State of California 

Staff Report 

Analysis of the South Coast Air Basin 

PM10 Redesignation Request, 

Maintenance Plan, and Conformity Budgets 

Release Date: February 22, 2010 

Scheduled for Consideration: March 25, 2010 

 

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. 
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February 22, 2010 

TABLE OF CONTENTS 

EXECUTIVE SUMMARY ................................................................................................ 1

I. BACKGROUND...................................................................................................... 3

II. REDESIGNATION REQUIREMENTS .................................................................... 4

III. EVALUATION OF THE SOUTH COAST AIR BASIN PLAN ................................. 4

A. The South Coast Air Basin Attains the 24-Hour PM10 Standard....................... 4

B. U.S. EPA Approved the South Coast Air Basin PM10 SIP and the State Has 

Met Applicable Act Requirements........................................................................... 6

C. Improvement in the South Coast Air Basin PM10 Air Quality is Due to 

Permanent and Enforceable Reductions in Emissions ........................................... 6

D. Maintenance Plan.............................................................................................. 6

1. Attainment Emission Inventory...................................................................... 6

2. Maintenance Demonstration.......................................................................... 7

3. PM10 Monitoring Network ............................................................................. 8

4. Verification of Continued Attainment ............................................................. 8

5. Contingency Plan .......................................................................................... 8

6. Transportation Conformity Budgets............................................................... 8

IV. STAFF RECOMMENDATION .............................................................................. 10
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February 22, 2010 

EXECUTIVE SUMMARY 

Background 

The South Coast Air Basin (South Coast) is currently designated as a serious 

nonattainment area for the 24-hour national ambient air quality standard (NAAQS or 

standard) for particulate matter of 10 microns in diameter or smaller (PM10). The South 

Coast Air Quality Management District (District) adopted the first PM10 attainment plan 

for the South Coast in 1991. The plan focused on fugitive dust as the primary control 

strategy for attaining the national 24-hour and the annual PM10 standards. The 1997 

plan revision requested extension of the attainment date to 2006. This revision was 

approved by the United States Environmental Protection Agency (U.S. EPA). In various 

plan revisions, the District adopted increasingly stringent dust measures. The 2003 

plan revision added control measures to reduce emissions of particulate matter 

precursors. Adoption of District controls in the South Coast resulted in this area 

attaining the 24-hour PM10 standard by the 2006 attainment date. 

On January 8, 2010, the District adopted the PM10 Redesignation Request and 

Maintenance Plan for the South Coast (South Coast PM10 Maintenance Plan). The 

plan officially requests this area be redesignated to attainment for the PM10 standard 

and charts the course for continued maintenance of the standard. 

Shortly before plan adoption, the District developed revised transportation conformity 

budgets (budgets) for the Maintenance Plan based on U.S. EPA comments that the 

budgets only include emission reductions from adopted control measures. Because 

transportation conformity budgets are subject to a 30-day public notice requirement, 

ARB staff has posted the revised budgets to provide for the required public review 

period. ARB staff proposes adoption of the updated budgets for the South Coast. 

Maintenance Plans Address Act Requirements 

The South Coast PM10 Maintenance Plan includes the following components: 

• Attainment emission inventories for directly emitted PM10 and for particulate 

matter precursor gases (NOx, SOx, and ROG); 

• Demonstration that PM10 attainment concentrations at federal reference 

monitoring stations will be maintained for ten years after redesignation; 

• Commitment to ongoing monitoring network operation for continued verification 

of attainment; and 

• Contingency provisions to address any future violations. 

In addition, eight years after the area is redesignated as attainment, the District will 

submit a revised South Coast PM10 Maintenance Plan providing for continued 

attainment for an additional ten years. 
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February 22, 2010 

Staff Recommendation 

Air Resources Board (ARB) staff concurs with the District’s PM10 Redesignation 

Request and Maintenance Plan for the South Coast Air Basin. ARB staff recommends 

that the Board approve the District’s South Coast PM10 Maintenance Plan, including 

the updated conformity budgets, as a revision to the California State Implementation 

Plan for submittal to U.S. EPA. In addition, ARB staff recommends that the Board 

approve the District’s request that the South Coast Air Basin be redesignated from 

nonattainment to attainment for the national PM10 standard. 
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February 22, 2010 

I. BACKGROUND 

The South Coast Air Basin (South Coast) is designated as a serious nonattainment area 

for the 24-hour PM10 national ambient air quality standard (NAAQS or standard). The 

area is under the jurisdiction of the South Coast Air Quality Management District 

(District). In 1987, the United States Environmental Protection Agency (U.S. EPA) 

adopted the PM10 NAAQS consisting of a 24-hour PM10 standard of 

150 micrograms per cubic meter (μg/m3) and an annual standard of 50 μg/m3. Effective 

December 18, 2006, U.S. EPA revoked the annual portion of the PM10 standard. 

PM10 is a complex mixture of primary or directly emitted particles (dust and soot), and 

secondary particles or aerosol droplets formed in the atmosphere from precursor gases 

(NOx, SOx, ROG, and ammonia). PM10 includes the subsets of fine particles with a 

diameter of 2.5 microns or less (PM2.5) and of coarse particles with a diameter between 

2.5 and 10 microns. Secondary particles are found mostly in the PM2.5 portion of 

PM10. 

In the South Coast, currently, the fine fraction contributes approximately 56 percent and 

the coarse fraction 44 percent of the average peak PM10 concentrations. Dust is the 

main component of the coarse fraction in this area. 

The District adopted the first PM10 Plan for the South Coast in 1991. This plan focused 

on a fugitive dust control strategy for attaining the national 24-hour and annual PM10 

standards. Control measures were adopted to address fugitive dust emissions from 

paved and unpaved roads, agricultural activities, construction and demolition activities, 

and open area wind erosion. The District subsequently adopted Plan revisions in 1994, 

1997, and 2003 providing dust control enhancements. The 2002 plan revision 

requested an extension of the PM10 attainment date to 2006. In addition to including 

control measures for directly emitted PM10, the 2003 Plan revision included controls for 

gaseous precursors of PM10. The 2007 revisions to the District’s Air Quality 

Management Plan (AQMP) included an attainment demonstration showing continuous 

attainment of the standard through 2020. 

On January 8, 2010, the District adopted the PM10 Redesignation Request and 

Maintenance Plan for the South Coast. The plan officially requests that the South Coast 

be redesignated to attainment for the PM10 standard and charts the course for 

continued maintenance of the standard through 2030. 

Shortly before plan adoption, the District developed revised transportation conformity 

budgets (budgets) for the Maintenance Plan based on U.S. EPA comments that the 

budgets only include emission reductions from adopted control measures. Because 

transportation conformity budgets are subject to a 30-day public notice requirement, 

ARB staff has posted the revised budgets to provide for the required public review 

period. ARB staff proposes adoption of the updated budgets for the South Coast. 
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February 22, 2010 

II. REDESIGNATION REQUIREMENTS 

ARB staff reviewed the South Coast PM10 Maintenance Plan within the context of the 

Clean Air Act (Act), which identifies the following requirements each area must meet to 

be redesignated to attainment: 

A. The PM10 standard has been attained; 

B. The District has an approved State Implementation Plan (SIP) and the State has 

met all applicable Act requirements for PM10 in the nonattainment area; 

C. The improvement in PM10 air quality is due to permanent and enforceable 

emission reductions; and 

D. U.S. EPA has approved a maintenance plan. 

The Act also sets the general framework for maintenance plans1. Each PM10 

maintenance plan must provide for continued maintenance of the PM10 standard for 

ten years after redesignation and includes the following components: 

1. Attainment emission inventory; 

2. Maintenance demonstration; 

3. Commitment to continue the monitoring network operation; 

4. Commitment for verification of continued attainment; and 

5. Contingency plan to promptly correct any violation of the PM10 NAAQS that 

occurs after the area has been redesignated. 

III. EVALUATION OF THE SOUTH COAST AIR BASIN PLAN 

Based on review of the South Coast PM10 Maintenance Plan and the District’s 

supporting technical analysis, ARB staff concurs that the Plan meets the requirements. 

The following sections describe the major elements of the Plan and the redesignation 

request. 

A. The South Coast Air Basin Attains the 24-Hour PM10 Standard 

In the South Coast, PM10 concentrations are measured at nineteen federal reference 

monitors (FRMs) that collect PM10 samples on a 24-hour basis and ten real-time 

monitors that collect PM10 samples on an hourly basis (Figure 1). Table 1 lists air 

quality data for the three-year period of 2005-2007 for the FRMs demonstrating that the 

South Coast attains the 24-hour PM10 standard. The 24-hour standard is met when the 

estimated number of exceedances measured over a three year period averages one or 

less per year. 

