The International Co-operative Programme on Effects on Materials including Historic and Cultural Monuments (ICP Materials) is an extensive field exposure programme within the United Nations Economic Commission for Europe (UN ECE). In its network of test sites, which presently includes 30 test sites in 14 European countries and in Israel, the United States and Canada, several one-year exposures of unalloyed carbon steel, zinc, copper, cast bronze, limestone and steel panel with alkyd paint have been performed during the period 1987–97. The present work summarizes and analyses the one-year exposures for trend effects in Europe and, in particular, quantifies the part of the trend attributable to changes in sulfur dioxide concentration. SO2 is the largest single contributing factor to the decreasing corrosion trends. The decreasing H+ in precipitation is also a contributing factor, its effect is, however, much smaller than that of dry deposition. In addition to the ICP Materials results, long term trend examples of zinc and carbon steel corrosion and SO2 concentration for the period 1946–1997 are shown for Stockholm, Moscow, Prague and Kopisty.