This book is a translation of the French book "Pollution atmospherique. Des p- cessus a la modelisation", published by Springer France (2007). The content is mainly derived from a course devoted to air pollution I taught at Ecole nationale des ponts et chaussees (ENPC; one of the foremost French high schools, at ParisTech Institute of Technology and University Paris-Est) during the decade 1997-2006. This book has of course been deeply in uenced by my research activity at CEREA, the Teaching and Research Center for Atmospheric Envir- ment, a joint laboratory between ENPC and the Research and Development Di- sion of Electricite de France (EDF R&D), that I created and then headed from 2002 to 2007. I want to thank many of my colleagues for discussions, help and review. Thanks to Vivien Mallet for his careful review, his availability and his pieces of advice (both for the content and the form of this book). Thanks to Marc Bocquet, Karine Sartelet- Kata, Irene Korsakissok for their help in reviewing chapters. I want also to thank a few colleagues for having provided me illustrations from their research work. Thanks to Bastien Albriet, Marc Bocquet, Edouard Debry, Irene Korsakissok, H- sein Malakooti, Denis Quelo, Yelva Roustan, Karine Sartelet, Christian Seigneur and Marilyne Tombette. Thanks also to the American family, Celine and Julien, for their review of the introduction.

This book collates the written contributions of the Second Conference on Air Pollution Modelling and Simulation (APMS 2001). A wide range of current topics is covered, focusing on three challenging issues: (1) the modelling issue of complex, multiphase, atmospheric chemistry; (2) the numerical issue associated with comprehensive three-dimensional chemistry-transport models; and (3) the key issues of data assimilation and inverse modelling. State-of-the art research is presented with many operational procedures applied at either forecast agencies or companies.

This book is a translation of the French book "Pollution atmospherique. Des p- cessus a la modelisation", published by Springer France (2007). The content is mainly derived from a course devoted to air pollution I taught at Ecole nationale des ponts et chaussees (ENPC; one of the foremost French high schools, at ParisTech Institute of Technology and University Paris-Est) during the decade 1997-2006. This book has of course been deeply in uenced by my research activity at CEREA, the Teaching and Research Center for Atmospheric Envir- ment, a joint laboratory between ENPC and the Research and Development Di- sion of Electricite de France (EDF R&D), that I created and then headed from 2002 to 2007. I want to thank many of my colleagues for discussions, help and review. Thanks to Vivien Mallet for his careful review, his availability and his pieces of advice (both for the content and the form of this book). Thanks to Marc Bocquet, Karine Sartelet- Kata, Irene Korsakissok for their help in reviewing chapters. I want also to thank a few colleagues for having provided me illustrations from their research work. Thanks to Bastien Albriet, Marc Bocquet, Edouard Debry, Irene Korsakissok, H- sein Malakooti, Denis Quelo, Yelva Roustan, Karine Sartelet, Christian Seigneur and Marilyne Tombette. Thanks also to the American family, Celine and Julien, for their review of the introduction.

These proceedings gather the written contributions presented during the second Conference APMS'2001 (Air Pollution Modeling and Simulation), which was jointly organized by the Ecole Nationale des Ponts et Chaussees (ENPC) and the Institut National de Recherche en Inforrnatique et en Automatique (INRIA). 3D comprehensive models are now widely used for Air Quality Modeling. They compute the distribution of trace gases in the troposphere by taking into account numerous processes simultaneously: transport (advection and diffusion), chemie al transformations, emissions and depositions processes. The applications range from physical understanding to forecast and we have to tackle many challenges. of each process, which is highly The first challenge concems the MODELING complex in itself. This inc1udes a key issue: multiphase modeling of gas-phase species, clouds and particulate matter (aerosols). A second challenge is numerical SIMULATION. These comprehensive models are computationally intensive due to the nonlinearity, the coupling and the wide range of scales to be handled with. The ability to use such models is subjected to the restrictions of today's computer technology. Appropriate numerical tools are necessary in order to benefit from the state of the art numeries. In addition, each phenomenon has to be supported by a large body of data, which are often difficult to describe with accuracy. This is related to the third challenge: DATA ASSIMILATION (more generally INVERSE MODELING) and all the relevant topics (use of adjoint models for instance).