EnviroNearby

Yolo County, California air quality history

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

58%
Good days in 2025
47
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 Yolo, California on 365 days. 213 of those days (58%) were in the Good range, and the median daily AQI was 47. 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 205 days. Across the years with fuller monitoring, the share of Good days fell: an average of 76% in 1980–1982 versus 64% 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 250 of 336 days1980: Moderate 52 of 336 days1980: Unhealthy for Sensitive Groups 21 of 336 days1980: Unhealthy 12 of 336 days1980: Very Unhealthy 1 of 336 days19801981: Good 256 of 364 days1981: Moderate 59 of 364 days1981: Unhealthy for Sensitive Groups 33 of 364 days1981: Unhealthy 12 of 364 days1981: Very Unhealthy 4 of 364 days1982: Good 298 of 363 days1982: Moderate 54 of 363 days1982: Unhealthy for Sensitive Groups 10 of 363 days1982: Unhealthy 1 of 363 days1983: Good 295 of 359 days1983: Moderate 46 of 359 days1983: Unhealthy for Sensitive Groups 15 of 359 days1983: Unhealthy 3 of 359 days1984: Good 274 of 366 days1984: Moderate 61 of 366 days1984: Unhealthy for Sensitive Groups 21 of 366 days1984: Unhealthy 10 of 366 days1985: Good 281 of 365 days1985: Moderate 60 of 365 days1985: Unhealthy for Sensitive Groups 18 of 365 days1985: Unhealthy 6 of 365 days19851986: Good 273 of 365 days1986: Moderate 66 of 365 days1986: Unhealthy for Sensitive Groups 22 of 365 days1986: Unhealthy 4 of 365 days1987: Good 233 of 365 days1987: Moderate 75 of 365 days1987: Unhealthy for Sensitive Groups 47 of 365 days1987: Unhealthy 8 of 365 days1987: Very Unhealthy 2 of 365 days1988: Good 271 of 366 days1988: Moderate 66 of 366 days1988: Unhealthy for Sensitive Groups 22 of 366 days1988: Unhealthy 7 of 366 days1989: Good 269 of 335 days1989: Moderate 55 of 335 days1989: Unhealthy for Sensitive Groups 11 of 335 days1990: Good 276 of 365 days1990: Moderate 67 of 365 days1990: Unhealthy for Sensitive Groups 17 of 365 days1990: Unhealthy 5 of 365 days19901991: Good 157 of 225 days1991: Moderate 56 of 225 days1991: Unhealthy for Sensitive Groups 11 of 225 days1991: Unhealthy 1 of 225 days1992: Good 238 of 352 days1992: Moderate 84 of 352 days1992: Unhealthy for Sensitive Groups 24 of 352 days1992: Unhealthy 6 of 352 days1993: Good 297 of 364 days1993: Moderate 55 of 364 days1993: Unhealthy for Sensitive Groups 11 of 364 days1993: Unhealthy 1 of 364 days1994: Good 279 of 365 days1994: Moderate 74 of 365 days1994: Unhealthy for Sensitive Groups 12 of 365 days1995: Good 293 of 365 days1995: Moderate 58 of 365 days1995: Unhealthy for Sensitive Groups 10 of 365 days1995: Unhealthy 4 of 365 days19951996: Good 270 of 366 days1996: Moderate 62 of 366 days1996: Unhealthy for Sensitive Groups 30 of 366 days1996: Unhealthy 4 of 366 days1997: Good 317 of 365 days1997: Moderate 44 of 365 days1997: Unhealthy for Sensitive Groups 3 of 365 days1997: Unhealthy 1 of 365 days1998: Good 297 of 365 days1998: Moderate 42 of 365 days1998: Unhealthy for Sensitive Groups 21 of 365 days1998: Unhealthy 5 of 365 days1999: Good 245 of 365 days1999: Moderate 87 of 365 days1999: Unhealthy for Sensitive Groups 25 of 365 days1999: Unhealthy 8 of 365 days2000: Good 263 of 366 days2000: Moderate 81 of 366 days2000: Unhealthy for Sensitive Groups 20 of 366 days2000: Unhealthy 2 of 366 days20002001: Good 264 of 365 days2001: Moderate 85 of 365 days2001: Unhealthy for Sensitive Groups 14 of 365 days2001: Unhealthy 2 of 365 days2002: Good 253 of 365 days2002: Moderate 89 of 365 days2002: Unhealthy for Sensitive Groups 17 of 365 days2002: Unhealthy 6 of 365 days2003: Good 231 of 365 days2003: Moderate 111 of 365 days2003: Unhealthy for Sensitive Groups 23 of 365 days2004: Good 204 of 366 days2004: Moderate 148 of 366 days2004: Unhealthy for Sensitive Groups 14 of 366 days2005: Good 194 of 365 days2005: Moderate 156 of 365 days2005: Unhealthy for Sensitive Groups 13 of 365 days2005: Unhealthy 2 of 365 days20052006: Good 197 of 365 days2006: Moderate 138 of 365 days2006: Unhealthy for Sensitive Groups 25 of 365 days2006: Unhealthy 5 of 365 days2007: Good 224 of 365 days2007: Moderate 130 of 365 days2007: Unhealthy for Sensitive Groups 9 of 365 days2007: Unhealthy 2 of 365 days2008: Good 200 of 366 days2008: Moderate 145 of 366 days2008: Unhealthy for Sensitive Groups 14 of 366 days2008: Unhealthy 7 of 366 days2009: Good 205 of 365 days2009: Moderate 150 of 365 days2009: Unhealthy for Sensitive Groups 10 of 365 days2010: Good 273 of 362 days2010: Moderate 86 of 362 days2010: Unhealthy for Sensitive Groups 3 of 362 days20102011: Good 135 of 365 days2011: Moderate 221 of 365 days2011: Unhealthy for Sensitive Groups 9 of 365 days2012: Good 201 of 366 days2012: Moderate 157 of 366 days2012: Unhealthy for Sensitive Groups 8 of 366 days2013: Good 249 of 365 days2013: Moderate 116 of 365 days2014: Good 215 of 365 days2014: Moderate 149 of 365 days2014: Unhealthy for Sensitive Groups 1 of 365 days2015: Good 185 of 365 days2015: Moderate 176 of 365 days2015: Unhealthy for Sensitive Groups 4 of 365 days20152016: Good 246 of 366 days2016: Moderate 116 of 366 days2016: Unhealthy for Sensitive Groups 4 of 366 days2017: Good 228 of 365 days2017: Moderate 130 of 365 days2017: Unhealthy for Sensitive Groups 6 of 365 days2017: Unhealthy 1 of 365 days2018: Good 216 of 365 days2018: Moderate 135 of 365 days2018: Unhealthy for Sensitive Groups 5 of 365 days2018: Unhealthy 7 of 365 days2018: Very Unhealthy 2 of 365 days2019: Good 252 of 365 days2019: Moderate 112 of 365 days2019: Unhealthy for Sensitive Groups 1 of 365 days2020: Good 215 of 366 days2020: Moderate 123 of 366 days2020: Unhealthy for Sensitive Groups 14 of 366 days2020: Unhealthy 13 of 366 days2020: Very Unhealthy 1 of 366 days20202021: Good 242 of 365 days2021: Moderate 117 of 365 days2021: Unhealthy for Sensitive Groups 4 of 365 days2021: Unhealthy 2 of 365 days2022: Good 283 of 365 days2022: Moderate 80 of 365 days2022: Unhealthy for Sensitive Groups 2 of 365 days2023: Good 246 of 365 days2023: Moderate 117 of 365 days2023: Unhealthy for Sensitive Groups 2 of 365 days2024: Good 238 of 366 days2024: Moderate 127 of 366 days2024: Unhealthy for Sensitive Groups 1 of 366 days2025: Good 213 of 365 days2025: Moderate 152 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 1011981: 90th percentile AQI 1081982: 90th percentile AQI 671983: 90th percentile AQI 741984: 90th percentile AQI 1001985: 90th percentile AQI 841986: 90th percentile AQI 901987: 90th percentile AQI 1191988: 90th percentile AQI 901989: 90th percentile AQI 711990: 90th percentile AQI 841991: 90th percentile AQI 871992: 90th percentile AQI 931993: 90th percentile AQI 711994: 