Air pollution in megacities represents one of the greatest environmental challenges. Our observed results show that the dramatic NOx decrease (77%) led to significant O3 increases (a factor of 2) during the COVID-19 lockdown in megacity Hangzhou, China. Model simulations further demonstrate large increases of daytime OH and HO2 radicals and nighttime NO3 radical, which can promote the gas-phase reaction and nocturnal multiphase chemistry. Therefore, enhanced NO3− and SO42− formation was observed during the COVID-19 lockdown because of the enhanced oxidizing capacity. The PM2.5 decrease was only partially offset by enhanced aerosol formation with its reduction reaching 50%. In particular, NO3− decreased largely by 68%. PM2.5 chemical analysis reveals that vehicular emissions mainly contributed to PM2.5 under normal conditions in Hangzhou. Whereas, stationary sources dominated the residual PM2.5 during the COVID-19 lockdown. This study provides evidence that large reductions in vehicular emissions can effectively mitigate air pollution in megacities.
Bibliographical noteFunding Information:
This work was funded by the National Natural Science Foundation of China (42075096 and 91844301), the National Key R&D Program of China (2017YFC0212700), Zhejiang Provincial Natural Science Foundation of China (LZ19D050001), Zhejiang Meteorological Science and Technology Program (2019YB11), LAC/CMA (2020B02), and China Postdoctoral Science Foundation (2020M681823). Gongda Lu thanks the PhD studentship funded by China Scholarship Council.
© 2020. The Authors.
- air pollution
- chemical composition
- fine particles
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)