Simulating the impact of urban sprawl on air quality and population exposure in the German Ruhr area. Part II: Development and evaluation of an urban growth scenario

The impact of uncontrolled urban growth (‘sprawl’) on air pollution and associated population exposure is investigated. This is done for the Ruhr area in Germany, by means of a coupled modelling system dealing with land use changes, traffic, meteorology, and atmospheric dispersion and chemistry. In a companion paper [De Ridder, K., Lefebre F., Adriaensen S., Arnold U., Beckroege W., Bronner C., Damsgaard O., Dostal I., Dufek J., Hirsch J., Int Panis L., Kotek Z., Ramadier T., Thierry A., Vermoote S., Wania A., Weber C., 2008. Simulating the impact of urban sprawl on air quality and population exposure in the German Ruhr area. Part I: reproducing the base state.], a description was given of the coupling of these models and of the validation of simulation results. In the present paper, a land use change scenario was implemented to mimic urban sprawl, relocating 12% of the urban population in the study domain to the green periphery. The resulting updated land use, population and employment density patterns were then used as input for traffic simulations, yielding an increase of total traffic volume by almost 17%. As a consequence, the domain-average simulated pollutant concentrations of ozone and particulate matter increased, though by a smaller amount, of approximately 4%. In a final step, population exposure to air pollution was calculated, both for the base case and the scenario simulations. A very slight domain-average exposure increase was found, of the order of a half percent. A compensating mechanism was identified, explaining this small figure. However, when stratifying the population into groups of individuals that were relocated to the urban periphery and those that were not, much larger exposure changes following urban sprawl emerged. Indeed, it was found that the relatively small proportion of relocated individuals benefited of a decrease of exposure to particulate matter by almost 13%, mainly because of their moving out of the most polluted areas; and that this came at the expense of an increase of exposure of 1.2% by the individuals not having moved.