EnviroNearby

Santa Clara County, California air quality history

Daily Air Quality Index summaries from EPA monitors in Santa Clara, California, 1980–2024.

55%
Good days in 2024
47
Median daily AQI, 2024
1
Days above 100 in 2024
363
Days with an AQI in 2024 (of 366)

In 2024, EPA reported a daily Air Quality Index (AQI) for Santa Clara, California on 363 days. 201 of those days (55%) 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 46.5 across 52 counties), and higher than the typical monitored U.S. county (41). The main pollutant was fine particles (PM2.5) on 334 days. Across the years with fuller monitoring, the share of Good days fell: an average of 61% in 1980–1982 versus 58% in 2022–2024.

The most recent year with data for this county is 2024; EPA's files for 2025–2025 contain no row for it, which usually means its monitors stopped reporting.

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 215 of 366 days1980: Moderate 97 of 366 days1980: Unhealthy for Sensitive Groups 25 of 366 days1980: Unhealthy 17 of 366 days1980: Very Unhealthy 12 of 366 days19801981: Good 220 of 365 days1981: Moderate 102 of 365 days1981: Unhealthy for Sensitive Groups 26 of 365 days1981: Unhealthy 15 of 365 days1981: Very Unhealthy 2 of 365 days1982: Good 231 of 365 days1982: Moderate 94 of 365 days1982: Unhealthy for Sensitive Groups 34 of 365 days1982: Unhealthy 6 of 365 days1983: Good 230 of 365 days1983: Moderate 92 of 365 days1983: Unhealthy for Sensitive Groups 17 of 365 days1983: Unhealthy 16 of 365 days1983: Very Unhealthy 10 of 365 days1984: Good 215 of 366 days1984: Moderate 96 of 366 days1984: Unhealthy for Sensitive Groups 29 of 366 days1984: Unhealthy 20 of 366 days1984: Very Unhealthy 6 of 366 days1985: Good 214 of 365 days1985: Moderate 95 of 365 days1985: Unhealthy for Sensitive Groups 37 of 365 days1985: Unhealthy 15 of 365 days1985: Very Unhealthy 4 of 365 days19851986: Good 216 of 365 days1986: Moderate 114 of 365 days1986: Unhealthy for Sensitive Groups 25 of 365 days1986: Unhealthy 10 of 365 days1987: Good 222 of 365 days1987: Moderate 98 of 365 days1987: Unhealthy for Sensitive Groups 22 of 365 days1987: Unhealthy 19 of 365 days1987: Very Unhealthy 4 of 365 days1988: Good 213 of 366 days1988: Moderate 111 of 366 days1988: Unhealthy for Sensitive Groups 25 of 366 days1988: Unhealthy 17 of 366 days1989: Good 189 of 365 days1989: Moderate 129 of 365 days1989: Unhealthy for Sensitive Groups 40 of 365 days1989: Unhealthy 7 of 365 days1990: Good 224 of 365 days1990: Moderate 112 of 365 days1990: Unhealthy for Sensitive Groups 26 of 365 days1990: Unhealthy 3 of 365 days19901991: Good 214 of 365 days1991: Moderate 120 of 365 days1991: Unhealthy for Sensitive Groups 26 of 365 days1991: Unhealthy 4 of 365 days1991: Very Unhealthy 1 of 365 days1992: Good 225 of 366 days1992: Moderate 117 of 366 days1992: Unhealthy for Sensitive Groups 21 of 366 days1992: Unhealthy 3 of 366 days1993: Good 235 of 365 days1993: Moderate 106 of 365 days1993: Unhealthy for Sensitive Groups 20 of 365 days1993: Unhealthy 3 of 365 days1993: Very Unhealthy 1 of 365 days1994: Good 239 of 365 days1994: Moderate 113 of 365 days1994: Unhealthy for Sensitive Groups 11 of 365 days1994: Unhealthy 2 of 365 days1995: Good 244 of 365 days1995: Moderate 97 of 365 days1995: Unhealthy for Sensitive Groups 11 of 365 days1995: Unhealthy 12 of 365 days1995: Very Unhealthy 1 of 365 days19951996: Good 244 of 366 days1996: Moderate 92 of 366 days1996: Unhealthy for Sensitive Groups 22 of 366 days1996: Unhealthy 8 of 366 days1997: Good 287 of 365 days1997: Moderate 72 of 365 days1997: Unhealthy for Sensitive Groups 6 of 365 days1998: Good 279 of 365 days1998: Moderate 67 of 365 days1998: Unhealthy for Sensitive Groups 12 of 365 days1998: Unhealthy 5 of 365 days1998: Very Unhealthy 2 of 365 days1999: Good 208 of 364 days1999: Moderate 120 of 364 days1999: Unhealthy for Sensitive Groups 25 of 364 days1999: Unhealthy 11 of 364 days2000: Good 178 of 366 days2000: Moderate 154 of 366 days2000: Unhealthy for Sensitive Groups 26 of 366 days2000: Unhealthy 8 of 366 days20002001: Good 180 of 365 days2001: Moderate 158 of 365 days2001: Unhealthy for Sensitive Groups 15 of 365 days2001: Unhealthy 12 of 365 days2002: Good 169 of 365 days2002: Moderate 165 of 365 days2002: Unhealthy for Sensitive Groups 23 of 365 days2002: Unhealthy 8 of 365 days2003: Good 174 of 365 days2003: Moderate 168 of 365 days2003: Unhealthy for Sensitive Groups 17 of 365 days2003: Unhealthy 6 of 365 days2004: Good 162 of 366 days2004: Moderate 180 of 366 days2004: Unhealthy for Sensitive Groups 24 of 366 days2005: Good 168 of 365 days2005: Moderate 175 of 365 