Response: We agree that knowledge of the initial NO 2 / NO X ratio is limited and that the ratio can be variable . Although we note that EPA’s new mobile source emissions model, MOVES, can provide separate estimates of NO, NO 2 , and NO X emissions. We also note that the importance of the accuracy of the initial ratio depends on the degree of conversion of NO to NO 2 predicted b y the model. That is, in cases where more complete conversion is predicted, the sensitivity of the final NO 2 /

NO X ratio to its initial value is minimized. In the present exposure assessment where the dispersion model predicts a high rate of conversion, this effect of this on the output concentration will be small. F urthermore, Carslaw (2005) attributes much of the observed increase in NO 2 / NO X emissions ratios to the increased use of diesel particulate filters (DPF) in London, UK. Even if this supposition is correct, it is unlikely to be relevant to the present mode ling results. For comparison, diesel vehicles make up over fifty percent of new light duty vehicles in the EU (Dieselnet, 2008) whereas the North American diesel passenger vehicle market share is less than 1 percent (Haight, 2003)

. Regardless, we agree that, generall y, improved characterization of this ratio would be advantageous in future modeling efforts. (1 6 ) Comment: On e commenter drew attention to a potential error that causes underestimation of NO 2 impacts using the m odeling software AERMOD ( CAAP COA ). They provided the following description this error and other modeling shortcomings that will affect the models used to inform the selection of a short

- term NO 2 standard: “The use of AERMOD with a more refined Conversion Tier (e.g., OLM [Ozone Limit ing Method] or PVMRM [Plume Volume Molar Ratio Method] ) produces lower 1

- hour NO 2 impacts than less refined methods do. However, California air district modelers have discovered that an error exists in the multi

- source, combined

- plume application of AERMO D (the OLMGROUP key word) thatbiases the results low. This means that 1

- hour NO 2 levels calculated using the

more refined methods may be underestimating the impact. Furthermore, the AERMOD model requires newer MET [meteorological] data sets that are more complicated and require data inputs that may not be readil y available for all areas in California. Consequently , not all air districts have converted to the AERMOD model.” The commenter urges EPA to address this potential model error prior to establish ing a 1

- hr NO 2 standard. Response: EPA was aware of this error while conducting the NO 2 exposure assessment. The version of AERMOD that was used in our analy sis had been corrected for this error. (17) Comment : In their October 22, 2008 memo, the ACC commented that the exposure assessment results for Philadelphia (1 st draft REA) were very different from results presented for Atlanta (Final REA). They specifically

noted “there are substantially higher numbers of exceedances and numbers of individuals e xposed to repeated exceedances for Atlanta compared to Philadelphia”. The commenter requested discussion or comparisons of the differences between the two locations. Response : EPA considered performing the exposure modeling in five locations described i n the Scope and Methods Plan (i.e., Atlanta, Detroit, Philadelphia, Phoenix, and L os Angeles) however there were limited data, time, and resources available to perform exposure modeling in all five locations. Following the CASAC review of the 1 st draft RE A and considering comments made on that document, EPA judged the model evaluations to be an important factor in selecting a location for an improved exposure assessment. Given the availability of personal exposure measurements within a similar time frame as the exposure modeling and a complementary quantitative risk assessment to be performed in the same location, EPA elected to focus the exposure modeling effort on Atlanta, GA rather than continue with the modeling that was initiated for the 1 st draft REA (i.e., Philadelphia County). The exposure modeling approach used for Philadelphia in the 1 st draft REA (and documented in Appendix B

- 3 of the final REA) is not directly comparable to the exposure modeling performed for Atlanta (REA, Chapter 8). Therefor e, a direct comparison of the exposure results obtained for each location would be unreasonable. As stated in REA Appendix B, section B

- 1, “due to differences in the approach used in the Philadelphia anal ys is, the results are not directly comparable to th e Atlanta case

- study .” For example, one of the most significant differences between the two assessments was how the emissions from minor roadway s were addressed. In Atlanta minor roadway s were modeled as area sources using AERMOD, considered b y EPA an important improvement to the modeling approach used for this assessment. In Philadelphia minor roads were not modeled as emission sources, but considered as part of the unaccounted concentration when comparing the modeled concentrations considering all othe r emission sources at the ambient monitor locations. It is possible that these differing model approaches used were related to another important difference: the derived distributions ofin

- vehicle and near

- road proximity factors. In Atlanta, the proximity distributions were stratified by

season and hour

- of

- day , having a time

- weighted geometric mean of about 2.7 (REA Appendix B, Table B

- 42). In Philadelphia, the proximity distributions were stratified only

by hour

- of

- day , having a time

- weighted geometric mean of about 1.4 (REA Appendix B, Figure B

- 11). These examples were just two of several important differences designed to improve the Atlanta assessment for the 2 nd draft and final REA, building upon what was learned from the 1 st draft approach used for Philadelphia. No improvements or adjustments were made to the exposure modeling approach used for Philadelphia, thus results for that assessment should only be considered as preliminary

. (1 8 ) Comment: Some commenters (e.g., API) noted that indoor NO 2 co ncentrations can be higher than the levels that EPA is considering for an hourly NO 2 NAAQS due to indoor emission sources. These commenters conclude that, given that people spend the majority of their time indoors, the Agency should consider NO 2 exposures indoors when evaluating whether the proposed NAAQS would have a meaningful effect on risk from NO 2 . Response: We agree that indoor concentrations of NO 2 can be elevated relative to ambient concentrations, particularl y in indoor environments containin g sources of NO 2 such as gas stoves (I SA, section 2.5.5). Indoor sources were considered as part of the exposure assessment presented in the REA. Even when indoor sources were included in modeling, the majority of exposures to peak NO 2 concentrations (i. e., 1

- hour concentrations at or above 100 ppb) were attributable to roadway

- associated sources (REA, Figures 8

- 17 and 8

- 18). (15)

## III. Responses to Significant Comments on the Adequacy of the

Curr ent Standard (1) Comment: CASAC agreed that, based on the available information, the current NO 2 standard is not requisite to protect public health with an adequate margin of safety and that revisions to the standard are appropriate. Their l etter to the Administrato r on the final REA (Samet, 2008 ) stated th at “CASAC concurs with EPA’s judgment that the current NAAQS does not protect the public’s health and that it should be revised.” In supporting adoption of a more stringent NAAQS for NO 2 , CASAC generally relied on the assessment of the scientific evidence presented in the I SA, the results of assessments presented in the REA, and the conclusions of the policy assessment chapter of the REA. A number of public commenters also called for revis ing the current standard . This included environmental groups ( e.g., CAC, EJ , EDF, NRDC, GASP); medical/public health organizations (e.g., AACPR , ALA, A MA, ATS, NAMDRC, NACPR, ACCP ); State, local , and tribal agencies and organizations (e.g, NACAA, NESCAUM, agencies in CA, IA, IL, MI, MO, NC, NM, NY, TX, VA, WI , and tribes including NTAA, Fon du Lac ); and a number of individual commenters. These commenters generally concluded that the current NO 2 standard needs to be revised and that a more stringent standard is needed to protect the health of sensitive population grou ps. In supporting this conclusion, these commenters ty pically relied upon the evidence and information presented in the proposal and on CASAC’s recommendation. Response: W e generall y agree with these commenters’ conclusions regarding the adequacy of the current standard. The Administrator’s conclusions regarding adequacy are discussed in more detail in section II.E. 3 of the final rule. (2) Comment: Some industry commenters ( e.g., AAM , API , Dow, INGAA , UARG ) , one State commenter (INDEM ) , and Roge r McClellan expressed support for retaining the current annual standard alone . In supporting this view, these commenters generall y concluded that available evidence supports a judgment that the current standard provides adequate protection of public health . They also t ypically concluded that the available evidence and information is not sufficient to support revision of the standard. These c ommenters generall y relied upon the ir judgments regarding the scientific evidence and exposure/risk information and on the uncertainties associated with that evidence and information, as discussed above (section II) in more detail

. For example, the UARG stated that “EPA has failed to demonstrate that the present NO 2 NAAQS is no longer at the level requisite to protect public health with an adequate margin of safety .” The IN GAA stated that “

... EPA should be compelled to retain the current standard and defer a decision on a new short

- term standard until the science is more clearl y defined.” Roger McClellan commented that “ there is a substantial body of scientific information to under

gird a policy judgment to re

- affirm the present annual standard set at 0.053 ppm NO 2 m easured at area

- wide monitoring sites.”Response: T hese comments and EPA’s responses are discussed in detail in section II.E.2

of the final rule. The Administrator’s conclusions on the adequacy of the current standard are described in section II.E.3 of the final rule. ( 3 ) Comment: T he Oklahoma Independent Petroleum Association (OIPA) pointed out that “since 1990, NO 2 emissions have decreased 35% despite the 63% increase in the gross domestic product, a 45% increase in the vehicle miles traveled, a 21% increase in population, and a 20% increase in energy consumption

. Between 2001 and 2007, NO 2 emis sions decreased b y 20%

. In addition, EPA anticipates that nitrogen oxide (NO x ) emissions will decrease substantially over the next 20 years as a result of the ongoing implementation of mobile source emissions standards. ” As a result of these and similar statements by

commenters , several groups concluded that a more stringent NO 2 standard is unnecessary

because the current standard is sufficient to protect against both long

- and short

- term exposures ( e.g., API , Dow, INGAA, VADOT, MODNR, INDEM). Response: As noted b y the commenters, NO X emissions have decreased and are expected to continue to decrease as a result of ongoing implementation of mobile source emissions standards. However, the Clean Air Act (section 109) requires that primary NAAQS “shall be ambient air quality standards the attainment and maintenance of which in the judgment of the Administrator, based on such criteria and allowing an adequate margin of safet y, are requisite to protect the public health.” Given this requirement, the primary NAAQS are set such that, in the Administrator’s judgment, public health is protected with an adequate margin of safety in locations that meet the standards. As discussed more fully

in the final rule (section II.E.3), the scientific evidence and the exposure/risk information support the Administrator’s conclusion that important NO 2 - related public health risks are present in some locations with ambient NO 2 concentrations below those allowed b y the current annual standard and that a new standard is needed to provide the requisite degree of protection for public health.

## IV. Comments on A N ew S hort - T erm NO 2 

## P rimary Standard This section discusses comments received on EPA’s proposed 1

- hour standard. Some commenters provided comments on the cost or economic impact of monitoring, implementation, or compliance associated with the proposed NO 2 NAAQS. As noted in section I .B of the preamble, the Clean Air Act bars consideration of costs in setting the NAAQS, and accordingly EPA has not considered costs, including the costs or economic impact of monitoring, implementation or compliance, in revising the NO 2 NAAQS. 

### A. Indicator CASAC and some public commenters addressed the issue of the indicator for the standard (AAM, API, Dow, an d MODNR). All of these commenters endor sed the proposal to continue to use NO 2 as the indicator for ambient NO x , though some commenters expressed the need for special considerations when using NO 2 as a surrogate for NO x. (1) Comment: API concluded that the proposed regulatory language would change the denomination of the standard from one regulating NO 2 to one regulating oxides of nitrogen, with compliance to be determined b y m easurement of NO 2 in the ambient air. APIrecommends that EPA clearl y st ate that this language is not a substantive change and merel y reflects the continuation of the Agency ’ s regulation of NO 2 (and only NO 2 ) as an indicator for all oxides of nitrogen. Response: We agree that no substantive change is being made with regard to the indicator and that NO 2 is the indicat or for the oxides of nitrogen. This is indicated in the regulatory

text for 50.11 in the final rule. (2) Comment: Some commenters (e.g., AAM) asserted that the tendency to overestimate NO 2 concentrations with the Federal Reference Method (FRM) should b e considered with regard to margin of safety , and that EPA should develop an FRM not prone to positive interference. Response: EPA is required to set the NAAQS at a level requisite to protect public health “allowing a margin of safety”. Thus, EPA take s “margin of safety” into consideration in setting the NAAQS. EPA separatel y considers the accuracy and precision of measurement methods in determining FRM and FEM requirements. The Administrator believes that the continued use of the chemiluminescence F RM is appropriate for comparison to the NAAQS. The issue of interference in FRM measurements and the discussion of the development of alternative method s that could be used in determining NO 2 concentrations are discussed in section III.A.1 of the preamble to the final rule. Although the FRM can be subject to positive artifacts resulting in varying degrees of overestimation of NO 2 concentrations, this overestimation should be minimized for monitors sited in urban locations, particularl y near NO X sources suc h as roads. Additionally , the ISA concluded that for monitors sited in urban locations near roadway s or other sources of NO X emissions, the overestimation of NO 2 concentrations is ty picall y less than 10% (ISA, section 2.3).

### B. Averaging t im e (1) Comment: CASAC endorsed the establishment of a new standard with a 1

- hour averaging time. CASAC stated the following in their comments on the proposal (Samet, 2009 b ) : In reviewing the REA, CASAC supported a short

- term standard for NO 2 and in reviewing the propo sal, CASAC supports the proposed one - hour averaging time in EPA's proposed rule. The rationale offered b y CASAC in support of a new 1

- hour standard was generall y the same as that put forward in the final REA and the proposal. Specificall y, that rational e considered the available scientific evidence, which supports a link between 1

- hour NO 2 concentrations and adverse respiratory effects, and air quality

information presented in the REA, which suggests that a 1

- hour standard can protect against effects linked to short

- term NO 2 exposures while an annual standard would not be an effective or efficient approach to protecting against these effects. A number of public commenters also endorsed the establishment of a new standard with a 1

- hour averaging time. These included a number of State agencies and organizations (e.g., NACAA, NESCAUM and agencies in CA, IL, NM, TX, VA); environmental, medical, and public health organizations (ACCP, ALA, AMA, ATS, CAC, EDF, EJ, GASP, NACPR, NAMDRC, NRDC); and a number of i ndividual commenters . The supporting rationale offered by these commenters often acknowledged the recommendations of CASAC and the Administrator’s rationale as discussed in the proposal.
Response: We agree with these comments on the need for a new 1

- h our standard. Comments on averaging time are discussed in section II.F.2.b of the final rule. The Administrator’s final decision on averaging time is discussed in section II.F.2.c of the final rule. (2) Comment: Though many industry commenters recomme nded not revising the current annual standard (see above), several of these groups did conclude that if a short

- term standard were to be set, a 1

- hour averaging time would be appropriate (e.g., CPA, Dow, NAM, PAW, UPA). Response: As discussed above, in dustry commenters who disagreed with setting a new 1

- hour standard generally based this conclusion on their interpretation of the s cientific evidence and their conclusion that this evidence does not support the need to revise the current annual standard. These comments are discussed in detail in section II. E.2 of the final notice. The Administrator’s conclusions regarding averaging time are discussed in section II.F.2.c of the final notice.(3) Comment: Two state commenters recommended that further studies be conducted to

determine whether the 24

- hr standard is as protective of human health as the 1

- hr standard ( e.g., NYDOH , SDDENR). One of these commenters specificall y noted that epidemiological studies do not provide sufficient evidence that disti nguishes effects between 1

- hour and 24

- hour exposure periods ( SDDENR). Response : The Administrator’s conclusion that available scientific evidence supports setting an NO2 standard with a 1

- hour averaging time is described in detail in section II.F.2.c of the final notice. In addition, EPA notes that the court

- ordered schedule for this review requires a notice of final rulemaking to be signed b y J anuary 22, 2010.


### C. Form (1) Comment: M an y commenters emphasized that , for a standard reflecting the maximum allowable NO 2 concentration any where in an area (i.e., the approach adopted in the final rule, section II.F.4.d), a form should be chosen that provides regulatory stability . To this end, CASAC favor s a 3

- ye ar average of the 98 th percentile (or 7 th or 8 th highest) of the distribution of annual 1

- hour daily maximum concentrations . Specificall y, CASAC commented that “the 98th percentile is preferred by CASAC for the form, given the likely instability

of measurements at the upper range and the absence of data from the proposed two

- t ier approach. ” A number of other commenters also recommended a form based on the 3

- ye ar average of the 98 th percentile (or 7 th or 8 th highest) of the distribution of annual 1

- hour daily maximum concentrations (e.g., Dow, SDDENR, NCDENR, API , PAW, VADOT, ACC, ExxonMobil , I

NDEM, NESCAUM, AQRL , and IPAMS) . These commenters ty picall y argue that the 98 th percentile form will provide a more stable statistic and, therefore, will better protect against unusual events and the possibility that concentrations measured b y near - road monitors will be highl y variable and responsive to small changes in monitor placement. Response: EPA agrees with the comments that a 98 th percentile form is appropriate. Her consideration of comments on form and her rationale for her final decision are discussed in detail in sections II.F.3.b and II.F.3.c, respectively. (2) Comment: Several commenters recommended either a 99 th percentile form or a more stringent form. For example, some commenters recommend e d a “no exceedance” form, claiming that such a form would provide “more coherence in the protection for a standard that targets peak exposures than a form based in the 98 th or 99 th percentile” (ALA, EJ, EDF, NRDC). These same commenters note d that if EPA is unwilling to accept a “no

exceedence” form, they

strongl y favor a 99 th percentile standard over a 98th percentile standard. They

point ed out that a 98 th percentile form would allow for as many as 21 exceedances in a three

- year period, and concluded that this would be unacceptable.Alternativel y, GASP recommends using a form allowing one exceedence per year over a

three

- ye ar period, arguing that this will prevent several of the top measurements that contribute to adverse health effects from being dismis sed. Several commenters prefer the 3

- ye ar average of the 99 th percentile (or 4 th highest) of the distribution of 1

- hour daily maximum concentrations (e.g., TXCEQ, HLI, RHAMC, MODNR, NMED, NESCAUM). Respons e: The Administrator recognizes that the public health protection provided b y th e 1

- hour NO 2 standard is based on the entire standard including the level of the standard (see below), in conjunction with the averaging time and form of the standard

. In light of her decision to set a new 1

- hour standard that reflects the maximum allowable NO 2 concentration an yw here in an area (see section II.F.4.d of the final rule) , she concludes (consistent with the advice of CASAC) that an appropriate consideration with regard to form is the extent to which specific statistics could be unstable in locations where maximum NO 2 concentrations are expected, such as near major roads. When considering alternative forms for the standard, the Administrator notes that an unstable form could result in areas shifting in and out of attainment, potentially disrupting ongoing air quality

planning without achieving public health goals. Given the limited available information on the variability in peak NO 2 concentrations near important sources of NO 2 such as major roadway s, and given the recommendation from CASAC that the potential for instability

in the 99 th percentile concentration is cause for supporting a 98 th percentile form, the Administrator judges it appropriate to set the form based on the 3

- ye ar average of the 9 8 th percentile of the annual distribution of 1

- hour dail y maximum NO 2 concentrations. This decision is discussed in section II.F.3.c of the final rule. (3) Comment: Some commenters stated a preference for expressing the form in terms of the nth highest concentration rather than in terms of a percentile. These commenters believe that using the nth highest f orm would increase transparency ( e.g., Dow, AQRL). AQRL noted that “it can provide an unambiguous determination of a ‘design value’ in the face of missing data if concentrations are high. The percentile form does not provide that certaint y if data are missing.” Response: We disagree that a percentile form does not provide certainty regarding the determination of the design value. As discussed above, and in the final rule (section II.F.3), the Administrator has determined it appropriate to set a form based on the 3

- year average of the 9 8 th percentile of the annual distribution of 1

- hour daily maximum NO 2 concentrations. The interpretation of this standard, inclu ding requirements for when data are missing, is described in Appendix S to 40 CFR part 50 and in section IV of the preamble to the final rule.


### D. Approach and l

evel 1. 

### Comments on the approach to setting the standard (1) Comment: We received a number of comments on the most appropriate approach to setting the 1

- hour NO 2 standard. In their comments on the proposal , CASAC was splitregarding the most appropriate approach to setting the 1

- hour standard . In their letter to

the Administrator on the proposal (Samet, 2009 b ), CASAC stated the following: There was a split view on the two approaches among both CASAC and CASAC panel members with a majority of each favoring the Agency 's proposed two

- tiered monitoring network because they thought this approach would b e more effective in limiting near

roadway exposures that may

reach levels in the range at which some individuals with asthma may be adversel y affected. Other members acknowledged the need for research and development of near - road monitoring data for criteria pollutants in general but favored retention of EPA's current area

- wide monitoring for NO 2 regulatory

purposes, due to the lack of epidemiological data based on near - roadway

exposure measurements and issues related to implementing a near

- road monitoring sy stem for NO 2 . As indicated in their letter, the majority of CASAC Panel members favored the proposed approach of setting a 1

- hour standard that reflects the maximum allowable NO 2 concentration an ywhere in an area and linking such a standard with a 2

- tie red monitoring network that would include both near

- road and area

- wide monitors. The recommendation of these CASAC Panel members was based on their conclusion that the proposed approach would be more effective than the alternative at limiting near

- roadway exposures to NO 2 concentrations that could adversely affect asthmatics

. In contrast, the minority of CASAC Panel members expressed support for the alternative approach of setting a 1

- hour standard that reflects the allowable area

- wide NO 2 concentration . These CASAC Panel members concluded that there would be important uncertainties associated with the proposed approach. Specificall y, they n oted that the key U.S. NO 2 epidemiologic studies relied upon area

- wide NO 2 concentrations and that this introduce s uncertainty

into the use of these studies to inform a standard that reflects the maximum allowable NO 2 concentration an ywhere in an area. As a result of this uncertainty, CASAC Panel members who favored the alternative approach noted that “it would be b etter to set the standard on the same area

- wide monitoring basis as employed in the epidemiologic studies upon which it now relies” (Samet, 2009 b ). These CASAC Panel member s also noted uncertainties associated with identifying appropriate monitoring sites near roads (see below and section III.B.2 of the final notice for more discussion of monitoring comments). Consistent with the views expressed by the majority

of CASAC members, a number of commenters concluded that the most appropriate approach would b e to set a 1

- hour standard that reflects the maximum allowable NO 2 concentration an ywhere in an area and to couple that standard with a requirement that monitors be placed in locations where maximum concentrations are expected, including near major roads. This view was expressed by

some State and local agencies (e.g., in CA, IA, NY, TX, WA, WI), b y the majority of environmental organizations (e.g., CAC, EDF, EJ, GASP, NRDC), by the ALA, and b y a number of individual commenters. Several additional medical and publichealth organizations ( ACCP, AMA , ATS , NADRC , NACPR) did not explicitly express a recommendation regarding the approach though these o rganizations did recommend that, in setting a 1

- hour standard, particular attention should be paid to NO X concentrations around major roadway s. In support of their recommendation to adopt the proposed approach and to focus monitoring around major roads, these commenters generall y concluded that a primary

consideration should be the extent to which the NO 2 NAAQS pro tects at
- risk populations that live and/or attend school near important sources of NO 2 such as major roads. As such, these comments were ty picall y consistent with the rationale discussed b y the Administrator in the proposal in support of setting a 1

- hour standard that reflects the maximum allowable NO 2 concentration an ywhere in an area. Consistent with the view of the minority of CASAC Panel members, several industry groups and an individual commenter (Roger McClellan) noted uncertainties associated wi th using epidemiologic studies to inform decisions on a standard reflecting the maximum allowable NO 2 concentration an ywhere in an area. Specifically, Roger McClellan stated the following: In considering the results of the six epidemiological studies th at are at the core of the EPA assessment, it is important to recognize all of them used NO 2 concentration data from central area monitors as a surrogate for personal exposure. These data are not applicable to establishing stand ards for near roadway

monitor s. Similar concerns with the proposed approach were expressed b y several industry groups. Response: As described in detail in section II.F.4.c of the final notice, the Administrator agrees with the majority

of CASAC Panel members and other commenters who concluded that the most appropriate approach to setting the 1

- hour NO 2 standard is to set a standard reflecting the maximum allowable NO 2 concentration an ywhere in an area. Her consideration of the uncertainties associated with this approach, as stat ed by the minority of CASAC Panel members and industry commenters , is also discussed in the final notice (sections II.F.4.b and II.F.4.c). ( 2 ) Comment: Some industry groups concluded that E PA is inappropriatel y combining decisions on the standard with decisions on the monitoring network. Specifically , AAM states the following with regard to the proposed approach [T] he effective stringency of a NAAQS depends on more than simply the numerical level selected. Italso depends on the sensitivity

of the m onitoring s ys tem, and the ability of that sy stem to determine accurately

the ambient levels of the pollutant in a consistent manner at monitoring stations across the country . By affixing the stringency

of a primary

NAAQS to a monitoring sy stem that does n ot now exist and will be subject to varying interpretation b y regional, state and local officials, EPA is in effect delegating the final decision on the NAAQS standard to thoseofficials, contrary to statutory

requirements that judgments concerning such st andards reside with the Administrator. Response : We disagree with this characterization of the standard. As discussed in detail in the final notice (section II.F.4.c), the Administrator is setting a 1

- hour standard reflecting the maximum allowable NO 2 concentration any where in an area. It follows from this standard that monitors should be placed in locations where maximum NO 2 concentrations are expected to occur. As discussed in the final notice (section II.A.2 and II.F.4.c), available information su pports the conclusion that these maximum concentrations will occur around major roads in many areas. Therefore, the Administrator is requiring monitors within 50 m of major roads (see section III of the final notice). In situations where maximum NO 2 conc entrations are expected to occur in locations other than near major roads (e.g., near multiple smaller roads and/or stationary sources), the Regional Administrator can also require monitors in these locations. EPA establishes criteria for the method of mo nitoring and for quality assurance/quality

control (QA/QC). An y hourl y data from monitors meeting FRM/FEM and QA/QC requirements will be considered in making designations. ( 3 ) Comment: Several industry and state commenters recommended that EPA select i ts alternate monitoring proposal of using area

- wide monitors to be used in conjunction with a new short

- term NO 2 standard ( e.g., EMA, SCCC, NMED). In their recommendation of the alternate monitoring network, NMED noted that the use of area

- wide monitors i s more applicable for measuring ambient air concentrations than near

- road monitors since few people live or work as close to major roadways as near

- road monitoring stations would be required to be located. Other commenters (e.g., Exxon) also concluded that monitor siting requirements should allow for consideration of population. Response : As noted in the proposal and the final notice (section II.F.4.c), millions of people in the United States live, work and/or attend school near important sources of NO 2 , including major roads. In addition, people commuting on major roads can be exposed to elevated NO 2 concentrations. As described in the preamble, the Administrator concludes that short

- term elevated NO 2 concentrations, including those occurring on or ne ar roads, pose public health risks. The Administrator further concludes it is appropriate to locate monitors where maximum concentrations are expected to occur, and that generall y it is appropriate to locate monitors near major roads. States are to consi der population in the site selection process if a state identifies multiple acceptable candidate sites where maximum hourly NO 2 concentrations are expected to occur. ( 4 ) Comment: AQRL commented that EPA’s alternative monitoring approach should not be chosen and implemented if one of the principal reasons for the proposed 1

- hr NO 2 standard is to develop the near

- road monitoring network. Response : The rationale supporting a 1

- hour standard reflecting the maximum allowable NO 2 concentration an yw here i n an area is discussed in detail in section II.F.4.d. This rationale does not include the development of a near

- road monitoring network.( 5 ) Comment: Several commenters (e.g., AAM, API) concluded that it is not appropriate to

use the information discu ssed in the proposal on the NO 2 concentration gradient around roads to inform decisions on the 1

- hour standard. AAM concluded that the focus of the proposed approach on NO 2 concentrations around major roadway s is not justified (and would result in a stand ard that is more stringent than necessary) because the REA and the proposal overstate the extent to which NO 2 concentrations near roads are higher than NO 2 concentrations farther away from the road. AAM used data from the existing NO 2 monitoring network a s the basis for their conclusion that “roadside monitors are not measuring high NO 2 concentrations.” Specifically , they claim that their analy ses suggest the following:

 Many of the presently

located urban monitoring sites are already located within 50 me ters of a major roadway

.
 These monitors are not measuring the high concentrations that are of concern to EPA.

 Consequently , there does not appear to be a need to initiate a massive deployment of new NO 2 monitors within 50 m of major roadway s. Other commenters also noted that the highest concentrations of NO 2 may be in urban can yons, near stationary sources, or near airports ( e.g., NESCAUM ). Response: With regard to the general point made by several commenters that maximum NO 2 concentrations may

no t alway s occur near major roads, we note that, although the Administrator concluded in the proposal that maximum NO 2 concentrations in many areas are likel y to occur around major roads, she also allowed for situations where this is not the case. Specifically , she proposed to set a 1

- hour NO 2 standard that reflects the maximum allowable NO 2 concentration an ywhere in an area, regardless of where that maximum concentration occurs. 7 Therefore, the proposed approach to setting the standard would be expected to limit the maximum NO 2 concentrations an ywhere in an area even if in some areas, as is contended b y AAM, those maximum NO 2 concentrations do not occur near roads. With regard to the anal ys es submitted by AAM, w e agree that there is uncertainty associated with estimates of roadway

- associated NO 2 concentrations (see REA, sections 7.4.6 and 8.4.8.3 for detailed discussion of these uncertainties) and in identifying locations where maximum concentrations are expected to occur. However, we note that the Adminis trator’s conclusions regarding the relationship between NO 2 concentrations near roads and those away from roads rel y on multiple lines of scientific evidence and information. Specifically , the administrator relied in the proposal on the following in drawi ng conclusions regarding the distribution of NO 2 concentrations across areas:

7 To measure maximum concentrations, the Administrator proposed monitoring provisions that would require monitors within 50 meters of major roads and to allow the Regional Administrator to r equire additional monitors in situations where maximum concentrations would be expected to occur in locations other than near major roads (e.g., due to the influence of multiple smaller roads and/or stationary

sources). Monitoring studies discussed in the I SA and REA that were designed to characterize the NO 2 concentration gradient around roads, which indicated that NO 2 concentrations near road s are elevated compared to concentrations in the same area but away from the road
 Air quality

and exposure anal ys es presented in the REA which estimate that NO 2 concentrations on roads could be 80% higher than away from the road, on average across locatio ns, and that roadway

- associated exposures account for the majority of exposures to NO 2 concentrations at or above 100 ppb In contrast, to support their conclusions about the NO 2 concentration gr adient, AAM relies largel y on an anal ysis of existing NO 2 mon itors that focused on 6 locations with a total of 42 monitors. While this analy sis does provide information on NO 2 concentrations at different distances from roads, the existing NO 2 monitoring network was not designed to characterize the spatial gradients in NO 2 concentrations surrounding roadway s. Rather, concentrations of NO 2 measured b y existing monitors may likel y reflect contributions from a combination of mobile and stationary sources, with one or the other dominating depending on the proximity of the monitors to these sources

. Specificall y, one example used b y the commenters to support their conclusion that NO 2 concentrations near roads are not elevated is that of St. L ouis, where the monitors closer to a road measured lower NO 2 concentrations th an a monitor farther away from the road. However, a closer look at the monitor classified as being away from the road provides a potential explanation for these observations and illustrates the limitations of relying exclusively

on the existing monitoring network to characterize the NO 2 concentration gradient around roads. The monitor used (ID 295100086) is characterized by EPA’s Air Quality S ys tem (AQS) as having a “high concentration” monitoring objective, is 133 m from a major road, and is surrounded b y 35 NO X emission sources within 10 km having median emissions of about 17 tons per year (see REA, Appendix A, Tables A

- 7 and A

- 8). Thus, the single site used in St. L ouis for the ≥ 100 m bin may not necessarily

reflect concentrations at a site distant from a roadway , is likely not exclusively

impacted by roadway emissions, and would likely not be useful in determining the relationship between near

- road NO 2 concentrations and those away from the road. The REA identified and discussed situations such as th is as an important uncertainty when estimating on

- road concentrations (REA, section 7.4.6, page 135). Given the considerations above , we conclude that the anal ys is submitted by AAM, which does not consider relevant lines of evidence and information other than their anal ys is of existing monitors , does not appropriatel y characterize the relationship between NO 2 concentrations near roads and those away from roads.

2. 

### Comments on standard level (1) Comment: In commenting on the proposal, CASAC discussed both the proposed range of standard levels (i.e., 80

- 100 ppb) and the alternative range of standard levels (i.e., 50

- 75 ppb). Though, as discussed above, they were split on which approach should be adopted for setting the 1

- hour standard, CASAC did express the co nsensus conclusionthat, if the Agency finalizes a 1

- hour standard in accordance with the proposed approach (i.e., standard level reflects the maximum allowable NO 2 concentration an ywhere in an area and a monitoring network is established that includes mon itors near major roads), then it is appropriate to consider the proposed range of standard levels from 80 to 100 ppb. Specificall y, the CASAC letter to the Administrator on the proposal (Samet, 2009 b ) stated the following with regard to the proposed appro ach: [T] he level of the one

- hour NO 2 standard should be within the range of 80

- 100 ppb and not above 100 ppb. In its letter of December 2, 2008, CASAC strongl y voiced a consensus view that the upper end of the range should not exceed 100 ppb, based on e vidence of risk at that concentration. The lower limit of 80 ppb was viewed as reasonable by CASAC; selection of a value lower than 80ppb would represent a policy judgment based on uncertainty and the degree of public health protection sought, given the li mited health

- based evidence at concentrations below 100 ppb. A number of State and local agencies and organizations also expressed support for setting the level of the 1

- hour NO 2 standard within the proposed range of 80 to 100 ppb , though only a few of these State and local agencies (e.g., in CA, IA, M I, NY, TX) made this recommendation in conjunction with a recommendation to focus monitoring near major roads and other important sources of NO 2 . Response: As is discussed in section II.F.4.d of the fina l rule, the Administrator has judged it appropriate to set a standard level of 100 ppb. Her rationale, which incorporates her consideration of the above comments, is discussed in detail in this section. (2) Comment: A number of environmental organizat ions (e.g., CAC, CSE, EDF, EJ, GASP, NRDC) and medical/public health organizations (e.g., ACCP, ALA, AMA, ATS, NACPR, NAMDRC) supported setting a standard level below 80 ppb for a standard that reflects the maximum allowable NO 2 concentration any where in an area. Several of these groups recommended a standard level of 50 ppb. This recommendation was ty picall y based on the commenters’ interpretation of the epidemiologic and controlled human exposure evidence as well as the NO 2 exposure and risk information

. Some of these commenters noted that the 98 th percentile area

- wide NO 2 concentration was below 80 ppb in the location of a single key U.S. epidemiologic study (i.e., 50 ppb in study by Delfino). Given this, commenters concluded that the standard level should be set at 50 ppb. Their comments on the monitoring network generall y favored a requirement to place monitors near major roads and, therefore, these commenters appeared to favor a standard level as low as 50 ppb and to recommend that such a standard level reflect the maximum allowable NO 2 concentration an ywhere in an area. In their comments, the ALA, EDF, EF, and NRDC stated the following:Considering the Delfino study alone on EPA’s terms, that is, focusing on the 98 th percentile of the 1

- hour d aily maximum concentrations, EPA reports a concentration of 50 ppb where asthma sy mptoms were observed. Based primaril y on this study , EPA concluded in the REA that it was appropriate to set the lower end of the range at 50 ppb, which corresponded to the l owest
observed effects level of airway hy perresponsiveness in asthmatics. To provide the strongest public health protection, we therefore urge the level of the standard be set at 50 ppb. In some cases, the same commenters also appeared to recommend setti ng a standard level below 50 ppb because mean area

- wide NO 2 concentrations reported in locations of key U.S. epidemiologic studies are below this concentration . Specificall y, with regard to the key U.S. epidemiologic studies, these commenters (e.g., ALA, EDF, EJ, NRDC) stated the following: These studies clearl y identify adverse health effects such as emergency

room visits and hospital admissions for respiratory causes at concentrations currentl y occurring in the U.S. Mean concentrations for all but two o f these studies are about or below 50 ppb, suggesting that the standard must be set below this level t o allow for a margin of safety

. Some of these commenters also concluded that the proposed range of standard levels fails to provide a margin of safety f or effects reported in controlled human exposure studies. Response: The Administrator’s decision to set a standard level of 100 ppb is discussed in detail in section II.F.4.d of the final rule. The rationale for this decision includes consideration of the above comments. Specific comments on standard level are discussed in section II.F.4.c of the final rule. (3) Comment: Several environmental and public health groups (e.g., ALA, EDF, EJ, NRDC) concluded that the REA anal ys es of NO 2 exposures and risks suggest that “only an hourl y standard of no more than 50 ppb would protect against harm from peak exposures.” Response: We disagree with this characterization. As discussed in sections II.C and II.F.4.d of the final rule, the anal ys es of differe nt potential alternative standards in the REA are based on the current monitoring network, which contains primarily area

- wide monitors. The Administrator concludes that the results of exposure and risk anal ys es provide support for limiting area

- wide NO 2 c oncentrations to no higher than 100 ppb. The Administrator is setting a new 1

- hour standard that reflects the maximum allowable NO 2 concentration an yw here in an area. Therefore, when considering the REA anal ys es in the context of such a standard, the Adm inistrator considered available information on the relationship between the higher NO 2 concentrations around roads and area

- wide NO 2 concentrations. Specifically , as described in detail in section II.F.4.d, she noted that astandard level of 100 ppb refle cting the maximum allowable NO 2 concentration

any where in an area would be expected to limit area

- wide NO 2 concentrations to approximately

50 to 75 ppb. Therefore, she concluded that a standard level of 100 ppb, for a standard that reflects the maximum al lowable NO 2 concentration an ywhere in an area, is consistent with conclusions based on the NO 2 exposure and risk information. (3) Comment: Several industry groups (e.g., AAM, Dow, NAM, NPRA) and Roger McClellan concluded that, if EPA does choose to se t a new 1

- hour standard, the level of that standard should be above 100 ppb. As a basis for this recommendation, these groups ty picall y emphasized uncertainties in the scientific evidence. Specificall y, these commenters t ypicall y concluded that available epidemiologic studies do not support the conclusion that NO 2 causes reported health effects. This was based on their assertion that the presence of co

- pollutants in the ambient air precludes the identification of a specific NO 2 contribution to reported e ffects. Some industry groups also concluded that epidemiologic studies should not be used to inform decisions on the standard level because these studies were based on area

- wide, rather than near

- road, NO 2 concentrations. As a result, these commenters re commended that a 1

- hour standard should be based on the controlled human exposure evidence and that, in considering that evidence, EPA should rely on the meta

- analy sis of NO 2 airway responsiveness studies conducted b y Goodman et al., (2009) rather than the meta
- anal ys is included in the final ISA. They

concluded that in relying on the I SA meta

- anal ys is, EPA has inappropriatel y reli ed on a new unpublish ed meta
- anal ys is that has not been peer

- reviewed, was not reviewed b y CASAC, and was not conducted in a transparent manner. Response: EPA recognizes the uncertainties in the scientific evidence that are discussed by these industry

commenters; however, we strongl y disagree with their conclusions regarding the implications of these uncertainties for decisions on the NO 2 NAAQS. These comments, and EPA’s responses, are discussed in detail in section II.E.2 of the final rule and above (section II) in this Response to Comments Document

. The Administrator’s conclusions on standard level are described in section I I.F.4.d of the final rule. (4) Comment: Some commenters argued that EPA should not adjust the standard level to account for postulated near

- road concentrations because, due to differences in concentration gradient, it would establish a level that is ar bitrary and variable across locations (e.g., NPRA, NYSDEC, AAM). AAM further argued that EPA’s information about the concentration gradient was not sufficiently precise or “factual” to inform EPA’s decision making. Response: As described in section II .F.4.d of the final rule, EPA has not adjusted the standard level to account for near

- road concentrations. Rather, the Administrator has considered the extent to which specific standard levels would be expected to protect against exposure to the distribut ion of NO 2 concentrations across an area and , therefore, against the array

of respiratory

effects that have been linked to short

- term NO 2 exposures. These considerations are described in detail in section II.F.4.d of the final rule. EPAdisagrees with AAM’s suggestion that information about the concentration gradient

should be disregarded in reviewing the standard. (5) Comment: One commenter (NYDOH) concluded that too much weight has been placed on clinical studies and that more emphasis should be place d on epidemiologic studies in setting the standard level. Response: As discussed in detail in section II.F.4.d of the final rule, the Administrator has considered both the controlled human exposure and epidemiologic evidence in setting the standard lev el. Both lines of evidence provide information on the extent to which specific NO 2 standards would be expected to protect against the range of respiratory effects that have been linked to short

- term exposures to NO 2 . (6) Comment: INGAA pointed out that the related health

- based standards (e.g., Short

- term Exposure L evel ( STEL ) or ceiling Permissible Exposure Level ( PEL ) from Occupational Safety and Health Association ( OSHA ) or the National In stitute of Occupational Safety and Health (NI OSH ) ) are highe r than the proposed NO 2 NAAQS. They claim ed that personnel have not been negativel y affected b y NO 2 exposures at th eir facility

. The commenter also observed that “when comparing the relative margin of OSHA or NIOSH standards to the NAAQS for other gases, the proposed NO 2 NAAQS is more stringent. F or example, the OSHA NO 2 PEL(ceiling) is 5 ppmv [parts per million by volume] (i.e., 5000 ppbv [parts per billion by volume] ) and the NIOSH STEL is 1 ppmv (1000 ppbv)

. These levels are one to two orders of mag nitude higher than ranges being considered b y EPA for the 1

- hour NO 2 NAAQS. By comparison, the CO [carbon monoxide] NAAQS 1

- hour average standard is 35 ppmv, compared to a NIOSH STELof 200 ppmv, a factor of 5.7

. This appears to indicate a more conservat ive approach for the proposed NO 2 NAAQS.” Response: The CAA requires that air quality criteria and NAAQS be reviewed periodicall y. After consideration of the latest scientific knowledge, the NAAQS must be set at levels that are, in the Administrator’s j udgment, requisite to protect public health, including the health of sensitive subpopulations, with an adequate margin of safety. The Administrator has considered this requirement in setting a new 1

- hour NO 2 standard as described in section II.F.4. In co ntrast, occupational standards, such as those mentioned by the commenter, are established based on different legal requirements and may not be updated in the same manner as the NAAQS. Therefore, there is no expectation that the ratio of the NAAQS to an oc cupational standard would be a basis for selecting a NAAQS. (7) Comment: N ESCAUM argues that “while ozone rapidly oxidizes NO to NO 2 , there is usually insufficient ozone to produce substantially elevated levels of NO 2 from this reaction in near

- roadway exposure scenarios during morning rush hours, nighttime, and at least half of the ye ar (during the non

- ozone season).” Response: While EPA acknowledges that the extent to which NO 2 concentrations near roads are elevated will vary with ozone concentratio ns, we disagree with the conclusionthat NO 2 concentrations near roads are not usually elevated substantiall y. As discussed in

the final rule (sections II.A.2 and II.F.4), elevated NO 2 concentrations do occur on and around roads and people who live, work, and/or attend school near major roads , or commute in vehicles on major roads, can be exposed to these elevated concentrations

. For example, based on NO 2 monitoring studies the I SA stated that NO 2 concentrations in heav y traffic or on freeways “can be twi ce the residential outdoor or residential/arterial road level,” that “exposure in traffic can dominate personal exposure to NO 2 ,” and that “NO 2 levels are strongly

associated with distance from major roads (i.e., the closer to a major road, the higher the NO 2 concentration)” (ISA, sections 2.5.4, 4.3.6). Inaddition, a considerable fraction of the population resides, works, or attends school near major roadway s and these populations are likel y to have increased exposure to NO 2 (I SA, section 4.4). Based on data from the 2003 American Housing Survey , approximately 36 million individuals live within 300 feet (~90 meters) of a four

- lane highway , railroad, or airport (ISA, section 4.4)

. 8 Furthermore, in California, 2.3% of schools with a total enrollment of mo re than 150,000 students were located within approximately 500 feet of h igh

- traffic roads (I SA, section 4.4). (8) Comment: Harris County Public Health and Environmental Services (HCPHES) note d that EPA’s REA “concludes that it is appropriate to focus o n studies that evaluated NO 2 health effect associations using both single

- and multi

- pollutant models. However, HCPHES believes that insufficient study and attention has been given to such sy nergistic effects. Because of this insufficiency , HCPHES believ es that EPA should include an adequate margin of safety and set the one

- hour standard sufficientl y below the upper limit of 100 ppb leaning more towards the bottom end of the proposed range.” Response: The Administrator’s decision on standard level, including her consideration of the requirement to provide an adequate margin of safety, is discussed in detail in section II.F.4.d of the final rule. ( 9 ) Comment: AASHTO recommended that EPA should not set its NO 2 standard below background concentrations o f NO 2 in order to avoid making the standard unattainable. Response: As described in detail in section II.F.4.d of the final rule, the Administrator has set an NO 2 NAAQS that, in her judgment, is requisite to protect public health, including the health of sensitive subpopulations, with an adequate margin of safety. In setting such a standard, the Administrator is prohibited from considering such factors as

8 The most current American Housing Survey (http://www.census.gov/hhes/www/housing/ahs/ahs.html ) is from 2007 and lists a higher fraction of housing units within the 300 foot boundary . According to Table 1A

- 6 from that report (http://www.census.gov/hhes/www/housing/ahs/ahs07/tab1a

- 6.pdf ) , out of 128 .2 million total housing units in the United States, about 20 million were reported b y the surveyed occupant or landlo rd as being within 300 feet of a 4

- or - more lane highway , ra ilroad, or airport. That constitutes 15.6% of the total housing units in the U.S. Assuming equal distributions, with a current population of 306 .3 million , that means that there would be 47.8 million people meeting the 300 foot criteria.projections of areas that will or will not attain the standard. However, EPA notes that we

are un aware of an y locations with nonanthropogenic background concentrations that would exceed the standard.

3. 

