EnviroNearby

Shasta County, California air quality history

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

76%
Good days in 2025
44
Median daily AQI, 2025
1
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 Shasta, California on 365 days. 276 of those days (76%) were in the Good range, and the median daily AQI was 44. 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 ozone on 285 days. Across the years with fuller monitoring, the share of Good days held roughly steady: an average of 73% in 1980–1982 versus 72% in 2023–2025.

Years with fewer than 120 monitored days (1983) 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 208 of 321 days1980: Moderate 51 of 321 days1980: Unhealthy for Sensitive Groups 44 of 321 days1980: Unhealthy 18 of 321 days19801981: Good 257 of 335 days1981: Moderate 35 of 335 days1981: Unhealthy for Sensitive Groups 24 of 335 days1981: Unhealthy 19 of 335 days1982: Good 250 of 327 days1982: Moderate 52 of 327 days1982: Unhealthy for Sensitive Groups 23 of 327 days1982: Unhealthy 2 of 327 days1983: Good 71 of 110 days1983: Moderate 25 of 110 days1983: Unhealthy for Sensitive Groups 10 of 110 days1983: Unhealthy 4 of 110 days1984: Good 219 of 269 days1984: Moderate 39 of 269 days1984: Unhealthy for Sensitive Groups 10 of 269 days1984: Unhealthy 1 of 269 days1985: Good 226 of 299 days1985: Moderate 46 of 299 days1985: Unhealthy for Sensitive Groups 18 of 299 days1985: Unhealthy 9 of 299 days19851986: Good 178 of 274 days1986: Moderate 55 of 274 days1986: Unhealthy for Sensitive Groups 36 of 274 days1986: Unhealthy 5 of 274 days1987: Good 234 of 363 days1987: Moderate 72 of 363 days1987: Unhealthy for Sensitive Groups 38 of 363 days1987: Unhealthy 18 of 363 days1987: Very Unhealthy 1 of 363 days1988: Good 269 of 353 days1988: Moderate 59 of 353 days1988: Unhealthy for Sensitive Groups 22 of 353 days1988: Unhealthy 3 of 353 days1989: Good 270 of 365 days1989: Moderate 76 of 365 days1989: Unhealthy for Sensitive Groups 19 of 365 days1990: Good 265 of 365 days1990: Moderate 70 of 365 days1990: Unhealthy for Sensitive Groups 18 of 365 days1990: Unhealthy 11 of 365 days1990: Very Unhealthy 1 of 365 days19901991: Good 254 of 365 days1991: Moderate 71 of 365 days1991: Unhealthy for Sensitive Groups 32 of 365 days1991: Unhealthy 8 of 365 days1992: Good 256 of 366 days1992: Moderate 79 of 366 days1992: Unhealthy for Sensitive Groups 23 of 366 days1992: Unhealthy 8 of 366 days1993: Good 301 of 365 days1993: Moderate 54 of 365 days1993: Unhealthy for Sensitive Groups 9 of 365 days1993: Unhealthy 1 of 365 days1994: Good 246 of 362 days1994: Moderate 76 of 362 days1994: Unhealthy for Sensitive Groups 33 of 362 days1994: Unhealthy 7 of 362 days1995: Good 257 of 339 days1995: Moderate 58 of 339 days1995: Unhealthy for Sensitive Groups 24 of 339 days19951996: Good 227 of 345 days1996: Moderate 78 of 345 days1996: Unhealthy for Sensitive Groups 28 of 345 days1996: Unhealthy 12 of 345 days1997: Good 265 of 360 days1997: Moderate 59 of 360 days1997: Unhealthy for Sensitive Groups 30 of 360 days1997: Unhealthy 5 of 360 days1997: Very Unhealthy 1 of 360 days1998: Good 209 of 365 days1998: Moderate 73 of 365 days1998: Unhealthy for Sensitive Groups 40 of 365 days1998: Unhealthy 40 of 365 days1998: Very Unhealthy 3 of 365 days1999: Good 189 of 364 days1999: Moderate 111 of 364 days1999: Unhealthy for Sensitive Groups 51 of 364 days1999: Unhealthy 13 of 364 days2000: Good 240 of 366 days2000: Moderate 100 of 366 days2000: Unhealthy for Sensitive Groups 25 of 366 days2000: Unhealthy 1 of 366 days20002001: Good 266 of 362 days2001: Moderate 78 of 362 days2001: Unhealthy for Sensitive Groups 18 of 362 days2002: Good 255 of 365 days2002: Moderate 84 of 365 days2002: Unhealthy for Sensitive Groups 26 of 365 days2003: Good 252 of 364 days2003: Moderate 87 of 364 days2003: Unhealthy for Sensitive Groups 18 of 364 days2003: Unhealthy 7 of 364 days2004: Good 248 of 366 days2004: Moderate 81 of 366 days2004: Unhealthy for Sensitive Groups 34 of 366 days2004: Unhealthy 3 of 366 days2005: Good 272 of 365 days2005: Moderate 75 of 365 days2005: Unhealthy for Sensitive Groups 15 of 365 days2005: Unhealthy 3 of 365 days20052006: Good 243 of 365 days2006: Moderate 99 of 365 days2006: Unhealthy for Sensitive Groups 22 of 365 days2006: Unhealthy 1 of 365 days2007: Good 258 of 365 days2007: Moderate 85 of 365 days2007: Unhealthy for Sensitive Groups 22 of 365 days2008: Good 244 of 366 days2008: Moderate 92 of 366 days2008: Unhealthy for Sensitive Groups 23 of 366 days2008: Unhealthy 6 of 366 days2008: Very Unhealthy 1 of 366 days2009: Good 272 of 365 days2009: Moderate 85 of 365 days2009: Unhealthy for Sensitive Groups 8 of 365 days2010: Good 269 of 365 days2010: Moderate 81 of 365 days2010: Unhealthy for Sensitive Groups 15 of 365 days20102011: Good 263 of 365 days2011: Moderate 96 of 365 days2011: Unhealthy for Sensitive Groups 5 of 365 days2011: Unhealthy 1 of 365 days2012: Good 256 of 366 days2012: Moderate 104 of 366 days2012: Unhealthy for Sensitive Groups 5 of 366 days2012: Unhealthy 1 of 366 days2013: Good 294 of 365 days2013: Moderate 69 of 365 days2013: Unhealthy for Sensitive Groups 2 of 365 days2014: Good 272 of 365 days2014: Moderate 87 of 365 days2014: Unhealthy for Sensitive Groups 6 of 365 days2015: Good 252 of 365 days2015: Moderate 100 of 365 days2015: Unhealthy for Sensitive Groups 12 of 365 days2015: Unhealthy 1 of 365 days20152016: Good 296 of 366 days2016: Moderate 56 of 366 days2016: Unhealthy for Sensitive Groups 14 of 366 days2017: Good 260 of 365 days2017: Moderate 91 of 365 days2017: Unhealthy for Sensitive Groups 12 of 365 days2017: Unhealthy 2 of 365 days2018: Good 272 of 365 days2018: Moderate 72 of 365 days2018: Unhealthy for Sensitive Groups 15 of 365 days2018: Unhealthy 5 of 365 days2018: Very Unhealthy 1 of 365 days2019: Good 306 of 364 days2019: Moderate 58 of 364 days2020: Good 286 of 366 days2020: Moderate 72 of 366 days2020: Unhealthy for Sensitive Groups 6 of 366 days2020: Unhealthy 2 of 366 days20202021: Good 222 of 365 days2021: Moderate 111 of 365 days2021: Unhealthy for Sensitive Groups 15 of 365 days2021: Unhealthy 12 of 365 days2021: Very Unhealthy 5 of 365 days2022: Good 253 of 365 days2022: Moderate 106 of 365 days2022: Unhealthy for Sensitive Groups 6 of 365 days2023: Good 247 of 365 days2023: Moderate 112 of 365 days2023: Unhealthy for Sensitive Groups 5 of 365 days2023: Hazardous 1 of 365 days2024: Good 268 of 366 days2024: Moderate 94 of 366 days2024: Unhealthy for Sensitive Groups 3 of 366 days2024: Very Unhealthy 1 of 366 days2025: Good 276 of 365 days2025: Moderate 88 of 365 days2025: Unhealthy 1 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 1331981: 90th percentile AQI 1191982: 90th percentile AQI 871983: 90th percentile AQI 1191984: 90th percentile AQI 671985: 90th percentile AQI 931986: 90th percentile AQI 1191987: 90th percentile AQI 1221988: 90th percentile AQI 931989: 90th percentile AQI 871990: 90th percentile AQI 