Uncertainty and sensitivity analysis of normalization factors to methodological assumptions

Abstract

Normalisation factors are calculated as results of regional/global inventories of emission and resources characterised trough impact assessment methods. Several methodological assumptions are needed for building the inventory. Sala et al 2015 presented a set of normalisation factors for the EU 2010 defining a methodological approach for sources selection and for building proxy indicators. Qualitative and quantitative uncertainty evaluation is needed for assessing the robustness of final figures. Five sources of uncertainty have been analysed in this work: (F1) the selection of the sources of data; (F2) the classification of data as life cycle inventory (LCI) elementary flows; (F3) the classification of substances for characterization; (F4) the specification of the emission compartments; and (F5) the use of spatially differentiated characterization factors. The sensitivity of the normalization factors to such uncertainties were assessed through a global sensitivity method, for the impact categories acidification (ACID), terrestrial eutrophication (ET), marine eutrophication (EM), photochemical ozone formation (POF), respiratory inorganics/particulate matter (RIPM) and water depletion (WD).The uncertainty associated with the methodological choices made for calculating normalization factors (Sala et al 2015) was assessed. Generally the value calculated by Sala et al (2015) compare well against average and median values estimated in this analysis for ACID, ET, EM and POF. Instead, the impact categories RIPM and WD show different patterns, for the former, although the average value is very similar, the median value is far lower than the normalization factor reported by Sala et al. (2015). For what concerns WD, the median value is much higher. Future improvements of the normalization factors should therefore prioritize the development of more detailed inventories of emissions by including: higher substance resolution, height of emission as well as the use of spatially differentiated characterization factors. The authors recommend that the normalization factors from Sala et al. (2015) are applied together with two additional sets of normalization factors i.e. the 'median values' and the set of 'average + standard deviation' values, so to better capture their uncertainty. Similarly, the interpretation of the results should build on the qualitative estimates of robustness provided by Sala et al. (2015).