San Luis Obispo County, California air quality history
Daily Air Quality Index summaries from EPA monitors in San Luis Obispo, California, 1980–2025.
52%
Good days in 2025
50
Median daily AQI, 2025
7
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 Luis Obispo, California on 365 days. 191 of those days (52%) were in the Good range, and the median daily AQI was 50. That median is higher than 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 ozone on 194 days. Across the years with fuller monitoring, the share of Good days fell: an average of 77% in 1980–1982 versus 54% 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
194
53%
Fine particles (PM2.5)
168
46%
Coarse particles (PM10)
3
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
191
167
7
0
0
0
50
67
119
Ozone
2024
366
193
163
10
0
0
0
49
80
122
Ozone
2023
365
207
152
6
0
0
0
47
77
122
Ozone
2022
365
117
245
3
0
0
0
55
75
115
PM2.5
2021
365
154
203
8
0
0
0
53
77
133
Ozone
2020
366
161
174
21
7
1
2
53
90
334
PM2.5
2019
365
196
166
3
0
0
0
49
74
108
Ozone
2018
365
147
209
9
0
0
0
53
77
133
Ozone
2017
365
107
250
8
0
0
0
58
82
133
PM2.5
2016
366
140
217
8
1
0
0
55
84
156
Ozone
2015
365
95
265
5
0
0
0
58
80
126
PM2.5
2014
365
81
270
14
0
0
0
60
87
126
PM2.5
2013
365
65
286
14
0
0
0
62
90
136
PM2.5
2012
366
113
216
35
2
0
0
57
101
154
Ozone
2011
365
78
268
19
0
0
0
61
93
133
PM2.5
2010
365
124
207
33
1
0
0
55
97
161
Ozone
2009
365
152
184
29
0
0
0
56
97
141
Ozone
2008
366
166
128
62
10
0
0
54
122
179
Ozone
2007
365
188
136
39
2
0
0
50
101
156
Ozone
2006
365
214
100
45
6
0
0
47
115
174
Ozone
2005
365
276
84
5
0
0
0
42
67
150
Ozone
2004
366
285
75
6
0
0
0
41
67
119
Ozone
2003
365
258
95
11
1
0
0
44
80
159
Ozone
2002
365
252
100
13
0
0
0
44
82
143
Ozone
2001
365
254
99
11
1
0
0
44
84
153
Ozone
2000
366
273
88
5
0
0
0
42
77
143
Ozone
1999
365
241
110
14
0
0
0
46
87
143
Ozone
1998
365
123
168
56
17
1
0
67
133
208
Ozone
1997
365
288
71
6
0
0
0
44
64
122
Ozone
1996
366
258
67
33
7
1
0
43
105
213
Ozone
1995
365
253
87
24
1
0
0
42
90
154
Ozone
1994
365
266
87
11
1
0
0
43
80
159
Ozone
1993
365
297
57
11
0
0
0
40
74
150
Ozone
1992
366
284
73
7
2
0
0
42
67
182
Ozone
1991
365
254
91
18
2
0
0
46
87
190
Ozone
1990
365
251
92
22
0
0
0
44
84
140
Ozone
1989
365
212
111
35
5
2
0
47
101
218
Ozone
1988
366
253
95
17
1
0
0
46
87
151
Ozone
1987
365
281
66
16
1
1
0
40
74
206
Ozone
1986
365
287
69
7
2
0
0
40
67
177
Ozone
1985
365
282
73
9
1
0
0
43
74
156
Ozone
1984
366
308
52
4
2
0
0
38
61
169
Ozone
1983
365
304
49
9
3
0
0
38
71
169
Ozone
1982
365
309
48
8
0
0
0
39
61
140
Ozone
1981
365
276
76
13
0
0
0
42
71
140
Ozone
1980
366
254
88
23
1
0
0
42
87
154
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 California with a similar median AQI in 2025