90th percentile AQI 801995: 90th percentile AQI 741996: 90th percentile AQI 1001997: 90th percentile AQI 541998: 90th percentile AQI 871999: 90th percentile AQI 972000: 90th percentile AQI 842001: 90th percentile AQI 792002: 90th percentile AQI 842003: 90th percentile AQI 862004: 90th percentile AQI 842005: 90th percentile AQI 802006: 90th percentile AQI 882007: 90th percentile AQI 752008: 90th percentile AQI 802009: 90th percentile AQI 802010: 90th percentile AQI 612011: 90th percentile AQI 772012: 90th percentile AQI 742013: 90th percentile AQI 652014: 90th percentile AQI 632015: 90th percentile AQI 772016: 90th percentile AQI 642017: 90th percentile AQI 712018: 90th percentile AQI 712019: 90th percentile AQI 632020: 90th percentile AQI 862021: 90th percentile AQI 682022: 90th percentile AQI 642023: 90th percentile AQI 652024: 90th percentile AQI 632025: 90th percentile AQI 631980: Median AQI 401981: Median AQI 371982: Median AQI 351983: Median AQI 331984: Median AQI 351985: Median AQI 371986: Median AQI 391987: Median AQI 431988: Median AQI 391989: Median AQI 371990: Median AQI 401991: Median AQI 391992: Median AQI 401993: Median AQI 381994: Median AQI 401995: Median AQI 371996: Median AQI 381997: Median AQI 371998: Median AQI 371999: Median AQI 442000: Median AQI 422001: Median AQI 412002: Median AQI 422003: Median AQI 442004: Median AQI 472005: Median AQI 482006: Median AQI 492007: Median AQI 452008: Median AQI 472009: Median AQI 462010: Median AQI 412011: Median AQI 562012: Median AQI 492013: Median AQI 422014: Median AQI 462015: Median AQI 502016: Median AQI 432017: Median AQI 452018: Median AQI 452019: Median AQI 432020: Median AQI 452021: Median AQI 422022: Median AQI 422023: Median AQI 432024: Median AQI 452025: Median AQI 471980198519901995200020052010201520202025
  • 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)20556%
Ozone16044%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
202536521315200004763100PM2.5
202436623812710004563118Ozone
202336524611720004365108Ozone
20223652838020004264101Ozone
202136524211742004268159Ozone
20203662151231413104586209PM2.5
201936525211210004363136Ozone
201836521613557204571260Ozone
201736522813061004571154Ozone
201636624611640004364115Ozone
201536518517640005077103PM2.5
201436521514910004663101PM2.5
20133652491160000426592Ozone
201236620115780004974133Ozone
201136513522190005677140PM2.5
20103622738630004161109Ozone
2009365205150100004680140Ozone
2008366200145147004780182Ozone
200736522413092004575164Ozone
2006365197138255004988172Ozone
2005365194156132004880154PM2.5
2004366204148140004784135Ozone
2003365231111230004486147Ozone
200236525389176004284164Ozone
200136526485142004179169Ozone
200036626381202004284159Ozone
199936524587258004497172Ozone
199836529742215003787192Ozone
19973653174431003754151Ozone
1996366270623040038100197Ozone
199536529358104003774164Ozone
199436527974120004080140Ozone
199336429755111003871179Ozone
199235223884246004093177Ozone
199122515756111003987164Ozone
199036527667175004084200Ozone
198933526955110003771143Ozone
198836627166227003990161Ozone
1987365233754782043119223Ozone
198636527366224003990187Ozone
198536528160186003784179Ozone
19843662746121100035100179Ozone
198335929546153003374169Ozone
198236329854101003567200Ozone
19813642565933124037108210Ozone
19803362505221121040101203Ozone

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