Temperature Dependence of Atmospheric Concentrations of Semivolatile Organic Compounds

Abstract

Reported data on the temperature dependence of atmospheric concentrations of semivolatile organic compounds (SOCs) are compiled and expressed as linear regressions of the logarithm of the partial pressure in air versus reciprocal temperature: ln pA = m/T + b. Two simple models are introduced to explain the dependence of these air concentrations on temperature. The first assumes equilibrium between the atmosphere and the earth's surface. In the second, air concentrations are established as a result of chemical inflow and outflow in advected air and reversible exchange with a soil or water surface. The model equations are rearranged to express the partial pressure of the chemical as a function of temperature. On the basis of these models, it is shown that only under selected circumstances, namely, if surface contamination is high and atmospheric background concentration low, does the slope m of the ln p vs 1/T relationship reflect the thermodynamics of air−surface partitioning. Generally, however, m is a m...