State of California 

AIR RESOURCES BOARD 

 

June 2011 

RECOMMENDED 

AREA DESIGNATIONS 

FOR THE 

 2010 FEDERAL 

SULFUR DIOXIDE (SO2) STANDARD 

STAFF REPORT 

California Environmental Protection Agency 

Air Resources Board
i 

TABLE OF CONTENTS 

 Page 

BACKGROUND .......................................................................................................... 1 

SULFURE DIOXIDE AIR QUALITY............................................................................. 1 

EMISSIONS ................................................................................................................ 3 

RECOMMENDED AREA DESIGNATIONS ................................................................. 4 

SULFUR DIOXIDE MONITORING NETWORK REQUIREMENTS ............................ 5 

SUMMARY .................................................................................................................. 6 

APPENDIX 1: FIVE FACTOR ANALYSES 

APPENDIX 2: 2009 1-HOUR SO2 DESIGN VALUES 
ii 

LIST OF TABLES AND FIGURES 

 Page 

FIGURE 1: Graph of 1-hour SO2 Design Values at Highest Monitoring 

 Sites in California ..................................................................................... 2 

 

TABLE 1: Recommended California Attainment Areas for the Federal 

 1-Hour Sulfur Dioxide Standard ............................................................ 5 

TABLE 2: Minimum Sulfur Dioxide Monitoring Requirements .................................... 6 
1 

BACKGROUND 

This report provides the Air Resources Board’s (ARB) recommendations on 

designations for the revised federal sulfur dioxide (SO2) standard, based on air quality 

monitoring data for California. 

On June 2, 2010, the United States Environmental Protection Agency (U.S. EPA) 

established a new primary 1-hour SO2 standard of 75 parts per billion (ppb). At the 

same time, U.S. EPA revoked the 24-hour and annual average standards. In addition to 

changing the averaging time and level of the standard, U.S. EPA revised the ambient air 

monitoring and data reporting requirements for SO2. The final rule for the SO2 standard 

was published in the Federal Register on June 22, 2010 and can be accessed via the 

link below: 

http://www.epa.gov/ttn/naaqs/standards/so2/fr/20100622.pdf

SULFUR DIOXIDE AIR QUALITY 

Routine Monitoring 

California has attained the 24-hour and annual average standards since the late 1980s. 

In the early 1970s, peak 1-hour SO2 concentrations in California were as high as 

230 ppb, but by the early 1990s, had decreased to less than 50 ppb. Based on 

California’s routine monitoring network, in 2009, 1-hour SO2 concentrations are one 

tenth of 1970 levels, ranging from 3 ppb to 35 ppb. Figure 1 below shows the trends in 

1-hour SO2 concentrations for the South Central Coast, San Francisco Bay Area and 

South Coast Air Basins. These urban areas have the highest level of SO2

concentrations in California. Although the Nipomo site in the South Central Coast once 

had concentrations above the level of the 1-hour standard, concentrations have 

decreased as a result of new emission control requirements and revised permit 

requirements for a nearby refinery. The 20 year trend shows that sites with the highest 

SO2 concentrations in 2009 are well below the standard. 
2 

FIGURE 1 

 1-hour SO2 Design Values at Highest Monitoring Sites in California 

Special Purpose Monitoring 

In addition to the routine monitoring network, several special purpose monitoring 

networks are operated in the South Coast and San Francisco Bay Area. In the South 

Coast, the Port of Long Beach/Los Angeles Air Quality Monitoring Program collects data 

on criteria air pollutants, including SO2, to estimate ambient levels of pollution that are 

due to Port operational activities. Together, the two Ports operate six monitoring sites. 

At the Port of Los Angeles these sites are the Wilmington Community Monitoring 

Station, the San Pedro Community Monitoring Station, the Outer Harbor site, and the 

Terminal Island Treatment Plant Station. The two sites at the Port of Long Beach are 

the Inner and Outer Port sites. Terminal Island Treatment Plant Station (at the Port of 

Los Angeles) and the Inner Port site (at the Port of Long Beach) are expected to have 

the highest exposure to emissions from port operations, as they are in direct proximity 

to terminal operations which use a large number of diesel engine sources. The 2010 

1-hour SO2 design value at the Terminal Island Treatment Station was 59 ppm. The 

1-hour SO2 2010 design value at the Inner Port site was 62 ppb. 

In the San Francisco Bay Area, 15 ground level monitors are deployed at the region’s 

five petroleum refineries. These ground level monitors, required under the Bay Area Air 

Quality Management District’s Regulation 9, are located near or outside the facility 

property boundaries and monitor downwind near-source concentrations as part of the 

facility operating permit requirements. Measurements were collected at all 15 sites 

during the 2008 through 2010 timeframe, and all but one have valid 2010 1-hour SO2
3 

design values. The highest design values were 56 ppb, measured near the Chevron 

facility and 53 ppb measured near the Conoco facility. 

EMISSIONS 

ARB maintains a comprehensive Oxides of Sulfur (SOx) inventory. Staff estimates that 

SO2 comprises 97% of the SOx inventory. Additionally, in most combustion categories 

almost all SOx will be SO2. Therefore, in this report, SOx emissions are used to 

represent SO2 emissions. 

Emissions of SOx declined tremendously in California between 1990 and today. 

Statewide, emissions have decreased by 45% since 1990. SOx emissions from 

stationary sources have decreased due to improved industrial source controls and 

switching from fuel oil to natural gas for electric generation and industrial boilers. The 

SOx emissions from land-based on- and off-road gasoline and diesel-fueled engines 

and vehicles have also decreased due to lower sulfur content in the fuel, and 

regulations to reduce the sulfur content in fuel used by commercial harbor craft. 

As SOx is emitted primarily from combustion of fuels, emission control efforts have 

focused largely on reducing the content of sulfur in fuels. California has required the 

use of ultra-low-sulfur diesel fuel for on-road vehicles since 2006. In 2007, the U.S. 

EPA followed suit, requiring the ultra-low sulfur content (15ppm) in on-road diesel fuel 

sold in the United States. Off-road diesel fuel was required to transition to ultra-low 

sulfur by 2010. Railroad locomotive and marine diesel fuel was reduced to 500 ppm 

sulfur in 2007, and will change to ultra-low sulfur in 2012. By the end of 2014, all 

highway, off-road, locomotive and marine diesel fuel produced will be ultra-low-sulfur 

diesel. 

Implementation of the revised SO2 standard is focused on large stationary sources. 

U.S. EPA guidance suggests initial focus on those emitting 100 tons per year or greater 

of SO2. States are required to identify and eventually conduct air quality modeling of 

any sources that may be anticipated to contribute to a violation of the revised SO2

standard. SOx emissions from stationary sources in California are a fraction of the 

levels in other parts of the country. The largest sources in the U.S. have emissions 

exceeding 100,000 tons per year. These are large fossil fuel electrical generation 

facilities located in the eastern and southern states. In contrast, the largest source of 

SOx emissions in California, a refinery in the Bay Area, has emissions of approximately 

5,000 tons per year, and ranks 350 on the list of top SO2 emitters in the nation. In total, 

there are 34 facilities in California with emissions greater than 100 tons per year. ARB 

staff is working with air districts to conduct additional dispersion modeling as required by 

U.S. EPA. 
4 

RECOMMENDED AREA DESIGNATIONS 

ARB staff evaluated the available ambient SO2 data and SOx emissions data to 

determine appropriate area designations throughout the State. The recommendations 

in this report are based on SO2 air quality data collected between 2007 and 2009. The 

analysis was conducted for each monitoring site in the State for which data are 

available. Generally, the 99th percentile is the fourth highest 1-hour SO2 concentration 

measured during a year. However, if data are incomplete, a higher value may be used, 

in accordance with established U.S. EPA criteria. 

ARB staff has conducted a five factor analysis to determine the appropriate 

designations and boundaries. The five factors recommended by U.S. EPA for the 

purposes of determining the appropriate attainment area boundaries include: 

jurisdictional boundaries, geography/topography, meteorology, emissions, and air 

quality data. No areas with monitors in California violate the federal 1-hour SO2

standard. 

Areas of the State where no monitors exist are generally more rural in nature. There 

are no facilities located in these air basins with significant SOx emissions (greater than 

100 tons per year), and only two facilities with SOx emissions greater than 50 tons per 

year. In comparison to the rest of the state, total SOx emissions are low. Since the 

existing monitoring network indicates that all areas with monitors are well below the 

level of the standard, ARB staff conclude that areas without monitors should also be 

below the standard. 

Therefore, ARB staff is recommending that all areas in California be designated 

attainment for the 1-hour SO2 standard. The recommended area designations are 

summarized in Table 1 below. Staff is recommending the air basin as the appropriate 

boundary for all of the attainment areas. Air basin boundaries were developed based 

on regions with similar meteorology and topography. The five factor analysis for each 

air basin is provided in Appendix 1. Design values for individual monitoring sites are 

provided in Appendix 2. 
5 

Table 1 

Area Designation Recommendations 

Air Basin Name Recommended Designation 2009 DV

SO2 

(ppb) 

Mojave Desert Attainment 10 

North Central Coast Attainment 11* 

North Coast Attainment 5 

Sacramento Valley Attainment 4* 

Salton Sea Attainment 10 

San Diego Attainment 17 

San Francisco Bay Area Attainment 25 

San Joaquin Valley Attainment 9* 

South Central Coast Attainment 35 

South Coast Attainment 20 

Great Basin Valleys Attainment n/a 

Lake County Attainment n/a

Mountain Counties Attainment n/a

Northeast Plateau Attainment n/a

Lake Tahoe Attainment n/a

*Design value is not considered complete under U.S. EPA criteria. While no other site exists in 

the basin with a valid design value, the indicated design value is representative of concentrations 

in the region.

SULFUR DIOXIDE MONITORING NETWORK REQUIREMENTS 

The final rule for the primary SO2 standard also specifies the minimum number of SO2

monitoring sites that State and local air agencies must operate. The monitoring 

regulations require SO2 monitors be placed in Core Based Statistical Areas (CBSAs) 

based on a population weighted emissions index (PWEI) for the area. The PWEI is 

calculated by multiplying the latest available SO2 emission data within each CBSA by 

the population of the CBSA, and then dividing the result by one million. The final rule 

requires: 

• Three SO2 monitors in CBSAs with PWEI values of one million or more; 

• Two SO2 monitors in CBSAs with PWEI values less than one million but 

greater than 100,000; and 

• One SO2 monitor in CBSAs with PWEI values greater than 5,000 but less than 

100,000. 
6 

California has thirty-five CBSAs with population ranging from 17,000 to more than 

12 million people. Table 2 lists the three CBSAs in California that require SO2

monitoring. In addition, Table 2 shows that these CBSAs either meet or exceed federal 

monitoring requirements for SO2. California’s monitoring network currently consists of 

39 monitors, in excess of the 4 required monitors. 

Table 2 

Minimum Monitoring Requirements for Sulfur Dioxide 

CBSA 

Counties in 

CBSA 

SO2 

emissions 

per CBSA 

(tpy) 

Population 

(2009) 

PWEI 

(Million 

personstpy) 

Required 

SO2 

Monitors 

Existing 

SO2 

monitors 

Los Angeles-Long 

Beach-Santa Ana 

Los Angeles, 

Orange 13,498 12,874,797 173,785 2 5 

Riverside-San 

BernardinoOntario Riverside, San 

Bernardino 2,478 4,143,113 10,266 1 4 

San FranciscoOakland-Fremont 

Alameda, 

Contra Costa, 

San 

Francisco, 

San Mateo, 

Marin 12,669 4,317,853 54,702 1 9 

SUMMARY 

ARB has used California’s air quality monitoring and emissions data to develop 

recommended area designations for U.S. EPA’s revised 1-hour SO2 standard. The 

statewide monitoring network shows no violations and the highest concentrations are far 

below the new federal standard. A review of the statewide monitoring data and SOx 

emissions shows that California attains the SO2 standard. Therefore, ARB recommends 

all air basins in California be designated as attainment. Additional dispersion modeling, 

for sources with SOx emissions greater than 100 tons per year, will be provided to the 

U.S. EPA. ARB is working with air districts to complete the required modeling and plans 

to submit the modeling results to the U.S. EPA later this year. 
APPENDIX 1 

FIVE FACTOR ANALYSES FOR 

CALIFORNIA AIR BASINS 

 
APPENDIX 1 Five Factor Analyses 

Air Basins Having Facilities Greater Than 100 Tons Per Year of SOx Emissions 

I. San Francisco Bay Area Air Basin 

II. South Coast Air Basin 

III. San Joaquin Valley Air Basin 

IV. Mojave Desert Air Basin 

V. South Central Coast Air Basin 

VI: Remaining Air Basins 

Sacramento Valley Air Basin 

San Diego Air Basin 

Salton Sea Air Basin 

North Central Coast Air Basin 

Mountain Counties Air Basin 

Great Basin Valleys Air Basin 

Lake County Air Basin 

Lake Tahoe Air Basin 

Northeast Plateau Air Basin 
A-1 

I. SAN FRANCISCO BAY AREA BASIN 

Recommendation 

Ambient air quality monitors in the San Francisco Bay Area Air Basin (Bay Area) show a 

2009 1-hour sulfur dioxide (SO2) design value of 25 parts per billion (ppb). Because this 

value is well below the level of the federal standard, staff recommends the Bay Area be 

designated as attainment, based on the assessment provided below. The assessment 

includes an evaluation of the five factors recommended by U.S. EPA for the purposes of 

determining the appropriate attainment area boundaries: jurisdictional boundaries, 

geography/topography, and meteorology (collectively referred to as nature of the 

region), emission data, and air quality data. Additional dispersion modeling results will 

be provided to the U.S. EPA later this year to further support the attainment designation 

recommendation. 

Nature of the Region 

The Bay Area is California’s second largest metropolitan region. The nine county area 

comprises all of Alameda, Contra Costa, Marin, Napa, San Francisco, San Mateo, and 

Santa Clara counties, the southern half of Sonoma County, and the southwestern 

portion of Solano County. It includes a number of large cities, for example, San 

Francisco, Oakland, and San Jose. Overall, approximately 20% of California’s 

population resides in the Bay Area. The entire nine county area falls under the 

jurisdiction of the Bay Area Air Quality Management District (Bay Area District or 

District), which has responsibility for developing and implementing rules and regulations 

to control SO2 emissions from stationary sources located in the region. 

Although the Bay Area comprises a diverse landscape, the unifying feature of this 

region is the Bay itself, which is one of the largest natural harbors in the world. The Bay 

is oriented north-south and covers about 400 square miles of the region’s total 5,340 

square miles. Surrounding the Bay are the Coast Range Mountains, oriented 

northwest/southeast with elevations up to about 2,500 feet. Along the western and 

northern shores of the Bay are numerous headlands and peninsulas separated by small 

bays which lead into valleys and canyons in the surrounding foothills. In contrast, much 

of the eastern side is bordered by a low plain that slopes up into the Berkeley Hills. The 

highest population densities occur in the heavily urbanized areas surrounding the Bay. 

These urban centers give way to more suburban areas, to the north, south, and east. 

Although these areas are less densely populated, they are home to a significant number 

of people. 

 
A-2 

As with most of California, the Bay Area exhibits the typical wet winter/dry summer 

meteorological regime. Rainfall varies from more than 20 inches along the coast to less 

than 15 inches at inland locations. Because of the variety of terrain, air flow in the 

region can be complex, especially at the lowest levels. This is particularly true when the 

airmass is stable and wind speeds are weak. Although flow patterns vary, the Bay Area 

shows a general sea breeze circulation pattern with onshore flow during the day and 

offshore flow during the evening and overnight hours. During the summer, surface 

temperatures over the Bay Area are determined in large part by the effect of differential 

heating between land and water surfaces. This process produces a large-scale gradient 

across the region. The temperature difference between coastal locations and inland 

locations can be 35 degrees Fahrenheit (F) or more on many summer afternoons. At 

night, the difference is usually less than 10 degrees F. The coastal versus inland 

temperature extremes reverse during the winter months, with smaller differences during 

the daytime and larger differences at night. 

