Monitoring air quality by using living organisms as biomonitors has received increasing attention in
recent years. However, rather few studies were based on the concomitant use of passive biomonitoring
(based on the different sensitivity of living organisms to air pollution) and active biomonitoring (based on
their capacity to accumulate pollutants in the tissues). We carried out a repeated survey of an urban area
in Northern Italy, with the objective of comparing temporal trends of different kinds of air pollutants with
bioindication (passive biomonitoring) and bioaccumulation (active biomonitoring) techniques. During a
five-year interval, temporal patterns of moss metal concentrations underwent significant changes probably
due to intercurring variations in the importance of different pollution sources. Nitrogen (N) concentration
in moss tissues also decreased and was paralleled by increasing diversity of epiphytic lichens.
Increasing d15N in moss tissues suggested a higher contribution of oxidized N species compared with
reduced N species.