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Haze caused by NOx oxidation under restricted residential and industrial activities in a mega city in the south of North China Plain.
Ma, Qingxia; Wang, Weisi; Wu, Yunfei; Wang, Fang; Jin, Liyuan; Song, Xiaoyan; Han, Yan; Zhang, Renjian; Zhang, Daizhou.
  • Ma Q; Key Laboratory of Geospatial Technology for the Middle and Lower Yellow River Regions, Ministry of Education, College of Geography and Environmental Science, Henan University, Kaifeng, 475004, China; Henan Key Laboratory of Integrated Air Pollution Control and Ecological Security, Kaifeng, 475004, C
  • Wang W; Henan Ecological and Environmental Monitoring Center, Zhengzhou, 450000, China.
  • Wu Y; Key Laboratory of Middle Atmosphere and Global Environment Observation (LAGEO), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China. Electronic address: wuyf@mail.iap.ac.cn.
  • Wang F; China West Normal University, Nanchong, 637000, China.
  • Jin L; Key Laboratory of Geospatial Technology for the Middle and Lower Yellow River Regions, Ministry of Education, College of Geography and Environmental Science, Henan University, Kaifeng, 475004, China.
  • Song X; College of Geosciences and Engineering, North China University of Water Resources and Electric Power, Zhengzhou, Henan, 450046, China.
  • Han Y; Key Laboratory of Geospatial Technology for the Middle and Lower Yellow River Regions, Ministry of Education, College of Geography and Environmental Science, Henan University, Kaifeng, 475004, China; Henan Key Laboratory of Integrated Air Pollution Control and Ecological Security, Kaifeng, 475004, C
  • Zhang R; Key Laboratory of Middle Atmosphere and Global Environment Observation (LAGEO), Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, 100029, China.
  • Zhang D; Faculty of Environmental and Symbiotic Sciences, Prefectural University of Kumamoto, Kumamoto, 862-8502, Japan. Electronic address: dzzhang@pu-kumamoto.ac.jp.
Chemosphere ; 305: 135489, 2022 Oct.
Article in English | MEDLINE | ID: covidwho-1906853
ABSTRACT
The formation of secondary aerosol species, including nitrate and sulfate, induces severe haze in the North China Plain. However, despite substantial reductions in anthropogenic pollutants due to severe restriction of residential and industrial activities in 2020 to stop the spread of COVID-19, haze still formed in Zhengzhou. We compared ionic compositions of PM2.5 during the period of the restriction with that immediately before the restriction and in the comparison period in 2019 to investigate the processes that caused the haze. The average concentration of PM2.5 was 83.9 µg m-3 in the restriction period, 241.8 µg m-3 before the restriction, and 94.0 µg m-3 in 2019. Nitrate was the largest contributor to the PM2.5 in all periods, with an average mass fraction of 24%-30%. The average molar concentration of total nitrogen compounds (NOx + nitrate) was 0.89 µmol m-3 in the restriction period, which was much lower than that in the non-restriction periods (1.85-2.74 µmol m-3). In contrast, the concentration of sulfur compounds (SO2 + sulfate) was 0.34-0.39 µmol m-3 in all periods. The conversion rate of NOx to nitrate (NOR) was 0.35 in the restriction period, significantly higher than that before the restriction (0.26) and in 2019 (0.25). NOR was higher with relative humidity in 40-80% in the restriction period than in the other two periods, whereas the conversion rate of SO2 to sulfate did not, indicating nitrate formation was more efficient during the restriction. When O3 occupied more than half of the oxidants (Ox = O3 + NO2), NOR increased rapidly with the ratio of O3 to Ox and was much higher in the daytime than nighttime. Therefore, haze in the restriction period was caused by increased NOx-to-nitrate conversion driven by photochemical reactions.
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Full text: Available Collection: International databases Database: MEDLINE Main subject: Air Pollutants / Air Pollution / COVID-19 Limits: Humans Country/Region as subject: Asia Language: English Journal: Chemosphere Year: 2022 Document Type: Article

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Full text: Available Collection: International databases Database: MEDLINE Main subject: Air Pollutants / Air Pollution / COVID-19 Limits: Humans Country/Region as subject: Asia Language: English Journal: Chemosphere Year: 2022 Document Type: Article