reported a positive, although imprecise, association between estimated PM2.5 concentrations and lung cancer mortality in males (HR per each 24.3 μg/m3 = 2.23; 95% CI, 0.56–8.94); however only 13 lung cancer deaths were observed (22). A previous 16-year follow-up of never-smoking CPS-II participants reported a positive, although statistically insignificant, association between PM2.5 and lung cancer death (6).