(Slip Opinion)              OCTOBER TERM, 2013                                       1

                                       Syllabus

         NOTE: Where it is feasible, a syllabus (headnote) will be released, as is
       being done in connection with this case, at the time the opinion is issued.
       The syllabus constitutes no part of the opinion of the Court but has been
       prepared by the Reporter of Decisions for the convenience of the reader.
       See United States v. Detroit Timber & Lumber Co., 200 U. S. 321, 337.


SUPREME COURT OF THE UNITED STATES

                                       Syllabus

  ENVIRONMENTAL PROTECTION AGENCY ET AL. v. 

    EME HOMER CITY GENERATION, L. P., ET AL. 


CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR
          THE DISTRICT OF COLUMBIA CIRCUIT

  No. 12–1182. Argued December 10, 2013—Decided April 29, 2014*
Congress and the Environmental Protection Agency (EPA or Agency)
  have, over the course of several decades, made many efforts to deal
  with the complex challenge of curtailing air pollution emitted in up-
  wind States, but causing harm in other, downwind States. As rele-
  vant here, the Clean Air Act (CAA or Act) directs EPA to establish
  national ambient air quality standards (NAAQS) for pollutants at
  levels that will protect public health. 42 U. S. C. §§7408, 7409. Once
  EPA settles on a NAAQS, the Agency must designate “nonattain-
  ment” areas, i.e., locations where the concentration of a regulated pol-
  lutant exceeds the NAAQS. §7407(d). Each State must submit a
  State Implementation Plan, or SIP, to EPA within three years of any
  new or revised NAAQS. §7410(a)(1). From the date EPA determines
  that a State SIP is inadequate, the Agency has two years to promul-
  gate a Federal Implementation Plan, or FIP. §7410(c)(1). Among
  other components, the CAA mandates SIP compliance with the Good
  Neighbor Provision, which requires SIPs to “contain adequate provi-
  sions . . . prohibiting . . . any source or other type of emissions activity
  within the State from emitting any air pollutant in amounts which
  will . . . contribute significantly to nonattainment in, or interfere with
  maintenance by, any other State with respect to any . . . [NAAQS].”
  §7410(a)(2)(D)(i).
     Several times over the past two decades, EPA has attempted to
  delineate the Good Neighbor Provision’s scope by identifying when
——————
  * Together with No. 12–1183, American Lung Association et al. v.
EME Homer City Generation, L. P., et al., also on certiorari to the same
court.
2            EPA v. EME HOMER CITY GENERATION, L. P.

                                 Syllabus

    upwind States “contribute significantly” to nonattainment downwind.
    The D. C. Circuit found fault with the Agency’s 2005 attempt, the
    Clean Air Interstate Rule, or CAIR, which regulated both nitrogen
    oxide (NOX) and sulfur dioxide (SO2) emissions, the gasses at issue
    here. The D. C. Circuit nevertheless left CAIR temporarily in place,
    while encouraging EPA to act with dispatch in dealing with problems
    the court had identified.
       EPA’s response to that decision is the Cross-State Air Pollution
    Rule (Transport Rule), which curbs NOX and SO2 emissions in 27 up-
    wind States to achieve downwind attainment of three NAAQS. Un-
    der the Transport Rule, an upwind State “contribute[d] significantly”
    to downwind nonattainment to the extent its exported pollution both
    (1) produced one percent or more of a NAAQS in at least one down-
    wind State and (2) could be eliminated cost-effectively, as determined
    by EPA. Upwind States are obliged to eliminate only emissions
    meeting both of these criteria. Through complex modeling, EPA cre-
    ated an annual emissions “budget” for each regulated State upwind,
    representing the total quantity of pollution an upwind State could
    produce in a given year under the Transport Rule. Having earlier de-
    termined each regulated State’s SIP to be inadequate, EPA, contem-
    poraneous with the Transport Rule, promulgated FIPs allocating
    each State’s emissions budgets among its in-state pollution sources.
       A group of state and local governments (State respondents), joined
    by industry and labor groups (Industry respondents), petitioned for
    review of the Transport Rule in the D. C. Circuit. The court vacated
    the rule in its entirety, holding that EPA’s actions exceeded the
    Agency’s statutory authority in two respects. Acknowledging that
    EPA’s FIP authority is generally triggered when the Agency disap-
    proves a SIP, the court was nevertheless concerned that States would
    be incapable of fulfilling the Good Neighbor Provision without prior
    EPA guidance. The court thus concluded that EPA must give States
    a reasonable opportunity to allocate their emission budgets before is-
    suing FIPs. The court also found the Agency’s two-part interpreta-
    tion of the Good Neighbor Provision unreasonable, concluding that
    EPA must disregard costs and consider exclusively each upwind
    State’s physically proportionate responsibility for air quality prob-
    lems downwind.
Held:
    1. The CAA does not command that States be given a second oppor-
 tunity to file a SIP after EPA has quantified the State’s interstate
 pollution obligations. Pp. 13–18.
       (a) The State respondents do not challenge EPA’s disapproval of
 any particular SIP. Instead, they argue that, notwithstanding these
 disapprovals, the Agency was still obliged to grant upwind States an
                   Cite as: 572 U. S. ____ (2014)                     3

                              Syllabus

additional opportunity to promulgate adequate SIPs after EPA had
set the State’s emission budget. This claim does not turn on the va-
lidity of the prior SIP disapprovals, but on whether the CAA requires
EPA do more than disapprove a SIP to trigger the Agency’s authority
to issue a FIP. Pp. 13–14.
      (b) The CAA’s plain text supports the Agency: Disapproval of a
SIP, without more, triggers EPA’s obligation to issue a FIP. The
statute sets precise deadlines for the States and EPA. Once EPA is-
sues any new or revised NAAQS, a State “shall” propose a SIP within
three years, 42 U. S. C. §7410(a)(1), and that SIP “shall” include, in-
ter alia, provisions adequate to satisfy the Good Neighbor Provision,
§7410(a)(2). If the EPA finds a SIP inadequate, the Agency has a
statutory duty to issue a FIP “at any time” within two years.
§7410(c)(1). However sensible the D. C. Circuit’s exception to this
strict time prescription may be, a reviewing court’s “task is to apply
the text [of the statute], not to improve upon it.” Pavelic & LeFlore v.
Marvel Entertainment Group, Div. of Cadence Industries Corp., 493
U. S. 120, 126. Nothing in the Act differentiates the Good Neighbor
Provision from the several other matters a State must address in its
SIP. Nor does the Act condition the duty to promulgate a FIP on
EPA’s having first quantified an upwind State’s good neighbor obliga-
tions. By altering Congress’ SIP and FIP schedule, the D. C. Circuit
allowed a delay Congress did not order and placed an information
submission obligation on EPA Congress did not impose. Pp. 14–17.
      (c) The fact that EPA had previously accorded upwind States a
chance to allocate emission budgets among their in-state sources does
not show that the Agency acted arbitrarily by refraining to do so
here. EPA retained discretion to alter its course provided it gave a
reasonable explanation for doing so. Motor Vehicle Mfrs. Assn. of
United States, Inc. v. State Farm Mut. Automobile Ins. Co., 463 U. S.
29, 42. Here, the Agency had been admonished by the D. C. Circuit
to act with dispatch in amending or replacing CAIR. Endeavoring to
satisfy that directive, EPA acted speedily, issuing FIPs and the
Transport Rule contemporaneously. Pp. 17–18.
   2. EPA’s cost-effective allocation of emission reductions among up-
wind States is a permissible, workable, and equitable interpretation
of the Good Neighbor Provision. Pp. 18–31.
      (a) Respondents’ attack on EPA’s interpretation of the Good
Neighbor Provision is not foreclosed by §7607(d)(7)(B), which pro-
vides that “[o]nly an objection to a rule . . . raised with reasonable
specificity during the period for public comment . . . may be raised
during judicial review.” Even assuming that respondents failed to
object to the Transport Rule with “reasonable specificity,” that lapse
is not jurisdictional. Section 7607(d)(7)(B) is a “mandatory,” but not
4            EPA v. EME HOMER CITY GENERATION, L. P.

                                  Syllabus

    “jurisdictional,” rule, see Arbaugh v. Y & H Corp., 546 U. S. 500, 510,
    which speaks to a party’s procedural obligations, not a court’s author-
    ity, see Kontrick v. Ryan, 540 U. S. 443, 455. Because EPA did not
    press this argument unequivocally before the D. C. Circuit, it does
    not pose an impassable hindrance to this Court’s review. Pp. 18–19.
         (b) This Court routinely accords dispositive effect to an agency’s
    reasonable interpretation of ambiguous statutory language. The
    Good Neighbor Provision delegates authority to EPA at least as cer-
    tainly as the CAA provisions involved in Chevron U. S. A. Inc. v.
    Natural Resources Defense Council, Inc., 467 U. S. 837. EPA’s au-
    thority to reduce upwind pollution extends only to those “amounts” of
    pollution that “contribute significantly to nonattainment” in down-
    wind States. §7410(a)(2)(D)(i). Because a downwind State’s excess
    pollution is often caused by multiple upwind States, however, EPA
    must address how to allocate responsibility among multiple contribu-
    tors. The Good Neighbor Provision does not dictate a method of ap-
    portionment. Nothing in the provision, for example, directs the pro-
    portional allocation method advanced by the D. C. Circuit, a method
    that works neither mathematically nor in practical application. Un-
    der Chevron, Congress’ silence effectively delegates authority to EPA
    to select from among reasonable options. See United States v. Mead
    Corp., 533 U. S. 218, 229.
       EPA’s chosen allocation method is a “permissible construction of
    the statute.” Chevron, 467 U. S., at 843. The Agency, tasked with
    choosing which among equal “amounts” to eliminate, has chosen sen-
    sibly to reduce the amount easier, i.e., less costly, to eradicate. The
    Industry respondents argue that the final calculation cannot rely on
    costs, but nothing in the Good Neighbor Provision’s text precludes
    that choice. And using costs in the Transport Rule calculus is an effi-
    cient and equitable solution to the allocation problem the Good
    Neighbor Provision compels the Agency to address. Efficient because
    EPA can achieve the same levels of attainment, i.e., of emission re-
    ductions, the proportional approach aims to achieve, but at a much
    lower overall cost. Equitable because, by imposing uniform cost
    thresholds on regulated States, EPA’s rule subjects to stricter regula-
    tion those States that have done less in the past to control their pol-
    lution. Pp. 20–28.
         (c) Wholesale invalidation of the Transport Rule is not justified
    by either of the D. C. Circuit’s remaining objections: that the
    Transport Rule leaves open the possibility that a State might be
    compelled to reduce emissions beyond the point at which every af-
    fected downwind State is in attainment, so-called “over-control”; and
    that EPA’s use of costs does not foreclose the possibility that an up-
    wind State would be required to reduce its emissions by so much that
                      Cite as: 572 U. S. ____ (2014)                     5

                                 Syllabus

  the State would be placed below the one-percent mark EPA set as the
  initial threshold of “significan[ce].” First, instances of “over-control”
  in particular downwind locations may be incidental to reductions
  necessary to ensure attainment elsewhere. As the Good Neighbor
  Provision seeks attainment in every downwind State, however, ex-
  ceeding attainment in one State cannot rank as “over-control” unless
  unnecessary to achieving attainment in any downwind State. Sec-
  ond, the EPA must have leeway in fulfilling its statutory mandate to
  balance the possibilities of over-control and “under-control,” i.e., to
  maximize achievement of attainment downwind. Finally, in a volu-
  minous record, involving thousands of upwind-to-downwind linkages,
  respondents point to only a few instances of “unnecessary” emission
  reductions, and even those are contested by EPA. Pp. 28–31.
696 F. 3d 7, reversed and remanded.

  GINSBURG, J., delivered the opinion of the Court, in which ROBERTS,
C. J., and KENNEDY, BREYER, SOTOMAYOR, and KAGAN, JJ., joined. SCAL-
IA, J., filed a dissenting opinion, in which THOMAS, J., joined. ALITO, J.,
took no part in the consideration or decision of the cases.
                        Cite as: 572 U. S. ____ (2014)                              1

                             Opinion of the Court


     NOTICE: This opinion is subject to formal revision before publication in the
     preliminary print of the United States Reports. Readers are requested to
     notify the Reporter of Decisions, Supreme Court of the United States, Wash­
     ington, D. C. 20543, of any typographical or other formal errors, in order
     that corrections may be made before the preliminary print goes to press.


SUPREME COURT OF THE UNITED STATES
                                   _________________

                         Nos. 12–1182 and 12–1183
                                   _________________


  ENVIRONMENTAL PROTECTION AGENCY ET AL.,
               PETITIONERS
12–1182             v.
  EME HOMER CITY GENERATION, L. P., ET AL.; AND

      AMERICAN LUNG ASSOCIATION ET AL.,
                PETITIONERS
12–1183              v.
    EME HOMER CITY GENERATION, L. P., ET AL.
ON WRITS OF CERTIORARI TO THE UNITED STATES COURT OF
    APPEALS FOR THE DISTRICT OF COLUMBIA CIRCUIT
                                 [April 29, 2014]

   JUSTICE GINSBURG delivered the opinion of the Court.
   These cases concern the efforts of Congress and the
Environmental Protection Agency (EPA or Agency) to cope
with a complex problem: air pollution emitted in one
State, but causing harm in other States. Left unregulated,
the emitting or upwind State reaps the benefits of the
economic activity causing the pollution without bearing all
the costs. See Revesz, Federalism and Interstate Envi­
ronmental Externalities, 144 U. Pa. L. Rev. 2341, 2343
(1996). Conversely, downwind States to which the pollu­
tion travels are unable to achieve clean air because of the
influx of out-of-state pollution they lack authority to con­
trol. See S. Rep. No. 101–228, p. 49 (1989). To tackle the
2        EPA v. EME HOMER CITY GENERATION, L. P.

                     Opinion of the Court

problem, Congress included a Good Neighbor Provision in
the Clean Air Act (Act or CAA). That provision, in its
current phrasing, instructs States to prohibit in-state
sources “from emitting any air pollutant in amounts which
will . . . contribute significantly” to downwind States’
“nonattainment . . . , or interfere with maintenance,” of
any EPA-promulgated national air quality standard. 42
U. S. C. §7410(a)(2)(D)(i).
   Interpreting the Good Neighbor Provision, EPA adopted
the Cross-State Air Pollution Rule (commonly and herein­
after called the Transport Rule). The rule calls for consid­
eration of costs, among other factors, when determining
the emission reductions an upwind State must make to
improve air quality in polluted downwind areas. The
Court of Appeals for the D. C. Circuit vacated the rule in
its entirety. It held, 2 to 1, that the Good Neighbor Provi­
sion requires EPA to consider only each upwind State’s
physically proportionate responsibility for each downwind
State’s air quality problem. That reading is demanded,
according to the D. C. Circuit, so that no State will be
required to decrease its emissions by more than its ratable
share of downwind-state pollution.
   In Chevron U. S. A. Inc. v. Natural Resources Defense
Council, Inc., 467 U. S. 837 (1984), we reversed a D. C.
Circuit decision that failed to accord deference to EPA’s
reasonable interpretation of an ambiguous Clean Air Act
provision. Satisfied that the Good Neighbor Provision
does not command the Court of Appeals’ cost-blind con­
struction, and that EPA reasonably interpreted the provi­
sion, we reverse the D. C. Circuit’s judgment.
                              I

                             A

  Air pollution is transient, heedless of state boundaries.
Pollutants generated by upwind sources are often trans­
ported by air currents, sometimes over hundreds of miles,
                    Cite as: 572 U. S. ____ (2014)                 3

                        Opinion of the Court

to downwind States. As the pollution travels out of state,
upwind States are relieved of the associated costs. Those
costs are borne instead by the downwind States, whose
ability to achieve and maintain satisfactory air quality is
hampered by the steady stream of infiltrating pollution.
   For several reasons, curtailing interstate air pollution
poses a complex challenge for environmental regulators.
First, identifying the upwind origin of downwind air pollu­
tion is no easy endeavor. Most upwind States propel
pollutants to more than one downwind State, many
downwind States receive pollution from multiple upwind
States, and some States qualify as both upwind and
downwind. See Brief for Federal Petitioners 6. The over­
lapping and interwoven linkages between upwind and
downwind States with which EPA had to contend number
in the thousands.1
   Further complicating the problem, pollutants do not
emerge from the smokestacks of an upwind State and
uniformly migrate downwind. Some pollutants stay with­
in upwind States’ borders, the wind carries others to
downwind States, and some subset of that group drifts to
States without air quality problems. “The wind bloweth
where it listeth, and thou hearest the sound thereof, but
canst not tell whence it cometh, and whither it goeth.”
The Holy Bible, John 3:8 (King James Version). In craft­
ing a solution to the problem of interstate air pollution,
regulators must account for the vagaries of the wind.
   Finally, upwind pollutants that find their way down­
wind are not left unaltered by the journey. Rather, as the
gases emitted by upwind polluters are carried downwind,
they are transformed, through various chemical processes,
into altogether different pollutants. The offending gases
——————
  1 For the rule challenged here, EPA evaluated 2,479 separate link­

ages between downwind and upwind States. Brief for Federal Petition­
ers 6.
4        EPA v. EME HOMER CITY GENERATION, L. P.

                     Opinion of the Court

at issue in these cases—nitrogen oxide (NOX) and sulfur
dioxide (SO2)—often develop into ozone and fine particu­
late matter (PM2.5) by the time they reach the atmos­
pheres of downwind States. See 76 Fed. Reg. 48222–
48223 (2011). See also 69 Fed. Reg. 4575–4576 (2004)
(describing the components of ozone and PM2.5). Down­
wind air quality must therefore be measured for ozone and
PM2.5 concentrations. EPA’s chore is to quantify the
amount of upwind gases (NOX and SO2) that must be
reduced to enable downwind States to keep their levels of
ozone and PM2.5 in check.
                               B
   Over the past 50 years, Congress has addressed inter­
state air pollution several times and with increasing rigor.
In 1963, Congress directed federal authorities to “encour­
age cooperative activities by the States and local govern­
ments for the prevention and control of air pollution.” 77
Stat. 393, 42 U. S. C. §1857a (1964 ed.). In 1970, Congress
made this instruction more concrete, introducing features
still key to the Act. For the first time, Congress directed
EPA to establish national ambient air quality standards
(NAAQS) for pollutants at levels that will protect public
health. See 84 Stat. 1679–1680, as amended, 42 U. S. C.
§§7408, 7409 (2006 ed.). Once EPA settles on a NAAQS,
the Act requires the Agency to designate “nonattainment”
areas, i.e., locations where the concentration of a regulated
pollutant exceeds the NAAQS. §7407(d).
   The Act then shifts the burden to States to propose
plans adequate for compliance with the NAAQS. Each
State must submit a State Implementation Plan, or SIP,
to EPA within three years of any new or revised NAAQS.
§7410(a)(1). If EPA determines that a State has failed to
submit an adequate SIP, either in whole or in part, the Act
requires the Agency to promulgate a Federal Implementa­
tion Plan, or FIP, within two years of EPA’s determina­
                    Cite as: 572 U. S. ____ (2014)                 5

                        Opinion of the Court

tion, “unless the State corrects the deficiency” before a FIP
is issued. §7410(c)(1).2
   The Act lists the matters a SIP must cover. Among SIP
components, the 1970 version of the Act required SIPs to
include “adequate provisions for intergovernmental coop­
eration” concerning interstate air pollution. §110(a)(2)(E),
84 Stat. 1681, 42 U. S. C. §1857c–5(a)(2)(E). This statutory
requirement, with its text altered over time, has come
to be called the Good Neighbor Provision.
   In 1977, Congress amended the Good Neighbor Provi­
sion to require more than “cooperation.” It directed States
to submit SIPs that included provisions “adequate” to
“prohibi[t] any stationary source within the State from
emitting any air pollutant in amounts which will . . .
prevent attainment or maintenance [of air quality stand­
ards] by any other State.” §108(a)(4), 91 Stat. 693, 42
U. S. C. §7410(a)(2)(E) (1976 ed., Supp. II). The amended
provision thus explicitly instructed upwind States to
reduce emissions to account for pollution exported beyond
their borders. As then written, however, the provision
regulated only individual sources that, considered alone,
emitted enough pollution to cause nonattainment in a
downwind State. Because it is often “impossible to say
that any single source or group of sources is the one which
actually prevents attainment” downwind, S. Rep. No. 101–
228, p. 21 (1989), the 1977 version of the Good Neighbor
Provision proved ineffective, see ibid. (noting the provi­
sion’s inability to curb the collective “emissions [of] multi­
ple sources”).
   Congress most recently amended the Good Neighbor
Provision in 1990. The statute, in its current form, re­
quires SIPs to “contain adequate provisions . . . prohibiting
——————
  2 FIPs and SIPs were introduced in the 1970 version of the Act; the

particular deadlines discussed here were added in 1990. See 104 Stat.
2409, 2422–2423, 42 U. S. C. §§7401(a)(1), 7410(c) (2006 ed.).
6        EPA v. EME HOMER CITY GENERATION, L. P.

                     Opinion of the Court

. . . any source or other type of emissions activity within
the State from emitting any air pollutant in amounts
which will . . . contribute significantly to nonattainment
in, or interfere with maintenance by, any other State with
respect to any . . . [NAAQS].” 42 U. S. C. §7410(a)(2)(D)(i)
(2006 ed.). The controversy before us centers on EPA’s
most recent attempt to construe this provision.
                             C
   Three times over the past two decades, EPA has at­
tempted to delineate the Good Neighbor Provision’s scope
by identifying when upwind States “contribute significantly”
to nonattainment downwind. In 1998, EPA issued a
rule known as the “NOX SIP Call.” That regulation lim­
ited NOX emissions in 23 upwind States to the extent such
emissions contributed to nonattainment of ozone stand­
ards in downwind States. See 63 Fed. Reg. 57356, 57358.
In Michigan v. EPA, 213 F. 3d 663 (2000), the D. C. Cir­
cuit upheld the NOX SIP Call, specifically affirming EPA’s
use of costs to determine when an upwind State’s contri­
bution was “significan[t]” within the meaning of the stat­
ute. Id., at 674–679.
   In 2005, EPA issued the Clean Air Interstate Rule, or
CAIR. 70 Fed. Reg. 25162. CAIR regulated both NOX and
SO2 emissions, insofar as such emissions contributed to
downwind nonattainment of two NAAQS, both set in 1997,
one concerning the permissible annual measure of PM2.5,
and another capping the average ozone level gauged over
an 8-hour period. See id., at 25171. The D. C. Circuit
initially vacated CAIR as arbitrary and capricious. See
North Carolina v. EPA, 531 F. 3d 896, 921 (2008) (per
curiam). On rehearing, the court decided to leave the rule
in place, while encouraging EPA to act with dispatch in
dealing with problems the court had identified. See North
Carolina v. EPA, 550 F. 3d 1176, 1178 (2008) (per curiam).
   The rule challenged here—the Transport Rule—is EPA’s
                     Cite as: 572 U. S. ____ (2014)                   7

                         Opinion of the Court

response to the D. C. Circuit’s North Carolina decision.
Finalized in August 2011, the Transport Rule curtails NOX
and SO2 emissions of 27 upwind States to achieve down­
wind attainment of three different NAAQS: the two 1997
NAAQS previously addressed by CAIR, and the 2006
NAAQS for PM2.5 levels measured on a daily basis. See 76
Fed. Reg. 48208–48209.
   Under the Transport Rule, EPA employed a “two-step
approach” to determine when upwind States “contribute[d]
significantly to nonattainment,” id., at 48254, and there­
fore in “amounts” that had to be eliminated. At step one,
called the “screening” analysis, the Agency excluded as de
minimis any upwind State that contributed less than one
percent of the three NAAQS3 to any downwind State
“receptor,” a location at which EPA measures air quality.
See id., at 48236–48237.4 If all of an upwind State’s con­
tributions fell below the one-percent threshold, that State
would be considered not to have “contribute[d] signifi-
cantly” to the nonattainment of any downwind State. Id.,
at 48236. States in that category were screened out and
exempted from regulation under the rule.
   The remaining States were subjected to a second in­
quiry, which EPA called the “control” analysis. At this
stage, the Agency sought to generate a cost-effective allo­
cation of emission reductions among those upwind States
“screened in” at step one.
   The control analysis proceeded this way. EPA first
calculated, for each upwind State, the quantity of emis­
sions the State could eliminate at each of several cost
——————
  3 With respect to each NAAQS addressed by the rule, the one-percent

threshold corresponded to levels of 0.15 micrograms per cubic meter
(µg/m3) for annual PM2.5, 0.35 µg/m3 for daily PM2.5, and 0.8 parts per
billion (ppb) for 8-hour ozone. See 76 Fed. Reg. 48236–48237.
  4 If, for example, the NAAQS for ozone were 100 ppb, a contribution of

less than 1 ppb to any downwind location would fall outside EPA’s
criteria for significance.
8          EPA v. EME HOMER CITY GENERATION, L. P.

                          Opinion of the Court

thresholds. See id., at 48248–48249. Cost for these pur­
poses is measured as cost per ton of emissions prevented,
for instance, by installing scrubbers on powerplant smoke­
stacks.5 EPA estimated, for example, the amount each
upwind State’s NOX emissions would fall if all pollution
sources within each State employed every control measure
available at a cost of $500 per ton or less. See id., at
48249–48251. The Agency then repeated that analysis at
ascending cost thresholds. See ibid.6
  Armed with this information, EPA conducted complex
modeling to establish the combined effect the upwind
reductions projected at each cost threshold would have on
air quality in downwind States. See id., at 48249. The
Agency then identified “significant cost threshold[s],”
points in its model where a “noticeable change occurred in
downwind air quality, such as . . . where large upwind
emission reductions become available because a certain
type of emissions control strategy becomes cost-effective.”
Ibid. For example, reductions of NOX sufficient to resolve
or significantly curb downwind air quality problems could
be achieved, EPA determined, at a cost threshold of $500
per ton (applied uniformly to all regulated upwind States).
“Moving beyond the $500 cost threshold,” EPA concluded,
“would result in only minimal additional . . . reductions [in
emissions].” Id., at 48256.7
  Finally, EPA translated the cost thresholds it had se­
——————
    5 Toillustrate, a technology priced at $5,000 and capable of eliminat­
ing two tons of pollution would be stated to “cost” $2,500 per ton.
   6 For SO2, EPA modeled reductions that would be achieved at cost

levels of $500, $1,600, $2,300, $2,800, $3,300, and $10,000 per ton
eliminated. See id., at 48251–48253.
   7 For SO2, EPA determined that, for one group of upwind States, all

downwind air quality problems would be resolved at the $500 per ton
threshold. See id., at 48257. For another group of States, however,
this level of controls would not suffice. For those States, EPA found
that pollution controls costing $2,300 per ton were necessary. See id.,
at 48259.
                     Cite as: 572 U. S. ____ (2014)                   9

                         Opinion of the Court

lected into amounts of emissions upwind States would be
required to eliminate. For each regulated upwind State,
EPA created an annual emissions “budget.” These budg­
ets represented the quantity of pollution an upwind State
would produce in a given year if its in-state sources im­
plemented all pollution controls available at the chosen
cost thresholds. See id., at 48249.8 If EPA’s projected
improvements to downwind air quality were to be realized,
an upwind State’s emissions could not exceed the level this
budget allocated to it, subject to certain adjustments not
relevant here.
   Taken together, the screening and control inquiries
defined EPA’s understanding of which upwind emissions
were within the Good Neighbor Provision’s ambit. In
short, under the Transport Rule, an upwind State “con­
tribute[d] significantly” to downwind nonattainment to the
extent its exported pollution both (1) produced one percent
or more of a NAAQS in at least one downwind State (step
one) and (2) could be eliminated cost-effectively, as deter­
mined by EPA (step two). See id., at 48254. Upwind
States would be obliged to eliminate all and only emis­
sions meeting both of these criteria.9
   For each State regulated by the Transport Rule, EPA
contemporaneously promulgated a FIP allocating that
State’s emission budget among its in-state sources. See
id., at 48271, 48284–48287.10 For each of these States,
——————
  8 In  2014, for example, pollution sources within Texas would be per­
mitted to emit no more than 243,954 tons of SO2, subject to variations
specified by EPA. See id., at 48269 (Table VI.F–1).
   9 Similarly, upwind States EPA independently determined to be “in­

terfer[ing] with [the] maintenance” of NAAQS downwind were required
to eliminate pollution only to the extent their emissions satisfied both
of these criteria. See id., at 48254.
   10 These FIPs specified the maximum amount of pollution each in­

state pollution source could emit. Sources below this ceiling could sell
unused “allocations” to sources that could not reduce emissions to the
necessary level as cheaply. See id., at 48271–48272. This type of “cap­
10         EPA v. EME HOMER CITY GENERATION, L. P.

