The long-term effects of ambient PM and chemical constituents on childhood pneumonia were still unknown. A cross-sectional study was conducted in 30,315 children in the China Children, Homes, Health (CCHH) project, involving 205 preschools in six cities in China, to investigate the long-term effects of PM constituents on lifetime-ever diagnosed pneumonia. Information on the lifetime-ever pneumonia and demographics were collected by validated questionnaires. The lifetime annual average ambient PM, ozone and five main PM constituents, including SO, NO, NH, organic matter (OM) and black carbon (BC), were estimated according to preschool addresses by a combination of satellite remote sensing, chemical transport modeling and ground-based monitors. The prevalence of lifetime-ever diagnosed pneumonia was 34.5% across six cities and differed significantly among cities (p = 0.004). The two-level logistic regression models showed that the adjusted odds ratio for PM (per 10 µg/m) and its constituents (per 1 µg/m)-SO, NO, NH, and OM were 1.12 (95% CI:1.07-1.18), 1.02 (1.00-1.04), 1.06 (1.04-1.09), 1.05 (1.03-1.07) and 1.09 (1.06-1.12), respectively. Children in urban area, aged < 5 years and breastfeeding time < 6 months enhanced the risks of pneumonia. Our study provided robust results that long-term levels of ambient PM and its constituents increased the risk of childhood pneumonia, especially NH, NO and OM.
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