Chiang Mai was again listed on Wednesday as the city with the worst air pollution in the world, according to pollution monitoring website IQAir.
At 10.30am, IQAir reported the PM2.5 level was at 239 microgrammes per cubic metre (µg/m³), which far exceeds standard safe levels.
"As a result, Chiang Mai continues to be the most polluted city in the world over the past several days," IQAir said.
Lahore in Pakistan was the second most polluted city with a US AQI value of 260, followed by New Delhi in India at 242, Beijing (181) and Wuhan in China (173).
Chiang Mai was blanketed by thick haze on Wednesday due to extensive outdoor burning and a large number of fire hotspots in neighbouring countries, with winds blowing smoke across the border into the northern city.
Of all 3,667 hotspots in 17 northern cities, 488 were detected in Chiang Mai in the past 24 hours.
In Chiang Mai, the worst PM2.5 level of 960 µg/m³ was recorded in Chiang Dao district yesterday morning.
On Tuesday, the Chiang Mai governor said he had opened a help centre to look after the health of residents affected by PM2.5, amid reports that hospital admissions for respiratory illnesses have increased.
Measures are also in place to distribute face masks to residents and arrange dust-free rooms across the northern province, the governor said.
The Pollution Control Department predicts the PM2.5 situation in Bangkok and surrounding provinces will improve from now until April 2, with southerly winds blowing the haze away from the provinces. However, between April 3-4, several areas in Bangkok may be affected by haze coming from the western part of the country.
