Linda S. Adams

Secretary for 

Environmental Protection

 

The energy challenge facing California is real. Every Californian needs to take immediate action to reduce energy consumption. 

For a list of simple ways you can reduce demand and cut your energy costs, see our website: http://www.arb.ca.gov. 

California Environmental Protection Agency

Printed on Recycled Paper

Air Resources Board 

 

Mary D. Nichols, Chairman 

1001 I Street • P.O. Box 2815 

Sacramento, California 95812 • www.arb.ca.gov Arnold Schwarzenegger

Governor 

March 11, 2009 

Ms. Laura Yoshii 

Acting Regional Administrator 

U.S. Environmental Protection Agency 

Region 9 

75 Hawthorne Street 

San Francisco, California 94105 

Dear Ms. Yoshii: 

We are transmitting our recommendations for area designations and boundaries under 

the revised federal 8-hour ozone standard, as required under the Federal Clean Air Act. 

Ozone Nonattainment Areas 

We base our recommendations on ambient ozone concentrations measured from 2006 

through 2008 by 180 Federal Reference Method (FRM) monitors located throughout 

California. The Air Resources Board’s (ARB) recommendation is that the 

U.S. Environmental Protection Agency (U.S. EPA) designate twenty-one areas as 

nonattainment for the revised ozone standard of 0.075 parts per million. Enclosure 1, 

included with this letter, lists the proposed nonattainment areas, which include all fifteen 

areas currently designated nonattainment for the 0.08 parts per million ozone standard, 

along with six new or expanded areas. 

We also recommend that U.S. EPA designate twelve areas as attainment, where air 

quality data are sufficient to determine that they meet the federal standard. Finally, five 

should be deemed unclassifiable, where air quality data are insufficient to make a 

determination. 

Nonattainment Area Boundaries 

Regarding nonattainment area boundaries, ARB makes the following recommendations: 

• Retain the existing nonattainment area boundaries for the fifteen areas that are 

currently designated as nonattainment for ozone. 
Ms. Laura Yoshii 

March 11, 2009 

Page 2 

• Expand the Eastern Kern County nonattainment area to include Indian Wells 

Valley and the town of Ridgecrest. 

• Establish our recommended nonattainment boundaries for new rural transport 

areas. These areas are Southern Inyo County, Northeast San Bernardino 

County, Eastern San Luis Obispo County, the high elevation site on the Tuscan 

Buttes and the specified portion of Pinnacles National Monument located in 

San Benito County. 

Enclosures 

We include the following materials in this package:

• Recommended nonattainment/attainment/unclassifiable areas (Enclosure 1). 

• Staff Report (Enclosure 2). 

• Information supporting recommendations for nonattainment areas (Enclosure 3). 

• Boundary descriptions (Enclosure 4). 

• 2006-2008 data for all of California’s ozone monitoring sites (Enclosure 5). 

Classification Process 

We are completing a technical evaluation of the how well the classification scheme used 

for the current 8-hour ozone standard worked for California. Upon completion we will 

share this information, and want to work with U.S. EPA on potential changes that would 

improve the ozone classification process. 

Please feel free to contact me at (916) 445-4383 if you have any questions regarding 

these recommendations, or have your staff contact Ms. Karen Magliano, Chief, 

Air Quality Data Branch, at (916) 322-7137. 

Sincerely, 

/s/ 

James N. Goldstene 

Executive officer 

Enclosures 
Ms. Laura Yoshii 

March 11, 2009 

Page 3 

cc: Ms. Deborah Jordan, Director 

 U.S. Environmental Protection Agency 

 Air Division – Region 9 

 75 Hawthorne Street 

 San Francisco, California 94105 

 Ms. Amy Zimpfer 

 Assistant Director 

 U.S. Environmental Protection Agency 

 Air Division – Region 9 

 75 Hawthorne Street 

 San Francisco, California 94105 

 Mr. Barry Wallerstein 

Air Pollution Control Officer 

 South Coast Air Quality Management District 

 21855 E. Copley Drive 

 Diamond Bar, California 91765-4182 

Mr. Michael J. Villegas 

Air Pollution Control Officer 

Ventura County Air Pollution Control District 

669 County Square Drive, 2nd Floor 

Ventura, California 93003-5417 

Ms. Rosa Abreu 

Acting Air Pollution Control Officer 

San Diego County Air Pollution Control District 

10124 Old Grove Road 

San Diego, California 92131-1649 

Mr. Larry Allen 

Air Pollution Control Officer 

San Luis Obispo Air Pollution Control District 

3433 Roberto Court 

San Luis Obispo, California 93401-7126 

Continued next page. 
Ms. Laura Yoshii 

March 11, 2009 

Page 4 

cc: (continued) 

Mr. Seyed Sadredin 

Air Pollution Control Officer 

San Joaquin Valley Air Pollution Control District 

1990 East Gettysburg 

Fresno, California 93726 

Mr. Larry Greene 

Air Pollution Control Officer 

Sacramento Metro Air Quality Management District 

777 12th Street, Third Floor 

Sacramento, California 95814-1908 

Ms. Marcella McTaggart 

Air Pollution Control Officer 

El Dorado County Air Quality Management District 

2850 Fairlane Court, Building C 

Placerville, California 95667-4100 

Mr. Tom Christofk 

Air Pollution Control Officer 

Placer County Air Pollution Control District 

3091 County Center Drive, Suite 240 

Auburn, California 95603 

Mr. Mat Ehrhardt 

Air Pollution Control Officer 

Yolo-Solano Air Quality Management District 

1947 Galileo Court, Suite 103 

Davis, California 95616-4882 

Mr. Dave Valler 

Air Pollution Control Officer 

Feather River Air Quality Management District 

938 14th Street 

Marysville, California 95901-4149 

Continued next page. 
Ms. Laura Yoshii 

March 11, 2009 

Page 5 

cc: (continued) 

Dr. Charles Mosher 

Air Pollution Control Officer 

Mariposa County Air Pollution Control District 

P.O. Box 5 

Mariposa, California 95338 

Mr. Gary Caseri 

Air Pollution Control Officer 

Tuolumne County Air Pollution Control District 

2 South Green Street 

Sonora, California 95370-4618 

Mr. Jim Harris 

Air Pollution Control Officer 

Amador County Air Pollution Control District 

665 New York Ranch Road, #4 

Jackson, California 95642 

Mr. Lakhmir Grewal 

Air Pollution Control Officer 

Calaveras County Air Pollution Control District 

Government Center 

891 Mountain Ranch Road 

San Andreas, California 95249-9709 

Mr. Doug Quetin 

Air Pollution Control Officer 

Monterey Bay Unified Air Pollution Control District

24580 Silver Cloud Court 

Monterey, California 93940-6536 

Mr. Jack Broadbent 

Air Pollution Control Officer 

Bay Area Air Quality Management District 

939 Ellis Street 

San Francisco, California 94109-7799 

Continued next page. 
Ms. Laura Yoshii 

March 11, 2009 

Page 6 

cc: (continued) 

Mr. W. James Wagoner 

Air Pollution Control Officer 

Butte County Air Quality Management District 

2525 Dominic Drive, Suite J 

Chico, California 95928-7184 

Mr. Alan Abbs 

Air Pollution Control Officer 

Tehama County Air Pollution Control District 

1750 Walnut Street 

Red Bluff, California 96080-0038 

Mr. Brad Poiriez 

Air Pollution Control Officer 

Imperial County Air Pollution Control District 

150 South 9th Street 

El Centro, California 92243-2801 

Mr. Eldon Heaston 

Executive Director 

Antelope Valley Air Quality Management District 

43301 Division Street, Suite 206 

Lancaster, California 93535-4649 

Mr. Ted Schade 

Air Pollution Control Officer 

Great Basin Unified Air Pollution Control District 

157 Short Street, Suite 6 

Bishop, California 93514-3537 

Mr. David L. Jones 

Air Pollution Control Officer 

Kern County Air Pollution Control District 

2700 M Street, Suite 302 

Bakersfield, California 93301-2370 

Continued next page. 
Ms. Laura Yoshii 

March 11, 2009 

Page 7 

cc: (continued) 

Mr. Eldon Heaston 

Executive Director 

Mojave Desert Air Quality Management District 

14306 Park Avenue 

Victorville, California 92392-2310 

Mr. Russ Mull 

Air Pollution Control Officer 

Shasta County Air Quality Management District 

1855 Placer Street, Suite 101 

Redding, California 96001-1759 

Ms. Gretchen Bennitt 

Air Pollution Control Officer 

Northern Sierra Air Quality Management District 

200 Litton Drive, Suite 320 

Grass Valley, California 95945-2509 
-1-

ENCLOSURE 1

Recommended California Nonattainment Areas for the Federal 8-Hour Ozone Standard 

Based on 2006-2008 Ozone Air Quality Data

Nonattainment Area

Design 

Value1

(ppm)

Area Included

Northeast San Bernardino 

County 0.080

Remainder of the Mojave Desert portion of 

San Bernardino County outside the Western 

Mojave ozone nonattainment area

Southern Inyo County 0.081

Inyo County portions of federal hydrologic units 

16060015, 18090202, 18090203, 18090204, and 

18090205

Eastern San Luis Obispo 

County 0.084 Eastern San Luis Obispo County

Pinnacles 0.079 San Benito County portion of Pinnacles National 

Monument

New

Areas

Tuscan Buttes 0.085 Tuscan Buttes in Tehama County above 1800’ 

Expanded

Area Eastern Kern County 0.086 Mojave Desert Air Basin portion of Kern County,including Indian Wells Valley

South Coast Air Basin 0.119

Western Los Angeles (including Catalina and 

San Clemente Islands), Orange, southwestern 

San Bernardino, and western Riverside counties

San Joaquin Valley 0.108 San Joaquin, Stanislaus, Merced, Madera, 

Fresno, Kings, Tulare, and western Kern counties

Sacramento Metro Area 0.102

Sacramento, Yolo, eastern Solano, southern 

Sutter, and western portions of El Dorado and 

Placer counties

San Francisco Bay Area 0.081

Marin, southern Sonoma, Napa, western Solano, 

Contra Costa, Alameda, Santa Clara, San 

Francisco, and San Mateo counties

Ventura County 0.088 Continental portion of Ventura County (excludes 

Anacapa and San Nicolas islands)

Western Mojave Desert 0.104 Central San Bernardino County

Antelope Valley 0.094 Northeastern Los Angeles County

Coachella Valley 0.097 Central Riverside County

San Diego County 0.092 San Diego County

Imperial County 0.082 Imperial County

Sutter Buttes 0.085 Sutter Buttes in Sutter County above 2000’

Central Mountain Counties 0.089 Amador and Calaveras counties 

Southern Mountain Counties 0.088 Tuolumne and Mariposa counties

Western Nevada County 0.091 Portion of Nevada County west of the crest of the 

Sierra Nevada

Continuing

Areas

Butte County 0.085 Butte County

1

The design value is the 3-year average (2006-2008 data) of the annual fourth highest 8-hour 

ozone concentration at the highest monitor (if greater than 0.075 ppm = nonattainment; if less 

than or equal to 0.075 = attainment). 2008 data are preliminary.
-2-

Recommended California Attainment Areas for the 

Federal 8-Hour Ozone Standard

Based on 2006-2008 Ozone Air Quality Data

Attainment Area

Design 

Value1

(ppm)

Area Included

North Coast Air Basin 0.058

Del Norte, Humboldt, Mendocino, and Trinity 

counties and the North Coast Air Basin 

portion of Sonoma County

Shasta County 0.073 Shasta County

Tehama County 0.075 Portion of Tehama County outside Tuscan 

Buttes area

Glenn County 0.065 Glenn County

2

Colusa County 0.069 Colusa County

Sutter and Yuba Counties 0.072

Yuba County and portion of Sutter County 

outside Sacramento Metro Area and Sutter 

Buttes area

Lake County 0.062 Lake County

Lake Tahoe Air Basin 0.070 Lake Tahoe Air Basin portions of El Dorado 

and Placer counties

North Central Coast Air 

Basin 0.069

Monterey County, Santa Cruz County, 

San Benito County outside Pinnacles 

National Monument boundary

Santa Barbara County 0.073

Continental portion of Santa Barbara County 

(excludes San Miguel, Santa Barbara, Santa 

Cruz, and Santa Rosa islands)

Western San Luis Obispo

County 0.068

Portion of County west of Eastern San Luis 

Obispo area

Eastern Riverside County 0.063 Portion of Riverside County in Mojave Desert 

Air Basin

1

The design value is the 3-year average (2006-2008 data) of the annual fourth highest 8-hour 

ozone concentration at the highest monitor (if greater than 0.075 ppm = nonattainment; if less 

than or equal to 0.075 = attainment). 2008 data are preliminary.

2 Reflects combined data from 2 monitoring sites.
-3-

Recommended California Unclassifiable Areas 

for the Federal 8-Hour Ozone Standard

Unclassifiable Area Area Included

Great Basin Valleys Air Basin

Alpine County, Mono County, portion of Inyo 

County outside Southern Inyo County 

nonattainment area

Northern Mountain Counties Plumas and Sierra counties 

Northern Channel Islands

The islands located in the South Central Coast Air 

Basin, including Anacapa, San Miguel, 

San Nicolas, Santa Barbara, Santa Cruz, and 

Santa Rosa

Eastern Nevada County Portion of Nevada County east of the crest of the 

Sierra Nevada mountains

Northeast Plateau Air Basin Lassen, Modoc, and Siskiyou counties
State of California

AIR RESOURCES BOARD

Revised: March 3, 2009

RECOMMENDED

AREA DESIGNATIONS 

FOR THE 2008 FEDERAL

8-HOUR OZONE STANDARD

STAFF REPORT

California Environmental Protection Agency 

Air Resources Board

i

TABLE OF CONTENTS

 Page

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

OZONE AIR QUALITY ............................................................................................................2

RECOMMENDED AREA DESIGNATIONS.........................................................................2

New Nonattainment Areas................................................................................................6

Northeast San Bernardino County.............................................................................6

Southern Inyo County..................................................................................................7

Pinnacles National Monument ...................................................................................8

San Luis Obispo County .............................................................................................9

Tuscan Buttes ...............................................................................................................9

Expanded Nonattainment Area......................................................................................10

Eastern Kern County .................................................................................................10

Existing Nonattainment Areas ........................................................................................11

South Coast Air Basin ...............................................................................................11

San Joaquin Valley ....................................................................................................11

Sacramento Metro......................................................................................................11

San Francisco Bay Area ...........................................................................................11

Ventura County...........................................................................................................11

Western Mojave Desert.............................................................................................12

Antelope Valley...........................................................................................................12

Coachella Valley.........................................................................................................12

San Diego County......................................................................................................12

Imperial County...........................................................................................................12

Sutter Buttes ...............................................................................................................12

Central Mountain Counties .......................................................................................12

Southern Mountain Counties....................................................................................13

Western Nevada County...........................................................................................13

Butte County ...............................................................................................................13

Attainment Areas..............................................................................................................13

Shasta County ............................................................................................................13

Eastern Riverside County .........................................................................................14

Other Areas .................................................................................................................14

Unclassifiable Areas ........................................................................................................16
ii

LIST OF TABLES AND FIGURES

 Page

FIGURE 1: Recommended Area Designations for the Federal 8-Hour 

Ozone Standard ...............................................................................................4

TABLE 1: Recommended California Nonattainment Areas for the Federal 8-Hour 

Ozone Standard Based on 2006-2008 Ozone Air Quality Data ...............5

TABLE 2: Recommended California Attainment Areas for the Federal 8-Hour 

Ozone Standard Based on 2006-2008 Ozone Air Quality Data .............15

TABLE 3: Recommended California Unclassifiable Areas for the Federal 

8-Hour Ozone Standard ................................................................................16

ATTACHMENT A: SUMMARY OF OZONE DATA POTENTIALLY IMPACTED BY

EXCEPTIONAL EVENTS

ATTACHMENT B: 2006-2008 FEDERAL 8-HOUR OZONE DESIGN VALUES

BY SITE
-1-

BACKGROUND

On March 12, 2008, U.S. EPA revised the federal 8-hour average air quality 

standard for ozone, lowering it from 0.08 parts per million (ppm) to 0.075 ppm. 

Both the primary and the secondary standard are set at the same level. Under 

the Clean Air Act, all states, including California, are required to develop 

recommendations for area designations and appropriate boundaries. The 

purpose of this report is to summarize the staff’s technical analyses and area 

designation recommendations which are due to U.S. EPA by March 12, 2009. 

U.S. EPA then has one year to review these recommendations and will 

promulgate final designations by March 12, 2010. State implementation plans 

are due three years after the effective date of the final designations, with 

attainment dates ranging from 2013 to 2030, depending on the severity of the 

ozone problem. 

ARB staff completed analyses to determine appropriate designation areas 

throughout the State using the criteria outlined in U.S. EPA’s guidance memo 

(December 4, 2008, Area Designations for the 2008 Revised Ozone National 

Ambient Air Quality Standards, Memorandum from Robert J. Meyers, Principal 

Deputy Assistant Administrator, Office of Air and Radiation to Regional 

Administrators, Regions I-X). Determining an area’s designation is based on 

comparing the design value to the level of the standard. The design value 

reflects a three-year average of the 4th highest 8-hour concentration. If the 

design value is 0.076 ppm or greater, it violates the federal standard. The 

recommendations in this report are based on design values reflecting 2006 

through 2008 ozone data. However, ARB anticipates that U.S. EPA will base the 

final designations on the most recent data, which will most likely be data 

collected during 2007 through 2009. 

Under U.S. EPA’s guidance, air quality data may be excluded from the design 

value calculation if they were affected by an exceptional event. An exceptional 

event is an event, such as a wildfire, that causes an exceedance that is not 

reasonable to control through the regulatory process. During 2007 and 2008, 

wildfires impacted air quality throughout California. However, there is only one 

area in the State, Shasta County, where excluding such data makes a difference 

between attainment and nonattainment based on the design value for the 2006 

through 2008 timeframe. Attachment A to this staff report includes a list of sites 

and dates for Shasta County that we are evaluating for identification as 

exceptional events. 

