Spatial Analysis of Air Quality Impacts from
Using Natural Gas for Road Transportation
Fan Tong, Paulina Jaramillo, Ines Azevedo
Department of Engineering and Public Policy
Carnegie Mellon University
33rd USAEE/IAEE North American Conference
Oct 28, 2015
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Use Natural Gas to Fuel Transportation?
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Unintended Consequences? GHGs?
• Previous work on greenhouse gas (GHG) emissions
• Tong et al. Environmental Science & Technology (2015).
• Tong et al. Energy & Fuels (2015).
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Unintended Consequences of GHGs? Key Factors
• Relative fuel efficiency w.r.t. gasoline/diesel vehicles.
• Life cycle methane leakage (well pads, gathering lines,
processing, pipelines, refueling, vehicle tanks, tailpipe).
15%
Current
FCEV
Break-even methane leakage rate
Current
CNG
vehicle
GH2 FCEV, 100-yr
Current
BEV
BEV,
100-yr
10.8%
10%
CNG, 100-yr
GH2 FCEV, 20-yr
5%
4.5%
CNG, 20-yr
BEV, 20-yr
2.8%
2.3%
1.2%
0.9%
0%
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100%
150%
200%
250%
300%
Energy economy ratio (EERs) of natural gas vehicles
350%
400%
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What about Criteria Air Pollutants?
• Criteria Air Pollutants (CAP)
• Regulated in the National Ambient Air Quality Standards (U.S. EPA).
• Particle pollution (often referred to as particulate matter), ground-level
ozone, carbon monoxide, sulfur oxides, nitrogen oxides, and lead.
• Health and environmental impacts
• Of the six pollutants, particle pollution and ground-level ozone are the
most widespread health threats.
• direct emissions (primary), or
• products of chemical reactions (secondary).
• Local, certain, near-term impacts.
• Health impacts dominate.
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Research Questions
• ‘Best’ use of natural gas?
• What are health and environmental damages of natural gas-based fuels
in a life cycle sense?
• How do they compare with conventional gasoline vehicles? Are there
opportunities to reduce the social damages from petroleum use?
• Location, location, location?
• Are there any good regions or bad regions in particular? How does
regional variation affect results?
• Do we trust the results?
• What cause uncertainty and variability?
• How do they impact the results?
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Comments on Existing Literature
• “Fuel pathway comparison” by examining marginal social costs in a
life cycle perspective.
• Hydrogen (FECVs), biomass (ethanol), electric vehicle, natural gas.
• A recent surge of literature (2014-2015).
• Almost all focused on passenger vehicles (except NRC (2010)).
• Almost all used GREET + APEEP (different versions).
• Knowledge gaps?
• Environmental damages of trucks, buses and other heavy-duty vehicles?
• Near-zero emission engine (0.02 g/bhp-hr) and California’s optional low-NOx standard.
• New Marginal damage estimates (social cost of SOx) emgerged.
• Emission inventory should be updated.
• Real world factors?
• Travel speed, road grade, ambient environment - Reyna et al. (2014), Yuksel et al. (2015).
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Damage Function Method
• Marginal damages from life cycle CAP emissions.
• Contiguous U.S.; Seasonal & annual average.
• Fuel and vehicle focus.
• Focus on natural gas pathways
• For both LDVs and MHDVs.
• Functional Unit.
• Normalized damages.
• Vehicle mile traveled (VMT).
• Passenger mile traveled (PMT).
• A ton of cargo moved over one mile (Cargo-ton-mile).
• Total damages
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Build an Emission Inventory
• A well-to-wheel emission inventory.
Modified from a GREET
model presentation
(Argonne National Lab)
Upstream: extraction of feedstock (e.g., natural gas, crude oil)
Production: natural gas -> CNG/LNG/electricity/hydrogen.
Transport: from plant sites to refueling stations.
Vehicle use: tailpipe emissions.
Vehicle manufacturing (e.g. batteries).
• Locations of emissions are very important information!
• Develop our own emission inventory and compare it with the GREET model.
• Source: National Emission Inventory (NEI), peer-reviewed literature.
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Marginal Damage Estimation
• Marginal/incremental damages ($/tonne of pollutant).
• Atmospheric chemistry, exposure (intake function), response function,
monetary valuation.
• APEEP/AP2 model, EASIUR model, BenMAP model, COBRA model.
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Different Pictures for Passenger Vehicles and Trucks
• Fuel pathway comparison with breakdown of life cycle stages.
• Median damages in U.S. counties (Unit: cent in year 2000/mile)
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Benefits of CNG over Gasoline (Passenger Vehicles)
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Preliminary Conclusions
• Choice of natural gas pathway matters.
• All natural gas pathways provide some damage reduction potentials but
their magnitudes differ.
• If NGCC power plant is on the margin, natural gas-electricity-BEV reduces
more social damages than CNG.
• Vehicle type matters.
• Reducing tailpipe emissions is more important for MHDVs than for LDVs.
• Location matters.
• Across fuel pathways, urban areas (LA, SF, NYC) see much larger
normalized damage reductions from natural gas pathways.
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Acknowledgements
• This work is financially supported by
• Center for Climate and Energy Decision-Making (CMU & NSF).
• 2013-14 Northrop Grumman Fellowship.
• 2013-14 Steinbrenner Institute Graduate Research Fellowship.
• Fuels Institute.
• Fuel Freedom Foundation.
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Questions?
Fan Tong
PhD candidate in Engineering & Public Policy
ftong@andrew.cmu.edu
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