EnviroNearby

Powder River County, Montana air quality history

Daily Air Quality Index summaries from EPA monitors in Powder River, Montana, 2010–2023.

69%
Good days in 2023
44
Median daily AQI, 2023
12
Days above 100 in 2023
355
Days with an AQI in 2023 (of 365)

In 2023, EPA reported a daily Air Quality Index (AQI) for Powder River, Montana on 355 days. 244 of those days (69%) were in the Good range, and the median daily AQI was 44. That median is higher than the typical monitored county in Montana (median 38 across 19 counties), and about the same as the typical monitored U.S. county (43). The main pollutant was ozone on 215 days. Across the years with fuller monitoring, the share of Good days fell: an average of 75% in 2010–2012 versus 71% in 2021–2023.

The most recent year with data for this county is 2023; EPA's files for 2024–2025 contain no row for it, which usually means its monitors stopped reporting.

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%2010: Good 308 of 364 days2010: Moderate 56 of 364 days20102011: Good 273 of 364 days2011: Moderate 91 of 364 days20112012: Good 236 of 358 days2012: Moderate 122 of 358 days20122013: Good 299 of 363 days2013: Moderate 64 of 363 days20132014: Good 286 of 347 days2014: Moderate 60 of 347 days2014: Unhealthy for Sensitive Groups 1 of 347 days20142015: Good 274 of 358 days2015: Moderate 78 of 358 days2015: Unhealthy for Sensitive Groups 5 of 358 days2015: Unhealthy 1 of 358 days20152016: Good 299 of 366 days2016: Moderate 67 of 366 days20162017: Good 243 of 358 days2017: Moderate 106 of 358 days2017: Unhealthy for Sensitive Groups 4 of 358 days2017: Unhealthy 5 of 358 days20172018: Good 272 of 362 days2018: Moderate 86 of 362 days2018: Unhealthy for Sensitive Groups 4 of 362 days20182019: Good 312 of 361 days2019: Moderate 48 of 361 days2019: Unhealthy for Sensitive Groups 1 of 361 days20192020: Good 254 of 350 days2020: Moderate 91 of 350 days2020: Unhealthy for Sensitive Groups 3 of 350 days2020: Unhealthy 2 of 350 days20202021: Good 230 of 358 days2021: Moderate 113 of 358 days2021: Unhealthy for Sensitive Groups 11 of 358 days2021: Unhealthy 4 of 358 days20212022: Good 292 of 365 days2022: Moderate 70 of 365 days2022: Unhealthy for Sensitive Groups 3 of 365 days20222023: Good 244 of 355 days2023: Moderate 99 of 355 days2023: Unhealthy for Sensitive Groups 6 of 355 days2023: Unhealthy 6 of 355 days2023
  • 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 year0501002010: 90th percentile AQI 532011: 90th percentile AQI 632012: 90th percentile AQI 652013: 90th percentile AQI 552014: 90th percentile AQI 592015: 90th percentile AQI 612016: 90th percentile AQI 572017: 90th percentile AQI 782018: 90th percentile AQI 672019: 90th percentile AQI 522020: 90th percentile AQI 682021: 90th percentile AQI 802022: 90th percentile AQI 562023: 90th percentile AQI 712010: Median AQI 392011: Median AQI 422012: Median AQI 432013: Median AQI 392014: Median AQI 382015: Median AQI 402016: Median AQI 392017: Median AQI 422018: Median AQI 412019: Median AQI 382020: Median AQI 412021: Median AQI 422022: Median AQI 392023: Median AQI 4420102011201220132014201520162017201820192020202120222023
  • Median daily AQI
  • 90th-percentile daily AQI

Main pollutant by day, 2023

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
Ozone21561%
Fine particles (PM2.5)10830%
Coarse particles (PM10)319%
Nitrogen dioxide (NO₂)1<1%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20233552449966004471195Ozone
20223652927030003956108Ozone
2021358230113114004280169Ozone
20203502549132004168159Ozone
20193613124810003852145Ozone
20183622728640004167117Ozone
201735824310645004278177Ozone
20163662996700003957100Ozone
20153582747851004061170Ozone
20143472866010003859110Ozone
2013363299640000395573Ozone
20123582361220000436594Ozone
2011364273910000426397Ozone
2010364308560000395380Ozone

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 2023

All monitored counties in Montana

Source: U.S. EPA AirData, “Annual AQI by County” files for 2010–2023 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem