The Challenge of Representing Sulfur Chemistry in the University of Hawaii Vog Model

Abstract:

Sulfur dioxide oxidizes to sulfate aerosol through numerous chemical pathways. There are gas-phase and aqueous-phase pathways, pathways that involve metals, and photolytic pathways. Considering all pathways in an atmospheric chemistry model is computationally expensive and unnecessary given certain pathway dependencies and limitations. Several sulfur chemistry parameterizations have been realized in the UH Vog model to convert sulfur dioxide to sulfate. These range in complexity from constant conversion rates to parameterizations that consider the dominant gas and aqueous-phase pathways. Past research has found that aqueous-phase pathways are the most dominant when cloud water is present, and conversion rates are higher in non-precipitating clouds than in precipitating clouds. This suggests that the input of a representative cloud field should produce improved sulfur dioxide and sulfate concentration forecasts. A liquid water content field from the Weather Research and Forecasting model is input into the existing sulfur chemistry module in the UH Vog model. Forecasts of sulfur dioxide and sulfate concentrations around the island of Hawaii are compared against in-situ observations, and model results using more simplified sulfur conversion schemes.