1. A critical evaluation of country-dependent impact factors for acidification in Europe summary of a scientific paper submitted for review -Do Not Quote or Cite - presentation of work by CCE and University of Groningen at the 29 th Meeting TFIAM, 10-12 May 2004, Amiens, by Jean-Paul Hettelingh Follow up of 28 th TFIAM; EB.AIR/GE.1/2003/4 para. 27 Paper authors: Jean-Paul Hettelingh Max Posch José Potting (Univ. Groningen)

2. Impact factors...establish a linear relationship between changes in European ecosystem area protection and a change in the emissions of S or N compounds in one country (emissions of all other countries remaining unchanged) …have been derived from (different) integrated assessment models, e.g. RAINS (Potting et al., 1998) and ECOSENSE (Krewitt et al., 2000)...are increasingly used (e.g. European Commission 2003) in applications to assess external costs of energy related activities and to assess surrogates for monetary assessments of changes in ecosystem protection caused by changes in country emissions (so called “avoidance costs”) …depend on (a) the reference year of the emissions, (b) the atmospheric transport model, and (c) the area and vulnerability of receptors or ecosystems. …should be scientifically sound and sufficient knowledge of their reliability/uncertainty should be communicated with them, if they are to be trusted, e.g., in cost benefit analysis of European air pollution policies…triggering this paper

3. Objective … describes results of a systematic analysis to derive European impact factors for acidification, Derive new impact factors for EU23 (EU25 ex. Malta and Cyprus) plus Norway, Switzerland and Rest-of-Europe emission regions, relative to the UNECE- European ecosystems … test their robustness, … make recommendations to delimit the usefulness of the impact factors for providing sound support to European air pollution policies.

4. Approach EXACT MODEL: using recent data on critical loads, on emissions of sulphur and nitrogen compounds for 2000 and 2010 and source-receptor matrices for atmospheric transport derived from the EMEP lagrangian model LINEAR MODEL: A-A 2000 = p i * (E i -E i 2000 ), p i = impact factor; i = country and pollutant = 1…3*26; A-A 2000 = change of unprotected ecosystem (km 2 ) relative to 2000; E-E 2000 = change of emission relative to 2000. Test conditions under which the LINEAR MODEL yields results similar to the EXACT MODEL Compare the result to impact factors p i which have (tentatively) been used in European cost benefit analysis e.g. where p i was derived from an emission change of +10% (to mimic Krewitt et al., 2000) and earlier published results using -10% (to mimic Potting, 1998)

5. Results of exact model computations of the impact factor p i =dA/de i (steps of 1% between -100% to +20% emission change) SO 2 NO 2 NH 3

6. Comparison of EXACT to LINEAR model for 200 random emission reductions Random sampling of emission changes: -70%<SO 2 <+30% -50%<NO 2 <+30% -30%<NH 3 <+30%

7. Conclusions More robust impact factors for acidification have been derived for 26 European emission regions. A linear model which is calibrated to emission changes of –50% is generally more reliable than impact factors which are based on emission changes of plus or minus 10%. Application of these impact factors are justified for emission reductions up to 30% in total European emissions, compared to 2000, which is within the range of currently agreed emission reductions in 2010 relative to 2000. Therefore, carefully derived impact factors can be used for the support of the revision of existing European air pollution agreements

8. Recommendations The application of linear approximations of exact models used in integrated assessment may expedite the analysis of the impact of individual country emissions on the protection of ecosystems in Europe. Generalisation to other well-known indicators used in the support of European air pollution policies, such as the average accumulated exceedance, requires further work (non-linear underlying function) The reliability of such simplified indicators in the assessment of, e.g., cost benefit analysis, requires a comprehensive understanding of possible error propagation. Careful consideration is required of the fact that critical loads are not based on dose-response relationships. Further research is needed to justify the use of impact factors based on critical loads as a surrogate for dose-response relations. ICP-M&M National Focal Centres need to be involved in understanding new applications of their critical load data.