Atmospheric Environment 40 (2006) 2089–2104 A process-oriented inter-comparison of a box model and an atmospheric chemistry transport model: Insights into model structure using a-HCH as the modelled substance Kaj M. Hansen a,Ã , Konstantinos Prevedouros b,1 , Andrew J. Sweetman b , Kevin C. Jones b , Jesper H. Christensen a a Department of Atmospheric Environment, National Environmental Research Institute, P.O. box 358, Frederiksborgvej 399, DK-4000 Roskilde, Denmark b Environmental Science Department, Institute of Environmental and Natural Sciences, Lancaster University, Lancaster, LA1 4YQ, UK Received 20 June 2005; received in revised form 5 November 2005; accepted 14 November 2005 Abstract Two models that use different approaches to model the environmental distribution and fate of persistent organic pollutants (POPs) and feature different approaches to the description of environmental processes are compared. The European Variant Berkeley–Trent model (EVn-BETR) is a fugacity based box model using long-term averaged environmental input to drive inter-compartmental and inter-regional exchange processes. The POP version of the Danish Eulerian Hemispheric Model (DEHM-POP) is a 3-D atmospheric chemistry transport model using dynamic meteorological input to drive atmospheric transport and deposition to the surface. It is expanded with surface modules to describe the post-depositional re-emission processes of POPs. Seasonally averaged air, soil and water a-hexaclorocyclohexane (a-HCH) concentrations and distribution patterns within the European region are compared for a number of emissions scenarios. There is generally a good agreement between the predicted distribution patterns of the two models. Discrepancies in environmental concentrations are attributed to the difference in efficiency of atmospheric removal processes arising from the differences in model parameterisation. r 2005 Elsevier Ltd. All rights reserved. Keywords: Model inter-comparison; Dynamic models; Fugacity models; Atmospheric chemistry transport models; a-hexachloro- cyclohexane 1. Introduction Mathematical models are increasingly used to simulate the environmental fate of persistent organic pollutants (POPs) to increase the knowledge of the involved physical processes, particularly in the absence of available monitoring data. Models of varying complexity in the description of the environmental matrices of interest are being devel- oped to investigate the environmental partitioning and chemical exchange between mobile and im- mobile media. Recently there has also been a shift of focus from regional to global modelling studies as ARTICLE IN PRESS www.elsevier.com/locate/atmosenv 1352-2310/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.atmosenv.2005.11.050 Ã Corresponding author. Tel.: +45 46 30 18 72; fax: +45 46 30 12 14. E-mail address: kmh@dmu.dk (K.M. Hansen). 1 Present address: Department of Applied Environmental Science (ITM), Stockholm University, 10691 Stockholm, Sweden.