A guide to the principles and methods of air quality assessment aimed at measuring population exposure to ambient air pollutants and estimating the effects on health. Addressed to policy-makers as well as scientists engaged in air quality monitoring, the book responds to the failure of most monitoring systems to provide data that are useful in estimating and managing threats to health. The need for exposure data on populations at special risk is also addressed. Throughout, emphasis is placed on methods of monitoring and modelling that are cost-effective, targeted, and appropriate to local and national conditions. The report has six chapters. The first introduces WHO activities related to air quality management and explains the need for monitoring systems capable of assessing health impact. The types of information required for health impact assessment are described in chapter two, which outlines several methods of monitoring and modelling that can be used to measure the level and distribution of exposure to air pollutants in populations, identify population groups with high exposure, and estimate adverse effects on health. Chapter three formulates a general concept of air quality assessment, offering advice on principles for designing a monitoring network, interpreting and reporting data, and solving problems with quality assurance. Also included is a comparison of the advantages, disadvantages, and costs of different methods for air quality monitoring. Against this background, the fourth and most extensive chapter describes specific methods for the monitoring of carbon monoxide, ozone, sulfur dioxide, nitrogen dioxide, particulate matter, benzene, polycyclic aromatic hydrocarbons, lead, and atmospheric cadmium. Monitoring strategies for each pollutant are presented according to a standard format, which covers health effects, sources and exposure patterns, monitoring methods, recommended strategies for monitoring and assessment, and a practical example. The remaining chapters offer advice on the collation, analysis, interpretation, and dissemination of data, and summarize the main conclusions and recommendations of the report. Detailed technical guidelines for the use of various methods and models are provided in a series of annexes. The report also reproduces the newly revised WHO air quality guidelines for Europe.