Impact of the clouds of volcanic aerosols in Italy during the last 7 centuries

Abstract

Intense natural pollution has occurred in the past in Italy corresponding to intense volcanic activity, which appears to have diminished somewhat in recent times. Between 1500 and 1900, Etna, Vesuvius, Vulcano and Stromboli, plus volcanoes outside Italy were very active and there are numerous, well documented episodes of atmospheric acidification which caused widespread damage, especially to the vegetation. Other than the acid rains, volcanic emissions also caused so calleddry fogs which consist of a more or less dense mist composed of foul smelling gases and aerosols, characterized by a reddish color, that could appear and persist when the relative humidity was low as shown by measurements taken on such occasions. This phenomenon appeared most frequently at the beginning of the hot season. In fact, volcanic clouds of gases and aerosols formed especially when the Tyrrhenian sea water was relatively cold giving rise to very stable atmospheric conditions locally and the summer anticyclone meant that the winds were calm. Under such conditions the emissions of Stromboli and Vulcano, especially those emitted at low levels, remained entrapped in the stable layer, which were then transported towards the land reaching Northern Italy at a distance on the order of 10³ km. Thedry fogs could persist for days or weeks. Harvests were seriously damaged and frequently the crops were subsequently attacked by parasites. The leaves of the vegetation became discoloured with numerous punctiform lesions or gangrene at the edges of the leaves. The phenomenon was so frequent that, in texts on agricultural meteorology of the 1800s, a distinction was made between the causticdry fogs which damaged the vegetation anddamp fogs which instead were good for it. The most important episode occurred in 1783 due to the activity of Laki Grímsvötn (Iceland) with the contribution of Italian volcanoes. This dry fog lasted many months and affected the greater part of the northern hemisphere including Europe and Asia, harming people, animals and vegetation. Apart from paroxysmal cases, from the 1300s up to today, some tens ofdry fogs have been noted, all of which have been sufficiently well documented. The frequency of these events culminated between the middle of the 1700s and the middle of the 1800s. There is reason to believe that this well documented phenomenon of the past, with sufficient volcanic activity, could recur on the meso and large scale; with present day activity the emissions continue to cause damage to vegetation, both in the Aspromonte mountains (Calabria, Southem Italy) as well as in other parts of Italy.