* Corresponding author. Tel.: #44-1524-594330; fax: #44- 1524-593985. E-mail address: c.halsall@lancaster.ac.uk (C.J. Halsall).  Present address: Atmospheric Sciences and Global Change. Resources, Paci"c Northwest National Laboratory (PNNL), 902 Battelle Boulevard, P.O. Box 999, Richland, WA 99362, USA. Atmospheric Environment 35 (2001) 255}267 Modelling the behaviour of PAHs during atmospheric transport from the UK to the Arctic C.J. Halsall*, A.J. Sweetman, L.A. Barrie, K.C. Jones Environmental Science Department, Institute of Environmental and Natural Sciences, Lancaster University, Lancaster LA1 4YQ, UK Atmospheric Environment Service, 4905 Duwerin St, Downsview, Ontario M3H 5T4, Canada Received 6 August 1999; received in revised form 23 March 2000; accepted 28 March 2000 Abstract Persistent organic pollutants (POPs) such as PAHs are subject to long-range atmospheric transport, which can result in the contamination of remote areas such as the Arctic. A simple model was developed to describe the removal processes of four PAHs; #uorene (FLU), phenanthrene (PHEN), #uoranthene (FLA) and benzo[a]pyrene (B[a]P) transported over a 5 day period from a source area over the UK to the Russian Arctic. The purpose of this model was to study processes a!ecting the PAHs within the atmosphere, rather than their interaction with the earth's surface. The components to the model included gas/particle partitioning, reaction with OH radicals and dry and wet deposition (both rain and snow). Atmospheric/meteorological parameters for the geographical region of interest were generated from three-dimensional atmospheric models. Air concentrations were prescribed in the source area with no additional PAH inputs along the transect, both winter and summer scenarios were modelled. Reaction with OH was a major removal mechanism for gas-phase FLU, PHEN and FLA, most notably in the temperate atmosphere. Wet deposition in the form of snow accounted for the majority of PAH loss in the winter, although the gas and particle scavenging ratios used in this model ranged over several orders of magnitude. Using a 5 day transport scenario in a &1-hop' event, the model predicted that a primary emission of FLA and B[a]P to the atmosphere of the southern UK, would not reach the Russian Arctic at a distance of &3500 km, assuming a constant windspeed of 10 m s. However, both FLU and PHEN with calculated half-lives of '60 h during the winter could be transported to this area under this scenario.  2000 Elsevier Science Ltd. All rights reserved. Keywords: Trajectory; Gas/particle partitioning; OH-radical breakdown; Deposition 1. Introduction In recent years concern has grown about transboun- dary atmospheric transport of persistent organic pollu- tants (POPs). This has resulted in a new protocol on POPs being added to the UN-ECE convention on long- range transboundary air pollution (CLRTAP), with the intention of reducing emissions of certain POPs such as PAHs and PCDD/Fs to below their 1990 emission levels (http://www.unece.org/env/). Long-range atmospheric transport (LRT) is responsible for the contamination of remote regions such as the Arctic. Multi-year systematic air sampling in the Canadian and Russian Arctic has revealed a seasonality in PAH concentrations, with levels being highest during the colder winter months, corre- sponding to elevated levels observed in temperate indus- trialised regions (Menichini, 1992; Halsall et al., 1994; Do K rr et al., 1996). The prevailing meteorology at this time of year results in anthropogenic pollutants being carried into the Arctic, giving rise to the haze period observed during polar sunrise in April (Heintzenberg, 1989; Barrie, 1996). Recent attempts to model PAH transport and 1352-2310/00/$ - see front matter  2000 Elsevier Science Ltd. All rights reserved. PII: S 1 3 5 2 - 2 3 1 0 ( 0 0 ) 0 0 1 9 5 - 3