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From: Lydia Wegman/RTP/USEPA/US To: nfrey@omb.eop.gov Cc: martin.karen@epa.gov, Scott Jenkins/RTP/USEPA/US@EPA, Joseph
- J Dougherty/DC/USEPA/US@EPA,

Beth Hassett - Sipple/RTP/USEPA/US@EPA, Susan Stone/RTP/USEPA/US@EPA, Alison Davis/RTP/USEPA/US@EPA, hannon.john@epa.gov, Steven Silverman/DC/USEPA/US@EPA Date: 06/08/2 012 05:02 PM Subject: Revisions to the AQI section of PM NAAQS preamble Nathan, Please find attached revisions to the AQI section of the PM NAAQS preamble. These revisions address the interagency comments we received both in meetings this week and in w riting on June 6. We can discuss these edits during our Monday meeting on the secondary standard if any of the reviewers have questions about these revisions. Thanks and have a good weekend. LydiaPage 2 of 10

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
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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
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that is generated through the periodic review, and revision when appropriate, of the NAAQS. In recognition of the proposed changes to the suite of primary PM 2.5 standards summarized in section I II.F above, the EPA propos es conforming changes to the AQI to be consistent with the proposed changes to the standards
. The health effects information that supports the proposed decisions on the PM 2.5 standards as dis cussed 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 primary annual and 24

- hou r 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 guidance (Harnett, 2 009 , 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 and the EPA see s no basis for deviating from this approach
. 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 sam e 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 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, 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 above, is to set an AQI value of 100 at the same level as the short

- term standard
. The EPA recognizes that some 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 standard
. These agencies typically express t he view that this linkage is useful for the purpose of communicating with the public

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 10

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
. The EPA is considering soliciting comment on this alternative approach in recognition that, as proposed, the 24

- hour PM 2.5 standard provides supplemental protecti on 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 alte rnative approach, 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 of 100 at the upper end of the range (35 μg/m 3 , 24

- hour average ) ) , which would be essential ly 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 within 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 s ignificant 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 appropr iate, andPage 6 of 10

then 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 set 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
. 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 beli eve that the health effects evidence indicates that the level of 55 μg/m 3 , 24

- hour average, is appropriate to use in conjunction with an AQI value of 100 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 app roach 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 values 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
. Therefo re, 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
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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

- hour 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 the British Smoke method measures PM with a cutpoint of approximately 4.5 microns (52 FR 24688, July 1, 19 87)
. In establishing this value for PM 10 , we assumed that concentrations of PM 10 , which includes both coarse and fine particles, during episodes of concern, 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 during the historical wintertime pollution episodes in London (500 μg/m 3 ) and adding a margin of 100 μg/m 3 to ac count for this measurement difference
. The current PM 2.5 concentration corresponding to an AQI value of 500 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 stated assumption that PM concentrations measured by the British Smoke method are 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 )

– 35.4Page 8 of 10 Unhealthy for Sensitive Groups 101

- 150 35.5

– 55.4 Unhealthy 151

- 200 55.5

- 140.4 Very Unhealthy 201

- 300 140.5

- 210.4 Hazardous 301

- 400 210.5

- 280.4

401

- 500 280.5

- 350.4 In considering revisions to an AQI value of 500 for PM 2.5 , the EPA has taken note that the propos ed and final action s in 1998 and 1999 were 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 h as a cutoff of 4.5 microns (52 FR 24688, July 1, 1987)
. Because of the dramatic increase in PM 2.5 monitoring data since that rulemaking, the EPA considers it appropriate to set the AQI value of 500 for PM 2.5 at a level below 500 μg/m 3 so that it is more co nsistent with the findings from the London episodes and with the AQI value of 500 for PM 10 . On average, about 60 percent of ambient PM 10 measured in the northeastern, southeastern, and industrial midwest portions of the U.S. consists of PM 2.5 . 4 Using the 60 percent factor to scale the AQI value of 500 for PM 10 (600 μg/m 3 ) results in an AQI value of 500 for PM 2.5 of about 350 μg/m 3

. 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 scali ng approach for translating the AQI value of 500 for PM 10 into an appropriate corresponding value for PM 2.5 The EPA has used the historical wintertime pollution episodes in London to propose setting an AQI value of 500 for PM 2.5 as described above because it is still the best available information

- -- there is little information about similar, more recent, air pollution episodes and associated impacts on 4 More specifically, in 2001 to 2003, the median of the ratio of 24

- hour PM 2.5 and PM 10 am ong 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).Page 9 of 10

community health upon which to base a decision
. However, the limited number of studies cited in the I nte grated S cience A ssessment that evaluated wood smoke health impacts 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 al., 2009; Schreuder et al., 2006) at much lower levels (US EPA, 2009a, sections 6.2 and 6.6)
. These recent health studies provide additional qualitative support for lowering the air quality level associated with an AQI value of 500 to 350 belo w 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
. 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 th e 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 being associated with increasingly larger numbers of people likely to experience such effects
. The generally linear r elationship 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 information does not suggest particular levels. I n proposing to 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 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 PollutionPage 10 of 10

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), 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.