Aerosol optical properties at Mt. Waliguan Observatory, China

Aerosol optical properties at the Mt. Waliguan Observatory (WLG) in Northwest China are investigated based on the measurements of aerosol optical depth (AOD) at 500 nm and Angstrom exponent (α) from September 2009 to August 2010. Mean values of 0.14 ± 0.07 and 0.59 ± 0.24 are observed for AOD and Angstrom exponent, respectively, both of which are characterized by a wide range of values from 0.02 to 1.13 and −0.03 to 1.37, respectively. A seasonal variation is found with high AOD and low Angstrom exponent values in spring which could be attributed to the effect of Asian dust events, and low ground AOD level of less than 0.10 in autumn and winter. The k-means cluster analysis separates the measurements into three aerosol modes based on the AOD and Angstrom exponent distributions with the frequency distribution of AOD centering about 0.07 ± 0.002, 0.11 ± 0.02, and 0.18 ± 0.12. AOD at WLG is significantly larger than those at Mauna Loa (MLO) and Izana (IZA) because of the contribution of the dust aerosol in spring from desert regions of Western China and fine particles transport from Central China in summer. In addition, the factors of nearby surface, geographic location and different aerosol components could also contribute to higher AOD at WLG than MLO and IZA.