Bad Air Days in Union County, North Carolina: 2 a Year

2 bad air days a year

Fewer bad air days than most monitored US counties. Ranked 525 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 Union

Most bad days here fall in June and July and October. 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.

Better or worse than it was

In 2000 to 2009 this county averaged 39 bad days a year; in 2016 to 2025, 2. The air has improved. The worst recent year was 2018, with 3 bad days on 189 monitored days.

Date	AQI	Main pollutant
2018-07-11	122	Ozone
2017-09-28	115	Ozone
2016-06-10	108	Ozone
2016-04-19	105	Ozone
2019-07-02	105	Ozone

Most days, not the worst ones

Across 2,334 monitored days from 2016 to 2025, the air in Union County rated Good on 85% of them, more often than the 72% typical of monitored counties, and Moderate on 14%. The median day sat at AQI 41; one day in ten went above 58.

The pollutant setting the AQI on an ordinary day here:

ozone100%2,334 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	245	223	22	0	0	40	90
2024	245	212	33	0	0	41	97
2023	245	201	43	1	0	43	101
2022	244	218	26	0	0	41	100
2021	244	209	34	1	0	42	101
2020	242	242	0	0	0	31	50
2019	235	175	57	3	0	45	105
2018	189	143	43	3	0	44	122
2017	236	204	31	1	0	43	115
2016	209	165	41	3	0	44	108
2015	209	153	55	1	0	44	101
2014	214	166	46	2	0	44	115
2013	205	182	23	0	0	38	84
2012	214	165	44	5	1	40	206
2011	209	133	62	14	0	45	126
2010	221	139	75	7	0	45	115

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

Elsewhere in North Carolina

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.