2023-20555. Second 10-Year Maintenance Plan for the 24-Hour PM10 Standards; Sacramento County Planning Area, California

AGENCY:

Environmental Protection Agency (EPA).

ACTION:

Proposed rule.

SUMMARY:

The Environmental Protection Agency (EPA) is proposing to approve the “Second 10-Year PM₁₀ Maintenance Plan for Sacramento County” (“Second 10-Year Maintenance Plan” or “Plan”) as a revision to the state implementation plan (SIP) for the State of California (“State”). The Second 10-Year Maintenance Plan includes, among other elements, a base year emissions inventory, a maintenance demonstration, contingency provisions, and motor vehicle emissions budgets for use in transportation conformity determinations, to ensure the continued maintenance of the national ambient air quality standards (NAAQS) for particulate matter of 10 microns or less (PM₁₀). With this proposed rulemaking, the EPA is beginning the adequacy process for the 2024, 2027, and 2033 motor vehicle emissions budgets. Additionally, as part of the technical basis for this approval, the EPA is taking comment on our August 1, 2022 concurrence on the wildfire exceptional events demonstration submitted by the California Air Resources Board (CARB) on April 26, 2021.

DATES:

Written comments must arrive on or before October 23, 2023.

ADDRESSES:

Submit your comments identified by Docket ID No. EPA–R09–OAR–2023–0267 at https://www.regulations.gov. For comments submitted at Regulations.gov, follow the online instructions for submitting comments. Once submitted, comments cannot be edited or removed from Regulations.gov. The EPA may publish any comment received to its public docket. Do not submit electronically any information you consider to be Confidential Business Information (CBI) or other information whose disclosure is restricted by statute. Multimedia submissions (audio, video, etc.) must be accompanied by a written comment. The written comment is considered the official comment and should include discussion of all points you wish to make. The EPA will generally not consider comments or comment contents located outside of the primary submission ( i.e., on the web, cloud, or other file sharing system). For additional submission methods, please contact the person identified in the FOR FURTHER INFORMATION CONTACT section. For the full EPA public comment policy, information about CBI or multimedia submissions, and general guidance on making effect comments, please visit https://www.epa.gov/​dockets/​commenting-epa-dockets. If you need assistance in a language other than English or if you are a person with a disability who needs a reasonable accommodation at no cost to you, please contact the person identified in the FOR FURTHER INFORMATION CONTACT .

FOR FURTHER INFORMATION CONTACT:

Michael Dorantes, Geographic Strategies and Modeling Section (AIR–2–2), EPA Region IX, (415) 972–3934, [e-mail].

SUPPLEMENTARY INFORMATION:

Throughout this document, “we,” “us,” and “our” refer to the EPA.

Table of Contents

I. Background

A. The PM₁₀ National Ambient Air Quality Standards

B. The Sacramento County Planning Area Nonattainment Designation and First PM₁₀ Maintenance Plan

II. Air Quality in the Sacramento County Planning Area

A. Exceedances in the Sacramento County Planning Area

B. Exceptional Events Demonstration for the 2018 Exceedances in the Sacramento County Planning Area

C. Exceedances Occuring After the 2019 Design Value Period

III. The Second 10-Year Maintenance Plan Submittal and Procedural Requirements

IV. Evaluation of the Second 10-Year Maintenance Plan

A. Emissions Inventory

B. Maintenance Demonstration

C. Monitoring Network Requirements

D. Verification of Continued Attainment

E. Contingency Provisions

F. Motor Vehicle Emissions Budgets for Transportation Conformity

V. Proposed Action and Request for Public Comment

VI. Statutory and Executive Order Reviews

I. Background

A. The PM₁₀ National Ambient Air Quality Standards

Under section 109 of the Clean Air Act (CAA), the EPA promulgates NAAQS for pervasive air pollutants, such as particulate matter, and conducts periodic review of these standards to determine whether they should be revised or whether new standards should be established. In 1987, the EPA established two PM₁₀ NAAQS: annual standards of 50 micrograms per cubic meter (μg/m^[3] ) and 24-hour standards of 150 μg/m^[3] .^[1] Upon further review, the annual PM₁₀ standards were subsequently revoked effective December 18, 2006, as the available evidence did not suggest an association between long-term exposure to coarse particles at ambient levels and detrimental health effects.^[2] However, the EPA announced that it was retaining the 24-hour PM₁₀ NAAQS at 150 micrograms per cubic meter (µg/m^[3] ) to provide continued protection against the effects associated with short-term exposure to coarse particles.^[3] In this document, “PM₁₀ NAAQS” or the singular “PM₁₀ standard” will henceforth refer to both the primary and secondary 24-hour PM₁₀ NAAQS, as they are the same.

B. The Sacramento County Planning Area Nonattainment Designation and First PM₁₀ Maintenance Plan

Under section 107 of the CAA, the EPA is required to designate all areas of the country as attainment, nonattainment, or unclassifiable for each of the NAAQS. Under the CAA Amendments of 1990, the Sacramento County planning area was initially designated as unclassifiable for the PM₁₀ NAAQS by operation of law. The EPA then redesignated and classified the area as a “Moderate” nonattainment area on January 20, 1994, due to PM₁₀ NAAQS violations recorded at two PM₁₀ monitors within the Sacramento County planning area during 1989 and 1990.^[4] This action established an attainment deadline of December 31, 2000.

On February 15, 2002, the EPA determined that the Sacramento County nonattainment area had attained the PM₁₀ NAAQS by the attainment date.^[5] The determination was based on complete, quality-assured, and certified ambient air monitoring data from 1998 to 2000. The 24-hour standard is attained when the recorded number of days with levels above 150 µg/m^[3] (averaged over a 3-year period) is less than or equal to one.^[6] The recorded number of exceedances averaged over a three-year period at any given monitor is known as the PM₁₀ design value, and the highest design value recorded within the nonattainment area is used as the area's PM₁₀ design value for the purposes of determining attainment.^[7]

Section 175A of the CAA dictates that any state that submits a request for redesignation of a nonattainment area to attainment shall also submit a SIP revision that provides for the maintenance of the pertinent NAAQS for at least 10 years after the redesignation. This maintenance plan must, among other requirements, ensure control measures are in place such that the area will continue to maintain the standard for a 10-year period after redesignation, and include contingency provisions to ensure that violations of the NAAQS will be promptly remedied.

In California, CARB is the agency responsible for the adoption and submission of California SIPs and SIP revisions to the EPA. Working jointly with CARB, local and regional air pollution control districts in California are responsible for the development of regional air quality plans. The Sacramento Metropolitan Air Quality Management District (“SMAQMD” or “District”) develops and adopts plans to address CAA planning requirements applicable to Sacramento County. SMAQMD adopts and submits its plans to CARB for state adoption and submission to the EPA as revisions to the California SIP.

On December 7, 2010, CARB requested that the EPA redesignate the Sacramento County PM₁₀ nonattainment area to attainment and concurrently submitted the Sacramento PM₁₀ Maintenance Plan and associated motor vehicle emissions budgets (“budgets”) to the EPA as a revision to the California SIP.^[8] On October 28, 2013, the EPA approved the Sacramento PM₁₀ Maintenance Plan, which provided for maintenance of the NAAQS for the area through October 28, 2023.^[9]

II. Air Quality in the Sacramento County Planning Area

A. Exceedances in the Sacramento County Planning Area

A recent design value showing a maintenance area is continuing to attain the PM₁₀ NAAQS ( i.e., the recorded number of days with levels above 150 µg/m³ , averaged over a 3-year period, is less than or equal to one) is the foundation of a second 10-year maintenance plan. As described in more detail in Section IV.A of this document, a base year emissions inventory from the design value period that represents attainment conditions is used as the basis for projecting emissions inventories into the future and to demonstrate that future emissions will not lead to an exceedance of the standards. The District used the data from calendar years 2017 through 2019 to calculate a 2019 design value to demonstrate the area had continued to attain the PM₁₀ standard and selected the 2017 emissions inventory as its base year inventory.

Table 1 of this document shows the design values for the Sacramento County PM₁₀ maintenance area at the monitoring sites active in the county between 2011 through 2022, accounting for all recorded exceedances during that time. Specifically, no exceedances of the PM₁₀ NAAQS were recorded in 2011–2017, numerous exceedances were recorded in 2018 across all active monitors, a single exceedance was recorded in 2019 at the Sacramento T Street monitoring site (AQS ID: 06–067–0010), several exceedances were recorded in 2020 across all active monitors, and in 2021–2022 no exceedances of the PM₁₀ NAAQS were recorded. As a result of the exceedance days recorded in 2018, the calculated 2019 design value for PM₁₀ is in violation of the standard.^[10] The District contends that the exceedances in 2018 were due to uncontrollable wildfire smoke and submitted a request to exclude the 2018 data from regulatory decisions on the basis that they are exceptional events.^[11]

Table 1—Sacramento County 2013–2022 PM ₁₀ Monitor Design Values Including 2018 Exceptional Events Exceedances

Design value period	Monitoring site
	North Highlands	Del Paso Manor	Sacramento T Street a	Sacramento Branch Center
2011–2013	0.0	0.0		0.0
2012–2014	0.0	0.0		0.0
2013–2015	0.0	0.0		0.0
2014–2016	0.0	0.0	0.0	0.0
2015–2017	0.0	0.0	0.0	0.0
2016–2018	4.1	4.1	2.0	2.0
2017–2019	4.1	4.1	2.3	2.0
2018–2020	6.0	6.0	3.7	4.6
2019–2021	1.9	1.9	1.7	2.6
2020–2022	1.9	1.9	1.3	2.6
a  The Sacramento T Street monitoring station came into active use in 2013. (North Highlands Air Quality System Site ID #:06–067–0002–1; Del Paso Manor (primary) AQS Site ID #: 06–067–0006–1; Sacramento T Street AQS Site ID #: 06–067–0010–4; Sacramento Branch Center AQS Site ID #: 06–067–0284–1).

B. Exceptional Events Demonstration for the 2018 Exceedances in the Sacramento County Planning Area

Congress has recognized that it may not be appropriate for the EPA to use certain monitoring data, collected by the ambient air quality monitoring network and maintained in the EPA's Air Quality System (AQS) database, in certain regulatory determinations. Thus, in 2005, Congress provided the statutory authority for the exclusion of data influenced by “exceptional events” meeting specific criteria by adding section 319(b) to the CAA. To implement this 2005 CAA amendment, the EPA promulgated the 2007 Exceptional Events Rule.^[12] The 2007 Exceptional Events Rule created a regulatory process codified at 40 CFR parts 50 and 51 (sections 50.1, 50.14, 51.930). These regulatory sections, which superseded the EPA's previous guidance on handling data influenced by exceptional events, contain definitions, procedural requirements, requirements for air agency demonstrations, criteria for EPA approval of the exclusion of event-affected air quality data from the data set used for regulatory decisions, and requirements for air agencies to take appropriate and reasonable actions to protect public health from exceedances or violations of the NAAQS. In 2016, the EPA promulgated a comprehensive revision to the 2007 Exceptional Events Rule (referred to herein as the “Exceptional Events Rule”).^[13] Under the Exceptional Events Rule, if, for example, a state demonstrates to the EPA's satisfaction that emissions from a wildfire smoke event caused specific air pollution concentration in excess of the PM₁₀ NAAQS at a particular air quality monitoring location and otherwise satisfies the requirements of 40 CFR 50.14, the EPA must exclude that data from use in determinations of exceedances and violations.^[14]

For the EPA to concur with excluding the air quality data from regulatory decision, the demonstration must satisfy all the Exceptional Events Rule criteria. Specifically, under 40 CFR 50.14(c)(3)(iv), the air agency demonstration to justify exclusion of data must include:

1. a narrative conceptual model that describes the event(s) causing the exceedance or violation and a discussion of how emissions from the event(s) led to the exceedance or violation at the affected monitors(s);

2. a demonstration that the event affected air quality in such a way that there exists a clear causal relationship between the specific event and the monitored exceedance or violation;

3. analyses comparing the claimed event-influenced concentration(s) to concentrations at the same monitoring site at other times to support requirement in 40 CFR 50.14(c)(3)(iv)(2);

4. a demonstration that the event was both not reasonably controllable and not reasonably preventable, and;

5. a demonstration that the event was a human activity that is unlikely to recur at a particular location or was a natural event.^[15]

In addition, the air agency must meet several procedural requirements, including:

1. submission of an Initial Notification of Potential Exceptional Event and flagging of the affected data in the EPA's Air Quality System (AQS) as described in 40 CFR 50.14(c)(2)(i);

2. completion and documentation of the public comment process described in 40 CFR 50.14(c)(3)(v); and

3. implementation of any relevant mitigation requirements as described in 40 CFR 51.930.

On August 21, 2019,^[16] CARB submitted an Initial Notification of Potential Exceptional Events prepared by SMAQMD for numerous exceedances of the PM₁₀ NAAQS that occurred at the Sacramento T Street, North Highland, Del Paso Manor, and Sacramento Branch Center PM₁₀ monitoring sites within the maintenance area on November 10–12 and November 14–16, 2018.

The EPA recommended that CARB and SMAQMD determine the relevant exceedances and associated monitoring sites that may have regulatory significance with respect to the PM₁₀ NAAQS, and submit an exceptional event demonstration to the EPA no later than March of 2021.^[17] On March 31, 2021, SMAQMD submitted the “Exceptional Event Demonstration for November 2018 Exceedances in Sacramento County due to Wildfires” to CARB for transmittal to the EPA.^[18] Then, on April 26, 2021,^[19] CARB submitted the exceptional event demonstration prepared by SMAQMD for 13 exceedances of the 1987 24-hour PM₁₀ NAAQS during November 10–12 and November 14–16, 2018.^[20] Table 2 of this document summarizes the exceedances that SMAQMD included in the demonstration.

Table 2—Sacramento County PM ₁₀ NAAQS Exceedance Summary for 2018

Exceedance date	Monitoring site	AQS ID a	PM 10 (µg/m3 )
November 10, 2018	Sacramento T Street	06–067–0010–4	189
November 10, 2018	North Highlands	06–067–0002–1	222
November 10, 2018	Del Paso Manor	06–067–0006–1	212
November 10, 2018	Del Paso Manor	06–067–0006–2	202
November 10, 2018	Sacramento—Branch Center	06–067–0284–1	200
November 11, 2018	Sacramento T Street	06–067–0010–4	176
November 12, 2018	Sacramento T Street	06–067–0010–4	183
November 14, 2018	Sacramento T Street	06–067–0010–4	181
November 15, 2018	Sacramento T Street	06–067–0010–4	292
November 16, 2018	Sacramento T Street	06–067–0010–4	252
November 16, 2018	North Highlands	06–067–0002–1	163
November 16, 2018	Del Paso Manor	06–067–0006–1	166
November 16, 2018	Del Paso Manor	b  06–067–0006–2	163
a  The last number in the AQS ID is the Parameter Occurrence Code (POC) and distinguishes between different monitors at the same site.
b  The Del Paso Manor (POC 2) monitor is a collocated monitor used for quality assurance purposes. Data from this monitor are not used for comparison to the NAAQS. However, for completeness, CARB, SMAQMD, and the EPA have included this monitor in the demonstration and concurrence process.
Source: Second 10-Year Maintenance Plan, Table 2–5.

The demonstration submitted by CARB and SMAQMD provides a narrative conceptual model to describe how emissions from the Camp Fire, in Butte County, California, caused the PM₁₀ exceedances at the listed monitoring sites on the listed dates. The narrative conceptual model includes a description of the Camp Fire and its progression, the general meteorological conditions in the affected area, and information regarding how PM₁₀ concentrations measured during this period compared to normal conditions across the Sacramento Valley. To support a clear causal relationship between the wildfire event and the monitored exceedances, the demonstration includes several analyses, specifically including the following: comparison with historical PM₁₀ concentrations; Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) analysis; satellite imagery of smoke; ceilometer data; ^[21] regional patterns of PM₁₀ concentrations and PM air quality index (AQI) values; fine particulate matter (PM_2.5 ) concentrations and comparison with historical data; concurrent increases in carbon monoxide, black carbon, and organic carbon concentrations; media reports of wildfire smoke affecting the monitoring area; and District-issued air quality advisories.^[22] The documentation also demonstrates that the wildfire event was not reasonably controllable and not reasonably preventable.^[23] Furthermore, the Camp Fire event meets the definition of a natural wildfire event, defined in 40 CFR 50.1(n) as “a wildfire that predominantly occurs on wildland.” ^[24]

In addition to the technical demonstration requirements, there are timing and procedural requirements an air agency must follow to request data exclusion. The demonstration submitted by CARB includes evidence of the following: SMAQMD provided prompt public notification of the events, CARB submitted an Initial Notification of Potential Exceptional Event in the EPA's AQS system ^[25] and met the deadline requirements for these submissions, and the District allowed for a documented public comment period in which feedback from the public was solicited, collected, submitted to the EPA, and considered along with the submission of the demonstration.

The EPA reviewed and concurred on the documentation provided by CARB and SMAQMD to support claims that the Camp Fire caused exceedances of the PM₁₀ NAAQS at the Sacramento T Street, North Highlands, Del Paso Manor, and Sacramento Branch Center monitoring sites on November 10–12 and November 14–16, 2018.^[26] The demonstration prepared by SMAQMD and submitted by CARB meets all criteria required by 40 CFR 50.14 (c)(3)(iv). Furthermore, the submittal satisfied all schedule and procedural requirements specified in 40 CFR 50.14(c) and 40 CFR 51.930. Thus, the EPA is relying on calculated values that exclude the event-influenced data for the purpose of demonstrating continued attainment of the PM₁₀ NAAQS. With the exclusion of the wildfire-related exceedances in 2018, the 2019 design value is no longer in violation of the PM₁₀ NAAQS.

EPA concurrence is a preliminary step in the regulatory process for actions that may rely on these data and does not constitute final agency action. Regulatory actions that rely on the exclusion of exceptional event data require the EPA to provide an opportunity for public comment on the technical basis of the proposed action, including the claimed exceptional events and all supporting data prior to the EPA taking final agency action. This proposed action provides the public with an opportunity to comment on the claimed exceptional events for the 2018 exceedances in Sacramento County and all supporting documents submitted by CARB, and the EPA's concurrence with the State's request with regards to our proposed action to approve the Second 10-Year Maintenance Plan.

C. Exceedances Occuring After the 2019 Design Value Period

In order to ensure that the area has continued to attain the standard after 2017–2019 design value period on which the Plan is based, the District calculated the 2020 design value (based on 2018–2020 data), and we independently calculated the 2021 and 2022 design values (based on 2019–2021, and 2020–2022 data, respectively). In all cases the design values are above the standard.^[27] The 2020 exceedances associated with these violations were initially flagged in AQS by SMAQMD as wildfire related and the District included information with the Plan to support these claims.^[28] Appendix A in the Second 10-Year Maintenance Plan (“Analysis of PM₁₀ Exceedance Days in 2020”) provides a conceptual narrative demonstrating how wildfire smoke also contributed to the PM₁₀ exceedances in 2020. Between September 8, 2020, and September 13, 2020, there was a total of seven recorded exceedances among all monitoring sites located within the county at the time,^[29] accounting for all exceedances recorded in 2020. Table 3 of this document summarizes the exceedances recorded during this period.

