| Atmospheric particles are primary problems of urban environment pollution in China,especially in eastern cities during heating period.And metal elements（MEs）in atmospheric particles exert adverse effects on ecological environment and human health.This study analyzed the variations of pollution characteristics of atmospheric particles and MEs before and after Three-year Action Plan to Win the Blue Sky Defense War worked through particles collections in winter 2016 and 2020 in Beijing.And the risks assessment models were further used to explore the ecological and health risk levels of MEs in atmospheric particles for two years,as well as the main contributing MEs and exposure pathways,combining with size distributions.Our researches showed that atmospheric particles in Beijing in winter 2016 and2020 were influenced by fine and coarse mode,where most serious fine mode particles originated from primary emissions such as combustions and secondary formations of gaseous precursors.And particles-bound MEs had high ecological risks,and caused cumulative non-carcinogenic and moderate carcinogenic risks for both adults and children for two years.In addition,the mass concentrations of atmospheric particles and MEs in different sizes all decreased in 2020 compared to2016,especially in fine mode.Health risks of MEs in 2020 were lower than 2016.And combined online PM2.5 and PM10 indicated the implementation of Three-Year Action Plan reduced absolute contributions of various emission sources significantly such as vehicles,dust,industry,and coal combustion,alleviating particles pollutions obviously.However,atmospheric particles in 2020 were shifted to larger size compared to 2016,and the proportions of MEs in particles all increased to a certain extent,especially in coarse mode.For reasons,there were floating dusts during sampling period in 2020,and the control effects of emission sources as vehicle exhaust,industry and coal combustion were greater than that of dust during Three-Year Action Plan,supporting ecological risks of MEs in 2020 were significantly higher than that in 2016.Thus,control of dusts need to be strengthened in future.As for ecological risks,the main contributions of MEs were successively Cd>>Tl>Zn>Pb in 2016,and Cd>>Zn>Cu in 2020.Additionally,for health risks,the contributions to non-carcinogenic risks were mainly Pb,As,Cr（VI）and Zn in2016,and As,Pb,Cr（VI）,Co,Zn in 2020.And MEs causing carcinogenic risks were mainly Ni,Cr（VI）,As,Pb in 2016,and Ni,Cr（VI）,As,Co in 2020.Moreover,the main exposure pathway for health risks was oral ingestion for As,Pb,Co,Zn but inhalation for Cr（VI）,Ni. |
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