Occupational asthma affects a variety of industry sectors, including agricultural and manufacturing. Currently, asthma pharmaceuticals are delivered via an inhaler and deposited in the respiratory system. The effectiveness of the medication depends partially on where the particle deposits in the lung.
The specific aims of this research were to (1) develop a system to measure hygroscopic particle growth under different environmental conditions; (2) determine the accuracy of a hygroscopic growth model during the growth phase of salt particles; and (3) determine whether the large-diameter particles of an aerosol, those that will most likely deposit in the upper airways, can be separated from the smaller particles.
Aim 1: A system was developed that satisfied the design criteria to measure particle growth within fractions of a second. The particles growth was measured every 0.03 seconds and had a relative humidity that only varied by a maximum of 1.3% over a 30 second trial.
Aim 2: The next step in the research was to determine how well the model compares to reality in the initial growth phase. The model that included the initial growth rate as a saturated solution had a lower root mean square of error (RMSE) than the model that did not include a maximum saturation value. The maximum reduction in RMSE was 0.254.
Aim 3: The analysis of a virtual impactor was conducted to see if aerosolized particles can be size separated at a cut point of 2.5 μm. The virtual impactor was designed to have small particles exit the device in one airflow and the large particles exit in a different airflow. Multiple trials were conducted however, there were only two trials that had any size separation between the two exiting flows. From these results, it was determined that large-diameter particles cannot be separated from smaller particles while remaining aerosolized. The cut-point was 2.3 μm, the small particles were split at 50% through both flows, and the flow that was supposed to contain 100% of all of the large particles only contained a maximum of 70%.