Bangkok was enveloped in a thick pollution haze yesterday, with the outlook set to worsen today, the authorities said. The amount of particulate matter in the air reached hazardous levels throughout the Thai capital yesterday morning, the Bangkok Metropolitan Administration said. People were advised to stay indoors or wear face masks if going out. Air quality could deteriorate today, especially on the streets, the Bangkok Post quoted the Pollution Control Department as saying. Bangkok Governor Aswin Khwanmuang attributed the pollution to a combination of exhaust emissions, railway and condominium construction, road works and dry season weather. He ordered district officials to clean roads, spray water and encourage people to use public transport instead of their cars, the Post quoted him as saying.