Ultra-fine PM 2.5 dust particles in the air exceeded the so-called safe level in three districts of Bangkok on Thursday, prompting concerns over a possible recurrence of hazardous smog in the capital.
Bang Phlat, Bang Khen and Bang Sue districts reported 60, 51 and 51 microgrammes per cubic metres (cu/m) of the dust particle respectively as of 8am on Thursday, according to a daily air-quality report by the Bangkok Metropolitan Administration's (BMA) environment office.
The "safe" level in Thailand of the PM 2.5 dust is no more than 50 microgrammes per cu/m.
The overall air quality in most parts of the city, however, was still rated as being between moderate to very good, said the same report.
Nevertheless, the high levels of ultra-fine dust in these three districts may pose a threat to the health of people living in these areas, said the report.
Chatri Watthanakhachon, director of the BMA's environment office, played downed fears over a possible recurrence of hazardous dust particles across the city, saying the particle levels in these districts may not be high all day long or every day.
The high PM 2.5 levels may only occur during rush hours and around large construction sites such as at electric rail route projects, he said.
The office will send out inspection teams to the affected areas to ensure construction projects strictly follow guidelines on air pollution control such as by spraying water more frequently on the ground to keep the levels of dust low, he said.
Meanwhile, the Public Health Ministry has distributed more face masks to three schools in the southern province of Trang where the PM 2.5 level was measured at 168 microgrammes per cu/m on Thursday.
The province is being hit by toxic haze blamed on forest fires in Indonesia.
The fires have been spewing smoke over Southeast Asia in recent weeks, closing schools and airports, with people rushing to buy face masks and seek medical treatment for respiratory ailments, according to international media reports.
The haze situation in Thailand's Yala, meanwhile, improved considerably on Thursday following a couple of rainy days, said Songkran Maichum, the province's chief health officer.
The level of PM 2.5 dust measured in Muang district of the province dropped to 26 microgrammes per cu/m on Thursday morning, he said.
At least 156,000 face masks have been handed out to groups of people highly susceptible to exposure to ultra-fine dust, including those with respiratory illnesses, he said.