1 Carnegie Mellon University Does using natural gas to power vehicles reduce greenhouse gas (GHG) emissions? - Comparison of Life Cycle Emissions from Natural Gas Pathways for On-Road Vehicles Fan Tong, Paulina Jaramillo, Ines Azevedo Department of Engineering and Public Policy Carnegie Mellon University May 23, 2016

2 Carnegie Mellon University Significant industry interests in using natural gas to power on-road vehicles 2

3 Carnegie Mellon University Significant industry interests in using natural gas to power on-road vehicles 3

4 Carnegie Mellon University Research Gaps Previous studies do not account for technological developments and emerging issues (e.g. methane leakage) of the natural gas system and of vehicle technologies. Existing findings on life cycle GHG emissions of natural gas pathways are incomplete: mixed and contradictory for transit buses and heavy-duty trucks, none for medium-duty trucks. Research Questions Which natural gas pathways or which vehicle segments provide GHG emissions reductions compared to petroleum fuels? How sensitive are the results to methane leakage rates and other factors? Does using natural gas to power vehicles reduce greenhouse gas emissions? 4

5 Carnegie Mellon University Emission Sources Resource extraction: natural gas and oil (baseline). Fuel production, transport, distribution. Vehicle operation (tailpipe). Vehicle manufacturing emissions (esp., battery and fuel cells). Emissions from infrastructure construction. Emissions from end-of-life disposal or treatment. Bottom-up Attributional Life Cycle Assessment (LCA) GHGs CO 2, CH 4, N 2 O Global warming potential (GWP) from IPCC AR5. Functional Unit Vehicle distance (kilometer). Freight distance (metric ton-km). 5

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7 Results 7

8 Carnegie Mellon University Sample Results - Natural Gas Pathways Are Worse. 8

9 Carnegie Mellon University Results: 9 vehicle types * 4 scenarios (methane leakage & GWP). 9 Many pathways do not achieve emissions reduction yet

10 Carnegie Mellon University If natural gas vehicles have the same fuel efficiency as diesel vehicles, then natural gas vehicles achieve emissions reduction for up to 3.1% of methane leakage rate. 10

11 Carnegie Mellon University Higher or lower relative vehicle fuel efficiency allows higher or lower methane leakage. 11

12 Carnegie Mellon University LNG/CNG vs. Diesel (Medium- and Heavy-Duty Vehicles) 12

13 Carnegie Mellon University LNG/CNG vs. Diesel (Medium- and Heavy-Duty Vehicles) 13

14 Carnegie Mellon University Natural Gas Pathways vs. Gasoline (Light-Duty Vehicles) 14

15 Carnegie Mellon University Conclusions Natural gas does not necessarily reduce GHG emissions. Key factors: vehicle fuel efficiency, methane leakage, global warming potential. Conclusions and Policy Implications 15 Policy implications Increase fuel efficiency of natural gas vehicles. Reduce methane leakage throughout the life cycle. How much efforts are enough? Need to account for uncertainty in emission estimates.

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17 Carnegie Mellon University My Ph.D. study is financially supported by Department of Engineering and Public Policy. Center for Climate and Energy Decision-Making (CMU & NSF) Northrop Grumman Fellowship Steinbrenner Institute Graduate Research Fellowship. Fuels Institute. Fuel Freedom Foundation. Richard K. Mellon Foundation Ji-Dian Liang Fellowship. I would also like to thank the comments and suggestions I have received during presentations the EPP qualifier, CEDM student seminars, CEDM annual meetings, ISSST conference, USAEE conference, ASCE conference, and invited talks at UC Davis. I would also like to thank the anonymous reviewers for reviewing our submissions at ES&T and Energy&Fuels. Acknowledgements 17

18 Carnegie Mellon University Questions? Fan Tong, 18