PoCP impact in CLT Structure Buildings

Hi CLF Community!

I’m aware that this is a “carbon” forum, but other impacts behind GWP should be also taken into account such as AP, EP, POCP, if we really want to adress the whole environmental issue. Hopefully you will find interesting this topic, I’d love to hear some feedback!

I’ve noticed that in a reinforced concrete structure builidng, PoCP impact is not nearly as important as in a CLT structure building, see graph bellow

Blue colums: Reinforced Concrete Structure
Red columns: CLT structure

Note that in previous graph, proposed building (CLT) demonstrates always a better environmental performance if compared with a baseline building (concrete) except in one impact category: Formation of ozone potential in lower atmosphere (PoCP)


When digging in for answers I could confirm that in the CLT structure building, indeed the CLT structure material was the most representative material contributing to the PoCP impact


Why PoCP is higger in CLT if compared with reinforced concrete?

In the following LCA “https://www.americanhardwood.org/sites/default/files/download/2017-11/Endless_Stair_LCA_final%20report.pdf” it’s mentioned that:

“The large percentage of PoCP during material production (wood) is due to emissions of terpene, a type of volatile organic compound (VoC) released from wood resins during kiln drying”

The Terpene issue

Terpene literacy is not as extensive as I would like, but the following report (from 2007) identifies interesting topics: https://www.researchgate.net/publication/271450371_Wood_processing_as_a_source_of_terpene_emissions_compared_to_natural_sources.

"Sawing and lumber drying are equally important terpene emitting processes. Emissions during pellets production can be as important as emissions from sawdust drying, although emissions during drying can also be considerably larger depending on drying technique.

The importance of natural versus anthropogenic emissions depends on the environmental issue. Climate change is global. The importance of the terpene contribution depends on the total amount of emitted terpenes. Natural sources of terpenes would therefore be more important than anthropogenic sources. Formation of photo-oxidants is a regional problem. Terpenes contribute in accordance with their concentration. Hence anthropogenic emissions would be more important. Effects on insects are local, with bark drying an interesting anthropogenic source”


Other reports have been found such as: Underestimation of terpene exposure in the Nordic wood industry - PubMed


Last thoughts

While it seems that “Wood Structure buildings” are being accepted as a general strategy to reduce GWP (and other environmental impacts), other strategies may be required to reduce PoCP.

Formation of ozone of lower atmosphere (PoCP) is measured with kg Ethenee, which contributes in connection with UV radiation to the formation of ozone in the lower atmopshere (summer smog) which is damaging to the respiratory system → not only environmental but also health issue

How do we adress the PoCP impact in CLT buildings?
Is the CLT industry aware of this?
Is there any “low PoCP CLT” available in the market?

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Hello Xavi,
First, I’d suggest you to identify which specific elementary process is contributing to the higher POCP result of the CLT structure considering the dataset you used. In simapro, this is possible using the process contribution function. I also recommend assessing this difference not only in relative values, but also in absolute terms. Just to confirm if it is really associated with terpene emission or not.
Fernanda

Hello @fbsilva, thanks for your answer!

The process that is contributing the most in higher POCP in CLT is A1-A3:

When checking into the EPD, we can confirm that the specific process most contributing to POCP is “A1:Raw material extraction and processing”:

Same happens with other EPD from a different manufacturer of CLT:


So, we can confirm that the higher POCP in CLT is due to the extraction and process (A1).

This is also demonstrated when checking the difference between the CLT building and the Reinforced Concrete in absolute numbers:

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What It’s hard to confirm with OneClick LCA or with the CLT EPD is the relation between POCP and Terpene, due to the fact that POCP is measured with kg of Ethenee.

The resource I have found to explain why POCP is higher in extraction and processing (A1) of wood products and the relation with Terpene are the reports mentioned:

When I have tried to find out more I really did not come across any other useful information, in fact other info seems to not even list “terpene” into the most POCPs

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The conclusions I have made so far:

Conclusion 1: POCP seems to be higher in a CLT structure if compared with a Reinforced Concrete structure.

Conclusion 2: POCP in CLT is produced in A1-A3, specifically in A1: extraction and process.

Conclusion 3 (to be confirmed): Terpene seems to be the responsible of higher POCP in CLT during A1 phase ¿?

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There are lots of “Carbon Contributing Materials” lists…
but what happens to POCP Contributing Materials?

Just for fun: bellow some POCP results of 1m2 of: CLT, concrete, XPS (insulation), paint and gypsum board. This is a quick exercise to have some results, the functional unit would be 1m2 of material with its own typical thickness

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