Opinion ID: 187302
Heading Depth: 2
Heading Rank: 1

Heading: Risk of Short-Term Exposure

Text: An agency's failure adequately to consider a relevant and significant aspect of a problem may render its rulemaking arbitrary and capricious. See Chamber of Commerce of U.S. v. SEC, 412 F.3d 133, 140 (D.C.Cir.2005); see also Motor Vehicle Mfrs. Ass'n v. State Farm Mut. Auto. Ins. Co., 463 U.S. 29, 43, 103 S.Ct. 2856, 77 L.Ed.2d 443 (1983) (agency must examine the relevant data and articulate a satisfactory explanation for its action). In setting the primary annual NAAQS for PM2.5, the EPA relied exclusively upon studies of long-term exposure, placing the greatest weight upon the Harvard Six Cities and the American Cancer Society (ACS) studies. See 2006 Final Rule, 71 Fed.Reg. at 61,176/2. The state and environmental petitioners argue the EPA did not adequately explain why, even if the studies of long-term exposure were most directly relevant to setting the annual standard, id. at 61,174/3, the studies of short-term exposure were not at all relevant. In the EPA's view, studies of long-term exposure are most directly relevant to the annual standard because the human body responds differently to long-term than to short-term exposure and because a long-term study evaluates periods of exposure closer to a year than the periods evaluated in a short-term study. See id. ; Proposed Rule: National Ambient Air Quality Standards for Particulate Matter, 71 Fed.Reg. 2620, 2627/2-3 (2006); U.S. ENVTL. PROT. AGENCY, AIR QUALITY CRITERIA FOR PARTICULATE MATTER (CRITERIA DOCUMENT) § 8.2.1, at 8-18 (2004). Be that as it may, the EPA did not assert that short-term studies provide no relevant information. The EPA concluded merely that it would be more appropriate to consider the shortterm exposure studies as a basis for ... the 24-hour standard and to consider the long-term exposure studies as a basis for the ... annual standard. 2006 Final Rule, 71 Fed.Reg. at 61,174/2. Two premises underlie this conclusion: the agency can (1) appropriately ... evaluate[] where to set the level of the annual standard based solely upon the long-term studies and (2) provide an appropriate degree of protection from short-term exposure through a daily standard alone. Id. at 61,174/3. The petitioners challenge both. As to the first, the petitioners start by pointing out that the staff and the CASAC, both of which relied upon three short-term studies, proposed an annual standard lower than 15 ¢g/m3. See OFFICE OF AIR QUALITY PLANNING AND STANDARDS, U.S. ENVTL. PROT. AGENCY, REVIEW OF THE NATIONAL AMBIENT AIR QUALITY STANDARDS FOR PARTICULATE MATTER: POLICY ASSESSMENT OF SCIENTIFIC AND TECHNICAL INFORMATION (STAFF PAPER) § 5.3.1.1, at 5-7 (2005); Letter from Dr. Rogene Henderson, CASAC, to Administrator Stephen L. Johnson, EPA 3-4 (Mar. 21, 2006) (Studies described in the PM Staff Paper indicate that short term effects of PM2.5 persist in cities with annual PM2.5 concentrations below [15 ¢g/m3]). By statute the EPA must explain its rejection of the CASAC's recommendation, 42 U.S.C. § 7607(d)(3), and the staff's analysis is something we consider when determining whether the EPA has adequately addressed the relevant considerations and reasonably reached its conclusions, see Natural Res. Def. Council v. EPA, 902 F.2d 962, 967-68, 970 (D.C.Cir. 1990) (noting staff paper's relevance as bridge over gap between criteria document and EPA's policy judgment). [] We reject the EPA's initial response, to wit, that its approach is consistent with those recommendations. See 2006 Final Rule, 71 Fed.Reg. at 61,174/3 n. 45. The CASAC directly challenged the EPA's proposal to retain the annual standard at 15 ¢g/m3. See Letter from Dr. Rogene Henderson, CASAC, to Administrator Stephen L. Johnson, EPA 7 (June 6, 2005). The staff recommended that if the agency kept the annual standard at 15 ¢g/m3 while setting the daily standard with a 98th percentile form, then it should set the daily standard at the middle to lower end of the range from 25 to 35 ¢g/m3. See STAFF PAPER § 5.3.7, at 5-46; see also id. § 5.3.5.1, at 5-32 ([S]taff continues to believe that an annual standard cannot be expected to offer an adequate margin of safety against the effects of all short-term exposures). The EPA instead set the daily standard at 35 ¢g/m3 with a 98th percentile form, see 2006 Final Rule, 71 Fed.Reg. at 61,165/2; id. at 61,171/3, while acknowledging it did not consider the short-term studies when setting the annual standard. As both the CASAC and the staff reasoned, the studies of Eight Canadian Cities, of Santa Clara County (CA), and of Phoenix are relevant to setting an annual standard because each reports adverse health effects associated with short-term exposures in places where the annual PM2.5 concentration is below 15 ¢g/m3. See CASAC Mar. 21 Letter at 3-4. The EPA failed adequately to explain its reason for not accepting the CASAC's recommendations, instead stating only that it did not disagree with CASAC's factual statements regarding the findings of [the short-term studies], but believes ... it ... more appropriate to consider the short-term exposure studies as a basis for the level of the 24-hour standard. 