The oxidative potential of atmospheric particulate matter as an indicator of health risk of air pollution: a review

Health impact of atmospheric particulate matter is traditionally assessed using mass concentrations of particulate matter, yet epidemiological findings reveal inconsistencies, and respiratory and cardiovascular diseases often correlate more strongly with the oxidative potential of particulate matter, which reflects its ability to generate reactive oxygen species and induce oxidative stress. Here we review the oxidative potential of particulate matter in more than 200 field studies, with focus on epidemiological evidence, methods, influencing factors, and the contribution of the emission sources. Methods to assess the oxidative potential include electron spin resonance, the dithiothreitol and dichlorofluorescein assays, antioxidant depletion, and hydroxyl radical production. Major influencing factors comprise particle size and the presence of metals and carbonaceous aerosols. We observed that the oxidative potential varies substantially depending on particle size, the presence of transition metals and quinones, and emission sources such as biomass burning and traffic. Existing assays vary in their sensitivity to specific components of particulate matter, making comparisons between studies challenging. Methodological decisions such as the choice of extraction solvents and filter types can significantly change the measured oxidative potential. Overall, there is a need for standardized protocols and longitudinal studies linking oxidative potential to health outcomes.