The Department of Disaster Prevention and Mitigation on Monday reported unhealthy levels of fine dust in seven northern provinces: Chiang Mai, Chiang Rai, Lampang, Mae Hong Son, Nan, Phayao and Phrae.
Director-general Chayapol Thitisak said the level of particulate matter 2.5 micrometres or less in diameter exceeded the safe threshold of 50 microgrammes per cubic metre of air in the past 24 hours in parts of the seven provinces.
Harmful levels were detected in tambon Chang Phuak and tambon Sri Phum of Chiang Mai's Muang district; tambon Wiang Phang Kham of Mae Sai district and tambon Wiang of Muang district in Chiang Rai; and tambon Phra Bat of Muang district and tambon Ban Dong of Mae Mo district in Lampang.
The same conditions prevailed in tambon Jong Kham of Muang district in Mae Hong Son; tambon Nai Wiang of Muang district and tambon Huai Kone in Chalerm Prakiat district of Nan; tambon Na Chak of Muang district in Phrae; and tambon Ban Tom of Muang district in Phayao.
The levels of fine dust ranged from 53 to 101mcg in these areas. The worst was in Chiang Rai province, Mr Chayapol said. He blamed the pollution on people burning off fields before planting crops, and forest fires.