北京秋季大气气溶胶光学厚度与Angstr?m指数观测研究

利用2010年10~11月CE318太阳光度计观测资料,得出了北京市秋季气溶胶光学厚度(AODλ=500nm),Angstr?m波长指数(α)和浑浊度(β).结果显示,气溶胶AOD,Angstr?m指数,浑浊度平均值分别为0.5(±0.69)、0.95(±0.33)、0.24(±0.31),变异系数分别为139%、35%和132%.非污染天,AOD变化较小,峰值出现在15:00,但大气中细粒子组分相对较高;污染天,AOD波动很大,没有明显的日变化,颗粒物以细粒子为主.非污染天,当α1.0,两者呈现正相关;污染天,两者无明显关系,但当AOD>1.0,α随AOD的增大而变小.当Vmax4m/s,AOD和α均出现小值,α与AOD呈负相关.风向也是影响α和AOD变化的重要因素,尤其ENE为主导风向时,α与AOD呈明显正相关.温度的变化并未对α和AOD的变化造成很大影响.局地扬尘或沙尘气溶胶呈非亲水性,但当α>0.5,AOD随相对湿度(RH)的增大有一定程度的增大.

A observational study of aerosol optical depth and angstrom wavelength exponent over Beijing in Autumn

The aerosol optical depth (AODλ= 500nm), Angstr?m wavelength exponent (α) and turbidity coefficient (β) are derived from sun photometer CE318measurements over Beijing from October to December 2010. The results show that, the mean values of AOD, Angstr?m wavelength exponent and turbidity coefficient are 0.5±0.69, 0.95±0.33, 0.24±0.31with coefficients of variation (CV) of 139%, 35% and 132%, respectively. AOD change little in polluted days with a peak at 15:00, but the concentrations of fine particles are relatively high. During polluted days, AOD fluctuate widely without a distinct diurnal variation, and the fine particles are the main components of the air pollutants. In addition, during the non-polluted days, positive and negative correlations are found between α and AOD when α smaller than 0.5and greater than 1.0, respectively. There is no clear correlation between α and AOD during the polluted days, while a decrease trend of α is detected with increase of AOD when α are lager than 1.0. It is indicated that wind speed would not play a critical role in the local changes of aerosol concentrations from similar variations between α and AOD when Vmax4m/s. Wind direction can also have large influence on the relationship between α and AOD, which shows a positive correlation especially for ENE direction. The temperature shift has little effect on variation of α and AOD. AOD increase with relative humidity when α is greater than 0.5though dust aerosols are hydrophobic in this study.