Briefing for Interagency ReviewJune 4, 2012

Draft Proposal for the Particulate Matter (PM) National Ambient Air Quality

Standards (NAAQS)

Washington, DC

Overview of Briefing

• Schedule• Current PM standards• Overview of proposed decisions• Primary standards for fine particles• Primary standard for thoracic coarse particles• Secondary standards

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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 PlansFinal

February 2009June/July 2010

Policy Assessment

Second DraftFinal

June 2010April 2011

Proposed Rule Signed June 7, 2012 (court ordered)

Final Rule Signed TBD

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Current PM Standards

• PM2.5 Primary– Annual standard with a level of 15 µg/m3

– 24-hour standard with a 98th percentile form and a level of 35 µg/m3

• PM10 Primary– 24-hour standard with a 1-expected-exceedance form and a

level of 150 µg/m3

• Secondary– Identical to primary PM2.5 standards

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Overview of Proposed Decisions

• Fine Particles – Primary PM2.5 Standards– Propose to revise annual standard level to 12 µg/m3 in conjunction

with retaining 24-hour standard level at 35 µg/m3

• Thoracic Coarse Particles - Primary PM10 Standard– Propose to retain the current standard

• Secondary PM2.5 Standard • Propose a new standard defined in terms of a PM2.5 visibility index,

with an averaging time of 24 hours, a 90th percentile form, and a level of either 30 or 28 dv

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Fine Particles: Significant Impacts on Public Health

• Nationally, based on PM2.5 air quality in 2005, we estimate:– 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 of age)• 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 hospitalizations for respiratory effects (all ages)

• In addition, recent research provides evidence that decreases in long-term PM2.5 exposures have been associated with an estimated increase in mean life expectancy of approximately 5 to 9 months

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Fine Particles: Estimated National Impacts…Premature Mortality

Percentage of total deaths due to PM2.5

Krewski et al. (2009) PM mortality estimate

<2.5%

2.5 to 3.9%

4 to 5%

5.1 to 6.1%

6.1 to 9%

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Fine and Coarse Particles: Susceptible Populations

• Primary standards are to be set to protect public health, including susceptible populations, with an “adequate margin of safety”

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

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Fine Particles: History of the Primary PM2.5 Standards

• 1997: Fine and coarse fractions of PM10 considered separately; EPA set initial fine particle standards using PM2.5 as indicator

• 2006: Retained level of annual standard (15 µg/m3); revised level of 24-hour standard (65 µg/m3 lowered to 35 µg/m3)

– Annual standard: Based level on long-term exposure studies only (Harvard Six Cities and American Cancer Society (ACS) studies); key morbidity studies in children judged to be too uncertain a basis for establishing a lower level (e.g., S. California Children’s Health Study)

– 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/m3 in

conjunction with revising 24-hour standard level within a range of 30-35 µg/m3; following final rule, CASAC expressed serious concerns with decision to retain annual PM2.5 standard level

• 2009: US Court of Appeals, DC Circuit issued decisions on 2006 PM standards– Concluded “EPA failed adequately to explain why, in view of risks posed by short-term exposures

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

– Remanded annual standard for further consideration of whether it provides an adequate margin of safety, especially in children and other susceptible populations

– Primary 24-hour PM2.5 standard, as revised in 2006, was not challenged by litigants9

Fine Particles: Overview of Health Effects Evidence

Based on ORD’s PM Integrated Science Assessment (ISA), which CASAC has endorsed:•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 toxicological studies

provide support for effects observed in epidemiological studies•Compelling evidence supports a causal relationship between PM2.5 and premature 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 for respiratory effects (long- and short-term exposures)– Suggestive of a causal relationship for developmental/reproductive effects, cancer (long-

term exposures)•Evidence is not sufficient to link health effects with any specific fine particle component or group of components associated with any source categories of fine particles nor to exclude any component(s) from the mix of particles included in PM2.5 indicator•No evidence of a discernible threshold below which health effects would not occur

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Fine Particles: Overview of Epidemiology EvidenceLong-term Exposure “Cohort” Studies• Follows a specific group of study participants (“cohort”) over time and across

urban areas; PM2.5 concentrations over years are associated with specific health events (e.g., deaths) across cities

• Extended follow-up of important studies as well as new studies are largely consistent with previous reports of premature mortality at lower ambient PM2.5 concentrations; provide stronger evidence of morbidity effects

• Studies of note include: – Extended analyses of ACS and Harvard Six City studies (premature mortality)– Extended analyses of S. California Children’s Health Study (decreased lung function growth)– Women’s Health Initiative Study (WHI, cardiovascular-related mortality and morbidity effects observed in

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., Medicare

participants) in a single city or across multiple cities over several years; daily changes in PM2.5 concentrations (one or more days) are associated with daily changes in events (e.g., deaths, hospitalizations)

• New multi-city studies greatly expand and reinforce evidence of mortality and morbidity effects available in last review; studies of note include:

– MCAPS (hospitalizations for cardiovascular and respiratory disease, older adults)– 112 U.S. Cities study (premature mortality)

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Fine Particles: Translating Evidence into Primary PM2.5 Standards (1)

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

– Recognize health effects may occur over the full range of concentrations observed in epidemiological studies; there is no evidence of a discernible threshold below which health effects would not occur

– Controlled human exposure studies help to demonstrate causality but, unlike in other recent 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 short-term PM2.5 exposures, with 24-hour standard providing supplemental protection against high peak concentrations

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

• Annual standard level (see figure on next slide)– Focus on identifying levels somewhat below long-term mean concentrations reported in

epidemiological studies (general approach used in previous reviews)– Consider broader distribution of PM2.5 concentrations beyond a point “somewhat below the

mean” to consider ranges of concentrations that were most influential in generating health effect estimates in epidemiological studies, as CASAC strongly advised us to do

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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)

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)

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

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)

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

9 10 11 12 13 14 15 16 17

Fine Particles: Translating Evidence into Primary PM2.5 Standards (2)

Long-term Mean PM2.5 Concentrations

(50th percentiles)

♦ = long-term exposure studies; causal or likely causal relationship▲= short-term exposure studies; causal or likely causal relationship■ = long-term exposure studies; suggestive of a causal relationship

25th percentile

10th percentile

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

Level of current annual PM2.5

standard

Distributional Statistics of Health Event and/or Study Population Data

Long –term mean PM2.5 concentration (µg/m3)

Source: Policy Assessment for the Review of the PM NAAQS, April 2011, Figure 2-8

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Fine Particles: Staff Conclusions in Final Policy Assessment

Annual Standard 24-Hour Standard Potential Implications

12 to 11 µg/m3 35 µg/m3

(retain current standard)

•Alternative suites of standards most strongly supported by evidence•Results in annual standard being the generally controlling standard, except in areas with particularly high peak-to-mean ratios (e.g., Northwest)•Results in more uniform public health protection

up to 13 µg/m3 somewhat below 35 µg/m3, such as down to 30 µg/m3

•More limited support for this suite of standards•Results in 24-hour standard being the controlling standard in a large number of areas in many geographic regions•Results in more uneven public health protection

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Fine Particles: CASAC Advice

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

public health consequences” at the current levels of the standard(s) that “justify 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 concluded that alternative annual standard levels within a range of 13 to 11

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 the risk and air quality information”– Based on 2nd draft Policy Assessment, which did not include consideration of analyses

of the broader distribution of PM2.5 concentrations beyond a point “somewhat below the mean” to consider ranges of concentrations that were most influential in generating health effect estimates in epidemiological studies

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Fine Particles: Draft Proposal and Considerations Propose to revise annual standard level to 12 µg/m3 in conjunction with retaining 24-

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- and short-term exposure studies providing

evidence of effects classified as having a causal or likely causal relationship– Below the lowest long-term mean concentrations reported in all multi-city studies that

reported statistically significant associations (i.e., below 12.8 µg/m3)• Places little weight on more limited evidence from multi-city, long-term exposure studies

for which we have suggestive evidence of a causal relationship for developmental effects• In conjunction with lowering the annual standard level to 12 µg/m3, the evidence most

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

– Changes in air quality designed to meet a lower annual standard would likely result not only in lower annual average PM2.5 concentrations but also in fewer and lower peak 24-hour PM2.5 concentrations

– Thus, additional protection would be provided by a revised annual standard such that revision to the 24-hour standard is not warranted

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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 for

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 down through which we continue to have confidence in observed associations or on the more limited evidence of serious effects in susceptible populations (e.g., infant mortality, low birth weight)

– Places substantial weight on the remaining uncertainties and limitations in the evidence– In conjunction with lowering the annual standard to 13 µg/m3, the evidence provides limited

support for also lowering the 24-hour standard level– An annual standard of 13 µg/m3 (absent a very low 24-hour standard level) could raise

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

• Requesting comment on an annual standard level down to 11 µg/m3:– Places greater weight on considering the range of PM2.5 concentrations below the long-

term mean concentrations down through which we continue to have confidence in observed associations

– Places considerably more weight on limited evidence of serious effects in susceptible populations providing evidence suggestive of a causal relationship

– Places less weight on the remaining uncertainties and limitations in the evidence– In conjunction with lowering the annual standard level to 11 µg/m3, the evidence most

strongly supports retaining 24-hour standard level 17

Costs and Benefits for Proposed Primary PM2.5 Standards (12/35)

• In setting NAAQS, EPA may not consider implementation costs. Per Executive Order 12866 and standard practice, EPA has conducted a Regulatory Impact Analysis for informational purposes only.

• Costs are low because they consider federal measures already in place including recently promulgated regulations (e.g., CSAPR and MATS) and controls applied to meet the current standards (15/35).

• Emission control measures were applied to sources of PM2.5, SO2, and NOx (few thousands of tons) for meeting proposed alternative standards (12/35).

Projected Costs and Benefits of Attainment of 12/35 Incremental to Attainment of Current Standards in 2020*

(Million 2006$, 7% Discount Rate)

Costs $69

Health Benefits $2,100 to $5,400

Net Benefits $2,000 to $5,300

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*Estimated costs and benefits are additional to those associated with meeting the current standards. Currently, we are performing QA on the cost and benefit estimates. A new version of the RIA with updated estimates will be provided in the next few weeks. We anticipate there will be an increase in the costs; however, the benefits are still expected to significantly exceed the costs.

Current and Projected PM2.5 Nonattainment

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Standard(s)

Current Standards (15/35)

Nonattainment Areas*

Proposed Standards (12/35)**

Estimated Using Recent Air Quality

(2008-2010)by County

Proposed Standards (12/35)**

Projected Considering ‘On the Books’ Federal

Controls (2020)by County

Both annual and 24-hour standards

16 14 8

Annual standard only 19 68 4

24-hour standard only 16 21 6

Total 51 103 18

*Nonattainment areas may include multiple counties or only a part of one county.**Estimated/projected conditions are for illustrative purposes only. Assuming revised PM NAAQS are promulgated in June 2013, designations would be based on 2011-2013 or 2012-2014 air quality data.

2008-2010 PM2.5 Concentrations by CountyProposed Standards: Annual NAAQS level = 12 µg/m3/24-hr NAAQS level = 35 µg/m3

20Note: This slide represents recent air quality conditions but not necessarily the areas likely to be designated as attainment/nonattainment. For illustrative purposes, assuming revised PM NAAQS are promulgated in June 2013, designations would be based on 2011-2013 or 2012-2014 air quality data.

2020 Projected PM2.5 Concentrations by County with ‘on the books’ Federal controls

21Projected design values indicate 18 counties are likely not to meet one or both of the proposed primary PM 2.5 standards in 2020.

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

Coarse Particles: History of the PM10 Standard• 1987: EPA first set PM10 standards in order to protect against exposures to particles

that can penetrate deeply into the respiratory system – 24-hour standard: Form set at one-expected-exceedance and level set at 150 µg/m3 – Annual standard: Level set at 50 µg/m3

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

long-term exposure to inhalable coarse particle pollution

– In subsequent litigation, DC Circuit court upheld decisions and supporting rationale for PM10 standard

• Today’s 24-hour PM10 standard is the same as that set in 1987

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Coarse Particles: ISA Conclusions

• Causality: The available evidence is “suggestive” of a causal relationship between short-term thoracic coarse particle exposures and mortality, respiratory effects, and cardiovascular effects– “Suggestive,” rather than “causal” or “likely causal”, reflects the

greater degree of uncertainty associated with the health evidence for PM10-2.5

• Composition: Evidence is not sufficient to link health effects with specific sources or components of PM10-2.5 (such as those typical of urban versus rural areas)

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Coarse Particles: Health Evidence• In epidemiologic studies, associations between PM10-2.5 and mortality/morbidity

were generally positive, with some being statistically significant– In the subset of studies that employed co-pollutant models to evaluate the potential for

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

• Single-city analyses reported positive and statistically significant associations in a few urban locations that would have met the current PM10 standard during the study period

– Detroit (Ito et al., 2003)– 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 mortality or morbidity and PM of non-urban, 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 the

current PM10 standard

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Coarse Particles: Uncertainties and Limitations• Extent to which thoracic coarse particles themselves, rather than one or more co-

occurring pollutants, are responsible for health effects reported in epidemiologic studies

