Programme of the I stage of the POP intercomparison study

Stage I is aimed at the comparison of descriptions of basic processes affecting POP fate in the environment (listed below). Such comparison is based on the analysis of process descriptions (approach and parameterisation) used in different POP models and computational experiments.

First, mathematical description of the selected processes and parameters needed for modelling are analysed. On the basis of this analysis the agreed sets of internally consistent key physical-chemical properties of PCBs referred below as "reference data sets" are worked out for model testing. These data sets will be used for evaluation of influence of differences in values of POP physical-chemical parameters on model output at Stage II. Then a number of computational experiments is carried out on the basis of physical-chemical data sets of the individual model (if possible). The results of the computational experiments are compared between models. This stage results in an intermediate report.

Basic processes. The following processes are considered:

Gas/particle partitioning of POPs in the atmosphere.
Scavenging from the atmosphere (wet deposition for gaseous and particulate phases and dry deposition of particulate phase onto forest, grass, bare soil, and water).
Gaseous exchange processes between the atmosphere and different types of underlying surface (soil, water, vegetation).
Degradation in various environmental compartments (the atmosphere, soil, vegetation, water).

Pollutants considered: At Stage I the following pollutants selected for the intercomparison study: PCB-153 (first priority), and PCB-28 and PCB-180 (second priority) are included into computational experiments

Physical-chemical properties. The physical-chemical parameters used in the description of the above processes can be presented in the form shown in table:

Computational experiments. The following computational experiments are performed:

Calculations of POP gas/particle partitioning in the atmosphere (particulate fraction for a range of temperatures).
Calculations of dry deposition fluxes to agreed types of underlying surfaces (forest, grass, bare soil, seawater).
Calculations of wet deposition fluxes both for gaseous and particulate phases and total POP concentrations in precipitation.
Calculations of POP concentrations in different environmental media and/or gaseous fluxes from and to underlying surfaces (soil, water, vegetation) at given atmospheric concentrations.
Calculations of temporal trends characterising POP concentrations in the soil at the stages of their accumulation and clearance (optional additional experiment).

The input data for modelling include several sets of given PCB air concentrations in different phases (if needed) and environmental conditions (averaged ambient temperatures, organic content in the atmospheric aerosol, TSP, precipitation intensity, mean wind velocity, etc.) relevant for each of the experiments. These data are considered as conventional (not strictly concerned with particular geographic location and time period). More detailed description of input data for computational experiments together with a number of tabular templates on each experiments to be filled in by all participants within Stage I.

Time-table for Stage I