天津城区大气气溶胶复折射指数的反演及消光贡献分析

The Retrieval of Aerosol Complex Refractive Index and the Contribution Rate Analyses of Extinction Coefficient in Urban Tianjin City

气溶胶的复折射指数是直接影响其散射特性和吸收特性的基本物理量之一.为深入研究城市大气气溶胶的复折射指数特征,引入一种具有高时间分辨率优点的反演方法来反演气溶胶复折射指数.依据辐射传输理论,将天津大气边界层观测站观测到的高精度散射系数、吸收系数和数浓度谱分布数据利用查表法代入Mie理论气溶胶粒子群消光计算公式,对大气气溶胶复折射指数进行反演.结果表明:①天津城区2011年4月观测地点0.55μm波长处的气溶胶复折射指数实部平均值为1.64,虚部平均值为0.015.②气溶胶复折射指数实部和虚部均有明显日变化规律,实部和虚部均与相对湿度呈正相关,与风速呈负相关.③利用反演得到的复折射指数对不同粒径大气气溶胶的消光特性进行计算发现,对散射特性而言,>0.25~1.00μm粒子对散射系数的贡献率达86%;对吸收特性而言,>0.25~2.50μm粒子对吸收系数的贡献率为53%,>2.50~32.00μm粒子对吸收系数的贡献率为47%.研究显示,>0.25~1.00和>1.00~32.00μm的粒子对吸收系数的贡献率均较高,但对散射系数而言,>0.25~1.00μm的粒子贡献率较高,因此综合考虑气溶胶散射系数、吸收系数和消光系数,控制>0.25~1.00μm的气溶胶粒子数浓度可有效改善大气能见度.

Aerosol complex refractive index is one of the most fundamental optical parameter,which can directly relate to aerosol properties such as scattering and absorption index.In this study,we retrieved the aerosol complex refractive index using an inversion method with fine resolution for time series.Based on high precision measured size distribution of aerosol,aerosol scattering and absorption coefficients,the aerosol complex refractive index was retrieved using the Lorenz-Mie scattering theory.The results indicated that:(1)In the urban area of Tianjin City in April 2011,the real part of averaged equivalent complex refractive index of the aerosol at the wavelength of 0.55μm was 1.64,and the imaginary part was 0.015.(2)An obvious daily variation regularity of aerosol complex refractive index is found in this study.Both the real part and imaginary part of complex refractive index were significantly positively correlated with relative humidity,and were negatively correlated with wind speed.(3)The contributions of different scale aerosol to total extinction coefficient were calculated,it showed that 86%of the scattering coefficient is from the small aerosols with radius>0.25-1.00μm.Meanwhile,the aerosols particles with radius from 0.25 to 2.50μm and from 2.50 to 32.00μm contribute 53%and 47%to the total absorption coefficient,respectively.Studies had shown that aerosol particles>0.25-1.00μm and particles>1.00-32.00μm have similarly higher contribution rate to the absorption coefficient,but for the scattering coefficient,aerosol particles with a contribution rate of>0.25-1.00μm are higher.Based on comprehensive consideration of aerosol scattering coefficient,absorption coefficient and extinction coefficient,controlling aerosol particles>0.25-1.00μm can effectively improve atmospheric visibility.