addressing uncertainty in oil and natural gas industry greenhouse

U ( abs) = (U( abs) +U( abs) +U( abs)
2 2 2
ECO2e ECO E
2 CH E
4 N2O
U ( abs) = (0.102× 551) + (1.00× 21× 0.00776) + (1.00× 310× 0.00628) = 56.2 tonnes CO e/yr
2 2 2
ECO2e
2
56.2 tonnes CO e/yr
2
( )
E
100% 10.2% tonnes C
CO2e
553 tonnes CO2e/yr
Urel
= × =± ( Oe/yr)
2
F.14 SUMMARY UNCERTAINTY – Propagating Uncertainty for the Example Facility
Total emissions for this facility are summarized in Table F-15, along with the summary uncertainty
propagation. The uncertainty of the total emissions is calculated by applying Equation 4-4 and using the
absolute uncertainty values. In practice, uncertainty values are usually displayed in relative terms, which are
provided in terms of upper and lower % uncertainty values in Table F-15 for those emissions sources with
an asymmetrical uncertainty.
As an example, the summed upper bound uncertainties for N 2 O combustion emissions for the facility are
calculated as follows, using absolute uncertainties:
U ( abs) = U ( abs) + U ( abs) + U ( abs) + U ( abs) + U ( abs)
U ( abs)
2 2 2 2 2
N2O CombustionTotal BoilersandHeaters Turbines Flare IC Fleet
N2O CombustionTotal
(0.0242× 1.50) + (0.325× 1.51) + (0.223× 2.00) + (0.00175×
1.51)
=
+ (0.0000467 ×
2 2
1.51) + (0.00871×
1.51)
0.663
Urel ( )
N
100% 114%
2O Combustion Total
= × =
0.582
2 2 2 2
= 0.663
U ( abs) = U ( abs) + U ( abs) + U ( abs) + U ( abs)
U abs
2 2 2 2
N2OTotal Combustion Vented Fugitive Indirect
= × + + + × =
2 2 2 2
( )
NOTotal
(0.582 1.14) 0 0 (0.00628 1.00) 0.663
2
0.663
Urel ( )
NOTotal= 100% × = 113%
2
0.582
This calculation was repeated for the sum of each category, and for the totals in that GHG gas type. The
gases were each converted to CO 2 e using the GWPs. As was stated previously, for the purpose of compiling
a facility-level GHG inventory, the GWP’s are assumed to have no uncertainty. The bottom row of
Table F-15 shows the emissions in CO 2 e.
Pilot Version, September 2009 F-37