Life cycle assessment (AQA GCSE Chemistry): Revision Notes
Life cycle assessment
What is a life cycle assessment?
A life cycle assessment (LCA) is a method used to work out the total environmental impact of a product. It looks at every stage of the product's life, from getting the raw materials to throwing it away at the end.
Think of it like following a product's complete journey and measuring how much it affects the environment at each step. This comprehensive approach helps us understand the true environmental cost of products we use every day.
The stages of a life cycle
The life cycle has six main stages that form a circle:
The Six Stages of Product Life Cycle
These stages form a continuous cycle because disposal often leads back to raw material extraction through recycling or decomposition:
- Raw material extraction - Getting materials from the Earth
- Raw material processing - Turning raw materials into useful materials
- Manufacturing and packaging - Making the product and putting it in packaging
- Transport - Moving the product to shops and customers
- Use and operation - When people actually use the product
- Disposal after use - What happens when the product is thrown away
Each stage uses energy and resources, and produces waste that can harm the environment.
What factors do we measure?
When doing an LCA, scientists look at four main things:
- Use of energy - How much electricity, fuel, or other energy is needed
- Use of raw materials - How many natural resources are used up
- Use of water - How much water is needed in the process
- Production of waste - How much rubbish and pollution is created
These factors help scientists get a complete picture of environmental impact rather than focusing on just one aspect.
Real example: Shopping bags
Worked Example: Government LCA Study on Shopping Bags
The government conducted a comprehensive LCA study comparing three types of shopping bags:
- Single-use plastic bags - Used once then thrown away
- Plastic bags for life - Stronger plastic bags used many times
- Cotton bags - Fabric bags that last a long time
Energy Use Results:
- Single-use plastic bag: 22.1 MJ of energy
- Plastic bag for life: 167.5 MJ of energy
- Cotton bag: 39.6 MJ of energy
Key Finding: A plastic bag for life uses 7.6 times more energy than a single-use plastic bag.
Waste Production Results:
- Single-use plastic bag: 420g of waste
- Plastic bag for life: 170g of waste
- Cotton bag: 1800g of waste
Key Finding: A cotton bag produces 10.6 times more waste than a plastic bag for life.
What this tells us
Key Insights from the LCA Study:
- Cotton bags use less energy than bags for life, but much more than single-use bags
- Cotton bags create far more waste than plastic bags
- You need to use a cotton bag many times to make it better for the environment than single-use plastic bags
Critical Point: This shows why claims like "cotton bags are better because they use less energy" can be misleading. The LCA looks at all the factors together, not just one.
Limitations of LCA
Important Limitations to Consider:
- LCA studies need to be checked by independent experts to make sure they're reliable
- Different studies might give different results
- It's hard to measure every single environmental impact
- The results depend on how many times you reuse the product
These limitations mean that LCA results should be interpreted carefully and compared with other studies when making environmental decisions.
Remember!
Key Points to Remember:
- Life cycle assessment measures the total environmental impact of a product from start to finish
- It looks at six stages: extraction → processing → manufacturing → transport → use → disposal
- Four main factors are measured: energy use, raw materials, water use, and waste production
- All factors must be considered together - looking at just one factor can be misleading
- LCA studies help us make better choices about which products are truly better for the environment