Emissions 

Based on the Air Resources Board’s (ARB) 2008 emission inventory, there were 

22,448 tons per year of total SOx emissions in the Bay Area. Petroleum refining and

combustion-related processes accounted for approximately 55% of the total emissions, 

while ocean going vessels accounted for an additional 20% of the total. Another 15% of 

the total SOx emissions was attributable to the mineral processes, chemical processes, 

and manufacturing and industrial fuel combustion categories. The remaining fraction of 

emissions was distributed over a number of small stationary, area-wide, off-road, and 

on-road source categories. 

Stationary sources are of particular interest because implementation of the federal 

1-hour SO2 standard is focused on determining whether large stationary sources have 

the potential to result in violations of the standard. U.S. EPA guidance suggest initial 

focus on sources emitting more than 100 tons of SOx per year. Stationary sources 

account for the majority of SOx emissions in the Bay Area, and emissions from these 

sources have decreased. Figure 1, based on data from ARB’s facility emissions 

database, shows total SOx emissions from all stationary source facilities in the Bay Area 

during 1998 and 2008. Overall, stationary source facility SOx emissions have been 

reduced by a third, down from 19,161 tons per year in 1998 to 12,744 tons per year in 

2008.

 
A-3 

FIGURE 1 

While the above information is based on ARB’s 2008 emission inventory, more recent 

data for specific large facilities are available from the Bay Area District. The remainder 

of this discussion centers on these large facilities because of EPA’s focus on their 

potential to violate the 1-hour standard. Based on the District’s 2009 emission data, 

there are nine stationary source facilities in the Bay Area with SOx emissions in excess 

of 100 tons per year. These sources are summarized in Table 1 and Figure 2. 

TABLE 1 

Bay Area Facilities with SOx Emissions Greater than 100 Tons per Year 

0

5,000

10,000

15,000

20,000

SF

Emissions (t/y)

Sulfur Oxides Emissions from ARB's

Facilities Database - San Francisco Bay Area

1998 SOx (t/y) 2008 SOx (t/y)

Facility Name City County SOx Emissions 

Valero Refining Company Benicia Solano 5,066.10 t/y

Shell Martinez Refinery Martinez Contra Costa 1,222.50 t/y 

Conoco Phillips Refining Rodeo Contra Costa 1,172.10 t/y 

Tesoro Refining Martinez Contra Costa 588.6 t/y 

ConocoPhillips Rodeo Contra Costa 500.4 t/y 

Chevron Products Company Richmond Contra Costa 470.4 t/y 

Rhodia, Inc. Martinez Contra Costa 307.5 t/y 

Lehigh Southwest Cement Cupertino Santa Clara 240.2 t/y 

General Chemical West LLC Richmond Contra Costa 163.5 t/y 
A-4 

FIGURE 2 

Six of the large Bay Area sources are petroleum refining and processing facilities. Five 

of these petroleum-related facilities are located in Contra Costa County, and one is 

located in Solano County. The remaining three facilities are a cement plant located in 

Santa Clara County and two chemical manufacturing facilities located in Contra Costa 

County. Together, these nine facilities emitted 9,731 tons of SOx in 2009, representing 

about 38% of the total 2009 Bay Area SOx emissions. 

The Bay Area District has reduced emissions from stationary facilities through a 

combination of District rules controlling SOx emissions, permitting requirements, and 

compliance with recent U.S. EPA consent agreements. The Bay Area District has two 

existing rules that control SO2 emissions: 

 
A-5 

* Regulation 9: Inorganic Gaseous Pollutants, Rule 1: Sulfur Dioxide

establishes emissions limits from stacks, as well as ground-level concentration 

limits (beyond the facility property) for sulfur dioxide-emitting operations. There 

are specific limits for sulfur content in fuels, sulfur recovery plants, sulfuric acid 

plants, fluid catalytic cracking units, fluid cokers and coke calcining kilns, catalyst 

manufacturing plants, fresh fruit sulfuring operations, sulfur removal operations at 

petroleum refineries, and ships. 

* Regulation 12: Miscellaneous Standards of Performance, Rule 12: Flares 

at Petroleum Refineries requires reporting and analysis of any flaring emission 

of over 500 lbs per day of sulfur dioxide. To reduce future emisisons, the 

analysis is incorporated into flaring minimization plans. 

In addition to these two rules, the Bay Area District implements two operating permit 

programs. Approximately 9,200 facilities have District operating permits which are 

renewed on an annual basis, in most cases. Permit renewal includes a review to 

determine if permit conditions are adequate to ensure compliance with, and the 

enforceability of, applicable rules and regulations. Requirements for projects that would 

increase SO2 emissions include Best Available Control Technology (for sources that 

emit 10 pounds per day or more), offsets (for major sources that increase emissions by 

more than 1 ton per year), and air quality impact analysis which includes review for the 

1-hour federal SO2 standard (for major sources that would increase emissions by more 

than 40 tons per year). The permit review also includes a compliance determination for 

other applicable rules and regulations. 

Finally, SO2 emissions from the largest SOx emission source in the Bay Area (as well as 

in California) have been significantly reduced as the result of a U.S. EPA consent 

decree. The 2005 U.S. EPA consent decree required the Valero refinery to reduce 

sulfur dioxide emissions at their fluid catalytic cracking unit (FCCU). Valero installed a 

pre-scrubber for PM and sulfate removal and a regenerative amine scrubber for sulfur 

dioxide. These controls abate emissions from the FCCU and from Valero’s coker, 

which are vented to a common stack. The new emissions control equipment reduced 

SO2 emissions more than 90% -- from a potential to emit of 6,222 tons per year to 

416 tons per year. 

In addition to existing controls, the Bay Area District included two upcoming rules in 

their 2010 Clean Air Act Plan. When formally adopted, these rules will further reduce 

SOx emissions: 

 
A-6 

SSM 8 - Coke Calcining: This measure will reduce SO2 emissions from coke 

calcining by requiring a minimum 80% sulfur capture. In combination, the two 

coke calcining kilns at District Plant 22 (ConocoPhillips Carbon Plant) emit 

1,232 tons of sulfur dioxide per year. The facility has committed to reducing SO2 

emissions by 42 tons per year to provide offsets for their Clean Fuels Expansion 

Project. The plant currently operates an abatement device to periodically trim 

SO2 emissions to maintain compliance with the current SO2 emission limit in 

Regulation 9, Rule 1 of 400 ppm by volume or 113 kg (250 pounds) per hour, 

whichever is more restrictive. 

Similar to the proposed rule described above, the South Coast Air Quality 

Management District also requires a minimum 80% sulfur capture. The Bay 

Area’s proposed SSM 8 - Coke Calcining measure is intended to replicate the 

South Coast measure. Bay Area District staff expect to take a proposed rule to 

their Board in mid-2012. 

SSM 9 - Cement Kilns: This control measure would reduce emissions of NOx, 

SOx, mercury, and other toxic air contaminants from cement kilns. There is one 

cement manufacturing facility in the Bay Area: Lehigh Southwest Cement 

(plant #17). The proposed rule would require Lehigh to use abatement 

technology to reduce NOx emissions and to consider a wet scrubber to reduce 

SO2 emissions if any synergies in installing SO2 controls along with NOx controls 

(or other controls) can be identified. Bay Area District staff expects to take a 

proposed rule for cement kilns to their Board in 2011. 

Air Quality Trends 

Ten SO2 monitors were operated in the Bay Area during the 2007 through 2009 time 

period. An additional monitor recently began operating near the Lehigh Southwest 

Cement facility in Cupertino. These air quality monitors, shown in Figure 2, collect 

quality-assured data for record. Most of the Bay Area monitors are located in and 

around the more heavily industrialized eastern portion of the region. Several others are 

located downwind of the major source areas (refer to Figure 2). Based on data 

collected during 2007 through 2009, six monitoring sites have valid design values. 

These design values range from 8 to 25 parts per billion (ppb), which is well below the 

level of the federal 1-hour standard. Although the remaining sites do not have valid 

design values for the three-year period, individual fourth high 1-hour measurements are 

well below the level of the standard, indicating that design values for these sites would 

also be below the standard. 
A-7 

The monitoring site with the highest 1-hour SO2 design value in the Bay Area is the 

Crockett-Kendall Avenue site in Contra Costa County. This site is located in the portion 

of the Bay Area that has the greatest density of stationary SO2 sources. The 2009 

design value for the Crockett site is 25 ppb, which is well below the 75 ppb standard. 

The next highest design value is 18 ppb, measured at both the Martinez-Jones Street 

and Richmond-7th Street sites. These sites are also located in Contra Costa County, 

also in the vicinity of the largest SO2 sources. 

One-hour ambient SO2 concentrations at Bay Area sites have decreased during the last 

20 years. Figure 3 shows the trend for the three highest sites from 1990 through 2009. 

Although concentrations are variable from year-to-year, they show a 50% overall 

decrease. Design values for these sites have never been more than two-thirds the level 

of the federal standard, and in 2009, were no more than one-third the level of the 

standard. Design values for other sites in the Bay Area are even lower, ranging from 

8 to 14 ppb in 2009. Monitoring sites in the Bay Area are located both upwind and 

downwind of the main source area, indicating that people living in this region of 

California are not exposed to SO2 concentrations above the level of the federal 

standard. 

FIGURE 3 

 

0

10

20

30

40

50

60

70

80

Federal 1-hour SO2 (ppb)

1-Hour Federal SO2 Design Value

San Francisco Bay Area

Crockett-Kendall Avenue Martinez-Jones Street

Richmond-7th Street Fed 1-hr SO2 NAAQS (75 ppb)
A-8 

In addition to the long-term ambient monitoring network, 15 ground level monitors are 

deployed at the five Bay Area petroleum refineries (refer to Figure 4). These ground 

level monitors, required under the District’s Regulation 9, are located near or outside the 

facility property boundaries and monitor downwind near-source concentrations as part 

FIGURE 4 

of the facility operating permit requirements. Measurements were collected at all 

15 sites during the 2008 through 2010 timeframe, and all but one have valid 2010 

1-hour SO2 design values. As summarized in Table 2, none of these sites had a design 

value above the level of the federal standard. The highest design values were 56 ppb, 

measured near the Chevron facility and 53 ppb measured near the Conoco facility (note 

that the monitor near the Conoco facility is missing data for one quarter, but based on 

the other data collected at this site, it is highly unlikely the design value exceeded the 

standard). 
A-9 

TABLE 2 

2010 1-Hour SO2 Design Values for Monitors 

Located Near Bay Area Petroleum Refineries 

* Missing data for 1 quarter 

Summary 

Staff evaluated the five factors recommended by U.S. EPA for the purposes of 

determining attainment status and appropriate boundaries for federal SO2 designations: 

jurisdictional boundaries, geography/topography, meteorology, emission data, and air 

quality data. Based on this analysis, violations of the 1-hour SO2 standard have not 

been measured over the last two decades, and violations are not expected to occur in 

the future. Therefore, staff recommends the San Francisco Bay Area be designated as 

attainment, with the San Francisco Bay Area Air Basin serving as the appropriate 

boundary for the attainment area. This recommendation is based on the following 

weight of evidence: 

• The San Francisco Bay Area has a comprehensive SO2 monitoring network, with 

monitoring sites located in the areas with the highest SOx emissions. Design 

values for all the Bay Area sites are well below the level of the standard, 

Refinery Site Design Value 

Chevron 

2201 56.3 ppb 

2202 17.7 ppb 

2203 31.7 ppb 

Conoco 

2263 53.3 ppb* 

2265 3.3 ppb 

2271 10.0 ppb 

2273 36.7 ppb 

2274 18.3 ppb 

Shell 2242 0.3 ppb 

Tesoro 

2251 36.7 ppb 

2252 20.0 ppb 

2253 10.0 ppb 

Valero 

8201 1.7 ppb 

8202 3.0 ppb 

8203 1.3 ppb 
A-10 

including air quality monitoring data for the east Bay region, which has the 

greatest density of SOx sources and emissions; 

• Emissions from SOx facilities have declined more than 30% since 1998 and are 

expected to continue declining as a result of continuing and anticipated District 

emission control programs; 

• The San Francisco Bay Area Air Basin falls under the control of one jurisdiction: 

the Bay Area Air Quality Management District, and the most effective air quality 

management will be achieved by including the entire air basin in the attainment 

area; 

• There are no specific meteorological, geographical, or topographic factors that 

warrant a different boundary for the attainment area; and 

• Bay Area District staff are in the process of conducting dispersion modeling for 

large local SO2 sources, as described in the March 2011 U.S. EPA guidance, 

and results of this modeling are expected to provide further support for the 

attainment designation. 

 
A-11 

II. SOUTH COAST AIR BASIN

Recommendation 

Ambient air quality monitors in the South Coast Air Basin (South Coast) show a 2009 

1-hour sulfur dioxide (SO2) design value of 20 parts per billion (ppb), which is less than 

one-third the level of the federal standard. Because this value is well below the 

standard, staff recommends the South Coast be designated as attainment, based on 

the assessment provided below. The assessment includes an evaluation of the five 

factors recommended by U.S. EPA for the purposes of determining the appropriate 

attainment area boundaries: jurisdictional boundaries, geography/topography, and 

meteorology (collectively referred to as nature of the region), emission data, and air 

quality data. Dispersion modeling results will be provided to the U.S. EPA later this year 

to further support the attainment designation recommendation. 

Nature of the Region 

The South Coast is California’s largest metropolitan region. The area includes the 

southern two-thirds of Los Angeles County, all of Orange County, and the western 

urbanized portions of Riverside and San Bernardino counties. It covers a total of 

6,480 square miles and is home to nearly 17 million people -- more than 40% of the 

State’s population. The South Coast falls under the jurisdiction of the South Coast Air 

Quality Management District (District), which has responsibility for developing and 

implementing rules and regulations to control SOx emissions from stationary sources 

located in the region. 

The South Coast region generally forms a lowland coastal plain, bounded by the Pacific 

Ocean on the west and by mountains on the other three sides. Although the coastal 

plain comprises only about a third of the region’s land area, more than 80% of the South 

Coast population lives in the coastal area. The region boasts a diverse economic base. 

Historically, the four South Coast counties collectively comprised one of the fastest 

growing local economies in the United States. However, the industrial base has 

realized significant changes over the last several decades. Similar to many other parts 

of the nation, a large segment of the heavy manufacturing sector, including steel and 

tire manufacturing and automobile assembly, has been phased out. These operations 

have been replaced by smaller service industries and businesses that have developed 

as a result of growth in the regional shipping and trade sectors. 

Overall, the South Coast region experiences more days of sunlight than any other major 

urban area in the nation except Phoenix. However, the climate does vary, from mild 

near the coast to more extreme at inland locations. The coastal area benefits from the 

 
A-12 

marine influence. This influence moderates temperatures, and the daily 

onshore/offshore circulation pattern tends to disperse pollutants, which keeps pollutant 

concentrations low. Average temperatures in the coastal area vary from lows in the 

mid-50s to highs in the mid-70s, with annual precipitation ranging from 12 to 15 inches. 

Further inland, temperatures increase and precipitation decreases. Average highs 

during the summertime can reach the mid- to high-90s, with maximum daily 

temperatures over 100 degrees Fahrenheit common in many inland areas. Rainfall in 

some areas averages less than 10 inches per year. In contrast to the low elevation 

inland areas, the surrounding inland mountains reach elevations of more than 10,000 

feet. These areas see temperatures below freezing in the winter and precipitation in the 

form of snow. 

Emissions 

There are 13,870 tons per year of total SOx emissions in the South Coast, based on 

the Air Resources Board’s (ARB) 2008 emission inventory. The major sources are 

ocean-going vessels and related port industrial and freight activities. The South Coast 

is home to two major port facilities. The Port of Long Beach is the second busiest 

container port in the country and is considered one of the largest shipping ports in the 

world. It is located approximately two miles from downtown Long Beach and twenty 

miles south of downtown Los Angeles. Occupying 3,200 acres of land, the Port of Long 

Beach adjoins the neighboring Port of Los Angeles. 

The remainder of this section addresses large SO2 stationary sources in the South 

Coast because implementation of the federal 1-hour SO2 standard is focused on 

determining whether large stationary sources have the potential to result in violations of 

the standard. U.S. EPA guidance suggests initial focus on sources emitting more than 

100 tons of SOx per year. Figure 5, based on data provided by the South Coast District, 

shows total SOx emissions from all stationary source facilities in the South Coast during 

1998 and 2008. Overall, stationary source SOx emissions have decreased 40%, down 

from 7,748 tons per year in 1998 to 4,570 tons per year in 2008. 

There are eleven stationary source facilities with SOx emissions greater than 

100 tons per year in the South Coast. All eleven facilities are located in Los Angeles 

County and most are related to petroleum processing and transportation. Together, 

these facilities represent 84% of the total stationary source component of the South 

Coast SOx inventory. The map in Figure 6 shows the locations of the large SOx

facilities. Seven of the facilities are located relatively close to one another, near the 

Port of Long Beach, south of the city of Los Angeles. The remaining four are scattered 

around the southern and central portions of the County. Table 3 provides a summary of 

the sources, their location, and their SOx emissions levels. 
A-13 

FIGURE 5 

FIGURE 6 

0

1,000

2,000

3,000

4,000

5,000

6,000

7,000

8,000

9,000

Emissions (t/y)

Sulfur Oxides Emissions from ARB's

Facilities Database - South Coast

1998 SOx (t/y) 2008 SOx (t/y)
A-14 

TABLE 3 

South Coast Facilities with SO2 Emissions Greater than 100 tons per year 

Facility Name City County SOx Emissions 

BP West Carson Refinery Carson Los Angeles 915 t/y 

Chevron Products Company El Segundo Los Angeles 429 t/y 

Rhodia Carson Los Angeles 426 t/y 

Tesoro Refining & Marketing Wilmington Los Angeles 368 t/y 

Ultramar Inc. (NSR use only) Wilmington Los Angeles 357 t/y 

Exxon Mobil Oil Corporation Torrance Los Angeles 328 t/y 

Conoco Phillips Company Carson Los Angeles 305 t/y 

Conoco Phillips Company Wilmington Los Angeles 270 t/y 

BP West Wilmington Wilmington Los Angeles 208 t/y 

LA County Sanitation District City of Industry Los Angeles 142 t/y 

Owens-Brockway Glass Vernon Los Angeles 100 t/y 

The South Coast has the most stringent SO2 control measures in the nation. These 

measures go far beyond what U.S. EPA has required in recent settlement agreements 

of similar facilities in California and the rest of the country. The South Coast District is 

in the process of submitting updates to their regulations. Under their Regional Clean Air 

Incentives Market (RECLAIM) program, these updates will ensure an additional 

2,080 tons per year reduction in SOx emissions. Of the total 2,080 ton reduction, more

than half (1,095 tons) will be reduced by 2013. All of the large SOx facilities, with the 

exception of the Los Angeles County Sanitation District, are covered by these updated 

regulations, which are both verifiable and enforceable. 

In addition to the stationary source SOx emission control measures adopted by the 

South Coast District, the ARB has a number of emission control measures that will 

reduce emissions from port-related sources including cargo handling, commercial 

harbor craft, port trucks, and ship auxiliary and main engines. There are additional 

substantial emission reduction efforts at the local level. The Ports of Long Beach and 

Los Angeles approved the San Pedro Bay Ports Clean Air Action Plan (Ports Plan) in 

2006, which provides an overall strategy for reducing air pollution emissions from 

port-related cargo movement. Among the main elements of the Ports Plan are 

requirements and incentives to reduce diesel truck-related emissions in the ports area 

and surrounding communities. 
A-15 

Air Quality Trends 

As mentioned earlier, there are seven SO2 monitors in the South Coast that collect 

quality-assured data for record (refer to Figure 7). Several of these monitors are 

located near (from 2 to 12 miles) the largest SOx facilities in Los Angeles County and 

are therefore well-sited for capturing the highest regional SO2 concentrations. In 

addition to these monitors, several others are located in Orange, Riverside, and 

San Bernardino counties. These sites monitor public SO2 exposure from smaller 

facilities and from area wide transportation sources. Based on data for record collected 

during 2007 through 2009, the South Coast attains the federal 1-hour SO2 standard with 

design values for individual sites ranging from 6 ppb to 20 ppb, with design values for 

most sites below 10 ppb.

The monitoring site with the highest design value in the South Coast is the North Long 

Beach site, located near the area with the highest density of major SOx emission 

sources. This site has a design value of 20 ppb, which is well below the level of the 

standard. The long-term trend in 1-hour SO2 design values at North Long Beach is 

graphed in Figure 7. The trend line shows the value is now less than half what it was in 

1998, and the design value has never violated the federal standard. Figure 7 also 

shows trend lines for two other long-term sites: Burbank and Riverside. These sites 

are located in the inland portions of Los Angeles and Riverside counties, respectively. 

In 2009, design values at these sites were less than half the value for North Long 

Beach, indicating that concentrations are much lower in areas further away from the 

main source area near the coast. 

In addition to the long-term SO2 monitoring network, the ports of Long Beach and 

Los Angeles conduct special monitoring to measure air quality at the ports and in 

nearby communities. The ports monitoring network collects air quality (including SO2) 

and weather data on a real-time basis to provide timely and accurate information on air 

quality in the ports region. The Port of Long Beach operates two monitoring stations: 

one in the Inner Port area, near West Long Beach (also called Superblock), and the 

second in the Outer Port area, near the breakwater (also called Gull Park). The Port of 

Los Angeles operates four monitoring stations, located in the Outer Harbor area at 

Berth 47, at the Terminal Island Treatment Plant, in the community of San Pedro, and in 

the community of Wilmington. The six-monitor network was developed under the Green 

Port Policy and is used to better manage air quality improvement efforts. As shown in 

the Table 4, the three-year average of the 99th percentile 1-hour concentration for the 

six ports sites ranged from 34 ppb to 62 ppb, all of which are below the level of the 

federal standard. 
A-16 

FIGURE 7 

TABLE 4 

1-Hour SO2 Design Values for Monitoring Sites Located at 

the Ports of Long Beach and Los Angeles 

Site Port 2008-2010 Design Value 

Inner Port (Superblock) Port of Long Beach 62 ppb 

Terminal Island Port of Los Angeles 53 ppb 

Outer Port (Gull Park) Port of Long Beach 47 ppb 

Outer Harbor Port of Los Angeles 47 ppb 

San Pedro Port of Los Angeles 44 ppb 

Wilmington Port of Los Angeles 34 ppb 

 

0

10

20

30

40

50

60

70

80

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009

Federal 1-hour SO2 (ppb)

1-Hour Federal SO2 Design Values

South Coast

North Long Beach Burbank-W Palm Avenue Riverside-Rubidoux Fed 1-hr SO2 NAAQS (75 ppb)
A-17 

Summary 

Staff evaluated the five factors recommended by U.S. EPA for the purposes of 

determining attainment status and appropriate boundaries for federal SO2 designations: 

jurisdictional boundaries, geography/topography, meteorology, emission data, and air 

quality data. Based on this analysis, violations of the 1-hour SO2 standard have not 

been measured over the last two decades, and violations are not expected to occur in 

the future. Therefore, staff recommends the South Coast be designated as attainment, 

with the South Coast Air Basin serving as the appropriate boundary for the attainment 

area. This recommendation is based on the following weight of evidence: 

• South Coast Air Basin has a comprehensive SO2 monitoring network, with 

monitoring sites in the areas with the highest SOx emissions and expected 

highest concentrations. Design values for all the South Coast monitoring sites 

are well below the level of the standard, including monitoring data collected in the 

Long Beach/San Pedro area, which has the greatest density of SOx sources and 

emissions; 

• The South Coast has the most stringent SOx control measures in the nation; 

• Stationary source SOx emissions decreased 40% between 1998 and 2008. The 

South Coast District is currently updating rules that will ensure an additional 

2,080 ton per year reduction in SOx emissions from large facilities participating in 

its RECLAIM program, and more than half the reduction will occur by 2013; 

• The South Coast Air Basin falls under the jurisdiction of a single agency, the 

South Coast Air Quality Management District, and effective air quality 

management is best achieved by including the entire air basin in the attainment 

area; 

• There are no specific meteorological, geographical or topographic factors that 

warrant a different boundary for the attainment area; 

• South Coast District staff are in the process of conducting dispersion modeling 

for large local SOx sources, as described in the March 2011 U.S. EPA guidance, 

and results of their modeling are expected to provide further support for the 

attainment designation. 

 
A-18 

III. SAN JOAQUIN VALLEY AIR BASIN 

Recommendation 

Ambient air quality monitoring in the San Joaquin Valley Air Basin (SJV or Valley) 

shows a 2009 1-hour sulfur dioxide (SO2) design value of 9 parts per billion (ppb). 

Although this value is not considered valid under U.S. EPA’s criteria because data for 

one quarter are incomplete, it provides a good indication of SO2 concentrations in 

relation to the standard. The preliminary design value for 2010, which is generally 

complete, is even lower, at 7 ppb. Because the two design values are so far below the 

level of the federal standard, staff recommends the San Joaquin Valley be designated 

as attainment, based on the assessment provided below. The assessment includes an 

evaluation of the five factors recommended by U.S. EPA for the purposes of 

determining the appropriate attainment area boundaries: jurisdictional boundaries, 

geography/topography, and meteorology (collectively referred to as nature of the 

region), emission data, and air quality data. Additional dispersion modeling results will 

be provided to the U.S. EPA later this year to further support the attainment designation 

recommendation. 

Nature of the Region 

The San Joaquin Valley Air Basin is one of California’s largest air quality control 

regions. The eight-county area includes all of Fresno, Kings, Madera, Merced, 

San Joaquin, Stanislaus, and Tulare counties, as well as the western portion of Kern 

County. Although the San Joaquin Valley (SJV or Valley) was once primarily 

agricultural, urban and industrial development has increased substantially over the last 

several decades. About 10% of the State’s population, or about three million people, 

now live in the Valley. The entire region falls under the jurisdiction of the San Joaquin 

Valley Air Pollution Control District (SJV District or District), which has responsibility for 

developing and implementing rules and regulations to control SO2 emissions from 

stationary sources. 

The SJV occupies the southern two-thirds of California’s Central Valley and comprises 

nearly 23,500 square miles. With very few exceptions, the SJV is flat, with most of the 

area lying below 400 feet elevation. The long flat valley area is bordered by the Coast 

Range to the west, the Sierra Nevada to the east, the Transverse Range to the south, 

and the Sacramento Valley to the north. In contrast to other California areas, the 

San Joaquin Valley is not dominated by one large urban area. Instead, there are a 

number of moderately sized urban areas spread along the main axis of the Valley. Most 

residents are distributed along the two major thoroughfares: Highway 99 and 

Interstate 5. The Valley’s major population centers include the Fresno, Bakersfield, and 

Stockton/Modesto urban areas. 
A-19 

In general, the San Joaquin Valley experiences a climate with cool wet winters and hot 

dry summers. The northern Valley experiences a more temperate climate than the rest 

of the SJV because it is located closer to the Pacific Ocean, and the marine influence 

extends into the area through gaps in the Coast Range Mountains. This keeps 

temperatures cooler and favors better air flow. Moving further down the Valley, 

maximum daily temperatures increase, and rainfall totals decrease. From north to 

south, average maximum July temperatures increase from about 94 degrees Fahrenheit 

(F) at Stockton to nearly 99 degrees F at Fresno and Bakersfield. In contrast, annual 

average rainfall decreases from north to south, averaging 14 inches at Stockton, 

11 inches at Fresno, and 6 inches at Bakersfield. The amount of stagnation and the 

complexity of local circulation patterns also increase from north to south. As a result, 

prevailing conditions in the central and southern portions of the SJV are more likely to 

trap pollutants and prevent their dispersal. 

Emissions 

Based on the Air Resources Board’s (ARB) 2008 emission inventory, there were a total 

of 8,413 tons per year of SOx emissions in the San Joaquin Valley. The SOx inventory 

is dominated by stationary source emissions. Among the various stationary source 

categories, fuel combustion from manufacturing and industrial operations, oil and gas 

production, electric utilities, and service and commercial operations account for more 

than half the SJV total. Industrial processes, including glass and related products, 

mineral processes, chemical processes, and food and agricultural processes account 

for another third of the total. The remaining SOx emissions are distributed over a wide 

range of fuel combustion and miscellaneous processes, including cogeneration, food 

and agricultural processes, petroleum refining, and managed burning and disposal 

operations. 

U.S. EPA guidance suggests initial focus on sources emitting more than 100 tons of 

SOx per year. In total, emissions from stationary sources in the SJV have decreased 

over the last decade. Figure 8, based on data from the ARB’s facility emission 

database, shows total SOx emissions from all stationary source facilities in the San 

Joaquin Valley during 1998 and 2008. Overall, stationary source SOx emissions 

decreased a little more than 50 percent between 1998 and 2008 – from 6,021 tons per 

year to 2,947 tons per year. 

 
A-20 

FIGURE 8

While the information in Figure 8 is based on ARB’s 2008 emission inventory, more 

recent data for the specific large local facilities are available from the SJV District. The 

remainder of this discussion centers on these large facilities because of EPA’s focus on 

their potential to violate the 1-hour standard. Based on the District’s 2009 emission 

data, there are eight stationary source facilities in the San Joaquin Valley with 

emissions in excess of 100 tons per year. These sources are summarized in Table 5 

and Figure 9. Together, these eight facilities emitted 1,899 tons of SOx in 2009, 

representing about 23% of the total SJV SOx inventory. 

