Ontology: update definitions for emission value / emission factor value

[stap-m]

Description of the issue

Update definitions for emission value / emission factor value.

Ideas of solution

Workflow checklist

• [x] I discussed the issue with someone else than me before working on a solution
• [x] I already read the latest version of the workflow for this repository
• [x] The goal of this ontology is clear to me

I am aware that

• [x] every entry in the ontology should have an annotation
• [x] classes should arise from concepts rather than from words
• [x] class or property names should follow the UpperCamelCase

[han-f]

Should this include a definition for _emission factor_ or _emission factor value_?
Suggestions for emission factor:
The emission factor is the ratio between the amount of pollution generated and the amount of a given raw material processed. The term may also refer to the ratio between the emissions generated and the outputs of production processes. https://stats.oecd.org/glossary/detail.asp?ID=761

[akleinau]

emission value can't be found and emission factor got deleted in #368 (as it's a quantity) so this can get moved to the second release

[l-emele]

I think we have to distinguish between different types of emission values.

1. An emission value that is _directly_ connected to the emission process. This is e.g. the combustion of fuels where the carbon content of the fuels is oxidized. A practical example is a CO2 emission value of 96 t/TJ for hard coal.
2. An emission value that is only _indirectly_ connected to the emission process as it is calculated from the emissions and some activity data that is not directly related to the combustion. A practical example is a CO2 emission value of 900 g/kWh for a coal power plant with the produced electrical energy as activity data.
3. An emission value that covers that e.g. greenhouse gases are directly emitted without a chemical conversion process. This can be e.g. methane leakage from a gas grid or emission of F-gases from air conditioning.

So the first and second emission value are related to combustion and other chemical conversion processes while the second one the leaking itself is the emission process. Maybe we need different types (subclasses?) of our emission process? Like _emission from a conversion process_ and _emission from leakage_?

In UNFCCC terminology the first and third emission value is called _emission factor_ while the second one is called _implied emission factor_.

[l-emele]

The IPCC defines emission factor as:

A coefficient that quantifies the emissions or removals of a gas per unit activity. Emission factors are often based on a sample of measurement data, averaged to develop a representative rate of emission for a given activity level under a given set of operating conditions.

(Glossary of the _2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories_)

[Vera-IER]

When it comes to modelling I can only use one general type of emission factor. So I would be fine with only one label emission factor and the definition from IPCC.
I think emission factor is also an example of what we call "attribute", so we would need to relate it to a process class.
A suggestion for this relation is: `energy transformation' has_process_attribute 'emission coefficient'

Or if the issue with the subclasses of energy transformation (#372) is solved than the relation could be for example:
'coal power unit' participates in 'energy transformation' has_process_attribute 'emission factor'
for all fossil power plants.

[l-emele]

An emission factor an also applied to combustion fuels, e.g. natural gas has an emission factor of about 56 t CO2/TJ.

[Vera-IER]

Yes true, but I think it should be related to the combustion fuel and the combustion process. As the definition says its "quantifies the emissions per unit activity." An activity is always a process in my understanding.
So we would need to relate combustion fuel to the combustion process and the emission factor. Additionally we could relate combustion fuel or specific power units to energy transformation and emission factor.

[l-emele]

Yes true, but I think it should be related to the combustion fuel and the combustion process. As the definition says its "quantifies the emissions per unit activity." An activity is always a process in my understanding.

Yes, exactly. An emission factor is always connected to a process.

So we would need to relate combustion fuel to the combustion process and the emission factor. Additionally we could relate combustion fuel or specific power units to energy transformation and emission factor.

The emission process does not necessarily be a combustion process. If you think e.g. about the methane leakage emissions from a gas well the relevant process is the production of gas and not the combustion. And if you think of some industrial process emissions like F-gas emissions they are not connected to any fuel at all.

[Vera-IER]

My suggestion would be to keep the definition of emission factor generic, for example use the one from IPCC and then relate it to the classes which are already included in the OEO. So an additional relation could be to made to primary energy mining.
We don't have a class industrial process ... Maybe we could put an editor note, that emission factors can also be applied to industrial processes?

[l-emele]

Adapting the IPCC definition I propose the following definition: _An emission factor is a quantity value that quantifies the emissions or removals of a gas per unit activity._ The superclass would then be quantity value.

[l-emele]

No one objected against my proposal from 27 August so I think it is ready for implementation. I'll do that.