                        Opinion of the Court

EPA had determined that the State had failed to submit
a SIP adequate for compliance with the Good Neighbor
Provision. These determinations regarding SIPs became
final after 60 days, see 42 U. S. C. §7607(b)(1)(2006 ed.,
Supp. V ), and many went unchallenged.11 EPA views the
SIP determinations as having triggered its statutory
obligation to promulgate a FIP within two years, see
§7410(c), a view contested by respondents, see Part II,
infra.
                              D
  A group of state and local governments (State respond­
ents), joined by industry and labor groups (Industry re­
spondents), petitioned for review of the Transport Rule in
the U. S. Court of Appeals for the D. C. Circuit. Over the
dissent of Judge Rogers, the Court of Appeals vacated the
rule in its entirety. See 696 F. 3d 7, 37 (2012).
  EPA’s actions, the appeals court held, exceeded the
Agency’s statutory authority in two respects. By promul­
gating FIPs before giving States a meaningful opportunity
to adopt their own implementation plans, EPA had, in the
court’s view, upset the CAA’s division of responsibility
between the States and the Federal Government. In the
main, the Court of Appeals acknowledged, EPA’s FIP
authority is triggered at the moment the Agency disap­
proves a SIP. See id., at 30. Thus, when a State proposes
——————
and-trade” system cuts costs while still reducing pollution to target
levels.
  11 Three States did challenge EPA’s determinations. See Petition for

Review in Ohio v. EPA, No. 11–3988 (CA6); Petition for Review in
Kansas v. EPA, No. 12–1019 (CADC); Notice in Georgia v. EPA, No. 11–
1427 (CADC). Those challenges were not consolidated with this pro­
ceeding, and they remain pending (held in abeyance for these cases) in
the Sixth and D. C. Circuits. See Twelfth Joint Status Report in Ohio
v. EPA, No. 11–3988 (CA6); Order in Kansas v. EPA, No. 11–1333
(CADC, May 10, 2013); Order in Georgia v. EPA, No. 11–1427 (CADC,
May 10, 2013).
                  Cite as: 572 U. S. ____ (2014)            11

                      Opinion of the Court

a SIP inadequate to achieve a NAAQS, EPA could promul­
gate a FIP immediately after disapproving that SIP. See
id., at 32.
   But the Court of Appeals ruled that a different regime
applies to a State’s failure to meet its obligations under
the Good Neighbor Provision. While a NAAQS was a
“clear numerical target,” a State’s good neighbor obligation
remained “nebulous and unknown,” the court observed,
until EPA calculated the State’s emission budget. Ibid.
Without these budgets, the Court of Appeals said, upwind
States would be compelled to take a “stab in the dark” at
calculating their own significant contribution to interstate
air pollution. Id., at 35. The D. C. Circuit read the Act to
avoid putting States in this position: EPA had an implicit
statutory duty, the court held, to give upwind States a
reasonable opportunity to allocate their emission budgets
among in-state sources before the Agency’s authority to
issue FIPs could be triggered. Id., at 37.
   The D. C. Circuit also held that the Agency’s two-part
interpretation of the Good Neighbor Provision ignored
three “red lines . . . cabin[ing the] EPA’s authority.” Id., at
19. First, the D. C. Circuit interpreted the Good Neighbor
Provision to require upwind States to reduce emissions in
“a manner proportional to their contributio[n]” to pollution
in downwind States. Id., at 21. The Transport Rule,
however, treated all regulated upwind States alike, re­
gardless of their relative contribution to the overall prob­
lem. See id., at 23. It required all upwind States
“screened in” at step one to reduce emissions in accord
with the uniform cost thresholds set during the step two
control analysis. Imposing these uniform cost thresholds,
the Court of Appeals observed, could force some upwind
States to reduce emissions by more than their “fair share.”
Id., at 27.
   According to the Court of Appeals, EPA had also failed
to ensure that the Transport Rule did not mandate up­
12       EPA v. EME HOMER CITY GENERATION, L. P.

                     Opinion of the Court

wind States to reduce pollution unnecessarily. The Good
Neighbor Provision, the D. C. Circuit noted, “targets [only]
those emissions from upwind States that ‘contribute sig­
nificantly to nonattainment’ ” of a NAAQS in downwind
States. Id., at 22. Pollution reduction beyond that goal
was “unnecessary over-control,” outside the purview of the
Agency’s statutory mandate. Ibid. Because the emission
budgets were calculated by reference to cost alone, the
court concluded that EPA had done nothing to guard
against, or even measure, the “over-control” potentially
imposed by the Transport Rule. See ibid.
   Finally, by deciding, at the screening analysis, that
upwind contributions below the one-percent threshold
were insignificant, EPA had established a “floor” on the
Agency’s authority to act. See id., at 20, and n. 13. Again
pointing to the rule’s reliance on costs, the Court of Ap­
peals held that EPA had failed to ensure that upwind
States were not being forced to reduce emissions below the
one-percent threshold. See ibid.
   In dissent, Judge Rogers criticized the majority for
deciding two questions that were not, in her view, properly
before the court. See id., at 40–46, 51–58. First, she
addressed the majority’s insistence that FIPs abide a
State’s opportunity to allocate its emission budget among
in-state sources. She regarded the respondents’ plea to
that effect as an untimely attack on EPA’s previous SIP
disapprovals. See id., at 40–46. Second, in Judge Rogers’
assessment, the respondents had failed to raise their
substantive objections to the Transport Rule with the
specificity necessary to preserve them for review. See id.,
at 51–58. On the merits, Judge Rogers found nothing in
the Act to require, or even suggest, that EPA must quan-
tify a State’s good neighbor obligations before it promul­
gated a FIP. See id., at 46–51. She also disagreed with
the court’s conclusion that the Transport Rule unreasona­
bly interpreted the Act. See id., at 58–60.
                 Cite as: 572 U. S. ____ (2014)          13

                     Opinion of the Court

  We granted certiorari to decide whether the D. C. Cir­
cuit had accurately construed the limits the CAA places on
EPA’s authority. See 570 U. S. ___ (2013).
                             II

                              A

   Once EPA has calculated emission budgets, the D. C.
Circuit held, the Agency must give upwind States the
opportunity to propose SIPs allocating those budgets
among in-state sources before issuing a FIP. 696 F. 3d, at
37. As the State respondents put it, a FIP allocating a
State’s emission budget “must issue after EPA has quanti­
fied the States’ good-neighbor obligations [in an emission
budget] and given the States a reasonable opportunity to
meet those obligations in SIPs.” Brief for State Respond­
ents 20.
   Before reaching the merits of this argument, we first
reject EPA’s threshold objection that the claim is untimely.
According to the Agency, this argument—and the D. C.
Circuit’s opinion accepting it—rank as improper collateral
attacks on EPA’s prior SIP disapprovals. As earlier re­
counted, see supra, at 9–10, EPA, by the time it issued the
Transport Rule, had determined that each regulated
upwind State had failed to submit a SIP adequate to
satisfy the Good Neighbor Provision. Many of those de­
terminations, because unchallenged, became final after 60
days, see 42 U. S. C. §7607(b)(1), and did so before the
petitions here at issue were filed. EPA argues that the
Court cannot question exercise of the Agency’s FIP author­
ity without subjecting these final SIP disapprovals to
untimely review.
   We disagree. The gravamen of the State respondents’
challenge is not that EPA’s disapproval of any particular
SIP was erroneous. Rather, respondents urge that, not­
withstanding these disapprovals, the Agency was obliged
to grant an upwind State a second opportunity to promul­
14         EPA v. EME HOMER CITY GENERATION, L. P.

                          Opinion of the Court

gate adequate SIPs once EPA set the State’s emission
budget. This claim does not depend on the validity of the
prior SIP disapprovals. Even assuming the legitimacy of
those disapprovals, the question remains whether EPA
was required to do more than disapprove a SIP, as the
State respondents urge, to trigger the Agency’s statutory
authority to issue a FIP.12
                             B
  Turning to the merits, we hold that the text of the stat­
ute supports EPA’s position. As earlier noted, see supra,
at 4–5, the CAA sets a series of precise deadlines to which
the States and EPA must adhere. Once EPA issues any
new or revised NAAQS, a State has three years to adopt a
SIP adequate for compliance with the Act’s requirements.
See 42 U. S. C. §7410(a)(1). Among those requirements is
the Act’s mandate that SIPs “shall” include provisions
sufficient to satisfy the Good Neighbor Provision.
§7410(a)(2).
  If EPA determines a SIP to be inadequate, the Agency’s
mandate to replace it with a FIP is no less absolute:
       “[EPA] shall promulgate a [FIP] at any time within
     2 years after the [Agency]
       “(A) finds that a State has failed to make a required
     submission or finds that the plan or plan revision
     submitted by the State does not satisfy the minimum
     [relevant] criteria . . . , or

——————
  12 The State respondents make a second argument we do not reach.

They urge that EPA could not impose FIPs on several upwind States
whose SIPs had been previously approved by the Agency under CAIR.
EPA changed those approvals to disapprovals when it issued the
Transport Rule, see 76 Fed. Reg. 48220, and the States assert that the
process by which EPA did so was improper. That argument was not
passed on by the D. C. Circuit, see 696 F. 3d 7, 31, n. 29 (2012), and we
leave it for the Court of Appeals to consider in the first instance on
remand.
                      Cite as: 572 U. S. ____ (2014)                    15

                          Opinion of the Court

       “(B) disapproves a [SIP] in whole or in part,
     “unless the State corrects the deficiency, and [EPA]
     approves the plan or plan revision, before the [Agency]
     promulgates such [FIP].” §7410(c)(1).
In other words, once EPA has found a SIP inadequate, the
Agency has a statutory duty to issue a FIP “at any time”
within two years (unless the State first “corrects the defi­
ciency,” which no one contends occurred here).
   The D. C. Circuit, however, found an unwritten excep­
tion to this strict time prescription for SIPs aimed at
implementing the Good Neighbor Provision. Expecting
any one State to develop a “comprehensive solution” to the
“collective problem” of interstate air pollution without first
receiving EPA’s guidance was, in the Court of Appeals’
assessment, “set[ting] the States up to fail.” 696 F. 3d, at
36–37. The D. C. Circuit therefore required EPA, after
promulgating each State’s emission budget, to give the
State a “reasonable” period of time to propose SIPs im­
plementing its budget. See id., at 37.
   However sensible (or not) the Court of Appeals’ posi­
tion,13 a reviewing court’s “task is to apply the text [of the
statute], not to improve upon it.” Pavelic & LeFlore v.
Marvel Entertainment Group, Div. of Cadence Industries
Corp., 493 U. S. 120, 126 (1989). Nothing in the Act dif­
——————
   13 On this point, the dissent argues that it is “beyond responsible

debate that the States cannot possibly design FIP-proof SIPs without
knowing the EPA-prescribed targets at which they must aim.” Post, at
18. Many of the State respondents thought otherwise, however, when
litigating the matter in Michigan v. EPA, 213 F. 3d 663 (CADC 2000).
See Final Brief for Petitioning States in No. 98–1497 (CADC), p. 34
(“EPA has the responsibility to establish NAAQS,” but without further
intervention by EPA, “States [have] the duty and right to develop . . .
SIPs . . . to meet those NAAQS.”). See also id., at 37 (“EPA’s role is to
determine whether the SIP submitted is ‘adequate’ . . . not to dictate
contents of the submittal in the first instance. . . . [E]ach State has the
right and the obligation to write a SIP that complies with §[74]10(a)(2),
including the ‘good neighbor’ provision.”).
16       EPA v. EME HOMER CITY GENERATION, L. P.

                     Opinion of the Court

ferentiates the Good Neighbor Provision from the several
other matters a State must address in its SIP. Rather, the
statute speaks without reservation: Once a NAAQS has
been issued, a State “shall” propose a SIP within three
years, §7410(a)(1), and that SIP “shall” include, among
other components, provisions adequate to satisfy the Good
Neighbor Provision, §7410(a)(2).
   Nor does the Act condition the duty to promulgate a FIP
on EPA’s having first quantified an upwind State’s good
neighbor obligations. As Judge Rogers observed in her
dissent from the D. C. Circuit’s decision, the Act does not
require EPA to furnish upwind States with information of
any kind about their good neighbor obligations before a
FIP issues. See 696 F. 3d, at 47. Instead, a SIP’s failure
to satisfy the Good Neighbor Provision, without more,
triggers EPA’s obligation to issue a federal plan within
two years. §7410(c). After EPA has disapproved a SIP,
the Agency can wait up to two years to issue a FIP, during
which time the State can “correc[t] the deficiency” on its
own. Ibid. But EPA is not obliged to wait two years or
postpone its action even a single day: The Act empowers
the Agency to promulgate a FIP “at any time” within the
two-year limit. Ibid. Carving out an exception to the Act’s
precise deadlines, as the D. C. Circuit did, “rewrites a
decades-old statute whose plain text and structure estab­
lish a clear chronology of federal and State responsibili­
ties.” 696 F. 3d, at 47 (Rogers, J., dissenting).
   The practical difficulties cited by the Court of Appeals
do not justify departure from the Act’s plain text. See
Barnhart v. Sigmon Coal Co., 534 U. S. 438, 461–462
(2002) (We “must presume that a legislature says in a
statute what it means and means in a statute what it says
there.” (internal quotation marks omitted)). When Con­
gress elected to make EPA’s input a prerequisite to state
action under the Act, it did so expressly. States develop­
ing vehicle inspection and maintenance programs under
                 Cite as: 572 U. S. ____ (2014)           17

                     Opinion of the Court

the CAA, for example, must await EPA guidance before
issuing SIPs. 42 U. S. C. §7511a(c)(3)(B). A State’s obli­
gation to adopt a SIP, moreover, arises only after EPA has
first set the NAAQS the State must meet. §7410(a)(1).
Had Congress intended similarly to defer States’ discharge
of their obligations under the Good Neighbor Provision,
Congress, we take it, would have included a similar direc­
tion in that section. See Jama v. Immigration and Cus-
toms Enforcement, 543 U. S. 335, 341 (2005) (“We do not
lightly assume that Congress has omitted from its adopted
text requirements that it nonetheless intends to apply,
and our reluctance is even greater when Congress has
shown elsewhere in the same statute that it knows how to
make such a requirement manifest.”).
   In short, nothing in the statute places EPA under an
obligation to provide specific metrics to States before they
undertake to fulfill their good neighbor obligations. By
altering the schedule Congress provided for SIPs and
FIPs, the D. C. Circuit stretched out the process. It al­
lowed a delay Congress did not order and placed an infor­
mation submission obligation on EPA Congress did not
impose. The D. C. Circuit, we hold, had no warrant thus
to revise the CAA’s action-ordering prescriptions.
                              C
   At oral argument, the State respondents emphasized
EPA’s previous decisions, in the NOX SIP Call and CAIR,
to quantify the emission reductions required of upwind
States before the window to propose a SIP closed. See Tr.
of Oral Arg. 37–39, 42–43, 45–46. In their view, by failing
to accord States a similar grace period after issuing States’
emission budgets, EPA acted arbitrarily. See ibid.
   Whatever pattern the Agency followed in its NOX SIP
call and CAIR proceedings, EPA retained discretion to
alter its course provided it gave a reasonable explanation
for doing so. Motor Vehicle Mfrs. Assn. of United States,
18         EPA v. EME HOMER CITY GENERATION, L. P.

                          Opinion of the Court

Inc. v. State Farm Mut. Automobile Ins. Co., 463 U. S. 29,
42 (1983). The Agency presented such an explanation in
the Transport Rule. As noted, see supra, at 6, the D. C.
Circuit’s North Carolina decision admonished EPA to act
with dispatch in amending or replacing CAIR, the
Transport Rule’s predecessor. See 550 F. 3d, at 1178
(warning EPA that the stay of the court’s decision to va­
cate CAIR would not persist “indefinite[ly]”). Given North
Carolina’s stress on expeditious action to cure the infir-
mities the court identified in CAIR, EPA thought
it “[in]appropriate to establish [the] lengthy transition
period” entailed in allowing States time to propose new or
amended SIPs implementing the Transport Rule emission
budgets. See 76 Fed. Reg. 48220 (citing North Carolina,
550 F. 3d 1176). Endeavoring to satisfy the D. C. Circuit’s
directive, EPA acted speedily, issuing FIPs contemporane­
ously with the Transport Rule. In light of the firm dead­
lines imposed by the Act, which we hold the D. C. Circuit
lacked authority to alter, we cannot condemn EPA’s deci­
sion as arbitrary or capricious.14
                             III

                              A

  The D. C. Circuit also held that the Transport Rule’s
two-step interpretation of the Good Neighbor Provision
conflicts with the Act. Before addressing this holding, we
take up a jurisdictional objection raised by EPA.
  The CAA directs that “[o]nly an objection to a rule . . .

——————
  14 Inlight of the CAA’s “core principle” of cooperative federalism, the
dissent believes EPA abused its discretion by failing to give States an
additional opportunity to submit SIPs in satisfaction of the Good
Neighbor Provision. Post, at 19. But nothing in the statute so restricts
EPA. To the contrary, as earlier observed, see supra, at 16, the plain
text of the CAA grants EPA plenary authority to issue a FIP “at any
time” within the two-year period that begins the moment EPA deter­
mines a SIP to be inadequate. §7410(c)(1) (emphasis added).
                 Cite as: 572 U. S. ____ (2014)          19

                     Opinion of the Court

raised with reasonable specificity during the period for
public comment . . . may be raised during judicial review.”
42 U. S. C. §7607(d)(7)(B). Respondents failed to state
their objections to the Transport Rule during the comment
period with the “specificity” required for preservation,
EPA argues. See Brief for Federal Petitioners 34–42.
This failure at the administrative level, EPA urges, fore­
closes judicial review. Id., at 34.
  Assuming, without deciding, that respondents did not
meet the Act’s “reasonable specificity” requirement during
the comment period, we do not regard that lapse as “juris­
dictional.” This Court has cautioned against “profligate
use” of the label “jurisdictional.” Sebelius v. Auburn Re-
gional Medical Center, 568 U. S. ___, ___ (2013) (slip op.,
at 6). A rule may be “mandatory,” yet not “jurisdictional,”
we have explained. See Arbaugh v. Y & H Corp., 546 U. S.
500, 510 (2006). Section 7607(d)(7)(B), we hold, is of that
character. It does not speak to a court’s authority, but
only to a party’s procedural obligations. See Kontrick v.
Ryan, 540 U. S. 443, 455 (2004). Had EPA pursued the
“reasonable specificity” argument vigorously before the
D. C. Circuit, we would be obligated to address the merits
of the argument. See Gonzalez v. Thaler, 565 U. S. ___,
___ (2012) (slip op., at 10). But EPA did not press the
argument unequivocally. Before the D. C. Circuit, it indi­
cated only that the “reasonable specificity” prescription
might bar judicial review. Brief for Respondent EPA et al.
in No. 11–1302 (CADC), p. 30. See also id., at 32. We
therefore do not count the prescription an impassable
hindrance to our adjudication of the respondents’ attack
on EPA’s interpretation of the Transport Rule. We turn to
that attack mindful of the importance of the issues re­
spondents raise to the ongoing implementation of the Good
Neighbor Provision.
20       EPA v. EME HOMER CITY GENERATION, L. P.

                      Opinion of the Court

                              B
    We routinely accord dispositive effect to an agency’s
reasonable interpretation of ambiguous statutory lan­
guage. Chevron U. S. A. Inc. v. Natural Resources Defense
Council, Inc., 467 U. S. 837 (1984), is the pathmarking
decision, and it bears a notable resemblance to the cases
before us. Chevron concerned EPA’s definition of the term
“source,” as used in the 1977 Amendments to the CAA.
Id., at 840, n. 1. Those amendments placed additional
restrictions on companies’ liberty to add new pollution
“sources” to their factories. See id., at 840. Although
“source” might have been interpreted to refer to an indi­
vidual smokestack, EPA construed the term to refer to an
entire plant, thereby “treat[ing] all of the pollution­
emitting devices within the [plant] as though they were
encased within a single ‘bubble.’” Ibid. Under the Agency’s
interpretation, a new pollution-emitting device would not
subject a plant to the additional restrictions if the “altera­
tion [did] not increase the total emissions [produced by]
the plant.” Ibid.
    This Court held EPA’s interpretation of “source” a rea­
sonable construction of an ambiguous statutory term.
When “Congress has not directly addressed the precise
[interpretative] question at issue,” we cautioned, a review­
ing court cannot “simply impose its own construction o[f]
the statute.” Id., at 843. Rather, the agency is charged
with filling the “gap left open” by the ambiguity. Id., at
866. Because “ ‘a full understanding of the force of the
statutory policy . . . depend[s] upon more than ordinary
knowledge’ ” of the situation, the administering agency’s
construction is to be accorded “controlling weight unless
. . . arbitrary, capricious, or manifestly contrary to the
statute.” Id., at 844 (quoting United States v. Shimer, 367
U. S. 374, 382 (1961)). Determining that none of those
terms fit EPA’s interpretation of “source,” the Court de­
ferred to the Agency’s judgment.
                    Cite as: 572 U. S. ____ (2014)                 21

                        Opinion of the Court

   We conclude that the Good Neighbor Provision delegates
authority to EPA at least as certainly as the CAA provi­
sions involved in Chevron. The statute requires States to
eliminate those “amounts” of pollution that “contribute
significantly to nonattainment” in downwind States. 42
U. S. C. §7410(a)(2)(D)(i) (emphasis added). Thus, EPA’s
task15 is to reduce upwind pollution, but only in “amounts”
that push a downwind State’s pollution concentrations
above the relevant NAAQS. As noted earlier, however, the
nonattainment of downwind States results from the collec­
tive and interwoven contributions of multiple upwind
States. See supra, at 3. The statute therefore calls
upon the Agency to address a thorny causation problem:
How should EPA allocate among multiple contributing up-
wind States responsibility for a downwind State’s excess
pollution?
   A simplified example illustrates the puzzle EPA faced.
Suppose the Agency sets a NAAQS, with respect to a
particular pollutant, at 100 parts per billion (ppb), and
that the level of the pollutant in the atmosphere of down­
wind State A is 130 ppb. Suppose further that EPA has
determined that each of three upwind States—X, Y, and
Z—contributes the equivalent of 30 ppb of the relevant
pollutant to State A’s airspace. The Good Neighbor Provi­
sion, as just observed, prohibits only upwind emissions
that contribute significantly to downwind nonattainment.
EPA’s authority under the provision is therefore limited to
eliminating a total of 30 ppb,16 i.e., the overage caused by

——————
  15 Though we speak here of “EPA’s task,” the Good Neighbor Provi­

sion is initially directed to upwind States. As earlier explained, see
Part II–B, supra, only after a State has failed to propose a SIP ade­
quate for compliance with the provision is EPA called upon to act.
  16 Because of the uncertainties inherent in measuring interstate air

pollution, see supra, at 3–4, reductions of exactly 30 ppb likely are
unattainable. See infra, at 30–31.
22         EPA v. EME HOMER CITY GENERATION, L. P.

                          Opinion of the Court

the collective contribution of States X, Y, and Z.17
   How is EPA to divide responsibility among the three
States? Should the Agency allocate reductions propor­
tionally (10 ppb each), on a per capita basis, on the basis of
the cost of abatement, or by some other metric? See Brief
for Federal Petitioners 50 (noting EPA’s consideration of
different approaches). The Good Neighbor Provision does
not answer that question for EPA. Cf. Chevron, 467 U. S.,
at 860 (“[T]he language of [the CAA] simply does not
compel any given interpretation of the term ‘source.’ ”).
Under Chevron, we read Congress’ silence as a delegation
of authority to EPA to select from among reasonable op­
tions. See United States v. Mead Corp., 533 U. S. 218, 229
(2001).18
   Yet the Court of Appeals believed that the Act speaks
clearly, requiring EPA to allocate responsibility for reduc­
ing emissions in “a manner proportional to” each State’s
“contributio[n]” to the problem. 696 F. 3d, at 21. Nothing
——————
  17 For  simplicity’s sake, the hypothetical assumes that EPA has not
required any emission reductions by the downwind State itself.
   18 The statutory gap identified also exists in the Good Neighbor Provi­

sion’s second instruction. That instruction requires EPA to eliminate
amounts of upwind pollution that “interfere with maintenance” of a
NAAQS by a downwind State. §7410(a)(2)(D)(i). This mandate con­
tains no qualifier analogous to “significantly,” and yet it entails a
delegation of administrative authority of the same character as the one
discussed above. Just as EPA is constrained, under the first part of the
Good Neighbor Provision, to eliminate only those amounts that “con­
tribute . . . to nonattainment,” EPA is limited, by the second part of the
provision, to reduce only by “amounts” that “interfere with mainte-
nance,” i.e., by just enough to permit an already-attaining State to
maintain satisfactory air quality. (Emphasis added.) With multiple
upwind States contributing to the maintenance problem, however, EPA
confronts the same challenge that the “contribute significantly” man­
date creates: How should EPA allocate reductions among multiple
upwind States, many of which contribute in amounts sufficient to
impede downwind maintenance? Nothing in either clause of the Good
Neighbor Provision provides the criteria by which EPA is meant to
apportion responsibility.
                 Cite as: 572 U. S. ____ (2014)           23

                     Opinion of the Court

in the text of the Good Neighbor Provision propels EPA
down this path. Understandably so, for as EPA notes, the
D. C. Circuit’s proportionality approach could scarcely be
satisfied in practice. See App. in No. 11–1302 etc.
(CADC), p. 2312 (“[W]hile it is possible to determine an
emission reduction percentage if there is a single down­
wind [receptor], most upwind states contribute to multiple
downwind [receptors] (in multiple states) and would have
a different reduction percentage for each one.”).
  To illustrate, consider a variation on the example set out
above. Imagine that States X and Y now contribute air
pollution to State A in a ratio of one to five, i.e., State Y
contributes five times the amount of pollution to State A
than does State X. If State A were the only downwind
State to which the two upwind States contributed, the
D. C. Circuit’s proportionality requirement would be easy
to meet: EPA could require State Y to reduce its emissions
by five times the amount demanded of State X.
  The realities of interstate air pollution, however, are not
so simple. Most upwind States contribute pollution to
multiple downwind States in varying amounts. See 76
Fed. Reg. 48239–48246. See also Brief for Respondent
Calpine Corp. et al. in Support of Petitioners 48–49 (offer­
ing examples). Suppose then that States X and Y also
contribute pollutants to a second downwind State (State
B), this time in a ratio of seven to one. Though State Y
contributed a relatively larger share of pollution to State
A, with respect to State B, State X is the greater offender.
Following the proportionality approach with respect to
State B would demand that State X reduce its emissions
by seven times as much as State Y. Recall, however, that
State Y, as just hypothesized, had to effect five times as
large a reduction with respect to State A. The Court of
Appeals’ proportionality edict with respect to both State A
and State B appears to work neither mathematically nor
in practical application. Proportionality as to one down­
24         EPA v. EME HOMER CITY GENERATION, L. P.

                          Opinion of the Court

wind State will not achieve proportionality as to others.
Quite the opposite. And where, as is generally true, up­
wind States contribute pollution to more than two down­
wind receptors, proportionality becomes all the more
elusive.
  Neither the D. C. Circuit nor respondents face up to this
problem. The dissent, for its part, strains to give meaning
to the D. C. Circuit’s proportionality constraint as applied
to a world in which multiple upwind States contribute
emissions to multiple downwind locations. In the dissent’s
view, upwind States must eliminate emissions by “what­
ever minimum amount reduces” their share of the overage
in each and every one of the downwind States to which
they are linked. See post, at 8. In practical terms, this
means each upwind State will be required to reduce emis­
sions by the amount necessary to eliminate that State’s
largest downwind contribution. The dissent’s formulation,
however, does not account for the combined and cumu-
lative effect of each upwind State’s reductions on attain­
ment in multiple downwind locations. See ibid. (“Under a
proportional-reduction approach, State X would be required
to eliminate emissions of that pollutant by whatever min­
imum amount reduces both State A’s level by 0.2 unit and
State B’s by 0.7 unit.” (emphasis added)). The result
would be costly overregulation unnecessary to, indeed
in conflict with, the Good Neighbor Provision’s goal of
attainment.19
——————
  19 To see why, one need only slightly complicate the world envisioned

by the dissent. Assume the world is made up of only four States—two
upwind (States X and Y), and two downwind (States A and B). Suppose
also, as the dissent allows, see post, at 9, that the reductions State X
must make to eliminate its share of the amount by which State A is in
nonattainment are more than necessary for State X to eliminate its
share of State B’s nonattainment. As later explained, see infra, at 29–
30, this kind of “over-control,” we agree with the dissent, is acceptable
under the statute. Suppose, however, that State Y also contributes to
pollution in both State A and State B such that the reductions it must
                    Cite as: 572 U. S. ____ (2014)                  25

                         Opinion of the Court

   In response, the dissent asserts that EPA will “simply
be required to make allowance for” the overregulation
caused by its “proportional-reduction” approach. Post, at
11. What criterion should EPA employ to determine
which States will have to make those “allowance[s]” and
by how much? The dissent admits there are “multiple
ways” EPA might answer those questions. Ibid. But
proportionality cannot be one of those ways, for the
proportional-reduction approach is what led to the over­
regulation in the first place. And if a nonproportional
approach can play a role in setting the final allocation of
reduction obligations, then it is hardly apparent why EPA,
free to depart from proportionality at the back end, cannot
do so at the outset.
   Persuaded that the Good Neighbor Provision does not
dictate the particular allocation of emissions among con­
tributing States advanced by the D. C. Circuit, we must
next decide whether the allocation method chosen by EPA
is a “permissible construction of the statute.” Chevron,
467 U. S., at 843. As EPA interprets the statute, upwind
emissions rank as “amounts [that] . . . contribute signifi­
cantly to nonattainment” if they (1) constitute one percent
——————
make to eliminate its proportion of State B’s overage exceed the reduc­
tions it must make to bring State A into attainment. In this case, the
dissent would have State X reduce by just enough to eliminate its share
of State A’s nonattainment and more than enough to eliminate its
share of State B’s overage. The converse will be true as to State Y:
Under the dissent’s approach, State Y would have to reduce by the
“minimum” necessary to eliminate its proportional share of State B’s
nonattainment and more than enough to eliminate its proportion of
State A’s overage. The result is that the total amount by which both
States X and Y are required to reduce will exceed what is necessary for
attainment in all downwind States involved (i.e., in both State A and
State B). Over-control thus unnecessary to achieving attainment in all
involved States is impermissible under the Good Neighbor Provision.
See infra, at 30, n. 23. The problem would worsen were the hypothet­
ical altered to include more than two downwind States and two upwind
States, the very real circumstances EPA must address.
26       EPA v. EME HOMER CITY GENERATION, L. P.

                      Opinion of the Court

or more of a relevant NAAQS in a nonattaining downwind
State and (2) can be eliminated under the cost threshold
set by the Agency. See 76 Fed. Reg. 48254. In other
words, to identify which emissions were to be eliminated,
EPA considered both the magnitude of upwind States’
contributions and the cost associated with eliminating
them.
   The Industry respondents argue that, however EPA
ultimately divides responsibility among upwind States,
the final calculation cannot rely on costs. The Good
Neighbor Provision, respondents and the dissent empha­
size, “requires each State to prohibit only those ‘amounts’
of air pollution emitted within the State that ‘contribute
significantly’ to another State’s nonattaintment.” Brief for
Industry Respondents 23 (emphasis added). See also post,
at 6. The cost of preventing emissions, they urge, is
wholly unrelated to the actual “amoun[t]” of air pollution
an upwind State contributes. Brief for Industry Respond­
ents 23. Because the Transport Rule considers costs,
respondents argue, “States that contribute identical
‘amounts’ . . . may be deemed [by EPA] to have [made]
substantially different” contributions. Id., at 30.
   But, as just explained, see supra, at 21–22, the Agency
cannot avoid the task of choosing which among equal
“amounts” to eliminate. The Agency has chosen, sensibly
in our view, to reduce the amount easier, i.e., less costly, to
eradicate, and nothing in the text of the Good Neighbor
Provision precludes that choice.
   Using costs in the Transport Rule calculus, we agree
with EPA, also makes good sense. Eliminating those
amounts that can cost-effectively be reduced is an efficient
and equitable solution to the allocation problem the Good
Neighbor Provision requires the Agency to address. Effi­
cient because EPA can achieve the levels of attainment,
i.e., of emission reductions, the proportional approach
aims to achieve, but at a much lower overall cost. Equita­
                     Cite as: 572 U. S. ____ (2014)                    27

                          Opinion of the Court

ble because, by imposing uniform cost thresholds on regu­
lated States, EPA’s rule subjects to stricter regulation
those States that have done relatively less in the past to
control their pollution. Upwind States that have not yet
implemented pollution controls of the same stringency as
their neighbors will be stopped from free riding on their
neighbors’ efforts to reduce pollution. They will have to
bring down their emissions by installing devices of the
kind in which neighboring States have already invested.
   Suppose, for example, that the industries of upwind
State A have expended considerable resources installing
modern pollution-control devices on their plants. Facto­
ries in upwind State B, by contrast, continue to run old,
dirty plants. Yet, perhaps because State A is more popu­
lous and therefore generates a larger sum of pollution
overall, the two States’ emissions have equal effects on
downwind attainment. If State A and State B are re­
quired to eliminate emissions proportionally (i.e., equally),
sources in State A will be compelled to spend far more per
ton of reductions because they have already utilized lower
cost pollution controls. State A’s sources will also have to
achieve greater reductions than would have been required
had they not made the cost-effective reductions in the first
place. State A, in other words, will be tolled for having
done more to reduce pollution in the past.20 EPA’s cost­
based allocation avoids these anomalies.
   Obligated to require the elimination of only those
“amounts” of pollutants that contribute to the nonattain­
ment of NAAQS in downwind States, EPA must decide
how to differentiate among the otherwise like contribu­
tions of multiple upwind States. EPA found decisive the
——————
  20 The dissent’s approach is similarly infirm. It, too, would toll those

upwind States that have already invested heavily in means to reduce
the pollution their industries cause, while lightening the burden on
States that have done relatively less to control pollution emanating
from local enterprises.
28         EPA v. EME HOMER CITY GENERATION, L. P.

                         Opinion of the Court

difficulty of eliminating each “amount,” i.e., the cost in­
curred in doing so. Lacking a dispositive statutory in­
struction to guide it, EPA’s decision, we conclude, is a
“reasonable” way of filling the “gap left open by Congress.”
Chevron, 467 U. S., at 866.21
                              C
   The D. C. Circuit stated two further objections to EPA’s
cost-based method of defining an upwind State’s contribu­
tion. Once a State was screened in at step one of EPA’s
analysis, its emission budget was calculated solely with
reference to the uniform cost thresholds the Agency selected
at step two. The Transport Rule thus left open the
possibility that a State might be compelled to reduce
emissions beyond the point at which every affected down­
wind State is in attainment, a phenomenon the Court of
Appeals termed “over-control.” 696 F. 3d, at 22; see supra,
at 12. Second, EPA’s focus on costs did not foreclose, as
the D. C. Circuit accurately observed, the possibility that
an upwind State would be required to reduce its emissions
by so much that the State no longer contributed one per­
——————
   21 The dissent, see post, at 12–13, relies heavily on our decision in

Whitman v. American Trucking Assns., Inc., 531 U. S. 457 (2001). In
Whitman, we held that the relevant text of the CAA “unambiguously
bars” EPA from considering costs when determining a NAAQS. Id., at
471. Section 7409(b)(1) commands EPA to set NAAQS at levels “requi­
site to protect the public health” with “an adequate margin of safety.”
This mandate, we observed in Whitman, was “absolute,” and precluded
any other consideration (e.g., cost) in the NAAQS calculation. Id., at
465 (internal quotation marks omitted). Not so of the Good Neighbor
Provision, which grants EPA discretion to eliminate “amounts [of
pollution that] . . . contribute significantly to nonattainment” down­
wind. On the particular “amounts” that should qualify for elimination,
the statute is silent. Unlike the provision at issue in Whitman, which
provides express criteria by which EPA is to set NAAQS, the Good
Neighbor Provision, as earlier explained, fails to provide any metric by
which EPA can differentiate among the contributions of multiple
upwind States. See supra, at 21–22.
                     Cite as: 572 U. S. ____ (2014)                  29

                         Opinion of the Court

cent or more of a relevant NAAQS to any downwind State.
This would place the State below the mark EPA had set,
during the screening phase, as the initial threshold of
“significan[ce].” See id., at 20, and n. 13.
   We agree with the Court of Appeals to this extent: EPA
cannot require a State to reduce its output of pollution by
more than is necessary to achieve attainment in every
downwind State or at odds with the one-percent threshold
the Agency has set. If EPA requires an upwind State to
reduce emissions by more than the amount necessary to
achieve attainment in every downwind State to which it is
linked, the Agency will have overstepped its authority,
under the Good Neighbor Provision, to eliminate those
“amounts [that] contribute . . . to nonattainment.” Nor
can EPA demand reductions that would drive an upwind
State’s contribution to every downwind State to which it is
linked below one percent of the relevant NAAQS. Doing
so would be counter to step one of the Agency’s interpreta­
tion of the Good Neighbor Provision. See 76 Fed. Reg.
48236 (“[S]tates whose contributions are below th[e]
thresholds do not significantly contribute to nonattain­
ment . . . of the relevant NAAQS.”).
   Neither possibility, however, justifies wholesale invali­
dation of the Transport Rule. First, instances of “over­
control” in particular downwind locations, the D. C. Cir­
cuit acknowledged, see 696 F. 3d, at 22, may be incidental
to reductions necessary to ensure attainment elsewhere.
Because individual upwind States often “contribute signif­
icantly” to nonattainment in multiple downwind locations,
the emissions reduction required to bring one linked
downwind State into attainment may well be large enough
to push other linked downwind States over the attainment
line.22 As the Good Neighbor Provision seeks attainment
——————
  22 The following example, based on the record, is offered in Brief for

Respondent Calpine Corp. et al. in Support of Petitioners 52–54. Ohio,
30         EPA v. EME HOMER CITY GENERATION, L. P.

                          Opinion of the Court

in every downwind State, however, exceeding attainment
in one State cannot rank as “over-control” unless unneces­
sary to achieving attainment in any downwind State.
Only reductions unnecessary to downwind attainment
anywhere fall outside the Agency’s statutory authority.23
  Second, while EPA has a statutory duty to avoid over­
control, the Agency also has a statutory obligation to avoid
“under-control,” i.e., to maximize achievement of attain­
ment downwind. For reasons earlier explained, see supra,
at 3–4, a degree of imprecision is inevitable in tackling the
problem of interstate air pollution. Slight changes in wind
patterns or energy consumption, for example, may vary
downwind air quality in ways EPA might not have antici­
pated. The Good Neighbor Provision requires EPA to seek
——————
West Virginia, Pennsylvania, and Indiana each contribute in varying
amounts to five different nonattainment areas in three downwind
States. Id., at 52. Implementation of the Transport Rule, EPA model­
ing demonstrates, will bring three of these five areas into attainment
by a comfortable margin, and a fourth only barely. See id., at 53, fig. 2.
The fifth downwind receptor, however, will still fall short of attainment
despite the reductions the rule requires. See ibid. But if EPA were to
lower the emission reductions required of the upwind States to reduce
over-attainment in the first three areas, the area barely achieving
attainment would no longer do so, and the area still in nonattainment
would fall even further behind. Thus, “over-control” of the first three
downwind receptors is essential to the attainment achieved by the
fourth and to the fifth’s progress toward that goal.
   23 The dissent suggests that our qualification of the term “over­

control” is tantamount to an admission that “nothing stands in the way
of [a] proportional-reduction approach.” Post, at 9. Not so. Permitting
“over-control” as to one State for the purpose of achieving attainment in
another furthers the stated goal of the Good Neighbor Provision, i.e.,
attainment of NAAQS. By contrast, a proportional-reduction scheme is
neither necessary to achieve downwind attainment, nor mandated by
the terms of the statute, as earlier discussed, see supra, at 21–25.
Permitting “over-control” for the purpose of achieving proportionality
would thus contravene the clear limits the statute places on EPA’s good
neighbor authority, i.e., to eliminate only those “amounts” of upwind
pollutants essential to achieving attainment downwind.
                  Cite as: 572 U. S. ____ (2014)           31

                      Opinion of the Court

downwind attainment of NAAQS notwithstanding the
uncertainties. Hence, some amount of over-control, i.e.,
emission budgets that turn out to be more demanding
than necessary, would not be surprising. Required to
balance the possibilities of under-control and over-control,
EPA must have leeway in fulfilling its statutory mandate.
   Finally, in a voluminous record, involving thousands of
upwind-to-downwind linkages, respondents point to only a
few instances of “unnecessary” emission reductions, and
even those are contested by EPA. Compare Brief for
Industry Respondents 19 with Reply Brief for Federal
Petitioners 21–22. EPA, for its part, offers data, contested
by respondents, purporting to show that few (if any) up­
wind States have been required to limit emissions below
the one-percent threshold of significance. Compare Brief
for Federal Petitioners 37, 54–55, with Brief for Industry
Respondents 40.
   If any upwind State concludes it has been forced to
regulate emissions below the one-percent threshold or
beyond the point necessary to bring all downwind States
into attainment, that State may bring a particularized, as­
applied challenge to the Transport Rule, along with any
other as-applied challenges it may have. Cf. Babbitt v.
Sweet Home Chapter, Communities for Great Ore., 515
U. S. 687, 699–700 (1995) (approving agency’s reasonable
interpretation of statute despite possibility of improper
applications); American Hospital Assn. v. NLRB, 499 U. S.
606, 619 (1991) (rejecting facial challenge to National
Labor Relations Board rule despite possible arbitrary
applications). Satisfied that EPA’s cost-based methodol-
ogy, on its face, is not “arbitrary, capricious, or manifestly
contrary to the statute,” Chevron, 467 U. S., at 844, we
uphold the Transport Rule. The possibility that the rule,
in uncommon particular applications, might exceed EPA’s
statutory authority does not warrant judicial condemna­
tion of the rule in its entirety.
32       EPA v. EME HOMER CITY GENERATION, L. P.

                     Opinion of the Court

   In sum, we hold that the CAA does not command that
States be given a second opportunity to file a SIP after
EPA has quantified the State’s interstate pollution obliga­
tions. We further conclude that the Good Neighbor Provi­
sion does not require EPA to disregard costs and consider
exclusively each upwind State’s physically proportionate
responsibility for each downwind air quality problem.
EPA’s cost-effective allocation of emission reductions
among upwind States, we hold, is a permissible, work-
able, and equitable interpretation of the Good Neighbor
Provision.
                        *   *    *
  For the reasons stated, the judgment of the United
States Court of Appeals for the D. C. Circuit is reversed,
and the cases are remanded for further proceedings con­
sistent with this opinion.
                                          It is so ordered.

  JUSTICE ALITO took no part in the consideration or
decision of these cases.
                 Cite as: 572 U. S. ____ (2014)           1

                     SCALIA, J., dissenting

SUPREME COURT OF THE UNITED STATES
                         _________________

                  Nos. 12–1182 and 12–1183
                         _________________


  ENVIRONMENTAL PROTECTION AGENCY ET AL.,
               PETITIONERS
12–1182             v.
  EME HOMER CITY GENERATION, L. P., ET AL.; AND

      AMERICAN LUNG ASSOCIATION ET AL.,
                PETITIONERS
12–1183              v.
    EME HOMER CITY GENERATION, L. P., ET AL.
ON WRITS OF CERTIORARI TO THE UNITED STATES COURT OF
    APPEALS FOR THE DISTRICT OF COLUMBIA CIRCUIT
                        [April 29, 2014]

   JUSTICE SCALIA, with whom JUSTICE THOMAS joins,
dissenting.
   Too many important decisions of the Federal Govern­
ment are made nowadays by unelected agency officials
exercising broad lawmaking authority, rather than by the
people’s representatives in Congress. With the statute
involved in the present cases, however, Congress did it
right. It specified quite precisely the responsibility of an
upwind State under the Good Neighbor Provision: to
eliminate those amounts of pollutants that it contributes
to downwind problem areas. But the Environmental
Protection Agency was unsatisfied with this system.
Agency personnel, perhaps correctly, thought it more
efficient to require reductions not in proportion to the
amounts of pollutants for which each upwind State is
responsible, but on the basis of how cost-effectively each
can decrease emissions.
2          EPA v. EME HOMER CITY GENERATION, L. P.

                        SCALIA, J., dissenting

  Today, the majority approves that undemocratic revi­
sion of the Clean Air Act. The Agency came forward with
a textual justification for its action, relying on a farfetched
meaning of the word “significantly” in the statutory text.
That justification is so feeble that today’s majority does
not even recite it, much less defend it. The majority
reaches its result (“Look Ma, no hands!”) without benefit
of text, claiming to have identified a remarkable “gap” in
the statute, which it proceeds to fill (contrary to the plain
logic of the statute) with cost-benefit analysis—and then,
with no pretended textual justification at all, simply ex­
tends cost-benefit analysis beyond the scope of the alleged
gap.
  Additionally, the majority relieves EPA of any obligation
to announce novel interpretations of the Good Neighbor
Provision before the States must submit plans that are
required to comply with those interpretations. By accord­
ing the States primacy in deciding how to attain the gov­
erning air-quality standards, the Clean Air Act is preg­
nant with an obligation for the Agency to set those
standards before the States can be expected to achieve
them. The majority nonetheless approves EPA’s promul­
gation of federal plans implementing good-neighbor
benchmarks before the States could conceivably have met
those benchmarks on their own.
  I would affirm the judgment of the D. C. Circuit that
EPA violated the law both in crafting the Transport Rule
and in implementing it.1
                     I. The Transport Rule
   “It is axiomatic that an administrative agency’s power to
promulgate legislative regulations is limited to the author­
ity delegated by Congress.” Bowen v. Georgetown Univ.

——————
  1 I agree with the majority’s analysis turning aside EPA’s threshold

objections to judicial review. See ante, at 13–14, 18–19.
                  Cite as: 572 U. S. ____ (2014)            3

                      SCALIA, J., dissenting

Hospital, 488 U. S. 204, 208 (1988). Yet today the major-
ity treats the text of the Clean Air Act not as the source
and ceiling of EPA’s authority to regulate interstate air
pollution, but rather as a difficulty to be overcome in
pursuit of the Agency’s responsibility to “craf[t] a solution
to the problem of interstate air pollution.” Ante, at 3. In
reality, Congress itself has crafted the solution. The Good
Neighbor Provision requires each State to eliminate what­
ever “amounts” of “air pollutant[s]” “contribute significantly
to nonattainment” or “interfere with maintenance” of
national ambient air-quality standards (NAAQS) in other
States. 42 U. S. C. §7410(a)(2)(D)(i)(I). The statute ad­
dresses solely the environmental consequences of emis­
sions, not the facility of reducing them; and it requires
States to shoulder burdens in proportion to the size of
their contributions, not in proportion to the ease of bearing
them. EPA’s utterly fanciful “from each according to its
ability” construction sacrifices democratically adopted text
to bureaucratically favored policy. It deserves no defer­
ence under Chevron U. S. A. Inc. v. Natural Resources
Defense Council, Inc., 467 U. S. 837 (1984).
         A. Alleged Textual Support: “Significantly”
   In the Government’s argument here, the asserted tex­
tual support for the efficient-reduction approach adopted by
EPA in the Transport Rule is the ambiguity of the word
“significantly” in the statutory requirement that each
State eliminate those “amounts” of pollutants that “con­
tribute significantly to nonattainment” in downwind
States. §7410(a)(2)(D)(i)(I) (emphasis added). As de­
scribed in the Government’s briefing:
    “[T]he term ‘significantly’ . . . is ambiguous, and . . .
    EPA may permissibly determine the amount of a
    State’s ‘significant’ contribution by reference to the
    amount of emissions reductions achievable through
    application of highly cost-effective controls.” Reply
4        EPA v. EME HOMER CITY GENERATION, L. P.

                     SCALIA, J., dissenting

    Brief for Federal Petitioners 15–16 (emphasis added;
    some internal quotation marks omitted).
And as the Government stated at oral argument:
    “[I]n terms of the language, ‘contribute significantly,’
    . . . EPA reasonably construed that term to include a
    component of difficulty of achievement [i.e., cost]; that
    is, in common parlance, we might say that dunking a
    basketball is a more significant achievement for
    somebody who is 5 feet 10 than for somebody who is 6
    feet 10.” Tr. of Oral Arg. 9 (emphasis added).
   But of course the statute does not focus on whether the
upwind State has “achieved significantly”; it asks whether
the State has “contributed significantly” to downwind
pollution. The provision addresses the physical effects of
physical causes, and it is only the magnitude of the rela­
tionship sufficient to trigger regulation that admits of
some vagueness. Stated differently, the statute is ambig­
uous as to how much of a contribution to downwind pollu­
tion is “significant,” but it is not at all ambiguous as to
whether factors unrelated to the amounts of pollutants
that make up a contribution affect the analysis. Just as
“[i]t does not matter whether the word ‘yellow’ is ambigu­
ous when the agency has interpreted it to mean ‘purple,’ ”
United States v. Home Concrete & Supply, LLC, 566 U. S.
___, ___, n. 1 (2012) (SCALIA, J., concurring in part and
concurring in judgment) (slip op., at 2, n. 1), it does not
matter whether the phrase “amounts which . . . contribute
significantly [to downwind NAAQS nonattainment]” is
ambiguous when EPA has interpreted it to mean
“amounts which are inexpensive to eliminate.”
   It would be extraordinary for Congress, by use of the
single word “significantly,” to transmogrify a statute that
assigns responsibility on the basis of amounts of pollut­
ants emitted into a statute authorizing EPA to reduce
interstate pollution in the manner that it believes most
                 Cite as: 572 U. S. ____ (2014)            5

                     SCALIA, J., dissenting

efficient. We have repeatedly said that Congress “does not
alter the fundamental details of a regulatory scheme in
vague terms or ancillary provisions—it does not, one
might say, hide elephants in mouseholes.” Whitman v.
American Trucking Assns., Inc., 531 U. S. 457, 468 (2001)
(citing MCI Telecommunications Corp. v. American Tele-
phone & Telegraph Co., 512 U. S. 218, 231 (1994); FDA v.
Brown & Williamson Tobacco Corp., 529 U. S. 120, 159–
160 (2000)).
   The statute’s history demonstrates that “significantly” is
not code for “feel free to consider compliance costs.” The
previous version of the Good Neighbor Provision required
each State to prohibit emissions that would “prevent at­
tainment or maintenance by any other State of any
[NAAQS].” 91 Stat. 693 (emphasis added). It is evident
that the current reformulation (targeting “any air pollut-
ant in amounts which will . . . contribute significantly to
nonattainment in, or interfere with maintenance by, any
other State with respect to any [NAAQS]”) was meant
simply to eliminate any implication that the polluting
State had to be a but-for rather than merely a contributing
cause of the downwind nonattainment or maintenance
problem—not to allow cost concerns to creep in through
the back door.
   In another respect also EPA’s reliance upon the word
“significantly” is plainly mistaken. The Good Neighbor
Provision targets for elimination not only those emissions
that “contribute significantly to nonattainment [of
NAAQS] in . . . any other State,” but also those that “inter­
fere with maintenance [of NAAQS] by . . . any other
State.” §7410(a)(2)(D)(i)(I). The wiggle-word “significantly”
is absent from the latter phrase.         EPA does not—
cannot—provide any textual justification for the conclu­
sion that, when the same amounts of a pollutant travel
downwind from States X and Y to a single area in State A,
the emissions from X but not Y can be said to “interfere
6        EPA v. EME HOMER CITY GENERATION, L. P.

                     SCALIA, J., dissenting

with maintenance” of the NAAQS in A just because they
are cheaper to eliminate. Yet EPA proposes to use the
“from each according to its ability” approach for nonat­
tainment areas and maintenance areas.
   To its credit, the majority does not allude to, much less
try to defend, the Government’s “significantly” argument.
But there is a serious downside to this. The sky-hook of
“significantly” was called into service to counter the crite­
rion of upwind-state responsibility plainly provided in the
statute’s text: amounts of pollutants contributed to down­
wind problem areas. See Brief for Federal Petitioners 42–
45. Having forsworn reliance on “significantly” to convert
responsibility for amounts of pollutants into responsibility
for easy reduction of pollutants, the majority is impaled
upon the statutory text.
                    B. The Alleged “Gap”
   To fill the void created by its abandonment of EPA’s
“significantly” argument, the majority identifies a sup­
posed gap in the text, which EPA must fill: While the text
says that each upwind State must be responsible for its
own contribution to downwind pollution, it does not say
how responsibility is to be divided among multiple States
when the total of their combined contribution to downwind
pollution in a particular area exceeds the reduction that
the relevant NAAQS requires. In the example given by
the majority, ante, at 21–22, when each of three upwind
States contributes 30 units of a pollutant to a downwind
State but the reduction required for that State to comply
with the NAAQS is only 30 units, how will responsibility
for that 30 units be apportioned? Wow, that’s a hard
one—almost the equivalent of asking who is buried in
Grant’s Tomb. If the criterion of responsibility is amounts
of pollutants, then surely shared responsibility must be
based upon relative amounts of pollutants—in the major­
ity’s example, 10 units for each State. The statute makes
                 Cite as: 572 U. S. ____ (2014)            7

                     SCALIA, J., dissenting

no sense otherwise. The Good Neighbor Provision con-
tains a gap only for those who blind themselves to the
obvious in order to pursue a preferred policy.
   But not only does the majority bring in cost-benefit
analysis to fill a gap that does not really exist. Having
filled that “gap,” it then extends the efficiency-based prin-
ciple to situations beyond the imaginary gap—that is,
situations where no apportionment is required. Even
where only a single upwind State contributes pollutants to
a downwind State, its annual emissions “budget” will be
based not upon the amounts of pollutants it contributes,
but upon what “pollution controls [are] available at the
chosen cost thresholds.” Ante, at 9. EPA’s justification
was its implausible (and only half-applicable) notion that
“significantly” imports cost concerns into the provision.
The majority, having abandoned that absurdity, is left to
deal with the no-apportionment situation with no de-
fense—not even an imaginary gap—against a crystal-clear
statutory text.
   C. The Majority’s Criticisms of Proportional Reduction
                       1. Impossibility
   The majority contends that a proportional-reduction
approach “could scarcely be satisfied in practice” and
“appears to work neither mathematically nor in practical
application,” ante, at 23—in essence, that the approach is
impossible of application. If that were true, I know of no
legal authority and no democratic principle that would
derive from it the consequence that EPA could rewrite the
statute, rather than the consequence that the statute
would be inoperative. “There are sometimes statutes
which no rule or canon of interpretation can make effec-
tive or applicable to the situations of fact which they
purport to govern. In such cases the statute must simply
fail.” 3 R. Pound, Jurisprudence 493 (1959) (footnote
omitted). In other words, the impossibility argument has
8         EPA v. EME HOMER CITY GENERATION, L. P.

                      SCALIA, J., dissenting

no independent force: It is relevant only if the majority’s
textual interpretation is permissible. But in any event,
the argument is wrong.
  The impossibility theorem rests upon the following
scenario: “Imagine that States X and Y . . . contribute air
pollution to State A in a ratio of one to five . . . .” Ante, at
23. And suppose that “States X and Y also contribute
pollutants to a second downwind State (State B), this time
in a ratio of seven to one.” Ibid. The majority concludes
that “[t]he Court of Appeals’ proportionality edict with
respect to both State A and State B appears to work nei­
ther mathematically nor in practical application.” Ibid.
But why not? The majority’s model relies on two faulty
premises—one an oversimplification and the other a mis­
apprehension.
  First, the majority’s formulation suggests that EPA
measures the comparative downwind drift of pollutants in
free-floating proportions between States. In reality, how­
ever, EPA assesses quantities (in physical units), not
proportions. So, the majority’s illustration of a 1-to-5 ratio
describing the relative contributions of States X and Y to
State A’s pollution might mean (for example) that X is
responsible for 0.2 unit of some pollutant above the
NAAQS in A and that Y is responsible for 1 unit. And
the second example, assuming a 7-to-1 ratio underlying
State X’s and Y’s contributions to State B’s pollution,
might mean that State X supplies 0.7 unit of the same pol­
lutant above the NAAQS and State Y, 0.1 unit. Under a
proportional-reduction approach, State X would be re­
quired to eliminate emissions of that pollutant by what-
ever minimum amount reduces both State A’s level by 0.2
unit and State B’s by 0.7 unit. State Y, in turn, would be
required to curtail its emissions by whatever minimum
amount decreases both State A’s measure by 1 unit and
State B’s by 0.1 unit.
  But, the majority objects, the reductions that State X
                 Cite as: 572 U. S. ____ (2014)            9

                     SCALIA, J., dissenting

must make to help bring State B into compliance may be
more than those necessary for it to help bring State A into
compliance, resulting in “over-control” of X with respect to
A. See ante, at 23–25, and n. 19. This objection discloses
the second flaw in the impossibility theorem. Echoing
EPA, see Brief for Federal Petitioners 47–48, the majority
believes that the D. C. Circuit’s interpretation of the Good
Neighbor Provision forbids over-control with respect to
even a single downwind receptor. That is the only way in
which the proportional-reduction approach could be
deemed “to work neither mathematically nor in practical
application” on its face. Ante, at 23. But the premise is
incorrect. Although some of the D. C. Circuit’s simplified
examples might support that conclusion, its opinion explic­
itly acknowledged that the complexity of real-world condi­
tions demands the contrary: “To be sure, . . . there may be
some truly unavoidable over-control in some downwind
States that occurs as a byproduct of the necessity of reduc­
ing upwind States’ emissions enough to meet the NAAQS
in other downwind States.” 696 F. 3d 7, 22 (2012). More­
over, the majority itself recognizes that the Good Neighbor
Provision does not categorically prohibit over-control. “As
the Good Neighbor Provision seeks attainment in every
downwind State, . . . exceeding attainment in one State
cannot rank as ‘over-control’ unless unnecessary to achiev­
ing attainment in any downwind State.” Ante, at 29–30.
The majority apparently fails to appreciate that, having
cleared up that potential point of confusion, nothing
stands in the way of the proportional-reduction approach.
   The majority relies on an EPA document preceding the
Transport Rule to establish the Agency’s supposed belief
that the proportional-reduction approach “could scarcely
be satisfied in practice.” Ante, at 23. But the document
says no such thing. Rather, it shows that the Agency
rejected a proportion-based, “air[-]quality-only” methodol­
ogy not because it was impossible of application, but be­
10       EPA v. EME HOMER CITY GENERATION, L. P.

                     SCALIA, J., dissenting

cause it failed to account for costs. See App. in No. 11–
1302 etc. (CADC), pp. 2311–2312. The document labels as
a “technical difficulty” (not an impossibility) the fact that
“most upwind states contribute to multiple downwind
[receptors] (in multiple states) and would have a different
reduction percentage for each one.” Id., at 2312. The
Clean Air Act is full of technical difficulties, and this one
is overcome by requiring each State to make the greatest
reduction necessary with respect to any downwind area.
                       2. Over-Control
   Apparently conceding that the proportional-reduction
approach may not be impossible of application after all,
the majority alternatively asserts that it would cause
“costly overregulation unnecessary to, indeed in conflict
with, the Good Neighbor Provision’s goal of attainment.”
Ante, at 24. This assertion of massive overregulation
assumes that a vast number of downwind States will be
the accidental beneficiaries of collateral pollution reduc­
tions—that is, nontargeted reductions that occur as a
consequence of required reductions targeted at neighbor­
ing downwind States. (Collateral pollution reduction is
the opposite of collateral damage, so to speak.) The major­
ity contends that the collateral pollution reductions en­
joyed by a downwind State will cause the required upwind
reductions actually targeting that State to exceed the level
necessary to assure attainment or maintenance, thus
producing unnecessary over-control. I have no reason to
believe that the problem of over-control is as extensive and
thus “costly” as the majority alleges, and the majority
provides none.
   But never mind that. It suffices to say that over-control
is no more likely to occur when the required reductions are
apportioned among upwind States on the basis of amounts
of pollutants contributed than when they are apportioned
on the basis of cost. There is no conceivable reason why
                    Cite as: 572 U. S. ____ (2014)                 11

                        SCALIA, J., dissenting

the efficient-reduction States that bear the brunt of the
majority’s (and EPA’s) approach are less likely to be over­
controlled than the major-pollution-causing States that
would bear the brunt of my (and the statute’s) approach.
Indeed, EPA never attempted to establish that the
Transport Rule did not produce gross over-control. See
696 F. 3d, at 27. What causes the problem of over-control
is not the manner of apportioning the required reductions,
but the composite volume of the required reductions in
each downwind State. If the majority’s approach reduces
over-control (it admittedly does not entirely eliminate it),
that is only because EPA applies its cost-effectiveness
principle not just to determining the proportions of re­
quired reductions that each upwind State must bear, but
to determining the volume of those required reductions.
See supra, at 7.
   In any case, the solution to over-control under a propor­
tional-reduction system is not difficult to discern. In
calculating good-neighbor responsibilities, EPA would
simply be required to make allowance for what I have
called collateral pollution reductions. The Agency would
set upwind States’ obligations at levels that, after taking
into account those reductions, suffice to produce attain­
ment in all downwind States. Doubtless, there are multi­
ple ways for the Agency to accomplish that task in accord­
ance with the statute’s amounts-based, proportional
focus.2 The majority itself invokes an unexplained device
to prevent over-control “in uncommon particular applica­
tions” of its scheme. Ante, at 31. Whatever that device is,
it can serve just as well to prevent over-control under the
approach I have outlined.
——————
  2 The majority insists that “proportionality cannot be one of those

ways.” Ante, at 25. But it is easy to imagine precluding unnecessary
over-control by reducing in a percent-based manner the burdens of each
upwind State linked to a given downwind area, which would retain the
proportionality produced by my approach.
12       EPA v. EME HOMER CITY GENERATION, L. P.

                     SCALIA, J., dissenting

   I fully acknowledge that the proportional-reduction
approach will demand some complicated computations
where one upwind State is linked to multiple downwind
States and vice versa. I am confident, however, that
EPA’s skilled number-crunchers can adhere to the stat-
ute’s quantitative (rather than efficiency) mandate by
crafting quantitative solutions. Indeed, those calculations
can be performed at the desk, whereas the “from each
according to its ability” approach requires the unwieldy
field examination of many pollution-producing sources
with many sorts of equipment.
                       D. Our Precedent
   The majority agrees with EPA’s assessment that
“[u]sing costs in the Transport Rule calculus . . . makes
good sense.” Ante, at 26. Its opinion declares that
“[e]liminating those amounts that can cost-effectively be
reduced is an efficient and equitable solution to the alloca-
tion problem the Good Neighbor Provision requires the
Agency to address.” Ibid. Efficient, probably. Equitable?
Perhaps so, but perhaps not. See Brief for Industry Re-
spondents 35–36. But the point is that whether efficiency
should have a dominant or subordinate role is for Con-
gress, not this Court, to determine.
   This is not the first time parties have sought to convert
the Clean Air Act into a mandate for cost-effective regula-
tion. Whitman v. American Trucking Assns., Inc., 531
U. S. 457 (2001), confronted the contention that EPA
should consider costs in setting NAAQS. The provision at
issue there, like this one, did not expressly bar cost-based
decisionmaking—and unlike this one, it even contained
words that were arguably ambiguous in the relevant
respect. Specifically, §7409(b)(1) instructed EPA to set
primary NAAQS “the attainment and maintenance of
which . . . are requisite to protect the public health” with
“an adequate margin of safety.” One could hardly over-
                     Cite as: 572 U. S. ____ (2014)                  13

                         SCALIA, J., dissenting

state the capaciousness of the word “adequate,” and the
phrase “public health” was at least equally susceptible
(indeed, much more susceptible) of permitting cost-benefit
analysis as the word “significantly” is here. As the re-
spondents in American Trucking argued, setting NAAQS
without considering costs may bring about failing indus-
tries and fewer jobs, which in turn may produce poorer
and less healthy citizens. See id., at 466. But we conclud-
ed that “in the context of ” the entire provision, that inter-
pretation “ma[de] no sense.” Ibid. As quoted earlier, we
said that Congress “does not alter the fundamental details
of a regulatory scheme in vague terms or ancillary provi-
sions—it does not . . . hide elephants in mouseholes.” Id.,
at 468.
   In American Trucking, the Court “refused to find im-
plicit in ambiguous sections of the [Clear Air Act] an
authorization to consider costs that has elsewhere, and so
often, been expressly granted,” id., at 467, citing a tradition
dating back to Union Elec. Co. v. EPA, 427 U. S. 246, 257,
and n. 5 (1976). There are, indeed, numerous Clean Air
Act provisions explicitly permitting costs to be taken into
account. See, e.g., §7404(a)(1); §7521(a)(2); §7545(c)(2);
§7547(a)(3); §7554(b)(2); §7571(b); §7651c(f)(1)(A). Ameri-
can Trucking thus demanded “a textual commitment of
authority to the EPA to consider costs,” 531 U. S., at 468—
a hurdle that the Good Neighbor Provision comes nowhere
close to clearing. Today’s opinion turns its back upon that
case and is incompatible with that opinion.3
——————
  3 The   majority shrugs off American Trucking in a footnote, reasoning
that because it characterized the provision there in question as “abso-
lute,” it has nothing to say about the Good Neighbor Provision, which is
not absolute. See ante, at 28, n. 21. This is a textbook example of
begging the question: Since the Good Neighbor Provision is not absolute
(the very point at issue here), American Trucking, which dealt with a
provision that is absolute, is irrelevant. To the contrary, American
Trucking is right on point. As described in text, the provision at issue
14         EPA v. EME HOMER CITY GENERATION, L. P.

                         SCALIA, J., dissenting

      II. Imposition of Federal Implementation Plans
   The D. C. Circuit vacated the Transport Rule for the
additional reason that EPA took the reins in allocating
emissions budgets among pollution-producing sources
through Federal Implementation Plans (FIPs) without
first providing the States a meaningful opportunity to
perform that task through State Implementation Plans
(SIPs). The majority rejects that ruling on the ground
that “the Act does not require EPA to furnish upwind
States with information of any kind about their good
neighbor obligations before a FIP issues.” Ante, at 16.
“[N]othing in the statute,” the majority says, “places EPA
under an obligation to provide specific metrics to States
before they undertake to fulfill their good neighbor obliga­
tions.” Ante, at 17. This remarkably expansive reasoning
makes a hash of the Clean Air Act, transforming it from a
program based on cooperative federalism to one of central­
ized federal control. Nothing in the Good Neighbor Provi­
sion suggests such a stark departure from the Act’s fun­
damental structure.
        A. Implications of State Regulatory Primacy
   Down to its very core, the Clean Air Act sets forth a
federalism-focused regulatory strategy. The Act begins by
declaring that “air pollution prevention (that is, the reduc­
tion or elimination, through any measures, of the amount
of pollutants produced or created at the source) and air
pollution control at its source is the primary responsibility
of States and local governments.” §7401(a)(3) (emphasis
added). State primacy permeates Title I, which addresses
the promulgation and implementation of NAAQS, in par­
ticular. Under §7409(a), EPA must promulgate NAAQS
for each pollutant for which air-quality criteria have been
—————— 

here is even more categorical (“absolute”) than the provision at issue in

American Trucking. 

                 Cite as: 572 U. S. ____ (2014)           15

                     SCALIA, J., dissenting

issued pursuant to §7408. Section 7410(a)(1), in turn,
requires each State, usually within three years of each
new or revised NAAQS, to submit a SIP providing for its
“implementation, maintenance, and enforcement.” EPA
may step in to take over that responsibility if, and only if,
a State discharges it inadequately. Specifically, if the
Agency finds that a State has failed to make a required or
complete submission or disapproves a SIP, it “shall prom­
ulgate a [FIP] at any time within 2 years . . . , unless the
State corrects the deficiency, and [EPA] approves the [SIP]
or [SIP] revision.” §7410(c)(1).
   To describe the effect of this statutory scheme in simple
terms: After EPA sets numerical air-quality benchmarks,
“Congress plainly left with the States . . . the power to
determine which sources would be burdened by regulation
and to what extent.” Union Elec. Co., 427 U. S., at 269.
The States are to present their chosen means of achieving
EPA’s benchmarks in SIPs, and only if a SIP fails to meet
those goals may the Agency commandeer a State’s author­
ity by promulgating a FIP. “[S]o long as the ultimate
effect of a State’s choice of emission limitations is compli­
ance with the [NAAQS], the State is at liberty to adopt
whatever mix of emission limitations it deems best suited
to its particular situation.” Train v. Natural Resources
Defense Council, Inc., 421 U. S. 60, 79 (1975). EPA, we
have emphasized, “is relegated by the Act to a secondary
role in the process of determining and enforcing the spe-
cific, source-by-source emission limitations which are
necessary if the [NAAQS] are to be met.” Ibid.
   The Good Neighbor Provision is one of the requirements
with which SIPs must comply. §7410(a)(2)(D)(i)(I). The
statutory structure described above plainly demands that
EPA afford States a meaningful opportunity to allocate
reduction responsibilities among the sources within their
borders. But the majority holds that EPA may in effect
force the States to guess at what those responsibilities
16        EPA v. EME HOMER CITY GENERATION, L. P.

                      SCALIA, J., dissenting

might be by requiring them to submit SIPs before learning
what the Agency regards as a “significan[t]” contribu­
tion—with the consequence of losing their regulatory
primacy if they guess wrong. EPA asserts that the D. C.
Circuit “was wrong as a factual matter” in reasoning that
States cannot feasibly implement the Good Neighbor
Provision without knowing what the Agency considers
their obligations to be. Brief for Federal Petitioners 29.
That is literally unbelievable. The only support that EPA
can muster are the assertions that “States routinely un­
dertake technically complex air quality determinations”
and that “emissions information from all States is publicly
available.” Ibid. As respondents rightly state: “All the
scientific knowledge in the world is useless if the States
are left to guess the way in which EPA might ultimately
quantify ‘significan[ce].’ ” Brief for State Respondents 50.
   Call it “punish[ing] the States for failing to meet a
standard that EPA had not yet announced and [they] did
not yet know,” 696 F. 3d, at 28; asking them “to hit the
target . . . before EPA defines [it],” id., at 32; requiring
them “to take [a] stab in the dark,” id., at 35; or “set[ting]
the States up to fail,” id., at 37. Call it “hid[ing] the ball,”
Brief for State Respondents 20; or a “shell game,” id., at
54. 	 Call it “pin the tail on the donkey.” Tr. of Oral Arg.
24. 	As we have recently explained:
     “It is one thing to expect regulated parties to conform
     their conduct to an agency’s interpretations once the
     agency announces them; it is quite another to require
     regulated parties to divine the agency’s interpre­
     tations in advance or else be held liable when the
     agency announces its interpretations for the first
     time . . . and demands deference.” Christopher v.
     SmithKline Beecham Corp., 567 U. S. ___, ___ (2012)
     (slip op., at 14).
That principle applies a fortiori to a regulatory regime
                 Cite as: 572 U. S. ____ (2014)           17

                     SCALIA, J., dissenting

that rests on principles of cooperative federalism.
                    B. Past EPA Practice
   EPA itself has long acknowledged the proposition that it
is nonsensical to expect States to comply with the Good
Neighbor Provision absent direction about what consti­
tutes a “significan[t]” contribution to interstate pollution.
   The Agency consistently adopted that position prior to
the Transport Rule. In 1998, when it issued the NOX SIP
Call under §7410(k)(5), EPA acknowledged that “[w]ithout
determining an acceptable level of NOX reductions, the
upwind State would not have guidance as to what is an
acceptable submission.” 63 Fed. Reg. 57370. EPA deemed
it “most efficient—indeed necessary—for the Federal
government to establish the overall emissions levels for
the various States.” Ibid. Accordingly, the Agency quanti­
fied good-neighbor responsibilities and then allowed
States a year to submit SIPs to implement them. Id., at
57450–57451.
   Similarly, when EPA issued the Clean Air Interstate
Rule (CAIR) in 2005 under §7410(c), it explicitly “recog­
nize[d] that States would face great difficulties in develop­
ing transport SIPs to meet the requirements of today’s
action without th[e] data and policies” provided by the
Rule, including “judgments from EPA concerning the
appropriate criteria for determining whether upwind
sources contribute significantly to downwind nonattain­
ment under [§74]10(a)(2)(D).” 70 id., at 25268–25269.
The Agency thus gave the States 18 months to submit
SIPs implementing their new good-neighbor responsibili­
ties. See id., at 25166–25167, 25176. Although EPA
published FIPs before that window closed, it specified that
they were meant to serve only as a “Federal backstop” and
would not become effective unless necessary “a year after
the CAIR SIP submission deadline.” 71 id., at 25330–
25331 (2006).
18          EPA v. EME HOMER CITY GENERATION, L. P.

                           SCALIA, J., dissenting

   Even since promulgating the Transport Rule, EPA has
repeatedly reaffirmed that States cannot be expected to
read the Agency’s mind. In other proceedings, EPA has
time and again stated that although “[s]ome of the ele­
ments of the [SIP-submission process] are relatively
straightforward, . . . others clearly require interpretation
by EPA through rulemaking, or recommendations through
guidance, in order to give specific meaning for a particular
NAAQS.” 76 id., at 58751 (2011). As an example of the
latter, the Agency has remarked that the Good Neighbor
Provision “contains numerous terms that require substan­
tial rulemaking by EPA in order to determine such basic
points as what constitutes significant contribution,” citing
CAIR. Ibid., n. 6. In fact, EPA repeated those precise
statements not once, not twice, but 30 times following
promulgation of the Transport Rule.4
   Notwithstanding what parties may have argued in other
litigation many years ago, it is beyond responsible debate
that the States cannot possibly design FIP-proof SIPs
without knowing the EPA-prescribed targets at which
they must aim. EPA insists that it enjoys significant
discretion—indeed, that it can consider essentially what­
ever factors it wishes—to determine what constitutes a
“significan[t]” contribution to interstate pollution; and it
simultaneously asserts that the States ought to know
what quantities it will choose. The Agency—and the
——————
  4 In  addition to the citations in text, see 77 Fed. Reg. 50654, and n. 7
(2012); id., at 47577, and n. 7; id., at 46363, and n. 7; id., at 46356, and
n. 9; id., at 45323, and n. 7; id., at 43199, and n. 7; id., at 38241, and
n. 6; id., at 35912, and n. 7; id., at 34909, and n. 7; id., at 34901, and n.
8; id., at 34310, and n. 7; id., at 34291, and n. 8; id., at 33384, and n. 7;
id., at 33375, and n. 7; id., at 23184, and n. 7; id., at 22543, and n. 4;
id., at 22536, and n. 7; id., at 22253, and n. 8; id., at 21915, and n. 7;
id., at 21706, and n. 6; id., at 16788, and n. 4; id., at 13241, and n. 5;
id., at 6715, and n. 7; id., at 6047, and n. 4; id., at 3216, and n. 7; 76 id.,
at 77955, and n. 7 (2011); id., at 75852, and n. 7; id., at 70943, and n. 6;
id., at 62636, and n. 3.
                     Cite as: 572 U. S. ____ (2014)                   19

                         SCALIA, J., dissenting

majority—cannot have it both ways.
                    C. Abuse of Discretion
   The majority attempts to place the blame for hollowing
out the core of the Clean Air Act on “the Act’s plain text.”
Ante, at 16. The first textual element to which it refers is
§7410(c)’s requirement that after EPA has disapproved a
SIP, it “shall promulgate a [FIP] at any time within 2
years.” That is to say, the Agency has discretion whether
to act at once or to defer action until some later point
during the 2-year period. But it also has discretion to
work within the prescribed timetable to respect the right­
ful role of States in the statutory scheme by delaying the
issuance or enforcement of FIPs pending the resubmission
and approval of SIPs—as EPA’s conduct surrounding
CAIR clearly demonstrates. And all of this assumes that
the Agency insists on disapproving SIPs before promulgat­
ing the applicable good-neighbor standards—though in
fact EPA has discretion to publicize those metrics before
the window to submit SIPs closes in the first place.
   The majority states that the Agency “retained discretion
to alter its course” from the one pursued in the NOX SIP
Call and CAIR, ante, at 17, but that misses the point.
The point is that EPA has discretion to arrange things so
as to preserve the Clean Air Act’s core principle of state
primacy—and that it is an abuse of discretion to refuse to
do so. See §7607(d)(9)(A); see also 5 U. S. C. §706(2)(A)
(identical text in the Administrative Procedure Act).
Indeed, the proviso in §7410(c)(1) that the Agency’s au­
thority to promulgate a FIP within the 2-year period
terminates if “the State corrects the deficiency, and [EPA]
approves the [SIP] or [SIP] revision” explicitly contem­
plates just such an arrangement.5
——————
   5 I am unimpressed, by the way, with the explanation that the major-

ity accepts for EPA’s about-face: that the D. C. Circuit admonished it to
“act with dispatch in amending or replacing CAIR.” Ante, at 18 (citing
20         EPA v. EME HOMER CITY GENERATION, L. P.

                         SCALIA, J., dissenting

   The majority’s conception of administrative discretion is
so sprawling that it would allow EPA to subvert state
primacy not only with respect to the interstate-pollution
concerns of the Good Neighbor Provision, but with respect
to the much broader concerns of the NAAQS program
more generally. States must submit SIPs “within 3 years”
of each new or revised NAAQS “or such shorter period as
[EPA] may prescribe.” §7410(a)(1) (emphasis added).
Because there is no principled reason to read that schedul­
ing provision in a less malleable manner than the one at
issue here, under the majority’s view EPA could demand
that States submit SIPs within a matter of days—or even
hours—after a NAAQS publication or else face the imme­
diate imposition of FIPs.
   The second element of “plain text” on which the majority
relies is small beer indeed. The Good Neighbor Provision
does not expressly state that EPA must publish target
quantities before the States are required to submit SIPs—
even though the Clean Air Act does so for NAAQS more
generally and for vehicle inspection and maintenance
programs, see §7511a(c)(3)(B). From that premise, the
majority reasons that “[h]ad Congress intended similarly
to defer States’ discharge of their obligations under the
Good Neighbor Provision, Congress . . . would have included
a similar direction in that section.” Ante, at 17. Per­
haps so. But EPA itself read the statute differently when
it declared in the NOX SIP Call that “[d]etermining the
overall level of air pollutants allowed to be emitted in a
State is comparable to determining [NAAQS], which the
courts have recognized as EPA’s responsibility, and is
——————
North Carolina v. EPA, 550 F. 3d 1176, 1178 (2008) (per curiam)).
Courts of Appeals’ raised eyebrows and wagging fingers are not law,
least so when they urge an agency to take ultra vires action. Nor can
the encouragement to act illegally qualify as a “good reaso[n]” for an
agency’s alteration of course under FCC v. Fox Television Stations, Inc.,
556 U. S. 502, 515 (2009).
                  Cite as: 572 U. S. ____ (2014)           21

                      SCALIA, J., dissenting

distinguishable from determining the particular mix of
controls among individual sources to attain those stand­
ards, which the caselaw identifies as a State responsibil­
ity.” 63 Fed. Reg. 57369 (emphasis added).
   The negative implication suggested by a statute’s failure
to use consistent terminology can be a helpful guide to
determining meaning, especially when all the provisions
in question were enacted at the same time (which is not
the case here). But because that interpretive canon, like
others, is just one clue to aid construction, it can be over­
come by more powerful indications of meaning elsewhere
in the statute. It is, we have said, “no more than a rule of
thumb that can tip the scales when a statute could be read
in multiple ways.” Sebelius v. Auburn Regional Medical
Center, 568 U. S. ___, ___ (2013) (slip op., at 9) (internal
quotation marks and brackets omitted). The Clean Air
Act simply cannot be read to make EPA the primary regu­
lator in this context. The negative-implication canon is
easily overcome by the statute’s state-respecting struc­
ture—not to mention the sheer impossibility of submitting
a sensible SIP without EPA guidance. Negative implica­
tion is the tiniest mousehole in which the majority discov­
ers the elephant of federal control.
                        *      *    *
   Addressing the problem of interstate pollution in the
manner Congress has prescribed—or in any other manner,
for that matter—is a complex and difficult enterprise. But
“[r]egardless of how serious the problem an administrative
agency seeks to address, . . . it may not exercise its author­
ity ‘in a manner that is inconsistent with the administra­
tive structure that Congress enacted into law.’ ” Brown &
Williamson, 529 U. S., at 125 (quoting ETSI Pipeline
Project v. Missouri, 484 U. S. 495, 517 (1988)). The major­
ity’s approval of EPA’s approach to the Clean Air Act
violates this foundational principle of popular government.
   I dissent.