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

• Extent to which PM10-2.5 concentrations measured at central-site monitors reflect exposures in study populations

– Relatively limited spatial coverage provided by existing PM10-2.5 monitors combined with the relatively large spatial variability in ambient PM10-2.5 concentrations

– Tends to decrease the likelihood that an association between PM10-2.5 and health effects would be detected, even if such an association exists

• Measurements of coarse particle concentrations at which reported health effects occur – Given the lack of a national monitoring network for PM10-2.5, different health studies have used

different approaches to estimate or measure thoracic coarse particles and it is not clear how 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 variability in

health effect associations with thoracic coarse particles • Lack of quantitative estimates of PM10-2.5-associated health risks

– Evidence judged insufficient to support quantitative risk assessment, adding to uncertainty regarding potential public health implications of retaining versus revising the current standard 25

Coarse Particles: Staff and CASAC Conclusions on the Current Standard

• Staff conclusion in Policy Assessment: Consider either retaining or revising the current standard, depending on the weight placed on the evidence and its associated uncertainties

– Retain: Focuses on the “suggestive” nature of the PM10-2.5 health evidence– Revise: Places more weight on the results of specific studies, particularly those

reporting associations with PM10-2.5 in locations that would have met the current PM10 standard, and less weight on the “suggestive” nature of the evidence

• CASAC concluded that the available evidence, while limited, is sufficient to call into question the level of protection provided by the current standard

– CASAC placed weight on studies reporting associations with PM10-2.5 in locations that would have met the current PM10 standard, results from co-pollutant models, and controlled human exposure studies

– CASAC did not discuss the role that the “suggestive” nature of the evidence played in reaching their conclusion on the adequacy of the current standard

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Coarse Particles: Staff Conclusions on Potential Alternative Standards

• Final Policy Assessment: Appropriate to consider revising the form and the level

• Form: 98th percentile of the annual distribution of 24-hour PM10 concentrations, averaged over 3 years

– Based on analyses in the final Policy Assessment, a 98th percentile form could better target public health protection to locations with higher coarse particle concentrations and to locations 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 concentrations 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 the strongest health evidence

– 98th percentile 24-hour PM10 concentrations in U.S. study locations were above 85 µg/m3 in locations where positive and statistically significant PM10-2.5 effect estimates have been reported

– Based on analyses in the final Policy Assessment, standard levels from 85 µg/m3 to just above 75 µg/m3 could be considered “generally equivalent” to the current PM10 standard

– Even such “generally equivalent” standard levels could better target public health protection, compared to the current standard

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Coarse Particles: CASAC Conclusions and Recommendations on Potential Alternative Standards

• CASAC recommendations are based on the 2nd draft Policy Assessment, which did not include the analyses of targeting public health protection

– These analyses were conducted in response to CASAC comments and were included in the final Policy Assessment

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

• Level: CASAC agreed that standard levels from 85 (a level that could be “generally equivalent” to current standard) to 65 µg/m3 could be justified; however, they 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 increased public

health protection across the U.S.– CASAC noted that margin of safety considerations could justify a PM10 standard level at or

below 75 µg/m3

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Coarse Particles: Draft Proposal and Considerations Propose to retain the current standard

In addition, in light of CASAC’s recommendations, the draft proposal welcomes the public’s views on different approaches to considering and accounting for the evidence and its limitations and uncertainties, as well as on the appropriateness of revising the PM10 primary standard

Considerations • Retaining the current standard places a large amount of weight on the ISA conclusions that the evidence is only “suggestive”

of a causal relationship – We conclude that “suggestive” evidence is sufficient to justify retaining the current standard 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 specific studies

• CASAC placed more weight on specific studies than we judge to be appropriate • Given the “suggestive” nature of the evidence, there is substantial uncertainty in the extent to which additional public health

benefits would result, beyond those provided by the current standard, if we set revised standard that targets protection to different areas

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Secondary Standards: History of Visibility Standards • 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 more stringent than primary standard

– 1987: Secondary NAAQS set identical to new primary PM10 standards; solicited comment on approaches to setting a distinct secondary standard

– 1997: Secondary NAAQS set identical to new primary PM2.5 standards; intended to address urban visibility impairment in conjunction with Regional Haze Program

• Regional Haze Program: – 1977: Congress established a national visibility goal to “remedy existing impairment and prevent

future impairment” in Class I areas– 1990: Clean Air Act Amendments emphasized regional haze issues and directed EPA to

establish Grand Canyon Visibility Transport Commission– 1999: Regional Haze Rule promulgated; specified use of an equation for calculating visibility

impairment (in terms of light extinction) as a function of PM components and relative humidity

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Secondary Standards: History of Visibility Standards (cont.)

