EnviroNearby

Lake County, Illinois air quality history

Daily Air Quality Index summaries from EPA monitors in Lake, Illinois, 1980–2025.

85%
Good days in 2025
39
Median daily AQI, 2025
3
Days above 100 in 2025
231
Days with an AQI in 2025 (of 365)

In 2025, EPA reported a daily Air Quality Index (AQI) for Lake, Illinois on 231 days. 196 of those days (85%) were in the Good range, and the median daily AQI was 39. That median is lower than the typical monitored county in Illinois (median 42 across 23 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was ozone on 231 days. Across the years with fuller monitoring, the share of Good days fell: an average of 86% in 1980–1982 versus 81% in 2023–2025.

EPA did not report an AQI for every day of 2025 here (231 of 365 days). Figures describe monitored days only; seasonal monitoring (for example, ozone measured only in warmer months) can make a county look cleaner or dirtier than a full-year record would.

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 291 of 342 days1980: Moderate 24 of 342 days1980: Unhealthy for Sensitive Groups 19 of 342 days1980: Unhealthy 6 of 342 days1980: Very Unhealthy 2 of 342 days19801981: Good 305 of 355 days1981: Moderate 31 of 355 days1981: Unhealthy for Sensitive Groups 11 of 355 days1981: Unhealthy 4 of 355 days1981: Very Unhealthy 4 of 355 days1982: Good 297 of 341 days1982: Moderate 35 of 341 days1982: Unhealthy for Sensitive Groups 4 of 341 days1982: Unhealthy 5 of 341 days1983: Good 312 of 364 days1983: Moderate 27 of 364 days1983: Unhealthy for Sensitive Groups 13 of 364 days1983: Unhealthy 10 of 364 days1983: Very Unhealthy 2 of 364 days1984: Good 318 of 366 days1984: Moderate 25 of 366 days1984: Unhealthy for Sensitive Groups 13 of 366 days1984: Unhealthy 6 of 366 days1984: Very Unhealthy 4 of 366 days1985: Good 297 of 361 days1985: Moderate 43 of 361 days1985: Unhealthy for Sensitive Groups 14 of 361 days1985: Unhealthy 5 of 361 days1985: Very Unhealthy 2 of 361 days19851986: Good 315 of 363 days1986: Moderate 31 of 363 days1986: Unhealthy for Sensitive Groups 14 of 363 days1986: Unhealthy 3 of 363 days1987: Good 294 of 364 days1987: Moderate 39 of 364 days1987: Unhealthy for Sensitive Groups 19 of 364 days1987: Unhealthy 7 of 364 days1987: Very Unhealthy 5 of 364 days1988: Good 261 of 343 days1988: Moderate 40 of 343 days1988: Unhealthy for Sensitive Groups 22 of 343 days1988: Unhealthy 11 of 343 days1988: Very Unhealthy 9 of 343 days1989: Good 304 of 364 days1989: Moderate 41 of 364 days1989: Unhealthy for Sensitive Groups 13 of 364 days1989: Unhealthy 5 of 364 days1989: Very Unhealthy 1 of 364 days1990: Good 319 of 365 days1990: Moderate 37 of 365 days1990: Unhealthy for Sensitive Groups 7 of 365 days1990: Unhealthy 2 of 365 days19901991: Good 294 of 365 days1991: Moderate 34 of 365 days1991: Unhealthy for Sensitive Groups 24 of 365 days1991: Unhealthy 12 of 365 days1991: Very Unhealthy 1 of 365 days1992: Good 321 of 352 days1992: Moderate 19 of 352 days1992: Unhealthy for Sensitive Groups 10 of 352 days1992: Unhealthy 1 of 352 days1992: Very Unhealthy 1 of 352 days1993: Good 323 of 364 days1993: Moderate 32 of 364 days1993: Unhealthy for Sensitive Groups 8 of 364 days1993: Unhealthy 1 of 364 days1994: Good 304 of 354 days1994: Moderate 36 of 354 days1994: Unhealthy for Sensitive Groups 8 of 354 days1994: Unhealthy 5 of 354 days1994: Very Unhealthy 1 of 354 days1995: Good 301 of 365 days1995: Moderate 41 of 365 days1995: Unhealthy for Sensitive Groups 12 of 365 days1995: Unhealthy 9 of 365 days1995: Very Unhealthy 2 of 365 days19951996: Good 326 of 366 days1996: Moderate 32 of 366 days1996: Unhealthy for Sensitive Groups 5 of 366 days1996: Unhealthy 1 of 366 days1996: Very Unhealthy 2 of 366 days1997: Good 318 of 365 days1997: Moderate 36 of 365 days1997: Unhealthy for Sensitive Groups 6 of 365 days1997: Unhealthy 4 of 365 days1997: Very Unhealthy 1 of 365 days1998: Good 297 of 365 days1998: Moderate 43 of 365 days1998: Unhealthy for Sensitive Groups 20 of 365 days1998: Unhealthy 4 of 365 days1998: Very Unhealthy 1 of 365 days1999: Good 300 of 365 days1999: Moderate 40 of 365 days1999: Unhealthy for Sensitive Groups 18 of 365 days1999: Unhealthy 7 of 365 days2000: Good 271 of 366 days2000: Moderate 89 of 366 days2000: Unhealthy for Sensitive Groups 6 of 366 days20002001: Good 263 of 365 days2001: Moderate 89 of 365 days2001: Unhealthy for Sensitive Groups 10 of 365 days2001: Unhealthy 3 of 365 days2002: Good 252 of 365 days2002: Moderate 86 of 365 days2002: Unhealthy for Sensitive Groups 16 of 365 days2002: Unhealthy 8 of 365 days2002: Very Unhealthy 3 of 365 days2003: Good 297 of 365 days2003: Moderate 57 of 365 days2003: Unhealthy for Sensitive Groups 11 of 365 days2004: Good 305 of 365 days2004: Moderate 55 of 365 days2004: Unhealthy for Sensitive Groups 5 of 365 days2005: Good 274 of 365 days2005: Moderate 69 of 365 days2005: Unhealthy for Sensitive Groups 16 of 365 days2005: Unhealthy 6 of 365 days20052006: Good 305 of 365 days2006: Moderate 54 of 365 days2006: Unhealthy for Sensitive Groups 6 of 365 days2007: Good 274 of 365 days2007: Moderate 80 of 365 days2007: Unhealthy for Sensitive Groups 9 of 365 days2007: Unhealthy 2 of 365 days2008: Good 302 of 366 days2008: Moderate 61 of 366 days2008: Unhealthy for Sensitive Groups 3 of 366 days2009: Good 297 of 353 days2009: Moderate 51 of 353 days2009: Unhealthy for Sensitive Groups 4 of 353 days2009: Unhealthy 1 of 353 days2010: Good 287 of 365 days2010: Moderate 67 of 365 days2010: Unhealthy for Sensitive Groups 10 of 365 days2010: Unhealthy 1 of 365 days20102011: Good 316 of 359 days2011: Moderate 36 of 359 days2011: Unhealthy for Sensitive Groups 6 of 359 days2011: Unhealthy 1 of 359 days2012: Good 296 of 361 days2012: Moderate 37 of 361 days2012: Unhealthy for Sensitive Groups 20 of 361 days2012: Unhealthy 8 of 361 days2013: Good 305 of 351 days2013: Moderate 39 of 351 days2013: Unhealthy for Sensitive Groups 7 of 351 days2014: Good 317 of 355 days2014: Moderate 33 of 355 days2014: Unhealthy for Sensitive Groups 5 of 355 days2015: Good 332 of 362 days2015: Moderate 27 of 362 days2015: Unhealthy for Sensitive Groups 3 of 362 days20152016: Good 306 of 346 days2016: Moderate 32 of 346 days2016: Unhealthy for Sensitive Groups 8 of 346 days2017: Good 316 of 358 days2017: Moderate 35 of 358 days2017: Unhealthy for Sensitive Groups 7 of 358 days2018: Good 304 of 352 days2018: Moderate 40 of 352 days2018: Unhealthy for Sensitive Groups 6 of 352 days2018: Unhealthy 2 of 352 days2019: Good 210 of 245 days2019: Moderate 33 of 245 days2019: Unhealthy for Sensitive Groups 2 of 245 days2020: Good 199 of 241 days2020: Moderate 31 of 241 days2020: Unhealthy for Sensitive Groups 10 of 241 days2020: Unhealthy 1 of 241 days20202021: Good 180 of 244 days2021: Moderate 55 of 244 days2021: Unhealthy for Sensitive Groups 9 of 244 days2022: Good 199 of 243 days2022: Moderate 41 of 243 days2022: Unhealthy for Sensitive Groups 2 of 243 days2022: Unhealthy 1 of 243 days2023: Good 182 of 243 days2023: Moderate 47 of 243 days2023: Unhealthy for Sensitive Groups 13 of 243 days2023: Unhealthy 1 of 243 days2024: Good 201 of 245 days2024: Moderate 39 of 245 days2024: Unhealthy for Sensitive Groups 5 of 245 days2025: Good 196 of 231 days2025: Moderate 32 of 231 days2025: Unhealthy for Sensitive Groups 3 of 231 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 year0501001501980: 90th percentile AQI 841981: 90th percentile AQI 