days2005: Unhealthy for Sensitive Groups 21 of 365 days2005: Unhealthy 1 of 365 days20052006: Good 151 of 365 days2006: Moderate 192 of 365 days2006: Unhealthy for Sensitive Groups 15 of 365 days2006: Unhealthy 7 of 365 days2007: Good 149 of 365 days2007: Moderate 203 of 365 days2007: Unhealthy for Sensitive Groups 12 of 365 days2007: Unhealthy 1 of 365 days2008: Good 120 of 366 days2008: Moderate 228 of 366 days2008: Unhealthy for Sensitive Groups 17 of 366 days2008: Unhealthy 1 of 366 days2009: Good 178 of 365 days2009: Moderate 177 of 365 days2009: Unhealthy for Sensitive Groups 10 of 365 days2010: Good 181 of 365 days2010: Moderate 172 of 365 days2010: Unhealthy for Sensitive Groups 10 of 365 days2010: Unhealthy 2 of 365 days20102011: Good 93 of 365 days2011: Moderate 266 of 365 days2011: Unhealthy for Sensitive Groups 6 of 365 days2012: Good 159 of 366 days2012: Moderate 201 of 366 days2012: Unhealthy for Sensitive Groups 6 of 366 days2013: Good 129 of 365 days2013: Moderate 228 of 365 days2013: Unhealthy for Sensitive Groups 7 of 365 days2013: Unhealthy 1 of 365 days2014: Good 216 of 365 days2014: Moderate 141 of 365 days2014: Unhealthy for Sensitive Groups 7 of 365 days2014: Unhealthy 1 of 365 days2015: Good 179 of 365 days2015: Moderate 179 of 365 days2015: Unhealthy for Sensitive Groups 7 of 365 days20152016: Good 187 of 366 days2016: Moderate 178 of 366 days2016: Unhealthy for Sensitive Groups 1 of 366 days2017: Good 174 of 365 days2017: Moderate 179 of 365 days2017: Unhealthy for Sensitive Groups 9 of 365 days2017: Unhealthy 3 of 365 days2018: Good 154 of 365 days2018: Moderate 194 of 365 days2018: Unhealthy for Sensitive Groups 6 of 365 days2018: Unhealthy 9 of 365 days2018: Very Unhealthy 2 of 365 days2019: Good 205 of 365 days2019: Moderate 156 of 365 days2019: Unhealthy for Sensitive Groups 4 of 365 days2020: Good 174 of 366 days2020: Moderate 172 of 366 days2020: Unhealthy for Sensitive Groups 11 of 366 days2020: Unhealthy 9 of 366 days20202021: Good 147 of 365 days2021: Moderate 211 of 365 days2021: Unhealthy for Sensitive Groups 7 of 365 days2022: Good 188 of 365 days2022: Moderate 172 of 365 days2022: Unhealthy for Sensitive Groups 5 of 365 days2023: Good 240 of 365 days2023: Moderate 121 of 365 days2023: Unhealthy for Sensitive Groups 4 of 365 days2024: Good 201 of 363 days2024: Moderate 161 of 363 days2024: Unhealthy for Sensitive Groups 1 of 363 days2024
  • 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 1331981: 90th percentile AQI 1081982: 90th percentile AQI 1011983: 90th percentile AQI 1191984: 90th percentile AQI 1331985: 90th percentile AQI 1221986: 90th percentile AQI 1001987: 90th percentile AQI 1221988: 90th percentile AQI 1081989: 90th percentile AQI 1051990: 90th percentile AQI 931991: 90th percentile AQI 1001992: 90th percentile AQI 901993: 90th percentile AQI 891994: 90th percentile AQI 791995: 90th percentile AQI 871996: 90th percentile AQI 971997: 90th percentile AQI 631998: 90th percentile AQI 801999: 90th percentile AQI 1002000: 90th percentile AQI 982001: 90th percentile AQI 902002: 90th percentile AQI 962003: 90th percentile AQI 902004: 90th percentile AQI 872005: 90th percentile AQI 892006: 90th percentile AQI 892007: 90th percentile AQI 812008: 90th percentile AQI 872009: 90th percentile AQI 782010: 90th percentile AQI 692011: 90th percentile AQI 752012: 90th percentile AQI 692013: 90th percentile AQI 802014: 90th percentile AQI 712015: 90th percentile AQI 712016: 90th percentile AQI 642017: 90th percentile AQI 752018: 90th percentile AQI 722019: 90th percentile AQI 682020: 90th percentile AQI 812021: 90th percentile AQI 722022: 90th percentile AQI 732023: 90th percentile AQI 632024: 90th percentile AQI 631980: Median AQI 431981: Median AQI 441982: Median AQI 441983: Median AQI 441984: Median AQI 451985: Median AQI 451986: Median AQI 461987: Median AQI 461988: Median AQI 461989: Median AQI 491990: Median AQI 471991: Median AQI 471992: Median AQI 471993: Median AQI 441994: Median AQI 441995: Median AQI 431996: Median AQI 431997: Median AQI 421998: Median AQI 421999: Median AQI 462000: Median AQI 512001: Median AQI 512002: Median AQI 522003: Median AQI 522004: Median AQI 532005: Median AQI 532006: Median AQI 542007: Median AQI 522008: Median AQI 562009: Median AQI 512010: Median AQI 512011: Median AQI 562012: Median AQI 522013: Median AQI 552014: Median AQI 462015: Median AQI 512016: Median AQI 502017: Median AQI 522018: Median AQI 532019: Median AQI 482020: Median AQI 522021: Median AQI 532022: Median AQI 492023: Median AQI 432024: Median AQI 471980198519901995200020052010201520202024
  • Median daily AQI
  • 90th-percentile daily AQI

