Impact categories help us make actionable statements about how Greenhouse Gas (GHG) emissions influence the environment.
Actionable is a very important aspect here. Environmental sciences are immensely complex. Thus, when companies try to become more sustainable, they have to define what they mean by that.
Definition: What are impact categories in LCA?
An impact category groups different emissions into one effect on the environment.
However, to fully understand impact categories, we need to have a basic understanding of Life Cycle Assessments.
Quick recap: Life-Cycle Assessment (LCA)
A Life Cycle Assessment (short LCA) is the standardized method of calculating the impact of, for example, a product on the environment.
During the course of the LCA, a large amount of emission data is collected: emissions from energy production, the waste produced, the raw material production, etc.
Role of Impact Categories in an LCA
These emissions come in different shapes and formats since the emissions from harvesting raw materials are very different from the emissions from producing electricity.
This is where impact categories come into place. During the Life Cycle Impact Assessment (LCIA) of an LCA, we try to unite these different emissions into actionable numbers. Meaning: different emissions that cause the same impact- are converted into one unit that translates into one impact category.
For example, the impact category ‘climate change’ is expressed in kg CO₂ equivalents (kg CO₂-eq). However, other greenhouse gas emissions than carbon emissions (CO₂) cause climate change as well. Such as methane (CH₄), or laughing gas (N₂O).
By expressing these other GHG emissions with different measuring units in kg CO₂ equivalents. An impact category makes it possible to come to a single metric for climate change.
KPI for the environment
You are probably familiar with the concept of Key Performance Indicators, or KPIs, that measure the success of a business.
Impact categories can serve a similar function. They group complex data into accessible numbers – numbers that give a concrete picture of what the impact actually is.
All the impact categories (overview)
Table 1 gives you an overview of the 15 environmental impact categories, which unit they are measured in, and what they describe. Below them, you will find Table 2-4 which includes additional parameters and indicators you have to report on for the use of resources, waste types and output flows of materials & energy.
Both the 15 categories and the parameters & indicators are all taken from the EN15804 (A1+A2) standard for LCA’s in the construction sector. Other impact assessment methods (such as the PEF 3.0) exist as well, which use slightly different categories. However, EN15804 +A2 gives a good general overview.
Good to note: last year the EN15804 standard was updated to EN15804 + A2 (2019). This resulted in quite some other changes. Find these new adaptations here.
Table 1. Environmental impacts
| Impact category / Indicator | Unit | Description |
| Climate change – total, fossil, biogenic and land use | kg CO2-eq | Indicator of potential global warming due to emissions of greenhouse gases to the air. Divided into 3 subcategories based on the emission source: (1) fossil resources, (2) bio-based resources and (3) land use change. |
| Ozone depletion | kg CFC-11-eq | Indicator of emissions to air that causes the destruction of the stratospheric ozone layer |
| Acidification | kg mol H+ | Indicator of the potential acidification of soils and water due to the release of gases such as nitrogen oxides and sulphur oxides |
| Eutrophication – freshwater | kg PO4-eq | indicator of the enrichment of the freshwater ecosystem with nutritional elements, due to the emission of nitrogen or phosphor-containing compounds |
| Eutrophication – marine | Kg N-eq | Indicator of the enrichment of the marine ecosystem with nutritional elements, due to the emission of nitrogen-containing compounds. |
| Eutrophication – terrestrial | mol N-eq | Indicator of the enrichment of the terrestrial ecosystem with nutritional elements, due to the emission of nitrogen-containing compounds. |
| Photochemical ozone formation | kg NMVOC-eq | Indicators of emissions of gases that affect the creation of photochemical ozone in the lower atmosphere (smog) catalysed by sunlight. |
| Depletion of abiotic resources – minerals and metals | kg Sb-eq | Indicator of the depletion of natural non-fossil resources. |
| Depletion of abiotic resources – fossil fuels | MJ, net calorific value | Indicator of the depletion of natural fossil fuel resources. |
| Human toxicity – cancer, non-cancer | CTUh | Impact on humans of toxic substances emitted to the environment. Divided into non-cancer and cancer-related toxic substances. |
| Eco-toxicity (freshwater) | CTUe | Impact on freshwater organisms of toxic substances emitted to the environment. |
| Water use | m3 world eq. deprived | Indicator of the relative amount of water used, based on regionalized water scarcity factors. |
| Land use | Dimensionless | Measure of the changes in soil quality (Biotic production, Erosion resistance, Mechanical filtration). |
| Ionising radiation, human health | kBq U-235 | Damage to human health and ecosystems linked to the emissions of radionuclides. |
| Particulate matter emissions | Disease incidence | Indicator of the potential incidence of disease due to particulate matter emissions |
Table 2. Parameters that describe resources used
| Parameter | Unit | Description |
| Primary renewable energy (materials) | MJ | Use of renewable primary energy resources as raw materials |
| Primary renewable energy (energy) | MJ | Use of renewable primary energy, excluding renewable primary energy resources used as raw materials |
| Primary renewable energy (total) | MJ | Sum of the two values above |
| Primary non-renewable energy (materials) | MJ | Use of non-renewable primary energy resources as raw materials |
| Primary non-renewable energy (energy) | MJ | Use of non-renewable primary energy, excluding renewable primary energy resources used as raw materials |
| Primary non-renewable energy (total) | MJ | Sum of the two values above |
| Use of secondary material | kg | Material recovered from previous use or from waste which substitutes primary materials |
| Use of freshwater | m3 | Freshwater use in absolute values |
| Use of renewable secondary fuels | MJ | Renewable fuel recovered from previous use or from waste which substitutes primary fuels |
| Use of non-renewable secondary fuels | MJ | Non-renewable fuel recovered from previous use or from waste which substitutes primary fuels |
Table 3. Other environmental information: Waste type
| Indicator | Unit | Description |
| Hazardous waste disposed | kg | Hazardous waste has a certain degree of toxicity that necessitates special treatment |
| Non-hazardous waste disposed | kg | Non-hazardous waste is non-toxic and similar to household waste. It consists of inert waste and ordinary household waste |
| Radioactive waste disposed | kg | Radioactive waste mainly originates from nuclear energy reactors |
Table 4. Other environmental information: Output flows
| Indicator | Unit | Description |
| Components for re-use | kg | Material or components leaving the modelled system boundary which is destined for reuse |
| Materials for recycling | kg | Material leaving the modelled system boundary which is destined for recycling |
| Materials for energy recovery | kg | Material leaving the modelled system boundary which is destined for use in power stations using secondary fuels (minimum energy efficiency 60% or 65% for installations opened after 2008) |
| Energy production | MJ | Energy exported from waste incineration and landfill |
Environmental Cost Indicator: One indicator for all impact categories
Impact categories are not the be-all and end-all of measuring environmental impacts. In many cases, it makes sense to translate them into one aggregated metric, that makes the data comparable.
One popular metric for this is the Environmental Cost Indicator (ECI). You can learn more about ECI in our article about it.
