Unhealthy levels of fine dust remained high in the northern provinces on Monday, held there by stagnant air, while a southerly wind was easing the pollution in Greater Bangkok.
The Pollution Control Department said levels of particulate matter up to 2.5 microns in diameter (PM2.5) ranged from 97 to 225 microgrammes per cubic metre (μg/m³) of air in many northern provinces over the previous 24 hours, as of Monday morning.
Unhealthy PM2.5 were reported in Chiang Mai, Chiang Rai, Mae Hong Son, Nan, Phitsanulok and Sukhothai provinces. The worst reading was in tambon Chong Kham of Muang district in Mae Hong Son province.
The safe threshold is set by the government at 50 μg/m³, higher than many other countries.
The department blamed the pollution on outdoor burning and stagnant air. It predicted fine dust levels would keep rising in the North through to Thursday.
The pollution was less serious in the Northeast where PM2.5 was measured at 51-69μg/m³ in Buri Ram, Loei, Nakhon Phanom and Nakhon Ratchasima provinces.
In Greater Bangkok, PM2.5 accumulation exceeded the safe threshold only in Bang Khun Thian and Bang Sue district of Bangkok, where fine dust was measured at 51-55μg/m³ of air over 24 hours. The area benefitted from rain and wind.
The Pollution Control Department expected better air quality in Greater Bangkok from Thursday onwards thanks to a southerly wind.
The Meteorological Department forecast scattered summer storms for the North, the Northeast, the East and the Central Plains, including Greater Bangkok, on Monday and Tuesday due to the collision of cold air from China and hot air above the country.
The department warned of hailstorms in some areas.