EnviroNearby

Stanislaus County, California air quality history

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

50%
Good days in 2025
51
Median daily AQI, 2025
3
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 Stanislaus, California on 365 days. 182 of those days (50%) were in the Good range, and the median daily AQI was 51. That median is higher than 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 ozone on 229 days. Across the years with fuller monitoring, the share of Good days fell: an average of 53% in 1980–1982 versus 47% 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 184 of 364 days1980: Moderate 133 of 364 days1980: Unhealthy for Sensitive Groups 40 of 364 days1980: Unhealthy 6 of 364 days1980: Very Unhealthy 1 of 364 days19801981: Good 178 of 365 days1981: Moderate 121 of 365 days1981: Unhealthy for Sensitive Groups 41 of 365 days1981: Unhealthy 20 of 365 days1981: Very Unhealthy 5 of 365 days1982: Good 216 of 365 days1982: Moderate 100 of 365 days1982: Unhealthy for Sensitive Groups 40 of 365 days1982: Unhealthy 9 of 365 days1983: Good 225 of 365 days1983: Moderate 81 of 365 days1983: Unhealthy for Sensitive Groups 29 of 365 days1983: Unhealthy 26 of 365 days1983: Very Unhealthy 4 of 365 days1984: Good 204 of 361 days1984: Moderate 82 of 361 days1984: Unhealthy for Sensitive Groups 30 of 361 days1984: Unhealthy 33 of 361 days1984: Very Unhealthy 12 of 361 days1985: Good 188 of 365 days1985: Moderate 87 of 365 days1985: Unhealthy for Sensitive Groups 50 of 365 days1985: Unhealthy 30 of 365 days1985: Very Unhealthy 10 of 365 days19851986: Good 195 of 365 days1986: Moderate 107 of 365 days1986: Unhealthy for Sensitive Groups 45 of 365 days1986: Unhealthy 18 of 365 days1987: Good 153 of 365 days1987: Moderate 110 of 365 days1987: Unhealthy for Sensitive Groups 39 of 365 days1987: Unhealthy 53 of 365 days1987: Very Unhealthy 10 of 365 days1988: Good 153 of 366 days1988: Moderate 116 of 366 days1988: Unhealthy for Sensitive Groups 54 of 366 days1988: Unhealthy 40 of 366 days1988: Very Unhealthy 3 of 366 days1989: Good 145 of 365 days1989: Moderate 140 of 365 days1989: Unhealthy for Sensitive Groups 59 of 365 days1989: Unhealthy 20 of 365 days1989: Very Unhealthy 1 of 365 days1990: Good 164 of 365 days1990: Moderate 135 of 365 days1990: Unhealthy for Sensitive Groups 50 of 365 days1990: Unhealthy 13 of 365 days1990: Very Unhealthy 3 of 365 days19901991: Good 179 of 365 days1991: Moderate 132 of 365 days1991: Unhealthy for Sensitive Groups 41 of 365 days1991: Unhealthy 13 of 365 days1992: Good 199 of 366 days1992: Moderate 112 of 366 days1992: Unhealthy for Sensitive Groups 46 of 366 days1992: Unhealthy 9 of 366 days1993: Good 214 of 365 days1993: Moderate 113 of 365 days1993: Unhealthy for Sensitive Groups 27 of 365 days1993: Unhealthy 9 of 365 days1993: Very Unhealthy 2 of 365 days1994: Good 200 of 365 days1994: Moderate 117 of 365 days1994: Unhealthy for Sensitive Groups 38 of 365 days1994: Unhealthy 10 of 365 days1995: Good 209 of 365 days1995: Moderate 107 of 365 days1995: Unhealthy for Sensitive Groups 28 of 365 days1995: Unhealthy 18 of 365 days1995: Very Unhealthy 3 of 365 days19951996: Good 209 of 366 days1996: Moderate 91 of 366 days1996: Unhealthy for Sensitive Groups 47 of 366 days1996: Unhealthy 17 of 366 days1996: Very Unhealthy 2 of 366 days1997: Good 228 of 365 days1997: Moderate 101 of 365 days1997: Unhealthy for Sensitive Groups 28 of 365 days1997: Unhealthy 8 of 365 days1998: Good 213 of 365 days1998: Moderate 90 of 365 days1998: Unhealthy for Sensitive Groups 32 of 365 days1998: Unhealthy 26 of 365 days1998: Very Unhealthy 4 of 365 days1999: Good 180 of 365 days1999: Moderate 131 of 365 days1999: Unhealthy for Sensitive Groups 30 of 365 days1999: Unhealthy 24 of 365 days2000: Good 184 of 366 days2000: Moderate 123 of 366 days2000: Unhealthy for Sensitive Groups 42 of 366 days2000: Unhealthy 16 of 366 days2000: Very Unhealthy 1 of 366 days20002001: Good 177 of 365 days2001: Moderate 141 of 365 days2001: Unhealthy for Sensitive Groups 31 of 365 days2001: Unhealthy 16 of 365 days2002: Good 168 of 365 days2002: Moderate 116 of 365 days2002: Unhealthy for Sensitive Groups 47 of 365 days2002: Unhealthy 33 of 365 days2002: Very Unhealthy 1 of 365 days2003: Good 182 of 365 days2003: Moderate 114 of 365 days2003: Unhealthy for Sensitive Groups 53 of 365 days2003: Unhealthy 16 of 365 days2004: Good 199 of 366 days2004: Moderate 132 of 366 days2004: Unhealthy for Sensitive Groups 31 of 366 days2004: Unhealthy 4 of 366 days2005: Good 231 of 365 days2005: Moderate 94 of 365 days2005: Unhealthy for Sensitive Groups 32 of 365 days2005: Unhealthy 8 of 365 days20052006: Good 211 of 365 days2006: Moderate 108 of 365 days2006: Unhealthy for Sensitive Groups 32 of 365 days2006: Unhealthy 14 of 365 days2007: Good 95 of 365 days2007: Moderate 218 of 365 days2007: Unhealthy for Sensitive Groups 37 of 365 days2007: Unhealthy 15 of 365 days2008: Good 73 of 366 days2008: Moderate 211 of 366 days2008: Unhealthy for Sensitive Groups 63 of 366 days2008: Unhealthy 15 of 366 days2008: Very Unhealthy 4 of 366 days2009: Good 100 of 365 days2009: Moderate 198 of 365 days2009: Unhealthy for Sensitive Groups 55 of 365 days2009: Unhealthy 12 of 365 days2010: Good 125 of 365 days2010: Moderate 202 of 365 days2010: Unhealthy for Sensitive Groups 32 of 365 days2010: Unhealthy 6 of 365 days20102011: Good 82 of 365 days2011: Moderate 212 of 365 days2011: Unhealthy for Sensitive Groups 57 of 365 days2011: Unhealthy 14 of 365 days2012: Good 95 of 366 days2012: Moderate 192 of 366 days2012: Unhealthy for Sensitive Groups 67 of 366 days2012: Unhealthy 11 of 366 days2012: Very Unhealthy 1 of 366 days2013: Good 117 of 365 days2013: Moderate 183 of 365 days2013: Unhealthy for Sensitive Groups 54 of 365 days2013: Unhealthy 11 of 365 days2014: Good 112 of 365 days2014: Moderate 194 of 365 days2014: Unhealthy for Sensitive Groups 53 of 365 days2014: Unhealthy 6 of 365 days2015: Good 92 of 365 days2015: Moderate 225 of 365 days2015: Unhealthy for Sensitive Groups 43 of 365 days2015: Unhealthy 5 of 365 days20152016: Good 102 of 366 days2016: Moderate 221 of 366 days2016: Unhealthy for Sensitive Groups 40 of 366 days2016: Unhealthy 3 of 366 days2017: Good 127 of 365 days2017: Moderate 175 of 365 days2017: Unhealthy for Sensitive Groups 55 of 365 days2017: Unhealthy 8 of 365 days2018: Good 109 of 365 days2018: Moderate 209 of 365 days2018: Unhealthy for Sensitive Groups 32 of 365 days2018: Unhealthy 11 of 365 days2018: Very Unhealthy 4 of 365 days2019: Good 168 of 365 days2019: Moderate 174 of 365 days2019: Unhealthy for Sensitive Groups 22 of 365 days2019: Unhealthy 1 of 365 days2020: Good 131 of 366 days2020: Moderate 198 of 366 days2020: Unhealthy for Sensitive Groups 21 of 366 days2020: Unhealthy 16 of 366 days20202021: Good 84 of 365 days2021: Moderate 234 of 365 days2021: Unhealthy for Sensitive Groups 42 of 365 days2021: Unhealthy 5 of 365 days2022: Good 108 of 365 days2022: Moderate 234 of 365 days2022: Unhealthy for Sensitive Groups 22 of 365 days2022: Unhealthy 1 of 365 days2023: Good 166 of 365 days2023: Moderate 176 of 365 days2023: Unhealthy for Sensitive Groups 23 of 365 days2024: Good 166 of 366 days2024: Moderate 162 of 366 days2024: Unhealthy for Sensitive Groups 38 of 366 days2025: Good 182 of 365 days2025: Moderate 180 of 365 days2025: Unhealthy for Sensitive Groups 3 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 year0501001502001980: 90th percentile AQI 1051981: 90th percentile AQI 1331982: 90th percentile AQI 1191983: 90th percentile AQI 1431984: 90th percentile AQI 