中国科学院地球环境研究所机构知识库

Ground and satellite remote sensing measurements have revealed heavy aerosol loading in China; however, aerosol optical properties and direct radiative forcing in Northeast China - important in climate modeling and remote sensing - have not been widely studied. We studied four years of continuous sun photometer measurements at Tongyu, a typical semi-arid rural site in Northeast China, to better understand column-integrated aerosol optical properties and direct radiative forcing. The annual average aerosol optical depth (AOD) at 500 nm was 0.20 +/- 0.26; the Angstrom exponent (AE) between 440 and 870 nm was 137 +/- 0.64; and the single scattering albedo (SSA) at 440 nm was 0.91 +/- 0.05. The AOD at this rural site was a quarter of that observed in the polluted North China Plain and Yangtze River Delta regions. Anthropogenic fine-mode particles were the dominant contributor to AOD. The AOD and AE showed generally opposite seasonal variation patterns. Relatively higher AOD values in summer (0.26 +/- 0.27) and spring (0.24 +/- 0.30) were likely related to long-range transportation of anthropogenic aerosols from southern industrial regions in summer, and the increased contribution of dust events in spring. The minimum AOD (0.16 +/- 0.22) was concurrent with the maximum AE (1.75 +/- 0.76), observed in winter. On average, the absorption AOD (MOD) at 440 nm and its absorption Angstrom exponent (AAE) between 440 and 870 nm were 0.06 +/- 0.03 and 1.04 +/- 0.43, respectively. The mean AAE was considerably higher than 1 in autumn and winter, indicating that brown carbon from biomass burning contributed greatly to aerosol absorption. The AAE was lower than 1 in summer and spring, related to the coating of black carbon particles. Large negative aerosol direct radiative forcing was estimated at the bottom of the atmosphere, with relatively lower values estimated at the top of the atmosphere; the means were -26.28 and -9.42Wm(-2), respectively. This resulted in a strong cooling effect on the surface, but warming in the atmosphere, potentially impacting the regional climate. (C) 2015 Elsevier B.V. All rights reserved.