ACPD Atmospheric Chemistry and Physics Discussions ACPD 1680-7375 Copernicus GmbH Göttingen, Germany 10.5194/acpd-4-5103-2004 A transboundary transport episode of nitrogen dioxide as observed from GOME and its impact in the Alpine region Schaub D. 1 Weiss A. K. 1 Kaiser J. W. 2 Petritoli A. 3 Richter A. 4 Buchmann B. 1 Burrows J. P. 4 Swiss Federal Laboratories for Materials Testing and Research (EMPA), Ueberlandstrasse 129, CH-8600 Duebendorf, Switzerland Remote Sensing Laboratories, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland Institute of Atmospheric Science and Climate (ISAC-CNR), Via Gobetti 101, I-40129 Bologna, Italy Institute of Environmental Physics, University of Bremen, P.O. Box 33 04 40, 28334 Bremen, Germany 08 09 2004 4 5 5103 5134 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys-discuss.net/4/5103/2004/acpd-4-5103-2004.html The full text article is available as a PDF file from http://www.atmos-chem-phys-discuss.net/4/5103/2004/acpd-4-5103-2004.pdf

High tropospheric NO<sub>2</sub> amounts are occasionally detected by satellite-borne spectrometers even though clouds shield the highly polluted boundary layer. We present a method to investigate such events and apply the model to the high NO<sub>2</sub> vertical tropospheric column densities (VTCs) over middle Europe observed from the Global Ozone Monitoring Experiment (GOME) instrument on 17 February 2001. Our case study shows that pollution originally residing near the ground has been advected to higher tropospheric levels by a passing weather front. With backward trajectories, the NO<sub>2</sub> source region is located in central Germany, the Ruhr area and adjacent parts of the Netherlands and Belgium. The highly polluted air masses are traced by forward trajectories starting from the GOME columns to move further to the Alpine region. Their impact on the air quality there is modeled by combining the NO<sub>2</sub> VTCs observed by GOME with the trajectory calculations and a given NO<sub>2</sub> lifetime. Considering ground-based in-situ measurements in the Alpine region we conclude that for this episode, 50% to 90% of the NO<sub>2</sub> concentration recorded at the sites can be attributed to transboundary transport during the frontal passage.