Some benefits from those reductions would be offset by increased driving. But the EPA expects the new standards to continue the overall downward trend in vehicle emissions for years to come. Despite increased travel, past air pollution control regulations have resulted in a steady decline in overall vehicle emissions within the Bay watershed. From 1987 to 1997, NOx emissions in the watershed decreased by 18 percent even as the number of miles driven increased by 41 percent, according to Bay Program figures. Motor vehicles account for about a third of all the NOx emissions in the Bay region.
Air pollution is estimated to contribute about a quarter of all the nitrogen that enters the Bay.
Citing evidence that sulfur in gasoline hinders the effectiveness of catalytic converters on cars, the EPA wants refiners to reduce the average sulfur level to 30 parts per million by 2004, down from the current average of more than 300 ppm. That will increase the price of gas by about 1 to 2 cents per gallon, according to the EPA Automakers had argued that they could not do much more to reduce emissions unless the sulfur content in gasoline was dramatically reduced. As a result, automakers are in the odd position of siding with environmental groups in supporting the regulations. Refiners, though, oppose the sulfur reductions, saying they will have to spend billions of dollars to change the refining process. At the least, they say the low sulfur gas should only be sold in the East, where smog is a major problem.