EnviroNearby

Big Horn County, Wyoming air quality history

Daily Air Quality Index summaries from EPA monitors in Big Horn, Wyoming, 2010–2024.

89%
Good days in 2024
39
Median daily AQI, 2024
2
Days above 100 in 2024
353
Days with an AQI in 2024 (of 366)

In 2024, EPA reported a daily Air Quality Index (AQI) for Big Horn, Wyoming on 353 days. 315 of those days (89%) were in the Good range, and the median daily AQI was 39. That median is about the same as the typical monitored county in Wyoming (median 41 across 19 counties), and about the same as the typical monitored U.S. county (41). The main pollutant was ozone on 353 days. Across the years with fuller monitoring, the share of Good days fell: an average of 98% in 2010–2012 versus 94% in 2022–2024.

The most recent year with data for this county is 2024; EPA's files for 2025–2025 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 286 of 292 days2010: Moderate 6 of 292 days20102011: Good 286 of 291 days2011: Moderate 5 of 291 days2012: Good 355 of 363 days2012: Moderate 8 of 363 days20122013: Good 299 of 348 days2013: Moderate 49 of 348 days2014: Good 306 of 352 days2014: Moderate 46 of 352 days20142015: Good 315 of 359 days2015: Moderate 44 of 359 days2016: Good 277 of 283 days2016: Moderate 6 of 283 days20162017: Good 326 of 345 days2017: Moderate 19 of 345 days2018: Good 311 of 348 days2018: Moderate 37 of 348 days20182019: Good 344 of 356 days2019: Moderate 12 of 356 days2020: Good 349 of 359 days2020: Moderate 8 of 359 days2020: Unhealthy for Sensitive Groups 2 of 359 days20202021: Good 324 of 364 days2021: Moderate 39 of 364 days2021: Unhealthy for Sensitive Groups 1 of 364 days2022: Good 356 of 362 days2022: Moderate 6 of 362 days20222023: Good 335 of 359 days2023: Moderate 24 of 359 days2024: Good 315 of 353 days2024: Moderate 36 of 353 days2024: Unhealthy for Sensitive Groups 2 of 353 days2024
  • 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 462011: 90th percentile AQI 452012: 90th percentile AQI 472013: 90th percentile AQI 542014: 90th percentile AQI 532015: 90th percentile AQI 512016: 90th percentile AQI 462017: 90th percentile AQI 492018: 90th percentile AQI 512019: 90th percentile AQI 462020: 90th percentile AQI 462021: 90th percentile AQI 512022: 90th percentile AQI 462023: 90th percentile AQI 492024: 90th percentile AQI 512010: Median AQI 382011: Median AQI 392012: Median AQI 362013: Median AQI 402014: Median AQI 412015: Median AQI 412016: Median AQI 382017: Median AQI 362018: Median AQI 392019: Median AQI 362020: Median AQI 382021: Median AQI 392022: Median AQI 382023: Median AQI 392024: Median AQI 3920102012201420162018202020222024
  • Median daily AQI
  • 90th-percentile daily AQI

Main pollutant by day, 2024

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
Ozone353100%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20243533153620003951119Ozone
2023359335240000394977Ozone
202236235660000384664Ozone
20213643243910003951101Ozone
2020359349820003846126Ozone
2019356344120000364677Ozone
2018348311370000395184Ozone
2017345326190000364974Ozone
201628327760000384684Ozone
2015359315440000415171Ozone
2014352306460000415374Ozone
2013348299490000405487Ozone
201236335580000364784Ozone
201129128650000394571Ozone
201029228660000384667Ozone

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 Wyoming with a similar median AQI in 2024

All monitored counties in Wyoming

Source: U.S. EPA AirData, “Annual AQI by County” files for 2010–2024 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem