The safety level for Thailand has been set at 50 micrograms per cubic metre (µg/m3).
The provinces with high air pollution included Chiang Rai, Mae Hong Son, Chiang Mai, Nan, Phrae, Uttaradit, Sukhothai, Phitsanulok, Kamphaeng Phet, Nong Khai Loei, Nakhon Phanom, Sakon Nakhon, Khon Kaen, Kalasin, Roi Et, Chaiyaphum, Ubon Ratchathani, Nakhon Ratchasima and Buriram.
The bureau added that the PM2.5 range in the North was between 35 to 145µg/m3, between 50 to 73µg/m3 in the Northeast, between 9 to 32µg/m3 in the Central and West, between 12 and 19µg/m3 in the East, and 9 to 22µg/m3 in the South.
The range of air pollution in Bangkok and its vicinity was between 13 to 35µg/m3.