Bad Air Days in Trinity County, California: 16 a Year
16 bad air days a year
Among the worst tenth of monitored US counties. Ranked 42 of 996 monitored counties, where 1 is worst.
What makes them bad: mostly particles: smoke and dust (100% particle days).
The bad-air season here
- J
- F
- M
- A
- M
- J
- J
- A
- S
- O
- N
- D
Most bad days here fall in August and September. Averaged over 2016 to 2025.
What to buy, and what not to
- 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.
The worst days on file
The worst recent year was 2021, with 46 bad days on 328 monitored days.
| Date | AQI | Main pollutant |
|---|---|---|
| 2021-08-07 | 1217 | PM2.5 |
| 2021-08-06 | 1111 | PM2.5 |
| 2021-08-13 | 1108 | PM2.5 |
| 2021-08-14 | 1012 | PM2.5 |
| 2017-09-03 | 844 | PM2.5 |
The air on a normal day
Across 2,954 monitored days from 2016 to 2025, the air in Trinity County rated Good on 62% of them, less often than the 72% typical of monitored counties, and Moderate on 33%. The median day sat at AQI 37; one day in ten went above 82.
The pollutant setting the AQI on an ordinary day here:
- fine particles (PM2.5)100%2,954 days
Year by year
| Year | Days monitored | Good | Moderate | Over 100 | Over 150 | Median AQI | Highest AQI |
|---|---|---|---|---|---|---|---|
| 2025* | 332 | 231 | 99 | 2 | 1 | 31 | 164 |
| 2024 | 357 | 258 | 98 | 1 | 0 | 31 | 113 |
| 2023 | 311 | 209 | 93 | 9 | 3 | 31 | 174 |
| 2022 | 353 | 227 | 111 | 15 | 10 | 34 | 342 |
| 2021 | 328 | 201 | 81 | 46 | 42 | 38 | 1217 |
| 2020 | 343 | 215 | 100 | 28 | 16 | 36 | 211 |
| 2019 | 269 | 225 | 42 | 2 | 0 | 23 | 113 |
| 2018 | 291 | 117 | 155 | 19 | 7 | 54 | 209 |
| 2017 | 203 | 76 | 116 | 11 | 5 | 57 | 844 |
| 2016 | 167 | 83 | 84 | 0 | 0 | 51 | 97 |
| 2015 | 68 | 67 | 1 | 0 | 0 | 12 | 56 |
| 2014 | 112 | 102 | 10 | 0 | 0 | 12 | 90 |
| 2013 | 218 | 140 | 62 | 16 | 0 | 34 | 143 |
| 2012 | 343 | 156 | 152 | 35 | 7 | 54 | 243 |
| 2011 | 210 | 116 | 61 | 33 | 2 | 34 | 160 |
| 2010 | 122 | 122 | 0 | 0 | 0 | 11 | 46 |
*2025 may be a partial year in EPA's file.
Nearby counties on file
- 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.