Bad Air Days in Dorchester County, Maryland: 2 a Year

2 bad air days a year

Fewer bad air days than most monitored US counties. Ranked 555 of 996 monitored counties, where 1 is worst.

What makes them bad: mostly ozone: summer smog (24% particle days).

The bad-air season here

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

The worst days on file

In 2000 to 2009 this county averaged 30 bad days a year; in 2016 to 2025, 2. The air has improved. The worst recent year was 2023, with 7 bad days on 365 monitored days.

Date	AQI	Main pollutant
2023-06-07	179	PM2.5
2023-06-08	166	PM2.5
2023-06-29	162	PM2.5
2018-07-10	151	Ozone
2019-09-12	126	Ozone

The air on a normal day

Across 3,652 monitored days from 2016 to 2025, the air in Dorchester County rated Good on 76% of them, more often than the 72% typical of monitored counties, and Moderate on 23%. The median day sat at AQI 42; one day in ten went above 57.

The pollutant setting the AQI on an ordinary day here:

ozone67%2,462 days
fine particles (PM2.5)33%1,190 days

Year by year

Year	Days monitored	Good	Moderate	Over 100	Over 150	Median AQI	Highest AQI
2025*	365	314	51	0	0	39	84
2024	366	294	71	1	0	40	108
2023	365	268	90	7	3	44	179
2022	365	274	91	0	0	43	93
2021	365	287	77	1	0	41	105
2020	365	339	26	0	0	36	84
2019	365	281	81	3	0	43	126
2018	365	283	80	2	1	40	151
2017	365	212	153	0	0	47	90
2016	366	236	127	3	0	45	122
2015	365	233	131	1	0	45	105
2014	365	218	147	0	0	46	90
2013	365	258	105	2	0	43	108
2012	365	253	94	18	4	41	208
2011	318	246	52	20	1	40	156
2010	355	272	74	9	1	40	182

*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.