| The optical properties of aerosols are important factors influencing the direct effects on climate and the environmental effects of aerosols,and the complex refractive index is one of important parameters determining the optical properties of aerosols.To study the optical properties and the complex refractive indices of atmospheric aerosols at the summit of Mt.Tai,we carry out a comprehensive ground-based observation experiment in high altitude area on optical properties of aerosols,atmospheric ice nuclei(IN),size distribution of aerosols and other projects from May to June,2017 at the riguan peak national benchmark climate station at the summit of Mt.Tai(36.25°N,117.10°E;1533.7 m).Basing on the data obtained from the observation experiment,we analyze and discuss the optical properties,the complex refractive index,color simulation and the relationship between color and optical properties of atmospheric aerosols at the summit of Mt.Tai,and some meaningful research results are obtained.During the observation from May to June,2017,the average scattering coefficient(?sca,550)of atmospheric aerosols at the summit of Mt.Tai is 40.3 Mm-1,and the range of variation is2.6?159.8 Mm-1.The average absorption coefficient(?abs,550)is 16.0 Mm-1,and the range of variation is 2.7?55.1 Mm-1.The average scattering coefficient of aerosols in this study is close to that observed at the Mt.Huang,which is about 15%of the scattering coefficients of aerosols in urban areas like Beijing and Shanghai.The average absorption coefficient of aerosols in this study is close to that observed in Shangdianzi and Nanjing,which is about 25%of the absorption coefficients of aerosols in Beijing and Shanghai.The average single scattering albedo(?550)of aerosols is 0.67,and the range of variation is 0.23?0.90.The average single scattering albedo in this study is close to the observation results in Delhi and Granada,which is about 20%smaller than that of aerosols in Beijing,Shanghai and other urban areas.The average backscattering ratio(?neph,550)is 0.17,and the range of variation is 0.11?0.44.The?neph,550 is relatively stable and low in most of the time.During this observation,the scattering coefficient and the absorption coefficient of aerosols at the summit of Mt.Tai have obvious diurnal variation,which is overall high in the daytime and low in the nighttime.Based on the data of the scattering coefficients,the absorption coefficients and numerical concentration size distributions which have high time resolution and high precision obtained during the observation experiment,the equivalent complex refractive indices of aerosols at the summit of Mt.Tai are calculated using the Mie scattering theory.The results show that the mean of the real parts of the equivalent refractive indices of aerosols at 550 nm is 1.38,and the range is 1.31?1.98.The mean of the imaginary parts of the equivalent refractive indices of aerosols at 550 nm is 0.049,and the range is 0.014?0.251.The real and imaginary parts of the equivalent refractive indices of aerosols at the summit of Mt.Tai keep at similar level in most of the time.The inversion results can represent the general values of the refractive indices of aerosols at the mount Taishan area.The average equivalent refractive index of aerosols at Mt.Tai is smaller than that of the light scattering aerosols(such as sulfate and nitrate),which is about 10%lower than that of Beijing and Tianjin.The k is larger than that of most kinds of aerosols,even larger than that of dust in some studies,but much smaller than that of black carbon.In summary,the aerosol average complex refractive index shows that the scattering properties of aerosols at the summit of Mt.Tai are relatively weak compared with those of other kinds of aerosols,and the absorption properties are relatively strong compared with those of other kinds of aerosols.The real part of the complex refractive index has obvious diurnal variation law,which is lower in the daytime and higher in the nighttime.No obvious diurnal variation of the imaginary part is found.By analyzing the correlation between the complex refractive indices and meteorological elements,it can be seen that the imaginary part of complex refractive index has significant correlation with wind speed,temperature and relative humidity.By simulating the colors of atmospheric aerosols theoretically,the microphysical and chemical properties of aerosols can relate to their macroscopic properties.We optimize the existing algorithm of the aerosol color simulation by introducing the actual solar radiation spectrum and the visual response function of the human eye to the color simulation in our model.The optimized algorithm of atmospheric aerosol color simulation not only describes the objective spectral selectivity of aerosols,but also considers the subjective biological characteristics of human eyes to light.Using the optimized color simulation algorithm,we simulate the colors of the aerosol layers with different absorption(?)ngstr(?)m exponents(AAEs),and quantitatively discusses of the relationship between the aerosol colors and their optical properties are also carried out.The simulation results of the colors of the aerosol layers with AAE values of 1?7 are also shown in this paper.When the difference between the transmittance of light at 400 nm and the transmittance of light at 730 nm in one aerosol layer is greater than0.2 and the AAE is greater than 2,the aerosol layer presents colors of brown or yellow instead of gray or black.The colors of the aerosol layers at the summit of Mt.Tai can be simulated effectively by using the properties of size distributions,the complex refractive indices and optical depths that are based on observation.The simulated color based on reasonable hypotheses of the atmospheric aerosol layer at the summit of Mt.Tai take on a hue of grey.The color of the scenery in the clean atmosphere overlaped with the simulated colored aerosol layer shows a similar scenery under the polluted atmosphere condition.The intrinsic relationships between the optical properties and other physical and chemical properties of atmospheric aerosols at the summit of Mt.Tai are analyzed in this paper,which provide effective parameters for the optimization of models such as climate patterns in this region and references for better understanding the relationships between aerosol microphysical and chemical properties,optical properties and aerosol color. |
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