Development Of A Broadband Aerosol Single Scattering Albedo Spectral Measurement System And Its Application

Aerosol single scattering albedo(?),defined as the ratio of the aerosol scattering to extinction coefficient,is a key optical parameter that governs the relative strength of aerosol scattering and absorption capacity.The bias of co directly affects the role in strengthening or weakening global warming.However,the uncertainty of co is still large due to the lack of in-situ measurement instrument and the lack of spectrum information.The sum of black carbon(BC)and brown carbon(BrC)in carbonaceous aerosols is the largest absorber in atmospheric aerosol,which has significant effects on the radiation balance of the climate system.Due to the complexities of their emission sources and aging processes,there are still debates on their mixing state and optical properties.In this thesis,a new method for real time in situ measurement of aerosol single scattering albedo has been developed.By using this method,the optical properties of carbonaceous aerosols,including the laboratory straw burning,optical properties under pollution condition in the winter in Beijing and high oxidation conditions in summer in Shouxian,Anhui,were investigated.The main contents and merits of this thesis are as follows:1.A broadband cavity-enhanced aerosol single scattering albedo measurement system was developed for simultaneous in situ measurement of aerosol extinction,scattering,absorption coefficients,and ? in the spectral range of 365 to 660 nm.The detection limits for extinction and scattering coefficients are better than 0.83 and 0.60 Mm-1,respectively,and the uncertainties of absorption coefficient and co are better than 4%and 5%,respectively.Laboratory-generated particles and ambient aerosol were used for the demonstration of the system performance.2.Laboratory study of the optical properties of straw burning aerosol.Open burning of four types of crop residues(wheat,rice,corn and soybean)that widely planted in China were studied.The evolution of the size distribution and? of straw burning aerosol during burning processes was studied.We found that the relationship between ? and Dg,n(geometric mean diameter of number contribution)can be used to distinguish the burning stage.A ?-Dg·s(geometric mean diameter of surface contribution)parameterization was developed.The ?of straw burning aerosol was wavelength dependent with an ?abs(absorption Angstrom exponent)of about 2,indicating the contribution of BrC to light absorption.3.Contribution of BC(or EC)light absorption to aerosol total extinction has been investigated at suburban site near Beijing.The mass extinction efficiency of BC in IMPROVE algorithm was modified by BC absorption enhancement(Eabs),which improves the accuracy of chemical apportionment.The results indicated that organic component was the largest contributor to the total extinction.After considering the coating-enhanced absorption by BC,the extinction contribution of EC was up to 17%.Moreover,Eabs was large(-2.4-4.0)and the light absorption of secondary organic aerosol can not be negligible at the wavelength of 470 nm.4.The influence of atmospheric oxidation on the mixing state and light absorption enhancement of BC-containing particles was studied in summer in a rural site at Shouxian,Anhui.Based on the measurements of BC light absorption enhancement and oxidant concentration,and the newly developed algorithm,we found that photochemical aging can result in the enhancement of BC absorption,but the mechanisms are different under different oxidizing conditions.Moreover,a linear relationship was first observed between Eabs and co,which provides a plausible,new method to better reconcile model-based and observation-constrained direct radiative forcing by BC.