Gasoline's Carbon Footprint

One gallon of conventional gasoline weighs approximately 6.25 pounds

Octane contains 8 carbon atoms (hence the oct- prefix) and 18 hydrogen atoms. Carbon has a molecular weight of 12 and hydrogen has a molecular weight of 1, so octane has a total molecular weight of 114 (8 x 12 + 18 x 1). Oxygen has a molecular weight of 16, so CO2 has a total molecular weight of 44 (12 + 16 + 16). When burned in an engine, every molecule of octane makes eight molecules of CO2, with a total molecular weight of 352 (44 x 8). 6.25 pounds x (352 / 114) = 19.3 pounds of CO2.

An acre of native forest grows at slightly less than 1 ton/ac/yr. An acre of native forest produces a maximum of 2,000 lbs of wood per year. 1 pound of wood is approximately 52% carbon. To produce 1 lb of wood a tree would take in approximately 1.5 pounds of CO2, absorbing the 1/2 pound of Carbon and releasing the other 1 pound of Oxygen to the air. An acre of native forest absorbs a maximum of 3,000 pounds of CO2 per year.

To absorb the CO2 emitted by burning 1 gallon of gasoline (19.3 pounds of CO2), 12.87 pounds of wood need to be grown.

An acre of native forest has to grow for 2.35 days (56.36 hours) to absorb the CO2 emitted from the burning of 1 gallon of gasoline.

Urban Trees (individual):

A medium growth coniferous tree, planted in an urban setting and allowed to grow for 10 years, sequesters 23.2 lbs of carbon or 69.6 lbs of CO2. This estimate is based on the following assumptions: the medium growth coniferous trees are raised in a nursery 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 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, 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.

From planting, one urban tree would have to grow for 8.32 years to absorb the amount of CO2 emitted from the burning of 1 gallon of gasoline. (19.3/23.2 = .831896 X 10 years)