Several types of natural gas emissions (soil gas, low temperature fumaroles, gas bubbling in mud pools) were collected monthly on Mt. Etna volcano between July 2000 and July 2003 both from its summit and its flanks. Samples were analysed for the determination of the concentrations of CO₂, CH₄, He, H₂, CO as well as the isotopic ratios of ¹³C/¹⁴C of CO₂ (δ¹³C) and He (R/Ra). The analysed gases were chemically divided into two groups: air-contaminated (from sites closer to the summit vents of Mt. Etna)and CO₂ - rich. Among the latter, samples from the lower SW flank of the volcano showed high contents of biogenic thermogenic and/or microbial CH₄. Isotopic shift in the δ¹³C values is caused by input of organic CO₂ and/or by interaction between magmatic CO₂ and shallow ground water as a function of water temperature and CO₂ flux from depth. Based on a graphic method applied to δ¹³C_TDIC of some ground water, the inferred isotopic composition of the pristine magmatic gas at Mt. Etna is characterised by δ¹³C values ranging from -2 to -1 ‰.

During the period July 2000 - July 2003 significant variations were observed in many of the investigated parameters almost at all monitored sites. Seasonal influences were generally found to be negligible, with only alimited effect of air temperature changes on soil CO₂ and ground temperature in only two of the air-contaminated sites. The largest chemical anomalies were observed in the air-contaminated sites, probably because of the strong buffering power of local ground water on gases released through the most peripheral areas where the CO₂-rich sites are located. The anomalous changes observed during the study period can be explained in terms of progressive gas release from separate batches of magma that ascend towards the surface in a step-wise manner. Data relevant to the period following the 2002-03 eruption suggest that magma kept accumulating beneath the volcano, thus increasing the probability of a new large eruption at Mt. Etna.