Visibility-Reducing Particles
This page reviewed November 24, 2009.
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| What are Visibility-Reducing Particles? |
| Visibility-reducing particles consist of suspended particulate matter, which
is a complex mixture of tiny particles that consists of dry solid fragments, solid cores with liquid
coatings, and small droplets of liquid. These particles vary greatly in shape, size and chemical composition,
and can be made up of many different materials such as metals, soot, soil, dust, and salt. |
| Welfare Effects from Presence of Visibility-Reducing Particles |
| The Statewide standard is intended to limit the frequency and severity of
visibility impairment due to regional haze. A separate standard for visibility-reducing particles that
is applicable only in the Lake Tahoe Air Basin is based on reduction in scenic quality. |
| History of Air Quality Standard for Visibility-Reducing Particles |
- In
1959, the California Department of Public Health adopted an air quality
standard for particulates, at the
"adverse" level, defined as the "level at which there will be
… reduction in visibility or similar effects." The
standard for particulates "sufficient to
reduce visibility to less than three mi[les] when relative
humidity is less than 70 percent."
- In 1969, the ARB adopted a standard for 'visibility reducing particles',
defined as particles "in sufficient amount to reduce the visibility to less than
ten miles when relative humidity is less than 70 percent."
- In 1976, the ARB adopted a standard for 'visibility reducing particles'
for the Lake Tahoe Air Basin only. This was defined as particles "in sufficient
amount to reduce the prevailing visibility to less than 30 miles when relative humidity is
less than 70 percent."
- In 1989, the ARB converted both the the general statewide 10-mile standard
and the 30-mile Lake Tahoe standards to "instrumental equivalents". The statewide standard,
"extinction of 0.23 per kilometer" is equivalent to the standard set in 1969.
The Lake Tahoe Air Basin standard, "extinction of 0.07 per kilometer" is equivalent to the standard
set in 1976.
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For more information on Ambient Air Quality Standards
please contact
Linda Smith at (916) 327-8225 or email at lsmith@arb.ca.gov.
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Ambient Air Quality Standards
