Changes in source-specific health risks of PM_2.5-bound trace elements after the residential "coal-to-gas" conversion...

The concentration of atmospheric fine particles (PM_2.5) has been considerably lowered in Beijing as a result of the implementation of a number of air pollution control initiatives. Nevertheless, the understanding of the impact of clean air measures on the health risks of PM_2.5-bound trace elements is still limited. In this study, the concentrations and chemical fractionation of 14 trace elements in PM_2.5 in Beijing after the "coal-to-gas" conversion measure were measured and compared with our previous study in Beijing before the measure. The major elements changed from Fe, Zn, and Pb before the measure to Fe, Ti, and Cu after the measure. The bioavailability of Pb, Zn, Cu, Sr, Ba, and Cr increased by approximately 5 %-44 % after the measure, while the bioavailability of Cd, Mn, As, Co, V, Fe, Ni, and Ti decreased by approximately 0.5 %-31 %, which may be mainly attributed to changes in their emission sources. After the measure, the relative contribution of traffic-related emissions to the total concentration of 14 elements increased by 12.1 %, and coal combustion decreased by 17.5 %. Traffic-related emissions (92.8 %) were the primary causes of carcinogenic risk after the measure, while traffic-related emissions (52.2 %) and coal combustion (41.4 %) dominated before the measure. This study elucidates changes in concentrations, chemical fractionation, bioavailability, sources, and health risks of PM_2.5-bound trace elements in Beijing before and after the "coal-to-gas" conversion measure and suggests that traffic-related emissions should still be the main focus in the future.