EnviroNearby

Mendocino County, California air quality history

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

74%
Good days in 2025
38
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 Mendocino, California on 365 days. 269 of those days (74%) were in the Good range, and the median daily AQI was 38. 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 fine particles (PM2.5) on 217 days. Across the years with fuller monitoring, the share of Good days fell: an average of 98% in 1980–1982 versus 60% in 2023–2025.

Years with fewer than 120 monitored days (1989, 1990, 1991, 1992) 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 347 of 353 days1980: Moderate 6 of 353 days19801981: Good 351 of 359 days1981: Moderate 8 of 359 days1982: Good 323 of 326 days1982: Moderate 3 of 326 days1983: Good 336 of 337 days1983: Moderate 1 of 337 days1984: Good 275 of 278 days1984: Moderate 3 of 278 days1985: Good 155 of 156 days1985: Moderate 1 of 156 days19851986: Good 169 of 179 days1986: Moderate 10 of 179 days1987: Good 159 of 187 days1987: Moderate 26 of 187 days1987: Unhealthy for Sensitive Groups 2 of 187 days1988: Good 118 of 135 days1988: Moderate 14 of 135 days1988: Unhealthy for Sensitive Groups 3 of 135 days1989: Good 59 of 65 days1989: Moderate 6 of 65 days1990: Good 65 of 69 days1990: Moderate 4 of 69 days19901991: Good 69 of 73 days1991: Moderate 4 of 73 days1992: Good 118 of 118 days1993: Good 360 of 365 days1993: Moderate 5 of 365 days1994: Good 347 of 365 days1994: Moderate 18 of 365 days1995: Good 359 of 365 days1995: Moderate 6 of 365 days19951996: Good 236 of 237 days1996: Moderate 1 of 237 days1997: Good 359 of 365 days1997: Moderate 6 of 365 days1998: Good 357 of 365 days1998: Moderate 7 of 365 days1998: Unhealthy for Sensitive Groups 1 of 365 days1999: Good 328 of 365 days1999: Moderate 36 of 365 days1999: Unhealthy for Sensitive Groups 1 of 365 days2000: Good 351 of 366 days2000: Moderate 15 of 366 days20002001: Good 347 of 365 days2001: Moderate 17 of 365 days2001: Unhealthy for Sensitive Groups 1 of 365 days2002: Good 328 of 365 days2002: Moderate 33 of 365 days2002: Unhealthy for Sensitive Groups 3 of 365 days2002: Unhealthy 1 of 365 days2003: Good 334 of 365 days2003: Moderate 31 of 365 days2004: Good 351 of 366 days2004: Moderate 15 of 366 days2005: Good 350 of 365 days2005: Moderate 15 of 365 days20052006: Good 333 of 365 days2006: Moderate 32 of 365 days2007: Good 356 of 365 days2007: Moderate 9 of 365 days2008: Good 340 of 365 days2008: Moderate 22 of 365 days2008: Unhealthy for Sensitive Groups 3 of 365 days2009: Good 107 of 365 days2009: Moderate 257 of 365 days2009: Unhealthy for Sensitive Groups 1 of 365 days2010: Good 250 of 361 days2010: Moderate 111 of 361 days20102011: Good 157 of 361 days2011: Moderate 204 of 361 days2012: Good 277 of 357 days2012: Moderate 80 of 357 days2013: Good 245 of 331 days2013: Moderate 86 of 331 days2014: Good 224 of 365 days2014: Moderate 141 of 365 days2015: Good 213 of 365 days2015: Moderate 148 of 365 days2015: Unhealthy for Sensitive Groups 2 of 365 days2015: Unhealthy 2 of 365 days20152016: Good 287 of 364 days2016: Moderate 77 of 364 days2017: Good 226 of 365 days2017: Moderate 131 of 365 days2017: Unhealthy for Sensitive Groups 7 of 365 days2017: Very Unhealthy 1 of 365 days2018: Good 217 of 364 days2018: Moderate 126 of 364 days2018: Unhealthy for Sensitive Groups 13 of 364 days2018: Unhealthy 6 of 364 days2018: Very Unhealthy 1 of 364 days2018: Hazardous 1 of 364 days2019: Good 290 of 361 days2019: Moderate 71 of 361 days2020: Good 240 of 366 days2020: Moderate 103 of 366 days2020: Unhealthy for Sensitive Groups 10 of 366 days2020: Unhealthy 10 of 366 days2020: Hazardous 3 of 366 days20202021: Good 210 of 365 days2021: Moderate 147 of 365 days2021: Unhealthy for Sensitive Groups 6 of 365 days2021: Unhealthy 2 of 365 days2022: Good 129 of 365 days2022: Moderate 234 of 365 days2022: Unhealthy for Sensitive Groups 2 of 365 days2023: Good 144 of 365 days2023: Moderate 216 of 365 days2023: Unhealthy for Sensitive Groups 5 of 365 days2024: Good 244 of 366 days2024: Moderate 122 of 366 days2025: Good 269 of 365 days2025: Moderate 96 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 year0501001980: 90th percentile AQI 421981: 90th percentile AQI 371982: 90th percentile AQI 381983: 90th percentile AQI 321984: 90th percentile AQI 371985: 90th percentile AQI 421986: 90th percentile AQI 441987: 90th percentile AQI 581988: 90th percentile AQI 511989: 90th percentile AQI 491990: 90th percentile AQI 391991: 90th percentile AQI 401992: 90th percentile AQI 351993: 90th percentile AQI 391994: 90th percentile AQI 451995: 90th percentile AQI 421996: 90th percentile AQI 361997: 90th percentile AQI 391998: 90th percentile AQI 421999: 90th percentile AQI 512000: 90th percentile AQI 412001: 90th percentile AQI 442002: 90th percentile AQI 512003: 90th percentile AQI 492004: 90th percentile AQI 442005: 90th percentile AQI 432006: 90th percentile AQI 502007: 90th percentile AQI 432008: 90th percentile AQI 442009: 90th percentile AQI 722010: 90th percentile AQI 582011: 90th percentile AQI 612012: 90th percentile AQI 572013: 90th percentile AQI 642014: 90th percentile AQI 622015: 90th percentile AQI 612016: 90th percentile AQI 542017: 90th percentile AQI 702018: 90th percentile AQI 692019: 90th percentile AQI 542020: 90th percentile AQI 792021: 90th percentile AQI 692022: 90th percentile AQI 692023: 90th percentile AQI 692024: 90th percentile AQI 572025: 90th percentile AQI 591980: Median AQI 281981: Median AQI 191982: Median AQI 281983: Median AQI 191984: Median AQI 251985: Median AQI 291986: Median AQI 321987: Median AQI 331988: Median AQI 311989: Median AQI 261990: Median AQI 191991: Median AQI 221992: Median AQI 211993: Median AQI 281994: Median AQI 311995: Median AQI 311996: Median AQI 281997: Median AQI 291998: Median AQI 311999: Median AQI 332000: Median AQI 302001: Median AQI 312002: Median AQI 322003: Median AQI 332004: Median AQI 322005: Median AQI 322006: Median AQI 342007: Median AQI 312008: Median AQI 312009: Median AQI 582010: Median AQI 422011: Median AQI 522012: Median AQI 382013: Median AQI 292014: Median AQI 442015: Median AQI 462016: Median AQI 392017: Median AQI 452018: Median AQI 462019: Median AQI 362020: Median AQI 402021: Median AQI 462022: Median AQI 542023: Median AQI 532024: Median AQI 432025: Median AQI 381980198519901995200020052010201520202025
  • 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)21759%
Ozone14740%
Coarse particles (PM10)1<1%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
2025365269960000385981PM2.5
20243662441220000435783PM2.5
202336514421650005369140PM2.5
202236512923420005469103PM2.5
202136521014762004669185PM2.5
20203662401031010034079716PM2.5
2019361290710000365480PM2.5
2018364217126136114669376PM2.5
201736522613170104570203PM2.5
2016364287770000395470PM2.5
201536521314822004661164PM2.5
20143652241410000446296PM2.5
2013331245860000296482PM10
2012357277800000385780PM2.5
20113611572040000526182PM2.5
20103612501110000425875PM2.5
200936510725710005872138PM2.5
20083653402230003144134Ozone
200736535690000314390Ozone
2006365333320000345097Ozone
2005365350150000324373Ozone
2004366351150000324469Ozone
2003365334310000334987Ozone
20023653283331003251154Ozone
20013653471710003144108Ozone
2000366351150000304176Ozone
19993653283610003351101Ozone
1998365357710003142101Ozone
199736535960000293971Ozone
199623723610000283651Ozone
199536535960000314284Ozone
1994365347180000314578Ozone
199336536050000283984Ozone
199211811800000213547PM10
1991736940000224060PM10
1990696540000193953PM10
1989655960000264964PM10
19881351181430003151119Ozone
19871871592620003358119Ozone
1986179169100000324482Ozone
198515615510000294254Ozone
198427827530000253774Ozone
198333733610000193258Ozone
198232632330000283884Ozone
198135935180000193774Ozone
198035334760000284267Ozone

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