Table 3—Sacramento County PM ₁₀ NAAQS Exceedance Summary for 2020

Exceedance date	Monitoring station	AQS ID a	PM 10 (µg/m3 )
September 8, 2020	Sacramento T Street	06–067–0010–4	298
September 11, 2020	Sacramento T Street	06–067–0010–4	231
September 12, 2020	Sacramento T Street	06–067–0010–4	186
September 12, 2020	Del Paso Manor	06–067–0006–1	186
September 12, 2020	Del Paso Manor	b  06–067–0006–2	188
September 12, 2020	North Highlands	06–067–0002–1	187
September 12, 2020	Sacramento—Branch Center	06–067–0284–1	201
September 13, 2020	Sacramento T Street	06–067–0010–4	169
a  The last number in the AQS ID is the Parameter Occurrence Code (POC) and distinguishes between different monitors at the same site.
b  The Del Paso Manor (POC 2) monitor is a collocated monitor for quality assurance purposes, and the data from this monitor is not used for comparison to the NAAQS. However, for completeness, CARB, SMAQMD, and the EPA included this monitor in the demonstration and concurrence process.
Source: Second 10-Year Maintenance Plan, Table A–1.

Similar to the exceptional event demonstration for the 2018 exceedances, Appendix A documents several wildfires in the vicinity of Sacramento County that were active during 2020 and attributes emissions from these wildfires, concurrent with wind gust events, as having caused the PM₁₀ exceedances listed in Table 3. ³⁰ The appendix includes an overview of the wildfires active at the time of the exceedances, including the start and containment dates, the geographic proximity and range of each wildfire, and fire containment levels during the date range of the exceedances. To support a clear causal relationship between these wildfire events, wind gusts, and the monitored exceedances, Appendix A includes several analyses including the following: HYSPLIT analysis; satellite imagery of smoke; regional patterns of PM₁₀ concentrations and PM AQI; PM_2.5 concentrations and comparison with historical data; concurrent increases in carbon monoxide, black carbon, and organic carbon concentrations; as well as media reports of wildfire smoke affecting the monitoring data. In addition, the District notes that the wildfires listed in Table A–2 of Appendix A were either a result of lightning strikes or were still under investigation, and the District contends these wildfire events were not reasonably controllable and not reasonably preventable. Therefore, in lieu of an exceptional event demonstration, the EPA proposes to find that this information provided in Appendix A of the Plan indicates that the 2020 exceedances were caused by uncontrollable wildfire smoke and wind gusts.

Because SMAQMD and CARB did not submit an exceptional event demonstration for the 2020 exceedances from wildfires, we have factored these exceedances into design value calculations, and the post-2019 design values (2020, 2021, and 2022) remain in violation of the PM₁₀ NAAQS, as summarized in Table 4 of this document. However, after reviewing the evidence provided by the District demonstrating that the exceedances in 2020 were caused by a combination of uncontrollable wildfire smoke and wind gust events, and therefore separate from trends in the ambient air quality for PM₁₀, we propose to find that these exceedances do not call into question the EPA's proposed approval of the Second 10-Year Maintenance Plan as providing for maintenance of the PM₁₀ NAAQS. No exceedances were recorded in 2021, nor 2022, lending additional support to the claim that the 2020 exceedances were caused by uncontrollable wildfire smoke and wind gust events. We find that these data are consistent with the EPA's proposed approval of the Second 10-Year Maintenance Plan as providing for maintenance of the PM₁₀ NAAQS. Prior to finalizing this action, we will examine all quality-assured and certified PM₁₀ monitoring data available to ensure this trend persists or that the District has implemented its contingency plan to address any exceedances.

Table 4—Sacramento County PM ₁₀ Monitor Design Values With 2018 Exceptional Events Exceedances Removed

Design value period	Monitoring site
	North Highlands	Del Paso Manor	Sacramento T Street a	Sacramento Branch Center
2011–2013	0.0	0.0		0.0
2012–2014	0.0	0.0		0.0
2013–2015	0.0	0.0		0.0
2014–2016	0.0	0.0	0.0	0.0
2015–2017	0.0	0.0	0.0	0.0
2016–2018	0.0	0.0	0.0	0.0
2017–2019	0.0	0.0	0.3	0.0
2018–2020	1.9	1.9	1.7	2.6
2019–2021	1.9	1.9	1.7	2.6
2020–2022	1.9	1.9	1.3	2.6
a  The Sacramento T Street monitoring station came into active use in 2013. (North Highlands AQS Site ID #:06–067–0002–1; Del Paso Manor (primary) AQS Site ID #: 06–067–0006–1; Sacramento T Street AQS Site ID #: 06–067–0010–4; Sacramento Branch Center AQS Site ID #: 06–067–0284–1).
Source: TSD for EPA Concurrence on PM 10 Exceedances Measured in Sacramento County on Nov 10–12 and Nov 14–16 as EE, found within the docket for this rulemaking.

III. The Second 10-Year Maintenance Plan Submittal and Procedural Requirements

CAA section 175A(b) requires states to submit a SIP revision to maintain the NAAQS for an additional ten years after the expiration of the 10-year period covered by the initial maintenance plan. The submittal is due eight years after the original redesignation request and maintenance plan was approved. The deadline to submit the SIP revision for the Sacramento County PM₁₀ NAAQS maintenance area was October 28, 2021. On October 21, 2021, CARB submitted the “Second 10-Year PM₁₀ Maintenance Plan for Sacramento County” (“Second 10-Year Maintenance Plan” or “Plan”) to meet the requirement for a subsequent maintenance plan under CAA section 175A(b).^[31] The Second 10-Year Maintenance Plan is intended to provide for continued maintenance of the PM₁₀ NAAQS for the 10-year period following the end of the first 10-year period, i.e., from 2024 through 2033.

In addition, CAA sections 110(a)(1), (2), and 110(l) require states to provide reasonable notice and opportunity for public hearing prior to adoption and submission of a SIP or SIP revision. To meet these procedural requirements, every SIP submission should include evidence that the state provided adequate public notice and opportunity for a public hearing consistent with the EPA's implementing regulations in 40 CFR 51.102. CARB's October 21, 2021 SIP submittal package includes documentation of the public processes used by the District and CARB to adopt the Second 10-Year Maintenance Plan. Prior to adoption of the plan, a reasonable notice of a public hearing was provided to the public, and a public hearing was conducted. Specifically, notices of a public hearing and the opening of a comment period for the Second 10-Year Maintenance Plan for Sacramento County were published within the “News and Notices” section of the District's website on July 23, 2021, in advance of the August 26, 2021 public hearing.^[32] No comments were received during the District's comment period.^[33] Following the adoption of a resolution to approve the Second 10-Year Maintenance Plan,^[34] the District requested that CARB review and adopt the Plan.^[35] On August 13, 2021, CARB published on its website a notice of a public hearing to be held on September 23, 2021, to consider adoption of the District's Plan.^[36] No comments were received during CARB's public comment period. CARB adopted the Plan,^[37] and subsequently submitted it to the EPA as a revision to the California SIP on October 21, 2021. Based on the documentation provided in the Second 10-Year Maintenance Plan submittal, we propose to find that the SIP revision satisfies the public notice procedural requirements of the Act.

Section 175A of the CAA provides the general framework for a maintenance plan. The initial 10-year maintenance plan must provide for maintenance of the NAAQS for at least 10 years after redesignation, including any control measures necessary to ensure such maintenance. In addition, maintenance plans are to contain contingency provisions necessary to ensure the prompt correction of a violation of the NAAQS that may occur after redesignation. The contingency measures must include, at a minimum, a requirement that the state will implement all control measures contained in the nonattainment SIP prior to redesignation. Beyond these provisions, section 175A of the CAA does not define the content of a second 10-year maintenance plan.

The primary guidance on maintenance plans and redesignation requests is the September 4, 1992 memorandum from John Calcagni, titled “Procedures for Processing Requests to Redesignate Areas to Attainment” (“Calcagni Memo”).^[38] The Calcagni Memo outlines the key elements of a maintenance plan, which include the following: attainment emissions inventory, maintenance demonstration, monitoring network requirements, verification of continued attainment, and contingency plan elements. We are evaluating the Second 10-Year Maintenance Plan based on the satisfactory fulfillment of these and all relevant procedural requirements of the CAA.

IV. Evaluation of the Second 10-Year Maintenance Plan

A. Emissions Inventory

A maintenance plan for the PM₁₀ NAAQS should include a comprehensive, accurate, and current emissions inventory of all sources of relevant pollutants in the area, to identify a level of emissions sufficient to attain the PM₁₀ NAAQS. The inventory should include emissions from stationary point sources, area sources, and mobile sources and must be based on actual emissions during the appropriate season, if applicable.^[39] This emissions inventory should be consistent with the EPA's most recent guidance available at the time and should represent emissions during the time period associated with the monitoring data showing attainment, in this case 2017–2019. The specific PM₁₀ emissions inventory requirements are set forth in the Air Emissions Reporting Requirements rule.^[40] The EPA has provided additional guidance for developing PM₁₀ emissions inventories in “PM₁₀ Emissions Inventory Requirements,” ^[41] and “Emissions Inventory Guidance for Implementation of Ozone and Particulate Matter National Ambient Air Quality Standards (NAAQS) and Regional Haze Requirements” (May 2017).

