Variations in the characteristics and sources of PM2.5 during the COVID-19 lockdown in Xiangyang, Hubei Province, central China

This study investigated the variations in the characteristics and sources of fine particulate matter (PM_2.5) during the COVID-19 lockdown. The research was conducted in Xiangyang, a city in Hubei Province, central China, which is influenced by air pollutant transport from northern China and was the last city in Hubei to implement lockdown measures following the COVID-19 outbreak. PM_2.5 samples were obtained between 19 January and April 19, 2020. A significant reduction in the average PM_2.5 concentration was observed, falling from 148 ± 33 μg m⁻³ prior to the lockdown to 93 ± 40 μg m⁻³ after its implementation. Consistent with expectations, concentrations of polycyclic aromatic hydrocarbons (PAHs) and elemental carbon (EC) also gradually declined. Interestingly, 1 p.m._2.5 pollution event was observed during the lockdown, attributed to enhanced atmospheric oxidation capacity, as indicated by the elevated sulfur oxidation ratio (SOR), nitrogen oxidation ratio (NOR) and secondary organic carbon (SOC) levels. Results of diagnostic ratios and principal component analysis multiple linear regression (PCA-MLR) indicated an increased contribution from secondary aerosol formation and residential combustion emission during the lockdown, while vehicle emissions decreased. Geographical and meteorological data further suggested non-negligible influence from regional transport. Our findings reveal a complicated evolution of PM_2.5 species and sources amidst the enforcement of pollution control strategies. This underscores the necessity for regional coordinated source management and synergistic control of O₃ and PM_2.5, and provides a critical case for the design of differentiated emission control strategies.