SmogRank / World / United States / Connecticut / 2025

Most polluted cities in Connecticut, United States, 2025

6 cities in Connecticut, United States ranked by their average PM2.5 over the 365 days; 6 above the WHO annual guideline (5.0 µg/m³). Worst: Hartford at 7.3 µg/m³, #1,947 of 2,624 cities in the world. Cleanest: New London at 5.8. A city needs measurements on 70% of the days to be ranked.

Ranked by unhealthy days: the share of each city's measured days with a daily mean over 35.4 µg/m³ (US AQI 101+), Unhealthy for Sensitive Groups or worse on the US EPA's scale. Ties go to the higher average.

← Danbury 1% 0.75%0
Every city in Connecticut, United States ranked for 2025, one column each, ranked by unhealthy days: height is the share of its measured days that were unhealthy, colour its average. Point at it to read a city; tap to open it.
  1. 1Danbury
    1%
  2. 2Hartford
    1%
  3. 3Waterbury
    1%
  4. 4New Haven
    0%
  5. 5Bridgeport
    0%
  6. 6New London
    0%
Good0–50
Moderate51–100
Sensitive groups101–150
Unhealthy151–200
Very unhealthy201–300
Hazardous301+

The US EPA's Air Quality Index for PM2.5 (2024 breakpoints). Show values as: µg/m³ · US AQI · India AQI · China AQI · European AQI · UK DAQI · Canada AQHI+. About the scales

All cities in the world, 2025 · All cities in United States, 2025 · Connecticut now

Use this board

SmogRank, most polluted cities in Connecticut, United States, PM2.5, 2025, smogrank.com/us/region/connecticut/history/2025 (accessed 6 Oct 2026).

Download top 10 (PNG)

You're welcome to reuse a single chart, image or figure with this citation and a link. Terms. Raw monitor readings in bulk are published by OpenAQ, under each provider's licence.