Assessments on emergy and greenhouse gas emissions of internal combustion engine automobiles and electric automobiles in the USA

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Perspective

Q7

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Assessments on emergy and greenhouse gas emissions of internal combustion engine automobiles and electric automobiles in the USA Ran Jing 1,2,a, Chen Yuan 2,a, Hamidreza Rezaei 2, Jin Qian 3, Zhen Zhang 1,* 1

College of Natural Resources and Environment, Joint Institute for Environmental Research & Education, South China Agricultural University, Guangzhou, 510642, China 2 Department of Civil and Environmental Engineering, University of Maryland at College Park, MD, 20742, USA 3 Research & Development Institute in Shenzhen & School of Natural and Applied Sciences, Northwestern Polytechnical University, Xi'an, 710072, China

article info

abstract

Article history:

Increasing energy consumption in the transportation sector results in challenging green-

Received 17 May 2019

house gas (GHG) emissions and environmental problems. This paper involved integrated

Received in revised form

assessments on GHG emissions and emergy of the life cycle for the internal combustion

20 November 2019

engine (ICE) and electric automobiles in the USA over the entire assumed fifteen-year

Accepted 25 November 2019

lifetime. The hotspots of GHG emissions as well as emergy indices for the major pro-

Available online xxx

cesses of automobile life cycle within the defined system boundaries have been investigated. The potential strategies for reducing GHG emissions and emergy in the life cycle of

Keywords:

both ICE and electric automobiles were further proposed. Based on the current results, the

Emergy

total GHG emissions from the life cycle of ICE automobiles are 4.48E þ 07 kg CO2-e which is

Emergy Index

320 times higher than that of the electric automobiles. The hotspot area of the GHG

Electric automobiles

emissions from ICE and electric automobiles are operation phase and manufacturing

Greenhouse gas emissions

process, respectively. Interesting results were observed that comparable total emergy of

Internal combustion engine

the ICE automobiles and electric automobiles have been calculated which were 1.54E þ 17

automobiles

and 2.20E þ 17 sej, respectively. Analysis on emergy index evidenced a better environmental sustainability of electric automobiles than ICE automobiles over the life cycle due to its higher ESI. To the authors’ knowledge, it is the first time to integrate the analysis of GHG emissions together with emergy in industrial area of automobile engineering. It is expected that the integration of emergy and GHG emissions analysis may provide a comprehensive perspective on eco-industrial sustainability of automobile engineering. © 2019 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V.

* Corresponding author. E-mail addresses: [email protected], [email protected] (Z. Zhang). a Both Ran Jing and Chen Yuan contributed equally to this study. https://doi.org/10.1016/j.jes.2019.11.017 1001-0742/© 2019 The Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences. Published by Elsevier B.V. Please cite this article as: Jing, R et al., Assessments on emergy and greenhouse gas emissions of internal combustion engine automobiles and electric automobiles in the USA, Journal of Environmental Sciences, https://doi.org/10.1016/j.jes.2019.11.017

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Abbreviation

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BTU Bryan Texas Utilities Carbon Dioxide Equivalent CO2-e Ematerial emergy of raw materials Eenergy emergy of energy total emergy Etotal ECi, GHG greenhouse gas GHG emission factors for different raw material EFj,CO2 GHG emission factors of CO2 for each type of energy EFj,CH4 GHG emission factors of CH4 for each type of energy EFj,N2O GHG emission factors of N2O for each type of energy ELR environmental loading ratio ESI emergy sustainability index EYR emergy yield ratio Gmaterial material related GHG emissions Genergy energy related GHG emissions total GHG emissions Gtotal F purchased resources of emergy GHGCO2 CO2 emissions during the life cycle of ICE automobiles and electric automobiles GHGCH4 CH4 emissions during the life cycle of ICE automobiles and electric automobiles GHGN2O N2O emissions during the life cycle of ICE automobiles and electric automobiles GWPCO2 the global warming potential for CO2 emissions GWPCH4 the global warming potential for CH4 emissions GWPN2O the global warming potential for N2O emissions HEV hybrid-electric vehicle ICE internal combustion engine PHEVs plug-in hybrid electric vehicles R renewable sources of emergy the corresponding transformity for energy Ti sources denotes the corresponding transformity for raw Tj materials N nonrenewable sources of emergy USEPA United States Environmental Protection Agency fraction renewable FR

The automobile has been widely used in daily life since the invention of the first modern car in 1886 (Happian-Smith, 2001). In 2017, the USA consumed 28.20 quadrillions BTU of energy in the transportation sector which accounts for more than 28.82% of total energy consumption in the USA (Bureau of Transportation Statistics, 2018). As a result, a large amount of greenhouse gas (GHG) emissions was emitted due to the large amount of energy consumption by automobiles. According to the United States Environmental Protection Agency (USEPA), it is estimated that the transportation sector has contributed 28.5% of total GHG emissions in the USA (USEPA, 2018). The increasing energy consumption in transportation sector results in a challenging GHG emissions and environmental problem.

In the past several decades, the use of ICE automobile in the transportation caused a significant amount of fossil fuels being consumed (Zou et al., 2016). A variety of promising alternative technologies such as electric automobiles have been developed (Bandivadekar et al., 2008). According to Granovskii et al. (2006) ‘s study, the electric automobiles have more advantages on environmental impacts as compared with ICE automobiles. However, the environmental impacts associated with the electric automobiles also depend on other parameters such as the source of the electricity (Hawkins et al., 2012; Hawkins et al., 2013; Bauer et al., 2015; Casals et al., 2016) and weight of vehicles (Del Pero et al., 2018; Girardi et al., 2015; Nanaki and Koroneos, 2013). A comprehensive analysis of GHG emission requires a large amount of data including different sources of energy consumption and the corresponding emission factors as well as a complicated algorithm to calculate (Liu et al., 2012). Several studies have been performed focusing on the quantitative evaluation of the GHG emissions from both ICE automobiles and electric automobiles, which considered different inputs of the energy and resources (Jhaveri et al., 2018; Silva et al., 2018; Delogu et al., 2018b). Even through some previous studies payed efforts on GHG emission investigation and reduction for automobiles, understanding on which parts of the life cycle for ICE automobiles and electric automobiles generating the largest proportion of GHG emissions (hotspots) remains sparse. In addition, GHG environmental impacts highly rely on the inputs from the manufacturing resources. As a consequence, it may largely underestimate the GHG emission contributed from the manufacturing and operations of the automobiles. Emergy could be an appropriate measurement that can quantify the energy (and resources) used during the entire life cycle of an automobile in units of one form of energy (usually solar) (Mu et al., 2011). In recent years, emergy has been used in the area of ecological engineering (Zhou et al., 2010). However, to the authors' knowledge, there are few attempts to employ emergy accounting in the industrial area of automobile engineering, which is however essential for obtaining a comprehensive perspective on eco-industrial sustainability of automobile engineering. Therefore, the objectives of this study are: (i) to perform an integrated analysis of both GHG emissions and emergy of ICE automobiles and electric automobiles in the USA; (ii) to investigate the hotspots of GHG emissions and emergy indices for major processes of automobile life cycle within the defined system boundaries (i.e., raw material extraction and processing, manufacturing, and operation processes); (iii) to provide appropriate strategic opportunities for GHG emissions reduction during the automobile life cycle, thus achieving a sustainable automobile engineering development.

1.

Methodology

1.1. System boundary of GHG emissions investigation for ICE automobiles and electric automobiles A typical life cycle of ICE automobiles and electric automobiles in the USA includes raw material extraction and processing, manufacturing, operation processes, and recycling and

Please cite this article as: Jing, R et al., Assessments on emergy and greenhouse gas emissions of internal combustion engine automobiles and electric automobiles in the USA, Journal of Environmental Sciences, https://doi.org/10.1016/j.jes.2019.11.017

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Fig. 1 e System boundary of GHG emissions investigation for life cycle of ICE automobiles and electric automobiles.

disposal (Samaras and Meisterling, 2008; Zamel and Li, 2006). In this study, the system boundary of the GHG emissions investigation was “Gate-to-Gate”, which covered from raw material extraction and processing, manufacturing, and operation processes as highlighted in the red box (Fig. 1). Firstly, raw materials (e.g., steel plate, aluminum ingot) were transferred to manufacturing plants to produce car parts. Then, these produced car parts were delivered to the production line and then constructed together with automobile frames. After that, the rest parts of the automobile such as rear axles and drive shafts, gear boxes, steering box components, and braking systems were sequentially installed. The assembled automobile body was sequentially painted by an electrostatically-charged undercoat paint, a base coat of color paint and a clear top coat followed by drying at temperatures exceeding 275 C. Finally, the painted automobile body was sent to the assembly area to install the automotive interiors such as dash panels, interior lights, seats, headliners, and glass (Kumar et al., 2016). The ICE automobiles in this study are light vehicles which include Four-door sedan of 2015 model year, sport utility vehicles (SUVs), truck SUVs, pickups, and vans. The LCI data of raw material and energy consumption for the light vehicles are the average value of year 2015 (Table S1, Supplementary Data) (Davis, 2018). The LCI data of the electric automobiles are based on Tesla Model S 85 (Table S2) (Klemola, 2016). The total GHG emissions were energy-related GHG emissions that consisted of the GHG emissions from the fossil fuel combustion and electricity consumption. The final results of the GHG emissions were

calculated in terms of carbon dioxide equivalent (CO2-e), with global warming potential (GWP) values over a 100-year time horizon (USEPA, 2018). In addition, the GHG emission factors were obtained from the EPA Center for Corporate Climate Leadership: Emission Factors for Greenhouse Gas Inventories (USEPA, 2018).

1.2. Calculation methods for GHG emissions from life cycle of ICE automobiles and electric automobiles GHG emissions of the raw materials were calculated by multiplying the material weight with the corresponding emission factors (Eq. (1)). Similarly, GHG emissions of the energy were calculated by multiplying the energy consumption data with their corresponding emission factors. The emission factors of the raw materials were obtained from the inventory of carbon and energy (ICE) database V2.0 (Table S3), which was published by the University of Bath (Hammond and Jones, 2011). In addition, the energy-related GHG emissions can be obtained based on the amount of various types of energy, such as coal, gasoline, electricity, natural gas, etc., and the corresponding emission factors (Table S4). The major sources of GHG emissions during the use stage is from the combustion of fossil fuel for the ICE automobiles. The major sources of GHG emissions of the electric automobiles during the use stage is the consumption of electricity. According to the IPCC guideline Chapter 2 Stationary Combustion, three types of GHG emissions (i.e., CO2, CH4 and N2O) are mainly generated during the stationary combustion process

Please cite this article as: Jing, R et al., Assessments on emergy and greenhouse gas emissions of internal combustion engine automobiles and electric automobiles in the USA, Journal of Environmental Sciences, https://doi.org/10.1016/j.jes.2019.11.017

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light fuel oil, and natural gas), Gmaterial (kg CO2-e) is the total GHG emissions for different raw material i, mi (kg) is the material consumption for different raw material, ECi (kg CO2-e/ kg) denotes the GHG emission factors for different raw material i, Genergy (kg CO2/J, kg CH4/J, kg N2O/J) is the energyrelated GHG emissions for different energy source j, ej (J) stands for the different energy source j, EFj, CO2, EFj,CH4, and EFj, N2O are the emission factors of CO2, CH4 and N2O for the different energy source j, Gtotal (kg CO2-e) is the total GHG emissions of the life cycle of ICE automobiles and electric automobiles.

(Eggleston et al., 2006). In addition, according to the EPA, the primary sources of greenhouse gas from electricity production in the United States is burning fossil fuels, mostly coal and natural gas which account for approximately 62.9% of total electricity generation (Davis et al., 2009). Therefore, only CO2, CH4 and N2O have been considered in this study. The results of the GHG emissions are expressed in terms of carbon dioxide equivalent (CO2-e) per vehicle, with global warming potential (GWP) values over a 100-year time horizon (Intergovernmental Panel on Climate Change, 2007). The GWP values of three types of GHG emission (i.e., CO2, CH4, and N2O) are 1, 25, and 298, respectively (USEPA, 2018). Gmaterial ¼

q X

mi  ECi

1.3. System boundary of emergy investigation for ICE automobiles and electric automobiles

(1)

i¼1 p X ðej  EFj;CO2  GWPCO2 þ ej  EFj;CH4  GWPCH4 Genergy ¼ i¼1

In the current study, emergy analysis was employed to calculate the direct and indirect energy consumption and convert the different types of energy and materials in the system to one equivalent (i.e., solar emergy joules (sej) which is the basic unit of emergy). Fig. 2 reveals the energy system diagram for emergy accounting which was developed by the energy system's language (Odum, 2007). It identified the input resources, which was required during the life cycle of ICE automobiles and electric automobiles, to define the system boundary. Consistent with the system boundary of GHG emission, the system boundary of emergy included raw

(2)

þ ej  EFj;N2 O  GWPN2 O Þ Gtotal ¼ Gm þ Ge

(3)

where, i (i ¼ 1∙∙∙13) denotes for the types of raw material input for ICE automobiles and electric automobiles which are summarized in Tables 1 and 2, j (j ¼ 1∙∙∙6) denotes the different types of energy (i.e., coal, gasoline, diesel, electricity,

Table 1 e Total GHG emissions generated from the life cycle of ICE automobiles. Q8

Item Raw materials extraction and processing

Manufacturing

Operation

Total GHG emissions a

b

þ þ þ þ þ þ þ þ þ þ þ þ þ

Steel Steel (recycled) Iron Aluminum Magnesium Copper Lead Plastics Lubricants Glass Rubber Lithium Graphite Total

7.43E 2.48E 1.13E 1.86E 4.99E 2.99E 1.59E 1.51E 1.03E 4.22E 9.03E 0.00E 0.00E

Item

Raw data (J)

Coal Natural Gas Diesel Gasoline Electricity (Mixed) Total Gasoline Diesel Total

Emission factora (kg CO2-e/kg)

Raw data (kg)

1.12E 1.31E 3.00E 4.90E 5.52E

þ þ þ þ þ

02 02 02 02 00 01 01 02 02 01 01 00 00

09 11 06 07 09

5.68E þ 11 1.89E þ 11

2.89E 4.70E 2.03E 1.81E 1.32E 3.81E 3.37E 3.31E 0.00E 9.10E 2.85E 5.30E 3.31E

Total GHG emissions (kg CO2-e)

þ 00 - 01 þ 00 þ 00 þ 00 þ 00 þ 00 þ 00 þ 00 - 01 þ 00 þ 00 - 01

2.15E þ 03 1.16E þ 02 2.29E þ 02 3.37E þ 02 6.59E þ 00 1.14E þ 02 5.35E þ 01 4.98E þ 02 0.00E þ 00 3.84E þ 01 2.57E þ 02 0.00E þ 00 0.00E þ 00 3.80E þ 03

Emission factorsb

Total GHG emissions

kg CO2/J

(kg CO2-e)

kg N2O/J

(kg CO2-e)

8.89E 5.01E 6.99E 6.53E 1.55E

1.04E 9.43E 5.48E 2.83E 3.04E

1.51E 9.43E 1.78E 5.66E 2.30E

1.05E þ 05 6.58E þ 06 2.12E - 01 3.29E þ 03 8.61E þ 02 6.69E þ 06 3.81E þ 07 1.32E þ 04 3.81E þ 07 4.48E þ 07

-

05 05 08 05 07

6.53E - 05 6.99E - 08

-

08 10 12 09 12

2.83E - 09 5.48E - 12

-

08 10 12 09 12

5.66E - 09 1.78E - 12

GHG emission factors collected from Inventory of Carbon & Energy V2.0. Data source: http://www.carbonsolutions.com/resources/ice%20v2. 0%20-%20jan%202011.xls. Accessed December 12, 2018; GHG emission factors collected from Emission Factors for Greenhouse Gas Inventories-EPA. Data source: https://www.epa.gov/sites/ production/files/2018-03/documents/emission-factors_mar_2018_0.pdf. Accessed December 12, 2018.

Please cite this article as: Jing, R et al., Assessments on emergy and greenhouse gas emissions of internal combustion engine automobiles and electric automobiles in the USA, Journal of Environmental Sciences, https://doi.org/10.1016/j.jes.2019.11.017

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Table 2 e Total GHG emissions generated from the life cycle of the electric automobiles. Item Raw materials extraction and processing

Manufacturing

Operation

1.13E 7.68E 1.08E 3.85E 0.00E 2.95E 0.00E 2.10E 1.23E 4.23E 3.31E 7.56E 1.00E

Item

Raw data (J)

01 02 01 02 00 02 00 02 00 01 01 00 02

2.89E 4.70E 2.03E 1.81E 1.32E 3.81E 3.37E 3.31E 0.00E 9.10E 2.85E 5.30E 3.31E

þ 00 - 01 þ 00 þ 00 þ 00 þ 00 þ 00 þ 00 þ 00 - 01 þ 00 þ 00 - 01

Total GHG emissions (kg CO2-e) 3.27E þ 01 3.61E þ 02 2.20E þ 01 6.96E þ 02 0.00E þ 00 1.13E þ 03 0.00E þ 00 6.96E þ 02 0.00E þ 00 3.85E þ 01 9.44E þ 01 4.01E þ 01 3.33E þ 01 3.14E þ 03

Emission factorsb

Total GHG emissions

kg CO2/J

kg CH4/J

kg N2O/J

(kg CO2-e)

2.22E þ 09 6.30E þ 07 7.70E þ 09

5.01E - 05 6.98E - 05 1.55E - 07

9.43E - 10 2.83E - 09 3.04E - 12

9.43E - 10 5.66E - 08 2.30E - 12

1.15E þ 11

1.55E - 07

3.04E - 12

2.30E - 12

1.12E þ 05 5.46E þ 03 1.20E þ 03 1.18E þ 05 1.80E þ 04 1.80E þ 04 1.39E þ 05

Total GHG emissions a

þ þ þ þ þ þ þ þ þ þ þ þ þ

Steel Steel (recycled) Iron Aluminum Magnesium Copper Lead Plastics Lubricants Glass Rubber Lithium Graphite Total

Natural Gas Light fuel oilc Electricity (Mixed) Total Electricity (Mixed) Total

Emission factora (kg CO2-e/kg)

Raw data (kg)

GHG emission factors collected from Inventory of Carbon & Energy V2.0. Data source: http://www.carbonsolutions.com/resources/ice%20v2. 0%20-%20jan%202011.xls. Accessed December 12, 2018.; bGHG emission factors collected from Emission Factors for Greenhouse Gas Inventories-EPA. Data source: https://www.epa.gov/sites/production/files/2018-03/documents/emission-factors_mar_2018_0.pdf. Accessed December 12, 2018.; cThe GHG emission factors of light fuel oil were substituted by the emission factors of distillate fuel oil. The values were calculated as the average of their GHG emission factors.

Fig. 2 e System boundary of emergy investigation for life cycle of ICE automobiles and electric automobiles. material extraction and processing, manufacturing (i.e., parts production, painting and vehicle assembly) and the operation of finished vehicle (Fig. 2). It should be noted that the disposal

of end-of-life vehicles was not included in the system boundary for both GHG emission and emergy analysis. The sources of emergy can be classified into three categories:

Please cite this article as: Jing, R et al., Assessments on emergy and greenhouse gas emissions of internal combustion engine automobiles and electric automobiles in the USA, Journal of Environmental Sciences, https://doi.org/10.1016/j.jes.2019.11.017

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renewable sources (R), nonrenewable sources (N), and the purchased resources (F). Renewable sources include water and the electricity generated by hydropower, wind, solar and biomass. Nonrenewable sources contain gasoline, diesel, light fuel oil, coal, natural gas, as well as the electricity generated by natural gas, petroleum, coal, nuclear and coal. Purchased resources included raw materials and highway construction.

the fraction of purchased (F) and nonrenewable (N) emergy which indicates the impacts on the environment during the life cycle of ICE automobiles and electric automobiles, as shown in Eq. (9). A larger value of the fraction renewable, emergy yield ratio, and environmental loading ratio normally indicate a higher environmental loading. Emergy sustainability index (ESI) is the ratio of EYR to ELR, which is a measure of the sustainability of a given process (Eq. (10)).

1.4. Calculation methods for emergy from life cycle of ICE automobiles and electric automobiles

p P

FR ¼ i¼1 The emergy transformity was used to convert the different types of energy and materials which were obtained from the emergy society database (Emergy Society Website, 2011). The data of raw materials for the ICE automobiles were collected from transportation energy data book edition 36 (Davis, 2018). The energy consumption data of the ICE automobiles during operation were obtained from highway statistics 2016 (US Department of Transportation, 2016). The raw materials and energy consumption data of the electric automobiles were obtained from the life cycle analysis report of the Tesla model S 85 (Klemola, 2017). The emergy of energy and the raw materials were calculated based on the product of energy and their transformities which are shown in Eqs. (4) and (5). Table S5 indicates the more detailed information. Finally, the total emergy of ICE automobiles and electric automobiles is the sum of the intermediate emergy of all types of energy and materials. The calculation of the total emergy is shown in Eq. (6).

EYR ¼

Ri ,Ti (7)

ET ET

q P

(8)

Fj ,Tj

j¼1

q P

ELR ¼

Fj ,Tj þ

o P

Nk ,Tk

k¼1

j¼1 p P

(9)

Ri ,Ti

i¼1

ESI ¼

EYR ELR

(10)

EEnergy ¼ ei þ Ti

(4)

Ematerial ¼ mj þ Tj

(5)

where, i (i ¼ 1∙∙∙5) denotes the types of renewable sources (i.e., water, electricity (hydropower), electricity (wind), electricity (solar), electricity (biomass)), j (j ¼ 1∙∙∙9) stands for the types of nonrenewable sources, k (k ¼ 1∙∙∙14) are the types of purchased sources, The p, q and o refer to the total number of different types of emergy sources, Ri, Fj, and Nk denote the renewable source i, purchased source j, and nonrenewable source k, Ti, Tj, and Tk denote their corresponding transformities.

(6)

2.

Etotal ¼

p X i¼1

ei  Ti þ

q X

mj  Tj

j¼1

where, i (i ¼ 1∙∙∙6) denotes the types of energy input (i.e., coal, gasoline, diesel, electricity, light fuel oil and natural gas), j (j ¼ 1∙∙∙13) denotes the types of raw materials input, Eenergy (sej) is the emergy of energy, ei (g, j, m3) stands for the energy consumption for different energy sources i, Ti (sej/g, sej/j, sej/ m3) is the corresponding transformity for different energy sources i, Ematerial (sej) refers to the emergy of raw materials, mj (g) denotes the raw material consumption for different types of materials j, Tj (sej/g) denotes the corresponding transformity for raw materials j, Etotal (sej) refers to the total emergy, p and q stand for the numbers of different types of energy and material respectively.

1.5.

Emergy indices

Emergy indices serve as the emergy-based indicators to identify the ecological feasibility and sustainability of the life cycle of ICE automobiles and electric automobiles (Mu et al., 2011). In this study, four indices were proposed to be discussed in this study. Eq. (7) indicts fraction renewable (FR), which is the fraction of renewable sources (R) in emergy outflow (Y); emergy yield ratio (EYR) is the fraction of purchased resources (F) in emergy outflow (Y) which describes the system's ability to use local resources, as shown in Eq. (8); environmental loading ratio (ELR) is

Results and discussion

2.1. Evaluation of GHG emissions and identification of hotspot areas from life cycle of ICE automobiles and electric automobiles As shown in Table 1, the total GHG emissions from the life cycle of the ICE automobiles were 4.48E þ 07 kg CO2-e. While the total GHG emissions generated from the life cycle of the electric automobiles were only 1.39E þ 05 kg CO2-e. The total GHG emissions of the life cycle of the ICE automobiles were around 320 times higher than that of the electric automobiles. This indicates that much more GHG were generated from ICE automobiles as compared with electric automobiles. According to a previous study by Del Pero et al. (2018), the GHG emissions of the ICE automobiles are 3.04E þ 04 kg CO2-e, while the GHG emissions of the electric automobiles are 1.92E þ 04 kg CO2-e. The total GHG emissions of the ICE automobiles are also higher than that of the electric automobiles, but to a less extent as compared with the current findings. The even higher value on the total GHG emissions of the ICE automobiles than the electric automobiles is mainly attributed to the long-term evaluation in our study. The current results were obtained in the view of a long-term operation period for 15 years, and as is known that the GHG emissions from operation period accounted for 85.06% of the

