Optical measurements of aerosol size distributions in Great Smoky Mountains National Park: dry aerosol characterization

Aerosol size distributions were measured during the summertime 1995 Southeastern Aerosol and Visibility Study (SEAVS) in Great Smoky Mountains National Park using an Active Scattering Aerosol Spectrometer (ASASP-X) optical particle counter. We present an overview of the experimental method, our data inversion technique, timelines of the size distribution parameters, and calculations of dry accumulation mode aerosol density and refractive index. Aerosol size distributions were recorded during daylight hours for aerosol in the size range 0.1 < Dp < 2.5 microns. The particle refractive index used for the data inversion was calculated with the partial molar refractive index approach using 12-hr measured aerosol chemical composition. Aerosol accumulation mode volume concentrations ranging from 1 to 26 micron 3 cm-3 were observed, with an average of 7 +/- 5 micron 3 cm-3. The study average dry accumulation mode geometric volume median diameter was 0.27 +/- 0.03 micron, and the mean geometric standard deviation was 1.45 +/- 0.06. Using an internally mixed aerosol model, and assuming chemical homogeneity across the measured particle distribution, an average accumulation mode dry sulfate ion mass scattering efficiency of 3.8 +/- 0.6 m2 g-1 was calculated.