ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-2-215-2002 The impact of multiphase reactions of NO<sub>2</sub> with aromatics: a modelling approach Lahoutifard N. 1 4 Ammann M. 2 Gutzwiller L. 2 Ervens B. 3 5 George Ch. 1 Laboratoire d’Application de la Chimie à l’Environnement (LACE), CNRS-UCBL, 43, boulevard du 11 Novembre 1918, F-69622 Villeurbanne Cedex, France Paul Scherrer Institute, Laboratory for Radio- and Environmental Chemistry, CH-5232 Villigen, Switzerland Institut für Troposphärenforschung Permoserstr. 15, D-04303 Leipzig, Germany *now at: Department of Chemistry, University of Ottawa, Ontario, Canada now at: Cooperative Institute for Research in the Atmosphere (CIRA), Colorado State University, Fort Collins, Colorado 80523, USA 05 09 2002 2 3 215 226 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/2/215/2002/acp-2-215-2002.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/2/215/2002/acp-2-215-2002.pdf

The impact of multiphase reactions involving nitrogen dioxide (NO<sub>2</sub>) and aromatic compounds was simulated in this study. A mechanism (CAPRAM 2.4, MODAC Mechanism) was applied for the aqueous phase reactions, whereas RACM was applied for the gas phase chemistry. Liquid droplets were considered as monodispersed with a mean radius of 0.1 µm and a liquid content (LC) of 50 µg m<sup>-3</sup>. The multiphase mechanism has been further extended to the chemistry of aromatics, i.e. reactions involving benzene, toluene, xylene, phenol and cresol have been added. In addition, reaction of NO<sub>2</sub> with dissociated hydroxyl substituted aromatic compounds has also been implemented. These reactions proceed through charge exchange leading to nitrite ions and therefore to nitrous acid formation. The strength of this source was explored under urban polluted conditions. It was shown that it may increase gas phase HONO levels under some conditions and that the extent of this effect is strongly pH dependent. Especially under moderate acidic conditions (i.e. pH above 4) this source may represent more than 75% of the total HONO/NO<sub>2</sub> <sup>-</sup> production rate, but this contribution drops down close to zero in acidic droplets (as those often encountered in urban environments).