Bad Air Days in Thurston County, Washington: 2 a Year
2 bad air days a year
About the middle of monitored US counties. Ranked 494 of 996 monitored counties, where 1 is worst.
What makes them bad: mostly particles: smoke and dust (95% particle days).
The bad-air season here
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Most bad days here fall in August and September and October. 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.
The record for Thurston
In 2000 to 2009 this county averaged 5 bad days a year; in 2016 to 2025, 2. The air has improved. The worst recent year was 2020, with 7 bad days on 366 monitored days.
| Date | AQI | Main pollutant |
|---|---|---|
| 2020-09-14 | 242 | PM2.5 |
| 2020-09-13 | 238 | PM2.5 |
| 2020-09-15 | 227 | PM2.5 |
| 2020-09-12 | 220 | PM2.5 |
| 2020-09-11 | 199 | PM2.5 |
The air on a normal day
Across 3,476 monitored days from 2016 to 2025, the air in Thurston County rated Good on 88% of them, more often than the 72% typical of monitored counties, and Moderate on 12%. The median day sat at AQI 28; one day in ten went above 51.
The pollutant setting the AQI on an ordinary day here:
- fine particles (PM2.5)68%2,373 days
- ozone32%1,103 days
Thurston County by year
| Year | Days monitored | Good | Moderate | Over 100 | Over 150 | Median AQI | Highest AQI |
|---|---|---|---|---|---|---|---|
| 2025* | 293 | 274 | 19 | 0 | 0 | 27 | 65 |
| 2024 | 362 | 338 | 24 | 0 | 0 | 26 | 85 |
| 2023 | 358 | 327 | 31 | 0 | 0 | 28 | 82 |
| 2022 | 348 | 309 | 36 | 3 | 2 | 28 | 157 |
| 2021 | 329 | 309 | 20 | 0 | 0 | 19 | 63 |
| 2020 | 366 | 316 | 43 | 7 | 7 | 28 | 242 |
| 2019 | 365 | 290 | 75 | 0 | 0 | 33 | 74 |
| 2018 | 343 | 291 | 46 | 6 | 5 | 29 | 181 |
| 2017 | 363 | 287 | 72 | 4 | 2 | 32 | 156 |
| 2016 | 349 | 308 | 41 | 0 | 0 | 31 | 91 |
| 2015 | 357 | 295 | 62 | 0 | 0 | 34 | 99 |
| 2014 | 363 | 294 | 69 | 0 | 0 | 32 | 95 |
| 2013 | 364 | 256 | 105 | 3 | 0 | 36 | 132 |
| 2012 | 361 | 271 | 86 | 4 | 1 | 35 | 153 |
| 2011 | 363 | 304 | 58 | 1 | 0 | 31 | 104 |
| 2010 | 355 | 330 | 25 | 0 | 0 | 27 | 83 |
*2025 may be a partial year in EPA's file.
Washington compared
- Yakima County13/yr
- Chelan County11/yr
- Okanogan County11/yr
- Stevens County9/yr
- Asotin County8/yr
- King County8/yr
- Snohomish County7/yr
- Benton County6/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.