This page describes the calculations used to convert greenhouse gas emission numbers into different types of equivalent units. (see also here) .

Electricity use (kilowatt-hours)

The Clean Energy Equivalencies Calculator uses an eGRID (Emissions & Generation Resource Integrated Database) non-baseload national average emissions rate when converting kilowatt-hours into avoided units of carbon dioxide emissions.

Calculation

7.12 x 10^-4 metric tons CO₂ / kWh
(eGRID 2005 Non-Baseload National Average Emissions Rate)

Note: Individual non-baseload subregion emissions rates are also available on the eGRID Web site.

Sources

• EPA's Emissions & Generation Resource Integrated Database (eGRID 2005)

Passenger vehicles per year

Passenger vehicles are defined as 2-axle 4-tire vehicles, including passenger cars, vans, pickup trucks, and sport/utility vehicles.

In 2005, the weighted average combined fuel economy of cars and light trucks combined was 19.7 miles per gallon (FHWA 2006). The average vehicle miles traveled in 2005 was 11,856 miles per year.

In 2005, the ratio of carbon dioxide emissions to total emissions (including carbon dioxide, methane, and nitrous oxide, all expressed as carbon dioxide equivalents) for passenger vehicles was 0.971 (EPA 2007).

The amount of carbon dioxide emitted per gallon of motor gasoline burned is 8.81*10^-3 metric tons, as calculated in the "Gallons of gasoline consumed" section.

To determine annual GHG emissions per passenger vehicle, the following methodology was used: vehicle miles traveled (VMT) was divided by average gas mileage to determine gallons of gasoline consumed per vehicle per year. Gallons of gasoline consumed was multiplied by carbon dioxide per gallon of gasoline to determine carbon dioxide emitted per vehicle per year. Carbon dioxide emissions were then divided by the ratio of carbon dioxide emissions to total vehicle greenhouse gas emissions to account for vehicle methane and nitrous oxide emissions.

Calculation

Note: Due to rounding, performing the calculations given in the equations below may not return the exact results shown.

8.81*10^-3 metric tons CO₂/gallon gasoline * 11,856 VMT _{car/truck average} * 1/19.7 miles per gallon _{car/truck average} * 1 CO₂, CH₄, and N₂O/0.971 CO₂ = 5.46 metric tons CO₂E /vehicle/year

Sources

• EPA (2007). Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2005. U.S. Environmental Protection Agency, Washington, DC. USEPA, Table 3-7 (p.3-9) (PDF) (59 pp, 1.47MB, About PDF) and Table A-108 (p.A-127) (PDF) (169 pp, 1.27MB, About PDF)
• FHWA (2006). Highway Statistics 2005. Office of Highway Policy Information, Federal Highway Administration. Table VM-1.

Gallons of gasoline consumed

Average heat content of conventional motor gasoline is 5.22 million btu per barrel (EPA 2007). Average carbon coefficient of motor gasoline is 19.33 kg carbon per million btu (EPA 2007). Fraction oxidized to CO₂ is 100 percent (IPCC 2006).

Carbon dioxide emissions per barrel of gasoline were determined by multiplying heat content times the carbon coefficient time the fraction oxidized times the ratio of the molecular weight ratio of carbon dioxide to carbon (44/12). A barrel equals 42 gallons.

Calculation

Note: Due to rounding, performing the calculations given in the equations below may not return the exact results shown.

5.22 mmbtu/barrel * 19.33 kg C/mmbtu * 1 barrel/42 gallons * 44 g CO₂/12 g C * 1 metric ton/1000 kg = 8.81*10^-3 metric tons CO₂/gallon

Sources

• EPA (2007). Inventory of U.S. Greenhouse Gas Emissions and Sinks: Fast Facts 1990-2005. Conversion Factors to Energy Units (Heat Equivalents) Heat Contents and Carbon Content Coefficients of Various Fuel Types. U.S. Environmental Protection Agency, Washington, DC. USEPA #430-R-07-002 (PDF) (2 pp, 216K, About PDF).
• IPCC (2006). 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Intergovernmental Panel on Climate Change, Geneva, Switzerland.

Therms of natural gas

Average heat content of natural gas is 0.1 mmbtus per therm (EPA 2007). Average carbon coefficient of natural gas is 14.47 kg carbon per million btu (EPA 2007). Fraction oxidized to CO₂ is 100 percent (IPCC 2006).

Carbon dioxide emissions per therm were determined by multiplying heat content times the carbon coefficient time the fraction oxidized times the ratio of the molecular weight ratio of carbon dioxide to carbon (44/12).

Calculation

Note: Due to rounding, performing the calculations given in the equations below may not return the exact results shown.

