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From: Lydia Wegman/RTP/USEPA/US To: nfrey@omb.eop.gov Cc: martin.karen@epa.gov, Beth Hassett
- Sipple/RTP/USEPA/US@EPA, Joseph
- J

Dougherty/DC/USEPA/US@EPA, hannon.john@epa.gov, Steven Silverman/DC/USEPA/US@EPA, Richard Wayland/RTP/USEPA/US@EPA, Pat Dolwick/RTP/USEPA/US@EPA, James Hemby/RTP/USEPA/US@EPA Date: 06/12/ 2012 05:22 PM Subject: Further revisions to AQI section of draft PM NAAQS preamble Nathan, We have given further consideration to the comments from the FLMs and others on the Air Quality Index. Based on our further thinking, we have made revisions tha t we believe fully accommodate the concerns that the interagency reviewers have expressed. The attached section from the preamble reflects these changes compared to the interagency review draft. We'd appreciate it if you would distribute this to the inte ragency review group as soon as possible. Please let me know if you have any questions. Thanks. LydiaPage 2 of 13

I. Communicati on of Public Health Information Sections 319(a)(1) and ( 3) of the CAA require the EPA to establish a uniform air quality index fo r reporting of air quality

. The s e section s specifically direct the Administrator to ‘‘promulgate regulations establishing an air quality monitoring system throughout the United States which utilizes uniform air quality monitoring criteria and methodology and measures such air quality according to a uniform air quality index’’ and ‘‘provides for daily analysis and reporting of air quality based upon such uniform air quality index...’’ In 1979, the EPA established requirements for index reporting (44 FR 27598, May 10, 1979)

. The requirement for State a nd local agencies to report the AQI appears in 40 CFR 58.50 and the specific requirements (e.g., what to report, how to report, reporting frequency, calculations) are in appendix G to 40 CFR part 58. Information on the public health implications of ambient concentrations of criteria pollutants is currently made available primarily through EPA’s AQI program

. The current AQI has been in use since its inception in 1999. 1 It provides accurate, timely, and easily understandable information about daily levels of pollution (40 CFR 58.50)

. The AQI establishes a nationally uniform system of indexing pollution levels for ozone, carbon monoxide, nitrogen dioxide, PM and sulfur dioxide

. The AQI is also recognized internationally as a proven tool to effectively communica te air quality information to the public

. In fact, many countries have created similar indices based on the AQI

. The AQI converts pollutant concentrations in a community’s air to a number on a scale from 0 to 500

. Reported AQI values enable the public to know whether air pollution levels in a particular location are characterized as good (0

– 50), moderate (51

– 100), unhealthy for sensitive groups (101

– 150), unhealthy (151

– 200), very unhealthy (201

– 300), or hazardous (300

– 500)

. The AQI index value of 100 typ ically corresponds to the level of the short

- term (e.g., daily or hourly standard) NAAQS for each

1 In 1976, the EPA established a nationally uniform air quality index, then called the Pollutant Standard Index (PSI), for use by State and local agencies on a voluntary basis (41 FR 37660, September 7, 1976)

. In August 1999, the EPA adopted revisions to this air quality index (64 FR 42530, August 4, 1999) and renamed the index the AQI

.Page 3 of 13

pollutant

. Below an index value of 100, an intermediate value of 50 was defined either as the level of the annual standard if an annual standard has been esta blished (e.g., PM 2.5 , nitrogen dioxide), or as a concentration equal to one

- half the value of the short

- term standard used to define an index value of 100 (e.g., carbon monoxide). An AQI value greater than 100 means that a pollutant is in one of the unheal thy categories (i.e., unhealthy for sensitive groups, unhealthy, very unhealthy, or hazardous) on a given day

. An AQI value at or below 100 means that a pollutant concentration is in one of the satisfactory categories (i.e., moderate or good)

. Decisions ab out the pollutant concentrations at which to set the various AQI breakpoints that delineate the various AQI categories draw directly from the underlying health information that supports the NAAQS review. Historically, s tate and local agencies have primarily used the AQI to provide general information to the public about air quality and its relationship to public health

. For more than a decade, many s tates and local agencies, as well as the EPA and other Federal agencies, have been developing new and innovative programs and initiatives to provide more information to the public, in a more timely way

. These initiatives, including air quality forecasting, real

- time data reporting through the AIRNow website 2 , and air quality action day programs, can serve to provide useful, up

- to

- date, and timely information to the public about air pollution and its effects

. Such information will help individuals take actions to avoid or to reduce exposures to ambient pollution at levels of concern to them and can encourag e the public to take actions that will reduce air pollution on days when levels are projected to be at levels of concern to local communities

. Thus, these programs have significantly broadened the ways in which s tate and local agencies can meet the nationa lly uniform AQI reporting requirements, and are

co ntributing to s tate and local efforts to provide community health protection and to attain or maintain compliance with the NAAQS

. The EPA and s tate and local agencies recognize that these programs are inter related with AQI reporting and with the information on the effects of air pollution on public health

2 See http://www.airnow.gov/index.cfm?action=airnow.showlocal&cityid= 204

.Page 4 of 13

that is generated through the periodic review, and revision when appropriate, of the NAAQS. In recognition of the proposed change s to the suite of primary annual PM 2.5 standard s summarized in section I II.F above, the EPA propos es a conforming change s to the AQI to be consistent with the proposed change s to the annual standard s . The health effects information that supports the proposed decisions on the PM 2.5 standards , as discussed in section I II.B above , is also the basis for the proposed changes in the AQI discussed below in this section

. The EPA intends to finalize conforming changes to the AQI in conjunction with the Agency’s final decisions on the primar y annual and 24

- hour PM 2.5 standards, if revisions to such standards are promulgated

. Note that , currently, we are cautioning members of sensitive groups at the AQI value of 100 at 35 μg/m 3 , 24

- hour average, because this is the level that was provided in g uidance (Harnett, 2009 , Attachment B ) which , in essence , superseded the AQI value of 100 established in 1999 (64 FR 42530, August 4, 1999). 3 With respect to an AQI value of 50, as discussed above, the historical approach is to set it at the same level of the annual standard, if there is one

. This is consistent with the current AQI sub

- index for PM 2.5 , in which the current AQI value of 50 is set at 15 μg/m 3 , consistent with the level of the current primary annual PM 2 .5 standard. and t T he EPA see s no basis for deviating from this approach in this review

. Thus, the EPA propos es to set an AQI value of 50 at within a range of 12 to 13 μg/m 3 , 24

- hour average, the same level as consistent with the proposed annual PM 2. 5 standard

. If the annual 5 standard is set at a different level , an (section III.F)

. The final AQI value of 50 will be set at the level of the annual PM 2.5 standard that is promulgated

. With respect to an AQI value of 100, which is the basis for advisories to individuals in sensitive groups , there are two general approaches that could be use d to select the associated PM 2.5 level

. By far the most common approach, which has been used with the other sub

- indices as discussed noted above, is to set an AQI value of 100 at the same level as the short

- term standard

. The EPA recognizes that some

3 In addition, this guidance document recommended an AQI value of 150 at 55 μg/m 3 , 24

- hour average, which is in use by many State and local agencies (Harnett, 2009, Attachment B).Page 5 of 13

s tate and local air quality agencies have expressed a strong preference that the Agency set an AQI value of 100 equal to any short

- term standar d

. These agencies typically express the view that this linkage is useful for the purpose of communicating with the public about the standard, as well as the health impacts associated with daily air quality

. The EPA propos es to use this approach to set the AQI value of 100 at 35 μg/m 3 , 24

- hour average, consistent with the proposal to retain the current 24

- hour PM 2.5 standard (section III.F). The second An alternative approach is to directly evaluate the health effects evidence to select th e level for an AQI value of 100 which is the basis for advisories to individuals in sensitive groups

. This was the approach used in the 1999 rulemaking to set the AQI value of 100 at a level of 40 μg/m 3 when the 24

- hour standard level was 65 μg/m 3

. 4 This alternative approach was used in the case of the PM 2.5 sub

- index because the annual and 24

- hour PM 2.5 standards set in 1997 were designed to work together , and the intended degree of health protection against short

- term risks was not defined by the 24

- hour standard alone, but by the combination of the two standards working in concert. Indeed, at that time, the 24

