Most provinces in the North were hit with dangerous levels of PM2.5 on Monday morning, with Chiang Mai rated the city with the worst air pollution in the world.

The Geo-Informatics and Space Technology Development Agency reported at 8am on Monday that 14 provinces were facing red (seriously harmful) levels of PM2.5.

The worst level, 173.6 microgrammes per cubic metre of air, was measured in Mae Hong Son, followed by 153.1µg/m³ in Chiang Mai, 152.2µg/m³ in Chiang Rai and 140.8µg/m³ in Lamphun.

Orange (initially unsafe) levels of PM2.5 were detected in 20 other provinces, mostly in the Northeast. They ranged from 39.2 to 74.6µg/m³.

Provinces in the lower Central Plain, the lower Northeast and the South had moderate and good air quality. Samut Prakan had the best air quality with 10.6µg/m³, followed by Bangkok with 11.5µg/m³.

IQAir rated Chiang Mai as the major city with the world's worst air pollution on Monday morning, followed by Jakarta, Hanoi and Hangzhou.