Wspolny raport o jakosci powietrza w trojgranicznym regionie Republiki Czeskiej, Polski i Niemeic w roku 2004 (byly region Czarnego Trojkata)

About 15 years ago the Tri-border Region of the Czech Republic, Poland and Germany was called the Black Triangle (covering Northern Bohemia, part of Lower Silesia and Saxony) and was characterised by the highest air pollution in Europe. So it was necessary to find an approach for solving the transboundary air quality problems. Consequently a joint declaration of cooperation in solving environmental problems in the Black Triangle Region was signed by the ministers of environment of former Czechoslovakia, Germany and Poland in June 1991.