Factors in geotropospheric particle-gas transport of semivolatile organic compounds
Semivolatile organic compounds (SVOCs) can exist in solid, liquid, or gas phases under ambient environmental conditions. The geotropospheric transport of SVOCs varies according to the particle type. Two classes of SVOCs and two types of particles were analyzed to determine possible transport mechanisms to the troposphere: dicarboximide compounds moving from a soil matrix to the troposphere and polycyclic aromatic hydrocarbons (PAHs) from airborne particles to the troposphere. Both classes of compounds are considered to be SVOCs, since their vapor pressures under most environmental conditions range between 10 -2 to 10-5 kP. The dicarboximide results were obtained from a laboratory chamber designed and used to determine the headspace flux of the dicarboximide fungicide, vinclozolin [3-(3,5-dichlorophenyl)-5-methyl-5- vinyl-oxzoli-dine-2,4-dione], and its three principal degradation products from chamber surfaces, sand, and sterilized and nonsterile North Carolina Piedmont aquic hapludult soils following dicarboximide applications. The PAH results were gathered from a high-volume air-sampling system used to measure particle and gas phase concentrations of SVOCs in the plume downwind from the World Trade Center fire. The comparison indicates that SVOC transport from the soil matrix can be influenced by the type and size of particles, their chemical composition, pH, oxygen, and microbial action. The study indicates that in the troposphere, molecular weight and structure are the principal factors affecting the geotropospheric flux of SVOCs from the particle to gas phase. Although experimentally determined equilibrium constants are more robust predictors of phase distribution in the troposphere (r2 = 0.81), published Henry's Law and vapor pressure constants also relate to particle-gas phase distribution (r2 = 0.73 and 0.72, respectively).
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