Introduction - Mathematics and Statistics for the Environment - page 36

per year (or -35.32 metric tons C per acre per year). To convert to carbon dioxide, multiply by the
ratio of the molecular weight of carbon dioxide to that of carbon (44/12), to yield a value of -320.01
metric tons CO 2 per hectare per year (or -129.51 metric tons CO 2 per acre per year).
1.7.11.2 Conversion Factor for Carbon Sequestered Annually by
1 Acre of Forest Preserved from Conversion to Cropland
Due to rounding, performing the calculations given in the equations below may not return the
exact results shown. Negative values indicate CO 2 that is not emitted.
(-35.32 metric tons C per acre per year) × (44 units CO 2 ÷ 12 units C) = -129.51 metric tons
CO 2 per acre per year.
To estimate CO 2 not emitted when an acre of forest is preserved from conversion to cropland, simply
multiply the number of acres of forest not converted by -129.51 metric tons CO 2 per acre per year.
Note that this calculation method assumes that all of the forest biomass is oxidized during clear-
ing (i.e., one of the burned biomass remains as charcoal or ash). Also note that this estimate only
includes mineral soil carbon stocks, as most forests in the contiguous United States are growing on
mineral soils. In the case of mineral soil forests, soil carbon stocks could be replenished or even
increased, depending on the starting stocks, how the agricultural lands are managed, and the time
frame over which lands are managed.
1.7.12 p ropane C ylinders u sed For h ome b arbeCues
Propane is 81.7% carbon. The fraction oxidized is 100% (IPCC, 2006; USEPA, 2013a). Carbon
dioxide emissions per pound of propane were determined by multiplying the weight of propane in
a cylinder times the carbon content percentage times the fraction oxidized times the ratio of the
molecular weight of carbon dioxide to that of carbon (44/12). Propane cylinders vary with respect to
size; for the purpose of this equivalency calculation, a typical cylinder for home use was assumed
to contain 18 pounds of propane.
1.7.12.1 Calculation
Due to rounding, performing the calculations given in the equations below may not return the
exact results shown.
(18 lb propane/1 cylinder) × (0.817 lb C per lb propane) × (0.4536 kg/lb) × (44 kg CO 2 per
12 kg C) × (1 metric ton/1000 kg) = 0.024 metric tons CO 2 per cylinder.
1.7.13 r ailCars oF C oal b urned
The average heat content of coal in 2009 was 27.56 mmbtu per metric ton. The average carbon coef-
ficient of coal in 2009 was 25.34 kg carbon per mmbtu (USEPA, 2011). The fraction oxidized to CO 2
is 100% (IPCC, 2006). Carbon dioxide emissions per ton of coal 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). The amount of coal in an average railcar was
assumed to be 100.19 short tons, or 90.89 metric tons (Hancock and Sreekanth, 2001).
1.7.13.1 Calculation
Due to rounding, performing the calculations given in the equations below may not return the
exact results shown.
(27.56 mmbtu/metric ton coal) × (25.34 kg C per mmbtu) × (44g CO 2 per 12g C) × (90.89
metric tons coal per railcar) × (1 metric ton/1000 kg) = 232.74 metric tons CO 2 per railcar.