D ft P l f th P ti l t M 

Draft Proposal for th

e Particula

te M

(PM) National Ambient Air Quali

Standards (NAAQS) 

Briefing for Interagency Review

J ne 4 2012 J

une 4, 2012 

Washington, DC
Overview of Briefing

• Schedule• Current PM standards• Overview of 

p p ro osed decisions

• Primary standards for fine particles• Primary standard for thoracic coarse particles• Secondary standards
Schedule

Major Milestones Completion Date

Workshops on Key Policy-Relevant Issues Jul y 2007

Integrated Review Plan Final March 2008

Integrated Science Assessment Final December 2009

Risk/Exposure Assessments Plans Final February 2009 June/July 2010

Policy Assessment Second Draft

Final

June 2010April 2011

Proposed Rule Signed June 7, 2012 (court ordered)Final Rule Signed TBD
Current PM Standards

• PM Primary 2.5

– Annual standard with a level of 15 μg/m3 – 24-hour standard with a 98th percentile form and a lev

μg/m3 

• PM10 Primary

– 24-hour standard with a 1-expected-exceedance form 

level of 150 μg/m3

• Secondary

– Identical to primary PM2.5 standards
Overview of Proposed Decisions

• Fine Particles 

– Primary PM2.5 Standards

– Propose to revise annual standard level to 12 μg/m

conjunction with retaining 24-hour standard level at μg/m3

• Thoracic Coarse Particles - Primary PM10 Stan

– Propose to retain the current standard

• Secondary PM2 5 Standard 

2.5

• Propose a new standard defined in terms of a PM2

visibility index, with an averaging time of 24 hours, a percentile form and a level of either 30 or 28 dv percentile form, and a level of either 30 or 28 dv
Fine Particles: Significant Impacts on Public 

• Nationally, based on PM2 5 at o a y, based o air quality in 2005, we estimate: 2.5 a qua ty 005, e est ate

– Premature mortality: 

• 130,000 - 320,000 excess deaths in adults• 5.4% of all deaths related to PM2.5 exposures

– Impacts among children:

• 110,000 emergency department visits related to asthma (less than 18 years • 200,000 cases of acute bronchitis (age 8-12) • 2,500,000 cases of exacerbation of asthma (age 6-18)

– Impacts among adults:

• 18,000,000 loss work days (age 18-65)• 180,000 heart attacks (age 17 and older)• 83,000 cases of chronic bronchitis (age 26 and older)• 62,000 hospitalizations for cardiovascular effects (age 17 and older)• 30 000 h it li ti f i t ff t ( ll ) 30,000 hospitalizations for respiratory effects (all ages)

• In addition, recent research provides evidence that decreases in long

exposures have been associated with an estimated increase in mexp y ectancy of app y roximately 5 to 9 months
Fine Particles: Estimated National Impacts...Premature 

Percentage of total deaths due to Percentage of total deaths due to Krewski et al. (2009) PM mortality 

<2.5%2.5 to 3.9%4 to 5%5.1 to 6.1%6.1 to 9%
Fine and Coarse Particles: Susceptible Popula

• P i d d b bli h l h i l di P

rimary standards are to be set to protect publi

c health, including

susceptible populations, with an “adequate margin of safety

”

• A variety of factors make people more susceptible to PM-related health 

effects including: effects, including:

– Pre-existing diseases (such as heart or lung disease, including asthma) or conditions (such as obesity)

– Lifestage

• Older adults • Children

– Persons with lower socio-economic status (SES) 

• New evidence available in this review provides stronger evidence for this 

population

• Emerging evidence for additional susceptible populations related to:

– Genetic differences– Additional pre-existing diseases and conditions (such as diabetes)– Pregnancy, newborns
Fine Particles: History of the Primary PM2.5 Sta

• 1997: Fine and coarse fractions of PM10 considered se

parately; EPA 

10 p y; fine particle standards using PM2.5 as indicator

• 2006: Retained level of annual standard (15 μg/m3); revised level of 

standard (65 μg/m3 lowered to 35 μg/m3)

