Air quality in cities around the world

This chapter provides an overview of air quality trends over the last one to two decades for selected major cities across the world. We examine a selection of major cities which face disparate challenges ranging from growing urban populations and vehicle ownership, changing emissions distributions, and prevailing weather patterns to higher frequency of wildfires and natural hazards from sand and dust storms. Not only do these case studies illustrate the pressures from poor air quality around the world, they also serve to highlight the progress that has been achieved. One clear message that comes across when examining the status of air quality in these cities, is that while there are common challenges affecting all cities, there are many that are specific to the regions where they are located.