I. EXECUTIVE SUMMARY
Catalytic emission control systems, used on passenger cars since 1975, have played a key role in substantially reducing exhaust pollutants from motor vehicles. Exhaust emission control is influenced not only by the emission control system, but by engine design and fuel quality as well. Since 1975, catalyst technology and engine designs have continued to advance dramatically. Changes in fuel quality, most notably eliminating lead in gasoline and reducing gasoline sulfur levels, have also contributed to achieving very low vehicular emissions. Currently the U.S. federal gasoline sulfur limits (30 ppm sulfur average) lag the gasoline sulfur limits found in California, the European Union, Japan, and South Korea (20 ppm sulfur cap in California, 10 ppm sulfur cap for the EU, Japan, South Korea).
Sulfur in gasoline inhibits the emission control performance of catalyst technology. A variety of factors influence the degree of this impact and the extent to which it is reversible. These factors include the sulfur level in the gasoline, the catalyst composition, the catalyst design, the catalyst location, the type and control of fuel metering, the engine calibration, and the manner in which the vehicle is operated.
Recent studies have shown that the effect of sulfur inhibition has a greater impact on the emission control systems of vehicles designed to meet SULEV-type standards and that the effects of sulfur may not be completely reversible on these vehicles. While catalyst manufacturers are continuing design efforts to reduce the effects of sulfur on catalyst technology, the growing body of technical information strongly indicates that reducing the sulfur level in gasoline would have a significant benefit to the emission control performance of past, current and future emission control systems.
MECA supports the adoption of U.S. federal gasoline fuel sulfur specifications that are in line with sulfur limits currently in place in California: a gasoline sulfur cap in the range of 20-25 ppm and a national average of 10 ppm or lower. The change should be brought about as quickly as possible, although adequate lead-time should be provided to implement these changes and the limits should include compliance flexibility strategies similar to those used in the past to facilitate cost effective compliance.