Authorities are blaming local residents for burning garbage that caused thick smoke to blanket wide areas of Chiang Mai.
Fire trucks and crews from the Mam Phrae municipality on Wednesday were sent to extinguish a fire on Klong Chonprathan Road in tambon Nam Phrae of Hang Dong district. Motorists drove cautiously and slowly due to poor visibility.
Local authorities believed thick smoke and dust was caused by the burning of garbage by local residents that quickly spread to roadside weeds.
Dust particles at Chiang Mai's provincial hall were reported at 103 microgrammes per cubic metre at noon against a health standard of 120 mg per cu/m. The air quality index was measured at 90, against a health safety standard of 100.
In another location, the particle level at Yupparaj Wittayalai School in this northern province was reported at 124, while the air quality index was measured at 102.