EnviroNearby

Butte County, California air quality history

Daily Air Quality Index summaries from EPA monitors in Butte, California, 1980–2025.

65%
Good days in 2025
46
Median daily AQI, 2025
0
Days above 100 in 2025
365
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Butte, California on 365 days. 238 of those days (65%) were in the Good range, and the median daily AQI was 46. That median is about the same as the typical monitored county in California (median 45.5 across 46 counties), and higher than the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 192 days. Across the years with fuller monitoring, the share of Good days fell: an average of 79% in 1980–1982 versus 60% in 2023–2025.

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%1980: Good 281 of 353 days1980: Moderate 68 of 353 days1980: Unhealthy for Sensitive Groups 4 of 353 days19801981: Good 293 of 365 days1981: Moderate 71 of 365 days1981: Unhealthy for Sensitive Groups 1 of 365 days1982: Good 285 of 365 days1982: Moderate 73 of 365 days1982: Unhealthy for Sensitive Groups 7 of 365 days1983: Good 315 of 365 days1983: Moderate 49 of 365 days1983: Unhealthy for Sensitive Groups 1 of 365 days1984: Good 288 of 366 days1984: Moderate 72 of 366 days1984: Unhealthy for Sensitive Groups 6 of 366 days1985: Good 245 of 365 days1985: Moderate 97 of 365 days1985: Unhealthy for Sensitive Groups 20 of 365 days1985: Unhealthy 3 of 365 days19851986: Good 230 of 365 days1986: Moderate 104 of 365 days1986: Unhealthy for Sensitive Groups 30 of 365 days1986: Unhealthy 1 of 365 days1987: Good 204 of 365 days1987: Moderate 130 of 365 days1987: Unhealthy for Sensitive Groups 28 of 365 days1987: Unhealthy 3 of 365 days1988: Good 235 of 366 days1988: Moderate 103 of 366 days1988: Unhealthy for Sensitive Groups 25 of 366 days1988: Unhealthy 3 of 366 days1989: Good 215 of 365 days1989: Moderate 131 of 365 days1989: Unhealthy for Sensitive Groups 18 of 365 days1989: Unhealthy 1 of 365 days1990: Good 251 of 365 days1990: Moderate 96 of 365 days1990: Unhealthy for Sensitive Groups 17 of 365 days1990: Unhealthy 1 of 365 days19901991: Good 239 of 365 days1991: Moderate 117 of 365 days1991: Unhealthy for Sensitive Groups 9 of 365 days1992: Good 263 of 366 days1992: Moderate 83 of 366 days1992: Unhealthy for Sensitive Groups 20 of 366 days1993: Good 277 of 365 days1993: Moderate 73 of 365 days1993: Unhealthy for Sensitive Groups 15 of 365 days1994: Good 227 of 365 days1994: Moderate 94 of 365 days1994: Unhealthy for Sensitive Groups 42 of 365 days1994: Unhealthy 2 of 365 days1995: Good 269 of 365 days1995: Moderate 87 of 365 days1995: Unhealthy for Sensitive Groups 8 of 365 days1995: Unhealthy 1 of 365 days19951996: Good 269 of 366 days1996: Moderate 83 of 366 days1996: Unhealthy for Sensitive Groups 14 of 366 days1997: Good 322 of 365 days1997: Moderate 42 of 365 days1997: Unhealthy for Sensitive Groups 1 of 365 days1998: Good 280 of 365 days1998: Moderate 74 of 365 days1998: Unhealthy for Sensitive Groups 8 of 365 days1998: Unhealthy 3 of 365 days1999: Good 234 of 365 days1999: Moderate 101 of 365 days1999: Unhealthy for Sensitive Groups 23 of 365 days1999: Unhealthy 7 of 365 days2000: Good 216 of 361 days2000: Moderate 98 of 361 days2000: Unhealthy for Sensitive Groups 40 of 361 days2000: Unhealthy 7 of 361 days20002001: Good 122 of 365 days2001: Moderate 192 of 365 days2001: Unhealthy for Sensitive Groups 43 of 365 days2001: Unhealthy 8 of 365 days2002: Good 91 of 365 days2002: Moderate 187 of 365 days2002: Unhealthy for Sensitive Groups 71 of 365 days2002: Unhealthy 16 of 365 days2003: Good 90 of 365 days2003: Moderate 224 of 365 days2003: Unhealthy for Sensitive Groups 43 of 365 days2003: Unhealthy 8 of 365 days2004: Good 152 of 366 days2004: Moderate 172 of 366 days2004: Unhealthy for Sensitive Groups 39 of 366 days2004: Unhealthy 3 of 366 days2005: Good 191 of 365 days2005: Moderate 135 of 365 days2005: Unhealthy for Sensitive Groups 38 of 365 days2005: Unhealthy 1 of 365 days20052006: Good 129 of 365 days2006: Moderate 168 of 365 days2006: Unhealthy for Sensitive Groups 59 of 365 days2006: Unhealthy 9 of 365 days2007: Good 177 of 365 days2007: Moderate 148 of 365 days2007: Unhealthy for Sensitive Groups 38 of 365 days2007: Unhealthy 2 of 365 days2008: Good 145 of 366 days2008: Moderate 185 of 366 days2008: Unhealthy for Sensitive Groups 24 of 366 days2008: Unhealthy 9 of 366 days2008: Very Unhealthy 3 of 366 days2009: Good 151 of 365 days2009: Moderate 182 of 365 days2009: Unhealthy for Sensitive Groups 31 of 365 days2009: Unhealthy 1 of 365 days2010: Good 167 of 365 days2010: Moderate 185 of 365 days2010: Unhealthy for Sensitive Groups 13 of 365 days20102011: Good 86 of 365 days2011: Moderate 255 of 365 days2011: Unhealthy for Sensitive Groups 24 of 365 days2012: Good 116 of 366 days2012: Moderate 219 of 366 days2012: Unhealthy for Sensitive Groups 23 of 366 days2012: Unhealthy 8 of 366 days2013: Good 104 of 365 days2013: Moderate 252 of 365 days2013: Unhealthy for Sensitive Groups 8 of 365 days2013: Unhealthy 1 of 365 days2014: Good 127 of 365 days2014: Moderate 224 of 365 days2014: Unhealthy for Sensitive Groups 12 of 365 days2014: Unhealthy 2 of 365 days2015: Good 138 of 365 days2015: Moderate 214 of 365 days2015: Unhealthy for Sensitive Groups 12 of 365 days2015: Unhealthy 1 of 365 days20152016: Good 115 of 366 days2016: Moderate 235 of 366 days2016: Unhealthy for Sensitive Groups 16 of 366 days2017: Good 100 of 365 days2017: Moderate 241 of 365 days2017: Unhealthy for Sensitive Groups 23 of 365 days2017: Unhealthy 1 of 365 days2018: Good 97 of 365 days2018: Moderate 228 of 365 days2018: Unhealthy for Sensitive Groups 22 of 365 days2018: Unhealthy 10 of 365 days2018: Very Unhealthy 3 of 365 days2018: Hazardous 5 of 365 days2019: Good 171 of 365 days2019: Moderate 189 of 365 days2019: Unhealthy for Sensitive Groups 3 of 365 days2019: Unhealthy 2 of 365 days2020: Good 149 of 366 days2020: Moderate 178 of 366 days2020: Unhealthy for Sensitive Groups 18 of 366 days2020: Unhealthy 16 of 366 days2020: Very Unhealthy 3 of 366 days2020: Hazardous 2 of 366 days20202021: Good 160 of 365 days2021: Moderate 174 of 365 days2021: Unhealthy for Sensitive Groups 18 of 365 days2021: Unhealthy 10 of 365 days2021: Very Unhealthy 3 of 365 days2022: Good 191 of 365 days2022: Moderate 171 of 365 days2022: Unhealthy for Sensitive Groups 3 of 365 days2023: Good 191 of 365 days2023: Moderate 174 of 365 days2024: Good 231 of 366 days2024: Moderate 133 of 366 days2024: Unhealthy 1 of 366 days2024: Very Unhealthy 1 of 366 days2025: Good 238 of 365 days2025: Moderate 127 of 365 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 year0501001501980: 90th percentile AQI 681981: 90th percentile AQI 671982: 90th percentile AQI 671983: 90th percentile AQI 571984: 90th percentile AQI 611985: 90th percentile AQI 871986: 90th percentile AQI 961987: 90th percentile AQI 931988: 90th percentile AQI 911989: 90th percentile AQI 871990: 90th percentile AQI 771991: 90th percentile AQI 741992: 90th percentile AQI 871993: 90th percentile AQI 711994: 90th percentile AQI 1011995: 90th percentile AQI 771996: 