Absorption Properties Of Brown Carbons In Fumes And Atmospheres And Contributions Of Nitrated Phenols

Brown carbon(BrC)is a kind of important light-absorbing compounds in atmospheric aerosols.It has significant effects on atmospheric photochemical processes and alters the regional climate.Investigating the optical properties of brown carbon from different pollution sources and locations is of great significance for improving the global radiative forcing model and accurately assessing the climate effects of atmospheric aerosols.In this study,the optical properties of brown carbon emitted from biomass burning,coal combustion,and vehicle exhausts were determined.In addition,the optical parameters of brown carbon and the contents of nitrated phenols,a major component of brown carbon,in ambient PM2.5 samples collected from six sites in eastern China were measured.The light absorption contribution,major sources,and influencing factors of brown carbon in the real ambient air were also analyzed.The measurement results show that the light absorption capability of brown carbon emitted from biomass burning was the strongest among the three primary emission sources,and the average mass absorption efficiency(MAE365)was up to 2.01 m2/gC.The MAE365 values of brown carbon released from coal combustion and vehicle exhausts were relatively low,with average values of 1.51 and 0.27 m2/gC,respectively.The lignin contents of biomass,the maturity and volatile components of coal,and burning conditions had large impacts on the optical properties of freshly emitted brown carbon.In addition,fuel type was the dominant factor that affected the optical properties of brown carbon in vehicle exhausts.Brown carbon in the exhaust of diesel trucks had the highest absorption coefficient(Abs36s)and the strongest light absorption capability.The absorption coefficient and the mass absorption efficiency of brown carbon in atmospheric fine particulate matters in typical areas in eastern China showed similar seasonal variation characteristics,with the highest values in winter and the lowest values in summer.Generally,the Abs365 of brown carbon in urban sites was larger than that in rural and mountain sites.The ranges of average Abs365 and MAE365 of brown carbon at the six sampling sites were 2.4-14.1 Mm-1 and 0.42-1.16 m2/gC,respectively.Anthropogenic activities had a significant influence on the optical properties of brown carbon.Specifically,biomass burning influenced the optical properties of brown carbon at Dongying site in summer,while coal combustion had a significant effect at Jinan and Dongying sites in winter.Nevertheless,vehicle exhausts had an apparent influence at the urban sites of Jinan and Nanjing in autumn.With comparison of the contributions of light absorption at 365 nm of brown carbon to carbonaceous aerosols in emission sources,it is found that the brown carbon released from coal combustion had the largest contribution,while the brown carbon in vehicle exhausts had the lowest contribution.The light absorption of brown carbon to carbonaceous aerosols in atmospheric PM2.5 samples contributed 12.2%to 41.2%at the sampling sites.Particularly,the absorption contribution of brown carbon was significantly higher in winter in northern China than that in other seasons due to the huge consumption of coal during the heating period.The MAE365 values of the twelve nitrated phenols ranged from 3.2 to 37.9 m2/gC,which was significantly higher than the brown carbon from the emission sources and ambient air.Nevertheless,due to the low concentrations of nitrated phenols,the proportion of light absorption at 365 nm of nitrated phenols in brown carbon in emission sources and atmospheric samples was relatively small(mostly less than 10%),indicating that the light absorption of brown carbon mostly came from other organic components.Other brown carbon components and the light absorption contributions require further identification and evaluation in the future.