Ambient
air quality standards (AAQS) define clean air, and are established to
protect even the most sensitive individuals in our communities. An air
quality standard defines the maximum amount of a pollutant
that can be present in outdoor air without harm to the
public's health. Both the California Air Resources Board (ARB) and the U.S. Environmental
Protection Agency (U.S. EPA) are authorized to set ambient air
quality standards
Federal Standards
EPA
has established standards (termed National Ambient Air Quality Standards
or NAAQS), under the authority of the Federal Clean Air Act, that
identify safe levels for ozone in the atmosphere to prevent and minimize
adverse impacts to human health and to crops, forests, and materials.
Ozone levels measured in the atmosphere at levels equal to or
lower than the standards are viewed as safe, whereas levels above the
standards represent a reasonable danger to public health and welfare
(non-health related damages), and thus require action to reduce
emissions of ozone precursors. EPA
ozone standard
is an 8-hour average of 0.08 parts per million by volume [ppm(v)]
This standard is subdivided into primary standards that protect public
health and secondary standards that protect public welfare (the numeric value of the standard is
the same for primary and secondary standards).
Areas
in the United States where ozone levels measured in the ambient air
exceed the 8-hour standard of 0.08 ppm(v) are said to be in
nonattainment of this standard. The 8-hour ozone NAAQS is based on the number of days per
year with a 8-hour average concentration of 0.08 ppm(v) or greater.
An area is in compliance with the ozone NAAQS when
measured 8-hour average ozone levels at any given monitoring station do
not exceed 0.08 ppm(v) more than one day per year over any consecutive
three-year period. Thus an
area with measured 8-hour average ozone levels greater than 0.08 ppm(v)
on four or more days over a three-year period has not attained the
standard, even if all of the days occurred in only one of the three
years.
The severity or
magnitude of a given area’s ozone nonattainment problem is given by
the ozone design value, which is based on the
3-year average of the fourth-highest daily maximum 8-hour average ozone
concentrations measured at
a given monitoring station. The overall design value for the San Joaquin Valley Air Basin
is given by the highest design value of all of the individual monitoring
stations in the Basin.
The San Joaquin Valley Air Basin, which is comprised of San Joaquin, Stanislaus, Merced, Madera, Fresno, Kings, Tulare and Kern (Valley portion only) counties, has a design value of 0.115 ppm (2005) and is classified as “serious” nonattainment for the 8-hour standard."
1 Hour Standards
The U.S.
EPA revoked the Federal 1-hour standard on April 15, 2005.
For more information, click
here.
California Standards
On
April 28, 2005, the California Air Resources Board (ARB) approved the nation's
most health protective ozone standard with special consideration for
children's health. The new 8-hour-average standard at 0.070 parts per million
(ppm) will further protect California's most vulnerable population from the
adverse health effects associated with ground-level ozone, or smog. The new
8-hour-average ozone standard is the first of its kind in the state.
For
more information on California Ambient Air Quality Standards click
here.
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Pollutant
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Concentration (parts per million)
|
Averaging Time
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Notes
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Ozone
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0.09* ppm
|
1 hour
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Standard set to prevent the following short-term health
effects: One-hour and multi-hour exposures - lung function
decrements, and symptoms of respiratory irritation. Multi-hour
exposures - airway hyperreactivity and airway inflammation.
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0.070* ppm
|
8 hour
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* Defined the highest level of ozone that can be
present without adverse health effects
**These concentrations were approved by the Air Resources Board on April
28, 2005 and are expected to become effective in early 2006
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