Association between
Long-Term Exposure to PM2.5 Inorganic Chemical Compositions
and Cardiopulmonary Mortality: A
22-Year Cohort Study in Northern China
Particulate
matter with diameters ≤2.5 μm (PM2.5) has
been identified as a significant air pollutant contributing
to premature mortality. Nevertheless, the specific compositions within
PM2.5 that play the most crucial role remain unclear, especially
in areas with high pollution concentrations. This study aims to investigate
the individual and joint mortality risks associated with PM2.5 inorganic chemical compositions and identify primary contributors.
In 1998, we conducted a prospective cohort study in four northern
Chinese cities (Tianjin, Shenyang, Taiyuan, and Rizhao). Satellite-based
machine learning models calculated PM2.5 inorganic chemical
compositions, including sulfate (SO42–), nitrate (NO3–), ammonium (NH4+), and chloride (Cl–). A time-varying
Cox proportional hazards model was applied to analyze associations
between these compositions and cardiorespiratory mortality, encompassing
nonaccidental causes, cardiovascular diseases (CVDs), nonmalignant
respiratory diseases (RDs), and lung cancer. The quantile-based g-computation
model evaluated joint exposure effects and relative contributions
of the compositions. Stratified analysis was used to identify vulnerable
subpopulations. During 785,807 person-years of follow-up, 5812 (15.5%)
deaths occurred from nonaccidental causes, including 2932 (7.8%) from
all CVDs, 479 (1.3%) from nonmalignant RDs, and 552 (1.4%) from lung
cancer. Every interquartile range (IQR) increase in SO42– was associated with mortality from nonaccidental
causes (hazard ratio: 1.860; 95% confidence interval: 1.809, 1.911),
CVDs (1.909; 1.836, 1.985), nonmalignant RDs (2.178; 1.975, 2.403),
and lung cancer (1.773; 1.624, 1.937). In the joint exposure model,
a simultaneous rise of one IQR in all four compositions increased
the risk of cardiorespiratory mortality by at least 36.3%, with long-term
exposure to SO42– contributing the most
to nonaccidental and cardiopulmonary deaths. Individuals with higher
incomes and lower education levels were found to be more vulnerable.
Long-term exposure to higher levels of PM2.5 inorganic
compositions was associated with significantly increased cardiopulmonary
mortality, with SO42– potentially being
the primary contributor. These findings offer insights into how PM2.5 sources impact health, aiding the development of more effective
governance measures.