1. A new way of looking at emission uncertainties
Joint Task Force on Emission Inventory & Projection / Task Force on Modeling and Measurement Workshop
A new way of looking at emission uncertainties
Carlo Trozzi
Larnaca (Cyprus), 12 May 2010

2. Topics Uncertainty in the actual Guidebook
The general methodology for uncertainties evaluation proposed by US EPA EIIP and referred as DARS as personalized for national and regional inventory
The new system (E2gov) developed for government of energy and environment, energy balances and pollutant emission inventory where methodology was integrated

3. Guidebook Uncertainties Chapter
The GB follows 2006 IPCC Guidelines to define uncertainty and was not essentially update from the previous release
The GB suggests a very simple approach to define uncertainty in activity levels (ALs); this approach is useful for IPCC estimates and for preliminary approach to uncertainty evaluation but must be specialized for detailed national and local inventory to evaluate the entire cycle of life of data
The basic consideration is that the process of define indicators and the selection of Emission Factors (EFs) it’s often more complex than simple GB approach

4. Guidebook Uncertainties AL approach

5. Key Issues
The uncertainty in emission inventories is not simply due to the uncertainty of emission factors as it is often said
The overall uncertainty of emissions should be expressed as weighted average of individual uncertainty of estimates
The uncertainty is largely influenced by methods of collecting and evaluating indicators of activity
The uncertainty of the indicators of activity is not limited to statistical error of the data but must also take account of the whole estimate process estimation at the territorial level chosen

6. Methodology
Inventory uncertainty in emission data is evaluated by adapting the methodology Data Attribute Rating System (DARS) of the EPA, the U.S. Agency responsible for environmental protection
The method was originally described by Beck in 1994, and modified in the Emission Inventory Improvement Program (EIIP)
The evaluation criteria, originally formulated for area sources, have been extended to the evaluation of point sources and mobile
The original methodology was adapted for the structure of national, regional and local inventories

7. Single activity or plant Uncertainty Evaluation Scheme
Four aspect of activity level (AL) and emission factors evaluation (EF) are selected:
measurement/method of determination (MM)
source specificity (SS)
spatial congruity (SC)
temporal congruity (TC)
For each criterion is assigned a score from 1 to 10 for
AL and EF (highest the score less the uncertainty)
Score is more appropriate to assign than % as often % uncertainty is a numeric expression of score

8. Single activity total uncertainty
The final score is then processed by calculating, for a set of criteria, the average score among the products on the emission factor and score on the given activity
Attribute
Factor
Activity
Emissions
Measurement/Method e1 a1
e1 * a1
Source Specificity e2 a2
e2 * a2
Spatial Congruity e3 a3
e3 * a3
Temporal Congruity e4 a4
e4 * a4
Composite
[Si=1,4 (ei * ai)] / 40

9. Measurement/method of determination
General criteria
The score is based on the quality of the factor itself, not on how it has been used
The best results are usually obtained by direct measurement of either emissions or by measurement of surrogate parameters that have a strong, statistically documented correlation with the pollutant of interest
In the original EPA work some decision diagrams are reported while in the following slide some examples of application of DARS criteria was presented

10. Measurement/method of determination
Activity score assignation criteria

11. Measurement/method of determination EF score assignation criteria
AP-42 uncertainty codes and corresponding DARS scores

12. Measurement/method of determination EF score assignation criteria
uncertainty codes assigned in GB

13. Source specificity General criteria
The source specificity attribute concerns how specific the original factor or activity surrogate is to the source being estimated
This attribute is easily confused with the previous one but the key point to ask is "was this emission factor (or activity parameter) specifically developed for this source category
The criteria can be specialized to differentiate the evaluation when Tier 1, Tier 2 or Tier 3 methodologies are used

14. Activity score assignation criteria
Source specificity
Activity score assignation criteria

15. EF score assignation criteria
Source specificity
EF score assignation criteria

16. Activity score assignation criteria
Temporal congruity
Activity score assignation criteria

17. EF score assignation criteria
Temporal congruity
EF score assignation criteria

18. Activity score assignation criteria
Spatial congruity
Activity score assignation criteria

19. EF score assignation criteria
Spatial congruity
EF score assignation criteria

20. Special case: point sources stacks measurement
If emissions are measured at the stacks of point sources, the scores are assigned to the emissions, without compute it from indicator and emission factor
For continuous measurement of emissions the scores are 10 for MM, 10 for SS, 10 for SC and 10 for TC (unless reference is to a different year; in this case the assigned score will be smaller as discussed for other sources)
For periodical measurements scores are 8 are 10 for MM, 10 for SS, 10 for SC and 10 for TC (only if the year of reference of the analyses is that in consideration).

21. Ιik = (Σj∈k Εij Ιij) / (Σj∈k Εij)
Cumulate uncertainty
After uncertainty is assigned to the single activities of the inventory, global uncertainty of group of activities or of the whole inventory can be computed as:
Ιik = (Σj∈k Εij Ιij) / (Σj∈k Εij)
where:
Ιik, uncertainty of the emission of pollutant i from the group k
Ιij, uncertainty of the emission of pollutant i from the single activity j belonging to group k,
Εij, emission of pollutant i from the single activity j.

22. Examples of evaluation

23. The methodology was integrated in a new system (E2gov) developed for government of energy and environment, energy balances and pollutant emission inventory