Students from Chulalongkorn University wear face masks to protect themselves from poor air quality as they wait at a bus stop in Bangkok.

Tourists ride in tuk-tuks wearing face masks to protect from the poor air quality in Bangkok.

BANGKOK — Unhealthy levels of smog have choked Bangkok for more than a week, as the Thai capital’s residents fume over the ineffectiveness of government measures to combat the problem.

As thick haze blanketed the city on Monday, pollution levels soared to 95 micrograms per cubic meter of PM 2.5 particle at noon in some areas, according to the government’s Pollution Control Department, which described that level as very unhealthy. The maximum level considered safe by the government is 50.

PM 2.5 particles are small enough to penetrate deeply into the lungs, which can cause both short-term bronchial problems as well as serious long-term health issues.

Bangkok’s smog crisis results from still air and an excessive amount of ultrafine dust from vehicle emissions and other activities, Pollution Control Department Director-General Pralong Damrongthai explained in a Monday press release. He said smog is being trapped close to the ground by a blanket of warm air in what meteorologists call an inversion.

Bangkok residents have grown frustrated with the lack of progress in improving the situation. A survey by the National Institute for Development Administration released on Sunday showed 81 percent of the 1,256 local residents questioned agreed the government is ineffective in solving the problem. Only 2.7 percent of respondents approved of the government’s efforts.

The Pollution Control Department issued a 52-page national action plan in October for combating dust pollution problems, but it is unclear how many, if any, of the measures it suggested were implemented. The plan mostly included guidelines for government agencies, but also discussed possible precautions and ways to measure pollutants.

Burning of fields is cited as the main reason for smog outside of Bangkok, with provinces in the central and northern regions of Thailand also blanketed in haze.

Tara Buakamsri of the environmental group Greenpeace said the current situation shows the government’s strategy is failing.

“They probably think that the situation happens just only few days or few weeks and then it’s gone, therefore, no concrete or long-term measures have been launched by the government,” he said.

Tara also said the official maximum “safe level” of PM 2.5 of 50 micrograms per cubic meter over 24 hours was set too high.

“That level cannot protect people’s health,” he said. He urged the maximum safe level be reduced to 35, as it is in other places such as the United States.