Characterization Factors in Life Cycle Impact Assessment

LCI ResultsRaw emission dataCharacterizationApply factorsImpact ScoreCO₂ equivalentsExample: Converting methane to CO₂e1 kg CH₄ × GWP₁₀₀ (28) = 28 kg CO₂e2 kg N₂O × GWP₁₀₀ (265) = 530 kg CO₂eTotal impact: 558 kg CO₂e

What Are Characterization Factors?

Characterization factors are multipliers that convert different substances into equivalent amounts of a reference substance for a specific environmental impact category. They are based on scientific models that describe the environmental mechanism between the emission of a substance and its potential impact.

Global Warming Potential (GWP)

Global Warming Potential is the most widely used characterization factor for climate change impact assessment. GWP measures how much heat a greenhouse gas traps in the atmosphere relative to carbon dioxide (CO₂) over a specific time period.

Example Calculation:

For a process that emits:

• 100 kg CO₂
• 5 kg CH₄
• 0.5 kg N₂O

Total GWP₁₀₀ = (100 × 1) + (5 × 28) + (0.5 × 265) = 372.5 kg CO₂e

Other Common Characterization Factors

• Acidification Potential (AP): Converts acidifying emissions to SO₂ equivalents
• Eutrophication Potential (EP): Converts nutrient emissions to PO₄³⁻ equivalents
• Ozone Depletion Potential (ODP): Converts ozone-depleting substances to CFC-11 equivalents
• Photochemical Ozone Creation Potential (POCP): Converts emissions to ethene equivalents

Applying Characterization Factors in LCIA

The application of characterization factors involves several steps:

1. Classification: Assigning inventory flows to impact categories
2. Characterization: Multiplying inventory data by appropriate factors
3. Optional normalization: Comparing results to reference values
4. Optional weighting: Applying value-based weighting factors

Key Considerations:

• Time horizons (e.g., GWP₂₀ vs. GWP₁₀₀)
• Regional variations in impact pathways
• Uncertainty in characterization models
• Regular updates to factor values

Best Practice: When using characterization factors, always document the source, version, and time horizon of the factors used. This ensures transparency and reproducibility of the impact assessment results.