addressing uncertainty in oil and natural gas industry greenhouse

• Fuel Economy (miles per gallon) = ±5% (assigned by expert judgment, based on some fuel
economy data for similar vehicle types).
• Heat Value of Gasoline = ±5% (determined by expert judgment).
• The number of trucks = ±0% (expert judgment determined that this count is perfectly known and
discreet).
• The CO 2 emission factor for this category, expressed in tonne CO 2 /MMBtu, has a provided
uncertainty of ±10%. The reference source CH 4 and N 2 O emission factors, while small, have
much larger uncertainties of +150%,–100%. Because it is not possible to have negative
emissions, the lower bound uncertainty will be truncated at zero. As a result, the lower and upper
bound uncertainties are estimated separately.
The energy content of the fuel consumed by the vehicles (V) must first be converted to an energy input
basis and is determined based on the annual miles and an average fuel economy.
6
40,000 mi gal bbl 5.25 × 10 Btu
V = × × ×
yr-truck 14 mi 42 gal bbl
6
V=1,790×
10 Btu/yr-truck
Uncertainty Estimate for Fleet Activity Data:
Equation 4-6 is applied using the relative uncertainty values.
U ( rel) = U( rel) +U( rel) +U( rel)
2 2 2
Energy of Fuel AF fuel economy Heat value of gasoline
Urel = + + =±
( )
2 2 2
( )
Energy of Fuel
15 5 5 16.6% Btu/yr-truck
Uncertainty Estimate for CO 2 Emissions from Fleet:
Carbon dioxide emissions are then calculated by applying the emission factor for vehicles.
6
1,790 × 10 Btu 0.0709 tonne CO
E
CO
= 5 trucks ×
×
2
6
yr-truck 1×10 Btu
E
CO 2
2
= 127 tonnes CO /yr
2
Equation 4-6 is applied using the relative uncertainty values.
U ( rel) = U( rel) +U( rel) +U( rel)
2 2 2
CO Emissions Vehicle Energy of Fuel EF
2
2
( )
Urel ( ) = 0 + 16.6 + 10 =± 19.4% tonnes CO /yr
2 2 2
CO Emissions
2
Uncertainty Estimate for CH 4 Emissions from Fleet:
Methane emissions are then calculated by applying the emission factor for vehicles.
Pilot Version, September 2009 F-17