• 2006 NAAQS: Secondary standards set identical to revised primary PM2.5 standards

– Not consistent with staff and CASAC advice to consider distinct sub-daily secondary standard

– CASAC expressed serious concerns with final decision; continuing to rely on primary standards to protect against welfare effects “assures neglect, and will allow substantial continued degradation, of visual air quality over large areas of the country”

• Court remand: Decision to set secondary standards identical to primary standards was unreasonable and contrary to the law

– EPA failed to identify a target level of protection, as required by CAA

– EPA acknowledged that a PM2.5 mass-based standard, with a 24-hour averaging time, would not address regional differences in relative humidity, yet EPA did not address this issue at all in final decision

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Secondary Standards: Key Visibility Science from the ISA• Public perception of haze depends on lighting and scene characteristics as well as

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 comfort and

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

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

• ISA concluded there is a causal association between PM and light extinction – Particle light extinction efficiency depends on particle size and composition– There is no consistent relationship between PM2.5 mass concentration and light extinction

• Determining PM2.5 light extinction – Directly measure by optical instrumentation, but no Federal Reference Method (FRM)

currently available– Calculate using a simple equation from routinely available ambient PM2.5 mass

concentration/composition and relative humidity data (as done for the Regional Haze Program)32

Secondary Standards: Urban-Focused Visibility Assessment• Urban visibility preference survey studies conducted in four areas: Denver, CO;

Vancouver, BC; Phoenix, AZ; and Washington, DC– Survey participants for each urban area consistently identified levels of unacceptable visibility – Results showed a range of values that divide visibility into acceptable and unacceptable

conditions, results varied depending on characteristics of selected urban scene (using a “deciview” (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 assessments

• Highest haze levels were observed for Eastern U.S. and California urban areas– Worst haze conditions were generally caused by sulfate, nitrate and carbonaceous PM2.5

• Assessed visibility impairment associated with just meeting the current PM2.5 standards for 14 urban areas

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

West to get adequate protection in East)

• Estimated improvements in visibility associated with alternative standards based on PM-related light extinction; resulted in uniform protection across all urban areas

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Secondary Standards: Staff and CASAC Conclusions on Adequacy of Current Standards

• In the Policy Assessment, staff concluded currently available information clearly calls into question the adequacy of the current suite of PM2.5 standards in the context of public welfare protection from visibility impairment, primarily in urban areas

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

– Current averaging times (24-hours and annual) are not well-suited to protect against PM-related visibility impairment

• Current averaging times include nighttime conditions, for which the science needed to support identification of appropriate levels of visibility protection is not well developed or understood

• CASAC concurred, concluding that: “current secondary PM standards are inadequate to protect visibility, as their levels are too high, their averaging times are too long, and their (dried) mass-based indicators do not fully represent PM effects on visual air quality in the ambient atmosphere”

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Secondary Standards: Staff and CASAC Conclusions on Alternative Standards

Alternative indicators:• Directly measured PM2.5 light extinction – while strongly supported by CASAC for the future

development of Federal Reference Method would take several years• Calculated PM2.5 light extinction – preferred alternative for this review -- build on existing monitoring

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 appropriate

(limited to daylight hours with relative humidity less than 90%); also recognized that up to 4-hour averaging time may be appropriate

• Final PA concludes that a 24-hour averaging time is a reasonable and appropriate surrogate for light extinction calculated on a sub-daily basis

– Based on recent analyses that identified data quality concerns with some hourly PM2.5 data – Also appropriate to consider a 4-hour averaging time to the extent that data quality issues can be

appropriately addressed

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

presented in the draft PA, and supported by CASAC, especially in light of the limited nature of the 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 35

Secondary Standards: Draft Proposal• With regard to current standards:

– Propose that the existing PM2.5 standards are not adequately protective nor appropriate to address PM-related visibility impairment

– Propose that a new standard is warranted to provide increased protection, primarily in urban areas, in conjunction with the Regional Haze Program, to achieve appropriate protection in areas across the country

• With regard to a new standard to address PM-related visibility impairment (and respond to the court’s remand):

– Propose a new standard defined in terms of a PM2.5 visibility index with an averaging time of 24 hours, a 90th percentile form (averaged over 3 years), 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 visibility

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

36