The industry ministry plans to cut the legally allowable density of sulfur in diesel oil to one-fiftieth of the current limit around fiscal 2008, ministry officials said.

The Ministry of Economy, Trade and Industry will cut the allowable density to 10 parts per million. The same figure and timing will also apply to sulfur in gasoline, the officials said.

The new rules are designed to cut the amount of nitrogen oxides (NOX) in automobile emissions, they said. The toxins have been blamed for causing asthma and other respiratory illnesses.

METI will task an advisory panel to the trade chief with drawing up details of the rules by the end of fiscal 2002 and instruct the panel to find ways to aid oil refiners.

Industry officials warn that adopting the new levels will force companies to invest several hundred billion yen in new facilities.

The government had earlier decided to cut the allowable density of sulfur in both diesel oil and gasoline to 50 ppm from the current limits of 500 ppm and 100 ppm, respectively, in three years.

But the ministry's latest plan was drafted in light of a recent European Union decision to regulate the corresponding sulfur density to 10 ppm, the officials said.

Sulfur in automobile fuel gradually undermines the efficacy of catalysts in mufflers and other equipment to help remove NOX. METI thus concluded the new cut was vital.

In a related set of rules under consideration, the government plans to stiffen regulations on the hydrocarbon and particulate matter discharged by automobiles by fiscal 2008 to 2010, they said.

The refining industry has been calling on the government to speedily specify the time frame for any new rules and the revised figures for sulfur density, so it can draw up research and investment plans to meet the new rules in a timely manner.