EnviroNearby

Johnson County, Wyoming air quality history

Daily Air Quality Index summaries from EPA monitors in Johnson, Wyoming, 2002–2025.

93%
Good days in 2025
41
Median daily AQI, 2025
0
Days above 100 in 2025
363
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Johnson, Wyoming on 363 days. 337 of those days (93%) were in the Good range, and the median daily AQI was 41. That median is about the same as the typical monitored county in Wyoming (median 41 across 17 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was ozone on 345 days. Across the years with fuller monitoring, the share of Good days held roughly steady: an average of 93% in 2003–2018 versus 93% in 2023–2025.

Years with fewer than 120 monitored days (2010, 2011, 2012, 2013, 2014, 2015…) 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%2002: Good 62 of 63 days2002: Moderate 1 of 63 days20022003: Good 115 of 120 days2003: Moderate 5 of 120 days2004: Good 117 of 118 days2004: Moderate 1 of 118 days20042005: Good 114 of 115 days2005: Moderate 1 of 115 days2006: Good 111 of 115 days2006: Moderate 4 of 115 days20062007: Good 105 of 111 days2007: Moderate 6 of 111 days2008: Good 105 of 107 days2008: Moderate 2 of 107 days20082009: Good 122 of 122 days2010: Good 107 of 107 days20102011: Good 103 of 105 days2011: Moderate 2 of 105 days2012: Good 108 of 117 days2012: Moderate 9 of 117 days20122013: Good 101 of 103 days2013: Moderate 2 of 103 days2014: Good 111 of 114 days2014: Moderate 3 of 114 days20142015: Good 56 of 57 days2015: Moderate 1 of 57 days2018: Good 190 of 228 days2018: Moderate 38 of 228 days20182019: Good 345 of 364 days2019: Moderate 19 of 364 days2020: Good 337 of 364 days2020: Moderate 27 of 364 days20202021: Good 304 of 365 days2021: Moderate 54 of 365 days2021: Unhealthy for Sensitive Groups 7 of 365 days2022: Good 350 of 365 days2022: Moderate 14 of 365 days2022: Unhealthy for Sensitive Groups 1 of 365 days20222023: Good 351 of 364 days2023: Moderate 13 of 364 days2024: Good 327 of 364 days2024: Moderate 36 of 364 days2024: Unhealthy for Sensitive Groups 1 of 364 days20242025: Good 337 of 363 days2025: Moderate 26 of 363 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 year0501002002: 90th percentile AQI 322003: 90th percentile AQI 342004: 90th percentile AQI 242005: 90th percentile AQI 232006: 90th percentile AQI 342007: 90th percentile AQI 332008: 90th percentile AQI 272009: 90th percentile AQI 242010: 90th percentile AQI 222011: 90th percentile AQI 262012: 90th percentile AQI 472013: 90th percentile AQI 282014: 90th percentile AQI 262015: 90th percentile AQI 242018: 90th percentile AQI 572019: 90th percentile AQI 492020: 90th percentile AQI 502021: 90th percentile AQI 642022: 90th percentile AQI 482023: 90th percentile AQI 472024: 90th percentile AQI 512025: 90th percentile AQI 492002: Median AQI 112003: Median AQI 92004: Median AQI 82005: Median AQI 82006: Median AQI 92007: Median AQI 112008: Median AQI 82009: Median AQI 82010: Median AQI 82011: Median AQI 92012: Median AQI 112013: Median AQI 92014: Median AQI 82015: Median AQI 82018: Median AQI 392019: Median AQI 402020: Median AQI 402021: Median AQI 402022: Median AQI 392023: Median AQI 402024: Median AQI 402025: Median AQI 41200220042006200820102012201420182020202220242025
  • 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
Ozone34595%
Coarse particles (PM10)164%
Nitrogen dioxide (NO₂)21%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
2025363337260000414984Ozone
20243643273610004051112Ozone
2023364351130000404764Ozone
20223653501410003948101Ozone
20213653045470004064126Ozone
2020364337270000405093Ozone
2019364345190000404980Ozone
2018228190380000395790Ozone
201557561000082461PM2.5
20141141113000082668PM2.5
20131031012000092873PM2.5
201211710890000114766PM2.5
20111051032000092655PM2.5
20101071070000082239PM2.5
20091221220000082433PM2.5
20081071052000082754PM2.5
200711110560000113375PM2.5
20061151114000093465PM2.5
20051151141000082352PM2.5
20041181171000082452PM2.5
20031201155000093462PM2.5
2002636210000113255PM2.5

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 2025

All monitored counties in Wyoming

Source: U.S. EPA AirData, “Annual AQI by County” files for 2002–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem