Eight pollution control stations in the upper northern provinces were on Tuesday blanketed with PM2.5 fine dust pollution, prompting urgent measures to be implemented to deal with the problem, according to the Department of Pollution Control (DPC).

The department reported yesterday that severe PM2.5 pollution was detected by eight air-quality monitoring stations in Chiang Rai, Chiang Mai, Phayao, Mae Hong Son and Nan.

The eight stations in "red" danger zones are in Chiang Rai, tambon Wiang in Muang district where the pollution was measured at 102 microgrammes per cubic metre (µg/m³) of air and tambon Wiang Phang Kham in Mae Sai district at 145 µg/m³; in Chiang Mai, tambon Chang Phueak where the PM2.5 level was recorded at 104µg/m³, the Sri Phum area of Muang district at 97µg/m³ and the Chiang Dao district at 180µg/m³; in Mae Hong Son, the pollution hit 109µg/m³ in Muang district; in Phayao, the dust surged to 116µg/m³ in Muang district; and in Nan, the pollution rose to 99µg/m³ in Chalerm Prakiat district.

Poor air was also lingering over other northern provinces including Lampang, Kamphaeng Phet and Uttaradit.

PM2.5 readings above 50µg/m³ are considered hazardous to health by the Thai government.

Pralong Dumrongthai, the department director-general, said in the summer when there is little wind and rain, the dust tends to hover over specific areas.

The problem is exacerbated by slash-and-burn farming practices which have continued despite repeated warnings by the authorities threatening tough legal action against offenders, he added.

The southwesterly monsoon wind that blows fine particulate matter from neighbouring countries into Thailand has also worsened the dust pollution in vast areas of the upper North.

The department chief said that it will ask the countries concerned to reduce forest burning activities on their sides of the borders.

At the same time, the department is looking to deploy water spraying techniques to increase humidity in the air. The fine mist will cause the dust particles flowing in the air to drop to the ground. Water trucks, as well as planes, will be used in the operation, Mr Pralong said.

Department chief said Chiang Mai provincial governor Charoenrit Sanguansat was working to enlist the air force's help in the mission.

In Phrao district of Chiang Mai, fire extinguishers are in short supply to combat bushfires which are raging deep in the mountains, he said.