Airflow Patterns Inside a Car Affect Transmission Risk of Covid-19 in Ridesharing

 

A team of researchers at Brown University, including graduate student of engineering Asimanshu Das and assistant professor of physics at University of Massachusetts Amherst Varghese Mathai, investigated how airflow inside a car affects Covid-19 transmission risk. Mathai, a former postdoctoral researcher at Brown University, specializes his research in dispersed multiphase fluids and soft matter. Some of his previous publications include “Bubbly and buoyant particle laden turbulence”, “Dynamics of heavy and buoyant underwater pendulums”, and “Experimental study of the heat transfer properties of self-sustained biphasic thermally driven turbulence”. In order to study how certain airflow patterns in cars can help mitigate the risk of Covid-19 when ride sharing, they used computer models to simulate airflow in multiple scenarios of windows open, windows closed, and the use of the car’s ventilation system. Their simulation consisted of a car similar to a Toyota Prius and two people, the driver and a passenger, who is sitting in the backseat on the opposite side of the driver to maximize social distancing. Mathai et al. examined the airflow around and inside a car moving at 50 miles per hour in their simulation, looking at the movement of concentration of aerosols. Aerosols are tiny particles that tend to remain for extended periods of time in the air, and thus are one of the ways in which Covid-19 is thought to be transmitted between people.  

Their research revealed that the more windows that were open in the car, the lower the risk for transmission of Covid-19. The car’s ventilation system did a poor job of conducting airflow patterns that would reduce the concentration of airborne particles. Having even two windows open was much better than the ventilation system for circulation. Mathai et al. found that opening the car windows increased the number of air changes per hour (ACH), and ACH reduces the concentration of aerosols. Different combinations of open and closed windows established different air currents that either increased or decreased exposure to aerosols. Since the air pressure near the rear windows of a car tends to be higher than the pressure near the front windows, air enters the car through the back windows and exits the cars through the front windows. When all of the car windows were open in the simulation, this created independent flows of air on either side of the car. Thus, particles were rarely transferred between driver and passenger. Mathai et al. noted that the driver is actually at a higher risk of transmission since the air flows from the back of the car to the front. These findings depict patterns of exposure to lingering aerosols, and it is important to note that the research did not include large respiratory droplets. Besides contributing findings valuable for slowing the transmission of Covid-19, Mathai et al. developed a model for air circulation patterns and the microclimate inside a car.