TABLE 5 

San Joaquin Valley Facilities with SOx Emissions Greater than 100 Tons per Year 

Facility Name City County SOx Emissions 

Chevron USA Inc. Kern County Kern 430.69 t/y 

J. R. Simplot Company Lathrop San Joaquin 359.13 t/y 

Gallo Glass Company Modesto Stanislaus 300.05 t/y 

Plains Exploration & Production Co Kern County Kern 231.25 t/y 

Owens-Brockway Glass Container, Inc. Tracy San Joaquin 226.46 t/y 

Chevron USA Inc. Kern County Kern 130.97 t/y 

Pilkington North America, Inc Lathrop San Joaquin 114.67 t/y 

Stockton Cogen Company Stockton San Joaquin 106.02 t/y 

0

5,000

10,000

15,000

20,000

Emissions (t/y)

Sulfur Oxides Emissions from ARB's

Facilities Database - San Joaquin Valley

1998 SOx (t/y) 2008 SOx (t/y)
A-21 

FIGURE 9

The large stationary source facilities reflect four general source types. The two Chevron 

facilities and the Plains Exploration and Production Company are crude oil and gas 

extraction facilities. All three use multiple boilers, steam generators, and flares in their 

extraction processes. Another three facilities, Owens-Brockway Glass Container, Inc., 

Pilkington North America, Inc., and Gallo Glass Company manufacture glass, including 

container glass and flat glass. The J. R. Simplot Company in San Joaquin County 

produces sulfuric acid, which is used in the manufacture of fertilizer. Finally, the 

Stockton Cogeneration Company is a solid fuels-fired combined heat and power facility 

that supplies power for sale to PG&E, as well as steam for local manufacturing. This 

facility has modified both its operations and its permit to include agriculturally-derived 

biomass in its fuel mix. The facility anticipates that an increased use of biomass will 

likely lower their SO2 emissions in the coming years. 
A-22 

The SJV District has reduced SOx emissions from large stationary sources through a 

combination of rules and the use of low-sulfur Public Utilities Commission-grade 

(PUC-grade) natural gas (natural gas that is low in sulfur and meets California PUC 

specifications). For many industries, the prevailing use of PUC-grade natural gas as the 

primary process fuel source minimizes SO2 emissions. But most importantly, the 

SJV District has adopted stringent rules regulating SO2 emissions. Table 6 summarizes 

the major District rules that apply to the Valley’s eight large stationary sources. 

TABLE 6 

San Joaquin Valley District Rules Applicable to Stationary Sources with 

SOx Emissions of 100 Tons per Year or More 

Rule Name 

4306 Boilers, Steam Generators & Process Heaters >5 MMBtu/nr 

4320 Advanced Emission Reduction Options for Boilers, Steam Generators 

& Process Heaters >5.0MMBtu/hr (AERO) 

4354 Glass Melting Furnaces 

4802 Sulfuric Acid Mist 

4311 Flares 

Rules 4306 and 4320 work together to require the most effective pollution controls for 

large boilers, steam generators, and process heaters. Although Rule 4306 is not 

directly aimed at reducing SOx emissions, SOx emissions may be reduced, depending 

on the control method utilized. In contrast, Rule 4320 does directly target SO2

emissions, with reductions estimated at 73% of baseline levels. 

Rule 4354 places stringent limits on NOx, VOC, CO, and SOx emissions from 

glass-melting furnaces. The Rule limits SOx emissions to between 0.9 and 1.7 pounds 

per ton of glass produced, depending on the type of glass furnace and firing technology. 

These limits are the most stringent in the nation. 

Rule 4802 limits sulfuric acid mist emissions from existing sulfuric acid production units 

by limiting the discharge of effluent process gas to no more than 0.30 pounds of gas per 

short ton of sulfuric acid produced. 

Rule 4311 regulates emissions from combustion in flares associated with oil and gas 

production. Amendments adopted in 2009 added SOx emission limits, which will reduce 

SOx emissions by 66% from baseline levels. 
A-23 

Air Quality Trends 

There is one monitor in the San Joaquin Valley that collects quality assured data for 

record. This monitor, Fresno-1st Street, is located in the downtown portion of Fresno. 

The map in Figure 9 shows the location of the Fresno-1st Street monitor. Based on 

available 2007 through 2009 data, the design value for the Fresno monitor is 9 parts per 

billion (ppb), which is well below the 75 ppb federal 1-hour standard. However, the 

design value is not considered complete under U.S. EPA criteria, because data for 

January and February 2007 are missing. Based on data for 2008 through 2010, which 

are generally complete, the site has a preliminary design value of 7 ppb. The long-term 

trend in SO2 design values for the Fresno-1st Street is shown in Figure 10 and shows 

that concentrations have decreased 70% since 1990, dropping from 30 ppb to 9 ppb. 

Throughout the entire time period, the design value has been less than half the level of 

the federal standard. 

Although Fresno-1st Street is the only SO2 monitor currently operating in the 

San Joaquin Valley, data are available from a number of other monitors that were in 

operation during the mid-1970s through late-1990s. Several sites located in and around 

the Bakersfield urban area showed 4th high 1-hour SO2 concentrations up to 130 ppb 

during the late-1970s to mid-1980s, but these concentrations dropped to the 10 to 

20 ppb range by the early 1990s. Other sites located throughout the Valley showed 

4

th high 1-hour measurements in the range of 10 to 20 ppb during the 1980s. 

Monitoring at most of these sites, including sites in Stockton, Modesto, Oildale, and 

Visalia, was discontinued by 1990. None of these historic sites violated the federal 

1-hour SO2 standard at the time monitoring was stopped. Because SOx emissions are 

now lower, it is unlikely the federal standard is currently violated anywhere in the 

San Joaquin Valley. As discussed earlier, in addition to these air quality data, 

dispersion modeling for large stationary sources in the SJV will be provided when 

available, to further support the recommended attainment designation. 
A-24 

FIGURE 10 

Summary 

Staff evaluated the five factors recommended by U.S. EPA for the purposes of 

determining attainment status and appropriate boundaries for federal SO2 designations: 

jurisdictional boundaries, geography/topography, meteorology, emission data, and air 

quality data. Based on this five factor analysis, violations of the 1-hour SO2 standard 

have not been measured over the last two decades, and violations are not expected to 

occur in the future. Therefore, staff recommends the San Joaquin Valley be designated 

as attainment, with the San Joaquin Valley Air Basin serving as the appropriate 

boundary for the attainment area. This recommendation is based on the following 

weight of evidence: 

• The design value for Fresno-1st Street decreased over the last two decades and 

is now well below the level of the federal 1-hour SO2 standard. Evaluation of 

historic data for other sites located throughout the San Joaquin Valley also 

indicate long-term levels below the standard; 

0

10

20

30

40

50

60

70

80

1990 1992 1994 1996 1998 2000 2002 2004 2006 2008

Federal 1-hour SO2 (ppb)

1-Hour Federal SO2 Design Value

San Joaquin Valley

Fresno-1st Street Fed 1-hr SO2 NAAQS (75 ppb)
A-25 

• SOx emissions from stationary source facilities in the SJV declined 50% in the 

last ten years as a result of District emission control measures, and they will 

continue to decline in the future; 

• The entire San Joaquin Valley falls under the jurisdiction of the San Joaquin 

Valley Air Pollution Control District, and effective air quality management is best 

achieved by including the entire Air Basin in the attainment area; 

• There are no specific meteorological or geographic/topographic factors that 

support an attainment area boundary different from the Air Basin boundary; and 

• SJV District staff are in the process of conducting dispersion modeling for large 

local stationary SO2 sources, as described in the March 2011 U.S. EPA 

guidance, and results of this modeling are expected to provide further support for 

the attainment designation. The District is also considering modeling additional 

facilities with SOx emissions under 100 tons per year. 

 
A-26 

IV. MOJAVE DESERT AIR BASIN 

Recommendation 

Ambient air quality monitoring in the Mojave Desert Air Basin (Mojave Desert) shows a 

2009 1-hour sulfur dioxide (SO2) design value of 10 parts per billion (ppb). Because this 

value is well below the level of the federal standard, staff recommends the Mojave 

Desert be designated as attainment, based on the assessment provided below. The 

assessment includes an evaluation of the five factors recommended by U.S. EPA for 

the purposes of determining the appropriate attainment area boundaries: jurisdictional 

boundaries, geography/topography, meteorology (collectively referred to as nature of 

the region), emission data, and air quality data. Additional dispersion modeling results 

will be provided to the U.S. EPA later this year to further support the attainment 

designation recommendation. 

Nature of the Region 

The Mojave Desert comprises portions of four counties: eastern Kern County, northeast 

Los Angeles County, eastern Riverside County, and all but a small southwestern portion 

of San Bernardino County. Although the region is adjacent to the South Coast, 

California’s largest metropolitan area, the Mojave Desert is sparsely populated, with 

only 2.4% of the State population. Four local agencies have jurisdiction over air quality 

in the Mojave Desert. Eastern Kern Air Pollution Control District (APCD) governs the 

Kern County portion of the region. South Coast Air Quality Management District 

(AQMD) governs the Coachella Valley portion of Riverside County, which adjoins the 

South Coast. The far eastern portion of Riverside County and the San Bernardino 

County portion of the Mojave Desert are governed by the Mojave Desert AQMD. 

Finally, the Antelope Valley AQMD has jurisdiction over the Los Angeles County portion 

of the region; however, they contract with the Mojave Desert AQMD for the day-to-day 

operations in this area. 

The Mojave Desert covers a total of 27,287 square miles and is California’s largest 

air basin. The region is bounded by the Colorado River Valley to the south and east 

and by mountains on its remaining sides. The landscape is quite diverse, including 

low elevation desert, high elevation desert, and mountain areas. Elevations range 

from below sea level on the desert floor to peaks of more than 7,000 feet. There 

are several scattered population centers, although the most heavily populated is the 

Palmdale/Lancaster area. These two communities are located closest to the South 

Coast and have grown over the last several decades as bedroom communities of the 

South Coast. Major thoroughfares, including Interstate 15, Interstate 40, U.S. Highway 

395, and California State Highway 58, carry significant amounts of commuter and truck 

traffic in and out of the Mojave Desert region. 
A-27 

Overall, the Mojave Desert has an arid climate with cool winters, hot summers, and little 

rainfall. Temperatures generally increase, while precipitation generally decreases from 

south to north and west to east in this region. For example, the average minimum 

temperature in Palmdale is 48 degrees Fahrenheit (F), while it is 61 degrees F in 

Needles. Similarly, the average maximum temperature in Palmdale is 81 degrees F, 

compared with 87 degrees F in Needles. Daily maximum temperatures in both cities 

can top 100 degrees F during Summer, and annual average rainfall is less than 

8 inches. In contrast to the desert portions of the region, both temperature and 

precipitation can be significantly different in the mountain areas, where snowcapped 

peaks are commonplace during Winter. Overall, the Mojave Desert tends to be windy, 

with winds blowing predominantly from the south and west. During the late spring 

months, high winds from the coastal areas of southern California blow into the Mojave 

Desert. In contrast, during Fall Santa Ana conditions, hot air from the desert blows into 

southern California. 

Emissions 

The Air Resources Board’s (ARB) 2008 emission inventory shows the Mojave Desert 

Air Basin with a total of 3,259 tons per year of SOx emissions. The largest source 

category is mineral processes, which comprises about 60% of the SOx emissions total. 

Cogeneration, electric utilities, aircraft, and trains are the next largest contributing 

categories, together accounting for another 20% of the inventory. The remaining SOx

emissions are attributable to a number of smaller area-wide, on-road, and off-road 

sources. 

Although the numbers above reflect the total SOx inventory for the Mojave Desert, 

stationary sources are of particular interest with respect to the federal 1-hour SO2

standard. Figure 11 shows the change in stationary source SOx emissions for the 

Mojave Desert between 1998 and 2008. The data reflect sources in ARB’s facility 

emissions database. As shown in Figure 11, stationary source SOx emissions 

decreased about 5%, from 2,063 tons per year in 1998 to 1,990 tons per year in 2008. 

The remainder of this discussion is focused on large stationary sources because 

implementation of the federal 1-hour SO2 standard is focused on determining whether 

large sources cause violations. U.S. EPA guidance suggests initial focus on sources 

emitting more than 100 tons of SOx per year. 

 
A-28 

FIGURE 11 

Within the Mojave Desert, four facilities have emissions exceeding 100 tons per year. A 

number of smaller sources are widely distributed throughout the region. Figure 12 

shows the relative locations of the four large facilities, while Table 7 provides a 

summary of their city/county location and 2008 level of SOx emissions. 

Two of the facilities, Mitsubishi Cement Company and California Portland Cement 

Company, manufacture, process, and distribute Portland cement. Cement 

manufacturing utilizes a mixture of raw materials such as limestone, clay, sand, and iron 

ore. These raw materials are ground and heated in a rotary kiln to produce “clinker.” 

After being cooled, the clinker is ground and then mixed with a small amount of gypsum 

to produce concrete. Most of the SOx emissions from this process result from the 

heating of the raw materials, with burning of fuels being a small contributing factor. 

The third facility in the Mojave Desert, Searles Valley Minerals, is a mining operation 

that uses a solvent extraction method to recover boric acid from weak Searle’s Lake 

brines, thus providing a variety of Boron minerals. The last of the four facilities is the 

Ace Cogeneration Company. Cogeneration is the practice of operating a boiler to 

produce steam that provides heat for industrial processes, as well as generates 

electricity. This facility uses a circulating fluidized bed combustion boiler, which reduces 

the amount of sulfur emitted. 

 

0

500

1,000

1,500

2,000

2,500

MD

Emissions (t/y)

Sulfur Oxides Emissions from ARB's Facilities 

Database - Mojave Desert Air Basin

1998 SOx (t/y) 2008 SOx (t/y)
A-29 

FIGURE 12 

TABLE 7 

Mojave Desert Facilities with SOx Emissions Greater than 100 Tons per Year 

 

Facility Name City County SOx Emissions 

California Portland Cement Company Mojave Kern 966 t/y 

Mitsubishi Cement Lucerne Valley San Bernardino 256 t/y 

Ace Cogeneration Company Trona San Bernardino 256 t/y 

Searles Valley Minerals Trona San Bernardino 134 t/y 
A-30 

Sulfur oxide emissions from the four large facilities located in San Bernardino and Kern 

counties are controlled through a combination of local district rules and permit 

conditions. Facilities in San Bernardino County comply with the Mojave Desert AQMD’s 

Rule 406, which limits SO2 emissions to 500 parts per million. The facility in Kern 

County complies with Eastern Kern APCD’s Rule 407. Under Rule 407, SOx emissions 

must not exceed a specified concentration limit at the point of discharge. This 

concentration limit is 0.2 percent by volume, calculated as SO2. 

In addition to these local rules, U.S. EPA recently amended two rules that apply 

specifically to Portland cement manufacturing and will significantly reduce SO2

emissions from these sources. The rules apply to both large and small, new and 

existing, cement kilns. Existing kilns, including those in the Mojave Desert, are required 

to comply in 2013. When fully implemented, U.S. EPA estimates a 78% percent 

reduction in SO2 emissions from affected cement kilns. 

Air Quality Trends 

Figures 13 and 14 show 1-hour SO2 design value trends for two locations with long-term 

data: Trona and Victorville. The trend for Trona (refer to Figure 13) shows a decrease 

in design value from 1990 to 1995 at the Trona-Market Street site. There is a gap in the 

data record between 1995 and 2000, as the site was moved, and data collected at the 

interim site are not complete enough to calculate a representative design value. The 

interim site was moved to the Trona-Athol & Telegraph location during 1997, and a 

representative three-year design value is available for 2000 and subsequent years. As 

shown on the graph, the design value for the Trona-Athol & Telegraph site continued 

the trend seen at the Trona-Market Street site, and the design value for the Trona area 

continues to hover around 10 ppb. The location of the monitoring site in the town of 

Victorville has also changed over time. Similar to the trend for Trona, the transition from 

the Victorville-Armagosa site to the Victorville-Park Avenue is also smooth, with both 

sites showing design values well below the standard over the entire 20-year trend 

period (refer to Figure 14). 

