Aurora Best & Worst AQI Days: Air Quality Guide
The worst air quality day on record for Aurora (Denver-Aurora-Lakewood, CO area) was March 8, 2022, when the daily AQI reached 190 (Unhealthy), set by ground-level ozone. Across 2,557 monitored days in 2019–2025, 10 of the 10 worst days were Unhealthy (AQI 151+) or worse; 9 of the 10 were driven by ground-level ozone and 1 by fine particulate matter (PM2.5), and 4 of them fell in 2021. The cleanest day was September 8, 2020 at AQI 23 (Good); the 10 best days span 6 different years.
Reduce Indoor Ozone in Aurora
Today's main pollutant in Aurora 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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When were Aurora's worst and best air quality days?
Worst: March 8, 2022, AQI 190 (Unhealthy, O3). Best: September 8, 2020, AQI 23 (Good). Based on 2,557 EPA-monitored days in the Denver-Aurora-Lakewood, CO area, 2019–2025.
- ✓10 of the 10 worst days were Unhealthy (AQI 151+) or worse; the 10th-worst was AQI 166 (Unhealthy).
- ✓Ground-level ozone drove 9 of the 10 worst days.
- ✓2021 accounts for 4 of the 10 worst days.
Frequently asked questions
What was the worst air quality day in Aurora?▾
March 8, 2022: the Denver-Aurora-Lakewood, CO area's daily AQI hit 190 (Unhealthy), driven by ground-level ozone. That is the highest of 2,557 monitored days in 2019–2025.
What was the best air quality day in Aurora?▾
September 8, 2020, with a daily AQI of 23 (Good). The daily AQI is the highest reading from any monitor in the area, so even the cleanest day reflects the area's worst monitor.
What was Aurora's worst air quality day in 2025?▾
July 12, 2025, AQI 122 (Unhealthy for Sensitive Groups), set by ground-level ozone, in peak ozone season.
Which pollutant causes Aurora's worst air days?▾
Ground-level ozone set the AQI on 9 of the 10 worst days; fine particulate matter (PM2.5) on 1. The tables above list the defining pollutant for every day.
Aurora's 10 worst air quality days, 2019–2025
Highest daily AQI recorded for the Denver-Aurora-Lakewood, CO area (EPA AQS). The daily AQI is the highest reading from any monitor in the area that day.
| # | Date | AQI | Category | Defining pollutant |
|---|---|---|---|---|
| 1 | (2022 page) | 190 | Unhealthy | O3 — ground-level ozone |
| 2 | (2023 page) | 179 | Unhealthy | PM2.5 — fine particulate matter (PM2.5) |
| 3 | (2021 page) | 177 | Unhealthy | O3 — ground-level ozone |
| 4 | (2021 page) | 177 | Unhealthy | O3 — ground-level ozone, in peak ozone season |
| 5 | (2024 page) | 174 | Unhealthy | O3 — ground-level ozone, in peak ozone season |
| 6 | (2024 page) | 172 | Unhealthy | O3 — ground-level ozone, in peak ozone season |
| 7 | (2021 page) | 172 | Unhealthy | O3 — ground-level ozone, in peak ozone season |
| 8 | (2021 page) | 172 | Unhealthy | O3 — ground-level ozone, in peak ozone season |
| 9 | (2022 page) | 169 | Unhealthy | O3 — ground-level ozone, in peak ozone season |
| 10 | (2024 page) | 166 | Unhealthy | O3 — ground-level ozone, in peak ozone season |
Worst day of each year in Aurora
The single highest-AQI day in each year on record. Click a year for its full month-by-month statistics.
| Year | Worst day | AQI | Category | Defining pollutant |
|---|---|---|---|---|
| 2019 | 154 | Unhealthy | O3 — ground-level ozone, in peak ozone season | |
| 2020 | 161 | Unhealthy | O3 — ground-level ozone, in peak ozone season | |
| 2021 | 177 | Unhealthy | O3 — ground-level ozone | |
| 2022 | 190 | Unhealthy | O3 — ground-level ozone | |
| 2023 | 179 | Unhealthy | PM2.5 — fine particulate matter (PM2.5) | |
| 2024 | 174 | Unhealthy | O3 — ground-level ozone, in peak ozone season | |
| 2025 | 122 | Unhealthy for Sensitive Groups | O3 — ground-level ozone, in peak ozone season |
Aurora's 10 best air quality days, 2019–2025
Lowest daily AQI recorded for the Denver-Aurora-Lakewood, CO area. Ties are listed most recent first.
| # | Date | AQI | Category | Defining pollutant |
|---|---|---|---|---|
| 1 | (2020 page) | 23 | Good | O3 — ground-level ozone |
| 2 | (2025 page) | 32 | Good | O3 — ground-level ozone |
| 3 | (2024 page) | 36 | Good | O3 — ground-level ozone |
| 4 | (2019 page) | 36 | Good | O3 — ground-level ozone |
| 5 | (2022 page) | 37 | Good | O3 — ground-level ozone |
| 6 | (2021 page) | 37 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 7 | (2019 page) | 37 | Good | O3 — ground-level ozone |
| 8 | (2019 page) | 37 | Good | O3 — ground-level ozone |
| 9 | (2025 page) | 38 | Good | O3 — ground-level ozone |
| 10 | (2025 page) | 38 | Good | O3 — ground-level ozone |
Right now in Aurora
The latest EPA AirNow observation puts Aurora's AQI at 43 (O3). The days above are historical records, not today's reading.
View current Aurora 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.