A method for estimating the ratio of aerosol mass concentration to the imaginary part of the atmospheric complex refractive index and its application

Based on the principle of light propagation, it is necessary to obtain the ratio (RMN) of atmospheric aerosol mass concentration to the imaginary part of the atmospheric equivalent refractive index for measuring aerosol mass vertical flux. In this paper, the factors affecting the RMN values are analyzed by numerical calculation under an ideal state and by using observational data. Numerical calculations show that the RMN is mainly determined by the aerosol particle size distribution (PSD), hygroscopicity parameters and relative humidity. With the same relative humidity, the smaller the geometric mean diameter (Dg) is, the larger the RMN, and when the aerosol particle hygroscopicity parameter is greater than 0.14, the greater the relative humidity is, the smaller the RMN. Comprehensive experiments were conducted in urban Hefei, and the results of observations at Hefei confirm the numerical results. Data from ten cities across China also confirm the numerical results. The order of geometric mean diameter of aerosol particles at the ten sites can be determined by the order of RMN, and the order of hygroscopicity parameters at the ten sites can be determined by the order of the change rate of RMN with relative humidity. The geometric mean diameters of aerosol particles are different among the ten sites, while the hygroscopicity parameters are similar.