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Box 7-A Diesel-powered Automobiles

Friday, April 1, 2016

Diesel-powered automobiles have been making the headlines following emission concerns raised by the U.S. Environmental Protection Agency (see the recent letter on these issues at: http://www3.epa.gov/). Diesel vehicles are a small percentage of the Nation’s motor vehicle fleet, mostly medium and heavy trucks. For example, 72 percent of the trucks with a gross vehicle weight rating 10,001 and above sold in the United States in 2013 were diesel-powered, up from 69 percent in 2009 [USDOE ORNL 2015].

Sales of Diesel-Powered Passenger Cars and Light Trucks

In Model Year 2014, over 16.4 million passenger cars and light trucks were sold in the United States [USDOC BEA 2015]. Only 1.5 percent of all light duty vehicles (including passenger cars, sport utility vehicles, minivans, and all but the largest pickup trucks and vans) were diesel-powered. This percentage is up from less than 0.1 percent in the mid-90s, but below the peak of 5.9 percent in Model Year 1981. In Model Year 2014 Volkswagen had the highest percentage with 20.1 percent of diesel-powered light duty vehicles in its fleet across all automakers in the United States. Daimler had the next highest percentage with 6.9 percent, followed by BMW (6.0 percent), Chrysler-Fiat (2.8 percent), and GM (0.5 percent) [USEPA 2014a].

Emissions from Diesel-Powered Motor Vehicles

Diesel-powered motor vehicles account for about 4 percent of the fleet, but they account for about half of the on-road NOx emissions. In 2013, gasoline-powered motor vehicles contributed 2,365 kilotons; in comparison, diesel-powered motor vehicles contributed 2,125 kilotons of on-road NOx emissions [USEPA 2015]. Diesel- powered vehicles generally have better fuel economy than gasoline-powered ones, thus their CO2  per vehicle-mile travelled is generally lower than a comparable gasoline-powered vehicle. However, diesel remains a major source of harmful pollutants (e.g., ozone forming emission, including nitrogen compounds NOx as well as particulate matter (PM), which is a mixture  of solid particles and liquid droplets found in the air) when burned. According to the U.S. Environmental Protection Agency, using ultra low sulfur diesel fuel and advanced emission control systems can reduce vehicle PM and NOx emissions [USDOE EIA 2014].