Lichens as bioindicators of air quality in Arezzo (central Italy)

Abstract

Epiphytic lichens were used as bioindicators of air quality in the town of Arezzo in central Italy. By means of 15 Index of Atmospheric Purity (IAP) relevés, a zone-map was drawn by automatic mapping programmes and the area was divided into four air quality zones. The worst air quality occurred in the centre of the town, inside the old medieval walls, i.e. in the part of the study area where air exchange due to winds is scanty and motorized traffic is more intense. On the contrary, the highest IAP values were found to the south-east, in areas more exposed to winds and with a lower burden of traffic. These results are in agreement with data on air pollutants measured by recording gauges, which showed that SO2 levels were very low, NOx and CO from car exhaust being the main pollutants. It was thus concluded that in the area the main source of air pollution is from motorized traffic and that changes in lichen frequencies are largely determined by nitrogen oxides. Other possible factors affecting the impoverishment of lichen frequency in the city centre may be carbon monoxide and the heat island effect. Furthermore, the results suggest that a high lichen recolonization should have taken place from 1979 under conditions of falling SO2 levels.