Aerosol Deposition in the Human Respiratory System from Distinct Urban Sources Using Multiple Exposure Metrics

Targeting specific aerosol sources offers more effective air-quality control than focusing solely on ambient concentrations. Using source apportionment, major contributors to particle number concentrations in the diameter range of 6–1000 nm in urban background of Budapest, Hungary were identified, and their size distributions applied in lung deposition modelling under reference breathing conditions. In this study, we find that most particles penetrate to the deep lung with a maximum deposition at airway generations 17 to 21 depending on physical activity. Deposition fractions vary substantially by source, ranging from 76% (new particle formation) to 27% (solid fuel combustion). Exercise enhances overall deposition, and redistributes the deposited particles within the respiratory tract by decreasing extra-thoracic deposition and increasing the alveolar fraction. Our results also show that deposition rates are more sensitive to physical activity than deposition fractions. These deposition curves exhibit a levelling-off tendency in the extra-thoracic region, while continuing to increase in the lung. Particle number and particle surface area deposition curves are similar in shape, although the relative importance of aerosol sources and the most affected respiratory regions differ. We point that surface-density deposition rates are three orders of magnitude higher in the nose and mouth than in the lung.