The protection of our environment is one of the major problems in society. More and more important physical and chemical mechanisms are to be added to the air pollution models. Moreover, reliable and robust control strategies for keeping pollution caused by harmful compounds under certain safe levels have to be developed and used in a routine way. Well based and correctly analyzed large mathematical models can successfully be used to solve this task. The use of such models leads to the treatment of huge computational tasks. The efficient solution of such problems requires combined research from specialists working in different fields. The NATO ARW held at Borovetz (Bulgaria), in the period 8-12 May, 2004 was devoted to the above questions. This book contains selected papers of the meeting in the following topics:- improving the abilities of air pollution models to calculate reliable predictions of the pollution levels in a given domain and in real time by using adequate description of the physical and chemical processes,- implementation of advanced numerical methods and algorithms in the models,- efficient utilization of up-to-date computer architectures,- development of mechanisms for studying particles (including here fine and ultra-fine particles), biogenic emissions, etc.- optimization techniques in the study of the pollution levels, etc.