Elementary flows are a fundamental concept in Life Cycle Assessment (LCA). They represent the exchanges between a product system and the environment, such as extracting raw materials or releasing emissions. These flows are crucial for understanding the environmental impact of a product throughout its life cycle. This article covers the following topics:
What are elementary flows?
What is the role of elementary flows in LCA?
How do elementary flows work in Ecochain software?
Feel like you're missing information? This article builds upon the following articles, check them out if you want to learn more:
On the LCI phase: Explained: Life Cycle Inventory (LCI) phase
On the LCIA phase: Explained: Lice Cycle Impact Assessment (LCIA) phase
On LCIA methods: Explained: LCIA methods
What are elementary flows?
Elementary flows are a fundamental concept in LCA, representing the smallest measurable interactions between a product system and the environment. These flows capture the substances emitted into the environment (e.g., carbon dioxide released into the air) or the natural resources extracted from it (e.g., groundwater for industrial use). They set the foundation for understanding the environmental impact of a product, helping to quantify and assess emissions and extractions at every stage of a product's life cycle.
The elements of elementary flows
Elementary flows refer to two concepts:
Resources or substances found in a specific environmental medium. This type of elementary flow is relevant to your model if you are extracting resources from the natural environment.
Emissions represent the exchange of substances between a product system and the environment. This type of elementary flow is relevant to your model if your products or production processes cause emissions during their product lifetime.
Substances can be simple (e.g., elements like carbon (C) or oxygen (O₂)), a bit more complex (e.g., compounds like water (H₂O) or methane (CH₄)), or a combination of those like mixtures (e.g., particulates (PM) or Volatile Organic Compounds (VOCs)). The flow of these substances can be either extracted from or emitted into environmental mediums such as air, water, or soil.
The environmental mediums of elementary flows
Elementary flows occur across different environmental mediums—air, water, and soil. Each medium can have multiple specifications (Table 1). For example, the water medium includes ocean water, groundwater, river water, etc. These specifications provide a detailed understanding of where and how elements interact with the environment. Use the term 'unspecified' if the specific medium is unknown.
Examples of elementary flows in a product’s life cycle:
1 kg (Ammonia) Emissions to air due to a step in your production process
1 kg (Ammonia) Leakage to the ground due to rain on your product during its use phase because it is constructed outside and exposed to the weather.
Table 1: Specifications of environmental flows through different environmental mediums
The impact of elementary flows on the environment
Elementary flows have significant environmental impacts, whether elements are emitted into the environment (e.g., CO₂ released into the air) or extracted from it (e.g., water drawn from groundwater). Understanding these flows is critical for assessing the environmental footprint of a product.
What is the role of elementary flows in LCA?
Elementary flows in the LCIA phase
Elementary flows are an important part of the Life Cycle Impact Assessment (LCIA) phase of LCA. During this phase, the elementary flows identified in the Life Cycle Inventory (LCI) are linked to specific environmental impacts. This process involves several steps:
Impact Categories, Indicators, and Characterization Models: During LCIA, you select impact categories (e.g., climate change), category indicators (e.g., kg CO₂-equivalent), and characterization models that define how the environmental impacts will be quantified.
Classification and Characterization: Elementary flows are assigned to one or more impact categories (classification). A characterization factor determines the extent to which an elementary flow contributes to an impact category. For example, methane (CH₄) has a higher global warming potential than carbon dioxide (CO₂), so 1 kg of CH₄ is equivalent to 34 kg of CO₂ in terms of impact.
This process can vary depending on the LCIA method used (e.g., EF 3.1, EN15804, TRACI 2.1). Different methods may treat the same elementary flow differently. For example, biogenic CO₂ has a characterization factor of 0 in the EF 3.1 method but a factor of +/-1 in the EN15804 method.
[Optional] Normalization, Grouping, and Weighting: These optional steps help further interpret the results of the LCIA. For example, normalization allows comparison across different impact categories, grouping can aggregate impacts for more straightforward reporting, and weighting assigns importance to the different impacts.
How do elementary flows work in Ecochain software?
Elementary flows in Helix
In Ecochain Helix, you can select elementary flows on the Usage & Emissions (U&E) page (Figure 1). It's important to use filters carefully to select the correct medium and specification (e.g., CO₂ to air rather than CO₂ to groundwater). These flows can also be used in specific life cycle stages, but this is more advanced and may require assistance from the helpdesk.
Figure 1: Selecting elementary flows in Helix.
Elementary flows in Mobius
In Mobius, elementary flows are managed under the 'Elementary flows' tab when selecting datasets (Figure 2). This allows for the precise customization of the environmental impacts considered in your LCA.
Note: Starting from Ecoinvent v3.9.1, elementary flow selection is only available for flows that have an environmental impact according to the selected LCIA method respectively. In other words, Mobius will only display characterized elementary flows - those without any impact are omitted. If you wish to include an uncharacterized elementary flow in your model, we recommend creating an object (e.g., "Oxygen to air") without connecting it to any flow.
Figure 2: Accessing elementary flows in Mobius.
Next steps
Elementary flows are key to understanding the environmental exchanges between a product system and its surroundings, helping you assess its overall environmental impact. Whether you’re working in Helix or Mobius, you can accurately select and classify these flows to ensure your LCA results reflect real-world environmental interactions. With a strong grasp of elementary flows, you can make more informed sustainability decisions and refine your LCA models as needed.
