北京市雾霾天气下气溶胶光学特性分析

Analysis of Aerosol Optical Properties in Beijing during Fog and Haze Days

依据中国PM2.5浓度的空气质量标准,对北京地区2010~2015年的空气质量进行了评估,以此结合天气报告选取历年不同季节的雾霾天气过程,利用AERONET提供的CE-318太阳光度计反演资料,对北京雾霾天气下的气溶胶光学特性进行了分析研究。结果表明:(1)2010~2015年北京城区PM2.5日均浓度历年均呈"U"型变化,空气质量为优良的天数略有增加,但改善不大,秋季和冬季空气污染比较严重,尤其是冬季,严重污染的比例接近25%;(2)2010~2015年,440、675、870、1020nm四个波长下的气溶胶光学厚度年际变化特征基本一致,均有下降的趋势,气溶胶光学厚度随波长的增大而减小,说明雾霾天气条件下气溶胶粒子对太阳光的衰减具有波长选择性;(3)雾霾天气期间的气溶胶光学厚度整体都表现出较高值,Angstrom波长指数通常高于0.69,并保持在0.69~1.55之间,说明雾霾天气时气溶胶主要以细的污染粒子为主;(4)北京冬季易发雾霾天气,气溶胶光学厚度较大,大气浑浊程度较高,Angstrom波长指数α随气溶胶光学厚度的增大而减小,呈负相关,这为依据气溶胶光学厚度估算α提供了一种可能的方法。

According to the air quality standard of PM2.5 concentration in China, the air quality of Beijing from 2010 to 2015 is evaluated and the weather report is combined to select the haze process in different seasons from different years. The aerosol optical properties during haze event in Beijing are analyzed by using the inversion data from CE--318 sun--photometer measurement on AERONET. The results show that, the daily average variation of PM2.5 concentration in Beijing varies in the form of ＂U＂ from 2010 to 2015. The number of days with good air quality increases slightly, but it does not improve much and the air pollution in autumn and winter is rather serious, especially in winter, the proportion of serious pollution is close to 25%. Moreover, the interannual variations of aerosol optical depth （AOD） in four wavelengths of 440, 675, 870 and 1020 nm be- tween 2010 and 2015 are basically the same, which show a downward trend. The AOD decreases as the wavelength increases, indicating that the aerosol particles have wavelength selectivity to the attenuation of sunlight in the haze condition. Further- more, the AOD generally shows a high value during the haze. The Angstrom wavelength exponent （a） is usually higher than 0.69 and remains between 0.69 and 1.55, indicating that the aerosol mainly consists of fine particles in the haze event. In addi- tion, the haze event usually occurs in winter, and the larger AOD is, the higher atmospheric turbidity is. The a decreases as the AOD increases, so they are negatively correlated, and this provides a possible method to estimate a based on AOD.