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The measurement of SO 2 flux from volcanoes is of major importance for monitoring and hazard assessment purposes, and for evaluation of the environmental impact of volcanic emissions. We propose here a novel technique for accurate and high time resolution estimations of the gas flux. We use two wide field of view UV spectrometers capable of collecting, instantaneously, light from thin parallel cross sections of the whole gas plume, obviating the need for either traversing, scanning or imaging. It enables tracking of inhomogeneities in the gas cloud from which accurate evaluation of the plume velocity can be made by correlation analysis. The method has been successfully applied on Mt. Erebus volcano (Antarctica). It yields estimations of the plume velocity and gas flux at unprecedented time resolution (1 Hz) and high accuracy (uncertainty of 33%). During a ∼2 h experiment on 26 December 2006, SO 2 flux varied between 0.17 and 0.89 ± 0.2 kg s −1 with a vertical plume velocity varying between 1 and 2.5 ± 0.1 m s −1. These

[1] Direct sampling (filter pack and impactor) and remote sensing (ultraviolet spectroscopy and Sun photometry) of the plumes of Lascar and Villarrica volcanoes, Chile, reveal that both are significant and sustained emitters of SO 2 (28 and 3.7 kg s À1 , respectively), HCl (9.6 and 1.3 kg s À1 , respectively), HF (4.5 and 0.3 kg s À1 , respectively) and near-source sulfate aerosol (0.5 and 0.1 kg s À1 , respectively). Aerosol plumes are characterized by particle number fluxes (0.08-4.0 mm radius) of $10 17 s À1 (Lascar) and $10 16 s À1 (Villarrica), the majority of which will act as cloud condensation nuclei at supersaturations >0.1%. Impactor studies suggest that the majority of these particles contain soluble SO 4 2À. Most aerosol size distributions were bimodal with maxima at radii of 0.1-0.2 mm and 0.7-1.5 mm. The mean particle effective radius (R eff ) ranged from 0.1 to 1.5 mm, and particle size evolution during transport appears to be controlled by particle water uptake (Villarrica) or loss (Lascar) rather than sulfate production.

[1] We report measurements of Hg, SO 2 , and halogens (HCl, HBr, HI) in volcanic gases from Masaya volcano, Nicaragua, and gaseous SO 2 and halogens from Telica volcano, Nicaragua. Mercury measurements were made with a Lumex 915+ portable mercury vapor analyzer and gold traps, while halogens, CO 2 and S species were monitored with a portable multi gas sensor and filter packs. Lumex Hg concentrations in the plume were consistently above background and ranged up to 350 ng m À3. Hg/SO 2 mass ratios measured with the real-time instruments ranged from 1.1 Â 10 À7 to 3.5 Â 10 À5 (mean 2 Â 10 À5