大气棕色碳测定方法研究进展
Research progress of determination methods of atmospheric brown carbon
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摘要: 大气棕色碳(brown carbon,BrC)是碳气溶胶中具有吸光性的有机碳(OC)的总称,与黑碳(black carbon,BC)相比,其吸光能力随波长变短增长更快,是近年大气气溶胶能量收支研究领域的热点之一。BrC来源广泛且并不特指一种化学物质,因而当前鲜有公认的BrC标准测定方法或参考物质。介绍了文献报道的BrC测定方法,包括通过溶剂萃取的方式将BrC分离的化学法,借助BrC与BC吸光性差别分离出BrC吸光贡献的光学法,在传统的热光学法碳分析仪上借助BrC与BC热稳定性差异从光学上分离BrC与其他物质的热光学法,以及面向分子水平的BrC表征方法质谱法。对各类测定方法的原理、特点、应用和研究进展进行了系统的总结和评述,指出当前几乎所有关于BrC的定量测定方法都是探索性的,具有很大的局限性,需构建一个不排斥多样性和独立性的包容性方法体系,以便使不同方法的测定结果具有一定程度的可比性。Abstract: Atmospheric brown carbon (BrC) is a category of organic carbon (OC) that is light-absorbing in carbon aerosols. Compared with black carbon (BC), BrC absorption capacity grows faster with shorter wavelengths, and has become one of the hot spots in the research field of atmospheric aerosol energy budget. Because BrC comes from a wide range of sources and does not specifically refer to a single substance, there are no widely-accepted standard methods or reference materials for the determination of BrC. Various approaches for the determination of BrC appearing in literature were described, including the chemical method of separating BrC by solvent extraction, the optical method of distinguishing the absorption contribution of BrC from total based on the difference in light-absorption features between BrC and BC, the thermal/optical method of optically separating BrC from other substances in a few wavelengths on the traditional thermal/optical carbon analyzer in reference to the difference of thermal stability between BrC and BC, and the mass spectrometry of characterizing BrC at molecular-level. The principle, characteristics, application and research progress of the methods were systematically summarized and reviewed. It was also noted that almost all the quantitative determination methods currently used for BrC qua.pngication were exploratory and had great limitations. Optimization measures were needed to make up for the defects of individual methods, including the need for an inclusive methodology that did not exclude diversity and independence of existing methods, in order to make different methods intercomparable to a certain extent.