ENCLOSURE 1

State of California State of California 

 

AIR RESOURCES BOARD AIR RESOURCES BOARD

 

January 2011 

RECOMMENDED 

AREA DESIGNATIONS 

FOR THE 2010 FEDERAL 

NITROGEN DIOXIDE 

STANDARDS 

Technical Support Document

California Environmental Protection Agency 

Air Resources Board

 i 

TABLE OF CONTENTS 

 Page 

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

NITROGEN DIOXIDE AIR QUALITY .......................................................................... 1 

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

NITROGEN DIOXIDE MONITORING NETWORK REQUIREMENTS ....................... 4 

SUMMARY.................................................................................................................. 5 
 ii 

LIST OF TABLES AND FIGURES 

 Page 

FIGURE I: South Coast Maximum 1-Hour NO2 Concentration 

 for the Federal Standard...................................................................... 2 

TABLE I: Recommended California Attainment Areas for the Federal 

 1-Hour and Annual Average NO2 Standard.......................................... 3 

TABLE II: Recommended California Unclassifiable Areas for the Federal 

 1-Hour and Annual Average NO2 Standard.......................................... 3 

TABLE III: Required Near-Roadway Monitors in California for the Federal NO2 Standard 

 Core Based Statistical Areas with a Population of 500,000 or more.... 4 
 1 

BACKGROUND 

This technical report provides Air Resources Board (ARB) recommendations on 

designations for the revised federal nitrogen dioxide (NO2) standard based on air quality 

monitoring data for California. 

On January 22, 2010, the United States Environmental Protection Agency (U.S. EPA) 

established a new national 1-hour NO2 standard of 100 parts per billion (ppb) and 

retained the annual average standard of 53 ppb. In addition, U.S. EPA added new 

near-roadway monitoring requirements. The final rule was published in the Federal 

Register on February 9, 2010. 

http://www.epa.gov/ttn/naaqs/standards/nox/fr/20100209.pdf

Under the Clean Air Act all states, including California, must develop recommendations 

for area designations and appropriate boundaries. These area designations specify the 

status of each area of the State with respect to compliance with the standards. These 

area designation recommendations are due to U.S. EPA by January 22, 2011. 

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

designations by January 22, 2012. 

NITROGEN DIOXIDE AIR QUALITY 

The first federal NO2 standard was established in 1971, which was an annual average 

NO2 standard of 53 ppb. The federal NO2 standard was not revised until 2010, when 

the new 1-hour standard of 100 ppb was added and the annual standard was retained. 

NO2 is emitted into the atmosphere from combustion processes which include boilers, 

furnaces, utilities, and mobile sources. U.S. EPA estimates that nationally mobile 

sources account for 58 percent of NO2 emissions. 

California has attained the annual average standard since 1998, with current annual 

average NO2 concentrations ranging from 1 to 28 ppb. In the early 1980’s, 1-hour NO2

concentrations in California were as high as 300 ppb, three times the level of the new 

1-hour standard. Today, 1-hour NO2 concentrations range from 6 to 85 ppb, well below 

the level of the federal 1-hour NO2 standard. The long-term trend in 1-hour NO2

concentrations, shown in Figure 1, shows a decline of 60 percent at two urban sites that 

currently measure some of the highest NO2 concentrations (Pomona and North Long 

Beach). Staff expects NO2 concentrations to continue to decline as a result of new 

emission control programs that will be implemented over the next decade to meet 

federal ozone and PM2.5 standards. 
 2 

FIGURE I 

South Coast Maximum 1-Hour NO2 Concentration 

for the Federal Standard 

South Coast 1 Hour NO2 Concentrations

0

50

100

150

200

250

300

1982 1985 1988 1991 1994 1997 2000 2003 2006 2009

1 hour NO2 (ppb)

North Long Beach Pomona Standard

RECOMMENDED AREA DESIGNATIONS 

ARB staff evaluated the available ambient NO2 data to determine appropriate area 

designations throughout the State. The recommendations in this report are based on 

NO2 air quality data collected between 2007 and 2009. The analysis was conducted for 

each monitoring site in the State for which data are available. Both annual average and 

1-hour NO2 concentrations were evaluated. The annual average is calculated by 

averaging all hourly NO2 concentrations measured during a year. Compliance with the 

1-hour standard is based on averaging the 98th percentile hourly NO2 concentration 

over a 3-year period. Generally, the 98th percentile is the eighth highest 1-hour NO2

concentration measured during a year. However, if data are incomplete, a higher value 

may be used, in accordance with established U.S. EPA criteria. 

Based on ARB staff’s analysis, no areas in California have monitored violations of either 

the federal 1-hour or annual average NO2 standards. Therefore, ARB staff is 

recommending that all areas with valid data be designated attainment for the revised 

NO2 standards, and areas with limited or no NO2 air quality data be designated 

unclassified. U.S. EPA has not yet issued guidance on determining the boundaries for 

attainment or nonattainment areas. In the absence of U.S. EPA guidance, our 

recommendations are based on a combination of district and district/county boundaries 

in order to maximize air quality management objectives. The NO2 federal design values 

for areas recommended as attainment are listed in Table I, while areas recommended 

as unclassified are listed in Table II. 
 3 

TABLE I 

Recommended California Attainment Areas 

for the Federal 1-Hour and Annual Average NO2 Standard 

Designation Attainment Area 1-hour Design 

Value (ppb) 

Annual Average 

Design Value (ppb)

Bay Area AQMD 54 16 

Butte County AQMD 38 8 

Feather River AQMD 49 9 

Imperial County APCD 72 14 

Mendocino County AQMD 32 5 

Mojave Desert AQMD 63 16 

Monterey County – Monterey Bay Unified APCD 34 6 

Santa Cruz County – Monterey Bay Unified APCD 22 2 

Placer County APCD 53 10 

Sacramento Metropolitan AQMD 56 13 

San Diego County APCD 85 21 

San Joaquin Valley Unified APCD 61 18 

San Luis Obispo County APCD 42 7 

Santa Barbara County APCD 35 10 

Los Angeles County - South Coast AQMD portion 81 28

Orange County – South Coast AQMD 69 21 

Riverside County – South Coast AQMD portion 63 20 

San Bernardino County – South Coast AQMD portion 74 24 

Ventura County APCD 45 11 

Attainment 

Yolo-Solano AQMD 36 7 

TABLE II 

Recommended California Unclassified Areas 

for the Federal 1-Hour and Annual Average NO2 Standard 

Designation Unclassified Area 

Antelope Valley AQMD 

Amador County APCD 

Calaveras County APCD 

Colusa County APCD 

Eastern Kern APCD 

El Dorado County AQMD 

Glenn County APCD 

Great Basin Unified APCD 

Lake County AQMD 

Lassen County APCD 

Mariposa County APCD* 

Modoc County APCD 

San Benito County – Monterey Bay Unified APCD 

North Coast Unified AQMD* 

Northern Sierra AQMD* 

Northern Sonoma County APCD 

Shasta County AQMD 

Siskiyou County APCD 

Tehama County APCD 

Unclassified 

Tuolumne County APCD 

*

 These areas have incomplete data. Remaining areas have no data. 
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NITROGEN DIOXIDE MONITORING NETWORK REQUIREMENTS 

In addition to revising the NO2 standard, U.S. EPA also established new monitoring

requirements that are oriented towards assessing the impact of emissions from mobile 

sources. The most significant change is the requirement for a new monitoring network 

to measure NO2 concentrations near major roadways in urban areas with a population 

of 500,000 or more. Sixteen new near-roadway monitoring sites will be required in 

California. These monitors are required to be deployed by January 2013. 

U.S. EPA is developing near-road monitoring guidance to address many technical 

issues related to deploying near-road monitors. In conjunction with the development of 

near-roadway guidance, U.S. EPA and the National Association of Clean Air Agencies 

are collaborating to conduct a near-road monitoring pilot study. The purpose of the pilot 

is primarily to allow U.S. EPA, state, and local air monitoring stakeholders to evaluate, 

improve, and document the near-road monitor siting process. 

Table III shows where new near-roadway monitors will be required in California. 

TABLE III 

Required Near-Roadway Monitors in California for the Federal NO2 Standard 

Core Based Statistical Areas (CBSA) with a Population of 500,000 or more 

Core Based Statistical Areas County(ies) Population Number of 

Monitors 

Bakersfield Kern 800,458 1 

Fresno Fresno 909,153 1 

Los Angeles-Long Beach-Santa Ana Los Angeles, Orange 12,872,808 2 

Modesto Stanislaus 510,694 1 

Oxnard-Thousand Oaks-Ventura Ventura 797,740 1 

Riverside-San Berd-Ontario Riverside, San Bernardino 4,115,871 2 

Sacramento-Arden Arcade-Roseville Sacramento, Placer 2,109,832 2 

San Diego-Carlsbad-San Marcos San Diego 3,001,072 2

San Francisco-Oakland-Fremont Alameda, Contra Costa, San 

Francisco, San Mateo, Marin 4,274,531 2 

San Jose-Sunnyvale-Santa Clara Santa Clara 1,819,198 1 

Stockton San Joaquin 672,388 1 

There are also two additional monitoring requirements. First, states are required to 

continue operating monitors to measure community-wide exposures. There are 99 NO2

monitors of this type in California, which far exceeds the minimum federal requirements. 

The second monitoring requirement will be implemented by the U.S. EPA. Working with 

the states, EPA Regional Administrators will specify at least 40 additional NO2 monitors 

across the United States to help protect communities that are susceptible and 

vulnerable to NO2-related health effects. The new monitoring data may result in a need 

to change area designations in the future. ARB will revise the area designation 

recommendations, as appropriate, once the new monitoring data becomes available. 
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SUMMARY 

ARB has used California’s air quality monitoring data to develop recommended area 

designations for U.S. EPA’s revised NO2 air quality standard. Currently no counties in 

California exceed the revised standard. All urban areas are recommended to be 

designated as attainment. Several rural areas are recommended to be unclassified at 

this time since additional data is needed to meet U.S EPA requirements for designation 

as attainment. U.S. EPA is expected to issue final designations by January 22, 2012. 

These designations may later need revision when the results of the newly required 

near-road monitoring are available.