Atmospheric Chemistry and Physics Discussions www.atmos-chem-phys-discuss.net 1680-7367 1680-7375 5 4 2005 10.5194/acpd-5-6127-2005 http://www.atmos-chem-phys-discuss.net/5/6127/2005/ http://www.atmos-chem-phys-discuss.net/5/6127/2005/acpd-5-6127-2005.html http://www.atmos-chem-phys-discuss.net/5/6127/2005/acpd-5-6127-2005.pdf 6127 6184 2005-08-17 Case studies of ozone transport between North America and Europe in summer 2000 G. Guerova I. Bey J.-L. Attié R. V. Martin Laboratoire de Modélisation de la Chimie Atmosphérique, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland Laboratoire d’Aérologie, Observatoire Midi Pyrénées, Toulouse, France Department of Physics and Atmospheric Science, Dalhousie University, Halifax, NS, B3H 3J5, Canada Harvard-Smithsonian Center for Astrophysics, Cambridge, Massachusetts, USA This paper reports on Long Range Transport (LRT) of ozone and related species over the North Atlantic ocean and its impact on Europe. Measurements of NO₂ and O₃ columns from the GOME and MOPITT satellite instruments are first used in conjunction with the GEOS-CHEM global model of transport and tropospheric chemistry to identify the major events of LRT that reach Europe over the course of the summer 2000. Model simulations are then used to examine surface O₃ observations at a European mountain site and O₃ vertical profiles over several European cities to quantify the impact of the LRT events on the European ozone distributions. Over the course of summer 2000, we identified nine major episodes of pollution transport between North America and Europe, which are in majority associated with WCB/post-frontal outflow (7 events) and zonal transport (2 events). We find that on average three episodes occur per month with the strongest ones being in June. The number and frequency of LRT events that reach Europe after leaving North America is strongly driven by the position and strength of the Azores anticyclone. After leaving North America, the plumes can either i) travel in the North American cyclones, mostly in the Warm Conveyor Belt (WCB), tracking poleward and thus reach Europe at high latitudes; ii) be transported zonally between 40° and 55° N directly to Europe; iii) be incorporated into the Azores anticyclone and reach Europe at mid-latitudes. Based on model sensitivity simulation it can be concluded that on average the North American sources of ozone contribute between 2–8 ppb in PBL and 10–13 ppb in FT. During particular episodes the North American sources resulted in O₃ enhancement up to 25–28 ppb in the layer between 800–600 hPa and 10–12 ppb in PBL. For some episodes a substantial North American contribution (30% or higher) does not translate into a well marked enhancement of the total O₃.