DOI 10.1393/ncc/i2005-10188-y IL NUOVO CIMENTO Vol. 28 C, N. 2 Marzo-Aprile 2005 Assessment of the numerical diffusion effect in the advection of a passive tracer in BOLCHEM( ∗ ) M. D’Isidoro( 1 )( 3 )( ∗∗ ), A. Maurizi( 1 ), F. Tampieri( 1 ), A. Tiesi( 2 ) and M. G. Villani( 1 ) ( 1 ) ISAC-CNR - Bologna, Italy ( 2 ) IMAA-CNR - Potenza, Italy ( 3 ) Dipartimento di Fisica, Universit` a di Ferrara - Via Paradiso 12, 44100 Ferrara, Italy (ricevuto il 7 Febbraio 2005; approvato il 27 Maggio 2005) Summary. — The effects of the numerical scheme implemented in the advection equation of BOLCHEM have been quantified with reference to the diffusion of a passive tracer. An equivalent horizontal diffusion coefficient has been measured and is found to be dependent on wind field and resolution. PACS 47.11.+j – Computational methods in fluid dynamics. PACS 47.27.Qb – Turbulent diffusion. PACS 92.60.Sz – Air quality and air pollution. PACS 01.30.Cc – Conference proceedings. 1. – Introduction Modelling of the spatial distribution and time evolution of the atmospheric minor components is a challenging step in the investigation, simulation and forecasting of air quality. It is well recognized that the atmospheric composition results from the combined effects of emissions, transformations, transport and removal. Thepresentpaperconcentratesonsomeaspectsoftheoverallproblem,concerningthe numerical simulation of transport and dispersion at the regional scale (namely, a space scale typically larger than a city, and a time scale of the order of more than one hour). At the space and time scales of interest, the transport is driven by the meteorological fields, and dispersion is treated as a “subgrid” process. Turbulent dispersion in the atmosphere is essentially a Lagrangian process, and therefore its simplified description is ( ∗ ) Paper presented at CAPI 2004, 8 ◦ Workshop sul calcolo ad alte prestazioni in Italia, Milan, November 24-25, 2004. ( ∗∗ ) E-mail: m.disidoro@isac.cnr.it c  Societ` a Italiana di Fisica 151 brought to you by CORE View metadata, citation and similar papers at core.ac.uk provided by Scientific Open-access Literature Archive and Repository