California Air Resources Board

Toxics Air Quality Data Description

Sampling Schedule
Toxics samples are collected every 12 days at 21 sites (20 sites before July 1995) throughout California. There is usually a maximum of 31 values for a given toxics substance at a given site each year.

Data Use
The toxics sampling network was designed to produce a statewide annual average to support the determination of a statewide risk assessment. Where fewer than 12 continuous months of data are present, we believe that it is seldom appropriate to calculate an annual average. Most of the toxics substances show some seasonal variation, and some substances differ by as much as two orders of magnitude between the high and low periods of the year. If a month's data are missing, the calculated average could be radically different from the real average, the average that would have been calculated had the missing month's data been available.

Since the sampling program was designed to produce statewide annual averages, it is important that the data from a single site not be used too broadly. We have observed that data from sites that are as little as 20 miles from each other can differ drastically. In addition, our knowledge of emission sources leads us to believe that in some instances the area that may be characterized by a sampling site could be as little as a mile or less from that site. As a result, we believe that it is not appropriate to use the data from one sampling site to characterize the annual average of a location beyond the general area of the sampling site.

Please direct your questions about the appropriate use of the data to AQDWeb at the California Air Resources Board.

Collection and Analysis Methods
Substances - Aromatics & 1,3-Butadiene
Benzene, 1,3-Butadiene, Chlorobenzene, ortho-Dichlorobenzene, para-Dichlorobenzene, Ethyl Benzene, Styrene, Toluene, meta/para-Xylene, and ortho-Xylene
Collection Method:
Xontech 910A/stainless steel canister
Laboratory Instrument:
Gas Chromatograph
Laboratory Detector:
Photo Ionization Detector

Substances - Non-Aromatic VOCs
Carbon Tetrachloride, Chloroform, Ethylene Dibromide, Ethylene Dichloride, Methyl Chloroform, Methylene Chloride, Perchloroethylene, and Trichloroethylene
Collection Method:
Xontech 910A/stainless steel canister
Laboratory Instrument:
Gas Chromatograph
Laboratory Detector:
Electron Capture Detector

Substances - Carbonyls
Acetaldehyde, Formaldehyde, Methyl Ethyl Ketone
Collection Method:
Xontech 920/adsorbent tube
Laboratory Instrument:
High Performance Liquid Chromatography
Laboratory Detector:
Ultraviolet Detector
Quality Assurance Seal See the Ethyl Benzene Quality Assurance Data page for results of laboratory and field audits and information on analytical and sampling method changes.

Please direct your questions about the ethyl benzene data or comments
about this page to AQDWeb at the California Air Resources Board.

This page last revised on July 30, 1997.

Ethyl Benzene Monitoring Sites Toxics Substance Chooser Ethyl Benzene Data Availability
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Statewide Ethyl Benzene Summary
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