EnviroNearby

Saint Clair County, Illinois air quality history

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

58%
Good days in 2025
47
Median daily AQI, 2025
3
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 Saint Clair, Illinois on 365 days. 213 of those days (58%) were in the Good range, and the median daily AQI was 47. That median is higher than the typical monitored county in Illinois (median 42 across 23 counties), and higher than the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 281 days. Across the years with fuller monitoring, the share of Good days fell: an average of 83% in 1980–1982 versus 51% 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 296 of 363 days1980: Moderate 45 of 363 days1980: Unhealthy for Sensitive Groups 13 of 363 days1980: Unhealthy 7 of 363 days1980: Very Unhealthy 2 of 363 days19801981: Good 314 of 364 days1981: Moderate 43 of 364 days1981: Unhealthy for Sensitive Groups 7 of 364 days1982: Good 294 of 358 days1982: Moderate 59 of 358 days1982: Unhealthy for Sensitive Groups 3 of 358 days1982: Unhealthy 2 of 358 days1983: Good 246 of 363 days1983: Moderate 77 of 363 days1983: Unhealthy for Sensitive Groups 24 of 363 days1983: Unhealthy 13 of 363 days1983: Very Unhealthy 3 of 363 days1984: Good 264 of 366 days1984: Moderate 81 of 366 days1984: Unhealthy for Sensitive Groups 13 of 366 days1984: Unhealthy 7 of 366 days1984: Very Unhealthy 1 of 366 days1985: Good 270 of 365 days1985: Moderate 86 of 365 days1985: Unhealthy for Sensitive Groups 6 of 365 days1985: Unhealthy 3 of 365 days19851986: Good 283 of 359 days1986: Moderate 65 of 359 days1986: Unhealthy for Sensitive Groups 9 of 359 days1986: Unhealthy 2 of 359 days1987: Good 261 of 364 days1987: Moderate 91 of 364 days1987: Unhealthy for Sensitive Groups 11 of 364 days1987: Unhealthy 1 of 364 days1988: Good 248 of 366 days1988: Moderate 102 of 366 days1988: Unhealthy for Sensitive Groups 11 of 366 days1988: Unhealthy 4 of 366 days1988: Very Unhealthy 1 of 366 days1989: Good 270 of 364 days1989: Moderate 90 of 364 days1989: Unhealthy for Sensitive Groups 4 of 364 days1990: Good 310 of 365 days1990: Moderate 48 of 365 days1990: Unhealthy for Sensitive Groups 4 of 365 days1990: Unhealthy 2 of 365 days1990: Very Unhealthy 1 of 365 days19901991: Good 294 of 365 days1991: Moderate 62 of 365 days1991: Unhealthy for Sensitive Groups 8 of 365 days1991: Unhealthy 1 of 365 days1992: Good 295 of 362 days1992: Moderate 59 of 362 days1992: Unhealthy for Sensitive Groups 8 of 362 days1993: Good 316 of 365 days1993: Moderate 46 of 365 days1993: Unhealthy for Sensitive Groups 2 of 365 days1993: Unhealthy 1 of 365 days1994: Good 298 of 365 days1994: Moderate 60 of 365 days1994: Unhealthy for Sensitive Groups 7 of 365 days1995: Good 286 of 365 days1995: Moderate 56 of 365 days1995: Unhealthy for Sensitive Groups 20 of 365 days1995: Unhealthy 2 of 365 days1995: Very Unhealthy 1 of 365 days19951996: Good 314 of 366 days1996: Moderate 47 of 366 days1996: Unhealthy for Sensitive Groups 5 of 366 days1997: Good 320 of 365 days1997: Moderate 35 of 365 days1997: Unhealthy for Sensitive Groups 8 of 365 days1997: Unhealthy 2 of 365 days1998: Good 300 of 365 days1998: Moderate 54 of 365 days1998: Unhealthy for Sensitive Groups 10 of 365 days1998: Unhealthy 1 of 365 days1999: Good 260 of 365 days1999: Moderate 76 of 365 days1999: Unhealthy for Sensitive Groups 27 of 365 days1999: Unhealthy 2 of 365 days2000: Good 214 of 366 days2000: Moderate 140 of 366 days2000: Unhealthy for Sensitive Groups 9 of 366 days2000: Unhealthy 3 of 366 days20002001: Good 187 of 365 days2001: Moderate 159 of 365 days2001: Unhealthy for Sensitive Groups 19 of 365 days2002: Good 203 of 365 days2002: Moderate 133 of 365 days2002: Unhealthy for Sensitive Groups 21 of 365 days2002: Unhealthy 8 of 365 days2003: Good 226 of 365 days2003: Moderate 126 of 365 days2003: Unhealthy for Sensitive Groups 10 of 365 days2003: Unhealthy 1 of 365 days2003: Very Unhealthy 2 of 365 days2004: Good 230 of 366 days2004: Moderate 131 of 366 days2004: Unhealthy for Sensitive Groups 5 of 366 days2005: Good 208 of 365 days2005: Moderate 128 of 365 days2005: Unhealthy for Sensitive Groups 24 of 365 days2005: Unhealthy 4 of 365 days2005: Very Unhealthy 1 of 365 days20052006: Good 220 of 361 days2006: Moderate 129 of 361 days2006: Unhealthy for Sensitive Groups 10 of 361 days2006: Unhealthy 2 of 361 days2007: Good 87 of 365 days2007: Moderate 267 of 365 days2007: Unhealthy for Sensitive Groups 10 of 365 days2007: Unhealthy 1 of 365 days2008: Good 156 of 366 days2008: Moderate 208 of 366 days2008: Unhealthy for Sensitive Groups 2 of 366 days2009: Good 192 of 365 days2009: Moderate 172 of 365 days2009: Unhealthy 1 of 365 days2010: Good 177 of 365 days2010: Moderate 181 of 365 days2010: Unhealthy for Sensitive Groups 7 of 365 days20102011: Good 141 of 365 days2011: Moderate 214 of 365 days2011: Unhealthy for Sensitive Groups 9 of 365 days2011: Unhealthy 1 of 365 days2012: Good 182 of 366 days2012: Moderate 153 of 366 days2012: Unhealthy for Sensitive Groups 27 of 366 days2012: Unhealthy 3 of 366 days2012: Very Unhealthy 1 of 366 days2013: Good 177 of 365 days2013: Moderate 186 of 365 days2013: Unhealthy for Sensitive Groups 2 of 365 days2014: Good 194 of 365 days2014: Moderate 169 of 365 days2014: Unhealthy for Sensitive Groups 2 of 365 days2015: Good 205 of 365 days2015: Moderate 158 of 365 days2015: Unhealthy for Sensitive Groups 2 of 365 days20152016: Good 226 of 366 days2016: Moderate 136 of 366 days2016: Unhealthy for Sensitive Groups 4 of 366 days2017: Good 237 of 365 days2017: Moderate 127 of 365 days2017: Unhealthy for Sensitive Groups 1 of 365 days2018: Good 152 of 364 days2018: Moderate 207 of 364 days2018: Unhealthy for Sensitive Groups 4 of 364 days2018: Unhealthy 1 of 364 days2019: Good 217 of 365 days2019: Moderate 147 of 365 days2019: Unhealthy for Sensitive Groups 1 of 365 days2020: Good 260 of 365 days2020: Moderate 105 of 365 days20202021: Good 141 of 365 days2021: Moderate 221 of 365 days2021: Unhealthy for Sensitive Groups 2 of 365 days2021: Unhealthy 1 of 365 days2022: Good 165 of 365 days2022: Moderate 199 of 365 days2022: Unhealthy for Sensitive Groups 1 of 365 days2023: Good 128 of 365 days2023: Moderate 223 of 365 days2023: Unhealthy for Sensitive Groups 12 of 365 days2023: Unhealthy 2 of 365 days2024: Good 218 of 366 days2024: Moderate 145 of 366 days2024: Unhealthy for Sensitive Groups 3 of 366 days2025: Good 213 of 365 days2025: Moderate 149 of 365 days2025: Unhealthy for Sensitive Groups 2 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 year0501001501980: 90th percentile AQI 801981: 90th percentile AQI 581982: 90th percentile AQI 611983: 90th percentile AQI 1021984: 90th percentile AQI 811985: 90th percentile AQI 671986: 90th percentile AQI 641987: 90th percentile AQI 711988: 90th percentile AQI 681989: 90th percentile AQI 661990: 90th percentile AQI 581991: 90th percentile AQI 611992: 90th percentile AQI 621993: 90th percentile AQI 541994: 90th percentile AQI 611995: 90th percentile AQI 711996: 90th percentile AQI 581997: 90th percentile AQI 521998: 90th percentile AQI 711999: 90th percentile AQI 892000: 90th percentile AQI 802001: 90th percentile AQI 892002: 90th percentile AQI 932003: 90th percentile AQI 802004: 90th percentile AQI 722005: 90th percentile AQI 902006: 90th percentile AQI 802007: 90th percentile AQI 812008: 90th percentile AQI 722009: 90th percentile AQI 682010: 90th percentile AQI 792011: 90th percentile AQI 772012: 90th percentile AQI 972013: 90th percentile AQI 672014: 90th percentile AQI 672015: 90th percentile AQI 622016: 90th percentile AQI 632017: 90th percentile AQI 602018: 90th percentile AQI 642019: 90th percentile AQI 642020: 90th percentile AQI 602021: 90th percentile AQI 682022: 90th percentile AQI 692023: 90th percentile AQI 772024: 90th percentile AQI 642025: 90th percentile AQI 631980: Median AQI 271981: Median AQI 291982: Median AQI 381983: Median AQI 411984: Median AQI 421985: Median AQI 401986: Median AQI 391987: Median AQI 411988: Median AQI 441989: Median AQI 401990: Median AQI 381991: Median AQI 381992: Median AQI 391993: Median AQI 371994: Median AQI 391995: Median AQI 391996: Median AQI 351997: Median AQI 371998: Median AQI 351999: Median AQI 402000: Median AQI 442001: Median AQI 492002: Median AQI 472003: Median AQI 422004: Median AQI 422005: Median AQI 462006: Median AQI 422007: Median AQI 592008: Median AQI 542009: Median AQI 492010: Median AQI 522011: Median AQI 542012: Median AQI 512013: Median AQI 512014: Median AQI 492015: Median AQI 482016: Median AQI 442017: Median AQI 452018: Median AQI 522019: Median AQI 472020: Median AQI 422021: Median AQI 532022: Median AQI 522023: Median AQI 542024: Median AQI 462025: Median AQI 471980198519901995200020052010201520202025
  • 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)28177%
Ozone7521%
Nitrogen dioxide (NO₂)92%

