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

Aerosol size distributions were measured during the summertime 1995 Southea stern Aerosol and Visibility Study (SEAVS) in Great Smoky Mountains Nationa l Park using an Active Scattering Aerosol Spectrometer (ASASP-X) optical pa rticle counter. We present an overview of the experimental method, our data inversion technique, timelines of the size distribution parameters, and ca lculations of dry accumulation mode aerosol density and refractive index. A erosol size distributions were recorded during daylight hours for aerosol i n the size range 0.1 < Dp < 2.5 mu m. The particle refractive index used fo r the data inversion was calculated with the partial molar refractive index approach using 12-hr measured aerosol chemical composition. Aerosol accumu lation mode volume concentrations ranging from 1 to 26 mu m(3) cm(-3) were observed, with an average of 7 +/- 5 mu m(3) cm(-3). The study average dry accumulation mode geometric volume median diameter was 0.27 +/- 0.03 mu m, and the mean geometric standard deviation was 1.45 +/- 0.06. Using an inter nally mixed aerosol model, and assuming chemical homogeneity across the mea sured particle distribution, an average accumulation mode dry sulfate ion m ass scattering efficiency of 3.8 +/- 0.6 m(2) g(-1) was calculated.