This book brings together the methods, models and formulae used for estimating air pollution concentrations in urban areas. From the Foreword The visible effects of pollution in most cities in the developed countries have been reduced dramatically in the past thirty years. This has been achieved to a large extent by the replacement of most of the low-level sources, which burnt raw coal, by more modern appliances using gas, electricity or low-sulphur oil. The killer smog of 1952 could not be repeated unless there were to be a massive return to old-fashioned heating methods, due, for example, to excessive environmental constraints being applied to the more modern energy sources. It is important, therefore, to judge the impact of a new source in terms of its effect on the pattern of existing sources. One should also consider the environmental consequences of rejecting the new installation and examine the alternatives—that its product may either be denied to the community at large, produced elsewhere or produced using existing facilities. These facilities are probably less efficient and may therefore produce more pollution per unit of product than the new plant would. An objective, quantitative, urban-air-pollution model is clearly an essential component in such a decision-making process. Dr. Benarie has produced a distillation of existing modelling techniques which will, I hope, become the launching pad for many future models. As each city is unique, it will need its own tailor-made model, drawing on the best and the most appropriate techniques developed previously. Agreement with observations is the only real test of validity, because the physics and chemistry are so complicated that theoretical arguments are reduced to the role of assisting in the best formulation of the problem. Numerical precision must always rely on measurement. This is the approach that Dr. Benarie has adopted.—David J. Moore, Central Electricity Research Laboratires, Leatherhead, Surrey, UK