The SMAQMD Second 10-Year Maintenance Plan includes inventories for total primary PM₁₀ and nitrogen oxide pollutants (NO_X) in the County for the years 2017, 2024, 2027, and 2033. NO_X emissions are discussed in this plan due to the significant contribution of NO_X as a precursor pollutant, especially toward wintertime ambient PM₁₀ concentrations, as demonstrated in the first maintenance plan by a chemical mass balance (CMB) study of PM₁₀ pollution in the County.^[42] Additionally, detailed emissions inventory data for sulfur oxides (SO_X) are not included, but SO_X emissions remain stable throughout the second maintenance period at about 1 ton per day (tpd).^[43] The Plan also states that volatile organic compounds (VOCs) are not identified in the CMB study analysis performed for the First Maintenance Plan as contributing to the PM₁₀ concentrations and therefore are not included in the emissions inventory. The District selected the inventory years to include the base year emissions inventory (2017), an inventory for the first year of the second maintenance period (2024), an interim year inventory (2027), and an inventory for the end of the second maintenance period (2033). The base year is the first year of the Plan's design value. Projected emissions inventories for future years must account for, among other factors, the ongoing effects of economic growth and adopted emissions control requirements, and the inventories are expected to be the best available representation of future emissions. The Plan includes emissions estimates from all the relevant stationary point, area, and mobile source categories, and further divides these main categories into more descriptive subcategories. As these emissions forecasts consider expected emissions reductions to the base year inventory resulting from adopted control measures, they similarly consider potential emissions increases, such as those associated with emissions reduction credits (ERCs). ERCs are allowances earned through voluntary pollutant emissions reductions such as equipment shutdowns or voluntarily installed controls. Emissions within the Plan are listed for an average winter day when concentrations were shown to be seasonally elevated. The SMAQMD analysis demonstrates a seasonal occurrence of higher ambient PM₁₀ concentrations in the fall and winter months.^[44] The District finds that this trend is a result of increased residential wood combustion, in conjunction with winter weather conditions conducive to PM₁₀ pollutant build up ( e.g., greater atmospheric stability, low wind dispersion, and colder temperatures).

The emissions inventories used in the Plan are from CARB's California Emissions Projection Analysis Model (CEPAM): CEPAM 2019: External Adjustment Reporting Tool—Version 1.02. Because the Second 10-Year Maintenance Plan depends on both PM₁₀ and NO_X emissions to demonstrate continued compliance (discussed in further detail in Sections III.C and D of this document), the EPA reviewed both PM₁₀ and NO_X emissions inventories.

Direct PM₁₀ and NO_X emissions estimates for stationary point sources reflect actual emissions reported to the District by owners or operators of industrial point sources in the Sacramento County planning area. This category is primarily composed of fuel combustion, waste disposal, petroleum production and marketing, and other industrial processes. Areawide sources, such as consumer products and agricultural burning, occur over a wide geographic area. Emissions for these categories are calculated from fuel usage, product sales, population, employment data, and other parameters for the pertinent range of activities across Sacramento County.

Emissions from on-road mobile sources, which include passenger vehicles, buses, and trucks, were estimated using outputs from CARB's EMFAC2017 model.^[45] Emissions inventories for aircraft, trains, boats, and off-road vehicles and equipment used for construction, farming, commercial, industrial, and recreational activities were included in the “Other Mobile” category.

The direct PM₁₀ emissions for the base year emissions inventory are presented within Table 5 of this document.

Table 5—Sacramento County Direct PM ₁₀ 2017 Base Year Emissions

[Tons per average winter day]

Source category	Subcategory	2017	2024	2027	2033
Stationary Point Sources	Fuel Combustion	0.26	0.24	0.25	0.24
	Waste Disposal	0.02	0.02	0.02	0.02
	Industrial Processes	1.14	1.18	1.31	1.35
Areawide	Residential Fuel Combustion	9.15	8.97	8.89	8.83
	Farming Operations	1.25	1.16	1.12	1.06
	Construction and Demolition	9.42	9.57	10.60	11.29
	Paved Road Dust	7.69	8.25	8.52	9.15
	Unpaved Road Dust	0.65	0.62	0.61	0.59
	Managed Burning and Disposal	0.16	0.17	0.17	0.16
	Cooking	0.88	0.94	0.96	1.00
	Fires	0.06	0.07	0.07	0.07
	Fugitive Windblown Dust	0.11	0.11	0.10	0.10
	Asphalt Paving/Roofing	0.01	0.01	0.01	0.01
On-Road Motor Vehicles		2.24	2.08	2.15	2.22
Other Mobile	Aircraft	0.07	0.08	0.08	0.08
	Trains	0.02	0.02	0.02	0.02
	Equipment (Off-Road/Farm)	0.29	0.20	0.17	0.15
	Recreational Boat	0.13	0.09	0.08	0.07
	Commercial Harbor Craft	0.01	0.01	0.01	0.01
	Off-road Recreational Vehicles	<0.01	<0.01	<0.01	<0.01
Total	All Stationary, Areawide, and Mobile Sources	33.58	33.78	35.15	36.43
Source: Second 10-Year Maintenance Plan, Table 3–1.

The direct NO_X emissions for the base year emissions inventory are presented within Table 6 of this document.

Table 6—Sacramento County NO _X 2017 Base Year Emissions

[Tons per average winter day]

Source category	Subcategory	2017	2024	2027	2033
Stationary Point Sources	Fuel Combustion	1.93	1.78	1.80	1.80
	Waste Disposal	0.07	0.07	0.08	0.08
	Industrial Processes	0.24	0.25	0.27	0.28
	Petroleum Processing and Marketing	<0.01	<0.01	<0.01	<0.01
Areawide	Residential Fuel Combustion	3.83	3.75	3.76	3.81
	Managed Burning and Disposal	0.06	0.06	0.06	0.05
	Fires	0.01	0.01	0.01	0.01
On-Road Motor Vehicles		21.45	10.66	9.33	7.46
Other Mobile	Aircraft	1.75	1.98	2.08	2.30
	Trains	0.85	0.99	1.02	1.05
	Equipment (Off-Road/Farm)	5.00	3.42	2.97	2.69
	Recreational Boat	0.39	0.36	0.35	0.34
	Commercial Harbor Craft	0.25	0.23	0.22	0.19
	Off-road Recreational Vehicles	0.01	0.01	0.01	0.01
Total	All Stationary, Areawide, and Mobile Sources	35.84	23.57	21,96	20.08
Source: Second 10-Year Maintenance Plan, Table 3–2.

Based on the estimates for the year 2017 in Table 5, areawide sources account for a majority (approximately 88 percent) of the total PM₁₀ emissions in the Sacramento County planning area. Residential fuel combustion, construction and demolition, and paved road dust account for the majority of the areawide emissions (approximately 89 percent). The future year emissions estimates in the Plan predict an increase in direct PM₁₀ emissions within the Sacramento County planning area over the second ten-year planning period. The main source of the overall predicted increase of PM₁₀ emissions is increased emissions of areawide sources, with increases from stationary source emissions also acting as a minor contributor to the overall trend (0.20 tpd). By 2033, total direct PM₁₀ emissions are estimated to be approximately 2.85 tpd (8.5 percent) higher than in the 2017 base year. These projected increases in PM₁₀ emissions are associated with increases in industrial activity and vehicle miles traveled (VMT) from expected population growth in the county.

For precursor NO_X emissions estimates, the Plan predicts an overall decrease of 15.8 tpd (44 percent) between the base year of 2017 and 2033. Reductions to the On-Road Motor Vehicle subcategory, the most significant contributor to total NO_X emissions, is the primary cause of this trend. Implementation of federal, state, and local regulations, including fleet turnover, result in a 14.0 tpd reduction in associated NO_X emissions.

Based on our review of the Second 10-Year Maintenance Plan, we find that the emissions inventories in the Plan are comprehensive in that they include estimates of PM₁₀ and its precursors from all the relevant source categories, which the Plan divides among stationary, areawide, on-road motor vehicles, and other mobile sources. The EPA considers the selection of the 2017 base year inventory to be appropriate given that it was the most recent emissions inventory associated with the reporting schedule required under the Air Emissions Reporting Requirements rule at the time of Plan drafting and because it represents attainment conditions. Moreover, preparation of a seasonal average daily inventory, as opposed to a yearly or episodic inventory, is also appropriate given that elevated PM₁₀ concentrations in Sacramento County exhibit a clear seasonal pattern, with ambient concentrations peaking in the fall and winter months. Additionally, we consider the continued use of the CMB analysis from the first maintenance plan as a technical basis for the emissions inventory to be appropriate as we have found no evidence that it is invalid or inaccurate. Based on our review of the documentation provided with the Plan, we are proposing to find that the 2017 emissions inventory for PM₁₀ and NO_X is based on reasonable assumptions and methodologies, and that the inventory is comprehensive, current, accurate, and consistent with applicable CAA provisions and the Calcagni Memo.

B. Maintenance Demonstration

Section 175A(a) of the CAA requires that the maintenance plan provide for maintenance of the NAAQS for such air pollutant in the area concerned for at least 10 years after the redesignation. A state may generally demonstrate maintenance of the NAAQS by either showing that future emissions of a pollutant or its precursors will not exceed the level of the attainment inventory, or by conducting modeling that shows that the future mix of sources and emissions rates will not cause a violation of the NAAQS.^[46]

The District demonstrates continued maintenance of the PM₁₀ NAAQS in its Second 10-Year Maintenance Plan by using a proportional rollback analysis to show that the future PM₁₀ source concentrations will not cause a violation of the 24-hour PM₁₀ NAAQS. The District's proportional rollback model relies on CMB modeling performed in 1995.^[47] In proportional rollback, each source category's associated proportion of the ambient PM₁₀ contribution scales with the emissions of the category, i.e., the source ambient contribution is “rolled back” according to source emissions reductions. Thus, the Plan aims to demonstrate continued maintenance of the standard by showing that the sum of the individual source category contributions for future years will not exceed the PM₁₀ NAAQS as those source category emissions change.

