Heavy haze pollution during the COVID-19 lockdown in the Beijing-Tianjin-Hebei region, China.

To investigate the characteristics of particulate matter with an aerodynamic diameter less than 2.5 μm (PM _2.5 ) and its chemical compositions in the Beijing-Tianjin-Hebei (BTH) region of China during the novel coronavirus disease (COVID-19) lockdown, the ground-based data of PM _2.5 , trace gases, water-soluble inorganic ions, and organic and elemental carbon were analyzed in three typical cities (Beijing, Tianjin, and Baoding) in the BTH region of China from 5-15 February 2020. The PM _2.5 source apportionment was established by combining the weather research and forecasting model and comprehensive air quality model with extensions (WRF-CAMx). The results showed that the maximum daily PM _2.5 concentration reached the heavy pollution level (>150 μg/m ³ ) in the above three cities. The sum concentration of SO ₄ ^2- , NO ₃ ^- and NH ₄ ⁺ played a dominant position in PM _2.5 chemical compositions of Beijing, Tianjin, and Baoding; secondary transformation of gaseous pollutants contributed significantly to PM _2.5 generation, and the secondary transformation was enhanced as the increased PM _2.5 concentrations. The results of WRF-CAMx showed obviously inter-transport of PM _2.5 in the BTH region; the contribution of transportation source decreased significantly than previous reports in Beijing, Tianjin, and Baoding during the COVID-19 lockdown; but the contribution of industrial and residential emission sources increased significantly with the increase of PM _2.5 concentration, and industry emission sources contributed the most to PM _2.5 concentrations. Therefore, control policies should be devoted to reducing industrial emissions and regional joint control strategies to mitigate haze pollution.
(Copyright © 2021. Published by Elsevier B.V.)