Lichens as biomonitors of air pollution in territory surrounding Lake Maggiore (Provinces of Novara and Varese). Pt. 1

The air quality in the territory surrounding Lake Maggiore (Italy)has been monitored by means of lichens used as bioindicators 143 stations were used for the monitoring in which a total of 497 surveys were made. These were carried out on the same number of lime (Tilia sp. pl. ) and oak trees (Quercus sp. pl. ) using the Calibrated Lichen Index of Air Quality proposed by Liebendoerfer et al. (1988). This index consists of the calculation, in each station, of an index of atmospheric purity, based on the sum of the frequency with which all the lichen species were found in a reference grid of ten units. The processing of the data including the cartographic surveys, was entirely made by computerized systems. The results of the inquiry are the following: a) the most polluted zone stretches were from the south-eastern part of the survey area to the north-west towards the basin of the Borromee Islands and the Toce Valley; b) small zones with a poor air quality are also to be found in the northern part of Lake Maggiore; c) from the analysis of the chart of the Air Quality compared with that of the prevailing direction of the winds it is clear that the pollution is mainly brought from neighboring areas and is only partly due to local sources; d) the zones with a better air quality are located primarily in the mountainous areas, above all in the North towards the Swiss border, at more than 700-80O metres above sea level