Hartford Best & Worst AQI Days: Air Quality Guide
The worst air quality day on record for Hartford (Hartford-West Hartford-East Hartford, CT area) was June 20, 2024, when the daily AQI reached 185 (Unhealthy), set by ground-level ozone, in peak ozone season. Across 2,557 monitored days in 2019–2025, 9 of the 10 worst days were Unhealthy (AQI 151+) or worse; 7 of the 10 were driven by ground-level ozone and 3 by fine particulate matter (PM2.5), and 4 of them fell in 2023. The cleanest day was July 3, 2021 at AQI 12 (Good); the 10 best days span 4 different years.
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When were Hartford's worst and best air quality days?
Worst: June 20, 2024, AQI 185 (Unhealthy, O3). Best: July 3, 2021, AQI 12 (Good). Based on 2,557 EPA-monitored days in the Hartford-West Hartford-East Hartford, CT area, 2019–2025.
- ✓9 of the 10 worst days were Unhealthy (AQI 151+) or worse; the 10th-worst was AQI 147 (Unhealthy for Sensitive Groups).
- ✓Ground-level ozone 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 Hartford?▾
June 20, 2024: the Hartford-West Hartford-East Hartford, CT area's daily AQI hit 185 (Unhealthy), driven by ground-level ozone, in peak ozone season. That is the highest of 2,557 monitored days in 2019–2025.
What was the best air quality day in Hartford?▾
July 3, 2021, with a daily AQI of 12 (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 Hartford's worst air quality day in 2025?▾
August 12, 2025, AQI 164 (Unhealthy), set by ground-level ozone, in peak ozone season.
Which pollutant causes Hartford's worst air days?▾
Ground-level ozone set the AQI on 7 of the 10 worst days; fine particulate matter (PM2.5) on 3. The tables above list the defining pollutant for every day.
Hartford's 10 worst air quality days, 2019–2025
Highest daily AQI recorded for the Hartford-West Hartford-East Hartford, CT area (EPA AQS). The daily AQI is the highest reading from any monitor in the area that day.
| # | Date | AQI | Category | Defining pollutant |
|---|---|---|---|---|
| 1 | (2024 page) | 185 | Unhealthy | O3 — ground-level ozone, in peak ozone season |
| 2 | (2023 page) | 166 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 3 | (2025 page) | 164 | Unhealthy | O3 — ground-level ozone, in peak ozone season |
| 4 | (2025 page) | 164 | Unhealthy | O3 — ground-level ozone, in peak ozone season |
| 5 | (2023 page) | 163 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 6 | (2023 page) | 156 | Unhealthy | O3 — ground-level ozone |
| 7 | (2023 page) | 155 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season |
| 8 | (2019 page) | 154 | Unhealthy | O3 — ground-level ozone, in peak ozone season |
| 9 | (2021 page) | 151 | Unhealthy | O3 — ground-level ozone, in peak ozone season |
| 10 | (2022 page) | 147 | Unhealthy for Sensitive Groups | O3 — ground-level ozone, in peak ozone season |
Worst day of each year in Hartford
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 | 129 | Unhealthy for Sensitive Groups | O3 — ground-level ozone, in peak ozone season | |
| 2021 | 151 | Unhealthy | O3 — ground-level ozone, in peak ozone season | |
| 2022 | 147 | Unhealthy for Sensitive Groups | O3 — ground-level ozone, in peak ozone season | |
| 2023 | 166 | Unhealthy | PM2.5 — fine particulate matter (PM2.5), in wildfire smoke season | |
| 2024 | 185 | Unhealthy | O3 — ground-level ozone, in peak ozone season | |
| 2025 | 164 | Unhealthy | O3 — ground-level ozone, in peak ozone season |
Hartford's 10 best air quality days, 2019–2025
Lowest daily AQI recorded for the Hartford-West Hartford-East Hartford, CT area. Ties are listed most recent first.
| # | Date | AQI | Category | Defining pollutant |
|---|---|---|---|---|
| 1 | (2021 page) | 12 | Good | O3 — ground-level ozone, in peak ozone season |
| 2 | (2023 page) | 14 | Good | NO2 — nitrogen dioxide |
| 3 | (2023 page) | 15 | Good | NO2 — nitrogen dioxide |
| 4 | (2023 page) | 15 | Good | O3 — ground-level ozone |
| 5 | (2024 page) | 16 | Good | O3 — ground-level ozone |
| 6 | (2021 page) | 17 | Good | O3 — ground-level ozone |
| 7 | (2020 page) | 17 | Good | O3 — ground-level ozone |
| 8 | (2024 page) | 19 | Good | NO2 — nitrogen dioxide |
| 9 | (2023 page) | 19 | Good | O3 — ground-level ozone |
| 10 | (2024 page) | 20 | Good | O3 — ground-level ozone |
Right now in Hartford
The latest EPA AirNow observation puts Hartford's AQI at 36 (PM2.5). The days above are historical records, not today's reading.
View current Hartford air quality →Source: EPA Air Quality System (AQS) pre-generated Daily AQI by CBSA files — daily AQI by CBSA (Hartford-West Hartford-East Hartford, CT), 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.