Manchester Best & Worst AQI Days: Air Quality Guide
The worst air quality day on record for Manchester (Manchester-Nashua, NH area) was July 26, 2021, when the daily AQI reached 144 (Unhealthy for Sensitive Groups), set by fine particulate matter (PM2.5), in wildfire smoke season. Across 2,557 monitored days in 2019–2025, 0 of the 10 worst days were Unhealthy (AQI 151+) or worse; 7 of the 10 were driven by fine particulate matter (PM2.5) and 3 by ground-level ozone, and 4 of them fell in 2023. The cleanest day was December 11, 2023 at AQI 1 (Good); the 10 best days span 4 different years.
Reduce Indoor Ozone in Manchester
Today's main pollutant in Manchester is ground-level ozone (AQI 12). 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 Manchester's worst and best air quality days?
Worst: July 26, 2021, AQI 144 (Unhealthy for Sensitive Groups, PM2.5). Best: December 11, 2023, AQI 1 (Good). Based on 2,557 EPA-monitored days in the Manchester-Nashua, NH area, 2019–2025.
- ✓0 of the 10 worst days were Unhealthy (AQI 151+) or worse; the 10th-worst was AQI 101 (Unhealthy for Sensitive Groups).
- ✓Fine particulate matter (PM2.5) drove 7 of the 10 worst days.
- ✓2023 accounts for 4 of the 10 worst days.
Frequently asked questions
What was the worst air quality day in Manchester?▾
July 26, 2021: the Manchester-Nashua, NH area's daily AQI hit 144 (Unhealthy for Sensitive Groups), driven by fine particulate matter (PM2.5), in wildfire smoke season. That is the highest of 2,557 monitored days in 2019–2025.
What was the best air quality day in Manchester?▾
December 11, 2023, with a daily AQI of 1 (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 Manchester's worst air quality day in 2025?▾
July 26, 2025, AQI 123 (Unhealthy for Sensitive Groups), set by fine particulate matter (PM2.5), in wildfire smoke season.
Which pollutant causes Manchester's worst air days?▾
Fine particulate matter (PM2.5) set the AQI on 7 of the 10 worst days; ground-level ozone on 3. The tables above list the defining pollutant for every day.
Manchester's 10 worst air quality days, 2019–2025
Highest daily AQI recorded for the Manchester-Nashua, NH area (EPA AQS). The daily AQI is the highest reading from any monitor in the area that day.
| # | Date | AQI | Category | Defining pollutant |
|---|---|---|---|---|
| 1 | (2021 page) | 144 | Unhealthy for Sensitive Groups | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 2 | (2025 page) | 123 | Unhealthy for Sensitive Groups | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 3 | (2023 page) | 119 | Unhealthy for Sensitive Groups | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 4 | (2023 page) | 112 | Unhealthy for Sensitive Groups | O3 — ground-level ozone |
| 5 | (2023 page) | 109 | Unhealthy for Sensitive Groups | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 6 | (2025 page) | 105 | Unhealthy for Sensitive Groups | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 7 | (2023 page) | 105 | Unhealthy for Sensitive Groups | O3 — ground-level ozone, in peak ozone season |
| 8 | (2021 page) | 105 | Unhealthy for Sensitive Groups | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 9 | (2025 page) | 103 | Unhealthy for Sensitive Groups | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 10 | (2025 page) | 101 | Unhealthy for Sensitive Groups | O3 — ground-level ozone, in peak ozone season |
Worst day of each year in Manchester
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 | 80 | Moderate | O3 — ground-level ozone, in peak ozone season | |
| 2020 | 90 | Moderate | O3 — ground-level ozone, in peak ozone season | |
| 2021 | 144 | Unhealthy for Sensitive Groups | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season | |
| 2022 | 100 | Moderate | O3 — ground-level ozone, in peak ozone season | |
| 2023 | 119 | Unhealthy for Sensitive Groups | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season | |
| 2024 | 97 | Moderate | O3 — ground-level ozone | |
| 2025 | 123 | Unhealthy for Sensitive Groups | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
Manchester's 10 best air quality days, 2019–2025
Lowest daily AQI recorded for the Manchester-Nashua, NH area. Ties are listed most recent first.
| # | Date | AQI | Category | Defining pollutant |
|---|---|---|---|---|
| 1 | (2023 page) | 1 | Good | CO — carbon monoxide |
| 2 | (2022 page) | 1 | Good | CO — carbon monoxide |
| 3 | (2022 page) | 1 | Good | CO — carbon monoxide |
| 4 | (2023 page) | 2 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 5 | (2023 page) | 2 | Good | CO — carbon monoxide |
| 6 | (2023 page) | 3 | Good | CO — carbon monoxide |
| 7 | (2019 page) | 3 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 8 | (2023 page) | 4 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 9 | (2023 page) | 6 | Good | PM2.5 — fine particulate matter (PM2.5) |
| 10 | (2021 page) | 6 | Good | PM2.5 — fine particulate matter (PM2.5) |
Right now in Manchester
The latest EPA AirNow observation puts Manchester's AQI at 12 (O3). The days above are historical records, not today's reading.
View current Manchester air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Manchester-Nashua, NH), 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.