A Comparison of Carbon Dioxide Emissions from Electric Vehicles to Emissions from Internal Combustion Vehicles

A Comparison of Carbon Dioxide Emissions from Electric Vehicles to Emissions from Internal Combustion Vehicles

Daniel J. Berger *† and Andrew D. Jorgensen ‡

† Department of Chemistry and Physics, Bluffton University, Bluffton, Ohio 45814, United States

‡ Department of Chemistry and Biochemistry, University of Toledo, Toledo, Ohio 43606, United States

J. Chem. Educ., Article ASAP

DOI: 10.1021/acs.jchemed.5b00125

Publication Date (Web): April 28, 2015

10 pages

Copyright © 2015 The American Chemical Society and Division of Chemical Education, Inc.

Supporting Information:

6 pages of sample worksheets, survey form, spreadsheet of data from various sources (US EPA, US DOE, IEA, etc.)

ABSTRACT: http://pubs.acs.org/doi/abs/10.1021/acs.jchemed.5b00125

This article describes a student activity where the carbon dioxide emissions of two categories of vehicles are quantitatively compared through calculations using publicly available data.  The two categories of vehicles are internal combustion vehicles (ICV’s) and electric vehicles (EV’s, including plug-in hybrid vehicles).  The authors note that this exercise is appropriate for students in introductory engineering, chemistry, or environmental science, whether for majors or non-majors.

The authors provide suggestions on how this material can be used in different courses:

·         In a General Chemistry class, students can be asked to carry out thermodynamic calculations for the combustion of methane as a model for natural gas, of octane as a model for gasoline, and carbon graphite as a model for coal.  These calculations will demonstrate to students the greater amount of energy produced using methane combustion per mole of carbon dioxide produced, “which is the chemical basis for the value of natural gas in generating electricity”. This can be coupled with the worksheets provided by the instructor in the supporting information (see below for a description).

·         In the supporting information (5 pages), the authors provide sample worksheets they used for a chemistry for liberal arts major course.  In these worksheets, the data have been analyzed and presented in the form of graphs of grams carbon dioxide emissions versus curb weight of different types of cars (ICV – gas, ICV – diesel, and HEV compared to the average US EV emissions and disaggregated data on EV emissions using coal or using natural gas for electricity generation).  The other graph compares the mg of carbon dioxide emission per pound of curb weight for gasoline vehicles, diesel vehicles, hybrid vehicles, and EV vehicles from a sampling of states (with varying sources for electricity generation).  The students are asked to analyze the graphs and to write about how their interpretations may affect what they think about electric vehicles (in Part I, students are asked to write about their ideas regarding electric vehicles without having seen the data presented later).

·         For more advanced students (like those in an environmental chemistry class) can use the publicly available data (given by the authors in the form of a spreadsheet in the supporting information) and convert them into similar graphs like the ones provided by the authors in the student worksheets for analysis.

In the Data and Calculations section, the authors describe how they used publicly available data from the US EPA, US DOE, International Energy Agency, and the Edmunds automobile database and individual car manufacturers’ websites.  They also detailed some assumptions they have to make to relate certain databases to come up with their own calculations, e.g. the EPA reports no CO2 emissions for EV’s (only for gasoline and PHEV’s) and so they had to combine information on kilowatt-hours consumed per 100 miles drive and the IEA’s data on CO2 emissions per kilowatt-hour. They also had to do some back-calculations for the EPA-reported emissions for PHEV’s.

Some notable items from the Results and Analysis Section: The authors presented two graphs:

·         Grams carbon dioxide emissions versus curb weight of different types of cars (ICV – gas, ICV – diesel, and HEV compared to the average US EV emissions and disaggregated data on EV emissions using coal or using natural gas for electricity generation).  (figure 1)

·         mg of carbon dioxide emission per pound of curb weight for gasoline vehicles, diesel vehicles, hybrid vehicles, and EV vehicles from a sampling of states (with varying sources for electricity generation).  (Figure 2)

·         Their calculations on the average showed that EV’s release 30% less carbon dioxide than comparable ICV-gasoline or ICV-diesel. (Figure 2)

·         The highest performing HEV’s have emissions comparable to EV’s using the current mix of electrical generation.

·         EV’s charged using electricity from mostly coal-powered plants have about the same carbon dioxide emissions as ICV-diesels.  Powering EV’s using electricity generated from natural gas substantially lowers the CO2 emissions. (Figure 2).  The mix generated in the state (given in one of the spreadsheets) may not be the same as the mix used in the state due to import and export but the authors assume that these are good approximations. They also only took into account sources that generate greater than 1 MW and assumed that electricity generated from biomass like wood have net zero emissions.

·         Although these calculations do not include carbon dioxide emissions from manufacturing, the authors used the assumption that EV production has 25-75% more CO2 emissions than ICV’s when normalized for total number of miles driven before being scrapped.

The authors also provided a summary of valid survey responses from 36 students (from a liberal arts course).  See article for details but the overall interpretation of the authors is, “Clearly the assignment achieved its primary purpose of introducing an aspect of sustainability into an introductory level course”.