In addition to Shasta County, other areas of California were also adversely 

impacted by wildfires. In some cases, the fire-impacted days may adversely 

impact design values, based on the 2007 through 2009 data that we expect 

U.S. EPA to use in determining the final area designations. Such measurements 

might also affect an area’s classification with respect to the 0.075 ppm ozone 
-2-

standard. ARB and the local districts are still investigating these impacts, and 

will submit documentation to U.S. EPA in accordance with established rules and 

regulations.

OZONE AIR QUALITY

ARB maintains a comprehensive network of federally sanctioned ozone monitors. 

This network comprises nearly 200 monitors, statewide. We are basing our initial 

recommendations on ambient ozone concentrations measured during 2006 

through 2008 at locations sited and operated in accordance with federal 

requirements. 

Ozone is not directly emitted, but is formed in the atmosphere via photochemical 

reactions. Because it takes time for these reactions to occur, high concentrations 

are often found at downwind locations, sometimes far away from the initial 

precursor emissions sources. In California, many of these transport-impacted 

areas do not have significant emissions sources of their own, and therefore are

dependent on emissions controls in the upwind region to mitigate their ozone 

problem. 

Our recommendations for several of California’s new nonattainment areas 

recognize the importance of transport. Recent photochemical modeling 

completed as part of the planning process for the 0.08 ppm federal 8-hour ozone 

standard showed that many of the State’s downwind transport-impacted areas 

will attain the standard as a result of upwind emissions controls. The modeling 

also showed that because ozone concentrations in the transport-impacted areas 

are generally lower, they should attain earlier than the upwind urban areas. This 

is particularly true for areas located downwind of the South Coast Air Basin. As a 

result, our recommended ozone nonattainment boundaries recognize these 

differences in the challenge, and also, differences in the level of control 

requirements, as well as local planning jurisdictions. 

RECOMMENDED AREA DESIGNATIONS

Section 107(d)(1)(A) of the Clean Air Act defines a nonattainment area as any 

area that does not meet or that contributes to nearby areas not meeting the 

ambient air quality standard. U.S. EPA guidance recommends that the Core 

Based Statistical Area (CBSA) or Combined Statistical Area (CSA), which 

includes two or more CBSAs, serve as the starting point or “presumptive” 

boundary for an ozone nonattainment area. When a violating monitor is not 

located in a CBSA or CSA, U.S. EPA recommends that the boundary of the 

county in which the monitor is located serve as the presumptive boundary. In 

further refining the extent of the boundaries, U.S. EPA recommends that states 

evaluate each area on a case-by-case basis, considering nine factors:
-3-

• Air quality data

• Emissions data 

• Population density and degree of urbanization

• Traffic and commuting patterns

• Growth rates and patterns

• Meteorology 

• Geography/topography 

• Jurisdictional boundaries 

• Level of control of emission sources

Evaluation of these factors may support nonattainment area boundaries that are 

either larger or smaller than the presumptive boundary. Although each of our 

recommended nonattainment areas is unique, the boundaries embody several 

broad principles: 

• For existing 8-hour ozone nonattainment areas, we retained the same 

nonattainment area boundaries, with the exception of expanding one 

area. 

• For new nonattainment areas, a single monitor showing violations of

the 8-hour ozone standard places the area into nonattainment status. 

While the starting point for a new nonattainment area is generally the 

county, our consideration of factors outlined in U.S. EPA guidance 

justified a smaller nonattainment area in many cases. 

As shown in Figure 1, most of California will be nonattainment for the 8-hour 

ozone standard. We are proposing the State be divided into 21 distinct 

nonattainment areas. We are also proposing that 12 areas be designated as 

attainment. Table 1 presents a summary of the recommended nonattainment 

areas and corresponding boundaries. Following the figure and table, we discuss 

each of the nonattainment area recommendations, followed by a discussion of 

areas that qualify as attainment and areas that qualify as unclassified.
-4-

FIGURE 1

Recommended Area Designations for the

Federal 8-Hour Ozone Standard

 South Coast 

 Air Basin

Western Mojave Desert

 San Francisco 

 Bay Area

Sutter Buttes Sacramento Metro Area

Western Nevada County

Southern Mountain Counties

San Joaquin Valley

Eastern Kern 

Coachella Valley

Imperial County

Antelope Valley

 San Diego County

 Ventura County

Tuscan Buttes

Pinnacles

Eastern

San Luis 

Obispo County

Southern Inyo County

Butte County

Central Mountain Counties

Unclassified

Existing Nonattainment

Attainment

Recommended New Nonattainment

NE San Bernardino County
-5-

TABLE 1

Recommended California Nonattainment Areas for the Federal 8-Hour Ozone Standard 

Based on 2006-2008 Ozone Air Quality Data

Nonattainment Area

Design 

Value1

(ppm)

Area Included

Northeast San Bernardino 

County 0.080

Remainder of the Mojave Desert portion of 

San Bernardino County outside the Western 

Mojave ozone nonattainment area

Southern Inyo County 0.081

Inyo County portions of federal hydrologic units 

16060015, 18090202, 18090203, 18090204, and 

18090205

Pinnacles 0.079 San Benito County portion of Pinnacles National 

Monument

Eastern San Luis Obispo 

County 0.084 Eastern San Luis Obispo County

New

Areas

Tuscan Buttes 0.085 Tuscan Buttes in Tehama County above 1800’ 

Expanded

Area Eastern Kern County 0.086 Mojave Desert Air Basin portion of Kern County,including Indian Wells Valley

South Coast Air Basin 0.119

Western Los Angeles (including Catalina and 

San Clemente Islands), Orange, southwestern 

San Bernardino, and western Riverside counties

San Joaquin Valley 0.108 San Joaquin, Stanislaus, Merced, Madera, 

Fresno, Kings, Tulare, and western Kern counties

Sacramento Metro Area 0.102

Sacramento, Yolo, eastern Solano, southern 

Sutter, and western portions of El Dorado and 

Placer counties

San Francisco Bay Area 0.081

Marin, southern Sonoma, Napa, western Solano, 

Contra Costa, Alameda, Santa Clara, San 

Francisco, and San Mateo counties

Ventura County 0.088 Continental portion of Ventura County (excludes 

Anacapa and San Nicolas islands)

Western Mojave Desert 0.104 Central San Bernardino County

Antelope Valley 0.094 Northeastern Los Angeles County

Coachella Valley 0.097 Central Riverside County

San Diego County 0.092 San Diego County

Imperial County 0.082 Imperial County

Sutter Buttes 0.085 Sutter Buttes in Sutter County above 2000’

Central Mountain Counties 0.089 Amador and Calaveras counties 

Southern Mountain Counties 0.088 Tuolumne and Mariposa counties

Western Nevada County 0.091 Portion of Nevada County west of the crest of the 

Sierra Nevada

Existing

Areas

Butte County 0.085 Butte County

1

The design value is the 3-year average (2006-2008 data) of the annual fourth highest 8-hour 

ozone concentration at the highest monitor (if greater than 0.075 ppm = nonattainment; if less 

than or equal to 0.075 = attainment). 2008 data are preliminary.
-6-

New Nonattainment Areas

Northeast San Bernardino County

San Bernardino County is the largest county in the nation, comprising over 

20,000 square miles. Because of its size, it encompasses a very diverse

landscape. Currently, the central portion of San Bernardino County, located in 

the Mojave Desert Air Basin, is defined as the Western Mojave Desert (WMD) 

nonattainment area. While the presumptive boundary for an expanded 

nonattainment area would include the entire Mojave Desert portion of 

San Bernardino County, ARB is recommending the area be designated as two 

separate areas, based on differences in the nature and severity of the ozone 

problems. 

With a population of more than 350,000 (2006 estimate), the WMD portion of 

San Bernardino County is adjacent to the South Coast Air Basin. Given its 

proximity to the South Coast, major highways traveling through the WMD carry 

significant commuter and truck traffic in and out of the South Coast region. 

Principal cities in the area include Hesperia, Phelan, Victorville, Apple Valley, and 

Twentynine Palms. Previous transport assessments show that ozone 

concentrations in the WMD portion of San Bernardino County are impacted by 

transport from the South Coast and SanJoaquin Valley air basins , which are the 

areas with the highest ozone levels in the state. Along with the transport impact, 

there is also a local component to the ozone problem in this area. The design 

value for the WMD is 0.104 ppm at the Joshua Tree-National Monument site. 

Design values for other sites in the area are similar in magnitude, though slightly 

lower.

 

In contrast to the WMD, the more remote northeast portion of San Bernardino 

County is sparsely populated. There are no sizable cities, and the area has few

significant emission sources. Because the area lacks significant population 

centers and emissions sources capable of generating ozone locally, the transport 

component is even more important. Furthermore, the design value for this part of 

San Bernardino County is 0.080 ppm, which is substantially lower than the WMD 

design value. 

Although the northeast portion of San Bernardino County is contiguous with the 

existing WMD nonattainment area and is part of the same county, ARB staff is 

recommending it be defined as a separate nonattainment area. The design 

value for the WMD portion of San Bernardino County is 30 percent higher than 

the design value for the northeast portion of the County. Although both areas will

rely on controls from upwind areas to reach attainment, because the magnitude 

of their problems is so different, the northeast portion of San Bernardino County 

should attain the standard in a shorter timeframe. Designating the area 

separately would give them a classification consistent with their overall air quality 

problem and facilitate a more timely attainment finding. 
-7-

Southern Inyo County

Inyo County is the second largest county in California and one of the largest 

counties in the nation. It encompasses more than 10,000 square miles, from the 

below sea level floor of Death Valley to the 14,000 foot peaks of the Sierra 

Nevada. The only long-term ozone monitor in Inyo County is located at the 

Death Valley National Monument in southeast Inyo County. The site is operated 

by the National Park Service and has a design value of 0.081 ppm, which 

exceeds the federal standard. The area has an extremely low population, with 

only 0.22 residents per square mile, and lacks industrial emissions sources. 

While the presumptive boundary for the nonattainment area would include all of 

Inyo County, ARB is recommending a smaller nonattainment area because of the 

diversity of the area’s geography and the nature of the ozone impact. 

Previous studies suggest that ozone concentrations at the Death Valley site are 

substantially impacted by transport. Wind flow into the southern portion of the 

County is generally from the southwest to northeast, carrying pollutants and 

emissions from the highly urbanized South Coast and southern San Joaquin 

Valley air basins into southern Inyo County. Although Death Valley is the only 

monitoring site in southern Inyo County, data are also collected at the Trona site 

in San Bernardino County, just 2 miles south of the Inyo County line. These data 

suggest that exceedances are also likely to occur in the southwest portion of Inyo 

County. During 2004 through 2008, about half of the exceedance days at Trona 

coincide with exceedance days at Death Valley, indicating that the nonattainment

area should include the southwest portion of Inyo County, as well as the Death 

Valley area. 

In addition to these data, limited 2008 ozone monitoring data are available for a 

site at Bishop, in the northern portion of Inyo County. The site is operated by the 

Bishop Piute Tribe. The Bishop data show several days with concentrations 

above the federal 8-hour standard, but because the data are incomplete, it is not 

possible to calculate a valid design value for this site and determine if it would 

violate the standard. Furthermore, an analysis completed by the Great Basin 

Unified Air Pollution Control District (APCD) shows that emissions and pollutants 

from this area do not likely contribute to the exceedances at Death Valley.

In determining the appropriate nonattainment area boundary, ARB staff 

consulted with the local Great Basin Unified APCD. The recommended 

boundary for this area is based on federal hydrologic units. Hydrologic units are 

based on topography and drainage, similar in many respects to the way 

California’s air basins are defined. Therefore, it is appropriate to use them in 

defining the nonattainment area boundary, since mountainous terrain affects the 

transport and mixing depth of pollution. In addition, hydrologic units have been 

used previously to define designated areas for ozone. ARB staff recommends 

the Southern Inyo County ozone nonattainment area comprise the Inyo County 
-8-

portions of federal hydrologic units 16060015, 18090202, 18090203, 18090204, 

and 18090205. These units cover not only the areas exceeding the standard, but 

also the areas most heavily impacted by transport from the major upwind urban 

areas.

Pinnacles National Monument

San Benito County is located in California’s north central coast region, just south 

of the San Francisco Bay Area (Bay Area). Although it is considered part of the 

coastal region, San Benito County is located inland. The federal ozone standard 

is exceeded at only one site in this area, the Pinnacles National Monument site, 

with a design value of 0.079 ppm. 

With the exception of 2008, the trend in the design value for Pinnacles has been 

consistently downward. In fact, the 2006 and 2007 design values for this site

(0.075 ppm and 0.074 ppm, respectively) show attainment. The higher value for 

2008 likely reflects the impact of wildfires that burned throughout the State during 

the summer of 2008. If the impacted days were removed from consideration, the 

2008 design value would be more consistent with values for previous years. 

However, the area would still be nonattainment. In contrast to Pinnacles, design 

values for sites in the surrounding north central coast region are all well below 

the level of the standard, ranging from 0.052 ppm to 0.069 ppm. 

Pinnacles is an elevated site (1000 feet) located in an area of complex terrain 

within the boundaries of Pinnacles National Monument. Previous transport study 

indicates that exceedances measured at Pinnacles can be overwhelmingly 

impacted by transport aloft from the Bay Area. Although the San Francisco Bay 

Area does not yet attain the standard, design values for Bay Area sites have 

decreased since the early 2000s, similar to those for Pinnacles. As emissions in 

the Bay Area continue to decrease, ozone concentrations in downwind areas 

such as Pinnacles will also improve. 

Because exceedances in SanBenito County are measured only at Pinnacles and 

nowhere else in the local area, ARB recommends limiting the nonattainment 

area. The ozone problem at Pinnacles is attributable to transport from the Bay 

Area, which is already designated as nonattainment. Designating Pinnacles as 

nonattainment, as well, would adequately reflect the impact region for the upwind 

urban area. Specifically, ARB recommends limiting the nonattainment area to 

that portion of Pinnacles National Monument located within San Benito County. 

Using the Monument boundary would provide for an easily identifiable 

nonattainment area. 
-9-

Eastern San Luis Obispo County

San Luis Obispo County is located in California’s south central coast region and 

encompasses coastal, as well as inland areas. The design value for the County 

is 0.084 ppm, measured at the Carrizo Plains School-9640 Carrizo site in the 

eastern part of the County. This site is located in a populated area and was 

originally sited to provide information on transport impacts from the San Joaquin 

Valley. The design value for a second inland, eastern County site, Red Hills, is 

also above the standard at a level of 0.088 ppm, but only two years of data are 

available. In contrast to Carrizo Plains , the Red Hills site is located in an

unpopulated area. Design values for all other sites in San Luis Obispo County 

are below the level of the standard, as are design values for sites in counties 

located both to the north and to the south of SanLuis Obispo County.

Previous studies have shown that ozone and ozone precursor emissions from 

the San Joaquin Valley are transported west, impacting sites in eastern SanLuis 

Obispo County, including Carrizo Plains and Red Hills. Ozone concentrations 

can also be impacted by transport south from the SanFrancisco Bay Area. In 

the absence of transport, it is likely that exceedances would not occur at these 

sites. Therefore, reducing the transport impact will be critical to attaining the 

federal standard. Given that exceedances are limited to the eastern portion of 

the County, and all other sites meet the standard, ARB recommends that only the 

eastern portion of San Luis Obispo County be designated as nonattainment.

Tuscan Buttes

Tuscan Buttes in Tehama County is located in the Sacramento Valley, where the 

majority of the land is near sea level. There are two monitors in the County. The 

first site, Red Bluff-Oak Street, is in the town of Red Bluff at an elevation of 

322 feet. While the design value for this site currently meets the standard, 

several of the high measurements at this site during 2008 may have been 

impacted by wildfires. The District and ARB are currently reviewing this data, 

and if warranted, ARB plans to include documentation to support the exclusion of 

these measurements as exceptional events when we submit our designation 

recommendations to U.S.EPA in March 2009. 

The second monitor in Tehama County, Tuscan Buttes, has a design value of 

0.085 ppm which exceeds the standard. Located at an elevation of 1,877 feet, 

the Tuscan Buttes monitor is similar to the Sutter Buttes monitor in 

Sutter County. Both of these monitors were sited to study high-elevation 

transport of pollutants from the Sacramento urban nonattainment region into the 

upper Sacramento Valley, and there are no pollution sources or populated areas

near either site. Furthermore, design values for low elevation sites in areas 
-10-

surrounding Tehama County (Colusa and Glenn counties and northern Sutter 

County) are below the level of the standard, lending additional support to the 

argument that the ozone problem at Tuscan Buttes is unique and isolated. 

Because of the elevated location and lack of population exposure at the Tuscan 

Buttes site, ARB recommends the geographic scope of the nonattainment area 

be limited to that portion of the Tuscan Buttes area with an elevation of 1800 feet 

or more. This approach is consistent with the approach U.S. EPA used in 

designating the Sutter Buttes ozone nonattainment area. 

Expanded Nonattainment Area

Eastern Kern County

Kern County is located in two different air basins: the San Joaquin Valley 

Air Basin and the Mojave Desert Air Basin. The eastern portion, located in the 

Mojave Desert Air Basin, falls under the jurisdiction of the Kern County 

Air Pollution Control District. Currently, the Eastern Kern nonattainment area, 

which does not include Indian Wells Valley, is designated as nonattainment 

based on a design value of 0.086 ppm for the Mojave-Poole Street site. 

In contrast, Indian Wells Valley (defined as the Kern County portion of hydrologic 

unit 18090205), in the northeastern portion of Kern County, is designated as 

attainment for the 0.08 ppm ozone standard. Indian Wells Valley is a desert 

region that includes the China Lake Naval Air Weapons Station and the town of 

Ridgecrest. Similar to the rest of Eastern Kern, Indian Wells Valley is sparsely 

populated, with few significant emissions sources. Furthermore, previous studies 

have shown that ozone concentrations in both of these areas are overwhelmingly 

impacted by transport from the San Joaquin Valley and South Coast air basins. 

