Natural Resources Defense Council v. Andrew Wheeler

United States Court of Appeals
FOR THE DISTRICT OF COLUMBIA CIRCUIT

Argued May 3, 2019 Decided April 7, 2020

No. 18-1172

NATURAL RESOURCES DEFENSE COUNCIL,
PETITIONER

v.

ANDREW WHEELER, ADMINISTRATOR, U.S. ENVIRONMENTAL
PROTECTION AGENCY AND ENVIRONMENTAL PROTECTION
AGENCY,
RESPONDENTS

ARKEMA INC. AND MEXICHEM FLUOR, INC.,
INTERVENORS

Consolidated with 18-1174

On Petitions for Review of an Action of the
United States Environmental Protection Agency

Peter J. DeMarco argued the cause for petitioner Natural
Resources Defense Council. With him on the briefs were
Melissa J. Lynch and David D. Doniger.
 2
Joshua M. Tallent, Assistant Attorney General, Office of the
Attorney General for the State of New York, argued the cause
for State Petitioners. With him on the briefs were
Letitia James, Attorney General, Barbara D. Underwood,
Solicitor General, Steven C. Wu, Deputy Solicitor General,
Michael J. Myers, Senior Counsel, and Morgan A. Costello,
Chief, Office of the Attorney General for the State of New
York; Kwame Raoul, Attorney General, and Daniel I.
Rottenberg, Assistant Attorney General, Office of the Attorney
General for the State of Illinois; Xavier Becerra, Attorney
General, David A. Zonana, Supervising Deputy Attorney
General, and Megan K. Hey, Deputy Attorney General, Office
of the Attorney General for the State of California; Maura
Healey, Attorney General, Christophe G. Courchesne,
Assistant Attorney General, and Megan M. Herzog, Special
Assistant Attorney General, Office of the Attorney General for
the Commonwealth of Massachusetts; Ellen F. Rosenblum,
Attorney General, and Paul A. Garrahan, Attorney-in-Charge,
Office of the Attorney General for the State of Oregon;
Kathleen Jennings, Attorney General, and Valerie M. Edge,
Deputy Attorney General, Office of the Attorney General for
the State of Delaware; Keith Ellison, Attorney General, and
Max H. Kieley, Assistant Attorney General, Office of the
Attorney General for the State of Minnesota; Robert A. Reiley,
Assistant Counsel, Commonwealth of Pennsylvania
Department of Environmental Protection; Karl A. Racine,
Attorney General, and Loren L. AliKhan, Solicitor General,
Office of the Attorney General for the District of Columbia;
Gurbir S. Grewal, Attorney General, and Lisa J. Morelli,
Deputy Attorney General, Office of the Attorney General for
the State of New Jersey; Thomas J. Donovan, Jr., Attorney
General, and Nicholas F. Persampieri, Assistant Attorney
General, Office of the Attorney General for the State of
Vermont; Robert W. Ferguson, Attorney General, and
 3
Katharine G. Shirey, Assistant Attorney General, Office of the
Attorney General for the State of Washington.

Benjamin Carlisle, Attorney, U.S. Department of Justice,
argued the cause for respondent. With him on the brief were
Jeffrey Bossert Clark, Assistant Attorney General, Jonathan
Brightbill, Deputy Assistant Attorney General, and Jan M.
Tierney and Diane E. McConkey, Attorneys, U.S.
Environmental Protection Agency.

Keith Bradley argued the cause for intervenors. With him
on the brief were W. Caffey Norman, Dan Himmelfarb, John S.
Hahn, Roger W. Patrick, and William J. Hamel.

Before: SRINIVASAN , Chief Judge, and TATEL and RAO,
Circuit Judges.

Opinion for the Court filed by Chief Judge SRINIVASAN .

Dissenting opinion filed by Circuit Judge RAO.

SRINIVASAN, Chief Judge: Thirty years ago, Congress
amended the Clean Air Act to require that users of ozone-
depleting substances transition to use of less harmful
substitutes. Many users replaced ozone-depleting substances
with hydrofluorocarbons (HFCs). Over time, though, scientists
came to understand that HFCs, while not ozone-depleting
substances, are powerful greenhouse gases that contribute to
climate change.

In 2015, EPA issued a regulation disallowing the use of
HFCs as a substitute for ozone-depleting substances. That rule
was challenged in our court in Mexichem Fluor, Inc. v. EPA,
866 F.3d 451 (D.C. Cir. 2017). We determined that EPA could
validly forbid current users of ozone-depleting substances from
 4
switching to HFCs. But we also concluded that EPA lacked
authority to force users who had already switched to HFCs to
make a second switch to a different substitute. We thus vacated
the rule in part and remanded to the agency.

On remand, even though we had sustained EPA’s bar
against use of HFCs with regard to entities who were still using
ozone-depleting substances, the agency decided to implement
our decision by suspending the rule’s listing of HFCs as unsafe
substitutes in its entirety, meaning that even current users of
ozone-depleting substances can now shift to HFCs. And EPA
did so without going through notice-and-comment procedures.

The Natural Resources Defense Council and a group of
states have now filed petitions for review in our court. They
argue among other things that EPA’s rule on remand
improperly amended the agency’s earlier rule without adhering
to notice-and-comment procedures. We agree, and we
therefore grant the petitions for review and vacate the
challenged rule.

I.

In the 1970s, scientists realized that some chemicals used
by humans deplete the layer of ozone gas above the Earth’s
surface that protects humans from ultraviolet radiation’s
harmful effects. See Nat. Res. Def. Council v. EPA, 464 F.3d
1, 3 (D.C. Cir. 2006). Based on those concerns, the United
States and other countries, in the late 1980s, developed the
Montreal Protocol on Substances that Deplete the Ozone
Layer, Sept. 16, 1987, S. Treaty Doc. No. 100–10, 1522
U.N.T.S. 29. The Protocol is an international agreement
requiring signatories to regulate ozone-depleting substances.
 5
In 1990, Congress implemented the United States’
obligations under that agreement by adding to the Clean Air
Act a new Title VI, 42 U.S.C. § 7671 et seq. Title VI requires
that, “[t]o the maximum extent practicable,” ozone-depleting
substances “be replaced by chemicals, product substitutes, or
alternative manufacturing processes that reduce overall risks to
human health and the environment.” Id. § 7671k(a). And to
help guard against the replacement of ozone-depleting
substances with alternatives that are themselves harmful, the
statute directs EPA to promulgate rules making it unlawful to
replace ozone-depleting substances with substances that “may
present adverse effects to human health or the environment.”
Id. § 7671k(c). To that end, EPA must maintain lists of
“prohibited” and “safe” substitutes for specific uses. Id.

EPA has promulgated a number of regulations approving
or prohibiting various substitutes for certain end-uses. See,
e.g., Protection of Stratospheric Ozone: Listing of Substitutes
for Ozone-Depleting Substances, 68 Fed. Reg. 4004 (Jan. 27,
2003); Protection of Stratospheric Ozone, 59 Fed. Reg. 13,044
(Mar. 18, 1994). One group of substitutes addressed in many
of those regulations is hydrofluorocarbons (HFCs), a family of
“substances that contain hydrogen, fluorine, and carbon.”
Mexichem, 866 F.3d at 455. In 1994, EPA “concluded that
certain HFCs were safe substitutes for ozone-depleting
substances when used in aerosols, motor vehicle air
conditioners, commercial refrigerators, and foams, among
other things.” Id. Over the following decade, EPA “added
HFCs to the list of safe substitutes for a number of other
products.” Id. Throughout the 1990s and 2000s, as businesses
transitioned away from ozone-depleting substances, they often
employed HFCs as a substitute. See id.

But over time, EPA became increasingly concerned about
HFCs. Although HFCs are not ozone-depleting substances,
 6
they are powerful greenhouse gases that, in EPA’s view, “may
contribute to climate change, increasing the incidence of
mortality and the likelihood of extreme weather events such as
floods and hurricanes.” Id. In 2015, after going through
notice-and-comment procedures, EPA promulgated a rule
moving some HFCs from the safe substitutes list to the
prohibited substitutes list. See Protection of Stratospheric
Ozone: Change of Listing Status for Certain Substitutes Under
the Significant New Alternatives Policy Program, 80 Fed. Reg.
42,870 (July 20, 2015). The 2015 Rule prohibited current users
of ozone-depleting substances from replacing those substances
with HFCs. But the Rule also went further, prohibiting the
continued use of certain HFCs by users who had already
switched from ozone-depleting substances to HFCs. See
Mexichem, 866 F.3d at 456.

The latter measure proved too ambitious. In Mexichem,
we determined that EPA’s attempt to regulate users who had
already switched from ozone-depleting substances to HFCs
exceeded the agency’s statutory authority. Title VI, we
concluded, only “makes it unlawful to ‘replace’ an ozone-
depleting substance that is covered . . . with a substitute
substance that is on the list of prohibited substitutes.” Id. at
458 (quoting 42 U.S.C. § 7671k(c)). And businesses “‘replace’
an ozone-depleting substance when they transition to making
[or using] the same product with a substitute substance. After
that transition has occurred, the replacement has been
effectuated,” and there is no longer an “ozone-depleting
substance to ‘replace.’” Id. at 459. And because HFCs are not
ozone-depleting substances, we concluded that once an entity
replaces ozone-depleting substances with HFCs, its HFC use is
no longer regulated by Title VI. In that situation, we held, EPA
lacks authority to require a second substitution in place of
HFCs. See id.
 7
At the same time, with regard to EPA’s decision to move
HFCs to the list of prohibited substitutes on a going-forward
basis, we reaffirmed that the agency may “move a substitute
from the list of safe substitutes to the list of prohibited
substitutes” and “may prohibit a manufacturer [or other
regulated entity] from replacing an ozone-depleting substance
that is covered under Title VI with a prohibited substitute.” Id.
at 457. We also rejected the petitioners’ myriad arbitrary-and-
capricious challenges, holding that “EPA reasonably removed
HFCs from the list of safe substitutes.” Id. at 462–63. For
those reasons, we granted the petitions for review of the 2015
Rule “in part,” by vacating the 2015 Rule only “to the extent it
requires manufacturers to replace HFCs with a substitute
substance.” Id. at 464.

