“The Chiang Mai University [CMU], in particular, should suspend its classes until the situation improves. The statement was released after AirVisual, an internationally recognised platform for air-quality data, ranked Chiang Mai as the world’s third-most polluted city on Tuesday afternoon. The sky in Chiang Mai has been of brownish hue for several days now. As for Chiang Mai, Lamphun, Mae Hong Son and Tak, the ban will run from March to April. After about 10 days of respite, Bangkok and its adjacent provinces saw a return of the smog crisis yesterday.

Source: The Nation Bangkok February 13, 2019 18:00 UTC