 

1

 Calcagni, John, Memorandum, Procedures for Processing Requests to Redesignate Areas to 

Attainment, Office of Air Quality Planning and Standards, Research Triangle Park, North Carolina, 

September 4, 1992. http://www.epa.gov/ttn/oarpg/t5/memoranda/redesignmem090492.pdf
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February 22, 2010 

Figure 1. PM10 Monitoring Stations in the South Coast Air Basin 

Table 1. South Coast Air Basin FRM PM10 Data from 2005 to 2007

Observed 

Maximum 24-hour 

Concentration(a)

(μg/m3)

Three-year 

Total Number of 

Days Exceeding 

the 

Standard 

Monitoring Station Name 

2005 2006 2007 2005-2007 

Los Angeles County 

Los Angeles-North Main 70 59 78 0 

Los Angeles-Westchester 44 45 128 0 

North Long Beach 66 78 75 0 

South Long Beach 131 117 123 0 

Burbank 92 71 109 0 

Azusa 76 81 82 0 

Santa Clarita 55 53 131 0 

Orange County 

Anaheim 65 104 75 0 

Mission Viejo 41 57 74 0 

Riverside County 

Norco 79 74 93 0 

Riverside-Rubidoux 123 109 118 0 

Mira Loma -- 124 142 N/A(b) 

Perris 80 125 120 0 

Banning Airport 76 75 78 0 

San Bernardino County 

Ontario 74 78 115 0 

Fontana 108 142 111 0 

San Bernardino 72 92 136 0 

Redlands 61 103 97 0 

Crestline 49 63 89 0 

a. Data do not include PM10 concentrations caused by natural/exceptional events which are excluded 

from regulatory consideration. 

b. Monitoring since 2006. 
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February 22, 2010 

On three days over the 2005 to 2007 period, the 24-hour standard was exceeded due to 

high wind events or fireworks on a national holiday. These exceedances can be 

excluded under the federal rule for exceptional events since they are not reasonably 

preventable or controllable. Documentation for these three events has been submitted 

to U.S. EPA for concurrence as exceptional events. 

B. U.S. EPA Approved the South Coast Air Basin PM10 SIP and the State 

Has Met Applicable Act Requirements 

On April 18, 2003, U.S. EPA approved the PM10 elements of the 1997 South Coast 

AQMP and the 2002 plan update with a December 31, 2006 attainment deadline for the 

South Coast. In addition, ARB and the District have met all of the Act requirements 

applicable for a serious PM10 nonattainment area to be considered for redesignation. 

C. Improvement in the South Coast Air Basin PM10 Air Quality is Due to 

Permanent and Enforceable Reductions in Emissions 

The District has adopted the tighter dust control rules committed to in the Basin’s 

2003 PM10 attainment plan revision. In addition, the District has adopted rules 

controlling emissions of particulate matter precursors (NOx, SOx, and ROG). These 

measures have provided for continuous attainment of the 24-hour PM10 standard 

(excluding exceptional or natural events) in the region since 2004, despite regional 

growth. Adopted measures are fully enforceable. 

Based on analyses of long-term meteorological variables, including rainfall, wind 

speeds, and stagnation, the District found that meteorological conditions during the 

2005-2007 period were not unusually favorable to lower PM10 levels. Therefore, air 

quality improvements leading to PM10 attainment in the Basin are due to emission 

reductions from adopted, fully enforceable control measures. 

D. Maintenance Plan 

The South Coast PM10 Maintenance Plan includes the following components: 

attainment emission inventory; maintenance demonstration; commitment to continue 

monitoring network operation; commitment for verification of continued attainment; and 

contingency plan. In addition, transportation conformity budgets have been updated. 

1. Attainment Emission Inventory 

An emission inventory is a critical tool used to support evaluation, control, and mitigation 

of air pollution which is comprised of a systematic listing of the sources of air pollutants 

along with the amount of pollutants emitted from each source or category over a given 

period of time. Emission inventories are estimates of the air pollutant emissions 

released into the environment – they are not direct ambient concentration 

measurements. To determine the expected emissions in future years, emission 

inventories incorporate the effects of growth and existing regulations (baseline 
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February 22, 2010 

inventories). An attainment inventory identifies the level of emissions during the period 

when air quality data show attainment. 

