Reshaping metal composition and sources to reduce PM_2.5 oxidative potential by clean energy policies in Xi'an, China

“Iron-fisted Smog Control '1 + 9' Action Plan” in Shaanxi Province in 2017 promoted clean heating in rural households including “coal-to-gas” and “coal-to-electricity” conversions. This study collected PM_2.5 samples in Xi'an during three periods (pre-, mid-, and post-policy implementation from 2016 to 2021) and quantified policy-driven changes in particulate toxicity and underlying influence factors through DCFH-based oxidative potential (OP) measurements. The results demonstrated significant decreases in characteristic metals from residential combustion sources (As, Pb, K) alongside increases in vehicular emission tracers (Cu, Mn) during policy implementation. A progressive decline in OP (16.28 ± 2.43, 14.41 ± 2.59, and 13.77 ± 2.62 nM H₂O₂ m⁻³ in pre-, mid-, and post-policy implementation periods) confirmed the efficacy of clean energy projects in reducing oxidative stress potential. OP showed strong positive correlations (R = 0.35–0.47, P < 0.01) with water-soluble toxic metals (Fe, Cu, Mn). The source apportionment of PM_2.5 OP was conducted using a combined approach of positive matrix factorization and multilayer perceptron. The results revealed that the contribution of residential combustion sources to OP decreased from 32.1 % before the policy implementation to 25.9 % afterward, showing a significant response to the clean energy policies enacted in the Guanzhong region. Meanwhile, in the post-policy period, vehicle emissions (37.3 %) surpassed residential combustion as a major contributor to OP. This study verifies that policy interventions focusing on replacing scattered coal and biomass burning effectively reduced PM_2.5 OP through decreasing toxic coal/biomass combustion components (As, Pb, K), achieving dual-control strategies targeting both mass concentration and toxicity reduction in precision air pollution management.