What Is the Air Quality in Jefferson, Colorado?

Jefferson, Colorado earns a D — air quality falls below the U.S. average, with a 5-year median AQI of 47. Residents with asthma, COPD, heart disease, or young children should watch daily AQI forecasts and limit outdoor exertion when alerts go out.

Jefferson, Colorado's 5-year median AQI of 47 is 6 points above the national average of 41 — meaningfully more polluted than the typical U.S. metro tracked here. Within Colorado, Jefferson, 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 Weld, Colorado sits at the bottom (D, AQI 53).

Air quality in Jefferson, 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, Jefferson, Colorado posted a median AQI of 46. By 2023 that figure was 49 — a rise of 3 AQI points dirtier across 10 years of EPA records.

Across the past five years, this area has logged 147 days where AQI rose into the "Unhealthy for Sensitive Groups" range or worse — about 29 days per year, or roughly one every five to seven days. That is well above the national norm and explains the D grade.

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.