The Pollution Control Department (PCD) has urged people in worst-affected areas to wear masks as air pollution is set to get worse over the next two to three days.
"The situation could drag on for a few days. People in high-risk areas should avoid outdoor activities or wear N95 masks for protection," said Thalerngsak Phetsuwan, deputy director-general of the department.
He blamed the transition from cool to warm weather for causing the poor air circulation which has been exacerbated by high traffic volumes as people returned to the city after the New Year break.
Poor air quality caused by hazardous PM2.5 particulates, which reduce visibility and cause the air to appear brown and hazy when levels are elevated, posed a danger on Monday to human health in 20 areas in and around Bangkok, according to information from PCD's air quality monitoring stations.
It stated that PM2.5 exceeded the acceptable Thai safety standard of 50 microgrammes per cubic metre (µg/m³) in some places, but did not rise above 90 µg/m³.
The worst-affected areas included Kanchanaphisek Road in Bang Khunthian district, Intharaphithak Road in Thon Buri district and Lat Phrao Road in Wang Thonglang district.
Meanwhile, 16 other areas nationwide were also found to have PM2.5 in excess of the safety limit, although at less critical levels.
They included parts of Bang Na, Din Daeng, Bang Kapi and Phaya Thai districts in the capital as well as Muang district of Nakhon Pathom, Bang Kruai district of Nonthaburi, Klong Luang district of Pathum Thani, Krathum Baen district of Samut Sakhon and Bang Sao Thong and Phra Pradaeng districts of Samut Prakan.
According to the PCD, air quality Tuesday will continue to pose a threat to human health with rising levels of dust expected.
Exposure to PM2.5 has been found to cause short-term adverse health effects such as eye, nose, throat and chest irritation, as well as being linked to long-term health conditions such as asthma and cardiovascular disease.
People at severe risk include children, the elderly, pregnant women and people with congenital diseases.
The department is working with the Bangkok Metropolitan Administration to usher in more stringent measures that could help tackle the pollution, including cleaning road surfaces and employing special cannons to spray water into the air, the PCD stated.