Chemical composition characteristics and source analysis of PM 2.5 in Jiaxing, China: Insights into the effect of COVID-19 outbreak.

Jiaxing is a medium-sized city in the Yangtze River Delta (YRD), which showed complex local and surrounding pollution sources. To study the COVID-19 impact on the ambient PM in Jiaxing, we collected the PM samples from January 2 to April 25, 2020 and analyzed their chemical compositions (including carbon components, water-soluble ions (WSIs), and inorganic elements). The concentration of PM was 83.13 30.93 μg/m before COVID-19 pandemic, and then remarkably decreased with COVID-19 outbreak due to the suspension of mobility and industrial activities. Meanwhile, the concentrations of main chemical species (carbon components, water-soluble ions and inorganic elements) of PM all decreased from period A (January 2 to 20, 2020) to period B (January 23 to February 10, 2020). Moreover, Trajectory clustering analysis showed that close-range transport was one of the dominant factors throughout all the period, except for period D (April 1 to 25, 2020). In addition, PSCF model indicated that the COVID-19 outbreak resulted in a significant decrease of WPSCF value. This study highlighted the differences in chemical compositions and sources of PM since COVID-19 pandemic were reported and provide a better understanding of the impact of COVID-19 outbreak on PM.