Absolute Respiratory Particle Number and Mass Exhalation Rates and Size Distributions during Breathing and Vocalizing

Justice Archer, Henry Symons, Lauren McCarthy, Joshua Harrison, Christopher Orton, Natalie Watson, William Browne, Ben Moseley, Kier Philip, James Calder, Pallav Shah, Declan Costello, Bryan R. Bzdek, JONATHAN P. REID, University of Bristol

     Abstract Number: 41
     Working Group: Aerosol Science of Infectious Diseases: What We Have Learned and Still Need to Know about Transmission, Prevention, and the One Health Concept

Abstract
The coronavirus disease (COVID-19) pandemic has reinforced the need to understand the transmission of respiratory pathogens by aerosols. Aerosol particles of varying size are exhaled during respiratory activities like breathing while at rest or during exercise, speaking and singing, and can transmit pathogens if emitted from an infected individual. Improved quantification of exhalation rates would support estimates of viral shedding and assessments of transmission risk. Previous studies report aerosol concentrations in an exhaled plume; we report here absolute particle exhalation rates from combined measurements using cardiopulmonary exercise testing with exhaled particle concentrations.

We will summarise measurements from the project PERFORM-2 (The Investigation of Particulate Respiratory Matter to Inform Guidance for the Safe Distancing of Performers in a COVID-19 Pandemic) and from these cohorts of participants: professional singers and wind instrumentalists, children (aged 12-14) singing, individuals undergoing speech and language therapy tasks, and adults exercising. Measurements were made in a zero-background orthopaedic operating theatre to ensure all aerosol particles detected (<20 μm diameter) originate from the participant. We will also summarise measurements of larger particle size using water sensitive paper (extending from 20 to >500 μm). We will address the unique challenges that must be overcome when measuring exhaled aerosols such as Poisson arrival statistics for particles at the very low concentrations present in exhaled breath.

All cohorts generate similar emission rates from the same activity, but vocalisation generates significantly more particles than breathing. Exhalation rates of particles (<20 μm diameter) are typically 0.01, 0.1 and 0.5 ng s^-1 from breathing, speaking and singing, increasing with loudness. Size distributions when exercising are similar to breathing, and mass emission rates are comparable to vocalising at conversational volume, despite increased minute ventilation. We will also examine the correlation between the exhaled flux of carbon dioxide and aerosol mass across all activities, including for high impact exercise.