Bangkok and its suburbs are experiencing one of the most polluted days today (Thursday) due to an unusually high accumulation of fine airborne dust being caused by stagnant air, producing a temperature inversion effect.

Normally, air temperature decreases with an increase in altitude.  An inversion traps airborne pollution, such as dust and smoke, close to the ground.  An inversion can also suppress convection by acting as a “cap”.  If this cap is broken, for any of several reasons, convection of any moisture present can erupt into violent thunderstorms.

According to the air flow simulation model of the Marine Meteorological Centre, at the Meteorological Department today, air circulation in and around Bangkok is minimal, causing fine dust particles to accumulate in the lower atmosphere, especially between noon and 11pm, when wind speed is forecast to be only 2-3 knots, which is too weak to disperse the dust.

The Pollution Control Department reported this morning that only four areas were found to have excessive amount of PM2.5 dust.  They are Rama IV Road in Pathumwan district, Intharapitak Road and Tambon Hirunrujee in Thon Buri district and Tambon Plabpla in Wang Thong Lang district.