Daily Air Quality Index summaries from EPA monitors in Washington, Maryland, 1980–2025.
79%
Good days in 2025
40
Median daily AQI, 2025
0
Days above 100 in 2025
361
Days with an AQI in 2025 (of 365)
In 2025, EPA reported a daily Air Quality Index (AQI) for Washington, Maryland on 361 days. 285 of those days (79%) were in the Good range, and the median daily AQI was 40. That median is about the same as the typical monitored county in Maryland (median 39.5 across 16 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was ozone on 195 days. Across the years with fuller monitoring, the share of Good days held roughly steady: an average of 79% in 1982–1984 versus 78% in 2023–2025.
Years with fewer than 120 monitored days (1981, 1985, 1992, 1993, 1994, 1995…) are shown in the table but left out of comparisons and trend statements.
How the days broke down each year
Each bar is one year. The colored segments show the share of monitored days that fell in each AQI category.
Good
Moderate
Unhealthy for Sensitive Groups
Unhealthy
Very Unhealthy
Hazardous
Typical and high-end AQI over time
The median is the middle day of the year. The 90th percentile is the level that only the highest 10% of days exceeded.
Median daily AQI
90th-percentile daily AQI
Main pollutant by day, 2025
On each monitored day, the AQI reflects whichever measured pollutant had the highest index. This counts how many days each pollutant set the AQI. A pollutant that was not measured here cannot appear.
Pollutant
Days as main pollutant
Share of monitored days
Ozone
195
54%
Fine particles (PM2.5)
166
46%
Year-by-year data
Annual AQI summary by year
Year
Days with AQI
Good
Moderate
Unhealthy for Sensitive Groups
Unhealthy
Very Unhealthy
Hazardous
Median AQI
90th pct.
Max AQI
Main pollutant
2025
361
285
76
0
0
0
0
40
58
90
Ozone
2024
362
287
75
0
0
0
0
40
58
90
Ozone
2023
355
267
82
4
2
0
0
42
60
172
Ozone
2022
344
283
61
0
0
0
0
40
54
87
Ozone
2021
360
244
115
1
0
0
0
44
65
115
PM2.5
2020
359
288
71
0
0
0
0
40
55
83
PM2.5
2019
360
279
81
0
0
0
0
42
58
93
PM2.5
2018
356
253
103
0
0
0
0
43
63
93
PM2.5
2017
357
221
135
1
0
0
0
45
61
101
PM2.5
2016
351
209
138
4
0
0
0
47
64
112
PM2.5
2015
345
166
178
1
0
0
0
51
71
101
PM2.5
2014
352
216
136
0
0
0
0
45
66
100
PM2.5
2013
362
214
142
6
0
0
0
47
67
126
PM2.5
2012
362
162
189
10
1
0
0
52
77
151
PM2.5
2011
348
135
207
6
0
0
0
54
75
147
PM2.5
2010
303
126
166
10
1
0
0
54
84
161
Ozone
2009
263
183
80
0
0
0
0
43
66
100
Ozone
2008
264
154
98
12
0
0
0
47
80
147
Ozone
2007
265
119
124
22
0
0
0
52
100
150
Ozone
2006
257
143
100
14
0
0
0
48
90
150
Ozone
2005
256
112
120
22
2
0
0
54
100
164
Ozone
2004
265
148
106
11
0
0
0
48
87
150
Ozone
2003
263
146
106
9
2
0
0
47
84
190
Ozone
2002
257
119
94
29
15
0
0
53
129
185
Ozone
2001
263
115
120
23
5
0
0
54
105
161
Ozone
2000
256
137
105
12
2
0
0
49
84
172
Ozone
1999
214
110
59
37
8
0
0
50
122
174
Ozone
1995
35
34
1
0
0
0
0
25
38
52
PM10
1994
57
53
4
0
0
0
0
19
49
56
PM10
1993
60
57
3
0
0
0
0
23
44
58
PM10
1992
42
42
0
0
0
0
0
24
35
38
PM10
1985
71
70
1
0
0
0
0
11
36
93
Ozone
1984
307
231
50
19
6
1
0
32
97
213
Ozone
1983
278
222
29
19
8
0
0
29
97
200
Ozone
1982
241
197
31
13
0
0
0
30
71
147
Ozone
1981
107
102
4
0
1
0
0
20
44
154
Ozone
1980
118
108
10
0
0
0
0
32
48
80
CO
What this data can and can’t tell you
It is a county-level summary. EPA reports one AQI per day for the county, based on the monitors operating there. Air at a particular street, school or home can differ, especially near roads, industry or wildfire smoke.
It is not a health assessment. The AQI is EPA’s scale for communicating daily air quality. A county’s history can’t tell you what the health risk is for any particular person. For daily conditions and health guidance, see AirNow.
Rules change over time. EPA has revised AQI breakpoints, most recently for fine particles in 2024, so some year-to-year change can reflect the scale rather than the air.
Counties in Maryland with a similar median AQI in 2025
