Committee for a Better Arvin v. United States Environmental Protection Agency

FOR PUBLICATION UNITED STATES COURT OF APPEALS FOR THE NINTH CIRCUIT No. 24-7270 COMMITTEE FOR A BETTER ARVIN, a nonprofit corporation; Agency No. MEDICAL ADVOCATES FOR EPA–R09–OAR– HEALTHY AIR, a nonprofit 2023–0477 corporation; NATIONAL PARKS CONSERVATION ASSOCIATION, Environmental a nonprofit corporation; SIERRA Protection Agency CLUB, a nonprofit corporation, OPINION Petitioners, v. UNITED STATES ENVIRONMENTAL PROTECTION AGENCY; MICHAEL REGAN, in his official capacity as Administrator of the U.S. Environmental Protection Agency; MARTHA GUZMAN ACEVES, Regional Administrator of Region 9 of U.S., in her official capacity as Regional Administrator for Region IX of the U.S. Environmental Protection Agency, Respondents, 2 COMM. FOR A BETTER ARVIN V. U.S. EPA ---------------------------------------- CALIFORNIA AIR RESOURCES BOARD; SAN JOAQUIN VALLEY UNIFIED AIR POLLUTION CONTROL DISTRICT, Intervenors. On Petition for Review of an Order of the Environmental Protection Agency Argued and Submitted November 19, 2025 San Francisco, California Filed August 5, 2026 Before: Sidney R. Thomas, Daniel A. Bress, and Salvador Mendoza, Jr., Circuit Judges. Opinion by Judge Mendoza, Jr.; Dissent by Judge Bress  COMM. FOR A BETTER ARVIN V. U.S. EPA 3 SUMMARY* Clean Air Act The panel remanded without vacatur in a case challenging a final rule issued by the United States Environmental Protection Agency concerning air quality in California’s San Joaquin Valley. The Clean Air Act delegates authority to the EPA to set national ambient air quality standards (“NAAQS”). A state is primarily responsible for maintaining air quality within its entire geographic area and must submit state implementation plans (“SIPs”) that specify how NAAQS will be met in each air quality control region of the state. The EPA designates regions as “attainment” or “nonattainment” based on whether they meet the NAAQS. Section 172(c)(9) of the Act requires that SIPs for nonattainment areas include contingency measures if the area fails to make reasonable further progress or fails to meet a NAAQS by the applicable attainment date. Petitioners contend that the contingency measures approved by the final rule fall short of the improvement required for the Valley’s air quality. The panel held that the EPA exceeded its authority when it grafted a feasibility exemption onto Section 172(c)(9). Applying Loper Bright Enters. v. Raimondo, 603 U.S. 369 (2024), the panel held that because the text of Section 172(c)(9) is ambiguous, it must use statutory * This summary constitutes no part of the opinion of the court. It has been prepared by court staff for the convenience of the reader. 4 COMM. FOR A BETTER ARVIN V. U.S. EPA interpretation to independently interpret the statute to determine its most faithful reading. Congress did not expressly provide that the EPA should consider feasibility in Section 172(c)(9). The panel held that the EPA erred by plucking a feasibility exemption out of thin air and reading it into Section 172(c)(9) when the language of the provision does not provide for one. The panel further held that the provision’s directive to design “specific” contingency measures that shall “take effect” did not implicitly grant the EPA discretion to consider feasibility. In addition, permitting a feasibility exemption for contingency measures undermines both the specific function of Section 172(c)(9) and the overarching purpose of the Act. The panel held that remand without vacatur was the appropriate remedy given the potential disruptive consequences of the Valley lacking contingency measures while the EPA reconsiders the rule. Dissenting, Judge Bress wrote that the majority’s interpretation of the Clean Air Act—that California’s contingency measures do not meet the requirements of Section 172(c)(9) because any consideration of feasibility is completely forbidden when it comes to meeting air quality benchmarks—reflects serious legal error, conflating a supposedly improper feasibility assessment with what are merely the statutory requirements for an emissions reduction measure to qualify as a contingency measure under Section 172(c)(9) of the Clean Air Act.  