90th percentile AQI 841997: 90th percentile AQI 511998: 90th percentile AQI 801999: 90th percentile AQI 972000: 90th percentile AQI 1082001: 90th percentile AQI 1112002: 90th percentile AQI 1332003: 90th percentile AQI 1082004: 90th percentile AQI 1052005: 90th percentile AQI 1052006: 90th percentile AQI 1222007: 90th percentile AQI 1012008: 90th percentile AQI 1002009: 90th percentile AQI 1002010: 90th percentile AQI 842011: 90th percentile AQI 902012: 90th percentile AQI 972013: 90th percentile AQI 902014: 90th percentile AQI 842015: 90th percentile AQI 842016: 90th percentile AQI 872017: 90th percentile AQI 952018: 90th percentile AQI 1042019: 90th percentile AQI 712020: 90th percentile AQI 1102021: 90th percentile AQI 902022: 90th percentile AQI 772023: 90th percentile AQI 712024: 90th percentile AQI 712025: 90th percentile AQI 611980: Median AQI 381981: Median AQI 331982: Median AQI 381983: Median AQI 341984: Median AQI 381985: Median AQI 421986: Median AQI 411987: Median AQI 471988: Median AQI 441989: Median AQI 441990: Median AQI 401991: Median AQI 441992: Median AQI 381993: Median AQI 381994: Median AQI 451995: Median AQI 391996: Median AQI 381997: Median AQI 341998: Median AQI 361999: Median AQI 442000: Median AQI 452001: Median AQI 612002: Median AQI 672003: Median AQI 612004: Median AQI 552005: Median AQI 492006: Median AQI 602007: Median AQI 522008: Median AQI 552009: Median AQI 552010: Median AQI 532011: Median AQI 602012: Median AQI 572013: Median AQI 592014: Median AQI 572015: Median AQI 552016: Median AQI 572017: Median AQI 592018: Median AQI 592019: Median AQI 512020: Median AQI 542021: Median AQI 532022: Median AQI 502023: Median AQI 502024: Median AQI 462025: Median AQI 461980198519901995200020052010201520202025
  • 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
Fine particles (PM2.5)19253%
Ozone17347%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20253652381270000466196PM2.5
202436623113301104671213Ozone
202336519117400005071100Ozone
202236519117130005077119Ozone
20213651601741810305390257PM2.5
202036614917818163254110508PM2.5
201936517118932005171180PM2.5
20183659722822103559104682PM2.5
2017365100241231005995155PM2.5
2016366115235160005787127PM2.5
2015365138214121005584153Ozone
2014365127224122005784156PM2.5
201336510425281005990169PM2.5
2012366116219238005797199Ozone
201136586255240006090149PM2.5
2010365167185130005384126Ozone
20093651511823110055100156Ozone
20083661451852493055100237Ozone
20073651771483820052101174Ozone
20063651291685990060122172Ozone
20053651911353810049105162Ozone
20043661521723930055105172Ozone
2003365902244380061108164PM2.5
20023659118771160067133190Ozone
20013651221924380061111159Ozone
2000361216984070045108181Ozone
1999365234101237004497187Ozone
19983652807483003680161Ozone
19973653224210003451105Ozone
199636626983140003884147Ozone
19953652698781003977151Ozone
1994365227944220045101164Ozone
199336527773150003871143Ozone
199236626383200003887122Ozone
199136523911790004474150Ozone
199036525196171004077174Ozone
1989365215131181004487154Ozone
1988366235103253004491166Ozone
1987365204130283004793156Ozone
1986365230104301004196154Ozone
198536524597203004287169Ozone
19843662887260003861125Ozone
19833653154910003457103NO2
19823652857370003867150Ozone
19813652937110003367126Ozone
19803532816840003868126Ozone

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 California with a similar median AQI in 2025

All monitored counties in California

Source: U.S. EPA AirData, “Annual AQI by County” files for 1980–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem