Staff Report 

2015 update to the South Coast Air Basin 

24-hour PM2.5 plan

Release Date: February 9, 2015

Scheduled for Consideration: February 18, 2015

California Environmental Protection Agency

AIR RESOURCES BOARD
This document has been reviewed by the staff of the California Air Resources 

Board and approved for publication. Approval does not signify that the contents 

necessarily reflect the views and policies of the Air Resources Board, nor does 

the mention of trade names or commercial products constitute endorsement or 

recommendation for use.

Electronic copies from this document are available for download from the Air 

Resources Board’s Internet site at:

http://www.arb.ca.gov/planning/sip/planarea/sanjqnvllysip.htm.

In addition, written copies may be obtained from the Public Information Office, Air 

Resources Board, 1001 I Street, 1st Floor, Visitors and Environmental Services 

Center, Sacramento, California 95814, (916) 322-2990.

For individuals with sensory disabilities, this document is available in Braille, 

large print, audiocassette or computer disk. Please contact ARB's Disability 

Coordinator at (916) 323-4916 by voice or through the California Relay Services 

at 711, to place your request for disability services. If you are a person with 

limited English and would like to request interpreter services, please contact 

ARB's Bilingual Manager at 

(916) 323-7053.

Please send written comments to:

Carol Sutkus, Manager

South Coast Air Quality Planning Section

Air Resources Board

P.O. Box 2815

Sacramento, California 95812

Phone: (916) 322-1229

Email: csutkus@arb.ca.gov

For general questions, contact:

Dr. Scott King, Air Pollution Specialist

South Coast Air Quality Planning Section

Phone: (916) 322-2832

Email: sking@arb.ca.gov
Table of Contents

I. Background ....................................................................................................1

II. PM2.5 Plan Supplement Elements Meet Subpart 4 Requirements ................3

2015 Attainment Demonstration ........................................................................3

Precursor Requirements....................................................................................4

Reasonably Available Control Measures (RACM)/Reasonable Available 

Control Technology (RACT) demonstration.......................................................4

2015 Transportation Conformity Budgets ..........................................................5

III. Other Elements in the PM2.5 Plan Supplement..........................................5

Update of 2012 AQMP Commitments ...............................................................5

IV. Other Subpart 4 Requirements ...................................................................5

Reasonable Further Progress (RFP).................................................................5

Contingency Requirements ...............................................................................5

New Source Review (NSR) Program.................................................................6

V. Staff Recommendation...................................................................................6
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1

This report documents the Air Resources Board (ARB) staff’s review of the Supplement 

to the 24-Hour PM2.5 State Implementation Plan for the South Coast Air Basin1(PM2.5 

Plan Supplement) adopted by the South Coast Air Quality Management District (District)

on February 6, 2015. The PM2.5 Plan Supplement demonstrates compliance with the 

requirements under Clean Air Act (Act) Subpart 4 for the 24-hour PM2.5 National 

Ambient Air Quality Standard (NAAQS). Submittal of the PM2.5 Plan Supplement will 

provide the information needed for the U.S. Environmental Protection Agency 

(U.S. EPA) to approve the PM2.5 portion of the South Coast 2012 Air Quality 

Management Plan2(2012 AQMP).

I. Background

In December 2012, the District adopted the 2012 AQMP, which included a 

demonstration that it met the planning requirements for the 35 ug/m3 24-hour PM2.5 

NAAQS under Subpart 1 of the Act. ARB approved the 2012 AQMP on 

January 25, 20133, and submitted it to U.S. EPA on February 13, 2013. 

The 2012 AQMP was developed to meet requirements of the U.S. EPA 2007 Fine 

Particle Implementation Rule4based on the Subpart 1 provisions of the Act. The 

2012 AQMP included all of the required planning elements of the Act under Subpart 1

for the 24-hour PM2.5 NAAQS, including:

 Emission inventories;

 Attainment demonstration based on air quality modeling for 2014;

 Reasonably Available Control Measures (RACM) analysis;

 Reasonable Further Progress (RFP) Demonstration;

 Contingency measures; and

 Transportation conformity budgets for 2014.

Shortly after the District adopted the 2012 AQMP, the D.C. Circuit Court of Appeals 

determined that U.S. EPA erred in developing its implementation rule for PM2.5 under 

the Subpart 1 general provisions of the Act without considering the more specific 

particulate matter provisions in Subpart 4. The Court remanded the rule back to 

U.S. EPA to address the Subpart 4 provisions.

