Siskiyou, California Air Quality Today
AirHistory tracks long-run EPA monitoring rather than live readings, so for the live number check AirNow.gov below. As a baseline, Siskiyou, California's most recent EPA year (2023) posted a median AQI of 43 (Good) against a 5-year median of 41 and an overall Grade of D. The dominant pollutant is Ground-Level Ozone, which tells you which days are most likely to spike.
Check Today's Live AQI in Siskiyou, California
AirHistory is built on 10 years of EPA Air Quality System records, so it shows you what air quality in Siskiyou, California typically looks like — not the live reading for this exact hour. For today's real-time AQI, check AirNow.gov (the EPA's official live index) or the AirNow Fire and Smoke Map during wildfire season.
That said, the history is the best predictor of a normal day. In 2023, Siskiyou, California posted a median AQI of 43 (Good), with 270 "Good" days and 17 days that crossed into "Unhealthy for Sensitive Groups" or worse. The dominant pollutant, Ground-Level Ozone, is the one most likely to push today's number up — Ground-level ozone forms when sunlight reacts with vehicle exhaust and industrial emissions. It is worst on hot, sunny, stagnant summer days. Ozone irritates the lungs, triggers asthma attacks, and reduces lung function — even healthy adults can feel chest tightness and shortness of breath after exercising in elevated ozone.
Siskiyou, California Air Quality Snapshot
| Air Quality Grade | D49/100 |
| 5-Year Median AQI | 41 (Good) |
| Most Recent Median AQI (2023) | 43 (Good) |
| Dominant Pollutant | Ground-Level Ozone |
| 10-Year Trend | Worsening (+1.20 AQI/yr) |
| Unhealthy Days (last 5 yr) | 82 |
| National Rank (cleanest = #1) | #546 of 1,020 (54th most polluted percentile) |
| California Rank | #15 of 53 |
What Does the D Grade Mean?
Siskiyou, California earns a D — air quality falls below the U.S. average, with a 5-year median AQI of 41. Residents with asthma, COPD, heart disease, or young children should watch daily AQI forecasts and limit outdoor exertion when alerts go out.
Siskiyou, California's 5-year median AQI of 41 is right around the national average of 41 across the 1,020 monitored U.S. cities tracked here. Within California, Siskiyou, California runs cleaner than the state average of 49 — a positive signal that local conditions (terrain, wind patterns, emission sources) are working in residents' favor.
For context within California: Humboldt, California currently holds the state's cleanest grade (A, AQI 28), while Inyo, California sits at the bottom (F, AQI 57).
What's in Siskiyou, California's Air?
The dominant pollutant in Siskiyou, California is Ground-Level Ozone. Ground-level ozone forms when sunlight reacts with vehicle exhaust and industrial emissions. It is worst on hot, sunny, stagnant summer days. Ozone irritates the lungs, triggers asthma attacks, and reduces lung function — even healthy adults can feel chest tightness and shortness of breath after exercising in elevated ozone.
Days by Dominant Pollutant (2023)
| Pollutant | Days as Dominant | Share of Year |
|---|---|---|
| Ground-Level Ozone | 207 | 57% |
| Fine Particulate Matter (PM2.5) | 158 | 43% |
Is the Air Getting Better or Worse?
Air quality in Siskiyou, California has been getting worse over the past decade, with median AQI climbing by roughly 1.2 points per year. That bucks the national trend of broad improvement, and most often reflects either growing wildfire smoke exposure (particularly across the West) or rising local emissions from population and freight growth.
In 2014, Siskiyou, California posted a median AQI of 37. By 2023 that figure was 43 — a rise of 6 AQI points dirtier across 10 years of EPA records.
Year-by-Year AQI in Siskiyou, California
| Year | Median AQI | Good Days | Unhealthy Days | Dominant Pollutant |
|---|---|---|---|---|
| 2014 | 37 | 330 | 2 | Ozone |
| 2015 | 36 | 330 | 4 | Ozone |
| 2016 | 27 | 351 | 0 | Ozone |
| 2017 | 28 | 198 | 4 | Ozone |
| 2018 | 42 | 247 | 40 | Ozone |
| 2019 | 38 | 302 | 4 | Ozone |
| 2020 | 39 | 272 | 23 | Ozone |
| 2021 | 43 | 237 | 31 | PM2.5 |
| 2022 | 41 | 269 | 7 | Ozone |
| 2023 | 43 | 270 | 17 | Ozone |
Health Context for Siskiyou, California
Across the past five years, this area has logged 82 days where AQI rose into the "Unhealthy for Sensitive Groups" range or worse — about 16 days per year. That is roughly typical for a U.S. metro, with most caution days clustered in summer (ozone) or wildfire season.
Treat daily AQI forecasts as essential input. On flagged days, sensitive groups (asthma, COPD, heart disease, pregnancy, young children, older adults) should limit outdoor exertion and keep windows closed. A HEPA air cleaner sized to a bedroom or family room can cut indoor PM2.5 by 80%+ during smoke or pollution events. Because ozone peaks in the afternoon on hot sunny days, plan outdoor exercise for early morning or after sunset on bad-air days.
How This Grade Is Calculated
The AirHistory Air Quality Grade combines four signals: the 5-year median AQI (40% of the score), the 10-year trend direction (30%), the count of unhealthy days per year (20%), and the dominant pollutant type (10%). All four come directly from the EPA Air Quality System (AQS), which aggregates readings from federally certified monitors. Read the full methodology.
More about Siskiyou, California
Siskiyou, California has an Air Quality Grade of D (poor) with a 5-year median AQI of 41. The dominant pollutant is Ground-Level Ozone, and air quality has been worsening over the past decade.
The data source behind this answer is the EPA Air Quality System (AQS). Every figure on the page traces back to that source; the methodology page describes the inputs and the refresh cadence in full detail.
For readers turning this answer into action: cross-reference against the underlying the EPA Air Quality System (AQS) record before acting on time-sensitive decisions. The site renders the data as it was published; subsequent revisions can shift the picture, and the live federal data is always the authoritative current reference.
Source: EPA Outdoor Air Quality Data, 2026.