Study On The Effect Of Physical And Chemical Parameters Of Aerosol Particles On Optical Properties

Aerosol plays a unique and important role in the earth’s climate system.For example,black carbon has a very high absorption efficiency of solar radiation,which is second only to CO₂ in causing global warming.However,non-absorbing aerosol particles such as ammonium sulfate and sodium chloride have strong light scattering ability and have a cooling effect on the atmosphere.The residence time of aerosol particles in the atmosphere is short,and the concentration of aerosol particles may change greatly in a short time,with large differences at different locations in different p.This would significantly alter the distribution of energy in the atmosphere,thus profoundly affecting the weather systems.Therefore,it is necessary to discuss the optical properties of aerosols in the atmospheric processes on global,regional and local scales.Mass extinction coefficient（MEC）,mass scattering coefficient（MSC）and mass absorption coefficient（MAC）represent the extinction,scattering and absorption ability of aerosols per unit mass,which can more directly reflect the optical properties of aerosols.In this study,the effects of the size distribution of aerosol particles,physical and chemical parameters,the mixing state and the wavelength of the light source on MEC,MSC and MAC of aerosols were quantitatively calculated using the program of Mie theory,and the following conclusions were drawn:1.MSC and MAC have different effects on MEC in different size ranges of particles.MAC of small particle size is much larger than MSC,so MEC is mainly determined by MAC.With the increase of particle size,the value of MSC increases rapidly,and its contribution is closer to that of MAC to MEC.2.The effects of the real and imaginary parts of the complex refractive index on MEC,MSC and MAC are different,and the influence rules change significantly with the particle size.For the real part of the complex refractive index,the MEC of small particle decreases with the increase of the real part,which mainly reflects that the absorption of small particles decreases with the increase of the real part.Near the peak particle size where MEC is near the maximum value,MEC increases with the increase of the real part,indicating that the peak value of MSC increases with the increase of the real part.MEC is not sensitive to complex refractive index in large particle size range.The imaginary part of complex refractive index has no obvious effect on the change of MSC,and the change of MEC is mainly determined by MAC.As for small particles,MAC increases with the increase of the imaginary part.As for large particles,MAC is not sensitive to the imaginary part.3.The influence of the wavelength of the light source on MEC,MSC and MAC has three characteristics:（1）The peak particle size of the MEC,MSC and MAC increases with the increase of observation wavelength;（2）The maximum values of the MEC,MSC and MAC decreased with the increase of the observed wavelength;（3）The change of the observation wavelength has different effects in different ranges of particle size.When the observation wavelength increases,both the MEC,MSC,MAC of black carbon and the MSC of non-absorbing particles and water particles decreased significantly when the particle size is small,but their values did not change significantly when the particle size is large.4.Mixing increases the MAC of aerosols on the whole.In general,the enhancement of internal mixing is greater than that of the core-shell model,and the latter is greater than that of the external mixing.This is consistent with the results in the literature.However,the range of the enhancement with different mixing states varies with the particle size.In some particle size ranges,the mixing even makes the MEC and MSC of mixing particles decrease,i.e.,less than that of the external mixing.