A Comparison of Air Emissions from Natural G as P athways for Road Transportation

1. A Comparison of Air Emissions from Natural Gas Pathways for Road Transportation Fan Tong, Paulina Jaramillo, Ines Azevedo Department of Engineering and Public Policy Carnegie Mellon University 2013-14 Northrop Grumman Fellowship

2. Natural Gas Use in the Transportation Sector • Potential benefits: cost savings, energy security, and cleaner combustion. • Barriers: lack of fueling infrastructure, high upfront cost. Both figures are drawn with data from EIA’s website

3. Research Questions • What are the life-cycle greenhouse gas emissions of natural gas pathways? • Which pathway or which vehicle application provides the largest greenhouse gas emission reduction compared to conventional liquid pathways? • How does methane leakage affect the life-cycle greenhouse gas emissions of natural gas pathways? • What are the key parameters/stages to reduce life-cycle greenhouse gas emissions of natural gas pathways?

4. Research Gap • Limitations of existing studies • Hard to compare the results because studies tend to use different assumptions and system boundaries. (Wang et al., 2002; Jaramillo et al., 2008; Samaras et al., 2008; Sioshansi et al., 2009; Michalek et al., 2011). • There are a few natural gas-centered studies on light-duty vehicles (LDVs), but they are either limited in pathways considered (Venkatesh et al., 2011; NRC, 2013) or comprehensive but outdated (Wang et al., 2000; NRC, 2010a). • There is relatively few existing studies on air emissions from alternative fuels for heavy-duty vehicles except for transit buses.(Beer et al., 2002; Ally, et al., 2007; Clark et al., 2007; Graham et al., 2008; Hesterberg, et al., 2013; Weigel, 2009; Krupnick, 2010; NRC, 2010b & 2014; EPA, 2011; Meyer et al., 2011; Meier, et al., 2013; MJB&A, 2014) • Few studies treated uncertainty and variability explicitly (Venkatesh et al., 2011). • Estimates of natural gas upstream GHG emissions have been controversial. However, new on-site measurements of natural gas upstream emissions (Allen et al., 2013; EPA GHGRP 2013) are available.

5. Functional unit: km Greenhouse gases: CO2, CH4, N2O Global warming potential: IPCC (2013)

12. Vehicle Specifications

13. Results - Passenger Vehicles

14. Results - Passenger Vehicles

15. Results – Line-haul Tractor Trailers

16. Results – Line-haul Tractor Trailers

17. What roles do leakage rate and fuel economy play for CNG and LNG pathways?

18. Break-even leakage rate is a linear function of relative fuel economy of NGVs

19. Conclusions • Not all natural gas pathways achieve GHG emission reductions compared to existing petroleum pathways. • Indirect use of natural gas to produce electricityutilized in BEVsachieves significant reductions in all applicable vehicle segments. • E85, M85, and Fischer-Tropsch liquids are very unlikely to achieve emission reductions while hydrogen fuel cell electric vehicles, CNG and LNG pathways are possible (to a varying extent). • Emission reduction potentials of CNG and LNG depend on two key parameters, life-cycle methane leakage rate and relative fuel economy of natural gas vehicles. • Assuming a 90% relative fuel economy, the break-even leakage rate is around 1.2% or around 3.0% for 20-year and 100-year GWP. • An efficiency-increasing technology, such as hybridization or electrification, allows higher leakage rate to achieve emission reductions.

20. Thank you!ftong@Andrew.cmu.edu Supported by 2013-14 Northrop Grumman Fellowship

21. Results - Passenger Vehicles

22. Results – Line-haul Tractor Trailers

23. Results – Transit Buses

24. Natural gas upstream GHG emissions

25. Natural gas upstream GHG emissions

26. Natural gas upstream GHG emissions

27. Natural gas upstream GHG emissions