Document ID: EPA-R09-OAR-2020-0425-0130
Agency: epa
Document Type: Rule
Title: Air Quality State Implementation Plans; Approvals and Promulgations: California; Sacramento Metro Area; 2008 8-Hour Ozone Nonattainment Area Requirements
Posted Date: 2021-10-22T04:00Z

[Federal Register Volume 86, Number 202 (Friday, October 22, 2021)]
[Rules and Regulations]
[Pages 58581-58592]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2021-22661]

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 52

[EPA-R09-OAR-2020-0425; FRL-8723-02-R9]

Approval of Air Quality Implementation Plans; California; 
Sacramento Metro Area; 2008 8-Hour Ozone Nonattainment Area 
Requirements

AGENCY: Environmental Protection Agency (EPA).

ACTION: Final rule.

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SUMMARY: The Environmental Protection Agency (EPA) is taking final 
action to approve portions of two state implementation plan (SIP) 
revisions submitted by the State of California to meet Clean Air Act 
(CAA or ``Act'') requirements for the 2008 8-hour ozone national 
ambient air quality standards (NAAQS or ``standards'') in the 
Sacramento Metro ozone nonattainment area (``Sacramento Metro Area''). 
These SIP revisions address the CAA nonattainment area requirements for 
the 2008 ozone NAAQS, such as the requirements for an emissions 
inventory, an attainment demonstration,

[[Page 58582]]

reasonable further progress, reasonably available control measures, and 
contingency measures, and it establishes motor vehicle emissions 
budgets. The EPA is taking final action to approve these revisions as 
meeting all the applicable ozone nonattainment area requirements, 
except for the State's contingency measures revision. The EPA is 
deferring action on this revision related to contingency measures.

DATES: This rule will be effective on November 22, 2021.

ADDRESSES: The EPA has established a docket for this action under 
Docket ID No. EPA-R09-OAR-2020-0425. All documents in the docket are 
listed on the https://www.regulations.gov website. Although listed in 
the index, some information is not publicly available, e.g., 
Confidential Business Information (CBI) or other information whose 
disclosure is restricted by statute. Certain other material, such as 
copyrighted material, is not placed on the internet and will be 
publicly available only in hard copy form. Publicly available docket 
materials are available through https://www.regulations.gov, or please 
contact the person identified in the FOR FURTHER INFORMATION CONTACT 
section for additional availability information. If you need assistance 
in a language other than English or if you are a person with 
disabilities who needs a reasonable accommodation at no cost to you, 
please contact the person identified in the FOR FURTHER INFORMATION 
CONTACT section.

FOR FURTHER INFORMATION CONTACT: Jerry Wamsley, Air Planning Office 
(AIR-2), EPA Region IX, 75 Hawthorne Street, San Francisco, CA 94105, 
(415) 947-4111 or [email protected].

SUPPLEMENTARY INFORMATION:

Table of Contents

I. Summary of the Proposed Action
II. Public Comments and EPA Responses
    A. Review of Ozone Chemistry and NOX Substitution 
Effects
    B. Response to Comments
III. Final Action
IV. Statutory and Executive Order Reviews

I. Summary of the Proposed Action

    On October 29, 2020, the EPA proposed to approve, under CAA section 
110(k)(3), and to conditionally approve, under CAA section 110(k)(4), 
portions of submittals from the State of California as revisions to the 
California SIP for the Sacramento Metro ozone nonattainment area.\1\ 
The principal submittals are as follows: ``Sacramento Regional 2008 
NAAQS 8-Hour Ozone Attainment Plan and Reasonable Further Progress 
Plan,'' (``2017 Sacramento Regional Ozone Plan''); and the Sacramento 
Metro portion of the California Air Resource Board's (CARB) ``2018 
Updates to the California State Implementation Plan'' (``2018 SIP 
Update'').\2\ In this notice, we refer to these submittals collectively 
as the ``Sacramento Metro Area Ozone SIP'' or the ``Plan,'' and we 
refer to our October 29, 2020 proposed action as the ``proposed rule.''
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    \1\ 85 FR 68509 (October 29, 2020).
    \2\ The State submitted the 2017 Sacramento Regional Ozone Plan 
and the 2018 SIP Update on December 18, 2017, and December 5, 2018, 
respectively. Our proposed rule provides our detailed review of CAA 
procedural requirements related to these submissions.
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    The Sacramento Metro Area consists of Sacramento and Yolo counties 
and portions of El Dorado, Placer, Solano, and Sutter counties.\3\ 
Several local air agencies have their jurisdictions within this area. 
Sacramento County is under the jurisdiction of the Sacramento 
Metropolitan Air Quality Management District (SMAQMD). Yolo County and 
the eastern portion of Solano County are under the jurisdiction of the 
Yolo-Solano AQMD (YSAQMD). The southern portion of Sutter County is 
under the jurisdiction of the Feather River AQMD (FRAQMD). The western 
portion of Placer County is under the jurisdiction of the Placer County 
Air Pollution Control District (PCAPCD). Last, the western portion of 
El Dorado County is under the jurisdiction of the El Dorado County AQMD 
(EDCAQMD). In this action, we refer to these five districts 
collectively as the ``Districts.'' Under California law, each air 
district is responsible for adopting and implementing stationary source 
rules, while CARB adopts and implements consumer products and mobile 
source rules. The Districts' and State's rules are submitted to the EPA 
by CARB.
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    \3\ For a precise description of the geographic boundaries of 
the Sacramento Metro Area for the 2008 ozone standards, refer to 40 
CFR 81.305. Specifically included portions are the eastern portion 
of Solano County, the western portions of Placer and El Dorado 
counties outside of the Lake Tahoe Basin, and the southern portion 
of Sutter County.
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    In our proposed rule, we provided background information on the 
ozone standards,\4\ area designations, related SIP revision 
requirements under the CAA, and the EPA's implementing regulations for 
the 2008 ozone standards, referred to as the 2008 Ozone SIP 
Requirements Rule (``2008 Ozone SRR''). To summarize, the Sacramento 
Metro Area is classified as Severe nonattainment for the 2008 ozone 
standards; consequently, the Sacramento Metro Area Ozone SIP was 
developed to address the CAA requirements for this Severe nonattainment 
area in meeting the 2008 ozone NAAQS.
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    \4\ Ground-level ozone pollution is formed from the reaction of 
volatile organic compounds (VOC) and oxides of nitrogen 
(NOX) in the presence of sunlight. The 1-hour ozone NAAQS 
is 0.12 parts per million (ppm) (one-hour average), the 1997 ozone 
NAAQS is 0.08 ppm (eight-hour average), and the 2008 ozone NAAQS is 
0.075 ppm (eight-hour average). CARB refers to reactive organic 
gases (ROG) in some of its ozone-related submittals. The CAA and the 
EPA's regulations refer to VOC, rather than ROG, but both terms 
cover essentially the same set of gases. In this final rule, we use 
the term VOC to refer to this set of gases.
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    In our proposed rule, we also discussed a decision issued by the 
D.C. Circuit Court of Appeals in South Coast Air Quality Management 
Dist. v. EPA (``South Coast II'') \5\ that vacated certain portions of 
the EPA's 2008 Ozone SRR. The only aspect of the South Coast II 
decision that affects this action is the vacatur of the provision in 
the 2008 Ozone SRR that allowed states to use an alternative baseline 
year for demonstrating reasonable further progress (RFP). To address 
this decision, CARB, in the 2018 SIP Update, submitted an updated RFP 
demonstration that relied on a 2011 baseline year, as required, along 
with updated motor vehicle emissions budgets (MVEBs or ``budgets'') 
associated with the new RFP milestone years.\6\
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    \5\ South Coast Air Quality Management Dist. v. EPA, 882 F.3d 
1138 (D.C. Cir. 2018). The term ``South Coast II'' is used in 
reference to the 2018 court decision to distinguish it from a 
decision published in 2006 also referred to as ``South Coast.'' The 
earlier decision involved a challenge to the EPA's Phase 1 
implementation rule for the 1997 ozone NAAQS. South Coast Air 
Quality Management Dist. v. EPA, 472 F.3d 882 (D.C. Cir. 2006).
    \6\ In a letter dated December 18, 2019, from Richard W. Corey, 
Executive Officer, CARB, to Michael Stoker, Regional Administrator, 
EPA Region 9, CARB requested withdrawal of the RFP demonstration 
included in the 2017 Sacramento Regional Ozone Plan submitted 
previously. The RFP demonstration in the 2018 SIP Update replaced 
the demonstration in the 2017 Plan.
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    Within our proposed rule, we reviewed the various SIP elements 
contained in the Sacramento Metro Area Ozone SIP, evaluated them for 
compliance with CAA statutory and regulatory requirements, and 
concluded that they met all applicable requirements, with the exception 
of the contingency measures element, for which the EPA proposed 
conditional approval. Below, we provide a summary review of our 
proposed rule, by SIP element.
     We found that CARB and the Districts met all applicable 
procedural requirements for public notice and hearing prior to the 
adoption and submittal of the components of the Sacramento Metro Area 
Ozone SIP, i.e.,

