The Mechanism of Breath Aerosol Formation
Open accessAbstract
BACKGROUND: Aerosol production during normal breathing is often attributed to turbulence in the respiratory tract. That mechanism is not consistent with a high degree of asymmetry between aerosol production during inhalation and exhalation. The objective was to investigate production symmetry during breathing. METHODS: The aerosol size distribution in exhaled breath was examined for different breathing patterns including normal breathing, varied breath-holding periods, and contrasting inhalation and exhalation rates. The aerosol droplet size distribution measured in the exhaled breath was examined in real time using an aerodynamic particle sizer. RESULTS AND CONCLUSIONS: The dependence of the particle concentration decay rate on diameter during breath holding was consistent with gravitational settling in the alveolar spaces. Also, deep exhalation resulted in a four- to sixfold increase in concentration, and rapid inhalation produced a further two- to threefold increase in concentration. In contrast, rapid exhalation had little effect on the measured concentration. A positive correlation of the breath aerosol concentration with subject age was observed. The results were consistent with the breath aerosol being produced through fluid film rupture in the respiratory bronchioles in the early stages of inhalation and the resulting aerosol being drawn into the alveoli and held before exhalation. The observed asymmetry of production in the breathing cycle with very little aerosol being produced by exhalation is inconsistent with the widely assumed turbulence-induced aerosolization mechanism.
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Normal physiological respiratory activities such as sneezing, coughing, talking and even breathing expel particles into the local environment.
“The literature is replete with examples showing that normal physiological respiratory activities such as sneezing, coughing, talking and even breathing, expel particles into the local environment where individuals socialise and work [6–11].”
From The protective performance of reusable cloth face masks, disposable procedure masks, KN95 masks and N95 respirators: Filtration and total inward leakage (2021) · cites this paper as [11]
The Introduction states that normal breathing produces aerosol particles and compares their concentrations with those produced by coughing. The Methods describe collecting aerosol emitted by subjects, supporting release into the surrounding air. The paper does not address sneezing or talking, so it supports only part of the list of activities. (LLM, conf=0.86)
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- Authors
- Johnson, G. R., & Morawska, L.
- Affiliations
- Queensland University of Technology (AU)
- International Laboratory for Air Quality and Health, Queensland University of Technology, Brisbane, Australia
- Venue
- Journal of Aerosol Medicine and Pulmonary Drug Delivery
- Publisher
- SAGE Publications
- Published
- 2009-09
- Volume
- 22
- Issue
- 3
- Pages
- 229-237
- ISSN
- 1941-2703 (ISSN-L)
- 1941-2711
- OpenAlex
- W1527782018
- Cited by
- 434
- References
- 18
- Citations by year
- 2026: 15 · 2025: 29 · 2024: 35 · 2023: 49 · 2022: 66 · 2021: 64 · 2020: 61 · 2019: 11 · 2018: 12 · 2017: 18 · 2016: 6 · 2015: 13 · 2014: 10 · 2013: 18 · 2012: 5
- FWCI
- 7.53
- Type
- journal article
- Language
- en
- Open access
- green
- eprints.qut.edu.au
- Locations
- Journal of Aerosol Medicine and Pulmonary Drug Delivery (publishedVersion)
- PubMed (publishedVersion)
- QUT ePrints (Queensland University of Technology) (submittedVersion)
- Faculty of Science and Technology; Institute of Health and Biomedical Innovation
- Funders
- Australian Research Council (DP0558410)
- Topics
- Health Sciences › Medicine › Pulmonary and Respiratory Medicine › Inhalation and Respiratory Drug Delivery
- Health Sciences › Medicine › Pulmonary and Respiratory Medicine › Infection Control and Ventilation
- Physical Sciences › Engineering › Ocean Engineering › Particle Dynamics in Fluid Flows
- Keywords
- aerosol formation mechanisms, aerosol size distribution, breath-holding, gravitational settling, respiratory bronchioles
- MeSH terms
- Adult, Aerosols, Age Factors, Inhalation, Gravitation, Humans, Middle Aged, Particle Size, Pulmonary Alveoli, Exhalation
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