Indoor ultrafine particles entering human respiratory regions: defining an index for maximum deposition dose probability in a university classroom case study

Abstract

Ultrafine particles (UFPs) are relevant for human health due to their ability to penetrate the respiratory tract. Although several diseases are related to UFPs exposure, no reference levels for protecting human health have been established yet. In this work, experimental size distribution and concentration of UFPs are used to model their deposition in five different regions of the respiratory tract. This has been achieved by introducing the concept of a resonant system between the modelling of human deposition of particles and the environmental data. Such resonant system is mathematically described by the resonance angle, a function linking the particle deposition efficiency for different particles size classes to the corresponding measured size distribution. From this resonance angle it is possible to calculate the probability of maximum deposition dose corresponding to the actual UFPs indoor contamination. This method has been applied to one-month measurements of UFPs in a university classroom in Rome, Italy. Results show that the average values of risk angle of deposition are time dependent and ranged between 46,4° and 62,6° for alveolar and bronchiole regions, respectively, confirming UFPs mainly impacting the deepest respiratory region. The risk of exposure to UFPs as described by the resonance angle resulted varying along the week and among the five pulmonary regions of concern. Moreover, the calculated maximum probability for dose deposition in the five regions of the respiratory tracts did not always occur in correspondence of high values for the total PNC of UFPs.