Life Cycle Impact Assessment: Impact Categories
Life cycle assessment is a tool used to identify the environmental performance of a product throughout its lifespan, from raw material extraction (the “cradle” stage) to disposal after use (the “end-of-life” phase). But what are these environmental impacts? How are they calculated? And which impacts are important to consider?
Let's understand these Impact Categories!
Impact categories are essentially groupings of emissions based on their common environmental damage. They provide quantitative measures for specific categories that can be further analyzed. The impact categories represent the potential impact and can be located anywhere between the LCI results (Life Cycle Inventory) and the category endpoints.
Currently, there are two main methods of Impact Assessment: problem-oriented IA and damage-oriented IA, commonly known as midpoint and endpoint categories. Problem-oriented impact assessment quantifies the amount of emissions that affect a single environmental problem and assigns them a common unit. Damage-oriented impact assessment groups these problem-oriented impact categories based on the overall system they will affect.
In this article, we will focus solely on the midpoint categories and provide some popular examples.
Global Warming Potential (GWP):
Also known as climate change or the greenhouse gas effect, GWP is a widely recognized impact category that quantifies greenhouse gas emissions using a common unit, CO2 equivalent (CO2 eq). The greenhouse effect is a natural occurrence that helps maintain the Earth’s temperature to sustain life on the planet.
Greenhouse gases have the ability to trap heat from the sun and regulate atmospheric temperature. However, due to various anthropogenic sources of greenhouse gases, this effect is accelerating rapidly, leading to higher global temperatures and resulting in climate change events such as heavy rains in some areas, droughts in others, melting ice caps, and rising sea levels.
Major greenhouse gases include CO2, CH4, N2O, O3, H2O, and CFCs. Each gas has its own characterization factor that is multiplied and converted into a common unit, such as kilograms of CO2 equivalent.
Acidification Potential (AP)
Water is the most vital resource stored in various forms, including rivers, wells, lakes, seas, and ice caps. These water bodies can become contaminated with various acidic compounds generated in the troposphere when acidic gases mix with rain. This renders the water unusable.
The sources of these acid-forming compounds are both anthropogenic and natural. Anthropogenic sources include emissions from industries, vehicles, and agricultural activities, while volcanic eruptions are a natural source.
Major acidification potential gases include SOx, NOx, and NH3. These gases are multiplied by their characterization factors to obtain a common unit value, such as kilograms of SO2 equivalent or moles of H+ equivalent.
Ozone Depletion Potential (ODP):
The ozone layer is a protective layer in the Earth’s atmosphere that shields it from harmful UV-B radiation. Exposure to UV-B radiation can cause crop damage, skin cancer, and damage to materials and properties. Therefore, it is crucial to protect this ozone layer from gases that deplete it.
Gases like CFCs and HCFCs, along with their variants, are responsible for damaging the ozone bonds in the stratosphere. ODP is typically reported as kilograms of CFC-11 equivalent.
Other important categories include:
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Impact Categories
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Description
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Unit
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Abiotic Depletion
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This category corresponds to mineral, and resources used. It refers to the measure of the use of nonrenewable sources for energy production.
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Kg Sb eq/ MJ
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Eutrophication
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Occurs when excess of nutrients enters water bodies leading to algal bloom. Affects aquatic ecosytem and water quality.
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kg PO4-eq
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Human toxicity
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Evaluate the toxicity of the emissions on human.
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Kg 1,4-DB eq
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Photochemical oxidation
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This category relates to the formation of tropospheric ozone due to pollutants reacting with sunlight.
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Kg C2H4 eq
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Ecotoxicity
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Assess the impact of emission on Ecosystem.
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Kg 1,4 -DB eq
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