Seasonal characteristics of aerosol vertical structure and autumn enhancement of non-spherical particle over the semi-arid region of northwest China

Abstract Assessments of the effects of aerosols on the climate and environment still feature large uncertainties, and a better understanding of the spatiotemporal variation in these effects is needed. In this study, coincident observations of ground-based lidar and sun photometer measurements from March 2010 to February 2011 were selected to examine the sensible seasonal characteristics of the aerosol vertical structure and the potential variations of aerosol properties before and during the wintertime heating period at SACOL (Semi-Arid Climate and Environment Observatory of Lanzhou University, 35.946oN, 104.137oE, 1961 m ASL), northwest of China. Our results suggest that the aerosol behavior during a year can be roughly divided into two major periods: the non-spherical particle dominated period and the spherical particle dominated period based on the depolarization ratio, or the dust-dominated period (spring and winter) and the non-dust-dominated period (summer and autumn) based on the aerosol angstrom exponent. The height and width of peak of aerosol scale height frequency distribution show the distribution of aerosol layers in summer is highest, then followed by spring, autumn and winter. The depolarization ratios at different heights in spring are higher than those in other seasons. A similar distribution of extinction coefficients above 2 km can be seen in four seasons, but relatively large differences exist below 2 km, especially within 1 km. The increase of the extinction coefficient is observed near surface in November 2010 with a sharp increase in depolarization ratio which is induced by the rising contribution of the dust events (up to 13%) and the mixed type aerosols (70%). These results not only provide detailed characteristics of aerosol variation over the SACOL region, but also remind us to take into account the potential contribution of dust aerosol to the severe regional air pollution during the wintertime heating period.