EnviroNearby

Glacier County, Montana air quality history

Daily Air Quality Index summaries from EPA monitors in Glacier, Montana, 1994–2025.

92%
Good days in 2025
23
Median daily AQI, 2025
3
Days above 100 in 2025
351
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Glacier, Montana on 351 days. 322 of those days (92%) were in the Good range, and the median daily AQI was 23. 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 351 days.

Years with fewer than 120 monitored days (2002, 2003, 2004, 2005, 2006, 2007…) 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%1994: Good 51 of 51 days19941995: Good 43 of 43 days1996: Good 41 of 42 days1996: Moderate 1 of 42 days19961997: Good 29 of 39 days1997: Moderate 10 of 39 days1998: Good 44 of 52 days1998: Moderate 8 of 52 days19981999: Good 53 of 58 days1999: Moderate 5 of 58 days2000: Good 55 of 59 days2000: Moderate 4 of 59 days20002001: Good 59 of 61 days2001: Moderate 2 of 61 days2002: Good 52 of 59 days2002: Moderate 7 of 59 days20022003: Good 38 of 42 days2003: Moderate 3 of 42 days2003: Unhealthy for Sensitive Groups 1 of 42 days2004: Good 66 of 66 days20042005: Good 61 of 61 days2006: Good 60 of 61 days2006: Moderate 1 of 61 days20062007: Good 57 of 60 days2007: Moderate 3 of 60 days2009: Good 127 of 138 days2009: Moderate 11 of 138 days20092010: Good 137 of 153 days2010: Moderate 16 of 153 days2023: Good 315 of 354 days2023: Moderate 33 of 354 days2023: Unhealthy for Sensitive Groups 5 of 354 days2023: Unhealthy 1 of 354 days20232024: Good 306 of 346 days2024: Moderate 40 of 346 days2025: Good 322 of 351 days2025: Moderate 26 of 351 days2025: Unhealthy for Sensitive Groups 3 of 351 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 year0501001994: 90th percentile AQI 321995: 90th percentile AQI 331996: 90th percentile AQI 441997: 90th percentile AQI 731998: 90th percentile AQI 541999: 90th percentile AQI 472000: 90th percentile AQI 422001: 90th percentile AQI 422002: 90th percentile AQI 562003: 90th percentile AQI 382004: 90th percentile AQI 232005: 90th percentile AQI 232006: 90th percentile AQI 312007: 90th percentile AQI 382009: 90th percentile AQI 492010: 90th percentile AQI 542023: 90th percentile AQI 522024: 90th percentile AQI 522025: 90th percentile AQI 441994: Median AQI 171995: Median AQI 191996: Median AQI 291997: Median AQI 311998: Median AQI 271999: Median AQI 192000: Median AQI 162001: Median AQI 202002: Median AQI 202003: Median AQI 162004: Median AQI 142005: Median AQI 132006: Median AQI 142007: Median AQI 132009: Median AQI 422010: Median AQI 412023: Median AQI 122024: Median AQI 232025: Median AQI 231994199619982000200220042006200920232025
  • 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)351100%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20253513222630002344117PM2.5
2024346306400000235299PM2.5
20233543153351001252166PM2.5
2010153137160000415474Ozone
2009138127110000424987Ozone
2007605730000133872PM10
2006616010000143166PM10
2005616100000132348PM10
2004666600000142336PM10
20034238310001638121PM10
2002595270000205682PM10
2001615920000204261PM10
2000595540000164288PM10
1999585350000194767PM10
1998524480000275477PM10
19973929100000317386PM10
1996424110000294454PM10
1995434300000193347PM10
1994515100000173247PM10

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 1994–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem