Respiratory and Cardiovascular Effects of Ozone Modified by PM2.5: Evidence from a Panel Study and a Meta-Regression...

Disease burden of ground-level ozone (O3) may be underestimated partly due to unresolved inconsistencies in O3 health effects reported in the literature. Inaccurate exposure assessment, copollutant confounding, and other methodological issues have not fully explained the inconsistencies. To explore an alternative explanation, we hypothesize that acute cardiorespiratory effects of O3 can be modified by longer-term PM2.5 exposure (30 day average), which may predispose people to heightened susceptibility. We tested the hypothesis by using two complementary approaches, including a panel study in healthy adults and a meta-regression analysis of O3 on cardiorespiratory effects reported in the literature. In the panel study, we observed significantly stronger associations between short-term O3 exposure and decreased lung function (FEV1, FEF25-75, and PEF) and increased systolic and diastolic blood pressure under higher PM2.5 exposure levels (>22 μg/m3). These findings were further supported by the meta-regression analysis, which showed that study areas with higher annual PM2.5 concentrations had greater effect sizes of short-term ozone exposure on both FEV1 and blood pressure. Together, our results suggest that higher background PM2.5 concentrations may amplify the acute adverse cardiorespiratory effects of O3, which may partly explain the inconsistent health effect of ozone exposure reported in prior studies.