EnviroNearby

Butte County, Idaho air quality history

Daily Air Quality Index summaries from EPA monitors in Butte, Idaho, 1992–2025.

90%
Good days in 2025
42
Median daily AQI, 2025
0
Days above 100 in 2025
364
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Butte, Idaho on 364 days. 328 of those days (90%) were in the Good range, and the median daily AQI was 42. That median is higher than the typical monitored county in Idaho (median 35 across 18 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was ozone on 359 days. Across the years with fuller monitoring, the share of Good days held roughly steady: an average of 90% in 1992–1994 versus 88% in 2023–2025.

Years with fewer than 120 monitored days (2005, 2006) 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%1992: Good 124 of 128 days1992: Moderate 4 of 128 days19921993: Good 327 of 340 days1993: Moderate 13 of 340 days1994: Good 275 of 356 days1994: Moderate 81 of 356 days1995: Good 330 of 351 days1995: Moderate 21 of 351 days1996: Good 272 of 329 days1996: Moderate 56 of 329 days1996: Unhealthy for Sensitive Groups 1 of 329 days1997: Good 289 of 308 days1997: Moderate 19 of 308 days19971998: Good 286 of 357 days1998: Moderate 71 of 357 days1999: Good 277 of 357 days1999: Moderate 78 of 357 days1999: Unhealthy for Sensitive Groups 2 of 357 days2000: Good 276 of 353 days2000: Moderate 76 of 353 days2000: Unhealthy for Sensitive Groups 1 of 353 days2001: Good 284 of 290 days2001: Moderate 6 of 290 days2002: Good 236 of 357 days2002: Moderate 119 of 357 days2002: Unhealthy for Sensitive Groups 2 of 357 days20022003: Good 259 of 346 days2003: Moderate 85 of 346 days2003: Unhealthy for Sensitive Groups 2 of 346 days2004: Good 298 of 349 days2004: Moderate 51 of 349 days2005: Good 111 of 111 days2006: Good 100 of 109 days2006: Moderate 9 of 109 days2007: Good 203 of 268 days2007: Moderate 64 of 268 days2007: Unhealthy for Sensitive Groups 1 of 268 days20072008: Good 294 of 363 days2008: Moderate 68 of 363 days2008: Unhealthy for Sensitive Groups 1 of 363 days2009: Good 338 of 364 days2009: Moderate 26 of 364 days2010: Good 286 of 331 days2010: Moderate 45 of 331 days2011: Good 295 of 363 days2011: Moderate 68 of 363 days2012: Good 287 of 358 days2012: Moderate 68 of 358 days2012: Unhealthy for Sensitive Groups 2 of 358 days2012: Unhealthy 1 of 358 days20122013: Good 325 of 360 days2013: Moderate 35 of 360 days2014: Good 325 of 349 days2014: Moderate 24 of 349 days2015: Good 325 of 360 days2015: Moderate 34 of 360 days2015: Unhealthy 1 of 360 days2016: Good 345 of 362 days2016: Moderate 16 of 362 days2016: Unhealthy for Sensitive Groups 1 of 362 days2017: Good 306 of 347 days2017: Moderate 38 of 347 days2017: Unhealthy for Sensitive Groups 3 of 347 days20172018: Good 311 of 363 days2018: Moderate 49 of 363 days2018: Unhealthy for Sensitive Groups 3 of 363 days2019: Good 347 of 361 days2019: Moderate 14 of 361 days2020: Good 334 of 364 days2020: Moderate 28 of 364 days2020: Unhealthy for Sensitive Groups 1 of 364 days2020: Unhealthy 1 of 364 days2021: Good 289 of 363 days2021: Moderate 71 of 363 days2021: Unhealthy for Sensitive Groups 3 of 363 days2022: Good 337 of 365 days2022: Moderate 28 of 365 days20222023: Good 320 of 362 days2023: Moderate 42 of 362 days2024: Good 303 of 357 days2024: Moderate 54 of 357 days2025: Good 328 of 364 days2025: Moderate 36 of 364 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 year0501001992: 90th percentile AQI 371993: 90th percentile AQI 481994: 90th percentile AQI 621995: 90th percentile AQI 481996: 90th percentile AQI 611997: 90th percentile AQI 481998: 90th percentile AQI 641999: 90th percentile AQI 582000: 90th percentile AQI 642001: 90th percentile AQI 462002: 90th percentile AQI 712003: 90th percentile AQI 672004: 90th percentile AQI 542005: 90th percentile AQI 242006: 90th percentile AQI 472007: 90th percentile AQI 612008: 90th percentile AQI 612009: 90th percentile AQI 502010: 90th percentile AQI 542011: 90th percentile AQI 582012: 90th percentile AQI 612013: 90th percentile AQI 502014: 90th percentile AQI 492015: 90th percentile AQI 502016: 90th percentile AQI 482017: 90th percentile AQI 512018: 90th percentile AQI 542019: 90th percentile AQI 482020: 90th percentile AQI 502021: 90th percentile AQI 672022: 90th percentile AQI 502023: 90th percentile AQI 512024: 90th percentile AQI 582025: 90th percentile AQI 501992: Median AQI 321993: Median AQI 391994: Median AQI 441995: Median AQI 401996: Median AQI 411997: Median AQI 411998: Median AQI 441999: Median AQI 442000: Median AQI 422001: Median AQI 382002: Median AQI 462003: Median AQI 432004: Median AQI 442005: Median AQI 112006: Median AQI 142007: Median AQI 392008: Median AQI 442009: Median AQI 422010: Median AQI 432011: Median AQI 452012: Median AQI 422013: Median AQI 422014: Median AQI 392015: Median AQI 402016: Median AQI 392017: Median AQI 422018: Median AQI 412019: Median AQI 402020: Median AQI 402021: Median AQI 422022: Median AQI 422023: Median AQI 442024: Median AQI 422025: Median AQI 4219921997200220072012201720222025
  • 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
Ozone35999%
Fine particles (PM2.5)51%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
2025364328360000425077Ozone
2024357303540000425897Ozone
2023362320420000445180Ozone
2022365337280000425079Ozone
20213632897130004267128Ozone
20203643342811004050152Ozone
2019361347140000404871Ozone
20183633114930004154115Ozone
20173473063830004251147Ozone
20163623451610003948108Ozone
20153603253401004050159Ozone
2014349325240000394993Ozone
2013360325350000425091Ozone
20123582876821004261155Ozone
2011363295680000455893Ozone
2010331286450000435477Ozone
2009364338260000425064Ozone
20083632946810004461101Ozone
20072682036410003961101Ozone
200610910090000144785PM2.5
200511111100000112438PM2.5
2004349298510000445484Ozone
20033462598520004367129Ozone
200235723611920004671105Ozone
200129028460000384671Ozone
20003532767610004264115Ozone
19993572777820004458112Ozone
1998357286710000446490Ozone
1997308289190000414880Ozone
19963292725610004161119Ozone
1995351330210000404862Ozone
1994356275810000446284Ozone
1993340327130000394887Ozone
199212812440000323766Ozone

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 Idaho with a similar median AQI in 2025

All monitored counties in Idaho

Source: U.S. EPA AirData, “Annual AQI by County” files for 1992–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem