Investigation of PM pollution during COVID-19 pandemic in Guangzhou, China.

The COVID-19 pandemic has raised awareness about various environmental issues, including PM pollution. Here, PM pollution during the COVID-19 lockdown was traced and analyzed to clarify the sources and factors influencing PM in Guangzhou, with an emphasis on heavy pollution. The lockdown led to large reductions in industrial and traffic emissions, which significantly reduced PM concentrations in Guangzhou. Interestingly, the trend of PM concentrations was not consistent with traffic and industrial emissions, as minimum concentrations were observed in the fourth period (3/01-3/31, 22.45 μg/m) of the lockdown. However, the concentrations of other gaseous pollutants, e.g., SO, NO and CO, were correlated with industrial and traffic emissions, and the lowest values were noticed in the second period (1/24-2/03) of the lockdown. Meteorological correlation analysis revealed that the decreased PM concentrations during COVID-19 can be mainly attributed to decreased industrial and traffic emissions rather than meteorological conditions. When meteorological factors were included in the PM composition and backward trajectory analyses, we found that long-distance transportation and secondary pollution offset the reduction of primary emissions in the second and third stages of the pandemic. Notably, industrial PM emissions from western, southern and southeastern Guangzhou play an important role in the formation of heavy pollution events. Our results not only verify the importance of controlling traffic and industrial emissions, but also provide targets for further improvements in PM pollution.