Since people spend more than 80% of their time indoors, indoor air quality measurement and control should be a top priority.
More and more research is showing a link between COVID-19 cases and low humidity and/or or high levels of pollution. In addition, high CO2 concentrations are linked to viral infections. The higher the proportion of CO2, the greater the proportion of air that has been exhaled several times, thus increasing the risk of cross-contamination.
The concentration of CO2 is a sort of measure indirect exposure to viral aerosols.