0.1 mmbtu/1 therm * 14.47 kg C/mmbtu * 44 g CO₂/12 g C * 1 metric ton/1000 kg = 0.005 metric tons CO₂/therm

Sources

• EPA (2007). Inventory of U.S. Greenhouse Gas Emissions and Sinks: Fast Facts 1990-2005. Conversion Factors to Energy Units (Heat Equivalents) Heat Contents and Carbon Content Coefficients of Various Fuel Types. U.S. Environmental Protection Agency, Washington, DC. USEPA #430-R-07-002 (PDF) (2 pp, 216K, About PDF).
• IPCC (2006). 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Intergovernmental Panel on Climate Change, Geneva, Switzerland.
  

Barrels of oil consumed

Average heat content of crude oil is 5.80 million btu per barrel (EPA 2007). Average carbon coefficient of crude oil is 20.33 kg carbon per million btu (EPA 2007). Fraction oxidized is 100 percent (IPCC 2006).

Carbon dioxide emissions per barrel of crude oil were determined by multiplying heat content times the carbon coefficient times the fraction oxidized times the ratio of the molecular weight of carbon dioxide to that of carbon (44/12).

Calculation

Note: Due to rounding, performing the calculations given in the equations below may not return the exact results shown.

5.80 mmbtu/barrel * 20.33 kg C/mmbtu * 44 g CO₂/12 g C * 1 metric ton/1000 kg = 0.43 metric tons CO₂/barrel

Sources

• EPA (2007). Inventory of U.S. Greenhouse Gas Emissions and Sinks: Fast Facts 1990-2005. Conversion Factors to Energy Units (Heat Equivalents) Heat Contents and Carbon Content Coefficients of Various Fuel Types. U.S. Environmental Protection Agency, Washington, DC. USEPA #430-R-07-002 (PDF) (2 pp, 216K, About PDF).
• IPCC (2006). 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Intergovernmental Panel on Climate Change, Geneva, Switzerland.

Tanker trucks filled with gasoline

Average heat content of conventional motor gasoline is 5.22 million btu per barrel (EPA 2007). Average carbon coefficient of motor gasoline is 19.33 kg carbon per million btu (EPA 2007). Fraction oxidized to CO₂ is 100 percent (IPCC 2006).

Carbon dioxide emissions per barrel of gasoline were determined by multiplying heat content times the carbon coefficient time the fraction oxidized times the ratio of the molecular weight ratio of carbon dioxide to carbon (44/12). A barrel equals 42 gallons. A typical gasoline tanker trunk contains 8,500 gallons.

Calculation

Note: Due to rounding, performing the calculations given in the equations below may not return the exact results shown.

Sources

• EPA (2007). Inventory of U.S. Greenhouse Gas Emissions and Sinks: Fast Facts 1990-2005. Conversion Factors to Energy Units (Heat Equivalents) Heat Contents and Carbon Content Coefficients of Various Fuel Types. U.S. Environmental Protection Agency, Washington, DC. USEPA #430-R-07-002 (PDF) (2 pp, 216K, About PDF).
• IPCC (2006). 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Intergovernmental Panel on Climate Change, Geneva, Switzerland.

Home electricity use

In 2001, there were 107 million homes in the United States; of those, 73.7 million were single-family homes* (EIA, 2003). On average, each single-family home consumed 11,965 kWh of delivered electricity (EIA 2003). The national average carbon dioxide output rate for electricity in 2000 was 1,392 lbs CO₂ per megawatt-hour (EPA 2003).

Annual single-family home electricity consumption was multiplied by the carbon dioxide emission rate (per unit of electricity delivered) to determine annual carbon dioxide emissions per home.

Calculation

Note: Due to rounding, performing the calculations given in the equations below may not return the exact results shown.

11,965 kWh per home * 1,392 lbs CO₂ per megawatt-hour delivered * 1 mWh/1000 kWh * 1 metric ton/2204.6 lb = 7.55 metric tons CO₂/home.

*A single-family home is defined in the U.S. Department of Energy’s Residential Energy Consumption Survey as follows: A housing unit, detached or attached, that provides living space for one home or family. Attached houses are considered single-family houses as long as they are not divided into more than one housing unit and they have independent outside entrance. A single-family house is contained within walls extending from the basement (or the ground floor, if there is no basement) to the roof. A mobile home with one or more rooms added is classified as a single-family home. Townhouses, rowhouses, and duplexes are considered single-family attached housing units, as long as there is no home living above another one within the walls extending from the basement to the roof to separate the units.

Sources

• EIA (2003). A Look at Residential Energy Consumption in 2001. Table CE1-4c, Total Energy Consumption in U.S. Households by Type of Housing Unit, 2001, Physical Units of Total Consumption per Household, Fuels Used (PDF) (2 pp, 12K, About PDF).
• EPA (2003). eGRID 2006 version 2.01. U.S. Environmental Protection Agency, Washington, DC.

