Air pollution in northern Lampang and Phayao provinces escalated to hazardous levels yesterday as fires spread in the region.
The PM10 level stood at between 81 and 104 microgrammes per cubic metre, up from Sunday's readings, according to information provided by the Pollution Control Department's (PCD) measuring stations in Lampang's Muang and Mae Mo districts.
Though the levels were still under the safe limit of 120 ug/m³, officials said they were treating the situation seriously as dust levels continue to rise.
Forest fires are a major cause of fine dust, or particulate matter known as PM10. These particles are less than 10 microns in diameter -- or about 1/7th as thick as a human hair. PM10 can trigger asthma attacks, cause or aggravate bronchitis and other lung diseases, and reduce the body's ability to fight infections, according to information from the PCD.
Hazy conditions in the North have been blamed on fires tied to agricultural burning practices and the extreme dryness seen from February to April, when rainfall is less common.
The situation in Lampang deteriorated Monday as brush fires in Chae Som forest reserve kept expanding, Ronnarong Koetnuan, head of the reserve's fire-forest prevention unit, told media outlets.
So far, 59 rai have been ravaged, including forest areas inside the Doi Phra Bat wildlife sanctuary and Mae Suk-Mae Soi forest reserve in Muang Pan district.
Mr Ronnarong pointed an accusing finger at local villagers for setting fires while collecting wild vegetables in the forests.
In Phayao, the air quality has barely improved despite showers that helped to keep the brush fires in check, with records showing the levels of dust pollutants were on the rise.
The levels of PM10 swung between 81 and 111 ug/cu³ from March 20 till yesterday, according to data from the PCD's monitoring stations.
Phayao governor Prachon Pratsakun has urged officials to keep a close watch on the practice of open burning, having already imposed a two-month ban on the scourge.
Mr Prachon has effectively declared war on air pollution triggered by forest fires.
He has issued statements suggesting that anyone found guilty of open burning before the middle of next month will face strict punishment.
Tak province has adopted a similar ban.
In February, local authorities launched a hunt for villagers after finding they defied the order to refrain from this by setting fire to a sugar cane field.
Violators can face severe penalties, including a jail term of between two and 15 years and/or a fine of up to 150,000 baht, according to officials.
But the haze problem has not led to any major health problems, said Dr Asdang Ruayarchin, deputy secretary-general of the Department of Disease Control (DDC).
He advised people to wear masks to combat the PM10 and said the DDC is monitoring the situation closely.