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OECD and EMEP Model Intercomparison Studies: Similarities, Differences, and Outlook

This study compares and contrasts the OECD and EMEP model intercomparison studies, analyzing the similarities and differences in their results and discussing the future direction of the research. The study focuses on the nine relevant box models and explores various indicators for persistence and long-range transport potential.

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OECD and EMEP Model Intercomparison Studies: Similarities, Differences, and Outlook

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  1. POP Model Intercomparison StudiesSupported by OECD and EMEPMartin ScheringerSwiss Federal Institute of Technology Zürich EMEP Task Force on Measurements and ModellingZagreb5 April 2005

  2. Overview • OECD model comparison study • EMEP model comparison study • Similarities and differences, outlook

  3. Nine Multimedia Box Models ChemRange (spatial range) coupled Globo-POP(eACP) SimpleBox Impact 2002 (outflow ratio) Mode of Transport CalTox CEMC L III CEMC L II (CTD) single-media BETR (GLTE) ELPOS(CTD) transport-oriented target-oriented LRTP metric

  4. Indicators for Pov and LRTP • Overall persistence • Residence time at steady state • Potential for long-range transport (LRTP) • Spatial range • Characteristic travel distance • Great lakes transport efficiency • Arctic contamination potential

  5. 3175 Hypothetical Chemicals • Variation of • half-life in air: 5 steps from 4 h to 8760 h (1 year) • half-life in water: 5 steps from 1 day to 10 years–> half-life in soil: t1/2,s = 2·t1/2,w–> half-life in sediment: t1/2,sed = 10·t1/2,w • log Kaw from –11 to 2 in units of 1 • log Kow from –1 to 8 in units of 1 • additional restriction: log Koa between – 1 and 15 • Result: 3175 combinations, called hypothetical chemicals

  6. Pov, ChemRange a: t1/2a = 4 h b: t1/2a = 1 d c: t1/2a = 7 d d: t1/2a = 42 d e: t1/2a = 1 y t1/2w = 1 day atmospheric lifetime of aerosol particles t1/2w = 7 days t1/2w = 42 days t1/2w = 365 days t1/2w = 10 years

  7. Results OECD Model Comparison • For many chemicals, models yield similar results. • Chemicals with strongly different results in two models: • What model environment is most appropriate for what context/purpose? • Land: freshwater and sediment; water shallow; no transport in water; high net deposition of POPs to soils • Ocean water: water much deeper; transport in water relevant; export to deep ocean relevant, net deposition of POPs to surface lower

  8. 1st Publication Environ. Sci. Technol. 39, 2005, in press.

  9. CCl4 HCB PCBs 2n Publication (in prep.) • Use reference chemicals to identify POP-type chemicals

  10. Definition of Pov/LRTP Categories

  11. Ending of OECD Study • Workshop at ETH Zürich, 30–31 August 2005 • Supported by Swiss and German Environmental Agencies and by OECD and UNEP • Presentation of a „unified“ multimedia box model for Pov and LRTP screening, based on the nine models of the OECD study.

  12. EMEP Model Intercomparison Study • 10 highly different models • Different purposes and „endpoints“ • Planned in three stages, start March 2002 (TFMM meeting Geneva) • Stage I: individual phase transfer processes • Stage II: mass balances and concentration and deposition fields; sensitivity analysis • Stage III: persistence and long-range transport potential • Three expert meetings in Moscow (2002–2005) • Current status: stage I finished, stage II nearly finished, stage III started

  13. Participating Models • GLOBO-POP (Canada) • HYSPLIT 4 (USA) • INERIS (France) • LOTOS (Netherlands) • MEDIA (Canada) • MSCE-POP (MSC-E) • POPCYCLING-Baltic (Norway) • SimpleBox (Netherlands) • ADEPT(Netherlands) • ADOM-POP (Germany) • CAM/POPs (Canada) • CliMoChem (Switzerland) • DEHM-POP (Denmark) • ELPOS (Germany) • EVN-BETR and UK-MODEL (UK) • G-CIEMS (Japan)

  14. Stage I: Individual Processes (I) concentration of PCB 153 in precipitation • Wet deposition T, °C

  15. Stage I: Individual Processes (II) concentration of PCB 153 in seawater • Air-seawater exchange 30 74

  16. Stage II: Mass Balances (I) • Mass fractions of PCB 153 in soil

  17. Stage II: Mass Balances (II) • Masses of PCB 153 in air

  18. Stage II: Spatial Distribution mean annual air concentrations of PCB 153 in 2000 (pg/m3) SimpleBox MSCE-POP EVN-BETR DEHM-POP

