Air Quality Index

Air Quality degradation has been linked to numerous diseases in humans and can damage buildings, crops, and ecosystems. The U.S. EPA monitors six common air pollutants that are of special concern and has developed standards for these pollutants to protect human and environmental health (https://www.epa.gov/criteria-air-pollutants). This indicator includes three of those pollutants:two different size categories of particulate matter and ozone. However, not all of these pollutants were available for all of the watersheds (Table 1).

Table 1. The air quality pollutants that were available for each watershed. We scored particulate matter with a diameter less than 2.5 microns (PM 2.5) and less than 10 microns (PM 10) and ozone (O₃) . ✔ = data was available, N/A = data were not available.

How is it scored?

Scores were calculated individually for the air quality metrics, with thresholds based on the EPA thresholds for the Air Quality Index (AQI; Table 1). If multiple air quality stations were located within the same watershed, they were scored separately and averaged at the watershed-scale. Watershed scores were population-weighted to calculate an overall region score.

Table 1. Air Quality Index (AQI) thresholds and narrative from the US EPA and their corresponding Report Card Scores and the equations used to convert scores to the report card scale.

Data source: Daily data was downloaded from the US EPA (US EPA Air Quality Data) for 2021.