The Pollution Control Department has warned that ultra fine dust levels will be worse this harvest season than last year because of drier weather, and will peak in February.
Pansak Thiramongkol, air and noise quality director at the department, said on Tuesday that stagnant air resulted in the accumulation of ultra-fine dust currently produced mainly by motor vehicles.
"Dust pollution this year may be worse than last year because of drier weather. The dust will gradually increase, become high in January and peak in February," he said.
Air pollution would continue afterwards, due to smog from the North, he said.
On Tuesday morning the Bangkok Metropolitan Administration reported unhealthy levels of particulate matter 2.5 micrometres and less in diameter (PM2.5) in parts of Bang Bon, Bang Khunthian, Bang Phlat, Bang Rak, Bangkok Noi, Bangkok Yai, Klong San, Nong Khaem, Pathumwan, Phasicharoen, Thawi Watthana, Taling Chan, Thon Buri and Thung Kru.
The levels of PM2.5 per cubic metre of air over past 24 hours ranged from 38.2 to 54.4 microgrammes. The highest level was recorded in Nong Khaem. The safe threshold is 37.5µg/m³, according to the government.
The Industry Ministry recently also blamed ultra-fine dust pollution on sugarcane burn-off, saying it affected about 44 million people for about six months every year.