Characterizing respiratory aerosol emissions during sustained phonation

Airborne respiratory aerosol transport and deposition in a two-person office using a novel diffusion-based numerical model

BACKGROUND

The COVID-19 pandemic was caused by the SARS-CoV-2 coronaviruses transmitted mainly through exposure to airborne respiratory droplets and aerosols carrying the virus.

OBJECTIVE

To assess the transport and dispersion of respiratory aerosols containing the SARS-CoV-2 virus and other viruses in a small office space using a diffusion-based computational modeling approach.

METHODS

A 3-D computational model was used to simulate the airflow inside the 70.2 m3 ventilated office. A novel diffusion model accounting for turbulence dispersion and gravitational sedimentation was utilized to predict droplet concentration transport and deposition. The numerical model was validated and used to investigate the influences of partition height and different ventilation rates on the concentration of respiratory aerosols of various sizes (1, 10, 20, and 50 µm) emitted by continuous speaking.

RESULTS

An increase in the hourly air change rate (ACH) from 2.0 to 5.6 decreased the 1 μm droplet concentration inside the office by a factor of 2.8 and in the breathing zone of the receptor occupant by a factor of 3.2. The concentration at the receptor breathing zone is estimated by the area-weighted average of a 1 m diameter circular disk, with its centroid at the center of the receptor mannequin mouth. While all aerosols were dispersed by airflow turbulence, the gravitational sedimentation significantly influenced the transport of larger aerosols in the room. The 1 and 10 μm aerosols remained suspended in the air and dispersed throughout the room. In contrast, the larger 20 and 50 μm aerosols deposited on the floor quickly due to the gravitational sedimentation. Increasing the partition between cubicles by 0.254 m (10") has little effect on the smaller aerosols and overall exposure.

IMPACT

This paper provides an efficient computational model for analyzing the concentration of different respiratory droplets and aerosols in an indoor environment. Thus, the approach could be used for assessing the influence of the spatial concentration variations on exposure for which the fully mixed model cannot be used.

Respiratory particle emission rates from children during speaking

The number of respiratory particles emitted during different respiratory activities is one of the main parameters affecting the airborne transmission of respiratory pathogens. Information on respiratory particle emission rates is mostly available for adults (few studies have investigated adolescents and children) and generally involves a limited number of subjects. In the present paper we attempted to reduce this knowledge gap by conducting an extensive experimental campaign to measure the emission of respiratory particles of more than 400 children aged 6 to 12 years while they pronounced a phonetically balanced word list at two different voice intensity levels ("speaking" and "loudly speaking"). Respiratory particle concentrations, particle distributions, and exhaled air flow rates were measured to estimate the respiratory particle emission rate. Sound pressure levels were also simultaneously measured. We found out that median respiratory particle emission rates for speaking and loudly speaking were 26 particles s-1 (range 7.1-93 particles s-1) and 41 particles s-1 (range 10-146 particles s-1), respectively. Children sex was significant for emission rates, with higher emission rates for males during both speaking and loudly speaking. No effect of age on the emission rates was identified. Concerning particle size distributions, for both respiratory activities, a main mode at approximately 0.6 µm and a second minor mode at < 2 µm were observed, and no differences were found between males and females. This information provides important input parameters in predictive models adopted to estimate the transmission risk of airborne pathogens in indoor spaces.

SARS-CoV-2 transmission modes: Why and how contamination occurs around shared meals and drinks?

In spite of prevention measures enacted all over the world to control the COVID-19 pandemic outbreak, including mask wearing, social distancing, hand hygiene, vaccination, and other precautions, the SARS-CoV-2 virus continues to spread globally at an unabated rate of about 1 million cases per day. The specificities of superspreading events as well as evidence of human-to-human, human-to-animal and animal-to-human transmission, indoors or outdoors, raise questions about a possibly neglected viral transmission route. In addition to inhaled aerosols, which are already recognized as key contributors to transmission, the oral route represents a strong candidate, in particular when meals and drinks are shared. In this review, we intend to discuss that significant quantities of virus dispersed by large droplets during discussions at festive gatherings could explain group contamination either directly or indirectly after deposition on surfaces, food, drinks, cutlery, and several other soiled vectors. We suggest that hand hygiene and sanitary practices around objects brought to the mouth and food also need to be taken into account in order to curb transmission.

Comparison of Aerosol Emissions during Specific Speech Tasks

OBJECTIVES/HYPOTHESIS

Recent investigations into the behavior of aerosolized emissions from the oral cavity have shown that particulate emissions do indeed occur during speech. To date, there is little information about the relative contribution of different speech sounds in producing particle emissions in a free field. This study compares airborne aerosol generation in participants producing isolated speech sounds: fricative consonants, plosive consonants, and vowel sounds.

STUDY DESIGN

Prospective, reversal experimental design, where each participant served as their own control and all participants were exposed to all stimuli.

METHODS

While participants produced isolated speech tasks, a planar beam of laser light, a high-speed camera, and image software calculated the number of particulates detected over time. This study compared airborne aerosols emitted by human participants at a distance of 2.54 cm between the laser sheet and the mouth.

RESULTS

Statistically significant increases in particulate count over ambient dust distribution for all speech sounds. When collapsed across loudness levels, emitted particles in vowel sounds were statistically greater than consonants, suggesting that mouth opening, as opposed to the place of vocal tract constriction or manner of sound production, might also be influential in the degree to which particulates become aerosolized during speech.

CONCLUSIONS

The results of this research will inform boundary conditions for computational models of aerosolized particulates during speech.