Heavy-duty trucks switching to run on natural gas will only contribute to reining in climate change impacts if methane leakage across the natural gas supply chain is plugged, according to research summarized in the current issue of Environmental Science & Technology, an American Chemical Society (ACS) publication.

As part of its national campaign focused on methane emissions, the Environmental Defense Fund (EDF) held a press briefing in Washington, DC, to tout its co-authored research aimed at the shift of heavy-duty vehicles away from diesel fuel to natural gas. A foursome of EDF representatives said the study has "important implications" for truck and engine manufacturers, shippers, fleet operators and policymakers.

EDF also said several policy solutions are in play that could improve the climate prospects for natural gas trucks, including upstream federal methane regulations and the upcoming second phase rulemaking for truck efficiency and greenhouse gas (GHG) emissions standards by the U.S. Environmental Protection Agency (EPA) and the National Highway Traffic Safety Administration.

"Natural gas trucks have the potential to reduce overall climate impacts compared to diesel, but only if we clean up the highly potent GHG emissions from the systems that produce and deliver the fuel," said Jonathan Camuzeaux, a lead author of the study and EDF's senior economic analyst. "Otherwise, the net warming effect is actually a negative one for 50 to 90 years after the fuel is burned."

Matthew Godlewski, president of the Washington, DC-based Natural Gas Vehicles for America (NGVAmerica), said the study clearly demonstrates the need for NGVs in helping reduce the impacts of climate change, but he was puzzled as to why EDF has conducted more research outside on the national study, "Pump to Wheels Methane Leakage," in which the environmental organization is taking part, along with member companies in NGVAmerica (see Daily GPIMarch 6, 2013).

Noting its results are soon-to-be-published, Godlewski said the national report "is based on extensive research and provides a critical baseline to end speculation about actual in-use methane leaks from natural gas stations and vehicles."

Camuzeaux said the latest study on heavy-duty vehicles is complementary to the broader, long-term study and it emphasizes the importance of "gathering more and better data on methane loss," along with allowing stakeholders long term to evaluate the climate impacts of fuel switching from diesel to natural gas."

Godlewski emphasized that the NGV industry has "been a leader" in driving new technologies to further reduce emissions and improve air quality. He cited renewable natural gas and near-zero emission engines as two examples that he thinks will play significant roles in the future of NGVs.

In responses to questions on a conference call, EDF lead senior scientist Ramon Alvarez contrasted earlier research by others that estimated the high potential range for methane emissions at 7-10% of the U.S. gas production with what may come out of the cumulative research done in the past few years that could show that the national value is closer to the 1-2% range on average.

Alvarez attributed the 7-10% range as the high end of estimates from other researchers' work completed several years ago before EDF completed its 2012 study. "There has been a lot of other work by us and other researchers over the last three years," he said. "Some of that work is still incomplete, but what we're seeing is that the levels on average could not be that high nationally."

He said the high figures can be found in some individual production basins, such as the Uintah (see Daily GPIAug. 6, 2013), but on a national basis they are much lower on average considering all aspects of the natural gas product/distribution/end-use chain.

"The work is still ongoing, but I think we are seeing that the range is closer to the lower end -- the 1-2% range -- than to the upper ranges," Alvarez said. "That's the current emerging insight, but we're not done yet. A lot of the work ongoing in the next year or so will have a lot more certainty around the conclusions."

NGVAmerica cites four separate university-based research projects on methane emission, along with one from Argonne National Laboratory that found NGVs produce 13-21% less GHG emissions compared to gasoline or diesel fueled vehicles.