Evaporation and dispersion of respiratory droplets from coughing

Abstract

Understanding how respiratory droplets become droplet nuclei and their dispersion is essential for understanding the mechanisms and control of disease transmission via droplet-borne and airborne routes. A theoretical model was developed to estimate the size of droplet nuclei and their dispersion as a function of the ambient humidity and droplet composition. The model-predicted dried droplet nuclei size was 32% of the original diameter, which agrees with the maximum residue size in the classic study by Duguid, 1946, Edinburg Med. J., 52, 335 and the validation experiment in this study, but is smaller than the 50% size predicted by Nicas et al., 2005, J. Occup. Environ. Hyg., 2, 143. The droplet nuclei size at a relative humidity of 90% (25°C) could be 30% larger than the size of the same droplet at a relative humidity of less than 67.3% (25°C). The trajectories of respiratory droplets in a cough jet are significantly affected by turbulence, which promotes the wide dispersion of droplets. We found that medium-sized droplets (e.g., 60 μm) are more influenced by humidity than are smaller and larger droplets, while large droplets (≥100 μm), whose travel is less influenced by humidity, quickly settle out of the jet.

Direct or indirect exposure of exhaled contaminants in stratified environments using an integral model of an expiratory jet

“…Similar results were also found by the numerical simulations of Chen et al and experimental works of Brohus and Nielsen . Liu et al studied the interpersonal exposure of exhaled droplets and droplet nuclei of two standing thermal manikins with a separation distance of 0.5‐3 m and suggested that the threshold distance of approximately 1.5 m distinguished the short‐range modes and the long‐range airborne route. The knowledge of this threshold distance is important for selecting the correct measures for controlling airborne transmission; however, very few studies have considered the impact of thermal stratification.…”

Generic aspects of the airborne spread of human pathogens indoors and emerging air decontamination technologies

“…Therefore, targeting airborne pathogens could entail additional benefits, such as preventing or reducing the deposition of harmful microbes on secondary vehicles that include frequently touched environmental surfaces and also preventing or reducing their resuspension from these surfaces back into the air via a variety of indoor activities (Fig 1). 8,12,17,75,76 Further studies should investigate the role air decontamination may play in reducing the contamination of environmental surfaces and its combined impact on interrupting the risk of pathogen spread in both domestic and institutional settings.…”

Human Cough as a Two-Stage Jet and Its Role in Particle Transport

“…The former is known as direct spray infection [2], in which relatively large (≥ 5 μm in diameter) droplets or droplet nuclei can be directly deposited on the nasal or oral mucosa of the new host. Short-range airborne exposure via smaller droplets or droplet nuclei is also important in close proximity infection [3]. Beyond 1–2 m, the exhaled air stream dissolves into the room airflow, and the pathogen-containing droplets or droplet nuclei are dispersed according to the global airflow in the room.…”