Year-by-year data

Annual AQI summary by year
YearDays with AQIGoodModerateUnhealthy for Sensitive GroupsUnhealthyVery UnhealthyHazardousMedian AQI90th pct.Max AQIMain pollutant
202536521314921004763161PM2.5
202436621814530004664112PM2.5
2023365128223122005477169PM2.5
202236516519910005269105PM2.5
202136514122121005368185PM2.5
202036526010500004260100PM2.5
201936521714710004764108PM2.5
201836415220741005264174PM2.5
201736523712710004560101PM2.5
201636622613640004463126PM2.5
201536520515820004862117PM2.5
201436519416920004967125PM2.5
201336517718620005167101PM2.5
2012366182153273105197281PM2.5
201136514121491005477151PM2.5
201036517718170005279150PM2.5
200936519217201004968177PM2.5
200836615620820005472117PM2.5
200736587267101005981169PM2.5
2006361220129102004280182Ozone
2005365208128244104690205Ozone
200436623013150004272126Ozone
2003365226126101204280206Ozone
2002365203133218004793195Ozone
2001365187159190004989142PM2.5
200036621414093004480161Ozone
199936526076272004089177Ozone
199836530054101003571187NO2
19973653203582003752151NO2
19963663144750003558143NO2
199536528656202103971207NO2
19943652986070003961150NO2
19933653164621003754192NO2
19923622955980003962119NO2
19913652946281003861159NO2
19903653104842103858201NO2
19893642709040004066129NO2
1988366248102114104468208NO2
198736426191111004171151NO2
19863592836592003964185NO2
19853652708663004067172NO2
198436626481137104281209NO2
19833632467724133041102206NO2
19823582945932003861164NO2
19813643144370002958136Ozone
198036329645137202780219Ozone

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