A few Notes on Life Cycle Analysis (LCA)
Definition
Why: How to measure environmental impact of a given product or process
LCA is a technique for assessing the environmental aspects and potential impacts associated with a product by:
- Compiling relevant inputs and outputs
- Evaluating the potential environmental impacts associated with those inputs and outputs
- Interpreting the results of the inventory analysis and impact assessment phases in relation to the objectives of the study
ISO 14040 - From [1] slide 5
! Throughout the whole product/process life cycle: i.e. “cradle-to-grave”
Steps of the methodology
4 stages
-
Goal and scope definition
What to measure, what boundaries, where it is measured…
-
Inventory analysis
All the relevant “streams”
-
Impact analysis
What are the env. impacts for the goals of the step 2.
-
Interpretation
Notes from [2] and [3]:
1. Goal and scope
Goal
Must contain per ISO [wiki] following items:
- Intended application
- Reasons for carrying out the study
- Audience
- “Whether the results will be used in a comparative assertions released publicly”
Scope
-
Product system: activities that transform inputs to outputs to produce the defined function and are within the system boundary.
-
Functional unit: definition of what is being studied. It enables comparison between functionally different systems (?? ex.: 1 m3 tank at standard conditions of methanol produced in the current year in Bavaria with max. 1 wt% impurities ??).
* Questions: what, how much, for how long/many times, where, how well.
-
Reference flow: amount of product or energy needed to realize the functional unit, i.e. to which al other input/outputs are related to. Ex: the X kg of methanol needed to fill the functional unit. This would be equivalent for several methanol production processes.
-
System boundary. Limits of inputs and outputs in accordance to goal.
-
Relevant concepts: technosphere (man-made) and ecosphere (the environment). Elementary flows go between both. These are the ideal boundaries.
-
Background and foreground system. Processes and products specific to product system vs not specific ones (ex.: electricity production of a given region)
-
-
Assumptions and limitations.
-
Data quality requirements. Temporal, geographical and technological coverage (ex: energy mix depending on region!); precision, completeness and representativeness of the data (ex: imports are rounded to …), consistency and reproducibility of the methods; sources (database accessible at european union db for primary electricity generation) ; uncertainty and data gaps (unknown other sources from imports).
-
Allocation procedure: a.k.a. multifunctionality of a product system i.e. the product system delivers other types of function in addition to the defined goal. There is a hierarchy of methods according to ISO 14044 [Hauschild]
- Avoid by Sub-division (divide into smaller processes to separate prod from co-prods)
- Avoid by System Expansion (integrate the secondary function into the system boundaries, avoiding the impacts)
- Allocation using physical causality
- Allocation using representative physical parameter
- Allocation w/ other parameters (e.g. economic)
1 is essentally increasing the resolution of the process model
2 searches for substitutes of each one which provide the env flows for each function.
3, 4 and 5 partition the environmental flows of primary and secondary and retain only the ones associated with the primery ones.
-
Impact Assessment: outline of the impact categories.
-
Documentation of data: Explicit documentation of IO
2. Life cycle inventory (LCI)
inventory of flows from and to ecosphere from the product system.
Desired: primary source data collection. Alternative: secondary data from databases, literary sources and past studies. All documented ofc.
Three different LCI methods:
- Process-based (we model the product system)
- Economic IO (use info on elementary flows of associated with one unit of economic act.)
- Hybrid (1 and 2)
3. LCI Assessment
Assessment of flows identified in LCI
Mandatory:
- Selection of impact categories, indicators and characterization models (which impacts do I need to assess??). Relevant to region. In practice: LCIA method such as TRACI, ReCiPe, AWARE.
- Classification of inventory results -> assign LCI results to impact categories of 1. Usage of LCA db and software.
- Characterization quantify 1 and 2 with category indicators (how much does each LCI results contribute??)
Optional: normalization, weighting, grouping.
4. Interpretation
ISO 14043. Include:
- Identification of issues of LCI and LCIA
- Evaluation with completeness, sensitivity and consistency analyses
- Conclusions, limitations and reccomendations
Here are included sensitvity and uncertainity evaluations (Hauschild Chapter 11).
Sensitvity and Uncertainity
Relevant topics:
- Precision vs accuracy
- Variability ()
- Sensitivity (extent to which the variation of an input influences the model results)
- Trade-off between simple and complex modeling -> complex does not always lower uncertainity (https://doi.org/10.1007/BF02994186)
Representation: probability distribution (PDF - PD function). Basic concepts:
- std dev
- average
- mode
- median
- percentiles
- confidence intervals
Many types available to use: in LCA generally log-normal. Useful to approximate unknown distribution and facilitates uncert. propagation methods. [Ch 11, p. 285-286]
Types: temporal, spatial, between objects variability, param uncertainty, model (structure) uncert., uncert. due to choices, …
Influences:
Propagation methods:
- Semiquantitative pedigree matrix (ecoinvent!) for uncert. of LCI data. ?Kind of expert based, but becoming less (more comparison between published data)?
- Monte Carlo (MC) (SimaPro, openLCA). Needs sufficiently (waht is that anyway?) number of runs: Latin hypercube sampling (LHS) or simple random sampling (SRS)
- Generate random samples of input vars
- Apply model and calculate LCA results
- Analyze the model outputs
- Taylor series expansion (CMLCA)
References
[1] Intro from MIT: https://www.youtube.com/watch?v=gpuvUU0Nl4k
[2] Great LCA book: Hauschild, M. Z., Rosenbaum, R. K., & Olsen, S. I. (2018). Life cycle assessment (Vol. 2018). Springer International Publishing, Cham. https://doi.org/10.1007/978-3-319-56475-3.
[3] Wikipedia article (checked with the book above): https://en.wikipedia.org/wiki/Life-cycle_assessment.