Sierra Club v. United States Environmental Protection Agency

RECOMMENDED FOR PUBLICATION
Pursuant to Sixth Circuit I.O.P. 32.1(b)
File Name: 25a0331p.06
UNITED STATES COURT OF APPEALS
FOR THE SIXTH CIRCUIT
SIERRA CLUB,
Petitioner,
v.
UNITED STATES ENVIRONMENTAL PROTECTION
AGENCY; LEE ZELDIN, Administrator, United States
Environmental Protection Agency,
Respondents.
┐
│
│
│
│
│
│
│
│
│
┘
Nos. 23-3581/3583
On Petition for Review from the Environmental Protection Agency.
No. EPA-R05-OAR-2023-0058.
Argued: December 12, 2024
Decided and Filed: December 5, 2025
Before: COLE, WHITE, and DAVIS, Circuit Judges.
_________________
COUNSEL
ARGUED: Nicholas Leonard, GREAT LAKES ENVIRONMENTAL LAW CENTER, Detroit,
Michigan, Elena Saxonhouse, SIERRA CLUB, Oakland, California, for Petitioner. Heather E.
Gange, UNITED STATES DEPARTMENT OF JUSTICE, Washington, D.C., for Respondents.
ON BRIEF: Nicholas Leonard, GREAT LAKES ENVIRONMENTAL LAW CENTER,
Detroit, Michigan, Elena Saxonhouse, Sanjay Narayan, SIERRA CLUB, Oakland, California, for
Petitioner. Heather E. Gange, UNITED STATES DEPARTMENT OF JUSTICE, Washington,
D.C., for Respondents. John Minode’e Petoskey, EARTHJUSTICE, Chicago, Illinois, Nicholas
J. Schroeck, DETROIT MERCY LAW ENVIRONMENTAL LAW CLINIC, Detroit, Michigan,
David M. Flannery, Keeleigh S. Huffman, STEPTOE & JOHNSON PLLC, Charleston, West
Virginia, Dallas F. Kratzer III, STEPTOE & JOHNSON PLLC, Columbus, Ohio, Gaëtan
Gerville-Réache, Joshua J. Reuter, WARNER NORCROSS + JUDD LLP, Grand Rapids,
Michigan, Elbert Lin, HUNTON ANDREWS KURTH LLP, Richmond, Virginia, for Amici
Curiae.
>

-- 1 of 21 --

Nos. 23-3581/3583 Sierra Club v. EPA et al. Page 2
_________________
OPINION
_________________
HELENE N. WHITE, Circuit Judge. Petitioner Sierra Club challenges two decisions of
Respondent Environmental Protection Agency (EPA) regarding the Detroit area’s attainment of
ambient air quality standards under the Clean Air Act (CAA): (1) the approval of Michigan’s
exceptional-events request, and (2) the redesignation of the Detroit area to attainment, based in
part on the EPA’s interpretation of the CAA, which allows an area to be redesignated to
attainment without meeting reasonably available control technology (RACT) requirements that
came due after the state filed an application for redesignation. We affirm the approval of
Michigan’s exceptional-events request and vacate the redesignation of the Detroit area to
attainment.
I.
A.
The CAA requires the EPA to identify air pollutants that “may reasonably be anticipated
to endanger public health or welfare” and whose “presence . . . in the ambient air results from
numerous or diverse mobile or stationary sources.” 42 U.S.C. § 7408(a)(1)(A), (B). It must then
issue “air quality criteria” that reflect “all identifiable effects on public health or welfare” that
may result from a given pollutant’s presence in the ambient air. Id. § 7408(a)(2). Next, it must
propose and promulgate National Ambient Air Quality Standards (NAAQS), “the attainment and
maintenance of which . . . allow[] an adequate margin of safety.” Id. § 7409(b)(1).
Once the EPA establishes new or revised NAAQS, it designates areas of the country as
“attainment” (meaning the area meets the NAAQS), “nonattainment” (meaning the area does not
meet the NAAQS), or “unclassifiable[.]” Id. § 7407(d)(1)(A). The EPA determines whether an
area has reached attainment by calculating its “design value,” which is the annual fourth-highest
daily maximum eight-hour ozone concentration averaged over three years. 40 C.F.R. § 50 app.
U (2015). States with nonattainment areas must develop a State Implementation Plan (SIP)
detailing how they will reach attainment. 42 U.S.C. § 7410(a). States must adopt SIPs through

-- 2 of 21 --

Nos. 23-3581/3583 Sierra Club v. EPA et al. Page 3
state-level notice-and-comment rulemaking and then submit them to the EPA for approval. Id.
The statute also provides a mechanism for states to revise SIPs to account for changes in the
environment or based on a nonattainment designation. See, e.g., id. § 7410(2)(h)-(i). Once the
EPA approves an SIP, it becomes binding on the state and is enforceable as federal law under the
CAA. Id. §§ 7413, 7604(a).
42 U.S.C. § 7511a creates five classifications of nonattainment areas (Marginal,
Moderate, Serious, Severe, and Extreme) and sets requirements for each classification. States
with Marginal nonattainment areas must submit a revision to their operative SIP concerning the
implementation of RACT. Id. § 7511a(a)(2)(A). The Administrator of the EPA issues guidance
specifying the RACT requirements that states with Marginal nonattainment areas must
implement. The EPA defines RACT as “the lowest emission limitation that a particular source is
capable of meeting by the application of control technology that is reasonably available
considering technological and economic feasibility.” State of Mich. v. Thomas, 805 F.2d 176,
180 (6th Cir. 1986). States with Moderate nonattainment areas must make additional revisions to
their SIPs, requiring the implementation of RACT with respect to sources that emit a type of
pollutant called volatile organic compounds (VOCs). 42 U.S.C. § 7511a(b)(2). The
Administrator of the EPA issues a document listing the VOC sources for which states with
Moderate nonattainment areas must implement RACT requirements. Id.
Section 7511 establishes attainment deadlines for areas based on their classification as
Marginal, Moderate, Serious, Severe, or Extreme nonattainment. When the deadline for
attainment expires, the EPA must determine whether the area met the NAAQS by the deadline.
Id. § 7511(b)(2). Excluding Severe and Extreme areas, if an area fails to meet the NAAQS by
the deadline, the area is reclassified to the higher of either the next highest classification or the
classification applicable to the area based on its actual air quality. Id. § 7511(b)(2)(A). The area
is then subject to the SIP requirements for its new classification, and a new deadline is set for
meeting the NAAQS based on the new classification. Id. § 7511a(i).
The EPA can make a determination that an area designated as nonattainment has met
specific ozone NAAQS (also known as a “Clean Data Determination”). 40 C.F.R. § 51.1318.
When the EPA makes this determination, some planning requirements relating to the ozone

-- 3 of 21 --

Nos. 23-3581/3583 Sierra Club v. EPA et al. Page 4
NAAQS are suspended until either the area is redesignated to attainment for the ozone NAAQS,
at which point the requirements no longer apply, or the EPA determines that the area has failed
to meet the ozone NAAQS, at which point the requirements go back into effect. Id.
When a nonattainment area is meeting the NAAQS, the Governor of the state where the
area is located can submit a request to the EPA for redesignation to attainment. 42 U.S.C.
§ 7407(d)(3)(D). The EPA Administrator cannot redesignate an area unless:
(i) the Administrator determines that the area has attained the national ambient
air quality standard;
(ii) the Administrator has fully approved the applicable implementation plan for
the area under section 7410(k) of this title;
(iii) the Administrator determines that the improvement in air quality is due to
permanent and enforceable reductions in emissions resulting from implementation
of the applicable implementation plan and applicable Federal air pollutant control
regulations and other permanent and enforceable reductions;
(iv) the Administrator has fully approved a maintenance plan for the area as
meeting the requirements of section 7505a of this title; and
(v) the State containing such area has met all requirements applicable to the area
under section 7410 of this title and part D.
Id. § 7407(d)(3)(E). Redesignations of areas constitute agency rulemaking. See 5 U.S.C.
§ 551(4)-(5). They are therefore governed by the Administrative Procedure Act (APA), which
requires agencies to provide “notice of proposed rule making” and “give interested persons an
opportunity to participate in the rule making through submission of written data, views, or
arguments.” 5 U.S.C. § 553(b)-(c).
When assessing a request for redesignation, the EPA can exclude air-quality data that was
influenced by an “exceptional event,” defined as an event that:
(i) affects air quality;
(ii) is not reasonably controllable or preventable;
(iii) is an event caused by human activity that is unlikely to recur at a particular
location or a natural event; and
(iv) is determined by the Administrator through the process established in the
regulations promulgated under paragraph (2) to be an exceptional event.

-- 4 of 21 --

Nos. 23-3581/3583 Sierra Club v. EPA et al. Page 5
42 U.S.C. § 7619(b); 40 C.F.R. § 50.14(a)(1)(i). To request that such data be excluded, a state
must notify the EPA that an exceptional event occurred, flag data that was affected by the event,
and submit a demonstration that includes:
(A) A narrative conceptual model that describes the event(s) causing the
exceedance or violation and a discussion of how emissions from the event(s) led
to the exceedance or violation at the affected monitor(s);
(B) A demonstration that the event affected air quality in such a way that there
exists a clear causal relationship between the specific event and the monitored
exceedance or violation;
(C) Analyses comparing the claimed event-influenced concentration(s) to
concentrations at the same monitoring site at other times . . . ;
(D) A demonstration that the event was both not reasonably controllable and not
reasonably preventable; and
(E) A demonstration that the event was a human activity that is unlikely to recur
at a particular location or was a natural event.
40 C.F.R. § 50.14 (c)(2)(i), (c)(3)(iv). The EPA must exclude air-quality data if the state
“demonstrates to the Administrator’s satisfaction that an exceptional event caused a specific air
pollution concentration at a particular air quality monitoring location and otherwise satisfies the
requirements of [§ 50.14].” Id. § 50.14(b)(1). The determination whether to exclude the data is
reached through public notice-and-comment rulemaking on the request for redesignation. Id.
§ 50.14(c)(3)(i).
B.
In June 2018, the EPA designated the Detroit area as Marginal nonattainment for the
NAAQS the EPA had set in 2015. Additional Air Quality Designations for the 2015 Ozone
National Ambient Air Quality Standards, 83 Fed. Reg. 25776, 25813 (June 4, 2018) (codified at
40 C.F.R. § 81.323 (2025)). The Detroit area’s deadline to reach attainment was August 3, 2021.
Determinations of Attainment by the Attainment Date, Extensions of the Attainment Date, and
Reclassification of Areas Classified as Marginal for the 2015 Ozone National Ambient Air
Quality Standards, 87 Fed. Reg. 21842, 21849 (Apr. 13, 2022). On April 13, 2022, the EPA
proposed to make a determination that the Detroit area had failed to attain the 2015 NAAQS by
the August 3, 2021 deadline. Id. at 21845, 21844. The proposed rule set a deadline of January 1,

-- 5 of 21 --

Nos. 23-3581/3583 Sierra Club v. EPA et al. Page 6
2023 for Michigan to submit SIP revisions for RACT and implement RACT for the Detroit area.
Id. at 21856. On February 1, 2023, the EPA finalized its April 2022 determination that the
Detroit area had failed to attain the 2015 NAAQS by the August 3, 2021 deadline. Finding of
Failure to Attain and Reclassification of the Detroit Area as Moderate for the 2015 Ozone
National Ambient Air Quality Standards, 88 Fed. Reg. 6633, 6635 (Feb. 1, 2023). As a result,
by operation of law, the Detroit area was redesignated from Marginal nonattainment to Moderate
nonattainment. Id. As explained, areas designated as Moderate nonattainment are subject to
additional RACT requirements. 42 U.S.C. § 7511a(b)(2). Although the proposed rule had set a
RACT deadline of January 1, 2023, the final rule moved the deadline to March 1, 2023 because
the original due date had already passed, and March was the beginning of the ozone season for
the Detroit area. 88 Fed. Reg. at 6634–5.
In the meantime, in January 2022, Michigan submitted an application to redesignate the
Detroit area from Marginal nonattainment to attainment of the 2015 NAAQS based on 2019–
2021 data. Air Plan Approval; Michigan; Redesignation of the Detroit, MI Area to Attainment
of the 2015 Ozone Standards, 87 Fed. Reg. 14210, 14210 (Mar. 14, 2022). The EPA proposed to
redesignate the Detroit area from nonattainment to attainment in March 2022. Id. at 14210–11.
The notice-and-comment deadline was April 13, 2022. Id. at 14210.
While Michigan’s application for redesignation was pending, the ozone data for the
Detroit area exceeded the 2015 NAAQS on June 24 and 25, 2022. See Air Plan Approval;
Michigan; Clean Data Determination for the Detroit Area for the 2015 Ozone Standard, 88 Fed.
Reg. 32584, 32587 (May 19, 2023). Michigan attributed the exceedances to smoke and other
ozone precursors from wildfires in Canada that reached the United States. Id. at 32586. In
January 2023, Michigan submitted a demonstration to the EPA seeking to exclude the data from
June 24 and 25 when determining whether the Detroit area had reached attainment. Id. at 32584.
The EPA concurred with the demonstration on January 30, 2023, id. at 32584, but under the
APA, it was required to provide an opportunity for public comment on the claimed exceptional
events and supporting data before taking final action. Air Plan Approval; Michigan; Clean Data
Determination for the Detroit Area for the 2015 Ozone Standard, 88 Fed. Reg. 7382, 7383 (Feb.
3, 2023).

-- 6 of 21 --

Nos. 23-3581/3583 Sierra Club v. EPA et al. Page 7
On February 3, 2023, the EPA published a proposed clean data determination stating that
the Detroit area had attained the 2015 NAAQS for the 2020–2022 period. Id. at 7382. This
constituted a proposed rule separate from the EPA’s proposal to designate the Detroit area to
attainment. The clean data determination proposal was based on calculations that excluded the
June 24 and 25 data, as Michigan had requested. Id. at 7383. The proposed rule suspended SIPs
and other planning requirements. Id. Comments on the proposal were due by March 6, 2023.
Id. at 7382. On May 19, 2023, the EPA finalized the redesignation of the Detroit area to
attainment. Air Plan Approval; Michigan; Redesignation of the Detroit, MI Area to Attainment
of the 2015 Ozone Standards, 88 Fed. Reg. 32594 (May 19, 2023). That same day, the EPA
finalized its clean data determination for the Detroit area. Air Plan Approval; Michigan; Clean
Data Determination for the Detroit Area for the 2015 Ozone Standard, 88 Fed. Reg. at 32584.
Michigan never submitted SIP revisions addressing the additional RACT requirements for
Moderate nonattainment areas. But the EPA determined that Michigan did not have to make and
implement those revisions in order for the Detroit area to be redesignated to attainment,
reasoning that the prerequisite in 42 U.S.C. § 7407(d)(3)(E)(v) for a state to have “met all
requirements applicable to the area under section 7410 of this title and Part D of this subchapter”
did not include requirements that “came due after the submittal of a complete redesignation
request.” Redesignation of the Detroit, MI Area to Attainment of the 2015 Ozone Standards, 88
Fed. Reg. at 32611.
II.
When evaluating a challenge to a federal agency’s action, courts must overturn the action
if it is “arbitrary, capricious, an abuse of discretion, or otherwise not in accordance with law,”
5 U.S.C. § 706(2)(A), or “in excess of statutory jurisdiction, authority, or limitations,” id.
§ 706(2)(C). To establish that a decision was not arbitrary or capricious, an agency must provide
a satisfactory explanation for the decision, including a rational connection between the relevant
facts and the decision made. Motor Vehicle Mfrs. Ass’n v. State Farm Mut. Auto. Ins. Co., 463
U.S. 29, 43 (1983). When assessing whether an agency’s action was arbitrary or capricious,
“[a] court simply ensures that the agency has acted within a zone of reasonableness and, in
particular, has reasonably considered the relevant issues and reasonably explained the decision.”

-- 7 of 21 --

Nos. 23-3581/3583 Sierra Club v. EPA et al. Page 8
Fed. Commc’ns Comm’n v. Prometheus Radio Project, 592 U.S. 414, 423 (2021). A court may
not vacate an agency’s decision unless the agency “has relied on factors which Congress has not
intended it to consider, entirely failed to consider an important aspect of the problem, offered an
explanation for its decision that runs counter to the evidence before the agency, or is [highly]
implausible[.]” Motor Vehicle Mfrs. Ass’n, 463 U.S. at 43. Courts are to be “most deferential
when reviewing an agency’s scientific determinations about issues within its expertise.” St.
Mary’s Cement, Inc. v. EPA, 782 F.3d. 280, 286 (6th Cir. 2015) (citation and internal quotation
marks omitted).
A.
Sierra Club first contends that the EPA’s exceptional-event approval following the June
2022 wildfires was arbitrary and capricious because (1) it ignored evidence that wildfire smoke
did not meaningfully affect ozone concentrations at a Detroit area air monitor; (2) local data does
not support the conclusion that wildfire smoke was present at the air monitor throughout June 24
and 25, 2022; (3) it failed to evaluate whether Michigan properly omitted several days from a
data analysis in its exceptional-event demonstration; and (4) it did not analyze how local
conditions contributed to high ozone levels on the exceptional-event days. These arguments all
pertain to the exceptional-event requirement that Michigan establish to the EPA’s satisfaction a
“clear causal relationship” between the Canadian wildfire emissions and the exceedances on the
relevant days. See 40 C.F.R. § 50.14(c)(3)(iv)(B) (2025).
Our review of the administrative record reveals that the EPA conducted a thorough
evaluation of Michigan’s exceptional-event demonstration and provided reasons for its decision.
The EPA concluded that the exceedances at the Detroit-area monitor on June 24 and 25 were due
to wildfire smoke based on the measurements of Brown Carbon (BrC) at the monitor, which is “a
by-product of incomplete combustion and thus an indicator of wildfire smoke.” Clean Data
Determination for the Detroit Area for the 2015 Ozone Standard, 88 Fed. Reg. at 32586. The
EPA further explained that “the meteorological conditions on the exceedance days examined in
conjunction with local and background emissions do not present the conditions conducive to
producing elevated ozone concentrations,” so it concluded that “the exceedances at issue were
due to wildfire smoke, rather than local pollution.” Id. Thus, the EPA provided a sufficient

-- 8 of 21 --

Nos. 23-3581/3583 Sierra Club v. EPA et al. Page 9
explanation for its decision to grant the exceptional-event approval, connecting the facts it found
to the decision it made.
Sierra Club argues that the EPA failed to consider relevant information. Sierra Club first
claims that the EPA ignored evidence that the wildfire smoke did not meaningfully affect ozone
concentrations at the relevant area air monitor. It notes that Michigan used a screening analysis
developed by the Lake Michigan Air Directors Consortium (LADCO) to find evidence from
local monitoring data that wildfire smoke affected the monitor. According to Sierra Club, the
undisputed fact that the standard deviations for the concentration of ozone, fine particulate matter
(PM2.5), and carbon monoxide were below 1 on the exceptional-event days suggests that wildfire
smoke did not affect this monitor.
However, in response to Sierra Club and the Great Lakes Environmental Law Center’s
comment that the LADCO screening analysis “does not support a finding that wildfire smoke
was present in the Detroit area during on June 24 or 25, 2022,” the EPA explained that it had
“evaluated and considered all the information provided in [Michigan]’s demonstration” and that
it “reviews exceptional events demonstrations on a case-by-case basis using a weight of evidence
approach considering the specifics of the individual event.” Clean Data Determination for the
Detroit Area for the 2015 Ozone Standard, 88 Fed. Reg. at 32589. It acknowledged that “[t]he
LADCO analysis does not show a high peak (representing high 24-hr PM2.5 concentrations) for
PM2.5 during this time period.” Id. However, despite this data, it decided under the weight-of-
evidence approach to grant the exceptional-event approval because other types of data, such as
an analysis of hourly BrC data from Michigan’s air monitoring network on June 24 and 25,
“provide[d] evidence that wildfire smoke was present in the Detroit area, as well as at the ground
level where measurements are made.” Id. Sierra Club contends that the fact that the LADCO
analysis contradicts the EPA’s conclusion should have prevented the EPA from granting the
approval. But the EPA’s explanation demonstrates that it did not ignore the contrary evidence,
as Sierra Club asserts, and also provides a satisfactory rationale for granting the approval despite
the LADCO evidence.

-- 9 of 21 --

Nos. 23-3581/3583 Sierra Club v. EPA et al. Page 10
Sierra Club next argues that the BrC and coarse particular matter (PM10) data on which
the EPA relied in granting the approval did not support a finding that wildfire smoke was present
at the relevant air monitor throughout June 24 and 25. It asserts that the EPA has cautioned
against relying on PM10 concentrations as an indicator of smoke because “PM10 generally tends
to ‘fall’ to ground level relatively quickly in the vicinity of the event and, in our experience, is
not usually subject to long range transport.” EPA-R05-OAR-2023-0058-0031, Ex. 16, at 20.
Sierra Club further notes that BrC pollution peaked on June 23, which was a day before the
alleged exceptional event. It contends that because there was no spike in BrC concentrations on
June 24 and merely a small spike in on June 25, the BrC data did not allow the EPA to conclude
that the Canadian wildfires affected ozone levels in the Detroit area.
The EPA explained that Michigan “evaluated . . . PM10 concentrations but did not rely
solely on PM10 concentrations for their multi-pollutant corroboration.” Clean Data
Determination for the Detroit Area for the 2015 Ozone Standard, 88 Fed. Reg. at 32589. It
further stated that it “recognizes that long-range transport of wildfire smoke would not typically
have an impact on nearby PM10.” Id. Therefore, it is clear that the EPA was aware of the
limitations of PM10 data.
Turning to the BrC data, the EPA explained why it concluded that wildfire smoke had
affected the relevant monitor on June 24 and 25 even though BrC levels peaked on June 23:
By June 23, 2022, smoke from these fires had reached southern Ontario at the
Michigan border. Northerly winds on June 23, 2022 transported the smoke to
Detroit, and a cold front moved through the Detroit area on June 23, 2022,
bringing air and wildfire emissions from Canada behind it. The air behind the
cold front subsided, which allowed the air containing wildfire emissions aloft to
sink to the surface. The presence of smoke from the Canadian wildfire behind
this cold front resulted in atypical air quality for such a frontal passage. Although
meteorological conditions were stagnant on June 24-25, 2022, under a surface
high pressure, the Canadian wildfire emissions had already been transported to the
area prior and contributed to elevated ozone concentrations.
Id. at 32586. This explanation indicates that the EPA did not ignore the fact that BrC peaked on
June 23 and provided a satisfactory rationale for its determination that the BrC data supported a
finding that Canadian wildfires affected ozone levels in the Detroit area.

-- 10 of 21 --

Nos. 23-3581/3583 Sierra Club v. EPA et al. Page 11
Next, Sierra Club contends that there was insufficient evidence connecting the wildfire
smoke to the exceedances because Michigan omitted several days of data from an analysis it
provided in its demonstration. Michigan provided a matching-day analysis, which compared
ozone concentrations on previous days that had meteorological conditions similar to those
present on June 24 and 25 with the actual ozone concentrations on June 24 and 25. If a
matching-day analysis reveals high ozone concentrations on days with meteorological conditions
that are not typically associated with elevated ozone, that discrepancy can constitute evidence
that a source such as wildfire smoke influenced the ozone levels.
Sierra Club notes that Michigan’s matching-day analysis omitted several days that had
meteorological conditions similar to those on June 24 and 25 on the basis that ozone levels on
those days may have also been influenced by smoke. Sierra Club argues that the evidence in the
administrative record did not permit the EPA to conclude that wildfire smoke affected ozone
levels on June 24 and 25 because Michigan did not provide any evidence that smoke affected
ozone levels on the days it omitted from the analysis and merely stated what methods it used to
analyze smoke influence. But Michigan’s failure to provide more fulsome evidence that smoke
affected ozone levels on the omitted days did not require the EPA to deny the exceptional-event
approval. The evidence Michigan provided was extensive, consisting of a comparison of the
June 24 and 25 exceedances with historical concentrations, figures showing the progression of
smoke plumes over North America using satellite imagery, calculations of trajectories
originating from the largest fire sites, BrC and PM10 concentration data, ozone and PM2.5
concentration data, information on local meteorological conditions, and a matching-day analysis.
Accordingly, the matching-day analysis, combined with all the other evidence Michigan
provided in its demonstration, allowed the EPA to determine that wildfire smoke affected ozone
levels at the relevant monitor on June 24 and 25.
Finally, Sierra Club argues that the EPA’s decision to grant the exceptional-event
approval was unlawful because it did not consider how local conditions may have contributed to
high ozone levels on June 24 and 25. It notes that significant sources of ozone precursor
pollutants recently began operating near the relevant mile marker and contends that the EPA
failed to differentiate the impacts of these sources from those of the wildfire smoke. But when

-- 11 of 21 --

Nos. 23-3581/3583 Sierra Club v. EPA et al. Page 12
assessing Michigan’s demonstration, the EPA specifically determined that the matching-day
analysis demonstrated that “the meteorological conditions on the exceedance days examined in
conjunction with local and background emissions do not present the conditions conducive to
producing elevated ozone concentrations[;] . . . the exceedances at issue were due to wildfire
smoke, rather than local pollution.” Clean Data Determination for the Detroit Area for the 2015
Ozone Standard, 88 Fed. Reg. at 32586. Thus, the EPA met the requirement to demonstrate that
it “reasonably considered the relevant issues and reasonably explained the decision.”
Prometheus Radio Project, 592 U.S. at 423.
For these reasons, the EPA’s decision to grant the exceptional-event approval was not
arbitrary or capricious.
B.
Sierra Club next argues that, by issuing a Redesignation Rule redesignating the Detroit
area to attainment, the EPA contravened 42 U.S.C. § 7407(d)(3)(E), which states:
(E) The Administrator may not promulgate a redesignation of a nonattainment
area (or portion thereof) to attainment unless—
(i) the Administrator determines that the area has attained the national
ambient air quality standard;
(ii) the Administrator has fully approved the applicable implementation
plan for the area under section 7410(k) of this title;
(iii) the Administrator determines that the improvement in air quality is
due to permanent and enforceable reductions in emissions resulting from
implementation of the applicable implementation plan and applicable
Federal air pollutant control regulations and other permanent and
enforceable reductions;
(iv) the Administrator has fully approved a maintenance plan for the area
as meeting the requirements of section 7505a of this title; and
(v) the State containing such area has met all requirements applicable to
the area under section 7410 of this title and part D.
Sierra Club disputes only requirements (i), (iii), and (v). We address each challenge in turn.

-- 12 of 21 --

Nos. 23-3581/3583 Sierra Club v. EPA et al. Page 13
1.
The first criterion for redesignation requires the EPA to find that “the area has attained
the national ambient air quality standard.” 42 U.S.C. § 7407(d)(3)(E)(i). The EPA determined
that the Detroit area attained the 2015 NAAQS from 2019 through 2022. Sierra Club contends
that the EPA lacked a rational basis to conclude that the Detroit area was meeting the NAAQS in
light of 2022 data. It asserts that because monitoring data showed enough exceedances of the
NAAQS to disqualify the area for attainment in 2022, the area could only qualify for attainment
for the period from 2019 to 2022 because of the exceptional-event approval. Therefore, it
argues, if this court determines that the exceptional-event approval was wrongly granted, it must
also find that the EPA had no rational basis for finding that the area had attained the NAAQS
during this period.
Because we conclude that the decision to grant the exceptional-event approval was not
arbitrary or capricious, this argument fails.
2.
Sierra Club also challenges the EPA’s determination that the air-quality improvement
during the period from 2019 to 2022 was “due to permanent and enforceable reductions in
emissions,” as required by 42 U.S.C. § 7407(d)(3)(E)(iii). It asserts that the EPA lacked a
rational basis for this conclusion because, given the lockdowns and economic downturn resulting
from the COVID-19 pandemic during this period, the EPA could not reasonably attribute air-
quality improvements to permanent emission reductions.
The record demonstrates that the EPA did, in fact, consider the pandemic’s impact on
emissions. The EPA examined analyses Michigan performed to determine whether air-quality
improvement during the pandemic was due to pandemic-related economic conditions.
Redesignation of the Detroit, MI Area to Attainment of the 2015 Ozone Standards, 87 Fed. Reg.
at 14217. One such analysis showed an overall downward trend in point-source (facilities that
report their emissions directly to the state, plus some additional sources) emissions in the Detroit
area from 2012 to 2020, which indicated that the downward trend in emissions was not entirely
attributable to the pandemic. Id. Another analysis showed that although the pandemic’s impact

-- 13 of 21 --

Nos. 23-3581/3583 Sierra Club v. EPA et al. Page 14
was apparent in data showing decreases in source emissions, miles of vehicle travel, and
employment between 2019 and 2020, these decreases were not associated with a corresponding
decline in ozone pollution—rather, ozone concentration increased from 2019 to 2020. Id. The
EPA concluded that “these analyses show that economic conditions associated with the COVID-
19 pandemic were not correlated with the improved air quality and strengthen Michigan’s
demonstration that the improved air quality is due to permanent and enforceable emissions
reductions.” Id. The EPA also pointed to several permanent and enforceable emission controls
that had successfully reduced emissions in the Detroit area, including regional oxides-of-nitrogen
controls, federal emission control measures, Detroit point-source oxides-of-nitrogen reductions,
and a Michigan program requiring the sale of gasoline with a low rate of evaporation in the
summer. Id. at 14214–16.
For these reasons, the EPA’s determination that the air-quality improvements in the
Detroit area were due to permanent and enforceable emission reductions was not arbitrary or
capricious.
3.
Sierra Club next argues that the EPA lacked the authority to redesignate the Detroit area
to attainment because Michigan did not satisfy the RACT requirements imposed when the area
was designated Moderate nonattainment. 42 U.S.C. § 7407(d)(3)(E)(v) states, “[t]he
Administrator may not promulgate a redesignation of a nonattainment area (or portion thereof) to
attainment unless” the state “has met all requirements applicable to the area under section 7410
of this title and part D [of this subchapter].” The EPA’s proposal to designate the Detroit area as
Moderate nonattainment, issued on April 13, 2022, required Michigan to submit SIP RACT
revisions and implement RACT requirements for the Detroit area by January 1, 2023.
Determinations of Attainment by the Attainment Date, Extensions of the Attainment Date, and
Reclassification of Areas Classified as Marginal for the 2015 Ozone National Ambient Air
Quality Standards, 87 Fed. Reg. at 21855. Michigan applied to redesignate the Detroit area as an
attainment area in January 2022, before the deadline for RACT implementation. After Michigan
submitted its application, the EPA issued a final rule, dated February 1, 2023, which designated
the Detroit area as Moderate nonattainment and moved the deadline for RACT implementation

-- 14 of 21 --

Nos. 23-3581/3583 Sierra Club v. EPA et al. Page 15
to March 1, 2023. Finding of Failure to Attain and Reclassification of the Detroit Area as
Moderate for the 2015 Ozone National Ambient Air Quality Standards, 88 Fed. Reg. at 6633. In
May 2023, the EPA then issued a final rule redesignating the Detroit area to attainment, despite
Michigan’s failure to implement RACTs for the Detroit area. Air Plan Approval; Michigan;
Redesignation of the Detroit, MI Area to Attainment of the 2015 Ozone Standards, 88 Fed. Reg.
at 32594.
Sierra Club argues that, because Michigan did not satisfy the RACT requirements
imposed when the area was designated Moderate nonattainment, the Detroit area had not met “all
requirements applicable to the area,” § 7407(d)(3)(E)(v), and thus could not satisfy the
prerequisites for redesignated to attainment. The EPA has taken the position, in its regulations
and this proceeding, that § 7407(d)(3)(E)(v) excludes requirements that “came due after the
submittal of a complete redesignation request,” Clean Data Determination for the Detroit Area
for the 2015 Ozone Standard, 88 Fed. Reg. at 32611, as was the case here, where the RACT
requirements came due while the redesignation request was pending. The EPA argues that it is
sufficient that the Detroit area was in compliance with the requirements applicable to the area at
the time of its application.
This argument presents a question of statutory interpretation. “For questions of statutory
interpretation, we look to the statutory language as ‘the starting point for interpretation, and []
the ending point if the plain meaning of that language is clear.’” Davenport v. Lockwood,
Andrews & Newnam, Inc., 854 F.3d 905, 909 (6th Cir. 2017) (quoting United States v. Henry,
819 F.3d 856, 870 (6th Cir. 2016)). “The ‘words of a statute must be read in their context and
with a view to their place in the overall statutory scheme.’” Greenbaum v. EPA¸ 370 F.3d 527,
537 (6th Cir. 2004) (quoting Davis v. Mich. Dep’t of Treasury, 489 U.S. 803, 809 (1989)). And
this court must “‘reject administrative constructions [] that are inconsistent with the statutory
mandate.’” Wall v. EPA, 265 F.3d 426, 435 (6th Cir. 2001) (quoting Sec. Indus. Ass’n v. Bd. of
Governors of the Fed. Rsrv. Sys., 468 U.S. 137, 143 (1984)).

-- 15 of 21 --

Nos. 23-3581/3583 Sierra Club v. EPA et al. Page 16
In Loper Bright Enterprises v. Raimondo, 603 U.S. 369 (2024), the Supreme Court
overruled Chevron, U.S.A., Inc. v. Natural Resources Defense Council, Inc., 467 U.S. 837 (1984)
and provided the following rule regarding agency interpretations of statutes:
Courts must exercise their independent judgment in deciding whether an agency
has acted within its statutory authority, as the APA requires. Careful attention to
the judgment of the Executive Branch may help inform that inquiry. And when a
particular statute delegates authority to an agency consistent with constitutional
limits, courts must respect the delegation, while ensuring that the agency acts
within it. But courts need not and under the APA may not defer to an agency
interpretation of the law simply because a statute is ambiguous.
Loper Bright, 603 U.S. at 412–13. We therefore must conduct our statutory analysis with the
“presumption [] that Congress expects courts to do their ordinary job of interpreting statutes,
with due respect for the views of the Executive Branch.” Id. at 403.
We begin with statutory text. The EPA “may not promulgate a redesignation of a
nonattainment area [] to attainment unless [] the State containing such area has met all
requirements applicable to the area under section 7410 of [Title I of the Act] and part D.” 42
U.S.C. § 7407(d)(3)(E)(v) (emphasis added). Since section 7407(d)(3)(E) commands the EPA
not to promulgate a redesignation unless the state “has met” (in the present-perfect tense) certain
statutory requirements, it follows that the statutory requirements must be met at the time of
redesignation. If the state was required to meet the statutory requirements only at the time it
submitted its redesignation request, the provision would operate more like an application
requirement. That construction might make sense if 42 U.S.C. § 7407(d)(3)(E)(v) employed past
perfect tense—prohibiting redesignation unless the state had met all applicable requirements (at
the time of the application). But “Congress’ use of a verb tense is significant in construing
statutes.” United States v. Wilson, 503 U.S. 329, 333 (1992). Congress elected to use the present
perfect “has met,” which “denotes past action with an abiding effect or continuing relevance”
and not “noncontinuing compliance.” Commonwealth of Ky. v. EPA, 165 F.3d 26, *3 (6th Cir.
Sept. 2, 1998) (unpublished table decision). And when considering 42 U.S.C. § 7407(d)(3)(E)(i),
this court found that “the phrase ‘has attained’ [] requires that the attainment must continue until
the date of redesignation.” Id. (internal quotation marks and citation omitted). Accordingly, the

-- 16 of 21 --

Nos. 23-3581/3583 Sierra Club v. EPA et al. Page 17
phrase “has met” in § 7407(d)(3)(E)(v) requires that all applicable requirements must be met
until the date of redesignation.
The Supreme Court’s recent analysis of Congress’s use of the present-perfect tense in the
First Step Act is also instructive. In Hewitt v. United States, 606 U.S. 419, 427 (2025), the Court
analyzed the operative statutory text of § 403(b) of the act, which “require[es] the evaluation of
whether ‘a sentence . . . has . . . been imposed’ upon the defendant.” The Court reasoned that the
use of “the present-perfect tense conveys to a listener that the event in question continues to be
true or valid” and therefore concluded that Congress’s use of the present-perfect tense indicated
“that § 403(b) covers only past sentences with continued legal validity[.]” Id. at 429.
Congress’s use of the present-perfect tense in 42 U.S.C. § 7407(d)(3)(E)(v) similarly conveys
that the event in question—here, the Detroit area’s implementation of the applicable RACT
requirements—must continue to be true until the date of redesignation.
The EPA notes that the present-perfect tense can both be used to denote events that began
in the past and continue to the present, or “events that occurred in the past that have significance
in the present day.” Respondent’s Br. at 54 (citing Present Perfect, Collins Cobuild English
Dictionary (2024); and Present Perfect, Cambridge Dictionary (2024)). The EPA therefore
argues that the use of the present perfect does not definitively resolve this issue because its
construction—that the state need meet only the requirements applicable at the time of
application—is consistent with one use of the present-perfect tense, while Sierra Club’s
construction—that the state’s obligation to meet applicable standards is ongoing—is consistent
with the other use of the present-perfect tense. But the EPA does not explain how its
construction gives full effect to the statute’s use of the present perfect. If the use of the present
perfect “has met” refers to past events with significance for the present, what significance is
accorded to the past compliance with the statute under its interpretation? Moreover, under the
EPA’s construction, the statute’s meaning would be unchanged with the elimination of the word
“has.” We disfavor statutory interpretations that render a word or phrase superfluous. See
Kungys v. United States, 485 U.S. 759, 778 (1988) (plurality opinion of Scalia, J.) (citing the
“cardinal rule of statutory interpretation that no provision should be construed to be entirely
redundant”).

-- 17 of 21 --

Nos. 23-3581/3583 Sierra Club v. EPA et al. Page 18
“Context confirms this reading.” Southwest Airlines Co. v. Saxon, 596 U.S. 450, 457
(2022). The statute clearly contemplates escalating requirements even when a state has
submitted a request to redesignate an area to attainment. The nonattainment scheme in the
CAA adjusts an area’s obligations based on its failure to comply with the statute’s deadline
for achieving attainment. It is the state’s failure to meet the deadline, not a finding that
the state’s air quality has worsened, that triggers a bump-up in the CAA requirements. When a
state fails to meet its deadline, it is bumped up, and the stricter requirements go into effect.
Those requirements remain in effect as a redesignation request is pending. Commonwealth, 165
F.3d at *3. Indeed, the statutory provision allowing redesignation requests expressly states that a
state’s submission of a redesignation request “shall not affect the effectiveness or enforceability
of the applicable implementation plan for the State.” 42 U.S.C. § 7407(d)(3)(D).
Here, the EPA ordered Michigan to submit a revised SIP implementing RACT by March
1, 2023. Had Michigan done so, that revised SIP would have been “the applicable
implementation plan.” See 42 U.S.C. § 7407(d)(3)(D). A state cannot avoid the requirements of
an amended SIP by simply failing to submit the amendment. That the statute both requires a
state to adjust its implementation based on a deadline and prohibits a state from relying on its
submission of a redesignation request to forestall compliance with the applicable SIP offers
strong support for the Sierra Club’s construction of § 7407(d)(3)(E)(v). Finally, the statute
contains no exception to the RACT requirements for states that had met the NAAQS at the
effective date of the new designation. The regulatory exception, which allows the EPA to make
a clean-data determination when the NAAQS are attained, suspends implementation of some
federal requirements but does not provide for the suspension of RACT implementation. See 40
C.F.R. § 51.1318. Excusing non-compliance with the statute’s deadlines would render toothless
the requirement that a state continue complying with the CAA even if it already submitted a
redesignation request and would allow states to simply request redesignation and ignore any
changes required after the date of the request.
The timeline of events in this case demonstrates the problem with the EPA’s preferred
construction. By the time of its redesignation on May 19, 2023, Michigan had failed to meet its
August 3, 2021 deadline to bring the Detroit area into attainment. That failure to meet the

-- 18 of 21 --

Nos. 23-3581/3583 Sierra Club v. EPA et al. Page 19
attainment deadline triggered the bump up from Marginal to Moderate on March 1, 2023. From
the time of the EPA’s initial determination that the Detroit area was not in attainment on April
13, 2022, Michigan knew that it had an impending deadline to submit and implement ozone
RACT requirements, first set at January 1, 2023, and later moved to March 1, 2023.1 That a
redesignation request was pending at the time of the bump up did not preserve the area’s
nonattainment classification at the Marginal level or suspend implementation of the RACT
requirements. See Air Plan Approval; Michigan; Redesignation of the Detroit, MI Area to
Attainment of the 2015 Ozone Standards, 88 Fed. Reg. at 32594, 32598.
The EPA makes an additional textual argument that 42 U.S.C. § 7407(d)(3)(E)(v) is
directed at states, whereas the requirements in § 7407(d)(3)(E)(i)-(iv) are directed at the EPA
itself. Because § 7407(d)(3)(E)(v) is directed at the states, and the state’s role in the
redesignation process concludes when it submits a redesignation request, the EPA argues §
7407(d)(3)(E)(v) only covers requirements in place prior to the submission of an application.
This argument fails for four reasons. First, the statute explicitly prohibits states from
relying on a redesignation request to excuse future compliance with the applicable SIP. See id.
§ 7407(d)(3)(D). The state therefore has continuing compliance obligations, even after
submitting a redesignation request. Second, the “[r]esponsibility for meeting the NAAQS rests
with the states.” Wall, 265 F.3d at 428. Therefore, the fact that § 7407(d)(3)(E)(v) notes the
states’ responsibility to meet the requirements is consistent with the CAA’s imposition of
compliance responsibility and does not suggest any timing-based exemption based on application
submittal. Third, although § 7407(d)(3)(E)(v) does indeed begin with different language than
subsections (i)-(iv), all five subsections serve as requirements for “the Administrator” to
promulgate a redesignation. All five subsections, including subsection (v), thus constrain the
EPA’s actions. We discern the ordinary meaning of contested statutory text by reading those
words “in their context, not in isolation.” Southwest Airlines, 596 U.S. at 455 (citation
1The RACT requirements are always imposed when an area is designated Moderate nonattainment or
higher. 42 U.S.C. § 7511a(b)(2); 40 C.F.R. § 51.1312(a)(1); Wall, 265 F.3d at 429 (“For a moderate ozone
nonattainment area, a SIP must include the following specific measures: (1) pollution limits that reflect the
‘reasonably available control technology’ (RACT) for existing factories that emit VOCs, and (2) procedures to
ensure that state and local transportation plans and projects conform to the clean air plans.” (internal citations
omitted)).

-- 19 of 21 --

Nos. 23-3581/3583 Sierra Club v. EPA et al. Page 20
modified). Here, the statute provides redesignation requirements imposed upon the agency, not
the states. See 42 U.S.C. § 7407(d)(3)(E) (“The Administrator may not . . .” (emphasis added)).
Fourth, the EPA’s interpretation finds no support in this court’s precedent, which has described
§ 7407(d)(3)(E)(v) consistently with the other provisions as a burden imposed on the EPA.
See, e.g., Greenbaum, 370 F.3d at 531 (“The EPA may not redesignate an area to attainment
unless: . . . (v) the EPA has determined that the State containing the area seeking redesignation
has met all applicable SIP requirements for that area under § 110 with respect to SIPs generally,
and under Part D with respect to SIP provisions for nonattainment areas.” (citing 42 U.S.C.
§ 7407(d)(3)(E)) (emphasis added)). We therefore reject the EPA’s contention that, because
§ 7407(d)(3)(E)(v) is framed as a state’s compliance obligation, it imposes no continuing
compliance obligations beyond the date of the redesignation request.
Finally, the EPA contends that an interpretation of the “applicable” requirements as those
requirements applicable at the time of redesignation would delay action on the redesignation
request beyond the 18-month time frame permitted for EPA to approve or deny the request, since
an intervening bump-up would require the state to make additional SIP submissions. But the
Sierra Club’s construction is not unworkable. The EPA can decline the redesignation request
pending before it within the 18-month time frame and require the state to resubmit a new
redesignation request based on attainment of the NAAQS and compliance with the requirements
applicable to the area. And, the EPA has some leeway in setting RACT compliance dates. The
EPA recognized that it could have extended the deadline for the RACT SIP for up to two years
after the final date of its determination. Determinations of Attainment by the Attainment Date,
Extensions of the Attainment Date, and Reclassification of Areas Classified as Marginal for the
2015 Ozone National Ambient Air Quality Standards, 87 Fed. Reg. at 21855. But it chose not to
do so because of a desire for consistency and to make the requirements effective at the beginning
of the compliance year. Id. at 21855–56; Finding of Failure to Attain and Reclassification of the
Detroit Area as Moderate for the 2015 Ozone National Ambient Air Quality Standards, 88 Fed.
Reg. at 6634. If the EPA grants a redesignation before the stricter requirements come due, the
problem is avoided entirely. The EPA cannot, however, require RACT implementation by a
certain date, and then ignore a state’s failure to comply in assessing a redesignation request.
Thus, Sierra Club’s proposed interpretation would not render the statutory scheme unworkable.

-- 20 of 21 --

Nos. 23-3581/3583 Sierra Club v. EPA et al. Page 21
For these reasons, we conclude that 7407(d)(3)(E)(v) permits redesignation only when a
state “has met all requirements applicable to the area” at the time of redesignation, rather than at
the time a state submits its application for redesignation.
V.
For the reasons set out above, we AFFIRM in part and VACATE in part.

-- 21 of 21 --