Zhong Haobin, Huang Ru-Jin, Chang Yunhua, Duan Jing, Lin Chunshui, Chen Yang
State Key Laboratory of Loess and Quaternary Geology (SKLLQG), Center for Excellence in Quaternary Science and Global Change, and Key Laboratory of Aerosol Chemistry and Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, China; University of Chinese Academy of Sciences, Beijing 100049, China.
State Key Laboratory of Loess and Quaternary Geology (SKLLQG), Center for Excellence in Quaternary Science and Global Change, and Key Laboratory of Aerosol Chemistry and Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061, China; Institute of Global Environmental Change, Xi'an Jiaotong University, Xi'an 710049, China.
Sci Total Environ. 2021 Jul 15;778:144947. doi: 10.1016/j.scitotenv.2021.144947. Epub 2021 Mar 9.
The COVID-19 pandemic has drastically affected the economic and social activities, leading to large reductions in anthropogenic emissions on a global scale. Despite the reduction of primary emissions during the lockdown period, heavy haze pollution was observed unexpectedly in megacities in North and East China. In this study, we conducted online measurements of organic aerosol in a background site before and during the lockdown in Guanzhong basin, Northwest China. The oxygenated organic aerosol (OOA) increased from 24% of total OA (3.2 ± 1.6 μg m) before lockdown to 54% of total OA (4.5 ± 1.3 μg m) during lockdown, likely due to substantial decrease of NO emissions during lockdown which resulted in large increase of O and thus atmospheric oxidizing capacity. OOA showed higher mass concentrations and fractional contributions during lockdown than before lockdown, and increased with the increase of O in both periods. In comparison, aqueous secondary organic aerosol (aqSOA) showed high mass concentrations and fractional contributions in both polluted periods before and during lockdown with the increase of aerosol liquid water content (ALWC). The increase of aqSOA under high ALWC conditions is very likely the reason of pollution events during lockdown. Combined with trajectory analysis, the absence of Guanzhong cluster in polluted period during lockdown may play a key role in the OA variations between two polluted periods. In addition, when comparing the clusters from the same transmission directions between before lockdown and during lockdown, the OA fractions showed similar variations during lockdown in all clusters, suggesting the OA variations are widespread in northwest China.
新冠疫情极大地影响了经济和社会活动，导致全球范围内人为排放量大幅减少。尽管在封锁期间一次排放有所减少，但中国北方和东部的特大城市却意外出现了严重的雾霾污染。在本研究中，我们在中国西北关中盆地的一个背景站点，对封锁前后的有机气溶胶进行了在线测量。含氧有机气溶胶（OOA）在封锁前占总有机气溶胶（OA）的24%（3.2±1.6微克/立方米），在封锁期间占总OA的54%（4.5±1.3微克/立方米），这可能是由于封锁期间NO排放量大幅减少，导致O大幅增加，从而使大气氧化能力增强。与封锁前相比，OOA在封锁期间的质量浓度和分数贡献更高，且在两个时期均随O的增加而增加。相比之下，水相二次有机气溶胶（aqSOA）在封锁前和封锁期间的两个污染期，均随着气溶胶液态水含量（ALWC）的增加而呈现出较高的质量浓度和分数贡献。在高ALWC条件下aqSOA的增加很可能是封锁期间污染事件的原因。结合轨迹分析，封锁期间污染期关中团簇的缺失可能在两个污染期之间的OA变化中起关键作用。此外，在比较封锁前和封锁期间来自相同传输方向的团簇时，所有团簇在封锁期间的OA分数都呈现出相似的变化，这表明OA变化在中国西北地区普遍存在。
