You're breathing in at least five carcinogenic substances

The air in Bangkok, Hat Yai and Chiang Mai contains at least five carcinogenic substances, the Pollution Control Department reveals.

Plus, the atmosphere in these cities exceeds pollution limits.

The department blames motor-vehicle emissions. Depart-ment 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.

Black smoke

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

He says 15 per cent of complaints lodged with the Land Transport Department involv-ed vehicles that belch black exhaust fumes - especially buses. Supat says 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 natural-gas-powered engines and will meet the Euro-4 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.