AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Predicting Hygroscopic Particle Growth in Upper Human Airways
LAWRENCE LEBLANC, Ralph Altmaier, Ching-Long Lin, Patrick O'Shaughnessy, University of Iowa
Abstract Number: 366 Working Group: Health Related Aerosols
Abstract Under high humidity, hygroscopic compounds attract, absorb, and retain water molecules resulting first in deliquescence followed by an increase in the resulting droplet solution up to an equilibrium size. The human airways provide an environment suitable for hygroscopic particle growth which will ultimately affect their deposition sites. A series of published coupled differential equations for predicting droplet growth with droplet temperature change were used in conjunction with predicted lung temperature and relative humidity profiles up to six generations to model the growth of sodium chloride aerosols with diameters in the nanometer range in the human lung. Differential equations were solved using a built in MATLAB ODE solver. Experimental validation of the models was accomplished with the use of differential mobility analyzer coupled with an optical particle counter to measure growth during the transient growth phase of the droplets. Numerical models were validated through comparison with experimental data over a time period of 0.2 seconds, consistent with the average residence time needed for transport of air from the top of the trachea to the first lung bifurcation. Numerical results under the condition of changing air temperature and relative humidity as a particle progresses through the upper airways indicated particle growth to a lesser magnitude than predicted when a consistent temperature and relative humidity associated with the deep lung (37 C and 99.5%) were applied to the model. Depending on initial diameter, final diameter size after 0.2 seconds were consistently 20-45% lower than predicted. Current numerical models in the literature do not incorporate the time needed for full deliquescence of the salt particle to a liquid solution droplet. Experimental data suggests that such a lag in overall growth occurs. The deliquescence phenomenon is therefore a critical component missing from currently published particle growth models.