Forty-eight of the 77 provinces had unsafe levels of ultra-fine dust on Tuesday morning, 21 of them reporting red-level air pollution.
The Geo-Informatics and Space Technology Development Agency (Gistda) at 9am reported red levels of PM2.5, ranging from 75.9 to 145.2 microgrammes per cubic metre of air, over the previous 24 hours.
On Monday morning hazardous levels of PM2.5 were between 38.1 and 112.3µg/m³ in 41 provinces. The safe threshold set by the government is 37.5µg/m³.
On Tuesday, the smog had expanded to cover 48 provinces.
The worst five provinces were Samut Sakhon (145.2µg/m³), Samut Songkhram (135.7µg/m³), Nakhon Pathom (120.1µg/m³), Nonthaburi (116.3) and Bangkok (111.8).
Twenty-seven provinces reported orange levels of PM2.5, meaning very unhealthy.
