Atmospheric chemists join battle against COVID-19

By Aadhishre Kasat
Department Communications & Student Researcher (Buller)

Experiment setup in room with heating pads
Using a classroom simulation set-up in Mechanical Engineering, the Bertram Group assessed the spatial variability in respiratory aerosol emitted from mannequins equipped to disperse aerosol particles into the room.

When COVID-19 first hit, many people hastily adopted work-from-home protocols. Trips outside were limited to grocery runs; suddenly, fruits and vegetables became synonymous with ramen and ready-to-eat food choices. Social lives compressed to the six inches of mobile phone screens. Facetime Fridays with steaming cups of coffee, arguably with three too many shots of espresso, became routine. Today, even with the pandemic running rampant, things are very different. Slowly people are participating in more in-person activities; however, often without a complete understanding of the risks.

According to the National Academies of Science, there is growing evidence that SARS-CoV-2 can also spread through airborne transmission; viral particles evaporate, instead of depositing to a surface, and enter the room’s circulation to spread beyond the six-foot radius.

To prevent airborne transmission, Tim Bertram, professor of chemistry and affiliate professor of Atmospheric and Oceanic Sciences, explained the importance of understanding how air moves inside and outside closed spaces and how airborne particulates can carry the virus. Bertram, along with assistant scientist Joe Gord and graduate student Stephanie Richards, has been trying to determine transmission pathways and vectors in a typical indoor environment and engineering controls that can be utilized to mitigate associated risks.

Bertram explained that there is greater evidence for airborne transmission in indoor environments than the outdoors or between rooms. This is because indoor environments, in comparison, are not as thoroughly ventilated. To understand the risks associated with sitting in such spaces, the relationship between actions such as laughing, singing, and the diameter and the number of the aerosol particles ejected needs to be resolved, as well as what percentages of those particles contain active forms of the virus. Answering this question will help evaluate how effective physical distancing strategies are and at what rate particles are lost from circulation through physical processes.

In collaboration with Prof. David Rothamer and Prof. Scott Sanders, from the mechanical engineering department, and Johnson Controls, Bertram’s team found that viral particles ejected in rooms with four times higher ventilation rates have a 10-15 percent lower initial concentration, reach a steady-state faster, and decay faster. Bertram’s team also found that wearing a mask reduces the ejected particle concentration by at least 20-30 percent in the near-field region.

“These experiments help us understand what is occurring in a room after it has been vacated, which is valuable information because it will help us assess the amount of buffer time required between consecutive classes,” Bertram said.

“From a research perspective, I want to track particulates and the viruses they may carry as they are being exhausted out into the room,” Bertram said. “This is challenging because there are pieces of the puzzle that we simply do not know. We do not know how many viruses are in an individual aerosol particle as a function of size. We do not know the dose-response curve for SARS-CoV-2. But we have not had this information for calculating risk for other types of airborne diseases, so the best we can do is set policies in place to control variables we understand.”

Bertram explained that the key principles are clear: physical distancing while wearing masks, even though they are not 100 percent efficient, makes a difference. Limiting the time spent indoors, increasing ventilation, and clean air delivery rates also make a difference