Air Quality Changes during the COVID-19 Lockdown in an Industrial City in North China: Post-Pandemic Proposals for Air Quality Improvement

To better understand the changes in air pollutants in an industrial city, Handan, North China, during the COVID-19 lockdown period, the air quality and meteorological conditions were recorded from 1 January to 3 March 2020 and the corresponding period in 2019. Compared to the corresponding period in 2019, the largest reduction in PM2.5-10, PM2.5, NO2 and CO occurred during the COVID-19 lockdown period. PM2.5-10 displayed the highest reduction (66.6%), followed by NO2 (58.4%) and PM2.5 (50.1%), while O-3 increased by 13.9%. Similarly, compared with the pre-COVID-19 period, NO2 significantly decreased by 66.1% during the COVID-19 lockdown, followed by PM2.5-10 (45.9%) and PM2.5 (42.4%), while O-3 increased significantly (126%). Among the different functional areas, PM2.5 and PM2.5-10 dropped the most in the commercial area during the COVID-19 lockdown. NO2 and SO2 decreased the most in the traffic and residential areas, respectively, while NO2 increased only in the township and SO2 increased the most in the industrial area. O-3 increased in all functional areas to different extents. Potential source contribution function analysis indicated that not only the local air pollution lessened, but also long-distance or inter-regional transport contributed much less to heavy pollution during the lockdown period. These results indicate that the COVID-19 lockdown measures led to significantly reduced PM and NO2 but increased O-3, highlighting the importance of the synergetic control of PM2.5 and O-3, as well as regional joint prevention and the control of air pollution. Moreover, it is necessary to formulate air pollution control measures according to functional areas on a city scale.