There is ample evidence to show that air pollution correlates with increased mortality, and a number of natural experiments have allowed researchers to compare populations with similar socioeconomic status and different levels of air pollution, in order to demonstrate that effects do not result from wealth disparities. The consensus on why air pollution correlates with mortality is that interaction between particulates and lung tissue provokes greater systemic inflammatory signaling. That raised chronic inflammation accelerates the progression of all of the common fatal age-related conditions.
We aimed to report real-world longitudinal ambient air pollutants levels compared to WHO Air Quality Guidelines (AQG) and analyze multiple air pollutants' joint effect on longevity, and the modification and confounding from the climate and urbanization with a focus on the oldest-old. This study included 13,207 old participants with 73.3% aged 80 and beyond, followed up from 2008 to 2018 in 23 Chinese provinces. We used the Cox-proportional hazards model and quantile-based g-computation model to measure separate and joint effects of the multiple pollutants. We adjusted for climate and area economic factors based on a directed acyclic graph.
In 2018, no participants met the WHO AQG for PM2.5 and O3, and about one-third met the AQG for NO2. The hazard ratio (HR) for mortality was 1.07 per decile increase in all three pollutants, with PM2.5 being the dominant contributor according to the quantile-based g-computation model. In the three-pollutant model, the HRs for PM2.5 and NO2 were 1.27 and 1.08 per 10 μg/m3 increase, respectively. The oldest-old experienced a much lower mortality risk from air pollution compared to the young-old. The mortality risk of PM2.5 was higher in areas with higher annual average temperatures. The adjustment of road density considerably intensified the association between NO2 and mortality. The ambient PM2.5 and O3 levels in China exceeded the WHO AQG target substantially. Multiple pollutants coexposure, confounding, and modification of the district economic and climate factors should not be ignored in the association between air pollution and mortality.