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Quantification of Expiratory Aerosol and Droplets Produced during Exercise
Henry Symons, Justice Archer, Christopher Orton, Natalie Watson, James Calder, Declan Costello, James Hull, Pallav Shah, BRYAN R. BZDEK, Jonathan P. Reid, University of Bristol
Abstract Number: 306
Working Group: Infectious Aerosols in the Age of COVID-19
Abstract
The COVID-19 pandemic has brought considerable attention to the role of different human expiratory events in airborne pathogen transmission. Concern and uncertainty surrounding these issues led to widespread suspension of sporting events and closure of gyms and other venues. Quantification of respiratory aerosol and droplets will aid in assessing the relative risks of different activities and inform mitigation strategies to minimise exposure risk. In this work, we aim to quantify the emission rate and size distributions of respired aerosol generated during differing levels of physical activity. We used cardiopulmonary exercise testing (CPET) as a means of standardising the intensity of exercise undertaken across a cohort of participants covering a broad range of athletic abilities and other demographics. After an initial test that quantifies the athletic ability of participants, we measured aerosol generation by breathing at three relative levels of activity: resting, moderate exercise and heavy exercise. To detect the relatively small amounts of aerosol produced by respirable activities, we carried out measurements in a laminar flow operating theatre, with a near-zero background aerosol concentration. Two aerodynamic particle sizers quantified the number concentrations and size distribution of particles with diameters in the range of 0.5 – 20 μm. The total particle flux is estimated by combining measured aerosol number concentrations with participant ventilatory data. Additionally, the production of large droplets >20 μm was assessed. Clear increases in the concentration of aerosols generated by breathing as a function of exercise intensity were observed. These increased concentrations are compounded by a concurrent increase in ventilation rate during greater levels of physical activity. The results highlight the need for careful consideration of mitigation strategies to minimise the risks of airborne pathogen transmission during exercise, particularly in indoor spaces such as gyms and sports halls where ventilation rates are relatively low.