Eight months later, in April 2018, EPA published in the
Federal Register a rule explaining its “response to the court’s
decision.” See Protection of Stratospheric Ozone: Notification
of Guidance and a Stakeholder Meeting Concerning the
Significant New Alternatives Policy (SNAP) Program, 83 Fed.
Reg. 18,431, 18,432 (Apr. 27, 2018). EPA issued the 2018
Rule without going through notice-and-comment procedures.
Although EPA recognized that Mexichem effected only a
“partial vacatur of the 2015 Rule,” the agency determined that
it would “not apply the HFC use restrictions or unacceptability
listings in the 2015 Rule for any purpose prior to completion”
of an anticipated future rulemaking on the subject. Id. at
18,433 (italics omitted). EPA’s decision to stop applying the
HFC restrictions in their entirety, rather than only with respect
to users who had already switched to HFCs (as Mexichem had
contemplated), rested primarily on two bases.

First, EPA explained that the “regulatory text promulgated
in the 2015 Rule” had consisted of “individual listing
decisions” that prohibited or restricted the use of a given HFC
 8
in a given end-use, without regard to the distinction drawn in
Mexichem between users who had already switched to HFCs
and users still using ozone-depleting substances. Id. at 18,434.
“[F]or each listing decision,” EPA reasoned, “there is no
language that could be understood as being removed or struck
out by the court so that some portion of the listing would
remain in effect pending EPA’s action on remand.” Id.
Second, EPA determined that “attempting to draw the
distinctions made by the court would present practical
difficulties for implementation.” Id. For example, the agency
posited, there could be “complex situations” in which a
regulated entity uses ozone-depleting substances in some
facilities and HFCs in other facilities, such that it would be
unclear whether the entity had already “replaced” ozone-
depleting substances with HFCs. Id. at 18,435.

In sum, EPA “recognize[d] that the court” in Mexichem
had “vacated the 2015 Rule ‘to the extent that’ it requires
manufacturers to replace HFCs.” Id. But given “its expertise
in administering the [relevant] regulations, and its
understanding of the 2015 Rule, EPA conclude[d] that the
vacatur [could not] be implemented” in the way contemplated
by our decision in Mexichem. Id. EPA instead decided to
“treat[]” the vacatur “as striking the HFC listing changes in the
2015 Rule in their entirety.” Id. And the agency thus
determined that it “will not apply the HFC use restrictions or
unacceptability listings in the 2015 Rule for any purpose.” Id.
EPA also announced that it was “prepar[ing] to undertake
notice-and-comment rulemaking” to address various issues
related to Mexichem, HFCs, and the safe substitutes program
more generally. Id. at 18,435–36.

Following publication of that 2018 Rule, both the Natural
Resources Defense Council and a group of states filed petitions
for review of EPA’s action in our court, which we consolidated.
 9
Petitioners contend that the 2018 Rule is invalid, both because
EPA improperly issued it without adhering to notice-and-
comment procedures and because it is substantively arbitrary
and capricious. In response, two intervenors (HFC
manufacturers Arkema Inc. and Mexichem Fluor, Inc.) argue
that we lack jurisdiction over the petitions for review because
petitioners fail to demonstrate their standing to seek relief. In
addition, the intervenors and EPA contend that we lack
jurisdiction because the 2018 Rule is not final agency action,
and they also defend the Rule on the merits.

II.

A.

We begin by considering petitioners’ standing. Because
Article III of the Constitution limits us to “resolving cases and
controversies, a showing of standing is an essential and
unchanging predicate to any exercise of our jurisdiction.” Nat.
Res. Def. Council v. EPA, 755 F.3d 1010, 1016 (D.C. Cir.
2014) (internal quotation marks omitted). To establish
standing, a party must demonstrate: “(1) an injury in fact that
is concrete and particularized as well as actual or imminent; (2)
a causal connection between the injury and the challenged
conduct; and (3) a likelihood, as opposed to mere speculation,
that the injury will be redressed by a favorable decision.” Id.
(internal quotation marks omitted). In addition, when a
representational organization like NRDC sues on behalf of its
members, it must also show that (1) “its members would
otherwise have standing to sue in their own right”; (2) “the
interests it seeks to protect are germane to the organization’s
purpose”; and (3) “neither the claim asserted nor the relief
requested requires the participation of individual members.”
Id. (citation omitted).
 10
Here, NRDC and at least one of the state petitioners have
satisfied their burden to show an injury both caused by the 2018
Rule and likely to be redressed by a favorable decision. To link
the 2018 Rule to an injury-in-fact, petitioners begin with the
contention that the 2018 Rule, by vacating the entirety of the
2015 Rule’s HFC listings, allows entities to switch from ozone-
depleting substances to HFCs and thus will cause an increase
in HFC emissions. While EPA does not contest that premise,
intervenors do. They argue that the 2018 Rule will not cause
any such increase because it is our decision in Mexichem, as
opposed to the 2018 Rule, that “effectively undid the” 2015
Rule. See Intervenors Br. 27–28.

But, as is discussed below, petitioners’ core contention in
this case is that Mexichem only partially vacated the 2015 Rule,
and that the 2018 Rule then had an independent legal effect by
vacating the rest of the HFC listings in the 2015 Rule. And for
purposes of determining standing, we must assume that
petitioners will prevail on the merits of their argument. See
Defs. of Wildlife v. Gutierrez, 532 F.3d 913, 924 (D.C. Cir.
2008). We thus assume that petitioners are correct that the
2018 Rule, and not Mexichem, completed the vacatur of the
2015 Rule’s HFC listings. And no party disputes petitioners’
contention that allowing additional entities to use HFCs will in
fact lead to additional use of HFCs.

Once we accept the premise that the 2018 Rule will lead
to an increase in HFC emissions, the rest of the standing
analysis falls readily into place. As the parties agree, the
release of HFCs contributes to climate change. And NRDC has
submitted a declaration from a member averring that he owns
coastal property in New Jersey that is especially vulnerable to
weather events caused or worsened by climate change, and
New York state similarly demonstrated its proprietary interest
in coastal lands threatened by climate change. See NRDC Br.
 11
S.A. 13–19; States Br. 23–24; Snyder Decl. ¶ 30; cf.
Massachusetts v. EPA, 549 U.S. 497, 519 (2007). Petitioners
then have adequately linked the 2018 Rule to an injury-in-fact:
the 2018 Rule will lead to an increase in HFC emissions, which
will in turn lead to an increase in climate change, which will
threaten petitioners’ coastal property. And of course, a vacatur
of the 2018 Rule would redress that injury by restoring the
2015 Rule’s HFC listings as applied to those entities that
Mexichem found EPA could validly regulate, thereby reducing
HFC emissions.

It follows that both NRDC and New York have established
the injury, causation, and redressability requirements of
standing, and New York has shown its standing. (Because New
York has demonstrated its standing, we need not address the
standing of the other state petitioners. See Massachusetts, 549
U.S. at 518). As noted above, however, NRDC must clear two
additional hurdles to establish standing to bring its own
separate petition because it is suing in a representational
capacity: NRDC must show that its petition is germane to its
purpose and that the claims asserted or relief sought do not
require the involvement of its individual members.

NRDC satisfies both of those requirements. As NRDC
explains in its brief, it is an environmental organization that is
“committed to reducing emissions of greenhouse gases” and
that has long “worked on multiple fronts to reduce HFC
pollution.” NRDC Br. 15–16; cf. Nat. Res. Def. Council, 755
F.3d at 1016 (allowing NRDC to proceed in a representational
capacity in an environmental lawsuit). And NRDC neither
seeks any individualized relief nor brings claims dependent on
any individual member’s factual circumstances, which means
that no individual member’s participation is necessary to its
petition. We therefore find that NRDC, like New York, has
established its standing to proceed.
 12
B.

We next consider whether the 2018 Rule amounts to final
agency action subject to judicial review. The Clean Air Act
provides for judicial review only of “final action,” 42 U.S.C.
§ 7607(b)(1), a limitation coterminous with the concept of
“final agency action” in the Administrative Procedure Act, 5
U.S.C. § 704. See Sierra Club v. EPA, 873 F.3d 946, 951 (D.C.
Cir. 2017). An action is “final if two independent conditions
are met: (1) the action ‘marks the consummation of the
agency’s decisionmaking process’ and is not ‘of a merely
tentative or interlocutory nature;’ and (2) it is an action ‘by
which rights or obligations have been determined, or from
which legal consequences will flow.’” Soundboard Ass’n v.
Fed. Trade Comm’n, 888 F.3d 1261, 1267 (D.C. Cir. 2018)
(alteration omitted) (quoting Bennett v. Spear, 520 U.S. 154,
177–78 (1997)). The 2018 Rule satisfies both of those criteria.

1.

The 2018 Rule represents the consummation of EPA’s
decisionmaking process. Neither EPA nor intervenors contend
otherwise, and for good reason.

