How the Numbers were Calculated
Conventional Gasoline (Internal Combustion Engine) Cars
Methane Emissions (in units of pounds of methane gas per mile): estimates of methane gas emissions associated with cars operated by internal combustion engines (ICE) burning conventional gasoline are based on EPA estimates of 3 grams of methane per mmBtu and 0.125 mmBtu per gallon of gasoline or 0.375 grams per gallon of gasoline. For a typical passenger car in the U.S. averaging 23.4 miles to the gallon, this leads to a net methane emissions factor of 0.016 grams of methane/mile or 0.0000353 (3.53 X 10-5) pounds of methane gas/mile.
Nitrous Oxide Emissions (in units of pounds of nitrous oxide per mile): estimates of nitrous oxide emissions associated with ICE cars burning conventional gasoline are based on EPA estimates of 0.0036 grams/mile or 7.94 X 10-6 pounds/mile for passenger vehicles produced in 2009 or later.
Sulfur Dioxide Emissions: sulfur dioxide emissions associated with ICE cars burning conventional gasoline are negligible.
Greenhouse Gas Emissions (in units of pounds of carbon dioxide equivalent gases per mile): estimates for greenhouse gas emissions associated with ICE cars burning conventional gasoline are based on EPA estimates of 19.6 pounds/gallon and an average fuel efficiency of 23.4 miles to the gallon for passenger cars. Using these numbers, net emissions of greenhouse gases are approximately 0.84 pounds/mile.
Arsenic, Lead, and Mercury (in units of billionths of pounds per mile): emissions for heavy metals (arsenic, lead, and mercury) associated with ICE cars burning conventional gasoline are based on average emission factors determined by Pulles et al. (2012) of 0.3 micrograms per kilogram of gasoline for arsenic; 1.5 micrograms per kilogram of gasoline for lead; and 8.4 micrograms per kilogram of gasoline for mercury. Using these numbers, accounting for gas mileage of 23.4 miles to the gallon (mpg) for a typical passenger car, and assuming a gallon of gasoline weighs about 6.3 pounds, the emissions factors for ICE cars are approximately:
Nitrous Oxide Emissions (in units of pounds of nitrous oxide per mile): estimates of nitrous oxide emissions associated with ICE cars burning conventional gasoline are based on EPA estimates of 0.0036 grams/mile or 7.94 X 10-6 pounds/mile for passenger vehicles produced in 2009 or later.
Sulfur Dioxide Emissions: sulfur dioxide emissions associated with ICE cars burning conventional gasoline are negligible.
Greenhouse Gas Emissions (in units of pounds of carbon dioxide equivalent gases per mile): estimates for greenhouse gas emissions associated with ICE cars burning conventional gasoline are based on EPA estimates of 19.6 pounds/gallon and an average fuel efficiency of 23.4 miles to the gallon for passenger cars. Using these numbers, net emissions of greenhouse gases are approximately 0.84 pounds/mile.
Arsenic, Lead, and Mercury (in units of billionths of pounds per mile): emissions for heavy metals (arsenic, lead, and mercury) associated with ICE cars burning conventional gasoline are based on average emission factors determined by Pulles et al. (2012) of 0.3 micrograms per kilogram of gasoline for arsenic; 1.5 micrograms per kilogram of gasoline for lead; and 8.4 micrograms per kilogram of gasoline for mercury. Using these numbers, accounting for gas mileage of 23.4 miles to the gallon (mpg) for a typical passenger car, and assuming a gallon of gasoline weighs about 6.3 pounds, the emissions factors for ICE cars are approximately:
- 0.071 billionths of pounds (0.071 X 10-9 pounds) per mile for arsenic
- 0.430 billionths of pounds (0.430 X 10-9 pounds) per mile for lead
- 1.690 billionths of pounds (1.690 X 10-9 pounds) per mile for mercury
Battery Electric Vehicle (BEV) Cars
Efficiencies for electric vehicles are based on averages provided by the U.S. Department of Energy and are given in units of kWh per 100 miles of driving and are estimated as an average among multiple models of BMW i3 (29 kWh/100 miles); the Nissan Leaf (30 kWh/100 miles); and the Tesla Model S (33.5 kWh/100 miles).
All estimates for BEV emissions are made by dividing the total emissions for a particular state in a year (based on 2014 data) by the total annual MWh generated in that state, multiplying by the efficiency of a particular BEV, and adjusting the units to pounds per mile (for methane, nitrous oxides, sulfur dioxide, and greenhouse gases) and to billionths of pounds per mile (for arsenic, lead, and mercury). Because of uncertainties in the amount of water that hydroelectric energy actually consumes, water usage is estimated from non-hydroelectric sources.
Emissions for a particular driver in a particular zip code may be different due to the fact that the electricity that a state generates is not the same as that which it consumes. Some states purchase electricity from adjacent states and some states sell electricity to adjacent states. Other estimates of emissions as a result of operating a BEV by the Union of Concerned Scientists are based on power grids (rather than individual states). Both estimates provide a reasonable comparison of how a state performs relative to other states, but neither method is completely accurate.
All estimates for BEV emissions are made by dividing the total emissions for a particular state in a year (based on 2014 data) by the total annual MWh generated in that state, multiplying by the efficiency of a particular BEV, and adjusting the units to pounds per mile (for methane, nitrous oxides, sulfur dioxide, and greenhouse gases) and to billionths of pounds per mile (for arsenic, lead, and mercury). Because of uncertainties in the amount of water that hydroelectric energy actually consumes, water usage is estimated from non-hydroelectric sources.
Emissions for a particular driver in a particular zip code may be different due to the fact that the electricity that a state generates is not the same as that which it consumes. Some states purchase electricity from adjacent states and some states sell electricity to adjacent states. Other estimates of emissions as a result of operating a BEV by the Union of Concerned Scientists are based on power grids (rather than individual states). Both estimates provide a reasonable comparison of how a state performs relative to other states, but neither method is completely accurate.
Resources Used:
Pulles, Tinus & Denier van der Gon, Hugo & Appelman, Wilfred & Verheul, Marc. (2012). Emission factors for heavy metals from diesel and petrol used in European vehicles. Atmospheric Environment. 61. 641–651. 10.1016/j.atmosenv.2012.07.022.
U.S. Department of Energy (2017). www.fueleconomy.gov
U.S. Department of Energy (2017). Alternative Fuels Data Center
U.S. Environmental Protection Agency (2017). Greenhouse Gas Equivalencies Calculator
U.S. Environmental Protection Agency (2012). Emissions Factors for Greenhouse Gas Inventories
U.S. Environmental Protection Agency (2008). Average Annual Emissions and Fuel Consumption for Gasoline-Fueled Passenger Cars and Light Trucks Emission Facts.
U.S. Department of Energy (2017). www.fueleconomy.gov
U.S. Department of Energy (2017). Alternative Fuels Data Center
U.S. Environmental Protection Agency (2017). Greenhouse Gas Equivalencies Calculator
U.S. Environmental Protection Agency (2012). Emissions Factors for Greenhouse Gas Inventories
U.S. Environmental Protection Agency (2008). Average Annual Emissions and Fuel Consumption for Gasoline-Fueled Passenger Cars and Light Trucks Emission Facts.