Seattle Air Quality in 2021
In 2021, Seattle's air quality (Seattle-Tacoma-Bellevue, WA area) had a median daily AQI of 48 (Good) across 365 monitored days. 7 days (1.9%) reached Unhealthy for Sensitive Groups or worse, 201 were Good, and the year's peak AQI was 177 (Unhealthy). Fine particulate matter (PM2.5) set the daily AQI on 215 of those days. The cleanest month of 2021 was May (median AQI 42, 0 days above 100) and the worst was June (median 42, 2 days above 100, peak 177).
- Good: 55.1%
- Moderate: 43.0%
- Unhealthy for Sensitive Groups: 1.4%
- Unhealthy or worse: 0.5%
Extra Protection for Seattle Homes
Air quality in Seattle is moderate (AQI 54), with fine particles (PM2.5) the main concern. A True-HEPA purifier gives sensitive groups — kids, seniors and anyone with asthma or allergies — cleaner air indoors on days like today.
Recommended: Coway AP-1512HH Mighty — True HEPA + carbon · CADR ~246 CFM · rooms up to 361 sq ft
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How was Seattle's air quality in 2021?
Good on a typical day: median AQI 48, with 7 days above AQI 100 out of 365 monitored — the 4th cleanest of 7 years on record for the area.
- ✓Peak AQI in 2021: 177 (Unhealthy).
- ✓Fine particulate matter (PM2.5) was the main pollutant on 215 days.
- ✓Cleanest month: May; worst: June.
Frequently asked questions
What was the average AQI in Seattle in 2021?▾
EPA's Air Quality System puts Seattle's (Seattle-Tacoma-Bellevue, WA) median daily AQI for 2021 at 48, which is Good. 7 days were Unhealthy for Sensitive Groups or worse and the year's highest AQI was 177.
Which month had the worst air quality in Seattle in 2021?▾
The cleanest month of 2021 was May (median AQI 42, 0 days above 100) and the worst was June (median 42, 2 days above 100, peak 177).
Was 2021 a good or bad year for Seattle's air?▾
Among the 7 years EPA has published for the area (2019–2025), 2021 ranks 4th cleanest by days above AQI 100. 2021's median of 48 is in line with the area's typical annual median of 49.
Seattle month by month in 2021
Seattle air quality month by month, 2021 (Seattle-Tacoma-Bellevue, WA, EPA AQS daily AQI)
| Month | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| January | 31 | 61 | 1 | 108 | PM2.5 |
| February | 28 | 44 | 0 | 66 | PM2.5 |
| March | 31 | 55 | 0 | 80 | PM2.5 |
| April | 30 | 51 | 0 | 72 | PM2.5 |
| Maycleanest | 31 | 42 | 0 | 64 | O3 |
| Juneworst | 30 | 42 | 2 | 177 | O3 |
| July | 31 | 45 | 1 | 126 | O3 |
| August | 31 | 46 | 2 | 148 | PM2.5 |
| September | 30 | 44 | 0 | 87 | O3 |
| October | 31 | 46 | 0 | 88 | PM2.5 |
| November | 30 | 51 | 0 | 88 | PM2.5 |
| December | 31 | 55 | 1 | 104 | PM2.5 |
How 2021 compares
Among the 7 years EPA has published for the area (2019–2025), 2021 ranks 4th cleanest by days above AQI 100.
2021's median of 48 is in line with the area's typical annual median of 49.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Seattle
The latest EPA AirNow observation puts Seattle's AQI at 54 (PM2.5). The figures above are multi-year annual statistics, not today's reading.
View current Seattle air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Seattle-Tacoma-Bellevue, WA), 2019–2025. Daily AQI per CBSA is the highest AQI reported by any monitor in the area that day; the defining parameter is the pollutant that set it. Month and season statistics pool every such day in the period across all years listed. Retrieved 2026-09-09.