Consideration of local geographical variations in PM2·5 concentrations in China – Authors' reply
Authors: Xiaoming Shi, Tiantian Li, Yi Zhang, Jiaonan Wang, Yuebin Lv
Journal: The Lancet Public Health (2018)

Haris Majeed commented on our study,1Li T Zhang Y Wang J et al.All-cause mortality risk associated with long-term exposure to ambient PM2.5 in China: a cohort study.Lancet Public Health. 2018; 3: e470-e477Summary Full Text Full Text PDF PubMed Scopus (148) Google Scholar pointing out that geographical variations in air pollution concentrations, even in low-population densities and rural regions, are important to understand the full effect of air pollution, and suggesting that not including nine provinces could affect our analysis. These are valid concerns, especially when a nationally representative cohort is used. Although some provinces were not included in the original cohort design, we do have coverage of about 800 counties and districts in 22 provinces, and this accounts for one-third of counties in China. We believe although some provinces were not included, the heterogeneity of the regions is captured through the diverse geographical dispersion of research subjects. We also agreed that indoor PM2.5 exposure could be an important variable that might influence the association of ambient PM2.5 exposure with mortality. In our Article,1Li T Zhang Y Wang J et al.All-cause mortality risk associated with long-term exposure to ambient PM2.5 in China: a cohort study.Lancet Public Health. 2018; 3: e470-e477Summary Full Text Full Text PDF PubMed Scopus (148) Google Scholar we used household income, which can be a proxy for exposure to indoor air pollution. Previous research reported that household income was a key factor related to biomass consumption.2Xing X Zhou Y Lang J et al.Spatiotemporal variation of domestic biomass burning emissions in rural China based on a new estimation of fuel consumption.Sci Total Environ. 2018; 626: 274-286Crossref PubMed Scopus (32) Google Scholar Additionally, sensitivity analysis showed our models were robust. Therefore, we think the hazard ratio (HR) of long-term PM2.5 and mortality in our study are representative of China. Additionally, although data from nine provinces were not used to calculate HR, we considered the concentration of PM2.5 and the populations of the nine provinces in the estimation of mortality burden from long-term PM2.5 exposure for the whole of China in 2010. Our estimation of the mortality burden attributable to PM2·5 (1·77 million) is higher than that in the Global Burden of Diseases Study (GBD; 1·11 million in total).3Cohen A J Brauer M Burnett R et al.Estimates and 25-year trends of the global burden of disease attributable to ambient air pollution: an analysis of data from the Global Burden of Diseases Study 2015.Lancet. 2017; 389: 1907-1918Summary Full Text Full Text PDF PubMed Scopus (3217) Google Scholar This might be because of the different endpoint in our study, which was total death. In the GBD study, only five cause-specific deaths were included: ischaemic heart disease, cerebrovascular disease, lung cancer, chronic obstructive pulmonary disease, and lower respiratory infection. In conclusion, even without the nine provinces, to our knowledge, our study has the largest coverage, with the widest range of the PM2.5 (7–113 μg/m3), compared with other studies in China, and provided crucial and representative information about the mortality risk associated with long-term exposure of people aged 65 years and older to PM2.5 in China. We declare no competing interests. All-cause mortality risk associated with long-term exposure to ambient PM2·5 in China: a cohort studyLong-term exposure to PM2·5 is associated with an increased risk of all-cause mortality among adults aged 65 years and older in China, but the magnitude of the risk declines as the concentration of PM2·5 increases. Full-Text PDF Open AccessConsideration of local geographical variations in PM2·5 concentrations in ChinaGlobal efforts have been made to reduce air pollution. The Lancet Commission on pollution and health estimates that in 2015, air pollution was responsible for 9 million premature deaths and 268 million disability-adjusted life-years, with the most severe effects on individuals residing in low-income and middle-income countries.1,2 Although various factors have been used to understand air pollution-related mortalities in low-income and middle-income countries,2 geographical variations of air pollution concentrations in low-population dense and rural regions are often overlooked. Full-Text PDF Open Access