Spatial-temporal responses of atmospheric pollutants to the COVID-19 lockdown across the Yangtze River Delta region

ABSTRACT

From January 1 to February 29, 2020, using hourly monitoring data of criteria pollutants in Shanghai, Nanjing, Hefei and Hangzhou, combined with the vertical columns of SO2 and NO2 from satellite inversions, we explore the pollution levels and response characteristics of urban atmospheric pollutants in the Yangtze River Delta region to the COVID-19 lockdown. The results show that, except O3, the average concentrations of air pollutants during the lockdown (from January 24 to February 10) were lower than that before the lockdown but higher than that after the lockdown, indicating that emission reduction was not the only factor in terms of governing air quality. The ratio of PM2.5/PM10 during the lockdown period was higher than before and after the lockdown, indicating that the secondary generation of aerosols has an important contribution to the fine particle pollution that still occurs during the lockdown period. We observed a significant increase of Ox levels (p <0.01) during the lockdown, suggesting that atmospheric oxidation capacity may be substantially enhanced in the context of NO2 reduction. Spatially, the O3 typically centered in individual city as hotspots, indicating its nature of local emission and formation. However, other pollutants (including PM2.5, PM10, CO, SO2, and NO2) demonstrated a gradual decrease gradient from north to south, satellite observations pinpointed that North China Plain was the major source of regional transport, which can be further validated by back-trajectory analysis. © 2021, Science Press. All right reserved.