An aerosol dynamic model including such processes of nucleation, condensation/evaporation, coagulation, sedimentation, hygroscopic growth and dry and wet deposition coupled with the gas-phase chemistry of the California Institute of Technology model and the aqueous-phase chemistry of the Regional Acid Deposition Model together with meteorological outputs of the MM5 model in a grid of 60 x 60 km(2) has been used to estimate anthropogenic aerosols in East Asia (95-145E, 20-50N) for the period of 2-30 April 2001 in the ACE-Asia experimental period. During this period an Asian dust event has been observed from 10 to 13 and 24-26 April in the Korean peninsula. The estimated anthropogenic aerosols excluding the Asian dust are implemented to estimate radiative forcing at the surface, at the top of atmosphere (TOA) and atmospheric aerosol absorption in East Asia using the National Center for Atmospheric Research column radiation model of the community climate model. The results indicate that the area averaged column integrated anthropogenic aerosol concentration in East Asia is estimated to be about 20 mg m(-2), of which 46%, 29%, 20%, 4% and 1% are contributed by mixed type, inorganic (IOC), sea salt, organic carbon and black carbon aerosol, respectively. The daytime area mean direct shortwave radiative forcing at the surface is found to be about -5.9 W m(-2), of which IOC and the mixed type aerosol contribute about 95% whereas that at TOA is about -4.1 W m(-2), of which the IOC and the mixed type aerosol contribute more than 90%. Consequently the area mean atmospheric absorption due to anthropogenic aerosol layer in East Asia is about 1.8 W m(-2). The result clearly confirms the existence of a cooling effect (negative forcing) due to the direct effect of anthropogenic aerosols at the surface and TOA in East Asia. However, the atmosphere of the troposphere above the ground is slightly heated due to absorbing aerosol layers that are composed of black carbon and the mixed type aerosol. (C) 2004 Elsevier Ltd. All rights reserved.

In an effort to reduce uncertainties in the quantification of aerosol direct radiative forcing (ADRF) in the southeastern United States (US), a field column experiment was conducted to measure aerosol radiative properties and effects at Mt. Mitchell, North Carolina, and at an adjacent valley site. The experimental period was from June 1995 to mid-December 1995. The aerosol optical properties (single scattering albedo and asymmetry factor) needed to compute ADRF were obtained on the basis of a procedure involving a Mie code and a radiative transfer code in conjunction with the retrieved aerosol size distribution, aerosol optical depth, and diffuse-to-direct solar irradiance ratio. The regional values of ADRF at the surface and top of atmosphere (TOA), and atmospheric aerosol absorption are derived using the obtained aerosol optical properties as inputs to the column radiation model (CRM) of the community climate model (CCM3). The cloud-free instantaneous TOA ADRFs for highly polluted (HP), marine (M) and continental (C) air masses range from 20.3 to -24.8, 1.3 to -10.4, and 1.9 to -13.4 W m(-2), respectively. The mean cloud-free 24-h ADRFs at the TOA (at the surface) for HP, M, and C air masses are estimated to be -8 +/-4 (-33 +/- 16), -7 +/- 4 (-13 +/- 8), and -0.14 +/- 0.05 (-8 +/- 3) W m(-2), respectively. On the assumption that the fractional coverage of clouds is 0.61, the annual mean ADRFs at the TOA and the surface are -2 +/- 1, and -7 +/- 2 W m(-2), respectively. This also implies that aerosols currently heat the atmosphere over the southeastern US by 5 +/- 3 W m(-2) on annual timescales due to the aerosol absorption in the troposphere. (C) 2001 Elsevier Science Ltd. All rights reserved.