COMM. FOR A BETTER ARVIN V. U.S. EPA 5 COUNSEL Colin C. O'Brien (argued) and Tyler B. Szeto, Earthjustice, San Francisco, California; Brent J. Newell, Law Office of Brent J. Newell, Petaluma, California; for Petitioners. Sarah Izfar (argued), Senior Trial Counsel, Environment and Natural Resources Division; Robert N. Stander, Deputy Assistant Attorney General; Adam R.F. Gustafson, Acting Assistant Attorney General; United States Department of Justice, Washington, D.C.; Yasmin P. Ortiz and Jefferson Wehling, Attorneys, United States Environmental Protection Agency, Washington, D.C.; for Respondents. Corey M. Moffat (argued), Deputy Attorney General; Jonathan A. Wiener, Acting Supervising Deputy Attorney General; Rob Bonta, California Attorney General; Office of the California Attorney General, San Francisco, California; Isela G. Welz, Assistant District Counsel; Annette A. Ballatore, District Counsel; San Joaquin Valley Unified Air Pollution Control District, Fresno, California; for Intervenors. Brian S. Tomasovic, Assistant Chief Deputy Counsel; Kathryn Roberts, Principal Deputy District Counsel; Barbara Baird, Chief Deputy Counsel; Bayron T. Gilchrist, General Counsel; Office of the General Counsel, South Coast Air Quality Management District, Diamond Bar, California; Kathrine Pittard, District Counsel, Sacramento Metropolitan Air Quality Management District, Sacramento, California; Piero C. Dallarda, Best Best & Krieger LLP, Riverside, California; Ann M. Siprelle, Best Best & Krieger LLP, Sacramento, California; for Amici Curiae South Coast Air Quality Management District, Sacramento Metropolitan Air Quality Management District, Mojave Desert Air 6 COMM. FOR A BETTER ARVIN V. U.S. EPA Quality Management District, and California Air Pollution Control Officers Association. Robyn Wille, First Assistant Attorney General; Rylie Slaybaugh, Assistant Attorney General II; Laura T. Mehew, Senior Assistant Attorney General; Kyle Davenport, Senior Assistant Attorney General II; Shannon Stevenson, Solicitor General; Natural Resources and Environment Section, Colorado Office of the Attorney General, Denver, Colorado; for Amicus Curiae Colorado Department of Public Health and Environment. OPINION MENDOZA, JR., Circuit Judge: The San Joaquin Valley’s unique bowl-shaped topography is both a cradle of abundance and home to over four million Californians. It also has “some of the worst air quality in the United States.” Comm. for a Better Arvin v. EPA, 786 F.3d 1169, 1173 (9th Cir. 2015). The Valley has repeatedly failed to meet the Clean Air Act’s air quality standards, a reality reflected by the numerous disputes about emissions regulation in that area that have reached this court. The Committee for a Better Arvin, Medical Advocates for Healthy Air, the National Parks Conservation Association, and the Sierra Club challenge a final rule issued by the United States Environmental Protection Agency, arguing that the contingency measures approved by the rule fall far short of the improvement required for the Valley’s air quality. We conclude that the EPA exceeded its authority  COMM. FOR A BETTER ARVIN V. U.S. EPA 7 when it grafted a feasibility exemption onto Section 172(c)(9) of the Clean Air Act, and we remand. I. A. Enacted in 1963, the Clean Air Act (“Act”) was designed to promote air quality improvement through a scheme of “cooperative federalism.” MacClarence v. EPA, 596 F.3d 1123, 1125 (9th Cir. 2010). In the Act, Congress recognizes that “air pollution prevention . . . and air pollution control at its source is the primary responsibility of States and local governments,” but provides for “[f]ederal financial assistance and leadership.” 42 U.S.C. § 7401(a). The Act delegates authority to the EPA to set national ambient air quality standards (“NAAQS”) for certain air pollutants. 42 U.S.C. § 7409; Whitman v. Am. Trucking Ass’ns, 531 U.S. 457, 462 (2001). A state is primarily responsible for maintaining air quality within its “entire geographic area,” a responsibility that entails submitting state implementation plans (“SIPs”) that specify how NAAQS will be met in each air quality control region of the state. 42 U.S.C. § 7407(a). Within this framework, the EPA designates regions as “attainment” or “nonattainment” based on whether they meet the NAAQS. 42 U.S.C. § 7407(d). Nonattainment areas are also classified by the severity of nonattainment—fine particulate matter (“PM2.5”) nonattainment areas are initially classified as “moderate” and can be subsequently reclassified as “serious.” 40 C.F.R. § 51.1002. 8 COMM. FOR A BETTER ARVIN V. U.S. EPA Section 172(c)(9)1 of the Act also requires that SIPs for nonattainment areas include contingency measures: “specific measures to be undertaken if the area fails to make reasonable further progress,” or fails to meet a NAAQS by the applicable attainment date. 42 U.S.C. § 7502(c)(9). Discussing the Section 172(c)(9) contingency measure requirement, the house report accompanying the 1990 amendments to the Act states that “[s]uch measures are to take effect without further action by the State o[r] Administrator, and are to be adequate to compensate for any emission reduction shortfall.” H.R. Rep. No. 101-490, reprinted in Cong. Rsch. Serv., A Legislative History of the Clean Air Act Amendments of 1990, at 3248 (1993). In this regard, these contingency measures function as a “backup” in case existing measures fall short. Ass’n of Irritated Residents v. EPA, 10 F.4th 937, 947 (9th Cir. 2021). B. The challenged rule approves two SIP submissions designed to meet three contingency measure requirements for the Valley. Petitioners argue that the rule violates the Act by applying a new, lowered progress standard for contingency measures and reading a feasibility exemption into the statute. The EPA maintains that it has applied the best interpretation of the Act’s requirements for contingency measures. The San Joaquin Valley Unified Air Pollution Control District (“District”) is primarily responsible for developing plans to provide for the Valley’s attainment of NAAQS. It works with the California Air Resources Board (“CARB”) to develop those plans. In June 2023, CARB submitted two 1 Section 172(c)(9) of the Act is codified at 42 U.S.C. § 7502(c)(9).  COMM. FOR A BETTER ARVIN V. U.S. EPA 9 SIPs to the EPA addressing PM2.5 and precursor pollutants, including nitrogen oxides (“NOx”), in the Valley. 2 They contained three contingency measures designed to collectively meet the contingency measure requirements for the 1997 annual, 2006 24-hour, and 2012 annual PM2.5 standards.3 One of these contingency measures would require stricter wood burning restrictions if triggered, the second would require more “fugitive dust” control measures in certain open areas in the Valley, and the third would require more vehicles in the area to undergo smog checks. Notably, the proposed rule required only “one year’s worth of progress.” This marked a departure from the EPA’s traditional requirement that contingency measures provide for “one year’s worth of reasonable further progress.” The proposed rule also recommended accepting “feasibility analyses” provided by CARB and the District to justify the emissions reductions for precursor pollutant NOx falling short of that lowered “progress” standard. It detailed CARB and the District’s analyses of “contingency measure opportunities,” including CARB’s arguments on technological limitations and time pressure. Accepting the professed infeasibility of additional contingency measures paved the way for the EPA to approve the SIPs, despite the fact that the contingency measures fell significantly short of 2 PM2.5 is fine particulate matter with a diameter of 2.5 micrometers or less. NOx is a precursor pollutant that causes the formation of PM2.5. 3 The EPA classified the San Joaquin Valley as a serious nonattainment area for the 1997 annual PM2.5 standard in 2015, as a serious nonattainment area for the 2006 24-hour PM2.5 standard in 2016, and as a serious nonattainment area for the 2012 annual PM2.5 standard in 2021. 10 COMM. FOR A BETTER ARVIN V. U.S. EPA required NOx emissions reductions, even under the lowered one year’s worth of progress standard. Environmental advocacy groups raised numerous concerns about the proposed rule in the subsequent notice- and-comment period. The groups characterized the rule as an attempt by the EPA to “completely abdicate its obligation to require meaningful contingency measures” by abandoning its longstanding interpretation of Section 172(c)(9) as requiring one year’s worth of reasonable further progress. They further criticized the rule’s inclusion of a feasibility demonstration which further lowers the progress required from contingency measures. On this point, they argued that such feasibility demonstrations contradict the “plain language” of the Act, which does not apply any feasibility standard to contingency measures. Despite these concerns, the EPA issued the final rule with the lowered progress standard and the feasibility demonstration intact. The rule acknowledged the EPA’s “long-standing approach” of requiring one year’s worth of reasonable further progress, but it argued that that standard was “unnecessarily conservative.” And it defended further lowering progress requirements for contingency measures in certain circumstances: [A]s stated in our proposed rule and the EPA’s Draft Revised Contingency Measures Guidance, where a state is unable to identify contingency measures that would provide approximately [one year’s worth] of emission reductions, the state should provide a reasoned justification (referred to herein as an “infeasibility demonstration”) that explains and documents how it has evaluated  COMM. FOR A BETTER ARVIN V. U.S. EPA 11 all existing and potential control measures relevant to the appropriate source categories and pollutants in the nonattainment area and has reached reasonable conclusions regarding whether such measures are feasible. II. The contingency measures create sufficient emission reductions for direct PM2.5 emissions to meet the EPA’s longstanding one year’s worth of reasonable further progress standard. But NOx emission reductions fall short of both one year’s worth of reasonable further progress and the rule’s lowered progress standard. The final rule reasons that the approved contingency measures nevertheless satisfy Section 172(c)(9) because CARB and the District provided “reasoned justifications for not adopting additional contingency measures.” So this challenge turns on whether Section 172(c)(9) allows the EPA to exempt contingency measures from progress standards if the air agency makes a feasibility demonstration.4 We find that it does not. A. Under the general standard set by Section 706 of the Administrative Procedure Act, the court sets aside an agency action if it is “arbitrary, capricious, an abuse of discretion, or otherwise not in accordance with the law.” 5 U.S.C. § 706(2)(A); see also Sierra Club v. EPA, 671 F.3d 955, 961 (9th Cir. 2012) (applying this general standard because the 4 We neither endorse nor reject the EPA’s use of “one year’s worth of progress” instead of the longstanding one year’s worth of reasonable further progress standard because this petition rises and falls on feasibility. 12 COMM. FOR A BETTER ARVIN V. U.S. EPA Act does not specify a standard for SIP approvals). “Section 706 makes clear that agency interpretations of statutes . . . are not entitled to deference.” Loper Bright Enters. v. Raimondo, 603 U.S. 369, 392 (2024). Until recently, we would have deferred to the EPA’s reasonable interpretation of ambiguous statutory language, even if it was not the only permissible construction. See Chevron, U.S.A., Inc. v. Nat. Res. Def. Council, Inc., 467 U.S. 837, 843 (1984), overruled by, Loper Bright, 603 U.S. at 412. But the Supreme Court now instructs courts to use their “full interpretive toolkit” to find the “best meaning” of ambiguous statutes rather than deferring to agency interpretations. Loper Bright, 603 U.S. at 408–09. Because the text of Section 172(c)(9) is ambiguous,5 we must dust off our well-worn tools of statutory interpretation to independently interpret the statute and to determine its most faithful reading. B. The text of Section 172(c)(9) is silent on feasibility. To support the EPA’s contention that feasibility demonstrations are nonetheless allowed by the provision, the challenged rule emphasizes that “the statutory provisions applicable to other nonattainment area plan control measure requirements . . . allow air agencies to exclude certain control measures that are deemed unreasonable or infeasible.” In other words, the EPA’s position is that explicit feasibility allowances elsewhere in the Act suggest that it can consider feasibility in this instance. But the fact that other provisions in the Act 5 “A statute is ambiguous if it gives rise to more than one reasonable interpretation.” Woods v. Carey, 722 F.3d 1177, 1181 (9th Cir. 2013) (citation modified).  COMM. FOR A BETTER ARVIN V. U.S. EPA 13 provide for infeasibility exemptions—and that Section 172(c)(9) does not—fatally undermines the EPA’s position. “Congress generally acts intentionally when it uses particular language in one section of a statute but omits it in another.” Dep’t of Homeland Sec. v. MacLean, 574 U.S. 383, 391 (2015). As the Supreme Court observed in an early Clean Air Act case, “[w]here Congress intended the Administrator to be concerned about economic and technological infeasibility, it expressly so provided.” Union Elec. Co. v. EPA, 427 U.S. 246, 257 n.5 (1976). And Congress has provided for feasibility considerations elsewhere in the Act. Section 112 directs the EPA to promulgate and enforce emissions standards to control certain hazardous air pollutants, but it provides that “if it is not feasible in the judgment of the Administrator to prescribe or enforce an emission standard for control of a hazardous air pollutant or pollutants, the Administrator may” promulgate other “design, equipment, work practice, or operational standard[s]” to meet the provision’s goals. 42 U.S.C. § 7412(h)(1) (emphasis added). Then Section 188(e) of the Act permits attainment date extensions for serious PM10 nonattainment areas if the state can show that “the plan for that area includes the most stringent measures that are included in the implementation plan of any State or are achieved in practice in any State, and can feasibly be implemented in the area.” 42 U.S.C. § 7513(e) (emphasis added). It also expressly permits the consideration of “the technological and economic feasibility of various control measures.” Id. (emphasis added). Section 202, which covers motor vehicle emissions, also makes several feasibility allowances. It provides that 14 COMM. FOR A BETTER ARVIN V. U.S. EPA regulations cannot go into effect until “it would be feasible to implement” them, requiring collaboration with the National Academy of Sciences to “conduct a comprehensive study and investigation of the technological feasibility of meeting” certain emissions standards required by the provision, and allowing the Administrator to adjust standards related to the “useful life” of vehicles and engines “if he determines that it is feasible for vehicles and engines subject to such standards to meet such standards for a longer useful life.” 42 U.S.C. § 7521(a)(5)(B), (c)(1), (j)(3) (emphases added). As in Department of Homeland Security v. MacLean, the interpretive canon that Congress acts deliberately by omitting language that is included elsewhere in a statute “applies with particular force here.” 574 U.S. at 392. Feasibility is expressly referenced numerous times throughout the Act and the term appears “in close proximity” to Section 172(c)(9). Id. Even elsewhere in Section 172, there is language providing that the Administrator can consider the “availability and feasibility of the pollution control measures” when classifying nonattainment areas and extending attainment dates. See 42 U.S.C. §§ 7502(a)(1)(A), (a)(2)(A) (emphasis added). But there is no such language in Section 172(c)(9). Congress did not expressly provide that the EPA should consider feasibility in Section 172(c)(9). It easily could have done so. Indeed, it has done so elsewhere in the Act. The EPA erred by plucking a feasibility exemption out of thin air and reading it into Section 172(c)(9) when the language of the provision does not provide for one. So the challenged rule is contrary to the Act’s best meaning and must be remanded to the EPA.  COMM. FOR A BETTER ARVIN V. U.S. EPA 15 III. The EPA also argues that Congress granted it “discretionary authority to consider feasibility” by stating in Section 172(c)(9) that contingency measures are “specific measures” that will “take effect” without any qualifying language. But the hazy language of Section 172(c)(9) does not automatically give the EPA the right to consider feasibility. The Supreme Court has specifically rejected the presumption “that statutory ambiguities are implicit delegations to agencies.” Loper Bright, 603 U.S. at 399. So we must determine whether the best reading of the provision’s directive to design “specific” contingency measures that shall “take effect” implicitly grants the EPA discretion to consider feasibility. We find that it does not. A. On this point, Union Electric is instructive. There, the Supreme Court considered whether the “operator of a regulated emission source” could “raise the claim that it is economically or technologically infeasible to comply with the plan.” Union Elec., 427 U.S. at 249. The petitioner, an electric utility company, argued that a provision of the Act required consideration of technological and economic infeasibility because it provided that air quality standards be met “as expeditiously as practicable,” and within a “reasonable time.” Union Elec., 427 U.S. at 257–58. The petitioner asserted that “what is ‘practicable’ or ‘reasonable’ cannot be determined without assessing whether what is proposed is possible.” Id. at 258. The Supreme Court soundly rejected the petitioner’s argument, reasoning that the Act set strict compliance requirements that were “expressly designed to force regulated sources to develop pollution control devices that 16 COMM. FOR A BETTER ARVIN V. U.S. EPA might at the time appear to be economically or techno[logically] infeasible.” Id. at 257. The Court went as far as concluding that “Congress intended claims of economic and technological infeasibility to be wholly foreign to the Administrator’s consideration of a state implementation plan.” Id. at 256. The Court cited senators’ remarks during the legislative process, including Senator Edmund Muskie’s statement that Congress was responsible for protecting public health, which “may mean that people and industries will be asked to do what seems to be impossible at the present time.” Id. at 258–59 (citation modified). While this petition concerns a different provision of the Act, Union Electric’s rationale nevertheless applies.6 The contested statutory language in Union Electric required evaluation of what time frames would be “reasonable” or “practicable.” Even that was not enough to allow for feasibility considerations that were not explicitly provided for in the statute. In contrast, Section 172(c)(9) is devoid of references to practicability, and the EPA points only to “specific measures to be undertaken” as evidence that Congress intended to provide discretion to consider feasibility. In other words, if the phrases “as expeditiously as practicable,” and “within a reasonable time” do not permit consideration of feasibility, it is difficult to see how “specific 6 The dissent spills much ink arguing that Union Electric is distinguishable from this petition for review. This argument misses the point of our analysis. It was never our contention that Union Electric was factually or procedurally identical to this case. Union Electric is an early example of the Supreme Court refusing to “read in” technological and economic infeasibility considerations into the Act when Congress did not expressly include them.  COMM. FOR A BETTER ARVIN V. U.S. EPA 17 measures to be undertaken,” a phrase even further disconnected from feasibility, would allow it. B. Department of Treasury, IRS v. FLRA is also instructive. 494 U.S. 922 (1990). In that case, the Supreme Court rejected the government’s argument that the term “applicable laws” in one provision of the Civil Service Reform Act of 1978 was equivalent to the phrase “any law, rule, or regulation,” which is used elsewhere in the statute. Id. at 931–33. The majority reasoned that a “statute that in one section refers to ‘law, rule or regulation,’ and in another section to only ‘laws’ cannot, unless we abandon all pretense at precise communication, be deemed to mean the same thing in both places.” Id. at 932. If we hold that “specific measures to be undertaken” means “feasibility,” a term that is used throughout the Act and which holds a particular meaning, then we will be choosing to “abandon all pretense at precise communication,” as the Supreme Court warned against in Department of Treasury. Reading a feasibility standard into a provision whose text plainly does not provide for one would undermine the clarity of the Act’s language and usurp Congress’s choices in favor of an agency’s preference. As discussed supra, Congress is perfectly capable of writing feasibility into statutory language; it has done so repeatedly throughout the Act. So we find that Congress did not implicitly grant the EPA discretion to consider feasibility with the language of Section 172(c)(9). IV. Turning to another tool in our statutory interpretation toolbox, “[i]t is a fundamental canon of statutory 18 COMM. FOR A BETTER ARVIN V. U.S. EPA construction that the words of a statute must be read in their context and with a view to their place in the overall statutory scheme.” West Virginia v. EPA, 597 U.S. 697, 721 (2022) (quoting Davis v. Mich. Dep’t of Treasury, 489 U.S. 803, 809 (1989)). “[W]e must interpret statutes as a whole, giving effect to each word and making every effort not to interpret a provision in a manner that renders other provisions of the same statute inconsistent, meaningless or superfluous.” Boise Cascade Corp. v. EPA, 942 F.2d 1427, 1432 (9th Cir. 1991). “By requiring contingency measures, the Act closes any potential gap in progress should a nonattainment area miss a milestone.” Ass’n of Irritated Residents, 10 F.4th at 942. The feasibility demonstrations approved by this rule effectively allow states to eliminate that statutory imperative on demand. Accepting such demonstrations is particularly harmful to the purpose of contingency measures because the EPA’s guidance anticipates that these demonstrations will allow for a substantial lowering of progress standards. The EPA has stated that “[w]ith sufficient justification, [contingency measures] representing a small amount of reductions may be reasonable.” Lowering or largely eliminating progress standards for Section 172(c)(9) contingency measures undermines their role in the Act’s overall statutory scheme. To maintain contingency measures’ function as a “plan B,” 7 they should 7 The dissent suggests that our use of the phrase “plan B” indicates a larger misunderstanding of contingency measures’ purpose. But whether we say “plan B” or some other term, contingency measures’ function as a backup should not be discounted. As we have explained, “the reason the statute requires contingency measures is to have a backup that can be put in place immediately in case already-implemented measures in a plan fail to achieve reasonable further progress. The agency may not avoid  COMM. FOR A BETTER ARVIN V. U.S. EPA 19 be designed to compel a nonattainment area to meet a consistent standard of progress. 8 Reading feasibility demonstrations into Section 172(c)(9), which does not provide for them, undermines that function. V. We end our analysis with statutory purpose. It is a “familiar canon of statutory construction that remedial legislation should be construed broadly to effectuate its purposes.” Tcherepnin v. Knight, 389 U.S. 332, 336 (1967). “The overriding purpose of the Clean Air Act is to force the states to do their job in regulating air pollution effectively so as to achieve baseline air quality standards, the NAAQS.” Exxon Mobil Corp. v. EPA, 217 F.3d 1246, 1255 (9th Cir. 2000). As Congressman Bob Carr stated during the legislative debate of the 1990 amendments, “[u]ltimately, the purpose of the Clean Air Act is to improve the public’s health through a cleaner environment.” House Debate on the Clean Air Act Amendments of 1990 Conference Report, reprinted in Cong. Rsch. Serv., A Legislative History of the Clean Air Act Amendments of 1990, at 1342 (1993). Section 172 of the Act furthers those goals of effective regulation and public health by setting general requirements for nonattainment areas. See 42 U.S.C. § 7502. Those requirements include nonattainment plans that “require reasonable further progress,” and contingency measures that pick up the slack if those nonattainment plans fail to meet the need for robust contingency measures by assuming that they will not be needed.” Ass’n of Irritated Residents v. EPA, 10 F.4th 937, 947 (9th Cir. 2021) (citation modified). 8 Again, we take no position as to whether that consistent standard should be one year’s worth of reasonable further progress or one year’s worth of progress. 20 COMM. FOR A BETTER ARVIN V. U.S. EPA the reasonable-further-progress standard. Id. at §§ (c)(2), (9). Contingency measures are required by the Act with the purpose of bringing nonattainment areas in line with PM2.5 NAAQS. Permitting a feasibility exemption for these contingency measures undermines both the specific function of Section 172(c)(9) and the overarching purpose of the Act. VI. This case is about a limited question of statutory interpretation: does the best meaning of Section 172(c)(9) include a feasibility exemption, even if the text does not expressly provide for one? The answer, based on our established canons of statutory interpretation, is no. The dissent extensively discusses policy concerns. It warns that this decision will lead to “regulatory freefall” and a “treacherous trail.” First, we will note that it is unlikely that this limited statutory interpretation decision will bring about an administrative law apocalypse. It is worth reiterating that the EPA, not the petitioners, is proposing a new path. Our decision not to allow a novel feasibility analysis maintains the status quo. The dissent suggests that we should discuss the “actual feasibility analyses,” and stresses that the EPA’s analysis is “173 single-spaced pages.” We do not discuss the depth of the feasibility analyses because that has no bearing on the best meaning of the statutory provision at issue. The thoroughness of the EPA’s individual feasibility analyses does not ex post facto justify reading a feasibility exemption into Section 172(c)(9). To consider that would be to improperly broaden the scope of our analysis. This is a statutory interpretation question. No more, no less.  COMM. FOR A BETTER ARVIN V. U.S. EPA 21 Much of the dissent’s argument boils down to the idea that we should make Section 172(c)(9) mean what the EPA and air quality districts say it should mean—and if we don’t, catastrophe will ensue. But we will not warp our statutory interpretation to reach a predetermined conclusion. However sincerely held the dissent’s concerns may be, we cannot substitute policy goals for neutral statutory interpretation. It is the prerogative of Congress, not this court, to amend legislation based on policy concerns. In the post-Chevron era, we are tasked with employing our “full interpretive toolkit” to find the “best meaning” of ambiguous statutes, without deferring to agency interpretations. Loper Bright, 603 U.S. at 408–09. We have done so. VII. Having concluded that the challenged rule violates the Act, we must now determine the appropriate remedy. Petitioners request that this court “remand[] the EPA’s approval” of the contingency measures so that “California will need to revisit its decision[-]making and adopt meaningful control measures in compliance with the Clean Air Act.” They also seek an award of litigation costs, including attorney’s fees. They do not request vacatur. “The traditional remedy for erroneous administrative decisions is vacatur, but we will leave invalid agency action in place when equity demands that we do so.” Migrant Clinicians Network v. EPA, 88 F.4th 830, 847 (9th Cir. 2023) (citation modified). The Ninth Circuit employs a two-factor balancing test to determine whether an agency action should stay in effect on remand—weighing the severity of the agency’s errors against “the disruptive consequences of an interim change that may itself be changed.” Cal. Cmtys. Against Toxics v. EPA, 688 F.3d 989, 