Key Laboratory of Tibetan Environment Changes and Land Surface Processes, Institute of Tibetan Plateau Research, Chinese Academy of Sciences (CAS), Beijing 100101, China; University of Chinese Academy of Sciences, Beijing 100049, China.
Institute of Environment and Sustainable Development, Banaras Hindu University, Varanasi 221005, India.
Environ Pollut. 2020 Feb;257:113616. doi: 10.1016/j.envpol.2019.113616. Epub 2019 Nov 14.
Brown carbon (BrC) has been proposed as an important driving factor in climate change due to its light absorption properties. However, our understanding of BrC's chemical and optical properties are inadequate, particularly at remote regions. This study conducts a comprehensive investigation of BrC aerosols in summer (Aug. 2013) and winter (Jan. 2014) at Southeast Tibetan Plateau, which is ecologically fragile and sensitive to global warming. The concentrations of methanol-soluble BrC (MeS-BrC) are approximately twice of water-soluble BrC (WS-BrC), demonstrating the environmental importance of water-insoluble BrC are previously underestimated with only WS-BrC considered. The mass absorption efficiency of WS-BrC (0.27-0.86 m g) is lower than those in heavily polluted South Asia, indicating a distinct contrast between the two sides of Himalayas. Fluorescence reveals that the absorption of BrC is mainly attributed to humic-like and protein-like substances, which broaden the current knowledge of BrC's chromophores. Combining organic tracer, satellite MODIS data and air-mass backward trajectory analysis, this study finds BrC is mainly derived from bioaerosols and secondary formation in summer, while long-range transport of biomass burning emissions in winter. Our study provides new insights into the optical and chemical properties of BrC, which may have implications for environmental effect and sources of organic aerosols.
棕碳（BrC）因其光吸收特性而被认为是气候变化的一个重要驱动因素。然而，我们对 BrC 的化学和光学性质的理解还不够充分，特别是在偏远地区。本研究对夏季（2013 年 8 月）和冬季（2014 年 1 月）青藏高原东南部的 BrC 气溶胶进行了综合调查，该地区生态脆弱，对全球变暖敏感。甲醇可溶 BrC（MeS-BrC）的浓度约为水溶 BrC（WS-BrC）的两倍，这表明以前只考虑 WS-BrC，对水不溶性 BrC 的环境重要性估计不足。WS-BrC 的质量吸收效率（0.27-0.86 m g）低于南亚污染严重地区，表明喜马拉雅山两侧存在明显差异。荧光表明 BrC 的吸收主要归因于腐殖质样和蛋白质样物质，这拓宽了对 BrC 发色团的现有认识。本研究结合有机示踪剂、卫星 MODIS 数据和大气质量后向轨迹分析，发现 BrC 主要来源于夏季的生物气溶胶和二次形成，而冬季则是生物质燃烧排放的长距离传输。本研究为 BrC 的光学和化学性质提供了新的见解，这可能对环境效应和有机气溶胶的来源有影响。
