Median AQI
18
Good
Montana · County air quality · 2025
Dawson County, Montana
Median AQI 18 (Good). 90.3% of monitored days rated Good, direct from EPA Air Quality System stations.
- 18
- Median AQI
- 90.3%
- Good-air days
- 2
- Unhealthy days
- 80%
- Cleaner than US counties
Dawson County's 2025 annual median AQI is 18 (Good), with 90.3% Good days
According to the U.S. EPA Air Quality System, Dawson County, Montana posted a 2025 median AQI of 18 (Good) across 300 monitored days, with 90.3% rated Good and 2 unhealthy or worse. This is an annual comparison, not today's advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US
- Dawson County's 90.3% Good-day share places it cleaner than 80% of US counties in 2025.
- Closest median-AQI peer
- Hughes County (93.0% Good, median AQI 18) is the closest nationwide median-AQI peer to Dawson County.
- 2024–2025 trend
- Dawson County's floor-qualifying Good-day share is stable from 2024 to 2025 (89.9% → 90.3%).
- Median AQI
- Median AQI: 18
The verdict
According to EPA Air Quality System monitoring data, Dawson County's air is good on balance, cleaner than most US counties, a median AQI of 18 with 90.3% of 300 monitored days in the Good band, driven mainly by PM2.5.
- 18
- median AQI · Good
- 90.3%
- days rated Good
- PM2.5
- main pollutant
- 80%
- cleaner than US counties
2 days reached Unhealthy or worse; the worst single reading hit AQI 165.
Annual release change
What changed in the 2025 EPA annual release
- Dawson County's peak single-day AQI rose from 120 to 165 between the 2024 and 2025 EPA annual releases, a change of +45 points.
- Dawson County's Unhealthy-category days rose from 0 to 2 between the 2024 and 2025 EPA annual releases, a change of +2 days.
- Dawson County's median AQI rose from 14 to 18 between the 2024 and 2025 EPA annual releases, a change of +4 points.
Data updated August 2026
- Good · 271 d · 90.3%
- Moderate · 26 d · 8.7%
- USG · 1 d · 0.3%
- Unhealthy · 2 d · 0.7%
How did Dawson County's air break down in 2025?
Across 300 monitored days, 271 fell in the Good band (AQI 0–50) and 2 reached Unhealthy or worse. The worst single day peaked at AQI 165 (Unhealthy).
EPA AQS →Air quality data from EPA Air Quality System (2025). 300 days monitored. Median AQI: 18 (Good).
Insights: Dawson County, Montana. EPA monitors recorded a median Air Quality Index of 18 across 300 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 271 (90%) fell in the Good band (AQI 0–50), 26 (9%) registered Moderate readings, and 1 (0%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 49, while the worst single-day peak hit 165 (Unhealthy). Residents averaged about 27.1 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (300 days). Across the 2024–2025 trend window, the share of monitored days rated Good shifted by +0.4 points (measured against 357 monitored days in 2024 and 300 in 2025, so raw day counts are not comparable) and the median AQI moved +4 points, placing the multi-year trajectory at stable. The annual record contains 2 days at Unhealthy or worse. On those days, the EPA recommends that sensitive groups limit prolonged outdoor exertion. Nearby counties show comparable readings: Beaverhead (94.7% good, AQI 13); Cascade (59.8% good, AQI 46); Custer (87.2% good, AQI 40); Fergus (90.7% good, AQI 41); Flathead (73.7% good, AQI 41); Gallatin (98.1% good, AQI 11).
Air Quality Summary
Good Days
90.3%
271 of 300 monitored days
15.3pp vs 75% target
Max AQI Recorded
165
Unhealthy
Health Grade
Excellent
90th-pct AQI 49
Dawson County, Good days share 90.3%
National avg
Share of monitored days at AQI 0-50 (Good band).
Dawson County, Unhealthy-or-worse share 6.7%
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 300 monitored days across EPA AQI categories.
Good
271
90%
Moderate
26
9%
USG
1
0%
Unhealthy
2
1%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Dawson County.
- PM2.5 · 300 days · 100.0%
Health Impact Assessment
Excellent
Dawson County's air quality is rated Excellent based on 90.3% good air days. There were 2 unhealthy days in 2025 when outdoor activity should be limited.
