Bad Air Days in Santa Clara County, California: 8 a Year
8 bad air days a year
More bad air days than three quarters of monitored counties. Ranked 122 of 996 monitored counties, where 1 is worst.
What makes them bad: mostly particles: smoke and dust (62% particle days).
When the bad days come in Santa Clara
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Most bad days here fall in September and August and November. Averaged over 2016 to 2025.
What actually helps here
- Particles (wildfire smoke, dust) cause enough bad days here to matter. A HEPA purifier sized to your bedroom removes them; run it with windows shut on bad days.
- Upgrade the furnace or AC filter to MERV 13 so the whole house is filtered, not just one room.
- Ozone drives many bad days here. Purifiers and filters do not remove ozone, so do not buy one for that. Ozone peaks on hot afternoons: exercise outside in the morning.
Better or worse than it was
In 2000 to 2009 this county averaged 22 bad days a year; in 2016 to 2025, 8. The air has improved. The worst recent year was 2020, with 20 bad days on 366 monitored days.
| Date | AQI | Main pollutant |
|---|---|---|
| 2018-11-16 | 214 | PM2.5 |
| 2018-11-15 | 209 | PM2.5 |
| 2020-09-11 | 198 | PM2.5 |
| 2020-09-14 | 192 | PM2.5 |
| 2020-09-12 | 186 | PM2.5 |
Most days, not the worst ones
Across 3,285 monitored days from 2016 to 2024, the air in Santa Clara County rated Good on 51% of them, less often than the 72% typical of monitored counties, and Moderate on 47%. The median day sat at AQI 50; one day in ten went above 70.
The pollutant setting the AQI on an ordinary day here:
- fine particles (PM2.5)69%2,271 days
- ozone30%995 days
- nitrogen dioxide1%18 days
Santa Clara County by year
| Year | Days monitored | Good | Moderate | Over 100 | Over 150 | Median AQI | Highest AQI |
|---|---|---|---|---|---|---|---|
| 2024 | 363 | 201 | 161 | 1 | 0 | 47 | 111 |
| 2023 | 365 | 240 | 121 | 4 | 0 | 43 | 134 |
| 2022 | 365 | 188 | 172 | 5 | 0 | 49 | 119 |
| 2021 | 365 | 147 | 211 | 7 | 0 | 53 | 147 |
| 2020 | 366 | 174 | 172 | 20 | 9 | 52 | 198 |
| 2019 | 365 | 205 | 156 | 4 | 0 | 48 | 136 |
| 2018 | 365 | 154 | 194 | 17 | 11 | 53 | 214 |
| 2017 | 365 | 174 | 179 | 12 | 3 | 52 | 182 |
| 2016 | 366 | 187 | 178 | 1 | 0 | 50 | 101 |
| 2015 | 365 | 179 | 179 | 7 | 0 | 51 | 147 |
| 2014 | 365 | 216 | 141 | 8 | 1 | 46 | 154 |
| 2013 | 365 | 129 | 228 | 8 | 1 | 55 | 153 |
| 2012 | 366 | 159 | 201 | 6 | 0 | 52 | 122 |
| 2011 | 365 | 93 | 266 | 6 | 0 | 56 | 138 |
| 2010 | 365 | 181 | 172 | 12 | 2 | 51 | 164 |
California compared
- San Bernardino County138/yr
- Riverside County132/yr
- Kern County109/yr
- Tulare County107/yr
- Los Angeles County106/yr
- Fresno County81/yr
- Kings County49/yr
- Imperial County40/yr
How this is counted
A bad air day is a day the county's daily AQI from EPA AirData went above 100, the level where EPA tells children, older adults and people with asthma or heart disease to cut back outdoors. Monitors do not run every day, so yearly counts are scaled to 365 days. This is the record, not today's air: for that, check AirNow. More on the method in how the county numbers are made, on the AQI 100 line in what counts as a bad air day.