Observational Study Of Aerosol Optical And Physical Properties Over Semi-Arid Region In Northwest China

The features of atmospheric aerosols, such as the transformation and long distance transport, and the effects on climate change, environment and human health, not only depend on the concentration, but also link to particle size distributions, optical properties, chemical composition, lifetime, and so on. In order to further understand the optical and physical properties of aerosols, some fundamental studies are necessary.The characteristics of aerosol optical parameters, particle sizes range of aerosol number concentration and the number of spectral distribution were analyzed, using the observational data collected at SACOL from January2010to February2012. The relationship between the parameters mentioned above and meteorological conditions, and the correlation between AOD and mass concentration of PM10were discussed as well. Meanwhile, the data-fitting between APS data and PM10mass concentration was explored. The main conclusions are as follows:The annual average of aerosol optical depth, turbidity coefficient, wave length exponent are0.410,0.231and0.840respectively. The seasonal averages of first two optical parameters are progressively decreasing, in order of spring, winter, summer, and autumn over SACOL, but the seasonal averages of wave length exponents are opposite. The aerosol total concentrations over SACOL mainly depend on number concentrations of PM2.5, especially as the particle size less than1.0μm (in the accumulation of mode) is in the majority. Among them, the number concentration of aerosol particles with size less than1μm in winter is far beyond in other seasons. The seasonal average of PM2.5, PMcoarse, PM10-20, reach to the maximum in winter, and minimum in summer. The frequent occurrence of spring dust weather and winter coal-fired heating may lead to heavy aerosol pollution in spring and winter over SACOL.Southeast and northwest wind are main directions in SACOL. In winter, pollutants derived from human activities in northwest are more than that in southeast. The effect of relative humidity on AOD is not obvious, and degree of correlation between AOD and mass concentration of PM10is not significant.Dust events occurred frequently in SACOL area in the spring of2010. The characteristics of aerosol had been changed significantly in dust weather and rainfall weather process. After dust the AOD was increased, with a trend of turbidity coefficient keeping consistently with AOD positively, and the AOD had a weak negative correlation with wave length exponent. The number concentration of PM2.5, PMcoarse and PM10-20changed dramatically under dust conditions. Before sandstorms occurred, PM2.5concentrations number increases rapidly, aerosol total number concentrations mainly depend on the number concentrations of the aerosol particles in size less than0.523. While dust storms appeared, PMcoarse number concentration increased dramatically, PMtotal mass concentrations depend on PMcoarse number concentration. The effect of precipitation on PMcoarse, PM10and PM2.5-20was very obvious, the overall reached96.4%.Single variable linear regression and multivariate linear regression mothods were used to fit APS data and mass concentration of PM10with the correlation coefficients great than0.95, under the conditions of spring dust weather and winter pollution weather respectively. Both theoritical and observed results show that the multiple linear fitting results is better, so after measuring aerosol particle number with APS, we can choose the appropriate multiple linear fitting equation to calculate the mass concentration.