Within-City Spatial Variations in Multiple Measures of PM_2.5 Oxidative Potential in Toronto, Canada

Few studies have characterized within-city spatial variations in the oxidative potential of fine particulate air pollution (PM_2.5). In this study, we evaluated multiple measures of PM_2.5 oxidative potential across Toronto, Canada (2016-2017), including glutathione/ascorbate-related oxidative potential (OP^GSH and OP^AA) and dithiothreitol depletion (OP^DTT). Integrated 2-week samples were collected from 67 sites in summer and 42 sites in winter. Multivariable linear models were developed to predict OP based on various land use/traffic factors, and PM_2.5 metals and black carbon were also examined. All three measures of PM_2.5 oxidative potential varied substantially across Toronto. OP^AA and OP^DTT were primarily associated with traffic-related components of PM_2.5 (i.e., Fe, Cu, and black carbon) whereas OP^GSH was not a strong marker for traffic during either season. During summer, multivariable models performed best for OP^AA ( R_CV² = 0.48) followed by OP^DTT ( R_CV² = 0.32) and OP^GSH ( R_CV² = 0.22). During winter, model performance was best for OP^DTT ( R_CV² = 0.55) followed by OP^GSH ( R_CV² = 0.50) and OP^AA ( R_CV² = 0.23). Model parameters varied between seasons, and between-season differences in PM_2.5 mass concentrations were weakly/moderately correlated with seasonal differences in OP. Our findings highlight substantial within-city variations in PM_2.5 oxidative potential. More detailed information is needed on local sources of air pollution to improve model performance.