5

In June 2014, U.S. EPA classified the South Coast Air Basin as a moderate

nonattainment area6for the 35 μg/m324-hour PM2.5 NAAQS under Subpart 4 of the

 

1

Supplement to the 24-Hour PM2.5 State Implementation Plan for the South Coast Air Basin, 

http://www.aqmd.gov/docs/default-source/Agendas/Governing-Board/2015/2015-feb6-022.pdf?sfvrsn=2

2

South Coast Air Quality District 2012 AQMP, http://www.aqmd.gov/home/library/clean-air-plans/airquality-mgt-plan/final-2012-air-quality-management-plan

3

2012 South Coast Ozone and PM2.5 State Implementation Plan

http://www.arb.ca.gov/planning/sip/planarea/scabsip.htm#2012_plan

4 U.S. EPA, Clean Air Fine Particle Implementation Rule; Final Rule. (20586 – 20667) April 25, 2007. 

http://www.epa.gov/fedrgstr/EPA-AIR/2007/April/Day-25/a6347.pdf

5 U.S. Court of Appeals for the District of Columbia Circuit, Case No. 08-1250, January 4, 2013. 

http://www.gpo.gov/fdsys/pkg/USCOURTS-caDC-08-01250/pdf/USCOURTS-caDC-08-01250-0.pdf

6 U.S. EPA, 79 FR 105, pp. 31566-31782 (June 2, 2014)

http://www.gpo.gov/fdsys/pkg/FR-2014-06-02/pdf/2014-10395.pdf
2

Act and directed the State to submit a new State Implementation Plan (SIP) that meets 

moderate area requirements. U.S. EPA directed states to apply the existing guidance 

for PM10 implementation under Subpart 4 to the PM2.5 NAAQS. The table below 

details the differences between Subpart 1 and Subpart 4 of the Act. 

Comparison of Subpart 1 and Subpart 4 Implementation Requirements

SIP 

Component Subpart 1 Subpart 4

Classifications None Moderate and Serious

Attainment 

Dates

 Five years from 

designation date 

(December 2014)

 May be extended up to ten 

years from designation 

date (December 2019)

 Moderate: attain by the end of the 

sixth year after designation 

(December 2015)

 Serious: attain by the end of the 

tenth year after designation 

(December 2019)

SIP 

Submission 

Deadlines 

Three years after 

designation 

 Moderate: submittal 18 months 

after designation

 Serious: submittal 18 months after 

classification to serious

Precursor 

Requirements

 Must address sources of 

directly emitted PM2.5, 

sulfur oxides (SOx), and 

nitrogen oxides (NOx).

 Address ammonia or 

reactive organic gases 

(ROG) if they significantly 

contribute to PM2.5 levels.

Must address sources of all 

PM2.5 and PM2.5 precursors. 

Level of 

Emission 

Controls

Reasonably Available 

Control Measures (RACM) 

including Reasonably 

Available Control 

Technology (RACT)

 Moderate Area: RACM/RACT

 Serious Area: Best Available 

Control Measures (BACM)

Reasonable 

Further 

Progress (RFP)

Linear progress towards 

attainment 

Quantitative milestones to be 

achieved every 3 years 

Permitting 

Program

 Major Sources are not 

required to control 

ammonia or ROG, unless 

demonstrated that they

contribute significantly to 

PM2.5 concentrations in 

the area.

 Major source is over 100 

tons per year (tpy).

 Major Sources must control all 

precursors of PM2.5, unless 

demonstrated that such 

precursors do not contribute to 

levels which exceed the NAAQS. 

 Major source is over 100 tpy for 

Moderate Area and over 70 tpy for 

Serious Area.
3

On February 6, 2015, the District adopted the PM2.5 Plan Supplement. The PM2.5 

Plan Supplement demonstrates that the existing 2012 AQMP along with minor revisions 

included in the PM2.5 Plan Supplement satisfies the Subpart 4 requirements of the Act 

for a moderate PM2.5 nonattainment area. Specifically, the minor revisions to the 

planning elements to meet Subpart 4 requirements are:

 Demonstration of attainment of the 24-hour PM2.5 NAAQS by 2015; 

 New transportation conformity budgets for 2015; 

 Subpart 4 precursor requirements, and

 RACM/RACT analysis for PM2.5 precursors. 

Each of the updated elements to satisfy Subpart 4 provisions are further described 

below. Additionally, the PM2.5 Plan Supplement clarifies the list of control strategy 

commitments that are providing emission reductions in the attainment demonstration,

and includes a discussion of the effects of the past few years of drought conditions on 

the 2012 AQMP attainment determination.

