Daily Air Quality Index summaries from EPA monitors in New Castle, Delaware, 1980–2025.
64%
Good days in 2025
44
Median daily AQI, 2025
4
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 New Castle, Delaware on 365 days. 235 of those days (64%) were in the Good range, and the median daily AQI was 44. That median is higher than the typical monitored county in Delaware (median 41 across 3 counties), and higher than the typical monitored U.S. county (40). The main pollutant was ozone on 203 days. Across the years with fuller monitoring, the share of Good days rose: an average of 57% in 1980–1982 versus 60% in 2023–2025.
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
203
56%
Fine particles (PM2.5)
162
44%
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
235
126
3
1
0
0
44
67
161
Ozone
2024
366
246
116
4
0
0
0
43
67
119
Ozone
2023
365
173
184
5
1
2
0
51
73
282
PM2.5
2022
365
208
157
0
0
0
0
48
63
93
PM2.5
2021
365
195
166
4
0
0
0
48
67
144
PM2.5
2020
366
231
133
2
0
0
0
46
63
105
PM2.5
2019
365
207
155
3
0
0
0
47
71
136
PM2.5
2018
365
212
147
6
0
0
0
48
71
150
PM2.5
2017
365
187
168
10
0
0
0
50
71
147
PM2.5
2016
366
173
183
9
1
0
0
52
74
154
PM2.5
2015
365
170
185
9
1
0
0
52
84
172
PM2.5
2014
365
140
214
10
1
0
0
54
80
153
PM2.5
2013
365
159
199
7
0
0
0
52
72
133
PM2.5
2012
366
125
221
18
2
0
0
55
85
151
PM2.5
2011
365
116
231
14
4
0
0
56
83
187
PM2.5
2010
365
131
201
28
5
0
0
55
97
158
PM2.5
2009
365
151
207
5
2
0
0
53
77
155
PM2.5
2008
366
122
220
21
2
1
0
57
93
202
PM2.5
2007
365
114
215
31
4
1
0
59
100
213
PM2.5
2006
365
116
221
25
3
0
0
58
96
174
PM2.5
2005
365
91
240
27
7
0
0
61
97
200
PM2.5
2004
366
81
269
15
1
0
0
60
90
172
PM2.5
2003
365
94
241
26
2
2
0
60
97
217
PM2.5
2002
365
65
250
33
14
3
0
61
119
217
PM2.5
2001
365
59
254
32
20
0
0
67
112
192
PM2.5
2000
366
61
273
25
6
1
0
61
96
214
PM2.5
1999
365
101
225
22
13
4
0
61
112
215
PM2.5
1998
365
244
75
27
18
1
0
42
112
217
Ozone
1997
365
271
51
26
14
3
0
41
115
217
Ozone
1996
366
265
73
23
4
1
0
41
87
203
Ozone
1995
365
238
81
23
17
6
0
43
122
232
Ozone
1994
365
233
80
34
15
3
0
44
119
216
Ozone
1993
365
241
72
27
22
3
0
43
122
212
Ozone
1992
366
288
49
20
8
1
0
37
93
204
Ozone
1991
365
236
75
37
9
8
0
44
119
220
Ozone
1990
357
201
110
34
9
3
0
47
108
215
NO2
1989
354
217
97
22
16
2
0
47
105
228
NO2
1988
358
206
85
27
16
24
0
47
161
266
NO2
1987
365
175
123
30
27
10
0
57
151
222
NO2
1986
365
199
119
22
22
3
0
47
112
216
NO2
1985
365
142
141
51
21
10
0
57
143
212
Ozone
1984
366
178
135
33
16
4
0
51
115
223
NO2
1983
365
181
96
43
27
18
0
51
166
256
Ozone
1982
359
218
83
34
17
7
0
47
126
212
Ozone
1981
351
256
58
33
4
0
0
34
103
169
CO
1980
361
136
140
55
23
7
0
59
143
228
NO2
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
