Figure 5From: Long-term monitoring of environmental change in German towns through the use of lichens as biological indicators: comparison between the surveys of 1970, 1980, 1985, 1995, 2005 and 2010 in Wetzlar and GiessenAnnual mean values of sulfur dioxide concentration in Wetzlar and Giessen. There are no data since 2004 for Giessen[12].Back to article page