Bad Air Days in Shelby County, Indiana: 2 a Year

2 bad air days a year

Fewer bad air days than most monitored US counties. Ranked 560 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 Shelby

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

What actually helps 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

The worst recent year was 2018, with 5 bad days on 361 monitored days.

Date	AQI	Main pollutant
2023-06-28	147	Ozone
2020-06-19	115	Ozone
2022-06-22	115	Ozone
2018-07-14	112	Ozone
2023-06-02	112	Ozone

The air on a normal day

Across 3,330 monitored days from 2016 to 2025, the air in Shelby County rated Good on 91% of them, more often than the 72% typical of monitored counties, and Moderate on 8%. The median day sat at AQI 36; one day in ten went above 51.

The pollutant setting the AQI on an ordinary day here:

ozone100%3,330 days

Shelby County by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	359	328	30	1	0	35	105
2024	365	331	34	0	0	36	87
2023	359	317	38	4	0	37	147
2022	364	336	26	2	0	36	115
2021	365	345	20	0	0	33	100
2020	366	347	18	1	0	32	115
2019	365	338	27	0	0	36	84
2018	361	331	25	5	0	34	112
2017	243	209	33	1	0	41	108
2016	183	153	29	1	0	39	101
2015	183	166	17	0	0	39	77
2014	182	157	25	0	0	42	100
2013	183	148	35	0	0	44	97
2012	183	95	70	18	2	49	159
2011	179	114	57	8	0	46	143
2010	181	130	51	0	0	44	93

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

Indiana 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.