NO(2) and PM(2.5) air pollution co-exposure and temperature effect modification on pre-mature mortality in advanced age: a longitudinal cohort study in China

BACKGROUND: There is a discourse on whether air pollution mixture or air pollutant components are causally linked to increased mortality. In particular, there is uncertainty on whether the association of NO(2) with mortality is independent of fine particulate matter (PM(2.5)). Furthermore, effect modification by temperature on air pollution-related mortality also needs more evidence. METHODS: We used the Chinese Longitudinal Healthy Longevity Study (CLHLS), a prospective cohort with geographical and socio-economic diversity in China. The participants were enrolled in 2008 or 2009 and followed up in 2011-2012, 2014, and 2017-2018. We used remote sensing and ground monitors to measure nitrogen dioxide (NO(2)), fine particulate matter (PM(2.5)) , and temperature. We used the Cox-proportional hazards model to examine the association between component and composite air pollution and all-cause mortality, adjusted for demographic characteristics, lifestyle, geographical attributes, and temperature. We used the restricted cubic spline to visualize the concentration–response curve. RESULTS: Our study included 11 835 individuals with an average age of 86.9 (SD: 11.4) at baseline. Over 55 606 person-years of follow-up, we observed 8 216 mortality events. The average NO(2) exposure was 19.1 μg/m(3) (SD: 14.1); the average PM(2.5) exposure was 52.8 μg/m(3) (SD: 15.9). In the single pollutant models, the mortality HRs (95% CI) for 10 μg/m(3) increase in annual average NO(2) or PM(2.5) was 1.114 (1.085, 1.143) and 1.244 (1.221, 1.268), respectively. In the multi-pollutant model co-adjusting for NO(2) and PM(2.5), the HR for NO(2) turned insignificant: 0.978 (0.950, 1.008), but HR for PM(2.5) was not altered: 1.252 (1.227, 1.279). PM(2.5) and higher mortality association was robust, regardless of NO(2). When acccounting for particulate matter, NO(2) exposure appeared to be harmful in places of colder climates and higher seasonal temperature variation. CONCLUSIONS: We see a robust relationship of PM(2.5) exposure and premature mortality in advance aged individuals, however, NO(2) exposure and mortality was only harmful in places of colder climate such as northeast China, indicating evidence of effect modification by temperature. Analysis of NO(2) without accounting for its collinearity with PM(2.5,) may lead to overestimation. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12940-022-00901-8.