Mortality Risk of Short-Term Air Pollution Exposure in Urban and Rural Chinese Populations: A Nationwide Time-Stratified Case-Crossover Study, 2008-2020

Abstract

Background Epidemiologic evidence underpinning the updated World Health Organization Air Quality Guidelines (WHO AQGs) is primarily derived from urban populations, which remains challenging for implementing the guidelines in low- and middle-income countries (LMICs) where most people reside in rural. Here, we aimed to characterize the associations between ambient air pollution and mortality in Chinese populations living in both urban and rural areas, where rural populations have not been studied previously at national level. Methods In this nationwide time-stratified case-crossover study, we extracted non-accidental death cases of all ages in both urban and rural areas during 2008-2020 from National Mortality Surveillance System, which covered 40,300 representative township-level administration units from 29 provinces, representing nearly 24% of Chinese population. The urban-rural classification of participants’ addresses was defined based on the China’s National Bureau of Statistics. Daily township-level exposures to ambient particulate matter in diameter less than 10 μm and 2.5 μm (PM10 and PM2.5), nitrogen dioxide (NO2), carbon monoxide (CO), sulfur dioxide (SO2), and 8-hour maximum ozone (O3) were estimated using the Nested Air Quality Prediction Modeling System. We applied conditional logistic regression models to characterize province-specific associations of mortality risks with air pollutants, and then combined the estimates using random-effects meta-analysis. ResultsA total of 61,228,962 all-cause deaths were compiled in the analysis. During the study period, 87.3% of the death cases had PM2.5 exposure on the same day of death above current short-term guideline level of 15 μg/m3, and 35.6% had O3 exposure above guideline level of 100 μg/m3. In this analysis, significant morality risks were observed in associations with short-term exposures to all six criteria pollutants. In specific, each 10 µg/m3 increase in PM2.5 exposure levels on the same day of death was associated with increased mortality risks of 0.22 (95% confidence interval [95CI%], 0.13 to 0.31). Notably, with emerging exposure of O3, we derived the nationwide estimate as of 0.18% (95CI%, 0.11 to 0.25), which is also comparable with global estimates. Nonetheless, the mortality risks for major criteria pollutants PM2.5, PM10, NO2, SO2, and O3 were slightly greater among urban populations than those observed in rural populations. ConclusionThis nationwide study firstly showed increased mortality risks of PM2.5 exposure below guideline level, as well as significant morality risks of O3 exposure. Our timely findings highlight the importance quantifying air pollution exposure associated risks in LMICs, and provide practical approaches supporting the global implementation of AQGs.

Note:
Funding declaration: The work was supported by National Natural Science Foundation of China (82273589), Beijing Natural Science Foundation (7234400, 7222246), and China Postdoctoral Science Foundation (2021M690249).

Conflict of Interests: The authors declare no competing interests.

Keywords: Air pollution, Risks assessment, Mortality, Urban and rural populations