Two Years of Aerosol Properties and Direct Radiative Effects Measured at a Representative Southeastern U.S. Site

The southeastern U.S. is one of only a small number of regions worldwide which has not exhibited warming over the past century. Recent studies (Goldstein et al., 2009) show that negative aerosol direct radiative effects are consistent with a warm-season regional cooling effect linked to secondary organic aerosol loading. Two years of NOAA-ESRL supported aerosol measurements made at the Appalachian Atmospheric Interdisciplinary Research (AppalAIR) facility at Appalachian State University (36.214 N, 81.693 W, 1080m ASL) are presented, along with satellite-based measurements (MODIS-Aqua) of aerosol optical depth, cloud fraction, and surface albedo. Aerosol optical property statistics are placed in the context of those made at other U.S. ESRL stations. Direct aerosol radiative effect calculations reveal high seasonal variability, with negative broadband summer forcing values of ~ -10 W/m2 (-4W/m2) when actual (standard) cloud fraction, surface albedo, and single-scattering albedo values are used. Hierarchical cluster analyses were used to broadly classify the aerosol source types that influence the Southeastern U.S. aerosol optical properties. Recently-added aerosol hygroscopic growth measurements (a sample of which are presented) will facilitate improved aerosol source type classification and aerosol light scattering humidity dependence scaling of direct radiative effect calculations.