Bad Air Days in Adams County, Illinois: 2 a Year

2 bad air days a year

Fewer bad air days than most monitored US counties. Ranked 509 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (0% particle days).

Which months to watch

Most bad days here fall in June and May. Averaged over 2016 to 2025.

Is a purifier worth it here?

Bad air days are rare here. A standard furnace filter is enough; no purifier needed for outdoor air.
On the odd bad day, check AirNow and keep windows shut.

Better or worse than it was

In 2000 to 2009 this county averaged 5 bad days a year; in 2016 to 2025, 2. The air has improved. The worst recent year was 2023, with 12 bad days on 245 monitored days.

Date	AQI	Main pollutant
2023-06-03	136	Ozone
2023-06-06	133	Ozone
2023-06-20	122	Ozone
2023-05-30	119	Ozone
2023-06-23	119	Ozone

An ordinary day in Adams

Across 2,389 monitored days from 2016 to 2025, the air in Adams County rated Good on 90% of them, more often than the 72% typical of monitored counties, and Moderate on 10%. The median day sat at AQI 39; one day in ten went above 53.

The pollutant setting the AQI on an ordinary day here:

ozone100%2,389 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	244	231	13	0	0	38	71
2024	233	210	23	0	0	42	97
2023	245	184	49	12	0	43	136
2022	237	230	7	0	0	39	71
2021	242	219	23	0	0	40	93
2020	244	220	24	0	0	38	84
2019	241	208	33	0	0	41	93
2018	245	228	17	0	0	35	87
2017	244	213	30	1	0	41	115
2016	214	199	15	0	0	36	80
2015	214	193	21	0	0	40	93
2014	213	192	21	0	0	37	90
2013	303	282	21	0	0	37	97
2012	364	322	37	5	1	35	151
2011	365	337	28	0	0	37	100
2010	353	300	52	1	0	37	122

*2025 may be a partial year in EPA's file.

Nearby counties on file

How this is counted

A bad air day is a day the county's daily AQI from EPA AirData went above 100, the level where EPA tells children, older adults and people with asthma or heart disease to cut back outdoors. Monitors do not run every day, so yearly counts are scaled to 365 days. This is the record, not today's air: for that, check AirNow. More on the method in how the county numbers are made, on the AQI 100 line in what counts as a bad air day, and on why a purifier does not touch ozone in smoke vs ozone.