Please cite this article as: Jing, R et al., Assessments on emergy and greenhouse gas emissions of internal combustion engine automobiles and electric automobiles in the USA, Journal of Environmental Sciences, https://doi.org/10.1016/j.jes.2019.11.017

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7

Fig. 3 e Distribution of each process to total GHG emissions for ICE automobiles and electric automobiles.

total GHG emissions during the life cycle. It can be seen from Fig. 3 that the total GHG emissions from the life cycle of the ICE automobiles were mainly contributed by the operation process. However, the total GHG emissions generated from the life cycle of the electric automobiles were mainly generated from the manufacturing process, accounting for 84.85% of the total GHG emissions (Fig. 3). Table 1 reveals that the GHG emissions from the raw material extraction and processing, manufacturing, and operation processes of ICE automobiles were 3.80E þ 03, 6.69E þ 06, and 3.81E þ 07 kg CO2-e, respectively. For electric automobiles, the GHG emissions from these three processes were 3.14E þ 03, 1.18E þ 05, and 1.80E þ 04 kg CO2-e, respectively (Table 2). Relatively smaller amount of GHG emissions were generated from raw material extraction and processing for both life cycles of the ICE automobiles and electric automobiles. For the ICE automobiles, the raw material extraction and processing generated 3.80E þ 03 kg CO2-e. The steel and recycled steel contributed 2.27E þ 03 kg CO2-e which contributed the highest GHG emissions from the ram material extraction and processing. For the electric automobiles, the steel and recycled steel were only generated 3.94E þ 02 kg CO2-e accounting for 12.5% of the total GHG emissions from the raw material extraction and processing. It should be noted that the embodied GHG emissions of copper were 1.13E þ 03 kg CO2-e which accounted for the highest proportion in raw material for the electric automobiles production. There was a large amount of CO2-e emission during the manufacturing process for both ICE automobiles and electric automobiles. According to the current results, the energy used to build the ICE automobiles and electric automobiles achieved 6.69E þ 06 and 1.18E þ 05 kg CO2-e. However, for the ICE automobiles, the GHG emissions generated from their operation processes were smaller than the GHG emissions from the operation process of the electric automobiles. In this study, the operation period of the ICE automobiles was set up as 15 years. According to Fig. 3, the operation process accounted for the highest GHG emissions (85.06%) during the life cycle of ICE automobiles, in which the combustion of gasoline generated

3.81E þ 07 kg CO2-e of the GHG emissions during the operation process. Over a consistent lifetime, the electric vehicles only emitted about 1.80E þ 04 kg CO2-e which was only 0.05% of GHG emissions than that generated from the operation process of the ICE automobiles. In addition, for the operation of an internal combustion engine, gasoline is not a sustainable energy source due to its relatively high GHG emission factors (Table 1). There are 6.53E - 05 kg CO2 emitted for each Joule gasoline combustion, in which the emission factors of CH4 and N2O are 2.83E - 09 kg CH4/J and 5.66E - 09 kg N2O/J, respectively. In contrast, the contribution of the electric vehicles to GHG emissions was the greatest when the electricity derived from coal resulting from large emission factors (i.e., 8.89E - 05 kg CO2/J, 1.04E - 08 kg CH4/J, and 1.51E - 08 kg N2O/J) as compared with other energy sources, even though they emit no tailpipe pollutants.

2.2. Evaluation of emergy generated from ICE automobiles and electric automobiles and comparison of emergy indices As shown in Tables 3 and 4, the total emergy of the ICE automobiles and electric automobiles is 1.54E þ 17 and 2.20E þ 17 sej, respectively. For the ICE automobiles, the emergy generated from the raw material processing, manufacturing process, and operation process were 2.84E þ 16, 7.14E þ 15, and 1.18E þ 17 sej, respectively. While the emergy of these three processes for the electric automobiles are 6.40E þ 16, 2.64E þ 15 and 9.56E þ 16 sej, respectively. The emergy of the raw material processing from the ICE automobiles and electric automobiles accounted for 18.50% and 39.45% of their total emergy, which were mainly contributed by the aluminum accounting for 42.25% (1.20E þ 16 sej) and 38.75% (2.48E þ 16 sej) of their raw material emergy, respectively. For the ICE automobiles, the second-highest emergy material was steel, containing 7.26E þ 15 sej of emergy and accounting for 25.56% of the emergy from the raw material extraction and processing. Rubber was the third-highest emergy material which

Please cite this article as: Jing, R et al., Assessments on emergy and greenhouse gas emissions of internal combustion engine automobiles and electric automobiles in the USA, Journal of Environmental Sciences, https://doi.org/10.1016/j.jes.2019.11.017

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Table 3 e Results of total emergy for ICE automobiles. Item Raw materials extraction and processing

Manufacturing

Operation

Steel Steel (recycled) Iron Aluminum Magnesium Copper Lead Plastics Lubricants Glass Rubber Total Water Coal Natural Gas Diesel Gasoline Electricity (Coal)b Electricity (Natural Gas)b Electricity (Petroleum)b Electricity (Nuclear)b Electricity (Hydropower)b Electricity (Wind)b Electricity (Biomass)b Electricity (Solar)b Total Highway Gasoline Diesel Total

Total emergy a

Raw data

Unit

Transformity (sej/unit)

7.43E 2.48E 1.13E 1.86E 4.99E 2.99E 1.59E 1.51E 1.03E 4.22E 9.03E

þ þ þ þ þ þ þ þ þ þ þ

05 05 05 05 03 04 04 05 05 04 04

g g g g g g g g g g g

5.80E 1.45E 5.40E 6.44E 6.14E 2.08E 4.80E 1.25E 2.64E 2.16E 7.22E

þ þ þ þ þ þ þ þ þ þ þ

09 09 09 10 09 10 11 10 09 09 09a

1.57E 1.12E 1.31E 3.00E 1.10E 1.68E 1.86E 3.27E 1.09E 3.62E 3.07E 8.49E 4.88E

þ þ þ þ þ þ þ þ þ þ þ þ þ

00 09 11 06 03 09 09 07 09 08 08 07 07

mc J J J g J J J J J J J J

1.60E 8.17E 4.00E 1.21E 2.92E 2.87E 2.86E 6.78E 3.36E 1.12E 1.89E 4.44E 1.58E

þ þ þ þ þ þ þ þ þ þ þ þ þ

12 04 04 05 09 05 05 05 05 05 04 06 04

p-km g J

1.74E þ 114 2.92E þ 09 1.21E þ 05

3.31E þ 05c 1.28E þ 07 1.89E þ 11

Emergy (sej) 4.31E þ 15 3.59E þ 14 6.10E þ 14 1.20E þ 16 3.06E þ 13 6.23E þ 14 7.62E þ 15 1.88E þ 15 2.71E þ 14 9.11E þ 13 6.52E þ 14 2.84E þ 16 2.52E þ 12 9.17E þ 13 5.23E þ 15 3.63E þ 11 3.22E þ 12 4.81E þ 14 5.33E þ 14 2.22E þ 13 3.66E þ 14 4.06E þ 13 5.80E þ 12 3.77E þ 14 7.71E þ 11 7.15E þ 15 5.76E þ 16 3.73E þ 16 2.29E þ 16 1.18E þ 17 1.53E þ 17

Data source: https://pdfs.semanticscholar.org/a154/02ead027e6db733cfc024328cebe41dde711.pdf. Accessed December 12, 2018; bThe sectors percentages of electricity is the national average value. Data source: https://www.eia.gov/electricity/data/browser/. Accessed December 12, 2018; cThe mileage of the light vehicle during lifespan ¼ 11,514 (mi/year)  11.6 (year) ¼ 1,33,562.4 miles. Data source: https://www.energy.gov/ eere/vehicles/articles/fact-997-october-2-2017-average-age-cars-and-light-trucks-was-almost-12-years. Accessed December 12, 2018. https://www.fhwa.dot.gov/policyinformation/statistics/2016/Accessed December 12, 2018. Assuming that each vehicle has 1.59 passenger. Data source: https://www.energy.gov/eere/vehicles/articles/fotw-1040-july-30-2018-average-vehicle-occupancy-remains-unchanged-20092017. Accessed December 12, 2018.

contributed 4.31E þ 15 sej of emergy and accounted for 15.18% of the emergy from the raw material extraction and processing. As for electric automobiles, the graphite and the lithium were the second- and third-highest emergy raw materials for the life cycle of electric automobiles. Graphite normally serves as the negative electrode of a lithium-ion battery for an electric automobile (i.e., an anode) so that the lithium ions could be sent from the anode to the cathode (Lipu et al., 2018). Some studies indicate that a large emergy generated from lithium rely on the large amount of energy demanding inputs (Franzese et al., 2014; Jia et al., 2017; Puca et al., 2017). The emergy of lithium was 7.01E þ 15 sej, accounting for 10.95% of the total emergy in raw material extraction and processing of the electric automobiles. Up to date, few studies discussed the emergy-based sustainability assessment of graphite productions, even though graphite together with lithium are considered two of the most crucial components in lithium-ion batteries. In the present study, the graphite generated 2.19E þ 16 sej of emergy, accounting for as high as 34.2% of the emergy from the raw material extraction and processing. In addition, it is unexpected that the manufacturing processes contained

the least proportion of emergy. For the ICE automobiles and electric automobiles, the emergy of their manufacturing processes only accounted for 4.66% and 1.21% of total emergy (Fig. 4). This is mainly attributed to the fact that relatively less energy consumed in this process as compared to the raw material extraction and processing, as well as operation process. The operation processes contributed the highest proportion of emergy for both life cycle of the ICE automobiles and electric automobiles which accounted for 76.85% and 58.93% of their total emergy generation respectively (Table 4). The emergy indices between ICE automobiles and electric automobiles were further compared. In this study, the fraction renewable (FR ) of ICE automobiles and electric automobiles were 2.78E - 03 and 5.37E - 02 (Table 5). The faction renewable of electric automobiles was 19.3 times higher than that of the ICE automobiles. This indicates that there are more nonrenewable resources inputs during the life cycle of the ICE automobiles as compared with electric automobiles. It is interesting that a larger EYR value of ICE automobiles (1.78) was observed as compared to that of the electric automobiles (1.52), even though the ICE automobiles have a lower value of

Please cite this article as: Jing, R et al., Assessments on emergy and greenhouse gas emissions of internal combustion engine automobiles and electric automobiles in the USA, Journal of Environmental Sciences, https://doi.org/10.1016/j.jes.2019.11.017

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Table 4 e Results of total emergy for electric automobiles. Item Raw materials extraction and processing

Manufacturing

Operation

Steel Steel (recycled) Iron Aluminum Magnesium Copper Lead Plastics Lubricants Glass Rubber Lithium Graphite Total Water Coal Natural Gas Diesel Gasoline Light fuel oil Electricity (Coal)d Electricity (Natural Gas)d Electricity (Petroleum)d Electricity (Nuclear)d Electricity (Hydropower)d Electricity (Wind)d Electricity (Biomass)d Electricity (Solar)d Total Highway Electricity (Coal)e Electricity (Natural Gas)e Electricity (Petroleum)e Electricity (Nuclear)e Electricity (Hydropower)e Electricity (Wind)e Electricity (Biomass)e Electricity (Solar)e Total

Total emergy a

Raw data

Unit

Transformity (sej/unit)

1.13E 7.68E 1.08E 3.85E 0.00E 2.95E 0.00E 2.10E 1.23E 4.23E 3.31E 7.56E 1.00E

þ þ þ þ þ þ þ þ þ þ þ þ þ

04 05 04 05 00 05 00 05 03 04 04 03 05

g g g g g g g g g g g g g

5.80E 1.45E 5.40E 6.44E 6.14E 2.08E 4.80E 1.25E 2.64E 2.16E 7.22E 9.27E 2.18E

þ þ þ þ þ þ þ þ þ þ þ þ þ

09 09 09 10 09 10 11 10 09 09 09 11 11a

3.22E 0.00E 2.22E 0.00E 0.00E 6.30E 2.34E 2.60E 4.57E 1.52E 5.06E 4.29E 1.19E 6.81E

þ þ þ þ þ þ þ þ þ þ þ þ þ þ

00 00 09 00 00 07b 09 09 07 09 08 08 08 07

mc J J J g J J J J J J J J J

1.60E 8.17E 4.00E 1.21E 2.92E 6.52E 2.87E 2.86E 6.78E 3.36E 1.12E 1.89E 4.44E 1.58E

þ þ þ þ þ þ þ þ þ þ þ þ þ þ

12 04 04 05 09 04c 05 05 05 05 05 04 06 04

3.31E 3.69E 3.47E 5.77E 2.31E 8.65E 8.08E 1.85E 1.50E

þ þ þ þ þ þ þ þ þ

05 10 10 08 10 09 09 09 09

p-km J J J J J J J J

1.74E 2.87E 2.86E 6.78E 3.36E 1.12E 1.89E 4.44E 1.58E

þ þ þ þ þ þ þ þ þ

11 05 05 05 05 05 04 06 04

Emergy (sej) 6.57E þ 13 1.11E þ 15 5.85E þ 13 2.48E þ 16 0.00E þ 00 6.14E þ 15 0.00E þ 00 2.63E þ 15 3.25E þ 12 9.14E þ 13 2.39E þ 14 7.01E þ 15 2.19E þ 16 6.40E þ 16 5.15E þ 12 0.00E þ 00 8.88E þ 13 0.00E þ 00 0.00E þ 00 4.11E þ 12 6.72E þ 14 7.45E þ 14 3.10E þ 13 5.12E þ 14 5.67E þ 13 8.11E þ 12 5.27E þ 14 1.08E þ 12 2.65E þ 15 5.76E þ 16 1.06E þ 16 9.93E þ 15 3.91E þ 14 7.75E þ 15 9.69E þ 14 1.53E þ 14 8.20E þ 15 2.37E þ 13 9.56E þ 16 1.62E þ 17

Data source: https://www.researchgate.net/publication/329252628_Emergy_accounting_on_natural_graphite_and_spherical_graphite. Accessed December 12, 2018; bData source: Life Cycle Assessment of Battery Electric Vehicles and Concept Cars; cData source: The solar transformity of petroleum fuels (Bastianoni, 2009); dThe sectors percentages of electricity is the national average value. Data source: https:// www.eia.gov/electricity/data/browser/. Accessed December 12, 2018; eEnergy consumption during lifespan: 1,33,562.4 (km)  0.24 (kwh/ km) ¼ 32,054.976 (kwh). Data source: life-cycle impacts of tesla models 85 and volkswagen passat (Klemola and Karvonen, 2016).

the total emergy. A higher EYR value of the ICE automobiles than that of the electric automobiles indicates a high ability/ efficiency in converting manufacturing resources into the final products (Arbault et al., 2013). The ELR of ICE automobiles was 359 which was 23.4 times higher than that of electric automobiles (15.3). A large ELR indicated a relatively small renewable energy during over the life cycle of the ICE automobiles as compare purchased energy and non-renewable energy. Therefore, the life cycle of the ICE automobiles is not sustainable process resulting a negative environmental impact. This is mainly due to the fact that the manufacturing process and operation process of the ICE automobiles are highly dependent on non-renewable energy such as gasoline and diesel (Yazdanie et al., 2014). Moreover, the life cycle of electric automobiles has more technology-intensive processes

with cleaner energy and resources, which translates into a lower ELR. Last but not the least, the ESI of ICE automobiles and electric automobiles are 4.97E - 03 and 9.93E - 02. A higher ESI of the electric automobiles obtained in our study evidenced its environmental sustainability over the life cycle.

2.3. Integrated analysis of GHG emissions and emergy generated from ICE automobiles and electric automobiles In this study, the total GHG emissions of the life cycle of the ICE automobiles and electric automobiles are mainly energyrelated GHG emissions, which consist of the GHG emissions from the fuel combustion and electricity consumption. The non-energy-related GHG emissions, mainly encompass the chemical reactions, accounted for an insignificant proportion

Please cite this article as: Jing, R et al., Assessments on emergy and greenhouse gas emissions of internal combustion engine automobiles and electric automobiles in the USA, Journal of Environmental Sciences, https://doi.org/10.1016/j.jes.2019.11.017

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Fig. 4 e Distribution of each process to total emergy for ICE automobiles and electric automobiles.

of the total GHG emissions in this study. Jing et al. (2019) reported that less than 2% of the GHG emissions were derived from the chemical reactions such as limestone decomposition and iron oxide reduction. Therefore, the total GHG emissions from the raw materials of the ICE automobiles and electric automobiles are mainly driven by the consumed energy thereby resulting in large emission factors. Most of the highGHG emission-embodied raw materials in the current study are energy-intensive (e.g., steel, lead, copper, and lithium) with their emission factors of 2.89, 3.37, 3.81, and 5.30 kg CO2e/kg, respectively. However, the GHG emissions were only calculated based on energy inputs which are accessible resources (Buonocore et al., 2015). While emergy could offer the additionally comprehensive donor-side assessment to provide an estimate of the total environmental support (Raugei et al., 2014; Buonocore et al., 2015). The relationship of these two approaches is then complementary from this point of view. Nine raw materials including steel, recycled steel, lubricants, glass, magnesium, iron, rubber, plastic and copper have relatively low emergy transformities which ranged from 1.45E þ 09 to 2.08E þ 10 sej/g. However, four raw materials (i.e.,

aluminum, lead, lithium, and graphite) have larger emergy transformities (6.44E þ 10 sej/g to 9.27E þ 10 sej/g). It should be noted that these four raw materials besides the lithium (5.30 kg CO2/kg) have smaller GHG emission factors especially for the aluminum (1.81 kg CO2/kg) and graphite (0.33 kg CO2/ kg). As above mentioned, the total GHG emissions of the life cycle of the ICE automobiles are much higher (around 320 times) than that of the electric automobiles. However, interesting results were observed that comparable total emergy of the ICE automobiles and electric automobiles have been calculated which were 1.54E þ 17 and 2.20E þ 17 sej, respectively. Relatively comparable total emergy of two different types of automobiles against the acknowledge of GHG emissions calculations and derivations, since the emergy was calculated based on the local input flows to the entire life cycles of two different automobiles by converting mass and energy flows into the total emergy. Therefore, one possible reason of the obtained comparable total emergy is attributed from the considerations of other local inputs during the production process in addition to the energy inputs such as the

Table 5 e Emergy indices for ICE and electric automobiles.

ICE automobiles Electric automobiles a

R (sej)

N (sej)

F (sej)

Y (sej)

FR

EYRa

ELRb

ESIc

4.27E þ 14 9.94E þ 15

6.69E þ 16 3.07E þ 16

8.60E þ 16 1.22E þ 17

1.53E þ 17 1.85E þ 17

2.78E - 03 5.37E - 02

1.78E þ 00 1.52E þ 00

3.59E þ 02 1.53E þ 01

4.97E - 03 9.93E - 02

EYR refers to emergy yield ratio; bELR refers to environmental loading ratio; cESI refers to emergy sustainability index.

Please cite this article as: Jing, R et al., Assessments on emergy and greenhouse gas emissions of internal combustion engine automobiles and electric automobiles in the USA, Journal of Environmental Sciences, https://doi.org/10.1016/j.jes.2019.11.017

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manufacturing resources Based on the above discussion, an emergy analysis could be an extension of the traditional GHG emission calculation via the GHG emission evaluation or the life cycle assessment.

2.4. Potential strategies for reducing GHG emissions and emergy in life cycle of ICE automobiles and electric automobiles On the basis of the above discussion in this study, potential strategies could be applied to reduce the energy consumption and GHG emissions during the entire life cycle of the ICE automobiles and electric automobiles. For the ICE automobiles, the highest GHG emissions were generated during the operation process which accounted for 85.06% of the total GHG emissions. Waste heat recovery technologies such as thermoelectric generators, rankine cycle and organic rankine cycle systems have rapid developments to overcome the challenging GHG emissions in recent years (Karvonen et al., 2016). Fuel injection could be a useful technology to improve the combustion efficiency of engine of the ICE automobiles (Kume et al., 1996). In addition, the hybrid-electric vehicle (HEV) was introduced in the year of 1999 and has also been considered to be a promising energysaving solution (Sovacool and Hirsh, 2009). A life cycle analysis showed that the plug-in hybrid vehicles (PHEV) consumed 40%e 60% less gasoline than the conventional ICE automobiles and it can reduce the GHG emissions by 30%e60% (Elgowainy et al., 2016). Therefore, the HEV and PHEV should be promising energy-saving alternatives for the ICE automobiles. On the other hand, the lightweight materials is another way to reduce the energy consumption and environmental impacts (Dattilo et al., 2017; Del Pero et al., 2017; Mayyas et al., 2017; Zanchi et al., 2018; Delogu et al., 2018a). The light vehicle vehicles with secondary mass reductions can reduce 16% of GHG emissions (Kim and Wallington, 2013; Lewis et al., 2014). According to Koffler's study, lightweighting materials would reduce the emission of greenhouse gases by the equivalent of combusting more than 10.2 million liters (2.7 million gallons) of gasoline over the life of the vehicles (Koffler, 2014). From 1995 to 2014, the usage of highand medium-strength steel has increased by 325 lb per ICE automobile and this can help manufacturers to keep structural integrity and reduce the vehicle's weight (Davis et al., 2016). Moreover, increasing the use of recycled materials could also reduce the total emergy during the life cycle manufacturing instead of using new materials since the energy consumption of the recycled material is normally lower than the new materials. For instance, the energy consumption of the recycled steel are 26% of the energy that be needed for steel (Chan et al., 2015). However, the current life cycle of the ICE automobiles is still significantly dependent on the non-renewable resources, leading to negative impacts on the environment. Last but not least, import of the ICE automobiles could also impact the total emergy, since the emergy transformities of the imported ICE automobiles are calculated based on the different manufacturing conditions from other countries. Even though the electric automobiles have lower GHG emissions than that of the ICE automobiles, there is still room for GHG emission reduction. As abovementioned, using recycled materials with lower GHG emission factors could reduce the emergy. In addition, copper has a relatively high GHG

11

emission factor (3.81 kg CO2-e/kg) and it usually the raw materials of the essential pars such as copper-and-brass automotive radiators. According to Table 1, copper accounted for 35.99% of the electric automobiles. This is mainly attributed the fact that the implementation of the electrical distribution systems in electric automobiles (Sortomme et al., 2011). A reliable high conductivity of copper allowing it has an extensive application such as motors, alternators, actuators and electrical chokes, and the wiring harness (Qu et al., 2011). Therefore, using alternative materials for replacing copper and the steel with the recycled steel can help to reduce GHG emission from the raw material extraction and processing. Implementation of composite material or alternative materials for the battery such as lead and lithium could reduce both emergy and GHG emissions. Last but not least, fuel cell vehicles could be a technology that reduce GHG emissions (Alaswad et al., 2016). Fuel cells can converts chemical potential energy into electrical energy using hydrogen gas (H2) and oxygen gas (O2) as fuel (O'hayre et al., 2016). As a result, the vehicles that use fuel cell can be considered as zero-emission. If hydrogen is completely produced by renewable energy sources (such as hydropower, wind power and solar power), the hydrogen fuel cells would be more environmentally benign (Dincer and Acar, 2015).

3.

Conclusions

In the present study, the total GHG emissions from the life cycle of the ICE automobiles and electric automobiles are 4.48E þ 07 and 1.40E þ 05 kg CO2-e, in which the hotspot areas of the GHG emissions from ICE automobiles and electric automobiles were operation phase and manufacturing process, respectively. Interesting results were observed that total emergy of the ICE automobiles and electric automobiles were comparable. The operation processes contributed the highest proportion of emergy for both life cycle of the ICE automobiles and electric automobiles which accounted for 76.85% and 58.93% of their total emergy generation respectively. Application of fuel injection, a hybrid-electric vehicle, and increasing the use of recycled materials and lightweight materials can reduce the energy consumption and GHG emissions in the life cycle of the ICE automobiles and electric automobiles. The assessment method proposed herein could be helpful in providing valuable policy insights to those decision-makers, so that more appropriate policies toward sustainable automobile industry can be raised.

Acknowledgments This work was financially supported by National Natural Science Foundation for Young Scientists of China (Grant No. 51608531). Q2

Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.jes.2019.11.017.

Please cite this article as: Jing, R et al., Assessments on emergy and greenhouse gas emissions of internal combustion engine automobiles and electric automobiles in the USA, Journal of Environmental Sciences, https://doi.org/10.1016/j.jes.2019.11.017

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Uncited references United States Department of Transportation, 2018

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references

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