Source-specific health risks induced by PM_2.5-bound metallic species under different pollution scenarios in a cold megacity of Northeast China

As minor fractions of PM_2.5, metallic species are particularly associated with health risks. Furthermore, the health risks and health risk-involved source contributions induced by them might be discrepant under different pollution scenarios. To this end, this study first sampled fine particulate matter (PM_2.5) in the Harbin city, China from May 2017 to April 2018, then compared the concentrations of 22 PM_2.5-bound metallic species in five pollution scenarios (heating season, non-heating season, clean days (C), slightly polluted days (SP), and heavily polluted days (HP)), and finally assessed the source-involved health risks. During the sampling period, the average concentration of metallic elements was 4.58 μg m⁻³, constituted a minor fraction (4.75%) in PM_2.5. The CR values induced by PM_2.5-bound metals were 6.72 × 10⁻⁴–8.07 × 10⁻⁴ for adults and 1.26 × 10⁻⁴–1.51 × 10⁻⁴ for children, while HQ values were 1.92–2.67 for adults and 0.36–0.50 for children. The comparative analysis indicates that most metallic elements recorded higher mass concentration and health risk values in the heating season than those in the non-heating season, and followed the ascending gradient of C–SP–HP. Using the positive matrix factorization model (PMF), coal combustion (12.14% ~ 43.50% for children and 11.96% ~ 43.21% for adults) and traffic emission (6.91% ~ 32.37% for children and 6.91% ~ 32.27% for adults) were the dominant sources of CR values; while coal combustion (6.49% ~ 53.40% for children and 12.03% ~ 38.23% for adults), traffic emission (5.55% ~ 34.91% for children and 11.78% ~ 31.34% for adults), and mineral dust (8.67% ~ 54.31% for children and 11.35% ~ 37.29% for adults) were the dominant sources of HQ values. Moreover, the health risks induced by sea salt were higher in non-heating season than those in heating season, while the health risks induced by traffic emission were on the contrary. The findings of this study may have significance in promoting metal-involved health risk alleviation and formulating health-oriented pollution mitigation measures.