Use of Models and Facility-Level Data in Greenhouse Gas Inventories

Use of Models and Facility-Level Data in Greenhouse Gas Inventories
Decision tool to guide consistent application of decisions
based on available information on the sample of facilityspecific
data
Given the broad nature of the IPCC guidance in this field, Australia has developed an approach to the use of plant
specific data that is consistent with the IPCC guidelines and which attempts to provide a more explicit framework for the
consistent determination as to how these data are used within the inventory.
With the preparation of Australia’s future inventories in mind, the framework incorporates a decision tree to guide
decision making to encourage consistent and coherent use of plant specific data throughout the inventory (see figure 1).
In particular, conditions have been established that should be satisfied before plant specific data is incorporated into the
national inventory.
These conditions include:
1) the sample of the population reporting plant specific data must be significant – both absolutely and relative to
the overall population (the IPCC Guidelines refer to a ‘reasonable proportion’);
2) the sample must be representative; and
3) the sample must be approximately normally distributed and homogenous.
Plant specific data are used to revise the tier 2 country-specific emission factor for the portion of the inventory with no
measurement data available when the conditions (1) – (3) above are satisfied while also taking into account whether: (4)
the mean of the sample of plant specific data is significantly different to the country-specific tier 2 factor.
If these conditions hold, then the NGER EF data will be used a) for those plants reporting measured emission factors
and b) to construct an NGER determined emission factor that is applied to all facilities for which there is no information
available in relation to their actual plant-specific factor (the uncovered portion of the source).
If conditions (1) – (3) hold but (4) does not, then the NGER data is taken to be valid for those plants reporting data and,
in relation to the unmeasured portion of the source, to have confirmed the pre-existing value of the country-specific
emission factor. In this case, the pre-existing representative country-specific emission factor will be maintained for those
facilities where no information is available on facility-specific factors.
If conditions (1) – (3) do not hold, further information is required to decide how the plant specific data should be used.
What if condition (1) is not maintained? – ie what if the sample of NGER EF data is not sufficiently large?
In this case, NGER data is taken to be insufficient to justify re-estimation of the country-specific emission factor for any
part of the whole population. The pre-existing representative country-specific emission factor will be maintained for all
facilities – ie the inventory will maintain a tier 2 method. The NGERs EF data will not be used in the inventory directly
but will be used as a QC tool to check the reasonableness of the country-specific factor.
What if condition (2) is not maintained? – ie what if the sample is not representative?
Under NGERs – like the EU ETS or the US EPA mandatory reporting rule – reporters are sometimes offered the
opportunity to select their method of emission estimation (under NGERs this is true in all cases except for electricity
generation or underground coal mines). Consequently, it is possible that reporters have self selected an emission factor
that minimises their emissions i.e. where a higher order method results in an emission factor that is higher than the
default a reporter has no incentive to use the higher order method. Due to this possible ‘choice bias’ the sample will not
necessarily be representative of the overall population in these cases and needs to be assessed in every case. This
‘choice bias’ is removed where higher order methods are mandated.
If a non-representative sample is detected, then the new information is not considered sufficient to justify a re-estimation
of the national implied emission factor. While the reported EFs may be incorporated for facilities for which they are
known, the emission factor applied to those facilities without EF information is amended to compensate. In this case, the
tier 2 /3 method produces a national inventory estimate that is equivalent to the tier 2 method.
What if condition (3) is not maintained? – ie what if the population is determined to be not homogenous?
In some cases, it is possible that sub-populations may exist for which representative samples may be obtained. Within
the NGER data obtained for the combustion of black coal, for example, two sub-populations were able to be
distinguished. In this case, the general approach identified above would be able to be applied to the sub-population – ie
IPCC Expert Meeting Report 104 TFI