Ozone data collected during 2006 through 2008 are available for a site located in 

the China Lake area of Indian Wells Valley. Although these data have not been 

reviewed or forwarded to U.S. EPA, the design value for the site, 0.081 ppm,

exceeds the federal standard and is comparable to the design value of 

0.086 ppm for the Mojave-Poole Street site in the existing Eastern Kern

nonattainment area. Because the design values for these two areas are similar 

in magnitude and both areas are impacted by ozone transported from the same 

upwind areas, ARB staff recommends that the existing Eastern Kern 

nonattainment area be expanded to include Indian Wells Valley. As a result, the 

Eastern Kern ozone nonattainment area would include the entire Mojave Desert 

Air Basin portion of Kern County. 
-11-

Existing Nonattainment Areas

South Coast Air Basin

The South Coast Air Basin nonattainment area would continue to include all of 

the South Coast Air Basin: western Los Angeles (including Catalina and 

San Clemente Islands, which are not part of the Channel Islands), Orange, 

southwestern San Bernardino, and western Riverside counties. This 

nonattainment area violates the 8-hour standard with a design value of 

0.119 ppm at the Crestline monitoring site in San Bernardino County. 

San Joaquin Valley

The San Joaquin Valley nonattainment area would continue to comprise the 

entire SanJoaquin Valley Air Basin: San Joaquin, Stanislaus, Merced, Madera, 

Fresno, Kings, Tulare, and western Kern counties. The San Joaquin Valley 

violates the federal 8-hour standard with a design value of 0.108 ppm at the 

Arvin-Bear Mountain Blvd. monitoring site in Kern County. 

Sacramento Metro Area

The Sacramento Metro nonattainment area would continue to include all of 

Sacramento and Yolo counties, southern Sutter County, the Sacramento Valley 

Air Basin portion of Solano County, the Sacramento Valley and Mountain 

Counties air basin portions of Placer County, and the Mountain Counties Air 

Basin portion of El Dorado County. This area violates the standard with a design 

value of 0.102 ppm at the Folsom-Natoma Street site in Sacramento County. 

Although the nonattainment area involves multiple local air pollution control 

agencies, all but the Solano County portion are covered by a single 

transportation planning agency. 

San Francisco Bay Area

The San Francisco Bay Area nonattainment area would continue to comprise all

of the San Francisco Bay Area Air Basin: Marin, Napa, Contra Costa, Alameda, 

Santa Clara, SanFrancisco, and San Mateo counties and the San Francisco Bay 

Area Air Basin portions of Solano and Sonoma counties. The area’s 

nonattainment designation is based on a design value of 0.081 ppm for the 

Livermore-793 Rincon Avenue site in Alameda County.

Ventura County

The Ventura County 8-hour nonattainment area would continue to include only 

the continental portion of Ventura County. Anacapa and San Nicolas Islands, 

two of the Channel Islands, would not be included. Ventura County violates the 
-12-

federal standard with a design value of 0.088 ppm at the Simi Valley-Cochran 

Street site. 

Western Mojave Desert

The Western Mojave Desert nonattainment area would continue to comprise the 

central portion of San Bernardino County that is located in the Mojave Desert 

Air Basin. Ozone concentrations at a number of sites in this area violate the 

federal 8-hour standard, and the area has a design value of 0.104 ppm at the 

Joshua Tree-National Monument site.

Antelope Valley

The Antelope Valley nonattainment area would continue to comprise the portion 

of Los Angeles County that is located in the Mojave Desert Air Basin. The area 

has a design value of 0.094 ppm at the Lancaster-43301 Division Street site.

Coachella Valley

The Coachella Valley ozone nonattainment area would continue to include the 

portion of Riverside County that is located in the Salton Sea Air Basin. The 

design value for this area is 0.097 ppm at the Palm Springs-Fire Station site. 

San Diego County

The 8-hour nonattainment area would continue to include all of San Diego 

County. Ozone concentrations in the County exceed the standard at several 

sites, and the design value is 0.092 ppm at Alpine-Victoria Drive. 

Imperial County

Similar to San Diego County, the Imperial County nonattainment area would 

continue to include the entire County. The design value for Imperial County is 

0.082 ppm at both El Centro-9

th Street and Westmorland-West 1st Street.

Sutter Buttes

The Sutter Buttes nonattainment area would continue to include that portion of 

the Sutter Buttes above 2000 feet elevation. Located in Sutter County, the 

design value for this area is 0.085 ppm at the Sutter Buttes site. 

Central Mountain Counties

The Central Mountain Counties nonattainment area would continue to include all 

of Amador and Calaveras counties. The design value for this two-county area is 

0.089 ppm at the San Andreas-Gold Strike Road site in Calaveras County.
-13-

Southern Mountain Counties

The Southern Mountain Counties nonattainment area would continue to include 

all of Mariposa and Tuolumne counties. The design value for this area is 

0.088 ppm at the Turtleback Dome site in Yosemite National Park, which is in 

Mariposa County.

Western Nevada County

This nonattainment area would continue to comprise the western portion of 

Nevada County, up to the crest of the Sierra Nevada. The current design value 

for western Nevada County is 0.091 ppm at the Grass Valley-Litton Building site.

Butte County

This nonattainment area would continue to comprise all of Butte County. There 

are two monitoring sites in Butte County, and both have design values that 

violate the standard. The Paradise-4405 Airport Road site has the higher value, 

with a design value of 0.085 ppm. 

Attainment Areas

A number of areas in California have ozone monitoring data that are in

attainment of the 2008 federal 8-hour standard according to the criteria 

established by U.S. EPA (U.S. EPA, December 1998, Guideline on Data 

Handling Conventions for the 8-Hour Ozone NAAQS). One of these areas, 

Shasta County, attained the 0.08 ppm standard but has ozone data showing 

violations of the federal 0.075 ppm standard. However, a number of days in this 

area during 2008 were impacted by wildfires, an exceptional event. If these days 

are excluded, Shasta County’s design value is below the 2008 federal 8-hour 

ozone standard. A second area, Eastern Riverside County, was previously 

designated as unclassified because of incomplete data. Now that complete data 

are available, the area qualifies as attainment. The remaining ten areas all have 

design values in attainment of the 0.075 ppm ozone standard, and ARB 

recommends they also be designated as attainment. All of the recommended 

attainment areas are summarized in Table 2, below. 

Shasta County

Currently, Shasta County in northern California is designated as attainment for 

the federal 0.08 ppm ozone standard. There are three monitoring sites in Shasta 

County: Anderson-North Street, Redding-Health Department Roof, and Lassen 

Volcanic National Park-Manzanita Lake. Using all data collected at these sites 

during 2006 through 2008, the design values for both Anderson (0.076 ppm) and 

Lassen (0.077 ppm) are just slightly above the federal standard. 
-14-

During the summer of 2008, a significant number of wildfires in California 

impacted ambient ozone readings at sites throughout the State. Shasta County 

Air Quality Management District has documented these impacts and requested 

that high ozone measurements during 16 days in June and July 2008 be 

excluded as impacted by exceptional events (refer to Attachment A). ARB is still 

in the process of reviewing these data. However, if the measurements are 

excluded in accordance with U.S. EPA’s exceptional events rule, the revised 

design value would be 0.073 ppm for all three sites in Shasta County.

If the impacted data are excluded, the design value for Shasta County is below 

the 2008 federal 8-hour ozone standard. Therefore, pending ARB concurrence 

with the District’s evaluation, we recommend that Shasta County be designated 

as attainment for the federal 8-hour ozone standard. 

Eastern Riverside County

Riverside County is subdivided among three air basins: South Coast Air Basin, 

Salton Sea Air Basin (Coachella Valley), and Mojave Desert Air Basin. The 

urbanized South Coast and Coachella Valley portions of the County have design 

values that violate the standard, and these areas are designated as 

nonattainment. In contrast, the eastern portion of Riverside County, located in 

the Mojave Desert Air Basin, is sparsely populated, with few emissions sources. 

This portion of the County is currently designated as unclassified for the federal 

8-hour ozone standard.

When U.S. EPA designated areas for the 0.08 ppm ozone standard, complete

ozone monitoring data were not available for eastern Riverside County, and the 

area was designated as unclassified. Since then, the ozone monitoring site at 

Blythe (Blythe-445 West Murphy Street) has continued to operate. The Blythe 

data show a design value of 0.063 ppm, based on data collected during 2006 

through 2008. Because this value is below the standard, ARB recommends that 

eastern Riverside County be designated as attainment for the 2008 federal 

8-hour ozone standard.

Other Areas

A number of other areas in California that were attainment or unclassified for the 

0.08 ppm standard also qualify as attainment for the revised federal ozone 

standard of 0.075 ppm. These areas are listed in Table 2, along with their design 

values, based on data collected during 2006 through 2008. ARB recommends 

that all these areas be designated as attainment for ozone.
-15-

TABLE 2

Recommended California Attainment Areas 

for the Federal 8-Hour Ozone Standard

Based on 2006-2008 Ozone Air Quality Data

Attainment Area

Design 

Value1

(ppm)

Area Included

North Coast Air Basin 0.058

Del Norte, Humboldt, Mendocino, and Trinity 

counties and the North Coast Air Basin 

portion of Sonoma County

Shasta County 0.073 Shasta County

Tehama County 0.075 Portion of Tehama County outside Tuscan 

Buttes area

Glenn County 0.065 Glenn County

2

Colusa County 0.069 Colusa County

Sutter and Yuba Counties 0.072

Yuba County and portion of Sutter County 

outside Sacramento Metro Area and Sutter

Buttes area

Lake County 0.062 Lake County

Lake Tahoe Air Basin 0.070 Lake Tahoe Air Basin portions of El Dorado 

and Placer counties

North Central Coast Air 

Basin 0.069

Monterey County, Santa Cruz County, 

San Benito County outside Pinnacles 

National Monument boundary

Santa Barbara County 0.073

Continental portion of Santa Barbara County 

(excludes San Miguel, Santa Barbara, Santa 

Cruz, and Santa Rosa islands)

Western San Luis Obispo

County 0.068

Portion of County west of Eastern San Luis 

Obispo area

Eastern Riverside County 0.063 Portion of Riverside County in Mojave Desert 

Air Basin

1

The design value is the 3-year average (2006-2008 data) of the annual fourth highest 8-hour 

ozone concentration at the highest monitor (if greater than 0.075 ppm = nonattainment; if less 

than or equal to 0.075 = attainment). 2008 data are preliminary.

2 Reflects combined data from 2 monitoring sites. 
-16-

Unclassifiable Areas

The areas listed in Table 3 have either no ozone monitoring data or the available 

monitoring data do not meet completeness criteria established by U.S. EPA. 

Therefore, ARB recommends they be considered unclassifiable at the current 

time.

TABLE 3

Recommended California Unclassifiable Areas 

for the Federal 8-Hour Ozone Standard

Unclassifiable Area Area Included

Great Basin Valleys Air Basin

Alpine County, Mono County, portion of Inyo 

County outside Southern Inyo County 

nonattainment area

Northern Mountain Counties Plumas and Sierra counties 

Northern Channel Islands

The islands located in the South Central Coast Air 

Basin, including Anacapa, San Miguel, 

San Nicolas, Santa Barbara, Santa Cruz, and 

Santa Rosa

Eastern Nevada County Portion of Nevada County east of the crest of the 

Sierra Nevada mountains

Northeast Plateau Air Basin Lassen, Modoc, and Siskiyou counties
ATTACHMENT A

SUMMARY OF OZONE DATA 

POTENTIALLY IMPACTED BY EXCEPTIONAL EVENTS

A-1

INTRODUCTION

Under U.S. EPA’s guidance, air quality data may be excluded from the 

designation process if they were affected by an exceptional event. During 2007 

and 2008, wildfires impacted air quality throughout California. However, there is 

only one area in the State, Shasta County, where excluding such data makes a 

difference between attainment and nonattainment based on the design value for 

the 2006 through 2008 timeframe. The dates and sites being considered for 

identification as exceptional events for this area are listed in Table A-1, below. 

In addition to Shasta County, there are other areas in California where it is 

uncertain if measurements impacted by wildfires would adversely affect their 

design values based on the 2007 through 2009 data that U.S. EPA is expected to 

use in determining the final area designations. It is also uncertain whether 

excluding such measurements would affect their classification with respect to the 

0.075 ppm ozone standard. Therefore, additional dates and sites may be 

identified. ARB anticipates that documentation of all exceptional events will be 

submitted to U.S. EPA in March 2009.

TABLE A-1

Summary of Data Being Evaluated as

Potentially Affected by Exceptional Events

COUNTY MONITORING SITE DATES

Anderson-North St Jun 14-15, 24-25, 28-30, 2008 

and Jul 2, 13, 17-19, 23-26, 2008

Lassen Vol NP_Manzanita Lk same dates as Anderson

Shasta

Redding-Health Dept Roof same dates as Anderson

ATTACHMENT B

2006-2008 FEDERAL 8-HOUR OZONE DESIGN VALUES BY SITE

B-1

TABLE B-1

SUMMARY OF DATA AND FEDERAL 8-HOUR OZONE DESIGN VALUES

FOR CALIFORNIA SITES BASED ON 2006 THROUGH 2008 DATA

Year

Basin Name County Name Site Name Statistic 2006 2007 2008*

2008* 

Design 

Value

4

th High 0.082 0.085 0.077 0.081

Inyo Death Valley Natl Monument

Valid Days 347 351 320

Alpine NO MONITORS

Great Basin 

Valleys

Mono NO MONITORS

4

th High 0.062 0.057 0.068 0.062

Lake County Lake Lakeport-Lakeport Blvd 

Valid Days 360 354 328

4

th High 0.069 0.070 0.072 0.070

El Dorado South Lake Tahoe-Airport 

Road Lake Tahoe Valid Days 160 169 151

Placer NO MONITORS

4

th High 0.089 0.078 0.093 0.086

Kern Mojave-923 Poole Street 

Valid Days 357 358 188

4

th High 0.098 0.091 0.095 0.094

Los Angeles Lancaster-43301 Division 

Street Valid Days 363 357 360

4

th High 0.057 0.066 0.067 0.063

Riverside Blythe-445 West Murphy Street

Valid Days 361 284 237

4

th High 0.086 0.084 0.090 0.086

Barstow

Valid Days 344 356 364

4

th High 0.095 0.098 0.098 0.097

Hesperia-Olive Street

Valid Days 358 356 362

4

th Joshua Tree-National High 0.103 0.104 0.105 0.104

Monument Valid Days 348 342 322

4

th Phelan-Beekley Rd & Phelan High 0.097 0.093 0.099 0.096

Rd' Valid Days 363 356 365

4

th High 0.080 0.077 0.084 0.080

Trona-Athol and Telegraph 

Valid Days 360 351 339

4

th High 0.091 0.087 0.089 0.089

Mojave Desert

San Bernardino

Victorville-14306 Park Avenue 

Valid Days 363 362 359

4

th High 0.085 0.073 0.101 0.086

Amador Jackson-Clinton Road

Valid Days 363 344 265

4

th High 0.098 0.076 0.094 0.089

Calaveras San Andreas-Gold Strike Road 

Valid Days 364 356 267

4

th High 0.099 0.093 0.102 0.098

Cool-Highway 193

Valid Days 183 181 150

4

th High 0.075 0.075 0.078 0.076

Echo Summit

Valid Days 148 135 135

4

th High 0.097 0.085 0.106 0.096

El Dorado 

Placerville-Gold Nugget Way

Valid Days 363 333 272

4

th High 0.080 0.083 0.089 0.084

Mountain 

Counties

Mariposa Jerseydale - 6440 Jerseydale

Valid Days 175 181 183
B-2

Year

Basin Name County Name Site Name Statistic 2006 2007 2008*

2008* 

Design 

Value

4

th Mariposa High 0.084 0.087 0.094 0.088

(continued) Yosemite NP-Turtleback Dome

Valid Days 292 334 317

4

th High 0.096 0.088 0.091 0.091

Grass Valley-Litton Building

Valid Days 328 365 247

4

th High 0.076 0.071 0.066 0.071

Truckee-Fire Station

Valid Days 225 281 265

4

th High 0.089 0.082 0.091 0.087

Nevada 

White Cloud Mountain

Valid Days 162 182 153

4

th High 0.105 0.079 0.084 0.089

Placer Colfax-City Hall

Valid Days 346 356 338

4

th High 0.064 0.064

Plumas Quincy-N Church Street

Valid Days 229

4

th High 0.079 0.084 0.098 0.087

Tuolumne Sonora-Barretta Street

Valid Days 365 360 271

Mountain 

Counties 

(continued)

Sierra NO MONITORS

4

th High 0.060 0.059 0.060 0.059

Carmel Valley-Ford Road

Valid Days 364 365 332

4

th High 0.054 0.06 0.057

King City-415 Pearl Street

Valid Days 215 304

4

th High 0.063 0.054 0.058

King City-750 Metz Road

Valid Days 360 134

4

th High 0.054 0.053 0.060 0.055

Monterey 

Salinas-#3

Valid Days 358 354 322

4

th High 0.071 0.068 0.068 0.069

Hollister-Fairview Road

Valid Days 359 352 329

4

th High 0.078 0.075 0.086 0.079

San Benito

Pinnacles National Monument

Valid Days 355 361 324

4

th High 0.052 0.049 0.056 0.052

Davenport

Valid Days 364 362 322

4

th High 0.054 0.053 0.057 0.054

Santa Cruz-2544 Soquel Ave

Valid Days 358 358 329

4

th High 0.062 0.059 0.064 0.061

Scotts Valley-Scotts Valley Dr

Valid Days 361 361 332

4

th High 0.054 0.054 0.058 0.055

North Central 

Coast

Santa Cruz

Watsonville-Airport Boulevard

Valid Days 363 364 334

4

th High 0.046 0.049 0.047

Humboldt Eureka-Jacobs

Valid Days 17 308 347

4

th High 0.060 0.053 0.061 0.058

Ukiah-E Gobbi Street

Valid Days 356 352 302

4

th High 0.049 0.046 0.045 0.046

North Coast

Mendocino

Willits-899 S Main Street

Valid Days 351 358 149
B-3

Year

Basin Name County Name Site Name Statistic 2006 2007 2008*

2008* 

Design 

Value

4

th High 0.056 0.060 0.055 0.057

Sonoma Healdsburg-Municipal Airport

Valid Days 338 341 271

Del Norte NO MONITORS

North Coast 

(continued)

