Study On Optical Absorption Property Of Black Carbon In A Complex Environment

Black carbon is emitted from incomplete combustion of hydrocarbon fuel,which widely exists in the atmosphere.It promotes the formation of the atmospheric pollution and haze weather.For its strong light absorption,the optical properties of black carbon are important input parameter of the atmospheric forcing radiation assessment models.When the black carbon particles are discharged into the atmosphere,they will undergo complex physical and chemical changes and become particles with coating,and their optical properties will also change.The changes of optical absorption properties and morphological parameters of black carbon in different aging environments were discussed by combining experiment and theoretical simulation.The core-shell model was used to calculate the absorption properties of black carbon which is coated with different substances,the effects of core size and coating thickness etc on black carbon optical absorption properties including the absorption efficiency and absorption exponent index are discussed.The results show that particle absorption efficiency Qabs and absorption ratio η of D0=20,50,100nm particle at 405nm,532nm and 781 nm decrease with the coating thickness regardless of the coating material.The absorption exponent index β of black carbon with inorganic coating increases first and then decreases when coating thickness increases while β of black carbon with organic coating increases during the whole process.The black carbon optical absorption in different aging environments were measured,combined with core-shell model simulation,the relation between black carbon absorption exponent index β(β is a parameter that describes the relationship between absorption coefficient and light wavelength)and its particle diameter Di/D0 was detailed discussed.The results shows that the relative absorption ability of short wavelength light of black carbon particles in different aging atmosphere is enhanced.The NO2/SO2/C7H8 aging environment changes the absorption properties of carbon black particle most,while the effect of zero air seems not that obvious.within a certain error range the relation between β of black carbon in NO2/SO2/C7H8 aging environment and its Di/D0 can be expressed as β= 0.349(Di/D0)+ 0.562,the trend of the Di/D0 estimation using β = 0.349(Di/D0)+0.562 and its measurement data is consistent.The average value of absolute error value is 17.3%.Strong absorption carbonaceous aerosol originates from fossil fuel whose βapproximates 1 while weak absortion carbonaceous aerosol originates combustion of biomass fuels and new particle formation whose β approximates 2.Based on the different wavelength dependence of light absorption by aerosols from different origins,the carbon aerosol classification analysis in Hangzhou was done by analyzing the aethalometer measurements of Zhaohui environmental monitoring site in 2015.The results show that the annual concentration of strong absorption carbonaceous aerosol in 2015 is 15.4 μg/m3,accounting for 71.8%of total carbonaceous aerosol.The monthly contribution of weak absortion carbonaceous aerosol to carbonaceous aerosol varies from 20%to 38%.To some extent,the above results reveals the energy consumption structure of Hangzhou city is largely depended on fossil fuels.