PARENT SESSION

1K - Tropospheric Fate
Hall 13
8:30 AM - 12:30 PM, Monday, 28 April 2003
Chair: Harner, T.¹, ¹
Co-chair: Halsall, C.¹, ¹

(MO13/1) The effects of atmospheric degradation, deposition, and transport on the global fractionation of PCBs.

Scheringer, Martin¹, Salzmann, Michael¹, Wegmann, Fabio¹, Stocker, Judith¹, Hungerbühler, Konrad¹, ¹ Swiss Federal Institute of Technology, Zürich, Zürich, Switzerland

ABSTRACT- Different PCB congeners exhibit highly different environmental fate, including their long-range transport and accumulation in polar regions. The efficiency of the long-range transport depends strongly on atmospheric degradation and deposition processes which, in turn, are governed by factors such as temperature, OH radical concentration, and aerosol concentration as well as their temporal and spatial variability. We present an analysis of the influence of these factors on the transport efficiency of different PCB congeners, performed with the global multimedia transport model CliMoChem. The model contains different latitudinal zones consisting of the media soil, vegetation, oceanic surface water, and tropospheric air; it provides chemical concentrations and mass flows for every latitudinal zone and environmental medium as functions of time. For selected PCB congeners with increasing degree of chlorination, the fractions bound to aerosol particles as well as the mass flows of degradation, deposition, revolatilization, and transport between latitudinal zones are analyzed as functions of place, time, and temperature. The interplay of these different processes defines a window of substance parameters that lead to maximum transport efficiency. The transport efficiency of the different congeners is used to discuss the global fractionation hypothesis. The model results show different aspects of the global fractionation phenomenon, depending on whether the transport of absolute amounts of different congeners or the latitudinal mass distribution of individual congeners is considered. In addition, the observed fractionation depends on the time that has elapsed since the release event because the different congeners have highly different transport velocities. Transport efficiencies and transport velocities are related to the physicochemical properties of the PCB congeners and the model results are discussed in the light of experimentally observed PCB concentration distributions.

Key words: global fractionation, long-range transport, PCBs, exposure modeling