POPs model intercomparison study

The work on POP model intercomparison is carried out in accordance with the recommendation of the Executive Body for the Convention on Long Range Transboundary Air Pollution (ECE/EB.AIR/75).

The study concerns a wide spectrum of models designed for simulating POP behaviour in the environment. These models can be spatially resolved or generic. Below, they are referred to as POP models.

Objectives

The main objectives of the intercomparison study are::

to strengthen the exchange of scientific expertise between different groups working in the field of POP modelling;
to increase the transparency of existing POP models and their results: model concept, parameterisations, temporal and spatial resolution and output and uncertainties;
to harmonise the output parameters of POP models of different types and complexity for obtaining comparable results at different levels of regulatory activities;
to consider model approaches to the evaluation of new substances.

Stages of the intercomparison

The model intercomparison study is performed in the following stages.

Stage I

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

Events
The first EMEP meeting on POP model intercomparison study 13-14 November 2002, Moscow, Russia

Second EMEP expert meeting on intercomparison of POP models 10-11 December 2003, Moscow, Russia
Minutes

MSC-E Technical Report 1/2004 "POP Model Intercomparison Study. 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.

Third EMEP expert meeting on intercomparison of POP models 10-11 February 2005, Moscow, Russia
Minutes

MSC-E Intermediate Technical Report 7/2005 "POP Model Intercomparison Study. Stage II. Comparison of Mass Balance Estimates and Sensitivity Studies"

Stage III

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

At Stage I, model descriptions of the main processes determining POP fate in the environment (scavenging, partitioning, degradation etc.) are compared. This implies the comparison between the approaches to parameterisation of these processes by the models and between the models' operation. The latter is performed via relevant computational experiments.

At Stage II, the balance values are compared (PCB masses in different environmental compartments: atmosphere, soil, water, vegetation; masses of PCB degraded in these compartments; mass fluxes of PCB transported in/out of the specified domain; mass fluxes of PCB transported from one compartment to another; and PCB concentrations at each interface). The comparison is carried out on agreed conditions (e.g., land cover data, leaf area index, organic matter content in the soil, environmental temperature regime etc.) and with the use of input data on emissions with zero initial concentrations of PCBs in environmental media and, as optional, with initial concentrations for the specified calculation domain (35°N - 70°N; 10°W - 30°E). Additionally, the comparison between spatial distribution patterns of depositions and PCBs concentrations in various environmental compartments as predicted by different models is performed; these characteristics can be also compared with monitoring data (optional). Sensitivity studies with respect to physical-chemical parameter values used in the process descriptions and mass balance estimates are carried out. The second intermediate report can be an output of this stage.

At Stage III, model estimates of the long-range transport potential and the overall environmental persistence data on POPs are compared. Such a comparison can be performed for chemicals proposed below. The results of the study should be published in the final report including the results of all stages, conclusions and recommendations.

Pollutant selected for the intercomparison: First priority: PCB-153. Second priority: B[a]P, lindane, PCB-28, PCB-180, as a new pollutant - PBDE (was proposed by R. Farret ).

Computational experiments with PCB-153 are agreed to be the subject of this intercomparison study. For other selected pollutants, it is proposed to carry out computational experiments on the voluntary basis.

Input data sets:

"Reference data set":
Taking into account recommendations of the first meeting, the internally consistent data sets of key physical-chemical properties and degradation rates of PCBs hereinafter referred to as "reference data sets" were proposed for model testing. Calculations within the sensitivity studies with respect to physical-chemical parameters should be performed at Stage II with the help of these data sets. For models using "reference data sets" as own physical-chemical properties, alternative data sets based on individual data of some other participating models are proposed for this sensitivity study.

Emission data:
Officially reported emission data on PCBs are still incomplete in terms of their spatial and temporal coverage to satisfy the data requirements for the calculation experiments to be performed at Stage II. Therefore, consistent global atmospheric emission estimates presented by [Breivik et al. 2002] (see also www.nilu.no/projects/globalpcb/) have been chosen. The higher (or worst-case) emission estimate is to be applied, as this particular scenario appears to be more reasonable on the global scale [Wania and Daly, 2002; Meijer et al. 2003].

Base year for the intercomparison: : 2000

Time-schedule: