Bad Air Days in Hendricks County, Indiana: under 1 a Year

under 1 bad air day a year

Rare: among the cleanest-air counties EPA monitors. Ranked 763 of 996 monitored counties, where 1 is worst.

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

Which months to watch

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

The record for Hendricks

In 2000 to 2009 this county averaged 26 bad days a year; in 2016 to 2025, under 1. The air has improved. The worst recent year was 2023, with 4 bad days on 360 monitored days.

Date	AQI	Main pollutant
2023-08-03	119	Ozone
2018-06-08	108	Ozone
2023-06-02	105	Ozone
2023-06-28	105	Ozone
2018-06-28	101	Ozone

An ordinary day in Hendricks

Across 3,307 monitored days from 2016 to 2025, the air in Hendricks County rated Good on 93% of them, more often than the 72% typical of monitored counties, and Moderate on 7%. The median day sat at AQI 35; one day in ten went above 49.

The pollutant setting the AQI on an ordinary day here:

ozone100%3,307 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Median AQI	Highest AQI
2025*	362	333	29	0	35	90
2024	353	331	22	0	35	80
2023	360	324	32	4	37	119
2022	352	338	14	0	34	87
2021	365	347	18	0	33	80
2020	366	348	18	0	32	87
2019	361	348	13	0	34	93
2018	365	335	28	2	33	108
2017	240	220	20	0	38	93
2016	183	146	37	0	40	100
2015	183	179	4	0	35	61
2014	183	175	8	0	36	77
2013	179	168	11	0	38	74
2012	182	122	56	4	45	143
2011	182	145	35	2	40	105
2010	183	146	37	0	41	100

*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.