Thornton, Colorado Air Quality
Thornton air quality today — the AQI, the main pollutant, and whether it’s safe to exercise outside right now
Thornton, CO · Air quality right now
The air quality index in Thornton, CO is 45 (Good) right now — safe for outdoor activity.
Is it safe to be outside in Thornton today?
AQI 45 Yes — air quality is Good
Air is clean — great for outdoor activity.Main pollutant: PM2.5Observed 9:00 AM MDT
Pollutants right now
- PM2.517 µg/m³Main pollutantfine particles — smoke, exhaust, soot
- PM1017 µg/m³coarse particles — dust, pollen, ash
- Ozone43 µg/m³smog — builds on hot, sunny days
- NO₂23 µg/m³nitrogen dioxide — traffic, combustion
ExerciseOK to run — no air-quality limits on outdoor exercise.
How to read Thornton’s air quality
Guides: The AQI Scale, Explained · Air Quality Alerts, Decoded · How to Read a Wildfire Smoke Map · Why Wildfire Smoke Travels 1,000 Miles.
Air quality over time in Thornton
Across the EPA’s county records from 2020 to 2025, Thornton’s cleanest year was 2020 (median AQI 49) and its most polluted was 2024 (median AQI 55); the typical (median) day has trended more polluted since 2020.
| Year | Median AQI | Unhealthy+ | Main pollutant | USG | Moderate | Good |
|---|---|---|---|---|---|---|
| 2020 | 49 | 1 | Ozone | 11 | 162 | 192 |
| 2021 | 49 | 1 | Ozone | 22 | 154 | 188 |
| 2022 | 51 | 0 | Ozone | 14 | 171 | 180 |
| 2023 | 51 | 2 | Ozone | 3 | 181 | 179 |
| 2024 | 55 | 2 | Ozone | 20 | 197 | 147 |
| 2025 | 49 | 0 | Ozone | 1 | 163 | 201 |
“USG” is Unhealthy for Sensitive Groups (AQI 101–150); “Unhealthy+” combines the Unhealthy, Very Unhealthy, and Hazardous days. In 2024 the EPA tightened the annual fine-particle (PM2.5) standard to 9 µg/m³ from the previous 12 µg/m³, so counties near the old limit read worse against the new one. Source: EPA AQS annual summaries, 2020–2025.
Frequently asked
- What was the worst year for air quality in Thornton?
- In the EPA's 2020–2025 county records, 2021 had the most days above AQI 100: 23 days (22 Unhealthy for Sensitive Groups, 1 Unhealthy or worse). The highest median AQI came in 2024 (55; 2021's was 49).
- How many unhealthy air days does Thornton have?
- Across 2020–2025, 4% of the days reported for Thornton's county had an AQI above 100 (77 of 2192), about 13 days a year. 2025 had 1 day.
- What's the main air pollutant in Thornton?
- Ozone: it drove Thornton's county AQI on the most days in every year of the EPA's 2020–2025 records.