Evaluating pesticide volatilization under field conditions is a critical aspect of understanding the fate, transport, and exposure risk associated with agricultural applications of these compounds. Three methods are currently recommended by EPA for the purpose of estimating volatile flux of pesticides from treated fields: the indirect method, the aerodynamic (AD) method, and the integrated horizontal flux (IHF) method. The objective of this talk is to present the basis for choosing an appropriate method, including requirements for each method to be valid and necessary data inputs (such as those related to surface roughness and fetch). The indirect method is based on back calculating the flux that best simulates observed air concentrations off-field, and makes use of the EPA-supported air dispersion modeling system, AERMOD. The AD method uses the Thornthwaite-Holzman equations (developed to estimate evaporation) and is based on a logarithmic wind profile. The IHF method is based on mass balance principles and requires no atmospheric stability corrections. Practical guidance for parameterization of semi-volatile compounds is offered, and the theoretical as well as practical limitations of each method discussed. Uncertainty propagation from the flux estimation methods to subsequent modeling of downwind deposition using AERMOD is also evaluated. By examining methods currently used in regulatory assessments for flux estimation, the goal is to identify areas in which improvements can be made or new tools developed to better understand the mechanisms driving volatilization from plant and soil surfaces.<br/>

Comparison of three regulatory methods for estimating volatile flux of pesticides from treated fields

256th National Meeting (2018)

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