The current monitors in both Trona and Victorville are located near two of the Mojave 

Desert facilities that have SOx emissions in excess of 100 tons per year and are sited to 

capture high SO2 concentrations. Based on data collected during 2007 through 2009, 

the 1-hour SO2 design values for these sites are 10 ppb and 6 ppb, both of which are 

well below the level of the 75 ppb standard. These data demonstrate that SO2

concentrations in the Mojave Desert attain the federal 1-hour SO2 standard. 
A-31 

FIGURE 13 

FIGURE 14 

0

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1990 1992 1994 1996 1998 2000 2002 2004 2006 2008

Federal 1-hour SO2 (ppb)

1-Hour Federal SO2 Design Value

Mojave Desert - Trona

Trona-Market Street Trona-Athol & Telegraph Fed 1-hr SO2 NAAQS (75 ppb)

0

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1990 1992 1994 1996 1998 2000 2002 2004 2006 2008

Federal 1-hour SO2 (ppb)

1-Hour Federal SO2 Design Value

Mojave Desert - Victorville

Victorville-Armagosa Road Victorville-14306 Park Avenue Fed 1-hr SO2 NAAQS (75 ppb)
A-32 

Summary 

Staff evaluated the five factors recommended by U.S. EPA for the purposes of 

determining attainment status and appropriate boundaries for federal SO2 designations: 

jurisdictional boundaries, geography/topography, meteorology, emission data, and air 

quality data. Based on this analysis, violations of the federal 1-hour SO2 standard have 

not been measured over the last two decades, and violations are not expected to occur 

in the future. Therefore, staff recommends the Mojave Desert be designated as 

attainment with the Mojave Desert Air Basin serving as the appropriate boundary for the 

attainment area. This recommendation is based on the following weight of evidence: 

• There are two air quality monitors in the Mojave Desert, located in areas with 

high expected SO2 concentrations. One-hour SO2 design values for both 

monitors are well below the level of the federal standard; 

• There are no geographical, topographic, or meteorological factors that warrant a 

different boundary for the attainment area. 

• Large stationary sources in the Mojave Desert comply with local rules that limit 

SOx emissions, based on SO2 concentrations; 

• Recent revisions to U.S. EPA rules for Portland cement manufacturers will 

significantly reduce emissions from cement kilns. Existing kilns, such as those in 

the Mojave Desert, must comply by 2013; 

• Dispersion modeling results for large SO2 emission facilities in the Mojave Desert 

will be provided to the U.S. EPA later this year to further support the attainment 

designation. 

 
A-33 

V. SOUTH CENTRAL COAST AIR BASIN 

Recommendation 

Ambient air quality monitors in the South Central Coast Air Basin (South Central 

Coast or SCC) show a 2009 1-hour sulfur dioxide (SO2) design value of 35 parts per 

billion (ppb), which is well below the level of the federal standard. Based on the 

following assessment, staff recommends the South Central Coast be designated as 

attainment. The assessment includes an evaluation of the five factors recommended by 

U.S. EPA for the purposes of determining the appropriate attainment area boundaries: 

jurisdictional boundaries, geography/topography, and meteorology (collectively referred 

to as nature of the region), emission data, and air quality data. Dispersion modeling 

results will be provided to the U.S. EPA later this year as additional support for the 

attainment designation recommendation. 

Nature of the Region 

The South Central Coast comprises all of San Luis Obispo, Santa Barbara, and Ventura 

counties. Overall, the region covers 7,887 square miles and is home to approximately 

4% of California’s population. More than half the region’s population lives in Ventura 

County, and the largest cities include Oxnard, Thousand Oaks, and Ventura. Each of 

the three counties in the South Central Coast is governed by its own air pollution control 

district (APCD): the Ventura County APCD, the Santa Barbara County APCD, and the 

San Luis Obispo County APCD. These agencies have responsibility for developing and 

implementing rules and regulations to control SOx emissions from stationary sources 

located in their local county area. 

The region is bounded by the Pacific Ocean on the west and south, and it includes six 

of the eight Channel Islands. All three counties comprise a relatively narrow coastal 

strip that gives way to inland mountains, with the highest elevations ranging from 6,000 

to over 8,000 feet. San Luis Obispo County, the northernmost county, covers 

3,304 square miles. The County is more rural and agricultural than many of California’s 

other coastal regions, with a number of small communities scattered along the beaches, 

coastal hills, and mountains. Santa Barbara County is the middle county, comprising 

2,737 square miles. In addition to the mainland area, the County includes Santa Cruz, 

San Miguel, Santa Rosa, and Santa Barbara islands. Similar to San Luis Obispo 

County, most Santa Barbara County residents live in or near the coastal area. Ventura 

County, which includes Anacapa and San Nicolas islands, is the most populated county 

in the South Central Coast. It is also the smallest, with an area of 1,845 square miles. 

Significant population centers are found along Ventura County’s coastline (Oxnard and 

Ventura), as well as inland (Simi Valley and Thousand Oaks). 
A-34 

In terms of climate, the South Central Coast generally has relatively wet winters and 

warm dry summers. Coastal areas benefit from the marine influence, where onshore 

breezes keep beach communities cooler in summer and warmer in winter than 

communities located further inland. Year-round temperatures near the coast are mild, 

with average minimums in the 40s and 50s and average maximums in the 60s and low 

70s. Average precipitation in this part of the region is between about 15 and 25 inches 

per year. In contrast, the inland areas are warmer and dryer. In these areas, average 

minimum temperatures are still in the 40s and 50s. However, average maximums can 

be in the high 70s, and daily summer maximums can exceed 100 degrees Fahrenheit. 

Rainfall totals in the inland portions of the South Central Coast are generally less than 

15 inches per year. 

Emissions 

Based on the Air Resources Board’s (ARB) 2008 emission inventory, there were 

4,646 tons of SOx emissions in the South Central Coast Air Basin. Two major source 

categories account for the majority of these emissions: petroleum refining operations 

(close to 60%) and mineral processes (about 30%). More than 90% of the SOx

emissions within the mineral processes source category are attributable to 

diatomaceous earth processing. 

The remainder of this discussion is focused on large stationary sources because 

implementation of the federal 1-hour SO2 standard is focused on determining whether 

large stationary sources are likely to cause violations of the standard. U.S. EPA 

guidance suggests initial focus on sources emitting more than 100 tons of SOx per year. 

Similar to other areas of California, most of the SOx emissions in the South Central 

Coast come from stationary sources. As shown in Figure 15, which is based on ARB’s 

facility emissions database, emissions from stationary sources decreased more than 

70% between 1998 and 2008. 

Facility SOx emissions were reduced even further in 2010, from a combination of more 

stringent rules and permit requirements, along with the implementation of federal 

consent decrees. There are two large SOx stationary sources in the South Central 

Coast (refer to Figure 16). These sources are the Conoco Phillips Santa Maria Refinery 

in San Luis Obispo County and the Celite Corporation, a facility in Santa Barbara 

County that processes diatomaceous earth. Both are discussed in more detail, below. 

SOx emissions from the remaining stationary sources in the South Central Coast are 

below 100 tons per year, with each emitting between 0 and 30 tons of SOx per year.
A-35 

FIGURE 15 

FIGURE 16 

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

20,000

Emissions (t/y)

Sulfur Oxides Emissions from ARB's

Facilities Database - South Central Coast

1998 SOx (t/y) 2008 SOx (t/y)
A-36 

Conoco Phillips Facility: The Conoco Phillips Santa Maria Refinery (Conoco Phillips 

SMR or SMR) facility is located near the town of Nipomo in San Luis Obispo County. 

The SMR facility was originally built by Union Oil Company of California in 1955 and has 

had several owners since then, including Tosco, Phillips Petroleum, and now Conoco 

Phillips. The refinery operates 24 hours per day, year-round, unless operations are shut 

down for maintenance. Over time, the San Luis Obispo County APCD has been 

successful in securing substantial emission reductions from this facility not just for SOx, 

but also for reactive organic gases and particulate matter. 

The estimated SOx emissions from this facility have decreased nearly 95% since 2006 –

 emissions were 2,668 tons per year in 2006 compared with only 154 tons per year in 

2010. These are verifiable reductions, attributable to emission control measures 

adopted by the San Luis Obispo County APCD and to compliance with a recent U.S. 

EPA consent decree. Of particular importance is the recent shutdown of the calciner 

kiln stack. 

When it was operating, the calciner unit accounted for over 90% of SOx emissions in 

San Luis Obispo County and almost 95% of the annual SO2 emissions from the entire 

SMR facility (refer to Table 8, below). On May 31, 2006, the San Luis Obispo County 

APCD Board took action and approved amendments to District Rule 440, Petroleum 

Coke Calcining and Storage Operations. This Rule required an 80% reduction in SO2

emissions from SMR coke calcining operations and limits the storage of green coke to 

the levels that were stored at the facility as of January 1, 2006. On March 13, 2007, 

Conoco Phillips SMR shut down the calciner unit. Only green petroleum coke is 

generated by the coker units, stored in greatly reduced storage piles, and shipped out. 

As shown in Table 8, total emissions from the SMR facility have been greatly reduced 

since 2006, but there is some year-to-year variation. This variation is attributable to 

year-to-year differences in feedstock and throughput. 

TABLE 8 

SO2 Emission History at Conoco Phillips Santa Maria Refinery 

Calendar Year Total SMR Facility SO2 Calciner Unit SO2

2006 2668 tons/year 2500 tons/year 

2007 789 tons/year 668 tons/year 

2008 176 tons/year 0 

2009 129 tons/year 0 

2010 154 tons/year 0 

 
A-37 

Other relevant measures contributing to the SOx emission reductions at the SMR facility 

are summarized below: 

• U.S. EPA Consent Decree: As part of U.S. EPA's on-going multi-company 

Refinery Initiative, SMR was issued a Consent Decree in 2004/2005 covering 

both emission reductions and procedural changes under various regulatory 

compliance requirements, including New Source Performance Standards (NSPS) 

and National Emissions Standards for Hazardous Air Pollutants (NESHAP). The 

San Luis Obispo County APCD and U.S. EPA partnered in writing and 

implementing the Consent Decree. SMR is still operating under this Consent 

Decree, working towards full compliance with its provisions. December 2011 and 

2013 mark upcoming milestone deadlines.

• Abatement Order: In 1989, the San Luis Obispo County APCD issued an 

Abatement Order for the SMR facility, addressing numerous neighborhood odor 

complaints and excessive emissions from operations at the refinery and carbon 

plant. The Abatement Order included conditions for new and modified emission 

controls, odor abatement projects, new monitoring equipment, and procedural 

changes. Odor complaints, which numbered over 350 during the year prior to the 

Abatement Order, are now sporadic and usually in conjunction with facility upset 

conditions. The San Luis Obispo County APCD considers the Abatement Order 

a success in curbing emissions and odors from processes at the SMR facility.

Celite Corporation: Celite Corporation is a diatomaceous earth processing plant 

located in the city of Lompoc in Santa Barbara County. In the recent past, SOx

emissions from the Celite facility exceeded 700 tons per year. Since then, Celite 

Corporation has permanently ceased operating two older processing lines. They 

recently installed a new processing line that includes SOx emission control equipment 

with a potential to emit restriction of 13 tons per year. The new processing line includes 

Best Available Control Technology (BACT), comprising a high energy venturi scrubber 

and packed bed scrubber combination SOx control unit. The Authority to Construct 

(ATC) permit contains specific SOx emission limitations, reflecting BACT control. 

The plant is currently going through a shake-out period under the ATC permit, and 

the new processing line limits reflecting BACT control will ultimately be federally 

enforceable under a Part 70 permit. One older line is being retained by Celite 

Corporation as a back-up, anticipated to operate for only brief periods if the new line 

breaks down. As a result, hourly SOx emissions will routinely be under 3 pounds/hour, 

consistent with the permit limitations. The Santa Barbara County APCD has provided a 

recent source test that demonstrates the SOx control equipment is meeting the required 

efficiency and SOx emissions are in compliance with the permit limits. Because 
A-38 

SOx emissions are now under 100 tons per year, the Celite Corporation facility will not 

require modeling. 

Air Quality Trends 

The South Central Coast has an extensive air quality monitoring network, including a 

number of monitors that collect quality-assured SO2 data for record. Several of these 

monitors are located near the two SOx facilities described above and therefore reflect 

high SO2 concentrations within the South Central Coast region. In addition, several 

other monitors are located along the coast, downwind of these facilities. These 

downwind sites monitor public exposure from smaller facilities and area-wide SOx

emissions from transportation sources (refer to Figure 16 for relevant monitor locations). 

Based on data for record, the South Central Coast attains the federal 1-hour SO2

standard, with 2009 design values ranging from 2 ppb to 35 ppb, which is well below the 

level of the federal standard. 

The highest design value is for the Nipomo-Guadalupe Road monitoring site, located 

near the Conoco Phillips SMR. The long-term design value for the Nipomo site is 

plotted in Figure 17. It shows a significant reduction between 2006 and 2009. As 

shown in Table 8, the SMR facility sharply reduced emissions from its calciner unit 

between 2006 and 2007. The facility then shut the calciner unit down, in March 2007. 

The design value at Nipomo reflects these emission reductions, dropping more than 

50% between 2006 and 2009 (from 86 ppb to 35 ppb). Design values for future years 

should be even lower, because the 2009 design value still includes data for 2007 and 

2008, before the calciner unit ceased operating. Maximum 1-hour SO2 concentrations 

provide a good illustration of the significant decrease in SO2 concentrations over the 

three-year period, with maximums of 151 ppb in 2007, 47 ppb in 2008, and 17 ppb in 

2009. 

In addition to Nipomo, Figure 17 also shows the long-term trend for the monitoring site 

nearest the Celite facility (Lompoc-South H Street). The 2009 design value for this site 

is 6 ppb, less than one-tenth the level of the federal standard. It should be noted that 

the three-year period reflected in this design value (2006-2009) includes a period of 

uncontrolled high emissions at the Celite facility. Even so, the design value does not 

violate the standard. The remaining trend plotted in Figure 17 reflects the downwind 

coastal site with the highest 2009 design value – Las Flores Canyon-#1, in Santa 

Barbara County. The design value for this site is also well below the level of the federal 

standard, at 6 ppb. Based on these data and data for other sites in the region, 

violations of the federal 1-hour SO2 standard are unlikely in the South Central Coast. 

 
A-39 

FIGURE 17 

Summary 

Staff evaluated the five factors recommended by U.S. EPA for the purposes of 

determining appropriate attainment status and boundaries for federal SO2 designations: 

jurisdictional boundaries, geography/topography, meteorology, emission data, and air 

quality data. This five factor analysis shows that violations of the federal 1-hour SO2

standard have not been measured over the last several years, and because of 

substantial verifiable and enforceable emission reduction measures, are not expected to 

occur in the future. Therefore, staff recommends the South Central Coast be 

designated as attainment, with the South Central Coast Air Basin serving as the 

appropriate boundary for the attainment area. This recommendation is based on the 

following weight of evidence: 

• The South Central Coast has a comprehensive SO2 monitoring network, with 

monitoring sites located in areas with the highest SOx emissions and highest 

expected SO2 concentrations; 

• 2009 design values for all sites in the South Central Coast region are well below 

the standard, including values for sites nearest the Conoco Phillips SMR and 

0

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100

120

140

Federal 1-hour SO2 (ppb)

1-Hour Federal SO2 Design Values

South Central Coast

Nipomo-Guadalupe Road Lompoc-S H Street

Las Flores Canyon #1 Fed 1-hr SO2 NAAQS (75 ppb)
A-40 

Celite Corporation facilities. The highest 2009 design value in the region was 

35 ppb, less than half the level of the federal 1-hour SO2 standard; 

• Emissions from SOx facilities in the South Central Coast decreased 30% 

between 1998 and 2008. 

• Since 2006, SOx emissions from the Conoco Phillips SMR facility have 

decreased close to 95%, from 2,668 tons per year to 154 tons per year; 

• SOx emissions are expected to decrease from 743 tons per year to 13 tons per 

year at the Celite Corporation in Santa Barbara County, once their permit to 

operate is finalized. Therefore, this facility will not require modeling; 

• There are no significant differences in geography, topography, or meteorology in 

the South Central Coast that warrant an attainment area boundary different from 

the Air Basin boundary; 

• Dispersion modeling results for the Conoco Phillips SMR facility will be provided 

to the U.S. EPA later this year, to further support the attainment designation; 

• Staff will work with the Santa Barbara APCD to update their emissions inventory, 

after the Celite Corporation’s final permit to operate has been issued and is fully 

implemented. 

 
A-41 

VI. REMAINING AIR BASINS 

Recommendation 

The staff recommends that the following areas be designated as attainment, based on 

the assessment provided below. The assessment includes an evaluation of the five 

factors recommended by U.S. EPA for purposes of determining the appropriate 

attainment area boundaries: air quality data, emissions data, meteorology, 

geography/topography, and jurisdictional boundaries. 

Staff recommends that air basins be used as the jurisdictional boundaries for the 

attainment areas. In some cases air basins consist of a single air district, but the 

majority of air basins are composed of one or more air districts, each containing one or 

more counties or portions of counties. Air basins were determined based on similar 

meteorology and geography of the area which they contain. 

The following air basins, and the counties included within, contain no large stationary 

sources of SOx emissions. 

Air Basin Counties 

Sacramento Valley Butte, Colusa, Glenn, Sacramento, Shasta, Sutter, 

Tehama, Yolo, Yuba, western Placer, northeastern 

Solano 

San Diego San Diego 

Salton Sea Imperial, central Riverside 

North Central Coast Santa Cruz, San Benito, Monterey 

North Coast Del Norte, Humboldt, Trinity, Mendocino, northern 

Sonoma 

Mountain Counties Plumas, Sierra, Nevada, central Placer, western El 

Dorado, Amador, Calaveras, Tuolumne, Mariposa 

Great Basin Valleys Inyo, Mono, Alpine 

Lake County Lake 

Lake Tahoe Portions of El Dorado and Placer 

Northeast Plateau Lassen, Modoc, Siskiyou 

In general, these air basins encompass regions of the state that are more rural in 

nature. Population tends to be concentrated in a small number of urban areas, most 

notably Sacramento and San Diego Counties. There are no facilities located in these 

air basins with significant SOx emissions (greater than 100 tons per year), and in

comparison to the rest of the state, total SOx emissions are low. SO2 monitoring data is 

available only in select areas where the highest SO2 concentrations are expected to 
A-42 

occur, and concentrations at these monitors are far below the standard. These 

monitors are located in the areas with the largest emissions. Since the existing 

monitoring network indicates that all areas are well below the level of the standard, we 

conclude that areas without monitors would also be considerably below the standard. 

Sacramento Valley Air Basin 

Nature of the Region 

The Sacramento Valley Air Basin (SVAB) is located in the northern portion of the 

Central Valley. It includes Butte, Colusa, Glenn, Sacramento, Shasta, Sutter, Tehama, 

Yolo, and Yuba Counties, the western urbanized portion of Placer County, and the 

northeastern portion of Solano County. The SVAB occupies nearly 15,000 square miles 

and has a population of more than 2.5 million people. More than half of the total 

population in the eleven-county air basin resides in Sacramento County. 

The SVAB is approximately 216 miles from north to south and 95 miles east to west at 

the widest part. It is bounded on the north and west by the Coast Range Mountains and 

on the east by the southern portion of the Cascade Mountain Range and the northern 

portion of the Sierra Nevada Mountains. Within the SVAB the elevations reach heights 

of approximately 3,500 feet in the southwest, 8,500 feet in the northwest, 1,700 feet in 

the southeast and 10,500 feet in the northeast. In contrast, the elevation in Sacramento 

County near the San Francisco Bay delta is barely above sea level. The mountain 

ranges provide a significant physical barrier to trap locally created pollution as well as 

pollution transported into the SVAB from elsewhere.

The Sacramento Valley’s usual summer daytime wind flow pattern is characterized by 

onshore flow from the Bay Area to Sacramento (known as the sea breeze). A portion of 

the wind flow turns south, blowing into the San Joaquin Valley, a portion continues 

eastward, across the southern Sacramento Valley, and a portion turns north, blowing 

into the upper Sacramento Valley. At night, the sea breeze weakens, and the wind 

direction in the Sacramento Valley changes. Typical downslope flow, known as 

nocturnal drainage, brings air from the Coast Range and Sierra Nevada Mountains into 

the Sacramento Valley. 

 
A-43 

FIGURE 18 

Emissions 

There are no facilities in the SVAB with SOx emissions greater than 100 tons per year. 

In 1998, the total facility SOx emissions were 595 tpy. By 2008, the facility SOx

emissions dropped to 410 tpy, a decrease of over 30%. Other sources of SOx

emissions in SVAB are of a more diffuse nature, such as residential burning, managed 

burning, trains, airplanes, and vehicles. Emissions from all sources totaled 1,240 tpy in 

2008, down from over 2,300 tpy in 1998, a 45% reduction. 

Air Quality Trends 

Based on quality-assured data for record, the SVAB attains the revised federal SO2

standard, with a 2009 design value of 4 ppb. The SVAB has monitoring data available 

from five sites, one in Butte County and four in Sacramento County. The monitor in 

Butte County was located at Chico-Manzanita Avenue and operated from 1981 to 1984. 

SO2 concentrations were very low, and never came close to the level of the revised 

standard (75 ppb). Monitors in Sacramento County include Citrus Heights-Sunrise 

Boulevard (1980-1983), Sacramento-P Street (1980-1982), Sacramento-Del Paso 
A-44 

Manor (1980-present), and North Highlands-Blackfoot Way (1980-2010). Monitors are 

located in areas of the air basin where we would expect the highest SO2 concentrations 

to occur. These are also the areas with the greatest population density, capturing 

emissions from area-wide sources, such as residential burning and vehicles, as well as 

stationary facility sources. As shown in Figure 19 below, design values have been 

steadily decreasing since 2000. The 2009 design value is just 4 ppb, down from 20 ppb 

in 2001. Since monitoring began in 1980, SO2 concentrations have been well below the 

level of the revised standard. 

FIGURE 19 

Sacramento Valley Air Basin SO2 1-Hour Design Values 

San Diego Air Basin 

Nature of the Region 

The San Diego Air Basin (SDAB) lies in the southwest corner of California and 

comprises the entire San Diego region. Population is concentrated mainly in the 

western portion of the county. The air basin covers 4,260 square miles, and is home to 

over three million residents. The City of San Diego covers approximately 330 square 

miles, and has a population of over 1.3 million, 42 percent of the total population of 

San Diego County. 

The topography in SDAB varies greatly, from beaches on the west to mountains and 

desert on the east. Much of the topography in between consists of mesa tops 

intersected by canyon areas. Topography, along with local meteorology, influences the 

0

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80

1990 1992 1994 1996 1998 2000 2002 2004 2006 2008

North Highlands-Blackfoot Way Sacramento-Del Paso Manor
A-45 

dispersal and movement of pollutants in the basin. The mountains to the east prohibit 

dispersal of pollutants and help trap them under inversion layers. 

The San Diego region typically has dry, warm summers and mild, occasionally wet 

winters. The average temperature ranges from the mid 40s to the high 90s. Most of the 

county’s precipitation falls from November to April, with infrequent precipitation during 

the summer. The average seasonal precipitation along the coast is approximately 

ten inches. 

FIGURE 20 

Emissions 

There are no facilities located in the SDAB that have emissions greater than 100 tons 

per year. Emissions from all facilities in SDAB totaled just 85 tpy in 2008. The largest 

sources of SOx emissions in SDAB are more regional, including trains, shipping ports, 

fuel combustion and residential burning. Total SOx emissions from all sources totaled 

730 tpy in 2008, down from 1030 tpy in 1998, a reduction of nearly 30%. 
A-46 

0

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19901991199219931994199519961997199819992000200120022003200420052006200720082009

Chula Vista Otay Mesa-Paseo International San Diego-1110 Beardsley Street San Diego-12th Avenue

Air Quality Trends 

Based on data for record, the SDAB attains the revised federal SO2 standard, with a 

valid 2009 design value of 17 ppb. The design value at Otay Mesa (22 ppb) is not 

considered valid under U.S. EPA criteria. SDAB has had several monitors operating at 

various times from 1980 to the present. Currently, there are three sites with SO2

monitors – San Diego-Beardsley Street, Otay Mesa-Paseo International, and Chula 

Vista. Otay Mesa and Chula Vista have long term data dating back to the early 1990s. 

Only Chula Vista has come close to the level of the revised standard in 1994 when the 

design value reached 72 ppb. However, emissions have dropped dramatically since 

then. The 2009 design value at Otay Mesa is just 22 ppb, 7 ppb at Chula Vista, 17 ppb 

at San Diego – Beardsley Street. 

The monitor at Otay Mesa is located near the California/Mexico border and captures 

emissions from international commerce. The monitors in Chula Vista and downtown 

San Diego are designed to measure community exposure. The three monitors are 

located in areas where the highest SO2 concentrations are expected to occur. 

FIGURE 21 

San Diego Air Basin SO2 1-hour Design Values 
A-47 

Salton Sea Air Basin 

Nature of the Region 

The Salton Sea Air Basin (SSAB) is composed of the central portion of Riverside 

County (Coachella Valley) and Imperial County. The Coachella Valley extends 

southeast from the San Bernardino Mountains to the Salton Sea, the largest saltwater 

lake in California. The Riverside County portion of the SSAB is separated from the 

South Coast Air Basin on the west by the San Jacinto Mountains and the Santa Rosa 

Mountains and from the Mojave Desert Air Basin to the east by the Little San 

Bernardino Mountains. Imperial County borders Mexico to the south. The SSAB has a 

population of approximately 650,000. 

The mountain peaks range from 3,000 to 11,000 feet in elevation, and prevent off-shore 

winds from flowing into the Coachella Valley and Imperial County. During the summer, 

high temperatures in the SSAB frequently exceed 100 degrees Fahrenheit. In the 

winter, daytime temperatures are generally over 70 degrees. The SSAB averages 

between three and seven inches of precipitation per year. 

FIGURE 22 
A-48 

Emissions 

There are no facilities located in the Salton Sea Air Basin with SOx emissions greater 

than 100 tons per year. The largest facility in the basin is the Palm Springs International 

Airport. Emissions from all facilities combined totaled 124 tpy in 2008. All other 

sources of emissions in the SSAB totaled 270 tpy in 2008, down from 590 tpy in 1998, a 

reduction of over 50 percent. The largest SOx sources are trains, fuel combustion and 

residential burning. 

Air Quality Trends 

Based on data for record, the Salton Sea Air Basin attains the revised federal SO2 

standard, with a 2009 design value of 10 ppb. Current monitoring is conducted at the 

Imperial Calexico site. Historic data is also available from the Riverside-Palm Springs 

Fire Station. No monitor in the SSAB has ever come close to the level of the standard 

since monitoring began in 1980. 

FIGURE 23 

Salton Sea Air Basin SO2 1-hour Design Values 

North Central Coast Air Basin 

Nature of the Region 

The North Central Coast Air Basin (NCCAB) consists of Santa Cruz, San Benito, and 

Monterey Counties. It covers an area of 5,159 square miles along the coast, and has a 

0

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1994199519961997199819992000200120022003200420052006200720082009

Imperial Calexico-East Imperial Calexico-Ethel Street
A-49 

population of over 750,000. The Santa Cruz Mountains dominate the northwest portion 

of NCCAB, and the Diablo Range marks the northeastern boundary. The Santa Clara 

Valley extends into the northeastern tip of the basin. Further south, the Santa Clara 

Valley becomes the San Benito Valley, which runs northwest-southeast, with the 

Gabilan Range as its western boundary. To the west of the Gabilan Range is the 

Salinas Valley, which extends from Salinas at the northwest end to south of King City. 

In the summer, a high-pressure system over the Pacific Ocean is dominant and causes 

persistent west and northwest winds over the entire California coast. The onshore wind 

brings fog and relatively cool air into the coastal valleys. The northwest-southeast 

orientation of the mountain ridges tends to restrict and channel the summer onshore air. 

In the fall, the surface winds become weak. The airflow is occasionally reversed in a 

weak offshore movement and the relatively stationary air mass is held in place. During 

the winter, the Pacific high-pressure system moves south and has less influence on the 

NCCAB. Air frequently flows in a southeasterly direction out of the Salinas and San 

Benito Valleys, especially during night and morning hours. 

FIGURE 24 
A-50 

Emissions 

As of 2009, there are no facilities in the NCCAB with SOx emissions greater than 

100 tons per year. Prior to 2009, the Cemex Cement Plant, operated in Davenport, had 

SOx emissions of 179 tpy. The Cemex Cement Plant closed at the end of 2008, and the 

permit to operate was forfeited. In 2008, SOx emissions from all facilities totaled 

261 tpy. In 2009, the total emissions dropped to just 69 tpy, due to the closure of the 

Cemex facility. SOx emissions from all sources in NCCAB totaled 908 tpy in 2008, 

down from 967 tpy in 1998, a 6% reduction. 

Air Quality Trends 

Based on available data for record from 2007 to September 2009, the NCCAB attains 

the revised federal SO2 standard with a design value of 11 ppb. The air basin had only 

one SO2 monitor in operation, located in the town of Davenport. After the closure of the 

Cemex Cement Plant, the Davenport monitor was shut down at the end of September 

2009. The design value is not considered complete under U.S. EPA criteria because 

data from October through December 2009 are missing. However, even with the 

Cemex Plant in operation, design values were generally in the 10 – 20 ppb range over a 

period of 20 years, never exceeding 30 ppb. With the closure of the Cemex Plant, we 

expect the design value will remain well below the level of the revised standard. 

FIGURE 25 

North Central Coast SO2 1-hour Design Values 

 

0

10

20

30

40

50

60

70

80

19901991199219931994199519961997199819992000200120022003200420052006200720082009

SO2 concentrations (ppb)

Davenport
A-51 

North Coast Air Basin 

Nature of the Region 

The North Coast Air Basin (NCAB) includes the counties of Del Norte, Humboldt, Trinity, 

Mendocino, and the northern portion of Sonoma County. It has a land area of more 

than 12,000 square miles, and a population of approximately 330,000. 

In general, the climate of the North Coast is characterized by cool summers with 

frequent fog and mild winters with lots of rain. In coastal areas, the ocean helps to 

moderate temperatures year-round. Further inland, the summers are hotter and drier 

and the winters colder and more snowy. At higher elevations in inland areas, it is cooler 

in the summers and snowier in the winter. In the summer months strong northwesterly 

winds are common. During the winter, storms from the south Pacific lead to winds from 

the south. 

FIGURE 26 
A-52 

Emissions 

There are no facilities in the NCAB with SOx emissions greater than 100 tons per year. 

Emissions from all facilities in NCAB totaled 140 tpy in 2008. SOx emissions from all 

sources in NCAB totaled 558 tpy in 2008, down from 615 tpy in 1998, a reduction of 

almost 10%. The largest sources of SOx emissions are residential burning and fuel 

combustion. 

Air Quality Trends 

Based on data for record, the NCAB attains the revised federal SO2 standard, with a 

2009 design value of 5 ppb, down from 25 ppb in 2006. Monitoring for SO2 in the NCAB 

is currently conducted at the Eureka-Jacobs site. Historic data is available from EurekaFort Avenue from 1981-1983, Ukiah-Gobbi Street from 1992-1995, Ukiah-Highway 101 

from 1988-1990, and Willits-S Main Street from 1994-1996. Design values at these 

sites have never been near the level of the revised standard. The highest design value 

in the NCAB was 30 ppb at the Ukiah-Highway 101 site in Mendocino in 1992. 

