A study published last month in the journal Environmental Science and Technology raises questions about truck fleets switching from diesel to natural gas.
The study, “The Influence of Methane Emissions and Vehicle Efficiency on the Climate Implications of Heavy-Duty Natural Gas Trucks,” was conducted by the Environmental Defense Fund (EDF) and Columbia University's Lenfest Center for Renewable Energy.
The study findings include the following: “Our results show that under our reference case assumptions, reductions in CH4 (methane) losses to the atmosphere are needed to ensure net climate benefits on all time frames when switching from diesel to natural gas fuel in the heavy-duty sector. By combining such reductions with engine efficiency improvements for natural gas HDTs (heavy duty trucks); it may be possible to realize substantial environmental benefits. However, until better data is available on the magnitude of CH4 (methane) loss, especially for in-use emissions, the precise climate impacts of a switch remains uncertain in this sector. Therefore, policymakers wishing to address climate change should use caution before promoting fuel switching to natural gas. Furthermore, diesel engine efficiency is likely to improve in the future (particularly as a result of current and upcoming HDT standards), and if this occurs without similar improvements in natural gas engine efficiency, a growing spread between these engines could worsen the impacts of diesel to natural gas fuel switching. Fleet owners and policymakers should continue to evaluate data on well-to-wheels CH4 (methane) losses and HDT efficiencies and work to ensure that the potential climate benefits of fuel switching are realized."
"This new report puts into perspective the complexity involved in evaluating alternative fuels in the transportation sector, and the importance in understanding the full picture before rushing to judgment about the merits of one technology over another," said Allen Schaeffer, executive director of the Diesel Technology Forum.
"With over 98 percent of all Class 8 trucks being diesel-powered, it is natural that alternative fuels such as natural gas are seeking and finding some niche markets in certain transportation sectors like waste management and urban-based delivery vehicles. As the authors suggest, this report does raise serious questions about whether large-scale moves to natural gas as a transportation fuel is truly a climate-positive consideration, or a move that could make things worse,” added Schaeffer.
"It is refreshing that this EDF and Columbia University study compares new clean diesel trucks with new natural gas trucks. Some have made inaccurate environmental and efficiency claims by comparing new technology alternative fueled vehicles to older diesel trucks. This new study compares ‘apples to apples’ to more accurately evaluate the two technologies,” he said.
Schaeffer said Environmental Protection Agency and other data confirms that new clean diesel technology and fuels have significantly lowered particulate matter and NOx emissions by more than 95 percent compared to older diesel vehicles, and these emissions are now virtually as low as natural gas technology.
Last month, the American Lung Association (ALA) highlighted new clean diesel technology and fuels as being one of the major reasons for improved air quality in the U.S.
In an April release of its State of the Air 2015, ALA cited clean diesel technologies as one of two areas of significant progress.
“The best progress showed in levels of year-round particle pollution, which have been steadily improving. For that you can thank the transition to cleaner diesel fuel and engines and steps taken to clean up power plants, especially in the eastern United States. ALA has pushed long and hard for these changes. We are pleased to see that those steps not only reduced particle pollution, but also helped many cities reduce their ozone pollution as well.”
Schaeffer said the industry is working in a cooperative fashion.
“Engine and equipment makers together with fuel refiners and emissions control technology companies have made significant investments to produce this new generation of clean diesel technology with near zero levels of emissions. It’s rewarding to see the benefits of this work reflected in the quality of our environment,” he said. “The diesel industry is continuing to build on these accomplishments and is increasingly focused on producing near zero emissions technology that also is more efficient and has lower greenhouse gas emissions as well,” he added.
ALA’s report found that more than half of all Americans live in counties in the U.S. where ozone or particulate emission levels are meeting EPA clean air standards. The downside is that about four in 10 Americans live in communities with unhealthy levels of either ozone or particle pollution.