A Numerical Model of Pollen Dispersion in an Allergen Exposure Chamber
LAURA HAYA, Nick Ogrodnik, Suzanne Kelly, Edgar Matida, William Yang, Red Maple Trials
Abstract Number: 53
Working Group: Health-Related Aerosols
Abstract
Allergen exposure chambers (AECs) are specialized facilities used to expose clinical study participants to a controlled environment containing specific aeroallergens at specific concentrations. AECs have been used to help characterize allergic respiratory disease and contribute to the clinical development of treatments (Pfaar and Zieglmayer, 2020). While AECs vary in size and in their mechanisms used to dispense and disperse allergen, they must all be able to maintain a stable and narrow allergen concentration, homogenous across participant seating (Pfaar et al. 2021). The necessary airflow and particle dynamics to achieve this can be complex, and it may not be possible to fully characterize them experimentally.
A 3D numerical simulation of the EnviroGold™ AEC (Ottawa, ON) has been developed to simulate the dispersion of Timothy grass pollen (38 μm mean diameter) at target concentration 3,500 ± 500 particles/m3 and was validated against experimental data collected with laser particle counters in the operational AEC. Simulations were performed using Unsteady Reynolds Averaged Navier Stokes equations with a Shear Stress Transport turbulence model, and Lagrangian particle tracking.
Time and grid sensitivity analyses established that a 5-million element grid, and 1-ms time-step adequately resolved the flow field and met stability criteria. The particle spatial distribution and room-average pollen concentration stabilized by 40 seconds and the simulation was run for an additional 20 seconds. Numerical room-average pollen concentration was within 9% of experimental average (3,934 vs. 3,613 ± 151% particles/m3, respectively). Location-specific results were within 14-19% of experimental.
This is the first known numerical framework of an AEC. It has elucidated certain features of the complex flow patterns in the EnviroGold AEC which contribute to the generation of uniform pollen distribution. The framework may be extended in future work to simulate the dispersion of other aeroallergens including irregularly-shaped pet dander or dust.