FIGURE 27 

North Coast 1-hour SO2 Design Values 

0

10

20

30

40

50

60

70

80

1990 1992 1993 1994 1995 1996 2006 2007 2008 2009

Mendocino Ukiah-E Gobbi Street Mendocino Willits-899 S Main Street Eureka-Jacobs
A-53 

Mountain Counties Air Basin 

Nature of the Region 

The Mountain Counties Air Basin (MCAB) includes Plumas, Sierra, Nevada, Placer 

(middle portion), El Dorado (western portion), Amador, Calaveras, Tuolumne, and 

Mariposa Counties. The basin lies along the northern Sierra Nevada Mountain Range, 

close to or contiguous with the Nevada border, and covers an area of roughly 11,000 

square miles. The population of the entire air basin is less than 500,000. The western 

slope of El Dorado County, from Lake Tahoe on the east to the Sacramento County 

boundary on the west, lies within the MCAB. Elevations range from over 10,000 feet at 

the Sierra crest down to several hundred feet above sea level at the Sacramento 

County boundary. Throughout the basin, the topography is highly variable, and includes 

rugged mountain peaks and valleys with extreme slopes and differences in elevation in 

the Sierras, as well as rolling foothills to the west. 

The general climate of the MCAB varies considerably with elevation and proximity to the 

Sierra ridge. The terrain features of the basin make it possible for various climates to 

exist in relatively close proximity. The Sierra Nevada receives large amounts of 

precipitation in the winter, with lighter amounts in the summer. Precipitation levels are 

high in the highest mountain elevations but decline rapidly toward the western portion of 

the basin. Winter temperatures in the mountains can be below freezing for weeks at a 

time, and substantial depths of snow can accumulate, but in the western foothills, winter 

temperatures usually dip below freezing only at night and precipitation is mixed as rain 

or light snow. In the summer, temperatures in the mountains are mild, with daytime 

peaks in the 70s to low 80s, but the western end of the basin can routinely exceed 

100 degrees. 

 
A-54 

FIGURE 28 

Emissions 

There are no facilities in the MCAB with SOx emissions greater than 100 tons per year. 

Total SOx emissions from all facilities totaled 162 tpy in 2008. The largest contribution 

to SOx emissions are from residential and managed burning, trains, and cogeneration 

plants. Total emissions in MCAB in 2008 were 858 tpy, down from 1555 tpy in 1998, a 

45% reduction. 

Air Quality Trends 

Currently, no SO2 monitors exist in MCAB. One monitor, San Andreas-Gold Strike 

Road, operated from 1980-1982. The design value at that time was 10 ppb. Due to the 

low SOx emissions throughout the MCAB, we conclude that the area would not exceed 

the level of the standard. 
A-55 

Great Basin Valleys Air Basin 

Nature of the Region 

The Great Basin Valleys Air Basin (GBVAB) includes Inyo, Mono and Alpine Counties. 

This basin is bounded on the west by the Sierra Nevada Mountains, on the east by the 

Nevada border, and on the south by the desert. As the transition from the Great Basin 

Valleys to the desert is somewhat indistinct, the Inyo-San Bernardino County line has 

been chosen as the basin boundary. 

The population in the GBVAB is approximately 35,000, approximately 2 people per 

square mile. Much of the land area is open desert. The land use varies from riparian 

areas along the Owens River to light industry, small commercial and residential in the 

City of Bishop (population 4,000). The topography varies from high desert to mountain 

peaks. 

FIGURE 29 
A-56 

Emissions 

There are no facilities in the Great Basin Valleys Air Basin with SOx emissions greater 

than 100 tons per year. SOx emissions from all facilities in 2008 were just 32 tpy. The 

largest contributors of SOx emissions in GBVAB are managed burning and fuel 

combustion. Emissions from all sources totaled 263 tpy in 2008, down from 375 tpy in 

1998, a 30% reduction. 

Air Quality Trends 

There is no monitoring data available for GBVAB. However, due to the very low SOx

emissions throughout the GBVAB, we conclude that the area would not exceed the level 

of the standard. 

Lake County Air Basin 

Nature of the Region 

Lake County Air Basin (LCAB) consists of only Lake County. It is located inland from 

the Pacific Ocean, north of the San Francisco Bay Area, covers an area of 1,327 square 

miles and has a population of nearly 65,000. The highest peak in LCAB is Snow 

Mountain at 7,056 feet in the wilderness area of the Mendocino National Forest. LCAB 

has just two incorporated cities, Clearlake and Lakeport, surrounded by several smaller 

communities. 

FIGURE 30 
A-57 

Emissions 

There are no facilities in LCAB with SOx emissions greater than 100 tons per year. All 

facilities in LCAB combined emit just 34 tpy SOx in 2008. The largest contributors of 

SOx emissions are agriculture production and processing and residential burning. The 

total emissions from all sources in LCAB were 153 tpy in 2008, down from 168 tpy in 

1998, a 9% reduction. 

Air Quality Trends 

There is no monitoring data available for LCAB. However, due to the very low SOx

emissions throughout the LCAB, we conclude that the area would not exceed the level 

of the standard. 

Lake Tahoe Air Basin 

Nature of the Region 

The Lake Tahoe Air Basin (LTAB) is comprised of the surface of Lake Tahoe (roughly 

20 miles long by 10 miles wide) and land up to the surrounding rim of mountain ridges. 

The southern portion of the air basin is in El Dorado County and the northern portion is 

in Placer County. The basin has a population of less than 60,000. The lake is at 

6,200 feet elevation, and the ridges climb to over 10,000 feet. The mountain slopes 

surrounding the lake are quite precipitous, and are broken by deep valleys carved by 

streams that drain into the lake. 

The meteorology of the LTAB in winter is typified by large amounts of precipitation from 

Pacific storms that fall mainly as snow, and temperatures below freezing accompanied 

by winds, cloudiness, and lake and valley fog. Winter days can also bring cool, 

brilliantly clear days between storms. In the summer, the LTAB experiences sunny, 

mild days, with daytime peaks in the upper 70s and low 80s, with an occasional 

thunderstorm from southern flows of moisture. 

 
A-58 

FIGURE 31 

Emissions 

There are no facilities in the Lake Tahoe Air Basin with SOx emissions greater than 

100 tons per year. There are virtually no SOx facility emissions, just over 1 tpy in the 

entire basin. The largest contribution of SOx emissions is from residential burning and 

airplanes. In 2008, SOx emissions totaled 40 tpy, down from 44 tpy in 1998, a 9% 

reduction. 

Air Quality Trends 

There is no monitoring data available for LTAB. However, due to the very low SOx 

emissions throughout the LTAB, we conclude that the area would not exceed the level 

of the standard. 

 
A-59 

Northeast Plateau Air Basin 

Nature of the Region 

The Northeast Plateau Air Basin (NEPAB) is located in the northeast corner of 

California and includes Lassen, Modoc, and Siskiyou Counties. The northern part of 

NEPAB has lofty volcanic peaks, such as Mount Shasta and Mount Lassen. Forested 

mountains dominate the southern and western regions. The NEPAB covers 

approximately 14,788 square miles and is bordered by the states of Oregon to the north 

and Nevada to the east. NEPAB’s population of nearly 95,000 predominately resides in 

rural towns, including Yreka, Mount Shasta, Alturas, and Susanville. 

The climate is dry, cool, and windy. The area is separated from the rest of the State by 

the Cascade Mountains to a degree that permits very little air movement to or from 

other regions in the State. 

FIGURE 32
A-60 

Emissions 

There are no facilities in the NEPAB with SOx emissions greater than 100 tons per year. 

All facilities combined emitted just 45 tpy in 2008. Emissions from all sources in NEPAB 

totaled 215 tpy in 2008, down from 533 tpy in 1998, a nearly 60% reduction. The 

largest sources of emissions are from trains and residential burning. 

Air Quality Trends 

There is no monitoring data available for NEPAB. However, due to the very low SOx

emissions throughout the NEPAB, we conclude that the area would not exceed the level 

of the standard. 

Summary 

ARB staff has evaluated the five factors recommended by U.S. EPA for purposes of 

determining the appropriate attainment status and boundaries: air quality data, 

emissions data, meteorology, geography/topography, and jurisdictional boundaries. 

Based on this five factor analysis, the above mentioned air basins should be designated 

as attainment areas for the federal 1- hour SO2 standard. This recommendation is 

based on the following weight of evidence: 

• There are no stationary source facilities in these areas with SO2 emissions 

greater than 100 tons per year. 

• ARB maintains a statewide monitoring network, with monitoring sites in the areas 

with the highest expected SOx emissions. All design values in areas with 

monitors are well below the standard; areas without monitors have significantly 

lower SOx emissions. Therefore, we conclude that areas without monitors would 

also attain the standard. 

• Stringent statewide SO2 control measures will reduce emissions from sources 

including diesel fuel, locomotives, and shipping. 

• There are no specific meteorological or topographical factors which would 

warrant different boundaries for the attainment areas. 
APPENDIX 2 

2009 SO2 1-HOUR DESIGN VALUES FOR

ALL SITES IN CALIFORNIA
This page intentionally left blank. 
APPENDIX 2: 2009 SO2 1-Hour Federal Design Values1

Basin County Site Name SO2 1-hr Fed DV (ppb) 

Mojave Desert San Bernardino Trona-Athol and Telegraph 10 

Victorville-14306 Park Avenue 6 

North Coast Humboldt Eureka-Jacobs 5 

North Central Coast Santa Cruz Davenport 11* 

South Coast 

Los Angeles 

Burbank-W Palm Avenue 8* 

Los Angeles-North Main Street 7 

Los Angeles-Westchester Parkway 15* 

North Long Beach 20 

Orange Costa Mesa-Mesa Verde Drive 7 

Riverside Riverside-Rubidoux 7 

San Bernardino Fontana-Arrow Highway 6 

South Central Coast 

San Luis 

Obispo Nipomo-Guadalupe Road 35 

Santa Barbara 

El Capitan Beach 4 

Exxon Site 10-UCSB West Campus 4 

Goleta-Fairview 3* 

Las Flores Canyon #1 6 

Lompoc-HSandP 2 

Lompoc-S H Street 4 

Vandenberg Air Force Base-STS Power 3 

San Diego San Diego 

Chula Vista 7 

Otay Mesa-Paseo International 22* 

San Diego-1110 Beardsley Street 17 

San Francisco Bay 

Area 

Alameda Berkeley-6th Street 12* 

Oakland-West 13* 

Contra Costa 

Bethel Island Road 8 

Concord-2975 Treat Blvd 14 

Crockett-Kendall Avenue 25 

Martinez-Jones Street 18 

Pittsburg-10th Street 20* 

Richmond-7th Street 18 

San Pablo-Rumrill Blvd 14* 

San Francisco San Francisco-Arkansas Street 15* 

Santa Clara San Jose-Jackson Street 5* 

Solano Benicia-East 2nd Street 26* 

Vallejo-304 Tuolumne Street 8 

San Joaquin Valley Fresno Fresno-1st Street 9* 

Salton Sea Imperial Calexico-Ethel Street 10 

Sacramento Valley Sacramento North Highlands-Blackfoot Way 4* 

Sacramento-Del Paso Manor 4* 

1

 Data were extracted on 11/23/2010 from AQMIS Merged. The 2009 SO2 1-hour Federal Design Values were calculated based on the 3-

year average of the annual 99th percentile of the 1-hour daily maximum concentrations (2007, 2008, 2009). The Federal 1-hour SO2 

standard is 75 ppb and was effective August 23, 2010. All SO2 1-hour Federal Design Values in California are below the standard of 75 ppb. 

* Sites do not meet the EPA's data completeness criteria. No monitoring data are available for the following air basins: Great Basin Valleys, 

Lake County, Lake Tahoe, Mountain Counties, Northeast Plateau. 
Enclosure 2 

California SO2 Attainment Area Boundary Descriptions 

1 

North Coast Basin 

a) All of Del Norte County 

b) All of Humboldt County 

c) All of Mendocino County 

d) All of Trinity County 

e) That portion of Sonoma County which lies north and west of a line described as 

follows: 

Beginning at the southeasterly corner of the Rancho Estero Americano, being on 

the boundary line between Marin and Sonoma Counties, California; thence 

running northerly along the easterly boundary line of said Rancho Estero 

Americano to the northeasterly corner thereof, being an angle corner in the 

westerly boundary line of Rancho Canada de Jonive; thence running along said 

boundary of Rancho Canada de Jonive westerly, northerly and easterly to its 

intersection with the easterly line of Graton Road; thence running along the 

easterly and southerly line of Graton Road, northerly and easterly to its 

intersection with the easterly line of Sullivan Road; thence running northerly 

along said easterly line of Sullivan Road to the southerly line of Green Valley 

Road; thence running easterly along the said southerly line of Green Valley Road 

and easterly along the southerly line of State Highway 116, to the westerly line of 

Vine Hill Road; thence running along the westerly and northerly line of Vine Hill 

Road, northerly and easterly to its intersection with the westerly line of Laguna 

Road; thence running northerly along the westerly line of Laguna Road and the 

northerly projection thereof to the northerly line of Trenton Road; thence running 

westerly along the northerly line of said Trenton Road to the easterly line of 

Trenton-Healdsburg Road; thence running northerly along said easterly line of 

Trenton-Healdsburg Road to the easterly line of Eastside Road; thence running 

northerly along said easterly line of Eastside Road to its intersection with the 

southerly line of Rancho Sotoyome; thence running easterly along said southerly 

line of Rancho Sotoyome to its intersection with the Township line common to 

Townships 8 and 9 North, M.D.M.; thence running easterly along said township 

line to its intersection with the boundary line between Sonoma and Napa 

Counties, State of California. 
Enclosure 2 

California SO2 Attainment Area Boundary Descriptions 

2 

San Francisco Bay Area Basin 

a) That portion of Sonoma County which lies south and east of a line described as 

follows: 

Beginning at the southeasterly corner of the Rancho Estero Americano, being on 

the boundary line between Marin and Sonoma Counties, California; thence 

running northerly along the easterly boundary line of said Rancho Estero 

Americano to the northeasterly corner thereof, being an angle corner in the 

westerly boundary line of Rancho Canada de Jonive; thence running along said 

boundary of Rancho Canada de Jonive westerly, northerly and easterly to its 

intersection with the easterly line of Graton Road; thence running along the 

easterly and southerly line of Graton Road, northerly and easterly to its 

intersection with the easterly line of Sullivan Road; thence running northerly 

along said easterly line of Sullivan Road to the southerly line of Green Valley 

Road; thence running easterly along the said southerly line of Green Valley Road 

and easterly along the southerly line of State Highway 116, to the westerly line of 

Vine Hill Road; thence running along the westerly and northerly line of Vine Hill 

Road, northerly and easterly to its intersection with the westerly line of Laguna 

Road; thence running northerly along the westerly line of Laguna Road and the 

northerly projection thereof to the northerly line of Trenton Road; thence running 

westerly along the northerly line of said Trenton Road to the easterly line of 

Trenton-Healdsburg Road; thence running northerly along said easterly line of 

Trenton-Healdsburg Road to the easterly line of Eastside Road; thence running 

northerly along said easterly line of Eastside Road to its intersection with the 

southerly line of Rancho Sotoyome; thence running easterly along said southerly 

line of Rancho Sotoyome to its intersection with the Township line common to 

Townships 8 and 9 North, M.D.M.; thence running easterly along said township 

line to its intersection with the boundary line between Sonoma and Napa 

Counties, State of California. 

b) All of Napa County 

c) That portion of Solano County which lies south and west of a line described as 

follows: 

Beginning at the intersection of the westerly boundary of Solano County and the 

1/4 section line running east and west through the center of Section 34, T6N, 

R2W, M.D.B. & M., thence east along said 1/4 section line to the east boundary 
Enclosure 2 

California SO2 Attainment Area Boundary Descriptions 

3 

of Section 36, T6N, R2W, thence south 1/2 mile and east 2.0 miles, more or less, 

along the west and south boundary of Los Putos Rancho to the northwest corner 

of Section 4, T5N, R1W, thence east along a line common to T5N and T6N to the 

northeast corner of Section 3, T5N, R1E, thence south along section lines to the 

southeast corner of Section 10, T3N, R1E, thence east along section lines to the 

south 1/4 corner of Section 8, T3N, R2E, thence east to the boundary between 

Solano and Sacramento Counties. 

d) All of Contra Costa County 

e) All of Alameda County 

f) All of Santa Clara County 

g) All of San Mateo County 

h) All of San Francisco County 

i) All of Marin County 

North Central Coast Basin 

a) All of Santa Cruz County 

b) All of San Benito County 

c) All of Monterey County 

South Central Coast Basin 

a) All of San Luis Obispo County 

b) All of Santa Barbara County 

c) All of Ventura County 

South Coast Air Basin 

a) All of Orange County 

b) That portion of Riverside County which lies west of a line described as follows: 

Beginning at the Riverside-San Diego County boundary and running north along 

the range line common to R. 4 E and R. 3 E; then east along the township line 
Enclosure 2 

California SO2 Attainment Area Boundary Descriptions 

4 

common to T. 8 S and T. 7 S; then north along the range line common to R. 5 E 

and R. 4 E; then west along the township line common to T. 6 S and T. 7 S to the 

southwest corner of Section 34, T. 6 S, R. 4 E; then north along the west 

boundaries of Sections 34, 27, 22, 15, 10, 3, T. 6 S, R. 4 E; then west along the 

township line common to T. 5 S and T. 6 S; then north along the range line 

common to R. 4 E and R. 3 E; then west along the south boundaries of Sections 

13, 14, 15, 16, 17 and 18, T. 5 S. R. 3 E; then north along the range line common 

to R. 2 E and R. 3 E to the Riverside-San Bernardino County line. 

c) That portion of San Bernardino County west and south of a line described as 

follows: 

Beginning at the San Bernardino-Riverside County boundary and running north 

along the range line common to R. 3 E and R. 2 E; then west along the township 

line common to T. 3 N and T. 2 N to the San Bernardino-Los Angeles County 

boundary. 

d) That portion of Los Angeles County which lies south and west of a line described 

as follows: 

Beginning at the Los Angeles-San Bernardino County boundary and running 

west along the township line common to T.3 N and T.2 N, San Bernardino Base 

and Meridian; then north along the range line common to R.8 W and R.9 W; then 

west along the township line common to T.4 N and T.3 N; then north along the 

range line common to R.12 W and R.13 W to the southeast corner of Section 12, 

T.5 N, R. 13 W; then west along the south boundaries of Sections 12, 11, 10, 9, 

8, 7, T.5 N, R. 13 W to the boundary of the Angeles National Forest which is 

collinear with the range line common to R. 13 W and R. 14 W; then north and 

west along the Angeles National Forest boundary to the point of intersection with 

the township line common to T.7 N and T. 6 N (point is at the northwest corner of 

Section 4 in T.6 N, R. 14 W); then west along the township line common to T.7 N 

and T.6 N; then north along the range line common to R. 15 W and R. 16 W to 

the southeast corner of Section 13, T.7 N, R. 16 W; then along the south 

boundaries of Sections 13, 14, 15, 16, 17, 18, T.7 N, R. 16 W; then north along 

the range line common to R.16 W and R. 17 W to the north boundary of the 

Angeles National Forest (collinear with township line common to T.8 N and T.7 

N); then west and north along the Angeles National Forest boundary to the point 

of intersection with the south boundary of the Rancho La Liebre Land Grant; then 
Enclosure 2 

California SO2 Attainment Area Boundary Descriptions 

5 

west and north along this land grant boundary to the Los Angeles-Kern County 

boundary. 

Northeast Plateau Basin 

a) All of Modoc County 

b) All of Lassen County 

c) All of Siskiyou County 

Sacramento Valley Basin 

a) All of Tehama County 

b) All of Glenn County 

c) All of Butte County 

d) All of Colusa County 

e) All of Yolo County 

f) All of Sutter County 

g) All of Yuba County 

h) All of Sacramento County 

i) All of Shasta County. 

j) That portion of Solano County which lies north and east of a line described as 

follows: 

Beginning at the intersection of the westerly boundary of Solano County and the 

1/4 section line running east and west through the center of Section 34, T6N, 

R2W, M.D.B. & M., thence east along said 1/4 section line to the east boundary 

of Section 36, T6N, R2W, thence south 1/2 mile and east 2.0 miles, more or less, 

along the west and south boundary of Los Putos Rancho to the northwest corner 

of Section 4, T5N, R1W, thence east along a line common to T5N and T6N to the 

northeast corner of Section 3, T5N, R1E, thence south along section lines to the 

southeast corner of Section 10, T3N, R1E, thence east along section lines to the 

south 1/4 corner of Section 8, T3N, R2E, thence east to the boundary between 

Solano and Sacramento Counties. 

k) That portion of Placer County which lies west of Range 9 east, M.D.B. & M. 
Enclosure 2 

California SO2 Attainment Area Boundary Descriptions 

6 

San Joaquin Valley Basin 

a) All of San Joaquin County 

b) All of Stanislaus County 

c) All of Merced County 

d) All of Madera County 

e) All of Fresno County 

f) All of Kings County 

g) All of Tulare County 

h) That portion of Kern County which lies west and north of a line described as 

follows: 

Beginning at the Kern-Los Angeles County boundary and running north and east 

along the northwest boundary of the Rancho La Libre Land Grant to the point of 

intersection with the range line common to R. 16 W. and R. 17 W., San 

Bernardino Base and Meridian; north along the range line to the point of 

intersection with the Rancho El Tejon Land Grant boundary; then southeast, 

northeast, and northwest along the boundary of the Rancho El Tejon Land Grant 

to the northwest corner of S. 3, T. 11 N., R. 17 W.; then west 1.2 miles; then 

north to the Rancho El Tejon Land Grant boundary; then northwest along the 

Rancho El Tejon line to the southeast corner of S. 34, T. 32 S., R. 30 E., Mount 

Diablo Base and Meridian; then north to the northwest corner of S. 35, T. 31 S., 

R. 30 E.; then northeast along the boundary of the Rancho El Tejon Land Grant 

to the southwest corner of S. 18, T. 31 S., R. 31 E.; then east to the southeast 

corner of S. 13, T. 31 S., R. 31 E.; then north along the range line common to R. 

31 E. and R. 32 E., Mount Diablo Base and Meridian, to the northwest corner of 

S. 6, T. 29 S., R. 32 E.; then east to the southwest corner of S. 31, T. 28 S., R. 

32 E.; then north along the range line common to R. 31 E. and R. 32 E. to the 

northwest corner of S. 6, T. 28 S., R. 32 E., then west to the southeast corner of 

S. 36, T. 27 S., R. 31 E., then north along the range line common to R. 31 E. and 

R. 32 E. to the Kern-Tulare County boundary. 

Great Basin Valleys Basin 

a) All of Alpine County 

b) All of Mono County 

c) All of Inyo County 
Enclosure 2 

California SO2 Attainment Area Boundary Descriptions 

7 

Mojave Desert Air Basin 

a) That portion of Riverside County which lies east of a line described as follows: 

That segment of the southwestern boundary line of Hydrologic Unit Number 

18100100 within Riverside County*, further described as follows: 

Beginning at the Riverside-Imperial County boundary and running north along the 

range line common to R. 17 E. and R. 16 E., San Bernardino Base and Meridian; 

then northwest along the ridge line of the Chuckwalla Mountains, through T. 8 S., 

R. 16 E. and T. 7 S., R. 16 E., until the Black Butte Mountain, elev. 4504 '; then 

west and northwest along the ridge line to the southwest corner of T. 5 S., R. 14 

E.; then north along the range line common to R. 14 E. and R. 13 E.; then west 

and northwest along the ridge line to Monument Mountain, elev. 4834 '; then 

southwest and then northwest along the ridge line of the Little San Bernardino 

Mountains to Quail Mountain, elev. 5814 '; then northwest along the ridge line to 

the Riverside-San Bernardino County line. 

b) That portion of San Bernardino County east and north of a line described as 

follows: 

Beginning at the San Bernardino-Riverside County boundary and running north 

along the range line common to R. 3 E and R. 2 E, San Bernardino Base and 

Meridian; then west along the township line common to T. 3 N and T. 2 N to the 

San Bernardino-Los Angeles County boundary. 

c) That portion of Los Angeles County which lies north and east of a line described 

as follows: 

Beginning at the Los Angeles-San Bernardino County boundary and running 

west along the township line common to T. 3 N and T. 2 N, San Bernardino Base 

and Meridian; then north along the range line common to R. 8 W and R. 9 W; 

then west along the township line common to T. 4 N and T. 3 N; then north along 

the range line common to R. 12 W and R. 13 W to the southeast corner of 

Section 12, T. 5 N, R. 13 W; then west along the south boundaries of Sections 

12, 11, 10, 9, 8, 7, T. 5 N, R. 13 W to the boundary of the Angeles National 

Forest which is collinear with the range line common to R. 13 W and R. 14 W; 

then north and west along the Angeles National Forest boundary to the point of 
Enclosure 2 

California SO2 Attainment Area Boundary Descriptions 

8 

intersection with the township line common to T. 7 N and T. 6 N (point is at the 

northwest corner of Section 4 in T. 6 N, R. 14 W); then west along the township 

line common to T. 7 N and T. 6 N; hen north along the range line common to R. 

15 W and R. 16 W to the southeast corner of Section 13, T. 7 N, R. 16 W; then 

along the south boundaries of Sections 13, 14, 15, 16, 17, 18, T. 7 N, R. 16 W; 

then north along the range line common to R. 16 W and R. 17 W to the north 

boundary of the Angeles National Forest (collinear with township line common to 

T. 8 N and T. 7 N) then west and north along the Angeles National Forest 

boundary to the point of intersection with the south boundary of the Rancho La 

Liebre Land Grant; then west and north along this land grant boundary to the Los 

Angeles-Kern County boundary. 

d) That portion of Kern County east and south of a line described as follows: 

Beginning at the Kern-Los Angeles County boundary and running north and east 

along the northwest boundary of the Rancho La Libre Land Grant to the point of 

intersection with the range line common to R. 16 W. and R. 17 W., San 

Bernardino Base and Meridian; north along the range line to the point of 

intersection with the Rancho El Tejon Land Grant boundary; then southeast, 

northeast, and northwest along the boundary of the Rancho El Tejon Land Grant 

to the northwest corner of S. 3, T. 11 N., R. 17 W.; then west 1.2 miles; then 

north to the Rancho El Tejon Land Grant boundary; then northwest along the 

Rancho El Tejon line to the southeast corner of S. 34, T. 32 S., R. 30 E., Mount 

Diablo Base and Meridian; then north to the northwest corner of S. 35, T. 31 S., 

R. 30 E.; then northeast along the boundary of the Rancho El Tejon Land Grant 

to the southwest corner of S. 18, T. 31 S., R. 31 E.; then east to the southeast 

corner of S. 13, T. 31 S., R. 31 E.; then north along the range line common to R. 

31 E. and R. 32 E., Mount Diablo Base and Meridian, to the northwest corner of 

S. 6, T. 29 S., R. 32 E.; then est to the southwest corner of S. 31 T. 28 S., R. 32 

E.; then north along the range line common to R. 31 E. and R. 32 E. to the 

northwest corner of S. 6, T. 28 S., R. 32 E., then west to the southeast corner of 

S. 36, T. 27 S., R. 31 E., then north along the range line common to R. 31 E. and 

R. 32 E. to the Kern-Tulare County boundary. 

San Diego Air Basin

All of San Diego County. 
Enclosure 2 

California SO2 Attainment Area Boundary Descriptions 

9 

Mountain Counties Air Basin 

a) All of Plumas County 

b) All of Sierra County 

c) All of Nevada County 

d) All of Amador County 

e) All of Calaveras County 

f) All of Tuolumne County 

g) All of Mariposa County 

h) All of El Dorado County except that portion included in the Lake Tahoe Air Basin, 

as defined in Section 60113(a). 

i) All of Placer County except that portion included in the Lake Tahoe Air Basin, as 

defined in Section 60113(b), and that portion included in the Sacramento Valley 

Air Basin, as defined in Section 60106(k). 

Lake County Air Basin

All of Lake County. 

Lake Tahoe Air Basin 

a) That portion of El Dorado County within the drainage area naturally tributary to 

Lake Tahoe including said Lake. 

b) That portion of Placer County within the drainage area naturally tributary to Lake 

Tahoe including said Lake, plus that area in the vicinity of the head of the 

Truckee River described as follows: commencing at the point common to the 

aforementioned drainage area crestline and the line common to Townships 15 

North and 16 North, M.D.B. & M., and following that line in a westerly direction to 

the northwest corner of Section 3, Township 15 North, Range 16 East, M.D.B. & 

M., thence south along the west line of Sections 3 and 10, Township 15 North, 

Range 16 East, M.D.B. & M., to the intersection with the said drainage area 

crestline, thence following the said drainage area boundary in a southeasterly, 

then northeasterly direction to and along the Lake Tahoe Dam, thence following 

the said drainage area crestline in a northeasterly, then northwesterly direction to 
Enclosure 2 

California SO2 Attainment Area Boundary Descriptions 

10 

the point of beginning. 

Salton Sea Air Basin 

a) All of Imperial County 

b) That portion of Riverside County which lies east of a line described as follows: 

Beginning at the Riverside-San Diego County boundary and running north along 

the range line common to R. 4 E and R. 3 E; then east along the township line 

common to T. 8 S and T. 7 S; then north along the range line common to R. 5 E 

and R. 4 E; then west along the township line common to T. 6 S and T. 7 S to the 

southwest corner of Section 34, T. 6 S, R. 4 E; then north along the west 

boundaries of Sections 34, 27, 22, 15, 10, 3, T. 6 S, R. 4 E; then west along the 

township line common to T. 5 S and T. 6 S; then north along the range line 

common to R. 4 E and R. 3 E; then west along the south boundaries of Sections 

13, 14, 15, 16, 17 and 18, T. 5 S. R. 3 E; then north along the range line common 

to R. 2 E and R. 3 E to the Riverside-San Bernardino County line; 

and west of a line described as follows: 

That segment of the southwestern boundary line of Hydrologic Unit Number 

18100100 within Riverside County*, further described as follows: 

Beginning at the Riverside-Imperial County boundary and running north along the 

range line common to R. 17 E. and R. 16 E., San Bernardino Base and Meridian; 

then northwest along the ridge line of the Chuckwalla Mountains, through T. 8 S., 

R. 16 E. and T. 7 S., R. 16 E., until the Black Butte Mountain, elev. 4504 '; then 

west and northwest along the ridge line to the southwest corner of T. 5 S., R. 14 

E.; then north along the range line common to R. 14 E. and R. 13 E.; then west 

and northwest along the ridge line to Monument Mountain, elev. 4834 '; then 

southwest and then northwest along the ridge line of the Little San Bernardino 

Mountains to Quail Mountain, elev. 5814 '; then northwest along the ridge line to 

the Riverside-San Bernardino County line. 

*Hydrologic Unit Map, 1978, State of California (Southern Half), Department of the 

Interior, Geological Survey, Reston, Virginia (Reprinted 1987), incorporated by 

reference herein.