Tracking airborne nuclei to determine air filtration efficacy in reducing viral spread

In the era of Covid-19, understanding the fluid mechanics of airborne viruses has become a pressing imperative. Better knowledge of air movement and suspended particles indoors helps to control contagions and informs policy around public health.

In poorly ventilated indoor spaces, the risk of airborne viral transmission is considerably higher. While introducing fresh pathogen-free air into these spaces will reduce risk, cost considerations often demand that some indoor air be recycled. This raises questions about the efficacy of air filters in preventing transmission.

Krishnaprasad et al. use a statistical framework to examine the fluid mechanics of airborne nuclei and the effects of recycling and filtration in indoor ventilation systems.

The authors distinguish between a direct route by which the nuclei travel from an infected source to a receiving host; and an indirect route, in which nuclei are removed from a room before being re-injected through ventilation inlets.

“What sets our study apart is a process known as statistical overloading to provide relevant results by accounting for practically all possible direct and indirect routes and all possible combinations of sick and susceptible locations, taking into account the turbulent chaotic nature of indoor air,” said author Nadim Zgheib.

Compared to traditional simulations, this process is computationally expensive, necessitating the tracking of tens of millions of droplet nuclei and can take up to two hours. However, it can be applied definitively to any type of filtration system.

The researchers demonstrate this approach in two settings — a classroom and a nursing home — revealing that proper filtration is indeed effective at reducing transmission risk.

Source: “Fluid mechanics of air recycling and filtration for indoor airborne transmission,” by K. A. Krishnaprasad, J. S. Salinas, N. Zgheib, and S. Balachandar, Physics of Fluids (2022). The article can be accessed at http://doi.org/10.1063/5.0135718 .

This paper is part of the Special Collection “Flow and the Virus”; learn more here .