AQA · GCSE · Chemistry
Course version: 8462 · Version from Sept 2018
Allocating numerical values to pollutant effects is less straightforward…
Full specification wording
Life cycle assessment: Allocating numerical values to pollutant effects is less straightforward and requires value judgements, so LCA is not a purely objective process.
Once an LCA has measured emissions, someone must decide how harmful each pollutant is.
Checked against the AQA 8462 specification (opens in a new tab) on .
- Point 3 of 5
- 2 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Once an LCA has measured emissions, someone must decide how harmful each pollutant is. Assigning a number to that harm is not a simple measurement. For example, 1 kg of carbon dioxide and 1 kg of sulfur dioxide have different effects: one contributes to climate change, the other to acid rain. Deciding that one is ten times worse than the other is a value judgement, not a reading from an instrument. Different people may weight health, habitats or cost differently, so two valid LCAs can reach different conclusions. This is why an LCA is not purely objective: the data collection can be objective, but the interpretation involves choices.
What earns the marks
- Explain that pollutant effects must be weighted or scored before they can be compared.
- State that weighting involves value judgements about which impacts matter most.
- Give an example of two pollutants with different effects, such as carbon dioxide and sulfur dioxide.
- Conclude that different weightings can lead to different LCA conclusions, so the process is not purely objective.
- Distinguish objective measured data from subjective interpretation.
Common mistakes and how to put them right
Claiming an LCA gives one definite correct answer.
Put it right by stating that weightings are choices.
Saying all pollution is equally harmful.
Put it right by explaining that effects differ in type and severity.
Confusing the measurement stage with the weighting stage.
Put it right by separating data collection from value judgements.
Exam tips
- Use the phrase 'value judgement' and explain what choice is being made.
- Contrast a measured quantity with a weighted score to show the difference.
- Refer to a named pollutant effect to make the judgement concrete.
Try the lesson
The start of the Life cycle assessment: Allocating numerical values to pollutant effects is less straightforward and requires value judgements, so LCA is not a purely objective process. lesson, made from checked teaching notes for this specification point.
Have a go first
Why is a Life Cycle Assessment (LCA) not considered a purely objective process?
Listen
Once an LCA has measured emissions, someone must decide how harmful each pollutant is. Assigning a number to that harm is not a simple measurement. For example, 1 kg of carbon dioxide and 1 kg of sulfur dioxide have different effects: one contributes to climate change, the other to acid rain. Deciding that one is ten times worse than the other is a value judgement, not a reading from an instrument. Different people may weight health, habitats or cost differently, so two valid LCAs can reach different conclusions. This is why an LCA is not purely objective: the data collection can be objective, but the interpretation involves choices. A strong answer earns marks for these points. Explain that pollutant effects must be weighted or scored before they can be compared. State that weighting involves value judgements about which impacts matter most. Give an example of two pollutants with different effects, such as carbon dioxide and sulfur dioxide. Conclude that different weightings can lead to different LCA conclusions, so the process is not purely objective. A common slip: Claiming an LCA gives one definite correct answer. Instead, stating that weightings are choices. Exam tip: Use the phrase 'value judgement' and explain what choice is being made.
Key words
Say what each word means before you turn the card.
Value judgements
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Weighting pollutant effects
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See every definition
- Value judgements
- Decisions about how harmful each pollutant is, which are choices rather than readings from an instrument.
- Weighting pollutant effects
- Assigning a number to the harm caused by each pollutant so that effects can be compared.
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