The Use of Model-Derived and Observed Precipitation in Long-Term Sulfur Concentration and Deposition Modeling


Glenn D. Rolph, Roland R. Draxler, and Rosa G. de Pena


Atmospheric Environment, Vol. 27A, No. 13, pp. 2017-2037, 1993


Abstract - As a continuation of a previous study for the winter of 1987, the Hybrid Single-Particle Lagrangian Integrated Trajectory Model (HY-SPLIT) with Atmospheric Chemistry Including Deposition (ACID) is run for each season of 1989. Two simulations for each season are run; one using forecast precipitation data from the Nested Grid Model (NGM), and the other using gridded measured precipitation data from observation stations of the National Weather Service (NWS). Modeled seasonal and annual sulfur dioxide (SO2) and sulfate (SO4) concentrations in air and SO4 wet deposition over the eastern United States are compared with observed values. The model does well predicting the seasonal and annual spatial pattern of SO2 and SO4 concentrations in air, and SO4 wet deposition when using NWS precipitation. In all but the spring season, the model tends to over-predict SO2 concentration in air, but is well within a factor of 2; mean relative errors (MREs) are less than 20%. SO4 concentration in air is slightly over-predicted during the fall and winter and under-predicted during the spring and summer; MREs are less than 12%.  SO4 wet deposition is under-predicted for all seasons; MREs are less than 30%. The model-predicted and measured values of the previous study are well within the scatter of the data in this study. Using NGM precipitation does not significantly affect the results for the 1989 study period. Although the NGM does over-predict the precipitation during the summer months along the Gulf states, thereby increasing slightly the SO4 wet deposition and further under-predicting the modeled SO4 air concentration, the differences are small enough to suggest that the use of model-forecast precipitation can be an adequate substitute for precipitation observations over a seasonal or longer period.



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