Articles | Volume 15, issue 5
Research article
09 Mar 2015
Research article |  | 09 Mar 2015

Quantification of the depletion of ozone in the plume of Mount Etna

L. Surl, D. Donohoue, A. Aiuppa, N. Bobrowski, and R. von Glasow

Abstract. Volcanoes are an important source of inorganic halogen species into the atmosphere. Chemical processing of these species generates oxidised, highly reactive, halogen species which catalyse considerable O3 destruction within volcanic plumes. A campaign of ground-based in situ O3, SO2 and meteorology measurements was undertaken at the summit of Mount Etna volcano in July/August 2012. At the same time, spectroscopic measurements were made of BrO and SO2 columns in the plume downwind.

Depletions of ozone were seen at all in-plume measurement locations, with average O3 depletions ranging from 11–35 nmol mol−1 (15–45%). Atmospheric processing times of the plume were estimated to be between 1 and 4 min. A 1-D numerical model of early plume evolution was also used. It was found that in the early plume O3 was destroyed at an approximately constant rate relative to an inert plume tracer. This is ascribed to reactive halogen chemistry, and the data suggests the majority of the reactive halogen that destroys O3 in the early plume is generated within the crater, including a substantial proportion generated in a high-temperature "effective source region" immediately after emission. The model could approximately reproduce the main measured features of the ozone chemistry. Model results show a strong dependence of the near-vent bromine chemistry on the presence or absence of volcanic NOx emissions and suggest that near-vent ozone measurements can be used as a qualitative indicator of NOx emission.

Short summary
We investigate the atmospheric chemistry that occurs in the plume of Mt. Etna shortly after emission. We measured O3 destruction in the plume. Using simultaneous measurements of SO2 and wind speed, we approximate the rate of this destruction. BrO, expected to be an indicator of ozone-destructive chemistry, is also detected. A computer model is able to approximately reproduce these results and is used to make inferences about the chemistry occurring that cannot be directly observed.
Final-revised paper