基于AERONET典型污染天气下香河气溶胶光学特性研究

Aerosol Optical Properties under Typical Pollution Episodes

气溶胶光学特性是研究气溶胶气候效应的基础,气溶胶辐射强迫估算中最大的不确定性源于对气溶胶光学特性估算的不确定性,详细了解气溶胶光学特性尤其是典型污染天气下的光学特性对研究气溶胶辐射强迫估算具有重要意义。为深入了解香河地区大气气溶胶光学特性,利用AERONET数据资料研究了香河冬、春季节气团来向、气溶胶光学厚度(AOD)以及气溶胶的类型,对比分析了春季沙尘和冬季雾霾天气条件下大气气溶胶光学性质的差异。结果表明:移动速度较慢的气团伴随着高AOD(AOD>1.0),而移动速度快的气团伴随着较低的AOD(AOD<0.5)。Gobbi气溶胶图解法分析显示,香河站沙尘和细粒子气溶胶都会产生高光学厚度。香河沙尘和雾霾期间粗、细粒子消光占比差异明显,其中细粒子消光分别占总消光的40%和95%,说明雾霾天气发生时细粒子消光对总消光具有重要贡献。沙尘期间,平均AOD稍高于雾霾天气,其中高AOD(>1.0)出现的频率达到86%,说明沙尘天大量的粗粒子对总消光具有强烈贡献。两种污染天气下的AOD和Angstrom波长指数(AE)的关系明显不同,其中雾霾污染下的AE随AOD增大表现出缓慢减小的趋势,而沙尘期间AE随AOD变化复杂,当AOD大于1.8时,AE约为0.05。沙尘期间,平均AE为0.45,其中低于0.1和大于0.6的AE分别占41%和32%,表明香河作为沙尘下游地区,沙尘发生时气溶胶主要源于长距离传输的粗粒子和局地产生的细颗粒的共同贡献。雾霾天气下平均AE(1.19)是沙尘天的2倍多,其中大于0.9的AE频率分布高达93%,说明香河雾霾期间气溶胶以细粒子为主。研究结果对香河地区大气污染控制具有重要作用,可为京津冀地区大气污染治理及气溶胶气候效应研究提供参考依据。

Aerosol optical properties are the basis for the study of aerosol climate effect.Aerosol optical properties are the largest sources of the uncertainties in estimating aerosol radiative forcing.The study of aerosol optical properties under typical pollution episodes is of great significance for studying aerosol radiative forcing.The purpose of this study is to investigate the aerosol optical properties in Xianghe.Air mass,aerosol optical depth(AOD)and aerosol type in spring and winter were studied based on the 2013-2017 data from Aerosol Robotic Network(AERONET).A comparison of aerosol optical properties was performed during dusty and haze-foggy days.In general,AOD wassignificantly higher when air masses moved slowly,while AOD was obviously lower when air masses moved quickly.The graphical method of Gobbi was applied in order to discriminate different aerosol types and quantify the contribution of them.The results showed that the high AOD was caused by the dust aerosols or the fine particles at Xianghe site.The proportions of fine and coarse particles of extinction out of the total particles extinction were obvious during dusty and haze-fogy days in Xianghe.The extinction of fine particles(r<0.6μm)accounted for about 40%and 95%of that of total particle during dusty and haze-foggy days respectively.This result indicated that aerosol extinction was dominated by fine particles during haze-foggy days.It was found that the frequency of high AOD(>1.0)was up to 86%during dusty days,and average AOD in dusty days was slightly higher than that of haze-foggy days.This might be attributed to a strong contribution to the solar light extinction of large amounts of coarse particles in dusty days.The relation between AOD and Angstrom exponent(AE)under polluted episodes was apparently different.AE showed a decrease trend with increasing AOD in haze-foggy days,while the relation between AOD and AE was complex in dusty days.The values of AE were about 0.05 when AOD were higher than 1.8.The proportions were up to 41%and 32%when AE below 0.1 and above 0.6,respectively with average AE was 0.45 in dusty days.When dust happened in Xianghe,as dust downwind region,aerosols were attributed to the common contribution of coarse particles from long-range transport and fine particles emitted from local sources.Average AE of haze-foggy days was over two times larger than that of dusty days.The frequency reached 93%when AE was larger than 0.9 during haze-foggy days,indicating aerosols were dominated by fine particles.