Respiratory Aerosol - Sources and Transformation
Respiratory particles emitted during human exhalatory events span a wide size range, from large macroscopic droplets to small aerosol particles. Although these droplets (>100 μm diameter) and aerosols (≤100 μm) are responsible for direct, indirect and airborne modes of respiratory disease transmission, the concentrations and fluxes expired during activities such as speaking, singing, playing musical instruments and exercising, are poorly quantified and, in some cases, remain completely unknown. During the COVID-19 pandemic, an absence of data essential to inform assessments of risk for various activities led to precautionary measures that severely restrict singing, musical performance and sport, across both the amateur and professional domains.
Building on preliminary work with a cohort of professional musicians, we have undertaken a comprehensive analysis of aerosol and droplet emissions from singers covering a broad range of genres, as well as woodwind and brass instruments. Working in an orthopaedic operating theatre, an environment of “zero aerosol” background, we have quantified respirable particles exhaled by amateur musicians, children and individuals undertaking exercise. We have explored the size distributions of aerosols and droplets, and estimated the absolute aerosol flux by performing aerosol measurements in tandem with cardio-pulmonary exercise testing. We have worked with speech and language therapists to understand the risks of aerosol generating procedures used during therapy. In a range of venue types, we have investigated the dynamics of aerosol dispersion and clearance using a combination of measurements with a low cost sensor network and computational fluid dynamics models of aerosol spread.
Once exhaled, aerosols and droplets contain considerable moisture and must equilibrate to the surrounding environment losing water and size, and possibly changing in phase and morphology. These dynamics are coupled to the transportation of the exhalation plume, with the speed and turbulence in the exhaled jet dependent on activity (e.g. coughing, sneezing, breathing) and the range of aerosol and droplet transport influenced by environmental conditions. Using single particle tools, particularly an electrodynamic balance, we are making measurements of the microphysical dynamics of single droplets composed of surrogate respiratory fluids. In particular, we can identify the conditions under which the particles crystallise and can explore the impact of the hygroscopic response of the exhaled aerosol transport, providing comprehensive models to improve our understanding of transmission.
Relevant Publications
[1] Gregson, F. K. A.; Sheikh, S.; Archer, J.; Symons, H. E.; Walker, J. S.; Haddrell, A. E.; Orton, C. M.; Hamilton, F. W.; Brown, J. M.; Bzdek, B. R.; Reid, J. P. Analytical Challenges When Sampling and Characterising Exhaled Aerosol. Aerosol Sci. Technol. 2022. pdf
[2] McCarthy, L. P.; Orton, C. M.; Watson, N. A.; Gregson, F. K. A.; Haddrell, A. E.; Browne, W. J.; Calder, J. D.; Costello, D.; Reid, J. P.; Shah, P. L.; Bzdek, B. R. Aerosol and Droplet Generation from Performing with Woodwind and Brass Instruments. Aerosol Sci. Technol. 2021, 55 (11) 1277-1287. pdf
[3] Gregson, F.; Watson, N.; Orton, C.; Haddrell, A.; McCarthy, L.; Finnie, T.; Gent, N.; Donaldson, G.; Shah, P.; Calder, J.; Bzdek, B.; Costello, D.; Reid, J. Comparing Aerosol Concentrations and Particle Size Distributions Generated by Singing, Speaking and Breathing. Aerosol Sci. Technol. 2021, 55 (6), 681–691. pdf
[4] Walker, J. S.; Archer, J.; Gregson, F. K. A.; Michel, S. E. S.; Bzdek, B. R.; Reid, J. P. Accurate Representations of the Microphysical Processes Occurring during the Transport of Exhaled Aerosols and Droplets. ACS Cent. Sci. 2021, 7 (1), 200–209. pdf
BARC Researchers
Prof. Jonathan Reid, Dr. Bryan Bzdek, Dr. Justice Archer, Dr. Henry Symons, Dr. Jim Walker, Lauren McCarthy, Joshua Harrison and Jianghan Tian
BARC Collaborators
Natalie Watson,1 Christopher Orton,2 Pallav Shah,2 James Calder,3 Declan Costello,4 and William Browne.5
1 Lewisham and Greenwich NHS Trust, 2 Department of Respiratory Medicine, Royal Brompton Hospital, London, United Kingdom; Department of Respiratory Medicine, Chelsea & Westminster Hospital, London, United Kingdom; National Heart and Lung Institute, Guy Scadding Building, Imperial College London, London, United Kingdom, 3 Department of Bioengineering, Imperial College London, United Kingdom; Fortius Clinic, London, United Kingdom, 4 Wexham Park Hospital, 5 School of Education, University of Bristol, Bristol, United Kingdom
Funding
UKRI COVID Urgency Grant, The Investigation of Particulate Respiratory Matter to Inform Guidance for the Safe Distancing of Performers in a COVID-19 Pandemic (PERFORM-2), £541,099
PROTECT COVID-19 National Core Study on transmission and environment, managed by the Health and Safety Executive on behalf of HM Government