The Environmental Protection Agency (EPA) recommends guidelines and thresholds for indoor air pollutants are as follows:
- Radon: Below 4 picocuries per liter (pCi/L) of air.
- Carbon monoxide (CO): Below 9 parts per million (ppm) for more than 8 hours, or 35 ppm for shorter periods.
- Nitrogen dioxide (NO2): Below 100 parts per billion (ppb) for NO2.
- Particulate matter (PM2.5): The EPA has established a primary standard of 12 micrograms per cubic meter.
- Formaldehyde: A chronic inhalation reference exposure level (REL) of 100 micrograms per cubic meter or less.
- Ozone (O3): No more than 70 parts per billion (ppb).
Sadly, these are only recommended guidelines. Different authorities may have different recommendations or standards. Also, some pollutants may not have established guidelines or standards due to limited research or knowledge about their health effects. It’s important to consult with a qualified indoor air quality professional to determine appropriate guidelines and thresholds for specific indoor air pollutants in a particular building or environment.