Median AQI
40
Good
Montana · County air quality · 2025
Richland County, Montana
Median AQI 40 (Good). 79.5% of monitored days rated Good, direct from EPA Air Quality System stations.
- 40
- Median AQI
- 79.5%
- Good-air days
- 3
- Unhealthy days
- 55%
- Cleaner than US counties
Richland County's 2025 annual median AQI is 40 (Good), with 79.5% Good days
According to the U.S. EPA Air Quality System, Richland County, Montana posted a 2025 median AQI of 40 (Good) across 273 monitored days, with 79.5% rated Good and 3 unhealthy or worse. This is an annual comparison, not today's advisory.
Data source EPA Air Quality System (AQS)
- Cleaner than US
- Richland County's 79.5% Good-day share places it cleaner than 55% of US counties in 2025.
- Closest median-AQI peer
- Anderson County (91.3% Good, median AQI 40) is the closest nationwide median-AQI peer to Richland County.
- 2020–2025 trend
- Richland County's floor-qualifying Good-day share is worsening from 2020 to 2025 (93.7% → 79.5%).
- Median AQI
- Median AQI: 40
The verdict
According to EPA Air Quality System monitoring data, Richland County's air is good on balance, cleaner than the median US county, a median AQI of 40 with 79.5% of 273 monitored days in the Good band, driven mainly by Ozone.
- 40
- median AQI · Good
- 79.5%
- days rated Good
- Ozone
- main pollutant
- 55%
- cleaner than US counties
3 days reached Unhealthy or worse; the worst single reading hit AQI 165.
Annual release change
What changed in the 2025 EPA annual release
- Richland County's peak single-day AQI rose from 118 to 165 between the 2024 and 2025 EPA annual releases, a change of +47 points.
- Richland County's Good-day share fell from 83.9% to 79.5% between the 2024 and 2025 EPA annual releases, a change of -4.4 percentage points.
- Richland County's Unhealthy-category days rose from 0 to 3 between the 2024 and 2025 EPA annual releases, a change of +3 days.
- Richland County's median AQI rose from 36 to 40 between the 2024 and 2025 EPA annual releases, a change of +4 points.
Data updated August 2026
- Good · 217 d · 79.5%
- Moderate · 49 d · 17.9%
- USG · 4 d · 1.5%
- Unhealthy · 3 d · 1.1%
How did Richland County's air break down in 2025?
Across 273 monitored days, 217 fell in the Good band (AQI 0–50) and 3 reached Unhealthy or worse. The worst single day peaked at AQI 165 (Unhealthy).
EPA AQS →Air quality data from EPA Air Quality System (2025). 273 days monitored. Median AQI: 40 (Good).
Insights: Richland County, Montana. EPA monitors recorded a median Air Quality Index of 40 across 273 measured days in 2025, earning a Good classification and a Good health grade. Of those days, 217 (79%) fell in the Good band (AQI 0–50), 49 (18%) registered Moderate readings, and 4 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 59, while the worst single-day peak hit 165 (Unhealthy). Residents averaged about 23.8 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as Ozone (175 days), PM2.5 (96 days), PM10 (2 days). Across the 2020–2025 trend window, the share of monitored days rated Good shifted by -14.2 points (measured against 366 monitored days in 2020 and 273 in 2025, so raw day counts are not comparable) and the median AQI moved +3 points, placing the multi-year trajectory at worsening. The annual record contains 3 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); Dawson (90.3% good, AQI 18); Fergus (90.7% good, AQI 41); Flathead (73.7% good, AQI 41).
Air Quality Summary
Good Days
79.5%
217 of 273 monitored days
4.5pp vs 75% target
Max AQI Recorded
165
Unhealthy
Health Grade
Good
90th-pct AQI 59
Richland County, Good days share 79.5%
National avg
Share of monitored days at AQI 0-50 (Good band).
Richland County, Unhealthy-or-worse share 11.0%
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 273 monitored days across EPA AQI categories.
Good
217
79%
Moderate
49
18%
USG
4
1%
Unhealthy
3
1%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Richland County.
- Ozone · 175 days · 64.1%
- PM2.5 · 96 days · 35.2%
- PM10 · 2 days · 0.7%
Health Impact Assessment
Good
Richland County's air quality is rated Good based on 79.5% good air days. There were 3 unhealthy days in 2025 when outdoor activity should be limited.
Air quality is acceptable most days, but 4 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 Ozone, driving AQI on 175 of 273 monitored days.
5-Year Air Quality Trend
Air quality is worsening in Richland County. Highest Good-day share: 2020 (93.7%, 343 of 366 monitored days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 343 | 23 | 0 | 0 | 37 | 72 |
| 2021 | 284 | 63 | 4 | 0 | 38 | 147 |
| 2022 | 322 | 39 | 0 | 0 | 39 | 79 |
| 2023 | 267 | 87 | 5 | 4 | 39 | 219 |
| 2024 | 307 | 54 | 5 | 0 | 36 | 118 |
| 2025 | 217 | 49 | 4 | 3 | 40 | 165 |
How does Richland County compare?
How Richland County compares
Good-day share better than typical
Richland County 79.5%
Anderson County, South Carolina 91.3%
Typical US county 76.0%
Median AQI worse than typical
Richland County 40
Anderson County, South Carolina 40
Typical US county 39
Unhealthy days / yr worse than typical
Richland County 3
Anderson County, South Carolina 0
Typical US county 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as Richland County (40), not geographic neighbors.
Anderson County, South Carolina
Median AQI 40 · 91.3% Good-day share
Andrew County, Missouri
Median AQI 40 · 86.9% Good-day share
Anne Arundel County, Maryland
Median AQI 40 · 87.6% Good-day share
Bergen County, New Jersey
Median AQI 40 · 71.1% Good-day share
Blair County, Pennsylvania
Median AQI 40 · 76.9% Good-day share
Brazos County, Texas
Median AQI 40 · 68.5% Good-day share
Same primary pollutant: Ozone
Ozone 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).
Walworth County, Wisconsin
79.4% Good-day share · median AQI 42
Ward County, North Dakota
79.4% Good-day share · median AQI 36
Woodbury County, Iowa
79.6% Good-day share · median AQI 39
Russell County, Alabama
79.4% Good-day share · median AQI 40
Canadian County, Oklahoma
79.3% Good-day share · median AQI 43
Kiowa County, Oklahoma
79.7% Good-day share · median AQI 43
Montana counties on the map
Geographic containment only, other monitored counties in Montana, independent of AQI or pollutant match.
What Richland County's air means for you
On most days the air here is fine, but Ozone drives 3 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-Ozone days, the guide explains what a median of 40 means for exposure. Health guidance
- See how Richland County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Richland County with its Montana neighbours before drawing a conclusion about the region. All of Montana
Based on 273 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 Richland County, Montana? ▼
Richland County has a median Air Quality Index (AQI) of 40, rated "Good." 79.5% of monitored days (217 out of 273) had good air quality in 2025.
What is the main pollutant in Richland County? ▼
The primary pollutant in Richland County is Ozone (O3), which was the main AQI driver on 175 days (64% of monitored days). Can trigger asthma, reduce lung function, and cause chest pain.
How many unhealthy air days does Richland County have? ▼
In 2025, Richland County recorded 3 unhealthy air days (3 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 165.
Is the air quality in Richland County getting better or worse? ▼
Air quality in Richland County is worsening across floor-qualifying years (2020-2025); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2020 at 93.7% (343 of 366 days). Lowest qualifying Good-day share: 2023 at 73.6% (267 of 364 days).
What does AQI 40 mean for health? ▼
Richland County's median AQI of 40 falls in the "Good" category. See the AQI category guide for what each range means for health.
How does Richland County compare to other counties in Montana? ▼
Richland County has 79.5% good air days. Nearby counties in Montana: Beaverhead (94.7% good), Cascade (59.8% good), Custer (87.2% good), Dawson (90.3% good), Fergus (90.7% good), Flathead (73.7% good).
What is the 90th percentile AQI in Richland County? ▼
The 90th percentile AQI for Richland County is 59, 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 Richland 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.