### Comments on the a nnual s tandard (1) Comment: With regard to an annual standard, CASAC and a number of public commenters (e.g., NACAA, NESCAUM; age ncies from States including CA, I N, MO, NC, NY, SC, TX, VA; tribal organizations including Fon du Lac and NTAO ; environmental/medical/public health groups including ACCP, ALA, AMA, ATS, CAC, EDF, EJ, GASP, NACPR, NAMDRC, NRDC; and industry groups including AAM, API, Dow, INGAA , UARG ) agreed with the proposed decision to maintain an annual standard, though their recommendations with regard to the level of that annual standard differed (see below). In their comments on the final REA, CASAC recommended “ ret aining the current stand ard based on the annual average” based on the “ limited evidence related to potential long

- term effects of NO 2 exposure and the lack of strong evidence of no effect ” and that
“ the findings of the REA do not provide assurance that a s hort

- term standard based on the one - hour maximum will necessarily protect the population from long

- term exposures at levels potentially lead ing to adverse health effects” (Samet, 2008 ). A number of State agencies and organizations and industry groups also recommended maintaining the current level of the annual standard (i.e., 53 ppb). This recommendation was based on the conclusion that, while some evidence supports a link between long

- term NO 2 exposures and adverse respiratory effects, that evidence is n ot sufficient to support a standard level either higher or lower than the current level. In contrast, some environmental organizations and medical/public health organizations as well as a small number of States (e.g., ALA, EDF, EJ, NRDC, and organizatio ns in CA) recommended setting a lower level for the annual standard. These commenters generally supported their recommendation by pointing to the State of California’s annual standard of 30 ppb and to studies where long

- term ambient NO 2 concentrations hav e been associated with adverse respiratory effects such as impairments in lung function growth. 9 Response: EPA’s response to these comments, and the Administrator’s conclusions on the annual standard, are discussed in section II.G of the final rule. (2) Comment: Several petroleum industry commenters (API , UPA, IPAMS, PAW, UARG) claimed that EPA did not provide a rationale for changing the units of the annual standard . These commenters assert that the proposal to express the level as 53 ppb is differ ent from the current standard which also expresses the level in terms of

9 These groups a lso cited a recent study by Karr et al. (Influence of Ambient Air Pollutant Sources on Clinical Encounters for Infant Bronchiolitis. Am

. J

. Respir

. Crit

. Care

. Med

. ( 2009 ), Aug. 27 , epub ahead of print).micrograms/m 3 (100 micrograms/m 3 ). These commenters claim that b y shifting to ppb,

the stringency

of the standard is increased for higher elevations (i.e., at sea level 53 ppb = 100 microgram/m 3 , but at 5 , 000 ft , 53 ppb = 84 micrograms/m 3 )

. PAW specificall y stated that “the change in the annual standard from the current mass and volume concentration to a strictly volume concentration represents a significant and unjustified tightenin g of the standard for high altitude areas, which includes many of the areas in which the oil & gas industry operates in the western states .” Response: The issue raised in the comments is attributed to the mathematical conversion between ppb (a mixing ratio, by volume) and micrograms per cubic meter (μg/m 3 ), which is a mass

- based metric. According to the ideal gas law (PV=nRT) the number of molecules (n) are proportional to their volumes (V) which in turn is proportional to their pressures (P). Since th e total air pressure , and hence the concentration of air, decreases with altitude, a constant mixing ratio will not translate into a constant concentration. Ty pically , when converting from ppb to μg/m 3 , scientists standardize the process b y using a standard pressure and temperature, e.g., 1 atm and 25 C , respectively, in the conversion calculations. This standardization results in the apparent difference in mass concentration provided as an example by the commenter. EPA notes that “parts per ” concentrat ion , such as parts per billion (ppb) or parts per million (ppm), etc., are mixing ratios, and are very common units for measuring gas phase species. Further, the use of mixing ratios is widespread for expressing the relative amounts of species at various altitudes . The chemiluminescence FRM for the NO 2 NAAQS provides in

- situ concentration information, in a mixing ratio by volume (e.g., ppb), that is compensated for both temperature and pressure. As a result, chemiluminescence FRM

- produced data, which mea sures concentrations from a known volume of air, is not subject to variation due to ambient temperature or pressure (e.g., altitude). The parenthetical in the existing standard was intended to be informative, indicating the mass - based measurement corresp onding to the level of the standard at standard temperature and pressure. The parenthetical did not create a second standard, allowing compliance with either measurement depending on ambient temperature or pressure, and therefore deletion of the parenthet ical is not a change to the standard. Since the FRM is not subject to variation due to ambient temperature or pressure, the ppb level is the only measurement relevant to attainment. However, EPA recognized that the presence of the parenthetical in the standard could be confusing, and determined it was appropriate to delete it to clarify

the standard.

## V. Te chnical I ssues with M onitoring R equir ements

A. Comments on n ear

-road m onitor s iting requirem ents (1) Comment : Some state agencies (e.g., AASHTO, NYSDOT, and WIDNR) recommended that the maximum horizontal distance be increased from the proposed 50 meters to as much as 200 meters, noting that a 50 meter limit would be infeasible for many locations and could create a serious safety hazard for monitoring staff and the general public. In contrast, several environmental, and industry groups (e.g., GASP and AQRL ) supported the proposed range, and in GASP’s case, supported reducing the maximum distance to 30 meters or less in order to reduce the potential variation in roadway distance between monitoring sites and subsequent measurements of near

- road NO 2 concentrations. Response: EPA’s decision on the siting criteria for NO 2 monitors requires, among others, that the near

- road NO 2 monitors be sited within 50 meters from the roadway . EPA discusses the basis for this decision in detail in section III.B.7 of the preamble to the final rule. (2) Comment : A limited number of comments were received recommending changes to the requirements for the vertical height of the NO 2 monitor inlet manifold. Two state organizations (NESCAUM and NYSDEC) noted that the proposed 2

- 7 meter vertical range could generate significant variation in the concentrations reported from monitors located at different heights. NESCAUM recommended that the height range be reduced to 2.5

- 3.5 meters

. NYSDEC commented that the proposed vertical height range may not be practical for man y sites, especiall y those located in urban areas. In addition, the ALA, EJ, EDF, and NRDC noted that: [T] he lower end of the proposed height of 2 to 7 meters appears to capture the highest NO 2 concentrations, and more accuratel y represents human exposure at the breathing zone. Additional monitors at other relationships to these sources may be needed for research purp oses, but they should be in addition to those designed to establish the peak exposures f or NAAQS compliance purposes. Response: EPA’s decision on the siting criteria for NO 2 monitors requires, among others, that the near

- road NO 2 monitors inlet manifold s be placed between 2 to 7 meters above the ground. EPA discusses the basis for this decision in detail in section III.B.7 of the preamble to the final rule. With regard to the ALA, EJ, EDF, and NRDC comment on needing additional monitors for research, EP A does not believe that this particular research issue is appropriate to address through this rulemaking, but rather through ongoing and future research that further characterizes the near

- road environment. For the purposes of supporting the revised 1

- hour NAAQS, EPA believes that the siting criteria are sufficient and appropriate.(3) C

omment : Several groups that support the proposed two

- tiered monitoring network requested modifications to the proposed criteria for determining where a near

- road monitor should be located

. Some environmental/public health organizations (ALA, EJ, NRDC, EDF) commented that “Near

- road monitor placement should be determined not only by the highest AADT [annual average dail y traffic] volumes in a given [core

- based statistica l area] CBSA, but also by the highest heavy

- dut y truck volumes.” T he NYDOH, IA DNR, and some industry groups (e.g., EE I and SRNS) recommend making population a prominent consideration when deciding where to locate monitors. HCPHES recommended that near

- ro ad monitoring stations should take into consideration the location of other major mobile and point sources for NO 2 emissions, such as airports, seaports, and power plants, or vulnerable population groups like children, when determining the appropriate locations for near

- road monitors. Response: EPA has clarified that the selection criteria should include the consideration of localized factors when identifying locations of expected maximum concentrations. Near

- road sites shall be selected b y ranking all road segments within a CBSA by AADT and then identifying a location or locations adjacent to those highest ranked road segments, considering fleet mix, roadway design, congestion patterns, terrain, and meteorology , where maximum hourly NO 2 concentrations are expected to be highest and the siting criteria can be met in accordance with 40 CFR Part 58 Appendix E. EPA discusses the basis for this decision in detail in section III.B.6 of the preamble to the final rule. (4) Comment : Many

state agencies comm ented that EPA needed to provide greater guidance to state and municipal agencies about where to site near

- road monitors. T he CAC recommended that state discretion over the location of near

- road monitors be limited “such that gaming is not tolerated.” Response: EPA agrees that guidance will be useful in aiding the implementation of a near - road network. As noted in the section III.B.5 of the preamble to the final rule, EPA plans to assist state agencies in the network implementation process, particularly through guidance documentation that the Agency intends to prepare and share with state and local agencies earl y enough in the overall implementation process to be useful to states in developing their NO 2 monitoring network. Further, EPA encourages state and local monitoring agencies to include or cooperate with transportation officials in the development of the near

- road network. EPA believes that state and local monitoring agencies may

benefit greatly

from working with federal, state, and/or local transp ortation officials during the development of and long

- term maintenance of a near

- road network. EPA believes that the commenter’s concern that the state discretion allowed in the placement of near

- road monitors may lead to installations in locations unlikely to violate the NAAQS, will be avoided due to the process outlined in 40 CFR §58.10 under which a state’s annual monitoring network plan must be made available for public inspection or comment and approved by the EPA Regional Administrator. This proce ss will permit scrutiny of the monitor siting locations and assist in identifying and siting monitors in appropriate locations within CBSAs.(5) Comment : CASAC advised that siting monitors based on traffic counts alone might miss

locations where maximum NO 2 concentrations would occur. CASAC recommends that EPA should use model results from Congestion Mitigation and Air Quality L and Use Regression modeling as well as Gaussian plume models and emissions inventories to determine where roadside monitors shou ld be located. Response: EPA does not intend for AADT counts to be the sole basis for choosing a near - road site. EPA has clarified rule language to reflect that required near - road NO 2 monitoring stations shall be selected b y ranking all road segments within a CBSA by AADT and then identifying a location or locations adjacent to those highest ranked road segments, considering fleet mix, roadway design, congestion patterns, terrain, and meteorology , where maximum hourly NO 2 concentrations are expected to occur and the siting criteria can be met in accordance with 40 CFR Part 58 Appendix E. This issue is discussed in section III.B.6 of the preamble to the final rule. EPA also notes that air quality models, which were noted b y the CASAC panel member to be considered for use in near

- road site selection, are tools that EPA believes will be useful, and likely used by some states to inform where near

- road sites need to be placed (6) Comment : EPA received a number of comments recommending using different pop ulation thresholds, or a different approach in requiring near

- road monitors . Several commenters (e.g., NESCAUM, NYSDOT, NYSDEC) recommended using a higher population threshold than that proposed, for example, NYSDEC suggested the population threshold be i ncreased to as much as 2.5 million. Conversel y, CAC suggested that the proposed threshold may

not be low enough. Other commenters (e.g., AASHTO and HCPHES) recommended that EPA use an AADT threshold (ranging from 100,000 to 250,000 AADT), in lieu of a po pulation threshold, to require near

- road monitoring. Another commenter, San Joaquin Air Pollution Control District suggested the using a combination of population and AADT thresholds to require near

- road monitors. Response: EPA’s decision is to requir e one near - road NO 2 monitor in CBSAs with a population greater than or equal to 500,000 persons and a second near

- road monitor is required in CBSAs with a population greater than or equal to 2,500,000 persons, or in any CBSAs with one or more road segments with an Annual Average Dail y Traffic (AADT) count greater than or equal to 250,000. EPA discusses the basis for this decision in detail in section III.B.2 of the preamble to the final rule. (7) Comment: EPA received comments suggesting that EPA requir e monitoring at sites non

near - road locations. One commenter (Center on Race, Poverty, and the Environment) recommended that EPA account for populations in rural areas, such as those impacted b y agricultural emissions. The Fond du Lac Band of Lake Superior Chippewa and the NTAA suggested that EPA expand monitoring coverage into rural areas and tribal lands. Other commenters (ATS, AMA, NAMDRC, NACPR, ACCP, and the Swinomish Tribe) also recommended that EPA consider sources other than mobile sources, such as large stationary sources.Response: As discussed in section II.F.4.d of the final rule, the Administrator has set a

new 1

- hour NO 2 standard that reflects the maximum allowable NO 2 concentration any where in an area. In her judgment, this new standard will protect public health, including the health of sensitive populations such as asthmatics, with an adequate margin of safet y. It follows from this standard that monitors should be placed in locations where maximum NO 2 concentrations are expected. T he Administrator has judged that, in many areas, these maximum concentrations are likel y to occur around major roads (final rule, sections II.A.2 and II.F.4.d). Therefore, she is requiring NO 2 monitors within 50 meters of major roads. In situations where maximum NO 2 concentrations are likely to occur in locations other than near a major road (e.g., near stationary point or area sources, whether agricultural or industrial (such as those noted b y the commenters), the Regional Administrator has the authority to require additional monitors in these locations. Further, the Administrator has also recognized that susceptible and vulnerable populations, which include asthmatics and disproportionately exposed groups, (as discussed in sections II.B.4 and II.F.4.d o f the preamble to the final rule) are at particular risk of NO 2 - related health effects . The Administrator is therefore requiring the Regional Administrators, working in collaboration with states, to site forty monitors in appropriate locations, focusing p rimaril y on protecting such susceptible and vulnerable communities. This decision is discussed in detail in section III.B.4. (8) Comment: Two tribal commenters ( Fond Du Lac Band of Lake Superior Chippewa and the National Tribal Association) recommended that more monitoring stations be required for rural or tribal roadways since EPA recognized Native Americans as an at

- risk population group. Response: As discussed in section II.F.4.d of the final rule, the Administrator has set a new 1

- hour NO 2 standard that reflects the maximum allowable NO 2 concentration any where in an area. In her judgment, this new standard will protect public health, including the health of sensitive populations such as asthmatics, with an adequate margin of safet y. It follows f

rom this standard that monitors should be placed in locations where maximum NO 2 concentrations are expected. The Administrator has judged that, in many areas, these maximum concentrations are likel y to occur around major roads (final rule, sections II.A.2 and II.F.4.d). Therefore, she is requiring NO 2 monitors within 50 meters of major roads. In situations where maximum NO 2 concentrations are likely to occur in locations other than near a major road (e.g., near multiple smaller roads and/or stationary so urces), the Regional Administrator will have the authority to require additional monitors in these locations . EPA notes that it is not in a position to require monitoring by tribes or on tribal land. However, EPA has and will continue to work with tribes in conducting ambient monitoring on tribal lands. (9) Comment : One state agency , NYSDEC requested that CBSAs with populations larger than 2.5 million be allowed to have more than two near

- road monitors. Response : EPA’s decision is to require, at a min imum, one near

- road NO 2 monitor in CBSAs with a population greater than or equal to 500,000 persons and a second near

-road monitor in CBSAs with a population greater than or equal to 2,500,000 persons, or

in any CBSAs with one or more road segments with an Annual Average Daily Traffic (AADT) count greater than or equal to 250,000. EPA discusses the basis for this decision in detail in section III.B.2 of the preamble to the final rule. EPA also notes that states alway s have the ability

to conduct additional monitoring above the minimum monitoring requirements at their discretion. (10) Comment : Some public health and environmental groups (e.g., ALA, CAC, and NRDC) suggested that near

- road monitors should be required to be located on the downwind side of the target road. Conversely , several commenters (AQRLand NYSDEC) suggested that such a requirement may be over restrictive and not necessary . AQRL commented that siting monitors in downwind locations would not be feasible for all locations and EPA should a llow upwind monitoring locations so long as upwind monitors are used in conjunction with air dispersion modeling. Response: EPA is not going to finalize a requirement that near

- road sites must be climatologicall y downwind of the target road segment becau se of the additional limitations this introduces to finding potential site candidates in exchange for what may be a small increase in the opportunity to monitor peak NO 2 concentrations. EPA discusses the basis for this decision in detail in section III.B. 7 of the preamble to the final rule. (11) Comment : Several commenters (e.g., CASAC, ACCP, ALA, AMS ATS, EDF, NACPR, NAMDRC, NRDC) made comments that the proposed network should form the basis for a broader near

- road monitoring network that would encompas s other pollutants as well, i.e., be a multi

- pollutant near

- road monitoring network. These organizations’ recommendations were based on the argument that it makes little sense to only monitor NO 2 concentrations near roads when it is well

- understood that m an y other pollutants, hazardous to the public’s health, are emitted by on - road vehicles along with NO 2 . Response: The scope of this rulemaking pertains to the NO 2 NAAQS and the monitoring associated with it. However, EPA agrees that multi

- pollutant moni toring is desirable, and believes that the sites required in the near

- road component of the NO 2 network design could also be suitable for monitoring other pollutants including carbon monoxide, particulate matter (especially ultra

- fine particulate matter), air toxics, and black carbon. (12) Comment : Comments were submitted, particularly from state agencies (e.g., Michigan, Mississippi, and Tennessee), noting that one of the challenges to developing a near

- road monitoring network was the potential safety h azard of having a monitoring station located within 50 meters of busy roadways. Response: EPA notes that in all instances of field work, safety is a top priority . EPA believes that the safety issue raised in public comments is something that is an imp ortant component of near

- road siting logistics, and that the near

- road network can be safel y implemented while still serving its intended purpose of providing data on the expected maximum NO2 concentrations that occur within 50 meters of heavily trafficked roads.EPA discusses this issue in further detail in section III.B.7 of the preamble to the final

rule. (13) Comment: The Clean Air Council (CAC) recommended the “EPA not permit alternative monitoring sy stems on a state
- by

- state basis if they would hind er uniformity to the extent that public understanding and accountability of government would be degraded.” In contrast, the Southeast Michigan Council of Governments (SEMCOG) suggested that, rather than requiring a near

- road monitoring network, EPA should enable states to select monitoring locations based on each state’s specific needs and issues as part of the state implementation plan (SIP) process. Response: EPA believes that it must use, and has chosen, a balanced approach in setting monitoring requ irements that recognizes the need to have as nationall y consistent monitoring network as possible, while allowing an appropriate amount of flexibility so that states are able to comply with monitoring requirements. EPA believes that the near

road site sele ction process must include certain considerations such as AADT, fleet mix, roadway design, congestion patterns, terrain, and meteorology to identify

where maximum hourly

NO 2 concentrations are expected occur. While states have flexibility in evaluating wh at specific thresholds or criteria are appropriate for their particular situations with respect to the metrics listed above, they are to make all effort to meet the primary objective of locating the site in a location of expected concentration. This flexi bility is necessary

when considering the reality of, for example, safety

or site access, and other logistical issues that are inherent to installing a monitoring network that can differ on a case

- by

- case basis. EPA discusses issues of site selection and si ting criteria in further detail in sections III.B.6 and III.B.7 of the preamble to the final rule. (14) Comment: The Spokane Regional Clean Air Authority (SRCAA) noted that it might not be necessary

for EPA to require an extensive near

- road monitoring ne twork if a smaller network can develop a strong statistical correlation between particular variables (i.e. traffic density , vehicle mix) and above

- standard NO 2 concentrations. Response : EPA believes that the currently available data, and the number of variables that influence the concentration and behavior of NO 2 in the near

- road environment, including fleet mix, roadway design, congestion patterns, terrain, and meteorology , do not allow the development of a “strong,” and nationally applicable, statisti cal correlation that would allow the avoidance of what the commenter states is an “extensive” near

- road network. (EPA estimates that approximately 126 near road monitors will be needed.) The reasoning behind the size and extent of the near

- road monitors re quired in the two

- tier network design, with respect to SRCAA’s comments, are discussed in detail in sections III.B.1 and III.B.2 of the preamble to the final rule.. (1 5 ) Comment: Several environmental and public health groups (e.g., ALA, EDF, EJ, NRDC) pointed out that “only

58 of 489 total NO 2 monitors are sited in areas o f expected peak concentrations.”Response: The relative current state of the NO 2 network is detailed in the NOx Network

Review and Background document (Watkins and Thompson, 2009), which is posted in the docket. This document provides information and summaries on what EPA believes the current monitoring network, according to state provided meta

- data, is addressing.


### B. Comments on a rea- wide m onitor requirem ents A number of comments wer e received, particularly from state agencies, in support of maintaining the existing area

- wide monitoring network. Comments specific to the siting or area

wide monitors tended to focus on either (1) the need for more area

- wide monitors than the proposed 5 2 or (2) the need to make sure that all area

- wide monitors were measuring ambient NO 2 concentrations rather than NO 2 concentrations near major NO 2 emissions sources. (1) Comment : Several industry groups and state agencies (e.g., AAM, EMA, INDEM, and NYSDOT) provided specific comments that they preferred the alternative monitoring approach of using area

- wide monitors to measure 1

- hour NO 2 concentrations due to the high cost of implementing, operating, and maintaining a near

- road monitoring network and the unce rtain benefits such a network would provide. In addition, one commenter recommended the area

- wide approach because it provided greater flexibility for monitors to be located in places where more people are likely to be exposed to high concentrations of NO 2 . Response: T he Administrator has set a new 1

- hour NO 2 standard that reflects the maximum allowable NO 2 concentration an ywhere in an area. In her judgment, this new standard will protect public health, including the health of sensitive populations such as asthmatics, with an adequate margin of safety. It follows from this standard that monitors should be placed in locations where maximum NO 2 concentrations are expected. The Administrator has judged that, in many areas, these maximum concentrations are likel y to occur around major roads (final rule, sections II.A.2 and II.F.4.d). Therefore, the Administrator has concluded that a two
- tier network design composed of (1) near

- road monitors which would be placed in locations of expected maximum 1

- hour NO 2 concentrations near heavily trafficked roads in urban areas and (2) monitors located to characterize areas with the highest expected NO 2 concentrations at the neighborhood and larger spatial scales (also referred to as “area

- wide” monitors) are needed to i mplement the 1

- hour NO 2 NAAQS. The rationale for this decision is discussed in section III.B.1 of the preamble to the final rule. (2) Comment : Several environmental, public health , and tribal organizations (ALA, EDF, EJ, NRDC, NTAA) commented that EPA shoul d require more monitors than currently proposed. Specifically , the ALA, EJ, NRDC, and EDF stated that they “oppose the proposed requirement to retain only 52 air monitors to measure area wide concentrations NO 2 ” In addition, they

commented :

“ [The] EPA s hould require states and local offices to review inventory data to identify any potential NO 2 hotspots outside of those large metropolitan areas. For instance, if a large power plant or an y other source is creating elevated NO 2 levels in proximity tohome s, schools or other sensitive sites, in an area of less than one million people, EPA

should consider requiring a monitor. In particular, certain large agricultural facilities may emanate high concentrations of NO 2 under certain conditions, such as wet weather. Many of these facilities are directly upwind of rural communities, meriting an NO 2 monitor.” Response: EPA recognizes a variety of exposure scenarios can occur in an area such as the ones described b y the commenters above. Therefore, the final rule authorizes Regional Administrators to require additional monitors above the minimum required number of monitors in circumstances such as those described b y the commenter above where there is a likelihood of high concentrations of NO 2 that approach or exceed the NAAQS. The size and extent of the required area

- wide monitors in the network design are discussed in section III.B.3 of the preamble to the final rule. A more detailed discussion of the Regional Administrator authority and some examples where such authority may be exercised is in section III.B.4 in the preamble to the final rule. (3) Comment : One state agency provided comments opposing using onl y an area - wide network for monitoring NO 2 on the grounds that the network represents an inadequate al ternative to the creation of a near

- road monitoring network. The commenter was critical of how useful dispersion modeling would be at identifying NO 2 concentrations beyond a monitor’s immediate area. The commenter claimed there were too many confounding factors to accuratel y estimate the NO 2 concentrations near roadway s and other NO 2 emissions sources from an area

- wide monitor. Response: T he Administrator has set a new 1

- hour NO 2 standard that reflects the maximum allowable NO 2 concentration an ywhere in an area. In her judgment, using only an area - wide network of NO 2 monitors would not adequatel y support this new standard because maximum concentrations of NO 2 are likely to occur around major roads (final rule, sections II.A.2 and II.F.4.d)]. The Administrator has concluded that a two
- tier network design composed of (1) near

- road monitors which would be placed in locations of expected maximum 1

- hour NO 2 concentrations near heavily trafficked roads in urban areas and (2) monitors located to characterize are as with the highest expected NO 2 concentrations at the neighborhood and larger spatial scales (also referred to as “area

wide” monitors) are needed to implement the 1

- hour NO 2 NAAQS. The rationale for this decision is discussed in section III.B.1 of the p reamble to the final rule. (4) Comment : One commenter, Dow, recommended that area - wide monitors should be located at least 1,000 m eters from an y major road s or intersection s to ensure that the concentration of NO 2 measured is representative of an area

- wide c oncentration instead of “peak” near

- road concentrations. Response: EPA believes that Table E

- 1 of 40 CFR Part 58 Appendix E, which provides roadway set
- back distances for neighborhood and larger scale sites is appropriate to use to ensure that an y NO 2 si te that is intended as an area

- wide site will be located at a sufficient distance from any major road. This issue is discussed section III. B.8.of the preamble to the final rule.(5) Comment: NYSDEC encourages EPA to develop a table for defining the mini mum

distance to the nearest major roadway that can be used to calculate the area

- wide NO 2 concentrations, since specific distances are unlikely to be appropriate for all core based statistical areas (CBSAs). Response: EPA believes that existing data i n 40 CFR Part 58 Appendix E, Table E

- 1, are appropriate for use in determining the minimum distance a monitoring site must be from a road with a given annual average dail y traffic count to be considered a neighborhood or larger spatiall y representative si te. If a state feels that an increased minimum distance compared to Table E

- 1 is appropriate for an area

- wide site in one or more of their particular CBSAs, or on a case

- by

- case basis, the state can elect to site their area

- wide monitors accordingl y, so l ong as they continue to meet siting and network design requirements specified in 40 CFR Part 58. (6) Comment: Several environmental and public health groups (e.g., ALA, EDF, EJ, NRDC) opposed the proposed requirement to retain onl y 52 air monitors to mea sure area wide concentrations NO 2 . Response: EPA is not requiring that the current NO 2 network be reduced; rather, EPA has introduced minimum monitoring requirements where there was previously no minimum NO 2 monitoring requirement. This issue is disc ussed in section III.B.8 of the preamble to the final rule. Further, the relative current state of the NO2 network is detailed in the NOx Network Review and Background document (Watkins and Thompson, 2009), which is posted in the docket. This document pro vides information and summaries on what EPA believes the current monitoring network, according to state provided meta

- data, is addressing. 

### C. Comments on the n eed for a research m onitoring n etwork A number of commenters, primarily from industry

groups and s tate agencies recommended that some form of near

- road research monitoring network be utilized before a full

- scale near

- road monitoring network is implemented. (1) Comment : A subset of CASAC p anel members recommended establishing a limited roadside monitorin g network (20 to 50 monitors in different cities) for the purpose of informing the development of a national network. Specificall y, these CASAC member recommended the following:

 A small roadside network could provide more information than a national netw ork of NO x monitors if the smaller network also monitored other roadway

- associated pollutants, including CO and continuous particulate matter (PM) with speciation, and if the network also included detailed meteorological measurements and automatic traffic counters. They

note that measuring onl y NO 2 could lead to the mistaken impression that air quality is deteriorating as diesel particulate filters, which can increase the fraction of NO x that is emitted as NO2, become more common. If EPA undertakes near

- r oad monitoring, the Agency should seek the advice of technical experts, such as those in the CASAC Ambient Air Monitoring and Methods (AA M M) s ubcommittee.

 Siting criteria should include consideration of such factors as vehicle mix, location of susceptible or vulnerable populations (e.g., schools, hospitals), local phy sical features such as urban street can yons .
 Such a network should be established quickl y to capture ongoing changes in mobile source emissions and should be funded primaril y by EPA.
Respo nse: The Administrator has judged that a regulatory , two
- tier network design, which includes near

- road monitors in urban areas (not a research network), is necessary to support the intent of the revised NAAQS to protect against risks associated with expos ures to peak concentrations of NO 2 any where in an area. This rationale is discussed in section III.B. 1 of the preamble to the final rule . EPA believes that it will be useful to provide guidance to ensure consistent implementation of the monitoring network and has committed to engage the CASAC AA M M s ubcommittee on this effort, and discusses this issue in section III.B.5 of the preamble to the final rule. In regard to measuring other roadway

- associated pollutants, the scope of this rulemaking pertains to the NO 2 NAAQS and the monitoring associated with it. However, EPA agrees that multi

- pollutant monitoring is desirable, and believes that the sites required in the near

- road network design could be suitable for other pollutants including carbon monoxide, parti culate matter (especiall y ultra

- fine particulate matter), air toxics, and black carbon. (2) Comment : Some industry commenters (e.g., CE, EEI , NAM, NPRA, NMC, OIPA, POH, SRNS, SCCC, and SCMA) provided support for a research monitoring network due to perceiv ed weaknesses in the scientific basis for implementing an extensive near

- road monitoring network. Generall y indicating that a research network would allow EPA to gain a better understanding of near

- road peak NO 2 concentrations and their impact on public h ealth before requiring the development of a large and expensive monitoring network. For example, NAM commented: If EPA concludes that NO 2 near roadway monitoring is required, the NAM recommends at a minimum, EPA should consider conducting a near roadway "special purpose" monitoring network program. Conducting such a near road monitoring program would allow EPA to collect necessary data that can be used to better understand the health impacts associated with short term NO 2 exposures. Response: The admin istrator has judged that a regulatory , two
- tier network design, which includes near

- road monitors in urban areas (not a research network), is necessary to support the intent of the revised NAAQS to protect against risks associated with exposures to peak co ncentrations of NO 2 any where in an area. EPA believes that the existing near

- road research provides a sufficient base of information to implement an appropriatel y designed near

- road monitoring network, and the collective experience thatexists in the ambi ent monitoring community will allow for successful implementation of that network. EPA discusses the basis and rationale for the two

- tier network design, which include near

- road monitors for regulatory purposes in section III.B.2 of the preamble to the fin al rule. (3) Comment : Some state groups (e.g., AASHTO, ILEPA, MIDEQ, MSDEQ, NACAA, NCDENR, NESCAUM, NMED, SCDHEC, SJAQMD, and VDOT) focused their support for a research monitoring program b y identifying a need to develop more experience siting near

- road mon itors. Creating greater certainty about where and how near

- road monitors ought to be used could reduce variations in measurement results driven solely by differences in monitor siting. These comments are exemplified by NACAA’s comment: ...a major new network

– particularl y one that is inherentl y complicated and untried

– should not be rolled out without the benefit of an effective near

- road monitoring research program that can address man y of the relevant data questions, and inform the specific siting req

uirements of the rule. Response: The Administrator has judged that a regulatory , two
- tier network design, which includes near

- road monitors in urban areas (not a research network), is necessary to support the intent of the revised NAAQS to protect agains t risks associated with exposures to peak concentrations of NO 2 any where in an area. EPA believes that the existing near

- road research provides a sufficient base of information to implement a appropriatel y designed near

- road monitoring network, and the co llective experience that exists in the ambient monitoring community will allow for successful implementation of that network. EPA discusses the basis and rationale for the two

