Pollution characteristics, ecological risk assessment and source apportionment of mental elements in PM_2.5 in Jiaxing City

In order to study the pollution characteristics, ecological risks and pollution sources of metal elements in PM_2.5 in Jiaxing, the 24-hour online monitoring data of Shanxi (SX) site in Jiaxing City from March 1, 2019 to February 29, 2020 were collected to investigate PM_2.5 and 12 metal elements (K, Ca, Fe, Zn, Mn, Cd, Pb, Cr, Ni, Ba, Cu and V) in PM_2.5 samples. The results indicated that the average concentration of PM_2.5 was 30.94 μg/m³ during the sampling period, which was better than the secondary concentration standard of Ambient Air Quality Standard (GB 3095-2012) (PM_2.5, 35 μg/m³). PM_2.5 concentrations in the samples were in the following order: winter > spring > autumn > summer. Meanwhile, the concentrations of metal elements were ranked as follows: K > Fe > Zn > Ca > Mn > Pb > Ba > Cu > Cr > Ni > Cd > V (the total concentration being 1.36 μg/m³), in which concentrations of Fe and Zn were affected by the COVID-19 outbreak and the Spring Festival. It was found that both the total metal concentration and each metal element concentration in PM_2.5 increased with the pollution increasing, while the proportion of most metal elements in PM_2.5 decreased. The enrichment factor (EF) method results indicated that K, Ca, Fe, Ba and V were considered almost with no elements enrichment, while Zn and Cd showed extremely heavy enrichment. The geoaccumulation index (I_geo) results implied that Cu, Pb, Zn and Cd were strongly influenced by anthropogenic activities. In addition, the ecological risk index (E_i) results of mental elements indicated that Mn, Cr and Ni showed slight ecological risk, and Zn, Cu, Pb and Cd showed high ecological risk. In addition, the principal component analysis indicated that industrial processes, coal combustion, vehicle traffic and crustal sources were the main sources of these metal elements in PM_2.5 in Jiaxing City.