Trinity NO MONITORS

4

th High 0.067 0.060 0.058 0.061

Siskiyou Yreka-Foothill Drive

Valid Days 318 332 264

Lassen NO MONITORS

Northeast Plateau

Modoc NO MONITORS

4

th High 0.076 0.074 0.080 0.076

Chico-Manzanita Avenue

Valid Days 360 363 262

4

th High 0.089 0.083 0.084 0.085

Butte

Paradise-4405 Airport Road

Valid Days 361 364 269

4

th High 0.069 0.066 0.072 0.069

Colusa Colusa-Sunrise Blvd

Valid Days 357 361 269

4

th High 0.059 0.069 0.067 0.065

Willows-720 N Colusa Street

Valid Days 106 361 271

4

th High 0.063 0.063

Glenn 

Willows-E Laurel Street

Valid Days 252

4

th High 0.098 0.079 0.095 0.090

Auburn-Dewitt-C Avenue

Valid Days 330 347 351

4

th High 0.094 0.082 0.094 0.090

Placer 

Roseville-N Sunrise Blvd

Valid Days 363 350 271

4

th High 0.087 0.078 0.082 0.082

Elk Grove-Bruceville Road

Valid Days 357 359 330

4

th High 0.102 0.090 0.114 0.102

Folsom-Natoma Street

Valid Days 358 354 327

4

th High 0.092 0.071 0.072 0.078

North Highlands-Blackfoot Way

Valid Days 356 341 245

4

th High 0.077 0.077 0.080 0.078

Sacramento-3801 Airport Road

Valid Days 311 299 201

4

th High 0.093 0.081 0.087 0.087

Sacramento-Del Paso Manor

Valid Days 349 362 323

4

th High 0.084 0.073 0.081 0.079

Sacramento-T Street

Valid Days 351 342 292

4

th High 0.104 0.080 0.102 0.095

Sacramento

Sloughhouse

Valid Days 214 208 212

4

th High 0.073 0.075 0.081 0.076

Anderson-North Street

Valid Days 327 365 274

4

th High 0.074 0.076 0.083 0.077

Lassen Vol NP-Manzanita Lk

Valid Days 353 362 316

4

th High 0.080 0.070 0.077 0.075

Sacramento 

Valley

Shasta 

Redding-Health Dept Roof

Valid Days 357 365 338
B

-4

Year

Basin Name County Name Site Name Statistic 2006 2007 2008*

2008* 

Design 

Value

4

th High 0.080 0.071 0.084 0.078

Solano Vacaville-Ulatis Drive

Valid Days 358 365 354 4

th High 0.090 0.077 0.088

0.085

Sutter Buttes-S Butte

Valid Days 184 183 153 4

th High 0.078 0.072 0.068 0.072

Sutter

Yuba City-Almond Street

Valid Days 352 343 264 4

th High 0.073 0.072 0.080 0.075

Red Bluff-Oak Street

Valid Days 330 357 319 4

th High 0.087 0.082 0.087

0.085

Tehama

Tuscan Butte

Valid Days 183 184 146 4

th High 0.078 0.075 0.077 0.076

Davis-UCD Campus

Valid Days 358 359 258 4

th High 0.088 0.073 0.076 0.079

Yolo

Woodland-Gibson Road

Valid Days 365 363 356

Sacramento 

Valley (continued)

Yuba NO MONITORS 4

th High 0.043 0.067 0.057 0.055

Brawley-220 Main Street

Valid Days 91 89 14 4

th High 0.078 0.083 0.078 0.079

Calexico-East

Valid Days 352 325 341 4

th High 0.068 0.087 0.087 0.080

Calexico-Ethel Street

Valid Days 362 353 363 4

th High 0.065 0.071 0.068

Calexico-Grant Street

Valid Days 356 205 4

th High 0.091 0.083 0.074 0.082

El Centro-9th Street

Valid Days 331 349 362 4

th High 0.072 0.078 0.075 0.075

Niland-English Road

Valid Days 354 355 362 4

th High 0.086 0.085 0.077 0.082

Imperial

Westmorland-W 1st Street

Valid Days 355 353 360 4

th High 0.085 0.087 0.088 0.086

Indio-Jackson Street

Valid Days 361 360 237 4

th High 0.079 0.076 0.084 0.079

Joshua Tree National Park

Valid Days 270 281 129 4

th High 0.099 0.097 0.096 0.097

Salton Sea

Riverside

Palm Springs-Fire Station

Valid Days 354 360 241 4

th High 0.094 0.086 0.098 0.092

Alpine-Victoria Drive

Valid Days 357 358 301 4

th High 0.072 0.071 0.070 0.071

Camp Pendleton

Valid Days 355 349 300 4

th High 0.065 0.070 0.074 0.069

Chula Vista

Valid Days 357 351 299 4

th High 0.067 0.072 0.075 0.071

San Diego San Diego

Del Mar-Mira Costa College

Valid Days 364 362 305
B

-5

Year

Basin Name County Name Site Name Statistic 2006 2007 2008*

2008* 

Design

Value

4

th High 0.076 0.073 0.082 0.077

El Cajon-Redwood Avenue

Valid Days 349 332 297 4

th High 0.078 0.075 0.089 0.080

Escondido-E Valley Parkway

Valid Days 352 355 291 4

th High 0.061 0.064 0.066 0.063

Otay Mesa-Paseo International

Valid Days 359 357 273 4

th High 0.061 0.060 0.063 0.061

San Diego-1110 Beardsley St

Valid Days 362 330 291 4

th High 0.07 0.073 0.082 0.075

San Diego 

(continued)

San Diego 

(continued)

San Diego-Overland Avenue

Valid Days 354 357 296 4

th High 0.029 0.045 0.037

Berkeley-6th Street 

Valid Days 23 269 4

th High 0.069 0.055 0.061 0.061

Fremont-Chapel Way 

Valid Days 358 352 271 4

th High 0.067 0.055 0.068 0.063

Hayward-La Mesa 

Valid Days 244 242 182 4

th High 0.089 0.067 0.087 0.081

Livermore-793 Rincon Avenue 

Valid Days 361 361 270 4

th High 0.034 0.057 0.045

Oakland-Davie 

Valid Days 60 268 4

th High 0.06 0.052 0.067

0.059

Alameda

San Leandro-County Hospital 

Valid Days 243 243 175 4

th High 0.081 0.071 0.076 0.076

Bethel Island Road 

Valid Days 358 360 271 4

th High 0.085 0.071 0.078 0.078

Concord-2975 Treat Blvd

Valid Days 360 360 270 4

th High 0.079 0.067 0.067 0.071

Pittsburg-10th Street

Valid Days 357 356 271 4

th High 0.045 0.049 0.057 0.050

Contra Costa

San Pablo-Rumrill Blvd

Valid Days 353 356 265 4

th High 0.047 0.048 0.055 0.050

Marin San Rafael 

Valid Days 353 356 266 4th

 High 0.064 0.055 0.067 0.062

Napa Napa-Jefferson Avenue

Valid Days 361 355 269 4

th High 0.044 0.047 0.049 0.046

San Francisco San Francisco-Arkansas Street

Valid Days 347 354 266 4

th High 0.051 0.052 0.058 0.053

San Mateo Redwood City 

Valid Days 354 357 266 4

th High 0.08 0.068 0.072 0.073

Gilroy-9th Street

Valid Days 229 240 183 4

th High 0.085 0.059 0.074 0.072

Los Gatos 

Valid Days 363 363 273 4

th High 0.073 0.057 0.067 0.065

San Francisco 

Bay Area

Santa Clara

San Jose-Jackson Street 

Valid Days 329 352 269
B

-6

Year

Basin Name County Name Site Name Statistic 2006 2007 2008*

2008* 

Design 

Value

4

th High 0.088 0.070 0.071 0.076

San Martin-Murphy Avenue 

Valid Days 238 239 182 4

th High 0.064 0.054 0.063 0.060

Santa Clara 

(continued)

Sunnyvale-910 Ticonderoga 

Valid Days 243 243 183 4

th High 0.063 0.075 0.069

Benicia-East 2nd Street 

Valid Days 270 266 4

th High 0.074 0.062 0.068 0.068

Fairfield-Chadbourne Road 

Valid Days 242 241 183 4

th High 0.06 0.054 0.067 0.060

Solano

Vallejo-304 Tuolumne Street 

Valid Days 346 354 267 4

th High 0.049 0.047 0.059 0.051

San Francisco 

Bay Area 

(continued)

Sonoma Santa Rosa-5th Street 

Valid Days 362 357 269 4

th High 0.094 0.092 0.108 0.098

Clovis-N Villa Avenue 

Valid Days 357 341 269 4

th High 0.101 0.094 0.108 0.101

Fresno-1st Street 

Valid Days 362 360 265 4

th High 0.085 0.079 0.093 0.085

Fresno-Drummond Street 

Valid Days 359 357 241 4

th High 0.097 0.088 0.101 0.095

Fresno-Sierra Skypark #2 

Valid Days 355 359 262 4

th High 0.099 0.090 0.094 0.094

Fresno

Parlier

Valid Days 339 356 231 4

th High 0.111 0.102 0.112 0.108

Arvin-Bear Mountain Blvd 

Valid Days 350 353 292 4

th High 0.107 0.085 0.101 0.097

Bakersfield-5558 California Ave

Valid Days 348 361 298 4

th High 0.091 0.08 0.094 0.088

Bakersfield-Golden State Hwy

Valid Days 362 358 209 4

th High 0.108 0.093 0.107 0.102

Edison

Valid Days 361 361 301 4

th High 0.09 0.086 0.084 0.086

Maricopa-Stanislaus Street

Valid Days 351 291 265 4

th High 0.100 0.090 0.104 0.098

Oildale-3311 Manor Street

Valid Days 354 357 303 4

th High 0.093 0.083 0.093 0.089

Kern

Shafter-Walker Street 

Valid Days 361 353 303 4

th High 0.086 0.080 0.083

Kings Hanford-S Irwin Street 

Valid Days 339 297 4

th High 0.081 0.077 0.091 0.083

Madera Madera-Pump Yard 

Valid Days 363 360 250 4

th High 0.086 0.087 0.105 0.092

Merced Merced-S Coffee Avenue 

Valid Days 167 363 256 4

th High 0.083 0.075 0.077 0.078

San Joaquin 

Valley

San Joaquin Stockton-Hazelton Street 

Valid Days 362 361 267
B-7

Year

Basin Name County Name Site Name Statistic 2006 2007 2008*

2008* 

Design 

Value

4

th San Joaquin High 0.093 0.079 0.090 0.087

(continued) Tracy-Airport 

Valid Days 355 354 269

4

th High 0.090 0.076 0.090 0.085

Modesto-14th Street 

Valid Days 358 362 268

4

th High 0.092 0.075 0.106 0.091

Stanislaus

Turlock-S Minaret Street 

Valid Days 363 361 265

4

th High 0.104 0.099 0.112 0.105

Sequoia & Kings Canyon NP

Valid Days 300 238 232

4

th High 0.097 0.091 0.101 0.096

Sequoia NP-Lower Kaweah

Valid Days 348 360 325

4

th High 0.092 0.086 0.105 0.094

San Joaquin 

Valley (continued)

Tulare

Visalia-N Church Street

Valid Days 361 361 301

4

th High 0.071 0.066 0.069 0.068

Atascadero-Lewis Avenue 

Valid Days 356 352 330

4

th High 0.086 0.080 0.088 0.084

Carrizo Plains School-Carrizo

Valid Days 340 349 322

4

th High 0.053 0.053 0.058 0.054

Morro Bay

Valid Days 351 343 320

4

th High 0.055 0.056 0.066 0.059

Nipomo-Regional Park

Valid Days 345 351 325

4

th High 0.072 0.068 0.064 0.068

Paso Robles-Santa Fe Avenue

Valid Days 360 363 190

4

th High 0.084 0.092 0.088

Red Hills

Valid Days 362 330

4

th High 0.055 0.057 0.060 0.057

San Luis Obispo

San Luis Obispo-S Higuera St

Valid Days 356 356 242

4

th High 0.058 0.066 0.072 0.065

Carpinteria-Gobernador Road

Valid Days 349 354 272

4

th High 0.056 0.057 0.066 0.059

El Capitan Beach

Valid Days 364 364 299

4

th High 0.055 0.055 0.058 0.056

Gaviota-GTC Site B

Valid Days 360 362 241

4

th High 0.064 0.057 0.062 0.061

Goleta-Fairview

Valid Days 364 358 301

4

th High 0.07 0.078 0.070 0.072

Las Flores Canyon #1

Valid Days 363 360 330

4

th High 0.062 0.066 0.067 0.065

Lompoc-HSandP

Valid Days 363 358 301

4

th High 0.051 0.056 0.062 0.056

Lompoc-S H Street

Valid Days 362 356 302

4

th High 0.075 0.077 0.068 0.073

Paradise Road-Los Padres NF

Valid Days 363 355 301

4

th High 0.056 0.063 0.062 0.060

South Central 

Coast

Santa Barbara

Santa Barbara-E Canon 

Perdido Valid Days 357 359 240
B-8

Year

Basin Name County Name Site Name Statistic 2006 2007 2008*

2008* 

Design 

Value

4

th High 0.048 0.048 0.056 0.050

Santa Maria-906 S Broadway

Valid Days 349 354 217

4

th High 0.064 0.063 0.067 0.064

Santa Ynez -Airport Road

Valid Days 364 363 301

4

th High 0.059 0.069 0.065 0.064

Santa Barbara 

(continued)

Vandenberg AFB-STS Power

Valid Days 356 358 331

4

th High 0.059 0.061 0.065 0.061

El Rio-Rio Mesa School #2

Valid Days 364 351 297

4

th High 0.094 0.076 0.081 0.083

Ojai-Ojai Avenue

Valid Days 363 361 301

4

th High 0.085 0.076 0.081 0.080

Piru-3301 Pacific Avenue

Valid Days 359 358 304

4

th High 0.089 0.086 0.090 0.088

Simi Valley-Cochran Street

Valid Days 360 357 295

4

th Thousand Oaks-Moorpark High 0.076 0.074 0.077 0.075

Road Valid Days 364 358 301

4

th High 0.062 0.065 0.067 0.064

Ventura

Ventura-Emma Wood State 

Bch Valid Days 362 350 294

South Central 

Coast (continued)

Channel Islands NO MONITORS

4

th High 0.091 0.096 0.101 0.096

Azusa

Valid Days 357 355 236

4

th High 0.098 0.088 0.092 0.092

Burbank-W Palm Avenue

Valid Days 358 356 235

4

th High 0.106 0.105 0.112 0.107

Glendora-Laurel

Valid Days 354 352 241

4

th High 0.095 0.063 0.079

Lebec-Peace Valley Road

Valid Days 321 82

4

th High 0.075 0.072 0.073 0.073

Los Angeles-North Main Street

Valid Days 355 337 224

4

th Los Angeles-Westchester High 0.062 0.067 0.065 0.064

Pkwy Valid Days 358 355 221

4

th High 0.064 0.057 0.055 0.058

Lynwood

Valid Days 357 357 235

4

th High 0.057 0.057 0.064 0.059

North Long Beach

Valid Days 354 350 236

4

th High 0.096 0.090 0.091 0.092

Pasadena-S Wilson Avenue

Valid Days 360 357 232

4

th High 0.078 0.079 0.077 0.078

Pico Rivera-4144 San Gabriel

Valid Days 222 352 233

4

th High 0.108 0.103 0.100 0.103

Pomona

Valid Days 354 352 238

4

th High 0.104 0.093 0.095 0.097

South Coast Los Angeles

Reseda

Valid Days 355 339 242
B-9

Year

Basin Name County Name Site Name Statistic 2006 2007 2008*

2008* 

Design 

Value

4

th High 0.112 0.102 0.103 0.105

Santa Clarita

Valid Days 357 351 235

4

th High 0.068 0.067 0.075 0.070

Los Angeles 

(continued)

West Los Angeles-VA Hospital

Valid Days 360 345 236

4

th High 0.071 0.074 0.076 0.073

Anaheim-Pampas Lane

Valid Days 361 357 239

4

th High 0.061 0.065 0.073 0.066

Costa Mesa-Mesa Verde Drive

Valid Days 362 341 236

4

th High 0.09 0.082 0.078 0.083

La Habra

Valid Days 349 355 238

4

th High 0.09 0.081 0.092 0.087

Orange

Mission Viejo-26081 Via Pera

Valid Days 353 358 239

4

th High 0.105 0.095 0.108 0.102

Banning Airport

Valid Days 353 359 237

4

th High 0.102 0.097 0.108 0.102

Lake Elsinore-W Flint Street

Valid Days 353 352 239

4

th High 0.114 0.103 0.106 0.107

Perris

Valid Days 348 362 243

4

th High 0.112 0.099 0.111 0.107

Riverside

Riverside-Rubidoux

Valid Days 358 356 236

4

th High 0.111 0.126 0.120 0.119

Crestline

Valid Days 363 365 234

4

th High 0.114 0.113 0.110 0.112

Fontana-Arrow Highway

Valid Days 351 346 234

4

th High 0.125 0.112 0.112 0.116

Redlands-Dearborn

Valid Days 364 362 244

4

th High 0.119 0.117 0.112 0.116

San Bernardino-4th Street

Valid Days 356 352 236

4

th High 0.112 0.112 0.108 0.110

South Coast 

(continued)

San Bernardino

Upland

Valid Days 360 354 236

* 2008 data are preliminary and may not be complete. Therefore, the 2008 Design Value should be 

 considered preliminary.
1

ENCLOSURE 3

STATE OF CALIFORNIA

INFORMATION TO SUPPORT 

NONATTAINMENT AREA BOUNDARY RECOMMENDATIONS 

FOR THE 2008 FEDERAL 8-HOUR OZONE STANDARD

CONTINUING NONATTAINMENT AREAS

Because the 2008 revised 8-hour ozone standard (0.075 parts per million (ppm)) 

is more stringent than the previous 8-hour standard (0.08 ppm), all areas that 

were nonattainment for the previous standard continue to be nonattainment 

under the revised standard. These continuing nonattainment areas and their 

respective boundaries were justified when they were designated for the previous 

standard. ARB staff recommends retaining the current boundaries for 15 of the 

16 areas, as summarized below. In addition, ARB staff recommends expanding 

the current Eastern Kern County nonattainment area, as described in the section 

titled “New and Expanded Nonattainment Areas,” below. 

