Predicting pesticide volatilization from soils

Due to concerns about public health and environmental contamination, there has been great interest in improving our understanding of the processes and mechanisms that affect pesticide emissions from fields. For many situations, predicting pesticide volatilization has been limited to simple situations that often neglect important environmental conditions such as changes in ambient temperature and/or the effect of micrometeorological conditions. Recent research has shown that changes in ambient temperature can strongly affect methyl bromide (Me Br) volatilization under field conditions. Little research has been conducted that couples atmospheric processes to the volatilization of pesticides from soils. A field study was conducted to measure the volatilization of methyl bromide from a 3.5 ha field. Four methods were used to obtain the volatilization rate as a function of time. A one-dimensional numerical model was developed and used to simulate the fate and transport of methyl bromide from the fumigated field. The numerical simulation simultaneously solves water, heat, and solute transport equations including chemical transport in the vapor phase. Three volatilization boundary conditions were used to assess their accuracy in predicting the volatilization rates. The first two boundary conditions follow stagnant boundary layer theory and use no atmospheric information. For these boundary conditions, one assumes isothermal conditions and the other assumes temperature-dependent conditions. The third boundary condition couples soil and atmospheric processes and was found to provide an accurate and credible simulation of the instantaneous volatilization rates compared to