Exposure to submicron particulate matter and long-term survival: Cross-cohort analysis of 3 Chinese national surveys.

Background: Cohort evidence linking increased mortality with airborne fine particulate matter (PM, particulate matter [PM] with aerodynamic diameter ≤2.5 μm) exposure was extensively validated worldwide. Nevertheless, long-term survival associated with submicron particulate matter (PM, PM with aerodynamic diameter ≤1 μm) exposure remained largely unstudied, particularly in highly exposed populations.

Methods: We performed a population-based investigation involving 86844 adults aged 16+ years from 3 national dynamic cohorts spanning from 2005 to 2018. Residential annual exposure to PM and PM was assigned for each follow-up year using satellite-derived spatiotemporal estimates at a 1-km resolution. The concentration of PM (PM with aerodynamic diameter between 1 and 2.5 μm) was calculated by subtracting PM from PM. Time-independent Cox proportional hazards regression models were applied to assess the associations of all-cause mortality with long-term exposure to size-specific particles. To investigate the effect of PM on PM-mortality associations, we categorized participants into low, medium, and high groups based on PM/PM ratio and examined the risk of PM-associated mortality in each stratum. Effect modifications were checked via subgroup analyses.

Results: A total of 18722 deaths occurred during 497069.2 person-years of follow-up (median 5.7 years). Participants were exposed to an average annual concentration of 31.8 μg/m³ (range: 7.6-66.8 μg/m³) for PM, 56.3 μg/m³ (range: 19.8-127.2 μg/m³) for PM, and 24.5 μg/m³ (range: 7.3-60.3 μg/m³) for PM. PM, PM, and PM were consistently associated with elevated mortality risks, with a hazard ratio (HR) of 1.029 (95% confidence interval [CI]: 1.013-1.046), 1.014 (95% CI: 1.005-1.023), and 1.019 (95% CI: 1.001-1.038) for each 10-μg/m increase in exposure, respectively. Compared with low (HR = 0.986, 95% CI: 0.967-1.004) and medium (HR = 1.015, 95% CI: 1.002-1.029) PM/PM ratio groups, PM-related risk of mortality was more pronounced in high PM/PM ratio stratum (HR = 1.041, 95% CI: 1.019-1.064). Greater risks of mortality associated with size-specific particles were found among the elderly (>80 years old), southeastern participants, and those living in warmer areas.

Conclusions: This study demonstrated that long-term exposure to PM, PM, and PM was associated with heightened mortality, and PM may play a predominant role in PM-induced risk. Our results emphasized the population health implications of establishing ambient PM air quality guidelines to mitigate the burden of premature mortality stemming from particulate air pollution.