Association of mortality and combined oxidative capacity of ozone and nitrogen dioxide

Ozone (O3) and nitrogen dioxide (NO2) are two common gaseous pollutants that both possess oxidizing properties with consequences for human health and have an inextricable chemical relationship that could have distinct public health impacts when considered in combination. We examined the short-term associations of the combined oxidative capacity of O3 and NO2 (represented by Oxwt, the average of O3 and NO2 concentrations weighted by their standard electrode potential) with total, cardiovascular and respiratory mortality in 380 cities across 23 countries or regions between 1985 and 2020. Over 2 days (LAG01), a 10-ppb increase in Oxwt concentration was associated with an increase of 0.82% (95% confidence interval (CI): 0.55%, 1.10%) in total mortality, 1.09% (95% CI: 0.83%, 1.35%) in cardiovascular mortality and 0.88% (95% CI: 0.31%, 1.45%) in respiratory mortality. We also observed variations in this association by geographic region and study period. More deaths were attributable to Oxwt than to either O3 or NO2 but fewer than the sum of the two. Thus, Oxwt might be a valuable indicator for use in public health efforts to capture the combined effects of O3 and NO2.