Study on the aerosol optical properties and their relationship with aerosol chemical compositions over three regional background stations in China Huizheng Che a, * , Zhifeng Yang a , Xiaoye Zhang a , Chize Zhu b , Qiangli Ma c , Huaigang Zhou d , Peng Wang e a Key Laboratory for Atmospheric Chemistry, Center for Atmosphere Watch and Services, Chinese Academy of Meteorological Sciences, CMA, 46 Zhong-Guan-Cun S. Ave., Beijing 100081, China b Zhejiang Meteorological Institute, Hangzhou 310017, China c Lin’an Atmospheric Background Station, Zhejiang Province 311307, China d Shangdianzi Atmospheric Background Station, Beijing 101507, China e Longfengshan Atmospheric Background Station, Heilongjiang Province, China article info Article history: Received 11 September 2008 Received in revised form 6 November 2008 Accepted 7 November 2008 Keywords: Aerosol optical depth (AOD) Angstrom wavelength exponent Angstrom turbidity parameter Chemical composition Regional background station China abstract The special and temporal characteristics of aerosol optical depth (AOD) and Angstrom wavelength exponent (Alpha) and their relationship with aerosol chemical compositions were analyzed by using the data of CE318 sun-photometer and aerosol sampling instruments at Lin’an, Shangdianzi and Long- fengshan regional atmospheric background stations. Having the highest AOD among the three stations, Lin’an shows two peaks in a year. The AOD at Shangdianzi station shows a single annual peak with an obvious seasonal variation. The AOD at Longfengshan station has obvious seasonal variation which peaks in spring. The Alpha analysis suggests that the aerosol sizes in Lin’an, Longfengshan and Shangdianzi change from fine to coarse categories. The relationship between the aerosol optical depths of the Lin’an and Longfengshan stations and their chemical compositions is not significant, which suggests that there is not a simple linear relationship between column aerosol optical depth and the near surface chemical compositions of atmospheric aerosols. The aerosol optical depth may be affected by the chemical composition, the particle size and the shape of aerosol as well as the water vapor in the atmosphere. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Aerosol particles could change the earth–atmosphere radiation balance and affect the climate directly by absorbing and scattering solar radiation and the radiation of the earth–atmosphere system (Ackerman and Toon, 1981; Charlson et al., 1992). Indirectly, aerosol particles can serve as cloud condensation nuclei (CCN) or ice nuclei (IN) to change the microphysical structure, the optical properties and the precipitation efficiency of clouds, which could affect the climate (Hansen et al., 1997). The impact of aerosol on climate and environment has been a hot issue for the international scientific research community (IPCC, 2001, 2007). To fully understand the aerosol physical properties, extensive sets of both in situ and remote measurements are required (Alados-Arboledas et al., 2008). Consequently, several observation networks of aerosol optical properties have been established internationally to observe aerosol optical characterization such as AErosol RObotic NETwork, PHOTONS, SKYNET, AEROCAN, RIMA, AGSNet and so on (Holben et al., 1998; Goloub et al., 2008; Uchiyama et al., 2005; Bokoye et al., 2001; Campanelli et al., 2007; O’Brien and Mitchell, 2003). Currently, the observation of aerosol optical property is deficient in China. AERONET has more than twenty stations in China, but only a few are in long-term operation (Eck et al., 2005; Xia et al., 2005). Luo et al. (2000) and Qiu and Yang (2000) have studied aerosol optical properties by using the data of ground-based direct solar radiation of China. Xin et al. (2007) has analyzed CHRSNET aerosol optical characterization by using a hand-held sun- photometer. These results play an important role in the optical characterization of Chinese regional aerosol and its climatic effect. China Meteorological Administration (CMA) has established the largest automatic observational network – China Aerosol Remote Sensing Network (CARSNET) in China since 2002. CARSNET has 37 stations at present with a CE318 sun-photometer installed at each station for the observation of regional aerosol optical property over China. Among them one is the global atmosphere watch (GAW) station (Waliguan) and six are regional atmosphere watch stations (Lin’an, Shangdianzi, Longfengshan, Shangrila, Akedala, and Jing- sha). Three CE318 sun-photometers have been running continu- ously at Lin’an, Shangdianzi and Longfengshan stations for three years. The aim of this paper is to analyze these observation results * Corresponding author. Tel.: þ86 10 58995247; fax: þ86 10 62176414. E-mail address: chehz@cams.cma.gov.cn (H. Che). Contents lists available at ScienceDirect Atmospheric Environment journal homepage: www.elsevier.com/locate/atmosenv 1352-2310/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2008.11.010 Atmospheric Environment 43 (2009) 1093–1099