Unraveling the Spatiotemporal Heterogeneity in the Oxidation Potential of Fine Particulate Matter in China

The oxidative potential (OP) of fine particulate matter (PM_2.5) is a more robust health impact indicator than mass concentration alone. While China's stringent air pollution controls have significantly reduced PM_2.5 levels, the temporal evolution of OP and its relationship with PM_2.5 remain unclear. This study establishes a national PM_2.5 OP database (2000-2020) using a source-oriented CMAQ model. Key findings reveal that OP decreases alongside PM_2.5 concentrations over the study period, but the decline in OP (16%) is less pronounced than that of PM_2.5 (37%) after 2012, leading to a 35% increase in mass-normalized OP (OP^m). Source apportionment analysis identifies distinct phase-specific drivers: anthropogenic secondary organic aerosols (ASOA) were the dominant contributor to OP increases (∼68%) prior to 2012, while reductions in transportation, power generation, and biomass burning emissions drove OP declines during 2012-2017. Post-2017, stringent controls on anthropogenic non-methane volatile organic compounds (NMVOCs) made ASOA the dominant declining source. Notably, urban-rural disparities in OP exposure exceed those of PM_2.5 mass concentrations, primarily reflecting differences in dominant emission sources. As the first nationwide study to systematically evaluate the decoupling of PM_2.5 mass and OP trends in China, these findings underscore the need for targeted strategies to mitigate PM-related health risks.