Size distribution and sites of origin of droplets expelled from the human respiratory tract during expiratory activities

Abstract

A new expiratory droplet investigation system (EDIS) was used to conduct the most comprehensive program of study to date, of the dilution corrected droplet size distributions produced during different respiratory activities. Distinct physiological processes were responsible for specific size distribution modes. The majority of particles for all activities were produced in one or more modes, with diameters below 0.8 m at average concentrations up to 0.75 cm −3 . These particles occurred at varying concentrations, during all respiratory activities, including normal breathing. A second mode at 1.8 m was produced during all activities, but at lower concentrations of up to 0.14 cm −3 . Speech produced additional particles in modes near 3.5 and 5 m. These two modes became most pronounced during sustained vocalization, producing average concentrations of 0.04 and 0.16 cm −3 , respectively, suggesting that the aerosolization of secretions lubricating the vocal chords is a major source of droplets in terms of number. For the entire size range examined of 0.3-20 m, average particle number concentrations produced during exhalation ranged from 0.1 cm −3 for breathing to 1.1 cm −3 for sustained vocalization. Non-equilibrium droplet evaporation was not detectable for particles between 0.5 and 20 m, implying that evaporation to the equilibrium droplet size occurred within 0.8 s.

Measuring the Short-Term Emission Rates of Particles in the “Personal Cloud” with Different Clothes and Activity Intensities in a Sealed Chamber

“…It has been proved that exhaled droplets can be a significant particle source from human, whose emission characteristics have been reported in many studies (e.g., Fabian et al, 2008;Chao et al, 2009;Morawska et al, 2009b). Therefore, it is important to assess the influence of exhaled droplets on the emission rates of particles from clothed human body measured in this study.…”

Violent expiratory events: on coughing and sneezing

“…Tang et al 2009) and droplet sampling (e.g. Morawska et al 2009b). Violent respiratory events release droplet-bearing turbulent momentum puffs of moist, buoyant air ejected in a direction that depends on the individual.…”

Origin of Exhaled Breath Particles from Healthy and Human Rhinovirus-Infected Subjects

“…As more recent studies of healthy subjects have shown, particles are also produced during tidal breathing, and approximately 98% of these particles are under 1 mm. (4)(5)(6)(7) Particle concentrations reported in these studies span several logs: one study measured particle concentrations between 14 and 3230 particles per liter, (6) and another reported concentrations between 20 and 400 particles per liter. (8) found that they produced 67 to 8500 particles per liter of air and that 87% of the particles were under 1 mm.…”