671982: 90th percentile AQI 611983: 90th percentile AQI 771984: 90th percentile AQI 741985: 90th percentile AQI 771986: 90th percentile AQI 671987: 90th percentile AQI 871988: 90th percentile AQI 1151989: 90th percentile AQI 711990: 90th percentile AQI 611991: 90th percentile AQI 1011992: 90th percentile AQI 481993: 90th percentile AQI 511994: 90th percentile AQI 671995: 90th percentile AQI 801996: 90th percentile AQI 581997: 90th percentile AQI 641998: 90th percentile AQI 801999: 90th percentile AQI 802000: 90th percentile AQI 702001: 90th percentile AQI 802002: 90th percentile AQI 922003: 90th percentile AQI 672004: 90th percentile AQI 632005: 90th percentile AQI 842006: 90th percentile AQI 622007: 90th percentile AQI 742008: 90th percentile AQI 642009: 90th percentile AQI 562010: 90th percentile AQI 712011: 90th percentile AQI 582012: 90th percentile AQI 932013: 90th percentile AQI 582014: 90th percentile AQI 512015: 90th percentile AQI 492016: 90th percentile AQI 542017: 90th percentile AQI 542018: 90th percentile AQI 582019: 90th percentile AQI 582020: 90th percentile AQI 742021: 90th percentile AQI 772022: 90th percentile AQI 642023: 90th percentile AQI 842024: 90th percentile AQI 672025: 90th percentile AQI 611980: Median AQI 291981: Median AQI 291982: Median AQI 291983: Median AQI 281984: Median AQI 311985: Median AQI 321986: Median AQI 311987: Median AQI 311988: Median AQI 311989: Median AQI 311990: Median AQI 291991: Median AQI 311992: Median AQI 291993: Median AQI 301994: Median AQI 311995: Median AQI 321996: Median AQI 311997: Median AQI 311998: Median AQI 331999: Median AQI 342000: Median AQI 362001: Median AQI 352002: Median AQI 382003: Median AQI 332004: Median AQI 322005: Median AQI 362006: Median AQI 332007: Median AQI 362008: Median AQI 352009: Median AQI 342010: Median AQI 382011: Median AQI 342012: Median AQI 342013: Median AQI 342014: Median AQI 352015: Median AQI 352016: Median AQI 342017: Median AQI 352018: Median AQI 352019: Median AQI 402020: Median AQI 392021: Median AQI 422022: Median AQI 392023: Median AQI 422024: Median AQI 402025: Median AQI 391980198519901995200020052010201520202025
  • 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
Ozone231100%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
20252311963230003961108Ozone
20242452013950004067140Ozone
202324318247131004284179Ozone
20222431994121003964159Ozone
20212441805590004277136Ozone
202024119931101003974185Ozone
20192452103320004058115Ozone
20183523044062003558164Ozone
20173583163570003554129Ozone
20163463063280003454140Ozone
20153623322730003549122Ozone
20143553173350003551129Ozone
20133513053970003458136Ozone
201236129637208003493195Ozone
20113593163661003458174Ozone
201036528767101003871156Ozone
20093532975141003456154Ozone
20083663026130003564105Ozone
20073652748092003674154Ozone
20063653055460003362150Ozone
200536527469166003684179Ozone
20043653055550003263147Ozone
200336529757110003367147Ozone
200236525286168303892212Ozone
200136526389103003580174Ozone
20003662718960003670136Ozone
199936530040187003480169Ozone
199836529743204103380202Ozone
19973653183664103164207Ozone
19963663263251203158205Ozone
199536530141129203280203Ozone
19943543043685103167214Ozone
19933643233281003051154Ozone
199235232119101102948218Ozone
19913652943424121031101201Ozone
19903653193772002961164Ozone
198936430441135103171202Ozone
19883432614022119031115240Ozone
198736429439197503187246Ozone
198636331531143003167159Ozone
198536129743145203277208Ozone
198436631825136403174234Ozone
1983364312271310202877227Ozone
19823412973545002961185Ozone
198135530531114402967217Ozone
198034229124196202984249Ozone

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 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