The application showed Chiang Mai’s average pollution at 193, with particulate matter less than 2.5 microns in diameter (PM2.5) at 137.8 micrograms per cubic metre. 
According to the Air Quality Index, air quality between 0 to 50 is healthy, 51 to 100 is moderate, 101 to 150 is unhealthy for sensitive groups, 151 to 200 is unhealthy, 201 to 300 is very unhealthy, and 301 to 500 is dangerous. 
Meanwhile, the Pollution Control Department (PCD) said via its website that the air quality (as of 7am) in Bangkok and nearby provinces was at healthy levels, and would get better. 
The PCD found PM2.5 at between 16 and 46 micrograms per cubic metre.

Chiang Mai’s air quality worst in the world

Chiang Mai’s air-quality ranking took a severe hit, with the city being named the worst in the world, followed by Mumbai, Kathmandu and Kolkata, the application Air Visual revealed on Saturday (February 29) as of 11.37am.