- tier network design, which include near

- road monitors for regulatory purposes in section III.B.2 of the preamble to the final rule. ( 4 ) Comment: The CASAC panel members who support the alternative approach, which is coupled to a monitoring network that includes only area

- wide monitors, stated that roadside monitors will likely detec t extreme concentrations of NO 2 at certain times (e.g., heav y traffic, idling truck near monitor) and more effort is needed to characterize these measurements and their relationship to traditional area

- wide measurements. Response: EPA believes that some urban areas that will have both area

- wide monitors (whether required or not) and near

- road monitors may be able to provide data to increase the understanding or possibly quantify the relationship (at least for that particular area) between near

- road and are a - wide concentrations. Intense investigation of the roadway gradient has been, and will continue to be best served by research studies that utilize transect monitoring and/or saturation monitoring around target road segments. (5) Comment: The CASAC pan el members who support the alternative approach, which is coupled to a monitoring network that includes only area

- wide monitors, stated that thesiting of the near

- road monitors will require consideration of many factors as the monitors will be sensitive t o the microscale environment of the location. Because the monitors will capture concentrations at the extreme end of the range, the data from any two given monitors may

not be directl y comparable if the characteristics of their sites vary greatly

. Respon se: EPA understands that near

- road sites will be microscale in nature, and concentrations at the site will be subject to factors including AADT, fleet mix, roadway design, congestion patterns, terrain, and meteorology . As a result, EPA would expect site t o site differences corresponding to variability in the above factors. However, the intent of the revised primary NO 2 NAAQS is to protect against the maximum allowable NO 2 con centration an ywhere in an area, which includes ambient air on and around roads

. The required near

- road monitoring sites are intended to measure the maximum expected concentrations, considering the above factors. (6) Comment: The CASAC panel members who support the alternative approach, which is coupled to a monitoring network that includes only area - wide monitors, stated that siting monitors based on traffic count alone may miss locations where maximum concentrations of NO 2 occur. EPA should investigate model results from Congestion Mitigation and Air Quality (CMAQ) Land Use Regre ssion modeling as well as Gaussian plume models and emissions inventories to determine where roadside monitors should be located. Response: As noted in section III.B.6 of the preamble to the final rule, EPA does not intend for AADT counts to be the sole b asis for choosing a near

- road site. EPA understands that there are other factors that can influence which road segment in a CBSA may be the actual location where the maximum NO 2 concentrations could occur. These factors include vehicle fleet mix, roadway design, congestion patterns, terrain, and meteorology . When states identify their top

- ranked road segments by AADT, EPA intends for states to evaluate all of the factors listed above, which influence where the location of expected maximum NO 2 concentrati on may occur, when evaluating a pool of candidate near

- road monitoring sites. Further, EPA expects that modeling will be a tool used by states to assist in informing where near

- road monitoring sites should go.

(7) Comment: The CASAC panel members who support the alternative approach, which is coupled to a monitoring network that includes only area

- wide monitors, commented that diesel particle filters increase the fraction of NO 2 in NO x and may lead to higher measured concentrations of NO 2 in places whe re vehicles are actually cleaner.
Response : EPA notes that the required near

- road NO 2 monitors are to be sited in locations that are expected to measure maximum NO 2 concentrations. The issue of whether the fleet, or a component of the fleet, travellin g on the target road is relativel y dirty or clean is part of consideration of fleet mix that states are to consider when identifying near

- road site locations.(8) Comment: Many state and industry

commenters (e.g., NACAA, NESCAUM, many states, Consumer s Energy , EA, EEI, NAM) recommended that a near

- road research monitoring program be implemented before a full

- scale near

- road monitoring network is required. Specificall y, EA recommended that a near

- road monitoring network not be required until enough near - road monitoring data was available to ensure that EPA’s proposed NO 2 level is not set below background NO 2 levels. Response : The EPA believes that is has sufficient understanding of the near

- road environment from existing research to propose a near

- road network that is appropriate for regulatory

use. This issue is discussed in issue in section III.B. 2 of the preamble to the final rule. In addition, as discussed in section II.F.4.d of the preamble to the final rule, the Administrator has set the leve l of the 1

- hour standard at 100 ppb to protect public health with an adequate margin of safety . Her decision is based on consideration of available health evidence, exposure/risk information, the advice of CASAC, and input from the public.


### D. Justification of m eteorological m easurements Most commenters did not mention the issue of meteorological measurements but the comments received on the subject were unanimousl y against requiring monitoring stations to include three

dimensional anemometry equipment. Com ment : CASAC Panel members and a number of state commenters (e.g., AKDEC, NCDENR, SCDHEC, and WIDNR) questioned the need for meteorological measurements at the NO 2 monitoring sites. These commenters called into question the ability of three

- dimensional an emometry to provide the microscale meteorological information EPA desires if the monitors are to be located close to the ground and other structures, and if they

are averaging measurements over hour long periods of time. SCDHEC commented that the recording of air turbulence data at monitor stations ought to be encouraged but not required unless EPA were willing to fully fund the purchase, installation, and operation of the necessary equipment. These commenters concluded that the requirement to include equipment for measuring meteorological characteristics would be an unnecessary

expense. Response: EPA has chosen not to finalize a requirement for meteorological measurements, including three

- dimensional anemometry , at near
- road NO 2 monitoring stations, but does encourage states to perform meteorological monitoring to better characterize the behavior of NO2 cocentrations in the near

- road environment. EPA discusses its rationale for this decision in section III.B.9 of the preamble to the final rule.


### E. Monitori

ng t echnologyCommenters (CASAC Panel members, some state agencies, and some industry groups) who expressed an opinion regarding monitoring techniques generally agreed that the proposed chemiluminescence approach is appropriate. However, some groups (e. g., CASAC and industry) recommended that EPA promote the development of additional methods for measuring true NO 2 that would not be subject to positive interference. (1) Comment : Several commenters (e.g., MODNR, SRNS, Teledy ne API, and UARG) recommended that EPA encourage the development of alternative monitoring technologies, which includes the photoly tic

- chemiluminescence method or cavity ring

down spectroscop y, and to permit the use of these technologies for monitoring if the new technologies provide comparable or better monitoring results than existing FRM/FEM [Federal Reference Method/Federal Equivalent Method]. NCDENR urged EPA to maximize the flexibility

in the choice of FRM and FEM technology available to demonstrate compliance so long as the tec hno logy provides comparable results. Response : The FRM/FEM program ensures that only evaluated and approved methods may be used for comparison to the NAAQS (see 40 CFR Part 53). EPA only approves a particular method for use in measuring oxides of nitrogen once it has been shown to meet requirement set forth in 40 CFR Part 50 Appendix F, with testing and data provided usually provided b y instrument vendors. The use of FRM/FEMs and furthering method technologies is discussed in section III.A.1 of the pr eamble to the final rule. (2) Comment : One industry commenter, Aerody

ne, expressed concern that current NO 2 monitoring equipment and siting protocols will not be suitable for use in near

- road applications without proper reconfiguration. The commenter not es that the method by which the chemiluminescence FRM determines NO 2 concentrations, using alternating measurements of NO and NO X and subsequently using the difference to indicate NO 2 , may not be appropriate because this technique does not possess the time response required to accuratel y track the plumes of combustion gas emitted b y passing vehicles. The commenter notes that these plumes “tend to be short

- lived, with durations on the order of 3 to 30 seconds.” As a result, the commenter asserts that the va lues reported b y chemiluminescence FRMs “...can be quite inaccurate because of the inability of the alternating channel monitors to properl y average these plumes.” The commenter goes on to note that this issue “...begs the question of whether any of this affec ts reported 1 hour average NO 2 concentrations, the subject of the proposed regulations.”
Response: The “alternating measurement” technique utilized by the chemiluminescence FRM is asserted b y the commenter to cause variability in measuring short durati on plumes or ‘bursts’ of NO 2 . EPA believes this variability would be most apparent when there is only

one plume, or a few individual plumes, that may pass the monitor for a short period of time, but is unlikely to cause a discernable effect in the 1

- hour average. EPA believes that this particular characteristic of the chemiluminescence FRM does not warrant a new measurement approach for near

- road monitors because the averaging time of the NAAQS is 1 hour. The NAAQS is a 1

- hour standard, which EPA believe s is a long enough averaging period where short

- term variations, on the order of 3 to 30seconds will be averaged out, an are not expected to have a discernible effect. The

commenter states that “It has alway s been (rightl y) assumed that when reporting 24 hour and /or yearly

averages, the short term upsets observed in the NO2 data have no discernible effect.” EPA notes that states calculate 24

- hour and annual averages from the 1 hour averages they

acquire each day

. The commenter suggests several alternatives to relyingon a single chemiluminescence analyzer at near

- road sites. EPA has expressed its desire to further the development of alternative methods in determining NO 2 concentrations, which is discussed in section III.A.1 of the preamble to the fina l rule, and also is open to alternative applications of existing methods, all of which would need to follow the process for submission and approval described in 40 CFR part 53. (3) Comment : Some industry commenters expressed concern that open path monit ors might not be appropriate for use in near

- road applications. Response: EPA notes that path integrated optical remote sensing techniques, also known as open - path methods, are not ty pically used b y states at State and Local Ambient Monitoring Station ( SLAMS) sites. However, there are approved open

- path methods capable of providing hourly NO2 concentrations that can be compared to both the annual and 1

- hour standard. EPA believes that an appropriate path length is between 50 meters to 300 meters, where 50 corresponds to the maximum distance away from the edge of the nearest traffic lane of a nearb y road segment and 300 meters corresponds to the traditional maximum path length at micro

- or middle scales site. EPA recognizes that if open path methods are going to be used in the near

- road environment, issues regarding path orientation, safety, and optimal path length within the allowable range will likely be considered in the monitoring guidance that will need to be developed to assist states in the imple mentation of the network design. (4) Comment : One industry commenter , AQRL, requested that EPA set guidelines for the maximum allowable inlet length and sample residence time. Response: EPA has onl y chosen to set a maximum residence time of NO 2 in the sample line between the inlet probe and the anal yz er of 20 seconds. EPA discusses this issue in section III.B.7 of the preamble to the final rule. (5) Comment : APIcommented that, because state and local air monitoring agencies have little experie nce in near

- road NO 2 monitoring, EPA needs to be prepared to support significant field validation and statistical anal ys is to assess monitor performance and dispersion and photochemical modeling analy ses to assist in siting monitors

. Response: EPA believes it has sy stems in place that can provide “field validation and statistical analy sis” of any ambient monitoring network. Field validation and statistical anal ys is starts with the initial testing of instruments to ensure that they are operating properl y and providing precise and unbiased measurements before monitoring begins. Allmonitoring organizations are required to have quality management plans and quality assurance project plans that provide the necessary elements to help in their achievement of the NO2 data quality

goals. In addition, the quality assurance (QA) requirements in 40 CFR part 58 Appendix A provide the quality control samples, the auditing activities and the appropriate statistical anal ys is that monitoring organizations and EPA can use to j udge whether the monitoring s ys tems are under control from a data quality standpoint. (6) Comment : Several state commenters (e.g., MODNR and NCDENR) suggest that the current bias measurement uncertainty criteria used for other NAAQS will be appropriate and acceptable for use with a 1

- hr NO 2 standard. Response: EPA is finalizing the approach to develop data quality objectives, and is changing the proposed goal for measurement uncertainty, to match those criteria of the NCore network and the historical ap proach for NO 2 , where the goal s for acceptable measurement uncertainty for NO 2 methods for precision i s an upper 90 percent confidence limit for the coefficient of variation (CV) of 1 0 percent and for bias i s an upper 95 percent confidence limit for the ab solute bias of 15 percent. This issue is discussed section III.C of the preamble to the final rule. (7) Comment : A state commenter, IADNR, recommend allowing provisions for mobile monitoring to determine NO 2 exposure to motorists. Response: The use of mobile monitoring may be a very beneficial tool to assist states in locating candidate near

- road NO 2 sites; however, EPA does not believe that mobile monitoring is suitable for regulatory monitoring. The network design is predicated on placing monitors in the location of expected maximum concentration, which is inherently in a generally

fixed location. Further, much consideration would have to be given to issues regarding the deviation from the standard practice of using fixed point (or fixed path

- inte grated) data for comparison to the NAAQS. Another issue that would arise would be regarding data completeness and representation, e.g. at what time and where the data are valid, and whether the data are representative of a given location. EPA is encourage d by

the interest in mobile monitoring, but we believe that such monitoring is currentl y best suited for non

- regulatory informational purposes.


### F. Tim ing of m onitor d eploy ment In general, the majority of comments about the timing of monitor deplo ym ent, State Implementation Plan (SIP) development, and determination of attainment were received from state agencies and industry groups recommending that EPA keep the proposed current implementation deadlines as proposed or extend the deadlines further. A few environment and public health groups provided comments urging EPA to move the implementation deadlines forward. [who were the commenters among the states, industry and enviros?] Comment: A lage majority of state and industry groups who made comments on networ k implementation recommended that the deadline for installing near

- road monitors remain January 1, 2013, or that EPA provide the maximum amount of time possible. Theyclaimed that the current January 1, 2013 deadline provides insufficient time to plan and implement such a complicated network of monitors. SJAQMD went further, recommending that EPA allow for schedule relief if a state can demonstrate that monitor installation delay s are the result of delay s in obtaining permits or rights

- of

- way for the near - road monitors. Conversel y, the environmental and public health groups who made comments on network implementation recommended that urged “EPA to seek Congressional funding for an expanded network and to set a deadline for deploy ment of no later than January

1, 2012.” Response : EPA recognizes the need to aid state agencies in the network implementation process, particularl y through guidance documentation that will be developed in partnership between EPA and various stakeholders including NACAA and the states. Further, EPA has modified the timelines for implementation by changing the date by which state and, when appropriate, local air monitoring agencies shall provide a plan for deploying monitors in accordance with required network design from July 1 , 2011 to July 1, 2012. However, EPA is finalizing the date b y which state and, when appropriate, local air monitoring agencies shall establish the required NO 2 monitoring network as January 1, 2013, as was proposed. The basis and rationale for this deci sion is discussed in section III.B.5 of the preamble to the final rule.


