From Nan to Mae Hong Son, Phrae, Chiang Mai and Chiang Rai, choking smog continues to be a persistent problem and part of daily life in the North, where more than 400 brushfire hotspots have now been identified.
Most of the fires are in Mae Hong Son, on the far north-west border with Myanmar, which counted 100.
Bangkok Airways has already cancelled its morning flights between Chiang Mai and Mae Hong Son until at least next Sunday, extending the deadline from this weekend, saying there had been no improvement in visibility so the situation was too risky for flights.
Yesterday morning visibility at Mae Hong Son was just 1,600 metres, whereas Bangkok Airways requires 6,000 metres. At this stage other flights are continuing their schedule.
The Pollution Control Department reported the level of PM2.5 – particulate matter 2.5 micrometres or less in diameter – in Mae Hong Son more than twice the safe limit of 50 micrograms per cubic metre.
Authorities say that deliberately set brushfires and plantation burn-offs are the main cause of the air pollution. With Mae Hong Son topping the list, Chiang Mai had 83 hotspots on Sunday, Phayao 54, Tak 49, Nan 38, Chiang Rai 37, Lampang 31, Phrae 24 and Lamphum 20.
Authorities in several provinces have declared total bans on outdoor burning, but farmers often risk the threatened fines because they have no other viable way to clear their land.
Several outdoor activities have been cancelled in Nan, such as sports tournaments, as a result of the danger to health.