Short-term joint effects of ambient PM_2.5 and O₃ on mortality in Beijing, China

In recent years, air pollution caused by co-occurring PM_2.5 and O₃, named combined air pollution (CAP), has been observed in Beijing, China, although the health effects of CAP on population mortality are unclear.

We employed Poisson generalized additive models (GAMs) to evaluate the individual and joint effects of PM_2.5 and O₃ on mortality (nonaccidental, respiratory, and cardiovascular mortality) in Beijing, China, during the whole period (2014-2016) and the CAP period. Adverse health effects were assessed for percentage increases (%) in the three mortality categories with each 10-μg/m³ increase in PM_2.5 and O₃. The cumulative risk index (CRI) was adopted as a novel approach to quantify the joint effects.

The results suggested that both PM_2.5 and O₃ exhibited the greatest individual effects on the three mortality categories with cumulative lag day 01. Increases in the nonaccidental, cardiovascular, and respiratory mortality categories were 0.32%, 0.36%, and 0.43% for PM_2.5 (lag day 01) and 0.22%, 0.37%, and 0.25% for O₃ (lag day 01), respectively. There were remarkably synergistic interactions between PM_2.5 and O₃ on the three mortality categories. The study showed that the combined effects of PM_2.5 and O₃ on nonaccidental, cardiovascular, and respiratory mortality were 0.34%, 0.43%, and 0.46%, respectively, during the whole period and 0.58%, 0.79%, and 0.75%, respectively, during the CAP period. Our findings suggest that combined exposure to PM_2.5 and O₃, particularly during CAP periods, could further exacerbate their single-pollutant health risks.

These findings provide essential scientific evidence for the possible creation and implementation of environmental protection strategies by policymakers.