Sensitivity of aerosol-borne Influenza A Virus to gaseous nitric acid and carbon dioxide

Transmission via aerosols is an important route of transmission of influenza A virus (IAV) in humans, whose control remains a global challenge. After exhalation, aerosol particles undergo rapid physicochemical changes that lead to substantial aerosol pH variations, which can impair the infectivity of IAV. Here, we investigate the aerostability of IAV, a key step of the transmission chain, using an aerosol chamber that allows assessing the influence of air composition on aerosol pH. At 55% relative humidity, we observe high sensitivity of IAV to nitric acid concentrations as low as 5 ppb, i.e., 400 times lower than the permissible exposure limit, with the time required to achieve a 99% reduction in active viruses being halved. In contrast, even an increase in carbon dioxide concentration to 250,000 ppm has a negligible effect on IAV. Our results underscore the crucial role of trace acids in transmitting aerosolized respiratory viruses, including strong synergies with air humidification.