Ultrafine particles: presence and generation indoors

The particle size distributions of indoor and outdoor aerosols cover a very wide size range, from single digit nanometers to tens of micrometers. Ultrafine particles (UFP), specified as PM0.1, have a nominal diameter (such as geometric, aerodynamic, mobility, etc.) smaller than 100 nm. The interest of their effect on human health has been steadily increasing for the following reasons: Their number concentration is extremely high in many instances, e.g. more than 150 million particles per cubic centimeter of outdoor air assuming an airborne concentration of 10 µg/m3; Their deposition pattern, clearance and transportation is different compared to PM2.5 fraction; Their high surface-to-volume ratio makes them extremely effective in transmitting any toxic chemical to the human body. Recent observations concluded that UFPs human health effects include respiratory system inflammation, cardiovascular morbidity, mortality and even DNA damages (increasing of DNA strand breaks). Studies conducted in Europe estimate that exposure to UFPs reduces from four to eight months life expectancy. To assess the health effects of UFPs, some investigators use as an indicator central-site monitoring data of PM2.5. However, this approach is questionable because ultrafine fraction represents only a small portion (less than 10%) of PM2.5 mass concentration. Moreover, UFPs concentration varies in space and time much more than PM2.5. For this reason, to assess UFP exposure, personal monitoring systems should be adopted. According to other studies, UFPs and PM2.5 affect human health in different ways. The former accounts more for cardiovascular diseases and the latter accounts more for respiratory ones. People spend most of their time in indoor environments. Therefore, using just outdoor particulate matter data to evaluate occupants’ exposure to UFPs indoors is not appropriate. We report available data in the scientific literature about UFP presence in indoor environments, together with the impact of outdoor pollution on UFP indoors. Long-term and personal exposure to UFPs indoors are not well understood yet. We summarize indoor activities generating ultrafine particles and their fate. Finally, we suggest some measurement techniques and instruments suitable for expanding the available knowledge about UFP presence indoors.