Synergistic Inactivation of Airborne Viruses by Low‐Concentration Ozone With High Humidity and Temperature

Ambient humidity, temperature, and ozone influence the viability of airborne viruses, but their synergistic effects are poorly understood, particularly regarding ozone with humidity/temperature changes. Therefore, we examined the inactivation of airborne influenza viruses and coronaviruses under combinations of low ambient ozone concentrations, relative humidity (RH) levels, and temperatures typical of daily life. Viral fluid was atomized in a closed chamber conditioned with different combinations of these factors. The atomized aerosol particles containing the virus were exposed to ambient air and then sampled for titration. Active virus levels in ambient air at 50%-85% RH with 15, 35, and 55 ppb ozone significantly decreased compared with those in ambient air with 0 ppb ozone, whereas those in ambient air at < 40% RH decreased only slightly, even with 100 ppb ozone. Viral gene copy numbers, assayed via quantitative real-time polymerase chain reaction, remained similar across all conditions. Inactivation increased with higher temperatures, although not at 15°C. These findings suggest that low concentrations of ambient ozone, when combined with high humidity and temperature, effectively inactivate airborne viruses, potentially influencing viral transmission in real-world environments.