- hour standard was set to provide supplemental prote ction relative to the principal protection provided by the annual standard. The EPA is considering soliciting comment on this alternative approach in recognition that, as proposed, the 24

- hour PM 2.5 standard is intended to continue to provide s supplemental protection against effects associat ed with short

- term exposures of PM 2.5 by working in conjunction with the annual standard to reduce 24

- hour exposures to PM 2.5 . The EPA recognizes that

some s tate and local air quality agencies have expressed support for this alternative approach in such a

case , when the annual standard provides some protection fr om effects associated with short

- term exposures . This alternative approach of evaluating the health evidence directly results would result in the

c onsideration of a range of 35 to 30 μg/m 3 , 24

- hour average, based on the discussion of the health information pertaining to the level of the 24

- hour standard in section I II.E.4 above

. Setting an AQI value

4 C urrently, we are cautioning members of sensitive groups at the AQI value of 100 at 35 μg/m 3 , 24

- hour average, consistent with more recent guidance from EPA with regard to the development of S tate emergency episode contingency plans (Harnett, 2009, Attachment B)

. Formatted: Tab stops: 2.19", Left

Formatted: Subscript
Formatted: SubscriptPage 6 of 13

of 100 at the upper end of the range (35 μg/m 3 , 24

- hour average ) ) , which would be essentiall y equivalent to the proposed approach, would place more weight on the multi

- city, short

- term exposure studies that generally support retaining the current 24

- hour standard level at 35 μg/m 3 in conjunction with lowering the level of the annual standard to w ithin a range of 12 to 13 μg/m 3

. Setting an AQI value of 100 at the lower end of the range (30 μg/m 3 , 24

- hour average) would place more weight on the limited evidence from one multi

- city study (Bell et al., 2008) that reported positive and statistically si gnificant effects with an overall 98 th percentile value below 35 μg/m 3 , 24

- hour average, in conjunction with an overall long

- term mean concentration slightly less than 13 μg/m 3 (US EPA, 2011a, p. 2

- 84)

. Both of these approaches result in the consideration of setting an AQI value of 100 for the PM 2.5 sub

- index within the range of 35 to 30 μg/m 3 , 24

- hour average

. In making a final decision on the air quality level for an AQI value of 100, the EPA will first decide on the approach that is appropriate, and the n the level that is consistent with that approach

. If the first approach is selected, the Agency will set the AQI value of 100 at the level of the 24

- hour PM 2.5 that is promulgated

. If the second approach is selected, the Agency will base the decision to s et the PM 2.5 level for an AQI value of 100 by evaluating the health effects evidence

. The EPA strongly The EPA encourages s tate and local air quality agencies that use the AQI to comment on both the approach and the level at which to set an AQI value of 100

. With respect to an AQI value of 150, this level is based upon the same health effects information that informs the selection of the level of the 24

- hour standard and the AQI value of 100

. The AQI value of 150 is currently set at a level of 65 μg/m 3

. As noted above, in guidance the EPA indicated that a 55 μg/m 3 , 24

- hour average, PM 2.5 level should be used for an AQI value of 150, in conjunction with an AQI value of 100 at 35 μg/m 3 , 24

- hour average (Harnett, 2009. , Attachment B )

. In considering what level to propose for an AQI value of 150, we still believe that the health effects evidence indicates that the level of 55 μg/m 3 , 24

- hour average, 5 is appropriate to use in conjunction with an AQI value of 100

5 We note that this level is consistent with the level recommended in the more recent EPA guidance (Harnett, 2009, Attachment B ) , which is in use by many S tate and local agencies

.Page 7 of 13

set at the proposed level of 35 μg/m 3

. Thus, if the EPA sets an AQI value of 100 at the PM 2.5 level of 35 μg/m 3 , 24

- hour average, the Agency proposes to set an AQI value of 150 at the PM 2.5 level of 55 μg/m 3 , 24

- hour average

. If, however, the EPA decides to set an AQI value of 100 at 30 μg/m 3 , using one of based on the two approaches alternative approach discussed above, then the EPA would adjust an AQI value of 150 proportionally to the PM 2.5 level of 50 μg/m 3 , 24

- hour average

. The Agency’s approach to selecting the levels at which to set the AQI value s of 100 and 150 inherently recognize s that the epidemiological evidence upon which these decisions are based provides no evidence of discern i ble thresholds, below which effects do not occur in either s ensitive group s or in the general population , at which to set these two breakpoints

. Therefore, EPA concludes the use of a proportional adjustment is appropriate

. Thus, if the EPA sets an AQI value of 100 at the PM 2.5 level of 35 μg/m 3 , 24

- hour average, the Agency proposes to set an AQI value of 150 at the PM 2.5 level of 55 μg/m 3 , 24

- hour average

. However, if the EPA sets an AQI value of 100 at the PM 2.5 level of 30 μg/m 3 , 24

- hour average, the Agency proposes to set an AQI value of 150 at the PM 2.5 level of 50 μg/m 3 , 24

- hour average

. would be appropriate

. With respect to an AQI value of 500, a The EPA also propos es to set an AQI value of 500 at 350 μg/m 3 , as discussed below, and propos es proportional revisions to the AQI breakpoints between the 150 and 500 levels

. The proposed breakpoints are shown in Table 2 below

. A review of the history of the AQI value of 500 for PM 10 and of the AQI value of 500 for PM 2.5 is useful background

. for explaining the basis for proposing to set an AQI value of 500 at 350 μg/m 3 , 24

- hou r average, for PM 2.5 . The current AQI value of 500 for PM 10 was set in 1987 at the level of 600 μg/m 3 , 24

- hour average, on the basis of increased mortality associated with historical wintertime pollution episodes in London (52 FR 24687 to 24688, July 1, 1987)

. P article concentrations during these episodes, measured by the British Smoke method, were in the range of 500 to 1000 μg/m 3

. In the 1987 rulemaking that established the upper bound index value for PM 10 , the EPA cited a generally held opinion that th e British Smoke method measures PM with a cutpoint of approximately 4.5 microns (52 FR 24688, July 1, 1987)

. In establishingPage 8 of 13

this value for PM 10 , we EPA assumed that concentrations of PM 10 , which includes both coarse and fine particles, during episodes of c oncern, would be about 100 μg/m 3 higher than the PM concentration measured in terms of British Smoke (52 FR 24688, July 1, 1987)

. The upper bound index value of 600 μg/m 3 was developed by selecting the lower end of the range of harmful concentrations durin g the historical wintertime pollution episodes in London (500 μg/m 3 ) and adding a margin of 100 μg/m 3 to account for this measurement difference

. The current PM 2.5 concentration corresponding to an AQI value of 500 set in the 1999 rulemaking is 500 μg/m 3 , 24

- hour average

. This was proposed in 1998 and finalized in 1999 (63 FR 67829, December 9, 1998, and 64 FR 42530, August 4, 1999, respectively)

. Because there were few PM 2.5 monitoring data available at that time, the proposal decision was based on the stat ed assumption that PM concentrations measured by the British Smoke method a we re approximately equivalent to PM 2.5 concentrations

.
Table 2. Proposed Revisions to Breakpoints for PM 2.5 Sub

- Index

AQI Category Index

Values Proposed Breakpoints (μg/m 3 , 24

- hour average) Good 0

- 50 0.0

– ( 12 .0

- 13. 0 )
Moderate 51

-

100 ( 12. 1

– 13. 1 )

– 35.4 Unhealthy for Sensitive Groups 101

-

150 35.5

– 55.4

Unhealthy 151

-

200 55.5

- 140.4 Very 201

- 140.5

- 210.4 Formatted: Indent: First line: 0.5", Line spacing: Double, No widow/orphan control, Don't adjust space between Latin and Asian text, Don't adjust space between Asian text and numbers Formatted: Left, Indent: First line: 0.5", Line spacing: Double

Formatted: Left, Indent: First line: 0.5", Line spacing: Double

Formatted: Left, Indent: First line: 0.5", Line spacing: Double

Formatted: Left, Indent: First line: 0.5", Line spacing: Double

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Unhealthy 300

Hazardous 301

-

400 210.5

- 280.4

401

- 500 280.5

- 350.4

In considering whether it is ap propriate to retain or revi se sion s to an the AQI value of 500 for PM 2.5 , the EPA has taken note s that the propos ed and final action s in 1998 and 1999 rulemaking w as ere based on an assumption of approximate equivalence between the British Smoke method and the current PM 2.5 method

