Unsafe levels of ultrafine dust were reported in 70 of the 77 provinces on Tuesday, with the worst air pollution detected in Greater Bangkok.
The Geo-Informatics and Space Technology Development Agency (Gistda) reported at 7am that PM2.5 was at red (hazardous-to-health) levels in 27 provinces, mostly in the middle of the country.
The highest level of PM2.5 recorded over the preceding 24 hours was 144.8 microgrammes per cubic metre of in Samut Sakhon province, west of Bangkok, followed by 125.1µg/m³ in Bangkok.
The government-set safe threshold is 37.5µg/m³.
Safe air was reported in seven provinces. Three of them - Phangnga (32.2µg/m³), Surat Thani (32.1) and Chumphon (29.7) – had moderate air quality.
Four others had good air quality - Krabi (24.9), Chiang Rai (24.6), Chiang Mai (21.4) and Mae Hong Son (12.4).
Forty-three other provinces faced orange levels (starting to affect health) of PM2.5 ranging from 37.7 to 75µg/m³.
