Modeling and experimental study of dispersion and deposition of respiratory emissions with implications for disease transmission

Abstract

The ability to model the dispersion of pathogens in exhaled breath is important for characterizing transmission of the SARS‐CoV‐2 virus and other respiratory pathogens. A Computational Fluid Dynamics (CFD) model of droplet and aerosol emission during exhalations has been developed and for the first time compared directly with experimental data for the dispersion of respiratory and oral bacteria from ten subjects coughing, speaking, and singing in a small unventilated room. The modeled exhalations consist of a warm, humid, gaseous carrier flow and droplets represented by a discrete Lagrangian particle phase which incorporates saliva composition. The simulations and experiments both showed greater deposition of bacteria within 1 m of the subject, and the potential for a substantial number of bacteria to remain airborne, with no clear difference in airborne concentration of small bioaerosols (<10 μm diameter) between 1 and 2 m. The agreement between the model and the experimental data for bacterial deposition directly in front of the subjects was encouraging given the uncertainties in model input parameters and the inherent variability within and between subjects. The ability to predict airborne microbial dispersion and deposition gives confidence in the ability to model the consequences of an exhalation and hence the airborne transmission of respiratory pathogens such as SARS‐CoV‐2.

Metabolic changes of VOCs in human caused by wearing masks: a preliminary study based on electronic nose

“…Some potential changes in expiratory metabolism occurred due to differences in wearing duration, quality of masks, and filtering effectiveness of masks. Some possible explanations including the fact that our exhalation components frequently contain germs [10,8,9,11,19]. Because of the masks' barrier, some germs begin to gather around the masks and then continue to move through the body with breath in and out.…”

Reflections on the past and perspectives on the future at the Healthcare Infection Society – 40th Anniversary special celebratory meeting

“…Professor Cath Noakes (University of Leeds) summarised our understanding of respiratory transmission over 40 years, including through droplets, aerosols, fomites and contact. She argued against simple categorisations of respiratory viral transmission as droplet or aerosol, emphasised how medium-sized particles are the most unpredictable, and she explained exciting new methodological approaches used in research in this field [ 15 ].…”

Modeling the effect of temperature and relative humidity on exposure to SARS‐CoV ‐2 in a mechanically ventilated room

“…This was applied as a surface heat flux of 25 W m −2 . This value is similar to that measured by Zhu et al 28 for a resting subject and was used in Coldrick et al 12 The heat flux was assumed to be the same for all the temperature and RH conditions. All walls, the floor and the ceiling were given adiabatic boundary conditions.…”

“…F I G U R E 3 Initial jet expansion angles for the cough, viewed from the front and side. 27 as described in Coldrick et al 12 The number of droplets emitted during each time step was determined by the fraction of the total volume exhaled during that time interval. Over the duration of the exhalation, the sampled distribution approached the specified BLO distribution.…”

“…As in Coldrick et al, 12 the bronchiolar, laryngeal and oral (BLO) model 29 was used to describe the distribution of exhaled droplets.…”