LCA Methodology Country-Dependent Characterisation Factors for Acidification and Terrestrial Eutrophication Based on Accumulated Exceedance as an Impact Category Indicator

Background, Aims and Scope. Several authors have shown that spatially derived characterisation factors used in life cycle impact assessment (LCIA) can differ widely between different countries in the context of regional impact categories such as acidification or terrestrial eutrophication. Previous methodology studies in Europe have produced country-dependent characterisation factors for acidification and terrestrial eutrophication by using the results of the EMEP and RAINS models and critical loads for Europe. The unprotected ecosystem area (UA) is commonly used as a category indicator in the determination of characterisation factors in those studies. However, the UA indicator is only suitable for large emission changes and it does not result in environmental benefits in terms of characterisation factors if deposition after the emission reduction is still higher than the critical load. For this reason, there is a need to search for a new category indicator type for acidification and terrestrial eutrophying in order to calculate site-dependent characterisation factors. The aim of this study is to explore new site-dependent characterisation factors for European acidifying and eutrophying emissions based on accumulated exceedance (AE) as the category indicator, which integrates both the exceeded area and amount of exceedance. In addition, the results obtained for the AE and UA indicators are compared with each other. Methods. The chosen category indicator, accumulated exceedance (AE), was computed according to the calculation methods developed in the work under the United Nations Economic Commission for Europe (UNECE) Convention on Longrange Transboundary Air Pollution (LRTAP). Sulphur and nitrogen depositions to 150x150 km2 grid cells over Europe were calculated by source-receptor matrices derived from the EMEP Lagrangian model of long-range transport of air pollution in Europe. Using the latest critical load data of Europe, the sitedependent characterisation factors for acidification and terrestrial eutrophication were calculated for 35 European countries and 5 sea areas for 2002 emissions and emissions predicted for 2010. In the determination of characterisation factors, the emissions of each country/area were reduced by various amounts in order to find stable characterisation factors. In addition, characterisation errors were calculated for the AE-based characterisation factors. For the comparison, the results based on the use of UA indicator were calculated by 10% and 50% reductions of emissions that corresponded to the common practice used in the previous studies. Introduction The purpose of characterisation in Life Cycle Impact Assessment (LCIA) is to estimate the potential contributions of different environmental intervention (emissions, resource extractions and land use) to different impact categories and to sum the amounts of interventions into a single number within each impact category. An impact category such as acidification or terrestrial eutrophication is a class repreAcidification and Terrestrial Eutrophication LCA Methodology 404 Int J LCA 11 (6) 2006 senting environmental issues into which Life Cycle Inventory (LCI) results (environmental interventions) may be assigned (ISO 2000). In characterisation, values of environmental interventions are converted to impact category indicator results by multiplying values of interventions by the corresponding characterisation factors. The determination of characterisation factors within a certain impact category is the core issue in order to produce scientifically-based characterisation results. The determination needs characterisation modelling in which appropriate physical, chemical and biological processes for the selected impact category, linking the LCI results to category indicators, are taken into account. A category indicator is a quantifiable representation of an impact category, being the object of characterisation modelling. Thus, characterisation means that values of environmental interventions are aggregated using the commensurate unit of the category indicator. The category indicator can be defined at any level of the chain of environmental mechanism. Acidification is one of the most commonly used impact categories in LCA applications. In the earlier stages of LCIA methodology, only site-generic (site-independent) characterisation factors for acidification were used (Heijungs et al. 1992). However, the location of the acidifying emission source can cause different responses in surrounding ecosystems, depending, for example, on local atmospheric conditions and sensitivity of ecosystems subject to deposition from that source (e.g. Hettelingh et al. 1995, Posch et al. 2001). For this reason, there have been research activities to derive site-dependent characterisation factors for acidifying compounds. In the context of the determination of site-dependent characterisation factors, many studies have used the RAINS model developed by the International Institute for Applied System Analysis (IIASA) (Amann et al. 1999). In addition, a similar type of model (EcoSense) developed in ExternE (External Costs of Energy) project (European Commission 1999) has been used together with critical load data (Posch et al. 1997) for the determination of site-dependent characterisation factors. Using the RAINS model, Potting et al. (1998) and Krewitt et al. (2001) using the Ecosense model produced country-specific characterisation factors for acidification in which the category indicator was the change in Area of Unprotected ecosystems (UA) based on critical loads. The calculations were based on a 10% acidifying emission reduction (Potting et al. 1998) or on a 10% emission increase in each country in Europe for a chosen assessment year (Krewitt et al. 2001). Huijbregts et al. (2001) calculated the results in which the indicator was the marginal change in the hazard index of all ecosystems in Europe, where the critical load is actually exceeded (only above scenario) and whether or not the critical load is actually exceeded (above and below scenario). Bare et al. (2003) quantified, in the United States of America, the share of emission depositing on land with the help of atmospheric fate and transport modelling to account for expected source-location-dependent differences in wet and dry deposition. However, they had no critical loads in the calculations and, thus, did not take into account the vulnerability of ecosystems. In terrestrial eutrophication, the determination of country-specific characterisation factors had been calculated according to the same principles as in acidification (Huijbregts et al. 2001, Krewitt et al. 2001, Potting and Hauschild 2004, see also Potting et al. 2002). Several site-dependent factors and alternative indicators affecting the characterisation factors have been preliminarily discussed from within-country viewpoints (Johansson and Seppälä 2004). In the case of the UA indicator, Hettelingh et al. (2005) showed that the calculations based on emission changes of minus 50% are generally more reliable for the determination of characterisation factors for acidification than the calculations based on emission changes of minus or plus 10%, because they enable one to reproduce the exact model over a wider range of emission changes. They also produced new country-dependent characterisation factors for acidification using emissions of the year 2000 and the latest critical load database. The method used avoids some shortcomings of the RAINS model, in which critical load exceedances can only be computed with a certain degree of approximation. This calculation improved the characterisation factors of acidification based on the earlier works of the UA indicator (Potting et al. 1998, Potting and Hauschild 2004, Krewitt et al. 2001). However, Hettelingh and his colleagues (2005) recommended that the possibilities to use alternative indicators used in the support of European air pollution policies, such as average accumulated exceedance, should be studied. Pleijel et al. (1997) had drawn the same kind conclusion earlier and calculated the characterisation factors for acidification based on the amount or share of emission depositing on ecosystems calculated for a limited number of Swedish and European regions for which the critical load is exceeded. Heijungs and Huijbregts (1999) criticised the calculation approach based on the changes in unprotected ecosystem areas, because even small changes in emissions may result in either no increase in the protected areas at all or in (large) jumps in the area protected. This applies to a situation in which only a few critical load functions are given for a grid cell (Posch et al. 2001). To avoid this feature, the difference between current deposition and critical loads should be reflected more strongly in the calculations. Therefore, there is a need to search for a new indicator for the calculations of characterisation factors for acidification and terrestrial eutrophication. The aim of this article is to address a category indicator accumulated exceedance, for emissions contributing to acidification and terrestrial eutrophication, and to compute the corresponding characterisation factors for European countries and five-sea areas. In addition, the new values are compared with the values produced by the earlier approaches based on the changes in unprotected ecosystem areas.