Particle Deposition in Human Respiratory Tract: Effect of Water- Soluble Fraction

In the nearly saturated human respiratory tract, the presence of water-soluble substances in inhaled aerosols can cause change in the size distribution of particles. This consequently alters the lung deposition profiles of the inhaled airborne particles. The magnitude of particle deposition in the lung is affected by the soluble component present in the particle. This is estimated by a numerical model. The model solves the condensation growth equation to determine the size evolution of respirable particles within the human respiratory tract. The water uptake by the particles in the respiratory tract results in change of size and density of the particles, and these changes are incorporated for estimating the particle deposition efficiency. The model results are compared with experimental results of sodium chloride particles. The model reproduces the major features of the experimental data. The simulations indicate that the particle can grow up to two times or more of its original size due to water uptake, depending on the quantity of the soluble matter it carries and thus can have significant effect on particle deposition efficiency. The study investigated the effect of soluble compounds in estimating total and regional lung dose of ambient particulate matter measured in Mumbai, India. The particle mass size distribution and composition considered for the ambient particulate matter, the variation in the total mass dose due to the growth was modest. But, the regional lung dose was significantly affected by the hygroscopic growth.