# Counties in Massachusetts by share of days with good air quality (US EPA AQI), 2025

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

- Indicator id: `aqi_good_days_share`
- Unit: %
- Definition: Days with a daily Air Quality Index of 0 to 50 (good) as a percentage of the days of the year with an AQI in a US county. Calculated by Invokely from the day counts in the EPA AirData annual summaries; both counts are stored with each value.
- Source: U.S. Environmental Protection Agency, EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts (https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual)
- Retrieved: 2026-10-12
- Citation: U.S. Environmental Protection Agency, Air Quality System, AirData. EPA AirData annual AQI by county: good days as a share of days with an AQI, calculated with stored counts. https://aqs.epa.gov/aqsweb/airdata/download_files.html#Annual. Retrieved 2026-10-12.
- Web page: https://invokely.ai/rankings/good-air-quality-days-share/massachusetts-counties

| Rank | Place | % |
|---:|---|---:|
| 1 | Dukes County | 95.9 |
| 2 | Barnstable County | 93.7 |
| 3 | Hampshire County | 85.5 |
| 4 | Norfolk County | 84.4 |
| 4 | Plymouth County | 84.4 |
| 6 | Bristol County | 83.8 |
| 7 | Middlesex County | 81.9 |
| 8 | Worcester County | 81.6 |
| 9 | Essex County | 81.1 |
| 10 | Berkshire County | 78.1 |
| 11 | Hampden County | 77 |
| 12 | Franklin County | 76.9 |
| 13 | Suffolk County | 76.4 |