Adsorption equilibrium of organic vapors on the surface of minerals, salts, water, snow and soot under ambient conditions
Goss, K.-U.
EAWAG/ETH, Switzerland

The fate of organic pollutants in the atmosphere is strongly influenced by their tendency to sorb to ambient aerosols. Besides absorption in the organic aerosol fraction, adsorption to various aerosol surfaces may also play role. Here, this adsorption process is examined in greater detail. Roughly 1500 equilibrium adsorption constants have been measured for a diverse set of organic compounds (40-60) on twelve different surfaces at various relative humidities and temperatures. The traditional correlation of the experimental data with the saturated liquid vapor pressure or octanol/air partition constant of the respective compounds is not suitable for explaining the observed variability. In contrast, a simple approach that considers van-der-Waals interactions and H-Bonding between the compounds and the surfaces allows a good mechanistic understanding of the factors governing the adsorption equilibrium. This approach also allows us to derive a quantitative prediction method for the adsorption equilibrium as a function of the type of surface, compound, temperature and relative humidity.

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