Small particle dust was at unsafe levels in 38 areas in Bangkok and its neighbouring provinces on Wednesday morning, prompting the Pollution Control Department to warn against non-essential outdoor activities.
The department and Bangkok Metropolitan Administration reported that levels of particulate matter 2.5 micrometres and less (PM2.5) in diameter were in the orange zone in 38 areas, with levels measured from 40-71 microgrammes per cubic metre of air.
Muang district of Samut Prakan was the worst polluted with 71, followed by Krathum Baen district in Samut Sakhon and Bung Kum district in the capital with 70.
Other unhealthy areas in Bangkok were Bang Khuntien, Bang Na, Pathumwan, Thon Buri and Wang Thonglang districts. Muang district of Nakhon Pathom, Pakkret district of Nonthaburi, Khlong Luang district in Pathum Thani, Phra Pradaeng district of Samut Prakan were also among the worst areas.
The PM2.5 levels have worsened since Monday. The government considers readings of 51 or more unsafe for health. Elsewhere in the world the safe level is usually much lower.
The department advised people in affected areas to stay inside if possible and wear a mask when they do go outside.