Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, School of Environmental Sciences and Engineering, Nanjing University of Information Science and Technology, Nanjing, 210044, China.
Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, School of Environmental Sciences and Engineering, Nanjing University of Information Science and Technology, Nanjing, 210044, China; School of Atmospheric Sciences, Nanjing University, Nanjing, 210023, China.
Chemosphere. 2020 Jul;251:126350. doi: 10.1016/j.chemosphere.2020.126350. Epub 2020 Feb 29.
Brown carbon (BrC), a significant wavelength-dependent atmospheric absorber of solar radiation, plays a key role in photochemistry and long-lasting haze episodes. Herein, two types of BrC extracted from one-year PM samples (June 2017-May 2018 in Nanjing), i.e. methanol-extracted organic carbon (MSOC) and ultrapure water-extracted organic carbon (WSOC), were obtained to investigate distinct optical properties of atmospheric BrC. The extraction efficiency of BrC was as high as 91% in methanol solution, and the corresponding light absorption coefficient (Abs) of MSOC at 365 nm (Abs, 7.75 ± 3.95 Mm) was approximately 1.6 times that of WSOC (Abs, 4.84 ± 2.97 Mm), indicating that the water-insoluble compounds mostly affected the light absorption of BrC. The seasonal variations of Abs and Abs were followed the sequence of winter > spring > autumn > summer, due to the dominated emissions from fossil fuel combustion and biomass burning in the cooling seasons. Additionally, four fluorescent chromophores in WSOC and MSOC, containing three humic-like chromophores and one protein-like chromophore, exhibited the highest fluorescent intensities in winter but weakest in summer. The lower humification index (HIX) in MSOC reflects that humic-like chromophores were preferentially water-soluble, in coordination with high degree of photo-oxidation and aromaticity. Fluorescence index (FI) of BrC was also higher in winter because of the effects of photo-bleaching, whereas biological index (BIX) remained stable throughout a year. Considering the correlation between primary organic carbon (POC) and secondary organic carbon (SOC), aside from the contribution of primary emissions, secondary formation has become another major source to atmospheric BrC in Nanjing.
棕色碳（BrC）是一种对太阳辐射具有显著波长依赖性的大气吸光物质，在光化学和长时间雾霾事件中起着关键作用。在此，我们从一年的 PM 样品（2017 年 6 月至 2018 年 5 月在南京采集）中提取了两种 BrC，即甲醇提取的有机碳（MSOC）和超纯水提取的有机碳（WSOC），以研究大气 BrC 的不同光学特性。在甲醇溶液中，BrC 的提取效率高达 91%，相应的 MSOC 在 365nm 处的吸光系数（Abs）（7.75±3.95Mm）约为 WSOC 的 1.6 倍（Abs，4.84±2.97Mm），表明水不溶性化合物主要影响 BrC 的光吸收。由于冷却季节化石燃料燃烧和生物质燃烧的排放占主导地位，Abs 和 Abs 的季节性变化顺序为冬季>春季>秋季>夏季。此外，WSOC 和 MSOC 中的四个荧光发色团，包含三个类腐殖质发色团和一个类蛋白发色团，在冬季表现出最高的荧光强度，而在夏季则最弱。MSOC 中的腐殖化指数（HIX）较低反映了类腐殖质发色团优先具有水溶性，与高度光氧化和芳香性相协调。由于光漂白的影响，BrC 的荧光指数（FI）在冬季也较高，而生物指数（BIX）在一年中保持稳定。考虑到一次有机碳（POC）和二次有机碳（SOC）之间的相关性，除了一次排放的贡献外，二次形成已成为南京大气 BrC 的另一个主要来源。
