Possible to use X-equivalents from previous LCAs as input to model?

Question

Hi,

When searching for data for my model, I usually come across results of previously made LCAs. They provide an answer in in equivalents, e.g. CO2 eq, rather than the amount of emissions themselves.

My question is if it is possible to use those results, provided in the form of equivalents, as input or output to a process in openLCA. If so, how would one do that practically? My intention is to create processes representing components or sub-components, of my product system, for which I have found LCAs like the ones described earlier.  I.e. create a process where the output is comprised of the reference flow plus the different equivalents (C02 eq, SO2 eq etc).

I am limited to the free databases if that is of any importance.

Thanks!

Nils

Answer 1

Hi Nils,

Technically speaking you could use this approach as a last resort, for processes which you cannot find suitable data for. You would not be modelling the “equivalents” as outputs per se, rather you would be expressing the environmental burden for each impact category via its designated pollutant. So for global warming potential using CO2 eq, you would use carbon dioxide as the output. However, this could introduce a lot of uncertainty into your model, as the equivalents will vary according to the chosen impact category.

Take climate change as an example using Global Warming Potential (GWP) (kg CO2-eq) as the characterization factor at midpoint level. The GWP for greenhouse gases will vary between studies depending on the impact method that was used. For ReCiPe 2016 using a 100-year perspective, the GWP of methane is 34 kg CO2-eq. This is based on the fifth assessment report from the IPCC. However, previous LCAs may use other impact methods for which the GWP values differ. For example, methane had a GWP of 25 in the fourth assessment report from the IPCC. Using several different reported “equivalents” from various studies which use different impact methods would make your model more uncertain.

You would also have to be careful if the equivalents in the studies are expressed in terms of the functional unit and whether that functional unit is compatible with what you want to model.

Relating the equivalents to their designated pollutant may be difficult and time consuming for other impact categories.

Hope this helps

Ciara

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Comments

Hi,

Thanks for the reply! I believe you are right about the uncertainty aspect of the situation. What still perplexes me a bit is that there seems to be no clear way to use the results of previously made LCAs  when creating one's own model. I was under the impression that it was a, to some extent, common and accepted practice to incorporate findings from other similar studies. It would be somewhat unfortunate if one could not use the results from a really thorough and recent report in the case that it does not provide the exact inventory data but only the LCIA.