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Samples of grass were collected at Masaya Volcano (Nicaragua; Rhynchelytrum repens and Andropogon angustatus) and the Piton de La Fournaise (around the April 2007 eruptive vent, La Réunion; Vetiveria zizanioides) to investigate the controls on major and trace element concentrations in plants around active volcanic vents. Samples were analysed using inductively coupled plasma mass spectrometry for a wide range of elements, and atomic absorption spectroscopy for Hg. At Masaya, As, Cu, Mo, Tl and K concentrations in both grass species showed a simple pattern of variability consistent with exposure to the volcanic plume. Similar variability was found in A. angustatus for Al, Co, Cs, Hg and Mg. At the Piton de La Fournaise, the patterns of variability in V. zizanioides were more complex and related to variable exposures to emissions from both the active vent and lava flow. These results suggest that exposure to volcanic emissions is, for many elements, the main control on compositional variability in vegetation growing on active volcanoes. Thus, vegetation may be an important environmental reservoir for elements emitted by volcanoes and should be considered as part of the global biogeochemical cycles. [ABSTRACT FROM AUTHOR]

We present the first application of a multi-stage impactor to study volcanic particle emissions to the troposphere from Masaya volcano, Nicaragua. Concentrations of soluble SO42-, Cl-, F-, NO3-, K+, Na+, NH4+, Ca2+ and Mg2+ were determined in 11 size bins from ∼0.07 μm to >25.5 μm. The near-source size distributions showed major modes at 0.5 μm (SO42-, H+, NH4+); 0.2 μm and 5.0 μm (Cl-) and 2.0–5.0 μm (F-). K+ and Na+ mirrored the SO42- size-resolved concentrations closely, suggesting that these were transported primarily as K2SO4 and Na2SO4 in acidic solution, while Mg2+ and Ca2+ presented modes in both <1 μm and >1 μm particles. Changes in relative humidity were studied by comparing daytime (transparent plume) and night-time (condensed plume) results. Enhanced particle growth rates were observed in the night-time plume as well as preferential scavenging of soluble gases, such as HCl, by condensed water. Neutralisation of the acidic aerosol by background ammonia was observed at the crater rim and to a greater extent approximately 15 km downwind of the active crater. We report measurements of re-suspended near-source volcanic dust, which may form a component of the plume downwind. Elevated levels of SO42-, Cl-, F-, H+, Na+, K+ and Mg2+ were observed around the 10 μm particle diameter in this dust. The volcanic SO42- flux leaving the crater was ∼0.07 kg s-1. [ABSTRACT FROM AUTHOR]