2006 Final Rule, 71 Fed.Reg. at 61,174/2. The petitioners also point to the EPA's unexplained change of position since it last dealt with this issue, which was in 1997. Then the EPA believed short-term studies were indeed relevant to the setting of an annual standard, stating, the strongest evidence for short-term PM2.5 effects occurs at concentrations near the long-term (e.g., annual) average. See Final Rule: National Ambient Air Quality Standards for Particulate Matter, 62 Fed.Reg. 38,652, 38,676/1 (1997). The agency did not thereby commit itself irrevocably, however if the relevant facts have changed or the EPA has reasonably made a different policy judgment, then it need only explain itself and we will defer. See State Farm, 463 U.S. at 57, 103 S.Ct. 2856 (An agency's view of what is in the public interest may change, either with or without a change in circumstances (internal quotation marks omitted)). The EPA's only explanation for its change of position is that it relied upon short-term studies in 1997 because the studies of long-term exposure then available were less reliable than the short-term studies. See 2006 Final Rule, 71 Fed.Reg. at 61,174/3. At the time, however, the agency also said, an annual standard that controls an area's attainment status is likely to reduce aggregate risks associated with both short- and longterm exposures with more certainty than a 24-hour standard. 1997 Final Rule, 62 Fed.Reg. at 38,670/3. Even if the longterm studies available today are useful for setting an annual standard, therefore, it is not clear why the EPA no longer believes it useful to look as well to short-term studies in order to design the suite of standards that will most effectively reduce the risks associated with short-term exposure. We conclude the EPA failed adequately to explain its first premise, viz. that an annual standard could be appropriately... evaluated based solely upon long-term studies. See 2006 Final Rule, 71 Fed.Reg. at 61,174/3. Therefore, we need not reach the state petitioners' argument that the EPA should have relied in part upon the short-term studies because, unlike the ACS Study, those studies do not underestimate the magnitude of risk from exposure to PM2.5. That argument does not rest upon the ACS Study having examined long-term rather than short-term exposure, but instead questions whether the ACS Study involved a representative cohort. If, however, the EPA can adequately explain why studies of short-term effects are not relevant to setting an annual standard, then it may disregard those studies regardless whether the short-term studies are based upon a more representative cohort than is the ACS Study. Nor do we consider the EPA's argument that the short-term studies showed an annual standard would not provide more protection against short-term exposure than would a daily standard. That argument was advanced for the first time in its brief and therefore is not properly before us. See SEC v. Chenery Corp., 332 U.S. 194, 196, 67 S.Ct. 1575, 91 L.Ed. 1995 (1947) ([A] reviewing court ... must judge ... [administrative] action solely by the grounds invoked by the agency when it acted); Ashland Oil, Inc. v. FTC, 548 F.2d 977, 981 & n. 6 (D.C.Cir.1976) (court cannot rely upon post hoc position unless no special agency expertise is involved). The petitioners also challenge the EPA's second premise, that a primary daily standard for PM2.5 at 35 ¢g/m3 with a 98th percentile form could provide an appropriate degree of protection from short-term exposure, thus eliminating the need to calibrate the annual standard to address short-term exposure. 2006 Final Rule, 71 Fed.Reg. at 61,174/3; see id. at 61,165/2 (selecting percentile form of standard); id. at 61,171/3 (selecting level of standard). The EPA's daily standard will require each state to make sure that the average of the seventh highest concentration measured each year for three years does not exceed 35 ¢g/m3, thus permitting approximately six days a year to have concentrations above that level. See id. at 61,164-65 (describing form of standard). The petitioners argue the EPA's reliance upon the daily standard to address all the health risks from short-term exposure was unreasonable for several reasons. First, the environmental petitioners contend the record shows that low- to mid-range concentrations of PM2.5 cause most health effects from short-term exposure, noting that both the staff and the CASAC warned of risks at ambient concentrations below 35 ¢g/m3. See STAFF PAPER § 5.3.5.1, at 5-31-32; CASAC June 6 Letter at 7. In