There is now a general awareness that the chemical compounds present in the atmosphere may pose problems to human health through exposure to them in the air we breathe, and in 1984 the California Legislature enacted AB 1807 to mandate the identification and control of toxic air contaminants in California. California's air toxics program is a two-step process which involves the identification of a toxic air contaminant, followed by the implementation of any necessary and appropriate control measures. An important element of the Air Resources Board's exposure assessment for potential toxic air contaminants concerns the atmospheric behavior of chemicals emitted into the troposphere. Specifically, for a given chemical it is necessary to have quantitative information concerning the nature and rate of its removal from the atmosphere and, if these removal processes are chemical, the products formed from these atmospheric reactions. Furthermore, since a number of potential toxic air contaminants are formed in situ in the atmosphere, a knowledge of these formation pathways together with as assessment of the relative balance between direct emission and in situ atmospheric formation is necessary. To provide the necessary information concerning the atmospheric chemistry and ambient concentrations of a series of potential toxic air contaminants, the following research tasks were conducted during this program.
A. Literature Review of the Atmospheric Chemistry of Potential Toxic Air Contaminants --
Literature reviews of the atmospheric chemistry of three potential toxic air contaminants was carried out (one of which was a class of related chemicals), and the reviews submitted to the ARB for use in its exposure documents. The chemical compounds whose atmospheric chemistry were reviewed were chosen by the ARB staff based on their priority list. The chemicals (or group of chemicals) which were dealt with in this program were:
For each chemical, or group of chemicals, the available literature data concerning the potentially important tropospheric removal processes were evaluated. Since chemical compounds emitted into the troposphere can be present solely in the gas phase, solely in the particle phase, or be distributed between the gas- and particle-phases, the phase distribution and the physical and chemical removal processes were considered.
In addition to these specific chemicals (or class of chemicals), the atmospheric lifetimes of a series of potential toxic air chemicals and the possible in situ atmospheric formation of toxic compounds were dealt with in report format.
B. Investigation of the Mutagenicity of HPLC-Separated Products of the Simulated Atmospheric Reactions of Gasoline and Terpenes --
Using a micro suspension modification to the standard plate incorporation assay in conjunction with HPLC separation of extracts of collected reaction samples (Arey et al., 1992), we have investigated the formation of mutagenic products of low-volatility from the simulated atmospheric reactions of vaporized gasolines, designed to mimic the emissions from gasoline-fueled vehicles, and of a synthetic mixture of terpenes designed to simulate hydrocarbon emissions from vegetation. The data obtained showed insignificant formation of mutagenic compounds over those formed in control experiments in the absence of the vaporized gasolines or a mixture of terpenes (Table 1) and indicate that, with the sample collection and bioassay methods used, these anthropogenic and biogenic emissions are not the major sources of mutagenic compounds observed in both the gas- and particle-phase in the atmosphere in southern California (Harger et al., 1992).
For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753
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