Thai PBS World

Chiang Mai Ranked World’s Most Polluted City by IQAir

IQAir’s latest air‑quality index placed Chiang Mai at the top of the world’s most polluted cities, with a 24‑hour PM2.5 concentration of 255.1 µg/m³ recorded in the Mangna sub‑district of Chiang Dao. That figure is roughly seven times Thailand’s legal limit of 35 µg/m³ and signals a severe health emergency. The spike reflects a combination of seasonal factors and human activity. During the dry months, accumulated vegetation and agricultural residues are routinely set ablaze, releasing massive particulate matter. Experts estimate that cross‑border emissions from neighboring countries contribute 30‑40 % of the haze, while domestic forest and farm burning remains the dominant source. Son Zantara, head of Chiang Mai University’s Academic Center for Air Pollution, noted that last year’s Lanina phenomenon brought rain that temporarily suppressed fires. “This year the rains stopped, multiple fires ignited simultaneously, and the air turned dry,” he said, underscoring the volatility of the situation. The ramifications extend beyond health, threatening tourism revenues, labor productivity, and regional cooperation on air‑quality management. Immediate policy action—tightening burn bans, enhancing cross‑border monitoring, and investing in early‑warning systems—is essential to curb the crisis.