High time resolution observation of PM2.5 Brown carbon over Xi'an in northwestern China: Seasonal variation and source apportionment
High time resolution observation of PM2.5 Brown carbon over Xi'an in northwestern China: Seasonal variation and source apportionment
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西安上空 PM2.5 褐碳高时间分辨率观测：季节变化与来源解析
DOI：
10.1016/j.chemosphere.2019.124530
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发表时间：
2019
期刊：
影响因子：
8.8
通讯作者：
Cao Junji
中科院分区：
文献类型：
--
作者：
Lei Yali;Shen Zhenxing;Zhang Tian;Lu Di;Zeng Yaling;Zhang Qian;Xu Hongmei;Bei Naifang;Wang Xin;Cao Junji
越来越多的证据表明，在严重的灰霾事件中，棕色碳（BrC）的增加。本文以西安市为研究对象，对冬、夏季PM2. 5中的BrC进行了逐时测量。甲醇在365 nm处的吸收系数（babs 365，甲醇，通常用作甲醇可溶性BrC的替代物）在冬季采样期间是夏季的7倍以上。甲醇提取物（MAC 365，甲醇，归一化为babs 365，甲醇-有机碳，OC）的质量吸收截面在冬季是夏季的近1.5倍。在冬季灰霾天气中，平均babs 365、methanol浓度在午夜达到峰值，上午最低，而非灰霾天气中，平均babs 365、methanol浓度在下午高，夜间低。与冬季的日变化模式不同，夏季霾天甲醇的日变化呈现中午高、下午低的特点。然而，在非烟霞天，模式显示上午高水平和夜间低水平。在冬季和夏季采样期间，化学物种水平、babs 365、甲醇和MAC 365、甲醇的有霾和无霾变化表明，大气老化的影响是复杂的，可以增强或减少BrC的光吸收。基于正矩阵因子受体模型和多元线性回归的源解析结果表明，在冬季采样期，一次排放是BrC排放的重要贡献者，而在夏季，次生排放起着重要作用。
There is growing evidence suggesting the enhancement of brown carbon (BrC) in severe haze episodes. In this study, hourly measurements of BrC in PM2.5were conducted in Xi'an, a typical city in northwestern China during winter and summer. The absorption coefficient for methanol exacts at 365 nm (babs365, methanol, which is typically used as a proxy of methanol-soluble BrC) in the winter sampling period was over 7 times than that in summer. The mass absorption cross-section for methanol extracts (MAC365, methanol, normalized bybabs365, methanolto organic carbon, OC) in winter sampling period was nearly 1.5 times of that in the summer. During the winter haze days, the averagebabs365,methanolpeaked at midnight and the lowest values in the morning, in contrast to high levels in afternoon and low levels at night in non haze days. Unlike the diurnal patterns in winter, summerbabs365, methanoldiurnal variation presented high midday and low afternoon levels in haze days. However, in non haze days, the pattern showed high morning levels and night low levels. Haze and non haze variations of chemical species levels,babs365, methanol, andMAC365, methanolduring winter and summer sampling time showed that the effects of atmospheric aging were complex and could either enhance or reduce light absorption of BrC. Source apportionment based on positive matrix factorization receptor model and multiple linear regressions showed that primary emission was an important contributor to BrC emissions during the winter sampling period, whereas secondary formation played an important role in summer.