Bangkok on Wednesday recorded the world's third worst air quality on Air Visual, a popular app monitoring pollution, while City Hall is on high alert for a predicted rise in PM2.5 levels until the end of this week.
The level of PM2.5 at 9.30am on Wednesday rose to over 119 microgrammes per cubic metre (µg/m³), placing the Thai capital third behind only Australia's Canberra and India's New Delhi in terms of air pollution.
However, by 6pm the level of PM2.5 had dropped to 33.9µg/m³, placing the city 32nd on the app's real-time ranking of the world's air quality.
In a related development, the Bangkok Metropolitan Administration (BMA) has put its health officials on high alert following a rise of PM2.5 -- hazardous ultra-fine dust -- in 38 of 50 areas in the capital and adjacent provinces.
According to the Pollution Control Department (PCD), the levels of fine particulate matter in the 38 areas ranged from 40 to 71µg/m³.
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 were Bang Khunthian, 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.
Chawin Sirinak, director of the BMA's Health Department, said the Communicable Diseases Control Division is closely following guidelines drawn up to help authorities effectively respond to air pollution concerns.
He said officials at mobile units led by 68 health offices were instructed to step up an awareness campaign among city residents, with a focus on vulnerable groups such as the elderly, children, pregnant women and people with heart and respiratory complaints.
The health mobile units are instructed to step up monitoring of vulnerable groups if PM2.5 levels register between 76-100µg/m³ for three consecutive days.
The PCD sets the so-called safe threshold of PM2.5 at 50µg/m³. The fine dust can cause severe respiratory disorders, especially among vulnerable groups. People with underlying health problems were advised to wear face mask and avoid non-essential outdoor activities.
To help relieve the situation, Interior Minister Anupong Paojinda has ordered the police to strictly monitor emissions from vehicles and factories and enforce the ban on open-air burning.