Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 2 3 2002 10.5194/acp-2-215-2002 http://www.atmos-chem-phys.net/2/215/2002/ http://www.atmos-chem-phys.net/2/215/2002/acp-2-215-2002.html http://www.atmos-chem-phys.net/2/215/2002/acp-2-215-2002.pdf 215 226 2002-09-05 The impact of multiphase reactions of NO₂ with aromatics: a modelling approach N. Lahoutifard M. Ammann L. Gutzwiller B. Ervens Ch. George 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 The impact of multiphase reactions involving nitrogen dioxide (NO₂) 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^-3. 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 NO₂ 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/NO₂ ^- production rate, but this contribution drops down close to zero in acidic droplets (as those often encountered in urban environments).