The simulation of dry deposition is an essential component of regional- and large-scale atmospheric chemistry models for estimating the concentrations and fates of many trace chemicals. The deposition velocity is typically generated with a specialized dry deposition module that can be incorporated into atmospheric chemistry models; the product of the deposition velocity and the simulated ambient chemical concentration yields estimates of the vertical mass flux density at the surface. Over extended areas and multiseasonal periods of time, however, an adequately detailed depiction of the variations in vegetative and soil moisture conditions that strongly affect deposition velocities is difficult to achieve. The common practice of using of fairly broad land use and seasonal categories often leads to unrealistic estimates of the deposition velocity for relatively small areas or over short periods of time. Here, previously developed methods to use surface spectral reflectances remotely sensed by environmental satellites are employed to improve parameterization of surface processes and applied to the United States. With this new approach, results are improved somewhat in comparison to a previous version of the dry deposition module that relied on land use and seasonal categories. The effects of drought conditions during the summer now more properly reduce the calculated deposition velocities of sulfur dioxide, ozone, and other substances whose uptake rate is controlled mostly by plant stomatal resistance. The use of satellite data eliminates the artificial abrupt change in deposition velocities seen at transitional periods between seasonal categories. In addition, more realistic values of deposition velocities are found for areas with low rainfall or irrigated areas
Symposium on Interdisciplinary Issues in Atmospheric Chemistry