Dr Stephen E Schwartz

Our work examines the chemistry of Atmospheric Energy-Related pollutants. The principal substances of our attention have been sulfur and nitrogen oxides emitted into the troposphere as byproducts of fossil fuel combustion, and their oxidation products, i.e., sulfuric acid and nitric acid and the salts of these species. These substances are of concern from the perspective of human health, acid deposition, visibility reduction, and radiative forcing of climate. Because these materials are introduced into the atmosphere in association with energy-related activities, the environmental consequences of these emissions are of concern to the Department of Energy, and much of the support for my research comes from the Environmental Sciences Division within the Office of Biological and Environmental Research of the Department of energy. Much of our recent research has focused on the radiative influence of anthropogenic aerosols on climate. Aerosols affect the earth's radiation budget directly, by scattering incoming shortwave (solar) radiation and thereby enhancing the earth's albedo, and indirectly, by modifying the microphysical properties and reflectivity of clouds. We and others have presented a body of work over the past decade that indicates that anthropogenic aerosols are exerting an influence on climate change that is comparable (but of opposite sign) to the anthropogenic greenhouse effect. However the magnitude of these aerosol influences is quite uncertain in comparison to that of longwave (thermal infrared) radiative forcing by incremental concentrations of greenhouse gases (mainly carbon dioxide and to lesser extent methane, nitrous oxide, and others) resulting from industrial activity. Reducing the uncertainty in aerosol forcing will require a major effort both in characterizing the present distribution and properties of aerosols and in developing understanding required to represent the processes controlling loading and properties of tropospheric aerosols in numerical models. Model-based descriptions of aerosol forcing need to be incorporated into climate models in order to represent this forcing not just for the present climate but also retrospectively over the industrial period and prospectively for various scenarios of future emissions. Much of our research is directed to developing and evaluating numerical models for representing the geographical distribution of loading of atmospheric aerosols. Our approach has been to use observationally derived meteorological data to drive our models, because the temporal and spatial variation in aerosol loading is governed to great extent by meteorological variability. Meaningful evaluation of the model by comparison with observations thus requires this approach. Much of this work is conducted within the Department of Energy's Atmospheric Chemistry Program (ACP).