Median AQI
18
Good
Montana · County air quality · 2025
Phillips County, Montana
Median AQI 18 (Good). 94.2% of monitored days rated Good, direct from EPA Air Quality System stations.
- 18
- Median AQI
- 94.2%
- Good-air days
- 1
- Unhealthy days
- 86%
- Cleaner than US counties
The verdict
According to EPA Air Quality System monitoring data, Phillips County's air is good on balance, cleaner than most US counties, a median AQI of 18 with 94.2% of 171 monitored days in the Good band, driven mainly by PM2.5.
- 18
- median AQI · Good
- 94.2%
- days rated Good
- PM2.5
- main pollutant
- 86%
- cleaner than US counties
1 day reached Unhealthy or worse; the worst single reading hit AQI 168.
Data updated July 2026
- Good · 161 d · 94.2%
- Moderate · 8 d · 4.7%
- USG · 1 d · 0.6%
- Unhealthy · 1 d · 0.6%
How did Phillips County's air break down in 2025?
Across 171 monitored days, 161 fell in the Good band (AQI 0–50) and 1 reached Unhealthy or worse. The worst single day peaked at AQI 168 (Unhealthy).
EPA AQS →Air quality data from EPA Air Quality System (2025). 171 days monitored. Median AQI: 18 (Good).
Insights: Phillips County, Montana. EPA monitors recorded a median Air Quality Index of 18 across 171 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 161 (94%) fell in the Good band (AQI 0–50), 8 (5%) registered Moderate readings, and 1 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 41, while the worst single-day peak hit 168 (Unhealthy). Residents averaged about 28.2 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (171 days). Across the 2020–2025 trend window, good days shifted by -135 and the median AQI moved -18 points, placing the multi-year trajectory at improving. Residents and visitors experienced 1 unhealthy-or-worse days combined, periods when the EPA recommends sensitive groups limit prolonged outdoor exertion. Nearby counties show comparable readings: Beaverhead (100.0% good, AQI 12); Custer (91.2% good, AQI 39); Dawson (95.0% good, AQI 14); Fergus (92.2% good, AQI 44); Flathead (82.1% good, AQI 40); Gallatin (99.1% good, AQI 14).
Air Quality Summary
Good Days
94.2%
161 of 171 monitored days
19.2pp vs 75% target
Max AQI Recorded
168
Unhealthy
Health Grade
Excellent
90th-pct AQI 41
Phillips County, Good days share 94.2%
National avg
Share of monitored days at AQI 0-50 (Good band).
Phillips County, Unhealthy-or-worse share 0.6%
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 171 monitored days across EPA AQI categories.
Good
161
94%
Moderate
8
5%
USG
1
1%
Unhealthy
1
1%
Very Unhealthy
0
0%
Hazardous
0
0%
Pollutant Breakdown
Days where each pollutant was the primary driver of AQI readings in Phillips County.
- PM2.5 · 171 days · 100.0%
Health Impact Assessment
Excellent
Phillips County's air quality is rated Excellent based on 94.2% good air days. There were 1 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 168. Sensitive groups should monitor real-time conditions at AirNow.gov.
The dominant pollutant is PM2.5, driving AQI on 171 of 171 monitored days.
5-Year Air Quality Trend
Air quality is improving in Phillips County. Best year: 2022 (344 good days).
| Year | Good | Moderate | USG | Unhealthy | Median AQI | Max AQI |
|---|---|---|---|---|---|---|
| 2020 | 296 | 68 | 2 | 0 | 36 | 140 |
| 2021 | 292 | 64 | 5 | 0 | 36 | 146 |
| 2022 | 344 | 21 | 0 | 0 | 36 | 89 |
| 2023 | 289 | 64 | 4 | 7 | 38 | 199 |
| 2024 | 323 | 37 | 2 | 0 | 21 | 147 |
| 2025 | 161 | 8 | 1 | 1 | 18 | 168 |
How does Phillips County compare?
How Phillips County compares
Good-day share better than US avg
Phillips County 94.2%
Beaverhead County, Montana 100.0%
US average 76.5%
Median AQI better than US avg
Phillips County 18
Beaverhead County, Montana 12
US average 38
Unhealthy days / yr worse than US avg
Phillips County 1
Beaverhead County, Montana 0
US average 0
Other Counties in Montana
Air quality comparison for nearby counties in Montana.
Counties with Similar Air Quality
Counties across the US with a similar median AQI to Phillips County.
Garfield County, Washington
AQI 18 · 95.9% good
Guayama County, Puerto Rico
AQI 18 · 100.0% good
Lewis County, Washington
AQI 18 · 93.3% good
Marquette County, Michigan
AQI 18 · 87.0% good
St John County, Virgin Islands
AQI 18 · 100.0% good
Adams County, Washington
AQI 19 · 94.7% good
What Phillips County's air means for you
On most days the air here is fine, but PM2.5 drives 1 unhealthy-or-worse day 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 Phillips County ranks against every monitored U.S. county on Good-day share. County rankings
- Compare Phillips County with its Montana neighbours before drawing a conclusion about the region. All of Montana
Based on 171 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 Phillips County, Montana? ▼
Phillips County has a median Air Quality Index (AQI) of 18, rated "Good." 94.2% of monitored days (161 out of 171) had good air quality in 2025.
What is the main pollutant in Phillips County? ▼
The primary pollutant in Phillips County is Fine Particles (PM2.5), which was the main AQI driver on 171 days (100% of monitored days). Penetrates deep into lungs and bloodstream. Linked to heart disease and premature death.
How many unhealthy air days does Phillips County have? ▼
In 2025, Phillips County recorded 1 unhealthy air days (1 Unhealthy, 0 Very Unhealthy, 0 Hazardous). The maximum AQI reached 168.
Is the air quality in Phillips County getting better or worse? ▼
Air quality in Phillips County is improving based on 5-year trends (2020-2025). Best year: 2022 with 344 good days. Worst year: 2025 with 161 good days.
What does AQI 18 mean for health? ▼
Phillips County's median AQI of 18 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 Phillips County compare to other counties in Montana? ▼
Phillips County has 94.2% good air days. Nearby counties in Montana: Beaverhead (100.0% good), Custer (91.2% good), Dawson (95.0% good), Fergus (92.2% good), Flathead (82.1% good), Gallatin (99.1% good).
What is the 90th percentile AQI in Phillips County? ▼
The 90th percentile AQI for Phillips County is 41, meaning 90% of monitored days had an AQI at or below this level. The maximum AQI recorded was 168 (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.
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.