PM2.5 pollution surged to moderate and high-risk levels in 21 areas of Bangkok and neighbouring Samut Prakan province yesterday, according to the Pollution Control Department.
The department released readings at 1pm which showed that this particularly hazardous type of particulate matter had surpassed the "safe" threshold of 50 microgrammes per cubic metre (µg/m³) in 18 spots in Bangkok as well as three in Samut Prakan.
The readings ranged between 51 and 72 µg/m³.
The worst-hit area was Samut Sakhon's tambon Mahachai where PM2.5 topped out at 74 µg/m³, followed by tambon Om Noi of Krathum Baen district and Samut Prakan's Muang district.
PM10, another harmful pollutant, also reached 132 µg/m³ in tambon Mahachai, surpassing the safe threshold of 120 µg/m³.
This accumulation of fine dust particles is the result of the influence of cold air from China, according to the department.
Acting director-general of the department, Suwannachai Wattanayingcharoenchai, warned this sharp rise in inhalable pollutants could have an impact on public health, particularly in the areas of Bangkok and Samut Prakan with the highest readings.
He said the department is doing all it can to mitigate the problem.
The Health Department, he said, has opened an emergency centre to provide air quality warnings as well as provide health care assistance to vulnerable groups, such as children and the elderly, who are most likely to be affected.