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

According to the 2025 EPA AQS county release on PlainAirData, Dawson County, Montana ranks #29 of 951 by median AQI (18) and #188 by good-day share (90.3%). Ponce County, Puerto Rico is #1 of 951 by median AQI (3, 91.4% Good days) at good-day-share #159 ≠ largest of 7 at 100.0% Good days #1 by good-day share (100.0%, median AQI 9) at median-AQI #7.

Annual release change

What changed in the 2025 EPA annual release

2024 → 2025
  • 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.

Compared against 357 monitored days in 2024 and 300 in 2025. These are arithmetic differences between two stored EPA annual summaries, not a cause claim or a live advisory.

National release changes Two-year CSV

Data updated August 2026

Dawson County AQI category distribution Stacked-segment bar showing the share of monitored days that fell in each EPA AQI category, Good, Moderate, USG, Unhealthy, Very Unhealthy, Hazardous, with median AQI marker. AQI category distribution 300 monitored days G Median AQI 18 0 50 100 150 200 300 500 Dawson County
  • 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 →
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).

Where Dawson County sits nationally

COUNT-derived placement among 951 US counties with at least 100 monitored days in 2025. Dawson County's Good-day share is 90.3% - cleaner than 80% of that comparison set.

Dawson County Good-day share vs. every US county

Share of monitored days in the Good band (AQI 0–50) - EPA AQS annual release

90.3% Cleaner than 80% higher than 80% of 951 US counties

0.0%–5.0%: 0 US counties (0%). Below this entry. 5.0%–10.0%: 1 US counties (0%). Below this entry. 10.0%–15.0%: 4 US counties (0%). Below this entry. 15.0%–20.0%: 4 US counties (0%). Below this entry. 20.0%–25.0%: 1 US counties (0%). Below this entry. 25.0%–30.0%: 5 US counties (1%). Below this entry. 30.0%–35.0%: 9 US counties (1%). Below this entry. 35.0%–40.0%: 4 US counties (0%). Below this entry. 40.0%–45.0%: 16 US counties (2%). Below this entry. 45.0%–50.0%: 16 US counties (2%). Below this entry. 50.0%–55.0%: 32 US counties (3%). Below this entry. 55.0%–60.0%: 50 US counties (5%). Below this entry. 60.0%–65.0%: 77 US counties (8%). Below this entry. 65.0%–70.0%: 93 US counties (10%). Below this entry. 70.0%–75.0%: 109 US counties (11%). Below this entry. 75.0%–80.0%: 114 US counties (12%). Below this entry. 80.0%–85.0%: 123 US counties (13%). Below this entry. 85.0%–90.0%: 99 US counties (10%). Below this entry. 90.0%–95.0%: 117 US counties (12%). This entry sits in this band. 95.0%–100.0%: 70 US counties (7%). Above this entry. 100.0%–105.0%: 7 US counties (1%). Above this entry. This county 0.0% 100% every floor-qualified US county, bucketed by value

Each bar is a band; taller bars hold more US counties. The dashed line + filled bar mark this entry. Hover or tap any bar for its full count, share, and where it sits relative to this entry.

Source U.S. Environmental Protection Agency, Air Quality System (AQS) · 2025

Pollutant Breakdown

Days where each pollutant was the primary driver of AQI readings in Dawson County.

Dawson County, Montana criteria pollutant distribution Stratified-band visualization showing the share of monitored days each criteria pollutant (PM2.5, PM10, O3, NO2, CO) was the primary AQI driver. PM2.5 · 100.0% 0% 25% 50% 75% 100% Dawson County, Montana · 300 monitored days Criteria pollutant column
  • PM2.5 · 300 days · 100.0%

2024 daily-monitor rhythm in Dawson County

Month-by-month median AQI from EPA day-level county monitors (357 reported days in 2024). Jul posted the highest typical readings (median AQI 49, peak 98); Dec was cleanest at median 5. Summer months (Jun–Aug) averaged median AQI 31 vs 8 in Dec–Feb.

0 10 20 30 40 50 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 9 10 19 14 10 10 49 35 16 17 10 5
Dawson County median daily AQI by calendar month (2024, EPA daily county file)

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
2024 321 33 3 0 14
2025 271 26 1 2 18

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

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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Download this county's annual AQI row as CSV , with the same EPA fields and denominator shown on this page.

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.