[[Page 58583]]

the 2017 Sacramento Regional Ozone Plan and the Sacramento Metro 
portion of CARB's 2018 SIP Update.\7\
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    \7\ 85 FR 68509, 68511-68512.
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     We proposed to approve the base year emissions inventory 
element in the 2017 Sacramento Regional Ozone Plan as meeting the 
requirements of CAA sections 172(c)(3) and 182(a)(1) and 40 CFR 51.1115 
for the 2008 ozone NAAQS. Based on our review, we proposed to find that 
the future year baseline projections in the 2017 Sacramento Regional 
Ozone Plan are properly supported by SIP-approved stationary and mobile 
source measures.\8\
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    \8\ Id. at 68513-68515.
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     We proposed to approve the reasonably available control 
measures (RACM) demonstration element in the 2017 Sacramento Regional 
Ozone Plan as meeting the requirements of CAA section 172(c)(1) and 40 
CFR 51.1112(c) for the 2008 ozone NAAQS. Based on our review of the 
State and Districts' RACM analyses and the Districts' and CARB's 
adopted rules, we proposed to find that there are, at this time, no 
additional RACM that would further advance attainment of the 2008 ozone 
NAAQS in the Sacramento Metro Area.\9\
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    \9\ Id. at 68516-68518.
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     We proposed to approve the attainment demonstration 
element for the 2008 ozone NAAQS in the 2017 Sacramento Regional Ozone 
Plan as meeting the requirements of CAA section 182(c)(2)(A) and 40 CFR 
51.1108. In our review provided in the proposed rule, we observed that 
the Plan followed the modeling procedures recommended in the EPA's 
Modeling Guidance and showed excellent performance in simulating 
observed ozone concentrations in the 2012 base year. Given the 
extensive discussion of modeling procedures, tests, and performance 
analyses called for in the modeling protocol, the good model 
performance, and the model response to emissions changes consistent 
with observations, we proposed to find that the modeling is adequate 
for purposes of supporting the attainment demonstration.\10\
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    \10\ Id. at 68518-68523.
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     We proposed to approve the rate of progress (ROP) 
demonstration element in the 2017 Sacramento Regional Ozone Plan as 
meeting the requirements of CAA 182(b)(1) and 40 CFR 51.1110(a)(2) for 
the 2008 ozone NAAQS.\11\ As noted in the proposed rule, in 2015, the 
EPA approved a 15 percent ROP plan for the Sacramento Metro Area for 
the 1-hour ozone NAAQS and 1997 8-hour ozone NAAQS.\12\
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    \11\ Id. at 68523-68525
    \12\ 80 FR 4795 (January 29, 2015).
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     We proposed to approve the RFP demonstration element in 
Section V--SIP Elements for the Sacramento Metropolitan Area of the 
2018 SIP Update (as clarified) as meeting the requirements of CAA 
sections 172(c)(2), 182(b)(1), and 182(c)(2)(B), and 40 CFR 
51.1110(a)(2)(ii) for the 2008 ozone NAAQS. We proposed to find that 
CARB and the Districts used the most recent planning and activity 
assumptions, emissions models, and methodologies in developing the RFP 
baseline and milestone year emissions inventories. Also, we proposed to 
find that the Districts and CARB used an appropriate calculation method 
to demonstrate RFP. Lastly, we proposed to find that the Districts' use 
of oxides of nitrogen (NOX) NAAQS substitution is warranted 
and appropriately implemented based on the NOX-limited 
conditions in the Sacramento Metro Area, and the area's greater 
responsiveness to NOX emissions reductions relative to VOC 
emissions reductions.\13\
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    \13\ 85 FR 68509, 68523-68525.
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     We proposed to approve the vehicle miles traveled (VMT) 
emissions offset demonstration element in the 2017 Sacramento Regional 
Ozone Plan as meeting the requirements of CAA section 182(d)(1)(A) and 
40 CFR 51.1102 for the 2008 ozone NAAQS. Based on our review of revised 
Sacramento Metro Area VMT emissions offset demonstration in the 2017 
Sacramento Regional Ozone Plan, we proposed to find that CARB's 
analysis is consistent with the August 2012 Guidance and with the 
emissions and vehicle activity estimates found elsewhere in the 2017 
Sacramento Regional Ozone Plan. Also, we proposed to find that CARB and 
the Sacramento Area Council of Governments (SACOG) have adopted 
sufficient transportation control strategies (TCSs) and transportation 
control measures (TCMs) to offset the growth in emissions from growth 
in VMT and vehicle trips in the Sacramento Metro Area for the purposes 
of the 2008 ozone NAAQS.\14\
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    \14\ Id. at 68525-68527.
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     We proposed to approve the MVEBs in Section V--SIP 
Elements for the Sacramento Metropolitan Area of the 2018 SIP Update 
for the RFP milestone year of 2023, and the attainment year of 2024 and 
find that these budgets are consistent with the RFP and attainment 
demonstrations for the 2008 ozone NAAQS proposed for approval and the 
budgets meet the other criteria in 40 CFR 93.118(e).\15\ We reviewed 
the budgets in the Sacramento Metro Area Ozone SIP and proposed to find 
that they are consistent with the attainment and RFP demonstrations for 
which we proposed approval, are based on control measures that have 
already been adopted and implemented, and meet all other applicable 
statutory and regulatory requirements including the adequacy criteria 
in 40 CFR 93.1118(e)(4) and (5).\16\
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    \15\ Table 9 in our proposed rule provides the VOC and 
NOX emissions budgets that we proposed for approval.
    \16\ 85 FR 68509, 68529-68531.
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    We also proposed to make the following findings related to other 
CAA requirements:
     The emissions statement element of the 2017 Sacramento 
Regional Ozone Plan satisfies the requirements under CAA section 
182(a)(3)(B) based on our prior approvals of the Districts' emission 
statement rules; \17\
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    \17\ Id. at 68515-68516.
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     The enhanced vehicle inspection and maintenance program in 
the Sacramento Metro Area meets the requirements of CAA section 
182(c)(3) and 40 CFR 51.1102 for the 2008 ozone NAAQS; \18\
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    \18\ Id. at 68531.
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     The California SIP revision to opt out of the Federal 
Clean Fuels Fleet Program meets the requirements of CAA sections 
182(c)(4)(A) and 246 and 40 CFR 51.1102 for the 2008 ozone NAAQS with 
respect to the Sacramento Metro Area; \19\ and,
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    \19\ Id.
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     The enhanced air quality monitoring in the Sacramento 
Metro Area meets the requirements of CAA section 182(c)(1) and 40 CFR 
51.1102 for the 2008 ozone NAAQS.\20\
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    \20\ Id. at 68531-68532.
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    Finally, under CAA section 110(k)(4), we proposed to approve 
conditionally the contingency measures element of the Sacramento Metro 
Area Ozone SIP as meeting the requirements of CAA sections 172(c)(9) 
and 182(c)(9) for RFP and attainment contingency measures. Our proposed 
approval was based on commitments by the Districts and CARB to 
supplement the element through submission, as a SIP revision within one 
year of our final conditional approval action, of new or revised rules 
with more stringent requirements sufficient to produce near to one 
year's RFP if an RFP milestone is not met, as well as continuing 
emission reductions from State mobile source control measures.\21\
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    \21\ Id. at 68527-68529.
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    Please see our proposed rule and the docket for more information 
concerning the background of this final action and

[[Page 58584]]

for a detailed discussion of the rationale for approval or conditional 
approval of the above-listed elements of the Sacramento Metro Area 
Ozone SIP.

II. Public Comments and EPA Responses

    The public comment period on the proposed rule opened on October 
29, 2020, the date of its publication in the Federal Register, and 
closed on November 30, 2020. During this period, the EPA received one 
comment letter submitted by Air Law for All on behalf of the Center for 
Biological Diversity and the Center for Environmental Health 
(collectively referred to as ``CBD'' herein). Before we provide a 
detailed summary of and response to each of these comments in Section 
II.B, we provide a brief review of ozone chemistry and terminology as 
it relates to our responses to comments concerning the Plan's use of 
NOX substitution and the NOX-limited conditions 
in the Sacramento Metro Area.

A. Review of Ozone Chemistry and NOX Substitution Effects

    As explained in the proposed rule, ground-level ozone pollution is 
formed from the reaction of volatile organic compounds (VOCs) and 
NOX in the presence of sunlight. When VOC is abundant 
compared to NOX, i.e., when there is a high ratio of VOCs 
relative to NOX (``VOC:NOX ratio''), 
NOX is a limiting ingredient for ozone formation, and 
reducing NOX emissions causes ozone to decrease. An area 
with these conditions may be described as ``NOX-limited,'' 
which is the terminology used in this notice. Elsewhere, 
``NOX-limited'' is sometimes used in a stronger, relative 
sense to mean that NOX emissions reductions are more 
effective than VOC reductions at reducing ozone, and an area may be 
described as ``NOX-limited'' or ``VOC-limited'' as a 
shorthand for whether NOX or VOC emissions reductions are 
more effective at reducing the area's ozone design value.\22\ In 
contrast, in a ``NOX-saturated'' area where NOX 
is abundant compared to VOC, i.e., when there is a low 
VOC:NOX ratio, ozone concentrations typically increase with 
NOX emission reductions, that is, there is a 
``NOX disbenefit.'' \23\ Between the NOX-limited 
and NOX-saturated ozone chemistry regimes, there is an 
intermediate ``transitional'' regime where ozone responds weakly to 
NOX emissions reductions. Which one of these three chemical 
regimes exists for an area can depend on the season, time of day, and 
the area's location relative to a source of NOX emissions. 
As one moves farther downwind from an urban center, ozone formation 
tends to become more NOX-limited, as the VOC:NOX 
ratio increases. While there are continued VOC emissions in rural 
areas, there are fewer new NOX emissions from combustion 
sources, and some NOX deposits out of the atmosphere (in the 
form of HNO3); as a result, peak ozone hours and downwind 
locations are more NOX-limited than non-peak hours and 
upwind or central locations.\24\ When an area reduces NOX 
emissions more than VOC emissions, the VOC:NOX ratio 
increases and the area can transition from NOX-saturated to 
NOX-limited conditions. In general, areas in the United 
States have become more NOX-limited over time, though 
NOX-saturated areas and seasons remain.\25\
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    \22\ For example, the Plan generally uses the term 
``NOX-limited'' to mean that NOX emission 
reductions in the Sacramento Metro Area are more effective than VOC 
at decreasing ozone; e.g., 2017 Sacramento Regional Ozone Plan, 
Appendix B-4, page B-146, Figure 13 (labeling as ``NOX-
limited'' the region of a typical ozone isopleth plot where 
NOX reductions are more effective than VOC reductions).
    \23\ A NOX disbenefit can occur under NOX-
saturated conditions because enough NOX is present to 
interfere with ozone formation via VOC. VOC radicals require the 
hydroxyl radical (OH) to form, but OH is made unavailable when 
NOX combines with it to form nitric acid 
(HNO3), which then deposits out of the atmosphere. A 
reduction in NOX emissions reduces this OH sink reaction, 
increasing the OH available to form VOC radicals and ozone.
    \24\ Barbara J. Finlayson-Pitts and James N. Pitts Jr., 
``Tropospheric Air Pollution: Ozone, Airborne Toxics, Polycyclic 
Aromatic Hydrocarbons, and Particles,'' Science, Vol. 276, May 16, 
1997; EPA, U. S., Health Risk and Exposure Assessment for Ozone 
Final Report. Office of Air Quality Planning and Standards: RTP, NC, 
2014; EPA-452/R-14-004a, https://www.epa.gov/naaqs/ozone-o3-standards-risk-and-exposure-assessments-review-completed-2015.
    \25\ Wolff, G.T., Kahlbaum, D.F., & Heuss, J.M., 2013. ``The 
vanishing ozone weekday/weekend effect,'' Journal of the Air & Waste 
Management Association), 63(3), 292-299, https://doi.org/10.1080/10962247.2012.749312 Jin et al., 2017, ``Evaluating a space-based 
indicator of surface ozone NOX VOC sensitivity over 
midlatitude source regions and application to decadal trends,'' 
Journal of Geophysical Research: Atmospheres, 122,10,439 10,461. 
https://doi.org/10.1002/2017JD026720; Sicard et al, 2020, ``Ozone 
weekend effect in cities: Deep insights for urban air pollution 
control,'' Environmental Research, 191, 110193. https://doi.org/10.1016/j.envres.2020.110193.
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    NOX is emitted primarily in the form of nitric oxide 
(NO), which becomes nitrogen dioxide (NO2) as it converts or 
``titrates'' ozone (O3) to regular oxygen (O2). 
Therefore, the initial effect of a NOX emissions increase 
can be to decrease ozone immediately downwind of a NOX 
source, such as downtown metropolitan areas or a large fossil fuel 
burning power plant.\26\ Farther downwind from the NOX 
source, however, the NOX can increase ozone, via reactions 
with VOC. Conversely, the initial effect of a NOX emissions 
reduction, which is mainly a NO reduction, can be to increase ozone 
immediately downwind from the NOX source because there is 
less remaining NO to titrate ozone to oxygen. Because of this 
phenomenon, it may be impossible for an area to be ``NOX-
limited'' at all locations, at least with respect to a given change in 
NOX emissions occurring just upwind of a given location or 
monitor. Titration can occur under any ozone chemistry regime whether 
NOX-saturation, NOX-transitional, or 
NOX-limited.
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    \26\ EPA, Health Risk and Exposure Assessment for Ozone Final 
Report, 2-5.
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    To summarize, under certain conditions, NOX emissions 
can reduce existing ozone concentrations in nearby downwind areas 
through titration and can interfere with the formation of ozone in 
NOX-saturated areas. Reducing NOX emissions can 
lessen these effects and lead to ozone increases. Reducing 
NOX by a larger amount can, however, change the ozone 
chemistry from NOX-saturated to NOX-limited, 
meaning that NOX emission reductions can again result in 
reduced ozone. The overall effect of NOX emissions on an 
area's ozone chemistry depends on the location's existing mix of ozone 
and VOCs, as well as the location relative to the source of 
NOX emissions.

B. Response to Comments

    Comment #1: CBD notes that CAA section 182(c)(2)(C) allows a state 
to substitute NOX emissions reductions for the VOC 
reductions otherwise required by CAA section 182(c)(2)(B) 
(``NOX substitution'') if it demonstrates that the combined 
VOC and NOX reductions ``would result in a reduction in 
ozone concentrations at least equivalent'' to the reduction in ozone 
concentrations achieved through VOC emissions reductions alone. CBD 
argues that CAA section 182(c)(2)(C)'s use of the plural ``ozone 
concentrations'' means that an equivalency demonstration at a single 
monitoring site would be insufficient, and therefore asserts that 
Congress intended the equivalence requirement to apply throughout the 
nonattainment area. CBD interprets statements in the proposal that the 
Sacramento Metro Area is NOX-limited to indicate that the 
EPA agrees that equivalence must be demonstrated throughout the 
nonattainment area and says that the EPA must confirm this 
understanding in a final rule.

[[Page 58585]]

    Response to Comment #1: The EPA disagrees that CAA section 
182(c)(2)(C)'s use of the term ``ozone concentrations'' warrants the 
commenter's narrow interpretation that equivalence must be specifically 
demonstrated throughout a nonattainment area. As an initial matter, we 
note that the Act commonly uses the term ``concentrations'' to refer 
generally to ambient pollution levels at one or more (but not 
necessarily multiple) monitors or locations.\27\ Moreover, CAA section 
182(c)(2)(C) grants the EPA discretion to define the conditions under 
which NOX reductions may be substituted for or combined with 
VOC reductions ``in order to maximize the reduction in ozone air 
pollution'' and does not further specify the conditions that represent 
an ``equivalent'' reduction in ozone; for instance, it does not require 
a specific concentration test at every monitor or at specific locations 
within an area. No such requirement appears in the Act's other 
provisions governing the RFP demonstration, which define specific 
percentage reductions aimed at ensuring timely attainment of the 
NAAQS,\28\ or in the EPA's 1993 NOX Substitution Guidance, 
which describes a recommended procedure for states to utilize 
NOX substitution.\29\ We interpret CAA 182(c)(2)(C) and 
these supporting authorities as properly reflecting Congress' intent to 
allow NOX reductions to be considered within an RFP 
demonstration so long as these reductions are at least as effective in 
reducing ozone consistent with the area's demonstration of timely 
attainment.\30\
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    \27\ E.g., CAA section 107(e)(2); CAA section 110(a)(5)(D).
    \28\ E.g., CAA 182(b)(1) and (c)(2)(B); see also CAA 171(1) 
(defining RFP as ``such annual incremental reductions in emissions 
of the relevant air pollutant as are required by this part or may 
reasonably be required by the Administrator for the purpose of 
ensuring attainment of the applicable national ambient air quality 
standard by the applicable date'').
    \29\ NOX Substitution Guidance, Office of Air Quality 
Planning and Standards, U.S. Environmental Protection Agency, 
December 1993, available at https://archive.epa.gov/ttn/ozone/web/html/index-13.html.
    \30\ See id. at 8, (quoting H. Rept. No. 490, 101st Cong., 2d 
Sess. 239 (1990)), (``NOX reductions may not be 
substituted for VOC reductions in a manner that delays attainment of 
the ozone standard or that results in lesser annual reductions in 
ozone concentration than provided for in the attainment 
demonstration.'').
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    Also, we disagree with the commenter's assertion that statements 
from the proposed rule describing the Sacramento Metro Area as 
NOX-limited convey the EPA's position that NOX 
substitution requires a specific demonstration of equivalence 
throughout all portions or monitors within a nonattainment area. As 
described in our proposed rule and discussed further in our responses 
below, NOX-limited conditions likely persist throughout the 
Sacramento Metro Area, suggesting that NOX reductions will 
generally be effective in reducing ozone concentrations; with these 
statements, we intended no other suggestion regarding the demonstration 
necessary to support NOX substitution. The EPA evaluates the 
appropriateness of NOX substitution on a case-by-case 
basis,\31\ considering the balance of available evidence to support the 
efficacy of NOX reductions in reducing ambient ozone 
concentrations as necessary for timely attainment, and consistent with 
the requirements of CAA section 182(c)(2)(C).
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    \31\ NOX Substitution Guidance at 3 (``The EPA will 
approve substitution proposals on a case-by-case basis. Generally 
speaking, any reasonable substitution proposal will be approved.''); 
also, id. at 1 (explaining that the Guidance's purpose is ``to 
provide a procedure that can be applied to meet the post-1996 
Section 182(c)(2)(B) RFP requirement as well as the Section 
182(c)(2)(C) equivalency demonstration requirements'' (emphasis in 
original).
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    In some areas, NOX emissions reductions may be needed 
for attainment, even though it may not be possible to decrease ozone 
concentrations simultaneously at all locations in the short term. For 
example, in some NOX-limited areas, reducing NOX 
emissions may represent the most effective or only approach to timely 
attainment, but may nonetheless generate temporary ozone increases in 
some locations due to NOX titration or local NOX-
saturated conditions. In these areas, we believe it is reasonable to 
implement NOX reductions in lieu of some portion of the VOC 
emissions reductions otherwise required for RFP as part of an area's 
strategy for timely NAAQS attainment and notwithstanding limited short-
term increases, as an alternative to pursuing relatively ineffective 
VOC controls. We discuss conditions for the Sacramento Metro Area in 
detail below, including the relative importance and efficacy of 
NOX reductions for attainment.
    Comment #2: CBD comments that the Plan's evidence is equivocal and 
insufficient to show that NOX substitution will result in 
equivalent reductions in ozone concentrations throughout the 
nonattainment area. According to the commenter, the Plan's analysis of 
the ``weekend effect'' in the years 2000-2014 shows a shift to more 
NOX-saturated conditions in the Western and Central 
subregions of the Sacramento Metro Area and more transitional 
conditions in the Eastern region, and this is not inconsistent with the 
independent study of conditions in the years 2001-2007 cited by the 
EPA. CBD says that this evidence is insufficient for the EPA to 
rationally conclude that the entire nonattainment area is currently 
NOX-limited, and that, at most, it can only be concluded 
that the Eastern region is still NOX-limited. Furthermore, 
CBD says that the EPA must consider changes in NOX emissions 
occuring by 2024, such as the replacement of natural gas power plants 
by less NOX-emitting sources, to determine whether the 
entire Sacramento Metro Area will be NOX-limited through 
2024.
    The commenter characterizes the Plan's evidence as qualitative, 
rather than quantitative. The commenter states that a qualitative 
analysis does not address the possibility that NOX 
reductions could change the characteristics of the area and argues that 
the definition of the word ``equivalent'' as used in CAA section 
182(c)(2)(C) requires a quantitative analysis, such as photochemical 
grid modeling. The commenter notes that the Plan uses photochemical 
grid modeling to analyze ozone sensitivity to NOX reductions 
in the context of the attainment demonstration. CBD then states that 
this modeling analysis is insufficient to support the Plan's conclusion 
that the entire area is NOX-limited or to show equivalence 
throughout the nonattainment area because the Plan includes one 
isopleth diagram only for the Folsom monitoring site in the Eastern 
subregion.\32\
---------------------------------------------------------------------------

