Hanoi, April 3 -- Air pollution across northern Thailand continues to deteriorate, posing serious risks to public health and adversely affecting economic and tourism activities in the region. According to global air quality monitoring platform IQAir, the city of Chiang Mai, the country's second-largest urban centre, has consistently ranked among the most polluted cities in the world in recent days. In the tourist town of Pai, pollution levels have reached hazardous levels. Data from monitoring stations indicate that concentrations of fine particulate matter (PM2.5) have at times exceeded 900 micrograms per cubic metre, approximately 60 times higher than the 24-hour average guideline set by the World Health Organisation. These microscopic pa...