Prime Minster Prayut Chan-o-cha has asked motorists not to use diesel-engine cars in Bangkok and neighbouring provinces, in a bid to lower ultra fine dust that shows few signs of subsiding.
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.
"Dear Thai people," the prime minister on Friday began his request, "despite a raft of short-term solutions, the PM2.5 situation has not improved. The persistence comes from diesel engine emissions in Bangkok coupled with the stagnant weather. The government wants to ask people for their cooperation in not using, or limiting their use of diesel engines for a certain period of time in Bangkok and its nearby provinces," Gen Prayut said.
It is obvious the combustion of bad diesel engines has contributed most to the surge in dust levels, he said, adding factories are not the culprits because inspections show none produce PM2.5.
PM2.5, fine dust measuring 1/20 of the width of a human hair, can easily lodge in the lungs.
The government has tried many measures to curb PM2.5 levels from cutting down on black smoke-belching vehicles, creating artificial rain, spraying water on the streets to calling a two-day break for schools in Bangkok to reduce traffic congestion.
Private companies have now started letting their employees work from home.
The efforts bore fruit but have not been enough to make Bangkokians breathe without fear. More people are wearing masks and and are trying to keep their outdoor activities to a minimum. Some have even bought air purifiers.
PM2.5 levels have dropped, but not significantly.
The PCD and weather monitoring websites say air quality in Bangkok still exceeds safe levels, posing a potential risk to vulnerable groups such as those with health problems, the elderly, pregnant women and young children.
Airvisual.com reported that on Friday PM2.5 soared to 146 microgrammes per cubic metre (µg/m³), against the country's safety level at 50 µg/m.³ However, the PCD expected air quality will improve today, given better weather conditions.
The PCD said it would ask the National Environment Board to approve more urgent action plans to fight PM2.5. If the NEB approves, the department will ask the cabinet to okay the steps at its meeting on Tuesday.
Among the the measures are banning large trailers from the capital's middle zone around the clock until March, using cleaner petrol, and allowing state officials to work at home.