People in Bangkok and its surrounding areas were warned Monday to take extra precautions against PM2.5 dust particles on Thursday and Feb 13-15 which the Meteorological Department expects to be the most heavily polluted days this month.

This is due to a phenomenon known as temperature inversion, when a layer of cool air is trapped under a layer of warmer air. This will suspend more dust particles in the lower atmosphere than usual.

The warning was issued by the permanent secretary of the Natural Resources and Environment Ministry, Wijarn Simachaya, after he emerged from a meeting on providing an update on the dust and air pollution situation and coming up with more effective measures to tackle the problem.

"We advise people not to go out on these particular days. But if you have to, don't forget to wear the N95 masks.

"I see a lot of people wearing N95 masks, but they do so loosely with only one strap secured around their faces. This will not protect you from the PM.2.5 dust particles at all," Mr Wijarn said.

Mr Wijarn also added that the ministry is coming up with long-term solutions, which aim at reducing biodiesel usage and applying European Emission Standards within Thailand.

Transport Minister Arkhom Termpittayapaisith said officials are expediting efforts to reopen traffic lanes closed for the construction of electric train projects to boost traffic flow and reduce PM 2.5 pollutants.

Water is also being sprayed around construction sites of these projects and expressway toll gates to minimise haze, Mr Arkhom said.

Meanwhile, since Friday, Department of Land Transport (DLT) officers have impounded 137 lorries and 24 public buses for spewing black exhaust smoke in excess of the safety limit.

DLT director-general Peerapol Tavornsuppacharoen said 4,616 trucks and lorries had been checked at 31 checkpoints set up in 15 provinces leading to the capital during the three-day inspection.

Operators of the 161 impounded vehicles will be fined 5,000 baht and must have their vehicles fixed and tested by the DLT before being they can be used again, Mr Peerapol said.