Median AQI
34
Good
Oregon · County air quality · 2025
Marion County, Oregon
Median AQI 34 (Good). 85.1% of monitored days rated Good, direct from EPA Air Quality System stations.
- 34
- Median AQI
- 85.1%
- Good-air days
- 0
- Unhealthy days
- 66%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Marion County's air is good on balance, cleaner than the median US county, a median AQI of 34 with 85.1% of 181 monitored days in the Good band, driven mainly by PM2.5.
- 34
- median AQI · Good
- 85.1%
- days rated Good
- PM2.5
- main pollutant
- 66%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 85.
Data updated July 2026
- Good · 154 d · 85.1%
- Moderate · 27 d · 14.9%
How did Marion County's air break down in 2025?
Across 181 monitored days, 154 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 85 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 181 days monitored. Median AQI: 34 (Good).
Insights: Marion County, Oregon. EPA monitors recorded a median Air Quality Index of 34 across 181 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 154 (85%) fell in the Good band (AQI 0–50), 27 (15%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 54, while the worst single-day peak hit 85 (Moderate). Residents averaged about 25.5 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (124 days), Ozone (57 days). Across the 2020–2025 trend window, good days shifted by -124 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 85, moderate but never Unhealthy. Nearby counties show comparable readings: Baker (89.0% good, AQI 25); Clackamas (93.9% good, AQI 27); Columbia (96.7% good, AQI 25); Crook (80.7% good, AQI 24); Deschutes (93.4% good, AQI 22); Grant (66.7% good, AQI 34).
Air Quality Summary
Good Days
85.1%
154 of 181 monitored days
10.1pp vs 75% target
Max AQI Recorded
85
Moderate
Health Grade
Good
90th-pct AQI 54
Marion County, Good days share 85.1%
National avg
Share of monitored days at AQI 0-50 (Good band).
Marion 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 181 monitored days across EPA AQI categories.
Good
154
85%
Moderate
27
15%
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 Marion County.
- PM2.5 · 124 days · 68.5%
- Ozone · 57 days · 31.5%
Health Impact Assessment
Good
Marion County's air quality is rated Good based on 85.1% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 85.1% of monitored days in 2025, with a median AQI of 34. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is PM2.5, driving AQI on 124 of 181 monitored days.
5-Year Air Quality Trend
Air quality is improving in Marion County. Best year: 2024 (298 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 278 | 76 | 1 | 0 | 36 | 1272 |
| 2021 | 280 | 83 | 0 | 0 | 36 | 93 |
| 2022 | 254 | 104 | 5 | 2 | 36 | 168 |
| 2023 | 268 | 93 | 4 | 0 | 38 | 128 |
| 2024 | 298 | 64 | 4 | 0 | 35 | 129 |
| 2025 | 154 | 27 | 0 | 0 | 34 | 85 |
How does Marion County compare?
How Marion County compares
Good-day share better than US avg
Marion County 85.1%
Baker County, Oregon 89.0%
US average 76.5%
Median AQI better than US avg
Marion County 34
Baker County, Oregon 25
US average 38
Unhealthy days / yr about average
Marion County 0
Baker County, Oregon 0
US average 0
Other Counties in Oregon
Air quality comparison for nearby counties in Oregon.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Marion County.
Belknap County, New Hampshire
AQI 34 · 87.9% good
Dyer County, Tennessee
AQI 34 · 79.4% good
Flagler County, Florida
AQI 34 · 97.4% good
Grant County, Oregon
AQI 34 · 66.7% good
Highlands County, Florida
AQI 34 · 93.2% good
Johnson County, Texas
AQI 34 · 91.6% good
What Marion County's air means for you
The air here stays in the breathable range year-round, with PM2.5 the main thing to watch.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-PM2.5 days, the guide explains what a median of 34 means for exposure. Health guidance
- See how Marion County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Marion County with its Oregon neighbours before drawing a conclusion about the region. All of Oregon
Based on 181 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 Marion County, Oregon? ▼
Marion County has a median Air Quality Index (AQI) of 34, rated "Good." 85.1% of monitored days (154 out of 181) had good air quality in 2025.
What is the main pollutant in Marion County? ▼
The primary pollutant in Marion County is Fine Particles (PM2.5), which was the main AQI driver on 124 days (69% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Marion County have? ▼
In 2025, Marion County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 85.
Is the air quality in Marion County getting better or worse? ▼
Air quality in Marion County is improving based on 5-year trends (2020-2025). Best year: 2024 with 298 good days. Worst year: 2025 with 154 good days.
What does AQI 34 mean for health? ▼
Marion County's median AQI of 34 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 Marion County compare to other counties in Oregon? ▼
Marion County has 85.1% good air days. Nearby counties in Oregon: Baker (89.0% good), Clackamas (93.9% good), Columbia (96.7% good), Crook (80.7% good), Deschutes (93.4% good), Grant (66.7% good).
What is the 90th percentile AQI in Marion County? ▼
The 90th percentile AQI for Marion County is 54, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 85 (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.