A study by Ritz et al. [36] ascertained PDcases based on medical record review and reported a positiveassociation between PD and long-term exposure to ambientair pollution (i.e., NO2), similarly as reported for CO andPM2.5 by other two studies using administrative data [31,36]. Physician-diagnosed PD has also been associated withmanganese component of PM [37]. However, a large prospective study in women found no association of PD with anyform of air pollution assessed [32] and recent prospectivestudy in both males and females failed to find any associationbetween living near traffic pollution and PD [41•]. Thus, whilethere is some support for a potential association of ambient airpollution with PD, additional research is needed for a clearconclusion