ABSTRACT
This chapter presents an overview of key concepts discussed in the subsequent chapters of this book. The book focuses on the composition of the atmosphere, how it changes through space and time, particularly as a result of human activities, and the effects these changes may have on humans, the natural environment and the global climate system. These changes are considered in the context of policy responses aimed at establishing standards and reducing emissions to bring the atmosphere and its surface exchange back towards something like a pre-disturbance state. The book also describes some of the methods and networks available for assessing concentrations of pollutants now and in the past. The lifetime of a compound is a key factor to understand and will be determined by its chemical reactivity and how readily it can be removed from the atmosphere by dry or wet deposition The book focus on global, regional and urban pollution issues.
