Bad Air Days in Macon County, Illinois: 3 a Year

3 bad air days a year

About the middle of monitored US counties. Ranked 363 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (26% particle days).

When the bad days come in Macon

Most bad days here fall in June and May and July. 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.

Better or worse than it was

In 2000 to 2009 this county averaged 8 bad days a year; in 2016 to 2025, 3. The air has improved. The worst recent year was 2023, with 16 bad days on 365 monitored days.

Date	AQI	Main pollutant
2023-06-28	287	PM2.5
2023-06-27	178	PM2.5
2023-07-16	148	PM2.5
2025-03-15	141	PM2.5
2023-06-03	140	Ozone

The air on a normal day

Across 3,641 monitored days from 2016 to 2025, the air in Macon County rated Good on 55% of them, less often than the 72% typical of monitored counties, and Moderate on 44%. The median day sat at AQI 48; one day in ten went above 64.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)69%2,523 days
ozone31%1,118 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	237	125	3	0	44	141
2024	366	238	127	1	0	43	101
2023	365	171	178	16	2	51	287
2022	365	209	154	2	0	46	115
2021	361	179	179	3	0	51	112
2020	362	214	148	0	0	46	90
2019	364	176	188	0	0	51	93
2018	365	162	200	3	0	52	126
2017	363	214	146	3	0	47	108
2016	365	201	164	0	0	49	97
2015	365	228	137	0	0	44	100
2014	365	214	151	0	0	45	90
2013	365	226	139	0	0	44	88
2012	366	164	192	10	0	52	126
2011	365	119	241	5	1	55	161
2010	365	167	198	0	0	52	99

*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.