Assessment of deposition of particulate matter in the human respiratory system

Abstract

The harmful health effects of Particulate matter (PM) can be better assessed by its deposition into the respiratory system rather than ambient exposed concentrations. This study quantified the PM mass deposition in the human respiratory tract (HRT) based on the exposure to PM fractions at different microenvironments inside a technical university. The Multiple Path Particle Dosimetry (MPPD-V 3.04) model was used to quantify the deposition levels and their clearance. The modelled results revealed increased physical exertion leading to greater deposition fraction (DF) in the extrathoracic or head region. In contrast, an opposite trend was observed in the pulmonary and tracheobronchial (TB) regions. Furthermore, with an increase in PM size, the DF in the head increased but declined in the TB region for all the activity patterns. The highest deposition was found in the head region for all PM sizes in all the activity levels. Among different age groups, the maximum deposition was found in adolescents followed by children, adults and least in toddlers. In the lobar region, the left lung received a slightly greater deposition than the right lung and because of the larger volume of lower lobes, they received higher deposition than the middle and upper lobes. Further, the sitting activity level was found most critical for the lobar deposition. The deposited mass showed pronounced seasonal variation in accordance with the PM levels monitored at various microenvironments during the three seasons, maximum deposition in winter and least in monsoon. For all the activity patterns, the deposited mass of coarse fraction (PM10) followed a similar trend: Pulmonary < TB < head, whereas a different trend (TB < pulmonary < head) was observed for the fine fraction (PM2.5 and PM1). The total deposited mass was maximum at outdoor while minimum at the library. The clearance rate in TB region was significantly higher compared to the pulmonary region. Considering all activities, the model predicted that around 64% and 1.5 % of the accumulated mass in the TB and pulmonary regions, respectively was remained even after six months. The study results concluded that microenvironment's criticality could not be decided solely by PM exposure concentrations. Activity levels, subject’s age and exposure period also play a crucial role.