Chiang Mai, Chiang Rai and Mae Hong Son are the provinces hardest hit by fine dust pollution which has caused people to fall ill with respiratory illnesses and skin diseases.
PM2.5 fine dust has blanketed 17 northern provinces although it has surged to critical levels in those three provinces, the Department of Health (DoH) said.
Of the three, Mae Hong Son was worst affected, at 194 microgrammes per cubic metre (µg/m3), far above the 50 microgrammes the Department of Pollution Control has set as Thailand's safe level but which is still double the World Health Organization's 25 µg/m3 limit.
DoH director-general Suwannachai Wattanayingcharoenchai said yesterday the PM2.5 pollution in the North is potentially harmful to people's health.
The dust level in Bangkok, the Northeast and the Central Plains provinces remains moderate.
From Jan 1 to March 7, the number of people in the North who had sought treatment at hospitals for respiratory and skin ailments was recorded at 255,077. Doctors said the condition of many people was caused or aggravated by dust pollution.
The DoH said a survey showed that from March 1-8, 19% of respondents in the North suffered from nose irritation, 18% from nasal congestion and 15% from eye irritation. Most affected are people aged between 45-54.
A 110 µg/m3 dust level was detected yesterday in Chiang Mai's Muang district, according to a reading by the AIR4THAI application designed by the Department of Pollution Control.
Hazy skies blocked sunlight over Chiang Mai's downtown area and obscured the view of the mountain-top Doi Suthep, the province's landmark attraction.