II. PM2.5 Plan Supplement Elements Meet Subpart 4 Requirements

The PM2.5 Plan Supplement includes a detailed comparison of PM2.5 implementation 

requirements under Subpart 1 and Subpart 4. These requirements are summarized in 

the previous table. Focusing on the requirements that differ between the Subparts, the 

PM2.5 Plan Supplement demonstrates that the 2012 AQMP adopted by the District and 

ARB with this minor revision will satisfy the Subpart 4 requirements.

2015 Attainment Demonstration

The lack of rainfall and associated drought conditions in 2013 and 2014 impacted 

24-hour PM2.5 concentrations in the South Coast Air Basin. The PM2.5 Plan 

Supplement Attachment B includes an analysis evaluating precipitation levels and the 

impact on current PM2.5 concentrations. The District analysis demonstrates that based 

on data in 2012 and 2013, and preliminary data for 2014, attainment of the 35 ug/m3 

24-hour NAAQS will not be achievable by the end of 2014 as anticipated in the 

2012 AQMP. 

However, under Subpart 4, moderate nonattainment areas must demonstrate 

attainment within six years after designation, or by 2015, not 2014. The PM2.5 Plan 

Supplement Attachment A demonstrates South Coast Air Basin attainment of the 

24-hour PM2.5 NAAQS in 2015 in conformance with Subpart 4 requirements. To

calculate a 2015 design value based on modeling in the 2012 AQMP, the District 

interpolated between projected 2014 and 2019 24-hour PM2.5 design values. 

To further support the 2015 attainment demonstration in the PM2.5 Plan Supplement, 

the District analyzed the PM2.5 and PM2.5 precursor emission reductions that will occur 

between 2014 and 2015. The 2012 AQMP control strategy focused on measures to 

bring the last nonattaining monitoring site, at Mira Loma, into attainment. The strategy 

included enhanced control measures to reduce emissions from wood burning and open 

burning on days when high PM2.5 levels are expected. These measures have now 

been adopted and implemented by the District. The reductions from implementation of 
4

these strategies provide the air quality improvements needed to demonstrate attainment 

of the 24-hour PM2.5 NAAQS in 2015. 

Precursor Requirements

Under Subpart 1, only SOx, and NOx were presumed to be significant precursors to 

ambient PM2.5. Under Subpart 4, all PM2.5 precursors (NOx, SOx, ROG and 

ammonia) must be considered unless these precursors do not contribute significantly to 

PM2.5 levels exceeding the standard. The PM2.5 Plan Supplement Attachment E

describes the District analysis of Subpart 4 precursor requirements and demonstrates 

that the 2012 AQMP and District rules presently meet the Subpart 4 criteria.

Major stationary sources of NOx and SOx are presently subject to District rules meeting 

emission offsets required by Subpart 4 Section 189(e). Thus, to demonstrate 

compliance with Subpart 4 Section 189(e) for the remaining precursors, the District 

performed an analysis of ROG and ammonia emissions from major stationary sources. 

Major sources of ROG and ammonia each contribute less than 2 percent of the overall 

emissions in the South Coast Air Basin. At these relatively small emission levels, major 

sources of ROG and ammonia do not contribute significantly to ambient PM2.5 levels. 

In addition, both ROG and ammonia are subject to requirements for Best Available 

Control Measures under existing New Source Review (NSR) rules at a zero threshold. 

Reasonably Available Control Measures (RACM)/Reasonable Available Control 

Technology (RACT) demonstration

For both Subpart 1 and Subpart 4 moderate areas, RACM/RACT is the required 

minimum level of control of emission sources. The RACM/RACT analysis compares 

District rules and regulations governing emission limits to those established by 

U.S. EPA guidance, other California air districts and representative agencies elsewhere 

throughout the U.S. Subpart 4 requires that RACM/RACT assessments cover rules for 

both PM2.5 and PM2.5 precursors.

The PM2.5 Plan Supplement RACM/RACT demonstration in Attachment D builds upon 

previous RACM and RACT analyses from recent SIP submittals to U.S. EPA7,8. In 

conjunction, the previous assessments along with the PM2.5 Plan Supplement

demonstrate that State and District rules are equivalent to or more stringent than rules 

in other districts and states with the exception of two District rules. For these rules that 

the District identified as having the potential for further reductions, the District has 

committed to their further evaluation as part of the 2016 AQMP control measure 

development.

With this analysis and commitment to further evaluate rules identified as having the

potential for further emission reductions, the District has met the moderate area 

RACM/RACT requirement. 

