Uncertainty Over Amount of Methane Emissions & Diesel Technology Efficiency Warrant Further Examination
A new study published said that switching from diesel to natural gas in heavy-duty trucks could worsen and accelerate negative climate impacts unless methane leakage can be lowered. The study also outlined the need for increased data and new policies to lower methane leakage in order for natural gas heavy duty trucks to have a possible environmental advantage over new and future clean diesel trucks.
The study – "Influence of Methane Emissions and Vehicle Efficiency on the Climate Implications of Heavy-Duty Natural Gas Trucks" - was conducted by scientists at the Environmental Defense Fund (EDF) and Columbia University's Lenfest Center for Renewable Energy and published today in the journal Environmental Science and Technology.
The report concludes:
"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 remain 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."
Over 98 Percent of Heavy Duty Trucks Are Diesel Powered
"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, the Executive Director of the Diesel Technology Forum (http://www.dieselforum.org/).
"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.
"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.
New Diesel Technology Has Reduced PM & NOx Emissions by Over 95%
"While not specifically cited in this report, 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.
"Just last month the American Lung Association highlighted new clean diesel technology and fuels as being one of the major reasons for improved air quality in the U.S.
"While this study does note the "likely future efficiency improvements in clean diesel trucks", unfortunately it does not consider the combined benefits of those technology improvements combined with increasing blends of advanced renewable biodiesel fuels. That would make a great comparison, and one we think would be even harder to beat."
Link to new study- http://pubs.acs.org/doi/abs/10.1021/acs.est.5b00412
Link to EDF Statement- Big Rigs: Will the Climate Benefit from Switching Diesel Trucks to Natural Gas?