Per capita ALO as m² yr⁻¹ and PMF as kg particulates <10 μm yr⁻¹ are shown on the left

Figure 5. Per capita ALO as m² yr⁻¹ and PMF as kg particulates <10 μm yr⁻¹ are shown on the left. Local air pollution issues in Beijing and Cape Town are disproportionately high relative to the amount of economic activity, particularly when the IP per unit of economic activity is taken into account as shown on the right. Wealthier cities show a tendency to minimize air pollution while the exported environmental pressure of ALO increases with the wealth of the residents.

Abstract

Cities now consume resources and produce waste in amounts that are incommensurate with the populations they contain. Quantifying and benchmarking the environmental impacts of cities is essential if urbanization of the world's growing population is to occur sustainably. Urban metabolism (UM) is a promising assessment form in that it provides the annual sum material and energy inputs, and the resultant emissions of the emergent infrastructural needs of a city's sociotechnical subsystems. By fusing UM and life cycle assessment (UM–LCA) this study advances the ability to quantify environmental impacts of cities by modeling pressures embedded in the flows upstream (entering) and downstream (leaving) of the actual urban systems studied, and by introducing an advanced suite of indicators. Applied to five global cities, the developed UM–LCA model provided enhanced quantification of mass and energy flows through cities over earlier UM methods. The hybrid model approach also enabled the dominant sources of a city's different environmental footprints to be identified, making UM–LCA a novel and potentially powerful tool for policy makers in developing and monitoring urban development policies. Combining outputs with socioeconomic data hinted at how these forces influenced the footprints of the case cities, with wealthier ones more associated with personal consumption related impacts and poorer ones more affected by local burdens from archaic infrastructure.