This study was designed to investigate changes in the characteristics and sources of air pollutants during the lockdown caused by the COVID-19 outbreak. The city of Xiangyang in Hubei Province, central China, was chosen as the study site. It received air pollutants from north China, and was the last city in the province to be closed during the COVID-19 outbreak. PM_2.5 samples were collected from 19^th January to 19^th April 2020, which covered the period before, during, and after the city’s lockdown. The PM_2.5 decreased from 148 ± 33 μg·m^-3 before the lockdown to 93 ± 40 μg·m^-3 during the lockdown. The change of polycyclic aromatic hydrocarbons (PAHs) and elemental carbon (EC) was consistent with the anticipation of city lockdown gradually decreasing. Diagnostic ratios and principal component analysis multiple linear regression (PCA-MLR) results showed that during the lockdown period, secondary sources and home combustion sources increased while vehicle emission sources decreased significantly. The influence of regional transport was observed through geographical and meteorological data. Interestingly, pollution sources/formation processes continued, even though emission sources were significantly reduced during the lockdown. Using the sulfur oxidation ratio (SOR), nitrogen oxidation ratio (NOR) and secondary organic carbon (SOC), this formation of pollution was caused by the increase of O₃, which led to the enhancement of atmospheric oxidation capacity and increased formation of secondary particulate matter. Meanwhile, regional transport also made a certain contribution. This study showed the complex variations in chemical species and sources of PM_2.5, highlighting the need for coordination of regional prevention and coordinated control of O₃ and PM_2.5.
 

COVID-19, PM2.5, chemical composition, source apportionment, regional transportation, secondary particles.