Parts of the upper North and Northeast remained cloaked in hazardous levels of smoke haze on Tuesday, with with the worst pollution still in Chiang Rai's Mae Sai district.
The Pollution Control Department reported unsafe and red-coded levels of particulate matter 2.5 micrometres and less in diameter (PM2.5) in the northern provinces of Chiang Mai, Chiang Rai, Lamphun, Lampang, Mae Hong Son, Nan, Phayao and Phrae.
Their PM2.5 levels ranged from 99 to 517 microgrammes per cubic metre (μg/m³) of air over 24 hours as of 10am on Tuesday. The government-set safe threshold is at 50μg/m³.
The worst level, 517μg/m³, was again reported in tambon Wiang Phang Kham in Mae Sai district of Chiang Rai.
Red levels of PM2.5 were detected at a few locations in the upper Northeast, including 93μg/m³ in Bueng Kan province, 95 in Nong Khai and 126 in Loei.
Pinsak Suraswadi, director-general of the Pollution Control Department, said that dense smog remained in these regions because of the large number of forest fires in the countryside, the many hotspots in neighbouring countries, and the stagnant air over the area.
He warned that air pollution would remain severe in the North until next Tuesday.
Interior Minister Anupong Paochinda said provincial governors had authority to impose harsh measures to control smoke haze in line with the guidelines of the Ministry of Natural Resources and Environment, but the key to the successful implementation depended on people's cooperation.