Research progress of determination methods of atmospheric brown carbon

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.