Air Standards
Ambient air standards (AAQS) define the maximum amount of pollutant that can be present in outdoor air without harming the public health. Both the Air Resources Board (ARB) and the U.S. Environmental Protection Agency (U.S. EPA) are authorized to set ambient air standards. The federal and California ambient air standards are listed below.
OZONE
Ozone, an important ingredient of smog, is a highly reactive and unstable gas capable of damaging the linings of the respiratory track. This pollutant forms in the atmosphere through complex reactions between chemicals directly emitted from vehicles, industrial plants, and many other sources. Key pollutants involved in ozone formation are hydrocarbon and nitrogen oxide gases. Elevated ozone levels can reduce crop and timber yields, as well as damage native plants. Ozone can also damage materials such as rubber, plastics, and fabrics.
| OZONE AMBIENT AIR QUALITY STANDARDS | ||
| Averaging Time | California Standards | National Standards |
| 1 hour | 0.09 ppm | ---- |
| 8 hour | 0.070 ppm | 0.08 ppm |
CARBON MONOXIDE (CO)
Carbon Monoxide (CO) is a colorless, odorless gas. It results from the incomplete combustion of carbon-containing fuels such as gasoline or wood, and is emitted by a wide variety of combustion sources. Exposure to CO near the levels of the ambient air quality standard can lead to fatigue, headaches, confusion, and dizziness. CO interferes with the blood's ability to carry oxygen.
Carbon Monoxide Air Quality Standards
- In 1955, the Los Angeles County Air Pollution Control District established an air pollution alert system to prevent disasters. The first alert level for CO was 100 ppm.
- In 1959, the California Department of Public Health adopted air quality standards for CO at the "serious" level. These were 30 ppm for an eight-hour exposure and 120 ppm for a nine-hour exposure.
- In 1969, the ARB adopted a standard for CO at 20 ppm for an eight-hour averaging period.
- In 1970, the ARB revised the CO standards to 10 ppm for 12 hours, and 40 ppm for one hour.
- In 1976, the ARB adopted a CO standard of 6 ppm for eight hours (for the Lake Tahoe Basin only).
- In 1982, the ARB revised the CO standards to 9 ppm for eight hours and 20 ppm for one hour.
- In 1989 the ARB retained these standards.
NITROGEN DIOXIDE
Nitrogen dioxide (NO2) is a reactive, oxidizing gas capable of damaging cells lining the respiratory tract. This is pollutant is also an essential ingredient in the formation of ground-level pollution. NO2 is one of the nitrogen oxides emitted for high-temperature combustion processes, such as those occuring in trucks, cars, and power plants. Home heaters and stoves also produce substantial amounts of NO2 in indoor settings.
| NITROGEN DIOXIDE (NO |
||
| Averaging Time | California Standard | Federal Standard |
| Annual * | ---- | 0.053 ppm |
| 1 hour | 0.025 ppm | ---- |
| * Annual Arithmetic Mean | ||
SULFUR DIOXIDE
Sulfur Dixoide (SO2) is a gaseous compound of sulphur and oxygen. SO2 is formed when sulphur-containing fuel is burned by mobile sources, such as locomotives, ships, and off-road diesel equipment. SO2 is also emitted from several industrial processes, such as petroleum refining and metal processing.
Sulfer Dioxide Air Quality Standards
- In 1955, the Los Angeles County Air Pollution Control District established an air pollution "first alert" level for sulfur dioxides (includes SO2, sulfur trioxide, and sulfates) at 3 ppm.
- In 1959, the California Board of Public Health adopted standards for SO2 at the "adverse" level. These were 0.3 ppm for 8 hours, and 1 ppm for 1 hour.
- In 1969, the ARB adopted an SO2 standard of 0.04 ppm for 24 hours, and 0.5 ppm for 1 hour.
- In 1974, the ARB adopted a 24-hour SO2 standard of 0.1 ppm. This standard was adjusted to 0.04 ppm in 1975 and then readjusted to 0.05 ppm in 1977.
- In 1984, the ARB adopted a 1-hour SO2 standard of 0.25 ppm, which was reviewed and retained in 1995.
- In 1991, the ARB adopted the current 24-hour SO2 standard of 0.04 ppm.
