FOR PUBLICATION
UNITED STATES COURT OF APPEALS
FOR THE NINTH CIRCUIT
SIERRA CLUB; MEDICAL ADVOCATES
FOR HEALTHY AIR,
Petitioners,
v.
UNITED STATES ENVIRONMENTAL
PROTECTION AGENCY; LISA JACKSON,
Administrator, U.S. Environmental
Protection Agency; JARED No. 10-71457
BLUMENFELD, Regional
Administrator, Region IX, U.S.
Environmental Protection Agency,
Respondents,
SAN JOAQUIN VALLEY UNIFIED AIR
POLLUTION CONTROL DISTRICT,
Respondent-Intervenor.
567
568 SIERRA CLUB v. UNITED STATES EPA
COMMITTEE FOR A BETTER ARVIN, a
California nonprofit corporation;
COMITE RESIDENTES ORGANIZADOS
AL SERVICIO DEL AMBIENTE SANO,
an unincorporated association;
ASSOCIATION OF IRRITATED
RESIDENTS, an unincorporated
association,
Petitioners,
v.
No. 10-71458
UNITED STATES ENVIRONMENTAL
OPINION
PROTECTION AGENCY; LISA JACKSON,
Administrator, U.S. Environmental
Protection Agency; JARED
BLUMENFELD, Regional
Administrator, Region IX, U.S.
Environmental Protection Agency,
Respondents,
SAN JOAQUIN VALLEY UNIFIED AIR
POLLUTION CONTROL DISTRICT,
Respondent-Intervenor.
On Petition for Review of an Order of the
United States Environmental Protection Agency
Argued and Submitted
November 16, 2011—San Francisco, California
Filed January 20, 2012
SIERRA CLUB v. UNITED STATES EPA 569
Before: Sidney R. Thomas, Ronald M. Gould, and
Jay S. Bybee, Circuit Judges.
Opinion by Judge Gould
570 SIERRA CLUB v. UNITED STATES EPA
COUNSEL
Paul R. Cort and Deborah S. Reames, Earthjustice for peti-
tioners Sierra Club and Medical Advocates for Healthy Air;
SIERRA CLUB v. UNITED STATES EPA 571
Sofia L. Parino and Brent Newell, Center on Race, Poverty &
the Environment for Petitioners Committee for a Better Arvin,
Association of Irritated Residents and Comite Residentes
Organizados al Servicio del Ambiente Sano.
Ignacia S. Moreno, John C. Cruden, Monica Derbes Gibson,
Jefferson Wehling, Jeanhee Hong, and Jan M. Tierney for
respondent United States Environmental Protection Agency.
Catherine T. Redmond for respondent-intervenor San Joaquin
Valley Unified Air Pollution Control District.
OPINION
GOULD, Circuit Judge:
Sierra Club and several environmental groups, (collec-
tively, “Petitioners”), petition for review of the United States
Environmental Protection Agency’s (“EPA”) approval of the
2004 State Implementation Plan (“2004 SIP”) for the San Joa-
quin Valley’s nonattainment area for the one-hour ozone
National Ambient Air Quality Standard (“NAAQS”). Peti-
tioners contend that 1) EPA acted arbitrarily and capriciously,
in violation of the Administrative Procedures Act (“APA”),
by approving the 2004 SIP knowing that the emissions inven-
tory data on which the plan relied were, as an actual matter,
outdated and inaccurate by the time EPA approved the plan
in 2010; 2) EPA violated the Clean Air Act (“CAA”) by
approving the 2004 SIP because the emissions inventory data
on which it relied were outdated and inaccurate within the
meaning of the statute; 3) EPA violated the CAA by approv-
ing the 2004 SIP without the inclusion of the State-adopted
regulations on which the plan relied; and 4) EPA violated the
CAA by approving the 2004 SIP knowing that attainment of
the one-hour ozone NAAQS by the 2010 deadline was impos-
sible. We have jurisdiction to review EPA’s action pursuant
572 SIERRA CLUB v. UNITED STATES EPA
to 42 U.S.C. § 7607(b)(1), section 307(b)(1) of the CAA, and
we hold that EPA’s 2010 approval of the 2004 SIP, which
was based on data current only as of 2004, was arbitrary and
capricious. Deciding that issue, we need reach no other.
I
“The CAA makes the States and the Federal Government
partners in the struggle against air pollution.” Jensen Family
Farms, Inc. v. Monterey Bay Unified Air Pollution Control
Dist., 644 F.3d 934, 938 (9th Cir. 2011) (quoting Gen. Motors
Corp. v. United States, 496 U.S. 530, 532 (1990) (internal
quotation marks omitted)). The CAA protects the nation’s air
quality by authorizing EPA to establish NAAQS that apply to
air pollutants that are dangerous to the general health of the
public. 42 U.S.C. § 7409. EPA designates areas that fail to
attain NAAQS as nonattainment areas. Id. §§ 7407(d)(1).
Based on the severity of the pollution problem, nonattainment
areas are further divided into five categories: marginal, mod-
erate, serious, severe, and extreme. Id. § 7511. Central Cali-
fornia’s San Joaquin Valley (“the Valley”)1 has been
designated as an extreme nonattainment area for the pollutant
ozone.2
EPA first established NAAQS for ozone in 1979. This air
quality standard limited the acceptable level of ozone in the
ambient air to a maximum of 0.12 parts per million (“ppm”)
as measured by monitored levels averaged over one hour
1
The Valley is made up of eight counties; San Joaquin, Stanislaus, Mer-
ced, Madera, Fresno, Kings, Tulare, and the valley portion of Kern.
Approval and Promulgation of Implementation Plans, 74 Fed. Reg. 33,933
(July 14, 2009).
2
“Ozone (O3) is a gas composed of three oxygen atoms. It is not usually
emitted directly into the air, but at ground-level is created by a chemical
reaction between oxides of nitrogen (NOx) and volatile organic com-
pounds (VOC) in the presence of sunlight.” Ground-Level Ozone, U.S.
Envtl. Prot. Agency, http://www.epa.gov/glo/ (last updated Sept. 23,
2011).
SIERRA CLUB v. UNITED STATES EPA 573
(“the 1-hour ozone standard”). 74 Fed. Reg. at 33,934. In
1997, EPA reset that maximum to 0.08 ppm as measured by
monitored levels over an eight-hour period (“the 8-hour ozone
standard”). Id. Although the 8-hour standard replaced the 1-
hour standard effective June 2005, as an “anti-backsliding”
measure, EPA retained some elements of the 1-hour ozone
standard for certain nonattainment areas that had yet to attain
the 1-hour ozone standard at the time of its revocation. Id. at
33,934-35 (“As a general matter, the planning and control
requirements that remain applicable following the revocation
of the 1-hour ozone standard derive from CAA sections 110,
172, and 182 . . . . Under the [anti-backsliding measure, non-
attainment] areas remain subject to the 1-hour requirements
until they attain the 8-hour ozone standard.”) The Valley is
subject to this anti-backsliding provision.
A. State Implementation Plans
The CAA requires the states to address nonattainment areas
by developing an SIP that sets out how a nonattainment area
will come into compliance with the requisite NAAQS. 42
U.S.C. §§ 7407(a), 7410. Generally, all SIPs for nonattain-
ment areas must include, inter alia, (1) an emissions inven-
tory, important for the required attainment demonstration and
the related “rate of progress” (“ROP”) demonstration, that
“include[s] a comprehensive, accurate, current inventory of
actual emissions from all sources of the relevant pollutant or
pollutants in such area”; (2) an attainment demonstration,
developed from the emissions inventory, consisting of a tech-
nical analysis to predict whether the area will attain the
NAAQS by the deadline and a control strategy for how the
State plans to actually meet the standard;3 (3) a means to mea-
3
“[A]n attainment demonstration [is] a technical analysis that through
air quality modeling demonstrates that the ‘control measures’ proposed by
the SIP will ensure that these nonattainment areas attain the NAAQS by
the applicable deadline.” El Comité para el Bienestar de Earlimart v.
Warmerdam, 539 F.3d 1062, 1066 (9th Cir. 2008) (quoting 42 U.S.C.
§ 7502(c)(1)).
574 SIERRA CLUB v. UNITED STATES EPA
sure reasonable further progress (“RFP”); (4) nonattainment
area permit requirements for new or modified stationary
sources; and (5) contingency measures to be implemented if
the nonattainment area does not make RFP or does not attain
the NAAQS by the required date. Id. § 7502(c). SIPs for
extreme ozone nonattainment areas, such as the Valley, must
include an attainment demonstration “based on photochemical
grid modeling4 or any other analytical method determined by
the Administrator, in the Administrator’s discretion, to be at
least as effective.” Id. § 7511a(c)(2)(A), (e).
After public notice and hearings, a state must adopt the SIP
and submit it to EPA for review and approval. Id. § 7410(a).
EPA must then “determine whether a SIP submission is com-
plete within 60 days of receipt . . . . [A]ny plan that has not
been affirmatively determined to be complete or incomplete
shall become complete within 6 months by operation of law.”
74 Fed. Reg. at 33,934 (discussing 42 U.S.C. § 7410(k)(1)).
EPA must then act on the SIP, either approving it in whole or
disapproving it in part or in whole. 42 U.S.C. § 7410(k)(3).
Once approved by EPA, an “SIP bec[o]me[s] federal law . . . ,
4
As the Second Circuit stated:
Photochemical grid modeling is a sophisticated computerized
method of predicting what ozone levels will be in the future. The
model creates a three-dimensional grid over the entire control
region and analyzes how emissions from various sources com-
bine in the atmosphere to create pollutants such as ozone. Photo-
chemical reactions can produce ozone when oxides of nitrogen
(NOx) and volatile organic compounds (VOCs) are released into
the air and combine with sunlight. See 40 C.F.R. pt. 58 app. D.
§ 2.5. Ozone production is affected by a variety of factors such
as temperature, wind, and emissions levels. By manipulating
other variables like meteorology, terrain, predicted population
growth, and the effect of planned emissions reductions, the model
attempts to predict ambient ozone concentrations on the applica-
ble attainment date. See 1000 Friends of Maryland v. Browner,
265 F.3d 216, 220-21 n.4 (4th Cir. 2001).
Envtl. Def. v. EPA, 369 F.3d 193, 197-98 (2nd Cir. 2004).
SIERRA CLUB v. UNITED STATES EPA 575
and c[annot] be changed unless and until EPA approve[s] any
change.” Safe Air for Everyone v. EPA, 488 F.3d 1088, 1096
(9th Cir. 2007). The CAA provides a private right of action
for citizens to enforce an SIP by bringing a civil action in fed-
eral district court. 42 U.S.C. § 7604.
