In-situ characterisation of aerosol and gases (SO 2 , HCl, ozone) in Mt Etna volcano plume

International audienceWe present findings from a measurement campaign that deployed a range of in-situ real-time atmospheric measurement techniques to characterise aerosols and gases in Mt Etna plume in October 2013. The LOAC (Light Optical Aerosol Counter) instrument for size-resolved particle measurements was deployed alongside two Multi-Gas instruments (measuring SO 2 , H2S, HCl, CO 2) and an ozone sensor. Measurements were performed at the summit craters (in cloudy-and non-cloudy conditions) and in grounding downwind plume on the volcano flank. These high frequency measurements (acid gases: 1 to 0.1 Hz, aerosol: 0.1 Hz) provide a detailed in-situ dataset for time-resolved plume characterisation and volcano monitoring. The LOAC measurement of sized-resolved aerosol (over a 0.2 to 50 µm particle diameter range) alongside SO 2 (10's ppbv to 10's ppmv) provides a valuable dataset for determining the volcanic aerosol volume and surface area to SO 2 ratios. These parameters are presently poorly defined but are important for atmospheric models of the reactive halogen chemistry that occurs on volcanic aerosol surfaces to convert volcanic HBr into reactive bromine, including BrO. The LOAC's patented optical design can also provide insights into particle properties. The two Multi-Gas SO 2 time-series show good agreement, detecting co-varying plume fluctuations in the downwind plume, which also correlate with the LOAC total aerosol volume time-series. An estimate of HCl/SO 2 in Etna emissions was made by Multi-Gas electrochemical sensor, using a novel design to limit absorption/desorption effects and low-noise electronics for improved resolution. The detection of volcanic HCl by electrochemical sensor brings new possibilities for Multi-Gas monitoring of volcanic halogen emissions. Electrochemical sensor response times are not instantaneous, particularly for sticky gases such as HCl (T90 ∼min), but also even for " fast " response (T90 ∼ 10 to 30 s) sensors such as SO 2 and H2S. However, in a volcanic plume environment, Multi-Gas instruments are exposed to very rapidly fluctuating gas concentrations due to turbulent plume eddies. The combination of these effects can introduce measurement errors, emphasizing a need for sensor response modelling approaches for accurate determination of gas ratios from Multi-Gas instruments

In situ measurement of the Icelandic Holuhraun/ Bárðarbunga volcanicplume in an early “young state” using a LOAC

International audienceVolcanic eruptions have huge societal and economic consequences. In Iceland, one of the best known examples isthe Laki eruption (1783-84 CE) (Thordarson and Self, 2003) which caused the death of > 20% of the Icelandicpopulations and likely increased European levels of mortality through air pollution (Witham and Oppenheimer,2004). The recent fissure eruption at Holuhraun (31 August 2014 – 27 February 2015) was a major source ofsulfur gases and aerosols and caused also both local and European-wide deteriorations to air quality (Gislason etal. 2015; Schmidt et al. 2015).The capability of atmospheric models to predict volcanic plume impacts is limited by uncertainties in thenear-source plume state. Most in-situ measurements of the elevated plume involve interception of aged plumesthat have already chemically or physically evolved. Small portable sensors airborne drone or balloon platformsoffer a new possibility to characterize volcano plumes near to source.We present the results of a balloon flight through the plume emitted by Baugur the main vent during the nightof the January 22th 2015. The balloon carrying a LOAC (Renard et al. 2015) has intercepted the plume at 8kmdistance downwind from the crater which represents a plume age of approximately 15 minutes. The plume waslocated in altitude between 2 and 3.1km above the sea level. Two layers were observed, a non-condensed lowerlayer and a condensed upper layer. The lower layer of 400m thick was characterized by a mode of fine particlescentered on 0.2m in diameter and a second mode centered on 2.3m in diameter and a total particle concentrationaround 100 particles per cubic centimeter. The upper layer of 800m thick was a cloud-like signature with dropletscentered on 20 m in diameter and a fine mode, the total particles concentrations was 10 times higher than thefirst layer. The plume top height was determined between 2.7 and 3.1 km, the plume height is in good agreementwith an estimate made by analysis of IASI satellite remote sensing data, thus demonstrating in-situ validation ofthis recent satellite algorithm (Carboni et al. 2015).This experimentation shows that under such difficult field campaign conditions (strong wind, low temperatures,only car batteries for power supply, night time and active volcano close to the launch site) it is possible to launchmeteorological balloons with novel payloads to directly sample in-situ the near-source plume, determine theplume altitude, identify dynamical phases of the plume and document the size distribution of particles inside aplume which is only a quarter of an hour old