About This Ranking
This ranking is based on Air Quality Index (AQI) measurements from EPA monitoring stations across the United States. Cities with higher AQI values have more polluted air.
What Makes Air Quality Poor?
Cities with poor air quality often face challenges like geographic basins that trap pollution, high population density, industrial emissions, heavy traffic, wildfire smoke, or unfavorable weather patterns like temperature inversions.
Data Sources
Rankings are based on current AQI data from the EPA AirNow system, which monitors pollution levels continuously.