Ultrafine particle emissions from a smouldering cigarette in a residence and its associated lung cancer risk

After smoking bans were enforced in most public spaces, residences became the major places for exposure to second-hand smoke. Since cigarette smoke contains mainly submicron and ultrafine particles (UFPs), the harmful effects of the particles in cigarette smoke might be correlated more with number and surface area concentrations of UFPs instead of their mass concentration. To assess these harmful effects, we investigated the size distribution of particles (20 nm to 600 nm) released from sidestream smoke. An experiment was carried out in a two-zone house which was divided into smoking and non-smoking areas. Particle concentrations were measured in both zones and the exposure doses of people in both zones were calculated. The lung cancer risk of UFPs was then analysed by a modified surface area-based risk assessment scheme, which was found to be much closer to the incidence rate of lung cancer. In most of the studied scenarios, the excess lifetime cancer risks to non-smoker occupants exceeded an acceptable level. Although closing a door separating the two zones is a common isolation measure, adequate protection for the non-smokers cannot be achieved unless sufficient ventilation in the smoking zone is provided.