Scientists at the University of Bristol have discovered critical insights into why airborne viruses lose their infectivity. The findings, which were published in the Journal of the Royal Society Interface, show that cleaner air kills the virus much faster and that opening a window may be more important than previously thought. The findings could influence future virus mitigation strategies.
Researchers from Bristol’s School of Chemistry show that the virus has become less capable of surviving in the air as it evolved from the original strain to the ‘Delta’ variant in the first study to measure differences in airborne stability of different variants of SARS-CoV-2 in inhalable particles.
Dr. Allen Haddrell, the study’s lead author and Senior Research Associate in Bristol’s School of Chemistry, explained: “Aerosol particles, exhaled when infected individuals breathe, speak or cough, can transmit viruses — but how and why viruses lose infectivity once they are circulating around in these airborne particles has been widely debated.”
Our findings expand our understanding of how environmental factors affect the airborne stability of SARS-CoV-2 and other viruses, which will help us design better disease prevention and mitigation strategies.
Dr Allen Haddrell
The team used a next-generation bioaerosol technology instrument called CELEBS (Controlled Electrodynamic Levitation and Extraction of Bioaerosols onto a Substrate) to investigate the survival of different SARS-CoV-2 variants in laboratory-generated airborne particles that mimic exhaled aerosol. Over a 40-minute period, they investigated how environmental factors such as temperature and humidity, particle composition, and the presence of acidic vapours such as nitric acid affect virus infectivity.
The team confirmed that the alkaline pH of the aerosol droplets containing the virus controls the virus’s aero-stability by manipulating the gaseous content of the air. They describe how each of the SARS-CoV-2 variants has different airborne stabilities, and how this stability is related to their sensitivity to alkaline pH conditions.
Because the high pH of exhaled SARS-CoV-2 virus droplets is likely a major driver of the virus’s loss of infectiousness, the less acid in the air, the more alkaline the droplet, and the faster the virus dies. Opening a window may be more important than previously thought because fresh air with lower carbon dioxide content reduces acid content in the atmosphere and causes the virus to die much faster.
“Our results indicate that the high pH of exhaled aerosol drives the loss of viral infectivity,” Dr. Haddrell added. As a result, any gas that alters aerosol pH may influence how long the virus remains infectious in the air. Bleach, for example, emits acidic vapour, which may increase SARS-CoV-2 stability in the aerosol phase. In contrast, ammonia, which produces alkaline vapour, may have the opposite effect.”
The findings shed light on why and how aerosolized viruses lose their infectivity, paving the way for the development of new risk-mitigation strategies.
“There are numerous factors that affect the transmission of airborne viruses, and these are often confounded with physical and environmental parameters that can affect viral longevity in the aerosol phase, such as temperature, relative humidity, air movement, and UV light,” said Jonathan Reid, Director of Bristol Aerosol Research Centre and Professor of Physical Chemistry in the School of Chemistry at the University of Bristol, and one of the corresponding authors.
“Our findings expand our understanding of how environmental factors affect the airborne stability of SARS-CoV-2 and other viruses, which will help us design better disease prevention and mitigation strategies. We now plan to investigate the role of pH further by investigating the effect of carbon dioxide on the risk of SARS-CoV-2 transmission.”