  19. Stage II: Comparison to Field Data mean annual air concentrations of PCB-153 in 2000 (pg/m3) Measured SimpleBox MSCE-POP DEHM-POP

  20. Main Results, Benefits • Improved understanding of individual environmental processes • Gaseous exchange air-soil • Wet deposition • … • Consistent sets of chemical property data and of process descriptions • Understanding of similarities and differences among models (box models vs. atmospheric dispersion models) • Model improvement

  21. Next Steps • Stage II: • Analysis of mechanistical causes of differences in mass balances, mass fluxes etc. • Stage III: • Use reference chemicals from OECD study • Rank reference chemicals according to Pov and LRTP in all models • Analyze reasons for differences

  22. OECD and EMEP Studies in Comparison • EMEP/MSC-East: • Very different models • Not more than 10 chemicals • Several quantities recorded, also Pov and LRTP • Ranges of model results along with statistical analysis • Analysis of mechanistic differences • OECD: • 9 relatively similar models • 3175 chemicals • 2 endpoints: Pov and LRTP • 92 lists of rank orders • RCCs and binning results • Chemical space plots • Analyses of mechanistic differences between models • Relevant factors: • model geometry • transport in water • degradation on particles • export to deep ocean • target- vs. transport- oriented LRTP metric

  23. OECD study vs. EMEP study OECD study chemical properties individual environmental processes mass balances for different compartments Pov and LRTP

  24. OECD study vs. EMEP study OECD study chemical properties individual environmental processes analysis mass balances for different compartments Pov and LRTP

  25. OECD study vs. EMEP study OECD study chemical properties individual environmental processes analysis mass balances for different compartments Pov and LRTP

  26. OECD study vs. EMEP study EMEP/MSC-East study chemical properties individual environmental processes stage I mass balances for different compartments stage II Pov and LRTP stage III

  27. OECD study vs. EMEP study EMEP/MSC-East study chemical properties individual environmental processes stage I mass balances for different compartments stage II Pov and LRTP stage III

  28. OECD study vs. EMEP study EMEP/MSC-East study chemical properties individual environmental processes stage I mass balances for different compartments stage II Pov and LRTP stage III

  29. OECD study vs. EMEP study EMEP/MSC-East study chemical properties individual environmental processes stage I methods? mass balances for different compartments stage II methods? Pov and LRTP stage III

  30. Reference Chemicals Reference Chemicals: Methods • Select POPs and non-POPs with known environmental distribution • Calculate Pov and LRTP for these chemicals, including variants with high/low half-lives and partition coefficients (parameter uncertainty) • Locate reference chemicals in plots of Pov vs. LRTP* and define fields of high/low Pov and LRTP • Pov: lowest Pov of POPs reference chemicals • LRTP: lowest LRTP of POPs reference chemicals *M. Scheringer, Environmental Science & Technology 31 (1997), 2891

  31. Reference Chemicals Pov-LRTP Plot: Structure

  32. Reference Chemicals Pov-LRTP Plot: Structure

  33. Reference Chemicals Pov-LRTP Plot: Structure

  34. Reference Chemicals Selection of Reference Chemicals POPs non-POPs

  35. CCl4 HCB PCBs Reference Chemicals Results for Reference Chemicals

  36. Reference Chemicals Definition of Pov/LRTP Categories

  37. Reference Chemicals Results Reference Chemicals (I) • In the Pov-LRTP plot, chemicals can be characterized with respect to: • volatility line, transport distance of aerosol particles • the selected reference POPs • atrazine as a compound sensitive to continuous rain • Influence of uncertain chemical properties can be investigated.

  38. Reference Chemicals Results Reference Chemicals (II) • Chemicals in field A should be considered as possible POPs. • Classification depends on lowest Pov and LRTP among reference POPs! • Refinement of these Pov and LRTP criteria? • Several hypothetical chemicals exceeding UNEP criteria do not fall into field A. • Some hypothetical chemicals not exceeding UNEP criteria do fall into field A.

  39. Overall Results: Recipe for POPs Screening • Select a multimedia model that is appropriate for your purpose. • Run your chemical through the model. • Take the maximum of Pov and LRTP from the three emssion scenarios. • Insert these values into the LRTP-Pov plot. • Compare the substance to reference chemicals. • Investigate the sensitivity to uncertain substance data and variable environmental parameters. • Classify, decide, stop, repeat with another model etc.

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