On June 1, the nation's refineries began making low-sulfur diesel fuel for off-road equipment. By December, locomotives, ships and boats, as well as farming, construction, and mining equipment will switch to the new diesel containing nearly 85% less sulfur. The fuel has a sulfur content of 500 ppm, reduced from about 3,000 ppm. By 2020, sulfur levels in most off-road diesel fuel will be reduced to 15 ppm, clearing the way for advanced exhaust systems that significantly reduce emissions.