A combined soil atmosphere model for evaluating the fate of surface-applied pesticides. 1. Model development and verification

Volatilization of soil-applied pesticides to the atmosphere and their vapor transport in the air are principal processes leading to their widespread d ispersion in the environment. A detailed one-dimensional nonisothermal mode l was developed to accommodate the impact of outdoors-dynamic behavior on t he fate of surface-applied pesticides. The model includes the effects of te mporal changes in weather conditions on the distribution of soil temperatur e and moisture in the soil profile and the latter two parameters' role on t he volatilization and persistence of the applied pesticides. The model is s olved numerically by the finite differences method. The performance of the numerical model was tested in two ways: by comparing its results with an an alytic solution for a simplified case and by comparing predicted volatiliza tion rates and soil residues of three pesticides (lindane, dieldrin, and tr ifluralin) with measured data. A good agreement was found between measured and simulated results. Hence, the model might be a useful tool for designin g pesticide application and to explore their behavior under various soil an d meteorological conditions. A sensitivity analysis of the model showed tha t volatilization of volatile pesticides such as lindane is most sensitive t o the estimation of vapor pressure as a function of temperature, less sensi ble to adsorption coefficient, and insensitive to water solubility (within the range of published data) and decomposition coefficient.