"We're hosting a meeting with refineries and agencies over the feasibility of the plan and the timetable to implement the guidelines," Energy Minister Piyasvasti Amranand said last week.

The ministry is coordinating with the Ministry of Natural Resources and Environment on the campaign for Bangkok, Samut Prakan, Chachoengsao

and Chon Buri, where the sulphur level is 2 per cent and sulphuric residue has been detected in the air and soil.

Switching to natural gas would also ease the sulphur problem, he said.

PTT's recently completed gas pipeline between Sai Noi in Ayutthaya and Samut Prakan will help the Electricity Generating Authority of Thailand's power plant in Samut Prakan to consume more natural gas instead of bunker oil.

The pipeline will also allow greater use of natural gas in industrial plants in and around Bangkok.

"Reducing sulphur in bunker oil will require expenditures by refineries. But this is necessary for better air quality," Piyasvasti said.

Pramote Yanthaksa, an official at the Business Energy Department, said the sulphur level in bunker oil for general use is limited by law to 2 per cent while bunker oil for power plants is capped at 0.5 per cent.

The Environment Ministry wants to confirm that air pollution is caused by sulphur and to ascertain where the problem is intensifying, he said.

Chainoi Puankosoom, president of Rayong Refinery and chairman of the Federation of Thai Industries' refinery club, said he had been informed of the general concept of the sulphur mitigation plan.

Refineries would discuss among themselves on the new limit, he said.

"This will require investments. Personally, I think the entire production process should be done now that we are improving our product quality to meet Euro 4 emission standards," he said.