Investigation of aerosol optical properties on regional climate forcing and Spatial and temporal distributions of aerosol and ozone associated with the Antarctic polar vortex processes

• Main Author: Im, Jung-Sun
• Other Authors: Dr. V.K. Saxena, Committee Chair, Dr. S.P. Arya, Committee Member, Dr. Y.-L. Lin, Committee Member, Dr. J. DeLuisi, Committee Member
• Language: unknown
• Published: 2002
• Subjects: aerosol; hygroscopic growth factor; black carbon; ozone depletion; polar stratospheric clouds; Antarctic; Mount Mitchell; The Antarctic; Antarc*
• Online Access: http://www.lib.ncsu.edu/resolver/1840.16/4677

Aerosols influence Earth's heat budget both directly by scattering and absorbing sunlight, and indirectly by acting as nuclei for cloud droplets. To reduce the uncertainties of current estimates of aerosol climate forcing, aerosol optical properties relevant to the computation of direct radiative forcing were measured at a regionally representative site near Mount Mitchell, North Carolina. On the basis of these measurements and model calculations, we have studied (1) the effects of relative humidity (RH) on aerosol optical properties and direct aerosol radiative forcing and (2) the influence of long-range transport on black carbon (BC) concentrations, its seasonal and weekly patterns, and the effects of BC on the regional climate of the southeastern US. The light scattering of aerosol is strongly dependent on RH at which it is measured, due to hygroscopic growth nature of most atmospheric aerosols. In this study, the hygroscopic growth factor (ratio of total scattering coefficient at RH=80% to that at RH=30%) was calculated to be almost constant value of 1.60 +/- 0.01 for polluted, marine, and continental air masses. In addition, it was found that as the RH increased from 30% to 80%, the backscatter fraction decreased by 23%. The patterns of direct radiative climate forcing by aerosols for various values of RH were similar for the three air masses, but the magnitudes of the forcing were larger for polluted air masses than for marine and continental air masses by a factor of nearly 2 due to higher sulfate concentration in polluted air masses. The averaged forcing for all the observed ambient RHs was -2.9 W m^(-2) (the negative forcing of -3.2 by aerosol scattering plus the positive forcing of +0.3 by aerosol absorption) for polluted air masses, -1.4 W m^(-2) (-1.5 plus +0.1) for marine air masses, and -1.5 W m^(-2) (-1.6 plus +0.1) for continental air masses. The BC mass concentration of the southeastern US showed the highest average concentration in polluted air masses and the lowest in marine air masses. During ...