The latest in Dr Gary Fuller's pollution watch series for the Guardian.

Thanks to presenters at the recent AirMonTech conference in Duisburg for highlighting Willy Brandt’s 1961 demand that the "sky above the Ruhr be made blue again" and to Peter Bruckmann (formerly of State Agency for Nature, Environment and Consumer Protection of Northrhine-Westphalia) for further background information on this interesting issue.

Item date 08/04/2013