Enhanced secondary pollution offset reduction of primary emissions during COVID-19 lockdown in China.

Xin Huang,Derong Zhou,Chuanhua Ren,Liangduo Chen,Weijing Liu,Wei Cheng,Qingyan Fu,Jian Gao,Aijun Ding,Ximeng Qi,Wei Nie,Baoxian Liu,Nini Pang,Xuguang Chi,Kebin He,Haikun Wang,Jiaping Wang,Bo Zheng,Dan Tong,Fei Che,Fahe Chai,Zheng Xu,Yuanyuan Li,Qiang Zhang,Rong Tang,Wei Qin,Steven J Davis

doi:10.1093/nsr/nwaa137

Abstract

To control the spread of the 2019 novel coronavirus (COVID-19), China imposed nationwide restrictions on the movement of its population (lockdown) after the Chinese New Year of 2020, leading to large reductions in economic activities and associated emissions. Despite such large decreases in primary pollution, there were nonetheless several periods of heavy haze pollution in eastern China, raising questions about the well-established relationship between human activities and air quality. Here, using comprehensive measurements and modeling, we show that the haze during the COVID lockdown was driven by enhancements of secondary pollution. In particular, large decreases in NOx emissions from transportation increased ozone and nighttime NO3 radical formation, and these increases in atmospheric oxidizing capacity in turn facilitated the formation of secondary particulate matter. Our results, afforded by the tragic natural experiment of the COVID-19 pandemic, indicate that haze mitigation depends upon a coordinated and balanced strategy for controlling multiple pollutants.

Highlights

Efforts to control the spread of the 2019 novel coronavirus (COVID-19) have drastically reduced human activities worldwide [1,2]
Our results show that the dramatic reductions in NOx and other air pollution emissions during China’s COVID lockdown led to substantial increases in O3, which in turn increased atmospheric a b c
Policies have focused on the reduction of primary emissions such as SO2, NOx and NH3 [14,46,47], while efforts have been proposed to reduce ozone pollution target VOCs [18]

Summary

INTRODUCTION

Efforts to control the spread of the 2019 novel coronavirus (COVID-19) have drastically reduced human activities worldwide [1,2]. By testing the sensitivity of our WRF-Chem simulations to different NOx reduction rates (10%– 90%), we find a non-linear response in both O3 and NO3 radical in eastern China (Fig. S13) These results show that the sudden and precipitous reduction in NOx emissions could cause a substantial increase of O3, NO3 radical and a nonlinear response of oxidation products like H2SO4, HNO3 and N2O5 and oxygen-containing organic compound, which have a direct linkage to the enhancement of secondary PM species. Based on matrix-type WRF-Chem simulations considering the synergetic effects from NOx and VOCs emission reduction, we obtained EKMA (empirical kinetic modeling approach) isopleths for main oxidants and gaseous oxidation products for eastern China (Fig. 5) They clearly demonstrate the high non-linear dependence of oxidants and secondary PM formation upon the reduction of primary emissions

CONCLUSION AND POLICY IMPLICATIONS

Findings

MATERIALS AND METHODS