[Characteristics, Sources, and Health Risk Changes of Heavy Metal Pollution Carried by PM2.5 in Beijing and Evaluation of Policy Effectiveness].

To evaluate the effectiveness of air pollution prevention and control measures in Beijing, this study measured the content of 13 metal elements, including seven heavy metal elements [As, Cd, Co, Cr（Ⅵ）, Ni, Pb, and V], through daily PM_2.5 sampling （n = 934） in the urban area of Beijing for four years. We analyzed the interannual changes in the concentration levels of various metals and the differences between heating and non-heating seasons, used a positive definite matrix factorization （PMF） model for quantitative source analysis, and used health risk assessment methods to evaluate the health risks of six metals. The results showed that, except for a few metal elements such as Cr（Ⅵ） and Ni, which showed an increase in concentration in individual years, the overall concentration of each element showed a downward trend. The concentrations of ten metals, including V, Co, Pb, and Mn, during the heating season were significantly higher than those during the non-heating season （P<0.05）. There were five main types of atmospheric heavy metal pollution sources in Beijing： dust sources, transportation sources, coal sources, industrial sources, and fuel oil combustion sources. Among them, the proportion of coal sources was generally decreasing. The HQ values of each metal were all less than 1, indicating no non-carcinogenic health risk. The carcinogenic risk of Ni and Cd could be ignored, while the R values of As, Co, and Cr（Ⅵ） in each year were between 10^-6 and 10^-4, indicating a certain carcinogenic risk. The interannual trends in atmospheric concentration, sources, and health risks indicate that the relevant measures for air pollution prevention and control in Beijing have achieved positive results.