Median AQI
38
Good
Oregon · County air quality · 2025
Multnomah County, Oregon
Median AQI 38 (Good). 82.4% of monitored days rated Good, direct from EPA Air Quality System stations.
- 38
- Median AQI
- 82.4%
- Good-air days
- 0
- Unhealthy days
- 58%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Multnomah County's air is good on balance, cleaner than the median US county, a median AQI of 38 with 82.4% of 182 monitored days in the Good band, driven mainly by Ozone.
- 38
- median AQI · Good
- 82.4%
- days rated Good
- Ozone
- main pollutant
- 58%
- cleaner than US counties
Not one day crossed into the Unhealthy tier; the worst single reading was AQI 87.
Data updated July 2026
- Good · 150 d · 82.4%
- Moderate · 32 d · 17.6%
How did Multnomah County's air break down in 2025?
Across 182 monitored days, 150 fell in the Good band (AQI 0–50) and 0 reached Unhealthy or worse. The worst single day peaked at AQI 87 (Moderate).
EPA AQS →Air quality data from EPA Air Quality System (2025). 182 days monitored. Median AQI: 38 (Good).
Insights: Multnomah County, Oregon. EPA monitors recorded a median Air Quality Index of 38 across 182 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 150 (82%) fell in the Good band (AQI 0–50), 32 (18%) registered Moderate readings, and 0 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 55, while the worst single-day peak hit 87 (Moderate). Residents averaged about 24.7 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (114 days), PM2.5 (67 days), CO (1 days). Across the 2020–2025 trend window, good days shifted by -125 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 87, 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
82.4%
150 of 182 monitored days
7.4pp vs 75% target
Max AQI Recorded
87
Moderate
Health Grade
Good
90th-pct AQI 55
Multnomah County, Good days share 82.4%
National avg
Share of monitored days at AQI 0-50 (Good band).
Multnomah 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 182 monitored days across EPA AQI categories.
Good
150
82%
Moderate
32
18%
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 Multnomah County.
- Ozone · 114 days · 62.6%
- PM2.5 · 67 days · 36.8%
- CO · 1 days · 0.5%
Health Impact Assessment
Good
Multnomah County's air quality is rated Good based on 82.4% good air days. No unhealthy air days were recorded in 2025.
Air quality was acceptable on 82.4% of monitored days in 2025, with a median AQI of 38. Unusually sensitive people can check real-time conditions at AirNow.gov during high-pollution events.
The dominant pollutant is Ozone, driving AQI on 114 of 182 monitored days.
5-Year Air Quality Trend
Air quality is improving in Multnomah County. Best year: 2024 (311 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 275 | 82 | 1 | 0 | 36 | 779 |
| 2021 | 294 | 70 | 1 | 0 | 36 | 105 |
| 2022 | 266 | 94 | 3 | 2 | 36 | 165 |
| 2023 | 267 | 97 | 1 | 0 | 38 | 117 |
| 2024 | 311 | 55 | 0 | 0 | 35 | 93 |
| 2025 | 150 | 32 | 0 | 0 | 38 | 87 |
How does Multnomah County compare?
How Multnomah County compares
Good-day share better than US avg
Multnomah County 82.4%
Baker County, Oregon 89.0%
US average 76.5%
Median AQI about average
Multnomah County 38
Baker County, Oregon 25
US average 38
Unhealthy days / yr about average
Multnomah 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 Multnomah County.
Adams County, Illinois
AQI 38 · 94.4% good
Anoka County, Minnesota
AQI 38 · 82.1% good
Atlantic County, New Jersey
AQI 38 · 79.6% good
Avery County, North Carolina
AQI 38 · 93.9% good
Barnstable County, Massachusetts
AQI 38 · 92.5% good
Bay County, Michigan
AQI 38 · 71.8% good
What Multnomah 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 38 means for exposure. Health guidance
- See how Multnomah County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Multnomah County with its Oregon neighbours before drawing a conclusion about the region. All of Oregon
Based on 182 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 Multnomah County, Oregon? ▼
Multnomah County has a median Air Quality Index (AQI) of 38, rated "Good." 82.4% of monitored days (150 out of 182) had good air quality in 2025.
What is the main pollutant in Multnomah County? ▼
The primary pollutant in Multnomah County is Ozone (O3), which was the main AQI driver on 114 days (63% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Multnomah County have? ▼
In 2025, Multnomah County recorded 0 unhealthy air days (0 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 87.
Is the air quality in Multnomah County getting better or worse? ▼
Air quality in Multnomah County is improving based on 5-year trends (2020-2025). Best year: 2024 with 311 good days. Worst year: 2025 with 150 good days.
What does AQI 38 mean for health? ▼
Multnomah County's median AQI of 38 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 Multnomah County compare to other counties in Oregon? ▼
Multnomah County has 82.4% 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 Multnomah County? ▼
The 90th percentile AQI for Multnomah County is 55, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 87 (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.