EPA air quality + NOAA smoke
California air quality by county
Bad-air days, typical county
9.6
per year, AQI over 100 (US: 2.4)
Smoke days, average county
15
per year, medium or heavy plume (US: 24)
Mold pros licensed?
No state license
found in our check
Wildfire smoke days by year
Days with a medium or heavy smoke plume overhead, averaged across California's 58 counties. Smoke days come from NOAA satellite analysts, who draw where smoke plumes are overhead each day. A plume overhead does not always reach the ground, so these days measure exposure risk, not what you breathed. We count only medium and heavy plumes.
Every monitored California county
Sorted by bad-air days. EPA monitors 52 of 58 counties; the rest have smoke data only.
| County | Good days | Bad days / yr | Main pollutant | Worst AQI | Smoke days / yr |
|---|---|---|---|---|---|
| San Bernardino | 9.6% | 129.6 | ozone | 593 (2024) | 7 |
| Riverside | 11.2% | 126.4 | ozone | 1683 (2022) | 6 |
| Los Angeles | 7.9% | 101.8 | fine particles (PM2.5) | 281 (2021) | 8 |
| Tulare | 20% | 96.8 | ozone | 961 (2021) | 15 |
| Kern | 16.8% | 95.8 | ozone | 314 (2021) | 11 |
| Fresno | 22.6% | 64.6 | ozone | 278 (2021) | 14 |
| Imperial | 25.1% | 43.4 | ozone | 791 (2022) | 7 |
| Kings | 27.7% | 35 | fine particles (PM2.5) | 685 (2021) | 11 |
| San Diego | 14.6% | 34.2 | ozone | 161 (2024) | 5 |
| Plumas | 44.6% | 30 | fine particles (PM2.5) | 654 (2021) | 20 |
| Inyo | 30.1% | 27.8 | ozone | 1551 (2022) | 12 |
| Stanislaus | 38.7% | 26.8 | ozone | 172 (2021) | 10 |
| Placer | 44.1% | 21.8 | ozone | 692 (2021) | 19 |
| Merced | 44.9% | 19.2 | ozone | 166 (2021) | 11 |
| Madera | 43.2% | 18.2 | ozone | 194 (2021) | 17 |
| Sacramento | 47.5% | 17.4 | ozone | 381 (2021) | 15 |
| Mariposa | 63.9% | 16.8 | ozone | 264 (2023) | 16 |
| Nevada | 68.8% | 15 | ozone | 326 (2021) | 17 |
| Trinity | 67% | 14.6 | fine particles (PM2.5) | 1217 (2021) | 24 |
| Mono | 83.9% | 13.2 | fine particles (PM2.5) | 8368 (2022) | 15 |
| Orange | 36.6% | 12.8 | fine particles (PM2.5) | 172 (2024) | 7 |
| Siskiyou | 74.4% | 11.8 | ozone | 454 (2022) | 29 |
| Ventura | 50.9% | 11.2 | ozone | 176 (2024) | 8 |
| El Dorado | 73.7% | 10 | ozone | 375 (2021) | 18 |
| Shasta | 69.3% | 9.8 | ozone | 1435 (2023) | 25 |
| Tehama | 67.4% | 9.6 | ozone | 193 (2021) | 24 |
| San Joaquin | 51.3% | 9 | fine particles (PM2.5) | 208 (2022) | 12 |
| Alameda | 50% | 7.2 | fine particles (PM2.5) | 151 (2021) | 9 |
| Butte | 55.4% | 7.2 | ozone | 257 (2021) | 20 |
| Sutter | 47.9% | 7 | ozone | 175 (2021) | 18 |
| San Luis Obispo | 47.2% | 6.8 | ozone | 133 (2021) | 9 |
| Santa Clara | 53.2% | 4.2 | fine particles (PM2.5) | 147 (2021) | 8 |
| Calaveras | 74.8% | 3.8 | ozone | 178 (2021) | 15 |
| Colusa | 45.1% | 3.4 | fine particles (PM2.5) | 225 (2021) | 18 |
| Glenn | 75% | 3.2 | ozone | 192 (2021) | 19 |
| Mendocino | 54.5% | 3 | fine particles (PM2.5) | 185 (2021) | 14 |
| Tuolumne | 83.2% | 2.3 | ozone | 136 (2021) | 19 |
| Amador | 87.2% | 2.2 | ozone | 143 (2024) | 17 |
| Contra Costa | 50.6% | 2.2 | fine particles (PM2.5) | 150 (2021) | 10 |
| Humboldt | 82.6% | 2.2 | ozone | 299 (2023) | 22 |
| Yolo | 66.9% | 2.2 | ozone | 159 (2021) | 14 |
| Del Norte | 82.7% | 2 | fine particles (PM2.5) | 187 (2023) | 30 |
| Solano | 74.7% | 1 | ozone | 126 (2021) | 12 |
| Santa Barbara | 56.2% | 0.6 | fine particles (PM2.5) | 146 (2024) | 10 |
| San Benito | 82.3% | 0.4 | ozone | 111 (2023) | 8 |
| Sonoma | 87.9% | 0.4 | fine particles (PM2.5) | 117 (2023) | 11 |
| Lake | 98.7% | 0.2 | ozone | 157 (2021) | 15 |
| Monterey | 78.9% | 0.2 | fine particles (PM2.5) | 115 (2023) | 8 |
| San Francisco | 74.8% | 0.2 | fine particles (PM2.5) | 117 (2023) | 9 |
| Santa Cruz | 82% | 0.2 | fine particles (PM2.5) | 130 (2023) | 8 |
| Marin | 80.3% | 0 | fine particles (PM2.5) | 99 (2023) | 11 |
| San Mateo | 84.5% | 0 | ozone | 90 (2021) | 9 |
Most smoke days in California: Del Norte (30 days), Siskiyou (29 days), Shasta (25 days), Modoc (25 days), Trinity (24 days).
