STATE OF CALIFORNIA

STAFF REPORT

ANALYSIS OF THE 

SAN DIEGO COUNTY AIR POLLUTION CONTROL DISTRICT

2012 REDESIGNATION REQUEST AND MAINTENANCE PLAN 

FOR THE 1997 NATIONAL OZONE STANDARD 

Date of Release: November 15, 2012

Scheduled for Consideration: December 6, 2012

This report 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 mention of trade 

names or commercial products constitute endorsement or recommendation for use.
2

TABLE OF CONTENTS

I. EXECUTIVE SUMMARY........................................................3

II. REDESIGNATION REQUIREMENTS.......................................3

III. EVALUATION OF THE SAN DIEGO OZONE PLAN....................4

A. San Diego County Attains the Ozone Standard............................4 

B. The State Has Met Applicable Act Requirements..........................5 

C. Improvement in San Diego Ozone Air Quality is Due to

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

D. Maintenance Plan 

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

2. Maintenance Demonstration..............................................6 

3. Ozone Monitoring Network................................................7 

4. Verification of Continued Attainment....................................7 

5. Contingency Provisions.....................................................7 

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

IV. STAFF RECOMMENDATION.................................................8
3

I. EXECUTIVE SUMMARY

On June 13, 2012, the U.S. Environmental Protection Agency (U.S. EPA) classified 

San Diego as a “Moderate” nonattainment area for the 1997 8-Hour Ozone National 

Ambient Air Quality Standard (standard), requiring a State Implementation Plan 

(SIP) addressing Moderate area control requirements to be submitted to U.S. EPA 

by June 13, 2013. The classification, which was made in response to a court order, 

was based on 2001 to 2003 air quality data. However, more recent data show that 

San Diego attained the standard in 2011. The San Diego Air Pollution Control 

District’s (District) 2012 Redesignation Request and Maintenance Plan

(Maintenance Plan) demonstrates that the region’s air quality now meets the federal 

standard, and that it will continue to do so through at least 2025. If approved by 

U.S. EPA, the Maintenance Plan will fulfill all applicable SIP requirements for the 

1997 8-Hour Ozone Standard. 

The District’s Governing Board is scheduled to consider adoption of the

Maintenance Plan on December 5, 2012. ARB staff has reviewed the Draft 

Maintenance Plan released on November 2, 2012 and finds that the Maintenance

Plan meets all applicable federal Clean Air Act (CAA) requirements for redesignation 

requests and maintenance plans. Staff recommends that the Board approve the 

Maintenance Plan contingent on ARB staff’s determination that the Maintenance 

Plan approved by the District Board does not differ significantly from that reviewed 

by ARB staff, and that the Board direct staff to submit the Maintenance Plan to 

U.S. EPA as a proposed revision to California’s SIP. 

II. REDESIGNATION REQUIREMENTS

ARB staff reviewed the Maintenance Plan within the context of the CAA, which 

identifies the following requirements that a nonattainment area must meet in order to 

be redesignated to attainment:

 Attainment of the standard has been demonstrated;

 The State has met all applicable CAA requirements for ozone in the 

nonattainment area;

 The area has an approved SIP;

 The area’s improvement in air quality is due to permanent and enforceable

ozone emission reductions; and

 The area has a U.S. EPA-approved maintenance plan.

The CAA also sets the general framework for maintenance plans. Each ozone 

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

10 years after redesignation, and must include the following components:

 A detailed emissions inventory;

 A maintenance demonstration;

 A commitment to continue operation of the monitoring network;
4

 A commitment to verify continued attainment; and

 A contingency plan to promptly correct any violation of the standard that

occurs after redesignation.

III. EVALUATION OF THE SAN DIEGO PLAN

Based on review of the Maintenance Plan and the District’s supporting technical 

analysis, ARB staff concurs that the Maintenance Plan meets the CAA requirements. 

The following sections describe the major elements of the Maintenance Plan.

A. Redesignation Request: San Diego Attains the 1997 8-hour Ozone Standard

The San Diego District operates an extensive ozone monitoring network that 

continuously monitors ambient ozone levels at numerous sites throughout San 

Diego County in compliance with federal requirements. The data generated at these 

monitors are used to define the nature and severity of ozone pollution in San Diego 

County, to identify ozone pollution trends, and to determine compliance with ozone 

air quality standards.