South Coast Air Basin

Based on 2006 through 2008 monitoring data, the South Coast Air Basin remains 

nonattainment for the revised 8-hour ozone standard with a design value of 

0.119 ppm for the Crestline (Lake Gregory) site in San Bernardino County. 

The recommended South Coast Air Basin ozone nonattainment area would 

continue to include western Los Angeles County (including SanClemente and 

Santa Catalina islands), Orange County, western Riverside County, and 

southwestern San Bernardino County. This area falls under the jurisdiction of the 

South Coast Air Quality Management District (AQMD).

San Joaquin Valley

The San Joaquin Valley nonattainment area would continue to comprise the 

entire SanJoaquin Valley Air Basin: SanJoaquin, Stanislaus, Merced, Madera, 

Fresno, Kings, Tulare, and western Kern counties. The San Joaquin Valley 

violates the federal 8-hour standard with a design value of 0.108 ppm at the 

Arvin-Bear Mountain Blvd. monitoring site in Kern County. This area is under the 

jurisdiction of the San Joaquin Valley Air Pollution Control District (APCD). 

Sacramento Metro Area

The Sacramento Metro nonattainment area would continue to include all of 

Sacramento and Yolo counties, southern Sutter County, the Sacramento Valley 

Air Basin portion of Solano County, the Sacramento Valley and Mountain

Counties air basin portions of Placer County, and the Mountain Counties 
2

Air Basin portion of El Dorado County. This area violates the standard with a 

design value of 0.102 ppm at the Folsom-Natoma Street site in Sacramento 

County. The Sacramento Metro nonattainment area involves multiple local air 

pollution control agencies, including the Sacramento Metro, ElDorado County, 

Feather River, and Yolo-Solano AQMDs and the Placer County APCD. 

However, all but the Solano County portion of the nonattainment area are 

covered by a single transportation planning agency. 

San Francisco Bay Area

The San Francisco Bay Area nonattainment area would continue to comprise all 

of the San Francisco Bay Area Air Basin: Alameda, Contra Costa, Marin, Napa, 

San Francisco, San Mateo, and Santa Clara counties and the San Francisco Bay 

Area Air Basin portions of Solano and Sonoma counties. The area’s 

nonattainment designation is based on a design value of 0.081 ppm for the 

Livermore-793 Rincon Avenue site in Alameda County. The nonattainment area 

falls under the jurisdiction of the Bay Area AQMD.

Ventura County

The Ventura County 8-hour nonattainment area would continue to include only 

the continental portion of Ventura County. Anacapa and San Nicolas Islands, 

two of the Channel Islands, would not be included. Ventura County violates the 

federal standard with a design value of 0.088 ppm at the Simi Valley-Cochran 

Street site. This area is under the jurisdiction of the Ventura County APCD.

Western Mojave Desert

The Western Mojave Desert nonattainment area would continue to comprise the 

central portion of San Bernardino County that is located in the Mojave Desert 

Air Basin. Ozone concentrations at a number of sites in this area violate the 

federal 8-hour standard, and the area has a design value of 0.104 ppm at the 

Joshua Tree-National Monument site. The Mojave Desert AQMD has jurisdiction 

over this area.

Antelope Valley

The Antelope Valley nonattainment area, under the jurisdiction of the Antelope 

Valley AQMD, would continue to comprise the portion of Los Angeles County that 

is located in the Mojave Desert Air Basin. The area has a design value of 

0.094 ppm at the Lancaster-43301 Division Street site.
3

Coachella Valley

The Coachella Valley ozone nonattainment area would continue to include the 

portion of Riverside County that is located in the Salton Sea Air Basin. The 

design value for this area is 0.097 ppm at the Palm Springs-Fire Station site. 

Coachella Valley is under the jurisdiction of the South Coast AQMD. 

San Diego County

This 8-hour nonattainment area falls under the jurisdiction of the SanDiego 

County APCD and would continue to include all of San Diego County. Ozone 

concentrations in the County exceed the standard at several sites, and the 

design value is 0.092 ppm at Alpine-Victoria Drive. 

Imperial County

Similar to San Diego County, the Imperial County nonattainment area would 

continue to include the entire County. The design value for Imperial County is 

0.082 ppm at both ElCentro-9

th Street and Westmorland-West 1st Street. The 

County is under the jurisdiction of the Imperial County APCD.

Sutter Buttes

The Sutter Buttes nonattainment area would continue to include that portion of 

the Sutter Buttes above 2000 feet elevation. Located in Sutter County, the 

design value for this area is 0.085 ppm at the Sutter Buttes site, and the area is 

under the jurisdiction of the Feather River AQMD.

Central Mountain Counties

The Central Mountain Counties nonattainment area would continue to include all 

of Amador and Calaveras counties, under the jurisdiction of the Amador County 

and Calaveras County APCDs, respectively. The design value for this 

two-county area is 0.089 ppm at the San Andreas-Gold Strike Road site in 

Calaveras County.

Southern Mountain Counties

The Southern Mountain Counties nonattainment area would continue to include 

all of Mariposa and Tuolumne counties. The design value for this area is 

0.088 ppm at the Turtleback Dome site in Yosemite National Park, which is in 

Mariposa County. The two counties are under the jurisdiction of the Mariposa 

County APCD and the Tuolumne County APCD.
4

Western Nevada County

This nonattainment area would continue to comprise the western portion of 

Nevada County, up to the crest of the Sierra Nevada. The Northern Sierra 

AQMD has jurisdiction over this area. The current design value for western 

Nevada County is 0.091 ppm at the Grass Valley-Litton Building site.

Butte County

This nonattainment area would continue to comprise all of Butte County, which 

falls under the jurisdiction of the Butte County AQMD. There are two monitoring 

sites in Butte County, and both have design values that violate the standard. The 

Paradise-4405 Airport Road site has the higher value, with a design value of 

0.085 ppm. 

NEW AND EXPANDED NONATTAINMENT AREAS

The following six areas represent new or expanded nonattainment areas under

the revised standard. Because the revised standard is set at a lower level, it 

brings in areas that increasingly rural in nature. In addition to being rural, ozone 

concentrations in all of the new and expanded areas are dominated by transport 

from an upwind urban area. With the addition of the new areas, California will 

have a total of 21 ozone nonattainment areas. 

Justification for each of the new and expanded areas is outlined below, using the 

nine factors U.S. EPA included in its guidance memo (December 4, 2008, Area 

Designations for the 2008 Revised Ozone National Ambient Air Quality 

Standards, Memorandum from Robert J. Meyers, Principal Deputy Assistant 

Administrator, Office of Air and Radiation to Regional Administrators, 

Regions I-X). These factors include air quality data, emissions data, population 

density and degree of urbanization, traffic and commuting patterns, growth rates 

and patterns, meteorology, geography and topography, jurisdictional boundaries, 

and level of control of emission sources. 

Northeast San Bernardino County

Jurisdictional Boundaries:

The southwest and central portions of SanBernardino County, which are under 

the jurisdiction of the South Coast AQMD and the Mojave Desert AQMD, 

respectively, were designated as nonattainment for the previous 8-hour ozone 

standard. ARB staff recommends these areas continue as two distinct 

nonattainment areas for the revised 2008 standard. 
5

In contrast, the northeast portion of the County did not violate the previous 

standard, but does violate the revised standard. Although this area also falls 

under the jurisdiction of the Mojave Desert AQMD, it is sufficiently different in 

terms of air quality, emissions, population, and other human, economic, and 

geographic factors that ARB staff recommends it be designated as a separate 

nonattainment area. Designating Northeast SanBernardino County separately 

will give this area a classification consistent with its overall air quality problem 

and will facilitate a more timely attainment finding. 

Geography / Topography:

San Bernardino County is the largest county in the United States (refer to 

Figure 1). At just over 20,000 square miles, it encompasses a very diverse set of 

geographic conditions, from the over 11,000 foot mountain peaks in the 

southwest (South Coast Air Basin) portion of the County, to the high desert areas 

of the central (Western Mojave Desert) portion, to the low desert areas in the 

eastern (Northeast San Bernardino County) portion. The variety of physical 

conditions has impacted the way the County has grown and resultant air quality.

FIGURE 1

SAN BERNARDINO COUNTY 
6

Meteorology:

The variety of landscapes within SanBernardino County makes for a variety of 

different climate areas. Rainfall and temperatures show substantial variation 

throughout the area. The South Coast portion of the County receives an average 

of 16 inches of rainfall each year, with a maximum monthly average temperature 

of 97 degrees Fahrenheit. In contrast, the central portion receives an average of 

6 inches of rainfall each year, with an average maximum summer temperature of 

102 degrees Fahrenheit. In the northeast portion of the County, rainfall averages 

4 inches per year, and the average maximum summer temperature is 

107 degrees Fahrenheit. 

Information about meteorology, ozone concentrations, and transport within the 

northeast portion of the County is based on data for Trona and for sites in the 

surrounding area at Ridgecrest, Mojave National Preserve, Jean (Nevada), 

Blythe, Barstow, and Mojave. Additional information is based on back 

trajectories constructed as part of an ozone transport assessment. 

Northeast San Bernardino County is rural in nature, with extremely low 

population and few significant emissions sources. Because local emissions are 

low, locally measured ozone concentrations reflect the impact of long range 

transport from upwind urban areas. Based on general wind patterns, Northeast 

San Bernardino County is downwind of several high emission source areas, 

including the highly urbanized South Coast and San Joaquin Valley air basins. 

Previous ARB transport assessments have found that the transport contribution 

from both the South Coast and the SanJoaquin Valley into the desert portions of 

San Bernardino County can be overwhelming. An evaluation of back trajectories 

corroborates these findings. 

Air Quality Data: 

There is one ozone monitor in Northeast SanBernardino County, located at

Trona (refer to Figure 1). The design value for this site is 0.080 ppm, based on 

data for 2006 through 2008. This value does not violate the previous 8-hour 

standard, but it is does violate the revised standard. As shown in Table 1, the 

design value for Northeast SanBernardino County is significantly lower than the 

design values for the Western Mojave Desert portion of the County and for the 

upwind areas of the South Coast and the San Joaquin Valley. The design value 

for the northeast portion of the County is less than 10 percent above the level of 

the standard, while design values for the other three areas are 40 to 60 percent 

above the standard. Because of the significant differences in design value, the 

northeast portion of the County should be designated separately and given a 

classification that is commensurate with the overall magnitude of the ozone 

problem in this area. 
7

TABLE 1

8-HOUR OZONE DESIGN VALUES FOR VARIOUS PORTIONS OF 

SAN BERNARDINO COUNTY AND UPWIND AREAS

BASED ON 2006 THROUGH 2008 DATA

AREA DESIGN SITE

DESIGN 

VALUE 

(ppm)

PERCENT 

ABOVE 

STANDARD

NE San Bernardino Portion of County Trona 0.080 7%

Western Mojave Desert Portion of County Joshua Tree-NM 0.104 39%

South Coast Air Basin Portion of County Crestline 0.119 59%

San Joaquin Valley Air Basin Arvin 0.108 44%

The design value trends for all four areas are shown in Figure 2. It is apparent 

from the graph that design values for the South Coast and Western Mojave 

Desert Air Basin portions of the County, as well as for the SanJoaquin Valley, 

are higher than that for Northeast SanBernardino County. However, regardless 

of level, the design value trends for the Western Mojave Desert and Northeast 

portions of San Bernardino County mirror those for the South Coast and 

San Joaquin Valley. This reflects the overwhelming impact of transport in these 

areas, where improvements in ozone air quality are tied to improvements in the 

upwind urban area. 

FIGURE 2

Ozone Design Values for Subareas of 

San Bernardino County and Upwind Areas

0.000

0.020

0.040

0.060

0.080

0.100

0.120

0.140

0.160

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Ozone DV (ppm)

Northeast San Bernardino County Western Mojave Desert Portion

South Coast Air Basin Portion San Joaquin Valley 
8

Past control strategies for both the South Coast and the San Joaquin Valley have 

relied heavily on reducing reactive organic gas (ROG) emissions. While this 

strategy has been effective in reducing ozone close to the urban areas, ozone in 

transport-impacted areas has not seen the same level of improvement. Future 

strategies will rely more heavily on reducing oxides of nitrogen (NOx) emissions. 

ARB expects ozone concentrations in the northeast and Western Mojave Desert 

portions of SanBernardino County will begin to decrease at a faster rate as 

emission control strategies contained in the recently submitted State 

Implementation Plan begin to be effective.

Population Density and Degree of Urbanization; Growth Rates and 

Patterns; and Traffic and Commuting Patterns:

Similar to air quality, there are vast differences among the population in each of 

the three San Bernardino County subareas. Based on an analysis of census 

data, Table 2 gives a summary of the size of each area and its population. More 

than three-quarters of the County population lives in the highly urbanized, South 

Coast portion of SanBernardino County. Most of the rest of the County 

population (20 percent) lives in the Western Mojave Desert portion. Less than 

2 percent live in Northeast SanBernardino County. Because Northeast 

San Bernardino County is so large, the population density is very low, with less 

than 2 people per square mile. This compares with more than 1,100 people per 

square mile in the South Coast portion of the County, and 47 people per square 

mile in the Western Mojave Desert portion.

With higher population numbers and densities comes a greater degree of 

urbanization and generally higher growth rates, because of the jobs and 

convenience associated with the urban area. San Bernardino County is no 

exception. The Western Mojave Desert portion of the County is closely linked to 

the South Coast portion because of its proximity to the larger urban area. Many

people within this area commute to jobs in the South Coast, while others work in 

the cities that have developed close to the South Coast / Western Mojave 

boundary. These ties are less obvious, as one moves further away from the 

South Coast area, into the northeast portion of the County. 

Over time, both the South Coast and Western Mojave Desert portions of 

San Bernardino County have seen much higher growth rates when compared 

with Northeast San Bernardino County. Table 2 shows these different rates from 

1990 to 2000. Growth rates in the urbanized portions of the County have been 

more than triple the rates in the northeast. This discrepancy in growth is 

expected to continue. 
9

TABLE 2

8-HOUR OZONE DESIGN VALUES FOR VARIOUS PORTIONS OF 

SAN BERNARDINO COUNTY BASED ON 2006 THROUGH 2008 DATA

AREA

SIZE 

(square 

miles)

POPULATION

GROWTH IN 

POPULATION

(1990-2000)

PEOPLE PER 

SQUARE 

MILE

NE San Bernardino County Portion 11,470 25,941 + 6% 2

Western Mojave Desert Portion 7,503 350,426 + 22 % 47

South Coast Air Basin Portion 1,132 1,333,067 + 20 % 1,178

Emissions Data and Level of Emission Controls

Similar to population, there are vast differences in ozone precursor emissions 

among the three County subareas (refer to Table 3). In terms of number, ARB’s

emissions inventory shows five times more facilities in the Western Mojave 

Desert portion (125 facilities) and more than 10 times more in the South Coast 

portion (320 facilities), as are located in Northeast San Bernardino County 

(26 facilities). Facilities tend to be concentrated in the urban areas and along the 

major roadways in the South Coast and Western Mojave Desert portions, in 

contrast to being scattered throughout the area in Northeast SanBernardino 

County. 

 

TABLE 3

TOTAL ROG AND NOx EMISSIONS IN VARIOUS PORTIONS

OF SAN BERNARDINO COUNTY

AREA TONS / DAY ROG TONS / DAY NOx

NE San Bernardino County Portion 10.4 19.5

Western Mojave Desert Portion 48.4 149.5

South Coast Air Basin Portion 81.6 92.3

In combination, facilities in the South Coast and Western Mojave Desert portions 

of the County emit three and ten times more NOx and ROG than facilities in the 

northeast portion of the County. When mobile source emissions are added in, 

the discrepancy is similar (refer to Table 3). Total emissions of ROG and NOx in 

the South Coast and Western Mojave Desert portions of the County are five to 

eight times higher than in Northeast SanBernardino County. In terms of mobile 

source emissions, the dense network of streets and freeways in the South Coast 

portion of SanBernardino County carry significant amounts of traffic, averaging 

over 38 million vehicle miles travelled (VMT) each day. In contrast, the more 
10

limited networks in the Western Mojave Desert and Northeast portions of 

San Bernardino County average less than half that amount (19.8 million VMT 

each day). The bulk of the daily VMT in these areas is concentrated near the 

South Coast portion of the County. 

In terms of emissions controls, the statewide mobile source and consumer 

product regulations form the cornerstone of the attainment strategy for rural 

transport-impacted areas, along with the emissions reduction controls in the 

upwind regions of the South Coast and San Joaquin Valley. In addition, the 

Mojave Desert AQMD has adopted rules to reduce emissions from existing, as 

well as new or modified stationary sources under its jurisdiction. 

Summary and Recommendation:

In summary, the air quality problem in Northeast SanBernardino County is much 

less severe than in the Western Mojave Desert portion of the County. Ozone 

concentrations in the northeast County are overwhelmed by transport, even more 

so than in the Western Mojave Desert portion. As a result, the primary 

attainment strategy will rely on statewide controls and control measures 

implemented by upwind districts. Although there are few stationary emissions 

sources in Northeast SanBernardino County, there are few significant 

differences in the control requirements for stationary sources under the 

jurisdiction of the Mojave Desert AQMD.

Although Northeast San Bernardino County is contiguous with the Western 

Mojave Desert nonattainment area, and both areas will rely on controls in upwind 

areas to reach attainment, the magnitude of their problems is substantially 

different. Therefore, ARB recommends Northeast San Bernardino County be 

designated as a separate nonattainment area. Designating the area separately 

will give them a classification consistent with the nature and severity of their 

overall air quality problem and will facilitate a more timely attainment finding. 

Southern Inyo County

Jurisdictional Boundaries:

Inyo County falls under the jurisdiction of the Great Basin Unified Air Pollution 

Control District (GBUAPCD). Whereas Inyo County attained the previous 8-hour 

standard, concentrations violate the revised ozone standard. Because of the 

transport-impacted nature of the air quality problem in Southern Inyo County, 

ARB staff recommends limiting the extent of the nonattainment area. 
11

Geography / Topography:

Inyo County is the second largest county in California, encompassing over 

10,000 square miles of varied terrain (refer to Figure 3). Within its borders lies 

the highest point in the continental United States, Mount Whitney, towering

nearly 14,500 feet above sea level. Less than 100 miles away is Death Valley. 

