THE STEM-II ACID DEPOSITION AND PHOTOCHEMICAL OXIDANT MODEL .2. A DIAGNOSTIC-ANALYSIS OF MESOSCALE ACID DEPOSITION

The MesoSTEM model is used to analyse data obtained during the Mesoscale Acid Deposition Study. The Mesoscale Acid Deposition Study was designed to investigate acid deposition on the urban-suburban scale by sampling well defined frontal storms around the city of Philadelphia using a surface based network. The MesoSTEM model was developed to provide diagnostic analysis of these data. The MesoSTEM model is a combination of the Mesoscale Atmospheric Simulation System (MASS) predictive mesoscale dynamic meteorological model and the STEM-II model, a three-dimensional Eulerian acid deposition model. The MesoSTEM model is described in this paper and applied to the analysis of the 2 May 1985 storm. Elevated sulfate and nitrate deposition is predicted downwind of the major source areas and nitrate deposition exceeds that for sulfate. However, much of the NO(x) and SO(x) emitted on the mesoscale escapes the storm and becomes available for long-range transport and subsequent deposition.