The Air Quality Index (AQI) for Carbon Monoxide (CO) - 8 Hour Standard, Ozone (0₃) - 1 Hour Standard, Ozone (0₃) - 8 Hour Standard, Particulate Matter less than 10 microns (PM₁₀) - 24 Hour Standard, Particulate Matter less than 2.5 microns (PM_2.5) - 24 Hour Standard, Sulfur Dioxide (SO₂) - 1 Hour Standard, and Nitrogen Dioxide (NO₂) - 1 Hour Standard is calculated from all monitoring sites in the City of Philadelphia's air monitoring network operated by Philadelphia's Air Management Services.  The highest measured pollutant is used to calculate the overall AQI.  Typically, when the AQI exceeds 100 in the Philadelphia region, the cause is either ozone or fine particulate matter pollution.  The sum of Nitric Oxide (NO) and NO₂ is commonly called NO_x.  NO_x reacts with volatile organic compounds to form ozone.

Above are Philadelphia Air Management Services (AMS) air monitoring locations used to calculate the AQI.  Not all pollutants are measured at each location.