Air quality measurements in Chiang Mai have registered above the 'healthy' spectrum for three consecutive days.
The air quality index is measured at two spots in the city - the provincial hall and Yupparaj Wittayalai School.
Air quality at the provincial hall stood at 104 and measured 102 at the school, exceeding the benchmark of 100.
The average mass of small particles in the air stood at 129 and 123 microgrammes per cubic metre at the two spots, also slightly higher than the 120 standard, according to a media report.
Chana Phaengpibul, deputy governor of Chiang Mai said more than 3,500 rai of land had been damaged by forest fires in the province, which is the primary cause of problems with haze across the North of the country.
Caretaker Prime Minister Yingluck Shinawatra on Friday went to inspect the progress of projects to solve forest fire and haze problems in the North.
The operation centre for controlling forest fires and haze organised a video conference with 25 districts in the province. The conference identified five districts as being 'haze hotspots', where many villagers openly burn agricultural waste, often the cause of forest fires.
Officials have been are instructed to launch an aggressive education campaign to stop villagers burning such waste and to try and tries to increase water supplies to areas most at risk of forest fires.
A file photo shows a forest fire on March 8 in Mae Taeng district, Chiang Mai. Forest fires are a major cause of air pollution in the area.