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 dispersion in the environment. A detailed one-dimensional nonisothermal model was developed to accommodate the impact of outdoors- dynamic behavior on the fate of surface-applied pesticides. The model includes the effects of temporal changes in weather conditions on the distribution of soil temperature and moisture in the soil profile and the latter two parameters role on the volatilization and persistence of the applied pesticides. The model is solved numerically by the finite differences method. The performance of the numerical model was tested in two ways: by comparing its results with an analytic solution for a simplified case and by comparing predicted volatilization rates and soil residues of three pesticides (lindane, dieldrin, and trifluralin) with measured data. A good agreement was found between measured and simulated results. Hence, the model might be a useful tool for designing pesticide application and to explore their behavior under various soil and meteorological conditions. A sensitivity analysis of the model showed that volatilization of volatile pesticides such as lindane is most sensitive to the estimation of vapor pressure as a function of temperature, less sensible to adsorption coefficient, and insensitive to water solubility (within the range of published data) and decomposition coefficient.