Its lowest point, near Badwater, lies 282 feet below sea level. This is not only the 

lowest point in the 48 contiguous states, but in the entire North American 

continent. With these extremes in elevation come extremes in temperature and 

precipitation, both of which can impact air quality. 

FIGURE 3

INYO COUNTY 

Meteorology:

The geographical extremes of Inyo County provide for extremes in weather. The 

southern portion of the County is a high desert area with a typical desert climate. 

Summers are hot, while winters are cool. Maximum daily temperatures during 

the summer months are frequently well over 100 degrees Fahrenheit. What little 

rainfall does occur, generally falls during the winter months. On average, rainfall 

in the Death Valley area is less than 2 inches per year. 
12

Information about ozone concentrations in Inyo County are based on data for 

Death Valley, Bishop, and the Trona air monitoring site, which is just south of the 

Inyo County line in SanBernardino County. Some additional information is 

based on back trajectories constructed for a transport assessment. 

Similar to Northeast San Bernardino County, Southern Inyo County is rural in 

nature with few ozone precursor emissions sources. Because the area lacks 

significant emissions sources capable of generating ozone locally, ozone 

concentrations measured in Southern Inyo County reflect the impact of long 

range transport. Based on general wind patterns, Southern Inyo County is 

downwind of two major emissions source areas: the South Coast Air Basin and 

the San Joaquin Valley Air Basin. 

General wind patterns suggest that ozone is transported into Southern Inyo 

County from the south to southwest. This transported ozone travels northward, 

up valleys bounded by tall north-south mountain ranges. The extent of this 

transport is limited by tall mountains that are transverse to these north-south 

ranges. These transverse ranges represent the northern extent of transported 

airflow. When air pollutants reach this point, they disperse vertically upslope, 

and concentrations are lowered considerably. Although there are several towns, 

such as Lone Pine and Bishop, that are located north of the recommended 

Southern Inyo County ozone nonattainment area, there is no evidence that 

emissions from these areas are transported south, thereby impacting Southern 

Inyo County. 

The extent of airflow into Southern Inyo County is limited by terrain. Similarly, 

federal hydrologic units are defined by terrain. These water drainage units 

generally follow the crests of mountain ranges. Hydrologic units are defined in a 

manner similar to the way air basins are defined, because water drainage is 

constrained by the same geographic features as airflow. As a result, hydrologic 

units provide an appropriate basis for defining the extent of ozone transport 

impacts in Southern Inyo County. 

Air Quality Data: 

There is only one ozone monitor in Inyo County for which complete, quality 

assured data are available. This monitor is located within the bounds of Death 

Valley National Park. The design value based on 2006 through 2008 data is 

0.081 parts per million, which exceeds the standard by 8 percent. The design 

value for Death Valley is similar to that for Trona in San Bernardino County 

(0.080 ppm) and the China Lake area of Kern County (0.081 ppm). Both of these 

areas are located near Inyo County’s southern boundary, and both are highly 

impacted by transport, as well. 

Figure 4 shows a trend line for design values at Death Valley since 1998. There 

has been little change in the trend over the years. Similar to the desert areas of 
13

southern California, Southern Inyo County is impacted by transport from the 

South Coast and southern San Joaquin Valley areas. 

Although air quality in these upwind areas has improved over the years, the 

same degree of improvement has not been seen in downwind areas. However, 

trends in downwind areas are expected to improve with the implementation of 

control strategies emphasizing greater NOx reductions. 

FIGURE 4

 

Ozone Design Values for 

Death Valley National Park in Southern Inyo County

0.000

0.020

0.040

0.060

0.080

0.100

0.120

0.140

0.160

1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Ozone DV (ppm)

Population Density and Degree of Urbanization; Growth Rates and 

Patterns; and Traffic and Commuting Patterns:

While population density is relatively sparse throughout Inyo County, it is even 

more spread out in the southern portion. The GBUAPCD estimates only 

0.22 people per square mile in the recommended Southern Inyo County 

nonattainment area. Over time, this area has actually seen a decrease in 

population, from 3,473 people in 1990 to 3,117 people in 2000. This represents 

an overall decrease of about 10 percent, and the population is not expected to 

grow significantly in the next several years. Although there are several roadways 

carrying traffic through Southern Inyo County, emissions related to commutes 

within the area are not significant because of the low population and scattered 

nature of development within the area. 
14

Emissions Data and Level of Emission Controls

Emissions in Southern Inyo County are very low in comparison to the upwind 

South Coast and San Joaquin Valley air basins. As shown in Figure 3, there are 

only a handful of industrial stationary sources in Southern Inyo County. 

Emissions from these sources total 181 tons per year of NOx, and there are no 

measurable ROG emissions. In addition to stationary sources, there are several 

highways traversing Inyo County that contribute mobile source emissions. 

Overall, countywide emissions for Inyo County total 1,699 tons per year of NOx 

and 2,184 tons per year of ROG. Since 1990, there has been a 21 percent 

reduction in countywide NOx emissions and a 9 percent reduction in ROG 

emissions. The statewide strategy will continue to reduce overall emissions in 

the future. These future emission reductions will place greater emphasis on NOx 

reductions. Photochemical modeling shows that a greater emphasis on NOx 

reductions will have a greater benefit in terms reducing ozone concentrations in 

downwind, transport-impacted areas such as Southern Inyo County. 

Summary and Recommendation:

Inyo County is one of the largest counties in the nation, and encompasses a 

variety of landscapes, from high mountain peaks to below sea level deserts. The 

revised ozone standard is exceeded in the southern portion of the County, which 

has an extremely low population and lacks significant industrial emissions 

sources. While the presumptive boundary for the nonattainment area would 

include all of Inyo County, ARB recommends a smaller nonattainment area 

because of the diversity of the area’s geography and the nature of the ozone 

impact. 

Previous studies suggest that ozone concentrations at the Death Valley site are 

substantially impacted by transport. Wind flow into the southern portion of the 

County is generally from the south to southwest, carrying pollutants and 

emissions from the highly urbanized South Coast and southern SanJoaquin 

Valley air basins into Southern Inyo County. Although Death Valley is the only 

monitoring site in Southern Inyo County, data are also collected at the Trona site 

in San Bernardino County and in the China Lake area of Kern County. These 

sites are close to the southern boundary of Inyo County and suggest that 

exceedances are likely to occur throughout Southern Inyo County. 

The recommended boundary for Southern Inyo County is based on federal 

hydrologic units. Hydrologic units are based on topography and water drainage, 

similar in many respects to the way California’s air basins are defined. 

Therefore, it is appropriate to use them in defining the nonattainment area 

boundary, since mountainous terrain affects the transport and mixing depth of 

pollution. In addition, hydrologic units have been used in the past, to define 

ozone designation areas. ARB staff recommends the Southern Inyo County 
15

ozone nonattainment area comprise the Inyo County portions of federal 

hydrologic units 16060015, 18090202, 18090203, 18090204, and 18090205. 

These units cover not only the areas exceeding the standard, but also the extent 

of the region expected to be impacted by transport from the major upwind urban 

areas.

Eastern San Luis Obispo County

Jurisdictional Boundaries:

San Luis Obispo County is part of California’s South Central Coast Air Basin. Air 

quality control in the County is under the jurisdiction of the San Luis Obispo 

County Air Pollution Control District (SLOAPCD) 

Geography / Topography:

Although San Luis Obispo County is generally considered a coastal area, this 

generalization applies only to the western portion of the County (refer to 

Figure 5). This western portion includes the major cities in the County such as 

San Luis Obispo, Atascadero, and Paso Robles. As one moves inland, the 

coastal plain gives way to the mountains of the Coast Ranges, interspersed with 

FIGURE 5

SAN LUIS OBISPO COUNTY
16

a series of valleys and high plains which range in elevation from about 2000 to 

more than 5000 feet. These rural, higher elevation areas separate SanLuis 

Obispo County from the SanJoaquin Valley. Although Eastern SanLuis Obispo 

County is sparsely populated, there are scattered settlements and public 

facilities, such as schools. This area also includes Carrizo Plains National 

Monument, with grinding rocks and rock paintings reflecting the historic Native 

American population. 

Meteorology:

San Luis Obispo County is a meteorologically diverse region. To the west, high 

summer temperatures average in the low to mid 60s. Toward the middle of the 

County, high summer temperatures average in the low to high 70s. In contrast to 

both these areas, Eastern San Luis Obispo County sees high summer 

temperatures, averaging in the 90s, and the mountains separating the eastern 

portion of the County from the western portion effectively block the tempering 

influence of the ocean. 

In terms of general wind patterns, Eastern San Luis Obispo is downwind of both 

the San Joaquin Valley and the SanFrancisco Bay Area air basins. Previous 

ARB transport assessments found these areas to have an overwhelming impact 

on ozone concentrations in San Luis Obispo County.

Air Quality Data: 

Ozone data are available for two sites in Eastern San Luis Obispo County: 

Carrizo Plains and Red Hills. Table 4 includes design values, based on data for 

2006 through 2008, for sites in both the eastern and western portions of San Luis 

Obispo County. Values for the eastern sites are 12 to 17 percent above the level 

of the standard, whereas values for the western sites attain the standard. 

TABLE 4

8-HOUR OZONE DESIGN VALUES FOR VARIOUS PORTIONS OF 

SAN LUIS OBISPO COUNTY BASED ON 2006 THROUGH 2008 DATA

SITE / COUNTY PORTION DESIGN VALUE 

(ppm)

PERCENT ABOVE 

STANDARD

Carrizo Plains / Eastern San Luis Obispo 0.084 12%

Red Hills / Eastern San Luis Obispo 0.088* 17%

Paso Robles / Western San Luis Obispo 0.068 0%

Atascadero / Western San Luis Obispo 0.068 0%

* Design Value based on 2 years of data (2007-2008).
17

Because long-term data are not available for either Carrizo Plains or Red Hills, 

design value trends are not available. However, long-term trends for high sites in 

the western portion of the County and for the upwind air basins are plotted in 

Figure 6. The trends for the San Luis Obispo sites, which are also impacted by 

transport from the San Francisco Bay Area and San Joaquin Valley air basins, 

track fairly well with the upwind areas and show similar rates of improvement. 

We expect sites in Eastern San Luis Obispo County would show similar trends. 

FIGURE 6

Ozone Design Values for 

Western San Luis Obispo Sites and 

Upwind Air Basins

0.00

0.02

0.04

0.06

0.08

0.10

0.12

1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Ozone DV (ppm)

Paso Robles Atascadero 

San Francisco Bay Area San Joaquin Valley 

Population Density and Degree of Urbanization; Growth Rates and 

Patterns; and Traffic and Commuting Patterns:

More than 250,000 people reside in San Luis Obispo County, with the majority 

living in the western portion of the County. Overall, more than 95 percent of the 

County’s population lives in Western San Luis Obispo County. Those that live in 

Eastern San Luis Obispo County are scattered throughout the area. Between 

1990 and 2000, the total number of people in the eastern portion of the County 

actually decreased, and the SLOAPCD expects little growth in the area over the 

next several years. In contrast, the number of people living in the western 

portion increased by about 15 percent between 1990 and 2000. Emissions 

related to commutes within the area are not significant because of the low 

population and scattered nature of development. 
18

Emissions Data and Level of Emission Controls:

Emissions in Eastern San Luis Obispo County are very low. The SLOAPCD 

estimates a total of 2.2 tons per year of ROG and 4.3 tons per year of NOx in the 

eastern portion of the County. These amounts are less than 1 percent of the 

total countywide ROG and NOx emissions. There are limited mobile source 

emissions from several highways traversing the eastern County area. Emissions 

from these sources are not expected to significantly impact ozone concentrations 

in Eastern San Luis Obispo County. Overall, emission sources located 

throughout San Luis Obispo County are subject to the rules and regulations of 

the SLOAPCD. In addition, mobile source emissions will continue to be reduced 

under the statewide strategy.

Summary and Recommendation:

San Luis Obispo County comprises coastal, as well as inland areas. However, 

the revised ozone standard is violated only at the inland sites, which are high 

elevation sites located in the rural, eastern portion of the County. This portion of 

the County is sparsely populated and lacks emissions sources. The design value 

for the eastern area is 0.084 ppm, measured at Carrizo Plains (Red Hills has a 

higher value, 0.088 ppm, but this value is based on only two years of data). Sites 

in Western San Luis Obispo County, as well as in counties to the north and to the 

south, all attain the standard. 

The high elevation sites in Eastern San Luis Obispo County were originally sited 

to provide information on transport impacts from upwind urban areas. Previous 

studies have shown that ozone and ozone precursor emissions from the 

San Joaquin Valley are transported west, impacting Eastern San Luis Obispo 

County, including the Carrizo Plains and Red Hills sites. Ozone concentrations 

can also be impacted by transport south from the SanFrancisco Bay Area. 

Because violations occur only at elevated sites in the eastern County, ARB 

recommends limiting the nonattainment area to Eastern San Luis Obispo County, 

which reflects the extent of the County influenced by transport sufficient to cause 

violations of the federal standard.

Pinnacles National Monument

Jurisdictional Boundaries:

Nearly all of Pinnacles National Monument is located in San Benito County, with 

a small portion in Monterey County. Air quality control throughout San Benito 

County falls under the jurisdiction of the Monterey Bay Unified Air Pollution 

Control District (MBUAPCD). All sites within the MBUAPCD region attained the 

previous 8-hour standard. The monitor at Pinnacles is the only one that violates 

the revised standard. 
19

Geography / Topography:

Pinnacles National Monument is located in an area of rugged terrain in 

California’s North Central Coast Air Basin (refer to Figure 7). It lies about 

40 miles inland from the Pacific Ocean, just east of the Salinas Valley, and about 

80 miles south of the San Francisco Bay Area. The monument is in the southern 

portion of the Gabilan Mountains, which are part of California's Central Coast 

Range. Elevations within the Monument boundaries range from 824 feet to 

3,304 feet at the top of North Chalone Peak. The landscape includes the 

spectacular remains of an ancient volcano. Massive monoliths, spires, 

sheer-walled canyons, and talus passages have been created through millions of 

years of erosion, faulting, and tectonic plate movement. Established in 1908, 

the Monument has increased by bits and pieces to its present size of about 

26,000 acres. It boasts over 30 miles of trails, but has no overnight facilities. 

FIGURE 7

PINNACLES NATIONAL MONUMENT IN SAN BENITO COUNTY

Meteorology:

Pinnacles National Monument has a Mediterranean climate with hot, dry 

summers and cool, moderately wet winters. Although the Monument is only 

40 miles inland from the Pacific Ocean, the Santa Lucia Mountains to the west 
20

strongly modify the ocean influence before it reaches Pinnacles. As a result, 

summer temperatures at Pinnacles might range from 50 degrees Fahrenheit at 

night to 100 degrees during the day, while those near the coast are a fairly 

steady 60 degrees. Similarly, winter temperatures at Pinnacles often drop below 

freezing while coastal temperatures remain moderate. Average rainfall at 

Pinnacles is 16 inches per year, with most of it occurring between January and 

March. Small amounts of snow fall at the higher elevations between 

mid-December and January.

Based on general wind patterns, Pinnacles National Monument is downwind of 

the San Francisco Bay Area, which has significant emissions sources. Pollutants 

and emissions from the Bay Area are transported aloft, impacting concentrations 

at high elevations in the Pinnacles area. Previous transport assessments found 

the transport contribution from the San Francisco Bay Area can have an 

overwhelming impact on ozone concentrations measured at Pinnacles. 

Air Quality Data: 

The monitor at Pinnacles National Monument was sited to measure high 

elevation transport from the San Francisco Bay Area. The location is isolated 

and remote. Ozone concentrations measured at Pinnacles exceed the revised 

federal 8-hour ozone standard, with a design value of 0.079 ppm. In contrast, 

design values for other sites in the surrounding north central coast region are all 

well below the level of the standard, ranging from 0.052 ppm to 0.069 ppm. All of 

these sites are located at lower elevations.

The design value trend for Pinnacles is shown in Figure 8. With the exception of 

2008, the design value for Pinnacles has shown an overall downward trend since 

1998. In fact, the 2006 and 2007 design values for this site (0.075 ppm and 

0.074 ppm, respectively) show attainment. The higher value for 2008 likely 

reflects the impact of wildfires that burned throughout the State during the 

summer of 2008. If the impacted days were removed from consideration, the 

2008 design value would be more consistent with values for previous years. 

However, the area would still be nonattainment. 

The trend for Pinnacles closely follows the trend for the SanFrancisco Bay Area, 

although at a slightly lower level. Previous transport study indicates that 

exceedances measured at Pinnacles are overwhelmingly impacted by transport 

aloft from the Bay Area. Although the San Francisco Bay Area does not yet 

attain the standard, design values for Bay Area sites have decreased at a rate 

similar to those for Pinnacles. As emissions in the SanFrancisco BayArea 

continue to decrease, ozone concentrations in downwind areas such as 

Pinnacles will also continue to improve. 
21

FIGURE 8

Population Density and Degree of Urbanization; Growth Rates and 

Patterns; and Traffic and Commuting Patterns:

There is no permanent population living at Pinnacles National Monument, and 

there are no overnight accommodations for those visiting the monument. 

Because there are no roads travelling through the Monument, traffic is limited to 

those visiting the Monument for day use.

Emissions Data and Level of Emission Controls

With the exception of the few roads, there are no significant emissions sources 

located within Pinnacles National Monument. As a result, the area lacks 

emissions for locally generating ozone. Previous analyses indicate that ozone 

concentrations measured at the Pinnacles monitor are attributable to the 

transport of pollutants and emissions from the SanFrancisco Bay Area. Ozone 

concentrations at Pinnacles should continue to decrease, with continued 

implementation of upwind district controls and the statewide strategy.

Ozone Design Values for 

Pinnacles National Monument and 

San Francisco Bay Area

0.00

0.02

0.04

0.06

0.08

0.10

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Ozone DV (ppm)

Pinnacles National Monument San Francisco Bay Area 
22

Summary and Recommendation:

The Pinnacles monitor is an elevated site (1000 feet) located in an area of 

complex terrain within the boundaries of Pinnacles National Monument. With the 

exception of a few roads, there are no local ozone precursor emissions sources. 

