Platform Presentation
Derivation of SO2 – SO42- transformation and deposition rate Coefficients over the
Eastern US using a Semi-Empirical Approach
Bret A. Schichtel
Rudolf Husar
Washington University
Center for Air Pollution Impact
and Trend Analysis
St. Louis, MO, 63130-4899
314-935-6099
314-935-6145
Bret@mecf.wustl.edu
Washington University
Center for Air Pollution Impact
Impact and Trend Analysis
St. Louis, MO, 63130-4899
314-935-6099
314-935-6145
Rhusar@mecf.wustl.edu
Abstract
A semi-empirical approach is described which allows for the derivation of a consistent set of
chemical and physical rate coefficient equations. The main thrust of this approach is to make
maximum use of existing meteorological, emission, and receptor data in conjunction with a
physico-chemical model to derive the best set of rate coefficient equations. Assuming the
pollutant transport and emission rates are known, only the transformation and removal rates are
unknown. These coefficients are then determined via a tuning process to obtain the best fit
between simulated and measured ambient and wet deposition data allowing the transformation
and removal rates to vary within physically reasonable limits. The spatial and temporal
variability of the rate coefficients are modeled by making them dependent upon meteorological,
and chemical variables. It is hypothesized that given sufficient quality and quantity of data, it
will be possible to identify a unique set of rate parameters, thereby properly simulating the
physical/chemical processes.
This approach is applied in the Eastern US during 1992 to derive SO2 to SO42- transformation
and SO2 and SO42- dry and wet deposition rate coefficients. A Monte Carlo long range transport
model is used to simulate the ambient SO2 and SO42- and the total wet deposited sulfur which is
compared to measured data. The resulting best fit spatial and seasonal patterns of the rate
coefficients are presented as well as the simulated SO2 and SO42- ambient concentrations and wet
deposition rates.