What Is the Air Quality in Denver, Colorado?
Denver, Colorado has an Air Quality Grade of C (fair) with a 5-year median AQI of 54. The dominant pollutant is Fine Particulate Matter (PM2.5), and air quality has been stable over the past decade.
Denver, Colorado Air Quality Snapshot
| Air Quality Grade | C52/100 |
| 5-Year Median AQI | 54 (Moderate) |
| Most Recent Median AQI (2023) | 54 (Moderate) |
| Dominant Pollutant | Fine Particulate Matter (PM2.5) |
| 10-Year Trend | Stable (0.00 AQI/yr) |
| Unhealthy Days (last 5 yr) | 68 |
| National Rank (cleanest = #1) | #983 of 1,020 (96th most polluted percentile) |
| Colorado Rank | #32 of 32 |
What Does the C Grade Mean?
Denver, Colorado earns a C — air quality is fair, but not great. With a 5-year median AQI of 54, the city sees a meaningful number of "Moderate" days each year, when the EPA flags air as a concern for unusually sensitive people.
Denver, Colorado's 5-year median AQI of 54 is 13 points above the national average of 41 — meaningfully more polluted than the typical U.S. metro tracked here. Within Colorado, Denver, Colorado runs more polluted than the state average of 39 — local sources or geography are concentrating pollution above the state's typical reading.
For context within Colorado: Alamosa, Colorado currently holds the state's cleanest grade (A, AQI 14), while Jefferson, Colorado sits at the bottom (D, AQI 47).
What's in Denver, Colorado's Air?
The dominant pollutant in Denver, Colorado 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 |
|---|---|---|
| Ground-Level Ozone | 166 | 45% |
| Fine Particulate Matter (PM2.5) | 135 | 37% |
| Nitrogen Dioxide | 64 | 18% |
Is the Air Getting Better or Worse?
Air quality in Denver, Colorado has held roughly steady over the past decade, with year-to-year shifts in median AQI of less than half a point. That stability makes the city's long-run grade a reliable signal of what residents can expect day-to-day.
In 2014, Denver, Colorado posted a median AQI of 53. By 2023 that figure was 54 — a rise of 1 AQI points dirtier across 10 years of EPA records.
Year-by-Year AQI in Denver, Colorado
| Year | Median AQI | Good Days | Unhealthy Days | Dominant Pollutant |
|---|---|---|---|---|
| 2014 | 53 | 152 | 3 | PM2.5 |
| 2015 | 54 | 119 | 9 | PM2.5 |
| 2016 | 54 | 127 | 4 | NO2 |
| 2017 | 53 | 149 | 2 | NO2 |
| 2018 | 54 | 124 | 10 | PM2.5 |
| 2019 | 54 | 139 | 3 | PM2.5 |
| 2020 | 53 | 137 | 17 | PM2.5 |
| 2021 | 55 | 128 | 35 | Ozone |
| 2022 | 52 | 161 | 7 | Ozone |
| 2023 | 54 | 131 | 6 | Ozone |
Health Context for Denver, Colorado
Across the past five years, this area has logged 68 days where AQI rose into the "Unhealthy for Sensitive Groups" range or worse — about 14 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.
Denver, Colorado has an Air Quality Grade of C (fair) with a 5-year median AQI of 54. The dominant pollutant is Fine Particulate Matter (PM2.5), and air quality has been stable 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.