An input-output-based life cycle inventory (IO-based LCI) is grounded on economic environmental input-output analysis (IO analysis). It is a fast and low-budget method for generating LCI data sets, and is used to close data gaps in life cycle assessment (LCA). Due to the fact that its methodological basis differs from that of process-based inventory, its application in LCA is a matter of controversy. We developed a German IO-based approach to derive IO-based LCI data sets that is based on the German IO accounts and on the German environmental accounts, which provide data for the sector-specific direct emissions of seven airborne compounds. The method to calculate German IO-based LCI data sets for building products is explained in detail. The appropriateness of employing IO-based LCI for German buildings is analyzed by using process-based LCI data from the Swiss Ecoinvent database to validate the calculated IO-based LCI data.
The extent of the deviations between process-based LCI and IO-based LCI varies considerably for the airborne emissions we investigated. We carried out a systematic evaluation of the possible reasons for this deviation. This analysis shows that the sector-specific effects (aggregation of sectors) and the quality of primary data for emissions from national inventory reporting (NIR) are the main reasons for the deviations. As a rule, IO-based LCI data sets seem to underestimate specific emissions while overestimating sector-specific aspects.