# Counties in Massachusetts by median Air Quality Index (US EPA), 2025

All 13 values come from U.S. Environmental Protection Agency for 2025, so the places are comparable.

- Indicator id: `aqi_median`
- Unit: index
- Definition: Median of the daily Air Quality Index (AQI) values of a US county over the days of the year with an AQI, from the EPA AirData annual summaries. The daily county AQI is the highest AQI among the monitors and pollutants reported that day (ozone, PM2.5, PM10, carbon monoxide and nitrogen dioxide). Lower is cleaner: 0 to 50 is good, 51 to 100 moderate and above 100 unhealthy for sensitive groups.
- Source: U.S. Environmental Protection Agency, EPA AirData annual AQI by county: median daily AQI (https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual)
- Publisher page: https://invokely.ai/en/publishers/environmental-protection-agency
- Retrieved: 2026-10-12
- Citation: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: median daily AQI. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
- Web page: https://invokely.ai/rankings/median-air-quality-index/massachusetts-counties

| Rank | Place | index |
|---:|---|---:|
| 1 | Essex County | 40 |
| 2 | Hampden County | 39 |
| 2 | Norfolk County | 39 |
| 2 | Worcester County | 39 |
| 5 | Berkshire County | 38 |
| 5 | Bristol County | 38 |
| 5 | Franklin County | 38 |
| 5 | Middlesex County | 38 |
| 9 | Plymouth County | 37 |
| 9 | Suffolk County | 37 |
| 11 | Barnstable County | 36 |
| 11 | Hampshire County | 36 |
| 13 | Dukes County | 35 |