Median AQI
44
Good
Washington · County air quality · 2025
Pierce County, Washington
Median AQI 44 (Good). 76.1% of monitored days rated Good, direct from EPA Air Quality System stations.
- 44
- Median AQI
- 76.1%
- Good-air days
- 0
- Unhealthy days
- 42%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Pierce County's air is good on balance, more polluted than the median US county, a median AQI of 44 with 76.1% of 243 monitored days in the Good band, driven mainly by Ozone.
- 44
- median AQI · Good
- 76.1%
- days rated Good
- Ozone
- main pollutant
- 42%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 100.
Data updated July 2026
- Good · 185 d · 76.1%
- Moderate · 58 d · 23.9%
How did Pierce County's air break down in 2025?
Across 243 monitored days, 185 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 100 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 243 days monitored. Median AQI: 44 (Good).
Insights: Pierce County, Washington. EPA monitors recorded a median Air Quality Index of 44 across 243 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 185 (76%) fell in the Good band (AQI 0–50), 58 (24%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 58, while the worst single-day peak hit 100 (Moderate). Residents averaged about 22.8 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (150 days), PM2.5 (92 days), NO2 (1 days). Across the 2020–2025 trend window, good days shifted by -71 and the median AQI moved +2 points, placing the multi-year trajectory at improving. The worst single reading over the 2020–2025 window was AQI 100, moderate but never Unhealthy. Nearby counties show comparable readings: Adams (94.7% good, AQI 19); Asotin (73.8% good, AQI 35); Benton (88.9% good, AQI 35); Chelan (87.2% good, AQI 27); Clallam (88.5% good, AQI 26); Clark (89.3% good, AQI 31).
Air Quality Summary
Good Days
76.1%
185 of 243 monitored days
1.1pp vs 75% target
Max AQI Recorded
100
Moderate
Health Grade
Good
90th-pct AQI 58
Pierce County, Good days share 76.1%
National avg
Share of monitored days at AQI 0-50 (Good band).
Pierce County, Unhealthy-or-worse share 0.0%
National avg
Share of monitored days above AQI 150 (Unhealthy or worse). Bar maxes at 10% (worst-county ceiling).
AQI Day Breakdown (2025)
Distribution of 243 monitored days across EPA AQI categories.
Good
185
76%
Moderate
58
24%
USG
0
0%
Unhealthy
0
0%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Pierce County.
- Ozone · 150 days · 61.7%
- PM2.5 · 92 days · 37.9%
- NO₂ · 1 days · 0.4%
Health Impact Assessment
Good
Pierce County's air quality is rated Good based on 76.1% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 76.1% of monitored days in 2025, with a median AQI of 44. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 150 of 243 monitored days.
5-Year Air Quality Trend
Air quality is improving in Pierce County. Best year: 2023 (273 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 256 | 99 | 4 | 3 | 42 | 256 |
| 2021 | 269 | 96 | 0 | 0 | 42 | 94 |
| 2022 | 239 | 115 | 9 | 2 | 44 | 178 |
| 2023 | 273 | 89 | 0 | 3 | 42 | 195 |
| 2024 | 265 | 100 | 0 | 1 | 44 | 166 |
| 2025 | 185 | 58 | 0 | 0 | 44 | 100 |
How does Pierce County compare?
How Pierce County compares
Good-day share about average
Pierce County 76.1%
Adams County, Washington 94.7%
US average 76.5%
Median AQI worse than US avg
Pierce County 44
Adams County, Washington 19
US average 38
Unhealthy days / yr about average
Pierce County 0
Adams County, Washington 0
US average 0
Other Counties in Washington
Air quality comparison for nearby counties in Washington.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Pierce County.
Baltimore County, Maryland
AQI 44 · 70.4% good
Baltimore (City) County, Maryland
AQI 44 · 68.7% good
Bartholomew County, Indiana
AQI 44 · 69.2% good
Berks County, Pennsylvania
AQI 44 · 65.6% good
Bolivar County, Mississippi
AQI 44 · 70.3% good
Brewster County, Texas
AQI 44 · 69.0% good
What Pierce County's air means for you
The air here stays in the breathable range year-round, with Ozone the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-Ozone days, the guide explains what a median of 44 means for exposure. Health guidance
- See how Pierce County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Pierce County with its Washington neighbours before drawing a conclusion about the region. All of Washington
Based on 243 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
More Air Quality Data
Air Quality Guides
Frequently Asked Questions
What is the air quality in Pierce County, Washington? ▼
Pierce County has a median Air Quality Index (AQI) of 44, rated "Good." 76.1% of monitored days (185 out of 243) had good air quality in 2025.
What is the main pollutant in Pierce County? ▼
The primary pollutant in Pierce County is Ozone (O3), which was the main AQI driver on 150 days (62% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Pierce County have? ▼
In 2025, Pierce County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 100.
Is the air quality in Pierce County getting better or worse? ▼
Air quality in Pierce County is improving based on 5-year trends (2020-2025). Best year: 2023 with 273 good days. Worst year: 2025 with 185 good days.
What does AQI 44 mean for health? ▼
Pierce County's median AQI of 44 falls in the "Good" category. See the <a href="/guides/understanding-aqi" class="underline">AQI category guide</a> for what each range means for health.
How does Pierce County compare to other counties in Washington? ▼
Pierce County has 76.1% good air days. Nearby counties in Washington: Adams (94.7% good), Asotin (73.8% good), Benton (88.9% good), Chelan (87.2% good), Clallam (88.5% good), Clark (89.3% good).
What is the 90th percentile AQI in Pierce County? ▼
The 90th percentile AQI for Pierce County is 58, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 100 (Moderate).
Data Sources
Primary Source: U.S. Environmental Protection Agency (EPA), Air Quality System (AQS), Annual AQI by County dataset, 2020–2025 (aqs.epa.gov). For current conditions (not shown here — this page is historical annual data), see EPA AirNow (airnow.gov). See our methodology for how AQI, median, and coverage figures are computed.
Informational only, not professional advice. Data from EPA AQS. See our disclaimer.
Every figure on PlainAir is rendered directly from EPA AQS air-quality monitoring data, no number is typed in by an editor. This page draws directly on EPA AQS air-quality monitoring data, no figure is typed in by an editor. See our editorial standards & corrections policy, the methodology behind these numbers, or report a data error.