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

2 bad air days a year

About the middle of monitored US counties. Ranked 436 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (24% particle days).

Which months to watch

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

What to buy, and what not to

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.

The record for Champaign

In 2000 to 2009 this county averaged 13 bad days a year; in 2016 to 2025, 2. The air has improved. The worst recent year was 2023, with 13 bad days on 365 monitored days.

Date	AQI	Main pollutant
2023-06-28	277	PM2.5
2023-06-27	179	PM2.5
2023-07-16	148	PM2.5
2025-08-01	138	PM2.5
2025-03-15	137	PM2.5

An ordinary day in Champaign

Across 3,653 monitored days from 2016 to 2025, the air in Champaign County rated Good on 63% of them, less often than the 72% typical of monitored counties, and Moderate on 36%. The median day sat at AQI 45; one day in ten went above 63.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)54%1,964 days
ozone46%1,689 days

Champaign County by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	240	121	4	0	43	138
2024	366	250	116	0	0	44	100
2023	365	196	156	13	2	48	277
2022	365	223	141	1	0	44	126
2021	365	236	129	0	0	44	99
2020	366	250	114	2	0	44	126
2019	365	225	140	0	0	45	100
2018	365	209	152	4	0	47	112
2017	365	233	131	1	0	45	105
2016	366	254	112	0	0	43	100
2015	365	217	148	0	0	46	90
2014	365	277	87	1	0	38	101
2013	365	294	71	0	0	39	100
2012	366	273	85	8	0	41	136
2011	348	256	85	7	1	40	156
2010	352	280	72	0	0	35	88

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

Illinois compared

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.