ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-4-169-2004 Role of the NO<sub>3</sub> radicals in oxidation processes in the eastern Mediterranean troposphere during the MINOS campaign Vrekoussis M. 1 Kanakidou M. 1 Mihalopoulos N. 1 Crutzen P. J. 2 Lelieveld J. 2 Perner D. 2 Berresheim H. 3 Baboukas E. 2 Environmental Chemical Processes Laboratory, Department of Chemistry, University of Crete, P.O. Box 1470, 71409 Heraklion, Greece Max-Planck-Institute for Chemistry, Air Chemistry Department, P.O. Box 3060, 55020 Mainz, Germany German Weather Service, Meteorological Observatory, Hohenpeissenberg, Albin-Schwaiger-Weg 10, Germany 03 02 2004 4 1 169 182 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.net/4/169/2004/acp-4-169-2004.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/4/169/2004/acp-4-169-2004.pdf

During the MINOS campaign (28 July-18 August 2001) the nitrate (NO<sub>3</sub>) radical was measured at Finokalia station, on the north coast of Crete in South-East Europe using a long path (10.4 km) Differential Optical Absorption Spectroscopy instrument (DOAS). Hydroxyl (OH) radical was also measured by a Chemical Ionization Mass-Spectrometer (Berresheim et al., 2003). These datasets represent the first simultaneous measurements of OH and NO<sub>3</sub> radicals in the area. NO<sub>3</sub> radical concentrations ranged from less than 3x10<sup>7</sup> up to 9x10<sup>8</sup> radicals· cm<sup>-3</sup> with an average nighttime value of 1.1x10<sup>8</sup> radicals· cm<sup>-3</sup>.<br> <br> The observed NO<sub>3</sub> mixing ratios are analyzed on the basis of the corresponding meteorological data and the volatile organic compound (VOC) observations which were measured simultaneously at Finokalia station. The importance of the NO<sub>3</sub> radical chemistry relatively to that of OH in the dimethylsulfide (DMS) and nitrate cycles is also investigated. The observed NO<sub>3</sub> levels regulate the nighttime variation of DMS. The loss of DMS by NO<sub>3</sub> during night is about 75% of that by OH radical during day. NO<sub>3</sub> and nitrogen pentoxide (N<sub>2</sub>O<sub>5</sub>) reactions account for about 21% of the total nitrate (HNO<sub>3(g)</sub>+NO<sup>-</sup><sub>3(g)</sub>) production.