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 for emissions from new diesel engines.
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. Most of the diesel fuel now sold in the United States for use in vehicles 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 to air pollution in the United States because it will take a long time for newer and cleaner diesel vehicles to replace older vehicles.
Carbon dioxide emissions
The U.S. Energy Information Administration (EIA) estimates that in 2017, diesel (distillate) fuel consumption in the U.S. transportation sector resulted in the emission of 451 million metric tons of carbon dioxide (CO2), a greenhouse gas. This amount was equal to 24% of total U.S. transportation sector CO2 emissions and equal to 9% of total U.S. energy-related CO2 emissions in 2017.