Characteristics And Sources Of Atmospheric Brown Carbon In Harbin

Brown carbon（BrC）has been recognized as organic compound with light absorption from the visible to the ultraviolet range.BrC has an impact on climate change,radiation balance,air quality,and human health.Harbin is located in the northeast of Northeast Plain in China.Harbin’s winter is long and cold,and the heating season lasts for six months.BrC study in Harbin is of significance due to the unique climatic conditions and air pollution characteristics.Based on long-term,continuous field measurement and a variety of qualitative and quantitative methods,the characteristics of BrC,the influencing factors,and the sources of BrC have been investigated in this study.The results provide a reference for investigating the characteristics and sources of atmospheric BrC in cold urban areas.By studying the characteristics of BrC,it was found that the Absorption （?）ngstr（?）m exponent（AAE）was 7.04±0.46,the absorption coefficient(Abs₃₆₅)was 26.63±26.28Mm^-1,and the mass absorption efficiency（MAE）was 1.19±0.31 m²/gC in the Harbin heating season.The characteristics of BrC have been influenced by biomass combustion,secondary reactions,the contribution of specific organic matter to light absorption,and other factors.The average concentration of BrC during the heating season in Harbin was20.88±18.29μgC/m³,which was much lower than Xi’an and similar to the concentration of BrC in Beijing and Yulin,but slightly higher than that in Nanjing.Further investigations on BrC sources suggested that biomass burning emission was the main source of BrC.Generally,the secondary sources of BrC were less significant than the primary sources.The results of the PMF model which quantified the contribution of BrC sources showed that biomass burning contributed 59.1%to BrC,with smoldering combustion of biomass as the main source.The mixed primary sources contributed 28.5%and the source related to nitrate and sulfate contributed less.