Main pollutant by day, 2024

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)33492%
Ozone288%
Nitrogen dioxide (NO₂)1<1%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
202436320116110004763111PM2.5
202336524012140004363134Ozone
202236518817250004973119PM2.5
202136514721170005372147PM2.5
2020366174172119005281198PM2.5
201936520515640004868136PM2.5
201836515419469205372214PM2.5
201736517417993005275182PM2.5
201636618717810005064101PM2.5
201536517917970005171147PM2.5
201436521614171004671154PM2.5
201336512922871005580153PM2.5
201236615920160005269122PM2.5
20113659326660005675138PM2.5
2010365181172102005169164PM2.5
2009365178177100005178140PM2.5
2008366120228171005687179PM2.5
2007365149203121005281152PM2.5
2006365151192157005489200PM2.5
2005365168175211005389154PM2.5
2004366162180240005387147PM2.5
2003365174168176005290190PM2.5
2002365169165238005296185Ozone
20013651801581512005190177PM2.5
2000366178154268005198190PM2.5
199936420812025110046100192Ozone
199836527967125204280206Ozone
19973652877260004263147Ozone
199636624492228004397195Ozone
1995365244971112104387204Ozone
1994365239113112004479174NO2
1993365235106203104489207NO2
1992366225117213004790190Ozone
19913652141202641047100203NO2
1990365224112263004793177Ozone
19893651891294070049105192Ozone
198836621311125170046108190Ozone
19873652229822194046122203Ozone
198636521611425100046100200Ozone
19853652149537154045122223Ozone
19843662159629206045133220Ozone
198336523092171610044119247Ozone
1982365231943460044101187Ozone
198136522010226152044108219Ozone
198036621597251712043133247Ozone

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 2024

All monitored counties in California

Source: U.S. EPA AirData, “Annual AQI by County” files for 1980–2024 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem