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

2 bad air days a year

About the middle of monitored US counties. Ranked 459 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (9% particle days).

Which months to watch

Most bad days here fall in June and May and July and September. 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 worst days on file

In 2000 to 2009 this county averaged 17 bad days a year; in 2016 to 2025, 2. The air has improved. The worst recent year was 2018, with 6 bad days on 365 monitored days.

Date	AQI	Main pollutant
2023-06-02	129	Ozone
2018-05-25	122	Ozone
2023-06-18	122	Ozone
2023-06-29	122	Ozone
2020-07-05	120	PM2.5

An ordinary day in Allen

Across 3,627 monitored days from 2016 to 2025, the air in Allen County rated Good on 64% of them, less often than the 72% typical of monitored counties, and Moderate on 35%. The median day sat at AQI 45; one day in ten went above 63.

The pollutant setting the AQI on an ordinary day here:

ozone55%2,000 days
fine particles (PM2.5)45%1,627 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	219	143	3	0	44	115
2024	366	229	137	0	0	45	100
2023	361	267	89	5	0	42	129
2022	351	326	23	2	0	35	115
2021	365	257	108	0	0	40	100
2020	366	232	132	2	0	45	120
2019	365	200	164	1	0	49	101
2018	365	193	166	6	0	50	122
2017	365	214	150	1	0	47	105
2016	358	194	161	3	0	48	119
2015	357	177	178	2	1	51	176
2014	359	112	241	6	0	55	147
2013	365	170	195	0	0	52	97
2012	362	91	255	16	1	60	179
2011	361	132	221	8	0	55	122
2010	365	78	279	8	0	61	121

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

Elsewhere in Indiana

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.