西安市大气颗粒物中棕碳的吸光性研究

摘要/Abstract

摘要： 利用离线滤膜-溶剂提取-连续光谱分析的方法在 2016 年 12 月 25 日到 2017 年 12 月 26 日期间对西安市大气颗粒物进行了连续一年的监测与分析。用石英纤维滤膜收集大气 PM2:5 样品, 再分别利用超纯水和甲醇超声萃取样品中的水溶性有机碳 (WSOC) 和甲醇可溶性有机碳 (MSOC), 最后进行紫外-可见吸收光谱分析获得样品光吸收特性。对西安市水溶性棕碳 (BrC) 和甲醇溶性 BrC 在 365 nm 下冬季和夏季的吸光贡献分析发现, 冬、夏两个季节甲醇提取的有机组分光吸收效率均高于水提取的, 甲醇溶性有机碳质量吸收效率 [MAE(MSOC)] 年均值 [(1.60±0.67) m2·g−1] 是水溶性有机碳质量吸收效率 [MAE(WSOC)] 年均值 [(0.90±0.47) m2·g−1] 的 1.17 倍, 表明有机溶剂萃取组分中含有更多的吸光能力更强的物质。冬季的 MAE(WSOC) 为 (2.05±0.86) m2·g−1, MAE(MSOC) 为 (1.53±0.36) m2·g−1; 夏季的 MAE(WSOC) 为 (1.06±0.24) m2·g−1, MAE(MSOC) 为 (0.51±0.17) m2·g−1。冬季的 MAE 值总体高于夏季的, 且冬季的 WSOC 的 E250/E265 值 (5.25) 相对低于夏季 (5.58), 可能因冬季燃煤取暖排放导致。对 BrC 中的水溶性有机碳与气象六要素浓度进行了线性拟合, 结果显示 WSOC 与 PM2:5 (R2 = 0.6417) 和 PM10 (R2 = 0.4035) 有一定的相关性, 但与 O3 (R2 = 0.0682) 没有显示出明显的相关性, 表明其二次光化学反应的来源占比很小。

关键词: 颗粒物, 吸光气溶胶, 棕碳, 质量吸收效率

Abstract: Off-line membrane filtration, solvent extraction and continuous spectral analysis were mainly used to monitor and analyze the atmospheric particulate matter in Xi’an city, China, for a continuous year from December 25, 2016 to December 26, 2017. Atmospheric PM2:5 samples were collected by quartz fiber filter firstly, and then water-soluble organic carbon (WSOC) and methanol-soluble organic carbon (MSOC) were ultrasonically extracted by ultra-pure water and methanol respectivelly. Finally, UV-vis absorption spectrum was used to obtain the light absorption characteristics of the samples. By analyzing the absorption contribution of water soluble brown carbon (BrC) and methanol soluble BrC in winter and summer in Xi′an at 365 nm, it was found that the absorption efficiency of methanol extraction was higher than that of water extraction in winter and summer, and the annual mean of methanol-soluble organic carbon mass absorption efficiency (MAE(MSOC)) ((1.60±0.67) m2·g−1) is 1.17 times of that of water-soluble organic carbon mass absorption efficiency (MAE(WSOC)) ((0.90±0.47) m2·g−1), indicating that there is a large amount of organics with stronger light absorption in MSOC. In winter, MAE(WSOC) and MAE(MSOC) are (2.05±0.86) m2·g−1 and (1.53±0.36) m2·g−1 respectivelly, while MAE(WSOC) and MAE(MSOC) in summer are (1.06±0.24)) m2·g−1 and (0.51±0.17) m2·g−1 respectivelly, which shows that MAE in winter is higher than that in summer. And the calculated E250/E265 value of WSOC in winter (5.25) is lower than that in summer (5.58), which may be caused by winter coal-fired heating emissions. The correlation analysis between WSOC and the six meteorological elements was carried out, and it is shown that WSOC is correlated with PM2:5 (R2 = 0.6417) and PM10 (R2 = 0.4035), while there is no obvious correlation between WSOC and O3 (R2 = 0.0682), indicating that the source of the secondary photochemical reaction accounts for a small proportion.

Key words: particulate, absorbing aerosols, brown carbon, mass absorption efficiency

中图分类号:

X131.1

朱鑫, 陈庆彩∗, 王擎雯, 李锦雯, 程静雯, 郎涵睿, 王茂颖. 西安市大气颗粒物中棕碳的吸光性研究[J]. 大气与环境光学学报, 2022, 17(1): 125-134.

ZHU Xin, CHEN Qingcai∗, WANG Qingwen, Li Jinwen, CHENG Jingwen, LANG Hanrui, WANG Maoying. Absorbance of brown carbon in atmospheric particulate matter in Xi′an[J]. Journal of Atmospheric and Environmental Optics, 2022, 17(1): 125-134.

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