Ultrafine dust levels were in the red (hazardous-to-health) in 46 out of the 77 provinces and in Greater Bangkok on Wednesday morning, with only 10 provinces reporting moderate to good air quality. 

The Geo-Informatics and Space Technology Development Agency (Gistda) reported at 8am that PM2.5 was at red levels in 46 provinces and at orange (starting to affect health) levels in 21 provinces. Most were in the Central Plain, the Northeast and the East.

The highest level of PM2.5 recorded over the preceding 24 hours was 151.1 microgrammes per cubic metre of air in Samut Sakhon province, with 100µg/m³ in Bangkok.

The government-set safe threshold is 37.5µg/m³.

Twenty-eight other provinces were at two-digit red levels of PM2.5, ranging from 76.6 to 98.3µg/m³.

Safe levels of PM2.5 were recorded in 10 northern and southern provinces.

Eight of them had moderate air quality with yellow levels of PM2.5 ranging from 26 to 36.4µg/m³.

Two provinces had good air quality (green levels of PM2.5) namely Chiang Mai (20.1µg/m³) and Mae Hong Son (16.1).

Twenty-one other provinces were shrouded with orange levels of PM2.5 ranging from 38 to 74.8µg/m³.