To determine the source category concentration contributions for future years, the District conducted proportional rollback in two steps. First the State adjusted the 1995 source apportionment (percent contributions) to yield an updated source apportionment for the 2017 base year; then the 2017 source concentrations were projected to future years, including 2033. The ratio of the 2017 base year and the 1995 emissions for each category yields a scaling factor (“2017 Emissions Projection Factor”), to be applied to the 1995 percentage. This provides a growth-adjusted source apportionment for 2017 PM₁₀ . This scaling factor accounts for the various changes in the PM₁₀ source categories that have occurred over the 1995–2017 period. For this purpose, the source categories were broad and included several individual categories with chemically similar emissions; for example, “wood burning” is the sum of Residential Fuel Combustion, Fires, and Managed Burning and Disposal in the California Emissions Projection Analysis Model (CEPAM) 2019 state emissions inventory system. The Plan lists ammonium nitrate, ammonium sulfate, motor vehicles, wood smoke, fugitive dust PM₁₀, and all leftover PM₁₀ from unidentified sources as PM₁₀ “source categories,” identified in the CMB. The growth-adjusted source apportionment percentages for 2017 were then applied to the peak PM₁₀ ambient measurement in 2017 to yield the individual source category concentration contributions for 2017. In a similar manner, projection factors for future years were calculated from the ratio of future emissions estimates and 2017 base year emissions. Those projection ratios were then applied to the 2017 peak measurement source category concentrations to yield the peak source category concentrations for future years, 2024, 2027, and 2033.

Table 7—Predicted Future Maintenance Year Concentrations Based on 2017 Peak Ambient PM ₁₀ Concentration in Sacramento County

PM 10 CMB source category	2017 Peak conc. (µg/m3 )	2024 Peak conc. (µg/m3 )	2027 Peak conc. (µg/m3 )	2033 Peak conc. (µg/m3 )
Ammonium Nitrate	27.1	21.7	20.6	19.6
Ammonium Sulfate	3.3	4.3	4.5	4.5
Motor Vehicles	32.3	29.0	29.4	29.7
Wood Smoke	27.9	27.4	27.2	27.0
Fugitive Dust	25.4	26.1	27.8	29.4
Unidentified Other	27.4	27.8	28.9	30.0
Total PM 10 —Background	144.3	136.4	138.4	140.3
Background	5.7	5.7	5.7	5.7
Total PM 10 (using peak concentration)	149	142	144	146
Source: Second 10-Year Maintenance Plan, p. 5–5, Table 5–4.

Table 7 of this document presents a summary of the predicted peak ambient PM₁₀ concentrations for the future maintenance years for the Second 10-Year Maintenance Plan. The proportional rollback model predicts a decrease of secondary ammonium nitrate PM₁₀ due to the decrease in NO_X emissions.^[48] This decrease offset the increases in other PM₁₀ source categories such as ammonium sulfate and fugitive dust for the duration of the second maintenance period. The resulting projections for the future 24-hour PM₁₀ concentrations were calculated to be 142 µg/m^[3] for 2024, 144 µg/m^[3] for 2027, and 146 µg/m^[3] for 2033, all of which demonstrate continued attainment of the PM₁₀ NAAQS of 150 µg/m^[3] . As discussed in Section 2.3.1 of the Plan, the peak concentration in 2017 was suspected to be influenced by natural events and may not represent ambient conditions in Sacramento.^[49] The District states that this is supported by CARB flagging the data with an informational flag, which indicated the data may have been influenced by wildfire.^[50]

Based on our review, we propose to find that the proportional rollback analysis performed to demonstrate continued attainment of the PM₁₀ NAAQS for the years 2017 through 2033 is based on reasonable methods, growth factors, and assumptions, and is based on the most current and accurate information available to CARB and SMAQMD at the time of plan drafting and inventory development. Given that the projections of combined PM₁₀ sources show continued attainment through 2033, we are proposing to find that the Second 10-Year Maintenance Plan provides an adequate basis to demonstrate maintenance of the PM₁₀ NAAQS within the Sacramento County planning area. Lastly, we propose to find that by providing projected peak concentrations through 2033, the Plan demonstrates maintenance of the PM₁₀ NAAQS for more than 10 years after the expiration of the first 10-year maintenance plan ( i.e., 2023), in accordance with section 175A(b) of the CAA.

C. Monitoring Network Requirements

Following redesignation, the EPA determines whether an area's air quality is maintaining compliance with the PM₁₀ NAAQS based upon complete, quality-assured, and certified data gathered at established state and local air monitoring stations (SLAMS) in the nonattainment area and entered in the EPA AQS database.^[51] SLAMS monitors produce data to be compared to the NAAQS, using an approved federal reference method (FRM), federal equivalent method (FEM), or an approved regional method. Data from air monitors operated by state, local, or tribal agencies in compliance with EPA monitoring requirements must be submitted to AQS. These monitoring agencies certify annually that these data are accurate to the best of their knowledge. Accordingly, the EPA relies primarily on data in AQS when determining the attainment status of an area.^[52] All valid data are reviewed to determine the area's air quality status in accordance with 40 CFR part 50, Appendix K.

SMAQMD and CARB work together to monitor ambient air quality in Sacramento County and to submit annual monitoring network plans to the EPA. The annual monitoring network plans submitted to the EPA describe the air monitoring network operated by the District and CARB and its status, as required under 40 CFR 58.10. Once received, the EPA reviews these annual monitoring network plans for compliance with the applicable reporting requirements in 40 CFR part 58. The EPA examined the Sacramento-Roseville-Folsom Metropolitan Statistical Area (MSA), in which Sacramento County is located, to determine if the MSA currently meets the requirements for the minimum number of SLAMS for PM₁₀ based on the MSA population and air quality as described in 40 CFR 58, Appendix D. EPA regulations require six to ten PM₁₀ monitors in an MSA with the population and air quality of the Sacramento-Roseville-Folsom MSA. At the time the District drafted the Plan and through July 31, 2022, there were eight monitoring sites in the MSA, four of which were in Sacramento County. In 2022, the North Highlands monitoring station in Sacramento County, which produced air pollution data through 2021 and part of 2022, was closed.^[53] Because we are evaluating the continued maintenance of the area using design values through 2022, we include discussion of the four monitoring sites. However, our evaluation of the adequacy of the monitoring network is based on the number of operational monitoring sites at the time of this rulemaking. With the temporary shutdown of the North Highlands monitoring site, the Sacramento-Roseville-Folsom MSA is operating a total of seven monitors; thus, the MSA meets the minimum monitoring requirements.

During the 2017–2019 design value period covered by the Plan, SMAQMD operated SLAMS monitors at three sites within Sacramento County (North Highlands, Del Paso Manor, and Sacramento Branch Center), and CARB operated a SLAMS monitor at one site (Sacramento T Street). Except for the North Highlands monitor, these monitors continue to operate. The Del Paso Manor monitoring site contains two collocated FRM monitors, while the Sacramento Branch site has, and the North Highlands site had, one FRM monitor each. The Sacramento T Street monitoring site has a single FEM monitor. The schedule for PM₁₀ sample collection is one in six days for the FRM filter-based high-volume samplers (Del Paso Manor, Sacramento Branch, and North Highlands monitoring site), while the FEM monitor operates on a daily 24-hour schedule (Sacramento T Street monitoring site).

SMAQMD and CARB jointly commit to continuing to operate a regulatory monitoring network in accordance with 40 CFR part 58 and the California SIP, to verify the attainment status of the area. The Plan contains provisions for the continued operation of air quality monitors that will provide such verification. These provisions include maintaining the operational procedures of data collection, routine calibrations, pre-run and post-run test procedures, and routine service checks. Continued adherence to the annual network plan and annual reviews of the entire air quality monitoring network will be performed to determine if the network is effectively meeting the objectives of the monitoring program. Furthermore, SMAQMD documents any modifications of its monitoring network in its annual network plan that is submitted and reviewed annually by the EPA.^[54]

Therefore, the EPA proposes to determine that the Second 10-Year Maintenance Plan contains adequate provisions for continued operation of an air quality monitoring network and a commitment to annually verify continued attainment of the PM₁₀ NAAQS for Sacramento County.

D. Verification of Continued Attainment

Once an area has been redesignated, the state should continue to operate an appropriate air quality monitoring network, in accordance with 40 CFR part 58, to verify the continued attainment status of the area.^[55] Data collected by the monitoring network during this time are also needed to implement the contingency provisions of the maintenance plan.

As discussed in Section IV.C of this document, SMAQMD monitors ambient concentrations of PM₁₀ in the Sacramento County planning area at three separate monitoring stations. In Section 5.5 of the Second 10-Year Maintenance Plan, the District commits to continue to operate a PM₁₀ ambient monitoring network to track maintenance of the PM₁₀ standard in accordance with 40 CFR part 58. The EPA also recommends that the state verify continued attainment through methods supplementary to the ambient air monitoring program, e.g., through periodic review of the factors used in the development of the attainment inventory to track any significant change.^[56] In the Second 10-Year Maintenance Plan, SMAQMD commits to perform periodic reviews of the air monitoring data and assumptions used to develop the emissions inventory as part of its effort to verify that the County will continue to meet the 24-hour PM₁₀ NAAQS. We are therefore proposing to determine that the Second 10-Year Maintenance Plan contains adequate provisions for continued ambient PM₁₀ monitoring and for periodic review of emissions inventory development assumptions to ensure the continued attainment through the maintenance period.