### G. Other m onitoring i

ssues Many comments about the monitoring network associated with a one

- hour standard were also submitted, including comments on what should be considered an excepti onal event and the appropriate requirements for using data from monitors for evaluating attainment. (1) Comment: Some commenters urged EPA to create criteria for defining exceptional events for near

- road monitors that included events like road construction. Response: The Exceptional Events Rule (EER) and the accompanying preamble ( 72 FR 13560, March 22, 2007) set forth and explain the criteria and procedures that must be used to determine whether an event qualifies as an exceptional event and the documentati on that must be submitted to support an exceptional events claim. For an exceptional event claim to be approved and data affected b y such an event to be excluded from consideration in any NAAQS attainment designations, the data would need to meet the crit eria and procedures established in the rule. EPA believes that these criteria and procedures are sufficient to address an y exceptional events claims that may arise for NO2 NAAQS. Additions or modifications to the EER are not needed for any exceptional ev ents claims that may

arise for NO2. In addition, the current exceptional event data flags available in the AQS

-- unique traffic disruption and other

-- provide sufficient flexibility to address near

- road exceptional events. (2) Comment: One state commenter, NYSDOT, recommended (if EPA chose to finalize the two
- tier network design which included near

- road monitoring) that “ EPA establish national guidance so there is reasonable uniformity among EPA regions in the implementation of these provisions.”Response : EPA notes that network consistency , from site to site, is achieved in ambient

monitoring networks b y the adherence to monitoring regulations and through the use of guidance. EPA has detailed siting criteri a as specific as we belie ve is necessary and app ropriate to develop a consistent monitoring network , while allowing some necessary flexibility for logistical considerations that will occur on a case

- by

- case basis . Further, EPA recognizes the need to aid state agencies in the network implementation pro cess, particularl y through guidance documentation that will be developed in partnership between EPA and various stakeholders including NACAA and the states. This issue is discussed in section III.B.5 of the preamble to the final rule. (3) Comment: Some comm enters recommended that the annual primary standard design value be calculated b y averaging all 1

- hour values for the year, while a third commenter recommended the design value be calculated b y averaging within calendar quarters before averaging across cal endar quarters

. Response : This issue is discussed in the final notice (Section IV.A). (4) Comment: Several comments were made in regard to EPA’s data completeness test

. For example, three commenters agreed that the completeness test ought to stay at 75% for each quarter while a fourth commenter recommended the percentage be increased to 82%. Response : This issue is discussed in the final notice (Section IV.B). (5) Comment: A comment from a S tate agency noted that the proposed 75% capture requirement was inappropriate and should not be used for a 1

- hr NO 2 standard. Response : This issue is discussed in the final notice (Section IV.B). (6) Comment: A commenter requested that EPA truncate NO 2 concentration measurements rather than rounding them. Respon se : EPA agrees with this comment, as reflected in the final notice. (7) Comment: An industry group requested that EPA further clarify the guidelines for situations where incomplete monitoring data could be considered valid

. Response : The rule text ident ifies factors for the administrator to consider in determining when to use such data. No further clarification is necessary because the variety

and uniqueness of such situations require that they be treated on a case by

case basis.(8) Comment: One commente r expressed concern that the use of near

- road monitoring

would lead to near

- source monitoring for other point sources of NO 2 and other pollutant emissions. Response: EPA is establishing a two

- tier monitoring network, which includes both near

road and are a - wide monitoring, under this rule. EPA does not believe that near

- road monitoring will directly

result in non

- near - road monitoring. However, EPA recognizes that in certain circumstances, there can be an area or areas of expected maximum concentrations of NO2 due to non

- road, point, or area sources, that may not be monitored even though a state is fulfilling its minimum monitoring requirements. EPA has included a mechanism to deal with such circumstances b y providing the Regional Administrator with the authority

to require additional monitors above those minimally required. This issue is discussed in section III.B.4 of the preamble to the final rule. (9) Comment: A S tate agency recommended that EPA allow averaging across monitors for design value calculatio ns and substitution of values from additional monitor s for the primary monitor, for example , if the primary monitor is taken offline for quality control ( QC ) during a high pollutant period

. Response : This issue is discussed in the final notice (Section IV.B).

## VI. Air

Quality Index (1) Comment: Man y State agency commenters discouraged the use of near

- road concentrations in calculating the AQI since near

- road NO 2 concentrations do not represent exposure of the general public to ambient NO 2 . Several other co mmenters, including NACAA, expressed concern that using near

- road monitors for calculating the AQI could diminish the value of the index as a metric for reporting air quality to the general public b y making it sensitive to NO 2 concentrations that are prese nt only in small areas. CASAC also raised questions about how the AQI would be affected by roadside monitors. An additional commenter noted that it would be difficult to forecast the AQI for regions where near

- road monitoring stations existed, since near

- road NO 2 concentrations are likel y to be unpredictable. Response: The response to this comment on the AQI is discussed in section VII of the final rule. (2) Comment: The ALA, EJ, EDF , NRDC support setting the 100 level of the AQI at 50 ppb and the lev el of the “moderate” category well below 50 ppb (i.e., 25 ppb). These commenters disagree with EPA’s proposal to maintain the breakpoints at the higher end of the AQI scale (i.e., 200 to 500). They note that the 500 level has not been changed in the last 22 years, and EPA cannot claim that it represents the most up

- to
- date scientific evidence without more extensive review. They also note that the proposed 200 level for NO 2 is too high, relative to the 100 level , given the relationship between these level s for other pollutants. As a result , these commenters recommend that EPA “establish a meaningful and practical scale of levels of concern and graduated cautionary statements for both sensitive groups as well as the general population” based on th e current scientific evidence. In addition, NACAA expressed support for the “EPA’s proposed range of 0.040 to 0.053 ppm for the AQI value of 50 and 0.360 and 0.370 ppm for the AQI value of 150.” But NACAA did express some concern that it might make for a “confusi ng outreach message if the AQI level of 50 is set below the annual standard of 0.053 ppm” since this would mean that state and local air agencies would “be forecasting moderate air quality even though an area is meeting the annual standard.” Response: Wi th respect to an AQI value of 100, EPA has concluded that it is appropriate in this case to set this value at 100 ppb NO 2 , 1

- hour average, the level of the short

- term standard. With respect to an AQI value of 50, EPA agrees with the NACAA comment which no ted it might make for a confusing outreach message if this value is set below the level of the annual standard. This method of structuring the index is appropriate in the case where a short

- term standard is set to protect against the health effects associ ated with short

- term exposures and /or an annual standard is set to protect against health effects associated with long

- term exposures. In such cases , the short

- term standard ineffect defines a level of health protection provided against short

- term risks and thus can

be a useful benchmark against which to compare daily air quality

concentrations. With respect to the breakpoints at the higher end of the AQI scale (i.e., 200 to 500), EPA acknowledges that these breakpoints have been in place for a long period of time, and that an AQI value of 200 is higher for NO 2 , relative to the 100 level, than it is for the other pollutants in the AQI. EPA does not agree that there is new health evidence that would provide support for changing these levels. The levels at the upper end of the AQI are linked to a related program designed to prevent air pollution emergencies. Some state and local air agencies are required to have plans to take actions at these levels, thus it is important to have a firm basis for revising these levels. Significant harm levels (SHL) are those ambient concentrations of air pollutants that present an imminent and substantial endangerment to public health or welfare, or to the environment, as established in 40 CFR part 51.151. The SHLis t ypicall y set at the same ambient concentration of a pollutant as the AQI value of 500. Appendix L of 40 CFR part 51 includes example emergency episode plans as part of the Prevention of Air Pollution Emergency

Episodes program. This program requires spec ified areas to have contingency

plans in place and to implement these plans during episodes when high levels of air pollution, approaching the SHL, are in danger of being reached or have been reached. The Appendix L example links the AQI with emergency ep isodes. AQI values of 200, 300 and 400 are the basis for the example Alert, Warning and Emergency episode levels included in 40 CFR part 51, Appendix L . In this guidance, the Alert level corresponds to the breakpoint between the Unh ealthy and Very Unhealthy

categories, and the Warning level corresponds to the breakpoint between the Very Unhealthy

and Hazardous categories. The Hazardous category ranges up to the SHL.

## VII. Comments on the Pr ocess for Reviewing the NO 2 

## Primary NAAQ S A number of comments were received recommending changes to the current rulemaking process, either for NAAQS in general or the NO 2 NAAQS in particular. (1) Comment: A number of industry groups and state agencies recommended that the proposed near

- road mon itoring network be considered in a separate rulemaking from the proposed new 1

- hr NO 2 standard, because it represents a dramatic shift in the method of monitoring ambient air quality from previous NAAQS. Response : EPA notes that separating the monitoring issues from the NAAQS revision is not consistent with recently finalized or planned NAAQS reviews. EPA has promulgated monitoring rules as part of, or simultaneously with the PM and Pb rules, and has proceeded to include the monitoring rule as part of thi s primary NO 2 , as well as the primary SO 2 , the secondary NOx/SOx, and CO revisions . Monitoring issues were handled separatel y from the 2008 ozone NAAQS revision, however EPA intends that future ozone NAAQS reviews will integrate monitoring into the action

. (2) Comment: Some commenters (e.g., NACAA, NESCAUM, Roger McClellan) noted that EPA had originally

intended to publish an advance notice of proposed rulemaking (ANPR) and that because no ANPR was published, the public and CASAC had limited opportunity

to c omment on the range of available options. Other comments expressed disapproval with the limited amount of time for stakeholders to comment on EPA’s I SA and REA; the late notifications that EPA provided when comment periods were extended; and the inclusion of new sections and studies in the final versions of the IS A and REA, which denied stakeholders the opportunity to comment on these additions. Response: The Clean Air Act requires EPA to review and to revise, as appropriate, the NAAQS every

five ye ars . As a result of a lawsuit challenging EPA’s failure to complete its review of the air quality criteria for NO X and the NAAQS for NO 2, inter alia , EPA agreed in a consent decree to a schedule for this review of the NO 2 primary NAAQS. Pursuant to CAA § 11 3, EPA provided an opportunity for comment on the consent decree. This schedule was approved b y the United States District Court for the District of Columbia. We disagree that EPA’s decision to not publish an ANPR limited the opportunity for meaningful c omment on the rulemaking. EPA on occasion uses an ANPR to seeking input from stakeholders before issuing a proposed rule, but EPA is not required to publish an ANPR. Moreover, EPA provided for stakeholder comment throughout the review process, including 60 days of comment and held two public hearings on the proposed rule. To the extent that “new sections and studies” were added to the final version of the ISA and REA, stakeholders had the opportunity to comment on this material following the notice of proposed rulemaking.(3) Comment: API commented that EPA did not not adequatel y address comments provided

by other government agencies on the draft proposed rule. Response: EPA engaged in extensive discussions with other agencies as part of the interagency review process prior to the publication of the proposed rule. Under section 307(d) of the CAA, EPA is under no obligation to provide written responses to comments provided b y other agencies during the interagency review process. The scientific rationale for the standards is clearl y provided in the record for the final rule. (4) Comment: AASHTO requested that if EPA creates a 1

- hr NO 2 standard more stringent than 80 ppb, an additional public comment period be created to allow stakeholders to comment direct ly

on the specific standard level selected. Response : As described in section II.F.4.d of the final rule, the Administrator has set the level of the 1

- hour standard at 100 ppb. (5) Comment: AGCA commented that EPA’s Regulatory Impact Anal ys is (RIA) did not provide enough information to predict which areas of the country will not be in attainment with a new standard if the proposed near

- road monitoring network is also included

. This lack of information has the potential to negativel y affect AGCA members because it prevents the organization from assessing the potential impact of a new near

road monitoring network on the road construction industry

. Response : We developed the best estimate we were able to develop of future design values at currentl y existing monitors, based on emission inventory projections for 2020, using the best available emission data and control strategy information. What we are not able to do is to credibl y estimate specific design values at locations where monitors do not currentl y exist, but will in the future. States will determine where to place those monitors as they

implement the NAAQS. In addition, we did not model near

- roadway concentrations as a function of traffic density ; this RIA is a national scale analy sis.

## VIII. Interpr e tation of the Clean Air A ct (1) Comment: Numerous comments were received from industry groups and state agencies expressing concern with EPA using near

- road measurements of NO 2 concentrations to evaluate area

- wide attainment with an NO 2 NAAQS

. Many of the c ommenters note that EPA’s proposed near

- road monitoring network focuses on monitoring roadway s likely to have high NO 2 concentrations without requiring any demonstration that large and adjacent populations are exposed to similarly high concentrations

. Con sequently , the commenters argue that EPA has proposed a monitoring network using rationale that does not reflect the purpose of the CAA and NAAQS, which is to protect the public from exposure to unhealthy

concentrations of pollutants found within “ambient air” rather than just “air”. Response : We note that ambient air includes the outdoor air present around roads as well as the air that intrudes from outdoors into homes, buildings, or vehicles on/near those roads. As discussed in the final rule, people who spend time on or around major roads (e.g., because they

live there, go to school there, or commute in vehicles on major roads) can be exposed to elevated concentrations of ambient NO 2 . (2) Comment: A number of industry groups provided comments maintain ing that EPA may have overstepped its regulatory authority with its proposed 1

- hr NO 2 standard

. Comments included claims that the health effects from short

- term exposure to high concentrations of NO 2 fail to constitute the “adverse health effects” called for in the CAA

. Other comments noted that EPA is authorized by the CAA to set its NAAQS at levels intended to protect sensitive subpopulations , not the most sensitive individual. In addition, some commenters noted that NAAQS are not intended to eliminate all risks. Response : The issues raised by these commenters are addressed in sections II.E.2, II.E.3, II.F.4 in the final rule. (3) Comment: Roger McClellan provided some general comments on the role of CASAC and concluded that

-- In offering recomme ndations for a specific upper bound for the Standard, the Committee moved beyond advising on the science informing the policy

judgments inherent in setting the Standard, to taking on a role reserved for the Administrator

– the setting of the Standard. The Clean Air Act wisel y delegates the setting of the Standard to the Administrator and calls for a Clean Air Scientific Advisory Committee, not a Clean Air Standard Setting Committee. Response: Section 109(d)(2)(B) of the Clean Air Act, and the charter o f CASAC, provide that CASAC shall review the air quality criteria and the NAAQS and “recommend to the Administrator any new national ambient air quality standards andrevisions of existing criteria and standards as may be appropriate.” EPA believes that CASAC fulfilled this duty and provided helpful advice as a committee on the science issues raised b y this review. Of course, the Administrator cannot, and did not, delegate the setting of the standard to CASAC. (4) Comment: NPRA commented that EPA lacks the legal authority to withhold a designation of “attainment” from districts unless the districts cannot be classified on the basis of available information as meeting or not meeting the national air quality standard

. The commenter argued that, at present, E PA cannot know whether it will lack the necessary information in 2012

. According to NPRA, “ it is clear from the statute that for NO 2 EPA must designate areas as in attainment that have attaining monitors absent an affirmative showing that such an area is contributing to downwind nonattainment in another area.. ” Inaddition, NPRA commented that section 107(d) of the CAA requires that EPA “consider the recommendations of States with regard to the designation of areas as attainment, nonattainment and unclass ifiable.” One state agency

agreed with EPA’s proposal to designate all areas currently in attainment with the NO 2 standard as “unclassifiable” until a near

- road network has been established and measurements have been evaluated. Response : (Implementatio n group) (5) Comment: Several environmental groups (e.g., ALA, EDF, EJ, NRDC) noted that the CAA requires that NAAQS be set to protect public health with an adequate margin of safet y without consideration of cost and that, in setting the NAAQS, EPA mus t err on the side of protecting public health. These groups stated that this includes protecting sensitive subpopulations and guarding against “potential ” health effects. Response: EPA agrees that the NAAQS must be requisite (i.e., no less and no more stringent than necessary) to protect the public health, including the health of sensitive populations, with an adequate margin of safety. The Administrator’s consideration of this issue in the current review is described in section II. F.4.d of the final rule.