PARTICULATE MATTER
Particulate Matter (PM) consists of tiny particles that are easily inhaled deep into the lungs, and may cause a variety of harmful health effects.
PM10
PM10 is a mixture of various substances. These substances occur in the form of solid particles or as liquid drops. Some particles result from gases that are transformed into particles through physical and chemical processes in the atmosphere. A variety of emission sources and meteorological conditions contribute to ambient PM10.
PM2.5
PM2.5 particulate matter, or "fine" particulate, is primarily a result of combustion products emitted into the atmosphere, as well as those particles that are formed in the atmosphere from gaseous pollutants as a result of atmospheric chemistry (secondary formation). This "fine" particulate poses a greater health risk because they can deposit deep in the lungs and contain chemicals that are particularly harmful to health. These particles can reside in the atmosphere for long periods of time and are the main contributors to reduced visibility.
| PARTICULATE MATTER AMBIENT AIR QUALITY STANDARDS | |||
| Averaging Time | PM10 | PM2.5 | |
| Annual * | 20 µg/m |
12 µg/m |
|
| 24 Hours | 50 µg/m |
See Below ** | |
| * Annual Arithmetic Mean | |||
| ** There is no seperate 24-hour PM2.5 standard in California, however the U.S. EPA promulgated a 24-hour PM2.5 ambient air quality standard of 65 µg/m |
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SULFATES
Sulfates (SO4
Sulfates Air Quality Standards
- In 1976, the ARB adopted a sulfates standard at 25 µg/m
- This standard was reviewed and retained in 1977 and again in 2002.
LEAD
Lead is a relatively soft and chemical resistant metal. Lead forms compounds with both organic and inorganic substances. As an air pollutant, lead is present in small particles. In California, lead emissions come from several industrial activities. Lead is also present in many soils and can get resuspended into the air. Because lead is excreted slowly, exposures to small amounts of lead can accumulate to harmful levels, which can impair blood formation and nerve conduction and has been shown to cause certain types of cancers.
Lead Air Quality Standards
- In 1970, the ARB set a standard for lead at 1.5 µg/m3 for a 30-day average.
- In 1976, the ARB reviewed and retained this standard.
- In 1993, the ARB identified lead compounds (including inorganic lead) as toxic air contaminates, due to cancer effects.
- In 1996, the ARB established a cancer potentcy value of 1.2 × 10 –5 per µg/m3 for inorganic lead exposure. This value also applies to lead acetate, lead phosphate, and lead subacetate.
HYDROGEN SULFIDE (H2S)
Hydrogen Sulfide (H2S) is a colorless gas with the odor of rotten eggs. It is formed during bacterial decomposition of sulfur-containing organic substances. It can also be present in sewer gas and some natural gas, and can be emitted as the result of geothermal energy exploitation.
Hydrogen Sulfide Air Quality Standards
- In 1962, the California Board of Public Health adopted an air quality standard at the "adverse" level for H2S of 0.1 ppm for one hour.
- In 1969, the ARB adopted a standard for H2S of 0.03 ppm for a one-hour average. The ARB retained this standard in 1984.
VINYL CHLORIDE (chloroethene)
Vinyl Chloride (chloroethene), a chlorinated hydrocarbon, is a colorless gas with a mild, sweet odor. Most vinyl chloride is used to make polyvinyl chloride (PVC) plastic and vinyl products. Vinyl chloride has been detected near landfills, sewage plants, and hazardous waste sites, due to microbial breakdown of chlorinated solvents. Vinyl chloride exposure has been shown to increase the risk of angiosarcoma, a rare form of liver cancer in humans.
Vinyl Chloride Ambient Air Quality Standards
- In 1978, the ARB established a standard for vinyl chloride because it is a known animal and human carcinogen. As a carcinogen, the ARB could not recommend any level of exposure to vinyl chloride, other than zero, as being safe. This standard, 0.01 ppm for a 24-hour duration, was chosen because it was the lowest level that could be detected at that time.
- In 1990, the ARB identified vinyl chloride as a toxic air contaminant, and established a vinyl chloride cancer unit risk factor.
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. 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.
Visibility-Reducing Particles Air Quality Standards
- 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 miles 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 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 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.