 

7

2012 AQMP, Appendix VI: Reasonably Available Control Measures (RACM) Demonstration

8

2016 AQMP RACT Analysis, http://www.aqmd.gov/docs/default-source/Agendas/GoverningBoard/2014/2014-jun6-031.pdf?sfvrsn=2
5

2015 Transportation Conformity Budgets

The Act requires that SIPs include transportation conformity budgets for the purpose of 

ensuring that transportation plans are consistent with the SIP attainment demonstration. 

The PM2.5 Plan Supplement Attachment C includes transportation conformity budgets 

for the revised 2015 attainment date. These budgets replace the transportation 

conformity budgets for the original 2014 attainment year in the 2012 AQMP. 

The on-road emissions for PM2.5 and PM2.5 precursors were derived from the South 

Coast Air Basin annual average emission inventory. The emissions budgets for PM2.5 

and its precursors were provided for the 2015 attainment year. Like the 2014 

transportation conformity budgets in the 2012 AQMP, the transportation conformity 

budgets used in the PM2.5 Plan Supplement were based on the 2012 Regional 

Transportation Plan (RTP) Final annual average Vehicle Miles Traveled (VMT) data 

provided by the Southern California Association of Governments (SCAG). The 2015 

VMT distribution was interpolated from the 2012 RTP 2014 and 2019 profiles provided 

by SCAG. The 2015 VMT derived from the interpolation was input into the California 

transportation model (EMFAC2011) to generate the 2015 transportation conformity

budgets listed in the PM2.5 Plan Supplement.

III. Other Elements in the PM2.5 Plan Supplement

Update of 2012 AQMP Commitments

The attainment strategy included as part of the 2012 AQMP and PM2.5 Plan 

Supplement reflects a combination of emission reductions from ARB and District 

ongoing regulations and programs, and proposed control measures with implementation 

dates. The amount of estimated reductions from each measure and the timing of the 

measure’s implementation are required information to show attainment of the NAAQS 

by the attainment date.

The 2012 AQMP included several control measures that did not include estimated

reductions or implementation dates

9

and were therefore not part of the strategy 

necessary to demonstrate attainment. The PM2.5 Plan Supplement Attachment F

updates the adoption dates for these measures.

IV. Other Subpart 4 Requirements

Reasonable Further Progress (RFP)

Under Subpart 1, a SIP must demonstrate generally linear progress to meet RFP 

requirements. Under Subpart 4, a SIP must include quantitative milestones to be 

achieved every three years until the area is redesignated to attainment. Since the plan 

demonstrates attainment at the next milestone, no quantitative milestones are included.

Contingency Requirements

The Act requires that a SIP provide contingency measures in the event of failure to 

attain the 24-hour PM2.5 NAAQS by the applicable attainment date. These contingency 

 

9

South Coast Air Quality District 2012 AQMP Chapter 4, Table 4-2
6

measures must be already adopted, take effect without further action, not be relied upon 

to demonstrate attainment for the time in which they serve as contingency measures, 

and contain trigger mechanisms for implementation. U.S. EPA guidance states that the 

contingency measure requirements can be satisfied with already adopted control 

measure provided those controls will achieve emission reductions above and beyond 

what is needed to demonstrate attainment. 

The 2012 AQMP contingency control measure, CMB-01, Further NOx Reductions from 

RECLAIM, will achieve an additional two tons per day of NOx emissions reductions from 

the RECLAIM market if the 24-hour PM2.5 standard is not attained by 2015. The 

PM2.5 SIP Supplement also includes CMB-01 as a contingency measure. The District 

anticipates bringing control measure CMB-01 to their board in the first quarter of 2015 

and includes the appropriate automatic trigger mechanism consistent with the Act

contingency measure requirements. 

New Source Review (NSR) Program

U.S. EPA also set a deadline of December 31, 2014 for the District to demonstrate their 

PM2.5 permitting program complies with Subpart 4 requirements. In December 2014, 

the District amended NSR Rule 1325 to satisfy the Subpart 4 requirements and ARB

submitted the rule to U.S. EPA. 

V. Staff Recommendation

The Supplement to the 24-Hour PM2.5 State Implementation Plan for the South Coast 

Air Basin demonstrates that the South Coast 2012 AQMP along with the current 

revisions satisfies requirements for a moderate PM2.5 nonattainment area under 

Subpart 4 of the Act. Once submitted to U.S. EPA, this revision together with the 

2012 AQMP will enable U.S. EPA to approve the amended 2012 AQMP as meeting 

Subpart 4 moderate area requirements.

Staff recommends that the Board approve the Supplement to the 24-Hour PM2.5 State 

Implementation Plan for the South Coast Air Basin and submit it to U.S. EPA as a

revision to the California SIP.