Fine-dust readings were slightly above the safe level in Bangkok's Bang Khen and Laksi districts on Wednesday morning, and also in northern Nan province, where farmers are burning off fields ahead of a ban starting on Friday.
The Pollution Control Department reported the average level of hazardous particulate matter 2.5 micrometres and less in diameter (PM2.5) was 51 microgrammes per cubic metre of air in the past 24 hours in Thung Song Hong sub-district of Laksi and at 61mcg on Phahon Yothin Road in Bang Khen. The safe threshold is set at 50mcg.
The department said it was caused by stagnant air and a high pressure zone trapping the dust.
In the northern province of Nan, the PM2.5 reading was 52mcg in Muang district. Farmers in the area are hurrying to burn off the trash in their sugar cane fields ahead of the harvest, especially in Song Khwer and Tha Wang Pha districts, before a local ban on burning kicks in from Feb 15-April 15.
The Department of Disaster Prevention and Mitigation reported unhealthy levels of PM2.5 in seven other northern provinces -- Chiang Rai (Muang and Mae Sai districts), Chiang Mai (Muang district), Lampang (Muang and Mae Mo districts), Lamphun (Muang district), Phrae (Muang district), Phayao (Muang district), and Tak (Mae Sot district).
PM2.5 levels ranged from 60 to 93mcg there.