In addition, there are no permanent residents, and overnight stays are not

allowed within the Monument boundaries. Ozone exceedances in the North 

Central Coast Air Basin are measured only at Pinnacles. All other sites in the 

surrounding areas attain the standard, with design values ranging from 0.052 to 

0.069 ppm in the surrounding three-county area (Monterey, Santa Cruz, and 

San Benito counties). Furthermore, the violations at Pinnacles are attributable to 

transport from the San Francisco Bay Area, which will continue to be designated 

as nonattainment. 

ARB recommends a focussed nonattainment area, limited to that portion of 

Pinnacles National Monument located within San Benito County. Using the 

Monument boundary provides an easily identifiable nonattainment area, and it 

adequately reflects the region impacted by the upwind urban area. 

Tuscan Buttes 

Jurisdictional Boundaries:

Tuscan Buttes is located in eastern Tehama County in the northern Sacramento 

Valley. All of Tehama County is under the jurisdiction of the Tehama County Air 

Pollution Control District.

Geography / Topography:

As shown in Figure 9, Tuscan Buttes is an isolated, elevated area in the Upper

Sacramento Valley, where the majority of the land is near sea level. Located 

about 10 miles northeast of Red Bluff, Tuscan Buttes is a narrow, small ridge on 

the eastern side of the Valley. The area at the top of the Buttes stands above 

1800 feet elevation.
23

FIGURE 9

TUSCAN BUTTES IN TEHAMA COUNTY

Meteorology:

Tuscan Buttes exhibits the typical climate pattern of the Sacramento Valley, with 

hot, dry summers and cooler, wetter winters. In terms of air quality, the Buttes 

are impacted by transport from the Sacramento urban area. Based on general 

wind patterns, this area is downwind of significant emissions sources within the 

Sacramento Metro Area. Previous transport assessments found that the 

transport contribution from the Sacramento Metro Area to the Upper Sacramento 

Valley can be overwhelming. Because there are no local population or emissions 

sources, ozone concentrations measured at Tuscan Buttes are attributable to 

transport.

Air Quality Data: 

Figure 10 shows the design value trends for Tuscan Buttes, as well as for the 

upwind Sacramento Metro Area. The graph also shows the trend line for 

Sutter Buttes, another high elevation, transport dominated site in the Upper 

Sacramento Valley. The trends for both Tuscan Buttes and Sutter Buttes are 

nearly identical. Both track well with the trend for the Sacramento Metro Area, 

illustrating the importance of transport at the two locations. 
24

FIGURE 10

Ozone Design Values for 

Tuscan Buttes, Sutter Buttes, and 

Sacramento Metro Nonattainment Area

0.00

0.02

0.04

0.06

0.08

0.10

0.12

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Ozone DV (ppm)

Tuscan Buttes Sutter Buttes Sacramento Metro Area 

Although all three areas show general improvement over the years, the values 

for 2008 are slightly higher than for previous years. These higher values likely 

reflect the impact of wildfires that burned throughout California during the 

summer of 2008. If the fire-impacted days were removed, the design values for 

2008 would be lower, but the areas would still be nonattainment. 

Because there is no population in either the Tuscan Buttes or Sutter Buttes 

areas, ozone concentrations measured at these sites do not represent population 

exposure. In contrast to these sites, design values for surrounding sites that are 

located in populated areas, such as the Red Bluff site in Tehama County and 

sites in the populated areas of Colusa, Glenn, and northern Sutter counties, 

show attainment of the revised standard.

Population Density and Degree of Urbanization; Growth Rates and 

Patterns; and Traffic and Commuting Patterns:

There is no population living at Tuscan Buttes or in the surrounding local area. 

This is not expected to change in the next several years. Access to the area is 

limited, and traffic-related emissions are insignificant.

Emissions Data and Level of Emission Controls

There are virtually no ozone precursor emissions sources in the Tuscan Buttes 

area. The only development on the Buttes is a radio facility and a fire lookout. 
25

Access to these facilities is very limited. The site is dominated by transport from 

the Sacramento Metro area, and attainment will depend on upwind district 

controls and the statewide strategy.

Summary and Recommendation:

There are two monitors in Tehama County. The first site, Red Bluff-Oak Street, 

is located in the town of Red Bluff at an elevation of 322 feet. The design value 

for this site reflects population exposures and meets the revised standard. In 

contrast, the design value for the Tuscan Buttes site violates the standard. There 

are no population or emissions in the Tuscan Buttes area. Ozone concentrations 

measured at the site are dominated by transport from the Sacramento Metro 

Area. 

Located at an elevation of 1,877 feet, the Tuscan Buttes monitor is similar to the 

Sutter Buttes monitor in Sutter County. Both of these monitors were sited to 

study high-elevation transport of pollutants from the Sacramento Metro Area into 

the Upper Sacramento Valley. There are no pollution sources or populated 

areas near either site. In both cases, design values for lower elevation sites in 

the surrounding populated areas all attain the standard, lending additional 

support to the argument that the ozone problems at the elevated sites are unique 

and isolated. 

Sutter Buttes is currently designated as nonattainment, and the nonattainment 

area includes the immediate area above 2000 feet elevation. Because of the 

elevated location and lack of population exposure at the Tuscan Buttes site, ARB 

recommends the geographic scope of this nonattainment area be limited to that 

portion of the Tuscan Buttes area with an elevation of 1800 feet or more. This 

approach is consistent with the approach U.S. EPA used in designating the 

Sutter Buttes ozone nonattainment area. 

Eastern Kern County

Jurisdictional Boundaries:

Kern County is located in two different air basins. The western portion of the 

County is located in the San Joaquin Valley Air Basin, while the eastern portion is 

located in the Mojave Desert Air Basin (refer to Figure 11). The eastern portion 

of the County falls under the jurisdiction of the Kern County Air Pollution Control 

District. Currently, the northeast corner of Eastern Kern County, which coincides 

with the Kern County portion of federal hydrologic unit #18090205, is designated 

as attainment for the old federal 8-hour standard. In contrast, the remainder of 

Eastern Kern County is designated as nonattainment.
26

FIGURE 11

EASTERN KERN COUNTY

Geography / Topography:

Eastern Kern County occupies the northwestern portion of the Mojave Desert, as 

well as portions of the Tehachapi Mountains and the southern end of the Sierra 

Nevada. The ozone monitors in Eastern Kern County are located in the desert 

portions of the region, which are classified as high desert. Elevations in this area 

range from about 2000 to 5000 feet above sea level. 

Meteorology:

Violations of the revised ozone standard are measured at two sites in the desert 

portion of Eastern Kern County. This desert region has a typical desert climate, 

with hot dry summers and cool winters with little rainfall. In the southern part of 

Eastern Kern County, maximum summer temperatures average 94 degrees 

Fahrenheit, and rainfall averages 6 inches per year. Values in the northeast 

corner (Indian Wells Valley area) are a little higher, with maximum summer 

temperatures averaging 100 degrees and rainfall averaging 7 inches each year. 

Based on general wind patterns, Eastern Kern County is downwind of two major 

urban source areas: the South Coast Air Basin and the San Joaquin Valley Air 

Basin. As a result, ozone concentrations throughout Eastern Kern County are 
27

impacted by long range transport from these areas. Previous transport 

assessments show that ozone concentrations in Eastern Kern County can be 

overwhelmed by transport from the upwind areas. 

Air Quality Data: 

Ozone data are available for a site at the China Lake Naval Air Weapons Station 

in the Indian Wells Valley and a site at Mojave-Poole Street in the current 

nonattainment area. The design value for China Lake is 0.081 ppm, while the 

design value for Mojave is 0.086 ppm. Both of these values violate the revised 

standard.

As mentioned previously, ozone air quality in Eastern Kern County is significantly 

impacted by transport from both the SanJoaquin Valley and the South Coast air 

basins. Figure 12 shows the trend in design values for Mojave, as well as for the 

San Joaquin Valley and South Coast Air Basin (long-term trend data are not 

available for the China Lake site). The trends show that although the design 

value for Mojave is lower, it tracks well with the South Coast and San Joaquin 

Valley trends. Because of the overwhelming transport impact, ozone air quality 

in Mojave has decreased at a rate similar to that in the upwind areas. Although

China Lake is not included on the graph, this site is also impacted by transport, 

and we would expect the trend to be similar to that for Mojave, but at a lower 

level, overall. 

FIGURE 12

Ozone Design Values for Eastern Kern County 

and Upwind Air Basins

0.000

0.020

0.040

0.060

0.080

0.100

0.120

0.140

0.160

1999 2000 2001 2002 2003 2004 2005 2006 2007 2008

Ozone DV (ppm)

Mojave-Poole South Coast Air Basin

San Joaquin Valley 
28

Population Density and Degree of Urbanization; Growth Rates and 

Patterns; and Traffic and Commuting Patterns:

Several towns are scattered throughout Eastern Kern County. The largest one in 

the Indian Wells Valley area is Ridgecrest. This town grew up around the China 

Lake Naval Air Weapons Center. Overall, population in all of Eastern Kern 

County is small, compared with that in the South Coast and SanJoaquin Valley 

areas. The total Eastern Kern County population in 2005 was about 132,000. 

The increase in population has also been small, increasing only 13 percent 

between 1995 and 2005. Because of the limited population, overall local,

traffic-related emissions are not expected to be significant.

Emissions Data and Level of Emission Controls

Relative to the South Coast and SanJoaquin Valley air basins, ozone precursor 

emissions in Eastern Kern County are insignificant. There are only a handfull of 

stationary sources (refer to Figure 11), and nearly all of these are located in the 

portion of Eastern Kern County that is already designated as nonattainment. In 

addition to these stationary sources, several highways traverse the region, 

carrying traffic in and out of the Eastern Kern County area. Because of the

sparse population and limited emissions sources, attainment in Eastern Kern 

County is dependent on emissions reductions in the upwind districts and from the 

statewide strategy. 

Summary and Recommendation:

Indian Wells Valley is a high desert area in the northeast corner of Kern County. 

It includes the China Lake Naval Air Weapons Station and the town of 

Ridgecrest. Similar to the rest of Eastern Kern County, Indian Wells Valley is 

sparsely populated and has few significant emissions sources. The design value 

for Indian Wells Valley (0.081 ppm) is similar to the design value for the current 

Eastern Kern County nonattainment area (0.086 ppm). Furthermore, previous 

studies have shown that ozone concentrations in both of these areas are 

overwhelmingly impacted by transport from the San Joaquin Valley and South 

Coast air basins. 

Because both areas are similar in terms of air quality, population, emissions, and 

transport impacts, ARB recommends the current Eastern Kern County 

nonattainment area be expanded to include the Indian Wells Valley area. As a 

result, the entire portion of Kern County within the Mojave Desert Air Basin would 

be included in the Eastern Kern County ozone nonattainment area.
1

ENCLOSURE 4

STATE OF CALIFORNIA BOUNDARY RECOMMENDATIONS 

FOR NEW NONATTAINMENT AREAS 

UNDER THE 2008 FEDERAL 8-HOUR OZONE STANDARD

NORTHEAST SAN BERNARDINO COUNTY

That portion of San Bernardino County that lies north and east of a line described 

as follows: latitude 35 degrees, 10 minutes north and longitude 115 degrees, 

45 minutes west.

 

SOUTHERN INYO COUNTY

That portion of Inyo County that lies within the bounds of Hydrologic Unit

Number 16060015, 18090202, 18090203, 18090204, and 18090205.

EASTERN SAN LUIS OBISPO COUNTY

That portion of San Luis Obispo County that lies east of a line described as 

follows: Beginning at the SanLuis Obispo County / Santa Barbara County 

boundary and running north along 120 degrees 24 minutes longitude to the 

intersection with 35 degrees 27 minutes latitude; east along 35 degrees 

27 minutes latitude to the intersection with 120 degrees 18 minutes longitude; 

then north along 120 degrees 18 minutes longitude to the SanLuis Obispo

County / Monterey County boundary. 

PINNACLES NATIONAL MONUMENT (SAN BENITO COUNTY)

That portion of San Benito County that lies within the boundary of Pinnacles 

National Monument as it existed on February 26, 2009.

TUSCAN BUTTES (TEHAMA COUNTY)

That portion of the immediate Tuscan Buttes area at or above 1,800 feet in 

elevation.
2

EASTERN KERN COUNTY

That portion of Kern County that lies east and south of a line described as 

follows: Beginning at the Kern County / Los Angeles County boundary and 

running north and east along the northwest boundary of the Rancho La Liebre 

Land Grant to the point of intersection with the range line common to Range 16 

West and Range 17 West, 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 Grant to the northwest corner of Section 3, Township 11 North, 

Range 17 West; 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 Section 34, Township 32 South, Range 30 East, Mount Diablo Base 

and Meridian; then north to the northwest corner of Section 35, Township 31 

South, Range 30 East; then northeast along the boundary of the Rancho 

El Tejon Land Grant to the southwest corner of Section 18, Township 31 South, 

Range 31 East; then east to the southeast corner of Section 13, Township 31 

South, Range 31 East; then north along the range line common to Range 31 

East and Range 32 East, Mount Diablo Base and Meridian, to the northwest 

corner of Section 6, Township 29 South, Range 32 East; then east to the 

southwest corner of Section 31, Township 28 South, Range 32 East; then north 

along the range line common to Range 31 East and Range 32 East to the 

northwest corner of Section 6, Township 28 South, Range 32 East, then west to 

the southeast corner of Section 36, Township 27 South, Range 31 East, then 

north along the range line common to Range 31 East and Range 32 East to the 

Kern County / Tulare County boundary.
1

ENCLOSURE 5

SUMMARY OF DATA AND FEDERAL 8-HOUR OZONE DESIGN VALUES

FOR CALIFORNIA SITES BASED ON 2006 THROUGH 2008 DATA

Year

Basin Name County Name Site Name Statistic 2006 2007 2008*

2008* 

Design 

Value

4

th High 0.082 0.085 0.077 0.081

Inyo Death Valley Natl Monument

Valid Days 347 351 320

Alpine NO MONITORS

Great Basin 

Valleys

Mono NO MONITORS

4

th High 0.062 0.057 0.068 0.062

Lake County Lake Lakeport-Lakeport Blvd 

Valid Days 360 354 328

4

th High 0.069 0.070 0.072 0.070

El Dorado South Lake Tahoe-Airport 

Road Lake Tahoe Valid Days 160 169 151

Placer NO MONITORS

4

th High 0.089 0.078 0.093 0.086

Kern Mojave-923 Poole Street 

Valid Days 357 358 188

4

th High 0.098 0.091 0.095 0.094

Los Angeles Lancaster-43301 Division 

Street Valid Days 363 357 360

4

th High 0.057 0.066 0.067 0.063

Riverside Blythe-445 West Murphy Street

Valid Days 361 284 237

4

th High 0.086 0.084 0.090 0.086

Barstow

Valid Days 344 356 364

4

th High 0.095 0.098 0.098 0.097

Hesperia-Olive Street

Valid Days 358 356 362

4

th Joshua Tree-National High 0.103 0.104 0.105 0.104

Monument Valid Days 348 342 322

4

th Phelan-Beekley Rd & Phelan High 0.097 0.093 0.099 0.096

Rd' Valid Days 363 356 365

4

th High 0.080 0.077 0.084 0.080

Trona-Athol and Telegraph 

Valid Days 360 351 339

4

th High 0.091 0.087 0.089 0.089

Mojave Desert

San Bernardino

Victorville-14306 Park Avenue 

Valid Days 363 362 359

4

th High 0.085 0.073 0.101 0.086

Amador Jackson-Clinton Road

Valid Days 363 344 265

4

th High 0.098 0.076 0.094 0.089

Calaveras San Andreas-Gold Strike Road 

Valid Days 364 356 267

4

th High 0.099 0.093 0.102 0.098

Cool-Highway 193

Valid Days 183 181 150

4

th High 0.075 0.075 0.078 0.076

Echo Summit

Valid Days 148 135 135

4

th High 0.097 0.085 0.106 0.096

El Dorado 

Placerville-Gold Nugget Way

Valid Days 363 333 272

4

th High 0.080 0.083 0.089 0.084

Mountain 

Counties

Mariposa Jerseydale - 6440 Jerseydale

Valid Days 175 181 183
2

Year

Basin Name County Name Site Name Statistic 2006 2007 2008*

2008* 

Design 

Value

4

th Mariposa High 0.084 0.087 0.094 0.088

(continued) Yosemite NP-Turtleback Dome

Valid Days 292 334 317

4

th High 0.096 0.088 0.091 0.091

Grass Valley-Litton Building

Valid Days 328 365 247

4

th High 0.076 0.071 0.066 0.071

Truckee-Fire Station

Valid Days 225 281 265

4

th High 0.089 0.082 0.091 0.087

Nevada 

White Cloud Mountain

Valid Days 162 182 153

4

th High 0.105 0.079 0.084 0.089

Placer Colfax-City Hall

Valid Days 346 356 338

4

th High 0.064 0.064

Plumas Quincy-N Church Street

Valid Days 229

4

th High 0.079 0.084 0.098 0.087

Tuolumne Sonora-Barretta Street

Valid Days 365 360 271

Mountain 

Counties 

(continued)

Sierra NO MONITORS

4

th High 0.060 0.059 0.060 0.059

Carmel Valley-Ford Road

Valid Days 364 365 332

4

th High 0.054 0.06 0.057

King City-415 Pearl Street

Valid Days 215 304

4

th High 0.063 0.054 0.058

King City-750 Metz Road

Valid Days 360 134

4

th High 0.054 0.053 0.060 0.055

Monterey 

Salinas-#3

Valid Days 358 354 322

4

th High 0.071 0.068 0.068 0.069

Hollister-Fairview Road

Valid Days 359 352 329

4

th High 0.078 0.075 0.086 0.079

San Benito

Pinnacles National Monument

Valid Days 355 361 324

4

th High 0.052 0.049 0.056 0.052

Davenport

Valid Days 364 362 322

4

th High 0.054 0.053 0.057 0.054

Santa Cruz-2544 Soquel Ave

Valid Days 358 358 329

4

th High 0.062 0.059 0.064 0.061

Scotts Valley-Scotts Valley Dr

Valid Days 361 361 332

4

th High 0.054 0.054 0.058 0.055

North Central 

Coast

Santa Cruz

Watsonville-Airport Boulevard

Valid Days 363 364 334

4

th High 0.046 0.049 0.047

Humboldt Eureka-Jacobs

Valid Days 17 308 347

4

th High 0.060 0.053 0.061 0.058

Ukiah-E Gobbi Street

Valid Days 356 352 302

4

th High 0.049 0.046 0.045 0.046

North Coast

Mendocino

Willits-899 S Main Street

Valid Days 351 358 149
3

Year

Basin Name County Name Site Name Statistic 2006 2007 2008*

2008* 

Design 

Value

4

th High 0.056 0.060 0.055 0.057

Sonoma Healdsburg-Municipal Airport

Valid Days 338 341 271

Del Norte NO MONITORS

North Coast 

(continued)

