Daily Air Quality Index summaries from EPA monitors in Suffolk, Massachusetts, 1980–2025.
76%
Good days in 2025
37
Median daily AQI, 2025
2
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 Suffolk, Massachusetts on 365 days. 279 of those days (76%) were in the Good range, and the median daily AQI was 37. That median is about the same as the typical monitored county in Massachusetts (median 38 across 13 counties), and lower than the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 201 days. Across the years with fuller monitoring, the share of Good days rose: an average of 19% in 1980–1982 versus 73% 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
Fine particles (PM2.5)
201
55%
Ozone
146
40%
Nitrogen dioxide (NO₂)
16
4%
Coarse particles (PM10)
2
1%
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
279
84
2
0
0
0
37
60
106
PM2.5
2024
366
291
75
0
0
0
0
36
57
78
PM2.5
2023
365
231
134
0
0
0
0
44
62
99
PM2.5
2022
365
261
102
2
0
0
0
41
60
112
PM2.5
2021
365
237
125
3
0
0
0
44
61
145
PM2.5
2020
366
229
137
0
0
0
0
45
57
84
PM2.5
2019
365
224
141
0
0
0
0
46
58
87
PM2.5
2018
365
119
245
1
0
0
0
53
65
108
PM2.5
2017
365
98
264
3
0
0
0
56
70
119
PM2.5
2016
366
180
186
0
0
0
0
51
66
90
PM2.5
2015
365
141
223
1
0
0
0
53
64
126
PM2.5
2014
365
122
243
0
0
0
0
53
65
85
PM2.5
2013
365
125
235
5
0
0
0
54
70
122
PM2.5
2012
366
140
224
1
1
0
0
53
68
163
PM2.5
2011
365
100
262
3
0
0
0
55
72
123
PM2.5
2010
365
128
233
3
1
0
0
54
72
156
PM2.5
2009
365
145
214
6
0
0
0
52
71
136
PM2.5
2008
366
77
282
7
0
0
0
58
79
143
PM2.5
2007
365
52
297
15
1
0
0
60
86
154
PM2.5
2006
365
103
241
21
0
0
0
56
89
148
PM2.5
2005
365
49
293
18
5
0
0
61
90
174
PM2.5
2004
366
50
307
8
1
0
0
61
84
172
PM2.5
2003
365
40
308
15
2
0
0
62
89
192
PM2.5
2002
365
87
247
20
9
2
0
59
95
222
PM2.5
2001
365
63
275
19
6
2
0
61
91
206
PM2.5
2000
366
78
277
11
0
0
0
61
80
147
PM2.5
1999
365
145
198
17
5
0
0
54
89
192
PM2.5
1998
365
235
121
5
4
0
0
44
71
174
NO2
1997
365
244
114
6
1
0
0
45
67
151
NO2
1996
366
211
145
10
0
0
0
48
82
121
NO2
1995
365
245
105
14
1
0
0
44
68
190
NO2
1994
365
185
171
6
3
0
0
50
77
159
NO2
1993
365
188
166
10
1
0
0
50
80
190
NO2
1992
366
223
130
8
5
0
0
47
73
187
NO2
1991
365
179
173
11
2
0
0
51
76
172
NO2
1990
365
205
143
15
2
0
0
48
74
200
NO2
1989
365
192
162
8
3
0
0
50
78
197
NO2
1988
366
166
164
21
10
5
0
52
100
221
NO2
1987
365
95
244
20
5
1
0
60
90
205
NO2
1986
365
141
189
32
3
0
0
55
99
190
NO2
1985
365
76
268
15
6
0
0
61
91
190
NO2
1984
366
43
248
69
6
0
0
73
107
192
NO2
1983
365
71
268
20
4
2
0
62
94
212
CO
1982
365
60
273
28
1
3
0
68
99
271
CO
1981
365
48
293
24
0
0
0
68
96
145
CO
1980
362
96
217
46
3
0
0
65
105
172
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 Massachusetts with a similar median AQI in 2025
