Comment on "Mortality effects assessment of ambient PM2.5 pollution in the 74 leading cities of China" by Die Fang, Qin'geng Wang, Huiming Li, Yiyong Yu, Yan Lu, Xin Qian.

In a recent publication in the journal Science of the Total Environment, Die Fang et al. (2016) reported health effects of current ambient PM2.5 (particulate matters with aerodynamic diameters <2.5μm) pollution in 74 leading cities in China. It is a meaningful original study using the latest air quality surveillance data. However, we suppose their results may over-estimate the long-term exposure-response coefficients for per 10μg/m(3) increase in PM2.5 concentration. Moreover, we have concern about the linear relationship the authors assumed for long-term exposure to PM2.5 and the health outcomes. We also have concern about the sufficiency of confounder adjustment. Our suggestions are mainly based on our previous research experience and previous literature. We believe that the debate is conducive to a more accurate and more reasonable estimation of the health effects of PM2.5.