Limited Regional Aerosol and Cloud Microphysical Changes Despite Unprecedented Decline in Nitrogen Oxide Pollution During the February 2020 COVID-19 Shutdown in China.

Abstract

Following the emergence of a novel coronavirus in Wuhan, China instituted shutdown measures starting in late January and continuing into February 2020 to arrest the spread of disease. This resulted in a sharp economic contraction unparalleled in recent Chinese history. Satellite retrievals show that nitrogen dioxide pollution declined by an unprecedented amount (~50% regionally) from its expected unperturbed value, but regional‐scale column aerosol loadings and cloud microphysical properties were not detectably affected. The disparate impact is tied to differential economic impacts of the shutdown, in which transportation, a disproportionate source of nitrogen oxide emissions, underwent drastic declines (~90% reductions in passenger traffic), whereas industry and power generation, responsible for >90% of particulate emissions, were relatively less affected (~20% reductions in electricity and thermal power generation). A combination of anomalously warm and humid meteorological conditions and complex chemical interactions further decreased nitrogen dioxide concentrations but likely enhanced secondary aerosol formation.