    \32\ An ``isopleth'' is a line connecting points having the same 
value of a quantity, such as ozone concentration. Ozone isopleth 
diagrams typically have a series of such lines to show the ozone 
concentration for any combination of NOX and VOC 
emissions, just as contour lines on a map show the elevation for any 
combination of latitude and longitude.
---------------------------------------------------------------------------

    According to the commenter, approving NOX substitution 
based on a demonstration of equivalence at only one monitor or 
subregion is arbitrary for two reasons, even if it does not cause other 
monitors to exceed the 2008 ozone NAAQS. First, it may cause, or 
interfere with resolving, violations of the more protective 2015 ozone 
NAAQS in NOX-saturated areas (which the commenter says would 
violate CAA section 110(l)). Second, increased ozone levels, even below 
the NAAQS, may still result in injury to public health and welfare.
    Response to Comment #2: The EPA disagrees that the Plan's evidence 
is insufficient to support the use of NOX substitution under 
CAA section 182(c)(2)(C). As discussed in our response to Comment 1, 
use of NOX

[[Page 58586]]

substitution within an RFP demonstration does not require establishing 
equivalent reductions in ozone concentrations throughout the 
nonattainment area. As discussed in detail below, the Plan shows that, 
overall, the area has transitioned from NOX-saturated to 
NOX-limited as NOX emissions have declined, and 
that NOX reductions are more effective than VOC reductions 
on a percentage basis. Consistent with these conditions, the Sacramento 
Metro Area has relied on, and continues to rely on, NOX 
reductions to demonstrate attainment. While decreases in ozone 
concentrations may have been delayed initially at some locations 
because of the location-specific and complex behavior of NOX 
in ozone formation, Sacramento Metro Area ozone design values have 
shown a general downward trend at all monitors from 1990 to the 
present, demonstrating that these locations have not experienced the 
increased ozone design values of concern to the commenter, and that the 
Plan demonstrates timely attainment of the NAAQS at all locations. For 
these reasons and as addressed below, we find that the Plan provides 
adequate evidence and justification for its use of NOX 
substitution.
    As we discussed in the proposed rule and our accompanying technical 
support document, the State concludes that NOX reductions 
are more effective than VOC reductions throughout the Sacramento Metro 
Area.\33\ The State supports this conclusion with modeling and 
monitoring of weekday-weekend differences in ozone formation and 
citations to published research papers that study these differences and 
the response to NOX reductions in detail, as described 
below. The State estimates weekday-weekend differences in ozone 
concentrations using the Community Multiscale Air Quality (CMAQ) 
photochemical model as part of the air quality model's performance 
evaluation for the 2012 base year, in conjunction with the attainment 
demonstration. As described in the Plan, in the early 2000's the 
western region of the Sacramento Metro Area exhibited a ``weekend 
effect,'' in which weekend ozone concentrations were higher despite 
having lower NOX emissions, suggesting a NOX 
disbenefit at that time.\34\ The modeling results in the Plan show that 
the average daily maximum ozone concentrations at all monitoring sites 
are higher on weekdays, indicating that maximum ozone concentrations 
are lower when NOX emissions are lower, and that peak ozone 
formation is NOX-limited, at all monitoring sites. This is 
illustrated in Figure 14 from Appendix B-4 of the 2017 Sacramento 
Regional Ozone Plan, which shows average modeled 2012 weekday-weekend 
ozone concentrations above a 1:1 line, i.e., higher weekday 
concentrations, for all monitoring sites in each subregion in the 
nonattainment area (Western, Central, and Eastern).
---------------------------------------------------------------------------

    \33\ 85 FR 68509, 68520 (October 29, 2020); ``Modeling TSD--2017 
Sacramento Regional Ozone Plan,'' September 14, 2020, Air and 
Radiation Division, EPA Region IX, 25-26.
    \34\ 2017 Sacramento Regional Ozone Plan, Appendix B-4, B-148; 
CARB Staff Report B-33.
---------------------------------------------------------------------------

    In addition, the modeled differences in ozone concentrations are 
generally consistent with the monitored ambient concentrations.\35\ 
Monitored ozone concentrations included in the Plan for each year from 
2000 to 2014 generally progressed from a NOX disbenefit, 
i.e., higher weekend concentrations, to a NOX-limited or 
transitional regime, i.e., weekend concentrations lower than or about 
the same as weekday concentrations.\36\ The Eastern subregion has shown 
higher concentration on weekdays than on weekends for the entire 
period, i.e., no ``weekend effect''; this is evidence that ozone 
formation is NOX-limited there. By 2014, the Western and 
Central subregions of the Sacramento Metro Area show nearly identical 
weekday and weekend concentrations, suggesting these areas had shifted 
to a transitional regime by that time.\37\ For the Western subregion, 
the Plan notes that the shift toward transitional conditions occurred 
at ozone levels under 50 parts per billion (ppb), well below the 2008 
ozone NAAQS of 75 ppb, meaning that these changes are not leading to 
NAAQS exceedances. Indeed, monitoring sites in the Western subregion 
have met the 75 ppb NAAQS from 2011 to the present day. Within the 
Central subregion, ambient ozone data recorded for 2011-2014 show ozone 
levels under 70 ppb.\38\
---------------------------------------------------------------------------

    \35\ 2017 Sacramento Regional Ozone Plan, Appendix B-4, B-149, 
Figure 14. For sites appearing just above the 1:1 line, modeled 
weekday ozone is higher by only a small amount.
    \36\ Id.
    \37\ Id. The commenter has interpreted the presence of points 
below the 1:1 line as evidence of NOX-saturated ozone 
formation, but that interpretation would be supported only by points 
much farther below the line.
    \38\ 2017 Sacramento Regional Ozone Plan, Appendix B-4, B-148.
---------------------------------------------------------------------------

    The Plan suggests that the shift to a transitional regime could be 
explained by natural year-to-year variability in biogenic VOC emissions 
and in local meteorology.\39\ This is consistent with the relatively 
low level of biogenic VOC emissions during 2011-2014,\40\ which would 
decrease the VOC:NOX ratio and shift the atmosphere toward a 
transitional ozone formation regime (though not necessarily all the way 
to NOX saturation). VOC emissions have also decreased 
steadily from 2000 to the present day,\41\ and biogenic VOC emissions 
in the Sacramento Metro Area, while variable, are about ten times 
higher than those from anthropogenic sources.\42\ Accordingly, the 
shift to smaller differences in weekday-weekend ozone concentrations 
seen in 2014 could be the result of natural variability in biogenic VOC 
emissions that causes some locations to be transitional or 
NOX-saturated on some days.
---------------------------------------------------------------------------

