POP Model Intercomparison Study. Stage II. Comparison of mass balance estimates and sensitivity studies.

EMEP/MSC-E Technical Report 4/2005
DRAFT

V.Shatalov, E.Mantseva, A.Baart, P.Bartlett, K.Breivik, J.Christensen, S.Dutchak, S.Gong, A.Gusev, K.M.Hansen, A.Hollander, P.Huang, K.Hungerbuhler, K.Jones, G.Petersen, M.Roemer, M.Scheringer, J.Stocker, N.Suzuki, A.Sweetman, D.van de Meent, F.Wegmann

ABSTRACT

Following the recommendations of the Executive Body for the Convention on Long-Range Transboundary Air Pollution UN ECE [ECE/EB.AIR/75], the POP model intercomparison study was initiated under EMEP in 2002. Three EMEP expert meetings on intercomparison of POP models have been held since that year (Moscow, Russia, 2002; 2003; 2005).

Main aim of POP model intercomparison study is to exchange scientific experience between different groups of POP modelers. National experts from a large number of countries take part in this study, which concerns a wide spectrum of models designed for the simulation of POP behaviour in the environment and differing by their type (box or spatially resolved), resolution and scope (from regional to global scales). According to the agreed programme, the POP model intercomparison study is performed within three stages:

Stage I. Comparison of descriptions of main processes determining POP behaviour in various environmental compartments.

Stage II. Comparison of mass balance estimates and calculated deposition and concentration fields of POPs in different environmental compartments. Sensitivity study with respect to physical-chemical parameter values used in basic process descriptions and mass balance estimates.

Stage III. Comparison of calculated overall environmental persistence and long-range transport potential for evaluation of new substances

Stage I of the intercomparison study was launched in 2002 and completed last year. Fourteen scientific groups from Canada, the Czech Republic, Denmark, France, Germany, Japan, the Netherlands, Norway, Switzerland, the United Kingdom, the USA and representatives of the OECD and MSC-E took part in the first stage. At which model approaches to the description of such processes as gas/particle partitioning, dry deposition of particulate phase, wet deposition, gaseous exchange between the atmosphere and different types of underlying surface (soil, water, vegetation) and degradation processes were considered. This implied the comparison of process descriptions as well as results of relevant computation experiments. Main outcome of Stage I was published in the joint Technical Report 1/2004 "POP Model Intercomparison Study. Stage I. Comparison of descriptions of main processes determining POP behaviour in various environmental compartments" [Shatalov et al., 2004].

Stage II of the POP model intercomparison study has been ongoing since 2004. The third EMEP expert meeting on intercomparison of POP models (Moscow, February, 2005) was attended by national experts from Canada, Germany, Japan, the Netherlands, Norway, Switzerland, the United Kingdom, the USA and MSC-E. Experts and their eleven models participating in the intercomparison study at present are given in "List of partisipants".

At the meeting results of computational experiments on calculation of mass balance and spatial distribution of depositions and concentrations together with a comparison of model results with monitoring data performed by participants in the framework of Stage II were discussed in depth. Sensitivity of each model to variation in physical-chemical parameter values used in mass balance estimates as well as in descriptions of basic processes was also considered. At this stage PCB-153 (first priority), and PCB-28, PCB-180 and B[a]P (second priority) are considered within the computational experiments.

Since the beginning of 2005 Stage III of the POP model intercomparison study has been started. This stage is aimed at the comparison of relative order in ranking a number of chemicals with respect to LRTP and Pover calculated by different models. An extended work-programme and time-schedule of Stage III were elaborated at the meeting.

The list of participating models

Model name Experts Institution
1 HYSPLIT 4 - P. Bartlett CBNS, Queens College, USA
2 EVN-BETR and UK-MODEL - K. Jones, A. Sweetman Lancaster University, UK
3 CliMoChem - M. Scheringer, J. Stocker,K. Hungerbuhler, F. Wegmann ETH Zurich, Switzerland
4 CAM/POPs - S. Gong, P. Huang Air Quality Research Branch, Canada
5 G-CIEMS - N. Suzuki National Institute for Environmental Studies, Japan
6 ADOM-POP - G. Petersen GKSS, Germany
7 DEHM-POP - J. Christensen, K.M. Hansen National Environmental Research Institute, Denmark
8 SimpleBox D. - van de Meent, A. Hollander RIVM Laboratory for Ecological Risk Assessment,the Netherlands
9 LOTOS - M.G.M. RoemerA.C. Baart TNO-MEP, the Netherlands
10 ADEPT - Delft Hydraulics, the Netherlands
11 MSCE-POP - S. Dutchak, V. Shatalov,A. Gusev, E. Mantseva EMEP/MSC-E
POP emissions and measurements - K. Breivik NILU, Norway

As it was agreed, a detailed analysis of similarities and distinctions between different models in results on Stage II calculations will be presented as a part of final report on the whole POP model intercomparison study. A sensitivity study on wet deposition process performed at Stage II includes a comparative model simulation of the atmospheric scavenging of particulate B[a]P over the entire troposphere containing a precipitating cumulus cloud with different precipitation rates. Model estimates obtained by ADOM-POP and MSCE-POP within this study will be discussed and presented also in the final report on the whole POP model intercomparison study.

In this Intermediate Technical Report a preliminary analysis of results obtained by participating models within Stage II up to May 2005 is presented. This report is organized in four chapters and five annexes. Brief outline of their contents is given below.

Chapter 1 is devoted to the description of the programme on Stage II of the POP model intercomparison study.

In Chapter 2 a brief overview of the input data used in Stage II calculation experiments is presented. Description of the calculation domain specified for the experiments (land cover data, leaf area index, organic matter content in the soil, parameters of the environmental compartments), physical-chemical properties and degradation rate constants for pollutants in question, emission scenario and measurement data is included. There is also information on initial concentrations of pollutant in main media obtained by the participating models for the end of 1999. In addition, alternative data set of physical-chemical properties for the three considered congeners is presented in Annex A.

Chapter 3 provides information on comparison of results of Stage II computational experiments for PCB-153 obtained by the participating models. Mass balance estimates, deposition and concentration fields in different environmental compartments and results of sensitivity study with respect to physical-chemical parameter values used for mass balance estimates are discussed in this chapter. The comparison of model results on POP depositions and concentrations in various environmental compartments with monitoring data is also presented. Comparison of results of Stage II computational experiments for PCB-28 and PCB-180 is given in Annexes B and C, respectively.

In Chapter 4 results of the sensitivity study with respect to substance-specific properties used in the description of basic processes are presented for PCB-153. Comparison of the similar results for PCB-28 and PCB-180 is given in Annexes D and E, respectively.

Main conclusions are drawn in the end of the Intermediate Technical Report.