Humidity could hinder spread of COVID from sneezes

Throughout the pandemic, research has been conducted on how COVID-19 is transmitted in the air. For example, studies showing respiratory droplets can travel several feet led to guidelines suggesting masking and physical distancing of six feet could reduce transmission.

Stiehl et al. added to this understanding of transmission by looking at how relative humidity in the air can affect COVID spreading through sneezes. While studies of sneezes have been done previously, none had accounted for relative humidity.

Using a wide-angle, high-speed camera, the authors imaged test subjects violently sneezing without a face mask. The images, showing the velocity of droplets from the sneezes, were analyzed with computational fluid dynamics models that employed detached eddy simulations. This allowed the team to study how the droplets broke up, evaporated, and dispersed.

The scientists found increasing the humidity led to a decrease in virus transmission. This is likely because droplets evaporate much slower at high humidities and tend to fall to the ground relatively quickly. In contrast, in dry environments, evaporation shrinks droplet size and allows them to remain airborne for longer.

“We hope this work could be used when considering safe distancing and guidance for the general public,” said author Kareem Ahmed.

Next, the researchers are interested in looking into further unstudied factors that could affect the transmission of COVID and other airborne viruses.

“We plan to examine the effect of food content, which would make our saliva thicker and control the transmission of aerosols and droplets,” Ahmed said.

Source: “The effect of relative air humidity on the evaporation timescales of a human sneeze,” by Bernhard Stiehl, Rajendra Shrestha, Steven Schroeder, Juanpablo Delgado, Alexander Bazzi, Jonathan Reyes, Michael Kinzel, and Kareem Ahmed, AIP Advances (2022). The article can be accessed at https://doi.org/10.1063/5.0102078 .