EPA's Air Quality Index runs from 0 to 500. Up to 50 is good and 51-100 is moderate. Above 100 the air is unhealthy for sensitive groups (children, older adults, and people with asthma or heart or lung disease), and above 150 it is unhealthy for everyone. We count a county's bad days as days above 100, averaged over 2021-2025.
Mold and indoor air in California
We found no California state license for mold inspectors or remediators. Only a handful of states (Texas, Florida, New York, Louisiana and DC) license them. In California, ask for a national certification and a written report, and avoid a company that profits from finding mold by also doing the cleanup.
No agency measures indoor air city by city, so nobody can tell you your home's numbers except a monitor in your home. What research does show: Americans spend about 90% of their time indoors (EPA's National Human Activity Pattern Survey, 2001), EPA studies in the 1980s often found indoor levels of some chemical vapors two to five times outdoor levels, and during wildfire smoke the particles get inside unless windows stay shut and a filter runs.
We may earn a commission from links below, at no cost to you. How we make money.
Radon + air quality monitor
Radon zone 2: one device answers radon and air quality.
One battery device that tracks radon alongside particles, CO2, humidity and VOCs. Worth it in a radon zone 1 or 2 county where you want both answers.
Airthings View Plus (radon + PM2.5, CO2, VOC)
Price at Airthings, checked Oct 5, 2026Sold directly by Airthings
Airthings Wave Plus (radon + CO2, VOC)
Price at Airthings, checked Oct 5, 2026Sold directly by Airthings
HEPA air purifier
More unhealthy-air days than most US counties.
A true HEPA purifier sized to the room removes fine particles such as smoke, dust and pollen. Check the CADR rating and skip anything that makes ozone.
Levoit Core 300 (bedroom-size HEPA)
BudgetWinix 5520 (large-room HEPA)
Mid-rangeCO2 monitor
Stuffy bedroom or home office? CO2 tells you when to open a window.
CO2 is the best quick check on whether a room gets enough fresh air. Look for an NDIR sensor; cheap 'eCO2' sensors estimate it from VOCs instead of measuring it.
Aranet4 Home CO2 monitor (NDIR)
PremiumTemtop portable CO2 monitor
BudgetMold test kit
Musty smell or a past leak: a cheap first look before calling a pro.
A cheap first look. Settle-plate kits grow whatever spores are in the air, so they almost always show something; a visible patch or musty smell matters more than the plate.
Mold Armor DIY mold test kit
Budget12-test home mold test kit (air, HVAC, surfaces)
BudgetCalifornia cities: water, radon and air
- Los AngelesLos Angeles County
- San DiegoSan Diego County
- San JoseSanta Clara County
- San FranciscoSan Francisco County
- FresnoFresno County
- SacramentoSacramento County
- Long BeachLos Angeles County
- OaklandAlameda County
- BakersfieldKern County
- AnaheimOrange County
- StocktonSan Joaquin County
- RiversideRiverside County
- IrvineOrange County
- Santa AnaOrange County
- Chula VistaSan Diego County
- Santa ClaritaLos Angeles County
- FremontAlameda County
- San BernardinoSan Bernardino County
- ModestoStanislaus County
- FontanaSan Bernardino County
- Moreno ValleyRiverside County
- OxnardVentura County
- Huntington BeachOrange County
- GlendaleLos Angeles County
- OntarioSan Bernardino County
- Elk GroveSacramento County
- Santa RosaSonoma County
- Rancho CucamongaSan Bernardino County
- Garden GroveOrange County
- OceansideSan Diego County
- LancasterLos Angeles County
- RosevillePlacer County
- PalmdaleLos Angeles County
- CoronaRiverside County
- SalinasMonterey County
- HaywardAlameda County
- SunnyvaleSanta Clara County
- EscondidoSan Diego County
- PomonaLos Angeles County
- VisaliaTulare County
- VictorvilleSan Bernardino County
- FullertonOrange County
- TorranceLos Angeles County
Questions
How often is there wildfire smoke in California?+
NOAA satellites placed a medium or heavy smoke plume over the average California county on about 15 days a year from 2021-2025, below the typical US county. The worst year was 2021 (45 days on average). Smoke overhead does not always reach the ground.
Do mold inspectors need a license in California?+
We found no California state license for mold inspectors or remediators. Only a handful of states (Texas, Florida, New York, Louisiana and DC) license them. In California, ask for a national certification and a written report, and avoid a company that profits from finding mold by also doing the cleanup.
Is indoor air worse than outdoor air?+
No agency measures indoor air city by city, so nobody can tell you your home's numbers except a monitor in your home. What research does show: Americans spend about 90% of their time indoors (EPA's National Human Activity Pattern Survey, 2001), EPA studies in the 1980s often found indoor levels of some chemical vapors two to five times outdoor levels, and during wildfire smoke the particles get inside unless windows stay shut and a filter runs.
Sources: EPA AirData annual AQI by county, 2021-2025; NOAA Hazard Mapping System smoke polygons, 2021-2025. Methodology.