PM2.5 dust particles have returned to Bangkok and its neighboring provinces, with nine areas found to contain levels exceeding the 50-micron standard level today, according to the latest air quality readings by the Pollution Control Department.

Blaming the poor air quality on weak low-altitude air flow, the department predicted that the situation might further deterioratetomorrow.

The department pleaded for cooperation from members of the public by not burning anything in open areas and suspending the use of smoke emitting vehicles.

Several northern provinces, including Chiang Mai, are facing a worsening haze problem, mainly due to man-made forest fires which have sent the level of PM2.5 dust over the 50-micron level.

PM2.5 particulate matter in the Sansai district of Chiang Mai was measured at 250 microns on Tuesday, whereas in Mae Sai district of Chiang Rai province, the level of fine dust particles was measured at 146 microns.