This dataset contains trends in days violating air quality standards by date for the Philadelphia-Camden-Wilmington Core-Based Statistical Area (CBSA).In order to convey the health impacts of air pollution to the general public, the US EPA has created a color-coded scale to identify pollutant levels in simple terms. This scale is referred to as the Air Quality Index (AQI). AQI levels are directly related to the federal air quality standards and pollutant concentrations in the air. The AQI reports pollutant levels for six different categories based on AQI: Good or green (0 to 50), Moderate or yellow (51 to 100), Unhealthy for Sensitive Groups or orange (101 to 150), Unhealthy or red (151 to 200), Very Unhealthy or purple (201 to 300), and Hazardous (301 to 500). Note that no day in 2000 or subsequent years has qualified as hazardous, so it is not present in the charts. Sensitive groups are defined as children, older adults, and those with breathing impairments. When the AQI reaches Code Orange or higher for any of the pollutants, an air quality standard violation has occurred.

Air quality standards have been revised a number of times since 1997, and the data in these charts is normalized to the current standard.