Study On The Characteristics Of Equivalent Complex Refractive Index Of "dry" Aerosols In Chengdu In Autumn And Winter

The"dry"aerosol equivalent complex refractive index is an important parameter for characterizing the optical properties of aerosols,and it is also an important source of uncertainty for atmospheric visibility prediction.Relevant research has important theoretical significance and application value.To this end,this paper uses the time-course observation data of the AURORA 3000 turbidity meter and the AE-31 black carbon detector from September to December 2017 in Chengdu and the monitoring data of the GRIMM180 environmental particulate matter analyzer,combined with the simultaneous environmental meteorological monitoring.Data,the atmospheric extinction coefficient and its composition of the study area,the inversion algorithm,variation characteristics and the genesis of the"dry"aerosol equivalent complex refractive index are systematically studied.The main conclusions are as follows:?1?Research results for atmospheric extinction and its composition:The atmospheric extinction coefficient during observation is?1173.42±641.21?Mm^-1,to which,the average contribution rate of“dry”aerosol scattering coefficient,“dry”aerosol absorption coefficient,dry and clean atmospheric scattering coefficient,gaseous pollutant absorption coefficient and aerosol hygroscopicity extinction coefficient is53.02%,6.54%,1.50%,1.65%and 37.29%,respectively.The daily variation of atmospheric extinction coefficient,"dry"aerosol scattering coefficient and aerosol hygroscopic extinction coefficient is of unimodality,while the daily variation of"dry"aerosol absorption coefficient and gaseous pollutant absorption coefficient of unimodality and bimodal pattern.The unit mass atmospheric extinction coefficient and the variation characteristics of its composition with relative humidity were clarified,and their respective genesis were analyzed.?2?The objective function is constructed by Mie scattering theory formula,and the real and imaginary parts of the aerosol equivalent complex refractive index are collaboratively optimized through immune evolution algorithm.Based on that,the new inversion method of"dry"aerosol equivalent complex refractive index is innovatively proposed.The immune evolutionary algorithm of inverting aerosol equivalent complex refractive index is not only universal,but also of high convergence rate,stable calculation and high accuracy.By comparing with other inversion methods of aerosol equivalent complex refractive index,the advantages of the new are further demonstrated,which provides an algorithmic guarantee for the evolution mechanism of aerosol equivalent complex refractive index and the subsequent study of aerosol hygroscopic growth model.?3?The real and imaginary parts of the"dry"aerosol equivalent refractive index are?1.547±0.0552?and?0.0197±0.00604?,respectively.The daily variation of the real and imaginary parts of the"dry"aerosol equivalent refractive index are almost the same,mainly characterized of unimodality,and the valley value of the two parts are located between 15:00 and 18:00.The most referential indexes of mass concentration on the real part variation of"dry"aerosol equivalent complex refractive index are PM₁/PM₁₀and PM₁/PM_2.5,and the corresponding determination coefficients R² are 0.53 and 0.21,respectively?by significance testing with?=0.01?.The mass concentration indicators that of most referential on the variation of the imaginary part of"dry"aerosol complex refractive index are BC/PM₁₀0 and BC/PM_2.5,and the corresponding determination coefficients R²are 0.47 and 0.42,respectively?by significance testing with?=0.01?.?4?Regarding the daily time scale,the real part of the equivalent complex refractive index plays a synergistic effect on"dry"aerosol scattering extinction with and the mass concentration statistics,and the same effect on"dry"aerosol absorption extinction of imaginary part with mass concentration,the imaginary part of"dry"aerosol equivalent complex refractive index is an important characterization of the absorption extinction ability"dry"aerosol per unit mass.The conclusions above laid the foundation for the construction of parameterization scheme on"dry"aerosol equivalent complex refractive index.