. This assumption is not entirely consistent with the view cited in 1987 that the British Smoke method has a cutoff of 4.5 microns (52 FR 24688, July 1, 1987) , such that it would be reasonable to expect that a level of 500 μg/m 3 based on the British Smoke method would generally be equivalent to a somewhat lower level based on the current PM 2.5 method

. However, the EPA recognizes that regardless o f measurement method, extremely high PM concentrations that would most likely be associated with combustion sources (e.g., coal burning in historic t he London event, wildfires in contemporary U.S. environments) are typically dominated b y fine particles, su ch that there may be very little difference bet ween these measurement methods. To further explore this issue, Because of the dramatic increase in PM 2.5 monitoring data since that rulemaking, the EPA concludes that considers it appropriate to consider the extent to which more recent air quality data can inform consideration of the appropriate level to set the AQI value of 500 for PM 2.5 at a level below 500 μg/m 3 so that it is more consistent with the findings from the London episodes and with the AQI value of 500 for PM 10 . In considering more recent air quality data, EPA notes that o O n average, about 60 percent of ambient PM 10 measured in the northeastern, southeastern, and industrial midwest portions of the U.S. Formatted: Left, Indent: First line: 0.5", Line spacing: Double

Formatted: SubscriptPage 10 of 13

consists of PM 2.5 . 6 Using the 60 percent factor to scale the AQI value of 500 for PM 10 (600 μg/m 3 ) would result s in an AQI value of 500 for PM 2.5 of about 350 μg/m 3

. 7 On the other hand, the EPA

rec ognizes that the ratio between PM 10 and PM 2.5 based on such regional average data is not likely to be representative of the ratio at the atypically high concentrations that may occur in some areas of the country , such as those associated with wildfires and biomass burning, that would be relevant to consider in conjunction with the range of AQI values between 300 and 500 that define s the “hazardous” category

. The Agency believes it is appropriate that this scaling approach results in a PM 2.5 value for the upper bound index value that is below the 500 μg/m 3 concentration of PM 4.5 by the British Smoke method

. The EPA therefore proposes this level for the upper bound level of the PM 2.5 sub

- index of the AQI

. The EPA solicits comment on this scaling approach for translating the AQI value of 500 for PM 10 into an appropriate corres ponding value for PM 2.5 Further, in considering the body of more recent health effects evidence available in this review,
t T he EPA concludes that there is little information about more recent air pollution episodes similar to the wintertime pollution episodes in London and associa ted impacts on community health upon which to base a decision . Thus, the EPA concludes that it remains appropriate to has use d the historical wintertime pollution episodes in London as the basis for to propose s s etting an AQI value of 500 for PM 2.5 as described above because it is still the best available directly relevant information

- -- there is little information about similar, more recent, air pollution episodes and associated impacts on community health upon which to base a decision

. However Nonetheless , the EPA takes note of the a limited number of studies cited in the I ntegrated S cience A ssessment that evaluated wood smoke health impacts which found effects such as cardiovascular morbidity and mortality (e.g., Delfino et al., 2009; Mar et al., 2000; Sarnat et al., 2008) as well as respiratory effects (e.g., Barregard et al., 2008; Delfino et

6 More specifically, in 2001 to 2003, the median of the ratio of 24

- hour PM 2.5 and PM 10 among monitoring sites in the northeastern, southeastern, and industrial midwest portions of the U.S to the annual average was between 0.60 and 0.65 (US EPA, 2005, Figure 2

- 19). 7 We note that this level is consistent with the level recommended in the mo re recent EPA guidance (Harnett, 2009, Attachment B ). Formatted: Subscript Formatted: SubscriptPage 11 of 13

al., 2009; Schreuder et al., 2006) , albeit at much low er levels (US EPA, 2009a, sections 6.2 and 6.6)

. The EPA believes that t T hese recent health studies may provide some additional qualitative support for considering lowering the air quality level associated with an AQI value of 500 to 350 below the current value of 50 0 μg/m 3 and, therefore, also lowering the other levels in the range of AQI value s between 150 and 500

