Substantial changes in gaseous pollutants and chemical compositions in fine particles in the North China Plain during the COVID-19 lockdown period: anthropogenic vs. meteorological influences

The rapid response to the COVID-19 pandemic led to unprecedented decreases in economic activities, thereby reducing the pollutant emissions. A random forest (RF) model was applied to determine the respective contributions of meteorology and anthropogenic emissions to the changes in air quality. The result suggested that the strict lockdown measures significantly decreased primary components such as Cr (inline-formula−67 inline-formula%) and Fe (inline-formula−61 inline-formula%) in inline-formulaPM2.5 (inline-formulap<0.01), whereas the higher relative humidity (RH) and inline-formulaNH3 level and the lower air temperature (inline-formulaT) remarkably enhanced the production of secondary aerosol, including inline-formula $M9inlinescrollmathmlchem{\mathrm{normal SO}}_{normal 4}^{normal 2-}$ 29pt17ptsvg-formulamathimg06a1e144313624090049b6627390d3e8 acp-21-8677-2021-ie00001.svg29pt17ptacp-21-8677-2021-ie00001.png (29 inline-formula%), inline-formula $M11inlinescrollmathmlchem{\mathrm{normal NO}}_{normal 3}^{-}$ 25pt16ptsvg-formulamathimgeb51cd45ba2a21283d090226a04e61ba acp-21-8677-2021-ie00002.svg25pt16ptacp-21-8677-2021-ie00002.png (29 inline-formula%), and inline-formula $M13inlinescrollmathmlchem{\mathrm{normal NH}}_{normal 4}^{+}$ 24pt15ptsvg-formulamathimg9d8f7ee8bf88d657d75cdcf077dbe3e2 acp-21-8677-2021-ie00003.svg24pt15ptacp-21-8677-2021-ie00003.png (21 inline-formula%) (inline-formulap<0.05). The positive matrix factorization (PMF) result suggested that the contribution ratios of secondary formation (SF), industrial process (IP), biomass burning (BB), coal combustion (CC), and road dust (RD) changed from 36 inline-formula%, 27 inline-formula%, 21 inline-formula%, 12 inline-formula%, and 4 inline-formula% before the COVID-19 outbreak to 44 inline-formula%, 20 inline-formula%, 20 inline-formula%, 9 inline-formula%, and 7 inline-formula%, respectively. The rapid increase in the contribution ratio derived from SF to inline-formulaPM2.5 implied that the intermittent haze events during the COVID-19 period were characterized by secondary aerosol pollution, which was mainly contributed by the unfavorable meteorological conditions and high inline-formulaNH3 level.

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Li, Rui / Zhao, Yilong / Fu, Hongbo / et al: Substantial changes in gaseous pollutants and chemical compositions in fine particles in the North China Plain during the COVID-19 lockdown period: anthropogenic vs. meteorological influences. 2021. Copernicus Publications.

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