Time-series analysis of impact of ground-level ozone exposure on resident mortality in Hohhot City from 2018 to 2023

Background Exposure to ozone (O₃) is closely associated with an increased risk of mortality in the population, but this association exhibits regional heterogeneity, and relevant research in northern and central-western China is limited. Hohhot, as a typical city in the northern and western region, has seen a significant upward trend in O₃ concentrations (an increase of 17.9 μg·m⁻³ in 2020 compared to 2016). Studies targeting this region can fill the regional research gap.

Objective To evaluate the health effects of ground-level O₃ exposure on resident mortality in Hohhot from 2018 to 2023.

Methods Air quality, meteorological, and mortality data in Hohhot from 2018 to 2023 were collected. A time-series analysis based on Quasi-Poisson generalized additive model (GAM) was employed, controlling for meteorological factors, day-of-week effects, and holiday effects, to assess the impact of O₃ on non-accidental mortality, mortality from circulatory system diseases (CSD), and mortality from respiratory system diseases (RSD).

Results From 2018 to 2023, the non-accidental, CSD, and RSD mortalities in Hohhot amounted to 89721, 47394, and 11378 cases, respectively. The daily maximum 8-hour average O₃ concentration (O₃-8 h) was 90.00 μg·m⁻³. According to the Class I limit (100 μg·m⁻³) of GB 3095—2012 Ambient Air Quality Standard, the annual average number of days exceeding the standard was 144 d. For single-day lag effects, O₃ had the strongest health impact on non-accidental mortality and CSD mortality on the current day (lag0), with effect sizes of 0.78% (95%CI: 0.33%, 1.24%) and 1.10% (95%CI: 0.50%, 1.71%), respectively. The strongest impact on RSD mortality occurred on the second day (lag2), with an effect size of 1.61% (95%CI: 0.61%, 2.62%). The subgroup analyses showed that for every 10 μg·m⁻³ increase in O₃-8 h concentration, the risk of non-accidental mortality in females increased by 0.70% (95%CI: 0.01%, 1.41%); for CSD mortality, the risk in males and individuals aged ≥65 years increased by 0.73% (95%CI: 0.01%, 1.47%) and 0.76% (95%CI: 0.13%, 1.39%), respectively. During the warm season, statistically significant risks were observed for non-accidental, CSD, and RSD mortalities, with increases of 1.07% (95%CI: 0.54%, 1.60%), 1.31% (95%CI: 0.59%, 2.04%), and 2.27% (95%CI: 1.07%, 3.49%), respectively. In the two-pollutant models incorporating sulfur dioxide (SO₂), nitrogen dioxide (NO₂), carbon monoxide (CO), particulate matter with an aerodynamic diameter of 10 micrometers or less (PM₁₀), and fine particulate matter (PM_2.5), the effect estimates (excess risk) of O₃ remained stable and statistically significant (P<0.05), indicating model robustness.

Conclusion Ground-level O₃ exposure in Hohhot increases mortalities due to non-accidental causes, CSD, and RSD, with more pronounced effects during the warm season. Females and individuals aged ≥65 years may be susceptible populations. Therefore, relevant authorities should prioritize the potential health risks of O₃ exposure, particularly to vulnerable groups, and promote targeted prevention and control strategies.