Inhalation of salt aerosol particles—II. growth and deposition in the human respiratory tract

Abstract

The growth of single dry salt aerosol particles during respiration in human airways is calculated with equations for the mass and heat transport to the particle surface (Ferron, J. Aerosol Sci. 8, 251, 1977) and with axial profiles for the temperature ( T) and relative humidity ( RH) of the air in the human respiratory tract as derived in a previous study (Ferron et al., J. Aerosol Sci. 19, 343, 1988). The calculations are performed for single dry NaCl, CoCl 2.6H 2O and ZnSO 4.7H 2O particles representing salts with large, medium and small increases of particle size in nearly saturated air. The growth of a salt particle is a function of the initial dry particle size, the molecular weight of the salt, its density, and its dissociation constant. It is affected by the profile of the RH of the air in the upper human respiratory tract. Pure salt particles with initial sizes below 1 μm reach their final size during inhalation, whereas particles with initial sizes larger than 7 μm change their size by less than 20% during inhalation. The growth of a salt particle with initial size below 3 μm is influenced by the inhalation airflow. The influence of the reduced transport of water vapor and heat in the lower bronchial tree simulated by a correction equation has hardly any effect on the growth of salt particles. The deposition of salt particles in the human respiratory tract is calculated with a model published before (Ferron et al., J. Aerosol Sci. 16, 133, 1985a). The model is adapted to calculate the deposition of particles with a changing particle diameter. The calculated total lung deposition is enhanced for particles with initial diameter larger than 0.2 μm and reduced for particles with initial diameter less than 0.15 μm with respect to the deposition of non-growing particles. The largest increase in total deposition is found for 1 μm-sized particles. As a first approximation the values for the regional deposition of growing and non-growing particles differ by the same factor as the total deposition is changed. Particles with an initial dry size between 1 and 7 μm have a deposition probability larger than 70% in the bronchial and pulmonary region. A recommendation to estimate the deposition of hygroscopic aerosol particles is derived.