Aerosol chemistry of emissions from three contrasting volcanoes in Italy

Volcanoes constitute an important source of aerosol. Here we report the size-resolved compositions of major water-soluble ions in particles collected in near-source emissions from three contrasting volcanoes (Solfatara, Vulcano and Stromboli, in Italy). Concentrations of soluble SO42−, Cl−, F−, NO3−, H+, K+, Na+, NH4+, Ca2+ and Mg2+ were determined in 11 particle size bins from 0.069 to >25.5 μm in diameter. Soluble ions were most concentrated in the emissions from Solfatara and Stromboli. At Solfatara the major ions were NH4+ and Cl−, tightly correlated in 0.8–1.5 μm diameter particles, strongly suggesting speciation as NH4Cl. At Stromboli enhanced levels of SO42−, H+, Na+, K+ and NH4+ were present in 0.5–1.5 μm diameter particles. Near-source soluble sulphate was observed in the plumes from Stromboli and Vulcano, with that from Stromboli in much higher concentration (0.94–2.14 compared with 0.07–0.13 μmol m−3). Comparing SO42− measurements from Vulcano to those from other volcanic systems suggests that near-source sulphate aerosol emissions scale with SO2 and contribute 0.03–0.05 Tg yr−1 of sulphur to the atmosphere. Simple calculations suggest that all the particles containing these soluble ions will act as cloud condensation nuclei at typical atmospheric supersaturations.