– Annual standard: Based level on long-term exposure studies only (Harvard Six Citi

American Cancer Society (ACS) studies); key morbidity studies in children judged to 

uncertain a basis for establishing a lower level (e.g., S. California Children’s Health S

– 24-hour standard: Based level on short-term exposure studies only– CASAC had recommended revising annual standard level within a range of 13-14 μg/– CASAC had recommended revising annual standard level within a range of 13-14 μg/

conjunction with revising 24-hour standard level within a range of 30-35 μg/m3; followin

CASAC expressed serious concerns with decision to retain annual PM2.5 standard leve

• 2009: US Court of Appeals, DC Circuit issued decisions on 2006 PM 

– Concluded “EPA failed adequately to explain Concluded “EPA failed adequately to explain why in view of risks posed by short , in view of risks posed by short-term 

term 

and the evidence of morbidity resulting from long-term exposures, its annual standard to protect public health with an adequate margin of safety”

– Remanded annual standard for further consideration of whether it provides an ade

marg y, in of safety, esp y eciall

y in children and other susce

p pp tible 

populations

– Primary 24-hour PM2.5 standard, as revised in 2006, was not challenged by litigants
Fine Particles: Overview of Health Effects Evi

Based on ORD’s PM Integrated Science Assessment (ISA), which CASAC has • Extensive new epidemiological evidence is now available, including:

– Extended analyses of seminal studies of long-term PM2.5 exposures – Substantial increase in new U.S. multi-city, long- and short-term exposure studies– Additional types of evidence from controlled human exposure and animal toxicolog

provide support for effects observed in epidemiological studies

• Compelling evidence supports a causal relationship between PM2.5 and pr

mortality and cardiovascular effects (long- and short-term exposures)

• Additional evidence for a broad range of PM2.5-related health effects supports

– Likely causal relationship Likely causal relationship for respiratory effects respiratory effects (long- and short and short-term exposur

term exposur

– Suggestive of a causal relationship for developmental/reproductive effects, c

term exposures)

• Evidence is not sufficient to link health effects with any specific fine particl

comp gp p onent or group of components associated with any g source categories 

particles nor to exclude any component(s) from the mix of particles included iindicator

• No evidence of a discernible threshold below which health effects would no
Fine Particles: Overview of Epidemiology Ev

Long-term Exposure “Cohort” Studies• Follows a specific group of study participants (“cohort”) over time an

urban areas; PM2.5 concentrations over years are associated with specific health 

deaths) across cities 

• Extended follow-up of important studies as well as new studies are largely consist

previous reports of premature mortality at lower ambient PM concentrations; pro

2.5 concentrations; pro

evidence of morbidity effects

• Studies of note include: 

– Extended analyses of ACS and Harvard Six City studies (premature mortality)– Extended anal

y y ses of S. California Children’s Health Stud

y ( g g

decreased lung function 

g

– Women’s Health Initiative Study (WHI, cardiovascular-related mortality and morbidity eff

healthy, post-menopausal women)

– Medicare Air Pollution Study (MCAPS, premature mortality, older adults)

Short-term Exposure Studies• “Time-series studies” consider general population or a subset (e.g., 

participants) in a single city or across multiple cities over several yeachanges in PM2.5 concentrations (one or more days) are associated with daily ch

events (e.g., deaths, hospitalizations)

• New multi New multi-city studies greatly expand city studies greatly expand and reinforce reinforce evidence of mortality and mo

evidence of mortality and mo

available in last review; studies of note include:

– MCAPS (hospitalizations for cardiovascular and respiratory disease, older adults)

– 112 U.S. Cities study (premature mortality)
Fine Particles: Translating Evidence into Primary PM2.5 

• In translating evidence into basis for standard levels, we focus on epidemiolo

evidence:

– Recognize health effects may occur over the full range of concentrations observe

epidemiological studies; there is no evidence of a discernible threshold below w

effects would not occur

– Controlled human exposure studies help to demonst Controlled human exposure studies help to demonstrate causality but rate causality but unlike in ot

