Cheyenne Best & Worst AQI Days: Air Quality Guide
The worst air quality day on record for Cheyenne (Cheyenne, WY area) was October 6, 2020, when the daily AQI reached 159 (Unhealthy), set by fine particulate matter (PM2.5), in wildfire smoke season. Across 2,554 monitored days in 2019–2025, 4 of the 10 worst days were Unhealthy (AQI 151+) or worse; 6 of the 10 were driven by fine particulate matter (PM2.5) and 4 by ground-level ozone, and 4 of them fell in 2020. The cleanest day was August 23, 2022 at AQI 0 (Good); the 10 best days span 4 different years.
Reduce Indoor Ozone in Cheyenne
Today's main pollutant in Cheyenne is ground-level ozone (AQI 31). 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 Cheyenne's worst and best air quality days?
Worst: October 6, 2020, AQI 159 (Unhealthy, PM2.5). Best: August 23, 2022, AQI 0 (Good). Based on 2,554 EPA-monitored days in the Cheyenne, WY area, 2019–2025.
- ✓4 of the 10 worst days were Unhealthy (AQI 151+) or worse; the 10th-worst was AQI 126 (Unhealthy for Sensitive Groups).
- ✓Fine particulate matter (PM2.5) drove 6 of the 10 worst days.
- ✓2020 accounts for 4 of the 10 worst days.
Frequently asked questions
What was the worst air quality day in Cheyenne?▾
October 6, 2020: the Cheyenne, WY area's daily AQI hit 159 (Unhealthy), driven by fine particulate matter (PM2.5), in wildfire smoke season. That is the highest of 2,554 monitored days in 2019–2025.
What was the best air quality day in Cheyenne?▾
August 23, 2022, with a daily AQI of 0 (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 Cheyenne's worst air quality day in 2025?▾
May 10, 2025, AQI 108 (Unhealthy for Sensitive Groups), set by ground-level ozone.
Which pollutant causes Cheyenne's worst air days?▾
Fine particulate matter (PM2.5) set the AQI on 6 of the 10 worst days; ground-level ozone on 4. The tables above list the defining pollutant for every day.
Cheyenne's 10 worst air quality days, 2019–2025
Highest daily AQI recorded for the Cheyenne, WY area (EPA AQS). The daily AQI is the highest reading from any monitor in the area that day.
| # | Date | AQI | Category | Defining pollutant |
|---|---|---|---|---|
| 1 | (2020 page) | 159 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 2 | (2023 page) | 156 | Unhealthy | PM2.5 — fine particulate matter (PM2.5) |
| 3 | (2020 page) | 153 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 4 | (2024 page) | 151 | Unhealthy | O3 — ground-level ozone, in peak ozone season |
| 5 | (2023 page) | 145 | Unhealthy for Sensitive Groups | PM2.5 — fine particulate matter (PM2.5) |
| 6 | (2024 page) | 136 | Unhealthy for Sensitive Groups | O3 — ground-level ozone, in peak ozone season |
| 7 | (2020 page) | 132 | Unhealthy for Sensitive Groups | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 8 | (2020 page) | 130 | Unhealthy for Sensitive Groups | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 9 | (2024 page) | 126 | Unhealthy for Sensitive Groups | O3 — ground-level ozone, in peak ozone season |
| 10 | (2021 page) | 126 | Unhealthy for Sensitive Groups | O3 — ground-level ozone, in peak ozone season |
Worst day of each year in Cheyenne
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 | 74 | Moderate | O3 — ground-level ozone, in peak ozone season | |
| 2020 | 159 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season | |
| 2021 | 126 | Unhealthy for Sensitive Groups | O3 — ground-level ozone, in peak ozone season | |
| 2022 | 90 | Moderate | O3 — ground-level ozone, in peak ozone season | |
| 2023 | 156 | Unhealthy | PM2.5 — fine particulate matter (PM2.5) | |
| 2024 | 151 | Unhealthy | O3 — ground-level ozone, in peak ozone season | |
| 2025 | 108 | Unhealthy for Sensitive Groups | O3 — ground-level ozone |
Cheyenne's 10 best air quality days, 2019–2025
Lowest daily AQI recorded for the Cheyenne, WY area. Ties are listed most recent first.
| # | Date | AQI | Category | Defining pollutant |
|---|---|---|---|---|
| 1 | (2022 page) | 0 | Good | CO — carbon monoxide |
| 2 | (2021 page) | 1 | Good | CO — carbon monoxide |
| 3 | (2021 page) | 1 | Good | CO — carbon monoxide |
| 4 | (2020 page) | 3 | Good | PM10 — coarse dust (PM10) |
| 5 | (2025 page) | 7 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 6 | (2021 page) | 7 | Good | NO2 — nitrogen dioxide |
| 7 | (2020 page) | 8 | Good | NO2 — nitrogen dioxide |
| 8 | (2025 page) | 9 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 9 | (2021 page) | 9 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 10 | (2025 page) | 10 | Good | PM2.5 — fine particulate matter (PM2.5) |
Right now in Cheyenne
The latest EPA AirNow observation puts Cheyenne's AQI at 31 (O3). The days above are historical records, not today's reading.
View current Cheyenne air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Cheyenne, WY), 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.