DYNAMIC AEROSOL MODEL - URBAN INDUSTRIAL AEROSOL/

Aerosol properties vary with the aerosol type, loading, or atmospheric conditions. We found that a dynamical aerosol model that describes th e variability of aerosol properties as a function of aerosol optical t hickness can address this issue. Ambient urban/industrial aerosol is m easured in the mid-Atlantic region of the United States during the sum mer of 1993 by automatic Sun/sky radiometers. The volume size distribu tions inverted from the measured sky radiance represent the entire col umn of ambient particles. These data depict an aerosol regime in which accumulation mode particle size and volume increases as optical thick ness increases. A dynamical aerosol model that is a function of optica l thickness is constructed by fitting lognormal functions to the volum e size distributions. It accounts for 60% of the variance in the aeros ol accumulation mode size distributions. The accumulation mode is repr esented as a linear combination of two modes: one with volume modal ra dius 0.11 mu m and the other with modal radius 0.21 mu m. The model is shown to recreate the correct independently measured sky radiance in the backscattering direction and to predict the phase function within model uncertainties of data collected in subsequent years. The model i s shown to be unbiased with respect to the time of day and to reproduc e the wavelength dependence measured by the independent Sun measuremen ts. The dynamic model has substantially different properties than a '' static'' continental model except for the limited optical thickness ra nge of 0.0-0.25.