Daily Air Quality Index summaries from EPA monitors in Pierce, Washington, 1980–2025.
73%
Good days in 2025
44
Median daily AQI, 2025
0
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 Pierce, Washington on 365 days. 267 of those days (73%) were in the Good range, and the median daily AQI was 44. That median is higher than the typical monitored county in Washington (median 28 across 30 counties), and higher than the typical monitored U.S. county (40). The main pollutant was ozone on 201 days. Across the years with fuller monitoring, the share of Good days rose: an average of 59% 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
Ozone
201
55%
Fine particles (PM2.5)
163
45%
Nitrogen dioxide (NO₂)
1
<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
267
98
0
0
0
0
44
58
100
Ozone
2024
366
265
100
0
1
0
0
44
59
166
Ozone
2023
365
273
89
0
3
0
0
42
62
195
Ozone
2022
365
239
115
9
2
0
0
44
70
178
Ozone
2021
365
269
96
0
0
0
0
42
61
94
Ozone
2020
366
256
99
4
3
4
0
42
66
256
Ozone
2019
365
234
129
2
0
0
0
44
67
142
PM2.5
2018
365
234
120
5
6
0
0
44
74
188
Ozone
2017
365
242
110
6
7
0
0
45
74
176
Ozone
2016
366
269
96
0
1
0
0
42
58
156
PM2.5
2015
365
235
123
6
1
0
0
44
67
166
PM2.5
2014
365
251
112
2
0
0
0
42
67
114
PM2.5
2013
365
217
143
5
0
0
0
46
74
113
PM2.5
2012
366
237
124
5
0
0
0
44
67
144
PM2.5
2011
365
236
119
9
1
0
0
44
71
152
PM2.5
2010
365
246
119
0
0
0
0
43
64
97
PM2.5
2009
365
193
164
7
1
0
0
48
73
165
PM2.5
2008
366
208
150
7
1
0
0
46
70
154
PM2.5
2007
365
168
177
17
3
0
0
52
82
160
PM2.5
2006
365
198
147
13
6
1
0
48
80
203
PM2.5
2005
365
137
214
14
0
0
0
54
86
134
PM2.5
2004
366
114
238
13
1
0
0
56
88
153
PM2.5
2003
365
104
229
32
0
0
0
55
96
150
PM2.5
2002
365
135
215
12
3
0
0
54
86
157
PM2.5
2001
365
117
224
23
1
0
0
55
91
154
PM2.5
2000
366
116
230
16
4
0
0
55
93
161
PM2.5
1999
365
159
196
8
2
0
0
53
80
164
PM2.5
1998
365
312
45
6
1
1
0
40
58
203
Ozone
1997
365
301
63
1
0
0
0
39
58
105
Ozone
1996
366
311
45
9
1
0
0
38
59
154
Ozone
1995
365
299
61
5
0
0
0
35
57
129
Ozone
1994
365
297
62
4
1
1
0
35
58
202
Ozone
1993
365
288
74
3
0
0
0
37
58
119
Ozone
1992
366
261
93
11
1
0
0
40
69
156
Ozone
1991
364
255
102
7
0
0
0
41
66
129
Ozone
1990
364
271
82
7
4
0
0
34
64
187
PM10
1989
365
248
111
6
0
0
0
41
70
140
CO
1988
366
216
127
17
6
0
0
45
82
183
CO
1987
364
191
143
24
4
2
0
49
96
215
CO
1986
363
213
138
10
2
0
0
45
77
159
CO
1985
365
212
124
26
3
0
0
47
90
154
CO
1984
366
247
112
6
1
0
0
43
76
154
CO
1983
365
259
99
6
1
0
0
41
71
154
CO
1982
365
247
100
13
5
0
0
43
80
182
CO
1981
365
177
163
11
8
6
0
51
87
223
CO
1980
366
223
126
14
3
0
0
45
86
161
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 Washington with a similar median AQI in 2025