    \39\ Id.
    \40\ 2017 Sacramento Regional Ozone Plan Appendix B-2, B-31 and 
B-34.
    \41\ CARB Staff Report, B-16.
    \42\ CARB Staff Report, B-7.
---------------------------------------------------------------------------

    The Plan also suggests variability in meteorology as a factor in 
shifting ozone chemistry between NOX-limited and 
NOX-disbenefit regimes.\43\ The Plan cites a research paper 
that examined the effect of temperature and found that ``the average 
O3 is higher on weekends than on weekdays only for the 
lowest temperature days.'' \44\ Natural annual variability also applies 
to the degree of pollutant carryover from one day to the next day; day-
to-day carryover can mix weekday and weekend pollutants, making 
weekdays and weekends appear to be more similar. In addition, the 
NOX emissions reductions that have occurred from 2000 to the 
present day have decreased the difference between weekday and weekend 
NOX emissions, which would also decrease the differences in 
weekday and weekend ozone concentrations.
---------------------------------------------------------------------------

    \43\ 2017 Sacramento Regional Ozone Plan Appendix B-4, B-148.
    \44\ LaFranchi, B.W., Goldstein, A.H., and Cohen, R.C., 2011, 
``Observations of the temperature dependent response of ozone to 
NOX reductions in the Sacramento, CA urban plume,'' 
Atmospheric Chemistry and Physics, 11, 6945-6960, https://doi.org/10.5194/acp-11-6945-2011, 6954 (``LaFranchi et al. 2011'').
---------------------------------------------------------------------------

    Although these plots of weekday-weekend ozone differences provide a 
useful indicator, they are not a definitive description of the ozone 
chemistry involved. The plots show only the resulting ozone 
concentrations, not any ozone precursors or meteorology whose 
interaction results in those concentrations. Furthermore, the weekday-
weekend plots show just a single point for each monitor-year 
combination, the average over a year's summer days of daily maximum 8-
hour ozone concentrations, rather than a point for each day. Ozone 
concentrations vary between the days of

[[Page 58587]]

a single year, not just between years. A data point near the 1:1 line 
may indicate that weekday-weekend differences are small due to 
transitional chemistry on every individual day. Alternatively, it could 
indicate that positive differences balance out negative ones, due to a 
mix of high-ozone NOX-limited days and low-ozone 
NOX-saturated or transitional days. This would mean that 
NOX-saturated days with lower ozone concentrations and less 
regulatory and health significance would be masking NOX-
limited days with higher ozone concentrations and greater significance. 
In the context of the analyses and evidence presented in the Plan, the 
smaller weekday-weekend differences in ozone concentrations in 2014 do 
not indicate a change in ozone chemistry that would suggest a control 
strategy failure or an unknown phenomenon. As the State explains, 
variability in biogenic VOC emissions and in meteorology provide an 
explanation for some locations being transitional or NOX-
saturated on some days. We agree with the State that the weekday-
weekend analyses support the conclusion that ozone formation in the 
Sacramento Metro Area is mainly in a NOX-limited regime, 
with some periods in a NOX-transitional regime, and that 
there is no disbenefit from NOX controls. Next, we review 
and present additional research evidence from the Plan that further 
supports our conclusion that the Sacramento Metro Area's ozone 
chemistry is NOX-limited.
    To supplement the analysis of weekday-weekend conditions, the Plan 
cites several research and analysis papers examining daily and hourly 
concentrations of ozone, NOX, and VOC in the years prior to 
2011, which support the conclusion that ozone formation in the 
Sacramento area is currently NOX-limited. Two related papers 
by Murphy et al., from 2006 and 2007, examine monitored data from 1998-
2002 for the Central and Eastern subregions of the Sacramento Metro 
Area.\45\ As described in these papers, the ``weekend effect,'' i.e., 
conditions in which ozone concentrations are higher on weekends, was 
observed for monitoring sites in the Sacramento Valley (corresponding 
to the Central subregion).\46\ The researchers attributed this largely 
to NOX titration from mobile source emissions in urban 
Sacramento.\47\ For the Mountain Counties of the Eastern subregion, the 
researchers found that weekday ozone concentrations were higher, 
consistent with NOX-limited conditions.\48\ The researchers' 
analysis suggests that under conditions of high concentrations of ozone 
and precursors flowing in from other urban areas, NOX 
emission reductions of 50 percent or more would be needed to guarantee 
lower rates of ozone production in the Sacramento Valley portions 
studied, corresponding to the Central and Eastern subregions.\49\ In 
comparison to this prospective analysis, NOX emissions in 
the Sacramento Metro Area have decreased by 58 percent between 2000 and 
2015. Thus, the work of Murphy et. al., along with subsequent 
NOX emissions reductions, suggest that the full Sacramento 
Metro Area should currently be NOX-limited.
---------------------------------------------------------------------------

    \45\ Murphy, J.G., Day, D.A., Cleary, P.A., Wooldridge, P.J., 
Millet, D.B., Goldstein, A.H., and Cohen, R.C., 2007, ``The weekend 
effect within and downwind of Sacramento--Part 1: Observations of 
ozone, nitrogen oxides, and VOC reactivity,'' Atmos. Chem. Phys., 7, 
5327-5339, https://doi.org/10.5194/acp-7-5327-2007 (``Murphy et al. 
2007''); Murphy, J.G., Day, D.A., Cleary, P.A., Wooldridge, P.J., 
Millet, D.B., Goldstein, A.H., and Cohen, R.C., 2006, ``The weekend 
effect within and downwind of Sacramento: Part 2. Observational 
evidence for chemical and dynamical contributions,'' Atmos. Chem. 
Phys. Discuss., 6, 11971-12019, https://doi.org/10.5194/acpd-6-11971-2006 (``Murphy et al. 2006'').
    \46\ Murphy et al., 2007 at 5332.
    \47\ Murphy et al., 2007 at 5336; Murphy et. al., 2006 at 11972.
    \48\ Murphy et al., 2007 at 5336.
    \49\ Murphy et al., 2006 at 11996.
---------------------------------------------------------------------------

    LaFranchi et al., 2011 examines monitored data from 2001-2007 for 
the Central and Eastern subregions.\50\ These researchers found 
NOX-saturated conditions in the urban core, but mainly at 
lower temperatures and lower ozone concentrations, and determined that 
NOX emissions reductions were effective at reducing maximum 
ozone concentrations.\51\ The researchers also found no evidence that 
NOX reductions have been detrimental to air quality. For 
example, the researchers found that the 30 percent decrease in 
NOX and other nitrogen photochemical products from 2001 to 
2007 was ``extremely effective in reducing the exceedance probability 
at all locations during the hottest days of the year'' when increases 
in biogenic emissions result in more NOX-limited 
conditions.\52\ Furthermore, the researchers note that:
---------------------------------------------------------------------------

    \50\ LaFranchi et al., 2011 at 6945-6960.
    \51\ Id. at 6954.
    \52\ Id.

    It has been argued . . . that NOX decreases cause 
O3 increases in the center of cities and are more 
detrimental to health because of the larger number of people who 
live in the urban core as opposed to the surrounding suburbs and 
rural regions. . . . We find that between 2001 and 2007, the average 
O3 is higher on weekends than on weekdays only for the 
lowest temperature days . . . well below the exceedance limit 
[California 1-hour standard of 90 ppb], increases in O3 
with decreasing NOX are not likely to lead to additional 
exceedances. Thus, we find no evidence that implementation of 
NOX emission controls has been detrimental to air 
quality, by any policy-relevant metric.\53\
---------------------------------------------------------------------------

    \53\ Id. at 6954-6955.

