ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-5-2539-2005 A Lagrangian Stochastic Model for the concentration fluctuations Mortarini L. 1 3 Ferrero E. 2 3 Dipartimento di Fisica Generale, Università di Torino, v. P. Giuria 1, 10125, Torino, Italy Dipartimento di Scienze e Tecnologie Avanzate, Univ. del Piemonte Orientale, Via Bellini, 25/G 15100 Alessandria, Italy ISAC-CNR, Corso Fiume 4, 10133, Torino, Italy 23 09 2005 5 9 2539 2545 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/5/2539/2005/acp-5-2539-2005.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/5/2539/2005/acp-5-2539-2005.pdf

A Lagrangian Stochastic Model for the two-particles dispersion, aiming at simulating the pollutant concentration fluctuations, is presented. Three model versions (1-D, 2-D and 3-D) are tested. Firstly the ability of the model to reproduce the two-particle statistics in a homogeneous isotropic turbulence is discussed, comparing the model results with theoretical predictions in terms of the probability density function (PDF) of the particles separation and its statistics. Then, the mean concentration and its fluctuations are considered and the results presented. The influence of the PDF of the particle separation on the concentration fluctuations is shown and discussed. We found that the separation PDF in the inertial subrange is not gaussian and this fact influences the predicted concentration fluctuations.