Bad Air Days in Snohomish County, Washington: 7 a Year
7 bad air days a year
More bad air days than three quarters of monitored counties. Ranked 149 of 996 monitored counties, where 1 is worst.
What makes them bad: mostly particles: smoke and dust (100% 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 September and August and October and January. Averaged over 2016 to 2025.
What to buy, and what not to
- Particles (wildfire smoke, dust) cause enough bad days here to matter. A HEPA purifier sized to your bedroom removes them; run it with windows shut on bad days.
- Upgrade the furnace or AC filter to MERV 13 so the whole house is filtered, not just one room.
The worst days on file
In 2000 to 2009 this county averaged 8 bad days a year; in 2016 to 2025, 7. Not much has changed. The worst recent year was 2022, with 23 bad days on 362 monitored days.
| Date | AQI | Main pollutant |
|---|---|---|
| 2022-10-19 | 362 | PM2.5 |
| 2022-10-18 | 257 | PM2.5 |
| 2020-09-14 | 250 | PM2.5 |
| 2022-10-14 | 250 | PM2.5 |
| 2022-10-20 | 229 | PM2.5 |
The air on a normal day
Across 3,649 monitored days from 2016 to 2025, the air in Snohomish County rated Good on 67% of them, less often than the 72% typical of monitored counties, and Moderate on 31%. The median day sat at AQI 37; one day in ten went above 68.
The pollutant setting the AQI on an ordinary day here:
- fine particles (PM2.5)100%3,649 days
Every recent year on file
| Year | Days monitored | Good | Moderate | Over 100 | Over 150 | Median AQI | Highest AQI |
|---|---|---|---|---|---|---|---|
| 2025* | 365 | 248 | 116 | 1 | 0 | 41 | 125 |
| 2024 | 366 | 262 | 104 | 0 | 0 | 38 | 99 |
| 2023 | 365 | 246 | 116 | 3 | 1 | 38 | 175 |
| 2022 | 362 | 210 | 129 | 23 | 10 | 39 | 362 |
| 2021 | 365 | 248 | 114 | 3 | 0 | 35 | 137 |
| 2020 | 366 | 234 | 122 | 10 | 7 | 40 | 250 |
| 2019 | 364 | 227 | 136 | 1 | 0 | 40 | 114 |
| 2018 | 365 | 260 | 96 | 9 | 4 | 33 | 186 |
| 2017 | 365 | 244 | 105 | 16 | 3 | 33 | 161 |
| 2016 | 366 | 278 | 85 | 3 | 0 | 32 | 120 |
| 2015 | 362 | 238 | 112 | 12 | 2 | 38 | 158 |
| 2014 | 365 | 241 | 120 | 4 | 0 | 39 | 133 |
| 2013 | 365 | 227 | 136 | 2 | 0 | 38 | 115 |
| 2012 | 366 | 250 | 114 | 2 | 1 | 38 | 157 |
| 2011 | 365 | 239 | 118 | 8 | 0 | 41 | 147 |
| 2010 | 363 | 266 | 97 | 0 | 0 | 36 | 87 |
*2025 may be a partial year in EPA's file.
Elsewhere in Washington
- Yakima County13/yr
- Chelan County11/yr
- Okanogan County11/yr
- Stevens County9/yr
- Asotin County8/yr
- King County8/yr
- Benton County6/yr
- Kittitas 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.