 United States Court of Appeals
         FOR THE DISTRICT OF COLUMBIA CIRCUIT



Argued December 10, 2018              Decided May 31, 2019

                       No. 16-1158

                       SIERRA CLUB,
                        PETITIONER

                             v.

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


       On Petition for Review of Final Action of the
      United States Environmental Protection Agency


     Tosh Sagar argued the cause for petitioner. With him on
the briefs were Seth L. Johnson and David S. Baron.

     Phillip R. Dupré, Attorney, U.S. Department of Justice,
argued the cause for respondents. With him on the brief were
Jeffrey H. Wood, Acting Assistant Attorney General, Jonathan
D. Brightbill, Deputy Assistant Attorney General, and
Jonathan Skinner-Thompson, Counsel, U.S. Environmental
Protection Agency.
                                2
   Before: GRIFFITH and WILKINS, Circuit Judges, and
WILLIAMS, Senior Circuit Judge.

   Opinion for the Court filed by Senior Circuit Judge
WILLIAMS.

     WILLIAMS, Senior Circuit Judge: To implement the Clean
Air Act, the Environmental Protection Agency oversees state
procedures for creating and running air monitoring networks.
In 2016, EPA adopted a rule, Revisions to Ambient Monitoring
Quality Assurance and Other Requirements, 81 Fed. Reg.
17,248 (Mar. 28, 2016) (“Final Rule”), modifying its
regulations on the subject, specifically Part 58 of Title 40 of the
Code of Federal Regulations. The amendments (1) tightened
procedures for state changes to annual monitoring network
plans, (2) authorized limited reductions in required sampling
frequency, and (3) proposed revisions to certain quality
assurance requirements related to monitoring for Prevention of
Significant Deterioration.

     Sierra Club raises three objections. Resting on EPA’s
language in the preamble to the rule, it attacks the divergence
between EPA’s procedures for reviewing SIPs and annual
monitoring network plans—a divergence embodied in a 2006
EPA regulation that has long since passed the deadline for
seeking judicial review. It challenges (on the merits) the new
authority on sampling frequency reductions. And it sees a fatal
procedural defect in the quality assurance adjustments in the
form of EPA’s statement—plainly and concededly mistaken—
that no commenter had criticized the changes.

    For the reasons below, however, we find that Sierra Club
(1) is barred from seeking review of the claimed legal
requirement that monitoring plans be assessed under the same
procedures as SIPs because the new rule and EPA’s preamble
                               3
did no more than echo a prior EPA regulation, (2) lacks
standing to attack the sampling frequency changes, and (3) has
made no showing that the asserted non-response on quality
assurance issues manifested any failure to consider factors
relevant to the changes. Thus we dismiss the first two claims
and deny the third.


                            * * *

     The Clean Air Act, 42 U.S.C. §§ 7401–7671q, establishes
a comprehensive system for regulating and improving the
nation’s air quality, divvying up responsibility between the
federal government and the states.

     First, EPA identifies air pollutants that endanger public
health or welfare, and sets National Ambient Air Quality
Standards, or NAAQS, that specify the maximum permissible
concentration of those pollutants in the ambient air. 42 U.S.C.
§§ 7408–09. Then, subject to EPA approval, states adopt State
Implementation Plans, or SIPs, id. § 7410(a)(1), which are to
bring areas into attainment with the NAAQS (if they are not
already), see id. § 7502(a)(2)(A), and to “prevent significant
deterioration of air quality,” id. § 7471.

     To make performance of these functions possible, EPA
“promulgate[s] regulations establishing an air quality
monitoring system throughout the United States.” 42 U.S.C.
§ 7619(a). Those regulations, among other things, require
states to submit an “annual monitoring network plan” that
documents “the establishment and maintenance of an air
quality surveillance system that consists of a network of” state
or local air monitoring stations. 40 C.F.R. § 58.10(a)(1).

    We now turn to Sierra Club’s three challenges to EPA’s
recent revisions to its monitoring regulations.
                               4
                             * * *

     First and foremost, Sierra Club attacks EPA’s revised
regulation governing the review and approval of annual
monitoring network plans, 40 C.F.R. § 58.10(a), on the ground
that it violates Sierra Club’s reading of the Clean Air Act.
Because the act, in Sierra Club’s view, renders a state’s
“monitoring network plan . . . part of a SIP,” such plans must
be subjected to the review procedures applicable to SIPs.
Sierra Club Br. 24.

