Thousands of faulty diesel-run buses, trucks and other vehicles and the 4,000 brick kilns around the city have turned it into a virtual "gas chamber", enveloping the metropolis with thick smog, the source said.

Deterioration of ambient air quality has reached such a level that the newly installed 80-megawatt Tongi power plant had to be shut down recently as its air filters were exhausted much ahead of its life span, said an official of the Power Development Board (PDB).

World Bank sources said that recent conversion of the brick kiln chimneys into 120 feet tall chimneys has 'not at all helped' the city environment. The kilns use 'worst quality coal', vehicle tyres, fuel wood and even discarded polythene bags as fuel. Fumes from the kilns contain an extremely high count of sulphur dioxide and ash.

Deterioration of air quality has reached its peak in the current lean period with scarcity of rain. People of all ages are exposed to various health hazards due to the toxic haze hanging in the atmosphere, another DoE source said.

City clinics and hospitals are swarmed with patients complaining of various respiratory problems.

According to Bangladesh standards the permissible level of particulate matters in the city air is 65 microgram per cubic metre (mpcm). But a recent study shows that the particulate count has reached 200 mpcm. The concentration of fine particulate matter in the air has also crossed its standard limit of 135 MPCM to more than 200 MPCM.

According to air quality experts, constant exposure to such high concentration of particulate matters can cause cancer and related diseases.

"In winter the air is stagnant and therefore the problem is even aggravated," said an expert requesting anonymity.

He added that the Air Quality Management Project (AQMP) of the DoE is currently devising an environment-friendly model for brick kilns.

"There is no alternative other than adopting a new environment-friendly technology," said the expert.

"We need bricks, but not at the cost of the environment," he added.

Immediately after the phasing out of two-stroke engines in the late 90s the city's air quality improved temporarily, but soon thousands of vehicles, many of which are old and faulty were added to the roads, polluting the air more and in lean periods, brick kilns largely contribute to air pollution.