Ambient air monitoring is the systematic, long-term assessment of pollutant levels by measuring the quantity and types of certain pollutants in the surrounding, outdoor air.
Air quality is measured with the Air Quality Index, or AQI. The AQI works sort of like a thermometer that runs from 0 to 500 degrees. However, instead of showing changes in the temperature, the AQI is a way of showing changes in the amount of pollution in the air.
The most basic is the Ambient Air Monitoring Program, which collects national air quality data on criteria pollutants: Carbon Monoxide (CO), Oxides of Nitrogen (NO2 and NO3), Ozone (O3), Lead (Pb), Particulate Matter (PM) – both particulates with aerodynamic diameters below 10 micrometers (PM-10) and particulates with aerodynamic diameters below 2.5 micrometers (PM-2.5).