The Microcosmic Properties Of East Asian Aerosols And Influences Of Surface Heterogeneous Reaction

The estimation of radiative forcing to atmospheric aerosols is considered more complex and larger uncertainties than greenhouse gases. This situation is mainly due to the complexity of aerosol radiative forcing mechanism and the lack of detailed information of aerosol properties, such as size distribution, chemical composition, atmospheric transport and removal processes, etc. East Asia is one of the major sources of wind-blown dust in the world, however, up to date the studies on the dust aerosol from this region are far from completeness. The objective of this study is to characterize and compare the physical, chemical and optical properties of aerosols emitted from East Asia in different seasons, especially in dust events. Moreover, the optical properties of aging mineral particles which transported from source areas to remote downwind regions e.g. ocean etc., because of SO₂ uptake and thus heterogeneous reaction on the surfaces of dust and their mixture with sea salt, were simulated in a laboratory facility.The content mainly includes 5 parts, as following:Partâ… . The physical, chemical and optical characteristics of aerosols in East Asia were summarized and analyzed through the published data of previous researches. PM_2.5, water-soluble ion, organic compounds (such as PAHs, OC and EC) and chemical element concentrations in northern China were higher than southern China, Korea and Japan, commonly higher in winter than summer. PM_2.5, PAHs, OC and EC concentrations in polluted regions were larger than clean and coastal regions, and the Na⁺, SO₄^2-, Mg²⁺ and Cl^- concentrations of coastal regions showed a higher value. Higher AOT and a occurred in polluted regions but clean regions.Partâ…¡. The physical, chemical and optical properties of dust aerosols were analyzed by the published data of former researches. The concentrations of mass, Ca²⁺, Na⁺ and element components showed a decreasing trend from west to east in East Asia. The concentrations of SO₄^2-,NO₃^- and Cl^- also showed a higher value in both polluted and coastal regions. Higher AOT and SSA occurred in dust source regions other than downwind regions, associated with lowerα.Partâ…¢. A comparison of dust properties was performed between Chinese continent as source regions and Korea, Japan as downwind regions during dust events. Higher AOT appeared at Chinese sites than Korean and Japanese sites associated with lowerα. The value ofαdecreased with increasing AOTs, and decreased to zero or negative when heavy dust events occurred especially in source regions. The aerosol volume size distributions showed a tri-modal structure, one accumulation mode with median radius 0.07μm and two coarse modes with radii 1.3, 2.9-3.8μm in source regions, and one accumulation mode with radius 0.09μm and two coarse modes with radii 1.3-2.2μm and 2.9-3.8μm in downwind regions. In view of climate, SSA at 440, 670, 870 and 1020 nm was about 0.95 in source regions of China, and 0.92 in downwind regions of Korea and 0.95 of Japan. The real parts of refractive index were 1.51 in China, and 1.45 in Korea and 1.39 in Japan, but the imaginary parts had values of 0.0015-0.0044 in source regions and 0.0018-0.0052 in downwind regions. The asymmetry factors were about 0.67 over source and downwind regions.Partâ…£. The climatology of aerosol microphysical properties in northern China was examined from 2001 to 2005. High AOTs occurred at dust source regions in spring or at serious polluted regions in summer. The aerosol size distributions showed a tri-modal structure, one accumulation mode with radius 0.07-0.15μm and two coarse modes with radii 1.3-1.7 and 3.8-5.0μm. SSA showed a low sensitivity to AOTs at the four wavelengths of 440, 670, 870 and 1020 nm, about 0.94 for fine particles (r<0.6μm) and 0.85 for coarse particles (r>0.6μm) in winter and spring, and 0.86 for fine particles and 0.73 for coarse particles in summer and autumn. The asymmetry factor was 0.58 for fine particles and 0.79 for coarse particles in all seasons. The scattering phase functions varied with scattering angles, with the minimum occurred at 120°.Partâ…¤. The particle optical property variation for heterogeneous reaction of SO₂ on iron oxides and hematite-NaCl mixture was investigated using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). After heterogeneous reactions, the absorption and backward scattering coefficients of hematite are higher than those of other iron oxides, and varied with reaction temperature. The absorption and backward scattering coefficients are commonly higher in hematite mixture with 50-70% NaCl than pure hematite and other mixtures, and larger magnitudes at high SO₂ concentration than low SO₂ concentration. Under reactions of 1-10% O₂ concentrations, the absorption and backward scattering coefficients are in a higher increase than those of 20-30% O₂ concentrations.