Hazardous levels of PM2.5 remained only in the upper North at noon on Sunday, with the worst air pollution in Chiang Dao district of Chiang Mai province.
The Pollution Control Department reported that hazardous levels of particulate matter 2.5 micrometre and less in diameter (PM2.5) were detected in Chiang Mai, Chiang Rai, Lampang, Lamphum, Mae Hong Son, Nan and Phayao provinces.
Over the 24 hours prior to 12pm on Sunday, PM2.5 levels ranged from 91 to 310 microgrammes per cubic metre of air. The peak reading was in Chiang Dao district of Chiang Mai.
The level was at 307µg/m³ in Mae Sai district of Chiang Rai.
Meanwhile, the Meteorological Department expected heavy rains in the upper part of the country from Sunday to Thursday due to a low pressure system there.
On Friday and Saturday a high pressure system from China will collide with hot and humid air in the upper part of the country, likely bringing summer storms with hail and thunder, the department said on Sunday.