To evaluate the sources, sinks, chemistry, and transport of organic compounds in the troposphere, one must define the distribution of several manmade and natural compounds between the gaseous and condensed phases. Currently there is little quantitative information available about the phase distribution of semivolatile organic compounds present in the atmosphere. The vapor/particle distribution of compounds has an important influence on their atmospheric lifetimes and the chemical reactions they undergo. Direct measurement of the phase distribution of semivolatile compounds in the atmosphere is a challenging analytical problem that requires additional research. In this project the distribution of semivolatile organic compounds (SOC) between the vapor phase and atmospheric particulate matter is to be determined through field and laboratory experiments. The objectives of this study are to: (1) determine the partitioning behavior of different classes of semi-volatile compounds; (2) test the hypothesis that the SOC liquid-phase vapor pressure largely controls adsorption to atmospheric particular matter; (3) investigate the influence of SOC molecular shape on adsorption; and (4) distinguish "exchangeable" and "non-exchangeable" SOC on particles. High volume air samples are to be collected in summer and winter using a glass fiber filter backed up by an adsorbent trap. Samples will be analyzed by chromatographic procedures. Vapor-particle partition coefficients are to be calculated from the SOC concentrations on the adsorbent trap and filter and the total suspended particle concentration. Field and laboratory estimates of heats of adsorption will be made. Estimates of the "non-exchangeable" fraction of SOC will be made by analyzing filters after stripping with SOC-free air.
