EnviroNearby

Monroe County, Illinois air quality history

Daily Air Quality Index summaries from EPA monitors in Monroe, Illinois, 1980–1990.

80%
Good days in 1989
36
Median daily AQI, 1989
16
Days above 100 in 1989
355
Days with an AQI in 1989 (of 365)

In 1989, EPA reported a daily Air Quality Index (AQI) for Monroe, Illinois on 355 days. 283 of those days (80%) were in the Good range, and the median daily AQI was 36. That median is about the same as the typical monitored county in Illinois (median 37 across 21 counties), and lower than the typical monitored U.S. county (39). The main pollutant was ozone on 355 days. Across the years with fuller monitoring, the share of Good days held roughly steady: an average of 80% in 1980–1982 versus 77% in 1987–1989.

The most recent year with data for this county is 1990; EPA's files for 1991–2025 contain no row for it, which usually means its monitors stopped reporting.

Years with fewer than 120 monitored days (1990) are shown in the table but left out of comparisons and trend statements.

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 233 of 328 days1980: Moderate 62 of 328 days1980: Unhealthy for Sensitive Groups 26 of 328 days1980: Unhealthy 6 of 328 days1980: Very Unhealthy 1 of 328 days19801981: Good 198 of 248 days1981: Moderate 40 of 248 days1981: Unhealthy for Sensitive Groups 9 of 248 days1981: Unhealthy 1 of 248 days19811982: Good 275 of 313 days1982: Moderate 36 of 313 days1982: Unhealthy for Sensitive Groups 2 of 313 days19821983: Good 279 of 359 days1983: Moderate 46 of 359 days1983: Unhealthy for Sensitive Groups 26 of 359 days1983: Unhealthy 8 of 359 days19831984: Good 240 of 331 days1984: Moderate 63 of 331 days1984: Unhealthy for Sensitive Groups 20 of 331 days1984: Unhealthy 8 of 331 days19841985: Good 270 of 357 days1985: Moderate 74 of 357 days1985: Unhealthy for Sensitive Groups 10 of 357 days1985: Unhealthy 2 of 357 days1985: Very Unhealthy 1 of 357 days19851986: Good 294 of 355 days1986: Moderate 46 of 355 days1986: Unhealthy for Sensitive Groups 14 of 355 days1986: Unhealthy 1 of 355 days19861987: Good 261 of 358 days1987: Moderate 79 of 358 days1987: Unhealthy for Sensitive Groups 12 of 358 days1987: Unhealthy 6 of 358 days19871988: Good 273 of 347 days1988: Moderate 60 of 347 days1988: Unhealthy for Sensitive Groups 10 of 347 days1988: Unhealthy 2 of 347 days1988: Very Unhealthy 2 of 347 days19881989: Good 283 of 355 days1989: Moderate 56 of 355 days1989: Unhealthy for Sensitive Groups 14 of 355 days1989: Unhealthy 2 of 355 days19891990: Good 85 of 85 days1990
  • 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 1011981: 90th percentile AQI 771982: 90th percentile AQI 581983: 90th percentile AQI 1001984: 90th percentile AQI 931985: 90th percentile AQI 741986: 90th percentile AQI 671987: 90th percentile AQI 871988: 90th percentile AQI 711989: 90th percentile AQI 741990: 90th percentile AQI 391980: Median AQI 381981: Median AQI 381982: Median AQI 301983: Median AQI 351984: Median AQI 341985: Median AQI 391986: Median AQI 331987: Median AQI 381988: Median AQI 361989: Median AQI 361990: Median AQI 2919801981198219831984198519861987198819891990
  • Median daily AQI
  • 90th-percentile daily AQI

Main pollutant by day, 1989

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
1990858500000293949Ozone
198935528356142003674187Ozone
198834727360102203671204Ozone
198735826179126003887185Ozone
198635529446141003367172Ozone
198535727074102103974208Ozone
198433124063208003493185Ozone
1983359279462680035100185Ozone
19823132753620003058115Ozone
19812481984091003877151Ozone
1980328233622661038101202Ozone

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.

All monitored counties in Illinois

Source: U.S. EPA AirData, “Annual AQI by County” files for 1980–1990 (EPA download page). EPA file dates: 2026-06-26. Imported into EnviroNearby November 5, 2026. How we use this data · Report a problem