, unlike in ot

NAAQS reviews, are not helpful for setting the level of the PM2.5 standards

• Rely primarily on annual standard to provide protection from both long- and s

PM2.5 exposures, with 24-hour standard providing supplemental protection agpeak concentrations

– Considered most effective and efficient approach for providing public health prote– Supported by results from quantitative risk assessment

• Annual standard level (g ) see figure on next slide)

– Focus on identifying levels somewhat below long-term mean concentrations r

epidemiological studies (general approach used in previous reviews)

– Consider broader distribution of PM2.5 concentrations beyond a point “somew

mean” to consider ranges of concentrations that were most influential in generatin

estimates in epidemiological studies, as CASAC strongly advised us to do
Fine Particles: Translating Evidence into Primary PM2.5 S

McConnell et al, 2003; Gauderman et al., 2004 (S CA CHS, 12 communities)

Goss et al., 2004 (Cystic Fibrosis)

Eftim et al., 2008 (MCAPS-ACS sites, 110 counties)

Miller et al., 2007 (WHI, 36 cities)

Causal / Likely Causal - Long-Term Exposure Studies

Level of custandard

Dockery et al 1996; Raizenne et al 1996 (24 Cities Study

Lipfert et al., 2006 (Veterans Study)

Eftim et al., 2008 (MCAPS-Harvard Six Cities sites)

Zeger et al., 2008 (MCAPS-East, 421 counties)

Krewski et al., 2009 (ACS-Reanalysis II, 116 MSAs)

McConnell et al, 2003; Gauderman et al., 2004 (S CA CHS, 12 communities) 

Z b tti & S h t 2009 (112 iti )

Bell et al., 2008 (MCAPS, 202 counties)

Burnett et al., 2004 (12 Canadian Cities)

Causal / Likely Causal - Short-Term Exposure Studies

Laden et al., 2006 (Harvard Six Cities)

Dockery et al., 1996; Raizenne et al., 1996 (24-Cities Study 

Franklin et al., 2008 (25 US cities)

Klemm & Mason, 2003 (Harvard Six Cities)

Dominici et al., 2006 (MCAPS, 204 counties)

Burnett & Goldberg, 2003 (8 Canadian cities)

Zanobetti & Schwartz, 2009 (112 cities)

Woodruff et al., 2008 (infant mortality)

Liu et al., 2007 (IUGR)

Bell et al., 2007 (low birthweight)

Suggestive - Long-Term Exposure Studies

Franklin et al., 2007 (27 US cities)

9 10 11 12 13 14 15 16 17

Additional studies report effects at higher long-term meansMore limited and mixed evidence is available from single-city, short-term exposure studies with long-term mean PM2.5 concentrations below 15 μg/m3

Long –term mean PM2.5 concentration (μg/m3)
Fine Particles: Staff Conclusions in Final Policy As

Annual Standard 24-Hour Standard Potential Implic

•Alternative suites of standa

strongly supported by evid

12 to 11 μg/m3 35 μg/m3 (retain current standard)

g y pp y

•Results in annual standard generally controlling standarareas with particularly high pratios (e.g., Northwest)•R lt i if 

Results in more uniform pu

protection•More limited support for t

standards

•Results in 24 hour standard 

up to 13 μg/m3 somewhat below 35 μg/m3, such as down to 30 μg/m3 •Results in 24-hour standard 

controlling standard in a largareas in many geographic re•Results in more uneven puprotection
Fine Particles: CASAC Advice 

Adequacy of Current Standards• CASAC concluded current standards are “not protective” and there are “si

public health consequences” at the current levels of the standard(s) that “j

consideration of lowering the PM2.5 NAAQS further”

Alternative Standards Appropriate to Consider• CASAC agreed with staff’s approach to focus on annual standard• CASAC concl ded that alternati e concluded that alternative ann al standard le els annual standard levels within a range of ithin a range of 

μg/m3 and 24-hour standards levels within a range of 35 to 30 μg/m3 “are 

supported by the epidemiological and toxicological evidence, as well as by thand air quality information”

– Based on 2nd draft Policy Assessment, which did not include consideration o

analyses of the broader distribution of PM2.5 concentrations beyond a point 

“somewhat below the mean” to consider ranges of concentrations that were influential in generating health effect estimates in epidemiological studies
Fine Particles: Draft Proposal and Considera

 Propose to revise annual standard level to 12 μg/m3 in conjunction with re

hour standard level at 35 μg/m3

• Solicit comment on alternative annual standard levels from 13 to 11 μg/m3

Considerations: A focus on an annual standard level of 12 μg/m3:• Places greatest weight on both long greatest weight on both long- and short and short-term exposure studies term exposure studies p

p

evidence of effects classified as having a causal or likely causal relationship

– Below the lowest long-term mean concentrations reported in all multi-city stud

reported statistically significant associations (i.e., below 12.8 μg/m3)

• Places little weight on more limited evidence from multi-city, long-term expo

for which we have suggestive evidence of a causal relationship for developm

• In conjunction with lowering the annual standard level to 12 μg/m3, the evide

strongly supports retaining 24-hour standard level at 35 μg/m3 strongly supports retaining 24-hour standard level at 35 μg/m

– Changes in air quality designed to meet a lower annual standard would likely resu

lower annual average PM2.5 concentrations but also in fewer and lower peak 24-h

concentrations

– Th dditi l t ti ld b id d b i d l t d d h 

Thus, additional protection would be provided by a revised annual standard such to the 24-hour standard is not warranted
Fine Particles: Considerations (Continued

• Requesting comment on an annual standard level up to 13 μg/m3 :

– Places weight on most, but not all, multi-city studies; however, we have no basis fo

excluding studies with long-term mean concentrations of 12.8 or 12.9 μg/m3

– Places no weight on considering the broader distribution of PM2.5 concentrations d

through which we continue to have confidence in observed associations or on the 

limited evidence of serious effects in susceptible populations (e g infant mortality 

(e.g., infant mortality, 

weight)

– Places substantial weight on the remaining uncertainties and limitations in the 

– In conjunction with lowering the annual standard to 13 μg/m3, the evidence provide

support for also lowerin

g the 24-hour standard level

– An annual standard of 13 μg/m3 (absent a very low 24-hour standard level) could r

issues similar to those which resulted in the remand of the 2006 PM2.5 annual stan

• Requesting comment on an annual standard level down to 11 μg/m3:

– Places greater weight on considering the range of PM2 5 Places greater weight on considering the range of PM concentrations below 

2.5 concentrations below 

term mean concentrations down through which we continue to have confidence 

observed associations

– Places considerably more weight on limited evidence of serious effects in su

populations providing evidence suggestive of a causal relationship 

– Places less weight less weight on the remaining on the remaining uncertainties and limitations uncertainties and limitations in the evidenc

in the evidenc

– In conjunction with lowering the annual standard level to 11 μg/m3, the evidence m

strongly supports retaining 24-hour standard level 
Costs and Benefits for Proposed Primary PM2.5 Stand

• In setting NAAQS, EPA may not 

consider implementation costs. Per 

Executive Order 12866 and standard 

practice EPA has conducted a 

Projected Costs and Benefits of At

Incremental to Attainment of Current 

(Million 2006$, 7% Discou

practice, EPA has conducted a Regulatory Impact Analysis for informational purposes only.

• Costs are low because they consider 

federal measures already in place 

Costs Health Benefits 

including recently promulgated regulations (e.g., CSAPR and MATS) and controls applied to meet the current standards (15/35).

Net Benefits 

*E ti t d t d b fit dditi 

• Emission control measures were 

applied to sources of PM2.5, SO

2, and NOx (few thousands of tons) for meeting proposed alternative 

*E

stima

ted costs and benefits are

additiona

with meeting the current standards. CurrentQA on the cost and benefit estimates. A new with updated estimates will be provided in th

meeting proposed alternative 

We

anti

cipa

te the

re will be

an increase in th

standards (12/35). 

e a c pa e e e be a c ease 

benefits are still expected to significantly ex
Current and Projected PM2.5 Nonattainm

Current Standards Pro

posed Standards Pro

pose

Standard(s)

(15/35)

Nonattainment

Areas*

p

(12/35)** 

Estimated Using 

Recent Air Quality

p

(1

Projected 

‘On the B

(2008-2010)

by County

Contr

by 

Both annual and 24-hour standards 16 14 Annual standard only 19 68 24-hour standard only 16 21 Total 51 103 

*Nonattainment areas may include multiple counties or only a part of one county.

**Estimated/projected conditions are for illustrative 

purposes onl

y. Assuming revised PM NAAQS are 

promul

gated in June 

pj pp y g p g 

designations would be based on 2011-2013 or 2012-2014 air quality data.
2008-2010 PM2.5 Concentrations by y Count

Proposed Standards: Annual NAAQS level = 12 μg/m3/24-hr NAAQS level = 35 μg/m3

Note: This slide represents recent air quality conditions but not necessarily the areas likely to be designated as attainment/nonattainment. 

purposes, assuming revised PM NAAQS are promulgated in June 2013, designations would be based on 2011-2013 or 2012-2014 air qual
2020 P j t d PM 2020 Projected PM C t ti b C t ith ‘ th b k ’ F 

2.5 Concentrations by County with ‘on the books’ F

Proposed Primary Standards: Annual NAAQS level = 12 μg/m3/24-hr NAAQS 

Projected design values indicate 18 counties are likely not to meet one or both of the proposed primary PM2.5 stand
Coarse Particles: History of the PM10 Stand

• 1987: EPA first set PM standards in order to protect against exposures to 

10 that can penetrate deeply into the respiratory system 

– 24-hour standard: Form set at one-expected-exceedance and level set at 150 μ– Annual standard: Level set at 50 μg/m3

• 1997: Given newly established fine particle standards, purpose of PM10 s

became to protect against the coarse fraction of PM10 (i.e., PM10-2.5)

– Following litigation, the 1987 PM10 standards remained in place

• 2006: EPA retained the 24-hour standard and revoked the annual standard 

– Decision on annual standard based on insufficient evidence linking health prob

long-term exposure to inhalable coarse particle pollution 

– In subsequent litigation, DC Circuit court upheld decisions and supporting ratio

PM d d 10 standard 

• Today’s 24-hour PM10 standard is the same as that set in 1987 
Coarse Particles: ISA Conclusions

• Causality: The available evidence is “suggestive” of 

causal relationship between short-term thoracic coarse particle exposures and mortality, respiratory effects, ancardi l ff t diovascular effects

– “Suggestive,” rather than “causal” or “likely causal”, refle

greater degree of uncertainty associated with the heal

evidence for PM10-2.5

• Composition: Evidence is not sufficient to link health e

with specific sources or components of PM10-2.5 (such athose typical of ) urban versus rural areas)
Coarse Particles: Health Evidence

• In epidemiologic studies, associations between PM10 2 5 and mortality/m

-2.5 and mortality/m

were generally positive, with some being statistically significant

– In the subset of studies that employed co-pollutant models to evaluate the pote

confounding, PM10-2.5 effect estimates remained positive, and in a few cases sta

significant

• Single-city analyses reported positive and statistically significant assoc

a few urban locations that would have met the current PM10 standard d

study period – Detroit (Ito et al., 2003)

– T t (Li t l 2002) Toronto (Lin et al., 2002)– Birmingham, Chicago, Pittsburgh (ISA, based on Zanobetti and Schwartz, 2009

• A few recent dust storm studies have reported associations between mor

morbidity and PM of non-urban, g crustal origin

– Associations were positive with some being statistically significant– Mostly non-U.S. studies – PM10 concentrations in these study locations likely well above those allowed by 

current PM10 standard 
Coarse Particles: Uncertainties and Limitatio

• Extent to which thoracic coarse particles themselves, rather than one or m

occurring pollutants occurring pollutants, are responsible for health effects reported in epidemiostudies

– Relatively small number of studies that have evaluated co-pollutant models and su

experimental studies

• Extent to which PM10 2 5 Extent to which PM concentrations measured at central

-site monitors r

10-2.5 concentrations measured at central site monitors r

exposures in study populations 

– Relatively limited spatial coverage provided by existing PM10-2.5 monitors combined 

relatively large spatial variability in ambient PM10-2.5 concentrations 

– Tends to decrease the likelihood that an association between PM10-2.5 and health e

b d d if h i i i be detected, even if such an association exists

• Measurements of coarse particle concentrations at which reported health effe

– Given the lack of a national monitoring network for PM10-2.5, different health studies 

different approaches to estimate or measure thoracic coarse particles and it is not 

these different methods relate to each other 

• Extent to which coarse particle composition affects particle toxicity

– Lack of information on PM10-2.5 composition makes it difficult to characterize the va

health effect associations with thoracic coarse particles

• L k f tit ti ti t f PM Lack 

of quantitative estima

tes

of PM i t d h lth i k 10-2.5-associa

ted health 

risks

– Evidence judged insufficient to support quantitative risk assessment, adding to unc

regarding potential public health implications of retaining versus revising the curren
Coarse Particles: Staff and CASAC Conclusions 

Current Standard

• Staff conclusion in Policy Assessment: Consider either retaining or 

the current standard, depending on the weight placed on the evidence associated uncertainties 

– Retain: Retain: Focuses on the Focuses on the “suggestive suggestive ” nature of the PM nature of the PM health eviden

10-2.5 health eviden

– Revise: Places more weight on the results of specific studies, particu

reporting associations with PM10-2.5 in locations that would have met the cu

standard, and less weight on the “suggestive” nature of the evidence

• CASAC concluded that the available evidence, while limited, is sufficie

into question the level of protection provided by the current standard 

– CASAC placed weight on studies reporting associations with PM10-2.5 in loc

would h t th t PM ld have met the current PM t d d lt f ll t t d 

10 standard, results from co-pollutant mode

controlled human exposure studies 

– CASAC did not discuss the role that the “suggestive” nature of the evi

played in reaching their conclusion on the adequacy of the current standar
Coarse Particles: Staff Conclusions on Potential Alt

Standards

• Final Policy Assessment: Appropriate to consider revising the form and th• Form: 98th percentile of the annual distribution of 24-hour PM10 concentratio

over 3 years

– Based on analyses in the final Policy Assessment, a 98th percentile form could be

public health protection to locations with higher coarse particle concentrations a

where we have more confidence in associations with health effects and...

– Could be less influenced by relatively rare events that can result in high PM10 y y co

on a small number of days in a year

• Level: 85 μg/m3 to 65 μg/m3 , with the upper end of the range supported by t

health evidence

– 98th percentile 24-hour PM10 concentrations in U S study locations were above 85 

98 percentile 24 hour PM 

10 concentrations in U.S. study locations were above 85 

locations where positive and statistically significant PM10-2.5 effect estimates have b

– Based on analyses in the final Policy Assessment, standard levels from 85 μg/m3 

75 μg/m3 could be considered “generally equivalent” to the current PM10 stand

– Even such “g yq enerally equivalent” standard levels could better targ p etublic he

protection, compared to the current standard
Coarse Particles: CASAC Conclusions and Recomm

on Potential Alternative Standards

• CASAC recommendations are based on the 2nd draft Policy Assessment, w

include the analyses of targeting public health protection

– These analyses were conducted in response to CASAC comments and were in

final Policy Assessment 

• Form: CASAC “strongly” recommended revising the form to the 98th pe

• Level: CASAC agreed that standard levels from 85 (a level that could be 

i l t” t t t d d) t 65 / 3 equivalent” to current standard) to 65 μg/m ld b j tifi d h 

3 could be justified; however, 

recommended setting the level in the range of 75 to 65 μg/m3 

– CASAC recommended revising to increase public health protection

• CASAC concluded that a level at or below 75 μg/m3 would result in increa

h lth t ti th U S health protection across the U.S.

– CASAC noted that margin of safety considerations could justify a PM10 standar

below 75 μg/m3
Coarse Particles: Draft Proposal and Consider

 Propose to retain the current standard 

 In addition, in light of CASAC’s recommendations, the draft proposal welcome

public’s views on different approaches to considering and accounting for the evits limitations and uncertainties, as well as on the appropriateness of revising t

primary standard 

C id ti Considerations• Retaining the current standard places a large amount of weight on the ISA 

conclusions that the evidence is only “suggestive” of a causal relations

– We conclude that “suggestive” evidence is sufficient to justify retaining the cur

st d d b t t ffi i t t j tif i i th t t d d tandard but not sufficient to justify revising that standard 

• In contrast to CASAC, our rationale places relatively more weight on the 

“suggestive” nature of the overall body of evidence in interpreting specifi

• CASAC placed more weight on specific studies than we judge to be 

appropriate

• Given the “suggestive” nature of the evidence, there is substantial uncer

the extent to which additional public health benefits would result, beyonprovided by the current standard, if we set revised standard that targets pr

to different areas
Secondary Standards: History of Visibility Stand

• Over time, NAAQS and Regional Haze Programs have worked together• NAAQS: CAA requires “secondary standards which, in the judgment of the 

Administrator” are “requisite to protect the public welfare from any known or anticipated adverse effects (welfare effects explicitly include visibility)

– 1971: Secondary PM NAAQS set to protect visibility at airports; distinct and mo

than primary standard

– 1987: Secondary NAAQS set identical to new primary PM10 standards; solicite

on approaches to setting a distinct secondary standard

– 1997: Secondary NAAQS set identical to new primary PM2 5 standards; intende

2.5 standards; intende

address urban visibility impairment in conjunction with Regional Haze Program

• Regional Haze Program: 

– 1977: Congress established a national visibility goal to “remedy existing impair

prevent f t i i t” i Cl I t future impairment” in Class I areas

– 1990: Clean Air Act Amendments emphasized regional haze issues and direct

establish Grand Canyon Visibility Transport Commission

– 1999: Regional Haze Rule promulgated; specified use of an equation for calcu

visibilit impairment (in terms of light e tin isibility impairment (in terms of light extinction) as a f ction) as a f nction of PM component

unction of PM component

relative humidity
Secondary Standards: History of Visibility Standard

• 2006 NAAQS: Secondary standards set identical to revised primary P

standards

– Not consistent with staff and CASAC advice to consider distinct sub-da

secondary standard 

– CASAC expressed serious concerns with final decision; continuing to rely 

primary standards to protect against welfare effects “assures neglect, anallow substantial continued degradation, of visual air quality over large athe country”

• Court remand: Decision to set secondary standards identical to prima

standards was unreasonable and contrary to the law

– EPA failed to identify a target level of protection, as required by CAA– EPA k l d d th t PM EPA acknowledged that a PM b d t d d ith 24 h 

2.5 mass-based standard, with a 24-hour av

time, would not address regional differences in relative humidity, yet EPA address this issue at all in final decision
Secondary Standards: Key Visibility Science from 

• Public p p erce tion of haze depends on lig g htin and scene characteristics 

on light extinction (i.e., fractional loss of light per unit distance)

• Good visibility is important to public welfare

– Air quality impacts on visibility negatively affect a person’s sense of personal com

wellbeing

– For a given scene and lighting conditions, people consistently rate visibility levels 

the amount of haze that is unacceptable when viewing photographs within a rangconditions from pristine to highly impaired

• ISA concluded there is a causal association between PM and light extinctio

– Particle light extinction efficiency depends on particle size and composition– There is no consistent relationship between PM2.5 mass concentration and light e

• Determining PM2.5 light extinction 

– Directly measure by optical instrumentation, but no Federal Reference Method (

currently available

– Cl l a cu ate usi i l i ing a simple equation f i l il bl bi PM from routinely available ambient PM2.5 mass

concentration/composition and relative humidity data (as done for the Regional H
Secondary Standards: Urban-Focused Visibility Asse

• Urban visibility preference survey studies conducted in four areas: Denv

V BC Ph i AZ d W hi t DC Vancouver, BC; Phoenix, AZ; and Washington, DC

– Survey participants for each urban area consistently identified levels of unaccep