The South Coast PM10 Maintenance Plan presents the updated 2007 AQMP baseline 

emission inventories for PM10, NOx, ROG, and SOx for 2002, 2006, and 2008, plus 

projected emissions for 2010 through 2012 (providing a bracket for the start of the 

maintenance period depending upon plan approval by U.S. EPA), 2014, 2020, and 2023 

(bracketing the expected 10-year maintenance period), and 2030. 2007 AQMP 

inventory updates include the latest point and area source emission information; ARB 

EMFAC 2007 mobile source emission outputs; and planning assumptions in the 

Southern California Association of Government’s (SCAG) Interim 2007 Regional 

Transportation Plan (2007 RTP). 

2. Maintenance Demonstration 

The 2003 PM10 attainment plan used linear rollback to demonstrate attainment of the 

24-hour PM10 standard. Linear rollback assumes that future PM10 levels above 

background concentrations will decrease in proportion to projected emission reductions. 

The linear rollback technique was based on PM10 chemical components. For the five 

sites where PM10 component species were sampled, the components were matched to 

the appropriate emission inventory categories in the rollback analysis. 

The South Coast PM10 Maintenance Plan demonstrates maintenance of the 24-hour 

PM10 standard by estimating the PM2.5 and the coarse portions of PM10 

concentrations using two separate methodologies: 1) the PM2.5 portion using regional 

photochemical modeling, 2) the coarse portion using linear rollback simulations. This 

analysis employed baseline emission inventories for 2005 and 2010 through 2030. The 

projected PM2.5 and coarse fractions were added to estimate future-year maximum 

24-hour PM10 concentrations. Table 2 lists the 2010 through 2012, 2014, 2020, 2023, 

and 2030 projected maximum 24-hour PM10 values per county, which demonstrate 

continued attainment of the 24-hour NAAQS throughout the Basin. 

Table 2. Projected Maintenance of 24-hour PM10 NAAQS in the 

South Coast Air Basin 

Year Predicted County Maximum 24-hour PM10 Concentration 

(μg/m3) 

Los Angeles Orange Riverside San 

Bernardino 

2010 102 79 120 126 

2011 101 79 119 125 

2012 101 78 118 125 

2014 102 79 117 126 

2020 102 80 117 126 

2023 103 81 118 128 

2030 109 86 125 136 
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February 22, 2010 

The South Coast is projected to maintain attainment with the PM10 standard due to 

ARB, District, and other local control measures already in place. In addition, future 

emissions in PM10 precursors are projected to decrease even further as a result of the 

implementation of controls in the 2007 AQMP for PM2.5 and ozone in the Basin. 

3. PM10 Monitoring Network 

The District commits to continue PM10 monitoring to verify sustained attainment of the 

PM10 standard in the South Coast. The existing PM10 monitoring network in the South 

Coast includes nineteen FRM and ten real-time PM10 monitors (Figure 1). Federal 

regulations require daily sampling at the site reporting peak PM10 concentrations. The 

real-time PM10 monitors will be used to meet the daily monitoring requirement. 

4. Verification of Continued Attainment 

To verify continued attainment of the PM10 standards, the District commits to 

reevaluate the South Coast PM10 Maintenance Plan as part of the AQMP revision 

currently scheduled for 2011. Eight years after the South Coast has been redesignated 

to attainment, the District will submit to U.S. EPA the required revision to the Plan 

demonstrating maintenance of the standard for the following ten year period. On a 

regular basis, the District will continue to analyze PM10 data from FRM and continuous 

monitors and compare daily PM10 values to the level of the 24-hour standard. 

5. Contingency Plan 

The Act requires the maintenance plan to include contingency provisions for prompt 

correction of any PM10 standard violation that might occur after the area has been 

redesignated to attainment. The maintenance plan is not required to contain fully 

adopted contingency measures that will go into effect without further state action as is 

required in attainment SIPs. Instead, for maintenance plans, the area must have a plan 

to ensure that contingency measures are adopted once they are triggered. 

Implementation of the 2007 AQMP serves as an on-going contingency measure for 

maintaining the PM10 standard in the South Coast, since emission reductions from 

control measures designed to attain the PM2.5 and ozone standards will effectively 

reduce PM10 concentrations. If nonetheless the 24-hour PM10 standard is exceeded, 

and data evaluation shows the violation is not due to a natural or exceptional event, the 

District will evaluate further enhancements to key existing PM10 measures to achieve 

necessary emission reductions as expeditiously as possible. 

