Denver Air Quality in April
Across 2019–2025, Denver's April air quality had a median AQI of 64 (Moderate) over 210 monitored days in the Denver-Aurora-Lakewood, CO area. 3.3% of April days (7 of 210) reached Unhealthy for Sensitive Groups or worse, and ground-level ozone set the daily AQI on 86.7% of days. The cleanest April on record here was 2021 (median AQI 58, 0 days above 100) and the worst was 2023 (median 76, 3 days above 100, peak AQI 147).
- Good: 16.2%
- Moderate: 80.5%
- Unhealthy for Sensitive Groups: 3.3%
- Unhealthy or worse: 0.0%
Reduce Indoor Ozone in Denver
Today's main pollutant in Denver is ground-level ozone (AQI 43). Important: standard HEPA filters do NOT remove ozone — only a purifier with a substantial activated-carbon bed adsorbs it. The biggest wins are cutting indoor sources (gas appliances, certain "ionizer" purifiers) and ventilating when outdoor ozone is low (early morning). A high-carbon unit helps with the gases and VOCs that linger indoors.
Recommended: Levoit Core 300 — True HEPA + activated carbon · CADR ~141 CFM · rooms up to 219 sq ft
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How is the air in Denver in April?
Moderate on a typical day: median AQI 64 across 2019–2025, with 3.3% of April days above AQI 100. Ground-level ozone is the main driver.
- ✓16.2% of April days were Good (AQI 0–50), 80.5% Moderate (51–100).
- ✓7 days of 210 reached AQI 101+; the April peak was 147.
- ✓Best April: 2021; worst April: 2023.
Frequently asked questions
What is the air quality like in Denver in April?▾
Across 2019–2025, the median daily AQI in Denver in April was 64 (Moderate). 16.2% of days were Good, 80.5% Moderate, and 3.3% reached Unhealthy for Sensitive Groups or worse, based on 210 monitored days in EPA's Air Quality System.
Is April a good time for outdoor exercise in Denver?▾
A typical April day in Denver is Moderate (median AQI 64): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 30 of April days (3.3%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
Which pollutant causes Denver's April air quality problems?▾
Ground-level ozone set the daily AQI on 86.7% of April days in Denver. The highest April AQI recorded in 2019–2025 was 147 (Unhealthy for Sensitive Groups), in 2023.
Denver April air quality, year by year
Denver April air quality by year (Denver-Aurora-Lakewood, CO, EPA AQS daily AQI)
| Year | Days monitored | Median AQI | Days above 100 | Peak AQI | Main pollutant |
|---|---|---|---|---|---|
| 2019 | 30 | 63 | 0 | 97 | O3 |
| 2020 | 30 | 61 | 0 | 87 | O3 |
| 2021cleanest | 30 | 58 | 0 | 80 | O3 |
| 2022 | 30 | 64 | 0 | 97 | O3 |
| 2023worst | 30 | 76 | 3 | 147 | O3 |
| 2024 | 30 | 74 | 3 | 126 | O3 |
| 2025 | 30 | 65 | 1 | 105 | O3 |
What April air means in Denver
A typical April day in Denver is Moderate (median AQI 64): outdoor exercise is acceptable for most people, but unusually sensitive individuals should watch for symptoms, and about 1 day in 30 of April days (3.3%) reached AQI 101+ — the level at which EPA advises people with asthma, children and older adults to shorten hard outdoor exertion.
April's median AQI of 64 is in line with Denver's whole-year median of 64, so this period is neither a clean nor a dirty stretch for the area. Nationally, the median April AQI across every EPA metro area (100,677 metro-days, 2019–2025) is 44, so Denver runs above the national April norm; 3.3% of its April days topped AQI 100 versus 0.7% nationally (above average).
April is part of Denver's spring season (March, April, May); the spring page pools all three months.
Activity-specific thresholds: running, cycling, kids' sports.
Right now in Denver
The latest EPA AirNow observation puts Denver's AQI at 43 (O3). The figures above are multi-year month statistics, not today's reading.
View current Denver air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Denver-Aurora-Lakewood, CO), 2019–2025. Daily AQI per CBSA is the highest AQI reported by any monitor in the area that day; the defining parameter is the pollutant that set it. Month and season statistics pool every such day in the period across all years listed. Retrieved 2026-09-09.