What is the cleanest city in the world by air quality?

Longyearbyen, Svalbard (Norway) ranks as the world's cleanest monitored city with a composite US AQI of 8 and PM2.5 of just 1.9 µg/m³ — well below the WHO guideline of 5 µg/m³. Other top contenders include Whitehorse (Canada), Yellowknife (Canada), and remote Pacific island capitals.

What does AQI mean and how is it calculated?

The US AQI (Air Quality Index) converts measured pollutant concentrations into a 0–500 scale. 0–50 is Good (green), 51–100 is Moderate, 101–150 is Unhealthy for Sensitive Groups, 151–200 is Unhealthy, and higher values are Very Unhealthy or Hazardous. This site uses a composite AQI calculated as the maximum AQI across PM2.5, PM10, NO2, ozone and CO for each city.

Which continent has the cleanest air overall?

Oceania and North America consistently rank as the continents with the cleanest air quality. Remote Pacific island nations (Palau, Tuvalu, Marshall Islands, Micronesia) record some of the lowest PM2.5 concentrations on Earth. In North America, cities in Canada's Yukon and Northwest Territories lead the global rankings.

What is a good PM2.5 level to live in?

The WHO 2021 annual guideline for PM2.5 is 5 µg/m³. Cities below this threshold offer the healthiest long-term air for residents. A US AQI of 0–50 (PM2.5 below 9 µg/m³) is classified as Good. For comparison, many European and North American cities with Good AQI average 5–15 µg/m³, while polluted Asian cities can exceed 50–100 µg/m³ annually.

Helena MT, United States of America — Air Quality & Clean City Guide 2026

Helena MT Air Quality Data

#	City	Continent	AQI	PM2.5
1	Helena MT, United States of America	North America	AQI 23	PM2.5 5.49 µg/m³