Trinity NO MONITORS

4

th High 0.067 0.060 0.058 0.061

Siskiyou Yreka-Foothill Drive

Valid Days 318 332 264

Lassen NO MONITORS

Northeast Plateau

Modoc NO MONITORS

4

th High 0.076 0.074 0.080 0.076

Chico-Manzanita Avenue

Valid Days 360 363 262

4

th High 0.089 0.083 0.084 0.085

Butte

Paradise-4405 Airport Road

Valid Days 361 364 269

4

th High 0.069 0.066 0.072 0.069

Colusa Colusa-Sunrise Blvd

Valid Days 357 361 269

4

th High 0.059 0.069 0.067 0.065

Willows-720 N Colusa Street

Valid Days 106 361 271

4

th High 0.063 0.063

Glenn 

Willows-E Laurel Street

Valid Days 252

4

th High 0.098 0.079 0.095 0.090

Auburn-Dewitt-C Avenue

Valid Days 330 347 351

4

th High 0.094 0.082 0.094 0.090

Placer 

Roseville-N Sunrise Blvd

Valid Days 363 350 271

4

th High 0.087 0.078 0.082 0.082

Elk Grove-Bruceville Road

Valid Days 357 359 330

4

th High 0.102 0.090 0.114 0.102

Folsom-Natoma Street

Valid Days 358 354 327

4

th High 0.092 0.071 0.072 0.078

North Highlands-Blackfoot Way

Valid Days 356 341 245

4

th High 0.077 0.077 0.080 0.078

Sacramento-3801 Airport Road

Valid Days 311 299 201

4

th High 0.093 0.081 0.087 0.087

Sacramento-Del Paso Manor

Valid Days 349 362 323

4

th High 0.084 0.073 0.081 0.079

Sacramento-T Street

Valid Days 351 342 292

4

th High 0.104 0.080 0.102 0.095

Sacramento

Sloughhouse

Valid Days 214 208 212

4

th High 0.073 0.075 0.081 0.076

Anderson-North Street

Valid Days 327 365 274

4

th High 0.074 0.076 0.083 0.077

Lassen Vol NP-Manzanita Lk

Valid Days 353 362 316

4

th High 0.080 0.070 0.077 0.075

Sacramento 

Valley

Shasta 

Redding-Health Dept Roof

Valid Days 357 365 338
4

Year

Basin Name County Name Site Name Statistic 2006 2007 2008*

2008* 

Design 

Value

4

th High 0.080 0.071 0.084 0.078

Solano Vacaville-Ulatis Drive

Valid Days 358 365 354 4

th High 0.090 0.077 0.088 0.085

Sutter Buttes-S Butte

Valid Days 184 183 153 4

th High 0.078 0.072 0.068 0.072

Sutter

Yuba City-Almond Street

Valid Days 352 343 264 4

th High 0.073 0.072 0.080 0.075

Red Bluff-Oak Street

Valid Days 330 357 319 4

th High 0.087 0.082 0.087 0.085

Tehama

Tuscan Butte

Valid Days 183 184 146 4

th High 0.078 0.075 0.077 0.076

Davis-UCD Campus

Valid Days 358 359 258 4

th High 0.088 0.073 0.076 0.079

Yolo

Woodland-Gibson Road

Valid Days 365 363 356

Sacramento 

Valley (continued)

Yuba NO MONITORS 4

th High 0.043 0.067 0.057 0.055

Brawley-220 Main Street

Valid Days 91 89 14 4

th High 0.078 0.083 0.078 0.079

Calexico-East

Valid Days 352 325 341 4

th High 0.068 0.087 0.087 0.080

Calexico-Ethel Street

Valid Days 362 353 363 4

th High 0.065 0.071 0.068

Calexico-Grant Street

Valid Days 356 205 4

th High 0.091 0.083 0.074 0.082

El Centro-9th Street

Valid Days 331 349 362 4

th High 0.072 0.078 0.075 0.075

Niland-English Road

Valid Days 354 355 362 4

th High 0.086 0.085 0.077 0.082

Imperial

Westmorland-W 1st Street

Valid Days 355 353 360 4

th Hig

h 0.085 0.087 0.088 0.086

Indio-Jackson Street

Valid Days 361 360 237 4

th High 0.079 0.076 0.084 0.079

Joshua Tree National Park

Valid Days 270 281 129 4

th High 0.099 0.097 0.096 0.097

Salton Sea

Riverside

Palm Springs-Fire Station

Valid Days 354 360 241 4

th High 0.094 0.086 0.098 0.092

Alpine-Victoria Drive

Valid Days 357 358 301 4

th High 0.072 0.071 0.070 0.071

Camp Pendleton

Valid Days 355 349 300 4

th High 0.065 0.070 0.074 0.069

Chula Vista

Valid Days 357 351 299 4

th High 0.067 0.072 0.075 0.071

San Diego San Diego

Del Mar-Mira Costa College

Valid Days 364 362 305
5

Year

Basin Name County Name Site Name Statistic 2006 2007 2008*

2008* 

Design 

Value

4

th High 0.076 0.073 0.082 0.077

El Cajon-Redwood Avenue

Valid Days 349 332 297 4

th High 0.078 0.075 0.089 0.080

Escondido-E Valley Parkway

Valid Days 352 355 291 4

th High 0.061 0.064 0.066 0.063

Otay Mesa-Paseo International

Valid Days 359 357 273 4

th High 0.061 0.060 0.063 0.061

San Diego-1110 Beardsley St

Valid Days 362 330 291 4

th High 0.07 0.073 0.082 0.075

San Diego 

(continued)

San Diego 

(continued)

San Diego-Overland Avenue

Valid Days 354 357 296 4

th High 0.029 0.045 0.037

Berkeley-6th Street 

Valid Days 23 269 4

th High 0.069 0.055 0.061 0.061

Fremont-Chapel Way 

Valid Days 358 352 271 4

th High 0.067 0.055 0.068 0.063

Hayward-La Mesa 

Valid Days 244 242 182 4

th High 0.089 0.067 0.087 0.081

Livermore-793 Rincon Avenue 

Valid Days 361 361 270 4

th High 0.034 0.057 0.045

Oakland-Davie 

Valid Days 60 268 4

th High 0.06 0.052 0.067 0.059

Alameda

San Leandro-County Hospital 

Valid Days 243 243 175 4

th High 0.081 0.071 0.076 0.076

Bethel Island Road 

Valid Days 358 360 271 4

th High 0.085 0.071 0.078 0.078

Concord-2975 Treat Blvd

Valid Days 360 360 270 4

th High 0.079 0.067 0.067 0.071

Pittsburg-10th Street

Valid Days 357 356 271 4

th High 0.045 0.049 0.057 0.050

Contra Costa

San Pablo-Rumrill Blvd

Valid Days 353 356 265 4

th High 0.047 0.048 0.055 0.050

Marin San Rafael 

Valid Days 353 356 266 4

th High 0.064 0.055 0.067 0.062

Napa Napa-Jefferson Avenue

Valid Days 361 355 269 4

th High 0.044 0.047 0.049 0.046

San Francisco San Francisco-Arkansas Street

Valid Days 347 354 266 4

th High 0.051 0.052 0.058 0.053

San Mateo Redwood City 

Valid Days 354 357 266 4

th High 0.08 0.068 0.072 0.073

Gilroy-9th Street

Valid Days 229240 183

4

th High 0.085 0.059 0.074 0.072

Los Gatos 

Valid Days 363 363 273 4

th High 0.073 0.057 0.067 0.065

San Francisco 

Bay Area

Santa Clara

San Jose-Jackson Street 

Valid Days 329 352 269
6

Year

Basin Name County Name Site Name Statistic 2006 2007 2008*

2008* 

Design 

Value

4

th High 0.088 0.070 0.071 0.076

San Martin-Murphy Avenue 

Valid Days 238 239 182 4

th High 0.064 0.054 0.063 0.060

Santa Clara 

(continued)

Sunnyvale-910 Ticonderoga 

Valid Days 243 243 183 4

th High 0.063 0.075 0.069

Benicia-East 2nd Street 

Valid Days 270 266 4

th High 0.074 0.062 0.068 0.068

Fairfield-Chadbourne Road 

Valid Days 242 241 183 4

th High 0.06 0.054 0.067 0.060

Solano

Vallejo-304 Tuolumne Street 

Valid Days 346 354 267 4

th High 0.049 0.047 0.059 0.051

San Francisco 

Bay Area 

(continued)

Sonoma Santa Rosa-5th Street 

Valid Days 362 357 269 4

th High 0.094 0.092 0.108 0.098

Clovis-N Villa Avenue 

Valid Days 357 341 269 4

th High 0.101 0.094 0.108 0.101

Fresno-1st Street 

Valid Days 362 360 265 4

th High 0.085 0.079 0.093 0.085

Fresno-Drummond Street 

Valid Days 359 357 241 4

th High 0.097 0.088 0.101 0.095

Fresno-Sierra Skypark #2 

Valid Days 355 359 262 4

th High 0.099 0.090 0.094 0.094

Fresno

Parlier

Valid Days 339 356 231 4

th High 0.111 0.102 0.112 0.108

Arvin-Bear Mountain Blvd 

Valid Days 350 353 292 4

th High 0.107 0.085 0.101 0.097

Bakersfield-5558 California Ave

Valid Days 348 361 298 4

th High 0.091 0.08 0.094 0.088

Bakersfield-Golden State Hwy

Valid Days 362 358 209 4

th High 0.108 0.093 0.107 0.102

Edison

Valid Days 361 361 301 4

th High 0.09 0.086 0.084 0.086

Maricopa-Stanislaus Street

Valid Days 351 291 265 4

th High 0.100 0.090 0.104 0.098

Oildale-3311 Manor Street

Valid Days 354 357 303 4

th High 0.093 0.083 0.093 0.089

Kern

Shafter-Walker Street 

Valid Days 361 353 303 4

th High 0.086 0.080

0.083

Kings Hanford-S Irwin Street 

Valid Days 339 297 4

th High 0.081 0.077 0.091 0.083

Madera Madera-Pump Yard 

Valid Days 363 360 250 4

th High 0.086 0.087 0.105 0.092

Merced Merced-S Coffee Avenue 

Valid Days 167 363 256 4

th High 0.083 0.075 0.077 0.078

San Joaquin 

Valley

San Joaquin Stockton-Hazelton Street 

Valid Days 362 361 267
7

Year

Basin Name County Name Site Name Statistic 2006 2007 2008*

2008* 

Design 

Value

4

th San Joaquin High 0.093 0.079 0.090 0.087

(continued) Tracy-Airport 

Valid Days 355 354 269

4

th High 0.090 0.076 0.090 0.085

Modesto-14th Street 

Valid Days 358 362 268

4

th High 0.092 0.075 0.106 0.091

Stanislaus

Turlock-S Minaret Street 

Valid Days 363 361 265

4

th High 0.104 0.099 0.112 0.105

Sequoia & Kings Canyon NP

Valid Days 300 238 232

4

th High 0.097 0.091 0.101 0.096

Sequoia NP-Lower Kaweah

Valid Days 348 360 325

4

th High 0.092 0.086 0.105 0.094

San Joaquin 

Valley (continued)

Tulare

Visalia-N Church Street

Valid Days 361 361 301

4

th High 0.071 0.066 0.069 0.068

Atascadero-Lewis Avenue 

Valid Days 356 352 330

4

th High 0.086 0.080 0.088 0.084

Carrizo Plains School-Carrizo

Valid Days 340 349 322

4

th High 0.053 0.053 0.058 0.054

Morro Bay

Valid Days 351 343 320

4

th High 0.055 0.056 0.066 0.059

Nipomo-Regional Park

Valid Days 345 351 325

4

th High 0.072 0.068 0.064 0.068

Paso Robles-Santa Fe Avenue

Valid Days 360 363 190

4

th High 0.084 0.092 0.088

Red Hills

Valid Days 362 330

4

th High 0.055 0.057 0.060 0.057

San Luis Obispo

San Luis Obispo-S Higuera St

Valid Days 356 356 242

4

th High 0.058 0.066 0.072 0.065

Carpinteria-Gobernador Road

Valid Days 349 354 272

4

th High 0.056 0.057 0.066 0.059

El Capitan Beach

Valid Days 364 364 299

4

th High 0.055 0.055 0.058 0.056

Gaviota-GTC Site B

Valid Days 360 362 241

4

th High 0.064 0.057 0.062 0.061

Goleta-Fairview

Valid Days 364 358 301

4

th High 0.07 0.078 0.070 0.072

Las Flores Canyon #1

Valid Days 363 360 330

4

th High 0.062 0.066 0.067 0.065

Lompoc-HSandP

Valid Days 363 358 301

4

th High 0.051 0.056 0.062 0.056

Lompoc-S H Street

Valid Days 362 356 302

4

th High 0.075 0.077 0.068 0.073

Paradise Road-Los Padres NF

Valid Days 363 355 301

4

th High 0.056 0.063 0.062 0.060

South Central 

Coast

Santa Barbara

Santa Barbara-E Canon 

Perdido Valid Days 357 359 240
8

Year

Basin Name County Name Site Name Statistic 2006 2007 2008*

2008* 

Design 

Value

4

th High 0.048 0.048 0.056 0.050

Santa Maria-906 S Broadway

Valid Days 349 354 217

4

th High 0.064 0.063 0.067 0.064

Santa Ynez -Airport Road

Valid Days 364 363 301

4

th High 0.059 0.069 0.065 0.064

Santa Barbara 

(continued)

Vandenberg AFB-STS Power

Valid Days 356 358 331

4

th High 0.059 0.061 0.065 0.061

El Rio-Rio Mesa School #2

Valid Days 364 351 297

4

th High 0.094 0.076 0.081 0.083

Ojai-Ojai Avenue

Valid Days 363 361 301

4

th High 0.085 0.076 0.081 0.080

Piru-3301 Pacific Avenue

Valid Days 359 358 304

4

th High 0.089 0.086 0.090 0.088

Simi Valley-Cochran Street

Valid Days 360 357 295

4

th Thousand Oaks-Moorpark High 0.076 0.074 0.077 0.075

Road Valid Days 364 358 301

4

th High 0.062 0.065 0.067 0.064

Ventura

Ventura-Emma Wood State 

Bch Valid Days 362 350 294

South Central 

Coast (continued)

Channel Islands NO MONITORS

4

th High 0.091 0.096 0.101 0.096

Azusa

Valid Days 357 355 236

4

th High 0.098 0.088 0.092 0.092

Burbank-W Palm Avenue

Valid Days 358 356 235

4

th High 0.106 0.105 0.112 0.107

Glendora-Laurel

Valid Days 354 352 241

4

th High 0.095 0.063 0.079

Lebec-Peace Valley Road

Valid Days 321 82

4

th High 0.075 0.072 0.073 0.073

Los Angeles-North Main Street

Valid Days 355 337 224

4

th Los Angeles-Westchester High 0.062 0.067 0.065 0.064

Pkwy Valid Days 358 355 221

4

th High 0.064 0.057 0.055 0.058

Lynwood

Valid Days 357 357 235

4

th High 0.057 0.057 0.064 0.059

North Long Beach

Valid Days 354 350 236

4

th High 0.096 0.090 0.091 0.092

Pasadena-S Wilson Avenue

Valid Days 360 357 232

4

th High 0.078 0.079 0.077 0.078

Pico Rivera-4144 San Gabriel

Valid Days 222 352 233

4

th High 0.108 0.103 0.100 0.103

Pomona

Valid Days 354 352 238

4

th High 0.104 0.093 0.095 0.097

South Coast Los Angeles

Reseda

Valid Days 355 339 242
9

Year

Basin Name County Name Site Name Statistic 2006 2007 2008*

2008* 

Design 

Value

4

th High 0.112 0.102 0.103 0.105

Santa Clarita

Valid Days 357 351 235

4

th High 0.068 0.067 0.075 0.070

Los Angeles 

(continued)

West Los Angeles-VA Hospital

Valid Days 360 345 236

4

th High 0.071 0.074 0.076 0.073

Anaheim-Pampas Lane

Valid Days 361 357 239

4

th High 0.061 0.065 0.073 0.066

Costa Mesa-Mesa Verde Drive

Valid Days 362 341 236

4

th High 0.09 0.082 0.078 0.083

La Habra

Valid Days 349 355 238

4

th High 0.09 0.081 0.092 0.087

Orange

Mission Viejo-26081 Via Pera

Valid Days 353 358 239

4

th High 0.105 0.095 0.108 0.102

Banning Airport

Valid Days 353 359 237

4

th High 0.102 0.097 0.108 0.102

Lake Elsinore-W Flint Street

Valid Days 353 352 239

4

th High 0.114 0.103 0.106 0.107

Perris

Valid Days 348 362 243

4

th High 0.112 0.099 0.111 0.107

Riverside

Riverside-Rubidoux

Valid Days 358 356 236

4

th High 0.111 0.126 0.120 0.119

Crestline

Valid Days 363 365 234

4

th High 0.114 0.113 0.110 0.112

Fontana-Arrow Highway

Valid Days 351 346 234

4

th High 0.125 0.112 0.112 0.116

Redlands-Dearborn

Valid Days 364 362 244

4

th High 0.119 0.117 0.112 0.116

San Bernardino-4th Street

Valid Days 356 352 236

4

th High 0.112 0.112 0.108 0.110

South Coast 

(continued)

San Bernardino

Upland

Valid Days 360 354 236

* 2008 data are preliminary and may not be complete. Therefore, the 2008 Design Value should be 

 considered preliminary.