Abstract：
Brown carbon (BrC), the light-absorbing component of organic aerosols, plays a significant role in climate change and atmospheric photochemistry. However, the water-insoluble fractions of BrC have not been extensively studied, limiting the assessment of the overall climate effects of BrC. In this study, water-soluble and -insoluble organic carbon (i.e., WSOC and WIOC) in wintertime aerosols in Hefei were subsequently fractionated, and their fluorescence properties were comparatively investigated with the excitation-emission matrix method. WIOC contributing 57.1 % was the major component of organic carbon. WSOC with the largest contribution from humic-like regions exhibited a redshift compared to WIOC. Three humic-like substances (HULIS) with different oxidation degrees and one protein-like substances (PRLIS) were identified as the major fluorescent components by the parallel factor analysis. WSOC had more highly oxygenated HULIS, whereas low-oxygenated HULIS dominated WIOC. Nighttime WIOC contained more less-oxygenated species. The positive matrix factorization analysis suggested that biomass burning (43 %) was the largest source of both fluorescent WSOC and WIOC. Coal combustion contributed much more to fluorescent WIOC (40 %), whereas secondary formation contributed more to fluorescent WSOC (12 %). During aerosol pollution episodes, the increase in fluorescence efficiency was much greater for WIOC (25 %) than for WSOC (12 %), and WSOC and WIOC experienced a redshift and blueshift in emission wavelength, respectively. WSOC had more highly oxygenated HULIS, while WIOC had more less-oxygenated HULIS in aerosol episodes than the non-episodic periods. In addition, aerosol pollution was accompanied by the increased contributions of biomass burning and coal combustion to both fluorescent WSOC and WIOC, while the decreased relative contribution of secondary formation to fluorescent WSOC. Our findings highlighted the different fluorescence properties, compositions and sources of fluorescent WSOC and WIOC, providing a comprehensive view of BrC aerosols.
摘要：
褐碳(BrC),有机气溶胶的光吸收成分，在气候变化和大气光化学中起着重要作用。然而,尚未对BrC的水不溶性部分进行广泛研究，限制对BRC整体气候影响的评估。在这项研究中,水溶性和不溶性有机碳(即，随后对合肥冬季气溶胶中的WSOC和WIOC）进行了分馏，用激发-发射矩阵法比较研究了它们的荧光性质。WIOC占57.1％是有机碳的主要成分。与WIOC相比，腐殖质样地区贡献最大的WSOC表现出红移。通过平行因子分析，确定了三种具有不同氧化程度的腐殖质（HULIS）和一种蛋白质样物质（PRLIS）为主要荧光成分。WSOC有更高的含氧HULIS，而低氧HULIS主导WIOC。夜间WIOC包含更多含氧化合物。正矩阵分解分析表明，生物质燃烧（43％）是荧光WSOC和WIOC的最大来源。燃煤对荧光WIOC的贡献更大(40%)，而次级形成对荧光WSOC的贡献更大(12%)。在气溶胶污染事件期间，WIOC（25％）的荧光效率的增加远远大于WSOC（12％），WSOC和WIOC在发射波长上经历了红移和蓝移，分别。WSOC有更高的含氧HULIS，而WIOC在气溶胶发作中的HULIS含量低于非发作期。此外,气溶胶污染伴随着生物质燃烧和煤炭燃烧对荧光WSOC和WIOC的贡献增加，而次级形成对荧光WSOC的相对贡献减少。我们的发现强调了不同的荧光特性，荧光WSOC和WIOC的组成和来源，提供BRC气溶胶的全面视图。
