San Joaquin County, California air quality history
Daily Air Quality Index summaries from EPA monitors in San Joaquin, California, 1980–2025.
60%
Good days in 2025
46
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 San Joaquin, California on 365 days. 219 of those days (60%) were in the Good range, and the median daily AQI was 46. That median is about the same as the typical monitored county in California (median 45.5 across 46 counties), and higher than the typical monitored U.S. county (40). The main pollutant was fine particles (PM2.5) on 196 days. Across the years with fuller monitoring, the share of Good days fell: an average of 63% in 1980–1982 versus 55% 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)
196
54%
Ozone
163
45%
Coarse particles (PM10)
6
2%
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
219
146
0
0
0
0
46
67
93
PM2.5
2024
366
178
177
11
0
0
0
51
79
140
PM2.5
2023
365
208
148
9
0
0
0
47
78
119
PM2.5
2022
365
192
164
8
0
1
0
48
86
208
Ozone
2021
365
140
209
15
1
0
0
55
84
153
PM2.5
2020
366
162
173
16
13
2
0
54
97
215
PM2.5
2019
365
202
151
11
1
0
0
47
82
190
Ozone
2018
365
91
241
20
8
4
1
59
99
365
PM2.5
2017
365
141
191
33
0
0
0
55
100
146
PM2.5
2016
366
62
278
25
1
0
0
60
93
166
PM2.5
2015
365
83
246
32
4
0
0
60
100
164
PM2.5
2014
365
112
219
33
1
0
0
58
99
152
PM2.5
2013
365
43
289
24
9
0
0
62
99
159
PM2.5
2012
366
88
236
38
4
0
0
60
101
182
PM2.5
2011
365
128
194
36
7
0
0
57
103
158
PM2.5
2010
365
168
184
12
1
0
0
52
83
174
PM2.5
2009
365
220
121
23
1
0
0
45
93
177
Ozone
2008
366
155
179
22
10
0
0
54
95
195
Ozone
2007
365
135
203
26
1
0
0
54
93
155
PM2.5
2006
365
211
117
30
7
0
0
45
101
195
Ozone
2005
365
266
84
13
2
0
0
40
73
156
Ozone
2004
366
251
101
13
1
0
0
44
84
179
Ozone
2003
365
222
116
25
2
0
0
44
97
159
Ozone
2002
365
202
125
34
4
0
0
48
101
177
Ozone
2001
365
226
115
19
5
0
0
45
87
166
Ozone
2000
366
216
116
27
7
0
0
46
97
172
Ozone
1999
365
213
103
34
13
2
0
48
115
208
Ozone
1998
365
262
70
25
8
0
0
41
100
187
Ozone
1997
365
280
72
11
2
0
0
41
74
185
Ozone
1996
366
229
81
43
13
0
0
44
112
177
Ozone
1995
365
255
78
22
9
1
0
42
87
202
Ozone
1994
365
219
111
29
6
0
0
46
100
190
Ozone
1993
365
234
101
26
4
0
0
46
100
179
Ozone
1992
366
217
108
33
8
0
0
47
105
161
Ozone
1991
365
193
123
42
7
0
0
48
108
174
Ozone
1990
365
212
119
27
7
0
0
47
100
192
Ozone
1989
365
221
118
23
3
0
0
47
93
195
Ozone
1988
366
196
118
32
20
0
0
48
126
195
Ozone
1987
365
170
109
58
27
1
0
54
143
205
Ozone
1986
365
200
102
49
13
1
0
47
115
210
Ozone
1985
365
217
92
33
20
3
0
44
122
207
Ozone
1984
358
199
94
33
26
6
0
47
143
209
Ozone
1983
365
263
72
23
6
1
0
38
89
210
Ozone
1982
365
228
110
25
2
0
0
47
90
192
NO2
1981
365
241
88
23
12
1
0
42
100
213
NO2
1980
366
220
102
29
13
2
0
47
106
219
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 California with a similar median AQI in 2025
