The present results provide no information as to whether there may be a critical exposure time window that may be most relevant for lung cancer etiology. However, previous work in a subset of the CPS-II using estimated yearly PM2.5 (1972–2000) concentrations, derived from concentrations of PM10 and total suspended particulates, examining the relative importance of different exposure time windows for all-cause and cause-specific mortality, including lung cancer, was largely uninformative because of limitations in study design and modest spatiotemporal variation in PM2.5 concentrations over time (15).