E. Contingency Provisions

Section 175A(d) of the CAA requires that maintenance plans include contingency provisions, as the EPA deems necessary, to promptly correct any violations of the NAAQS that occur after the redesignation of the area. Such provisions must include a requirement that the state will implement all measures with respect to the control of the relevant air pollutants that were contained in the SIP for the area before redesignation of the area as an attainment area. These contingency provisions are distinguished from contingency measures required for nonattainment areas under CAA section 172(c)(9), in that they are not required to be fully adopted measures that take effect without further action by the state. However, the contingency provisions of a maintenance plan are an enforceable part of the SIP and should ensure that contingency measures are adopted expeditiously once they are triggered. The maintenance plan should clearly identify the measures to be adopted, include a schedule and procedure for adoption and implementation of the measures, and contain a specific timeline for action by the state. In addition, the state should identify the specific indicators or triggers that will be used to determine when the contingency measures need to be implemented.

The District has adopted a contingency plan to address possible future PM₁₀ air quality problems in the Sacramento County planning area. The contingency plan is included in Section 6 of the Plan. As noted by the District in the Second 10-Year Maintenance Plan, contingency measures are to be triggered to promptly correct any violation of the standard that occurs during the maintenance period. In this case, these contingency measures will be triggered when the number of monitored exceedances, averaged over three years, is greater than 1.05. However, the contingency plan also includes a detailed screening process that allows the District and CARB, subject to EPA review and agreement, to exclude exceedances from the trigger calculation if the agencies collectively determine that information developed by the District is sufficient to support exclusion. The purpose of the screening process is to differentiate between exceedances that are not within the District's or State's control ( i.e., exceedances that occur despite the implementation of reasonable measures), and exceedances that are within the District's or State's control and therefore should be included in the trigger calculation. Should the District or State exclude an exceedance from the contingency trigger calculation using this process, it would not constitute the EPA's concurrence that the exceedance was caused by an exceptional event. The exceedance would therefore continue to be included in design value calculations for the planning area, unless CARB, following opportunity for public comment, submits a request for the EPA to concur on the exceedance as an exceptional event pursuant to 40 CFR 50.14, and the EPA reviews the submittal and formally concurs.

Under the contingency trigger screening process described in the Plan, the District will analyze any exceedance(s) within the District's or State's control that leads to a violation of the NAAQS on a quarterly basis, in order to determine the possible causes and take appropriate action.^[57] The District will evaluate future emissions reductions from already-adopted rules to determine if those reductions would be sufficient to correct any exceedance(s). These rules could include previously-adopted CARB or District PM₁₀ or NO_X measures used to address ozone or PM₁₀ SIP requirements. Should the additional reductions resulting from these measures be insufficient to correct the exceedance(s), the District has committed to consider the implementation of new rules and/or modifications to existing rules that would bring the area back into maintenance.^[58] The District will complete its analysis of the exceedance(s) that caused the violation and evaluate the most appropriate control measures to adopt or implement within 6 months of identifying the violation. This is followed by a 12-month period, in which the District will adopt and implement the control measures identified from this process to achieve the necessary reductions. In total, the District will act to implement the contingency measures within 18 months of a violation of the PM₁₀ NAAQS. Based on our review of the Second 10-Year Maintenance Plan, we propose to find that the contingency provisions of the Plan clearly identify potential contingency measures, contain a triggering mechanism to determine when contingency measures are needed, contain a description of the process of recommending and implementing contingency measures, and contain specific and appropriate timelines for action. We also propose to find that the contingency trigger screening process, including the associated EPA review, is reasonably designed to distinguish between exceedances that were not within the District or State control, and exceedances that were within the District or State control and for which new or tightened control measures might be effective. Thus, we propose to conclude that the contingency plan in the Plan is adequate to ensure correction of any violation of the PM₁₀ NAAQS that occurs after redesignation, as required by section 175A(d) of the CAA.

F. Motor Vehicle Emissions Budgets for Transportation Conformity

Section 176(c) of the CAA requires federal actions in nonattainment and maintenance areas to conform to the SIP's goals of eliminating or reducing the severity and number of violations of the NAAQS and achieving expeditious attainment of the standards. Conformity to the SIP's goals means that such actions will not: (1) cause or contribute to violations of the NAAQS, (2) worsen the severity of an existing violation, or (3) delay timely attainment of any NAAQS or any interim milestone.

Actions involving Federal Highway Administration (FHWA) or Federal Transit Administration (FTA) funding or approval are subject to the EPA's transportation conformity rule codified at 40 CFR part 93, subpart A. Under this rule, metropolitan planning organizations (MPOs) in nonattainment and maintenance areas coordinate with state and local air quality and transportation agencies, the EPA, FHWA, and FTA to demonstrate that an area's regional transportation plans and transportation improvement programs conform to the applicable SIP. This demonstration is typically done by showing that estimated emissions from existing and planned highway and transit systems are less than or equal to the budgets contained in submitted or approved control strategy SIPs and maintenance plans.^[59]

These control strategy SIPs and maintenance plans typically set budgets for criteria pollutants and/or their precursors to address pollution from on-road vehicles such as cars and trucks. Budgets are generally established for specific years for those specific pollutants or precursors. PM₁₀ maintenance plan submittals must identify budgets for transportation related PM₁₀ emissions for the last year of the maintenance period.^[60]

For budgets in a maintenance plan to be approvable, they must meet, at a minimum, the EPA's adequacy criteria.^[61] To meet these requirements, the budgets must be consistent, when considered with emissions from all other sources, with maintenance of the NAAQS and reflect all the motor vehicle control measures relied upon for the maintenance demonstration.

The EPA also determines the adequacy of budgets in certain submitted SIPs. The adequacy process is separate from the approval process. The EPA's process for determining adequacy of a budget consists of three basic steps: (1) notifying the public of a SIP submittal, (2) providing the public the opportunity to comment on the budget during a public comment period, and (3) making a finding of adequacy or inadequacy. The process for determining the adequacy of a submitted budget is codified at 40 CFR 93.118(f). The EPA can notify the public by either posting an announcement that the EPA has received SIP budgets on the EPA's adequacy website,^[62] or via a Federal Register notice of proposed rulemaking when the EPA reviews the adequacy of a maintenance plan budget simultaneously with its review and action on the SIP submittal itself.^[63]

The Second 10-Year Maintenance Plan includes budgets for direct PM₁₀ and NO_X, on an average winter day, for the first year of the maintenance plan (2024), an interim year (2027), and the last year (2033) of the maintenance plan. The applicable source categories within the budget for PM₁₀ include direct exhaust (includes tire and brake wear), transportation related (road) construction emissions, re-entrained paved and unpaved road dust. NO_X budgets are based on combustion activity from on-road motor vehicles. In developing the budgets, the District also rounded up the motor vehicle emissions estimates to the nearest tenth of a ton and included a safety margin of 0.5 tpd of NO_X to the 2024 NO_X budgets.^[64] The conformity budgets for these categories and years are provided in Table 8 of this document.

Table 8—Transportation Conformity Budgets for the Sacramento County PM ₁₀ Area

[PM ₁₀ tons per average winter day]

Source category	2024		2027		2033
	NO X	PM 10	NO X	PM 10	NO X	PM 10
Vehicular Exhaust a (includes tire and break wear for PM 10 )	10.68	2.09	9.57	2.17	8.30	2.27
Re-Entrained Paved Road Dust b (Total)	N/A	8.25	N/A	8.52	N/A	9.15
Re-Entrained Unpaved Road Dust (City and Country Roads)	N/A	0.62	N/A	0.61	N/A	0.59
Road Construction Dust	N/A	3.65	N/A	4.04	N/A	4.31
Safety Margin	0.5	N/A	N/A	N/A	N/A	N/A
Total c	11.18	14.62	9.57	15.34	8.30	16.32
Motor Vehicle Emissions Budgets d	11.2	14.7	9.6	15.4	8.4	16.4
a  This reflects the adjustment factor for SAFE Vehicle Rule using EMFAC 2017.
b  Paved road dust was not measured directly and is based on CARB's Miscellaneous Process Methodology, which computed paved road dust using the emission factor equation provided by EPA's AP–42: Compilation of Air Emissions Factors document.65
c  Values from California Emissions Projection Analysis Model (CEPAM) 2019: External Adjustment Reporting Tool Version 1.02 may not add up due to rounding.
d  This reflects the adjustment factor for SAFE Vehicle Rule using EMFAC 2017.
Source: Second 10-Year Maintenance Plan, Table 7–1, extracted from CEPAM 2019: External Adjustments Reporting Tool Version 1.02 and EMFAC2017.

The District, the Sacramento County MPO, and CARB jointly developed the budgets, taking into consideration the expected population-related growth trends for the county since the first maintenance plan. Specifically, Sacramento Council of Governments (SACOG), the MPO for the six county Sacramento region,^[66] used both the Sacramento Activity-Based Simulation Model (SACSIM) program and data contained within the 2020 Metropolitan Transportation Plan/Sustainable Communities Strategy (“2020 MTP/SCS”) to develop a travel demand model to forecast VMT for future years within the area.^[67] Transportation activity data from the 2020 MTP/SCS and emissions modeling generated by CARB's EMFAC 2017 model were used to calculate the budgets. CARB further adjusted the budgets in the Plan to account for the Safer Affordable Fuel-Efficient Vehicle Rule Part 1.^[68]

In contrast to PM_2.5, where road dust applies in transportation conformity only if found to be significant or if budgets include it, for PM₁₀ road dust is always considered.^[69] The EPA requires road dust emissions to be included in all transportation conformity analyses of direct PM₁₀ emissions because fugitive dust from roadways and other sources dominate PM₁₀ on-road emissions inventories. The budgets in the Second 10-Year Maintenance Plan, therefore, include paved and unpaved road emissions.

