In our recent study, we compared the in vitro toxicity ofmainstream cigarette smoke PM from nano- to microsize, andthe results indicate that the toxicity of mainstream cigarettesmoke PM decreases with an increase in particle size (Linet al. 2014). Sidestream cigarette smoke PM is small enoughto be inhaled into the respiratory tracts of smokers and nearbynon-smokers. Toxic particulate components inhaled into thebody are associated with significant carcinogenic and non-carcinogenic health effects (Behera et al. 2014). Althoughmany studies provide evidence for the relationship betweensidestream tobacco smoke and several human diseases (U.S.DHHS 2010), the difference in the size-dependent toxicolog-ical effects of PM remains poorly understood