The maximum limit on sulfur in light oil used for diesel fuel may be reduced to about one-tenth the current level as early as this fall, according to the Environment Agency.

Although the limit on sulfur in light oil was increased last year to 0.05 percent of the oil's weight, the new limit sets a 0.005 percent maximum, agency officials said. A stricter regulation on sulfur in diesel fuel is direly needed in order to curb the levels of nitrogen oxides and suspended particulate matter in the air, the officials said.

Diesel engine emissions, which contain nitrogen oxides, are known to be a main source of air pollution. Sulfur can weaken the effectiveness of catalysts that reduce the level of nitrogen oxides contained in car exhaust.

Before setting a new figure, the agency will hold a series of hearings for the oil industry and consult with the Central Environment Council, an advisory panel to the prime minister, the officials said.

The agency is expected to decide on the new level of sulfur in light oil sometime around autumn.

However, the new regulation may not be implemented for about 10 years, because light oil producers will have to invest in new facilities, they said.