A high-resolution model for estimating the environmental fate of multi-species chemicals: Application to malathion and pentachlorophenol

A high-resolution multi-species (HR-MS) model is presented that assesses the fate of up to four inter-converting chemical species. The current model has a more detailed environmental description than previous multi-species models in order to give a more accurate description of environmental fate. Improvements to the model environment include stratified air, soil and sediment compartments, the inclusion of a vegetation compartment, and the separation of the aerosol phase from the gas phase of the atmosphere. Such detailed environmental descriptions are particularly valuable when chemical heterogeneity is expected within environmental media as occurs with more reactive chemicals or local-scale simulations. The HR-MS model is illustratively applied to two situations for which a detailed environmental description is needed to describe the chemical fate accurately. The first example is the estimation of the atmospheric concentrations of malathion and its degradation product malaoxon following a local-scale application. The second example is a regional simulation of pentachlorophenol, which benefits from the more detailed treatment of ionizing chemical in the atmosphere. In both these cases, the HR-MS model is shown to be in good agreement with observed field data and provides a more accurate description of environmental fate than simpler multi-species models.