EnviroNearby

Phillips County, Montana air quality history

Daily Air Quality Index summaries from EPA monitors in Phillips, Montana, 1990–2025.

91%
Good days in 2025
19
Median daily AQI, 2025
5
Days above 100 in 2025
314
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Phillips, Montana on 314 days. 287 of those days (91%) were in the Good range, and the median daily AQI was 19. That median is lower than the typical monitored county in Montana (median 25.5 across 18 counties), and lower than the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 314 days. Across the years with fuller monitoring, the share of Good days fell: an average of 96% in 2012–2014 versus 87% in 2023–2025.

Years with fewer than 120 monitored days (1992, 1993, 1994, 1995, 1996, 1997…) are shown in the table but left out of comparisons and trend statements.

How the days broke down each year

Each bar is one year. The colored segments show the share of monitored days that fell in each AQI category.

Share of monitored days in each AQI category, by year0%25%50%75%100%1990: Good 42 of 42 days19901991: Good 80 of 82 days1991: Moderate 2 of 82 days1992: Good 97 of 99 days1992: Moderate 2 of 99 days19921993: Good 93 of 93 days1994: Good 87 of 91 days1994: Moderate 4 of 91 days19941995: Good 91 of 91 days1996: Good 91 of 91 days19961997: Good 92 of 92 days2012: Good 150 of 153 days2012: Moderate 3 of 153 days20122013: Good 356 of 365 days2013: Moderate 9 of 365 days2014: Good 335 of 362 days2014: Moderate 26 of 362 days2014: Unhealthy for Sensitive Groups 1 of 362 days20142015: Good 317 of 364 days2015: Moderate 39 of 364 days2015: Unhealthy for Sensitive Groups 4 of 364 days2015: Unhealthy 3 of 364 days2015: Very Unhealthy 1 of 364 days2016: Good 348 of 366 days2016: Moderate 18 of 366 days20162017: Good 316 of 360 days2017: Moderate 41 of 360 days2017: Unhealthy for Sensitive Groups 3 of 360 days2018: Good 309 of 360 days2018: Moderate 47 of 360 days2018: Unhealthy for Sensitive Groups 3 of 360 days2018: Unhealthy 1 of 360 days20182019: Good 342 of 365 days2019: Moderate 23 of 365 days2020: Good 296 of 366 days2020: Moderate 68 of 366 days2020: Unhealthy for Sensitive Groups 2 of 366 days20202021: Good 292 of 361 days2021: Moderate 64 of 361 days2021: Unhealthy for Sensitive Groups 5 of 361 days2022: Good 344 of 365 days2022: Moderate 21 of 365 days20222023: Good 289 of 364 days2023: Moderate 64 of 364 days2023: Unhealthy for Sensitive Groups 4 of 364 days2023: Unhealthy 7 of 364 days2024: Good 323 of 362 days2024: Moderate 37 of 362 days2024: Unhealthy for Sensitive Groups 2 of 362 days20242025: Good 287 of 314 days2025: Moderate 22 of 314 days2025: Unhealthy for Sensitive Groups 3 of 314 days2025: Unhealthy 2 of 314 days2025
  • Good
  • Moderate
  • Unhealthy for Sensitive Groups
  • Unhealthy
  • Very Unhealthy
  • Hazardous

Typical and high-end AQI over time

The median is the middle day of the year. The 90th percentile is the level that only the highest 10% of days exceeded.

Median and 90th-percentile daily AQI, by year0501001990: 90th percentile AQI 291991: 90th percentile AQI 261992: 90th percentile AQI 241993: 90th percentile AQI 201994: 90th percentile AQI 361995: 90th percentile AQI 211996: 90th percentile AQI 181997: 90th percentile AQI 182012: 90th percentile AQI 462013: 90th percentile AQI 432014: 90th percentile AQI 462015: 90th percentile AQI 522016: 90th percentile AQI 442017: 90th percentile AQI 542018: 90th percentile AQI 542019: 90th percentile AQI 482020: 90th percentile AQI 682021: 90th percentile AQI 662022: 90th percentile AQI 452023: 90th percentile AQI 592024: 90th percentile AQI 522025: 90th percentile AQI 471990: Median AQI 161991: Median AQI 141992: Median AQI 111993: Median AQI 111994: Median AQI 161995: Median AQI 91996: Median AQI 71997: Median AQI 82012: Median AQI 312013: Median AQI 332014: Median AQI 342015: Median AQI 362016: Median AQI 342017: Median AQI 342018: Median AQI 372019: Median AQI 342020: Median AQI 362021: Median AQI 362022: Median AQI 362023: Median AQI 382024: Median AQI 212025: Median AQI 19199019921994199620122014201620182020202220242025
  • Median daily AQI
  • 90th-percentile daily AQI

Main pollutant by day, 2025

On each monitored day, the AQI reflects whichever measured pollutant had the highest index. This counts how many days each pollutant set the AQI. A pollutant that was not measured here cannot appear.

PollutantDays as main pollutantShare of monitored days
Fine particles (PM2.5)314100%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20253142872232001947168PM2.5
20243623233720002152147PM2.5
20233642896447003859199Ozone
2022365344210000364589Ozone
20213612926450003666146Ozone
20203662966820003668140Ozone
2019365342230000344871Ozone
20183603094731003754160Ozone
20173603164130003454113Ozone
2016366348180000344495Ozone
20153643173943103652209Ozone
20143623352610003446101Ozone
201336535690000334361Ozone
201215315030000314658Ozone
199792920000081831PM10
199691910000071833PM10
199591910000092146PM10
1994918740000163661PM10
1993939300000112028PM10
1992999720000112474PM10
1991828020000142658PM10
1990424200000162944PM10

What this data can and can’t tell you

It is a county-level summary. EPA reports one AQI per day for the county, based on the monitors operating there. Air at a particular street, school or home can differ, especially near roads, industry or wildfire smoke.

It is not a health assessment. The AQI is EPA’s scale for communicating daily air quality. A county’s history can’t tell you what the health risk is for any particular person. For daily conditions and health guidance, see AirNow.

Rules change over time. EPA has revised AQI breakpoints, most recently for fine particles in 2024, so some year-to-year change can reflect the scale rather than the air.

Counties in Montana with a similar median AQI in 2025

All monitored counties in Montana

Source: U.S. EPA AirData, “Annual AQI by County” files for 1990–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem