Challenges in tackling PM2.5 crisis

This aerial photo taken yesterday shows Doi Suthep temple as heavy pollution engulfs Chiang Mai, caused in part by seasonal agricultural burning. (Photo: AFP)

Chiang Mai has repeatedly been named the world's most air-polluted city this year. Not exactly a title to be envious about.

The city was hit hard by PM2.5 ultra-fine dust on March 31. IQair.com, an air quality reporting website, reported Chiang Mai had an air quality index of 320 with an ultra-fine PM2.5 dust level of 269.2 microgrammes per cubic metre (μg/m3), far beyond the World Health Organization (WHO)'s "safe" limit of 25 μg/m3.