Harsh measures such as school closures, and use of water canons brought down PM2.5 levels slightly on Friday. The Pollution Control Department (PCD) warned levels still exceed the safety limit, forcing Gen Prayut to beg the public for more cooperation. The persistence comes from diesel engine emissions in Bangkok coupled with the stagnant weather. PM2.5, fine dust measuring 1/20 of the width of a human hair, can easily lodge in the lungs. PM2.5 levels have dropped, but not significantly.

Source: Bangkok Post February 01, 2019 23:26 UTC