Move workouts to the morning
Ozone peaks on hot, sunny afternoons. Mornings are usually cleaner.
Ozone guide →Air quality in San Luis Obispo County, CA
Includes San Luis Obispo and Paso Robles · EPA monitor readings, 2021 to 2025 · 282,000 people
For today's air and tomorrow's forecast, check AirNow by ZIP code.
Bad-air days a year
7
days with an AQI over 100
About 1 day in 54. In the early 2000s it was about 10 a year. San Luis Obispo County has the 22nd fewest bad-air days of the 52 California counties with monitors.
0days unhealthy for everyoneAQI over 150, a year
51AQI on a typical dayModerate: fine for most people
Aug to Octworst monthsOzone on hot afternoons
334worst day since 2016Aug 20, 2020, fine particles
How to read the AQIThe EPA's air score runs from 0 to 500. Higher is worse. Over 100 counts as a bad-air day.
Typical day 51 (Moderate)Worst day 334 (Hazardous)
Good0 to 50Moderate51 to 100Sensitive groups101 to 150Unhealthy151 to 200Very unhealthy201 to 300Hazardous301 to 500
When bad air happens in San Luis Obispo County
Average bad-air days in each month, from 10 years of daily readings since 2016. Most fall in August, September and October.
Jan0
Feb0
Mar0
Apr0
May0.7
Jun0.3
Jul1.4
Aug2.3
Sep2.3
Oct1.9
Nov0.5
Dec0
Fine particles (smoke, soot)Ozone (smog)Bars stack in that order, from the bottom.
See the numbers by month
| Month | Ozone | Fine particles | All |
|---|---|---|---|
| January | 0 | 0 | 0 |
| February | 0 | 0 | 0 |
| March | 0 | 0 | 0 |
| April | 0 | 0 | 0 |
| May | 0.7 | 0 | 0.7 |
| June | 0.3 | 0 | 0.3 |
| July | 1.4 | 0 | 1.4 |
| August | 1.5 | 0.8 | 2.3 |
| September | 1.8 | 0.5 | 2.3 |
| October | 1.6 | 0.3 | 1.9 |
| November | 0.5 | 0 | 0.5 |
| December | 0 | 0 | 0 |
The worst day since 2016 was August 20, 2020: AQI 334, from fine particles.
What causes it
The pollutant that pushed the AQI over 100 on each of the 94 bad-air days since 2016.
83%Ozone: smog that forms in sunlight on hot days
17%Fine particles: smoke and soot
Most bad days here are ozone days: smog that builds on hot, sunny afternoons.
CDC estimates by month, 2001 to 2022
The CDC's model counts bad-air days at the county's worst spot, from monitors and satellites. Particles (brown) fill the inside of the ring and ozone (blue) the outside.
See the numbers by month
| Month | Fine particles | Ozone |
|---|---|---|
| January | 0.5 | 0 |
| February | 0.6 | 0 |
| March | 0 | 0 |
| April | 0 | 0 |
| May | 0 | 0.6 |
| June | 0 | 0.7 |
| July | 0.1 | 1.4 |
| August | 0.3 | 0.4 |
| September | 0.2 | 1.0 |
| October | 0.1 | 0 |
| November | 0.9 | 0 |
| December | 1.0 | 0 |
What helps in San Luis Obispo County
Most bad days here are ozone, which builds on hot afternoons. Timing helps most; filters don't remove ozone.
Check tomorrow's forecast
AirNow posts an air quality forecast by ZIP code, usually the day before.
AirNow →Keep one room clean on smoky days
Shut the windows and run an air purifier sized for the room.
Choosing a purifier →For today's reading and tomorrow's forecast, check AirNow by ZIP code. Its fire and smoke map adds smoke plumes.
Purifiers catch smoke but don't remove ozone, and smoky days are rare here. If you want one for wildfire season anyway, see the 3 models we'd buy, each with a verified smoke rating.
Every year since 2000
Bad-air days each year. The striped part is days unhealthy for everyone, over AQI 150. The worst recent year was 2024, with 10 bad-air days.
Unhealthy for sensitive groups (101 to 150)Unhealthy or worse (over 150)
See the numbers by year
| Year | Bad-air days | Over 150 |
|---|---|---|
| 2000 | 5 | 0 |
| 2001 | 12 | 1 |
| 2002 | 13 | 0 |
| 2003 | 12 | 1 |
| 2004 | 6 | 0 |
| 2005 | 5 | 0 |
| 2006 | 51 | 6 |
| 2007 | 41 | 2 |
| 2008 | 72 | 10 |
| 2009 | 29 | 0 |
| 2010 | 34 | 1 |
| 2011 | 19 | 0 |
| 2012 | 37 | 2 |
| 2013 | 14 | 0 |
| 2014 | 14 | 0 |
| 2015 | 5 | 0 |
| 2016 | 9 | 1 |
| 2017 | 8 | 0 |
| 2018 | 9 | 0 |
| 2019 | 3 | 0 |
| 2020 | 31 | 10 |
| 2021 | 8 | 0 |
| 2022 | 3 | 0 |
| 2023 | 6 | 0 |
| 2024 | 10 | 0 |
| 2025 | 7 | 0 |
San Luis Obispo County and its neighbors
Bad-air days a year, 2021 to 2025. California counties with monitors averaged about 53 bad-air days a year, weighted by population.
Questions people ask about air in San Luis Obispo County
How often is the air bad in San Luis Obispo County?
From 2021 to 2025, monitors in San Luis Obispo County recorded about 7 bad-air days a year with an AQI above 100, which is unhealthy for sensitive groups or worse. The worst year in that stretch was 2024, with 10 bad-air days.
What causes bad air in San Luis Obispo County?
Most bad days here are ozone days: smog that builds on hot, sunny afternoons. Bad days cluster in August, September and October.
Where can I see today's air quality in San Luis Obispo County?
AirNow, run by the EPA and its partners, shows the current AQI and tomorrow's forecast for your ZIP code. Its fire and smoke map adds smoke plumes. On a typical day the AQI in San Luis Obispo County is about 51, which is moderate, fine for most people. Check it most in August, September and October, when bad days here cluster.
About these numbers
Day counts come from the EPA's county air quality summaries, which take the worst reading across a county's monitors each day. Monitors here reported on about 365 days a year from 2021 to 2025. A county is large, and your street can be cleaner or worse. CDC's model, which estimates every county from monitors and satellites, gives the worst spot in San Luis Obispo County about 3 high-particle days and almost no high-ozone days a year from 2018 to 2022.
Sources: EPA AirData county AQI summaries (2000 to 2025) and daily county AQI (2016 to 2025); CDC Environmental Public Health Tracking Network modeled PM2.5 and ozone (2001 to 2022). Updated November 8, 2026.