Theoretical models for dynamic shape factors and lung deposition of small particle aggregates originating from combustion processes

Abstract

A theoretical model was developed which allows the generation of irregularly shaped aggregate particles due to the stepwise joining of spherical components with variable diameters. The mathematical approach is mainly thought to act as a supporting tool for the simulation of the transport and deposition behaviour of combustion aerosols in the atmosphere and the human respiratory tract. In combination with aggregate construction essential particle parameters (dynamic shape factor χ, aerodynamic diameter d(ae)) are computed using the model. As a main result of aggregate generation, an increasing particle size, expressed by an increasing number of spherical components, leads to an enhancement of χ and d(ae), whereby values of the first parameter range from 2 to 70. Deposition of small aggregates (sizes between 2 and 200nm) in the human respiratory tract is commonly marked by high rates of bronchial particle accumulation (40-60%) and declined rates of extrathoracic (20-30%) and alveolar accumulation (2-15%). Concerning aggregate deposition by airway generation, increased cluster size causes a significant decrease of particle accumulation in the proximal airways, whilst accumulation in the intermediate to distal airways is dramatically enhanced. The model was validated using experimental deposition data of tobacco smoke. An excellent correspondence between experimental and theoretical results was found.