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

2 bad air days a year

About the middle of monitored US counties. Ranked 450 of 996 monitored counties, where 1 is worst.

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

When the bad days come in Effingham

Most bad days here fall in June. 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 10 bad days a year; in 2016 to 2025, 2. The air has improved. The worst recent year was 2023, with 10 bad days on 242 monitored days.

Date	AQI	Main pollutant
2023-06-06	140	Ozone
2023-06-28	136	Ozone
2023-06-10	129	Ozone
2023-05-30	126	Ozone
2023-06-24	122	Ozone

Most days, not the worst ones

Across 2,314 monitored days from 2016 to 2025, the air in Effingham County rated Good on 89% of them, more often than the 72% typical of monitored counties, and Moderate on 11%. 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%2,314 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	242	231	11	0	0	35	84
2024	240	217	22	1	0	41	101
2023	242	182	50	10	0	44	140
2022	239	215	24	0	0	38	100
2021	237	226	11	0	0	37	77
2020	166	156	10	0	0	37	84
2019	245	224	21	0	0	40	84
2018	245	214	30	1	0	39	112
2017	244	206	35	3	0	43	112
2016	214	181	33	0	0	39	93
2015	203	184	19	0	0	40	84
2014	212	187	25	0	0	38	90
2013	213	184	29	0	0	41	97
2012	192	125	58	9	1	46	166
2011	211	175	35	1	0	43	108
2010	195	157	32	6	0	44	105

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

Elsewhere in Illinois

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.