Bad Air Days in Knox County, Nebraska: 3 a Year

3 bad air days a year

About the middle of monitored US counties. Ranked 417 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 Knox

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

Is a purifier worth it 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

In 2000 to 2009 this county averaged under 1 bad days a year; in 2016 to 2025, 3. Not much has changed. The worst recent year was 2023, with 14 bad days on 341 monitored days.

Date	AQI	Main pollutant
2023-06-08	151	Ozone
2023-06-07	147	Ozone
2023-06-04	140	Ozone
2023-05-24	122	Ozone
2023-06-15	122	Ozone

Most days, not the worst ones

Across 3,494 monitored days from 2016 to 2025, the air in Knox County rated Good on 91% of them, more often than the 72% typical of monitored counties, and Moderate on 9%. The median day sat at AQI 36; one day in ten went above 52.

The pollutant setting the AQI on an ordinary day here:

ozone100%3,494 days

Knox County by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	348	320	24	4	0	36	115
2024	327	300	26	1	0	36	108
2023	341	271	56	14	1	41	151
2022	355	319	36	0	0	37	100
2021	358	317	36	5	0	37	112
2020	365	341	24	0	0	35	84
2019	355	342	13	0	0	35	80
2018	357	329	28	0	0	34	93
2017	338	304	34	0	0	36	100
2016	350	323	26	1	0	35	101
2015	348	322	26	0	0	36	87
2014	342	318	24	0	0	35	80
2013	364	339	25	0	0	36	100
2012	352	262	77	13	0	38	133
2011	329	299	29	1	0	37	101
2010	349	324	25	0	0	36	90

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

Elsewhere in Nebraska

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.