Carbon dioxide helps extend life of airborne viruses like COVID

Carbon dioxide has a vital role in determining the lifespan of airborne viruses like SARS-CoV-2, the virus that caused COVID-19, a new study has revealed.

The Nature Communications study also highlights the importance of keeping tabs on CO₂ levels to reduce virus survival and minimise the risk of infection.

CELEBS technology

Researchers developed a unique bioaerosol technology called CELEBS – Controlled Electrodynamic Levitation and Extraction of Bioaerosols onto a Substrate – to show how CO₂ is a contributing factor in extending the life of SARS-CoV-2 variants.

CELEBS allows the survival of different SARS-CoV-2 variants to be measured in lab-generated airborne particles designed to mimic exhaled aerosol. By varying the concentration of CO₂ in the air between 400 parts per million (ppm), the level in normal outdoor air, and 6,500 ppm, the team confirmed a link between increases in CO₂ concentrations and the aerostabilities of different SARS-CoV-2 variants.

“We knew SARS-CoV-2, like other viruses, spreads through the air we breathe. But this study represents a huge breakthrough in our understanding of exactly how and why that happens, and crucially, what can be done to stop it,” explains lead author Dr Allen Haddrell, Senior Research Associate in Aerosol Science at the University of Bristol.

Haddrell says the research also shows opening a window “may be more powerful than originally thought, especially in crowded and poorly ventilated rooms, as fresh air will have a lower concentration of CO₂, causing the virus to become inactivated much faster.”

Super spreader events

Increasing CO₂ concentrations to just 800 ppm, a level considered as well ventilated, resulted in an increase in viral aerostability. After 40 minutes, around 10 times as much virus remained infectious when the air has a CO₂ concentration similar to that of a crowded room (3,000 ppm) compared to clean air.

“This relationship sheds important light on why super spreader events may occur under certain conditions,” Haddrell explains. “The high pH of exhaled droplets containing the SARS-CoV-2 virus is likely a major driver of the loss of infectiousness. CO₂ behaves as an acid when it interacts with droplets. This causes the pH of the droplets to become less alkaline, resulting in the virus within them being inactivated at a slower rate.”

He says that’s why opening a window is an effective mitigation strategy – it physically removes the virus from the room and makes the aerosol droplets more toxic to the virus.

Climate research

Recent climate science research suggests that between now and the end of the century, the concentration of CO₂ in the atmosphere is expected to reach more than 700 ppm.

“These findings therefore have broader implications not only in our understanding of the transmission of respiratory viruses, but how changes in our environment may exacerbate the likelihood of future pandemics,” says Haddrell. “Data from our study suggests that rising levels of CO₂ in the atmosphere may coincide with an increase in the transmissibility of other respiratory viruses by extending how long they remain infectious in the air.”

“While there is much we still do not understand, we are now gaining a much more complete picture of the role exhaled respiratory aerosols play in transporting infectious viruses between people and the mechanisms that control their survival,” adds Professor Jonathan Reid, Director of the EPSRC Centre for Doctoral Training in Aerosol Science at the University of Bristol. “These findings can serve as a scientific basis for the design of mitigation strategies that could save lives in any future pandemic.”

News Reference

Allen Haddrell, Jonathan P. Reid et al, (2024) Ambient carbon dioxide concentration correlates with SARS-CoV-2 aerostability and infection risk, Nature Communications