DANGEROUS ATMOSPHERIC SULPHUR DIOXIDE CONCENTRATIONS AT CRATERIC AREAS OF ITALIAN ACTIVE VOLCANOES

Volcanic activity is the main natural sources of sulphur dioxide (SO2) to the atmosphere. Although total anthropogenic sources are overwhelming greater, volcanoes like Mt. Etna and many others are considered to be among the biggest point sources of SO2 also during intereruptive periods. Apart from being one of the most impressive geodynamic expressions, volcanoes are also an important tourist attraction. During the summer season the number of tourists visiting the summit craters each day is on average many tens at Stromboli, hundreds at Vulcano and thousands at Mt. Etna. Of course touristic exploitation of active volcanic areas cannot exempt from warranting a reasonable security to the visiting persons. But while many risks in these areas have been since long time considered, gas hazard, a very subtle risk, is often disregarded. For healthy persons, about 1000 µg m-3 of sulphur dioxide is sensed by smell, 2000 to 4000 µg m-3 cause eye, nose and throat irritation, and 10,000 to 15,000 µg m-3 cause respiratory failure. For individuals with bronchial asthma or lung diseases, exposure to much lower doses could be fatal. Generally, a 700 µg m-3 level is considered to be a safe limit for such persons. The atmospheric concentrations of naturally emitted SO2 were measured at three volcanoes of southern Italy (Mt. Etna, Vulcano and Stromboli). Measurements were made with a network of passive samplers positioned at about 1.5 m above the ground, which gave time-integrated values for periods from few days to 1 month. Samplers were placed in zones of the volcanoes with high tourist frequentation. Measured concentrations reach values as high as 2700, 2400 and 10,000 µg m-3 for Etna, Vulcano and Stromboli respectively. Such values are absolutely dangerous to people affected by bronchial asthma or lung diseases. But considering that these are average values over periods from few days up to one month, SO2 concentrations could reach much higher peak values that could be dangerous also to healthy people. The present study evidences a peculiar volcanic risk connected to the touristic exploitation of active volcanic areas. Such risk is particularly enhanced at Mt.Etna where elderly and not perfectly healthy people can easily reach, with cableway and off-road vehicles, areas with dangerous SO2 concentrations