Bad Air Days in Washington County, Maine: under 1 a Year
under 1 bad air days a year
Rare: among the cleanest-air counties EPA monitors. Ranked 895 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 Washington
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Most bad days here fall in May and June. Averaged over 2016 to 2025.
What to buy, and what not to
- 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 1 bad days a year; in 2016 to 2025, under 1. Not much has changed. The worst recent year was 2017, with 2 bad days on 362 monitored days.
| Date | AQI | Main pollutant |
|---|---|---|
| 2017-05-18 | 147 | Ozone |
| 2018-05-02 | 122 | Ozone |
| 2017-06-11 | 101 | Ozone |
| 2025-08-13 | 100 | Ozone |
| 2017-06-12 | 97 | Ozone |
The air on a normal day
Across 3,598 monitored days from 2016 to 2025, the air in Washington County rated Good on 97% of them, more often than the 72% typical of monitored counties, and Moderate on 3%. The median day sat at AQI 34; one day in ten went above 45.
The pollutant setting the AQI on an ordinary day here:
- ozone91%3,272 days
- fine particles (PM2.5)9%326 days
Every recent year on file
| Year | Days monitored | Good | Moderate | Over 100 | Over 150 | Median AQI | Highest AQI |
|---|---|---|---|---|---|---|---|
| 2025* | 364 | 333 | 31 | 0 | 0 | 34 | 100 |
| 2024 | 365 | 351 | 14 | 0 | 0 | 34 | 60 |
| 2023 | 362 | 343 | 19 | 0 | 0 | 36 | 74 |
| 2022 | 364 | 355 | 9 | 0 | 0 | 34 | 58 |
| 2021 | 360 | 348 | 12 | 0 | 0 | 33 | 90 |
| 2020 | 353 | 351 | 2 | 0 | 0 | 33 | 61 |
| 2019 | 363 | 360 | 3 | 0 | 0 | 34 | 71 |
| 2018 | 339 | 327 | 11 | 1 | 0 | 36 | 122 |
| 2017 | 362 | 351 | 9 | 2 | 0 | 35 | 147 |
| 2016 | 366 | 360 | 6 | 0 | 0 | 32 | 74 |
| 2015 | 356 | 340 | 16 | 0 | 0 | 33 | 90 |
| 2014 | 359 | 355 | 4 | 0 | 0 | 33 | 84 |
| 2013 | 362 | 346 | 15 | 1 | 0 | 34 | 129 |
| 2012 | 342 | 337 | 5 | 0 | 0 | 32 | 67 |
| 2011 | 316 | 307 | 8 | 1 | 0 | 31 | 105 |
| 2010 | 301 | 293 | 7 | 1 | 0 | 35 | 126 |
*2025 may be a partial year in EPA's file.
Nearby counties on file
- York County2/yr
- Hancock County2/yr
- Cumberland County2/yr
- Aroostook County2/yr
- Knox County1/yr
- Penobscot Countyunder 1/yr
- Sagadahoc Countyunder 1/yr
- Oxford Countyunder 1/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.