Sustainability for Shrinking Cities

Ultrafine particles (UFPs; diameter less than 100 nm) are ubiquitous in urban air, and an acknowledged risk to human health. Globally, the major source for urban outdoor UFP concentrations is motor traffic. Ongoing trends towards urbanisation and expansion of road traffic are anticipated to further increase population exposure to UFPs. Numerous experimental studies have characterised UFPs in individual cities, but an integrated evaluation of emissions and population exposure is still lacking. Our analysis suggests that the average exposure to outdoor UFPs in Asian cities is about four-times larger than that in European cities but impacts on human health are largely unknown. This article reviews some fundamental drivers of UFP emissions and dispersion, and highlights unresolved challenges, as well as recommendations to ensure sustainable urban development whilst minimising any possible adverse health impacts. Copyright © 2014 Elsevier Ltd. All rights reserved.

Urban shrinkage is not a new phenomenon. It has been documented in a large literature analyzing the social and economic issues that have led to population flight, resulting, in the worse cases, in the eventual abandonment of blocks of housing and neighbourhoods. Analysis of urban shrinkage should take into account the new realization that this phenomenon is now global and multidimensional — but also little understood in all its manifestations. Thus, as the world's population increasingly becomes urban, orthodox views of urban decline need redefinition. The symposium includes articles from 10 urban analysts working on 30 cities around the globe. These analysts belong to the Shrinking Cities International Research Network (SCIRN), whose collaborative work aims to understand different types of city shrinkage and the role that different approaches, policies and strategies have played in the regeneration of these cities. In this way the symposium will inform both a rich diversity of analytical perspectives and country-based studies of the challenges faced by shrinking cities. It will also disseminate SCIRN's research results from the last 3 years.