Scientists Track Cough Droplets' Flight Trajectory
Researchers from Singapore's A*STAR Institute of High Performance Computing conducted a study on cough droplets' flight trajectory using air simulation. To put it simply, they calculated how far cough droplets go in various wind speeds.
Using computers to handle the mathematical formulation challenges, the researchers were able to pinpoint the airflow and the airborne cough droplets around humans at different wind speeds under the influence of other environmental factors such as weather. The study was published in the journal Physics of Fluids.
A cough usually emits thousands of cough droplets and they spread around a wide range. Researchers discovered that even without any wind, large cough droplets traveled 3 feet (1 meter) away from the coughing subject, and smaller droplets that can evaporate easier in the air traveled even further.
Study author Hongying Li explained the situation by saying “An evaporating droplet retains the nonvolatile viral content, so the viral loading is effectively increased, this means that evaporated droplets that become aerosols are more susceptible to be inhaled deep into the lung, which causes infection lower down the respiratory tract, than larger unevaporated droplets.” according to the paper.
Later on, the team tested the droplets with various winds speeds and found that under a wind speed of 6 feet (2 meters) per hour, cough droplets can actually travel up to over 19 feet (6 meters) and maybe even further according to the weather. If the air is drier, the droplets evaporate faster, making them travel to further distances.
Regarding the relationship between flight trajectories of cough droplets and wearing masks, study author Fong Yew Leong stated that "In addition to wearing a mask, we found social distancing to be generally effective, as droplet deposition is shown to be reduced on a person who is at least 3 feet (1 meter) from the cough."
Please note that these findings and this study is based on outdoor airborne transmission in a tropical setting. To track cough droplets' flight trajectory in different settings, the results would be highly dependent on the weather, wind speed, air humidity, and temperature.
While this study is the result of limited research, the team is working to develop their study into a more general one in order to optimize the comfort and safety of the public, especially for those who are receiving COVID-19 treatments in hospitals and medical units.