SmogRank / World / Switzerland / September 2025

Most unhealthy days in Switzerland, September 2025

9 cities in Switzerland ranked by their share of unhealthy days over the 30 days. The most unhealthy days: Winterthur, Switzerland, 0 of 30 measured days. 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.

← Winterthur 0% 0.75%0
Every city in Switzerland ranked for September 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. 1Winterthurlow-cost sensorsZurich
    0 of 30
  2. 2BaselBasel-City
    0 of 30
  3. 3GiubiascoTicino
    0 of 28
  4. 3BernBern
    0 of 28
  5. 5ZürichZurich
    0 of 28
  6. 6KreuzlingenThurgau
    0 of 27
  7. 7LuganoTicino
    0 of 28
  8. 8PayerneVaud
    0 of 28
  9. 9KüssnachtSchwyz
    0 of 28

Low-cost sensors: consumer units, counted only in cities with no government-grade monitor; they read close to reference monitors on the whole, but 15 to 25% high in humid air. How we use them.

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, September 2025 · Switzerland now

Regions

Basel-City 1Bern 1Schwyz 1Thurgau 1Ticino 2Vaud 1Zurich 2

Ranked cities in each region, September 2025.

Use this board

SmogRank, most polluted cities in Switzerland, by unhealthy days, PM2.5, September 2025, smogrank.com/ch/history/2025-09?by=days (accessed 10 Oct 2026). Some readings from Uzhydromet (Uzbekistan's Hydrometeorological Service); Department of Environment, Nepal; Vietnam's government monitors; Aurassure; Umhverfisstofnun (Environment Agency of Iceland); RMCAB (Secretaría Distrital de Ambiente, Bogotá); Love My Air (City and County of Denver), no reuse terms published.

Download top 10 by average (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.