Quantitative analysis of PM_2.5 oxidative potential: Insights into the role of organic compounds and sources

This study evaluates the oxidative potential (OP) of PM_2.5 and its chemical drivers across three contrasting environments in South Korea: a residential area, a cement factory, and a charcoal kiln facility. Mass-normalized OP (OPm, reflecting intrinsic particle reactivity) ranged from 9.5 to 13.1 pmol min⁻¹ μg⁻¹ and volume-normalized OP (OPv, reflecting exposure-related oxidative burden) ranged from 197 to 403 pmol min⁻¹ m⁻³ , with the highest OPv observed at the charcoal kiln site. Seasonal variation was evident, particularly in the residential area where OPm increased in warmer seasons. Machine learning models (XGBoost with SHAP interpretation) identified dicarboxylic acids and specific secondary organic aerosol (SOA) tracers, including toluene-derived products, as major contributors to OPm and OPv, underscoring the dominant role of chemically reactive organic components. Source apportionment using Positive Matrix Factorization (PMF) identified seven major sources, among which aged organic aerosol (19 % of PM_2.5 mass) and industrial sources (8 % of PM_2.5 mass) were the top two contributors to OPv. In contrast, biomass burning plus cooking emissions contributed the most to PM mass (24 %) but ranked only fourth in OPv contribution. These findings highlight the importance of identifying chemically reactive sources beyond traditional mass-based metrics to better assess the potential health relevance of PM_2.5. Understanding the sources of redox-active organic species, such as aged organic aerosol, may be more effective in reducing the oxidative potential of ambient PM_2.5, a property linked to its capacity for redox activity.