Ambient Concentrations of CO2(g) Affects the Aero-Stability of SARS-CoV-2
ALLEN E. HADDRELL, Henry Oswin, Tristan Cogan, Joshua Robinson, Jianghan Tian, Robert Alexander, Jamie Mann, Darryl Hill, Adam Finn, Andrew Davidson, Jonathan P. Reid,
University of Bristol Abstract Number: 322
Working Group: Aerosol Science of Infectious Diseases: Lessons and Open Questions on Models, Transmission and Mitigation
AbstractThe length of time that SARS-CoV-2 remains infectious while suspended in the aerosol phase will affect its overall spread. Thus, a detailed mechanistic understanding of how infectious viral particles lose infectivity in the aerosol phase is critical in predicting viral degradation across a broad range of environmental conditions.
It has been recently demonstrated that the high alkalinity a respiratory aerosol reaches immediately after exhalation (pH>10) is caustic enough to irreversibly inactivate SARS-CoV-2(1). The high pH reached by the aerosol results from the massive flux of dissolved bicarbonate from the droplet in the form of CO2(g):
Eq1. H+ + HCO3- ↔ H2CO3 ↔ CO2(g) + H2O
The peak pH the aerosol reaches is functions of many factors, such acidic gases/vapours (including CO2(g)) and aerosol size.
In this study, next generation bioaeorol technology (CELEBS) is used to explore the buffering effect that ambient concentrations of CO2(g) (<3,000 ppm) have on the aero-stability of the Delta and Omicron variants of SARS-CoV-2.
Under ambient conditions, the Omicron variant was found to be significantly more aero-stable than the Delta variant. The increase in aero-stability correlates with the variants alkalinity sensitivity.
At a high relative humidity, any excess concentration of CO2(g) is found to improve the aero-stability of SARS-CoV-2 in a dose dependent fashion. Increases in the concentration of CO2(g) improved viral aero-stability across the entire relative humidity range. Elevated levels of CO2(g) reduces the rate in which SARS-CoV-2 loses infectivity in the aerosol phase; after 40 minutes, elevated CO2(g) resulted in an order of magnitude increase in infectious load. The consequence of this change in viral aero-stability on the risk of transmission is estimated with a Wells-Riley model.
[1] Oswin, H. et al., (2022)PNAS, 119(27), e2200109119.