Data from the San Diego monitoring network show that the area attained the 1997 

8-hour ozone standard, which is 0.08 parts per million (ppm), in 2011. Figure 1 

maps the ozone monitors operating in the nonattainment area during the 2009

through 2011attainment period. Table 1 shows the fourth-highest daily maximum 

8-hour average ozone concentration recorded at each monitoring site in each of the 

past three consecutive years. U.S. EPA regulations specify that the three-year 

average of the fourth-highest daily concentrations recorded at each site must be 

used to determine whether a region attains the standard. The highest resulting 

averaged value is known as the ozone "design value" for the region; the 1997 8-hour 

ozone standard is attained when a region's design value is less than or equal to 

0.084 ppm. Table 1 shows that San Diego County's ozone design value is 0.082 

ppm. San Diego’s design value is established at the Alpine monitoring station, 

which has historically recorded the highest ozone concentrations in the region. As 

shown in Table 1, the 1997 8-hour ozone standard has been attained throughout the 

San Diego County Planning Area. 

Data from the 2012 ozone season have not yet been fully reviewed. Preliminary 

data indicate that the area continues to be in attainment of the 1997 ozone standard

to date. 
5

Figure 1. Ozone Monitoring Stations in San Diego County

Table 1. San Diego County Ozone Data: Annual Fourth-Highest Daily 

Maximum Concentrations (ppm)

Monitor Site 2009 2010 2011 3-Year 

Average

Alpine 0.085 0.081 0.082 0.082

Camp Pendleton 0.071 0.064 0.067 0.067

Chula Vista 0.067 0.068 0.055 0.063

Del Mar 0.067 0.063 0.064 0.064

Downtown 0.060 0.058 0.060 0.059

El Cajon 0.071 0.073 0.070 0.071

Escondido 0.074 0.075 0.068 0.072

Kearny Mesa 0.069 0.070 0.069 0.069

Otay Mesa 0.061 0.056 0.059 0.058

B. The State Has Met Applicable Clean Air Act Requirements

ARB and the District have met all of the CAA requirements applicable for a Moderate

ozone nonattainment area to be considered for redesignation. U.S. EPA fully 

approved San Diego’s 1-hour Ozone Maintenance Plan on July 28, 2003; this plan 

remains the applicable ozone SIP for San Diego until U.S. EPA approves a

subsequent ozone SIP submittal (San Diego’s 2012 Redesignation Request and 

Maintenance Plan). No SIP provisions are currently disapproved, conditionally 

approved, or partially approved.
6

C. Improvement in San Diego’s Ozone Air Quality is Due to Permanent and

Enforceable Reductions in Emissions

The Maintenance Plan projects that ozone precursor emissions will continue to 

decline through the maintenance period despite projected increases in population, 

motor vehicle use, meteorological fluctuations, and economic recovery. The benefits

of the adopted rules and regulations are projected to continue through the

maintenance period as older vehicles, engines, and equipment are replaced with 

newer units subject to more stringent emission control requirements. The 

Maintenance Plan also identifies the adopted State and local regulations that, 

together with federal controls, brought the area into attainment of the 1997 ozone 

standard. 

D. Maintenance Plan 

The Maintenance Plan also includes the components needed to demonstrate that 

the area will remain in attainment of the 1997 ozone standard: an attainment 

emission inventory that is projected to decline through 2025; a commitment to 

continue operation of the monitoring network; a commitment for verification of 

continued attainment; and a contingency plan.

1. Attainment Emission Inventory

Ozone is formed in the air by reactions of ozone precursor emissions, volatile 

organic compounds (VOC) and oxides of nitrogen (NOx), in the presence of sunlight 

and heat. Because San Diego attained the 8-hour ozone standard in 2011, total 

daily VOC and NOx emissions in 2011 represent the attainment inventory (see 

Table 2). The attainment inventory shows average total ozone precursor emissions 

of 142.6 tons per day (tpd) VOCs and 137.5 tpd NOx. 

Table 2. San Diego County 2011 Ozone Attainment Inventory

Summer Planning Inventory, tpd

Precursor Emissions 

Volatile organic compounds (VOC) 142.6

Nitrogen oxides (NOx) 137.5

2. Maintenance Demonstration

In addition to the 2011 adjusted baseline inventory of ozone precursor emissions, 

the Maintenance Plan provides emission projections through the year 2025. These 

projections incorporate the effects of projected growth in population, vehicle travel, 

and economic activity, as well as the effects of adopted regulations. As shown in 

Table 3, emissions of ozone precursors will continue to decline through 2025.

Because potential changes in military activities do not follow socioeconomic factors, 

the District included a projection of future mobile source emissions from potential 
7

additional military activity, obtained from the Department of the Navy, in its inventory 

projections. The projected inventory also includes banked emission reduction 

credits as a line item to demonstrate that the use of banked emissions credits will 

not interfere with maintenance.

Table 3. Emissions Trends

Emissions Source Category 2002 2011 2015 2020 2025

VOCs

Stationary Sources 28.4 31.1 33.1 35.8 36.8

Areawide Sources 42.2 35.9 35.3 36.7 37.5

On-Road Motor Vehicles 63.4 35.3 26.4 20.5 18.3

Non-Road Mobile Sources 49.1 40.3 37.1 35.4 36.1

Banked Emission Credits 0.9 0.9 0.9

Potential Future Military Activity 1.0 1.0 1.0

Total VOCs 183.1 142.6 133.9 130.3 130.6

NOx

Stationary Sources 8.2 6.3 5.6 5.5 5.6

Areawide Sources 1.9 1.7 1.8 1.9 2.0

On-Road Motor Vehicles 119.9 70.9 52.5 35.9 27.6

Non-Road Mobile Sources 68.0 58.6 54.9 50.4 47.5

Banked Emission Credits 0.7 0.7 0.7

Potential Future Military Activity 4.4 4.4 4.4

Total NOx 198.1 137.5 119.9 98.9 87.8

The declining inventory indicates that San Diego will maintain attainment of the 1997 

ozone standard due to ARB, District, and federal control measures that are already 

in place.

3. Ozone Monitoring Network

San Diego County’s nine-station ozone monitoring network substantially exceeds 

U.S. EPA requirements, which call for two ozone monitoring sites in an area of this 

size.

4. Verification of Continued Attainment

In the Maintenance Plan, the District commits to continue ozone monitoring to verify 

continued attainment of the 1997 ozone standard. The Maintenance Plan also 

includes a commitment to continue air monitoring data collection, verification, and 

submittal in compliance with federal guidelines.

5. Contingency Plan

The CAA requires that a maintenance plan include contingency provisions for 

prompt correction of any violation of an air quality standard that might occur after the 

area has been redesignated to attainment for that standard. U.S. EPA’s 
8

requirements specify that the area must have a plan ensures that contingency 

measures will be adopted if the area goes out of attainment.

The San Diego Maintenance Plan cites ARB mobile source control regulations that 

were not included in the emission projections as contingency measures that will 

provide significant continuing emissions reductions through the maintenance period.

The Maintenance Plan also includes a District commitment to adopt and implement 

additional emission control measures needed to ensure maintenance if a violation of 

the 1997 ozone standard is recorded. ARB staff concurs that the Maintenance Plan 

meets CAA contingency plan requirements.

6. Transportation Conformity Budgets

The CAA’s transportation conformity requirements are designed to ensure that 

transportation planning is consistent with air quality goals. Conformity is determined 

by comparing emissions from proposed projects and transportation system plans to 

the transportation conformity budgets established in the SIP. 

The Maintenance Plan includes the transportation conformity budgets shown in 

Table 5. The San Diego Association of Governments and District staffs agreed to 

use the projected on-road motor vehicle inventories for 2020 and 2025, rounded up 

to the nearest ton and increased by two tons, to develop the transportation

conformity budgets. These budgets provide room for economic recovery that 

exceeds current projections, but are still substantially lower than the 2011 on-road 

emissions levels that resulted in attainment of the 1997 ozone standard. If approved 

by the District Board in December 2012, these budgets will meet CAA requirements. 

Table 5. Emissions Budgets for Transportation Conformity

Ozone Precursor 2020 (Interim Year) 2025 (Horizon) and 

Subsequent Years

VOC 23 tpd 21 tpd

NOx 38 tpd 30 tpd

IV. STAFF RECOMMENDATION

ARB staff has reviewed the Maintenance Plan for San Diego and consulted with 

District staff during this review. ARB staff finds that the Maintenance Plan meets all 

applicable CAA requirements. ARB staff believes that implementation of this 

Maintenance Plan will continue to maintain ozone levels below the 1997 8-hour 

ozone National Ambient Air Quality Standard in the San Diego County Planning 

Area. Therefore, staff recommends that the Board adopt the San Diego County 

2012 Redesignation Request and Maintenance Plan as a revision to the California 

SIP for submittal to U.S. EPA. Staff further recommends that the Board approve the 

District’s request that the San Diego County Planning Area be redesignated from 

nonattainment to attainment for the national ozone standard.