Bad Air Days in Washington County, Maryland: 1 a Year

1 bad air day a year

Fewer bad air days than most monitored US counties. Ranked 631 of 996 monitored counties, where 1 is worst.

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

When the bad days come in Washington

Most bad days here fall in June. 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 25 bad days a year; in 2016 to 2025, 1. The air has improved. The worst recent year was 2023, with 6 bad days on 355 monitored days.

Date	AQI	Main pollutant
2023-06-29	172	PM2.5
2023-06-08	158	PM2.5
2023-06-28	126	PM2.5
2023-06-07	118	PM2.5
2023-06-30	118	PM2.5

The air on a normal day

Across 3,565 monitored days from 2016 to 2025, the air in Washington County rated Good on 73% of them, close to the 72% typical of monitored counties, and Moderate on 26%. The median day sat at AQI 42; one day in ten went above 60.

The pollutant setting the AQI on an ordinary day here:

fine particles (PM2.5)52%1,840 days
ozone48%1,725 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	361	285	76	0	0	40	90
2024	362	287	75	0	0	40	90
2023	355	267	82	6	2	42	172
2022	344	283	61	0	0	40	87
2021	360	244	115	1	0	44	115
2020	359	288	71	0	0	40	83
2019	360	279	81	0	0	42	93
2018	356	253	103	0	0	43	93
2017	357	221	135	1	0	45	101
2016	351	209	138	4	0	47	112
2015	345	166	178	1	0	51	101
2014	352	216	136	0	0	45	100
2013	362	214	142	6	0	47	126
2012	362	162	189	11	1	52	151
2011	348	135	207	6	0	54	147
2010	303	126	166	11	1	54	161

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

Elsewhere in Maryland

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.