6. Transportation Conformity Budgets 

Under section 176(c) of the Act, transportation plans, programs, and projects that 

receive federal funding or require federal approval must be found to be fully consistent 
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February 22, 2010 

with the SIP. The federal transportation conformity regulation2 found in 40 CFR parts 

51 and 93 requires SIPs to specify on-road motor vehicle emission budgets (budgets) 

that are consistent with attainment and maintenance of NAAQS. The conformity 

regulation requires metropolitan planning organizations to demonstrate that emissions 

from regional transportation plans and programs do not exceed these “emission 

budgets.” 

The District updated the South Coast transportation conformity budgets using ARB’s 

latest on-road mobile source emission factor model EMFAC2007 and transportation 

activity data from the 2008 RTP, Amendment 1 as adopted by SCAG in December 

2008. The budgets U.S. EPA previously approved as part the 2003 PM10 Attainment 

Plan were based on EMFAC 2002 and SCAG’s 2001 RTP. 

The District conducted an attainment modeling sensitivity analysis to evaluate the 

impact of increased motor vehicle emissions from potential growth on ambient PM10 

concentrations. Even if PM10 baseline emissions from motor vehicles were to increase 

by up to 20 tons per day (tpd), the South Coast would continue to show attainment 

through 2030 (Table 3). 

Table 3. Projected 24-hour PM10 Concentrations Assuming a 20 tpd Increase in 

the South Coast Air Basin Baseline PM10 Emissions 

Year Predicted County Maximum 24-hour PM10 Concentration 

(μg/m3) 

Los Angeles Orange Riverside San 

Bernardino 

2010 105 81 124 131 

2011 105 82 123 131 

2012 105 81 122 130 

2014 105 82 121 131 

2020 106 83 121 132 

2023 107 84 123 133 

2030 113 89 129 141 

Prior to the District’s Board hearing, the District revised the transportation conformity 

budgets in the South Coast PM10 Maintenance Plan, to reflect U.S. EPA‘s comment 

that the budgets only include emission reductions from already adopted control 

measures. Table 4 lists the revised on-road motor vehicle emission budgets for 

transportation conformity established for the years 2010, 2020, and 2030. After 

consultation with the District and SCAG, 5 tpd of PM10 were added to the conformity 

budget for 2030 and 7 tpd, 4 tpd, and 3 tpd of ROG to the budgets for 2010, 2020, and 

2030, respectively. Appendix C of the ARB Staff Report for the 2007 South Coast 

 

2

 U.S. EPA maintains online information on its transportation conformity program, including access to 

relevant rulemakings, policy guidance, and reports at: 

http://www.epa.gov/otaq/stateresources/transconf/index.htm
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February 22, 2010 

PM2.5 SIP presented the relative emissions contribution to the South Coast PM2.5 

formation from precursor gases, including ROG. Based on the established ratios, the 

additional ROG emissions translate to adding 1 tpd of PM10 emissions (rounding to 

whole tpd) for 2010, 2020, and 2030, respectively. Total additions for the 2030 budget 

are therefore the equivalent of 6 tpd of PM10. The additional 6 tpd of PM10 represents 

only 30 percent of the 20 tpd PM10 included in the District’s attainment modeling 

sensitivity analysis. The 6 tpd of PM10 facilitates anticipated growth while setting an 

emissions budget that ensures continued maintenance of the standard. ARB staff 

posted the revised budgets on ARB’s website to provide for the required 30-day public 

review. The revised emission budgets fulfill the requirements of the Act and U.S. EPA 

regulations to ensure that transportation activities support continued maintenance of the 

PM10 standard. 

Table 4. Transportation Conformity Emissions Budgets for PM10 in the 

South Coast Air Basin 

(Annual average)

Emission Budget 

(tons per day) 2010 2020 2030 

PM10 159 164 175 

NOx 372 180 116 

ROG 182 110 81 

IV. STAFF RECOMMENDATION 

ARB staff has reviewed the PM10 Redesignation Request and Maintenance Plan for the 

South Coast Air Basin and consulted with the District staff during this review. ARB staff 

finds that the South Coast Air Basin PM10 Maintenance Plan meets all applicable Act 

requirements. ARB staff believes that implementation of this plan will continue to 

maintain PM10 levels below the national air quality standard in the South Coast. 

Therefore, we recommend that the Board adopt the South Coast PM10 Maintenance 

Plans and the updated transportation conformity budgets for the South Coast, as a 

revision to the California SIP for submittal to U.S. EPA. In addition, ARB staff 

recommends that the Board approve the District’s request that the South Coast Air 

Basin be redesignated from nonattainment to attainment for the national PM10 

standard.