Oxidative Potential of Atmospheric Particulate Matter: A Review of the Role of Metal−Organic Interactions, Mechanistic Insights, and Key Determinants

Oxidative stress, resulting from antioxidant depletion or excessive reactive oxygen species (ROS) production, is a key mechanism linking ambient particulate matter (PM) exposure to adverse health effects. The oxidative potential (OP) of PM, a measure of inhaled PM's capacity to deplete antioxidants or generate ROS, is largely driven by transition metals (TMs) such as iron and copper. However, coexisting organic matter also modulates OP, both directly through its own redox activity and indirectly via interactions with TMs that alter redox cycling. This review synthesizes current understanding of TM-organic interactions and their influence on the OP of PM, as assessed by acellular assays. We discuss mechanistic insights, key determinants, and the complexity of these interactions. The importance of considering TM-organic interactions in evaluating aggregate OP from individual components and apportioning OP to specific chemical species is highlighted, with implications for mechanistic studies and health risk assessment.