棕色碳气溶胶来源、性质、测量与排放估算

Origin,Properties,Measurement and Emission Estimation of Brown Carbon Aerosols

随着对碳气溶胶吸光性认识的提高,近年来吸光有机碳——BrC（brown carbon,棕色碳）的吸光问题成为继BC（black carbon,黑碳）之后国际大气环境领域的新热点.基于已有的研究报道,将BrC大体分为焦油类物质、类腐殖质（HULIS）和其他吸光性有机气溶胶三大类,其来源包括一次排放和二次生成2种.由于BrC缺少BC所具有的类石墨烯结构,致使颗粒间较为分散,加之含氧官能团比重较高,因而在水及有机溶剂中均有较强的可溶性.BrC的光学性质通常借助AAE（ngstrm吸收波长指数）、MAE（质量吸收效率）、RI（折射率）及SSA（单次散射反照率）来表示,其中由于BrC分子结构中缺少sp2杂化成分,形成了区别于BC的典型特征,即AAE〉1（而对于BC,其AAE=1））.虽然已有借助于光学法、热光法、化学法和质谱法进行BrC测定的报道,但目前没有公认的标准测定方法和参考物质,测定结果实际依赖于选定的测定方式.在排放估算研究方面,BrC远落后于BC,致使有些排放估算方法多以相伴的BC排放量作为参照.建议今后对BrC研究应主要面向气候影响、生成机理、测定方法、排放因子与控制策略等领域来展开.

As understanding of the light absorption of carbonaceous aerosols increases,brown carbon（ Br C,i. e.,light-absorbing organic carbon）,another species of light-absorbing carbon in addition to black carbon（ BC）,has been highlighted in recent years and has become a new hotspot in the research field of atmospheric environment internationally. However,research on Br C in China is not common until now. Based on existing literature,Br C can be roughly divided into three categories,i. e.,tarry materials,humic-like substances（ HULIS） and other light-absorbing organic aerosols,and can originate from two pathways,i. e.,primary emission and secondary formation. In addition,Br C is in a weakly-bound aggregate morphology because of the shortage of graphitic structure,and is usually highly soluble because of the richness of oxygen content. The optical properties of Br C are often characterized by ngstrm absorption exponent（ AAE）,mass absorption efficiency（ MAE）,refractive index（ RI） and single scattering albedo（ SSA）,with a distinctive feature of AAE 1,in contrast to BC（ for BC,AAE = 1）,due to the deficiency of sp2 hybrid orbital structure in Br C. Although Br C is by some researchers quantified through methods based on the optical,thermal/optical,chemical and mass-spectrometric principles,there are no widelyaccepted standard methods and reference materials for Br C quantification, which makes Br C measurements operationallydependent. Given that the history of BC emission estimation is longer than that of Br C＇s,some researchers have tried estimating Br C emissions by referencing concurrently released BC emissions.Future research on Br C is proposed towards Br C＇s climate effects,formation mechanisms,emission factors,measurement methods and emissions abatement.