Home energy use

In 2001, there were 107 million homes in the United States; of those, 73.7 million were single-family homes* (EIA, 2003). On average, each single-family home consumed 11,965 kWh of delivered electricity, 52,429 cubic feet of natural gas, 57.3 gallons of fuel oil, 46.6 gallons of liquid petroleum gas, and 2.6 gallons of kerosene. (EIA 2003).

The national average carbon dioxide output rate for electricity in 2000 was 1,392 lbs CO₂ per megawatt-hour (EPA 2003).

The average carbon dioxide coefficient of natural gas is 0.0546 kg CO₂ per cubic foot (EPA 2007). Fraction oxidized to CO₂ is 100 percent (IPCC 2006).

The average carbon dioxide coefficient of distillate fuel oil is 462.1 kg CO₂ per 42-gallon barrel (EPA 2007a). Fraction oxidized to CO₂ is 100 percent (IPCC 2006).

The average carbon dioxide coefficient of liquefied petroleum gases is 231.9 kg CO₂ per 42-gallon barrel (EPA 2007). Fraction oxidized is 100 percent (IPCC 2006).

The average carbon dioxide coefficient of kerosene is 410.0 kg CO₂ per 42-gallon barrel (EPA 2007). Fraction oxidized to CO₂ is 100 percent (IPCC 2006).

Total single-family home electricity, natural gas, distillate fuel oil, and liquefied petroleum gas consumption figures were converted from their various units to metric tons of CO₂ and added together to obtain total CO₂ emissions per home.

Calculation

Note: Due to rounding, performing the calculations given in the equations below may not return the exact results shown.

*A single-family home is defined in the U.S. Department of Energy’s Residential Energy Consumption Survey as follows: A housing unit, detached or attached, that provides living space for one home or family. Attached houses are considered single-family houses as long as they are not divided into more than one housing unit and they have independent outside entrance. A single-family house is contained within walls extending from the basement (or the ground floor, if there is no basement) to the roof. A mobile home with one or more rooms added is classified as a single-family home. Townhouses, rowhouses, and duplexes are considered single-family attached housing units, as long as there is no home living above another one within the walls extending from the basement to the roof to separate the units.

Sources

• EIA (2003). A Look at Residential Energy Consumption in 2001. Table CE1-4c, Total Energy Consumption in U.S. Households by Type of Housing Unit, 2001, Physical Units of Total Consumption per Household, Fuels Used (PDF) (2 pp, 12K, About PDF). Per-home averages were obtained by dividing the physical units of total consumption for each fuel used by the total number of single-family homes.
• EPA (2003). eGRID 2006 version 2.01. U.S. Environmental Protection Agency, Washington, DC.
• EPA (2007). Inventory of U.S. Greenhouse Gas Emissions and Sinks: Fast Facts 1990-2005. Conversion Factors to Energy Units (Heat Equivalents) Heat Contents and Carbon Content Coefficients of Various Fuel Types. U.S. Environmental Protection Agency, Washington, DC. USEPA #430-R-07-002 (PDF) (2 pp, 216K, About PDF).
• IPCC (2006). 2006 IPCC Guidelines for National Greenhouse Gas Inventories. Intergovernmental Panel on Climate Change, Geneva, Switzerland.

Number of tree seedlings grown for 10 years

A medium growth coniferous tree, planted in an urban setting and allowed to grow for 10 years, sequesters 23.2 lbs of carbon. This estimate is based on the following assumptions:

• The medium growth coniferous trees are raised in a nursery for one year until they become 1 inch in diameter at 4.5 feet above the ground (the size of tree purchased in a 15-gallon container).
• The nursery-grown trees are then planted in a suburban/urban setting; the trees are not densely planted.
• The calculation takes into account "survival factors" developed by U.S. DOE (1998). For example, after 5 years (one year in the nursery and 9 in the urban setting), the probability of survival is 68 percent; after 10 years, the probability declines to 59 percent. For each year, the sequestration rate (in lb per tree) is multiplied by the survival factor to yield a probability-weighted sequestration rate. These values are summed for the 10-year period, beginning from the time of planting, to derive the estimate of 23.2 lbs of carbon per tree.

Please note the following caveats to these assumptions:

• Seedlings may require more than 1 year to reach 1 inch diameter; it may take 4-5 years or longer depending on species and conditions.
• Average survival rates in urban areas are unknown, and the rates will vary significantly depending upon site conditions.
• Carbon sequestration is dependent on growth rate, which varies by location and other conditions.

To convert to units of metric tons CO₂ per tree, we multiplied by the ratio of the molecular weight of carbon dioxide to that of carbon (44/12) and the ratio of metric tons per pound (1/2204.6).

Calculation

Note: Due to rounding, performing the calculations given in the equations below may not return the exact results shown.

23.2 lbs C/tree * (44 units CO₂ / 12 units C) * 1 metric ton / 2204.6 lbs = 0.039 metric ton CO₂ per urban tree planted