1. Measurement report of the change of PM2.5 composition during the COVID-19 lockdown in urban Xi'an: Enhanced secondary formation and oxidation
- Author
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Thorsten Hoffmann, Haobin Zhong, Colin D. O'Dowd, Yifang Gu, Jing Duan, Chunshui Lin, Ru-Jin Huang, and Yunhua Chang
- Subjects
Environmental Engineering ,010504 meteorology & atmospheric sciences ,Coronavirus disease 2019 (COVID-19) ,Chemistry ,010501 environmental sciences ,01 natural sciences ,Pollution ,Inorganic sulfate ,Aerosol ,chemistry.chemical_compound ,Nitrate ,Environmental chemistry ,Environmental Chemistry ,Haze pollution ,Relative humidity ,Composition (visual arts) ,Sulfate ,Waste Management and Disposal ,0105 earth and related environmental sciences - Abstract
Enhanced secondary aerosol formation was observed during the COVID-19 lockdown in Xi'an, especially for polluted episodes. More oxidized‑oxygenated organic aerosol (MO-OOA) and sulfate showed the dominant enhancements, especially in large particle-mode. Meanwhile, relative humidity (RH) showed a positive promotion on the formation of sulfate and MO-OOA during the lockdown, but had no obvious correlation with less oxidized‑oxygenated organic aerosol (LO-OOA) or nitrate. Organosulfurs (OS) displayed a higher contribution (~58%) than inorganic sulfate to total sulfate enhancement in the polluted episode during the lockdown. Although the total nitrate (TN) decreased during the lockdown ascribing to a larger reduction of inorganic nitrate, organic nitrate (ON) showed an obvious increase from pre-lockdown (0.5 ± 0.6 μg m-3 and 1 ± 2% of TN) to lockdown (5.3 ± 3.1 μg m-3 and 17 ± 9% of TN) in the polluted case (P < 0.05). In addition, RH also displayed a positive promotion on the formation of ON and OS, and the increases of both OS and ON were much efficient in the nighttime than in the daytime. These results suggest that higher RH and stagnant meteorology might facilitate the sulfate and MO-OOA enhancement, especially in the nighttime, which dominated the secondary aerosol enhancement in haze pollution during the lockdown.
- Published
- 2021
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