Exposure assessment for respirable hygroscopic particulate matter
D.M. Broday, P.G. Georgopoulos (EOHSI, UMDNJ - R.W. Johnson Medical School and Rutgers University)
Inhalation is a common route of human exposure to airborne pollutants. Anthropogenic particulate matter (PM) is of particular concern because of its potential irritant and toxic effects, and the possibility to use control strategies to limit its ambient concentrations.
To study the transport and fate of aerosols in the human respiratory tract, a new model is being developed within the MENTOR (Modeling Environment for Total Risk) project. The aerosol general dynamic equation, with terms accounting for growth, transport, and deposition, is used to track the evolution of the size distribution of an inhaled aerosol within a Weibel's symmetric lung model and under realistic breathing conditions. The initial particle size represents a discretized bimodal lognormal distribution, since anthropogenic aerosols often have number and mass distributions that closely follow such a distribution. Each mode may have different initial physicochemical properties (chemical composition and thermodynamic state).
Results reveal the significance of the initial parameters of the size distribution, the particle composition, and the thermodynamic state for lung dosimetry calculations. Specifically, only submicron-sized hygroscopic particles reach their equilibrium size during the respiration cycle. The slower growth of larger particles leads to an evolution of the particle size pdf, where increased number and mass fractions of the inspired particles are found in the PM10-PM2.5 size range. Non-hygroscopic particles, originally from the intermediate size range 0.1<d<1um, tend to persist in the inspired air and deposit to a lesser extent by the major deposition mechanisms than similar hygroscopic particles.