Bad Air Days in Barnstable County, Massachusetts: 2 a Year
2 bad air days a year
About the middle of monitored US counties. Ranked 466 of 996 monitored counties, where 1 is worst.
What makes them bad: mostly ozone: summer smog (0% particle days).
When the bad days come in Barnstable
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Most bad days here fall in May and June and July and August. Averaged over 2016 to 2025.
Is a purifier worth it here?
- Bad air days are rare here. A standard furnace filter is enough; no purifier needed for outdoor air.
- On the odd bad day, check AirNow and keep windows shut.
Better or worse than it was
In 2000 to 2009 this county averaged 23 bad days a year; in 2016 to 2025, 2. The air has improved. The worst recent year was 2017, with 5 bad days on 358 monitored days.
| Date | AQI | Main pollutant |
|---|---|---|
| 2017-05-18 | 150 | Ozone |
| 2023-04-13 | 140 | Ozone |
| 2017-06-13 | 136 | Ozone |
| 2018-05-02 | 133 | Ozone |
| 2017-06-12 | 129 | Ozone |
The air on a normal day
Across 3,584 monitored days from 2016 to 2025, the air in Barnstable County rated Good on 94% of them, more often than the 72% typical of monitored counties, and Moderate on 6%. The median day sat at AQI 36; one day in ten went above 47.
The pollutant setting the AQI on an ordinary day here:
- ozone96%3,457 days
- fine particles (PM2.5)4%127 days
Year by year
| Year | Days monitored | Good | Moderate | Over 100 | Over 150 | Median AQI | Highest AQI |
|---|---|---|---|---|---|---|---|
| 2025* | 364 | 341 | 20 | 3 | 0 | 36 | 129 |
| 2024 | 353 | 333 | 19 | 1 | 0 | 36 | 101 |
| 2023 | 358 | 331 | 24 | 3 | 0 | 37 | 140 |
| 2022 | 360 | 341 | 19 | 0 | 0 | 36 | 93 |
| 2021 | 359 | 331 | 25 | 3 | 0 | 36 | 126 |
| 2020 | 351 | 339 | 10 | 2 | 0 | 36 | 108 |
| 2019 | 359 | 346 | 13 | 0 | 0 | 36 | 93 |
| 2018 | 360 | 335 | 21 | 4 | 0 | 36 | 133 |
| 2017 | 358 | 332 | 21 | 5 | 0 | 37 | 150 |
| 2016 | 362 | 334 | 27 | 1 | 0 | 36 | 115 |
| 2015 | 317 | 289 | 24 | 4 | 0 | 34 | 122 |
| 2014 | 363 | 347 | 16 | 0 | 0 | 35 | 84 |
| 2013 | 315 | 288 | 23 | 4 | 0 | 36 | 129 |
| 2012 | 258 | 223 | 28 | 7 | 1 | 37 | 156 |
| 2011 | 275 | 246 | 26 | 3 | 0 | 36 | 112 |
| 2010 | 267 | 221 | 39 | 7 | 1 | 40 | 151 |
*2025 may be a partial year in EPA's file.
Massachusetts compared
- Bristol County4/yr
- Hampden County3/yr
- Essex County3/yr
- Dukes County2/yr
- Hampshire County2/yr
- Norfolk County2/yr
- Worcester County2/yr
- Plymouth County2/yr
How this is counted
A bad air day is a day the county's daily AQI from EPA AirData went above 100, the level where EPA tells children, older adults and people with asthma or heart disease to cut back outdoors. Monitors do not run every day, so yearly counts are scaled to 365 days. This is the record, not today's air: for that, check AirNow. More on the method in how the county numbers are made, on the AQI 100 line in what counts as a bad air day, and on why a purifier does not touch ozone in smoke vs ozone.