What is an Environmental Exchange?
In Life Cycle Assessment (LCA), an environmental exchange is any flow that goes between a human activity and the natural environment.
It can be something taken from nature (like minerals, water, or air) or something released back into nature (like emissions to air or water).
These exchanges are the building blocks used to calculate environmental impacts.
Examples
Emission example:
When fossil fuels are burned, carbon dioxide (CO₂) is released into the air.
This contributes to Climate Change, where 1 kg of CO₂ emitted equals 1 kg CO₂-equivalent of impact.Resource use example:
When 1 liter of freshwater is extracted from a river and eventually used as tap water, it contributes to Water Use,
with an impact of 0.001 m³ in that category.
The Five Main Parts of an Environmental Exchange
Every environmental exchange includes a few key pieces of information:
Name – what the flow is called (for example, “Carbon dioxide” or “Water”).
Context – where it happens:
Primary context: whether it’s an emission or a resource taken from the the main environmental media - air, water, or ground
Secondary context: extra detail, like whether it happens indoors, at which altitude (e.g. ground level, stratosphere), whether it occurs in an human dominated environment, or whether it occurs in a higly or sparcely populated area (rural vs urban)
Unit – how it’s measured (e.g., kg, m³, MJ).
Amount – how much of it is emitted or extracted.
Impact – how much it contributes to a specific environmental impact category, like Climate Change or Water Use.
Figure 1: Some of the properties of an environmental exchange
Environmental exchanges in external LCA data
The data you use in Earthster LCA software comes from a great variety of sources. In LCA databases, each exchange has a structured name that describes what it is and where it happens. For example:
Table 1: Typical structure of an exchange
Flow name | Context | Unit |
Carbon dioxide | emission/air/troposphere/rural/ground-level | kg |
Water | resource/water/fresh water body/river | kg |
Environmental exchanges may be called also elementary exchanges, elementary flows, etc. The concept and components are always present though.
Database curators (Ecoinvent, Exiobase, USLCI…) provide data about the environmental exchanges of each dataset (e.g. kg of CO2 emitted). Impact assessment method developers provider data about the emission factors of each chemical (e.g. kg CO2 equivalent per kg of carbon dioxide).
In order to compile it all together, Earthster needs to make sure that the same chemicals are treated as such (CO2 and carbon dioxide). For that we curate an extended version of the Federal Elementary Flow List (FEDEFL), with extensions to account for supported databases and methods. You can read more about the advantages of the extended standard and how we curate it in the section Environmental exchanges in Earthster.