B. Mobile Source Emissions Regulation
The CAA also regulates mobile source emissions.5 “[T]he
regulation of mobile source emissions is a federal responsibil-
ity, [and] Congress has expressly preempted states from set-
ting emissions standards for mobile sources.” Jensen Family
Farms, 644 F.3d at 938 (citing 42 U.S.C. § 7543(a)). Califor-
nia, however, is a “notable exception to this general rule,” and
the CAA permits EPA to authorize California “to set its own
mobile source emissions standards so long as it obtains EPA
approval.” Id. at 938 n.3 (citing 42 U.S.C. § 7543(b) (motor
vehicles); id. § 7543(e)(2) (nonroad sources)); see also Nat’l
Ass’n of Home Builders v. San Joaquin Valley Unified Air
Pollution Control Dist., 627 F.3d 730, 733 (9th Cir. 2010)
(“[T]he [CAA] gives the states the job of regulating stationary
sources of pollution, but the EPA, and with the EPA’s permis-
sion California, are responsible for regulating emissions from
motor vehicles and other mobile sources.”). California thus
relies on its own mobile source standards in the development
of its SIPs.
C. The San Joaquin Valley 2004 SIP
In 1991, the Valley was classified as a “serious” nonattain-
ment area under the 1-hour ozone standard. Designation of
Areas for Air Quality Purposes, 56 Fed. Reg. 56,694, 56,699
5
“ ‘Mobile sources’ is a term used to describe a wide variety of vehicles,
engines, and equipment that generate air pollution and that move, or can
be moved, from place to place.” What Are Mobile Sources?, U.S. Envtl.
Prot. Agency, http://www.epa.gov/otaq/invntory/overview/examples.htm
(last updated Jan. 3, 2012).
576 SIERRA CLUB v. UNITED STATES EPA
(Nov. 6, 1991). The State timely submitted its SIP to EPA in
1994, and in January 1997, EPA approved the plan, which set
November 1999 as the attainment deadline. Approval and
Promulgation of Implementation Plans; California—Ozone,
62 Fed. Reg. 1150 (Jan. 8, 1997).
In 2001, EPA determined that the Valley did not attain the
1-hour ozone standard by the deadline. CAA Reclassification,
San Joaquin Valley Nonattainment Area, 66 Fed. Reg. 56,476
(Nov. 8, 2001). Consistent with the CAA, EPA automatically
reclassified the Valley as a “severe” nonattainment area, set
May 31, 2002 as the deadline by which the State had to sub-
mit appropriate revisions to the SIP, and set November 15,
2002 as the Valley’s new attainment deadline. Id. at 56,481;
see also 42 U.S.C. § 7511(a)(1), (b)(2).
The State did not meet its May 2002 deadline for submis-
sion of the SIP revision. Findings of Failure to Submit SIP
Revisions for 1-Hour Standard, 67 Fed. Reg. 61,784 (Oct. 2,
2002). Under the CAA, EPA then issued a finding that the
State did not meet its obligation, which “trigger[ed] the 18-
month clock for mandatory application of sanctions and 2-
year clock for a Federal implementation plan (FIP) under the
[CAA].” Id.; see also 42 U.S.C. § 7509; 40 C.F.R. § 52.31.
The State effectively gained an 18-month extension in which
it was required to revise the SIP before EPA would impose
sanctions. 67 Fed. Reg. 61,784-85.
Once more, the State did not meet this deadline. To avoid
sanctions, the State requested that EPA reclassify the Valley
as an “extreme” one-hour ozone nonattainment area. CAA
Reclassification, 69 Fed. Reg. 20,550 (Apr. 16, 2004); see
also 42 U.S.C. § 7511(a)(5). This voluntary reclassification
gave the State extra time to submit its revised SIP by resetting
the State’s submission deadline for a revised SIP consistent
with the Valley’s reclassification as an extreme ozone nonat-
tainment area. 69 Fed. Reg. at 20,550. The new deadline was
November 15, 2004, and the new attainment deadline was
SIERRA CLUB v. UNITED STATES EPA 577
November 15, 2010. Id. The State submitted the 2004 SIP for
EPA approval in November 2004. 74 Fed. Reg. at 33,933-34.
In 2003, the State adopted the “State and Federal Strategy
for the California State Implementation Plan,” (“the State
Strategy”), which set forth California’s regulatory agenda to
reduce ozone and specific commitments to reduce emissions
in the Valley. Id. at 33,934. The State Strategy “includes
defined statewide control measures that were to be reflected
in future SIPs and provisions specific to air quality plans for
the San Joaquin Valley.” Id. The 2004 SIP relied on the State
Strategy’s mobile source emissions data, developed by the
State, for its attainment demonstration and rate of progress.
Id.
D. EPA Action on the 2004 SIP
The State amended the 2004 SIP in October 2005 to substi-
tute into the plan a new control strategy and to synchronize
the rulemaking schedule with that in the Valley’s plan for the
NAAQS for particulate matter less than or equal to 10
micrometers in diameter. Id. The State submitted these
amendments to the plan to EPA in March 2006. Id. In Sep-
tember 2008, the State submitted “Clarifications Regarding
the 2004 Extreme Ozone Attainment Demonstration Plan”
(“2008 Clarifications”), which updated information on certain
control programs, ROP demonstration, and contingency mea-
sures in the 2004 SIP. Id. By operation of law, the original
2004 SIP was deemed complete on May 15, 2005, the subse-
quent amendments on September 6, 2006, and the 2008 Clari-
fications on September 23, 2008. Id.; see also 42 U.S.C.
§ 7410(k)(1)(B). Together, the SIP as submitted in 2004, the
2006 Amendments, and the 2008 Clarifications constitute the
2004 SIP, now at issue.
In October 2008, EPA issued a proposed rule to approve
the 2004 SIP and sought public comment. Approval and Pro-
mulgation of Implementation Plans, 73 Fed. Reg. 61,381
578 SIERRA CLUB v. UNITED STATES EPA
(Oct. 16, 2008). After comments were received, EPA with-
drew its proposed rule approving the 2004 SIP, and instead
proposed to approve the 2004 SIP in part, disapproving only
the attainment contingency measures. 74 Fed. Reg. at 33,947.
In response, the State submitted supplemental technical infor-
mation, and EPA withdrew its proposed disapproval and pro-
posed to approve the attainment contingency measures, and
thus the 2004 SIP in full, in October 2009. Approval and Pro-
mulgation of Implementation Plans, 74 Fed. Reg. 50,936
(Oct. 2, 2009). EPA finally approved the 2004 SIP on March
8, 2010, six years after its original submission and just eight
months before the plan’s November 15, 2010 attainment
deadline. Approval and Promulgation of Implementation
Plans, 75 Fed. Reg. 10,420 (Mar. 8, 2010).
II
“We have jurisdiction to review EPA’s approval of the
[2004 SIP] under 42 U.S.C. § 7607(b)(1).” Vigil v. Leavitt,
381 F.3d 826, 833 (9th Cir. 2004). Because the CAA “does
not specify a standard of review, . . . we apply the general
standard of review for agency actions set forth in the [APA],
5 U.S.C. §§ 701-06.” Latino Issues Forum v. EPA, 558 F.3d
936, 941 (9th Cir. 2009) (citing Vigil, 381 F.3d at 833)).
“Under the APA, we consider whether the EPA’s action was
‘arbitrary, capricious, an abuse of discretion, or otherwise not
in accordance with law.’ ” Id. (quoting 5 U.S.C. § 706(2)(A)).
“This standard requires the EPA to ‘articulate[ ] a rational
connection between the facts found and the choice made.’ ”
Id. (quoting Ariz. Cattle Growers’ Ass’n v. U.S. Fish & Wild-
life, 273 F.3d 1229, 1236 (9th Cir. 2001)). “[We] review the
record to ensure that agency decisions are founded on a rea-
soned evaluation of the relevant factors, and may not rubber-
stamp . . . administrative decisions that [are] inconsistent with
a statutory mandate or that frustrate the congressional policy
underlying a statute . . . .” Id. (quoting Friends of Yosemite
Valley v. Norton, 348 F.3d 789, 793 (9th Cir. 2003)).
SIERRA CLUB v. UNITED STATES EPA 579
Chevron, U.S.A., Inc. v. Natural Res. Def. Council, Inc.,
467 U.S. 837 (1984) generally sets forth the framework by
which we review an agency’s interpretation of a statute. Id. at
842-44. Under this framework at the first step we determine
“whether Congress has directly spoken to the precise question
at issue. If the intent of Congress is clear, that is the end of
the matter; for the court, as well as the agency, must give
effect to the unambiguously expressed intent of Congress.” Id.
at 842-43. “[I]f the statute is silent or ambiguous with respect
to the specific issue, the question for the court is whether the
agency’s answer is based on a permissible construction of the
statute.” Id. at 843.
Not all agency statutory interpretations are entitled to Chev-
ron deference, however. Rather, Chevron deference is appro-
priate where “the agency can demonstrate that it has the
general power to ‘make rules carrying the force of law’ and
that the challenged action was taken ‘in the exercise of that
authority.’ ” The Wilderness Soc’y v. U.S. Fish & Wildlife
Serv., 353 F.3d 1051, 1067 (9th Cir. 2003) (quoting United
States v. Mead Corp., 533 U.S. 218, 226-27 (2001)); see also
Vigil, 381 F.3d at 834 (finding that Chevron deference did not
apply to EPA statutory interpretations where “EPA has not, in
fact, exercised its general rulemaking authority to define these
terms”). “A very good indicator of delegation meriting Chev-
ron treatment [is] express congressional authorizations to
engage in the process of rulemaking or adjudication that pro-
duces regulations or rulings for which deference is claimed.”
Mead, 533 U.S. at 229.
[1] With respect to the CAA, “Congress has given EPA
general rulemaking authority, 42 U.S.C. § 7601(a)(1), which,
when exercised, requires our deference in accordance with
Chevron.” Vigil, 381 F.3d at 834. But EPA has not exercised
its authority to make rules carrying the force of law to fill in
the meaning of “current” and “accurate,” the terms in the
CAA we now ponder. Instead, EPA’s interpretation of the
CAA in its material terms here is largely based on a policy
580 SIERRA CLUB v. UNITED STATES EPA
guidance document issued by the Office of Air Quality Plan-
ning and Standards and the Office of Transportation and Air
Quality in 2002 along with the agency’s past practices. See
Memorandum from John S. Seitz, Office of Air Quality Plan-
ning & Standards, and Margo Tsirigotis Oge, Office of
Transp. & Air Quality, Policy Guidance on the Use of
MOBILE6 for SIP Development and Transportation Confor-
mity (Jan. 18, 2002), available at http://www.epa.gov/otaq/
models/mobile6/m6policy.pdf (“Seitz Memo”). “ ‘Interpreta-
tions such as those . . . contained in policy statements, agency
manuals, and enforcement guidelines, all of which lack the
force of law—do not warrant Chevron-style deference.’ ”
Vigil, 381 F.3d at 835 (quoting Christensen v. Harris Cnty.,
529 U.S. 576, 587 (2000). Indeed, “[t]hey are beyond the
Chevron pale.” Mead, 533 U.S. at 234.