871991: 90th percentile AQI 1051992: 90th percentile AQI 931993: 90th percentile AQI 691994: 90th percentile AQI 1051995: 90th percentile AQI 841996: 90th percentile AQI 1081997: 90th percentile AQI 1011998: 90th percentile AQI 1541999: 90th percentile AQI 1262000: 90th percentile AQI 932001: 90th percentile AQI 862002: 90th percentile AQI 872003: 90th percentile AQI 902004: 90th percentile AQI 1012005: 90th percentile AQI 842006: 90th percentile AQI 902007: 90th percentile AQI 902008: 90th percentile AQI 932009: 90th percentile AQI 792010: 90th percentile AQI 842011: 90th percentile AQI 712012: 90th percentile AQI 772013: 90th percentile AQI 642014: 90th percentile AQI 712015: 90th percentile AQI 842016: 90th percentile AQI 742017: 90th percentile AQI 842018: 90th percentile AQI 842019: 90th percentile AQI 542020: 90th percentile AQI 672021: 90th percentile AQI 932022: 90th percentile AQI 712023: 90th percentile AQI 642024: 90th percentile AQI 672025: 90th percentile AQI 611980: Median AQI 401981: Median AQI 351982: Median AQI 371983: Median AQI 441984: Median AQI 351985: Median AQI 351986: Median AQI 441987: Median AQI 381988: Median AQI 381989: Median AQI 401990: Median AQI 431991: Median AQI 431992: Median AQI 411993: Median AQI 391994: Median AQI 431995: Median AQI 431996: Median AQI 431997: Median AQI 421998: Median AQI 461999: Median AQI 502000: Median AQI 442001: Median AQI 442002: Median AQI 442003: Median AQI 432004: Median AQI 442005: Median AQI 432006: Median AQI 452007: Median AQI 442008: Median AQI 452009: Median AQI 442010: Median AQI 432011: Median AQI 442012: Median AQI 442013: Median AQI 422014: Median AQI 432015: Median AQI 442016: Median AQI 412017: Median AQI 442018: Median AQI 432019: Median AQI 422020: Median AQI 412021: Median AQI 462022: Median AQI 452023: Median AQI 452024: Median AQI 442025: Median AQI 441980198519901995200020052010201520202025
  • 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
Ozone28578%
Fine particles (PM2.5)8022%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20253652768801004461154Ozone
20243662689430104467232Ozone
2023365247112500145641435Ozone
202236525310660004571119Ozone
20213652221111512504693240Ozone
20203662867262004167171Ozone
20193643065800004254100Ozone
201836527272155104384206Ozone
201736526091122004484159Ozone
201636629656140004174140Ozone
2015365252100121004484157Ozone
20143652728760004371126Ozone
20133652946920004264105Ozone
201236625610451004477180Ozone
20113652639651004471153Ozone
201036526981150004384119Ozone
20093652728580004479122Ozone
200836624492236104593275Ozone
200736525885220004490133Ozone
200636524399221004590151Ozone
200536527275153004384159Ozone
2004366248813430044101177Ozone
200336425287187004390177Ozone
200236525584260004487147Ozone
200136226678180004486134Ozone
2000366240100251004493154Ozone
199936418911151130050126182Ozone
19983652097340403046154222Ozone
1997360265593051042101202Ozone
19963452277828120043108187Ozone
199533925758240004384143Ozone
1994362246763370043105197Ozone
19933653015491003969156Ozone
199236625679238004193164Ozone
1991365254713280043105174Ozone
1990365265701811104387205Ozone
198936527076190004087143Ozone
198835326959223003893200Ozone
19873632347238181038122203Ozone
1986274178553650044119179Ozone
198529922646189003593200Ozone
198426921939101003567164Ozone
198311071251040044119169Ozone
198232725052232003787164Ozone
19813352573524190035119187Ozone
19803212085144180040133179Ozone

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