Abstract
Contact and inhalation of virions-carrying human aerosols represent the primary transmission pathway for airborne diseases including the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Relative to sneezing and coughing, non-symptomatic aerosol-producing activities such as speaking are highly understudied. The dispersions of aerosols from vocalization by a human subject are hereby quantified using high-speed particle image velocimetry. Syllables of different aerosol production rates were tested and compared to coughing. Results indicate aerosol productions and penetrations are not correlated. E.g. ‘ti’ and ‘ma’ have similar production rates but only ‘ti’ penetrated as far as coughs. All cases exhibited a rapidly penetrating “jet phase” followed by a slow “puff phase.” Immediate dilution of aerosols was prevented by vortex ring flow structures that concentrated particles toward the plume-front. A high-fidelity assessment of risks to exposure must account for aerosol production rate, penetration, plume direction and the prevailing air current.
Highlights
Contact and inhalation of virions-carrying human aerosols represent the primary pathway of transmission for many airborne diseases, including the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)[1,2] of 2020
Extrapolations of existing cough and sneeze models to estimate the dispersion of speech aerosols is untenable, due to the wide range of human vocalizations; e.g. different syllables are associated with vastly different mouth shapes and potentially different aerosol ejection velocities, whose influences on the dispersion pattern are unknown
Aerosol production rates increased with Sound intensity level (SIL), as expected
Summary
Contact and inhalation of virions-carrying human aerosols represent the primary transmission pathway for airborne diseases including the severe acute respiratory syndrome coronavirus 2 (SARSCoV-2). A recent study found that pre-symptomatic persons can shed SARS-CoV-2 virus at a higher rate than symptomatic individuals[16] Exacerbating this issue, asymptomatic persons are less likely to observe transmission-mitigating measures enacted by health agencies like the United States’ Centers for Disease Control and Prevention (CDC)[17], thereby increasing their transmission probability. In one series of emerging studies, researchers found that certain vowels and consonants consistently exhibit very high rates of aerosol production, while other vocalizations generated low amounts of a erosols[21,22] The sizes of these aerosol droplets can range from the lower measurement limit of 0.5 μm to approximately ~ 10 μm, peaking at ~ 1 μm[21,22]. Extrapolations of existing cough and sneeze models to estimate the dispersion of speech aerosols is untenable, due to the wide range of human vocalizations; e.g. different syllables are associated with vastly different mouth shapes and potentially different aerosol ejection velocities, whose influences on the dispersion pattern are unknown
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