EnviroNearby

DuPage County, Illinois air quality history

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

64%
Good days in 2025
42
Median daily AQI, 2025
6
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 DuPage, Illinois on 365 days. 233 of those days (64%) were in the Good range, and the median daily AQI was 42. That median is about the same as 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 fine particles (PM2.5) on 240 days. Across the years with fuller monitoring, the share of Good days fell: an average of 89% in 1980–1982 versus 56% 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%1980: Good 260 of 290 days1980: Moderate 25 of 290 days1980: Unhealthy for Sensitive Groups 4 of 290 days1980: Very Unhealthy 1 of 290 days19801981: Good 235 of 268 days1981: Moderate 24 of 268 days1981: Unhealthy for Sensitive Groups 7 of 268 days1981: Unhealthy 2 of 268 days1982: Good 293 of 329 days1982: Moderate 35 of 329 days1982: Unhealthy for Sensitive Groups 1 of 329 days1983: Good 310 of 358 days1983: Moderate 28 of 358 days1983: Unhealthy for Sensitive Groups 17 of 358 days1983: Unhealthy 2 of 358 days1983: Very Unhealthy 1 of 358 days1984: Good 182 of 201 days1984: Moderate 16 of 201 days1984: Unhealthy for Sensitive Groups 2 of 201 days1984: Very Unhealthy 1 of 201 days1985: Good 322 of 350 days1985: Moderate 24 of 350 days1985: Unhealthy for Sensitive Groups 4 of 350 days19851986: Good 321 of 347 days1986: Moderate 20 of 347 days1986: Unhealthy for Sensitive Groups 4 of 347 days1986: Unhealthy 2 of 347 days1987: Good 307 of 348 days1987: Moderate 29 of 348 days1987: Unhealthy for Sensitive Groups 11 of 348 days1987: Unhealthy 1 of 348 days1988: Good 272 of 366 days1988: Moderate 77 of 366 days1988: Unhealthy for Sensitive Groups 14 of 366 days1988: Unhealthy 3 of 366 days1989: Good 265 of 365 days1989: Moderate 88 of 365 days1989: Unhealthy for Sensitive Groups 10 of 365 days1989: Unhealthy 2 of 365 days1990: Good 328 of 359 days1990: Moderate 30 of 359 days1990: Unhealthy for Sensitive Groups 1 of 359 days19901991: Good 327 of 364 days1991: Moderate 27 of 364 days1991: Unhealthy for Sensitive Groups 7 of 364 days1991: Unhealthy 3 of 364 days1992: Good 346 of 364 days1992: Moderate 17 of 364 days1992: Unhealthy for Sensitive Groups 1 of 364 days1993: Good 347 of 362 days1993: Moderate 15 of 362 days1994: Good 334 of 359 days1994: Moderate 21 of 359 days1994: Unhealthy for Sensitive Groups 3 of 359 days1994: Unhealthy 1 of 359 days1995: Good 323 of 363 days1995: Moderate 30 of 363 days1995: Unhealthy for Sensitive Groups 8 of 363 days1995: Unhealthy 2 of 363 days19951996: Good 339 of 364 days1996: Moderate 19 of 364 days1996: Unhealthy for Sensitive Groups 6 of 364 days1997: Good 335 of 365 days1997: Moderate 25 of 365 days1997: Unhealthy for Sensitive Groups 5 of 365 days1998: Good 331 of 362 days1998: Moderate 29 of 362 days1998: Unhealthy for Sensitive Groups 1 of 362 days1998: Unhealthy 1 of 362 days1999: Good 294 of 359 days1999: Moderate 59 of 359 days1999: Unhealthy for Sensitive Groups 6 of 359 days2000: Good 268 of 365 days2000: Moderate 95 of 365 days2000: Unhealthy for Sensitive Groups 2 of 365 days20002001: Good 251 of 362 days2001: Moderate 102 of 362 days2001: Unhealthy for Sensitive Groups 9 of 362 days2002: Good 252 of 363 days2002: Moderate 97 of 363 days2002: Unhealthy for Sensitive Groups 11 of 363 days2002: Unhealthy 3 of 363 days2003: Good 269 of 360 days2003: Moderate 88 of 360 days2003: Unhealthy for Sensitive Groups 3 of 360 days2004: Good 315 of 362 days2004: Moderate 46 of 362 days2004: Unhealthy for Sensitive Groups 1 of 362 days2005: Good 277 of 361 days2005: Moderate 75 of 361 days2005: Unhealthy for Sensitive Groups 8 of 361 days2005: Unhealthy 1 of 361 days20052006: Good 312 of 364 days2006: Moderate 51 of 364 days2006: Unhealthy for Sensitive Groups 1 of 364 days2007: Good 117 of 365 days2007: Moderate 240 of 365 days2007: Unhealthy for Sensitive Groups 8 of 365 days2008: Good 137 of 366 days2008: Moderate 227 of 366 days2008: Unhealthy for Sensitive Groups 2 of 366 days2009: Good 119 of 365 days2009: Moderate 244 of 365 days2009: Unhealthy for Sensitive Groups 2 of 365 days2010: Good 132 of 365 days2010: Moderate 230 of 365 days2010: Unhealthy for Sensitive Groups 3 of 365 days20102011: Good 110 of 365 days2011: Moderate 252 of 365 days2011: Unhealthy for Sensitive Groups 3 of 365 days2012: Good 158 of 366 days2012: Moderate 201 of 366 days2012: Unhealthy for Sensitive Groups 7 of 366 days2013: Good 177 of 301 days2013: Moderate 123 of 301 days2013: Unhealthy for Sensitive Groups 1 of 301 days2014: Good 183 of 234 days2014: Moderate 49 of 234 days2014: Unhealthy for Sensitive Groups 2 of 234 days2015: Good 196 of 259 days2015: Moderate 62 of 259 days2015: Unhealthy for Sensitive Groups 1 of 259 days20152016: Good 176 of 241 days2016: Moderate 56 of 241 days2016: Unhealthy for Sensitive Groups 9 of 241 days2017: Good 210 of 311 days2017: Moderate 99 of 311 days2017: Unhealthy for Sensitive Groups 2 of 311 days2018: Good 136 of 361 days2018: Moderate 221 of 361 days2018: Unhealthy for Sensitive Groups 4 of 361 days2019: Good 196 of 352 days2019: Moderate 153 of 352 days2019: Unhealthy for Sensitive Groups 2 of 352 days2019: Unhealthy 1 of 352 days2020: Good 213 of 366 days2020: Moderate 149 of 366 days2020: Unhealthy for Sensitive Groups 3 of 366 days2020: Unhealthy 1 of 366 days20202021: Good 179 of 365 days2021: Moderate 184 of 365 days2021: Unhealthy for Sensitive Groups 2 of 365 days2022: Good 199 of 365 days2022: Moderate 165 of 365 days2022: Unhealthy for Sensitive Groups 1 of 365 days2023: Good 146 of 365 days2023: Moderate 202 of 365 days2023: Unhealthy for Sensitive Groups 11 of 365 days2023: Unhealthy 4 of 365 days2023: Very Unhealthy 2 of 365 days2024: Good 230 of 366 days2024: Moderate 136 of 366 days2025: Good 233 of 365 days2025: Moderate 126 of 365 days2025: Unhealthy for Sensitive Groups 5 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 year0501001980: 90th percentile AQI 541981: 90th percentile AQI 581982: 90th percentile AQI 541983: 90th percentile AQI 741984: 90th percentile AQI 501985: 90th percentile AQI 471986: 90th percentile AQI 471987: 90th percentile AQI 541988: 90th percentile AQI 771989: 90th percentile AQI 711990: 90th percentile AQI 501991: 90th percentile AQI 511992: 90th percentile AQI 431993: 90th percentile AQI 441994: 90th percentile AQI 461995: 90th percentile AQI 551996: 90th percentile AQI 471997: 90th percentile AQI 481998: 90th percentile AQI 501999: 90th percentile AQI 642000: 90th percentile AQI 692001: 90th percentile AQI 762002: 90th percentile AQI 772003: 90th percentile AQI 682004: 90th percentile AQI 552005: 90th percentile AQI 712006: 90th percentile AQI 582007: 90th percentile AQI 782008: 90th percentile AQI 712009: 90th percentile AQI 762010: 90th percentile AQI 752011: 90th percentile AQI 742012: 90th percentile AQI 742013: 90th percentile AQI 622014: 90th percentile AQI 652015: 90th percentile AQI 642016: 90th percentile AQI 642017: 90th percentile AQI 712018: 90th percentile AQI 722019: 90th percentile AQI 652020: 90th percentile AQI 642021: 90th percentile AQI 692022: 90th percentile AQI 672023: 90th percentile AQI 772024: 90th percentile AQI 632025: 90th percentile AQI 671980: Median AQI 261981: Median AQI 251982: Median AQI 251983: Median AQI 241984: Median AQI 211985: Median AQI 261986: Median AQI 251987: Median AQI 251988: Median AQI 391989: Median AQI 421990: Median AQI 311991: Median AQI 261992: Median AQI 251993: Median AQI 271994: Median AQI 271995: Median AQI 271996: Median AQI 271997: Median AQI 281998: Median AQI 271999: Median AQI 312000: Median AQI 312001: Median AQI 342002: Median AQI 342003: Median AQI 322004: Median AQI 292005: Median AQI 312006: Median AQI 302007: Median AQI 572008: Median AQI 542009: Median AQI 552010: Median AQI 542011: Median AQI 562012: Median AQI 522013: Median AQI 452014: Median AQI 392015: Median AQI 422016: Median AQI 422017: Median AQI 442018: Median AQI 532019: Median AQI 482020: Median AQI 472021: Median AQI 512022: Median AQI 472023: Median AQI 532024: Median AQI 452025: Median AQI 421980198519901995200020052010201520202025
  • 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
Fine particles (PM2.5)24066%
Ozone12534%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
202536523312651004267158PM2.5
20243662301360000456397PM2.5
2023365146202114205377234PM2.5
202236519916510004767129PM2.5
202136517918420005169105PM2.5
202036621314931004764154PM2.5
201935219615321004865174PM2.5
201836113622140005372112PM2.5
20173112109920004471129Ozone
20162411765690004264136Ozone
20152591966210004264115Ozone
20142341834920003965101Ozone
201330117712310004562115PM2.5
201236615820170005274136PM2.5
201136511025230005674119PM2.5
201036513223030005475110PM2.5
200936511924420005576115PM2.5
200836613722720005471106PM2.5
200736511724080005778147PM2.5
20063643125110003058105Ozone
20053612777581003171164Ozone
20043623154610002955115Ozone
20033602698830003268143Ozone
200236325297113003477164Ozone
200136225110290003476135Ozone
20003652689520003169112Ozone
19993592945960003164140Ozone
19983623312911002750151Ozone
19973653352550002848126Ozone
19963643391960002747143Ozone
19953633233082002755187Ozone
19943593342131002746164Ozone
1993362347150000274490Ozone
19923643461710002543126Ozone
19913643272773002651182Ozone
19903593283010003150115Ozone
198936526588102004271161NO2
198836627277143003977169NO2
198734830729111002554166Ozone
19863473212042002547161Ozone
19853503222440002647150Ozone
19842011821620102150204Ozone
198335831028172102474202Ozone
19823292933510002554108Ozone
19812682352472002558179Ozone
19802902602540102654216Ozone

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