[Concentration Variation and Source Analysis of Metal Elements in PM_2.5 During COVID-19 Control in Suzhou]

To study the variation in concentration and source analysis of metal elements during COVID-19 control in Suzhou, a multi-metal online monitor was used to determine hourly online data of 14 metal elements from December 1, 2019 to March 31, 2020. This study analyzed variation in concentration and source analysis of metal elements using a PMF model before, during, and after shutdown during COVID-19 control. The results showed that the concentrations of Cr, Mn, Zn, and Fe during shutdown decreased the most, by 87.6%, 85.6%, 78.3%, and 72.2%, respectively, compared with those before shutdown. The concentrations of Mn, Cr, Zn, and Fe after shutdown increased the most, by 227.0%, 215.4%, 147.4%, and 113.4%, respectively, compared with those of the previous stage. The diurnal variation in K differed at three stages. Zn showed a single peak shape at three stages, but the peak width and peak time were different. Unlike the concentrations, the diurnal variations in Fe, Mn, Pb, Se, and Hg were not significantly changed. The daily variation characteristics of Ca, Ba, Cu, As, Cr, and Ni during and after shutdown were significantly different from those before shutdown. The results of source analysis by the PMF model showed that metal elements mainly came from dust, motor vehicle, coal burning, industrial smelting, and mixed-combustion sources. Among them, the concentration of industrial smelting sources changed greatly, with the concentration decreasing by 89.0% during shutdown and increasing by 358.0% after shutdown.