Skip to main content Accessibility help

Violent expiratory events: on coughing and sneezing

  • Lydia Bourouiba (a1) (a2), Eline Dehandschoewercker (a3) and John W. M. Bush (a1)


Violent respiratory events such as coughs and sneezes play a key role in transferring respiratory diseases between infectious and susceptible individuals. We present the results of a combined experimental and theoretical investigation of the fluid dynamics of such violent expiratory events. Direct observation of sneezing and coughing events reveals that such flows are multiphase turbulent buoyant clouds with suspended droplets of various sizes. Our observations guide the development of an accompanying theoretical model of pathogen-bearing droplets interacting with a turbulent buoyant momentum puff. We develop in turn discrete and continuous models of droplet fallout from the cloud in order to predict the range of pathogens. According to the discrete fallout model droplets remain suspended in the cloud until their settling speed matches that of the decelerating cloud. A continuous fallout model is developed by adapting models of sedimentation from turbulent fluids. The predictions of our theoretical models are tested against data gathered from a series of analogue experiments in which a particle-laden cloud is ejected into a relatively dense ambient. Our study highlights the importance of the multiphase nature of respiratory clouds, specifically the suspension of the smallest drops by circulation within the cloud, in extending the range of respiratory pathogens.


Corresponding author

Email address for correspondence:


Hide All
Blanchette, F. A.2003 Sedimentation in a stratified ambient. PhD thesis, MIT, Cambridge.
Bourouiba, L. & Bush, J. W. M. 2012 Drops and bubbles. In Handbook of Environmental Fluid Dynamics Volume One: Overview and Fundamentals Taylor & Francis.
Bush, J. W. M., Thurber, B. A. & Blanchette, F. 2003 Particle clouds in homogeneous and stratified environments. J. Fluid Mech. 489, 2954.
Cardoso, S. S. S. & Woods, A. W. 1993 Mixing by a turbulent plume in a confined stratified region. J. Fluid Mech. 250, 277305.
Clark, R. P. & de Calcina-Goff, M. L. 2009 Some aspects of the airborne transmission of infection. J. R. Soc. Interface 6, S767S782.
Clarke, J. C., Bush, A. B. G. & Bush, J. W. M. 2009 Freshwater discharge, sediment transport, and modeled climate impacts of the final drainage of glacial lake Agassiz. J. Climate 22, 21612180.
Crowder, T. M., Rosati, J. A., Schroeter, J. D., Hickey, A. J. & Martonen, T. B. 2001 Fundamental effects of particle morphology on lung delivery: predictions of Stokes’ law and the particular relevance to dry powder inhaler formulation and development. Pharm. Res. 19, 239245.
Cunningham, E. 1910 On the velocity of steady fall of spherical particles through fluid medium. Proc. R. Soc. Lond. A 83 (563), 357365.
Duguid, J. P. 1945 The numbers and the sites of origin of the droplets expelled during expiratory activities. Edinburgh Med. J. LII (II), 385401.
Duguid, J. P. 1946 The size and the duration of air-carriage of respiratory droplets and droplet-nuclei. J. Hyg. 44 (6), 471479.
Edwards, D. A., Ben-Jebria, A. & Langer, R. 1998 Recent advances in pulmonary drug delivery using large, porous inhaled particles. J. Appl. Physiol. 85, 379385.
Ghosh, S., Dávila, J., Hunt, J., Srdic, A., Fernando, H. & Jonas, P. 2005 How turbulence enhances coalescence of settling particles with applications to rain in clouds. Proc. R. Soc. A: Math. Phys. Engng 461 (2062), 30593088.
Gonnermann, H. M. & Manga, M. 2007 The fluid mechanics inside a volcano. 321356.
Gupta, J. K., Lin, C. H. & Chen, Q. 2009 Flow dynamics and characterization of a cough. Indoor Air 19, 517525.
Hinds, W. C. 1999 Aerosol Technology: Properties, Behavior, and Measurement of Airborne Particles. John Wiley & Sons, Inc..
Holterman, H. J.2003 Kinetics and evaporation of water drops in air. Tech. Rep. IMAG Report 2003, Wageningen, Netherlands.
Höppe, P. 1981 Temperatures of expired air under varying climatic conditions. Intl J. Biometeorol. 25, 127132.
Hunt, J. C. R., Delfos, R., Eames, I. & Perkins, R. J. 2007 Vortices, complex flows and inertial particles. Flow Turbul. Combust. 79, 207234.
Hunt, G. R. & Kaye, N. G. 2001 Virtual origin correction for lazy turbulent plumes. J. Fluid Mech. 435, 377396.
IMF/World Bank, 2006 Press briefing: Avian flu. In Proc. IMF/World Bank Annual Meetings Suntec.
Johnson, G., Morawska, L., Ristovski, Z., Hargreaves, M., Mengersen, K., Chao, C., Wan, M., Li, Y., Xie, X., Katoshevski, D. & Corbett, S. 2011 Modality of human expired aerosol size distributions. J. Aerosol Sci. 42, 839851.
Jonassen, D. R., Settles, G. S. & Tronosky, M. D. 2006 Schlieren PIV for turbulent flows. Opt. Lasers Engng 44, 190207.
Kajihara, M. 1971 Settling velocity and porosity of suspended particle. J. Oceanogr. Soc. Japan 27, 158162.
Lai, A., Zhao, B., Law, A. -K. & Adams, E. 2013 Two-phase modeling of sediment clouds. Environ. Fluid Mech. 129.
Lauga, E., Brenner, M. P. & Stone, H. A. 2005 Microfluidics: the no-slip boundary condition. Handbook of Experimental Fluid Dynamics. Springer.
Lee, W. Y., Li, A. C. Y., Lee, J. H. W. & Asce, F. 2013 Structure of a horizontal sediment-laden momentum jet. J. Hydraul. Engng 139, 124140.
Loudon, R. & Roberts, M. 1967 Relation between the airborne diameters of respiratory droplets and the diameter of the stains left after recovery. Nature 213, 9596.
Martin, D. & Nokes, R. 1988 Crystal settling in a vigorously convecting magma chamber. Nature 332, 534536.
McCool, F. D. 2006 Global physiology and pathophysiology of cough. Chest 129 (1 Suppl), 48S53S.
McCutchan, J. W. & Taylor, C. L. 1981 Respiratory heat exchange with varying temperature and humidity of inspired air. J. Appl. Physiol. 4, 121135.
Melikov, A. K. & Kaczmarczyk, J. 2012 Air movement and perceived air quality. Build. Environ. 47, 400409.
Morawska, L. 2006 Droplet fate in indoor environments, or can we prevent the spread of infection?. Indoor Air 16, 335347.
Morawska, L., Johnson, G., Ristovski, Z., Hargreaves, M., Mengersen, K., Corbett, S., Chao, C., Li, Y. & Katoshevski, D. 2009a Size distribution and sites of origin of droplets expelled from the human respiratory tract during expiratory activities. Aerosol Sci. 40, 256259.
Morawska, L., Johnson, G., Ristovski, Z., Hargreaves, M., Mengersen, K., Corbett, S., Chao, C., Li, Y. & Katoshevski, D. 2009b Size distribution and sites of origin of droplets expelled from the human respiratory tract during expiratory activities. J. Aerosol Sci. 40, 256269.
Morton, B. R., Taylor, G. I. & Turner, J. S. 1956 Turbulent gravitational convection from maintained and instantaneous sources. Proc. R. Soc. Lond. 234, 123.
Nicas, M., Nazaroff, W. W. & Hubbard, A. 2005 Toward understanding the risk of secondary airborne infection: emission of respirable pathogens. J. Occup. Environ. Hyg. 2, 143154.
Papineni, R. S. & Rosenthal, F. S. 1997 The size distribution of droplets in the exhaled breath of healthy human subjects. J. Aerosol Med. 10, 105116.
Park, J., Kang, S., Lee, S. & Kim, W. C. D. 2010 How respiratory muscle strength correlates with cough capacity in patients with respiratory muscle weakness. Yonsei Med. J. 51, 392397.
Picard, A., Davis, R. S., Gläser, M. & Fujii, K. 2008 Revised formula for the density of moist air (CIPM-2007). Metrologia 45, 149155.
Richards, J. M. 1961 Experiments on the penetration of an interface by buoyant thermals. J. Fluid Mech. 11, 369384.
Richards, J. M. 1965 Puff motions in unstratified surroundings. J. Fluid Mech. 21, 97106.
Scorer, R. S. 1957 Experiments on convection of isolated masses of buoyant fluid. J. Fluid Mech. 2, 583594.
Scorer, R. S. 1978 Environmental Aerodynamics. Ellis Horwood.
Settles, G. S. 2006 Fluid mechanics and homeland security. Annu. Rev. Fluid Mech. 38, 87110.
Socolofsky, S. A., Crounse, B. C. & Adams, E. E.Environmental fluid mechanics: theories and applications. In Multi-Phase Plumes in Uniform, Stratified, and Flowing Environments American Society of Civil Engineers.
Sonkin, L. S. 1951 The role of particle size in experimental airborne infection. Am. J. Hyg. 53, 337354.
Tang, J. W., Li, Y., Eames, I., Chan, P. & Ridgway, G. 2006 Factors involved in the aerosol transmission of infection and control of ventilation in healthcare premises. J. Hosp. Infect. 64, 100114.
Tang, J. W., Liebner, T. J., Craven, B. A. & Settles, G. S. 2009 A schlieren optical study of the human cough with and without wearing masks for aerosol infection control. J. R. Soc. Interface 6, S727S736.
Tang, J. W., Path, F. R. C. & Settles, G. S. 2008 Coughing and aerosols. New Engl. J. Med. 359, e19.
Tellier, R. 2006 Review of aerosol transmission of influenza A virus. Emerg. Infect. Dis. 12, 16571662.
Tellier, R. 2009 Aerosol transmission of influenza A virus: a review of new studies. J. R. Soc. Interface 6, S783S790.
Turner, J. S. 1979 Buoyancy Effects in Fluids. Cambridge University Press.
Weber, T. P. & Stilianakis, N. I. 2008 Inactivation of influenza A virus in the environment and modes of transmission: a critical review. J. Infect. 57, 361373.
Wells, W. F. 1934 On air-born infection. Study II. Droplet and droplet nuclei. Am. J. Hyg. 20, 611618.
Wells, W. F. 1955 Airborne Contagion and Air Hygiene: An Ecological Study of Droplet Infection. Harvard University Press.
Wong, T. W., Lee, C. K., Tam, W., Lau, J. T., Yu, T. S., Lui, S. F., Chan, P. K., Li, Y., Bresee, J. S., Sung, J. J. & Parashar, U. D. 2004 Cluster of SARS among medical students exposed to single patient—Hong Kong. Emerg. Infect. Dis. 10, 269276.
Woods, A. W. 2010 Turbulent plumes in nature. Annu. Rev. Fluid Mech. 42, 391412.
Yang, S., Lee, G. W. M., Chen, C. -M., Wu, C. -C. & Yu, K. -P. 2007 The size and concentration of droplets generated by coughing in human subjects. J. Aerosol Med. 20, 484494.
Yu, I. T., Li, Y., Wong, T. W., Tam, W., Chan, A. T., Lee, J. H., Leung, D. Y. & Ho, T. 2004 Evidence of airborne transmission of the severe acute respiratory syndrome virus. New Engl. J. Med. 350, 17311739.
Zayas, G., Chiang, M., Wong, E., MacDonald, F., Lange, C., Senthilselvan, A. & King, M. 2012 Cough aerosol in healthy participants: fundamental knowledge to optimize droplet-spread infectious respiratory disease management. BMC Pulmonary Med. 12 (1), 11 doi:10.1186/1471-2466-12-11.
Recommend this journal

Email your librarian or administrator to recommend adding this journal to your organisation's collection.

Journal of Fluid Mechanics
  • ISSN: 0022-1120
  • EISSN: 1469-7645
  • URL: /core/journals/journal-of-fluid-mechanics
Please enter your name
Please enter a valid email address
Who would you like to send this to? *

JFM classification


Full text views

Total number of HTML views: 0
Total number of PDF views: 0 *
Loading metrics...

Abstract views

Total abstract views: 0 *
Loading metrics...

* Views captured on Cambridge Core between <date>. This data will be updated every 24 hours.

Usage data cannot currently be displayed