Conclusions: The present findings strengthen the evidence that ambient concentrations of PM2.5 measured in recent decades are associated with small but measurable increases in lung cancer mortality.Time-series and prospective studies provide compelling evidence that acute and chronic exposure to ambient fine particulate matter (PM2.5) air pollution is associated with increased cardiopulmonary mortality (1). However, the role of PM2.5 in the etiology of lung cancer is less clear, particularly at concentrations that prevail in developed countries (∼ 5–35 μg/m3) and in never-smokers (2). In China, high levels of indoor air pollution caused by coal and biomass burning contribute to high lung cancer rates observed even among nonsmoking women (3). There are also high background concentrations (>100 μg/m3) of outdoor air pollution in some industrial regions of the country (2).