What Is the Air Quality in Mendocino, California?
Mendocino, California has an Air Quality Grade of C (fair) with a 5-year median AQI of 46. The dominant pollutant is Fine Particulate Matter (PM2.5), and air quality has been worsening over the past decade.
Mendocino, California Air Quality Snapshot
| Air Quality Grade | C52/100 |
| 5-Year Median AQI | 46 (Good) |
| Most Recent Median AQI (2023) | 53 (Moderate) |
| Dominant Pollutant | Fine Particulate Matter (PM2.5) |
| 10-Year Trend | Worsening (+0.89 AQI/yr) |
| Unhealthy Days (last 5 yr) | 38 |
| National Rank (cleanest = #1) | #805 of 1,020 (79th most polluted percentile) |
| California Rank | #24 of 53 |
What Does the C Grade Mean?
Mendocino, California earns a C — air quality is fair, but not great. With a 5-year median AQI of 46, the city sees a meaningful number of "Moderate" days each year, when the EPA flags air as a concern for unusually sensitive people.
Mendocino, California's 5-year median AQI of 46 is 5 points above the national average of 41 — meaningfully more polluted than the typical U.S. metro tracked here. Within California, Mendocino, 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 Mendocino, California's Air?
The dominant pollutant in Mendocino, California is Fine Particulate Matter (PM2.5). Fine particulate matter — particles less than 2.5 micrometers across — comes mostly from combustion: vehicle exhaust, wildfire smoke, residential wood burning, and industrial emissions. Because these particles are small enough to enter the bloodstream, PM2.5 is the pollutant most strongly linked to cardiovascular disease, respiratory illness, and premature death.
Days by Dominant Pollutant (2023)
| Pollutant | Days as Dominant | Share of Year |
|---|---|---|
| Fine Particulate Matter (PM2.5) | 336 | 92% |
| Ground-Level Ozone | 29 | 8% |
Is the Air Getting Better or Worse?
Air quality in Mendocino, California has been getting worse over the past decade, with median AQI climbing by roughly 0.9 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, Mendocino, California posted a median AQI of 44. By 2023 that figure was 53 — a rise of 9 AQI points dirtier across 10 years of EPA records.
Year-by-Year AQI in Mendocino, California
| Year | Median AQI | Good Days | Unhealthy Days | Dominant Pollutant |
|---|---|---|---|---|
| 2014 | 44 | 224 | 0 | PM2.5 |
| 2015 | 46 | 213 | 4 | PM2.5 |
| 2016 | 39 | 287 | 0 | PM2.5 |
| 2017 | 45 | 226 | 8 | PM2.5 |
| 2018 | 46 | 217 | 21 | PM2.5 |
| 2019 | 36 | 290 | 0 | PM2.5 |
| 2020 | 40 | 240 | 23 | PM2.5 |
| 2021 | 46 | 210 | 8 | PM2.5 |
| 2022 | 54 | 129 | 2 | PM2.5 |
| 2023 | 53 | 144 | 5 | PM2.5 |
Health Context for Mendocino, California
Across the past five years, this area has logged 38 days where AQI rose into the "Unhealthy for Sensitive Groups" range or worse — about 8 days per year. That is roughly typical for a U.S. metro, with most caution days clustered in summer (ozone) or wildfire season.
Healthy adults can continue normal outdoor activity in most weather, but should pay attention to AQI alerts during the worst pollution windows. People with asthma, heart disease, or pregnancy should reduce prolonged or intense outdoor exertion on flagged days, and consider running an indoor HEPA air cleaner during peak season. Because PM2.5 penetrates deep into the lungs and bloodstream, an N95 or KN95 mask provides meaningful protection on smoky or high-particulate days — surgical masks do not.
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.
Mendocino, California has an Air Quality Grade of C (fair) with a 5-year median AQI of 46. The dominant pollutant is Fine Particulate Matter (PM2.5), 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.
A practical caveat: the headline answer above reflects the most recent the EPA Air Quality System (AQS) vintage; underlying data is often revised for months after first publication, and the right reference for any specific decision is whichever vintage is current at the time of the decision. The as-of date is stamped on every page.
Source: EPA Outdoor Air Quality Data, 2026.