    Since NOX emissions examined in the Plan and today are 
now lower \54\ than during the periods examined in these research 
papers, ozone formation is now expected to be within a more 
NOX-limited regime. As a result, current conditions are 
consistent with and fit the predictions in LaFranchi et al., that 
NOX emissions reductions decrease ozone concentrations in 
the Eastern subregion and more recently in the Central subregion; the 
possible exception being when ozone levels are already low, i.e., well 
below the 2008 NAAQS.
---------------------------------------------------------------------------

    \54\ Anthropogenic VOC emissions have also decreased, but 
because biogenic emissions are so much greater, the overall effect 
of the NOX and VOC reductions has been to increase the 
VOC/NOX ratio, resulting in more NOX-limited 
ozone chemistry.
---------------------------------------------------------------------------

    Overall, the State's evidence presented in the Plan suggests that 
NOX reductions are more effective than VOC reductions at 
decreasing ozone concentrations in the Sacramento Metro Area. For 
example, LaFranchi et al., observe that ``the intensity of biogenic VOC 
emissions have made NOX emission reductions more effective 
than anthropogenic VOC emission reductions in the region, at least 
downwind of Del Paso [i.e., within the Central and Eastern 
subregions].'' \55\ The Plan's ozone isopleth diagram for the Folsom 
monitor \56\ also provides strong evidence that NOX emission 
reductions are more effective than VOC reductions. The State generated 
this diagram using photochemical grid modeling to simulate various 
combinations of NOX and VOC emissions reductions and 
plotting the resulting ozone concentrations for the Folsom monitor, the 
ambient ozone monitor with the highest ozone design value in the 
Sacramento Metro Area. The diagram shows a nearly horizontal slope of 
the isopleth lines, indicating that ozone formation in the Folsom area 
is much more responsive to NOX emission reductions than to 
VOC reductions.\57\ As discussed in the proposed rule for this action, 
the EPA estimated from the ozone isopleth diagram in the Plan that 
ozone formation is about 14 times as

[[Page 58588]]

sensitive to NOX reductions than to VOC reductions on a 
percentage basis, and about 24 times as sensitive on a tons-per-year 
basis.\58\ Because the Plan demonstrates a shift to NOX-
limited conditions throughout all subregions in the area through its 
review of relevant research and includes additional modeling evidence 
at the Folsom monitor to support the Plan's reliance on NOX 
emissions reductions to achieve attainment, we disagree with CBD that 
additional evidence is needed to support the use of NOX 
substitution under CAA section 182(c)(2)(C).
---------------------------------------------------------------------------

    \55\ LaFranchi et al. 2011 at 6958. Id. at 6946-6947, which 
notes that VOC reactivity is controlled primarily by biogenic 
emissions, including the urban core. This suggests that reducing 
anthropogenic VOC emissions may be relatively ineffective for 
reducing ozone.
    \56\ 2017 Sacramento Regional Ozone Plan Appendix B-4, B-158, 
Figure 16.
    \57\ Id.
    \58\ 85 FR 68509, 68522 (October 29, 2020).
---------------------------------------------------------------------------

    We also disagree with the commenter's assertion that our proposed 
approval does not consider emissions changes through 2024. The Folsom 
isopleth diagram that supports the Plan's comparison of pre-2015 
monitored weekday-weekend data shows that NOX reductions are 
far more effective than VOC emissions based on 2026 emissions and 
including changes through and after 2024.\59\ Furthermore, the changes 
in emissions through 2024 posited by the commenter would not alter the 
EPA's conclusion that NOX substitution is appropriate. 
Indeed, we anticipate that the replacement of NOX combustion 
sources with wind and solar electricity generation, as well as 
continuing mobile source NOX reductions through 2024 and 
beyond, will make the Sacramento Metro Area even more NOX-
limited, thereby further strengthening the Plan's conclusions regarding 
the efficacy of NOX emissions reductions compared to VOC 
reductions.
---------------------------------------------------------------------------

    \59\ Plan Appendix B-4, B-158.
---------------------------------------------------------------------------

    The EPA also disagrees that an equivalence demonstration requires a 
quantitative analysis. Depending on the facts and circumstances of a 
given nonattainment area, analytical information that establishes 
equivalence may be quantitative or qualitative, or both. In this 
instance, some of the evidence relied upon could be termed qualitative, 
such as the shape of curves in the isopleth diagram.\60\ The Plan's 
modeling and monitoring analyses, and the analyses used in the cited 
research papers, are predominantly quantitative, with qualitative 
aspects and some qualitative conclusions. Qualitative evidence can be 
just as useful as quantitative evidence. For NOX 
substitution to yield an equivalent ozone decrease, as required in CAA 
section 182(c)(2)(C), a demonstration is adequate if it shows that 
NOX reductions are more effective than VOC reductions--it 
does not need to quantify an exact amount by which these reductions are 
more effective.
---------------------------------------------------------------------------

    \60\ These curves are partly quantified by the proposed rule's 
estimate that NOX emissions reductions are 14 times as 
effective as VOC reductions.
---------------------------------------------------------------------------

    We also disagree with CBD's suggestion that the overall geographic 
distribution of NOX and VOC emissions would be significantly 
affected by realistic and incremental changes in these emissions. 
Incremental changes resulting from the construction or closing of 
NOX point sources would not affect the preponderance of 
NOX emissions from mobile sources in the developed urban 
area, when compared to the lower NOX emissions in suburban 
and rural areas. These changes would also not significantly affect the 
reverse pattern of relatively more VOC emissions (from biogenic 
sources) in rural areas compared to urban areas. Such small changes in 
overall NOX or VOC emissions would merely affect the degree 
and amount by which NOX reductions are shown to be more 
effective than VOC reductions. Consequently, the EPA's overall 
conclusion that NOX substitution within the Plan meets the 
requirements of CAA section 182(c)(2)(C) remains unchanged.
    Regarding CBD's concern that ambient ozone data from a single 
monitoring site is inadequate to demonstrate equivalency, we agree that 
this could be problematic in some circumstances but disagree that this 
is a problem for the Sacramento Metro Area, for two reasons. First, as 
discussed previously, in concluding that NOX emissions 
reductions are more effective than VOC reductions at reducing ozone, 
the State considered studies of ozone response at monitoring sites 
throughout the nonattainment area as part of the Plan. Second, the Plan 
demonstrates attainment at all monitoring sites, and its conclusion 
that NOX reductions are more effective than VOC for the site 
with the highest design value, i.e., the Folsom monitoring site, the 
``controlling'' site for determining whether or not the NAAQS is 
attained in the Sacramento Metro Area, therefore ensures that 
NOX reductions will be effective in achieving ozone 
reductions that will help the nonattainment area toward attainment in 
all sub-regions. We anticipate that any increase in ozone 
concentrations that might result from NOX emission 
reductions would be only small, transient, and affect locations with 
ozone concentrations well below the NAAQS. These ozone increases would 
typically occur under low temperature conditions, with corresponding 
low ozone concentrations well below the NAAQS, not at elevated ozone 
concentrations that could affect public health or interfere with 
attainment of the 2015 ozone NAAQS. As noted above, ambient ozone data 
recorded in the Central subregion of the Sacramento Metro Area between 
2011 and 2014 already show ozone levels under 70 ppb, the concentration 
that the EPA has established as the 2015 ozone NAAQS.
    Concerning future air quality planning for the 2015 ozone NAAQS, 
the State has requested that the EPA reclassify the Sacramento Metro 
nonattainment area as a Serious nonattainment area, and the attainment 
plan for Serious areas is not yet due. The EPA has proposed to require 
that the State submit an attainment plan for the 2015 ozone NAAQS for 
the Sacramento Metro Area by August 3, 2022.\61\ As proposed, this plan 
will be required to demonstrate, through photochemical grid modeling 
and other demonstrations, that all portions of the Sacramento Metro 
Area will attain the 2015 NAAQS by no later than August 3, 2027. Based 
on conditions in this area as described above and in the proposed rule 
and the Plan, we anticipate that NOX reductions, including 
those used to demonstrate attainment of the 2008 ozone NAAQS, will 
remain a critical piece of the State's control strategy to meet the 
2015 ozone NAAQS. Accordingly, we disagree with CBD's assertion that 
the Plan's use of NOX substitution will interfere with 
attainment of the newer and more stringent ozone standards in the 
Sacramento Metro Area or violate CAA section 110(l).
---------------------------------------------------------------------------

    \61\ 86 FR 44677, 44678 (August 13, 2021).
---------------------------------------------------------------------------

    Comment #3: CBD states that an equivalence demonstration should be 
as rigorous as an attainment demonstration; as such, an equivalence 
demonstration should be based on photochemical modeling or another 
equally rigorous technique. The commenter suggests that the State could 
compare modeled relative response factors (RRFs) for each RFP milestone 
year for the 3 percent per year VOC reductions to corresponding RRFs 
from the control strategy, or the State could use ozone isopleth 
diagrams together with conservative assumptions about the amount of 
allowable NOX substitution. The commenter acknowledges that 
section 182(c)(2)(C) does not explicitly prescribe the use of 
photochemical grid modeling or an equally rigorous method and argues 
that this does not mean that section 182(c)(2)(C) is worthy of a less 
rigorous demonstration. The commenter argues that Congress added the 
RFP provisions to the CAA in response to the EPA's failure to address 
ozone pollution under

[[Page 58589]]

the general requirements for attainment demonstrations in subpart 1 of 
the CAA. The commenter states that, in any case, it would be arbitrary 
for the EPA to ignore the entire nonattainment area except for the 
isopleths at the Folsom monitor and the Eastern region weekend effect 
in assessing the equivalence demonstration.
    Response to Comment #3: The EPA disagrees that an equivalence 
demonstration for purposes of CAA section 182(c)(2)(C) must be as 
technically rigorous as a NAAQS attainment demonstration. As the 
commenter notes, CAA section 182(c)(2)(C) does not require the use of 
photochemical grid modeling to demonstrate the relative effectiveness 
of NOX and VOC emissions reductions in reducing ozone 
concentrations, whereas CAA section 182(c)(2)(A) explicitly requires 
photochemical grid modeling or another equivalent analytical method as 
part of the attainment demonstration. Instead, Congress provided the 
EPA with discretion to evaluate state demonstrations supporting 
NOX substitution, and to define the conditions under which 
NOX substitution is appropriate ``in order to maximize the 
reduction in ozone air pollution.'' \62\ We believe that this approach 
reflects an appropriate balance in the level of analysis required for 
demonstrating attainment by the attainment date, and for the supporting 
evaluation of the relative effectiveness of potential measures and 
reductions used to meet RFP milestones. Consequently, we disagree that 
a NOX equivalence demonstration for RFP purposes must 
reflect the same or equally rigorous analytical methods as used in the 
attainment demonstration. As discussed previously, a qualitative 
analysis may show that NOX reductions are more effective 
than VOC reductions and be adequate for purposes of allowing 
NOX substitution under section 182(c)(2)(C). As described 
above, we proposed to approve the RFP demonstration and its use of 
NOX substitution based on our analyses of the photochemical 
modeling results included in the attainment demonstration and the 
Folsom isopleth diagram, the other monitoring data from the Plan, and 
the research papers and analyses cited within. Collectively, these 
analyses and data show that NOX emissions reductions are 
effective at reducing ozone throughout the Sacramento Metro Area and 
are more effective than VOC reductions at bringing the area into 
attainment of the NAAQS. Accordingly, we support the Plan's use of 
NOX substitution.
---------------------------------------------------------------------------

    \62\ CAA section 182(c)(2)(C).
---------------------------------------------------------------------------

    Comment #4: CBD comments that the EPA has not demonstrated that the 
approval of NOX substitution complies with Executive Order 
12898, which expresses the EPA's obligation to identify and address 
disproportionate impacts of its actions on minority populations and 
low-income populations, i.e., environmental justice (EJ) communities. 
The commenter asserts that because the EPA is not applying the 
NOX Substitution Guidance in evaluating the Plan's use of 
NOX substitution, it is exercising discretion, and should 
use this discretion to require the State to demonstrate equivalence at 
each monitoring site through photochemical modeling of the relevant 
scenarios. Furthermore, the commenter says that because the record does 
not support the EPA's conclusion that NOX substitution will 
result in equivalent reductions in ozone concentrations throughout the 
area, EJ communities may be disproportionately and adversely impacted 
by the EPA's action by experiencing fewer reductions in ozone than 
would be achieved through VOC reductions alone, or even ozone 
increases. The commenter suggests that the EPA could exercise 
discretion to disapprove the Plan on this basis, and that this 
disapproval could result in the EPA issuing a Federal implementation 
plan requiring additional emissions reductions to ensure equivalent 
reductions in ozone concentrations. The commenter states that it is not 
a sufficient response to say that approving the Plan will have no 
adverse impact to EJ communities because it improves the status quo by 
making State law federally enforceable. The commenter provides a map 
generated using CalEnviroScreen, showing EJ communities concentrated in 
the Central subregion where the commenter asserts that the Plan does 
not demonstrate equivalence.
    Response to Comment #4: As explained in our previous responses, the 
EPA and the State have determined that NOX reductions are 
critical to the Sacramento Metro Area's attainment of the 2008 ozone 
NAAQS and we anticipate that any localized increase in ozone 
concentrations resulting from these NOX reductions would be 
minor, transitory, and occur well below the limits established by the 
NAAQS. Furthermore, we find that the Plan appropriately focuses on 
ozone reductions in the regions subject to the highest ozone 
concentrations, e.g., the eastern region and design value monitor at 
Folsom, where adverse health impacts are most likely to occur. In this 
context, we disagree that the use of NOX substitution is 
inappropriate even if it may generate disproportionate reductions in 
ozone concentrations within high ozone and NOX-limited 
areas.
    Executive Order 12898, ``Federal Actions To Address Environmental 
Justice in Minority Populations and Low-Income Populations,'' directs 
Federal agencies to identify and address ``disproportionately high and 
adverse human health or environmental effects'' of their actions on 
minority populations and low-income populations to the greatest extent 
practicable and permitted by law.\63\ Given our conclusion that the 
Plan satisfies all applicable CAA requirements related to demonstrating 
expeditious attainment of the ozone NAAQS, including the requirements 
for RFP and NOX substitution,\64\ we have no basis to 
conclude that this action will cause disproportionately high or adverse 
human health or environmental effects on any population, including any 
minority, low-income, or indigenous population. Under the CAA, the EPA 
is required to approve a SIP submission that satisfies the requirements 
of the Act and applicable Federal regulations,\65\ and Executive Order 
12898 does not provide an independent basis for disapproving such a SIP 
submission. The EPA remains committed, however, to working with CARB 
and the local air districts in the Sacramento Metro Area to ensure that 
the ozone attainment plans for this area satisfy CAA requirements for 
attainment and RFP and thereby protect all populations in the area, 
including minority, low-income, and indigenous populations, from 
disproportionately high or adverse air pollution impacts.
---------------------------------------------------------------------------

    \63\ 59 FR 7629 (February 16, 1994).
    \64\ Our response to Comment #7 discusses our reasons for 
deferring action on the State's contingency measures revision.
    \65\ CAA section 110(k); 40 CFR 52.02(a).
---------------------------------------------------------------------------

    Comment #5: CBD comments that the proposed rule fails to 
acknowledge the EPA's NOX Substitution Guidance, and that 
the EPA should explicitly disavow the guidance and its justifications. 
The commenter says that there is no basis for this guidance and 
suggests that the EPA's prior use of the guidance may have caused 
increases in asthma, hospital and emergency room visits, and premature 
mortality. An appendix to the comments provides numerous comments 
directed at the NOX Substitution Guidance, asserting 
generally that this guidance contradicts CAA section 182(c)(2)(C) by 
recommending a procedure that fails to

[[Page 58590]]

demonstrate any equivalence between VOC and NOX reductions, 
relies on incorrect policy assumptions, and gives legal justifications 
that are without merit.
    Response to Comment #5: Our proposed approval of the Plan's use of 
NOX substitution is compatible with the NOX 
Substitution Guidance, which, while non-binding and not having the 
force of regulation, provides a recommended procedure for substituting 
NOX emission reductions for VOC reductions on a percentage 
basis, consistent with a state's ozone attainment plan, control 
strategy, modeled attainment demonstration, and RFP milestones and 
requirements. The NOX Substitution Guidance specifies that 
the EPA will review NOX substitution on a case-by-case basis 
and will generally approve reasonable NOX substitution 
proposals.\66\ As noted in our proposed rule and described above, our 
approval of the State's reasonable use of NOX substitution 
is supported by local conditions and needs as documented in the 
modeling and analyses included in the Sacramento Metro Ozone SIP and is 
consistent with the requirements in CAA section 182(c)(2)(C).\67\
---------------------------------------------------------------------------

    \66\ NOX Substitution Guidance at 3 (``The EPA will 
approve substitution proposals on a case-by-case basis. Generally 
speaking, any reasonable substitution proposal will be approved.'').
    \67\ See id. at 1 (recognizing that ``NOX controls 
may effectively reduce ozone in many areas, and that the design of 
strategies is more efficient when the characteristic properties 
responsible for ozone formation and control are evaluated for each 
area'').
---------------------------------------------------------------------------

    To be clear, our action on the Plan is not intended to disavow or 
rescind any portion of the NOX Substitution Guidance. 
Comments relating solely to the NOX Substitution Guidance 
are outside the scope of this rulemaking action.
    Comment #6: CBD argues that, because the Plan does not meet the 
requirements for RFP, the EPA cannot determine that the MVEBs are 
allowable as a portion of the total allowable emissions for 
demonstrating RFP. The commenter asserts that because there is no 
measure of total allowable emissions for RFP in the absence of an 
approvable plan, the EPA has no basis for approval of the MVEBs.
    Response to Comment #6: For the reasons described above in our 
previous responses to comments, we have determined that the State's use 
of NOX substitution is appropriate and adequately supported 
within the Plan, consistent with the RFP and attainment demonstrations, 
and that the Plan's RFP demonstration is approvable. Consequently, we 
disagree with the commenter and their rationale suggesting that our 
approval of the MVEBs is inappropriate.
    Comment #7: CBD challenges the EPA's proposed conditional approval 
of the contingency measures as arbitrary and capricious and contrary to 
law, based on CAA requirements and interpreting case law. The commenter 
asserts that the EPA must disapprove the contingency measures.
    Response to Comment #7: As explained in the proposed rule, our 
proposed conditional approval of the State's RFP and attainment 
contingency measures was based on commitments from the State and 
Districts in the context of additional emissions reductions in the RFP 
milestone years and in the year following the attainment year. 
Following publication of the proposed rule, the Ninth Circuit Court of 
Appeals issued a decision in Association of Irritated Residents v. U.S. 
Environmental Protection Agency, which remanded the EPA's conditional 
approval of contingency measures for another California nonattainment 
area.\68\ Based on this decision, we are not finalizing our proposed 
conditional approval of the Plan's contingency measures at this time. 
Consequently, CBD's comments on this issue are outside the scope of 
this final action and we are not providing specific responses to these 
comments.
---------------------------------------------------------------------------

    \68\ Association of Irritated Residents v. U.S. Environmental 
Protection Agency, No. 19-71223 (9th Cir. Aug. 26, 2021).
---------------------------------------------------------------------------

III. Final Action

    For the reasons discussed in detail in the proposed rule and 
summarized herein, under CAA section 110(k)(3), the EPA is taking final 
action to approve as a revision to the California SIP the following 
portions of the Sacramento Metro Area Ozone SIP, as provided within the 
2017 Sacramento Regional Ozone Plan and the Sacramento Metro portion of 
CARB's 2018 SIP Update:
     The base year emissions inventory element in the 2017 
Sacramento Regional Ozone Plan meets the requirements of CAA sections 
172(c)(3) and 182(a)(1) and 40 CFR 51.1115 for the 2008 ozone NAAQS;
     The RACM demonstration element in the 2017 Sacramento 
Regional Ozone Plan meets the requirements of CAA section 172(c)(1) and 
40 CFR 51.1112(c) for the 2008 ozone NAAQS;
     The attainment demonstration element for the 2008 ozone 
NAAQS in the 2017 Sacramento Regional Ozone Plan meets the requirements 
of CAA section 182(c)(2)(A) and 40 CFR 51.1108;
     The ROP demonstration element in the 2017 Sacramento 
Regional Ozone Plan meets the requirements of CAA 182(b)(1) and 40 CFR 
51.1110(a)(2) for the 2008 ozone NAAQS;
     The RFP demonstration element in Section V--SIP Elements 
for the Sacramento Metropolitan Area of the 2018 SIP Update (as 
clarified) meets the requirements of CAA sections 172(c)(2), 182(b)(1), 
and 182(c)(2)(B), and 40 CFR 51.1110(a)(2)(ii) for the 2008 ozone 
NAAQS;
     The VMT emissions offset demonstration element in the 2017 
Sacramento Regional Ozone Plan meets the requirements of CAA section 
182(d)(1)(A) and 40 CFR 51.1102 for the 2008 ozone NAAQS; and
     The motor vehicle emissions budgets in Section V--SIP 
Elements for the Sacramento Metropolitan Area of the 2018 SIP Update 
for the RFP milestone year of 2023, and the attainment year of 2024 are 
consistent with the RFP and attainment demonstrations for the 2008 
ozone NAAQS, and the budgets meet the other criteria in 40 CFR 
93.118(e). In approving the budgets, we are also finding them adequate 
for use in transportation conformity determinations, consistent with 40 
CFR 93.118(f)(2).

 Table 1--Transportation Conformity Motor Vehicle Emissions Budgets for
            the 2008 Ozone NAAQS in the Sacramento Metro Area
                [Summer planning inventory, tons per day]
------------------------------------------------------------------------
               Budget year                      VOC             NOX
------------------------------------------------------------------------
2023....................................              15              22
2024....................................              15              21
------------------------------------------------------------------------
Source: 85 FR 68509; Id. at 68530, Table 9; and 2018 SIP Update, Table V-
  4.

[[Page 58591]]

    We also find that the:
     Emissions statement element of the 2017 Sacramento 
Regional Ozone Plan satisfies the requirements under CAA section 
182(a)(3)(B) based on our prior approval of the Districts' emissions 
statement rules;
     Enhanced vehicle inspection and maintenance program in the 
Sacramento Metro Area meets the requirements of CAA section 182(c)(3) 
and 40 CFR 51.1102 for the 2008 ozone NAAQS;
     California SIP revision to opt out of the Federal Clean 
Fuels Fleet Program meets the requirements of CAA sections 182(c)(4)(A) 
and 246 and 40 CFR 51.1102 for the 2008 ozone NAAQS with respect to the 
Sacramento Metro Area; and
     Enhanced monitoring in the Sacramento Metro Area meets the 
requirements of CAA section 182(c)(1) and 40 CFR 51.1102 for the 2008 
ozone NAAQS.
    To conclude, we are deferring final action on the contingency 
measures element of the Sacramento Metro Area Ozone SIP as meeting the 
requirements of CAA sections 172(c)(9) and 182(c)(9).

IV. Statutory and Executive Order Reviews

    Under the Clean Air Act, the Administrator is required to approve a 
SIP submission that complies with the provisions of the Act and 
applicable Federal regulations. 42 U.S.C. 7410(k); 40 CFR 52.02(a). 
Thus, in reviewing SIP submissions, the EPA's role is to approve state 
choices provided they meet the criteria of the Clean Air Act. 
Accordingly, this action merely approves state plans as meeting Federal 
requirements and does not impose additional requirements beyond those 
imposed by state law. For that reason, this action:
     Is not a ``significant regulatory action'' subject to 
review by the Office of Management and Budget under Executive Orders 
12866 (58 FR 51735, October 4, 1993) and 13563 (76 FR 3821, January 21, 
2011);
     Does not impose an information collection burden under the 
provisions of the Paperwork Reduction Act (44 U.S.C. 3501 et seq.);
     Is certified as not having a significant economic impact 
on a substantial number of small entities under the Regulatory 
Flexibility Act (5 U.S.C. 601 et seq.);
     Does not contain any unfunded mandate or significantly or 
uniquely affect small governments, as described in the Unfunded 
Mandates Reform Act of 1995 (Pub. L. 104-4);
     Does not have federalism implications as specified in 
Executive Order 13132 (64 FR 43255, August 10, 1999);
     Is not an economically significant regulatory action based 
on health or safety risks subject to Executive Order 13045 (62 FR 
19885, April 23, 1997);
     Is not a significant regulatory action subject to 
Executive Order 13211 (66 FR 28355, May 22, 2001);
     Is not subject to requirements of Section 12(d) of the 
National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 
note) because application of those requirements would be inconsistent 
with the Clean Air Act; and
     Does not provide the EPA with the discretionary authority 
to address disproportionate human health or environmental effects with 
practical, appropriate, and legally permissible methods under Executive 
Order 12898 (59 FR 7629, February 16, 1994).
    In addition, the SIP is not approved to apply on any Indian 
reservation land or in any other area where the EPA or an Indian tribe 
has demonstrated that a tribe has jurisdiction. Four Indian tribes have 
areas of Indian country located within the boundaries of the Sacramento 
Metro ozone nonattainment area. In those areas of Indian country, the 
rule does not have tribal implications and will not impose substantial 
direct costs on tribal governments or preempt tribal law as specified 
by Executive Order 13175 (65 FR 67249, November 9, 2000).
    The Congressional Review Act, 5 U.S.C. 801 et seq., as added by the 
Small Business Regulatory Enforcement Fairness Act of 1996, generally 
provides that before a rule may take effect, the agency promulgating 
the rule must submit a rule report, which includes a copy of the rule, 
to each House of the Congress and to the Comptroller General of the 
United States. The EPA will submit a report containing this action and 
other required information to the U.S. Senate, the U.S. House of 
Representatives, and the Comptroller General of the United States prior 
to publication of the rule in the Federal Register. A major rule cannot 
take effect until 60 days after it is published in the Federal 
Register. This action is not a ``major rule'' as defined by 5 U.S.C. 
804(2).
    Under section 307(b)(1) of the Clean Air Act, petitions for 
judicial review of this action must be filed in the United States Court 
of Appeals for the appropriate circuit by December 21, 2021. Filing a 
petition for reconsideration by the Administrator of this final rule 
does not affect the finality of this action for the purposes of 
judicial review nor does it extend the time within which a petition for 
judicial review may be filed, and shall not postpone the effectiveness 
of such rule or action. This action may not be challenged later in 
proceedings to enforce its requirements. (See section 307(b)(2)).

List of Subjects in 40 CFR Part 52

    Environmental protection, Air pollution control, Incorporation by 
reference, Intergovernmental relations, Nitrogen dioxide, Ozone, 
Reporting and recordkeeping requirements, Volatile organic compounds.

    Authority: 42 U.S.C. 7401 et seq.

    Dated: October 9, 2021.
Deborah Jordan,
Acting Regional Administrator, Region IX.

    Chapter I, title 40 of the Code of Federal Regulations is amended 
as follows:

PART 52--APPROVAL AND PROMULGATION OF IMPLEMENTATION PLANS

0
1. The authority citation for part 52 continues to read as follows:

    Authority: 42 U.S.C. 7401 et seq.

Subpart F--California

0
2. Section 52.220 is amended by adding paragraphs (c)(514)(ii)(A)(10) 
and (c)(566) to read as follows:

Sec.  52.220  Identification of plan--in part.

* * * * *
    (c) * * *
    (514) * * *
    (ii) * * *
    (A) * * *
    (10) 2018 Updates to the California State Implementation Plan, 
adopted on October 25, 2018, chapter V (``SIP Elements for the 
Sacramento Metropolitan Area''), excluding section V.D (``Contingency 
Measures''); and pages A-15 through A-18 of Appendix A (``Nonattainment 
Area Inventories'').
* * * * *
    (566) The following plan was submitted on December 18, 2017 by the 
Governor's designee.
    (i) [Reserved]
    (ii) Additional materials. (A) Sacramento Metropolitan Area 2008 8-
Hour Ozone National Ambient Air Quality Standard Planning Area.
    (1) Sacramento Regional 2008 NAAQS 8-Hour Ozone Attainment and 
Reasonable Further Progress Plan, dated July 24, 2017, excluding the 
following portions: Subchapter 7.9, ``Contingency Measures''; 
subchapter 10.5, ``Proposed New Motor Vehicle Emissions Budgets''; and 
chapter 12 (regarding reasonable further progress).

[[Page 58592]]

    (2) [Reserved]
    (B) [Reserved]

[FR Doc. 2021-22661 Filed 10-21-21; 8:45 am]
BILLING CODE 6560-50-P