- Captain Cook, Kailua Kona
- 2.5 microgram(s) per cubic metre
- United States ()
According to the IQAir 2019 World Air Quality Report, covering 4,680 cities globally, the two least polluted cities in the world are Captain Cook and Kailua Kona, both in Hawaii, USA, with an average PM2.5 level of just 1.9 µg/m³ in 2019. PM2.5s are very small particles such as soot, dust and ash, prolonged exposure to which can cause cancer, lung and heart conditions.