United States Court of Appeals, District of Columbia Circuit
October 3, 2018
Petitions for Review of Final Action of the United States
Environmental Protection Agency
Gormley argued the cause for petitioners Conservation Groups.
Valerie S. Edge, Deputy Attorney General, Office of the
Attorney General for the State of Delaware, argued the cause
for petitioner State of Delaware. With them on the briefs
were David Baron, Charles McPhedran, Joshua R. Stebbins, and
Zachary M. Fabish. Seth L. Johnson entered an appearance.
Tseytlin, Solicitor General, Office of the Attorney General
for the State of Wisconsin, and Harvey M. Sheldon argued the
causes for State Petitioners, Cedar Falls Utilities, and City
of Ames, Iowa. With them on the briefs were Brad D. Schimel,
Attorney General, Luke N. Berg, Deputy Solicitor General,
Peter Michael, Attorney General, Office of the Attorney
General for the State of Wyoming, James Kaste, Deputy
Attorney General, Erik Petersen, Senior Assistant Attorney
General, Leslie Sue Ritts, Steve Marshall, Attorney General,
Office of the Attorney General for the State of Alabama,
Robert D. Tambling, Assistant Attorney General, Leslie
Rutledge, Attorney General, Office of the Attorney General
for the State of Arkansas, Nicholas J. Bronni, Deputy
Solicitor General, Michael DeWine, Attorney General, Office
of the Attorney General for the State of Ohio, Eric E.
Murphy, State Solicitor, Ken Paxton, Attorney General, Office
of the Attorney General for the State of Texas, Priscilla M.
Hubenak, and Craig J. Pritzlaff and Linda B. Secord,
Assistant Attorneys General. Andrew L. Brasher, Deputy
Solicitor, Office of the Attorney General for the State of
Alabama, Michael J. McGrady, Senior Assistant Attorney
General, Office of the Attorney General for the State of
Wyoming, Lee P. Rudofsky, Solicitor, Office of the Attorney
General for the State of Arkansas, and Ryan Walsh entered
W. Fichthorn, Aaron M. Streett, and C. Grady Moore, III
argued the causes for Industry Petitioners. With them on the
briefs were E. Carter Chandler Clements, Peter S. Glaser,
Margaret Claiborne Campbell, M. Buck Dixon, Scott C. Oostdyk,
E. Duncan Getchell, Jr., Michael H. Brady, Jane E.
Montgomery, J. Michael Showalter, Amy Antoniolli, P. Stephen
Gidiere, III, Julia B. Barber, David W. Mitchell, Daniel J.
Kelly, David M. Flannery, Kathy G. Beckett, Edward L. Kropp,
Megan H. Berge, Charles T. Wehland, Todd E. Palmer, John A.
Sheehan, Valerie L. Green, Ben H. Stone, Terese T. Wyly, M.
Brant Pettis, Louis E. Tosi, Cheri A. Budzynski, and Michael
A. Born. Alina Fortson and Jordan Hemaidan entered
Dona and Chloe H. Kolman, Attorneys, U.S. Department of
Justice, argued the causes for respondents. With them on the
brief were Jonathan Brightbill, Deputy Assistant Attorney
General, and Stephanie L. Hogan, Attorney, U.S. Environmental
Carter Chandler Clements argued the cause for Industry
Respondent-Intervenors. With her on the brief were Norman W.
Fichthorn, Peter S. Glaser, Margaret Claiborne Campbell, M.
Buck Dixon, Scott C. Oostdyk, E. Duncan Getchell, Jr.,
Michael H. Brady, Robert A. Manning, and Joseph A. Brown.
G. Frank, Assistant Attorney General, argued the cause for
State Intervenors. With him on the brief were Eric T.
Schneiderman, Attorney General at the time the brief was
filed, Office of the Attorney General for the State of New
York, Barbara D. Underwood, Solicitor General, Steven C. Wu,
Deputy Solicitor General, Michael J. Myers, Senior Counsel,
Maura Healey, Attorney General, Office of the Attorney
General for the Commonwealth of Massachusetts, Jillian M.
Riley, Assistant Attorney General, Environmental Protection
Division, Peter F. Kilmartin, Attorney General, Rhode Island
Department of Attorney General, Gregory S. Schultz, Special
Assistant Attorney General, Brian E. Frosh, Attorney General,
Office of the Attorney General for the State of Maryland,
Michael F. Strande, Assistant Attorney General, Gordon J.
MacDonald, Attorney General, K. Allen Brooks, Assistant
Attorney General, New Hampshire Office of the Attorney
General, Thomas J. Donovan, Jr., Attorney General, Office of
the Attorney General for the State of Vermont, and Nicholas
F. Persampieri, Assistant Attorney General. Morgan A.
Costello, Assistant Attorney General, Office of the Attorney
General for the State of New York, entered an appearance.
Charles McPhedran argued the cause for Public Health and
Environmental Intervenors. With him on the brief were Sean H.
Donahue, Susannah L. Weaver, Graham G. McCahan, Vickie L.
Patton, Ann Brewster Weeks, Neil Gormley, David Baron, Howard
Fox, Joshua R. Stebbins, and Zachary M. Fabish.
M. Babcock was on the brief for amicus curiae American
Thoracic Society in support of respondent-intervenors
American Lung Association, Appalachian Mountain Club,
Environmental Defense Fund, and Sierra Club.
Before: Srinivasan, Millett and Wilkins, Circuit Judges.
upwind States pollute, downwind States can suffer the
consequences. Congress addressed that problem in the Clean
Air Act by enacting a "Good Neighbor Provision."
The Provision requires upwind States to eliminate their
significant contributions to air quality problems in downwind
2016, the Environmental Protection Agency implemented that
requirement by promulgating a regulation addressing the
interstate transport of ozone, or smog. A number of parties
brought challenges to the Rule, some contending that the Rule
is too strict and others contending that it is too lenient.
conclude that, in one respect, the Rule is inconsistent with
the Act: it allows upwind States to continue their
significant contributions to downwind air quality problems
beyond the statutory deadlines by which downwind States must
demonstrate their attainment of air quality standards. In all
other respects, though, we determine that EPA acted lawfully
Clean Air Act tasks EPA with setting national ambient air
quality standards, or NAAQS. See 42 U.S.C. §
7409(a). Individual States must ensure that their ambient air
quality complies with the national standard. To that end, the
Clean Air Act requires States to adopt State implementation
plans, or SIPs, that provide for implementation, maintenance
and enforcement of the national standard. Id. §
7410(a)(1). If a State fails to submit a SIP, or if EPA
disapproves it, EPA must issue a federal implementation plan,
or FIP, to correct any deficiency. Id. §
regulation of air quality faces a confounding variable. Air
pollution, once emitted, drifts with the wind. Upwind
pollutants affect air quality in downwind States via various
chemical processes. Ozone, for example, forms from the
interaction of nitrogen oxides (NOx) and volatile organic
compounds (VOCs) in the presence of sunlight. For downwind
States, upwind emissions of these ozone precursors can pose a
significant problem. According to a study referenced by EPA,
on average, over three-quarters of the ground-level ozone in
downwind States comes from upwind emissions. 81 Fed. Reg. at
included a Good Neighbor Provision in the Clean Air Act to
address the problem of upwind States' pollution impairing
downwind States' air quality. The Provision prohibits
States from "emitting any air pollutant in amounts"
that will "contribute significantly to
nonattainment" or "interfere with maintenance"
of air quality in other States. 42 U.S.C. §
addressed the Good Neighbor Provision's requirements in a
series of rulemakings. In 2011, EPA promulgated the
Cross-State Air Pollution Rule (CSAPR), which applied to
States whose upwind pollution violated good neighbor
obligations under the 1997 ozone NAAQS and the 1997 and 2006
fine particulate matter NAAQS. See 76 Fed. Reg. 48,
208 (Aug. 8, 2011).
