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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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• Previous work on greenhouse gas (GHG) emissions• Tong et al. Environmental Science & Technology (2015).• Tong et al. Energy & Fuels (2015).

Unintended Consequences? GHGs?

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• Relative fuel efficiency w.r.t. gasoline/diesel vehicles.• Life cycle methane leakage (well pads, gathering lines,

processing, pipelines, refueling, vehicle tanks, tailpipe).

Unintended Consequences of GHGs? Key Factors

100% 150% 200% 250% 300% 350% 400%0%

5%

10%

15%

Energy economy ratio (EERs) of natural gas vehicles

Bre

ak-e

ven

met

han

e le

akag

e ra

te

2.3%

0.9%

2.8%

1.2%

10.8%

4.5%

CurrentCNGvehicle

CNG, 100-yr

CNG, 20-yr

BEV,100-yr

CurrentBEV

CurrentFCEV

GH2 FCEV, 100-yr

GH2 FCEV, 20-yr

BEV, 20-yr

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• 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.

What about Criteria Air Pollutants?

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• ‘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?

Research Questions

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• “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).

Comments on Existing Literature

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• 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

Damage Function Method

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• A well-to-wheel emission inventory.

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.

Build an Emission Inventory

Modified from a GREET model presentation (Argonne National Lab)

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• Marginal/incremental damages ($/tonne of pollutant).• Atmospheric chemistry, exposure (intake function), response function,

monetary valuation.• APEEP/AP2 model, EASIUR model, BenMAP model, COBRA model.

Marginal Damage Estimation

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• Fuel pathway comparison with breakdown of life cycle stages.• Median damages in U.S. counties (Unit: cent in year 2000/mile)

Different Pictures for Passenger Vehicles and Trucks

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Benefits of CNG over Gasoline (Passenger Vehicles)

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• 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.

Preliminary Conclusions

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• 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.

Acknowledgements

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Questions?

Fan TongPhD candidate in Engineering & Public Policy

ftong@andrew.cmu.edu

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