The consummation prong of the finality inquiry requires
us to determine “whether an action is properly attributable to
the agency itself and represents the culmination of that
agency’s consideration of an issue,” or is, instead, “only the
ruling of a subordinate official, or tentative.” Id. (citation
omitted); see id. at 1269 (analyzing whether agency action is
“subject to further agency review” (citation omitted)). Here,
the 2018 Rule was issued under the authority of the
Administrator himself, was published in the Federal Register,
and was the culmination of EPA’s consideration of the issue of
how to treat the 2015 Rule’s HFC listings pending any further
 13
formal rulemaking. The 2018 Rule thus is far removed from
the types of agency action—such as informal letters issued by
subordinate officials—that we have held do not amount to the
culmination of an agency’s decisionmaking process. See id. at
1267–68.

The 2018 Rule marks the culmination of EPA’s
decisionmaking for finality purposes notwithstanding the
agency’s characterization of the Rule as an interim resolution:
EPA has stated its intention to commence another rulemaking
that will address the use of HFCs as replacements for ozone-
depleting substances on a permanent basis, and the outcome of
such a process could displace the 2018 Rule going forward.
See 83 Fed. Reg. at 18,435–36. But even if the 2018 Rule were
to be displaced by another rule at some point, our precedents
make clear that an interim agency resolution counts as final
agency action despite the potential for a different permanent
decision, as long as the interim decision is not itself subject to
further consideration by the agency. In that event, the interim
resolution is the final word from the agency on what will
happen up to the time of any different permanent decision.

For example, in Clean Air Council v. Pruitt, 862 F.3d 1
(D.C. Cir. 2017) (per curiam), we held that a stay of a
regulation pending the resolution of a petition for
reconsideration of the regulation qualified as final action: “In
effect, the Administrator has granted a modification of the
mandatory [regulation] for the entire period of time that the
petition is pending. There is no indication that the
[Administrator] intends to reconsider this decision or to vacate
the grant of interim relief. Thus, the [Administrator’s] decision
represents the final agency position on this issue . . . .” Id. at 6
(citation omitted). Similarly, in International Union, United
Mine Workers of America v. Mine Safety & Health
Administration, 823 F.2d 608 (D.C. Cir. 1987), we held that we
 14
had jurisdiction over a petition for review of the MHSA’s
decision to grant a mine operator interim relief from a safety
standard pending resolution of the operator’s petition for
permanent modification of the standard. In that case too, we
determined that the grant of relief was “final” notwithstanding
its interim nature because there was “no indication that the
Secretary intends to reconsider . . . or to vacate the grant of
interim relief.” Id. at 614–15.

Here, the 2018 Rule is even more final than were the
interim decisions in Clean Air Council and International
Union. In those cases, a proceeding that could result in an
alteration of the interim resolution—a petition for
reconsideration in Clean Air Council, and a petition for
permanent modification in International Union—had already
been commenced. Here, by contrast, EPA has indicated that it
intends to undertake a further rulemaking at some point but has
not formally initiated the process. And even if EPA in the
future were to do so and were to promulgate a new rule
addressing the treatment of HFCs under Title VI, the 2018 Rule
firmly establishes EPA’s current position that the 2015 Rule’s
HFC listings are unenforceable, and that position will continue
to govern unless and until the agency issues a new rule. That
counts as consummation of agency decisionmaking for finality
purposes.

A contrary conclusion would be incompatible with our
usual practice when an agency informs us that it wishes to
reconsider a rule that is the subject of a pending petition for
review before our court. In such a circumstance, we face a
choice between remanding to the agency or continuing with our
review. See Utility Solid Waste Activities Grp. v. EPA, 901
F.3d 414, 436–38 (D.C. Cir. 2018). But if the prospect of an
agency’s reconsideration of a rule sufficed to render the rule
non-final, then when an agency tells us it wants to reconsider a
 15
rule that is before us on review, we could neither remand to the
agency nor continue our review. Instead, we would be
compelled to dismiss for lack of jurisdiction, which we have
never done (or thought it necessary to do) in that situation.

Additionally, if an agency’s indication of an intent to
reconsider an interim (or other) action sufficed to render the
action non-final, agencies could evade judicial review of their
actions even if they impose substantial obligations on regulated
parties over a considerable period of time. Consider, in that
regard, a recent case in our court, Exhaustless v. FAA, 931 F.3d
1209 (2019). That case involved the Federal Aviation
Administration’s regulation of take-off and landing slots at
LaGuardia and John F. Kennedy Airports. Id. at 1210. In 2006
(for LaGuardia) and 2008 (for Kennedy), the FAA published
“interim” regulations governing distribution of those slots
ostensibly for a limited time, and professed an intent to finalize
a permanent rule in the near future. Id. at 1210–12. More than
a decade later, however, those “interim” regulations have been
extended multiple times and remain in effect. Id. It would
make little sense to deem such “interim” rules non-final—and
hence non-challengeable—merely because of the prospect that
they could be displaced at some point by further agency action.

Here, for instance, assuming that EPA has a good-faith
intent to engage in a rulemaking that will settle the treatment
of HFCs on an ostensibly permanent basis, it is wholly
uncertain what the resulting regime will look like or when it
will be in place. It could take the agency considerable time to
gather the necessary input and settle on a solution. And for all
we know, at the end of that process, EPA might even come to
the conclusion that the 2018 Rule already embodies the proper
resolution of the issue (or it could reach any of an unknown
number of other potential solutions). Regardless, until then,
EPA will continue to apply the 2018 Rule. That Rule marks
 16
the consummation of the agency’s decisionmaking about the
governing framework unless and until it is superseded.

Finally, any agency action is always subject to
displacement by a future rulemaking. If the mere possibility of
displacement rendered a governing agency rule non-final for
purposes of judicial review, no rule would ever count as final.
Our precedents understandably prescribe a contrary approach,
under which, as long as an agency has completed its
decisionmaking on a challenged rule—even one interim in
nature—the rule satisfies the first prong of the finality test. See
Clean Air Council, 862 F.3d at 6; Int’l Union, 823 F.2d at 614–
15. It follows that, as both EPA and petitioners agree, the 2018
Rule marks the consummation of the agency’s decisionmaking
process.

2.

The 2018 Rule also determined legal rights and obligations
and gave rise to legal consequences for purposes of the second
prong of the finality test. As we have recognized, an agency’s
suspension of regulatory requirements ordinarily “affects
regulated parties’ rights or obligations.” Clean Air Council,
862 F.3d at 7 (internal quotation marks omitted). Here, no
party disputes that, to the extent the 2018 Rule suspends the
2015 Rule’s HFC listings, the 2018 Rule determines legal
rights and obligations and carries legal consequences by giving
regulated parties the legal right to replace ozone-depleting
substances with HFCs.

EPA and intervenors, though, contend that the 2018 Rule
does not determine legal rights and obligations or effect legal
consequences. In their view, it was our decision in Mexichem,
not the 2018 Rule, that suspended the 2015 Rule’s HFC
listings. According to that account, the 2018 Rule “simply
 17
applies and implements” Mexichem and “therefore has no
independent legal consequences.” EPA Br. 19. That is
incorrect.

Our decision in Mexichem makes clear that it did not
vacate the HFC listings in the 2015 Rule in their entirety. The
decision rested on an understanding of EPA’s statutory
authority to regulate entities’ replacement of ozone-depleting
substances. We reasoned that an entity “replaces” an ozone-
depleting substance when it switches to a substitute substance,
and that EPA’s statutory authority thus extends only to
regulating the initial switch. See 866 F.3d at 458–59. And
because HFCs are not themselves ozone-depleting substances,
we concluded, EPA had no statutory authority to compel an
entity already using HFCs to replace them with alternate
substitutes. See id. We thus held that EPA cannot permissibly
apply the 2015 Rule’s HFC listings to entities already using
HFCs. Id. We made no suggestion, though, that EPA cannot
apply the 2015 Rule to entities still using ozone-depleting
substances. Our decision accordingly did not vacate the 2015
Rule’s HFC listings in toto.

To the contrary, the Mexichem decision repeatedly evinced
our understanding that we were vacating the HFC listings only
in part. Four distinct times, we emphasized that we were
vacating the 2015 Rule only “to the extent” the Rule requires
replacements of HFCs, id. at 454, 462, 464, confirming that we
otherwise sought to leave the HFC listings intact. Similarly,
when discussing EPA’s theory that it could apply the 2015 Rule
to all parties that had previously used ozone-depleting
substances but had since switched to HFCs, we explained that
the agency had not met the necessary requirements to allow
retroactive rulemaking and that, “[u]nless and until” it did so,
“EPA may not apply the 2015 Rule to require manufacturers to
replace one non-ozone-depleting substitute with another
 18
substitute.” Id. at 462. Again, the straightforward implication
of our statement is that EPA may apply the 2015 Rule in other
circumstances.

We echoed the same understanding when, after concluding
that EPA lacked statutory authority to apply the 2015 Rule’s
listings to entities that had already switched to HFCs, we went
on to consider—and reject—the manufacturers’ various
arguments that “EPA’s decision to remove HFCs from the list
of safe substitutes was arbitrary and capricious.” Id. at 462–
63. That entire discussion would have been wholly
unnecessary had we believed that the first part of our opinion
(about EPA’s statutory authority) meant we were vacating the
2015 HFC listings in their entirety.

In short, our decision in Mexichem reinforced throughout
an intention only to forbid EPA from applying the 2015 Rule’s
HFC listings to a discrete set of regulated parties (those that
had already switched from ozone-depleting substances to
HFCs), not to set aside the 2015 Rule’s HFC listings in their
entirety. The 2018 Rule goes further than Mexichem by
instituting a complete vacatur of the 2015 Rule’s HFC listings.
And vacating those listings has the effect of suspending
regulatory requirements, which qualifies as determining legal
rights or obligations and carrying legal consequences for
purposes of the second finality prong.

EPA and intervenors contend that the 2018 Rule
nonetheless has no independent legal effect because “the aspect
of the 2015 Rule that exceeded EPA’s authority” per Mexichem
“flow[s] from the exact same regulatory text” as “the aspect
that did not.” EPA Br. 24. According to EPA and intervenors,
“[t]he listings in the 2015 Rule are thus one, integral action
that” must “necessarily stand or fall as a whole because there
are no components to the regulatory text that can be treated
 19
independently and severed.” Id. (internal quotation marks
omitted). Therefore, they argue, even if the Mexichem court
intended to invalidate the 2015 Rule’s HFC listings only in
part, the decision necessarily had the effect of invalidating
those listings in their entirety because there is no discrete,
severable text in the listings that could be struck to implement
the court’s intended partial vacatur.

EPA errs in focusing on the question whether the HFC
listings contained discrete, severable text that Mexichem could
have struck to implement a partial vacatur. It is a routine
feature of severability doctrine that a court may invalidate only
some applications even of indivisible text, so long as the “valid
applications can be separated from invalid ones.” Fallon et al.,
Hart & Wechsler’s: The Federal Courts and the Federal System
170 (7th ed. 2015). As the Supreme Court has explained, when
a court encounters statutory or regulatory text that is “invalid
as applied to one state of facts and yet valid as applied to
another,” it should “try to limit the solution to the problem” by,
for instance, enjoining the problematic applications “while
leaving other applications in force.” Ayotte v. Planned
Parenthood of N. New England, 546 U.S. 320, 328–29 (2006)
(citation omitted) (statute); see Greater New Orleans Broad.
Ass’n v. United States, 527 U.S. 173, 195–96 (1999)
(regulation). Otherwise, a court would be compelled to grant
facial relief in any successful as-applied challenge to a
statutory or regulatory provision. That of course is not the law.

Here, the Mexichem court followed the Supreme Court’s
guidance to “limit the solution to the problem” by vacating the
2015 Rule’s HFC listings only as applied to entities that EPA
lacks authority to regulate (those who had already switched
from ozone-depleting substances to HFCs), leaving the listings
intact as applied to other entities (those who had not). And in
vacating only certain applications of the 2015 Rule without
 20
regard to whether the regulatory text is divisible in a
corresponding way, the Mexichem court acted in accordance
with our precedents.

Consider, in that regard, our decision in National Corn
Growers Ass’n v. EPA, 613 F.3d 266 (D.C. Cir. 2010). There,
we considered an EPA regulation that revoked all “tolerances”
(i.e., permissible residues in food) of the pesticide carbofuran,
thereby effectively banning use of carbofuran in food for
human consumption. Id. at 270. We vacated EPA’s rule as
applied to imported foods but left the rule in place as applied
to food produced domestically. See id. at 275. And we did so
without pausing to examine whether the regulatory text was
divisible in a manner corresponding to our partial vacatur. The
pertinent text in fact was not divisible in that way: it revoked
“all of the existing tolerances for residues of carbofuran,”
making no reference to—and drawing no distinction
between—import and domestic tolerances. Carbofuran; Final
Tolerance Revocations, 74 Fed. Reg. 23,046–23,052 (May 15,
2009). We nonetheless “vacate[d] EPA’s final rule” only “to
the extent it revoked the import tolerances for carbofuran,” 613
F.3d at 275, and we rejected challenges to the rule’s application
to domestic tolerances, id. at 272–74.

In Mexichem, we similarly did not engage in any express
severability analysis about the text of the 2015 Rule. Rather,
the decision makes clear its intention to separate unlawful
applications of the 2015 HFC listings from lawful ones, and to
vacate the 2015 Rule only as to the former. If EPA disagreed
with Mexichem’s invalidation only of certain applications
because the agency believed the 2015 Rule’s HFC listings
should be treated as an inseverable whole, see Carlson v. Postal
Regulatory Comm’n, 938 F.3d 337, 351 (D.C. Cir. 2019);
MD/DC/DE Broad. Ass’n v. FCC, 236 F.3d 13, 23 (D.C. Cir.
2001), the agency could have sought a full (rather than partial)
 21
vacatur of the rule in a petition for rehearing. Indeed, our court
routinely entertains rehearing petitions about the appropriate
scope of relief. See, e.g., MD/DC/DE Broad. Ass’n v. FCC,
253 F.3d 732 (D.C. Cir. 2001); Davis Cty. Solid Waste Mgmt.
v. EPA, 108 F.3d 1454, 1455 (D.C. Cir. 1997) (per curiam);
Virginia v. EPA, 116 F.3d 499 (D.C. Cir. 1997) (per curiam).
But EPA did not do so.

The upshot is that, after Mexichem, the 2015 Rule’s HFC
listings remained applicable to the class of regulated entities
that continued to use ozone-depleting substances. The 2018
Rule, by suspending the HFC listings as applied to that group
of entities, changed those parties’ legal rights and obligations
from the status quo established by Mexichem. And because the
2018 Rule meets both prongs of the Bennett test for finality, we
have jurisdiction to consider the petitions for review before us
in this case.

III.

We now proceed to assess petitioners’ challenges to EPA’s
adoption of the Rule. Petitioners contend that the 2018 Rule
was a legislative rule and was thus improperly promulgated
without the required notice-and-comment procedures. They
further contend that the Rule is arbitrary and capricious. We
agree with the first of those arguments and therefore have no
occasion to consider the second one.

The Clean Air Act calls for EPA to employ notice-and-
comment procedures whenever it engages in the “promulgation
or revision of regulations under” Title VI. 42 U.S.C. § 7607(d);
see 5 U.S.C. § 553. That requirement, though, applies to the
promulgation only of legislative rules, not interpretive rules.
See Am. Mining Congress v. Mine Safety & Health Admin., 995
F.2d 1106, 1108–12 (D.C. Cir. 1993). Because the 2018 Rule
 22
was not promulgated via notice and comment, the pivotal
question is whether the rule is legislative or interpretive.

The “line between interpretive and legislative rules” is
“fuzzy” and “enshrouded in considerable smog.” Id. at 1108
(citation omitted). Our decisions, however, set out a basic
taxonomy. A “legislative rule” is one that has “legal effect” or,
alternately, one that an agency promulgates with the “intent to
exercise” its “delegated legislative power” by speaking with
the force of law. Id. at 1109, 1112 (internal quotation marks
omitted). An “interpretive rule,” meanwhile, is one that
“derive[s] a proposition from an existing document,” such as a
statute, regulation, or judicial decision, “whose meaning
compels or logically justifies the proposition.” Catholic Health
Initiatives v. Sebelius, 617 F.3d 490, 494 (D.C. Cir. 2010)
(citation omitted). An interpretive rule, instead of creating
legal effects, thus puts the public on notice of pre-existing legal
obligations or rights. Here, the 2018 Rule has independent
legal effect beyond that compelled by Mexichem and reflects
EPA’s intent to exercise its delegated legislative power.

First, while EPA now describes the 2018 Rule as merely
interpretive, the Rule itself evinces the agency’s intent to speak
with the force of law. EPA concluded that “attempting to draw
the distinctions made by the court [in Mexichem] would present
practical difficulties,” that those distinctions were not reflected
in the text of the 2015 Rule, and that Mexichem’s partial
vacatur had generated “substantial confusion and uncertainty”
among regulated entities. 83 Fed. Reg. 18,433–35. EPA thus
relied “on its expertise . . . and its understanding of the 2015
Rule” to conclude that the 2015 HFC listings should be
suspended “in their entirety.” Id at 18,435. That manner of
action—identifying a practical problem ostensibly created by a
judicial decision and relying on agency expertise to put forward
a new and different resolution—is quintessentially legislative,
 23
manifesting EPA’s intent to exercise its delegated legislative
power and speak with the force of law.

The 2018 Rule has the force of law because it suspends the
2015 Rule’s HFC listings for a class of regulated entities (those
continuing to use ozone-depleting substances) to whom the
2015 Rule still applied after Mexichem. Suspension of a rule
is “tantamount to amending or revoking a rule,” Clean Air
Council, 862 F.3d at 6, and “an agency action which has the
effect of suspending a duly promulgated regulation” (like the
2015 Rule) “is normally subject to APA rulemaking
requirements,” including notice-and-comment procedures.
Envtl. Def. Fund, Inc. v. Gorsuch, 713 F.2d 802 (D.C. Cir.
1983). Indeed, because the 2018 Rule had the effect of
amending what is undisputedly a legislative rule (the 2015
Rule), it too is a legislative rule subject to notice-and-comment
obligations: an “amendment to a legislative rule must itself be
legislative.” Sierra Club v. EPA, 873 F.3d 946, 952 (D.C. Cir.
2017).

Our dissenting colleague, while agreeing that the 2018
Rule constitutes final agency action, believes that the Rule is
interpretive rather than legislative, such that notice-and-
comment procedures should be inapplicable. But even
assuming an agency rule can determine “legal rights and
obligations” or carry “legal consequences” (so as to amount to
final agency action) but still lack “legal effects” (so as to fall
short of a legislative rule), see Cal. Cmtys. Against Toxics v.
EPA, 934 F.3d 627, 635 (D.C. Cir. 2019), the 2018 Rule is not
such a needle-threading rule. The 2018 Rule did not merely
interpret Mexichem’s partial vacatur of the 2015 Rule. The
2018 Rule instead expanded Mexichem’s partial vacatur into a
full vacatur, revoking those applications of the 2015 Rule’s bar
on use of HFCs that had remained standing after Mexichem.
 24
Our colleague suggests that, insofar as Mexichem vacated
only certain applications of the 2015 Rule while leaving other
applications standing, our decision in that case disregarded the
regulatory history (specifically, a previous EPA rule referred to
as the “1994 Framework Rule”), and reached a resolution
inconsistent with severability principles. See Dissenting Op. 4,
11–15. As explained, however, Mexichem’s partial vacatur of
the 2015 Rule—its invalidation only of certain applications
without examining the severability of the regulatory text—
cohered with our precedents. See National Corn Growers, 613
F.3d 266; see also Illinois Commerce Comm’n v. ICC, 776 F.2d
355, 358–60 (D.C. Cir. 1985).

At any rate, the question for us is not whether Mexichem’s
partial vacatur of the 2015 Rule was correct at the time, or if
we should have examined the regulatory text’s severability in
that opinion. Mexichem’s partial vacatur, whether correct or
incorrect, is now final. And the question for us is whether EPA
in the 2018 Rule merely interpreted Mexichem’s partial vacatur
in the manner of an interpretive rule or instead altered the
decision’s legal effect in the manner of a legislative rule.

The agency did the latter, transforming Mexichem’s partial
vacatur into an across-the-board invalidation of the 2015
Rule’s HFC listings. The agency in fact affirmatively declined
“to draw the distinctions made by the court” in Mexichem. 83
Fed. Reg. 18,434. And the agency expressly “recognize[d] that
the court vacated the 2015 Rule [only] ‘to the extent that’ it
requires manufacturers to replace HFCs” and that the court had
otherwise “rejected the arbitrary and capricious challenges to
the HFC listing changes.” Id. at 18,435. But the agency
nonetheless opted to “implement the court’s vacatur by treating
it as striking the HFC listing changes in the 2015 Rule in their
entirety.” Id. (emphasis added). In other words, EPA “treated”
the decision as having a legal effect—full vacatur—that the
 25
decision disclaimed. That is a legislative rule subject to notice-
and-comment procedures.

Intervenors submit that the agency’s failure to abide by
notice-and-comment requirements amounts to harmless error.
See Intervenors Br. 34–36. Of course, though, the entire
premise of notice-and-comment requirements is that an
agency’s decisionmaking may be affected by concerns aired by
interested parties through those procedures. For that reason,
we have “not been hospitable to government claims of
harmless error in cases in which the government . . . fail[ed] to
provide notice.” Allina Health Servs. v. Sebelius, 746 F.3d
1102, 1109 (D.C. Cir. 2014). And we have found cases “in
which a government agency seeks to promulgate a rule by
another name—evading altogether the notice and comment
requirements”—to be the “most egregious” breaches of notice-
and-comment obligations. Id.

This is such a case. EPA wholly failed to provide
petitioners (or any other interested parties) the opportunity to
comment on the best way to implement the distinctions drawn
by our court in Mexichem. Indeed, the very fact that EPA plans
to engage in full notice-and-comment rulemaking in the future
when developing a permanent replacement for the 2018 Rule
suggests that the agency, too, believes that comments from
interested parties may provide valuable input on the matter.
EPA’s failure to abide by notice-and-comment procedures
when promulgating the 2018 Rule then cannot be considered
harmless.

For substantially similar reasons, EPA’s error requires us
to vacate the 2018 Rule. In general, “vacatur is the normal
remedy” for a procedural violation, although we may remand
to the agency without vacatur based on “the seriousness of the
order’s deficiencies and the likely disruptive consequences of
 26
vacatur.” Allina Health Servs., 746 F.3d at 1110 (internal
quotation marks omitted). Here, both considerations counsel
in favor of vacatur. First, “[f]ailure to provide the required
notice and to invite public comment—in contrast to the
agency’s failure . . . adequately to explain why it chose one
approach rather than another for one aspect of an otherwise
permissible rule—is a fundamental flaw that normally requires
vacatur of the rule.” Heartland Reg’l Med. Ctr. v. Sebelius,
566 F.3d 193, 199 (D.C. Cir. 2009) (internal quotation marks
omitted). And second, neither EPA nor intervenors have
identified any serious disruptive consequences of vacatur,
resting instead on the regulatory uncertainty that typically
attends vacatur of any rule. See EPA Br. 38–39.

None of this means that EPA was powerless to act in the
face of what it perceived to be practical difficulties and
regulatory uncertainty engendered by Mexichem’s partial
vacatur. First, as noted, EPA could have petitioned the
Mexichem court for rehearing, explaining that it believed the
HFC listings were inseverable and asking the court to vacate
the 2015 Rule in full. Second, EPA could have issued an
interpretive rule (without engaging in notice and comment) to
explain how it understood the Mexichem decision’s partial
vacatur to apply to certain gray areas identified in the 2018
Rule. See 5 U.S.C. § 553(b); 83 Fed. Reg. 18,434–35. Third,
EPA could have exercised its enforcement discretion to focus
its enforcement efforts on entities still subject to regulation
after Mexichem, or it could have resolved difficult questions
through case-by-case adjudications, cf. Blanca Tel. Co. v. FCC,
743 F.3d 860, 867 (D.C. Cir. 2014). Finally, EPA perhaps
could have attempted to invoke the good-cause exception to
promulgate an interim legislative rule without notice and
comment, pending its undertaking a full legislative rulemaking.
See 5 U.S.C. § 553(b).
 27
We do not mean to prejudge the ultimate permissibility or
efficacy of any of those options. Rather, we mean only to
highlight that EPA had several options by which it could have
attempted to address the perceived difficulties associated with
implementing our decision in Mexichem. But the one option
EPA could not permissibly pursue was the one it chose:
promulgating a legislative rule without abiding by notice-and-
comment requirements and without invoking any exception to
those obligations.

* * * * *

For the foregoing reasons, we grant the petitions for
review, vacate the 2018 Rule, and remand to EPA for further
proceedings consistent with this opinion.

So ordered.
 RAO, Circuit Judge, dissenting: In 2018, the
Environmental Protection Agency issued a guidance document
to provide clarity and regulatory certainty for stakeholders
affected by EPA’s 2015 Rule regulating hydrofluorocarbons
(“HFCs”) and our related decision in Mexichem Fluor, Inc. v.
EPA, 866 F.3d 451 (D.C. Cir. 2017). The majority classifies
the 2018 Guidance as a final legislative rule that should have
been promulgated through notice and comment procedures. I
agree that the 2018 Guidance is a final agency action subject to
our review. Unlike the majority, however, I would classify the
2018 Guidance as an interpretive rule that did not create new
rights or obligations and did no more than articulate the EPA’s
view of what was required by Mexichem in the “near term” and
pending further rulemaking. Because the 2018 Guidance was
an interpretive rule, notice and comment was not necessary. In
addition, EPA’s decision to treat Mexichem as vacating the
entire 2015 Rule was not arbitrary and capricious because it
was effectively compelled by Mexichem. In characterizing the
2018 Guidance as a legislative rule, the majority misinterprets
the EPA’s regulatory framework and unravels Mexichem’s
mandate. I respectfully dissent.

I.

The dispute in this case turns on the interplay between
Mexichem and the EPA’s implementation of that decision in
the 2018 Guidance. To understand the scope and consequences
of the 2018 Guidance requires analyzing “the idiosyncratic
regime of statutes and regulations that govern it.” Cal.
Communities Against Toxics v. EPA, 934 F.3d 627, 632 (D.C.
Cir. 2019). I begin with the original regulatory framework EPA
promulgated in 1994, because this provides essential context
for understanding the 2015 Rule, Mexichem, and the 2018
Guidance.

As the majority explains, the United States ratified the
Montreal Protocol in 1987 to help address the deterioration of
 2
the ozone layer. After ratification, Congress amended the Clean
Air Act in 1990 by adding Title VI. See 42 U.S.C. § 7671 et
seq. The amendments require manufacturers and end-users to
phase out various substances that deplete the ozone layer. See
Mexichem, 866 F.3d at 454. For our purposes, the most relevant
provision is Section 612(c), which authorizes EPA to regulate
which chemicals can be used “to replace” ozone-depleting
substances. 42 U.S.C. § 7671k(c). 1

In 1994, the EPA promulgated a framework explaining
how the EPA will regulate HFCs and other substitutes for
ozone-depleting substances. See Protection of Stratospheric
Ozone, 59 Fed. Reg. 13,044 (Mar. 18, 1994) (“1994
Framework Rule”). As relevant here, the Framework Rule
specified that when a chemical is listed as an unacceptable
substitute, no person can continue to use it, even if that person
has already stopped using ozone-depleting substances. Id. at
13,148 (“No person may use a substitute after the effective date
of any rulemaking adding such substitute to the list of
unacceptable substitutes.”). For more than 20 years, EPA
interpreted “replace” under Section 612(c) to apply on an
ongoing basis, each time a person uses the substitute. Id. at
13,048. Under this interpretation, if EPA reclassifies an
acceptable substitute as unacceptable, no one may use it, even
persons who had previously stopped using ozone-depleting
substances. Id. (“[O]nce EPA identifies an unacceptable
substitute, any future use of such substitute is prohibited. Under
any other interpretation, EPA could never effectively prohibit
the use of any substitute, as some user could always start to use

1
The full text reads: “[T]he Administrator shall promulgate rules
under this section providing that it shall be unlawful to replace any
class I or class II substance with any substitute substance which the
Administrator determines may present adverse effects to human
health or the environment, where the Administrator has identified an
alternative.” 42 U.S.C. § 7671k(c).
 3
it prior to EPA’s completion of the rulemaking required to list
it as unacceptable.”).

The EPA initially listed HFCs as acceptable substitutes for
ozone-depleting substances. See, e.g., Protection of
Stratospheric Ozone: Listing of Substitutes for Ozone-
Depleting Substances, 68 Fed. Reg. 4,004, 4,005–06 (Jan. 27,
2003). In 2015, the agency changed course and listed HFCs as
unacceptable because they have a significant effect on global
warming. See Protection of Stratospheric Ozone: Change of
Listing Status for Certain Substitutes Under the Significant
New Alternatives Policy Program, 80 Fed. Reg. 42,870 (July
20, 2015) (“2015 Rule”). The 2015 Rule applied to everyone,
including people who had already stopped using ozone-
depleting substances and had “replaced” them with HFCs. As
EPA emphasized, this consequence followed directly from the
1994 Framework Rule. Id. at 42,936–37.

In Mexichem, we rejected EPA’s longstanding
interpretation that the term “replace” encompasses the
continued use of a substitute by people who have already
stopped using ozone-depleting substances. We explained that
EPA’s “reading stretche[d] the word ‘replace’ beyond its
ordinary meaning.” Mexichem, 866 F.3d at 458. We held that
the EPA has no authority under Section 612(c) to prohibit the
use of HFCs by people who adopted them as a substitute for
ozone-depleting substances before the 2015 Rule went into
effect. See 866 F.3d at 456–61. As we explained, a party
“replaces” an ozone-depleting substance when it transitions to
an acceptable substitute; once it does that, the replacement is
over. Because people who have already made the switch to
HFCs are no longer using ozone-depleting substances, the EPA
cannot require them to stop using HFCs—at least not under
Section 612(c), which regulates only the initial replacement of
ozone-depleting substances. Indeed, we emphasized that the
 4
EPA’s “boundless interpretation” “border[ed] on the absurd”
because it would give the agency “indefinite authority.” Id. at
459. While we rejected EPA’s interpretation of “replace,” we
held that EPA’s decision to list HFCs as unacceptable
substitutes was, as a general matter, not arbitrary and
capricious. See id. at 462–64. As a remedy, we “vacate[d] the
2015 Rule to the extent it require[d] manufacturers to replace
HFCs with a substitute substance.” Id. at 464.

After Mexichem, the 1994 Framework Rule remains in
effect, although its reasoning was substantially undermined by
our opinion. The majority overlooks this fact—perhaps
because Mexichem never discusses the 1994 Rule and suggests
in passing that the EPA’s interpretation of “replace” was “new”
to the 2015 Rule. See 866 F.3d at 458. The 2015 Rule, however,
did not articulate a “new” interpretation. Rather, before
Mexichem, the EPA consistently maintained that it could
prohibit the use of substitutes like HFCs regardless of whether
a person had already made the substitution before the
regulation went into effect.

In the wake of Mexichem, regulated entities were unsure
of the practical consequences of our remedy and
“experience[ed] substantial confusion and uncertainty
regarding the meaning of the vacatur in a variety of specific
situations.” See Protection of Stratospheric Ozone: Notification
of Guidance and a Stakeholder Meeting Concerning the
Significant New Alternatives Policy (SNAP) Program, 83 Fed.
Reg. 18,431, 18,434 (Apr. 27, 2018) (“2018 Guidance”). In the
2018 Guidance, the EPA sought to clarify how it would
implement Mexichem. In doing so, EPA reiterated that the 1994
Framework Rule—not the 2015 Rule—required that “[n]o
person may use a substitute after the effective date of any
rulemaking adding such substitute to the list of unacceptable
substitutes.” See id. at 18,433 (quoting 40 C.F.R. § 82.174 (the
 5
1994 Framework Rule)). The 2018 Guidance emphasized that
prior to Mexichem, the 2015 Rule had operated exactly “like all
other actions EPA has taken implementing the 1994
Framework Rule over the last quarter-century”—namely to
require everyone to stop using the unacceptable substance,
irrespective of whether they had switched to the substitute prior
to the listing. Id. In other words, the agency maintained that the
interpretation invalidated by Mexichem originated in the 1994
Framework Rule.

In the 2018 Guidance, EPA recognized that Mexichem
vacated “the 2015 Rule ‘to the extent that’ it requires
manufacturers to replace HFCs.” Id. at 18,435. EPA proceeded
to analyze how to implement this directive with respect to the
2015 Rule, which “is comprised solely of tables listing …
certain substitutes for specific end-uses.” Id. at 18,434. While
Mexichem suggests that the 2015 Rule could apply to people
still using ozone-depleting substances, the tables in the Rule do
not “draw a distinction between persons using HFCs and those
using an [ozone-depleting substance].” Id. The agency
concluded that the “regulations as currently written do not
provide the distinctions that would be necessary to
accommodate the letter of the court’s vacatur.” Id. After all,
under the 1994 Framework Rule, every listing necessarily
applies to current and future users of a given substance. See id.
at 18,435 (“[T]the listing of HFC’s as unacceptable, or
acceptable subject to use restrictions, is the means by which the
2015 Rule ‘require[d] manufacturers to replace HFCs with a
substitute substance.’”). EPA explained that “[t]he narrower
language used by the court does not exist in either the 2015
Rule or the 1994 Framework Rule; nor do the distinctions
discussed above emerge when those two rules are read
together.” Id. at 18,434. Indeed, the EPA emphasized that to
implement a partial vacatur would require it “to drastically
rewrite the 2015 Rule,” which “would not be appropriate to
 6
undertake … without undergoing notice and comment
rulemaking.” Id. at 18,435.

Pending additional notice and comment rulemaking, EPA
determined that the only way to implement Mexichem and to
provide guidance to regulated entities was to read our opinion
as vacating the HFC listing in its entirety. See id. EPA thus
interpreted and implemented Mexichem’s vacatur in the only
way it believed permissible given the indivisible listings in the
2015 Rule and the interpretation set forth in the 1994
Framework Rule. With this more complete regulatory context,
I turn to the appeal before us.

II.

We face two interrelated, yet distinct, inquiries in this case.
First, we must decide whether the EPA’s action was final, a
question about the availability of judicial review. See 5 U.S.C.
§ 704. Second, if the action was final, we must determine
whether it is a legislative or interpretive rule, a question about
the procedures the agency must follow. As our court has
recently observed, “although all legislative rules are final, not
all final rules are legislative, and the finality analysis is
therefore distinct from the test for whether an agency action is
a legislative rule.” Cal. Communities Against Toxics, 934 F.3d
at 631; cf. Nat’l Mining Ass’n v. McCarthy, 758 F.3d 243, 251
(D.C. Cir. 2014) (“[E]ven interpretive rules may be subject to
pre-enforcement judicial review.”). 2

2
As the majority frames these questions, the standards for finality
and legislative rules are essentially the same. Indeed, the majority
leaves open the possibility that the category of final, interpretive
rules may be a conceptual null set. Maj. Op. 23. This has no support
in the APA and is foreclosed by Supreme Court precedent. See U.S.
 7
The majority conflates aspects of these two standards. For
the purposes of this case’s finality inquiry, we need ask only
whether the agency’s interpretation of Mexichem had “direct
and appreciable legal consequences.” Bennett v. Spear, 520
U.S. 154, 178 (1997). While I agree with the majority that the
EPA’s action is final under this standard, it does not matter
whether the 2018 Guidance created new legal obligations. A
final agency action can include interpretive rules that merely
state the agency’s interpretation of a statute, regulation, or
judicial decision.

The question of whether the 2018 Guidance created new
legal obligations is, however, relevant to the second inquiry—
whether this is legislative rule. Here I part ways with the
majority. Because the 2018 Guidance merely interpreted the
necessary consequences of our vacatur in Mexichem, the
Guidance is a final, interpretive rule that was reasonable and
not arbitrary and capricious.

A.

We have jurisdiction under the Clean Air Act to review the
2018 Guidance only if it was a “final action.” See 42 U.S.C.
§ 7607(b)(1). The term “final action” “is synonymous with the
term ‘final agency action’ as used in Section 704 of the”
Administrative Procedure Act (“APA”). Sierra Club v. EPA,
873 F.3d 946, 951 (D.C. Cir. 2017). To determine whether an
agency action is final, we apply the two-prong test set forth in
Bennett v. Spear: the action must both “mark the
consummation of the agency’s decisionmaking process,” and it
“must be one by which rights or obligations have been
determined, or from which legal consequences will flow.” 520
U.S. 154, 178 (1997) (quotation marks omitted). The parties

Army Corps of Eng’rs v. Hawkes Co., 136 S. Ct. 1807, 1815 (2016)
(observing that the Court frequently reviews interpretive rules).
 8
and the majority all agree that the 2018 Guidance reflects the
consummation of the agency’s decisionmaking process, Maj.
Op. 12, so I focus on the second prong.

The central dispute is whether an agency action can have
a sufficiently concrete legal effect for the purposes of Bennett’s
second prong if it simply interprets a legal obligation that stems
from a different legal source. The majority focuses on whether
it was “Mexichem, not the 2018 Rule, that suspended the 2015
Rule’s HFC listings.” Maj. Op. 16. In the finality context,
however, it is unnecessary to determine whether Mexichem
directs suspension of the 2015 Rule or whether the 2018
Guidance independently creates that result. Under Bennett, a
final action is “one by which rights or obligations have been
determined, or from which legal consequences will flow.” 520
U.S. at 178 (quotation marks omitted). The legal consequences
do not necessarily have to flow from the rule itself. If they did,
an interpretive rule could never be final and reviewable, and
we have explicitly held that “even interpretive rules may be
subject to pre-enforcement judicial review.” Nat’l Mining
Ass’n, 758 F.3d at 251; see also U.S. Army Corps of Eng’rs v.
Hawkes Co., 136 S. Ct. 1807, 1815 (2016) (observing that the
Court frequently reviews agency decisions that simply “give
notice of how the [agency] interpret[s] the relevant statute”
(quotation marks omitted)) (discussing Frozen Food Express v.
United States, 351 U.S. 40, 41–44 (1956)). 3

3
The Supreme Court made clear in Hawkes that interpretive rules
can be final actions subject to review, which supersedes any
suggestion in Association of Flight Attendants-CWA, AFL-CIO v.
Huerta, that interpretive rules are not reviewable. See 785 F.3d 710,
713 (D.C. Cir. 2015) (“The guidance offered in Notice N8900.240
reflects nothing more than a statement of agency policy or an
interpretive rule. The Notice is therefore unreviewable.”).
 9
An interpretive rule by definition does not create new
obligations, but instead interprets existing legal obligations
under statutes, regulations, and judicial decisions. To be final,
a rule simply has to determine which rights a party has under
the law, and a rule determines rights or obligations if its impact
is “sufficiently direct and immediate” and if it will have a
“direct effect” on “day-to-day” affairs. Abbott Labs. v.
Gardner, 387 U.S. 136, 152 (1967). Put slightly differently,
“[t]he core question is … whether the result of th[e] process is
one that will directly affect the” regulated parties. Franklin v.
Mass., 505 U.S. 788, 797 (1992); accord Dalton v. Specter, 511
U.S. 462, 470 (1994).

The 2018 Guidance was an action “by which rights or
obligations have been determined.” Bennett, 520 U.S. at 178
(quotation marks omitted). In Mexichem’s aftermath, there was
considerable confusion across several industries as to the
meaning of the court’s remedy. See 83 Fed. Reg. at 18,434. The
2018 Guidance explained how the EPA would implement
Mexichem. The agency’s interpretation directly affected
regulated parties: “EPA will not apply the HFC use restrictions
or unacceptability listings in the 2015 Rule for any purpose.”
Id. at 18,433. Thus, irrespective of whether the obligations
followed from our Mexichem decision or an independent
decision by EPA, the 2018 Guidance had an immediate and
practical impact and thus was a final agency action subject to
our review.

B.

The finality of the 2018 Guidance, however, does not
answer the question of whether it is a legislative or interpretive
rule. This question turns on whether the 2018 Guidance merely
articulated the agency’s understanding of Mexichem’s legal
implications, or whether the agency went further than
 10
Mexichem and thus created new legal obligations. If the 2018
Guidance was an interpretive rule, the EPA’s decision to skip
notice and comment was perfectly acceptable. See Shalala v.
Guernsey Mem’l Hosp., 514 U.S. 87, 99 (1995) (“Interpretive
rules do not require notice and comment.”); see also 5 U.S.C.
§ 553(b)(3)(A) (“Except when notice or hearing is required by
statute, this subsection [about notice and comment] does not
apply—(A) to interpretative rules.”). On the other hand, if the
2018 Guidance was a legislative rule that brought about a
substantive change to the agency’s Title VI regulations, then
the procedures used were inadequate. See 42 U.S.C.
§ 7607(d)(1)(I) (requiring notice and comment rulemaking for
regulations promulgated under Title VI).

To determine whether a rule is legislative, we ask whether
the agency is exercising its statutory rulemaking authority to
promulgate rules that have the force of law and “impose legally
binding obligations or prohibitions.” Nat’l Mining Ass’n, 758
F.3d at 251; see also Am. Mining Cong. v. Mine Safety &
Health Admin., 995 F.2d 1106, 1109 (D.C. Cir. 1993).
Interpretive rules, on the other hand, “derive a proposition from
an existing document whose meaning compels or logically
justifies the proposition.” Catholic Health Initiatives v.
Sebelius, 617 F.3d 490, 494 (D.C. Cir. 2010). “[T]he critical
feature of interpretive rules is that they are issued by an agency
to advise the public of the agency’s construction of the statutes
and rules which it administers.” Perez v. Mortg. Bankers Ass’n,
135 S. Ct. 1199, 1204 (2015) (quotation marks omitted). Thus,
legislative rules impose new legally binding requirements,
whereas interpretive rules set forth the agency’s explanation of
existing legal requirements. Evaluating EPA’s action in light
of the Mexichem remedy as well as the existing regulatory
scheme demonstrates that the 2018 Guidance was an
interpretive rule.
 11
As the majority recognizes, “EPA could have issued an
interpretive rule (without engaging in notice and comment) to
explain how it understood the Mexichem decision’s partial
vacatur to apply to certain gray areas identified.” Maj. Op. 26.
That is precisely what EPA did in the 2018 Guidance when it
stated why Mexichem compelled a prohibition on the use of
HFCs, absent further rulemaking. Mexichem held that EPA
could not interpret Section 612(c) to require people who had
already “replaced” ozone-depleting substances with HFCs to
make another replacement. Mexichem, 866 F.3d at 459
(“EPA’s strained reading of the term ‘replace’ contravenes the
statute and thus fails at Chevron step 1.”). In addition, our court
held that EPA had reasonably chosen to list HFCs as
unacceptable substitutes going forward. Id. at 462–64. The
resulting public confusion and uncertainty stemmed in part
from the fact that our court vacated the 2015 Rule “to the extent
that” it applied to people who had already switched to HFCs
from ozone-depleting substances. Our court remanded to the
EPA for further proceedings without conducting a severability
analysis or otherwise explaining how to implement the vacatur.

Thus, after Mexichem, a practical question remained about
how to implement the decision. Recognizing that “the agency
cannot remain silent on the implications of the court’s vacatur
until such time as the agency can complete a notice-and-
comment rulemaking,” the EPA provided a “near term”
interpretation of our decision. 83 Fed Reg. at 18,435. EPA
concluded that in light of the 2015 and 1994 Rules, the 2015
HFC listings could not be applied “for any purpose prior to
completion of rulemaking.” Id. Although our remedy in
Mexichem could arguably be read to suggest some type of
partial vacatur, the EPA concluded that “[t]he narrower
language used by the court does not exist in [ ] the 2015 Rule.”
Id. at 18,434. According to the EPA, because the Rule is
composed of nothing more than tables—tables that did not
 12
make the distinction drawn by our court—the Rule could not
be vacated only in part. “[T]he listing of HFC’s as
unacceptable, or acceptable subject to use restrictions, is the
means by which the 2015 Rule ‘require[d] manufacturers to
replace HFCs with a substitute substance.’” See id. at 18,435
(quoting Mexichem, 866 F.3d at 462). Listing HFCs as
unacceptable necessarily had the effect our court said went
beyond EPA’s statutory authority, so there was nothing that
could be severed from the listing to separate those who had
already switched to HFCs from those who may switch in the
future. “Vacating the 2015 Rule ‘to the extent’ that it imposed
that requirement means vacating the listings. To apply the
court’s holding otherwise would be to drastically rewrite the
2015 Rule.” Id.

The EPA recognized that it could eventually create
sublistings for different types of HFC users, but “such additions
to the 2015 Rule would require notice-and-comment
rulemaking.” Id. at 18,434. Additional rulemaking would be
required not only to address the 2015 Rule’s indivisible
listings, but also to revisit EPA’s interpretation of “replace” in
the 1994 Framework Rule, which was never addressed by
Mexichem and therefore remained on the books, even if its
reasoning was substantially undermined. Id. Thus, pending
further rulemaking, EPA interpreted Mexichem as vacating the
entire list of HFCs. The majority says that the 2018 Guidance
is a legislative rule because the EPA “identif[ied] a practical
problem” and “rel[ied] on agency expertise to put forward a
new resolution.” Maj. Op. 22–23. Yet EPA never suggested it
was crafting a practical solution to a new problem. Rather, EPA
concluded this was the only course of action that was legally
permissible in light of the vacatur in Mexichem.

The majority today provides a different interpretation of
Mexichem, one that rewrites our decision and ignores the
 13
regulatory framework still in place after Mexichem. To the
extent the majority seeks to provide a severability analysis not
provided by Mexichem, the majority’s conclusion is
inconsistent with our regulatory severability precedents and
also with the clear vacatur set forth in Mexichem. When
determining whether a regulation may be severed, the court
considers a two-part test. “First, the court must find that ‘the
agency would have adopted the same disposition regarding the
unchallenged portion [of the regulation] if the challenged
portion were subtracted.’” Carlson v. Postal Regulatory
Comm’n, 938 F.3d 337, 351 (D.C. Cir. 2019) (quoting Sierra
Club v. FERC, 867 F.3d 1357, 1366 (D.C. Cir. 2017)).
“Second, the parts of the regulation that remain must be able to
‘function sensibly without the stricken provision.’” Id. (quoting
Sorenson Commc’ns. Inc. v. FCC, 755 F.3d 702, 710 (D.C. Cir.
2014)). The “entire rule must be vacated” if severing only the
unlawful aspects “would severely distort the [agency’s]
program and produce a rule strikingly different from any the
[agency] has ever considered or promulgated in the lengthy
course of these proceedings.” MD/DC/DE Broads. Ass’n v.
FCC, 236 F.3d 13, 23 (D.C. Cir. 2001). Moreover, an agency
action should be vacated in its entirety if “[t]he intertwined
character of the … component parts gives rise to a substantial
doubt that a partial affirmance would comport with the
[agency’s] intent.” Tel. & Data Sys. Inc. v. FCC, 19 F.3d 42,
50 (D.C. Cir. 1994).

Here, the lawful and unlawful “parts” of the 2015 Rule
were not just “intertwined.” Id. They stemmed from the exact
same listing—indeed, the exact same words. The 2015 Rule’s
lawful applications could not survive independently when
Mexichem interpreted the statute in a manner fundamentally at
odds with the underlying 1994 Framework Rule. EPA noted in
the 2018 Guidance that it plans to consider to what extent the
1994 Framework Rule must be modified through future notice
 14
and comment rulemaking. Until that occurs, however, the
majority’s solution produces a rule inconsistent with the
agency’s existing regulatory framework for classifying
replacements for ozone-depleting substances.

If the agency had chosen to adopt the majority’s
interpretation after Mexichem, the EPA would have been
required to engage in notice and comment rulemaking. In the
2018 Guidance, EPA noted numerous difficult questions raised
by our decision in Mexichem that the agency planned to
address. See, e.g., 83 Fed. Reg. at 18,435–36 (listing the
questions the agency plans on considering in the future,
including “whether EPA should revisit specific provisions of
the 1994 Framework Rule … to establish distinctions between
users still using [ozone-depleting substances] and those who
have already replaced” them; “[w]hether EPA should
distinguish between product manufacturers and other users”;
and “[w]hether EPA should clarify when the replacement of an
[ozone-depleting substance] occurs: e.g., on a facility-by-
facility basis, or on a product-by-product basis”). As the EPA
reiterated in the 2018 Guidance, the 2015 Rule functioned the
same way as every other listing since 1994: The listing of a
substance as unacceptable would apply to everyone
manufacturing or using that substance. Because the majority
overlooks the existing regulatory framework, it fails to
appreciate that notice and comment rulemaking would be
required to implement its interpretation of Mexichem.

Under the majority’s holding, the 2015 Rule will now
function differently from every other rule promulgated by EPA
under Section 612(c). Instead of following our precedents in
the context of regulatory severability, 4 the majority interprets
4
Many of the cases relied on by the majority do not involve
severability at all. See, e.g., Ayotte v. Planned Parenthood of
Northern New England, 546 U.S. 320 (2006); Greater New Orleans
 15
what it considers to be our court’s “intention” in Mexichem.
Even though Mexichem did not engage in any express
severability analysis, the majority concludes that “the decision
makes clear its intention to separate unlawful applications of
the 2015 HFC listings from lawful ones, and to vacate the 2015
Rule only as to the former.” Maj. Op. 20; see also id. at 18
(“[O]ur decision in Mexichem reinforced throughout an
intention only to forbid EPA from applying the 2015 Rule’s
HFC listings to a discrete set of regulated parties.”). Yet
Mexichem did not enjoin particular applications of the 2015
Rule. Nor did it hold the regulation unlawful as applied to
specific parties. Nor did it remand without vacatur for the EPA
to determine how to apply our holding.

Instead, our court repeatedly stated that it was vacating the
2015 Rule insofar as it applies to people who have already
switched to HFCs. See Mexichem, 866 F.3d at 462. To vacate
is to do more than enjoin or modify; it is to invalidate. Not only
did we vacate the Rule, we said that by promulgating it, the
EPA exceeded its statutory authority to a degree that
“border[ed] on the absurd.” Id. at 459.

As EPA explained, “The court clearly intended to vacate
the 2015 Rule to some ‘extent.’” 83 Fed Reg. at 18,434. A
different remedy—for instance, one enjoining particular

Broad. Ass’n v. United States, 527 U.S. 173 (1999). Relatedly, the
majority claims National Corn Growers v. EPA is relevant because
the court vacated a rule “to the extent” it applied to imports, even
though the rule in question did not draw a distinction between
imports and other goods. Maj. Op. 20. (citing 613 F.3d 266, 275
(D.C. Cir. 2010)). That case also failed to address severability. While
National Corn Growers, like Mexichem, vacated a rule “to the
extent” it had unlawful applications, the case said nothing about the
interpretive question that necessarily followed—namely, what it
means to vacate a rule to that extent.
 16
applications—would have been inconsistent with the question
presented in Mexichem, which was “whether Section 612 of the
Clean Air Act authorizes the 2015 Rule.” Id. at 456. The
question presented did not concern the application of the 2015
Rule to particular persons, but instead raised a challenge to the
2015 Rule as a whole.

Nothing in Mexichem suggested that EPA could use
enforcement discretion to implement our holding that EPA’s
interpretation exceeded the authority in Section 612(c). 5 Today
the majority chooses to “sever” the 2015 Rule, not by vacating
as Mexichem directed, but by rewriting the Rule to apply to a
subset of regulated entities. Under the majority’s interpretation,
not a single word of the 2015 Rule is vacated; instead, the Rule
will apply as written in some cases but not others. See Maj. Op.
21 (“[A]fter Mexichem, the 2015 Rule’s HFC listings remained
applicable to the class of regulated entities that continued to use
ozone-depleting substances.”). As a formal matter, the text of
the 2015 Rule remains exactly the same. Yet as a practical
matter, it must be read with a judicial asterisk, directing the
agency to execute the 2015 Rule in a manner at odds with both

5
The majority suggests enforcement discretion as an alternative for
implementing Mexichem. Maj. Op. 26. To permit an agency to
implement a partial vacatur through enforcement discretion—thus
leaving the offending rule on the books—undermines this court’s
authority and produces further uncertainty. We should encourage
agencies to distinguish between regulated parties through clear
interpretive guidance, rather than through ad hoc discretion. For
similar reasons, EPA should be wary of the majority’s suggestion to
attempt using the good-cause exception for interim legislative rules,
Maj. Op. 26, another limited regulatory practice this court has
cautioned against abusing. See Mack Trucks, Inc. v. EPA, 682 F.3d
87, 93 (D.C. Cir. 2012) (“We have repeatedly made clear that the
good cause exception is to be narrowly construed and only
reluctantly countenanced.” (quotation marks omitted)).
 17
the plain meaning and EPA’s existing regulatory framework.
By contrast, the EPA’s 2018 Guidance is consistent with
Mexichem, the text and structure of the 2015 Rule, and other
regulations under Section 612(c). I would therefore hold that
the 2018 Guidance was an interpretive rule for which no notice
and comment was required.

C.

The petitioners also argue that the EPA’s decision to delist
HFCs was arbitrary and capricious. The majority does not
reach this issue because it concludes that the 2018 Guidance
was a legislative rule and therefore must be vacated because
the EPA did not follow notice and comment procedures.
Because I classify the 2018 Guidance as an interpretive rule, I
proceed to explain why petitioners’ arbitrary and capricious
challenge lacks merit.

The APA mandates that the federal courts “hold unlawful
and set aside agency action, findings and conclusions found to
be—(A) arbitrary, capricious, an abuse of discretion, or
otherwise not in accordance with the law.” 5 U.S.C.
§ 706(2)(A). We must ask whether the agency “examine[d] the
relevant data and articulate[d] a satisfactory explanation for its
action[,] … whether the decision was based on a consideration
of the relevant factors and whether there has been a clear error
of judgment.” Motor Vehicle Mfrs. Ass’n of U.S., Inc. v. State
Farm Mut. Auto. Ins. Co., 463 U.S. 29, 43 (1983); see also
Encino Motorcars, LLC v. Navarro, 136 S. Ct. 2117, 2125
(2016) (“One of the basic procedural requirements of
administrative rulemaking is that an agency must give adequate
reasons for its decisions.”).

The petitioners argue that the EPA’s analysis was arbitrary
and capricious because it did not “show that there are good
reasons for the new policy,” NRDC Br. at 36 (quoting Encino
 18
Motorcars, LLC, 136 S. Ct. at 2126), and because it failed to
account for the contribution of additional HFCs to “climate
change or its attendant harms.” Id. at 40. An action is arbitrary
and capricious, however, only if the agency failed to consider
“the relevant data.” State Farm Mut. Auto. Ins., 463 U.S. at 43.
We look to “whether the decision was based on a consideration
of the relevant factors and whether there has been a clear error.”
Marsh v. Ore. Nat. Res. Council, 490 U.S. 360, 378 (1989).
The petitioners essentially argue the EPA should have
addressed policy considerations. Policy considerations,
however, were not relevant to interpreting Mexichem, and
therefore EPA was not required to consider them. See Black
Citizens for a Fair Media v. FCC, 719 F.2d 407, 431 n.15 (D.C.
Cir. 1983) (explaining that agencies can “ignore those factors
it considers irrelevant to the statutory scheme”); TransCanada
Pipelines Ltd. v. FERC, 878 F.2d 401, 413 (D.C. Cir. 1989)
(“FERC acknowledged this evidence and ignored it as
irrelevant. We agree that this evidence, by itself, fails to
contradict FERC’s [ ] theory.” (citation omitted)).

As discussed, the 2018 Guidance did nothing more than
interpret Mexichem, and EPA’s interpretation properly
implemented our court’s mandate. In interpreting our opinion,
it simply would not have been relevant to consider what
environmental impacts our decision may have had. The EPA
could not choose to disregard our mandate because it thought a
different outcome was better on policy grounds. An agency
does not act arbitrarily or capriciously when it takes an action
that is required by law. See US Magnesium, LLC v. EPA, 630
F.3d 188, 193 (D.C. Cir. 2011) (holding that an agency’s action
could not have been arbitrary or capricious because the agency
did not have discretion to adopt a different choice); Fitts v. Fed.
Nat. Mortg. Ass’n, 236 F.3d 1, 6 (D.C. Cir. 2001) (explaining
that the exercise of agency “discretion” is necessary to “justify
the application of arbitrary and capricious review”).
 19
Ultimately, the petitioners’ argument that the EPA should
have given more reasons for its “new policy” is premised on
their view that the 2018 Guidance was a legislative rule that
created new obligations. Because it was instead an interpretive
rule, additional policy considerations were not relevant, so the
agency’s failure to consider them was not arbitrary and
capricious.

***

Notice and comment rulemaking is a central part of the
administrative framework set forth in the APA and the Clean
Air Act. When an agency issues a legislative rule by exercising
its delegated authority to establish new obligations with the
force of law, it must follow these procedures. In the 2018
Guidance, however, EPA simply interpreted the immediate and
necessary consequences of our decision in Mexichem and left
rewriting the regulatory framework for future notice and
comment rulemaking. Because the 2018 Guidance advised the
public of the EPA’s interpretation of legal obligations created
by this court, it was an interpretive rule properly issued without
notice and comment procedures. I respectfully dissent.