## IX. Comments on Implementation

(1) Comment: A minority of CASAC Panel members posed the question of what would be an effective control strategy to reduce NO 2 concentrations around major roads. A number of public commenters also expressed the con cern that states have little ability to reduce on

- road emissions from motor vehicles. Several went on to opine that it is the role of the federal government to reduce emissions from motor vehicles. One pointed out that their state has already implemented measures to reduce on

- road emissions of NO X as part of their plan to attain the ozone standard. One commenter opined that states have few options to reduce on

- road emissions beyond federal requirements. Another commenter suggested that one option for st ates would be to adopt California’s mobile source regulations including those that appl y to non
- road equipment. The commenter is concerned that adoption of California’s non

- road regulations would place a significant burden on the construction industry . T he commenter is also concerned that states may attempt to reduce emissions from non

- road equipment by imposing operating restrictions, requiring older equipment to be replaced or mandating retrofits for older equipment. Response: EPA agrees that it is a federal responsibility to implement regulations that reduce emissions from new light

- and heav y - dut y vehicles. However, states have authority that can be used to reduce emissions from in

- use light

- and heav y - duty vehicles. For example, states can impleme nt programs to retrofit heav y - dut y diesel vehicles to reduce their NO X emissions. States can implement regulations to reduce or eliminate long

- duration idling of heavy

- dut y diesel vehicles. They can implement an inspection and maintenance program for light

- dut y vehicles. Additionally , states can implement a wide range of programs to improve travel efficiency. States can implement strategies such as congestion pricing, programs to reduce trips for commuting purposes, and measures to improve the operation al efficiency of the transportation network. States can also work with freight shippers to improve the efficiency of goods movement in an area. EPA agrees that a number of states have already i mplemented controls on on

- road sources. The emissions reduct ions attributable to those measures will help such areas to attain the NO 2 NAAQS and can be included in a SIP for NO 2 . If such an area was designated nonattainment for NO 2 , EPA would expect the state to evaluate mobile source controls that it had not yet implemented and to evaluate the potential for controlling emissions from other sources that are contributing to the nonattainment problem. With regard to the comments related to the adoption of California’s on

- road and non

road regulations by

other state s and the possibility that some states may choose to reduce NO X emissions by

requiring older non

- road equipment to be replaced or equipped with retrofits or impose operating restrictions on non

- road equipment, EPA expects each state with a designated NO 2 n onattainment area to develop a SIP that brings the area into attainment by

the applicable deadline and that each state would evaluate the potential for controlling emissions from all sources that are contributing to the nonattainment problem. CAA section 177 allows states to adopt California’s standards that appl y to new motor vehicles or new motor vehicle engines and CAA section 209(e)(2)(B) allows states toadopt California’s standards that apply to new or used non

- road engines and equipment. California , and therefore other states, are prohibited by CAA section 209(e)(1) from promulgating standards for new construction and farm equipment with engines smaller than 175 hp and from new locomotives and locomotive engines. Itis possible that a state could c hoose to adopt California’s standards that apply to new on
- road and/or other non

road equipment in order to attain the NO 2 NAAQS. States may also choose to reduce emissions from non

- road equipment through operating restrictions, or requiring older equipme nt to be replaced to the extent that such measures are not federall y pre - empted. EPA would expect that before an y state included any of these types of measures in a SIP for NO 2 the state would have evaluated a wide range of potential control measures and concluded that such measures are necessary to bring the area into attainment by the applicable deadline. (2) Comment: Some commenters stated that modeling for permitting of the short term 1

- hr NO 2 standard could likely show that stationary

sources violat e the standard as opposed to near - road mobile sources. Others requested that if EPA requires near

- roadway monitoring for NO 2 , it should provide clarifying guidance stating that near

- road monitors would not be applicable for NSR or other point source permi t applications. Response: The permitting regulations for Prevention of Significant Deterioration of Air Quality (PSD) require applicants to provide 1 year of air qualit y data representative of the air quality

in the area that the proposed new or modifi ed source will impact. Ty pically , such monitoring data is used to represent background air quality levels that are considered along with modeled concentrations of a pollutant to show that the source’s predicted impact will not cause or contribute to a vio lation of any NAAQS. We agree that the ambient data collected from near

- road monitoring sites for NO 2 may not be represent ative of background air quality levels throughout the area of concern. However, if used correctl y, such data could be useful in asse ssing the source’s contribution in specific areas of potentially high ambient NO 2 concentrations largely attributable to near

road mobile source emissions. EPA will give further consideration to this comment as we evaluate an y NSR guidance and regulations that may be needed to implement a 1

- hour NO 2 NAAQS. (3) Comment: API recommends that EPA update the Guidelines on Air Quality Models to address screening and refined models for modeling peak short

- term concentrations in order to accuratel y predict short

- term NO 2 concentrations in diverse environmental settings. Response: The EPA agrees with this comment and intends to review the need to revise the Guideline on Air Quality Models to address issues associated with the promulgation of a short

- term NO 2 NAAQS. (4) Comment: API also recommends that EPA develop a database of NO 2 to NO X emissions ratios for the variety of sources that would be affected b y an y new NO 2 standards. The database could also include methods to make use of data from existing amb ientmonitoring networks to provide realistic background ozone and NO 2 concentrations

required for the short

- term NO 2 modeling framework. Response: The EPA will review the need for the development of a database of NO 2 to NO X emissions ratios sources fol lowing the promulgation of the NO 2 NAAQS. (5) Comment: CAC disagrees with EPA’s decision not to impose non

- attainment classifications on areas with measured near

- road NO 2 concentrations in excess of the new NO 2 standard, and urges EPA to provide a gradu ated non

- attainment classification sy stem for the new standard. According to the Council, “a classification s ys tem defining higher levels of non

- attainment with increasingl y stringent requirements at those levels is one that allows for finer calibration o f air quality regulatory response defined at the federal level.” Response: As stated in the proposed rule, Section 192(a), of part D, of the CAA specificall y provides an attainment date for areas designated as nonattainment for the NO 2 NAAQS. Therefor e, EPA has legal authorit y to classify NO 2 nonattainment areas, but the 5 year attainment date addressed under section 192(a) cannot be extended pursuant to section 172(a)(2)(D). Based on this limitation, EPA proposed not to establish classifications with in the 5 year interval for attaining an y new or revised NO 2 NAAQS. See the preamble to the final rule for consequences for areas failing to meet the attainment date. Once EPA makes a determination that an area has failed to meet it s attainment date, the S tate will be requested to submit a SIP revision which must show that it can attain the standard as expeditiously as practicable, but no later than 5 years from the determination of failure to attain. (6) Comment : One commenter opined that states that f ail to develop SIPs or meet EP A’s CAA deadlines would be subject to “numerous federal sanctions” including emissions caps, limiting economic development and the loss of federal highway transportation dollars. The commenter specificall y states that a construction ban would impede projects that would improve municipal water supplies and wastewater treatment. Response: CAA section 179 provides EPA with only two sanctions. These are the 2:1 offset sanction that applies to new or modified major stationary so urces and the highway funding sanction. These sanctions are onl y applied in specific circumstances, such as when a state has failed to submit a required SIP or when a SIP revision is disapproved. The CAA no longer contains a sanction specifically aimed at limiting development. The CAA Amendments of 1990 do not include the construction ban that applied in certain situations under the 1977 CAA. Therefore, EPA disagrees that, if the available sanctions are imposed in an NO2 nonattainment area, they would result in a de facto construction ban and they

would not delay

municipal water or wastewater projects. It must be noted that there is no sanction for failing to reach attainment by the CAA deadline. For areas that fail to attain by

the applicable deadli ne CAA section 179(d) requires that such areas submit a revised SIP within one year after EPA publishes a notice finding that the area failed to attain. In the case of NO2, this revised SIP would have to demonstrateattainment as expeditiously as practica

ble, but no later than 5 ye ars after the date of the Federal Register notice in which EPA made the finding that the area had failed to attain. ( 7 ) Comment: One commenter pointed out that a new 1

- hr standard for NO 2 will complicate permitting of small sources that may contribute to local NO 2 emissions. Response: Section 110(a)(2)(C) of the CAA requires states to regulate the construction and modification of an y s tationary source as necessary

to assure that NAAQS are achieved. Consequently , the addition of a 1

- hour NO 2 NAAQS would require that the necessary consideration be given to preventing sources from violating a 1

- hour NO 2 NAAQS. We do not, however, view this as a complication of the permitting process. In some instances, a modeling anal ys is may be required to make the necessary compliance demonstration, while in other cases modeling may not be required. Such decisions as to the level of analy sis needed to make the necessary compliance demonstration must be made b y the applicable state or local agen cy permitting authority

. (8) Comment: Several industry commenters requested that EPA slow the timeline for implementing a near

- road monitoring network and designating roadway areas, because they believe EPA lacks significant information about the implem entation and performance of a national, near

- road monitoring network. Response: EPA believes that there is sufficient information to implement a near

- road NO 2 network and that the timeline for implementation will allow EPA to consult CASAC and collaborate with states in the development of guidance that will assist in the implementation of a network that is as consistent as possible. This issue is discussed in section III.B.5 of the preamble to the final rule. (9) Comment: Numerous comments were re ceived, primarily from state agencies, noting the significant cost of a near

- road monitoring networks and requesting that the federal government pay

for a large percentage of the network’s cost by funding the monitors through Section 103 of the CAA, rather than section 105. Many commenters claimed that without federal funds, and because of the tight budgets faced b y state governments presentl y, the funding of a near

- road monitoring network would result in less spending on other valuable environmental programs. Response: EPA understands the resource concerns of the states and intends to work with states in identifying available funds and assess the increased resource needs that may be needed for network implementation. This issue is discussed in section I II.B.1 of the preamble to the final rule. (10) Comment: Several commenters claim that EPA significantl y underestimates the cost of near - road monitors for m any locations where monitors are likel y to be installed. Response : EPA used direct quotes or its best estimate for the variety of capital and logistical costs that will be associated with implementing the network design. EPA must make its estimates as nationally applicable as possible, and cannot anticipate theindividual variations in resource need s, or in the actual costs themselves, that may occur from one location of the country to the next. EPA intends to work with states in identifying available funds and consider the increased resource needs that may be needed for network implementation. (1 1 ) Comment: State agencies requested that EPA provide additional guidelines for the criteria that would be used by Regional Administrators in determining when additional near - road monitors would be required or when requests for additional monitors will be granted. An additional comment requested that EPA provide further guidance and oversight of Regional Administrators to ensure the consistent implementation of any near - road monitoring network across the country . State agencies also requested that the Reg ional Administrator be required to coordinate with the state government in deciding where near

- road monitors would be placed. Response : EPA has provided multiple examples of situations where Regional Administrator may

use their discretion to require addi tional monitors above the minimum required in section III.B.4 of the preamble to the final rule. In particular, EPA notes that in situations where a Regional Administrator may consider the need for additional monitoring, EPA expects that the state and the Regional Administrator would work together to evaluate quantitative evidence that suggests an area may warrant additional monitoring. (12) Comment: AASHTO recommended that state and local air monitoring agencies be required to coordinate with their re spective DOTs when developing a near

- road monitoring plan. Response : Although can not require state and local air agencies to work with another state or local entity, EPA believes that state and local air monitoring agencies can greatl y benefit from col laboration with their counterparts in state or local transportation authorities. Such collaboration may help in site identification, site access, and ensuring public and worker safety

at near
- road sites. (13) Comment: Several State Agencies commented on the interaction between NO X and O 3 . For example, AASHTO requested that EPA clarify how areas can overcome potential negative impacts on ambient O 3 of increased control of NO X emissions. In contrast, one State Agency

(HCPHES) commented that a more string ent NO 2 standard will help them attain the O 3 NAAQS because NO 2 is a precursor to O 3 . Response: It has long been recognized that reducing NO X emissions will result in lower concentrations of regional O 3 (National Research Council , 1991). This has been confirmed in numerous photochemical model simulations and assorted ambient data anal ys es over the past two decades (EPA 2005 b ; EPA, 200 8 d). As a result, efforts to reduce NO X emissions are the foundation of Federal and State actions to attain the ozone NAAQS. However, because of the complex chemistry of ozone formation, there are some specific instances in which certain NO X reductions can lead to localized ozone increases. In these areas, the local planning process will need to consider themultipollutant aspects of air quality management and derive the most appropriate set of

local control measures needed to attain multiple NAAQS simultaneously

. (15) Comment: One state agency recommended that state and local DOTs should be required to perform air qua lity

impact anal ys es for NO 2 prior to road construction projects as well as conduct regular mobile monitor testing to demonstrate that the construction projects are not causing violations of the 1

- hr NO 2 standard. Response : An y such requirement for state and local DOT’s to perform air quality impact anal ys is prior to road construction or to conduct any testing would have to be established and carried out under state or local authority

. (1 6 ) Comment: One commenter encouraged EPA to develop a 1

- hr NO 2 s ignificant impact level (SIL) without which, “any increase in NO 2 in a nonattainment area (or a near non - attainment area) could result in denial of the proposed permit, even if the increase is not significant or offset with offsite emission reduction credi ts” ( CAAPCOA ). Response: This issue is discussed in section VI.D.2 of the preamble to the final rule. (17) Comment: The North Carolina Department of Environment and Natural Resources (NCDENR) s upports the use of a weighted annual mean (quarterl y avera ge) for the annual primary

standard

. Response: This issue is discussed in the final notice (Section IV.A). (1 8 ) Comment: SJVAPCD recommended that EPA include guidelines for near

- road monitoring that allows for monitoring to stop at locations where suf ficient data has been collected to conclude that measured concentrations of NO 2 are less than 85% of the standard level. Response : 40 CFR § 58.14(c), explains the process by which states may

request approval for discontinuing monitoring at an individual site. The discontinuation is subject to Regional Administrator approval, and requires the satisfaction of multiple requirements which are spelled out in the regulation text. ( 19 ) Comment: CASAC Panel members who supported the alternative approach , as w ell as some public commenters (e.g., States) also raised questions related to how non

attainment areas would be designated if roadside monitors measure violations

. For example, some commenters questioned whether an entire county could be out of attainment based on a roadside monitor. Response: This comment is addressed in sections V.B and V.C of the final notice.(20) Comment: The ALA, EJ, EDF, and NRDC also recommended that EPA “formulate a

rational basis for re

- designation based on limited monito ring data and available information on mobile source emissions from the relevant roadway s.” Under this approach, EPA is encouraged to “commit to designating near roadway areas no later than the end of 2013.” These same groups also commented, “We believe it is reasonable to...promulgate a nonattainment SIP submittal deadline of no later than the end of 2015.” Other environmental groups (e.g., CAC) also commented that the timing for designations should be accelerated. Response : Section 110(d)(1)(B) of the CAA requires the EPA to designate areas as attainment, nonattainment or unclassifiable no later than 2 years following promulgation of a new or revised NAAQS (the CAA provides the Agency an additional third year from promulgation should there be insu fficient information on which to make compliance determinations). The EPA intends to finalize initial designations for the revised NO2 NAAQS in January 2012. A near

- roadway

monitoring network is not expected to be fully deployed until January 2013

. For this reason , EPA will proceed with initial desi gnations using air quality data from the exist ing, area

- wide NO 2 monitoring network in order to complete designations by January 2012

. Once the near - roadway network is fully deplo yed and 3 years of ai r quality data are available, the EPA intends to redesignate areas, as appropriate, based on the most recent air quality data from the new monitoring network. For both initial designations and redesignations, EPA will use monitoring data to identify vio lations of the standards. EPA would then consider a variety of other factors in determining which nearb y areas contribute to a violation in setting the boundaries. The response to commenters’ requests that EPA both shorten and extend SIP and att ainment deadlines is provided in the implementation section of the preamble. (21) Comment: One commenter (City of NY) recommended that EPA should develop a screening approach to estimate short

- term NO 2 concentrations, and provide source

- ty pe specific N 0 2 /NO X ratios with the NO X emission factors. Response : It is EPA's intention to utilize the current guidance and policies to implement the revised NAAQS for NO 2 . However, we will be reviewing the need to provide additional technical as well as policy guidance following the promulgation of the NAAQS. ( 22) Comment: API recommended that EPA “follow the precedent that was set for PM 2.5 by postponing the use of dispersion modeling to evaluate short

- term ambient NO 2 concentrations until appropriate model ing tools are developed, evaluated, peer

- reviewed, and subjected to public comment and review. Response: It is EPA's intention to utilize the current guidance and policies to implement the revised NAAQS for NO 2 . However, we will be reviewing the need to provideadditional technical as well as policy guidance following the promulgation of the NAAQS.

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