Regional PM₁₀ emissions analyses for transportation conformity determinations in PM₁₀ nonattainment and maintenance areas must also account for highway and transit project construction-related fugitive PM₁₀ emissions if the control strategy or maintenance plan identifies such emissions as a contributor to the air quality problem.^[70] Emissions estimates developed for the Second 10-Year Maintenance Plan show that fugitive PM₁₀ emissions from highway and transit project construction are a significant portion of total regional PM₁₀ emissions for the Sacramento County planning area. Consequently, the budgets in the Plan reflect highway and transit project construction-related fugitive dust.

We evaluated the budgets against our adequacy criteria in 40 CFR 93.118(e)(4) and (5) as part of our review of the budget's approvability. While adequacy and approval are two separate actions, reviewing the budgets in terms of the adequacy criteria informs the EPA's decision to propose to approve the budgets. We have completed our detailed review of the Second 10-Year Maintenance Plan for Sacramento County and are proposing herein to approve the Plan including the demonstration of maintenance of the PM₁₀ NAAQS in the area through the year 2033. We have also reviewed the budgets in the Plan and found that they are consistent with the maintenance demonstration for which we are proposing approval, are clearly identified and precisely quantified, 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 93.118(e)(4) and (5).^[71] For these reasons, the EPA proposes to approve the 2024, 2027, and 2033 budgets in the Second 10-Year Maintenance Plan.

In addition, in this document the EPA is announcing the beginning of the adequacy process for these budgets. Under the transportation conformity regulation, the EPA can begin this process with our proposed action on the second maintenance plan.^[72] The public has 30 days to comment on the adequacy of the budgets, per the transportation conformity rule at 40 CFR 93.118(f)(2)(i) and (ii). Any comments on the adequacy of the budgets should be submitted to the docket for this proposed rulemaking.

When we finalize our proposed approval of the budgets, they must be used by SACOG ( i.e., the MPO for this area) for transportation conformity determinations for the Sacramento County planning area effective upon the publication date of our finalized approval.^[73]

V. Proposed Action and Request for Public Comment

Under CAA section 110(k)(3), and for the reasons set forth in this document, the EPA is proposing to approve the Second 10-Year Maintenance Plan submitted by CARB by letter dated October 21, 2021, as a revision to the California SIP. We are proposing to approve the maintenance demonstration and contingency provisions as meeting all applicable requirements for maintenance plans and related contingency provisions in CAA section 175A, and the motor vehicle emissions budgets for 2024, 2027, and 2033 (shown in Table 8) for transportation conformity purposes, as we propose to find they meet all applicable criteria for such budgets including the adequacy criteria under 40 CFR 93.118(e).

We are soliciting comments on these proposed actions, including our concurrence on the exceptional events demonstration for the 2018 exceedances in Sacramento County as part of the technical basis for the approval of the Second 10-Year Maintenance Plan, as well as the adequacy of the motor vehicle emissions budgets. We will accept comments from the public for 30 days following publication of this proposal in the Federal Register and will consider any relevant comments before taking final action.

VI. 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 that they meet the criteria of the Clean Air Act. Accordingly, this proposed action merely approves state law as meeting federal requirements and does not impose additional requirements beyond those imposed by state law. For that reason, this proposed 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 14094 (88 FR 21879April 11, 2023);

• 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); and
• 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.

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. In those areas of Indian country, this rulemaking 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).

Executive Order 12898 (Federal Actions To Address Environmental Justice in Minority Populations and Low-Income Populations, 59 FR 7629, Feb. 16, 1994) 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. The EPA defines environmental justice (EJ) as “the fair treatment and meaningful involvement of all people regardless of race, color, national origin, or income with respect to the development, implementation, and enforcement of environmental laws, regulations, and policies.” The EPA further defines the term fair treatment to mean that “no group of people should bear a disproportionate burden of environmental harms and risks, including those resulting from the negative environmental consequences of industrial, governmental, and commercial operations or programs and policies.”

The State did not evaluate environmental justice considerations as part of its SIP submittal; the CAA and applicable implementing regulations neither prohibit nor require such an evaluation. The EPA did not perform an EJ analysis and did not consider EJ in this action. If finalized, this action is expected to have a neutral to positive impact on the air quality of the affected area. Consideration of EJ is not required as part of this action, and there is no information in the record inconsistent with the stated goal of E.O. 12898 of achieving environmental justice for people of color, low-income populations, and Indigenous peoples.

List of Subjects in 40 CFR Part 52

• Environmental protection
• Air pollution control
• Incorporation by

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

Dated: September 18, 2023.

Martha Guzman Aceves,

Regional Administrator, Region IX.

Footnotes

1.  52 FR 24634 (July 1, 1987). The EPA established both primary and secondary standards for the annual NAAQS and the 24-hour NAAQS. Primary standards provide public health protection, including protecting the health of “sensitive” populations such as asthmatics, children, and the elderly. Secondary standards provide public welfare protection, including protection against decreased visibility and damage to animals, crops, vegetation, and buildings. The primary and secondary standards were the set at the same level for the annual PM₁₀ NAAQS ( i.e., at 50 μg/m3. ) and for the 24-hour NAAQS ( i.e., at 150 μg/m3. ).

2.  71 FR 61144 (October 17, 2006).

3.  78 FR 3086 (January 15, 2013).

4.  The nonattainment area for PM₁₀ was set as the same boundaries as Sacramento County, 58 FR 67334 (December 21, 1993).

5.  67 FR 7082 (February 15, 2002).

6.  An exceedance is defined as a daily value that is above the level of the 24-hour standard ( i.e., 150 µg/m3. ) after rounding to the nearest 10 µg/m3. ( i.e., values ending in five or greater are to be rounded up.) Thus, a recorded value of 154 µg/m3. would not be an exceedance as it would be rounded to 150 µg/m3. . A recorded value of 155 µg/m3. would be an exceedance because it would be rounded to 160 µg/m3. . 40 CFR part 50, Appendix K, section 1.0.

7.  40 CFR 50.6 and 40 CFR part 50, appendix K. The comparison with the allowable expected exceedance rate of one per year is made in terms of a number rounded to the nearest tenth; e.g., an exceedance rate of 1.05 would be rounded to 1.1, which is the lowest rate for nonattainment. 40 CFR part 50, appendix K, section 2.1(b).

8.  Letter dated December 7, 2010, from James Goldstene, Executive Officer, CARB, to Jared Blumenfeld, Regional Administrator, EPA Region IX.

9.  78 FR 59261 (September 26, 2013).

10.  See EPA AQS Design Value Report, AMP480, for 2011–2022 PM₁₀ Design Values for Sacramento County (Report accessed August 9, 2023), included in the docket for this rulemaking, for full details.

11.  Letter dated March 31, 2021, from Mark Loutzenhiser, Division Manager, Program Coordination Division, SMAQMD, to Richard Corey, Executive Officer, CARB, Subject: “Exceptional Event Demonstration for November 2018 PM₁₀ Exceedances in Sacramento County due to Wildfires.”

12.  72 FR 13560 (March 22, 2007).

13.  81 FR 68216 (October 3, 2016).

14.  40 CFR 50.14(b)(4).

15.  A natural event is further described in 40 CFR 50.1(k) as “[a]n event and its resulting emissions, which may recur at the same location, in which human activity plays little or no direct causal role. For purposes of the definition of a natural event, anthropogenic sources that are reasonably controlled shall be considered to not play a direct role in causing emissions.”

16.  Email dated August 21, 2019, from Sylvia Vanderspek (CARB) to Gwen Yoshimura (EPA Region IX) Subject: “INI Form for Submittal to EPA—SMAQMD PM₁₀.”

17.  See letter dated March 3, 2020, from Elizabeth Adams, Air and Radiation Division Director, EPA Region IX, to Sylvia Vanderspek, Air Quality Planning Branch Chief, CARB.

18.  Letter dated March 31, 2021, from Mark Loutzenhiser, Division Manager, Program Coordination Division, SMAQMD, to Richard Corey, Executive Officer, CARB, Subject: “Exceptional Event Demonstration for November 2018 PM₁₀ Exceedances in Sacramento County due to Wildfires.”

19.  Letter dated April 26, 2021, from David Edwards for Michael Benjamin, Air Quality Planning and Science Division Chief, CARB, to Elizabeth Adams, Air and Radiation Division Director, EPA Region IX, Subject: “Submittal of Final Documentation for 2018 Exceptional Events.”

20.  SMAQMD Exceptional Event Demonstration For November 2018 PM₁₀ Exceedances in Sacramento County Due to Wildfires, March 31, 2021.

21.  A ceilometer measures the attenuated backscatter of light due to gradients in particulate matter or other aerosols.

22.  See Sections 3 and 4, and Appendices A, B, C, and D of the Demonstration for full details.

23.  Id. at pp. 3–1 to 3–3 and Section 5: p. 5–1.

24.  Id. at Section 6: p. 6–1.

25.  SMAQMD Exceptional Event PM₁₀ Initial Notification Summary Information 2016–2018, submitted August 21, 2019.

26.  Details included in “Technical Support Document for EPA Concurrence on PM₁₀ Exceedances Measured in the Sacramento County Maintenance Area on November 10–12 and November 14–16, 2018 as Exceptional Events,” found within the docket for this rulemaking, and letter dated July 27, 2022, from Elizabeth Adams, Director, Air and Radiation Division, EPA Region IX, to Sylvia Vanderspek, Chief, Air Quality Planning Branch and Air Quality Planning and Science Division, CARB, Subject: “EPA Concurrence with EE exclusion of PM₁₀ exceedances on November 10–12 and 14–16, 2018.”

27.  “Second 10-Year PM₁₀ Maintenance Plan for Sacramento County,” Appendix A.

28.  EPA AQS Report of Flagged PM₁₀ Values due to Wildfire Events in Sacramento County, Report Prepared February 13, 2023.

29.  See Section IV.C of the rulemaking for additional details on the present status of the Sacramento County PM₁₀ monitoring network.

30.  During the late summer and early fall of 2020, the Slater/Devils Fire, Red Salmon Complex Fire, August Complex Fire, North Complex Fire (composed of the Baer and Claremont fires), Fork Fire, and the Creek Fire were all active at the time of the exceedances.

31.  Letter dated October 20, 2021, from Richard Corey, Executive Officer, CARB, to Deborah Jordan, Acting Regional Administrator, EPA Region IX (submitted electronically October 21, 2021).

32.  SMAQMD affidavit of publication of “Public Hearing for Approval of the Second 10-Year PM₁₀ Maintenance Plan for Sacramento County” on the District's website on July 23, 2021.

33.  See SMAQMD Transmittal Letter from Mark Loutzenhiser, Division Manager, Program Coordination Division, SMAQMD, to Richard Corey, Executive Officer, CARB, dated September 2, 2021.

34.  SMAQMD Board of Directors Public Hearing and Resolution No. 2021–009 Adopting the “Second 10-Year PM₁₀ Maintenance Plan for Sacramento County,” dated August 26, 2021.

35.  Letter dated September 2, 2021, from Mark Loutzenhiser, Division Manager, Program Coordination Division, SMAQMD, to Richard Corey, Executive Officer, CARB.

36.  CARB Notice of Public Meeting to Consider Sacramento County PM₁₀ Maintenance Plan State Implementation Plan Submittal, dated August 13, 2021.

37.  CARB Board Resolution 21–20: Sacramento County PM₁₀ Maintenance Plan State Implementation Plan Submittal, dated September 23, 2021.

38.  Memorandum dated September 4, 1992, from John Calcagni, Director, Air Quality Management Division, EPA, to Regional Office Air Division Directors, Subject: “Procedures for Processing Requests to Redesignate Areas to Attainment.”

39.  CAA section 172(c)(3).

40.  40 CFR part 51, subpart A.

41.  EPA–454/R–94–033, September 1994.

42.  SMAQMD PM₁₀ Implementation/Maintenance Plan and Redesignation Request for Sacramento County, p. 4–4. Source contributions used in the CMB study were based on a technical paper on wintertime PM_2.5 and PM₁₀ source apportionment for Sacramento (Motallebi, Nehzat. “Wintertime PM_2.5 and PM₁₀ Source Apportionment at Sacramento California.” Air and Waste Management Association, 1999). The CMB study calculated source contributions for ambient air quality samples (>40 μg/m3) collected from November to January for 1991–1996.

43.  Second 10-Year Maintenance Plan, Table 5–1.

44.  Second 10-Year Maintenance Plan For Sacramento County, Section 2.8.

45.  EMFAC is short for EMission FACtor. The EPA approved EMFAC2017 for SIP development and transportation conformity purposes in California on August 15, 2019. 84 FR 41717. EMFAC2017 was the most recently approved version of the EMFAC model that was available at the time of preparation of the Second 10-Year Maintenance Plan.

46.  Calcagni Memo, p. 9–11.

47.  Motallebi, Nahzat. “Wintertime PM_2.5 and PM₁₀ Source Apportionment at Sacramento California.” Air and Waste Management Association [1999]. CMB receptor monitor results from the 1991–1996 wintertime ambient 24-hour PM₁₀ samples from the Sacramento T Street monitor were used to determine a CMB for the 1995 ambient PM₁₀ . The CMB modeling used the chemical components of ambient PM₁₀ concentrations, such as fugitive dust, carbonaceous materials from burning, nitrate, and sulfate, and associated them with broad emissions source categories having those chemical signatures. This is a source apportionment, giving a percent ambient contribution for each source category.

48.  In its analysis, the District applied a scaling factor of 0.7 to reflect the change in ambient ammonium nitrate due to the change in NO_X emissions. i.e., ammonium nitrate concentration changed by 0.7 percent for every 1 percent change in NO_X emissions. This ratio was based on San Joaquin Valley Air Pollution Control District photochemical modeling results. The District cites SJVAPCD, “2007 PM₁₀ Maintenance Plan and Request for Redesignation,” Appendix F. Modeling Analysis, p.61.

49.  The District performed additional proportional rollback analysis using the second highest ambient PM₁₀ value recorded in 2017 (87 µg/m3. ), which yielded predicted peak concentrations for 2024, 2027, 2033 that were substantially lower than those yielded using the highest ambient PM₁₀ concentration for 2017. However, as the future peak values yielded from the peak 2017 concentration already demonstrated continued maintenance, the District did not use this additional rollback analysis to demonstrate continued maintenance of the PM₁₀ NAAQS.

50.  Additional discussion of evidence in support of the impact of natural events on the peak 2017 ambient PM₁₀ concentration is found within Section 2.3.1 of the Plan.

51.  For PM₁₀, a “complete” set of data include a minimum of 75 percent of the scheduled PM₁₀ samples per quarter. See 40 CFR, part 50, appendix K, section 2.3(a).

52.  40 CFR 50.6; 40 CFR part 50, Appendix J; 40 CFR part 53; and 40 CFR part 58, Appendices A, C, D, and E.

53.  On August 1, 2022, the North Highlands monitoring site (AQS ID: 06–067–0002) was dismantled at the request of the owner of the property, following a withdrawal of permission for the continued placement of the monitor on the property. Due to the deteriorating condition of the station, immediate relocation was deemed not feasible, and the District discontinued the monitor. SMAQMD will work with the EPA to identify a relocation site. See email dated July 28, 2022, from Janice Lam Snyder (SMAQMD) to Gwen Yoshimura (Air Quality Analysis Office, EPA Region IX), Subject: “Notification of Shut down of North Highlands Station due to property owner request.”

54.  SMAQMD 2022 Annual Network Plan, August 1, 2022.

55.  Calcagni Memo, p. 11.

56.  Id.

57.  While not explicitly stated within the Plan, the District later confirmed that analysis of PM₁₀ monitoring data for any violation that would trigger the District's contingency plan or the exceptional event evaluation process would occur on a quarterly basis. See email dated June 12, 2023 from Michael Dorantes (EPA) to Janice Lam Snyder (SMAQMD). Subject: “Sacramento County 2nd PM₁₀ Maintenance Plan; Inquiry regarding the Contingency Action Trigger.”

58.  Appendix C of the Plan compiles possible control measures to reduce windblown dust and wood combustion.

59.  Control strategy SIPs refer to reasonable further progress and attainment demonstration SIPs. 40 CFR 93.101.

60.  Transportation-related emissions of VOC and NO_X must also be specified in PM₁₀ maintenance plans if the EPA or the state finds that transportation-related emissions of one or both of these precursors within the nonattainment area are a significant contributor to the PM₁₀ nonattainment problem and has so notified the MPO and the U.S. Department of Transportation (DOT), or the applicable SIP (or SIP revision submission) establishes an approved (or adequate) budget for such emissions as part of the reasonable further progress, attainment, or maintenance strategy. 40 CFR 93.102(b)(2)(iii). An analysis of precursors to PM₁₀ emissions, performed in the first maintenance plan, indicates that while NO_X emissions contributed significantly to wintertime ambient PM₁₀ concentration, VOCs did not. (See Section 7.4 of the Plan.) Further, 40 CFR 93.118(b)(2)(i) requires that motor vehicle emissions budgets must be established, at a minimum, for the last year of the maintenance plan.

61.  40 CFR 93.118(e)(4).

62.  40 CFR 93.118(e)(4).

63.  40 CFR 93.118(f)(2).

64.  The District has determined, based on proportional rollback analysis, that the addition of 0.5 tpd of NO_X in 2024 will increase the future PM₁₀ concentrations by less than 0.3 μg/m3. , which satisfies the requirements outlined in 40 CFR 93.124(a).

65.  AP–42 is the EPA's Compilation of Air Pollutant Emission Factors. It has been published since 1972 as the primary source of the EPA's emission factor information. It contains emission factors and process information for more than 200 air pollution source categories. A source category is a specific industry sector or group of similar emitting sources. The emission factors have been developed and compiled from source test data, material balance studies, and engineering estimates.

66.  The six counties are El Dorado, Placer, Sacramento, Sutter, Yolo, and Yuba counties.

67.  Information on SACSIM is located at: https://www.sacog.org/​modelingandthe2020MTP/​SCS is located at: https://www.sacog.org/​2020-metropolitan-transportation-plansustainable-communities-strategy-update.

68.  85 FR 24174 (June 29, 2020).

69.  See 40 CFR 93.102(b)(3).

70.  40 CFR 93.122(e).

71.  Technical Support Document for the Adequacy Review of the Motor Vehicle Emissions Budgets within the Second 10-Year PM₁₀ Maintenance Plan for Sacramento County can be found within the docket for this rulemaking.

72.  See the transportation conformity regulation at 40 CFR 93.119(f).

73.  40 CFR 93.118(f)(2)(iii).