Grade A means consistently clean air with minimal health risk and improving or stable trends. These cities are scored using EPA Air Quality System data spanning 10 years of daily AQI readings.
Grade A (Excellent) indicates consistently clean air with minimal health risk and improving or stable trends. The grade is based on 5-year average AQI (40%), trend direction (30%), unhealthy days per year (20%), and worst pollutant severity (10%).
50 of 1,020 monitored US cities currently have a Grade A Air Quality rating, representing 4.9% of all tracked areas.
Grade A cities generally have safe air quality for most people most of the time. However, sensitive groups should still monitor AQI on high-pollution days.