The results of long-term biomonitoring of nine elements (Cd, Cr, Ni, Pb, V, Cu, Zn, Fe and Al) with the epiphytic lichen Xanthoria parietina over a seven year time span are reported. A total of 51 sampling stations were monitored in two surveys, obtaining information about heavy metal concentrations in a large area characterized by a high impact of industrial and urban sources of air pollution. The results showed that the approach adopted is indeed a reliable tool to assess environmental alteration, pinpointing not only the trends of the nine elements analysed but also their reciprocal correlations. As a consequence it was possible to characterize changes in air pollution composition and the common origin and behavior of several groups of elements.