– Results showed a range of values that divide visibility into acceptable and unacc

conditions, results varied depending on characteristics of selected urban scene (“deciview deciview (dv) scale to characterize visibility) ” (dv) scale to characterize visibility)

• Low end of the range – 20 dv (based on Denver study) • Middle of the range – 25 dv (based on Phoenix study) • High end of the range – 30 dv (based on Washington, DC study) 

– These values define three target protection levels used in subsequent assessm

• Highest haze levels were observed for Eastern U.S. and California urban ar

– Worst haze conditions were generally caused by sulfate, nitrate and carbonaceo

• Assessed visibility impairment associated with just meeting the current PM2.

for 14 urban areas

– Target protection levels exceeded in most urban study areas– Resulted in substantially uneven visibility protection (i.e., significant over prot

West to get adequate protection in East)

• Estimated improvements in visibility associated with alternative standards ba

PM-related light extinction; resulted in uniform protection across all urban 
Secondary Standards: Staff and CASAC Conclusio

Adequacy of Current Standards

• I h P li A ff l d d l il bl i f i In the Policy Assessment, staff concluded currently available information cl 

calls into question the adequacy of the current suite of PM2.5 standard

context of public welfare protection from visibility impairment, primarily in urareas

– L t f d d t t t ti l l if ll t th 

Large percentage of days exceed target protection levels if all areas met the cuof PM2.5 standards

– Current averaging times (24-hours and annual) are not well-suited to protect ag

related visibility impairment

• Current averaging times include nightti Current averaging times include nighttime conditions me conditions for which the scienc

, for which the scienc

to support identification of appropriate levels of visibility protection is not wdeveloped or understood

• CASAC concurred, concluding that:

“ t d PM t d d “current secondary PM standards are i d t t t t i ibilit inadequate to protect visibility, th 

as the

are too high, their averaging times are too long, and their (dried) mass-baindicators do not fully represent PM effects on visual air quality in the amatmosphere”
Secondary Standards: Staff and CASAC Conclusi

Alternative Standards

Al i i di Alternative indicators:• Directly measured PM2.5 light extinction – while strongly supported by CASAC for th

development of Federal Reference Method would take several years

• Calculated PM2.5 light extinction – preferred alternative for this review -- build on exis

network and calculate light extinction similar to Regional Haze Program

Alternative averaging times:• In draft PA, staff concluded, and CASAC concurred, that 1-hour averaging time was ap

(limited to daylight hours with relative humidity less than 90%); also recognized that up 

averaging time may be appropriate

• Final PA concludes that a 24-hour averaging time is a reasonable and appropriate su

extinction calculated on a sub-daily basis

– Based on recent analyses that identified data quality concerns with some hourly PM2.5 data – Also app p ro riate to consider a 4-hour averag g in time to the extent that data q y ualit issues c

appropriately addressed

Level and form:• Final PA concludes that consideration should be given to the upper part of the range of 

presented in the draft PA, and supported by CASAC, especially in light of the limited na

information available from the public preference studies

– Range from 28 – 25 dv, in conjunction with a 24-hour averaging time and 90th percentile form

– Range from 30 – 25 dv, in conjunction with a 4-hour averaging time and 90th percentile form 
Secondary Standards: Draft Proposal

• With regard to current standards:

– Propose that the existing PM2.5 standards are not adequately protec

appropriate to address PM-related visibility impairment

– Propose that a new standard is warranted to provide increased pro

primarily in urban areas in conjunction with the Regional Haze Progrprimarily in urban areas, in conjunction with the Regional Haze Prograchieve appropriate protection in areas across the country

• With regard to a new standard to address PM-related visibility impa

(p ) and respond to the court’s remand): 

– Propose a new standard defined in terms of a PM2.5 visibility index 

averaging time of 24 hours, a 90th percentile form (averaged over 

and a level of either 30 or 28 dv

• Solicit comment on a range of levels down to 25 dv • Also solicit comment on alternative standards to address PM-related visib

impairment, including a sub-daily averaging time (e.g., 4 hours) and assoalternative levels in the range of 30 to 25 dv