Bad Air Days in Hardin County, Kentucky: under 1 a Year

under 1 bad air day a year

Rare: among the cleanest-air counties EPA monitors. Ranked 770 of 996 monitored counties, where 1 is worst.

What makes them bad: a mix of particles and ozone (50% particle days).

The bad-air season here

Most bad days here fall in June 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.

The worst days on file

In 2000 to 2009 this county averaged 17 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 365 monitored days.

Date	AQI	Main pollutant
2023-06-28	151	PM2.5
2023-07-16	111	PM2.5
2023-06-09	103	PM2.5
2016-06-16	101	Ozone
2021-07-28	101	Ozone

An ordinary day in Hardin

Across 3,368 monitored days from 2016 to 2025, the air in Hardin County rated Good on 63% of them, less often than the 72% typical of monitored counties, and Moderate on 37%. The median day sat at AQI 46; one day in ten went above 61.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)69%2,322 days
ozone31%1,046 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	304	223	81	0	0	43	97
2024	154	129	25	0	0	41	67
2023	365	225	136	4	1	45	151
2022	362	242	120	0	0	44	86
2021	364	238	125	1	0	43	101
2020	366	268	98	0	0	43	80
2019	363	261	102	0	0	44	72
2018	361	191	170	0	0	49	100
2017	365	178	187	0	0	51	87
2016	364	152	211	1	0	52	101
2015	365	175	189	1	0	51	105
2014	341	172	169	0	0	50	88
2013	364	154	210	0	0	53	90
2012	307	171	129	7	2	47	161
2011	339	197	141	1	0	47	112
2010	343	143	195	5	0	53	115

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

Elsewhere in Kentucky

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.