2024-27517. Clean Data Determination and Proposed Approval of Base Year Emissions Inventory; California; Los Angeles-South Coast Air Basin; 189(d) Plan for the 2006 24-Hour PM2.5 NAAQS

Table 1—2021-2023 24-Hour PM _2.5 Design Values for the South Coast PM _2.5 Nonattainment Area

General location	Site (AQS ID)	Annual 98th percentile (μg/m3 )			2021-2023 24-hour design value (μg/m3 )
		2021	2022	2023
Los Angeles County
East San Gabriel Valley	Azusa (06-037-0002)	36.1	17.8 (Inc)	No Data (Inc)	27 (Inv).
Central Los Angeles	Los Angeles (Main Street) (06-037-1103)	45.2	21.9	23.4	30.
West San Fernando Valley	Reseda (06-037-1201)	36.1	19.5	19.2	25.
South Central Los Angeles County	Compton (06-037-1302)	42.5	32.6	28.1	34.
South San Gabriel Valley	Pico Rivera #2 (06-037-1602)	47.9	25.6	27.8	34.
West San Gabriel Valley	Pasadena (06-037-2005)	29.9	19.0	17.7	22.
South Coastal Los Angeles County	Long Beach (North) (06-037-4002)	31.2	18.0 (Inc)	No Data (Inc)	25 (Inv).
South Coastal Los Angeles County	South Long Beach (06-037-4004)	32.8	23.1 (Inc)	No Data (Inc)	28 (Inv).
South Coastal Los Angeles County	Long Beach-Route 710 Near Road (06-037-4008)	34.8	25.5	25.4	29.
South Coastal Los Angeles County	Signal Hill (Lbsh) (06-037-4009)	No Data (Inc)	19.3 (Inc)	22.3	21 (Inv).
Orange County
Central Orange County	Anaheim (06-059-0007)	37.1	22.1	22.6	27.
Saddleback Valley	Mission Viejo (06-059-2022)	24.9	16.9 (Inc)	No Data (Inc)	21 (Inv).
Riverside County
Temecula Valley	Pechanga (06-065-0009)	16.5	11.4	12.0 (Inc)	13 (Inv).
Metropolitan Riverside County	Rubidoux (06-065-8001)	37.5	23.2	24.5	28.
Mira Loma	Mira Loma (Van Buren) (06-065-8005)	42.8	26.2	30.2	33.
San Bernardino County
Southwest San Bernardino Valley	Ontario-Route 60 Near Road (06-071-0027)	49.4	26.4	26.4	34.
Central San Bernardino Valley	Fontana (06-071-2002)	33.4	28.1	25.0	29.
East San Bernardino Mountains	Big Bear (06-071-8001)	21.5	23.2	18.0	21.
Central San Bernardino Valley	San Bernardino (06-071-9004)	34.2	25.8	21.8	27.
Source: EPA, AQS Design Value Report (AMP480), Report Request ID: 2218164, August 23, 2024.
Notes: Inc = Incomplete Data. Inv = Invalid design values due to incomplete data.

Preliminary data available in AQS for 2024 (January through June) indicate that the South Coast area continues to show concentrations below the 2006 24-hour PM_2.5 NAAQS.^[38] Consequently, the EPA is proposing to determine based upon three years of complete, quality-assured, and certified data from 2021 through 2023 that the South Coast PM_2.5 nonattainment area has attained the 2006 24-hour PM_2.5 NAAQS and to issue a CDD.

If we finalize this proposed CDD, the requirements for the State to submit an attainment demonstration, an RFP plan, quantitative milestones and quantitative milestone reports, and contingency measures for the area will be suspended until such time as: (1) the area is redesignated to attainment, after which such requirements are permanently discharged; or, (2) the EPA determines that the area has re-violated the 24-hour PM_2.5 NAAQS, after which time the state shall submit such attainment plan elements for the Serious nonattainment area by a future date to be determined by the EPA and announced through publication in the Federal Register at the time the EPA determines the area is violating the 24-hour PM_2.5 NAAQS.^[39]

A CDD does not suspend the requirements for an emissions inventory. As discussed in Section III of this document, this document includes our proposed approval of the 2018 base year emissions inventory included in the attainment plan for the South Coast PM_2.5 nonattainment area, submitted on December 29, 2020.

III. Review of the 2018 Base Year Emissions Inventory in the South Coast PM 2.5 Plan

A. Statutory and Regulatory Requirements

1. Requirements for Emissions Inventories

CAA section 172(c)(3) requires that each nonattainment plan SIP submission include a comprehensive, accurate, current inventory of actual emissions from all sources of the relevant pollutant or pollutants in the nonattainment area. The EPA discussed the emissions inventory requirements that apply to PM_2.5 nonattainment areas in the PM_2.5 SIP Requirements Rule and ( print page 92878) codified these requirements in 40 CFR 51.1008.^[40] The EPA has also issued guidance concerning emissions inventories for PM_2.5 nonattainment areas.^[41]

The base year emissions inventory for an attainment plan under CAA section 189(d) must provide a state's best estimate of actual emissions from all sources of the relevant pollutants in the area ( i.e., all emissions that contribute to the formation of a particular NAAQS pollutant). For the PM_2.5 NAAQS, the base year inventory must include direct PM_2.5 emissions, separately reported filterable and condensable PM_2.5 emissions,^[42] and emissions of all chemical precursors to the formation of secondary PM_2.5 ( i.e., NO_X, SO₂ , VOC, and ammonia).^[43]

The emissions inventory base year for a Serious PM_2.5 nonattainment area subject to CAA section 189(d) must be one of the three years for which the EPA used monitored data to determine that the area failed to attain the PM_2.5 NAAQS by the applicable Serious area attainment date, or another technically appropriate year justified by the state in its Serious area SIP submission.^[44]

A state's nonattainment plan SIP submission must include documentation explaining how it calculated emissions data for the inventory. In estimating mobile source emissions, a state should use the latest emissions models and planning assumptions available at the time the SIP is developed. At the time the South Coast PM_2.5 Plan was developed, the latest EPA-approved version of California's mobile source emissions factor model for estimating tailpipe, brake and tire wear emissions from on-road mobile sources was EMFAC2017.^[45] States are also required to use the EPA's “Compilation of Air Pollutant Emission Factors” (AP-42) road dust method for calculating re-entrained road dust emissions from paved roads.^[46]

2. Procedural Requirements for SIPs and SIP Revisions

CAA sections 110(a)(1) and (2) and 110(l) require each state to provide reasonable public notice and opportunity for public hearing prior to the adoption and submission of a SIP or SIP revision to the EPA. To meet this requirement, every SIP submission should include evidence that the State provided adequate public notice and an opportunity for a public hearing consistent with the EPA's implementing regulations in 40 CFR 51.102.

The District provided a public comment period and held a public hearing prior to the adoption of the South Coast PM_2.5 Plan on October 7, 2020.^[47] The SIP submission includes proof of publication of notices for the District's public hearing. Therefore, we find that the South Coast PM_2.5 Plan meets the procedural requirements for public notice and hearing in CAA sections 110(a) and 110(l).

CAA section 110(k)(1)(B) requires the EPA to determine whether a SIP submittal is complete within 60 days of receipt. This section of the CAA also provides that any plan that the EPA has not affirmatively determined to be complete or incomplete will become complete by operation of law six months after the date of submittal. The EPA's SIP completeness criteria are found in 40 CFR part 51, appendix V. On June 29, 2021, the South Coast PM_2.5 Plan was deemed complete by operation of law under CAA section 110(k)(1)(B).

B. Base Year Emissions Inventory in the Plan

The annual average planning emissions inventories for direct PM_2.5 and all PM_2.5 precursors (NO_X, SO_X, VOC, and ammonia) for the South Coast PM_2.5 nonattainment area, together with documentation for the inventories, are included in Chapter 3 (“Base-Year and Future Emissions”) of the Plan. More detailed emissions inventories for the South Coast PM_2.5 nonattainment area are included in appendix I (“Emissions Inventory”) of the Plan.

Each emissions inventory is divided into two source classifications: Stationary sources ( i.e., point sources and area sources) and mobile sources ( i.e., on-road and off-road sources). Point sources in the South Coast Air Basin that emit four tons per year (tpy) or more of PM, NO_X, SO_X , or VOC report annual emissions to the District. Point source emissions for the 2018 base year emissions inventory are generally based on reported data from facilities using the District's Annual Emissions Reporting program.^[48] Area sources include small emissions sources distributed across the nonattainment area. CARB and the District estimate emissions for about 400 area source categories using established inventory methods, including publicly available emissions factors and activity information. Activity data may come from national survey data such as from the Energy Information Administration or from local sources such as the Southern California Gas Company, paint suppliers, and District databases. Emissions factors can be based on a number of sources including source tests, compliance reports, and the EPA's AP-42.

On-road emissions inventories are calculated using CARB's EMFAC2017 model and the travel activity data provided by the Southern California Association of Governments (SCAG) in “The 2016-2040 Regional Transportation Plan/Sustainable Communities Strategy.” ^[49] CARB used the Spatial and Temporal Allocator tool to distribute emissions spatially and temporally.^[50]

( print page 92879)

CARB provided emissions inventories for off-road equipment, which includes construction and mining equipment, industrial and commercial equipment, lawn and garden equipment, locomotives, aircraft, tractors, harbor craft, off-road recreational vehicles, construction equipment, forklifts, cargo handling equipment, and various other mobile equipment types. CARB uses several models to estimate emissions for more than one hundred off-road equipment categories.^[51]

Finally, the South Coast PM_2.5 Plan provides separate estimates of filterable and condensable PM_2.5 emissions, expressed as annual average PM_2.5 emissions, for all of the identified source categories for the 2018 base year, as well as subsequent relevant years.^[52]

Table 2 provides a summary of the annual average inventories in tons per day (tpd) of direct PM_2.5 and PM_2.5 precursors for the 2018 base year. For a detailed breakdown of the inventories, see Chapter 3 and appendix I of the South Coast PM_2.5 Plan.

Table 2—Summary of Emissions by Major Source Category in the South Coast Air Basin: 2018 Base Year Average Annual Day

[tpd] ^a

Source category	Direct PM 2.5	NO X	SO X	VOC	Ammonia
Stationary Sources	44.8	57.7	8.2	206.8	58.6
On-Road Mobile	11.4	177.9	1.7	81.6	14.2
Off-Road Mobile	6.3	134.9	4.1	80.8	0.2
Total	62.4	370.5	14.0	369.2	72.9
a  Values may not sum due to rounding.
Source: South Coast PM 2.5 Plan, Chapter 3, Table 3-1.