EnviroNearby

Jo Daviess County, Illinois air quality history

Daily Air Quality Index summaries from EPA monitors in Jo Daviess, Illinois, 1994–2025.

95%
Good days in 2025
33
Median daily AQI, 2025
0
Days above 100 in 2025
341
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Jo Daviess, Illinois on 341 days. 325 of those days (95%) were in the Good range, and the median daily AQI was 33. That median is lower than the typical monitored county in Illinois (median 42 across 23 counties), and lower than the typical monitored U.S. county (40). The main pollutant was ozone on 341 days. Across the years with fuller monitoring, the share of Good days rose: an average of 75% in 1994–1996 versus 92% 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%1994: Good 246 of 314 days1994: Moderate 56 of 314 days1994: Unhealthy for Sensitive Groups 10 of 314 days1994: Unhealthy 2 of 314 days19941995: Good 175 of 252 days1995: Moderate 55 of 252 days1995: Unhealthy for Sensitive Groups 20 of 252 days1995: Unhealthy 2 of 252 days1996: Good 161 of 205 days1996: Moderate 30 of 205 days1996: Unhealthy for Sensitive Groups 10 of 205 days1996: Unhealthy 4 of 205 days1997: Good 303 of 351 days1997: Moderate 42 of 351 days1997: Unhealthy for Sensitive Groups 6 of 351 days1998: Good 270 of 335 days1998: Moderate 52 of 335 days1998: Unhealthy for Sensitive Groups 12 of 335 days1998: Unhealthy 1 of 335 days1999: Good 294 of 362 days1999: Moderate 51 of 362 days1999: Unhealthy for Sensitive Groups 14 of 362 days1999: Unhealthy 3 of 362 days19992000: Good 306 of 349 days2000: Moderate 38 of 349 days2000: Unhealthy for Sensitive Groups 5 of 349 days2001: Good 291 of 351 days2001: Moderate 50 of 351 days2001: Unhealthy for Sensitive Groups 9 of 351 days2001: Unhealthy 1 of 351 days2002: Good 285 of 352 days2002: Moderate 56 of 352 days2002: Unhealthy for Sensitive Groups 10 of 352 days2002: Unhealthy 1 of 352 days2003: Good 272 of 354 days2003: Moderate 67 of 354 days2003: Unhealthy for Sensitive Groups 15 of 354 days2004: Good 336 of 356 days2004: Moderate 18 of 356 days2004: Unhealthy for Sensitive Groups 2 of 356 days20042005: Good 280 of 361 days2005: Moderate 62 of 361 days2005: Unhealthy for Sensitive Groups 18 of 361 days2005: Unhealthy 1 of 361 days2006: Good 222 of 244 days2006: Moderate 22 of 244 days2007: Good 300 of 358 days2007: Moderate 46 of 358 days2007: Unhealthy for Sensitive Groups 12 of 358 days2008: Good 326 of 363 days2008: Moderate 36 of 363 days2008: Unhealthy for Sensitive Groups 1 of 363 days2009: Good 289 of 311 days2009: Moderate 22 of 311 days20092010: Good 327 of 357 days2010: Moderate 28 of 357 days2010: Unhealthy for Sensitive Groups 2 of 357 days2011: Good 287 of 315 days2011: Moderate 27 of 315 days2011: Unhealthy for Sensitive Groups 1 of 315 days2012: Good 275 of 341 days2012: Moderate 56 of 341 days2012: Unhealthy for Sensitive Groups 10 of 341 days2013: Good 284 of 317 days2013: Moderate 32 of 317 days2013: Unhealthy for Sensitive Groups 1 of 317 days2014: Good 324 of 353 days2014: Moderate 28 of 353 days2014: Unhealthy for Sensitive Groups 1 of 353 days20142015: Good 309 of 327 days2015: Moderate 18 of 327 days2016: Good 331 of 350 days2016: Moderate 18 of 350 days2016: Unhealthy for Sensitive Groups 1 of 350 days2017: Good 303 of 324 days2017: Moderate 21 of 324 days2018: Good 323 of 344 days2018: Moderate 19 of 344 days2018: Unhealthy for Sensitive Groups 2 of 344 days2019: Good 351 of 363 days2019: Moderate 12 of 363 days20192020: Good 337 of 353 days2020: Moderate 16 of 353 days2021: Good 336 of 362 days2021: Moderate 26 of 362 days2022: Good 328 of 343 days2022: Moderate 15 of 343 days2023: Good 302 of 353 days2023: Moderate 42 of 353 days2023: Unhealthy for Sensitive Groups 8 of 353 days2023: Unhealthy 1 of 353 days2024: Good 327 of 349 days2024: Moderate 21 of 349 days2024: Unhealthy for Sensitive Groups 1 of 349 days20242025: Good 325 of 341 days2025: Moderate 16 of 341 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 year0501001994: 90th percentile AQI 801995: 90th percentile AQI 931996: 90th percentile AQI 801997: 90th percentile AQI 581998: 90th percentile AQI 771999: 90th percentile AQI 742000: 90th percentile AQI 512001: 90th percentile AQI 672002: 90th percentile AQI 802003: 90th percentile AQI 802004: 90th percentile AQI 462005: 90th percentile AQI 802006: 90th percentile AQI 492007: 90th percentile AQI 642008: 90th percentile AQI 512009: 90th percentile AQI 492010: 90th percentile AQI 492011: 90th percentile AQI 502012: 90th percentile AQI 712013: 90th percentile AQI 512014: 90th percentile AQI 492015: 90th percentile AQI 472016: 90th percentile AQI 462017: 90th percentile AQI 462018: 90th percentile AQI 472019: 90th percentile AQI 472020: 90th percentile AQI 442021: 90th percentile AQI 472022: 90th percentile AQI 462023: 90th percentile AQI 582024: 90th percentile AQI 482025: 90th percentile AQI 461994: Median AQI 371995: Median AQI 391996: Median AQI 381997: Median AQI 361998: Median AQI 371999: Median AQI 392000: Median AQI 352001: Median AQI 362002: Median AQI 362003: Median AQI 362004: Median AQI 332005: Median AQI 362006: Median AQI 302007: Median AQI 362008: Median AQI 362009: Median AQI 322010: Median AQI 372011: Median AQI 352012: Median AQI 362013: Median AQI 372014: Median AQI 352015: Median AQI 342016: Median AQI 332017: Median AQI 342018: Median AQI 332019: Median AQI 342020: Median AQI 322021: Median AQI 362022: Median AQI 342023: Median AQI 362024: Median AQI 362025: Median AQI 3319941999200420092014201920242025
  • 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
Ozone341100%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
2025341325160000334687Ozone
20243493272110003648101Ozone
20233533024281003658154Ozone
2022343328150000344684Ozone
2021362336260000364797Ozone
2020353337160000324487Ozone
2019363351120000344774Ozone
20183443231920003347119Ozone
2017324303210000344687Ozone
20163503311810003346108Ozone
2015327309180000344790Ozone
20143533242810003549108Ozone
20133172843210003751105Ozone
201234127556100003671129Ozone
20113152872710003550105Ozone
20103573272820003749105Ozone
2009311289220000324993Ozone
20083633263610003651105Ozone
200735830046120003664143Ozone
2006244222220000304993Ozone
200536128062181003680151Ozone
20043563361820003346105Ozone
200335427267150003680129Ozone
200235228556101003680172Ozone
20013512915091003667156Ozone
20003493063850003551143Ozone
199936229451143003974169Ozone
199833527052121003777156Ozone
19973513034260003658126Ozone
199620516130104003880185Ozone
199525217555202003993154Ozone
199431424656102003780169Ozone

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 Illinois with a similar median AQI in 2025

All monitored counties in Illinois

Source: U.S. EPA AirData, “Annual AQI by County” files for 1994–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem