EnviroNearby

Richland County, Montana air quality history

Daily Air Quality Index summaries from EPA monitors in Richland, Montana, 2008–2025.

79%
Good days in 2025
40
Median daily AQI, 2025
7
Days above 100 in 2025
273
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Richland, Montana on 273 days. 217 of those days (79%) were in the Good range, and the median daily AQI was 40. That median is higher than the typical monitored county in Montana (median 25.5 across 18 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was ozone on 175 days. Across the years with fuller monitoring, the share of Good days fell: an average of 83% in 2009–2011 versus 79% in 2023–2025.

EPA did not report an AQI for every day of 2025 here (273 of 365 days). Figures describe monitored days only; seasonal monitoring (for example, ozone measured only in warmer months) can make a county look cleaner or dirtier than a full-year record would.

Years with fewer than 120 monitored days (2008) 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%2008: Good 79 of 83 days2008: Moderate 4 of 83 days20082009: Good 298 of 363 days2009: Moderate 65 of 363 days2010: Good 322 of 365 days2010: Moderate 43 of 365 days20102011: Good 283 of 363 days2011: Moderate 80 of 363 days2012: Good 228 of 365 days2012: Moderate 137 of 365 days20122013: Good 268 of 365 days2013: Moderate 95 of 365 days2013: Unhealthy for Sensitive Groups 2 of 365 days2014: Good 297 of 365 days2014: Moderate 67 of 365 days2014: Unhealthy for Sensitive Groups 1 of 365 days20142015: Good 298 of 364 days2015: Moderate 60 of 364 days2015: Unhealthy for Sensitive Groups 3 of 364 days2015: Unhealthy 3 of 364 days2016: Good 327 of 366 days2016: Moderate 39 of 366 days20162017: Good 297 of 358 days2017: Moderate 59 of 358 days2017: Unhealthy for Sensitive Groups 1 of 358 days2017: Unhealthy 1 of 358 days2018: Good 298 of 364 days2018: Moderate 65 of 364 days2018: Unhealthy for Sensitive Groups 1 of 364 days20182019: Good 322 of 365 days2019: Moderate 43 of 365 days2020: Good 343 of 366 days2020: Moderate 23 of 366 days20202021: Good 284 of 351 days2021: Moderate 63 of 351 days2021: Unhealthy for Sensitive Groups 4 of 351 days2022: Good 322 of 361 days2022: Moderate 39 of 361 days20222023: Good 267 of 364 days2023: Moderate 87 of 364 days2023: Unhealthy for Sensitive Groups 5 of 364 days2023: Unhealthy 4 of 364 days2023: Very Unhealthy 1 of 364 days2024: Good 307 of 366 days2024: Moderate 54 of 366 days2024: Unhealthy for Sensitive Groups 5 of 366 days20242025: Good 217 of 273 days2025: Moderate 49 of 273 days2025: Unhealthy for Sensitive Groups 4 of 273 days2025: Unhealthy 3 of 273 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 year0501002008: 90th percentile AQI 422009: 90th percentile AQI 542010: 90th percentile AQI 512011: 90th percentile AQI 562012: 90th percentile AQI 622013: 90th percentile AQI 582014: 90th percentile AQI 572015: 90th percentile AQI 572016: 90th percentile AQI 512017: 90th percentile AQI 582018: 90th percentile AQI 582019: 90th percentile AQI 512020: 90th percentile AQI 472021: 90th percentile AQI 712022: 90th percentile AQI 512023: 90th percentile AQI 642024: 90th percentile AQI 552025: 90th percentile AQI 592008: Median AQI 312009: Median AQI 392010: Median AQI 382011: Median AQI 382012: Median AQI 442013: Median AQI 422014: Median AQI 372015: Median AQI 392016: Median AQI 372017: Median AQI 392018: Median AQI 412019: Median AQI 372020: Median AQI 372021: Median AQI 382022: Median AQI 392023: Median AQI 392024: Median AQI 362025: Median AQI 402008201020122014201620182020202220242025
  • 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
Ozone17564%
Fine particles (PM2.5)9635%
Coarse particles (PM10)21%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20252732174943004059165Ozone
20243663075450003655118Ozone
20233642678754103964219Ozone
2022361322390000395179Ozone
20213512846340003871147Ozone
2020366343230000374772Ozone
2019365322430000375193Ozone
20183642986510004158139Ozone
20173582975911003958154Ozone
2016366327390000375199Ozone
20153642986033003957181Ozone
20143652976710003757107Ozone
20133652689520004258110Ozone
20123652281370000446290PM2.5
2011363283800000385694PM2.5
2010365322430000385184Ozone
2009363298650000395476Ozone
2008837940000314263Ozone

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 2008–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem