Critical fine particles in road dust: oxidative potential, distribution, and driving factors

Urban road dust act as both a sink and a secondary source of airborne fine particles (FPs), yet the components that determine their oxidative potential (OP), a metric of particle-induced reactive oxygen species, remain poorly understood. Here, we combined acellular OP measurements using the dithiothreitol assay with single particle ICP time-of-flight mass spectrometry to analyze FPs from Shanghai road dust. Samples collected in 2013 and 2022, spanning a period of major energy and emission transitions in China. The OP of road dust FPs decreased by approximately 28% between 2013 and 2022, significantly in industrial areas but not in traffic areas. Among all measured particle components, Fe-rich FPs associated with toxic metals (e.g., Cr, Zn, and Pb) emerged as the strongest correlates of OP. Notably, magnetite-rich FPs, a proxy for such Fe-rich toxic carriers, accounted for only 7.0% of the FP mass in selected dust samples but contributed 29%-68% of OP, highlighting their disproportionate oxidative activity. Variable importance analysis for Fe-rich FPs associated with toxic metals showed that the highest ranked factors shifted from industrial-related factors in 2013 to traffic-related factors in 2022. Our findings suggest that traffic-related emissions warrant particular attention in future mitigation strategies.