Fine dust was at unsafe levels in many districts of Bangkok and some districts in Samut Prakan and Samut Sakhon provinces.
Pralong Damrongthai, director-general of the Pollution Control Department, said on Tuesday that the levels of particulate matter 2.5 micrometres and less (PM2.5) in diameter measured 32-84 microgrammes per cubic metre of air in greater Bangkok over the 24 hours to 9am Tuesday. The safe threshold is set at 50mcg by the government.
Fine dust breached the safe level in Bangkok's Din Daeng, Bang Phlad (Charan Sanitwong Road), Bang Khunthian (Rama II Road), Pathumwan (Chamchuri Square), Phasicharoen (Phetkasem Road), and Bang Sue districts.
For the adjacent provinces, PM2.5 levels were unhealthy in tambon Song Khanong of Phra Pradaeng and tambon Pak Nam of Muang districts of Samut Prakan, and tambon Maha Chai of Muang district and tambon Om Noi of Krathum Baen district of Samut Sakhon, Mr Pralong said.
He attributed the air pollution to a high pressure system from China that caused stagnant air.