Atmospheric Processes

In cities, complex interactions take place between urban morphology, climate, atmospheric emissions, and human health. Scientists in various disciplines have started to uncover those interactions by examining the relationships among the major chemical, physical, biological, and human processes that drive urban air quality (Figure 7.1). But we will need to develop coupled human-natural models of urban regions before we can fully understand their interactions and feedback mechanisms. For example, we have long known that urban areas affect microclimate; in fact, the urban heat island was first described nearly two centuries ago. We also know that human activities generate emissions that are precursors of ozone, a primary constituent of photochemical smog in cities, and we have increasing evidence that such smog affects the health of both humans and ecosystems. At the same time, as the heat island effect continues to increase in many cities, people demand more energy for cooling, which increases the amount of both fuel combustion and atmospheric emissions.