|dc.description.abstract||The optical effects of atmospheric aerosol would influence solar radiation received and reflected by earth, therefore, the assessment of atmospheric aerosol optical properties on global warming is an important project. Lulin Atmosphere Background Station (LABS) at Mt. Lulin (2,862 m a.s.l.) in central Taiwan aims to observe the East Asian background atmospheric aerosol properties. Although Mt. Lulin is an elevated background station, it would still be affected by the Asian continental pollution and Indochina biomass burning through long-range transport. The purpose of this study is to analyze the impact of aerosol size distribution and aerosol chemical composition on the effects of changes in aerosol optical properties and use different models to estimate aerosol direct radiative effects for different air masses arriving at Mt. Lulin from October 2008 to April 2010.
The air masses were classified into four types as air masses from source area of biomass burning (BB), source area of biomass burning during non-BB period (SNBB), free atmosphere (FT), and Anthropogenic sources (Anthropogenic). The BB type of air masses bring high concentrations of sulfate aerosol and carbon content of aerosol through the long-range transport. PM10 aerosol scattering coefficient and absorption coefficient could reach 127.2 Mm-1 and 24.6 Mm-1 respectively. For SNBB, aerosol scattering coefficient and absorption coefficient were 23.2 Mm-1 and 3.1 Mm-1 respectively. The FT type represented the East Asian clean background atmosphere properties. For FT, aerosol scattering coefficient and absorption coefficient were 25.0 Mm-1 and 4.2 Mm-1, respectively. For Anthropogenic type, air masses lower atmosphere of Asian continent and valley-breeze driven local pollution caused 15.1 Mm-1 and 1.6 Mm-1 for aerosol scattering coefficient and absorption coefficient, respectively. The direct radiative effects for BB, SNBB, FT, and Anthropogenic were -0.25, -0.22, -0.17, -0.60 W m-2, respectively. Lower single scattering albedo and higher aerosol optical depth would reduce the cooling effect of direct solar radiation during the biomass burning period. In addition, taking into account the aerosol water content affected by aerosol chemical compositions, the resulting aerosol scattering effect would increase by 30.7%, 2.5%, 63.8%, 37.7% for BB, SNBB, FT, and Anthropogenic, respectively.