San Francisco, California vs Denver, Colorado Air Quality
Side-by-side air quality comparison using 10 years of EPA monitoring data. San Francisco, California has the edge with an Air Quality Grade of B (70/100).
| Metric | San Francisco, California | Denver, Colorado |
|---|---|---|
| Air Quality Grade | B (70/100) | C (52/100) |
| Current Median AQI | 32 (Good) | 54 (Moderate) |
| 5-Year Average AQI | 38 | 54 |
| 10-Year Trend | ↓ Improving (-7) | → Stable (+1) |
| Unhealthy Days/Year | 2 | 14 |
| Primary Pollutant | Fine Particulate Matter (PM2.5) | Fine Particulate Matter (PM2.5) |
Side-by-Side Analysis
San Francisco, California outperforms Denver, Colorado on overall air quality with a Grade B (70/100) versus C (52/100). San Francisco, California's 5-year median AQI of 38 sits in the "Good" range, while Denver, Colorado averages 54 ("Moderate") — a 16-point gap that shows up consistently in year-over-year readings, not just in a single year.
The two cities are moving in opposite directions: San Francisco, California is improving (-0.6 AQI/yr) while Denver, Colorado is stable (0.0 AQI/yr). Over time, today's ranking may flip if these trends hold.
What's in the Air
Both cities share the same dominant pollutant: Fine Particulate Matter (PM2.5). These cities' dominant issue is fine particulate matter — typically driven by combustion (vehicles, wildfire smoke, industry, residential wood burning). PM2.5 is the air pollutant most strongly linked to long-term cardiovascular and respiratory disease because the particles penetrate the bloodstream.
Health Implications
Over a 5-year window, San Francisco, California averages roughly 2 unhealthy air days per year (AQI above 100, where sensitive groups should limit outdoor exertion) versus 14 for Denver, Colorado. That 12-day gap matters most for residents with asthma, COPD, heart disease, or pregnancy — and for outdoor workers, who accumulate the most cumulative exposure. The city with fewer unhealthy days offers a meaningfully different baseline risk picture for sensitive populations. For long-term residents, the cleaner-air city is associated with measurably better outcomes on respiratory disease, cardiovascular events, and life expectancy — Harvard cohort research consistently finds 0.5 to 1.0 years of additional life expectancy for each 10-µg/m³ reduction in long-term PM2.5 exposure.
Frequently Asked Questions
San Francisco, California has better air quality with a Grade B (70/100) compared to Denver, Colorado's Grade C (52/100). San Francisco, California has a current median AQI of 32 and is improving over the past decade.
San Francisco, California averages 2 unhealthy air days per year (5-year average), while Denver, Colorado averages 14. Unhealthy days are those when AQI exceeds 100 and sensitive groups should limit outdoor activity.
San Francisco, California's primary pollutant is Fine Particulate Matter (PM2.5), while Denver, Colorado's is Fine Particulate Matter (PM2.5). Both cities share the same dominant pollutant.
Source: EPA Outdoor Air Quality Data, 2026.
The side-by-side above pulls the EPA Air Quality System data data for both entity A and entity B. What follows is the interpretation — which specific axes carry the most weight for entity A versus entity B, and which differences are large enough to influence a real decision.
For households or analysts using this comparison as a decision input, the right framing is usually not "which is better" in aggregate but "which is better for the specific decision in front of you." EPA Air Quality System data captures the raw data; the framing depends on whether the question is investment, residency, planning, or research.