水溶性大気エアロゾルによる地球温暖化抑制効果の評価

抄録

To estimate indirect radiative forcing of water soluble aerosols, we measured critical supersaturations of dicarboxylic acid aerosols which are major components of water soluble organic aerosols in laboratory experiments, and then calculated albedo of marine stratiform cloud and downward net flux at tropopause within stratiform cloud area under clean and polluted (concentrations of water soluble aerosols enhanced) conditions. Experimental results indicated that critical supersaturations of oxalate, malic acid and phtharic acid were found to be comparable to that of sulfate aerosol which is easily activated to cloud droplets at naturally occuring supersaturations in the atmosphere, in contrast to high critical supersaturation of adipic acid. Caluculations indicated that at polluted condition cloud-top albedo was enhanced and downward net flux at tropopause decreased by 40-60W/m² from clean condition. Although these estimates are confined within polluted and stratus cloud aera, the indirect forcing is so high compared with global averaged radiative forcing (+2.5W/m²) of greenhouse gases, that it is possible that the forcing offsets the greenhouse effect to a large extent.