Policy-driven changes in the health risk of PM_2.5 and O₃ exposure in China during 2013-2018

China issued a series of control measures to mitigate PM_2.5 pollution, including long-term (i.e., Air Pollution Prevention and Control Action Plan, APPCAP) and short-term (emergency measures in autumn and winter) acts. However, the O₃ concentration increased significantly as PM_2.5 levels sharply decreased when these measures were implemented. Therefore, the policy-driven positive/negative health effects of PM_2.5/O₃ need to be comprehensively estimated. The health impact function (HIF) is applied to evaluate the health burden attributable to long- and short-term PM_2.5 and O₃ exposure. The results show that the PM_2.5 concentration decreased by 42.95% in 74 cities, whereas O₃ pollution is increased by 17.56% from 2013 to 2018. Compared with 2013, the number of premature deaths attributable to long- and short-term PM_2.5 exposure decreased by almost 5.31 × 10⁴ (95% confidence interval [CI]: 2.87 × 10⁴-4.71 × 10⁴) (10.13%) and 3.00 × 10⁴ (95% CI: 1.66 × 10⁴-4.39 × 10⁴) (72.49%), respectively, in 2018. In contrast, O₃-attributable deaths, increased by 1.98 × 10⁴ (95% CI: 0.31 × 10⁴-3.59 × 10⁴) (130.57%) and 0.91 × 10⁴ (95% CI: 0.50 × 10⁴-1.33 × 10⁴) (76.16%) for long- and short-term exposure, respectively. The number of avoidable deaths attributed to PM_2.5 reduction is larger than the level of premature deaths related to increasing O₃. Although annual mean PM_2.5 concentrations have fallen rapidly, the benefits of reducing long-term exposure are limited, whereas the deaths associated with acute exposure decrease more significantly due to the reduction of heavy-pollution days by implementing emergency measures. The results show appreciable effectiveness in protecting human health and illustrate that synchronous control of PM_2.5 and O₃ pollution should be emphasized.