This paper presents a contribution to the Regional Material Balance Approaches to Long-Term Environmental Policy Planning project (IND project). The policy part of this project - the Ruhr/Katowice Policy Comparison - aims at a better understanding of policy options for cleaning up the Black Triangle. The comparison focuses on the Ruhr Area and the Katowice voivodship which were both identified as hot spots of heavy metal pollution. The Ruhr/Katowice Policy Comparison comprises a historical analysis of the Ruhr Area, which draws heavily on the evidence collected in IIASA's previous Rhine Basin study and which investigates past policies to reduce heavy metal pollution in this area. The investigation was performed by Sander de Bruyn and Simone Schucht during their participation in IIASA's Young Scientists' Summer Program. This paper describes, both quantitatively and qualitatively, the determinants of the reduction of atmospheric heavy metal emissions in Northrhine-Westfalia. It develops methods to describe quantitatively industrial transformation and applies these methods to the analysis of industrial change in Northrhine-Westfalia during the 1955 to 1988 period
