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Background: Oxidative stress plays an important role in the health impacts of both outdoor fine particulate air pollution (PM2.5) and thermal stress. However, it is not clear how the oxidative potential of PM2.5 may influence the acute cardiovascular effects of temperature. Methods: We conducted a case-crossover study of hospitalization for cardiovascular events in 35 cities across Canada during the summer months (July-September) between 2016 and 2018. We collected three different metrics of PM2.5 oxidative potential each month in each location. We estimated associations between lag-0 daily temperature (per 5°C) and hospitalization for all cardiovascular (n = 44,876) and ischemic heart disease (n = 14,034) events across strata of monthly PM2.5 oxidative potential using conditional logistical models adjusting for potential time-varying confounders. Results: Overall, associations between lag-0 temperature and acute cardiovascular events tended to be stronger when outdoor PM2.5 oxidative potential was higher. For example, when glutathione-related oxidative potential (OPGSH) was in the highest tertile, the odds ratio (OR) for all cardiovascular events was 1.040 (95% confidence intervals [CI] = 1.004, 1.074) compared with 0.980 (95% CI = 0.943, 1.018) when OPGSH was in the lowest tertile. We observed a greater difference for ischemic heart disease events, particularly for older subjects (age >70 years). Conclusions: The acute cardiovascular health impacts of summer temperature variations may be greater when outdoor PM2.5 oxidative potential is elevated. This may be particularly important for ischemic heart disease events. [ABSTRACT FROM AUTHOR]

Background: Populations are simultaneously exposed to outdoor concentrations of oxidant gases (i.e., O 3 and NO 2 ) and fine particulate air pollution (PM 2.5 ). Since oxidative stress is thought to be an important mechanism explaining air pollution health effects, the adverse health impacts of oxidant gases may be greater in locations where PM 2.5 is more capable of causing oxidative stress.Methods: We conducted a cohort study of 2 million adults in Canada between 2001 and 2016 living within 10 km of ground-level monitoring sites for outdoor PM 2.5 components and oxidative potential. O x exposures (i.e., the redox-weighted average of O 3 and NO 2 ) were estimated using a combination of chemical transport models, land use regression models, and ground-level data. Cox proportional hazards models were used to estimate associations between 3-year moving average O x and mortality outcomes across strata of transition metals and sulfur in PM 2.5 and three measures of PM 2.5 oxidative potential adjusting for possible confounding factors.Results: Associations between O x and mortality were consistently stronger in regions with elevated PM 2.5 transition metal/sulfur content and oxidative potential. For example, each interquartile increase (6.27 ppb) in O x was associated with a 14.9% (95% CI = 13.0, 16.9) increased risk of nonaccidental mortality in locations with glutathione-related oxidative potential (OP GSH ) above the median whereas a 2.50% (95% CI = 0.600, 4.40) increase was observed in regions with OP GSH levels below the median (interaction P value <0.001).Conclusion: Spatial variations in PM 2.5 composition and oxidative potential may contribute to heterogeneity in the observed health impacts of long-term exposures to oxidant gases. [ABSTRACT FROM AUTHOR]

Background: The association between fine particulate matter (PM2.5) and mortality widely differs between as well as within countries. Differences in PM2.5 composition can play a role in modifying the effect estimates, but there is little evidence about which components have higher impacts on mortality.Methods: We applied a 2-stage analysis on data collected from 210 locations in 16 countries. In the first stage, we estimated location-specific relative risks (RR) for mortality associated with daily total PM2.5 through time series regression analysis. We then pooled these estimates in a meta-regression model that included city-specific logratio-transformed proportions of seven PM2.5 components as well as meta-predictors derived from city-specific socio-economic and environmental indicators.Results: We found associations between RR and several PM2.5 components. Increasing the ammonium (NH4+) proportion from 1% to 22%, while keeping a relative average proportion of other components, increased the RR from 1.0063 (95% confidence interval [95% CI] = 1.0030, 1.0097) to 1.0102 (95% CI = 1.0070, 1.0135). Conversely, an increase in nitrate (NO3-) from 1% to 71% resulted in a reduced RR, from 1.0100 (95% CI = 1.0067, 1.0133) to 1.0037 (95% CI = 0.9998, 1.0077). Differences in composition explained a substantial part of the heterogeneity in PM2.5 risk.Conclusions: These findings contribute to the identification of more hazardous emission sources. Further work is needed to understand the health impacts of PM2.5 components and sources given the overlapping sources and correlations among many components. [ABSTRACT FROM AUTHOR]