Meteorol. Atmos. Phys. 57, 115-133 (1995) Meteorology and Atmospheric Physics 9 Springer-Verlag 1995 Printed in Austria Aristotle University, Thessaloniki, Greece The EUMAC Zooming Model, a Tool for Local-to-Regional Air Quality Studies N. Moussiopoulos With 17 Figures Received March 8, 1994 Revised August 23, 1994 Summary The EUMAC Zooming Model (EZM) is a comprehensive model system for simulations of wind flow and air pollutant transport and transformation at the local-to-regional scale. Core models of the EZM are the nonhydrostatic mesoscale model MEMO and the photochemical dispersion model MARS. Manifold air quality studies, primarily for large urban agglomerations, have been already performed with the EZM. In most of these studies the results of the EZM agree fairly well with available observations. An example for a successful study with the EZM is its application to simulate the formation of photochemical smog in the case of stagnant meteorological conditions in Athens. By applying a suitable nesting technique, MEMO reproduces satisfactorily the observed diurnal wind pattern in Athens. The results of MARS elucidate the characteristics of a severe photosmog episode in Athens and are in general very similar to available observations. 1. Introduction In the last decades, the mechanisms of air pollutant transport and transformation are the subject of intense scientific research. One of the principle aims of this research is to establish source/receptor relationships, i.e., to quantify to what extent various emission sources contribute to the occurrence of air pollution episodes. Nowadays most of the physical and chemical processes leading to high air pollution levels seem to be understood. Never- theless, air pollution still causes serious problems in many countries all over the world. Such problems may be classified depending on their characteristic length scale. Usually, global, continental, regional and local scale problems are distinguished. Observational evidence is only rarely sufficient to describe atmospheric transport and transfor- mation of air pollutants. For this reason mathe- matical models have been developed to simulate wind flow and the dispersion of chemically reacting pollutants in the atmosphere. Over the past few years there has been considerable progress in the practical applications of mathematical models at all above mentioned scales. Model development in Europe is coordinated in the frame of EUROTRAC's subproject EUMAC (European Modelling of Atmospheric Constituents). The objective of EUMAC is to develop a complete set of models and to apply them to scientific problems and environmental planning. The central model of EUMAC is the large-scale model EURAD (Hass et al., 1990) aiming primarily at the analysis of long-range transport and transformation phe- nomena. The local-to-regional nature of several air pollution problems, however, led to the develop- ment of the EUMAC Zooming Model (EZM) which may be used to cover scientific and appli- cational issues down to urban and local domains. The present paper contains an introduction to the EZM structure and illustrative examples for recent applications showing the capabilities of the EZM. More details on the material covered in this