EnviroNearby

Colusa County, California air quality history

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

79%
Good days in 2025
40
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 Colusa, California on 365 days. 289 of those days (79%) were in the Good range, and the median daily AQI was 40. That median is lower than the typical monitored county in California (median 45.5 across 46 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was ozone on 180 days. Across the years with fuller monitoring, the share of Good days fell: an average of 67% in 1981–1983 versus 43% in 2023–2025.

Years with fewer than 120 monitored days (1980, 1988, 1989, 1990) 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%1980: Good 30 of 31 days1980: Moderate 1 of 31 days19801981: Good 228 of 320 days1981: Moderate 55 of 320 days1981: Unhealthy for Sensitive Groups 37 of 320 days1982: Good 101 of 153 days1982: Moderate 42 of 153 days1982: Unhealthy for Sensitive Groups 9 of 153 days1982: Unhealthy 1 of 153 days1983: Good 116 of 182 days1983: Moderate 54 of 182 days1983: Unhealthy for Sensitive Groups 11 of 182 days1983: Unhealthy 1 of 182 days1984: Good 56 of 142 days1984: Moderate 52 of 142 days1984: Unhealthy for Sensitive Groups 29 of 142 days1984: Unhealthy 5 of 142 days1985: Good 129 of 214 days1985: Moderate 64 of 214 days1985: Unhealthy for Sensitive Groups 18 of 214 days1985: Unhealthy 3 of 214 days19851986: Good 107 of 208 days1986: Moderate 64 of 208 days1986: Unhealthy for Sensitive Groups 33 of 208 days1986: Unhealthy 4 of 208 days1987: Good 82 of 236 days1987: Moderate 86 of 236 days1987: Unhealthy for Sensitive Groups 52 of 236 days1987: Unhealthy 16 of 236 days1988: Good 45 of 55 days1988: Moderate 10 of 55 days1989: Good 56 of 60 days1989: Moderate 4 of 60 days1990: Good 66 of 73 days1990: Moderate 7 of 73 days19901991: Good 102 of 126 days1991: Moderate 19 of 126 days1991: Unhealthy for Sensitive Groups 5 of 126 days1992: Good 252 of 360 days1992: Moderate 74 of 360 days1992: Unhealthy for Sensitive Groups 33 of 360 days1992: Unhealthy 1 of 360 days1993: Good 286 of 357 days1993: Moderate 57 of 357 days1993: Unhealthy for Sensitive Groups 14 of 357 days1994: Good 234 of 365 days1994: Moderate 97 of 365 days1994: Unhealthy for Sensitive Groups 32 of 365 days1994: Unhealthy 2 of 365 days1995: Good 248 of 362 days1995: Moderate 91 of 362 days1995: Unhealthy for Sensitive Groups 21 of 362 days1995: Unhealthy 2 of 362 days19951996: Good 259 of 366 days1996: Moderate 78 of 366 days1996: Unhealthy for Sensitive Groups 25 of 366 days1996: Unhealthy 4 of 366 days1997: Good 287 of 365 days1997: Moderate 66 of 365 days1997: Unhealthy for Sensitive Groups 12 of 365 days1998: Good 292 of 365 days1998: Moderate 60 of 365 days1998: Unhealthy for Sensitive Groups 12 of 365 days1998: Unhealthy 1 of 365 days1999: Good 229 of 365 days1999: Moderate 116 of 365 days1999: Unhealthy for Sensitive Groups 20 of 365 days2000: Good 296 of 365 days2000: Moderate 64 of 365 days2000: Unhealthy for Sensitive Groups 5 of 365 days20002001: Good 226 of 363 days2001: Moderate 114 of 363 days2001: Unhealthy for Sensitive Groups 21 of 363 days2001: Unhealthy 2 of 363 days2002: Good 257 of 365 days2002: Moderate 95 of 365 days2002: Unhealthy for Sensitive Groups 12 of 365 days2002: Unhealthy 1 of 365 days2003: Good 279 of 365 days2003: Moderate 85 of 365 days2003: Unhealthy for Sensitive Groups 1 of 365 days2004: Good 265 of 365 days2004: Moderate 92 of 365 days2004: Unhealthy for Sensitive Groups 8 of 365 days2005: Good 165 of 365 days2005: Moderate 196 of 365 days2005: Unhealthy for Sensitive Groups 4 of 365 days20052006: Good 185 of 365 days2006: Moderate 177 of 365 days2006: Unhealthy for Sensitive Groups 2 of 365 days2006: Unhealthy 1 of 365 days2007: Good 227 of 365 days2007: Moderate 130 of 365 days2007: Unhealthy for Sensitive Groups 7 of 365 days2007: Unhealthy 1 of 365 days2008: Good 168 of 366 days2008: Moderate 180 of 366 days2008: Unhealthy for Sensitive Groups 11 of 366 days2008: Unhealthy 6 of 366 days2008: Very Unhealthy 1 of 366 days2009: Good 181 of 365 days2009: Moderate 184 of 365 days2010: Good 307 of 353 days2010: Moderate 45 of 353 days2010: Unhealthy for Sensitive Groups 1 of 353 days20102011: Good 199 of 365 days2011: Moderate 164 of 365 days2011: Unhealthy for Sensitive Groups 2 of 365 days2012: Good 130 of 366 days2012: Moderate 229 of 366 days2012: Unhealthy for Sensitive Groups 3 of 366 days2012: Unhealthy 2 of 366 days2012: Very Unhealthy 2 of 366 days2013: Good 176 of 364 days2013: Moderate 186 of 364 days2013: Unhealthy for Sensitive Groups 2 of 364 days2014: Good 163 of 365 days2014: Moderate 202 of 365 days2015: Good 141 of 365 days2015: Moderate 218 of 365 days2015: Unhealthy for Sensitive Groups 4 of 365 days2015: Unhealthy 1 of 365 days2015: Very Unhealthy 1 of 365 days20152016: Good 222 of 366 days2016: Moderate 144 of 366 days2017: Good 237 of 365 days2017: Moderate 120 of 365 days2017: Unhealthy for Sensitive Groups 7 of 365 days2017: Very Unhealthy 1 of 365 days2018: Good 206 of 365 days2018: Moderate 131 of 365 days2018: Unhealthy for Sensitive Groups 10 of 365 days2018: Unhealthy 17 of 365 days2018: Very Unhealthy 1 of 365 days2019: Good 260 of 365 days2019: Moderate 105 of 365 days2020: Good 218 of 366 days2020: Moderate 116 of 366 days2020: Unhealthy for Sensitive Groups 9 of 366 days2020: Unhealthy 22 of 366 days2020: Very Unhealthy 1 of 366 days20202021: Good 111 of 365 days2021: Moderate 238 of 365 days2021: Unhealthy for Sensitive Groups 9 of 365 days2021: Unhealthy 6 of 365 days2021: Very Unhealthy 1 of 365 days2022: Good 240 of 363 days2022: Moderate 122 of 363 days2022: Unhealthy for Sensitive Groups 1 of 363 days2023: Good 115 of 365 days2023: Moderate 250 of 365 days2024: Good 68 of 366 days2024: Moderate 298 of 366 days2025: Good 289 of 365 days2025: Moderate 76 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 281981: 90th percentile AQI 1011982: 90th percentile AQI 901983: 90th percentile AQI 901984: 90th percentile AQI 1221985: 90th percentile AQI 1001986: 90th percentile AQI 1221987: 90th percentile AQI 1431988: 90th percentile AQI 571989: 90th percentile AQI 471990: 90th percentile AQI 491991: 90th percentile AQI 611992: 90th percentile AQI 931993: 90th percentile AQI 671994: 90th percentile AQI 1001995: 90th percentile AQI 841996: 90th percentile AQI 971997: 90th percentile AQI 711998: 90th percentile AQI 771999: 90th percentile AQI 872000: 90th percentile AQI 642001: 90th percentile AQI 872002: 90th percentile AQI 792003: 90th percentile AQI 642004: 90th percentile AQI 712005: 90th percentile AQI 732006: 90th percentile AQI 742007: 90th percentile AQI 702008: 90th percentile AQI 842009: 90th percentile AQI 692010: 90th percentile AQI 542011: 90th percentile AQI 662012: 90th percentile AQI 742013: 90th percentile AQI 672014: 90th percentile AQI 672015: 90th percentile AQI 732016: 90th percentile AQI 642017: 90th percentile AQI 672018: 90th percentile AQI 842019: 90th percentile AQI 612020: 90th percentile AQI 872021: 90th percentile AQI 762022: 90th percentile AQI 592023: 90th percentile AQI 662024: 90th percentile AQI 632025: 90th percentile AQI 561980: Median AQI 161981: Median AQI 351982: Median AQI 431983: Median AQI 441984: Median AQI 671985: Median AQI 441986: Median AQI 491987: Median AQI 671988: Median AQI 251989: Median AQI 281990: Median AQI 311991: Median AQI 351992: Median AQI 371993: Median AQI 371994: Median AQI 431995: Median AQI 401996: Median AQI 381997: Median AQI 391998: Median AQI 381999: Median AQI 442000: Median AQI 372001: Median AQI 442002: Median AQI 422003: Median AQI 392004: Median AQI 412005: Median AQI 522006: Median AQI 502007: Median AQI 442008: Median AQI 522009: Median AQI 512010: Median AQI 392011: Median AQI 462012: Median AQI 562013: Median AQI 512014: Median AQI 522015: Median AQI 532016: Median AQI 452017: Median AQI 432018: Median AQI 462019: Median AQI 412020: Median AQI 422021: Median AQI 552022: Median AQI 442023: Median AQI 552024: Median AQI 542025: Median AQI 401980198519901995200020052010201520202025
  • 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
Ozone18049%
Fine particles (PM2.5)17648%
Coarse particles (PM10)92%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
2025365289760000405696Ozone
2024366682980000546390PM2.5
20233651152500000556698PM2.5
202236324012210004459105Ozone
202136511123896105576225PM2.5
2020366218116922104287221PM2.5
20193652601050000416185PM2.5
20183652061311017104684299PM2.5
201736523712070104367213PM2.5
20163662221440000456492Ozone
201536514121841105373208PM2.5
20143651632020000526799PM2.5
201336417618620005167126PM2.5
201236613022932205674227PM2.5
201136519916420004666105PM2.5
20103533074510003954119Ozone
20093651811840000516997PM2.5
2008366168180116105284245PM2.5
200736522713071004470153Ozone
200636518517721005074155PM2.5
200536516519640005273130PM2.5
20043652659280004171123Ozone
20033652798510003964101Ozone
200236525795121004279152Ozone
2001363226114212004487156Ozone
20003652966450003764105Ozone
1999365229116200004487150Ozone
199836529260121003877156Ozone
199736528766120003971136Ozone
199636625978254003897164Ozone
199536224891212004084161Ozone
1994365234973220043100161Ozone
199335728657140003767150Ozone
199236025274331003793166Ozone
19911261021950003561147Ozone
1990736670000314970PM10
1989605640000284759PM10
19885545100000255772PM10
1987236828652160067143192Ozone
1986208107643340049122156Ozone
1985214129641830044100164Ozone
198414256522950067122169Ozone
198318211654111004490151Ozone
19821531014291004390164Ozone
1981320228553700035101150Ozone
1980313010000162867Ozone

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