2008, EPA reduced the ozone NAAQS from 80 parts per billion
(ppb) to 75 ppb. As a result, EPA promulgated the rule at
issue in this case: an update to the CSAPR for eastern States
that accounts for the stricter 2008 ozone NAAQS. See
Cross-State Air Pollution Rule Update for the 2008 Ozone
NAAQS, 81 Fed. Reg. 74, 504 (Oct. 26, 2016) (Update Rule).
Under the Update Rule, EPA proceeded in four steps.
first step, EPA identified downwind States expected to have
problems attaining or maintaining air quality in compliance
with the 2008 ozone NAAQS. To identify those States, EPA had
to estimate the future air quality in each State.
Id. at 74, 516-17. EPA devised a measure to turn
2011 ozone measurements into 2017 projections.
started with 2011 modeled data from "receptors,"
devices in each State that measure air quality. EPA modeled
ozone concentrations in a three-by-three grid around each
receptor. EPA chose the ten days with the highest projected
ozone concentration, noted which of the nine 12-km2 grid
cells had the highest ozone concentration on that day, and
averaged the ten observations. See id. at 74,
526-27. EPA then ran the model for 2017, inputting 2011
environmental conditions (like rainfall and fire emissions)
but projected 2017 NOx emissions rates. The percentage change
from 2011 to 2017 was deemed a receptor's "relative
response factor," which measures the sensitivity of an
area to ozone formation. Multiplying a 2011 observation by
the relevant response factor yielded a projection for 2017
for the receptor.
projected 2017 ozone levels for each receptor by applying the
relative response factor to three "design values"
from a receptor across a five-year period. A "design
value" is a three-year historical average of monitored
ozone data. The selected design values represented 2009-2011,
2010-2012, and 2011-2013. See id. at 74, 532.
Multiplying the three design values by the applicable
relative response factor resulted in three different ozone
projections for 2017.
light of the 2008 ozone NAAQS of 75 ppb, EPA considered any
projected value of up to 75.9 ppb to constitute attainment.
Id. EPA defined a receptor to be in
"nonattainment" status if the average of its three
projected design values and its most recent monitored design
value (2013-2015) exceeded the NAAQS. Id. EPA also
identified a third category (beyond attainment and
nonattainment): a receptor would be deemed in
"maintenance" status if the highest of the three
projected design values exceeded the NAAQS but the other two
values did not. Id.
second step, EPA identified those upwind States whose
pollution was linked to nonattainment or nonmaintenance at
downwind receptors. EPA quantified the impact of each
State's pollution on downwind receptors using a model
that apportioned responsibility for ozone formation at a
given receptor to various categories of emitters. See
id. at 74.536. EPA then multiplied a given State's
contribution factor by the projected average ozone
concentration at each receptor (calculated in Step 1) to
yield each State's contribution to ozone formation at
each downwind receptor.
EPA screened out States whose contributions to ozone
formation in a downwind State comprised less than 1% of the
NAAQS (0.75 ppb) in that downwind State. See id. at
74.537. In other words, EPA construed "contribute
significantly" and "interfere with" in the
Good Neighbor Provision to require an upwind State's
pollution to cause at least 0.75 ppb of ozone formation in a
downwind State. EPA's analysis concluded that
twenty-three States and the District of Columbia were linked
to nonattainment or nonmaintenance in at least one downwind
State. Fourteen States' contributions fell below the 1%
threshold and thus were screened out at this step. See
third step, EPA quantified the amount of emissions reductions
that the twenty-three upwind States and the District of
Columbia would be required to make under the Good Neighbor
Provision. To do so, EPA applied a multifactor test that
balanced costs against benefits.
first measured the emissions reductions that would occur at
various levels of cost controls. It began with a baseline
case (i.e., a cost-control level of $0). It then ran
the model for a cost-control level of $800 per ton-in other
words, measuring the emissions reductions that would occur if
EPA required all States to apply all possible emissions
controls at its EGUs (electric generating units, or power
plants) up to the marginal price of $800 per ton of NOx.
See id. at 74, 540-41. EPA then ran the model for
higher cost-control levels of $1, 400/ton, $3, 400/ton, $5,
000/ton, and $6, 400/ton. For each of these cost-control
levels, EPA also estimated the air quality improvements that
would occur at each receptor in downwind States. Comparing
the cost-control levels against the resulting emissions
reductions and air quality improvements, EPA concluded that
the cost-control level of $1, 400 per ton represented the
point at which upwind "NOx reduction potential and
corresponding downwind ozone air quality improvements are
maximized with respect to marginal cost" - that is, the
point at which EPA would get the biggest bang for its buck.
Id. at 74, 550.
of that analysis, EPA also performed an
"overcontrol" analysis to ensure that no upwind
State would be required to reduce its emissions more than
called for by the Good Neighbor Provision. Overcontrol would
occur if either (1) a State's downwind receptors all
reduced their ozone concentrations below the NAAQS, or (2) a
State's contributions to all downwind receptors was
reduced below the 1% contribution threshold of 0.75 ppb.
See EME Homer City Gen., L.P. v. EPA, 572 U.S. 489,
521 (2014) ("EME Homer II"). EPA concluded
that neither of those indicia of overcontrol existed at the
$800/ton and $1, 400/ton cost-control levels. See 81
Fed. Reg. at 74, 551-52.
fourth step, EPA quantified State emissions
"budgets" by calculating the emissions amount that
would occur under $1, 400/ton cost controls. Under the CSAPR,
States may emit more NOx than permitted by their budgets by
acquiring allowances from other States, and States may sell
allowances to other States if they reduce their emissions
more than required by their budgets. Id. at 74, 554.
But to ensure that a State does not entirely skirt its good
neighbor obligations by buying a large number of allowances,
each State is limited to emitting no more than 121% of the
emissions budget (the "assurance level"),
irrespective of allowances. See id.
EPA promulgated the original CSAPR, various parties brought a
challenge to that rule. We initially vacated the rule,
see EME Homer City Generation, L.P. v. EPA, 696 F.3d
7 (D.C. Cir. 2012) ("EME Homer I"), but
the Supreme Court reversed our decision and upheld the rule
in its entirety, although it left open the possibility of
as-applied challenges, see EME Homer II, 572 U.S. at
495. On remand, we found that emissions budgets for thirteen
States were invalid due to overcontrol. EME Homer City
Generation, L.P. v. EPA, 795 F.3d 118, 124 (D.C. Cir.
2015) ("EME Homer III").
2016, EPA promulgated the Update Rule at issue here. A number
of parties have petitioned for review of the Rule in this
court. See 42 U.S.C. § 7607(d)(9). One group of
petitioners, including environmental groups and the State of
Delaware (collectively, Environmental Petitioners), contends
that EPA was required to adopt a more stringent rule. Another
group of petitioners, including various States and industry
groups (collectively, State and Industry Petitioners), argues
that EPA was required to issue a more lenient rule.
begin by addressing Environmental Petitioners' claims.
Environmental Petitioners challenge the Update Rule on the
grounds that it: (i) fails to square with the statutory
attainment deadlines, (ii) makes impermissible modeling and
implementation choices, and (iii) incorrectly classifies
Delaware as an attaining downwind State.
Rule must be set aside if it is "arbitrary, capricious,
an abuse of discretion, or otherwise not in accordance with
law" or "in excess of statutory jurisdiction,
authority, or limitations." 42 U.S.C. § 7607(d)(9).
That standard is "essentially the same" as the
familiar standard of review contained in § 706(2) of the
Administrative Procedure Act. Ethyl Corp. v. EPA, 51
F.3d 1053, 1064 (D.C. Cir. 1995).
that standard, we agree with Environmental Petitioners that
the Rule is inconsistent with the Act's attainment
deadlines. We reject Environmental Petitioners' remaining
first consider Environmental Petitioners' argument that
the Update Rule infringes the Good Neighbor Provision by
permitting upwind States to continue their significant
contributions to downwind air quality problems for too long-
i.e., past the statutory deadlines for nonattaining
downwind areas to meet the NAAQS for ozone. In fact, EPA set
no concrete deadline at all for upwind States to eliminate
their contributions to downwind States' nonattainment.
Good Neighbor Provision requires States to submit SIPs that
"prohibit, consistent with the provisions of this
subchapter [i.e., Title I of the Act], any source .
. . from emitting any air pollutant in amounts which will . .
. contribute significantly to nonattainment in . . . any
other State with respect to any" NAAQS. 42 U.S.C. §
7410(a)(2)(D)(i). If a State fails to submit a SIP or submits
one deemed inadequate, such that EPA must then prepare a FIP,
EPA must likewise satisfy the Good Neighbor Provision in the
FIP. See EME Homer II, 572 U.S. at 512-14 &
question we face is one of timing: the Good Neighbor
Provision calls for upwind States to eliminate their
significant contributions to air pollution in downwind
States, but by when must upwind States do so? In particular,
does the Provision call for upwind States to eliminate their
significant contributions to downwind pollution by the
deadlines for downwind areas to comply with the relevant
NAAQS-here, the 2008 NAAQS for ozone?
deadlines are prescribed by the Act. The Act first tasks EPA
with designating as "nonattainment" any area that
does not meet a NAAQS. See 42 U.S.C. §
7407(d)(1)(A). For areas designated as nonattainment for
ozone, the Act specifies that each State must secure
compliance "as expeditiously as practicable but not
later than" a date certain. Id. §
7511(a)(1) (emphasis added). That date is July 20, 2018, for
areas in "moderate" nonattainment with respect to
the 2008 NAAQS (and was July 20, 2015 for areas in
"marginal" nonattainment). See Nat. Res. Def.
Council v. EPA, 777 F.3d. 456, 465-66 (D.C. Cir. 2014);
Implementation of the 2008 National Ambient Air Quality
Standards for Ozone: State Implementation Plan Requirements,
80 Fed. Reg. 12, 264, 12, 268 (Mar. 6, 2015).
Update Rule does not require upwind States to eliminate their
significant contributions to downwind ozone pollution by that
date-or by any date, for that matter. EPA acknowledges that,
except for one State (Tennessee), it "is only
quantifying a subset of each State's emission
reduction obligation pursuant to the good neighbor
provision." 81 Fed. Reg. at 74, 520 (emphasis added);
see id. at 74, 508 n.19. And the Rule states that it
represents only a "first, partial step to addressing a
given upwind State's significant contribution to downwind
air quality impacts for the 2008 ozone NAAQS."
Id. at 74, 522. That is in large part because the
Update Rule confines itself to addressing upwind
contributions from EGUs due to an ostensible lack of
information about non-EGUs. EPA "expects that a full
resolution of upwind transport obligations would require
emission reductions from sectors besides EGUs," along
with "further EGU reductions that are achievable after
2017." Id. The upshot is that, while the Rule
calls for a certain level of reductions in upwind
contributions by the 2017 ozone year-"in time to assist
downwind states to meet the July 2018 attainment
deadlines"-the Rule does not purport to require upwind
States to fully meet their good neighbor obligations by that
the Update Rule, then, downwind States face a dilemma. On one
hand, they operate under a statutory obligation to secure
compliance with the ozone NAAQS by July 20, 2018. But on the
other hand, the Rule does not require upwind States to
eliminate their significant contributions to downwind
pollution by that deadline. Environmental Petitioners argue
that the Rule is inconsistent with the Act in failing to
require upwind States to eliminate their significant
contributions in accordance with the deadline by which
downwind States must come into compliance with the NAAQS. We
conclusion follows from our decision in North Carolina v.
EPA, 531 F.3d 896 (D.C. Cir. 2008). There, we considered
essentially the same question we now face here: whether EPA
can allow upwind States to continue their significant
contributions to downwind pollution beyond the statutory
deadlines for downwind States to meet the NAAQS. North
Carolina involved the Clean Air Interstate Rule (CAIR),
a prior EPA effort to implement the Good Neighbor Provision
with regard to the then-applicable NAAQS for two pollutants,
fine particulate matter (PM2.5) and ozone. See
id. at 903-06. Although the statutory deadline for
nonattaining areas to comply with those NAAQS was 2010, CAIR
gave upwind States until 2015 to eliminate their significant
contributions to downwind nonattainment. See id. at
that CAIR's "deadline of 2015 [was] unlawful."
Id. at 913. We explained that, under the terms of
the Good Neighbor Provision, upwind States must eliminate
their significant contributions "consistent with the
provisions" of Title I of the Act. See id. at
911-12; 42 U.S.C. § 7410(a)(2)(D)(i). And the
incorporated provisions of Title I, we further explained,
include ones setting the attainment deadlines for downwind
areas. See 42 U.S.C. § 7502(a)(2)(A)
(PM2.5); id. § 7511 (ozone). But
under CAIR, "downwind nonattainment areas [were required
to] attain NAAQS for ozone and PM2.5" by
2010, "without the elimination" by then "of
upwind states' significant contribution to downwind
nonattainment, forcing downwind areas to make greater
reductions than [the Good Neighbor Provision] requires."
North Carolina, 531 F.3d at 912. As a result, we
concluded, "EPA ignored its statutory mandate to
promulgate CAIR consistent with the provisions in Title I
mandating compliance deadlines for downwind states in
that is equally true here. Just as with CAIR, the CSAPR
Update Rule we consider in this case fails to eliminate
upwind States' significant contributions to downwind
pollution by the statutory deadline for downwind States to
meet the NAAQS for ozone. That in turn "forc[es]
downwind areas to make greater reductions than [the Good
Neighbor Provision] requires." Id. Indeed, CAIR
at least imposed some deadline for upwind States to
fully satisfy their good neighbor obligations, albeit a
deadline we held was too late. Here, by contrast, EPA
established no deadline at all for upwind States to eliminate
their significant contributions. And while EPA concluded that
requiring upwind States to meet their good neighbor
obligations by the 2018 attainment deadline "simply
[was] not feasible in the existing timeframe," 81 Fed.
Reg. 74, 523, in North Carolina, EPA had likewise
sought (unsuccessfully) to rely "on reasons of
feasibility." 531 F.3d at 911.
contends that North Carolina required it only to
"consider" the attainment deadline in some fashion
when establishing upwind States' good neighbor
responsibilities, not to align the attainment deadline with
the deadline for satisfying good neighbor obligations. And
EPA argues that the Update Rule gives the requisite
consideration to the July 2018 attainment deadline by
requiring at least some level of good neighbor reductions by
Carolina, though, requires more than merely
"considering" attainment deadlines in that manner.
In fact, CAIR provided for a first phase of reductions in
upwind contributions to take place before the attainment
deadlines. See id. at 903. But that was not enough
to satisfy the statute. The problem was that the eventual
elimination of significant upwind contributions in the second
phase of reductions would occur only long after the
attainment deadlines had passed.
explained that EPA needed to "harmonize" the
"Phase Two deadline for upwind contributors to
eliminate their significant contribution with the
attainment deadlines for downwind areas." Id.
at 912 (emphasis added). Otherwise, downwind areas would need
to attain the NAAQS "without the elimination of upwind
states' significant contribution." Id. The
Rule here creates the same situation. (And we note it does so
with respect to both the 2018 and 2015 deadlines. Although
EPA contends that the claim as to the 2015 deadlines was
forfeited, we disagree. See Comment of Sierra Club
et al., at 8-9, EPA Docket No. 2015-0500-0287 (Feb. 1, 2016),
notes that, when we addressed the issue of the appropriate
remedy at the conclusion of our opinion in North
Carolina, we observed that EPA would need to
"decide what date, whether 2015 or earlier, is
as expeditious as practicable for states to eliminate their
significant contributions to downwind nonattainment."
561 F.3d at 930 (emphasis added). But our reference to 2015
did not suggest that EPA could delay the deadline for upwind
States to eliminate their significant contributions until 5
years after the 2010 attainment deadline. The entire object
of our analysis was to reject the notion that the Phase Two
deadline of 2015 could be squared with the Good Neighbor
Provision. See id. at 913 (EPA operated "under
the assumption that 2015 was an appropriate deadline for CAIR
compliance. It is not."). Rather, we presumably referred
to 2015 because, as we had earlier specifically noted, EPA
has separate statutory authority to extend the deadline for
attaining the NAAQS for PM2.5-and thereby
correspondingly also extend the good neighbor deadline-for up
to five years, or until 2015. See id. at 911 (citing
42 U.S.C. § 7502(a)(2)(A)).
under our decision in North Carolina, the Good
Neighbor Provision calls for elimination of upwind
States' significant contributions on par with the
relevant downwind attainment deadlines. The Update Rule fails
to do so.
Carolina's understanding of the Good Neighbor
Provision is confirmed by examining the Update Rule under the
framework set out in Chevron U.S.A. Inc. v. Nat. Res.
Def. Council, Inc., 467 U.S. 837 (1984). See EME
Homer II, 572 U.S. at 512-14 (evaluating previous EPA
implementation of the Good Neighbor Provision under
Chevron); see also Util. Air Regulatory Grp. v.
EPA, 573 U.S. 302, 315 (2014) ("We review EPA's
interpretations of the Clean Air Act using the standard set
forth in Chevron.").
Chevron, we presume that when an agency-administered
statute is ambiguous with respect to what it prescribes,
Congress has empowered the agency to resolve the
ambiguity." Util. Air. Regulatory Grp., 573
U.S. at 315. The question then "is whether in doing so
the agency has acted reasonably and thus has 'stayed
within the bounds of its statutory authority.'"
Id. (quoting Arlington v. FCC, 569 U.S.
290, 296 (2013)). Here, the Update Rule's open-ended
compliance timeframe exceeds the bounds of EPA's
statutory authority by allowing upwind States to continue
their significant contributions to downwind nonattainment
well past the deadline for downwind areas to comply with the
threshold question under Chevron ordinarily would be
whether the statute is ambiguous on that issue, such that the
agency then would have discretion to choose among reasonable
interpretations. E.g., id. But there is no need to
resolve that threshold issue in this case, because,
regardless of ambiguity, the Update Rule amounts to an
unreasonable-and hence impermissible-interpretation of the
statute in any event. See Michigan v. EPA, 135 S.Ct.
2699, 2707 (2015); Massachusetts v. U.S. Dep't of
Transp., 93 F.3d 890, 892 (D.C. Cir. 1996) (declining to
resolve how Chevron might apply because "the
agency's determination here cannot be upheld with or
Good Neighbor Provision, as North Carolina
emphasized, requires upwind States to eliminate their
significant contributions to downwind pollution
"consistent with the provisions of this
subchapter," i.e., Title I of the Clean Air
Act. 42 U.S.C. § 7410(a)(2). One of the "provisions
of this subchapter" is § 7511(a)(1), which in turn
requires downwind areas in moderate nonattainment to attain
the NAAQS by July 20, 2018. See id. §
7511(a)(1); 81 Fed. Reg. at 74, 507. The statute cannot
reasonably be understood to enable upwind States to continue
their significant contributions ...