Median AQI
19
Good
Montana · County air quality · 2025
Phillips County, Montana
Median AQI 19 (Good). 91.4% of monitored days rated Good, direct from EPA Air Quality System stations.
- 19
- Median AQI
- 91.4%
- Good-air days
- 2
- Unhealthy days
- 83%
- Cleaner than US counties
Phillips County's 2025 annual median AQI is 19 (Good), with 91.4% Good days
According to the U.S. EPA Air Quality System, Phillips County, Montana posted a 2025 median AQI of 19 (Good) across 314 monitored days, with 91.4% 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
- Phillips County's 91.4% Good-day share places it cleaner than 83% of US counties in 2025.
- Closest median-AQI peer
- Cass County (95.9% Good, median AQI 19) is the closest nationwide median-AQI peer to Phillips County.
- 2020–2025 trend
- Phillips County's floor-qualifying Good-day share is improving from 2020 to 2025 (80.9% → 91.4%).
- Median AQI
- Median AQI: 19
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 19 with 91.4% of 314 monitored days in the Good band, driven mainly by PM2.5.
- 19
- median AQI · Good
- 91.4%
- days rated Good
- PM2.5
- main pollutant
- 83%
- cleaner than US counties
2 days reached Unhealthy or worse; the worst single reading hit AQI 168.
Annual release change
What changed in the 2025 EPA annual release
- Phillips County's Good-day share rose from 89.2% to 91.4% between the 2024 and 2025 EPA annual releases, a change of +2.2 percentage points.
- Phillips County's peak single-day AQI rose from 147 to 168 between the 2024 and 2025 EPA annual releases, a change of +21 points.
- Phillips County's Unhealthy-category days rose from 0 to 2 between the 2024 and 2025 EPA annual releases, a change of +2 days.
Data updated August 2026
- Good · 287 d · 91.4%
- Moderate · 22 d · 7.0%
- USG · 3 d · 1.0%
- Unhealthy · 2 d · 0.6%
How did Phillips County's air break down in 2025?
Across 314 monitored days, 287 fell in the Good band (AQI 0–50) and 2 reached Unhealthy or worse. The worst single day peaked at AQI 168 (Unhealthy).
EPA AQS →Air quality data from EPA Air Quality System (2025). 314 days monitored. Median AQI: 19 (Good).
Insights: Phillips County, Montana. EPA monitors recorded a median Air Quality Index of 19 across 314 measured days in 2025, earning a Good classification and a Excellent health grade. Of those days, 287 (91%) fell in the Good band (AQI 0–50), 22 (7%) registered Moderate readings, and 3 (1%) reached Unhealthy for Sensitive Groups. The 90th-percentile AQI settled at 47, while the worst single-day peak hit 168 (Unhealthy). Residents averaged about 27.4 clean-air days per 30-day window during the monitoring year.
The full pollutant mix ranks as PM2.5 (314 days). Across the 2020–2025 trend window, the share of monitored days rated Good shifted by +10.5 points (measured against 366 monitored days in 2020 and 314 in 2025, so raw day counts are not comparable) and the median AQI moved -17 points, placing the multi-year trajectory at improving. 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); Dawson (90.3% good, AQI 18); Fergus (90.7% good, AQI 41); Flathead (73.7% good, AQI 41).
Air Quality Summary
Good Days
91.4%
287 of 314 monitored days
16.4pp vs 75% target
Max AQI Recorded
168
Unhealthy
Health Grade
Excellent
90th-pct AQI 47
Phillips County, Good days share 91.4%
National avg
Share of monitored days at AQI 0-50 (Good band).
Phillips County, Unhealthy-or-worse share 6.4%
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 314 monitored days across EPA AQI categories.
Good
287
91%
Moderate
22
7%
USG
3
1%
Unhealthy
2
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 · 314 days · 100.0%
Health Impact Assessment
Excellent
Phillips County's air quality is rated Excellent based on 91.4% good air days. There were 2 unhealthy days in 2025 when outdoor activity should be limited.
Air quality is acceptable most days, but 3 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 314 of 314 monitored days.
5-Year Air Quality Trend
Air quality is improving in Phillips County. Highest Good-day share: 2022 (94.2%, 344 of 365 monitored 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 | 287 | 22 | 3 | 2 | 19 | 168 |
How does Phillips County compare?
How Phillips County compares
Good-day share better than US avg
Phillips County 91.4%
Cass County, Nebraska 95.9%
US average 76.0%
Median AQI better than US avg
Phillips County 19
Cass County, Nebraska 19
US average 39
Unhealthy days / yr worse than US avg
Phillips County 2
Cass County, Nebraska 0
US average 1
Counties with a similar median AQI
Nationwide peers within about the same annual median AQI as Phillips County (19), not geographic neighbors.
Cass County, Nebraska
Median AQI 19 · 95.9% Good-day share
Garfield County, Washington
Median AQI 19 · 92.5% Good-day share
Marquette County, Michigan
Median AQI 19 · 82.4% Good-day share
Pitkin County, Colorado
Median AQI 19 · 92.3% Good-day share
Dawson County, Montana
Median AQI 18 · 90.3% Good-day share
Hughes County, South Dakota
Median AQI 18 · 93.0% 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).
Ponce County, Puerto Rico
91.4% Good-day share · median AQI 3
Lewis County, Washington
91.3% Good-day share · median AQI 20
Matanuska-Susitna County, Alaska
91.5% Good-day share · median AQI 9
Alamosa County, Colorado
91.5% Good-day share · median AQI 25
Glacier County, Montana
91.7% Good-day share · median AQI 23
Douglas County, Nevada
91.1% Good-day share · median AQI 22
Montana counties on the map
Geographic containment only, other monitored counties in Montana, independent of AQI or pollutant match.
What Phillips 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 19 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 314 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 Phillips County, Montana? ▼
Phillips County has a median Air Quality Index (AQI) of 19, rated "Good." 91.4% of monitored days (287 out of 314) 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 314 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 2 unhealthy air days (2 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 across floor-qualifying years (2020-2025); years with fewer than 100 monitored days are excluded from that direction. Highest qualifying Good-day share: 2022 at 94.2% (344 of 365 days). Lowest qualifying Good-day share: 2023 at 79.4% (289 of 364 days).
What does AQI 19 mean for health? ▼
Phillips County's median AQI of 19 falls in the "Good" category. See the AQI category guide for what each range means for health.
How does Phillips County compare to other counties in Montana? ▼
Phillips County has 91.4% 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 Phillips County? ▼
The 90th percentile AQI for Phillips County is 47, 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. Spotted a figure that looks wrong? Report a correction.
Source: U.S. EPA Air Quality System (AQS) Annual AQI by county summary files for Phillips 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.