The 20th International Technical Meeting on Air Pollution Modelling and Its Application was held in Valencia, Spain, during late 1993. At this conference, a new record of abstracts was submitted, a new record of scientists participated, and a new record of countries was represented. This clearly indicates society's continuous and growing interest in, as well as importance of, the complexities associated with the modelling of air pollution. The conference addressed the following main subjects: integrated regional modelling, global and long-range transport, new modelling developments, accidental releases, and model assess­ ment and verification. In addition, two project-oriented workshops were organized as part of the conference. The many contributing authors and scientists taking active part in the discussions following the papers, have made this proceeding a record of the current status in the field of air pollu­ tion modelling. We want to express our gratitude to their efforts. We also wish to extend our gratitude to the sponsors that made this conference possible. In addition to financial support from NATOjCCMS the conference received contributions from CEAM, the European Asso­ ciation for the Science of Air Pollution, Danish Center for Air Research, and Ris0 National Laboratory. A special grant was given by NATOjCCMS to facilitate attendance of scientists from Central and Eastern Europe. We also wish to express our gratitude to Rosa Salvador and Pilar Zamora of CEAM, who laboriously organized the conference pre-proceedings, and to Anne N0rregaard and Ulla Riis Christiansen of Ris0 National Laboratory, who seved as conference secretariat.

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Integrated Regional Modelling: Experimental and Numerical Study of High Ozone Events in the Alpine Region; J. Graf, et al. Global and Longrange Transport: A Three Dimensional Hemispheric Air Pollution Model Used for the Arctic; J. Christensen. New Developments: A Fast Lagrangian Particle Model for Use with Three-dimensional Mesoscale Models; W. Physick, P. Hurley. Accidental Release: A Mesoscale Boundary Layer Meteorological Model for Inhomogeneous Terrain; S.M. Daggupaty, et al. Model Assessment and Verification: Improving the Science of Regulatory Dispersion Models for Shortrange Applications; J.C. Weil. Video Session: Designing an Air Quality Network for Brisbane Using a Mesoscale Model; W. Physick, et al. Poster Session: Vertical Diffusion Parameter in the Atmospheric Boundary Layer; L.E. Venegas. Special Session: Athenian Photochemical Smog Intercomparison of Simulations (APSIS). Special Session: Air Pollution Transport and Diffusion over Coastal Urban Areas (Athens). 94 additional articles. Index.