Abstract View
Exploring Approaches to Characterize Respiratory Droplets >20 μm Diameter
JOSHUA HARRISON, Henry Symons, Justice Archer, Jonathan P. Reid, Bryan R. Bzdek, University of Bristol
Abstract Number: 115
Working Group: Infectious Aerosols in the Age of COVID-19
Abstract
Respiratory aerosol emissions are likely key to elucidating the transmission of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). These emissions span a wide size range, from < 1 μm diameter to >> 100 μm diameter, with significant variability in number concentration with droplet size. The current view of these emissions is that they consist of three distinct modes. The bronchiolar mode is centered around < 1 μm diameter and arises from aerosol produced in the bronchioles during breathing. The laryngeal mode is centered around 1-2 μm diameter and is associated with vocalization. These two modes represent the vast majority of the aerosol number concentration. The oral mode is generated in the oral cavity, is associated with significantly larger droplet sizes (~200 μm diameter), and contributes relatively few droplets but most of the mass. Whereas the droplets in the bronchiolar and laryngeal modes are well within the size range accessible by commercial aerosol measurement equipment, robust approaches to measure the oral mode do not currently exist. This contribution describes efforts to characterize the robustness of two new approaches to characterize the oral mode. In one approach, droplets are deposited onto water-sensitive paper and droplet size inferred from a color change. In the other, a fluorescein rinse is used before respiratory maneuvers, and droplets deposited onto target paper are then imaged using ultraviolet light to reveal the droplets. Both approaches are highly sensitive to spreading coefficients on their respective substrates. To calibrate these approaches, droplets reproducibly ejected from a microdroplet dispenser were deposited onto the appropriate substrate, permitting quantification of the relationship between deposited spot size and droplet diameter. Challenges of interpreting these measurements and their limitations will also be discussed.