LCA Results - marc-vdm/activity-browser GitHub Wiki

Activity Browser has two contribution analysis approaches available to assess results, Elementary Flow (EF) Contributions and Process contributions.

Before we discuss the different approaches, we introduce a small example for the production of 'steel':

The amounts we use are:

activity	product	technosphere exchanges	biosphere exchanges
coal production	10 kg coal		0.02 kg CH4
electricity production	10 kWh electricity	10 kg coal	10.808 kg CO2
steel production	10 kg steel	5 kWh electricity 5 kg coal	10 kg CO2

^{Note: These numbers are used for ease of understanding, not for realism.}

To produce 1 kg of steel, we get a climate change impact of 1.6 kg CO2 eq with the 'IPCC 2021' impact category. In the way Brightway (and thus Activity Browser) calculate results, a contribution matrix is calculated with all impacts from all EFs and all activities. For the system and functional unit above, this would be:

	coal prod.	elec. prod.	steel prod.
CO2	-	0.5404...	1
CH4	0.0596...	-	-

The contribution matrix show the dis-aggregated results for each individual biosphere flow for each activity.

If we take sum the rows to one row, we get the EF contributions (the contribution of all CO₂ and CH₄ impacts together). In the case above, the EF contributions are:

• CO₂: 1.5404... (96.3%)
• CH₄: 0.0596... (3.7%)

If we take the sum of the columns to one column, we get the process contributions (the contribution of all coal, electricity and steel production impacts together). In the case above, the process contributions are:

• coal production: 0.0596... (3.7%)
• electricity production: 0.5404... (62.5%)
• steel production: 1 (33.8%)

To summarize, the difference between EF and process contributions is the direction the contribution matrix is summed.

In this section we generalize a little bit for the different contribution approaches, we call the from part of the contributions (the EFs or activities above) entities.

There are several ways Activity Browser manipulates your results by default.

• The results are sorted so that the largest (absolute) values are shown first
• A cut-off of 5% is applied to group all entities with an impact below that value.
• The contributions are normalized to the impact of that reference flow, meaning they are show as a percentage, counting up to 100%

These actions are taken to show you the most relevant results.

You can manually manipulate the contribution results in the next menu, which we explain bit by bit below.

You can manually change the cut-off of the results in two ways, Relative or Top #. The Relative option shows contributions from entities of x% or higher. The Top # options shows contributions from the x entities that contribute the most (as absolute).

You can change the value of the cut-off in the menu shown below.

The Compare menu allows you to compare different dimensions of results. You can compare between:

• Reference flows
• Impact categories
• Scenarios (only available in scenario LCA, see scenarios)

The compare mode defines what is shown in the figure.

The Aggregate by menu can be used to group results based on field names. As an example, EF contributions can be grouped on the name, for example to group all flows with the same name. Another example for process contributions can be grouped based on their reference product name.

By default, Activity Browser shows a plot and a table. You can disable one of them if you want to focus on one of them.

Finally, you can choose between Relative and Absolute results. The Relative results will sum to 100%, the Absolute results will sum to the impact score.

The Sankey tab shows results from graph traversal. Graph traversal calculates results step-by-step for nodes (activites) in the graph (supply chain/product system).

In the Sankey tab, you can configure, you can set the Reference flow, Impact category and Scenario (only available in scenario LCA, see scenarios) to be shown. you can also set a cutoff and calculation depth setting.

The cutoff setting will stop traversing the supply chain once the impact is below the percentage specified. The calculation depth will stop traversing the supply chain once that number of calculations have been performed.

In the Sankey, the red arrows show the cumulative impact of the product flow (direct from that process and indirect from all upstream processes involved in producing that product), the boxes show the direct (process contribution) impact of that process.

Using the example above in the contribution analysis section, we show the sankey below. The process contribution results are also shown in the boxes below.

The Monte Carlo and Senstivity Analysis tabs are explained on the Uncertainty page.