Air quality is acceptable most days, but 1 days reached "Unhealthy for Sensitive Groups" (AQI 101-150) and peak AQI reached 165. Sensitive groups should monitor real-time conditions at AirNow.gov.
The dominant pollutant is PM2.5, driving AQI on 300 of 300 monitored days.
5-Year Air Quality Trend
Air quality is stable in Dawson County. Highest Good-day share: 2025 (90.3%, 271 of 300 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2024 | 321 | 33 | 3 | 0 | 14 | 120 |
| 2025 | 271 | 26 | 1 | 2 | 18 | 165 |
How does Dawson County compare?
How Dawson County compares
Good-day share better than typical
Dawson County 90.3%
Hughes County, South Dakota 93.0%
Typical US county 76.0%
Median AQI better than typical
Dawson County 18
Hughes County, South Dakota 18
Typical US county 39
Unhealthy days / yr worse than typical
Dawson County 2
Hughes County, South Dakota 0
Typical US county 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as Dawson County (18), not geographic neighbors.
Hughes County, South Dakota
Median AQI 18 · 93.0% Good-day share
Blaine County, Idaho
Median AQI 17 · 96.6% Good-day share
Cass County, Nebraska
Median AQI 19 · 95.9% Good-day share
Garfield County, Washington
Median AQI 19 · 92.5% Good-day share
Luna County, New Mexico
Median AQI 17 · 84.7% Good-day share
Marquette County, Michigan
Median AQI 19 · 82.4% Good-day share
Same primary pollutant: PM2.5
PM2.5 led the AQI on the most monitored days here. These peers share that driver and the closest Good-day share (a second relationship type beyond median-AQI neighbors).
Cowlitz County, Washington
90.4% Good-day share · median AQI 22
Mason County, Washington
90.4% Good-day share · median AQI 23
Adams County, Washington
90.5% Good-day share · median AQI 21
Mono County, California
90.1% Good-day share · median AQI 21
Sherman County, Kansas
90.1% Good-day share · median AQI 27
Putnam County, Tennessee
90.0% Good-day share · median AQI 30
Montana counties on the map
Geographic containment only, other monitored counties in Montana, independent of AQI or pollutant match.
What Dawson County's air means for you
On most days the air here is fine, but PM2.5 drives 2 unhealthy-or-worse days a year that sensitive groups should plan around.
- Sensitive groups (asthma, heart conditions, children, older adults) should check the AQI on high-PM2.5 days, the guide explains what a median of 18 means for exposure. Health guidance
- See how Dawson County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Dawson County with its Montana neighbours before drawing a conclusion about the region. All of Montana
Based on 300 EPA-monitored days in 2025; figures reflect only days the monitors reported. Source: EPA Air Quality System annual summaries.
Keep exploring the annual AQI record
Air-quality reading list
Frequently Asked Questions
What is the air quality in Dawson County, Montana? ▼
Dawson County has a median Air Quality Index (AQI) of 18, rated "Good." 90.3% of monitored days (271 out of 300) had good air quality in 2025.
What is the main pollutant in Dawson County? ▼
The primary pollutant in Dawson County is Fine Particles (PM2.5), which was the main AQI driver on 300 days (100% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Dawson County have? ▼
In 2025, Dawson County recorded 2 unhealthy air days (2 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 165.
Is the air quality in Dawson County getting better or worse? ▼
Air quality in Dawson County is stable across floor-qualifying years (2024-2025); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2025 at 90.3% (271 of 300 days). Lowest qualifying Good-day share: 2024 at 89.9% (321 of 357 days).
What does AQI 18 mean for health? ▼
Dawson County's median AQI of 18 falls in the "Good" category. See the AQI category guide for what each range means for health.
How does Dawson County compare to other counties in Montana? ▼
Dawson County has 90.3% good air days. Nearby counties in Montana: Beaverhead (94.7% good), Cascade (59.8% good), Custer (87.2% good), Fergus (90.7% good), Flathead (73.7% good), Gallatin (98.1% good).
What is the 90th percentile AQI in Dawson County? ▼
The 90th percentile AQI for Dawson County is 49, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 165 (Unhealthy).
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. Spotted a figure that looks wrong? Report a correction.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files for Dawson County, Montana · 2020–2025
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Every figure on PlainAirData 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.