addressing uncertainty in oil and natural gas industry greenhouse

2.0 SOURCES OF UNCERTAINTY
There are a myriad of sources that contribute to the
uncertainty of an emission inventory. Whether at the national,
entity, or facility level, the ability to quantify emissions and
understand their associated uncertainty hinges on two main
factors:
Section Focus
This section discusses the major sources
affecting the uncertainty of GHG inventories.
It moves from general concepts to issues that
are germane to GHG inventories in the O&G
industry. It also describes factors that could
− Readily available data for emission quantification; and
introduce errors into the emission
measurements process and contribute to the
−
range of uncertainties of estimated emissions.
Knowledge of input parameters for statistical
The subsections address:
calculation of uncertainty.
• Overview of emissions inventory
uncertainty;
The overall range of uncertainty associated with an entity
GHG inventory usually is determined primarily by the
• Emission inventories uncertainties in the
O&G industry;
uncertainty associated with the largest (“key”) sources of • Sources of measurements uncertainty;
emissions. Although very large confidence intervals may be • Emission estimation approaches; and
associated with the data used to characterize some small • Inventory steps and data aggregation.
sources, the overall impact on the range of uncertainty at the
entity, or installation level, may often be very small. In turn, the confidence interval associated with each
individual source depends on the availability of sufficient data to estimate emissions, or on the quality of
the data in order to properly account for emission variability.
2.1 Overview of Emissions Inventory Uncertainty
Uncertainties in inventories are the result of three error categories:
−
−
−
Spurious errors, which may be due to incomplete, unclear, or faulty definitions of emission
sources that result from human error or machine malfunction;
Systematic errors, which may be due to the methods (or models) used to quantify emissions for
the process under consideration; and
Random errors, which may be due to natural variability of the process that produces the
emissions.
When assessing the process or quantity under consideration, uncertainties might be associated with one or
more factors such as: sampling, measuring, incomplete reference data, or inconclusive expert judgment.
Uncertainties due to models or equations are related to the proper application of estimation methodologies
to the respective source categories. These errors are typically eliminated as far as possible in advance,
Pilot Version, September 2009 2-1