The air quality in Chiang Mai has continued to deteriorate over the past several days due to wildfires spreading in the province, according to local authorities.
The province has the most hotspots in the northern region and is ranked among the cities with the poorest air quality in the world. The city's downtown area has been shrouded by heavy smog every day over the past month.
The province's Wildfire and Pollution Control Command Centre reported 52 additional hotspots in Chiang Mai yesterday morning, on top of the 166 hotspots detected by the Geo-Informatics and Space Technology Agency (Gistda) on Sunday.
The news came despite Chiang Mai's Wildfire and Pollution Control Command Centre reporting a reduction in burning activities in the province.
The province's six air quality monitoring stations -- three in Muang district and one each in Chiang Dao, Hot and Mae Chaem districts -- recorded unhealthy levels of ultra-fine particulate matter (PM2.5) in the air, with readings ranging from 53.3 microgrammes per cubic metre (μg/m³) to 102.7 μg/m³.
Any PM2.5 reading higher than the safe threshold for 24-hour exposure of 37.5 μg/m³ is considered unhealthy.
According to the air quality monitoring website IQAir.com, Chiang Mai's air quality index reached 161 while its PM2.5 level measured 74.1 μg/m³ at 10am yesterday, making it the world's fourth most polluted city.
Chiang Mai regularly appeared on the list of the world's most polluted cities between April 1 and 29 this year, the website's data showed.
Chiang Mai governor Nirat Phongsitthithawon yesterday said authorities are doing their best to curb wildfires in the region. He asked all relevant agencies to roll out anti-pollution measures help combat the fine dust pollution, which is detrimental to health and hurts the local tourism industry.