ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-6-1389-2006 Relative humidity impact on aerosol parameters in a Paris suburban area Randriamiarisoa H. 1 Chazette P. 1 Couvert P. 1 3 Sanak J. 1 Mégie G. 2 4 Laboratoire des Sciences du Climat et de l’Environnement/Institut Pierre-Simon Laplace, Orme des Merisiers Bât 701, C.E.Saclay, 91191 Gif-sur-Yvette Cedex, France Service d’Aéronomie/Institut Pierre-Simon Laplace, 4 place Jussieu, 75252 Paris, France deceased, June 2005 deceased, June 2004 02 05 2006 6 5 1389 1407 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/6/1389/2006/acp-6-1389-2006.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/6/1389/2006/acp-6-1389-2006.pdf

Measurements of relative humidity (RH) and aerosol parameters (scattering cross section, size distributions and chemical composition), performed in ambient atmospheric conditions, have been used to study the influence of relative humidity on aerosol properties. The data were acquired in a suburban area south of Paris, between 18 and 24 July 2000, in the framework of the "Etude et Simulation de la Qualit&#233; de l'air en Ile-de-France" (ESQUIF) program. According to the origin of the air masses arriving over the Paris area, the aerosol hygroscopicity is more or less pronounced. The aerosol chemical composition data were used as input of a thermodynamic model to simulate the variation of the aerosol water mass content with ambient <i>RH</i> and to determine the main inorganic salt compounds. The coupling of observations and modelling reveals the presence of deliquescence processes with hysteresis phenomenon in the hygroscopic growth cycle. Based on the H&#228;nel model, parameterisations of the scattering cross section, the modal radius of the accumulation mode of the size distribution and the aerosol water mass content, as a function of increasing RH, have been assessed. For the first time, a crosscheck of these parameterisations has been performed and shows that the hygroscopic behaviour of the accumulation mode can be coherently characterized by combined optical, size distribution and chemical measurements.