Diesel fuel engines are getting cleaner
Diesel fuel (refined from crude oil) produces many harmful emissions when it is burned, and diesel fueled vehicles are major sources of harmful pollutants such as ground-level ozone and particulate matter. To address this problem, the U.S. Environmental Protection Agency (EPA) established standards for the sulfur content of diesel fuel and standards for emissions from new diesel engines.
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EPA fuel standards require a major reduction in the sulfur content of diesel fuels. To meet the EPA standards, the petroleum industry is producing Ultra Low Sulfur Diesel (ULSD) fuel, a cleaner burning diesel fuel containing a maximum 15 parts-per-million (ppm) sulfur. All diesel fuel sold in the United States since 2014 is ULSD fuel.
The EPA also established emissions standards for diesel engine highway vehicles for model year 2007 and later. These engines are designed to operate only with ULSD fuel. Using ULSD fuel and advanced exhaust emission control systems can reduce vehicle particulate emissions by up to 90% and emissions of nitrogen compounds (NOx) by 25–50%. ULSD fuel helps reduce emissions in older engines as well.
Even with these advances, diesel fuel still contributes significantly to air pollution in the United States because it will take a long time for new cleaner burning diesel vehicles to replace older vehicles.
Carbon dioxide emissions
About 22 pounds of carbon dioxide (CO2) are produced when a gallon of diesel fuel is burned. Carbon dioxide is a greenhouse gas that is linked to global climate change. Diesel engines get better fuel economy than gasoline powered engines, so the amount of CO2 produced for each mile traveled may be lower in a vehicle with a diesel engine.