Objectives A theoretical comparison of modeled particle depositions in the human respiratory tract has been performed by taking into account different particle number and mass size distributions and physical activity in an urban environment.

Methods Urban air data on particulate concentrations in the size range 10 nm-10 µm were used to estimate the hourly average particle number and mass size distribution functions. The functions were then combined with the deposition probability functions obtained from a computerized ICRP 66 deposition model of the International Commission on Radiological Protection to calculate the numbers and masses of particles deposited in five regions of the respiratory tract of a male adult, the man`s physical activity and minute ventilation during the day being taken into account.

Results Two different mass and number size distributions of aerosol particles with equal (computed) <10 µm particle mass concentrations gave significantly different deposition patterns in the central and peripheral regions of the human respiratory tract. The deposited particle numbers and masses were much higher during the day (0700-1900) than during the night (1900-0700) because an increase in physical activity and ventilation were temporally associated with highly increased traffic-derived particles in urban outdoor air.

Conclusions In future analyses of the short-term associations between particulate air pollution and health, it would not only be important to take into account the outdoor-to-indoor penetration of different particle sizes and human time-activity patterns, but also actual lung deposition patterns and physical activity in significant microenvironments.

Key terms aerosol size distribution; human lung; modeling; particle deposition; particulate matter; physical activity; pulmonary deposition; urban aerosol