Column-integrated aerosol optical and physical properties at a regional background atmosphere in North China Plain

The AERONET level 2.0 data at Xinglong station from February 2006 to July 2011 were used to characterize the aerosol optical and physical properties, including temporal variability, aerosol absorption, classification and properties under dust and haze conditions. The annual mean aerosol optical depth (AOD) and extinction Angstrom exponent (EAE) are 0.28 ± 0.30 and 1.07 ± 0.38, respectively. The seasonal variations of AOD440nm are higher in spring (0.40 ± 0.3) and summer (0.40 ± 0.42) than in autumn (0.20 ± 0.22) and winter (0.19 ± 0.21). The EAE is low in spring (0.96 ± 0.43) and high in summer (1.22 ± 0.38). The EAE is ∼1.25 with an absorption Angstrom exponent (AAE) of ∼1.0-1.5 in Xinglong, which indicates that the dominant type is mixed aerosol (accounting for 88.2% at AAE > 1.0). Almost all of the dust observations occurred in spring. The volume concentrations of both fine and coarse mode particles increase with increasing AOD. In spring, the increase of coarse particles is greater than that of fine aerosols; however, the reverse phenomenon is observed for other seasons. The high AOD at Xinglong could be associated with the growth of fine mode aerosols and addition of coarse mode particles. This background station is not only impacted by dust aerosols from northwest China and south Mongolia but also influenced by long-range transportation of anthropogenic aerosols from south urban and industrialized regions. The mean AOD was 1.49 on the dust day, while AOD was 1.10 on the haze day. The mean EAEs were 0.09 and 1.43 on dust and haze days, respectively.