The dual role of tropospheric ozone in controlling COVID-19 outbreaks

The coronavirus disease COVID-19 is primarily transmitted through person-to-person contact, but meteorological conditions may influence its spread and severity. High levels of indoor ozone are known to inactivate the virus, yet the impact of low-level tropospheric ozone remains unclear. We thus hypothesized that tropospheric ozone, influenced by seasonal conditions, may mitigate viral spread. We studied the influence of ozone concentration, temperature, and humidity on the COVID-19 reproduction number in three large Israeli cities during 2020–2021. The effect of these parameters was also analyzed in laboratory experiments on viral inactivation. Field results show that in winter, under low temperature and low humidity, the COVID-19 reproduction number decreases with an increase in ozone concentration. In contrast, in the summer, under high temperature and high humidity, the COVID-19 reproduction number increases weakly with an increase in ozone concentration. This seasonal variation is attributed to ozone’s dual effects. Indeed, in winter, ozone inactivates the virus, whereas in summer, ozone primarily impacts human respiratory health, which indirectly favors COVID-19 transmission. Nonetheless, experimental results did not fully align with the field survey, showing increased virus inactivation with an increase in temperature.