particular, the CASAC observed that, because some cities have relatively high annual PM concentrations but would rarely exceed ambient concentrations of 35 ¢g/m3, it would be necessary to lower the annual standard below 15 ¢g/m3 to provide sufficient protection from the risks associated with short-term exposure. CASAC June 6 Letter at 7. The EPA maintains lowering the daily standard to 35 ¢g/m3 will provide additional protection in all areas where it is required, but as we discuss below, it is not clear why the EPA believes areas that already meet the daily standard either do not require additional protection or will enjoy improved protection against short-term exposure. Second, the environmental petitioners question the EPA's methodology. The EPA focused upon the 98th percentile air quality values in the short-term studies, concluding those values would shed light upon which overall distributions of air quality likely cause harm from short-term exposure. Because some studies did not find a statistically significant association between short-term exposure and health effects when the 98th percentile values were below 35 ¢g/m3, the EPA selected 35 ¢g/m3 as the level, and the 98th percentile as the form, of the primary daily standard. 2006 Final Rule, 71 Fed.Reg. at 61,169. The EPA does not contend, however, that lowering the peak concentrations to 35 ¢g/m3 would provide sufficient protection. Indeed, the EPA acknowledges that to provide adequate protection against short-term exposure, it must lower a broad distribution of PM2.5 air quality values in an area, but explains that lowering the daily standard will lower concentrations not only at the peak of the distribution curve, but also those at the trough because state implementation plans, [a]lthough... not yet defined, ... are likely to require the necessary improvements in air quality. Id. at 61,168/3. In support of this prediction the EPA points to a study finding that as peak daily levels of PM2.5 decreased from one year to the next in Philadelphia and Los Angeles, all off-peak air quality values, or low daily PM2.5 levels[,] decreased proportionally. See ABT ASSOCS., INC., PARTICULATE MATTER HEALTH RISK ASSESSMENT FOR SELECTED URBAN AREAS (RISK ASSESSMENT) 17 (2005); see also STAFF PAPER § 4.3.1.2, at 4-18 (study showed concentrations at different points in the distribution of 24-hour PM2.5 values... decreased by approximately the same percentage). Although the EPA is entitled to rely upon its experience, it must have a reasonable explanation of how its experience supports its conclusion. See DSE, Inc. v. United States, 169 F.3d 21, 30 (D.C.Cir.1999) (court will defer to [agency's] experience provided that the agency has offered a reasoned explanation ... [and] the result is in accord with material facts ... in the administrative record). The environmental petitioners rightly question the EPA's conclusion based upon past trends in Philadelphia and Los Angeles; according to the same study, they point out, the proportional decline in peak and off-peak daily levels of PM2.5 in those cities was not ... the result of a PM2.5 control strategy, but likely result[ed] from control programs for PM,2.5 and control programs for other pollutants. RISK ASSESSMENT at 17. The EPA offers no basis in the experience of those two citiesthus understoodfor expecting controls on the peak levels of fine particles will lead to a proportional decline in levels of PM2.5 at off-peak times simply because controls for coarse particles and for other pollutants did so in the past. The EPA may not and perhaps need not fully understand why off-peak PM2.5 levels decreased as peak PM2.5 levels decreased in the past, but it nevertheless needs plausibly to explain why it believes future controls for PM2.5 will, like other controls for other pollutants in the past, trigger the phenomenon. Even assuming off-peak levels of PM2.5 will decrease in proportion to decreases at peak levels, the environmental petitioners argue there will be no such decline in areas that already comply with the daily standard and therefore will not have to reduce ambient daily concentrations. It is not enough for the EPA to respond that, as it implied during the rulemaking, those areas do not need further improvement; the agency itself observed that short-term health effects occur across a broad distribution of PM2.5 air quality values. See 2006 Final Rule, 71 Fed.Reg. at 61,168/3. We conclude the EPA has failed reasonably to explain why it believes its daily standard will provide an appropriate degree of protection from health effects associated with short-term exposures to PM2.5. Id. at 61,174/3. We therefore remand the annual standard to the EPA for further consideration of whether it is set at a level requisite to protect the public health while providing an adequate margin of safety from the risk of short-term exposure to PM2.5.