Bad air

Plus, the atmosphere in these cities exceeds pollution limits.

The department blames motorvehicle emissions. Department tests found levels of benzo(a)pyrene from incomplete combustion of diesel fuel to be too high. It also detected carbon monoxide, sulphur dioxide, nitrogen dioxide and ozone.

Department chief Supat Wangwongwatana said checks between May and this month found the air quality in all other cities to be acceptable. He credits wetseason rains.

He said 15 per cent of the complaints lodged with the Land Transport Department involved vehicles that belch black exhaust fumes - especially city buses.

Supat said Bangkok suffers badly from this problem. There are 6 million vehicles on its roads, up from 2 million in 1992.

However, with a reduction in sulphur content in diesel from 350 to 50 parts per million, this problem will reduce.

But, a campaign to have motorists check their vehicles for engine efficiency and regular police checkpoints do not attack the problem at its root.

The government is encouraging the use of naturalgaspowered engines and will meet the Euro4 fuel standard by 2012.

 Two retail oil companies are selling B5, fuel with a 5 per cent biofuel content. For this they receive tax incentives.