Chiang Mai was ranked the worst among polluted major global cities on Monday, as the northern province continues to be hit by forest and man-made fires.
IQAir reported the Air Quality Index (AQI) in the northern city at 263, a level marked "very unhealthy", as of 10am on Monday. The level of PM2.5 was measured at 188.0 microgrammes per cubic metre.
Extremely smoggy conditions in Chiang Mai were forecast to improve Monday evening and at least until Wednesday.
Chiang Mai province also led the nation in the number of hot spots, at 480 on Sunday. Hot spots are due to natural bushfires in the dry season and burning-off by farmers.
The fires continue despite repeated legal warnings from authorities.
Authorities warned that starting a fire in a state-protected area could result in a fine of 400,000 to 2 million baht and/or 4 to 20 years in prison.
