Air quality response in China linked to the 2019 novel Coronavirus (COVID-19) mitigation

Abstract:

Efforts to stem the spread of COVID-19 in China hinged on severe restrictions to human movement starting January 23rd, 2020 in Wuhan and subsequently to other provinces. We quantified the ancillary impacts on air pollution and human health based on inverse emissions estimates using an assimilation of multiple satellite observations including TROPOMI NO2 and OMI SO2. Chinese NOx emissions were reduced by 36% from early January to mid-February, with more than 80% of reductions occurring after their respective lockdown in most provinces, which corresponds to about 9 % of the global total emissions. The reduction in NO2 concentrations have significantly different spatial patterns than emissions, underscoring the importance of non-linear chemistry. These emissions declines lead to a bifurcated response in MDA8 ozone, which increased over central and northern China by up to 16 ppb but decreased over southern China. The PM2.5 response to emissions decreases everywhere, with reductions of up to 23 μgm^-3. Corresponding to the emission changes in northern and eastern China, MDA8 and PM2.5 outside the regions were increased by up to 7 ppb and decrease by up to 6 μgm^-3, respectively, across East Asia including western Japan and Korean peninsula. In southern China, the increases in ozone due to the non-local impacts compensated for parts of the ozone decreases due to the local emission reductions. Consequently, health impacts, which we compute based upon population and exposure-response relationships, account for the effect of both local and non-local emissions changes. Air pollution appears to have substantially offset hospital admissions related to COVID-19 in China, augmenting mitigation efforts, such as in the Hubei province with about 400 reduced admissions. Changes in human exposure are associated with about 2,100 increased ozone-related morbidity incidences and avoidance of at least 60,000 PM2.5-related morbidity incidences in China. This framework can be readily extended to global responses that can situate these regional changes with worldwide lockdowns.