. Based on the above considerations, the EPA provisionally concludes that it is appropriate to propose both to retain the curr ent level of 5 0 0 μg/m 3 for the AQI value of 150 and, in the alternative , to propose to revise the level to within a range from below 500 μg/m 3 down to a level of 350 μg/m 3

. A decision to retain the current level would reflect placing significant weight on the uncertainties associated with characterizing an appropriate scaling factor to translate the historic London air quality data into corresponding PM 2.5 levels , and on the uncertainties in t ranslating the more recent health effects studies , cond ucted at relatively low PM 2.5 levels, into a ba sis for selecting a level for an AQI value of 500 . A decision to lower the level for the AQI value of 500 to within the pro p osed range would reflect placing more weight on the overall body of recent health effects information and on studies available in this review that specifically examine health impacts related to exposure to wood smoke. The EPA solicits comment on whether it is appropriate to retain or revise the current level of 500 μg/m 3 for the AQI value of 500 . To the extent that support is expressed for revising the current level to a level within the proposed range, the EPA solicits comment on the recommended level and on the rationale that would support such a level. The EPA also s olicits any additional information that may be useful to inform a final decision on the a ppropriate level to set the AQI value of 500

. For the intermediate breakpoints in the AQI between the values of 150 and 500, the EPA propos es PM 2.5 concentrations that generally reflect a linear relationship between increasing index values and increasing PM 2.5 values (Table 2 above )

. The available scientific evidence of health effects related to population exposures to PM 2.5 concentrations between the level of the 24

- hour standard and an AQI value of 500 suggest a continuum of effects in this range, with increasing PM 2.5 concentrations Formatted: Subscript
Formatted: SubscriptPage 12 of 13

being associated with increasingly larger numbers of people likely to experience such effec ts
. The generally linear relationship between AQI values and PM 2.5 concentrations in this range is consistent with the health evidence

. This also is consistent with the Agency’s practice of setting breakpoints in symmetrical fashion where health effects in formation does not suggest particular levels. Based on the proposed levels discussed above, Table 2 below summarizes the proposed breakpoint for the PM 2.5 subinde x. Table 2 shows the proposed level of 500 μg/m 3 for the AQI value of 500 , which is consistent with retaining the curren t AQI value , and the associated intermediate breakpoints between AQI values of 1 50 and 500. Intermediate breakpoints that would be associated with

an AQI value of 500 set a different level with in the range proposed in the alternative would be calculated based on a linear relationship between the selected l evels for AQI values of 150 and 500.

Table 2. Proposed Breakpoints for PM 2.5 Sub

- Index AQI Category Index Values Proposed Breakpoints (μg/m 3 , 24

- hour average) Good 0

- 50 0.0

– ( 12 .0

- 13.0) Moderate 51

- 100 ( 12. 1

– 13.1)

– 35.4 Unhealthy for Sensitive Groups 101

- 150 35.5

– 55.4 Unhealthy 151

- 200 55.5

- 1 5 0.4 Very Unhealthy 201

- 300 15 0.5

- 2 5 0.4 Hazardous 301

- 400 25 0.5

- 35 0.4

401

- 500 350 .5

- 500 .4

I n proposing to retain or revi se the 500 level for the AQI as described above , we note that the EPA is not proposing to establish a Significant Harm Level (SHL) for PM 2.5 . The SHL is an important part of air pollution Emergency Episode Plans, which are required for certain areas by CAA section 110(a)(2)(G) and associated regulations at 40 CFR 51.150, under the Prevention of Air Pollution Emergency Episodes program

. The Agenc y believes that air quality responses established through an Formatted: SubscriptPage 13 of 13

Emergency Episode Plan should be developed through a collaborative process working with State and Tribal air quality, forestry and agricultural agencies, Federal land management agencies, private land managers and the public. Therefore, if in future rulemaking EPA proposes revisions to the Prevention of Air Pollution Emergency Episodes program, the proposal will include a SHL for PM 2.5 that is developed in collaboration with these organizations. As discussed in the Air Quality Index Reporting Rule (64 FR 42530 ; August 4, 1999 ), if such a rulemaking process results in a SHL that is different from the 500 level of the AQI for PM 2.5 , the AQI will be revised accordingly.