Daily Air Quality Index summaries from EPA monitors in Sussex, Delaware, 1980–2025.
82%
Good days in 2025
39
Median daily AQI, 2025
1
Days above 100 in 2025
365
Days with an AQI in 2025 (of 365)
In 2025, EPA reported a daily Air Quality Index (AQI) for Sussex, Delaware on 365 days. 300 of those days (82%) were in the Good range, and the median daily AQI was 39. That median is about the same as the typical monitored county in Delaware (median 41 across 3 counties), and about the same as the typical monitored U.S. county (40). The main pollutant was ozone on 269 days. Across the years with fuller monitoring, the share of Good days rose: an average of 47% in 1983–1985 versus 74% in 2023–2025.
Years with fewer than 120 monitored days (1980) 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
269
74%
Fine particles (PM2.5)
96
26%
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
365
300
64
1
0
0
0
39
57
105
Ozone
2024
365
298
67
0
0
0
0
40
55
90
Ozone
2023
365
215
144
3
2
1
0
47
68
203
PM2.5
2022
365
274
91
0
0
0
0
43
58
87
Ozone
2021
365
277
88
0
0
0
0
40
57
100
Ozone
2020
366
286
80
0
0
0
0
42
56
87
Ozone
2019
365
251
114
0
0
0
0
44
61
93
Ozone
2018
365
256
105
4
0
0
0
42
61
140
Ozone
2017
365
251
113
1
0
0
0
44
61
119
Ozone
2016
366
259
104
3
0
0
0
43
61
129
Ozone
2015
365
231
131
3
0
0
0
45
67
115
Ozone
2014
365
199
165
1
0
0
0
49
67
105
PM2.5
2013
365
245
116
4
0
0
0
43
63
136
Ozone
2012
366
271
77
14
4
0
0
41
74
200
Ozone
2011
365
263
86
15
1
0
0
42
80
172
Ozone
2010
304
170
113
17
4
0
0
48
93
182
Ozone
2009
258
168
88
2
0
0
0
46
74
105
Ozone
2008
260
127
112
20
1
0
0
52
97
164
Ozone
2007
261
125
113
23
0
0
0
51
97
147
Ozone
2006
267
118
128
19
2
0
0
53
93
159
Ozone
2005
263
118
115
23
6
1
0
54
105
206
Ozone
2004
263
131
114
16
2
0
0
51
97
154
Ozone
2003
270
148
98
19
3
2
0
48
93
218
Ozone
2002
272
120
114
22
16
0
0
55
115
185
Ozone
2001
277
127
123
18
8
1
0
54
100
201
Ozone
2000
278
130
118
25
5
0
0
52
101
187
Ozone
1999
282
138
100
25
19
0
0
51
133
197
Ozone
1998
276
149
82
26
16
3
0
48
133
205
Ozone
1997
260
174
49
26
9
2
0
44
122
210
Ozone
1996
219
145
45
24
5
0
0
39
112
187
Ozone
1995
239
154
57
23
5
0
0
42
108
197
Ozone
1994
246
155
65
23
3
0
0
44
101
172
Ozone
1993
182
100
42
28
12
0
0
48
129
182
Ozone
1992
238
170
57
7
4
0
0
41
90
172
Ozone
1991
239
140
55
32
8
4
0
44
133
235
Ozone
1990
197
103
55
26
12
1
0
49
133
228
Ozone
1989
187
132
41
11
3
0
0
43
93
169
Ozone
1988
175
106
35
15
11
8
0
44
151
218
Ozone
1987
214
109
58
28
17
2
0
49
136
203
Ozone
1986
172
92
55
16
9
0
0
48
119
182
Ozone
1985
202
92
54
40
15
1
0
54
143
214
Ozone
1984
199
113
60
15
11
0
0
46
119
187
Ozone
1983
176
70
42
32
20
12
0
74
182
248
Ozone
1980
69
29
17
17
5
1
0
71
143
208
Ozone
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 Delaware with a similar median AQI in 2025