     But no later than 2006 EPA’s regulations pursued the non-
SIP path.      See Revisions to Ambient Air Monitoring
Regulations, 71 Fed. Reg. 61,236 (Oct. 17, 2006). A decade
later, Sierra Club cannot force EPA back up the trail. The
Clean Air Act requires that petitions for review be filed “within
sixty days” of a challenged action appearing in the Federal
Register. 42 U.S.C. § 7607(b)(1). Accordingly (absent EPA’s
reopening the issue), Sierra Club’s time for challenging EPA’s
adoption of a non-SIP approach to reviewing annual
monitoring network plans has passed. And because the issue
is jurisdictional, Sierra Club v. EPA, 895 F.3d 1, 16 (D.C. Cir.
2018), we must raise it ourselves, see, e.g., Gonzalez v. Thaler,
565 U.S. 134, 141 (2012), and dismiss the petition, Medical
Waste Inst. & Energy Recovery Council v. EPA, 645 F.3d 420,
427 (D.C. Cir. 2011).

     EPA’s decision to place annual monitoring network plans
outside the SIP-review process was evident. For example,
while the statute requires EPA approval of SIP revisions to be
preceded by notice and an opportunity for comment, see 42
U.S.C. § 7607(d)(1)(B), (3), (4)(B)(i), (5), (6)(B); see also
Sierra Club Br. 8, the 2006 rulemaking provided that, for
certain monitoring plans, “the Regional Administrator is not
required to provide a separate opportunity for comment,” 40
                               5
C.F.R. § 58.10(a)(2) (2007) (emphasis added); see also 71 Fed.
Reg. at 61,248/1.

     The 2006 rulemaking also embodied the same disconnect
between state processes for formulating monitoring plans and
for formulating SIPs—at least under Sierra Club’s reading of
the statute. Sierra Club complains that the current provision on
the subject is unlawful because it diverges from the statutory
requirement applicable to SIP submissions—namely, that
states act only after providing “reasonable notice and public
hearings,” 42 U.S.C. § 7410(a)(1), (a)(2), (l). See Sierra Club
Br. 37. But EPA created that divergence no later than the 2006
rulemaking, which similarly fell short of that standard,
demanding only that a monitoring “plan must be made
available for public inspection.” 40 C.F.R. § 58.10(a)(1)
(2007).

     Thus, by at least 2006 EPA had necessarily concluded that
annual monitoring network plans were not components of a
SIP.

     In the rulemaking currently under review EPA simply
continued the same approach. In 2014 it proposed two modest
revisions to 40 C.F.R. § 58.10(a). See Revisions to Ambient
Monitoring Quality Assurance and Other Requirements, 79
Fed. Reg. 54,356, 54,359/1–2 (Sept. 11, 2014) (“Proposed
Rule”). The proposal gave no indication that EPA intended to
address the relationship between annual monitoring network
plans and SIPs, or the requirements applicable to SIPs, which
are addressed (in great detail) elsewhere, see 40 C.F.R. pt. 51
(concerning the “Requirements for Preparation, Adoption, and
Submittal of [SIPs]”). In proposing and adopting these tweaks,
EPA never purported to close the gap in review procedures
between the two types of plans. Rather, it maintained (with
                                6
slight edits) the non-SIP approach it adopted, at the latest, in
2006.

     Accordingly, if Sierra Club disagreed with EPA’s
disjuncture between monitoring plans and SIPs, it should have
raised its objection at the conclusion of the 2006 rulemaking,
“within sixty days of EPA’s first use of the [non-SIP-style]
approach.” Medical Waste Inst., 645 F.3d at 427; see also, e.g.,
Am. Iron & Steel Inst. v. EPA, 886 F.2d 390, 397 (D.C. Cir.
1989) (holding that the time for filing a petition started when
“EPA first set out its understanding” of its authority).

     In an effort to tie the monitoring-plan-is-really-a-SIP issue
to the 2016 rulemaking, Sierra Club points to a single statement
EPA made in the preamble to the Final Rule:

    [S]ection 110(a)(2)(B) [of the Clean Air Act, 42
    U.S.C. § 7410(a)(2)(B),] simply requires that
    monitoring agencies have the legal authority to
    implement 40 CFR part 58 [concerning monitoring
    network plans]; it does not treat annual monitoring
    network plans . . . as “integral parts” of a SIP subject
    to public participation whenever such network plans
    are established or modified.

Final Rule, 81 Fed. Reg. at 17,251/3.

