Ambient carbon dioxide concentration correlates with SARS-CoV-2 aerosolability and infection risk

An improved understanding of the underlying physicochemical properties of respiratory aerosol that influence viral infectivity may open new avenues to mitigate the transmission of respiratory diseases such as COVID-19. Previous studies have shown that an increase in the pH of respiratory aerosols following generation due to changes in the gas-particle partitioning of pH buffering bicarbonate ions and carbon dioxide is a significant factor in reducing SARS-CoV-2 infectivity. We show here that a significant increase in SARS-CoV-2 aerosolability results from a moderate increase in the atmospheric carbon dioxide concentration (e.g. 800 ppm), an effect that is more marked than that observed for changes in relative humidity. We model the likelihood of COVID-19 transmission on the ambient concentration of CO₂, concluding that even this moderate increase in CO₂ concentration results in a significant increase in overall risk. These observations confirm the critical importance of ventilation and maintaining low CO₂ concentrations in indoor environments for mitigating disease transmission. Moreover, the correlation of increased CO₂ concentration with viral aerosolability needs to be better understood when considering the consequences of increases in ambient CO₂ levels in our atmosphere.