First, a disclaimer. We understand that sulfur (or sulphur for you Brits) isn't the only less-than-desirable thing in or about petroleum diesel. There's nitrogen oxide (NOx), particulate matter (soot) and carbon dioxide, to name a few other pollutants. And, of course, petroleum diesel does come from petroleum in the first place. And petroleum, no matter how clean it gets, is why that large body of water off our southern coast is starting to resemble the parking lot of a Jiffy Lube after a rain storm.
Still, one of diesel's nastiest ingredients, and one that, once removed, allows manufacturers to install better "clean diesel" particulate filters, is sulfur – and diesel used to have a lot of sulfur. Off-road diesel (used by farm vehicles, construction equipment and the occasional tax-dodging rancher) used to be limited to 3400 parts-per-million. But then came Low-Sulfur Diesel (LSD) which limited sulfur content to 500 ppm. And then, starting in late 2006, Ultra-Low-Sulfur Diesel (ULSD), which limited sulfur to just 15ppm, became the new standard for on-road diesel. As of this week, 100 percent of diesel fuel refined in the U.S. for on-road use and at least 80 percent of the diesel fuel refined in the U.S. for off-road use has to be ULSD.
Allen Shaeffer, executive director of the Diesel Technology Forum, said meeting the 80 percent mandate was an environmental milestone:
Today is another milestone for clean diesel and clean air, as our nation's farm tractors and construction machines will now have access to cleaner ultra-low sulfur diesel fuel. Two-thirds of all farm and construction equipment rely on diesel engines due to their unique combination of power, fuel efficiency, economical ownership and operation and legendary reliability and durability.