Air quality is a topic of discussion for all types of areas including indoors and/or outdoors depending on where you live in the world. Pollutant levels can be monitored from indoor and outdoor air. Today we have sophisticated devices that can give us accurate readings for a number of pollutants within air. The general composition of outdoor air is made up of 78% nitrogen, 20.9% oxygen, 0.9% argon, 0.04% carbon dioxide, a number of other gases that make up less than 1% of air composition.
In addition, to air composition there a natural substances such as pollen, mold spores, dust, radon gas, formaldehyde, along with anthropogenic (human made) origins. Anthropogenic emissions are particularly important, because they can be decreased by regulatory and voluntary actions. The six most important pollutant criteria are carbon monoxide, lead, nitrogen dioxide, ozone, particulate matter of different size fractions, and sulfur dioxide), which are common in outdoor air and can harm human health and the environment. The Clean Air Act requires the Environmental Protection Agency (EPA) to set National Ambient Air Quality Standards (NAAQS) for these pollutants. EPA is required to periodically review and update the NAAQS to reflect the latest scientific information on how outdoor air quality affects human health and the environment. You can find more about air quality at https://www.epa.gov/report-environment/outdoor-air-quality.