992 (9th Cir. 2012) 22 COMM. FOR A BETTER ARVIN V. U.S. EPA (quoting Allied–Signal, Inc. v. U.S. Nuclear Regul. Comm’n, 988 F.2d 146, 150–51 (D.C. Cir. 1993)); Migrant Clinicians Network, 88 F.4th at 848. Evaluating agency error includes considering whether “vacating a faulty rule could result in possible environmental harm.” Pollinator Stewardship Council v. EPA, 806 F.3d 520, 532 (9th Cir. 2015). Petitioners have not requested vacatur, and we find that remand alone is appropriate given the potential disruptive consequences of the Valley lacking contingency measures while the EPA reconsiders this rule. So we remand without vacatur. As for costs, the Act provides that “[i]n any judicial proceeding under this section, the court may award costs of litigation (including reasonable attorney and expert witness fees) whenever it determines that such award is appropriate.” 42 U.S.C. § 7607(f). We find that such an award is appropriate in this case. REMANDED.  COMM. FOR A BETTER ARVIN V. U.S. EPA 23 BRESS, Circuit Judge, dissenting: The majority opinion holds that Section 172(c)(9) of the Clean Air Act, 42 U.S.C. § 7502(c)(9), requires States to adopt technologically and economically infeasible contingency measures for meeting air quality benchmarks. This alarming ruling is mistaken, sending States into a regulatory freefall in which they must either adopt infeasible emission control measures or else face severe, escalating sanctions. California and the federal government do not always see eye to eye, but they both agree the Clean Air Act was never meant to operate in this Kafkaesque way. In this case, California and the EPA exhaustively explained why further contingency measures beyond the ones California has adopted do not meet the requirements of Section 172(c)(9) because they could not take effect automatically and yield emissions reductions promptly— precisely the analysis that Section 172(c)(9) requires. The majority takes issue with none of these extensive findings. Nor does it point to other possible contingency measures that California and the EPA failed to consider. Instead, California’s contingency measures fail because any consideration of feasibility is completely forbidden when it comes to meeting these air quality benchmarks. That interpretation of the Clean Air Act reflects serious legal error, conflating a supposedly improper feasibility assessment with what are merely the statutory requirements for an emissions reduction measure to qualify as a contingency measure under Section 172(c)(9). Because the majority rests on a fundamental misapprehension of the statutory scheme and puts States in an untenable stranglehold, I must respectfully dissent. 24 COMM. FOR A BETTER ARVIN V. U.S. EPA I A Before turning to the facts of this case, I begin with an explanation of how Section 172(c)(9) contingency measures fit into the broader Clean Air Act apparatus, which is important in understanding where the majority goes wrong. To protect public health, the Clean Air Act instructs the EPA to establish national ambient air quality standards (NAAQS) for various pollutants. See EPA v. EME Homer City Generation, L.P., 572 U.S. 489, 498 (2014); see 42 U.S.C. § 7409(a); 40 C.F.R. § 50.7(a). If a region meets NAAQS for a given pollutant, the EPA classifies that region as “attainment.” 42 U.S.C. § 7407(d)(1)(A)(ii). If a region does not meet NAAQS, the EPA classifies it as “nonattainment” and sets a deadline by which the region must reach compliance. Id. §§ 7407(d)(1)(A)(i), 7502(a). Under the Act, “[t]here are several degrees of nonattainment, ranging from marginal to extreme, and each classification imposes increasingly stringent requirements to reduce emissions and promote progress toward attainment.” Ass’n of Irritated Residents v. EPA, 10 F.4th 937, 942 (9th Cir. 2021) (citations omitted). For fine particulate matter, the pollutant at issue here, nonattainment areas are initially classified as “moderate” and are reclassified as “serious” if the EPA finds that the area failed to attain the NAAQS by the moderate-area attainment date. 40 C.F.R. § 51.1002(a), (b)(2). When a region is designated “nonattainment” for a given pollutant, the state must create a State Implementation Plan (SIP), which the EPA must approve. See Bahr v. Regan, 6 F.4th 1059, 1065 (9th Cir. 2021); 42 U.S.C. §§ 7410, 7502(b). “Each SIP must include enforceable emission  COMM. FOR A BETTER ARVIN V. U.S. EPA 25 limitations and other control measures necessary to attain the NAAQS, as well as timetables for compliance.” Bayview Hunters Point Cmty. Advocs. v. Metro. Transp. Comm’n, 366 F.3d 692, 695 (9th Cir. 2004), as amended on denial of reh’g and reh’g en banc (June 2, 2004). The SIP must “provide for the implementation