Bad Air Days in Frederick County, Virginia: 1 a Year

1 bad air day a year

Fewer bad air days than most monitored US counties. Ranked 673 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly particles: smoke and dust (90% particle days).

The bad-air season here

Most bad days here fall in June and November. 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 17 bad days a year; in 2016 to 2025, 1. The air has improved. The worst recent year was 2023, with 9 bad days on 363 monitored days.

Date	AQI	Main pollutant
2023-06-29	185	PM2.5
2023-06-08	157	PM2.5
2023-11-16	156	PM2.5
2023-06-28	152	PM2.5
2023-11-17	146	PM2.5

The air on a normal day

Across 3,502 monitored days from 2016 to 2025, the air in Frederick County rated Good on 72% of them, close to the 72% typical of monitored counties, and Moderate on 27%. The median day sat at AQI 42; one day in ten went above 58.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)64%2,236 days
ozone36%1,266 days

Every recent year on file

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	270	95	0	0	39	85
2024	355	264	90	1	0	41	102
2023	363	240	114	9	4	44	185
2022	334	234	100	0	0	43	89
2021	362	222	140	0	0	44	98
2020	304	249	55	0	0	39	81
2019	365	277	88	0	0	42	96
2018	352	267	85	0	0	40	87
2017	344	253	91	0	0	42	80
2016	358	256	102	0	0	42	90
2015	342	213	129	0	0	45	86
2014	362	222	140	0	0	45	93
2013	365	229	135	1	0	45	115
2012	361	180	178	3	0	51	119
2011	365	183	181	1	0	50	101
2010	261	155	102	4	1	46	159

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

Nearby counties on file

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.