1611985: 90th percentile AQI 1541986: 90th percentile AQI 1261987: 90th percentile AQI 1661988: 90th percentile AQI 1611989: 90th percentile AQI 1351990: 90th percentile AQI 1261991: 90th percentile AQI 1191992: 90th percentile AQI 1221993: 90th percentile AQI 1011994: 90th percentile AQI 1121995: 90th percentile AQI 1191996: 90th percentile AQI 1331997: 90th percentile AQI 1001998: 90th percentile AQI 1471999: 90th percentile AQI 1262000: 90th percentile AQI 1222001: 90th percentile AQI 1122002: 90th percentile AQI 1472003: 90th percentile AQI 1262004: 90th percentile AQI 1002005: 90th percentile AQI 1052006: 90th percentile AQI 1082007: 90th percentile AQI 1152008: 90th percentile AQI 1302009: 90th percentile AQI 1192010: 90th percentile AQI 1022011: 90th percentile AQI 1222012: 90th percentile AQI 1252013: 90th percentile AQI 1182014: 90th percentile AQI 1142015: 90th percentile AQI 1122016: 90th percentile AQI 1032017: 90th percentile AQI 1122018: 90th percentile AQI 1082019: 90th percentile AQI 922020: 90th percentile AQI 1022021: 90th percentile AQI 1052022: 90th percentile AQI 952023: 90th percentile AQI 932024: 90th percentile AQI 1012025: 90th percentile AQI 801980: Median AQI 481981: Median AQI 541982: Median AQI 471983: Median AQI 471984: Median AQI 471985: Median AQI 491986: Median AQI 471987: Median AQI 611988: Median AQI 581989: Median AQI 611990: Median AQI 571991: Median AQI 511992: Median AQI 471993: Median AQI 471994: Median AQI 471995: Median AQI 461996: Median AQI 461997: Median AQI 461998: Median AQI 461999: Median AQI 512000: Median AQI 502001: Median AQI 512002: Median AQI 552003: Median AQI 512004: Median AQI 482005: Median AQI 432006: Median AQI 452007: Median AQI 602008: Median AQI 672009: Median AQI 612010: Median AQI 582011: Median AQI 672012: Median AQI 642013: Median AQI 642014: Median AQI 602015: Median AQI 622016: Median AQI 592017: Median AQI 612018: Median AQI 592019: Median AQI 522020: Median AQI 602021: Median AQI 612022: Median AQI 572023: Median AQI 542024: Median AQI 532025: Median AQI 511980198519901995200020052010201520202025
  • 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
Ozone22963%
Fine particles (PM2.5)13236%
Coarse particles (PM10)41%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
202536518218030005180115Ozone
20243661661623800053101150Ozone
2023365166176230005493150Ozone
2022365108234221005795166PM2.5
2021365842344250061105172PM2.5
202036613119821160060102195PM2.5
2019365168174221005292177Ozone
201836510920932114059108265PM2.5
20173651271755580061112185Ozone
20163661022214030059103164PM2.5
2015365922254350062112187PM2.5
20143651121945360060114164Ozone
201336511718354110064118170Ozone
20123669519267111064125201PM2.5
20113658221257140067122169PM2.5
20103651252023260058102177PM2.5
200936510019855120061119192PM2.5
20083667321163154067130226PM2.5
20073659521837150060115187PM2.5
200636521110832140045108179Ozone
2005365231943280043105174Ozone
20043661991323140048100159Ozone
200336518211453160051126187Ozone
200236516811647331055147208Ozone
200136517714131160051112187Ozone
200036618412342161050122202Ozone
199936518013130240051126197Ozone
19983652139032264046147221Ozone
19973652281012880046100187Ozone
19963662099147172046133206Ozone
199536520910728183046119206Ozone
199436520011738100047112187Ozone
19933652141132792047101203Ozone
19923661991124690047122192Ozone
199136517913241130051119192Ozone
199036516413550133057126205Ozone
198936514514059201061135216Ozone
198836615311654403058161222Ozone
1987365153110395310061166223Ozone
198636519510745180047126192Ozone
198536518887503010049154218Ozone
198436120482303312047161233Ozone
19833652258129264047143203Ozone
19823652161004090047119187NO2
198136517812141205054133222NO2
19803641841334061048105202NO2

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