    But far from indicating that EPA intended to reconsider
the separation of monitoring plans and SIPs, this statement
merely responded (quite briefly) to a comment lodged by Sierra
Club’s counsel, Earthjustice, in an attempt to reopen the issue.
See Earthjustice & American Lung Association Comments,
EPA-HQ-OAR-2013-0619-0034, at 2 (Nov. 10, 2014)
(“Earthjustice Comments”), J.A. 96. Petitioners, however,
cannot “comment on matters other than those actually at issue,
goad an agency into a reply, and then sue on the grounds that
                               7
the agency had re-opened the issue.” United Transp. Union-
Ill. Legislative Bd. v. Surface Transp. Bd., 132 F.3d 71, 76
(D.C. Cir. 1998) (quoting Massachusetts v. ICC, 893 F.2d
1368, 1372 (D.C. Cir. 1990)).

     Of course, Sierra Club’s submissions might be read as an
invitation to EPA to reopen that issue, but agencies are free to
decline such invitations. Given “the entire context of the
rulemaking,” it is clear that EPA declined and did not reopen
consideration of the SIP-monitoring-plan divide. Am. Road &
Transp. Builders Ass’n v. EPA, 588 F.3d 1109, 1115 (D.C. Cir.
2009) (citation omitted). In sum, EPA’s rejection of Sierra
Club’s extraneous comment did not give Sierra Club the right
to challenge longstanding aspects of EPA’s regulations that the
agency did not open for reconsideration. (We take no position
on the merits of Sierra Club’s view that monitoring plans are a
subset of SIPs, nor on whether Sierra Club may challenge
EPA’s refusal to adopt SIP-style-review procedures in another
context, such as in a petition for rulemaking.)


                            * * *

     Sierra Club next challenges EPA’s decision to permit
Regional Administrators to give case-by-case approval to
reductions in the minimum required sampling frequency of
monitoring for fine particulate matter. Known as PM2.5, fine
particulate matter consists of airborne particles that are 2.5
micrometers in diameter or smaller—less than one-thirtieth the
thickness of human hair. Air Quality Designations and
Classifications for the Fine Particles (PM2.5) National
Ambient Air Quality Standards, 70 Fed. Reg. 944, 945/2 (Jan.
5, 2005).

     Under prior regulations, certain air monitoring stations
that track PM2.5 were required to operate on at least a 1-in-3
                               8
day sampling frequency. Proposed Rule, 79 Fed. Reg. at
54,360/2; see 40 C.F.R. § 58.12(d) (2015). On this, there is no
immediate change.

     Rather, EPA’s revisions created the possibility of
exceptions—enabling possible reductions from 1-in-3 days to
1-in-6 days (or for seasonal sampling). EPA sought to address
the sort of situation where a particular monitor was “highly
unlikely” to record an otherwise undetected violation of the
PM2.5 NAAQS. Final Rule, 81 Fed. Reg. at 17,254/1. One
example it noted was a monitor located in an area with “very
low PM2.5 concentrations relative to the NAAQS.” Id. Another
was a monitor in an urban environment surrounded by a
superabundance of other monitors, all with higher readings. Id.
Accordingly, EPA reasoned that in such instances the 1-in-3
sampling frequency might be unnecessary. Id.

    To counteract the possibility of excessive redundancy,
EPA gave Regional Administrators a cautiously hedged
authority to approve state requests to reduce specific monitors’
sampling frequency to 1-in-6 days or to seasonal sampling. 40
C.F.R. § 58.12(d)(1)(ii) (2018). Under the rule, the Regional
Administrator must first conduct a case-by-case analysis,
considering factors “including but not limited to the historical
PM2.5 data quality assessments” and the location of other PM2.5
monitors. Id. He must also “determine[] that the reduction in
sampling frequency will not compromise data needed for
implementation of the NAAQS.” Id. Only then may approval
be granted.

    Sierra Club, nevertheless, finds much to fear. Even with
an EPA gatekeeper, it says, a reduction in mandatory sampling
frequency “creates an increased risk that excessive daily PM2.5
levels will go undetected.” Earthjustice Comments at 4, J.A.
                               9
98. Sierra Clubs claims that EPA arbitrarily failed to consider
this risk increase.

     But our jurisdiction to consider the issue requires that
Sierra Club establish its standing. Sierra Club v. EPA, 292
F.3d 895, 898 (D.C. Cir. 2002). Here, it appears to assert only
associational standing. See Sierra Club Br. 31; Sierra Club
Reply Br. 25–26. In this context, it must demonstrate, not
merely allege, that there is a “substantial probability” that one
of its members will suffer an injury if the court does not take
action, i.e., prevent EPA from allowing regional administrators
to consider reductions in sampling frequency. Sierra Club v.
EPA, 754 F.3d 995, 1001 (D.C. Cir. 2014) (quoting Natural
Resources Defense Council v. EPA, 464 F.3d 1, 6 (D.C. Cir.
2006)). This demonstration must be made “by affidavit or
other evidence.” Sierra Club, 292 F.3d at 899 (quoting Lujan
v. Defenders of Wildlife, 504 U.S. 555, 561 (1992)). Sierra
Club has failed to make the requisite showing.

    For a Sierra Club member to face an increased risk of
harm, the following conditions would have to be fulfilled. (1)
A state must request a reduction in sampling frequency; (2) the
request must concern a monitor near one of Sierra Club’s
members; (3) the request must be approved by the Regional
Administrator; (4) there must be a likelihood that a spike in
PM2.5 levels near that monitor will occur at a time when the
monitor would have been sampling but for the approved
reduction; (5) and conditions must be such that no nearby
monitor would pick up the spike.

     To suggest even a minimally credible possibility of the
above occurring, Sierra Club identifies three monitors that are
(i) eligible for a reduction in sampling and (ii) placed near a
Sierra Club member. One is in Texas (Houston); two are in
Oregon (Oakridge and Klamath Falls). Sierra Club Reply Br.
                               10
26; see Joshua Berman Decl. ¶¶ 34–38 (Mar. 16, 2018). But is
Texas or Oregon likely to request any reductions in sampling
frequency? Courts are generally “hesitant” to base standing on
a chain of events that “‘depends on the unfettered choices made
by independent actors not before the courts,’” R.J. Reynolds
Tobacco Co. v. FDA, 810 F.3d 827, 831 (D.C. Cir. 2016)
(quoting Lujan, 504 U.S. at 562), such as state regulators, see,
e.g., Masias v. EPA, 906 F.3d 1069, 1074 (D.C. Cir. 2018);
Scenic Am., Inc. v. U.S. Dep’t of Transp., 836 F.3d 42, 50 (D.C.
Cir. 2016); Miami Bldg. & Constr. Trades Council v. Secretary
of Defense, 493 F.3d 201, 205–06 (D.C. Cir. 2007). In any
case, even if Texas or Oregon were likely to request reductions,
how likely is it that they would do so for monitors at the sites
identified by Sierra Club as near specific members, to wit, sites
482011039, 410350004, or 410392013? Berman Decl. ¶¶ 35–
37.

     Sierra Club seeks to fill this gap in state motivation by
pointing out that “states . . . lobbied for these changes to save
money.” Sierra Club Reply Br. 26–27. The inference may be
sound—for states that lobbied. But Sierra Club fails to point
us to any evidence that Texas or Oregon was among the
unspecified states that did so. See id. at 27 (citing Final Rule,
81 Fed. Reg. at 17,254/2, which simply states that all
comments, save one, were supportive of the rule change);
Berman Decl. ¶ 33 (same). And we need not scour the
administrative record ourselves. See, e.g., Masias, 906 F.3d at
1080 (citing Fed. R. App. P. 28(a)(8)(A)). In any event,
nothing suggests that the monitors at the three numbered sites
are prime candidates for reduction, whatever Texas’s or
Oregon’s general plans may be. Cf. Sierra Club v. EPA, 755
F.3d 968, 974 (D.C. Cir. 2014) (finding standing where EPA,
effectively reinforcing petitioners’ assertions, pointed to
specific refineries near Sierra Club’s members that were
“expected to take advantage” of the rule).
                                     11
     Further, the eligible monitors appear to be located at rather
low-risk sites. In 2016, not one of them recorded a violation of
the 24-hour PM2.5 NAAQS—or even came particularly close
to doing so. See Berman Decl. ¶¶ 31, 35–37. Nor did any come
within even 10% of an annual PM2.5 NAAQS violation—for
three reporting periods in a row. See Berman Decl. ¶¶ 31–32,
35–37. Far from it. As the table below indicates, the monitors
have consistently—year after year—fallen well below the
PM2.5 annual NAAQS.

                                 Monitor’s
                    Design                       Annual
   Monitor                        Design                           %
                    Value*                       NAAQS
   Location                       Value*                         Diff.**
                    Years                        (μg/m3)
                                  (μg/m3)
  482011039        2012-14          9.6             12.0          - 20%
   (Houston,       2013-15          9.6             12.0          - 20%
     TX)           2014-16          9.2             12.0          - 23%
  410350004        2012-14          10.2            12.0          - 15%
   (Klamath        2013-15          10.0            12.0          - 17%
  Falls, OR)       2014-16          8.3             12.0          - 31%
  410392013        2012-14          9.2             12.0          - 23%
  (Oakridge,       2013-15          9.6             12.0          - 20%
     OR)           2014-16          8.5             12.0          - 29%
      * “Design values” are “the 3-year average NAAQS metrics that are
compared to the NAAQS levels to determine when a monitoring site meets
or does not meet the NAAQS . . . .” The table references the annual
NAAQS—the “3-year average of PM2.5 annual mean mass concentrations
for each eligible monitoring site.” 40 C.F.R. pt. 50, app. N(1.0)(c).

     ** “The national primary ambient air quality standard[] for PM2.5 [is]
12.0 micrograms per cubic meter (μg/m3) annual arithmetic mean
concentration . . . .” 40 C.F.R. § 50.18(a); see also id. pt. 50, app. N(4.4).
The “% Diff.” is the difference between the design value calculated using
the monitor’s data and the national standard, divided by the national
standard. For the underlying data, see Berman Decl. ¶¶ 31, 35–37.
                               12
Sierra Club identifies no reason to believe that an abrupt
reversal in PM2.5 fortunes near these sites is likely, much less
“certainly impending.” Nat’l Ass’n of Home Builders v. EPA,
667 F.3d 6, 15 (D.C. Cir. 2011) (quoting Am. Chem. Council v.
Dep’t of Transp., 468 F.3d 810, 819 (D.C. Cir. 2006)).

     Finally, Sierra Club does nothing to build into its theory of
harm the analytical exercise that the Regional Administrator
must undertake before granting approval, such as determining
whether “continuous PM2.5 monitors” exist nearby, and
whether an unexpected spike in fine particulate matter would
really have registered at one of the sites (had it been kept at 1-
in-3) and yet evaded all other monitors. Final Rule, 81 Fed.
Reg. at 17,254/1; see also 40 C.F.R. § 58.12(d)(1)(ii).

     At bottom, Sierra Club’s claim to standing “stacks
speculation upon hypothetical upon speculation.” Kansas
Corp. Comm’n v. FERC, 881 F.3d 924, 931 (D.C. Cir. 2018)
(quoting N.Y. Regional Interconnect, Inc. v. FERC, 634 F.3d
581, 587 (D.C. Cir. 2011)). In these circumstances, Sierra Club
has failed to establish standing. Accordingly, the portion of the
petition for review challenging EPA’s revisions of minimum
sampling frequency is dismissed.


                             * * *

    Finally, Sierra Club protests adjustments EPA made to
four quality assurance requirements for Prevention of
Significant Deterioration, or PSD, air monitoring. See Sierra
Club Br. 55–56 & n.18; see also Final Rule, 81 Fed. Reg. at
17,271–75. As the name implies, PSD monitoring is designed
to evaluate whether new or significantly modified sources of
pollution will bring about significant deteriorations in air
quality.
                              13
     Until adoption of the Final Rule, the quality assurance
requirements for PSD monitoring had generally been the same
as the requirements for monitoring used to measure compliance
with the NAAQS. Final Rule, 81 Fed. Reg. at 17,271/1.
Compare 40 C.F.R. pt. 58, app. A (NAAQS), with 40 C.F.R.
pt. 58, app. B (PSD). In 2014, however, EPA proposed some
revisions relating to PSD monitoring. See Proposed Rule, 79
Fed. Reg. at 54,369–72.

     Earthjustice (Sierra Club’s counsel here) and the American
Lung Association jointly objected to that proposal, saying that
EPA should apply the same requirements to the PSD monitors
as it does to monitors ensuring NAAQS compliance. The
protest identified four specific ways in which the rule would
make the PSD quality assurance requirements weaker than
those for the NAAQS, and argued that such relaxations were
wrong, primarily because PSD monitoring was “required for
the purpose of determining whether the proposed facility will
cause or contribut[e] to exceedances of . . . NAAQS.”
Earthjustice Comments at 8, J.A. 102; see also Sierra Club Br.
57. EPA overlooked this comment. As the agency now admits,
in discussing the Final Rule it inaccurately stated that it had
received only favorable comments on its proposed changes.
See EPA Br. 49–50; see also, e.g., Final Rule, 81 Fed. Reg. at
17,271/3.

    Sierra Club argues that EPA could not meaningfully have
“respond[ed] to significant points raised by the public,” as EPA
must, as it failed even to recognize that anyone made adverse
comments. Sierra Club Br. 58 (quoting Lake Carriers’ Ass’n
v. EPA, 652 F.3d 1, 11 (D.C. Cir. 2011)).

    But a “failure to respond to comments is significant only
insofar as it demonstrates that the agency’s decision was not
based on a consideration of the relevant factors.” Sierra Club
                              14
v. EPA, 353 F.3d 976, 986 (D.C. Cir. 2004) (Roberts, J.)
(emphasis added) (quoting Thompson v. Clark, 741 F.2d 401,
409 (D.C. Cir. 1984)). The principle, of course, applies
whether EPA expressly acknowledged Earthjustice’s comment
or not. Here EPA plainly addressed the factors that the
comment had said must be considered. See generally Final
Rule, 81 Fed. Reg. at 17,271–75.

     Take     Sierra    Club’s     first   example—“waiving
implementation of the National Performance Evaluation
Program (‘NPEP’).” Sierra Club Br. 55 n.18. EPA in fact
addressed the substance of Earthjustice’s NAAQS-
requirements-must-meet-PSD-requirements concern in this
context, saying that NPEP requirements could not be waived
“if a PSD reviewing authority intended to use PSD data for any
official comparison to the NAAQS beyond” some limited PSD
uses. Final Rule, 81 Fed. Reg. at 17,271/2. And it explained,
in detail, why PSD monitoring otherwise needed more
“flexibility.” Id. For instance, because PSD monitoring is
shorter term (usually a year or less), it may, EPA elaborated,
“be more difficult” to arrange the specialized equipment,
personnel, and relationships that would be needed to
implement the NPEP. Id. at 17,271/1–2. This “explanation
makes it evident that [EPA] did consider the relevant factors.”
Sierra Club, 353 F.3d at 986.

    The same is true for each of the remaining changes to
which Earthjustice objected. Compare Sierra Club Br. 55–56
& n.18, with Final Rule, 81 Fed. Reg. at 17,271–75. As
detailed in the table below, for each of the changes identified
by Sierra Club, EPA explained why it was altering the PSD
requirements (relative to the NAAQS requirements):
                              15
Changes described
                         Excerpt from EPA’s Explanation
in Sierra Club Br.
                                  of each change
    55–56 n.18
“(2) [E]liminating      “Since PSD does not implement
lead quality assur-     NCore sites, the EPA proposed to
ance requirements       eliminate the [lead] [quality assur-
for collocated sam-     ance] language specific to non-source
pling and lead per-     oriented NCore sites from PSD while
formance evalua-        retaining the PSD [quality assurance]
tion procedures for     requirements for routine [lead] moni-
non-source oriented     toring.” 81 Fed. Reg. at 17,272/1.
NCore sites.”
“(3) [R]elaxing data    “Realizing that PSD monitoring may
quality objectives      have different monitoring objectives,
for PSD monitoring      the EPA proposed to . . . allow deci-
organizations.”         sions on [data quality objectives] to be
                        determined through consultation be-
                        tween the appropriate PSD reviewing
                        authority and PSD monitoring organ-
                        ization.” 81 Fed. Reg. at 17,272/3.
“(4) [W]aiving the      “Due to the relatively short-term na-
concentration valid-    ture of most PSD monitoring, the like-
ity threshold for im-   lihood of measuring low concentra-
plementation of the     tions in many areas attaining the
PM2.5 performance       PM2.5 standard and the time required
evaluation in the       to weigh filters collected in perfor-
last quarter of PSD     mance evaluations, a PSD monitoring
monitoring.”            organization[] . . . [may waive the]
                        threshold for validity of performance
                        evaluations conducted in the last
                        quarter of monitoring . . . .” 81 Fed.
                        Reg. at 17,275/1.
                              16
     To be sure, all these explanations may, as a substantive
matter, suffer from some infirmity that renders them
inadequate. But Sierra Club has not raised that argument, much
less developed it. Rather, it steadfastly maintains that EPA
“cannot identify any consideration” of Earthjustice’s concerns,
Sierra Club Reply Br. 30, a claim that is transparently
mistaken.


                            * * *

    For the foregoing reasons, the petition for review is
dismissed in part and denied in part.

                                                   So ordered.
