Very unsafe smog levels were reported in nine northern provinces on Wednesday - Chiang Mai, Chiang Rai, Kamphaeng Phet, Lampang, Mae Hong Son, Nan, Phayao, Phrae and Sukhothai - and worst was in Nan.
The Pollution Control Department reported hazardous levels of particulate matter 2.5 micrometres and less in diameter (PM2.5) over the previous 24 hours in the North. The government-set safe threshold is 50 microgrammes per cubic metre of air.
In Chiang Mai, the levels were at 119mcg in tambon Chang Phuak of Muang district and 234mg in tambon Muang Khong of Chiang Dao district.
In Lampang, the levels were at 107mcg in tambon Phra Bat of Muang district, 106mcg in tambon Mae Moh of Mae Moh district.
In Chiang Rai, the levels were at 119mcg in tambon Wiang of Muang district and 197mcg in tgambon Wiang Phang Kham of Mae Sai district. In Mae Hong Son, the level was in 92mcg in tambon Jong Kham of Muang district.
In Nan, the levels were at 139mcg in tambon Nai Wiang of Muang district and 275mcg in tambon Huai Kone of Chalerm Phrakiat district.
PM2.5 measured 121mcg in tambon Na Chak of Muang district in Phrae, 116mcg in tambon Ban Tom of Muang district in Phayao, 97mcg in tambon Thani of Muang district in Sukhothai, and 114mcg in tambon Nai Muang of Muang district in Kamphaeng Phet.
Lower unsafe levels of smog were also reported in other areas of Mae Chaem and Muang districts in Chiang Mai, Mae Moh district of Lampang, Muang district of Nakhon Sawan, Mae Sot district of Tak, Muang district of Phitsanulok, Muang district of Phichit, Muang district of Uttaradit and Wichan Buri district of Phetchabun.