EnviroNearby

Clark County, Illinois air quality history

Daily Air Quality Index summaries from EPA monitors in Clark, Illinois, 2001–2025.

94%
Good days in 2025
33
Median daily AQI, 2025
0
Days above 100 in 2025
355
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Clark, Illinois on 355 days. 333 of those days (94%) 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 355 days. Across the years with fuller monitoring, the share of Good days rose: an average of 72% in 2001–2003 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%2001: Good 149 of 205 days2001: Moderate 48 of 205 days2001: Unhealthy for Sensitive Groups 8 of 205 days20012002: Good 126 of 196 days2002: Moderate 45 of 196 days2002: Unhealthy for Sensitive Groups 20 of 196 days2002: Unhealthy 5 of 196 days2003: Good 155 of 195 days2003: Moderate 38 of 195 days2003: Unhealthy for Sensitive Groups 2 of 195 days20032004: Good 183 of 198 days2004: Moderate 15 of 198 days2005: Good 156 of 205 days2005: Moderate 45 of 205 days2005: Unhealthy for Sensitive Groups 4 of 205 days20052006: Good 158 of 177 days2006: Moderate 18 of 177 days2006: Unhealthy for Sensitive Groups 1 of 177 days2007: Good 143 of 196 days2007: Moderate 46 of 196 days2007: Unhealthy for Sensitive Groups 7 of 196 days20072008: Good 175 of 196 days2008: Moderate 21 of 196 days2009: Good 183 of 205 days2009: Moderate 22 of 205 days20092010: Good 176 of 210 days2010: Moderate 34 of 210 days2011: Good 151 of 176 days2011: Moderate 24 of 176 days2011: Unhealthy for Sensitive Groups 1 of 176 days20112012: Good 107 of 152 days2012: Moderate 39 of 152 days2012: Unhealthy for Sensitive Groups 6 of 152 days2013: Good 190 of 207 days2013: Moderate 17 of 207 days20132014: Good 185 of 211 days2014: Moderate 26 of 211 days2015: Good 182 of 210 days2015: Moderate 28 of 210 days20152016: Good 175 of 203 days2016: Moderate 27 of 203 days2016: Unhealthy for Sensitive Groups 1 of 203 days2017: Good 211 of 241 days2017: Moderate 29 of 241 days2017: Unhealthy for Sensitive Groups 1 of 241 days20172018: Good 337 of 359 days2018: Moderate 21 of 359 days2018: Unhealthy for Sensitive Groups 1 of 359 days2019: Good 314 of 327 days2019: Moderate 13 of 327 days20192020: Good 347 of 363 days2020: Moderate 16 of 363 days2021: Good 344 of 363 days2021: Moderate 19 of 363 days20212022: Good 296 of 312 days2022: Moderate 15 of 312 days2022: Unhealthy for Sensitive Groups 1 of 312 days2023: Good 320 of 358 days2023: Moderate 33 of 358 days2023: Unhealthy for Sensitive Groups 5 of 358 days20232024: Good 332 of 363 days2024: Moderate 31 of 363 days2025: Good 333 of 355 days2025: Moderate 22 of 355 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 year0501001502001: 90th percentile AQI 772002: 90th percentile AQI 1082003: 90th percentile AQI 642004: 90th percentile AQI 502005: 90th percentile AQI 772006: 90th percentile AQI 512007: 90th percentile AQI 772008: 90th percentile AQI 512009: 90th percentile AQI 542010: 90th percentile AQI 642011: 90th percentile AQI 642012: 90th percentile AQI 802013: 90th percentile AQI 492014: 90th percentile AQI 512015: 90th percentile AQI 612016: 90th percentile AQI 542017: 90th percentile AQI 512018: 90th percentile AQI 482019: 90th percentile AQI 472020: 90th percentile AQI 452021: 90th percentile AQI 462022: 90th percentile AQI 452023: 90th percentile AQI 512024: 90th percentile AQI 492025: 90th percentile AQI 482001: Median AQI 432002: Median AQI 452003: Median AQI 402004: Median AQI 382005: Median AQI 422006: Median AQI 392007: Median AQI 432008: Median AQI 392009: Median AQI 362010: Median AQI 402011: Median AQI 412012: Median AQI 432013: Median AQI 382014: Median AQI 392015: Median AQI 392016: Median AQI 382017: Median AQI 392018: Median AQI 322019: Median AQI 342020: Median AQI 312021: Median AQI 342022: Median AQI 342023: Median AQI 362024: Median AQI 362025: Median AQI 332001200320052007200920112013201520172019202120232025
  • 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
Ozone355100%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
2025355333220000334887Ozone
2024363332310000364990Ozone
20233583203350003651136Ozone
20223122961510003445101Ozone
2021363344190000344684Ozone
2020363347160000314597Ozone
2019327314130000344774Ozone
20183593372110003248101Ozone
20172412112910003951101Ozone
20162031752710003854101Ozone
2015210182280000396187Ozone
2014211185260000395190Ozone
2013207190170000384980Ozone
20121521073960004380129Ozone
20111761512410004164108Ozone
2010210176340000406490Ozone
2009205183220000365493Ozone
20081961752100003951100Ozone
20071961434670004377140Ozone
20061771581810003951101Ozone
20052051564540004277112Ozone
2004198183150000385080Ozone
20031951553820004064129Ozone
2002196126452050045108169Ozone
20012051494880004377136Ozone

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 2001–2025 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem