
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 particulate matter 2.5 micrometres and less in diameter (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 air.
It was measured in Samut Sakhon province, west of Bangkok, followed by 125.1µg/m³ in Bangkok city, 119.3µg/m³ in Nakhon Pathom, 116.3 in Nonthaburi, 115.3 in Samut Prakan, 109.4 in Samut Songkhram, 108.4 in Pathum Thani, 107.7 in Sing Buri, 106.4 in Ratchaburi, 104.8 in Ayutthaya, 103 in Sukhothai and 101.2 in Ang Thong.
Fifteen other provinces were at two-digit red levels of PM2.5, ranging from 75.4 to 95 µg/m³.
In descending order, they were Lop Buri, Chon Buri, Phetchaburi, Saraburi, Suphan Buri, Rayong, Chai Nat, Chachoengsao, Kanchanaburi, Sa Kaeo, Uthai Thani, Nakhon Sawan, Phitsanulok, Phetchabun and Prachuap Khiri Khan.
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.