Oxidative potential of fresh vs. O₃-aged PM_2.5 across urban and rural sources in China

Fine particulate matter (PM_2.5) is a major health risk, yet its impacts are still largely assessed using mass concentration, which does not capture toxicity. Recently, oxidative potential (OP) has emerged as a more relevant metric, reflecting the ability of particles to generate reactive oxygen species. A current challenge, especially in China, is understanding how emission sources and ozone (O₃) aging affect PM_2.5 toxicity, given that O₃ is an increasingly important pollutant there. A work by Ma and co-workers published in J. Environ. Sci. (doi.org/10.1016/j.jes.2024.04.023) addressed this by evaluating the OP of fresh and O₃-aged PM_2.5 from multiple sources in China using the dithiothreitol (DTT) assay. Biomass burning particles exhibited the highest OP, up to 35 times greater than suburban PM_2.5, driven by water-soluble organics and transition metals. While O₃ aging generally reduced OP, it also induced complex chemical transformations. These findings highlight that PM_2.5 toxicity is dynamic and source-dependent, underscoring the need to move beyond mass-based air quality metrics.