Kingchan said Bangkok Airways flight to Chiang Mai would depart Mae Hong Son at 1pm instead of the usual 10.30am, as the haze would lessen in the afternoon, while Kan Air, which uses a 66-seat aircraft, has temporarily opted for a 12-seater Cessna to service passengers who had made advance bookings.

Meteorological Station official Sunthorn Kanthamala said Mae Hong Son, with a minimum temperature of 14.5 degrees Celsius, had a visibility of 1,500 metres at 7am and 2,000 metres at 8am, which were too low for a large aircraft that require a minimum of 5,000 metres visibility.

According to the Pollution Control Department website, the amount of small particulate matter up to 10 microns in diameter (PM10) in Mae Hong Son in the last 24 hours peaked at 120 micrograms per cubic metre of air, while the readings on Sunday and Monday were beyond 150 micrograms.