BANGKOK • The Thai capital was expected to be blanketed in smog until at least today despite the authorities' deployment of water cannon to combat air pollution.

The Pollution Control Department said yesterday that this was because cool weather continued to retain smoke and dust particles in the air around Bangkok and the nearby provinces, the Bangkok Post news website reported.

The department said air quality around parts of Bangkok as well as the provinces of Nonthaburi, Pathum Thani, Samut Prakan and Samut Sakhon would be affected by the hazardous dust particles, which are known as PM 2.5.

PM2.5 is harmful because its very fine dust particles are small enough to pass through a person's lungs and enter the bloodstream.

The Thai authorities on Monday turned to firing water cannon into the air and hosing down streets to tackle the smog that has been blanketing the atmosphere since last Saturday, news agency Reuters reported.

The Air Quality Index (AQI) on Monday morning in Bangkok was 180, according to the website airvisual.com, putting it among the top 10 polluted cities worldwide. The city's AQI yesterday evening was 154. Any level above 150 is considered unhealthy.

The air force yesterday deployed two BT-67 aircraft from the north to spray water in Bangkok's Don Muang and Chatuchak districts. Government spokesman Puttipong Punnakanta said its agencies had taken urgent measures such as controls on construction sites and strict inspection of polluting vehicles, Bloomberg reported.