Air Quality Standards

State and National Ambient Air Quality Standards

The California Air Resources Board (ARB) and the U.S. Environmental Protection Agency (EPA) have promulgated ambient air quality standards. These standards were established to protect human health and/or welfare. The levels of the State and National standards may differ because the Board and the U.S. EPA considered different reports or information, and the Board chose to provide a wider margin of safety in the State standards than did the U.S. EPA in the National standards.

An ambient air quality standard is a concentration level expressed in either parts per million or micrograms per cubic meter and averaged over a specific time period such as one-hour, eight-hours, 24-hours, or one year. The different averaging times and concentrations are meant to protect against different exposure effects. Some ambient air quality standards are expressed as a concentration that is not to be exceeded. Others are expressed as a concentration that is not to be equaled or exceeded.

The National standards are further categorized as primary standards and secondary standards. The primary National standards are meant to protect public health. The secondary National standards are meant to protect the public welfare from any known or anticipated adverse effects of the pollutant.

The following table lists the applicable pollutant levels, averaging times, and analytical measurement methods for both the State standards and the National standards, including the new National ozone, PM10, and PM2.5 standards promulgated by the U.S. EPA in July 1997.    Visit the EPA Air Quality Standards web site at: http://ttnwww.rtpnc.epa.gov/naaqsfin.

  

Ambient Air Quality Standards

Pollutant

Averaging Time

California Standards 1

Federal Standards 2

Concentration 3

Method 4

Primary 3,5

Secondary 3,5

Method 7

Ozone (O3)

1 Hour

0.09 ppm (180 ug/m3)

Ultraviolet Photometry

0.12 ppm
(235 ug/m3)8

Same as Primary Standard

Ethylene Chemiluminescence

8 Hour

-

0.08 ppm
(157 ug/m3)

 

Respirable Particulate Matter (PM10)

Annual Geometric Mean

20 ug/m3

 

Size Selective Inlet Sampler ARB Method P (8/22/85)

-

 

Same as Primary Standard

 

Inertial Separation and Gravimetric Analysis

24 Hour

50 ug/m3

150 ug/m3

Annual Arithmetic Mean

-

50 ug/m3

Fine Particulate Matter (PM2.5)

24 Hour

No Separate State Standard

          12 ug/m3

65 ug/m3

Same as Primary Standard

Inertial Separation and Gravimetric Analysis

Annual Arithmetic Mean

15 ug/m3

 

Carbon Monoxide (CO)

8 Hour

 9.0 ppm (10 mg/m3)

 

Non-dispersive Infrared Photometry (NDIR)

9 ppm
(10 mg/m3)

 

None

 

Non-dispersive Infrared Photometry (NDIR)

1 Hour

 20 ppm (23 mg/m3)

35 ppm
(40 mg/m3)

8 Hour (Lake Tahoe)

 6 ppm (7 mg/m3)

-

Nitrogen Dioxide (NO2)

Annual Arithmetic Mean

-

 Gas Phase Chemiluminescence

0.053 ppm
(100 ug/m3)

Same as Primary Standard

Gas Phase Chemiluminescence

1 Hour

 0.25 ppm (470 ug/m3)

-

 

Lead

30 days average

1.5 ug/m3

AIHL Method 54 (12/74) Atomic Absorption

-

-

  

Calendar Quarter

-

1.5 ug/m3

Same as Primary Standard

High Volume Sampler and Atomic Absorption

 

Sulfur Dioxide (SO2)

Annual Arithmetic Mean

-

 

Fluorescence

0.030 ppm
(80 ug/m3)

-

 

Pararosoaniline

24 Hour

 0.04 ppm (105 ug/m3)

0.14 ppm
(365 ug/m3)

-

3 Hour

-

-

0.5 ppm
(1300 ug/m3)

1 Hour

 0.25 ppm (655 ug/m3)

-

-

Visibility Reducing Particles

8 Hour
(10 am to 6 pm, PST)

 In sufficient amount to produce an extinction coefficient of 0.23 per kilometer-visibility of ten miles or more (0.07-30 miles or more for Lake Tahoe) due to particles when the relative humidity is less than 70 percent. ARB Method V (8/18/89)

 

No

Federal

Standards

Sulfates

24 Hour

25 ug/m3

Turbidimetric Barium Sulfate-AIHL Method 61 (2/76)

Hydrogen Sulfide

1 Hour

0.03 ppm (42 ug/m3)

Cadmium Hydroxide STRactan

Footnotes:

  1. California standards for ozone, carbon monoxide (except Lake Tahoe), sulfur dioxide (1 and 24 hour), nitrogen dioxide, suspended particulate matter-PM10 , and visibility reducing particles, are values that are not to be exceeded. All others are not to be equaled or exceeded. California ambient air quality standards are listed in the Table of Standards in Section 70200 of Title 17 of the California Code of Regulations.

    2. In addition, Section 70200.5 lists vinyl chloride (chloroethene) under "Ambient Air Quality Standards for Hazardous Substances." In 1978, the California Air Resources Board (ARB) adopted the vinyl chloride Standard of 0.010 ppm (26 ug/m3) averaged over a 24-hour period and measured by gas chromatography. The standard notes that vinyl chloride is a "known human and animal carcinogen" and that "low-level effects are undefined, but are potentially serious. Level is not a threshold level and does not necessarily protect against harm. Level specified is lowest level at which violation can be reliably detected by the method specified. Ambient concentrations at or above the standard constitute an endangerment to the health of the public."

    In 1990, the ARB identified vinyl chloride as a Toxic Air Contaminant and determined that there was not sufficient available scientific evidence to support the identification of a threshold exposure level. This action allows the implementation of health-protective control measures at levels below the 0.010 ppm ambient concentration specified in the 1978 standard.

  2. National standards (other than ozone, particulate matter, and those based on annual averages or annual arithmetic mean) are not to be exceeded more than once a year. The ozone standard is attained when the fourth highest eight hour concentration in a year, averaged over three years, is equal to or less than the standard. For PM10, the 24 hour standard is attained when 99 percent of the daily concentrations, averaged over three years, are equal to or less than the standard. For PM 2.5 the 24 hour standard is attained when 98 percent of the daily concentrations, averaged over three years, are equal to or less than the standard. Contact U.S. EPA for further clarification and current federal policies.
  3. Concentration expressed first in units in which it was promulgated. Equivalent units given in parentheses are based upon a reference temperature of 25° C and a reference pressure of 760 mm of mercury. Most measurements of air quality are to be corrected to a reference temperature of 25° C and a reference pressure of 760 mm of mercury (1,013.2 millibar); ppm in this table refers to ppm by volume, or micromoles of pollutant per mole of gas.
  4. Any equivalent procedure which can be shown to the satisfaction of the ARB to give equivalent results at or near the level of the air quality standard may be used.
  5. National Primary Standards: The levels of air quality necessary, with an adequate margin of safety to protect the public health.
  6. National Secondary Standards: The levels of air quality necessary to protect the public welfare from any known or anticipated adverse effects of a pollutant.
  7. Reference method as described by the EPA. An "equivalent method" of measurement may be used but must have a "consistent relationship to the reference method" and must be approved by the EPA.
  8. New federal 8-hour ozone and fine particulate matter standards were promulgated by U.S. EPA on July 18, 1997. The federal 1-hour ozone standard continues to apply in areas that violated the standard. Contact U.S. EPA for further clarification and current federal policies.

                                                       

 

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