Unsafe smog levels covered most of greater Bangkok on Monday morning, with the worst air in Bangkok's Lat Krabang district and Samut Prakan's Muang district, the Pollution Control Department reported.
The levels of particulate matter 2.5 micrometre and less in diameter (PM2.5) ranged from 42-77 microgrammes per cubic metre of air over the previous 24 hours. The government-set safe threshold is 50mcg.
Unsafe levels were reported in many districts -- Bang Kapi, Bang Khunthian, Bang Na, Din Daeng, Pathumwan, Phaya Thai, Thon Buri, Wang Thonglang and Yannawa districts of Bangkok; Bang Kruai and Pak Kret districts of Nonthaburi; Klong Luang district of Pathum Thani; Muang and Phra Pradaeng districts of Samut Prakan; and Krathum Baen district of Samut Sakhon.
In other provinces, PM2.5 levels ranged from 15 to 128mcg. The lowest was in Betong district of Yala and the highest in Si Maha Phot district of Prachin Buri.
Unsafe levels were detected in some districts of Ayutthaya, Chachoengsao, Chon Buri, Kanchanaburi, Khon Kaen, Lampang, Loei, Nakhon Ratchasima, Nakhon Sawan, Nan, Phayao, Phrae, Ratchaburi, Rayong, Sa Kaeo, Saraburi, Suphan Buri and Tak provinces.
The Meteorological Department said the gentle breeze allowed the smog to accumulate.