“Such views, however, even if not authoritative for pur-
poses of Chevron, are entitled to so-called Skidmore defer-
ence insofar as they ‘constitute a body of experience and
informed judgment to which courts and litigants may properly
resort for guidance.’ ” Vigil, 381 F.3d at 835 (quoting Skid-
more v. Swift & Co., 323 U.S. 134, 140 (1944)). “Under Mead
and Skidmore, the weight that we are to give an administrative
interpretation not intended by an agency to carry the general
force of law is a function of that interpretation’s thorough-
ness, rational validity, and consistency with prior and subse-
quent pronouncements.” Wilderness Soc’y, 353 F.3d at 1068
(citing Skidmore, 323 U.S. at 140). Moreover, “ ‘[c]ogent
administrative interpretations . . . not the products of formal
rulemaking . . . nevertheless warrant respect.’ ” Vigil, 381
F.3d at 835 (quoting Alaska Dep’t of Envtl. Conservation v.
EPA, 540 U.S. 461, 488 (2004).
[2] Here, the Seitz Memo was not issued by EPA under
rulemaking authority, but, in promulgating the memo, EPA
followed “relatively formal administrative procedure tending
to foster the fairness and deliberation that should underlie a
pronouncement of . . . force.” Mead, 533 U.S. at 230. Before
SIERRA CLUB v. UNITED STATES EPA 581
its issuance, “EPA provided state, local, and tribal agencies an
opportunity to comment on the draft policy guidance in the
fall of 2001.” Seitz Memo at 1. To the extent that EPA relies
on the Seitz Memo, along with EPA’s past practices that have
not been codified through EPA’s rulemaking authority, to
support its interpretation of the statute, we give limited defer-
ence to EPA’s interpretation of the statutory provisions at
issue here. See Mead, 533 U.S. at 234 (“Chevron did nothing
to eliminate Skidmore’s holding that an agency’s interpreta-
tion may merit some deference whatever its form, given the
‘specialized experience and broader investigations and infor-
mation’ available to the agency and given the value of unifor-
mity in its administrative and judicial understandings of what
a national law requires.” (citations omitted) (quoting Skid-
more, 323 U.S. at 140)).
III
The crux of the case for us is whether EPA’s actions were
arbitrary and capricious, for if so, EPA needs to conduct its
process anew and other issues concerning statutory interpreta-
tion need not be reached. In assessing whether EPA’s agency
action approving the SIP is arbitrary and capricious, we con-
sider whether EPA “examine[d] the relevant data and articu-
late[d] a satisfactory explanation for its action including a
‘rational connection between the facts found and the choice
made.’ ” Motor Vehicle Mfrs. Ass’n of the U.S., Inc. v. State
Farm Mut. Auto. Ins. Co., 463 U.S. 29, 43 (1983) (quoting
Burlington Truck Lines, Inc. v. United States, 371 U.S. 156,
168 (1962)).
[3] Section 172(c)(3) of the CAA requires that nonattain-
ment plans “include a comprehensive, accurate, current
inventory of actual emissions from all sources of the relevant
pollutant or pollutants in such area .” 42 U.S.C. § 7502(c)(3)
(emphasis added). Petitioners contend that by the time EPA
approved the 2004 SIP in 2010, the mobile source data on
which the emissions inventory in the 2004 SIP relied were
582 SIERRA CLUB v. UNITED STATES EPA
neither “accurate” nor “current,” as shown by the emissions
inventory data that the State submitted in connection with its
2007 SIP for the 8-hour ozone standard. Petitioners further
contend that EPA’s approval of the 2004 SIP was arbitrary
and capricious because, in approving the 2004 SIP, EPA did
not reconcile the differences in the emissions data produced
by the two models. EPA also did not explain why it chose not
to consider the 2007 data in approving the 2004 SIP. We
agree that the use of stale data was not adequately reconciled
with the more current data.
The State based the 2004 SIP emissions inventory data on
mobile source data estimated through the use of the State’s
computer modeling tool released in 2002, called
EMFAC2002. EMFAC2002 estimated emissions from heavy-
duty diesel trucks based on where the trucks were registered.
The 2007 SIP emissions inventory data were compiled using
mobile source data estimated using the next generation of that
computer modeling tool, EMFAC2007, released in November
2006 and approved by EPA in January 2008. Official Release
of EMFAC2007 Motor Vehicle Emission Factor Model, 73
Fed. Reg. 3464, 3465-66 (Jan. 18, 2008). EMFAC2007
improved mobile source emission estimates by basing them
on where the trucks were being driven, which better
accounted for the amount of pollution from trucks driven in,
but not necessarily registered in, the Valley. The change in
computer modeling tool resulted in disparities in NOx emis-
sions estimates between the 2004 SIP emissions inventory and
the 2007 SIP emissions inventory. For example, the 2004 SIP
emission inventory estimate for total Valley NOx emissions
in 2008 was 429.1 tons per day, but the same estimate for
2008 rose to 597.8 tons per day in the 2007 SIP.
Although it knew of the disparities in mobile source emis-
sions estimates between the 2004 SIP and the 2007 SIP, EPA
did not address those differences or their likely impact, if any,
on the validity of the 2004 SIP in its final rule approving the
2004 SIP. Instead, EPA relied on its past practice and inter-
SIERRA CLUB v. UNITED STATES EPA 583
pretation of the CAA, as stated in the Seitz Memo, in which
emissions inventory data are considered “current” and “accu-
rate” within the meaning of § 172(c)(3) as long as the data are
current and accurate when the State submits an SIP to EPA
for approval and not necessarily when EPA approves an SIP.6
See Seitz Memo at 2.
EPA relies principally on the Seitz Memo and on the D.C.
Circuit’s holding in Sierra Club v. EPA, 356 F.3d 296 (D.C.
Cir. 2004), to support its interpretation that emissions inven-
tory data satisfy the “accurate” and “current” requirements of
the CAA as long as they are accurate and current when the
SIP is submitted for EPA approval, and that no further review
of the 2007 data was necessary.
The Seitz Memo, published in 2002, gives policy guidance
issued to address “when to use MOBILE67 in [SIP] develop-
6
As a preliminary matter, Respondent-Intervenor, San Joaquin Valley
Unified Air Pollution Control District (“the District”) argues that this court
cannot give relief to petitioners because the 1-hour ozone standard was
supplanted by the 8-hour ozone standard, and EPA has no obligation “to
take affirmative action to demonstrate attainment of the [1-hour ozone
standard].” As petitioners point out, however, EPA does not similarly
argue that the court may not provide a remedy here. Moreover, 40 C.F.R.
§§ 51.900(f), 51.905 set forth the ongoing obligations for 1-hour ozone
nonattainment areas after the adoption of the 8-hour standards. They
include ROP reductions and, here, a 1-hour NAAQS ozone attainment
demonstration because the State apparently has not met the other alterna-
tives for compliance with the regulations. See 40 C.F.R. § 51.905(a)(ii);
Adequacy Status of Motor Vehicle Emissions: 8-hour Ozone, 74 Fed. Reg.
4032, 4033 (Jan. 22, 2009) (stating that the Valley’s 8-hour ozone plan did
not show reasonable further progress for the year 2008).
Ultimately, the State is still required to submit, and EPA to approve, a
valid plan including measures relating to 1-hour NAAQS, although
revoked. To that end, the 2004 SIP contained these measures, “including
control measures, rate-of-progress (ROP) and attainment demonstrations,
and contingency measures,” and the panel may remand the matter to EPA
for action consistent with its holding. 74 Fed. Reg. at 33,934.
7
“MOBILE is EPA’s highway vehicle emissions [computer modeling
tool] for predicting gram-per-mile emissions of hydrocarbons (HC), car-
584 SIERRA CLUB v. UNITED STATES EPA
ment and transportation conformity determinations.” Seitz
Memo at 1. In 2001, MOBILE6 supplanted MOBILE5 as the
most current iteration of EPA’s federally-developed computer
modeling tool for highway vehicle emissions for “state and
local agencies outside of California.” Id. In the Seitz Memo,
EPA expressed its “belie[f] that the [CAA] would not require
states that have already submitted SIPs or will submit SIPs
shortly after MOBILE6’s release to revise these SIPs simply
because a new motor vehicle emissions model is now avail-
able.” Seitz Memo at 2. In coming to this conclusion, EPA
seemed concerned that requiring States to rework previously
submitted or recently approved SIPs whenever a new model
becomes available would pose “an obstacle to EPA approval.”
Id. EPA stated that, “[i]t would be unreasonable to require the
States to revise [recently submitted or approved] SIPs with
MOBILE6 since significant work has already occurred, and
EPA intends to act on these SIPs in a timely manner.” Id.
(emphasis added).
[4] Contrary to EPA’s argument, however, the Seitz Memo
does not appear unequivocally to stand for the proposition
that EPA action comports as a matter of course with
§ 172(c)(3) whenever EPA approves an SIP based on an old
emissions computer modeling tool as long as the modeling
tool was the most current and accurate at the time of SIP sub-
mission. That is because at least part of the Seitz Memo’s
rationale on not requiring an updated SIP when a new com-
puter modeling tool arrives appears to rest on the timeliness
of EPA’s subsequent action on the SIP in question. See id.
Indeed, the latter part of the statement quoted above suggests
that while there is some period of time after the release of a
bon monoxide (CO), nitrogen oxides (NOx), carbon dioxide (CO2), partic-
ulate matter (PM), and toxics from cars, trucks, and motorcycles under
various conditions.” Mobile, Office of Planning, Env’t, & Realty, http://
www.fhwa.dot.gov/environment/air_quality/conformity/methodologies/
mobile.cfm (last updated July 6, 2011). The most current version is
MOBILE6.2, released in 2004. Id.
SIERRA CLUB v. UNITED STATES EPA 585
new computer modeling tool in which the CAA does not
require a finding that SIPs based on the previous version are
not current and accurate, there comes a time after which reli-
ance on outdated models and data is inconsistent with requi-
site guidelines for ensuring that agency action is timely and
responsive to current public needs. The Seitz Memo itself fur-
ther supports this perspective as it states the following:
EPA also believes that the legal basis for approving
a MOBILE5-based SIP is less clear the longer that
MOBILE6 is in place and available for use. Since
SIPs must be based on applicable models and data
inputs, it could be difficult for EPA to approve a SIP
developed with MOBILE5 significantly after
MOBILE6 becomes available.
Id. at 2-3 (emphasis added). It appears then that EPA, when
it promulgated its guidance, contemplated, not surprisingly,
that relying on an outdated computer modeling tool after a
significant amount of time has passed since the introduction
of a newer model would pose a problem. Here, EMFAC2007
was released to the public in November 2006, submitted to
EPA for approval in April 2007, and approved by EPA in Jan-
uary 2008. See 73 Fed. Reg. at 3465. EPA, however, did not
approve the 2004 SIP until 2010, more than 3 years after the
release of EMFAC2007. By March of 2010, EPA knew that
a new computer modeling tool was available and had access
to data compiled through the use of the more current tool.
That data told a different story than that told by the earlier
data about projected emissions of NOx from mobile sources
in the Valley, which undermined the accuracy and currency
of the 2004 SIP emissions inventory data. EPA, in its final
rule approving the 2004 SIP, however, did not analyze this
new data or explain why it chose not to analyze the data in
considering the 2004 SIP. EPA did not “cogently explain why
it . . . exercised its discretion” not to consider the new and
available data. State Farm, 463 U.S. at 48. Instead, EPA
merely repeated its mantra that, despite availability of the
586 SIERRA CLUB v. UNITED STATES EPA
2007 emissions inventory data three years before the 2010
approval of the 2004 SIP, EPA had no duty under the CAA
to consider new data so long as the data relied upon was cur-
rent and accurate when submitted. But we think the agency in
the public’s interest should have considered that six years had
passed between the State’s submission of the 2004 SIP and its
approval by the agency.
EPA also relies on the D.C. Circuit’s holding in Sierra
Club to support its contention that reliance on the currency
and accuracy of the data at the time of submission renders its
approval of the 2004 SIP valid. In Sierra Club, the D.C. Cir-
cuit considered, inter alia, the significance of EPA’s introduc-
tion of MOBILE6 on EPA’s approval of the D.C.-area’s 1-
hour ozone SIPs, which were based on emissions data com-
plied using MOBILE5. 356 F.3d at 308. The ROP plans for
the years 1996-1999, based on MOBILE5, were originally
submitted for EPA approval in 1999 and then resubmitted as
part of the D.C.-area SIPs in February 2002, even though
MOBILE6 was made available one month earlier in January
2002. EPA approved the SIPs one year later in April 2003. Id.
The Sierra Club argued that EPA’s approval of the SIPs
there was arbitrary and capricious in light of the availability
of the newer modeling tool. Id. at 307-08. Relying on the
Seitz Memo, the D.C. Circuit concluded, however, that “[t]o
require states to revise completed plans every time a new
model is announced would lead to significant costs and poten-
tially endless delays in the approval processes.” Id. at 308.
Accordingly, the D.C. Circuit held that “EPA’s decision to
. . . accept the use of MOBILE5 . . . was neither arbitrary nor
capricious.” Id.
Contrary to EPA’s argument, our conclusion today is not
inconsistent with the D.C. Circuit’s holding in Sierra Club
because the facts here are not alike; there are marked differ-
ences between the plans’ submissions and their approvals. In
Sierra Club, the new modeling tool was available for only one
SIERRA CLUB v. UNITED STATES EPA 587
year before EPA approved the D.C.-area SIPs that were based
on the previous iteration. Here, EMFAC2007 was available to
the public as early as November 2006, and the 2004 SIP was
not approved until more than three years later in March 2010.
Thus as the Seitz Memo itself suggests, EPA stands on shaky
legal ground relying on significantly outdated data, given the
amount of time that EMFAC2007 was available and autho-
rized for use before EPA approved the 2004 SIP. See Seitz
Memo at 2-3.8
Second, in Sierra Club, the D.C. Circuit noted the Seitz
Memo’s argument that requiring a new compilation of emis-
sion data based on the new computer modeling tools would
place an onerous burden on and unnecessarily prolong
approval. Indeed, in that case, no new data based on
MOBILE6 were available and a new study just to collect the
raw data would have had to be commissioned. Here, by con-
trast, the State had already collected the emissions data using
EMFAC2007, and had presented to EPA the 2007 SIP that
relied on that updated data. There was no need for a new
study to be commissioned, and the burden and expense of
commissioning a new study was minimized as one had
already been completed with respect to the 8-hour ozone stan-
dard 2007 SIP. Based on these factual differences then, the
D.C. Circuit’s opinion in Sierra Club does not support EPA’s
8
In another example cited by EPA to support the proposition that it is
EPA’s policy to approve SIPs based on MOBILE5, although MOBILE6
was available for use, there was also a relatively short period of time
between the plan submission and EPA approval. Specifically, in July 2001
the state of Georgia submitted a revised attainment demonstration for the
1-hour ozone nonattainment area in Atlanta which replaced the previous
attainment demonstration submitted in October 1999. Approval and Pro-
mulgation of Georgia SIPs, 67 Fed. Reg. 30,574 (May 7, 2002). EPA
approved the attainment demonstration effective June 2002, about 6
months after MOBILE6 was available. Id. This example does not speak
to the Seitz Memo’s own observation regarding the legality of relying on
an old version of the computer modeling tool when a new version has
been available for a significant amount of time.
588 SIERRA CLUB v. UNITED STATES EPA
contention that its approval of the 2004 SIP here, without con-
sideration of the long available updated emissions inventory
data, was not arbitrary or capricious.
Moreover, EPA’s decision not to evaluate the EMFAC2007
data, of which EPA had actual knowledge and which could
reasonably be described as relevant to the efficacy of the 2004
SIP, is also inconsistent with our holding in Ass’n of Irritated
Residents v. EPA (A.I.R.), 632 F.3d 584 (9th Cir. 2011). In
A.I.R., we considered whether EPA’s decision not to evaluate
the adequacy of California’s South Coast nonattainment
area’s previously approved 1997/1999 SIP was arbitrary and
capricious after the State, upon new modeling, submitted a
2003 attainment demonstration revision that made clear that
the attainment demonstration in the 1997/1999 SIP was inac-
curate. 632 F.3d at 589-90. EPA ultimately disapproved the
2003 SIP revision’s attainment demonstration, but took no
further action to evaluate the 1997/1999 SIP’s extant attain-
ment demonstration. We held that EPA’s “failure to evaluate
the adequacy of the existing [1997/1999] SIP was arbitrary
and capricious,” because California, in its 2003 SIP revision,
acknowledged that the attainment demonstration in EPA-
approved 1997/1999 SIP was inaccurate. Id. at 590. We stated
that, “[t]hrough the 2003 SIP Revision, EPA knew, or should
have known, of the inadequacy of the 1997/1999 SIP,” and
that “even if EPA did not actually know the extent to which
the new modeling undermined the existing SIP, it has a duty
to evaluate the adequacy of the existing SIP as a whole when
approving SIP revisions.” Id. at 590-91.
In reasoning that EPA’s “obligation to take further action
[could] be derived from the statutory requirement that the
Administrator issue a SIP call upon a finding that the existing
SIP is substantially inadequate,” we noted:
[T]he question is not whether EPA has discretion in
determining substantial inadequacies exist, but
whether EPA has unlimited discretion to ignore evi-
SIERRA CLUB v. UNITED STATES EPA 589
dence indicating an existing SIP might be substan-
tially inadequate and choose to do nothing. We
believe EPA’s failure to act in light of the strong evi-
dence provided in the 2003 SIP Revision demon-
strating the substantial inadequacies of the 1997/
1999 Plan is arbitrary and capricious.
Id. at 593 (emphasis added). While A.I.R. addressed EPA’s
obligation to monitor the accuracy and efficacy of approved
SIPs, its holding is relevant because it supports the proposi-
tion that if new information indicates to EPA that an existing
SIP or SIP awaiting approval is inaccurate or not current,
then, viewing air quality and scope of emissions with public
interest in mind, EPA should properly evaluate the new infor-
mation and may not simply ignore it without reasoned expla-
nation of its choice.
The District argues that it was appropriate for EPA to
ignore the 2007 8-hour ozone emissions inventory data
because they were not relevant to the 2004 1-hour ozone
emissions inventory data, and that any comparison would not
be “an apples to apples comparison.” We are not persuaded
for several reasons. First, while the conclusions presented
within the two SIPs might vary, the undisputed fact is that the
EMFAC2007 revealed a significantly different measurement
of expected NOx emissions (e.g., 597.8 tons per day in 2008)
than did the data observed with EMFAC2002 (e.g., 429.1 tons
per day in 2008). Given NOx’s integral role in the creation of
harmful ground-level ozone, this disparity should have alerted
EPA to the possibility that the 2004 Plan may have been sig-
nificantly flawed.
Second, although the District characterizes the 8-hour
ozone NAAQS as being so different from the 1-hour ozone
standard as to make any comparison unreasonable, there is
evidence that the two standards are significantly close enough
that the above-noted differences in NOx emissions should
have reasonably alerted EPA to the real possibility that the
590 SIERRA CLUB v. UNITED STATES EPA
data on which the 2004 SIP was based were inaccurate and
ineffective. National Ambient Air Quality Standards for
Ozone, 62 Fed. Reg. 38,856, 38,858 (July 18, 1997) (stating
that the 8-hour standard (0.09 ppm) “generally represents the
continuation of the present level of protection”); see also S.
Coast Air Quality Mgmt. Dist., 472 F.3d 882, 888 (D.C. Cir.
2006) (citing 62 Fed. Reg. at 38,858 for the proposition that
the 8-hour ozone standard is only “marginally more stringent”
than the 1-hour ozone standard it replaced).
Third, and most importantly, EPA, in its final rule, did not
bother to address substantively the apparent disparities
between the 2007 emissions inventory data and the 2004
emissions inventory data, leaving us with no means of deter-
mining whether there is any merit to the District’s argument.
In this light, the District’s conclusions in its briefing that the
2007 emissions inventory data should have had no bearing on
EPA’s approval of the 2004 SIP are unpersuasive insofar as
they are presented for the purposes of litigation rather than
framed objectively and scientifically. See State Farm, 463
U.S. at 50 (“[T]he courts may not accept appellate counsel’s
post hoc rationalizations for agency action.”). EPA did not
“bring its expertise to bear on” the updated emissions inven-
tory data in the 2004 SIP approval process. Id. at 54. The
agency did not adequately address the staleness of its data and
availability of more current data before reaching its conclu-
sion.
[5] Our role is not to substitute our conclusions based on
the facts presented for those of the agency, and we express no
opinion as to what conclusion EPA should have reached, with
respect to the validity of the 2004 SIP, upon consideration of
the 2007 data. But we should not silently rubber stamp agency
action that is arbitrary and capricious in its reliance on old
data without meaningful comment on the significance of more
current compiled data. We hold that EPA’s failure to even
consider the new data and to provide an explanation for its
choice rooted in the data presented was arbitrary and capri-
SIERRA CLUB v. UNITED STATES EPA 591
cious. Indeed, it was unreasonable for EPA summarily to rely
on the point of view taken under markedly different circum-
stances in the Seitz Memo and in Sierra Club, without
advancing an explanation for its action based on “the facts
found and the choice made.” Burlington Truck Lines, 371
U.S. at 168.
[6] Concluding that the agency’s action in approving the
challenged SIP was arbitrary and capricious under the APA,
we need not and do not reach petitioners’ other arguments.
We grant the petition for review and remand the matter to
EPA for further proceedings consistent with our decision.9
PETITION GRANTED.
9
Upon EPA’s reconsideration and subsequent final action, petitioners
may again seek review of that EPA action, but shall file a new petition in
order to do so. In such an instance, petitioners, where appropriate, may
raise the issues not reached by us today.