Airborne observations of the Eyjafjalla volcano ash cloud over Europe during air space closure in April and May 2010

Abstract

Airborne measurements of Lidar backscatter, aerosol concentrations (particle diameters of 4 nm to 50 μm), trace gas mixing ratios (SO<sub>2</sub>, CO, O<sub>3</sub>, H<sub>2</sub>O), single particle properties, and meteorological parameters have been performed in volcanic ash plumes with the Falcon aircraft operated by Deutsches Zentrum für Luft- und Raumfahrt (DLR). A series of 17 flights was performed over Europe between Southern Germany and Iceland during the eruption period of the Eyjafjalla<sup>1</sup> volcano between 19 April and 18 May 2010. Flight planning and measurement analyses were supported by a refined Meteosat ash product and trajectory model analysis. The volcanic ash plume was observed with Lidar directly over the volcano and up to a distance of 2700 km downwind. Lidar and in-situ measurements covered plume ages of 7 h to 120 h. Aged ash layers were between a few 100 m to 3 km deep, occurred between 1 and 7 km altitude, and were typically 100 to 300 km wide. Particles collected by impactors had diameters up to 20 μm diameter, with size and age dependent composition. Ash mass concentration was evaluated for a material density of 2.6 g cm<sup>−3</sup> and for either weakly or moderately absorbing coarse mode particles (refractive index 1.59+0<i>i</i> or 1.59+0.004<i>i</i>). In the absorbing case, the ash concentration is about a factor of four larger than in the non-absorbing limit. Because of sedimentation constraints, the smaller results are the more realistic ones for aged plumes. The Falcon flew in ash clouds up to about 1 mg m<sup>−3</sup> for a few minutes and in an ash cloud with more than 0.2 mg m<sup>−3</sup> mean-concentration for about one hour without engine damages. In fresh plumes, the SO<sub>2</sub> concentration was correlated with the ash mass concentration. Typically, 0.5 mg m<sup>−3</sup> ash concentration was related to about 100 nmol mol<sup>−31</sup> SO<sub>2</sub> mixing ratio and 70 nmol mol<sup>−1</sup> CO mixing ratio increases for this volcano period. In aged plumes, layers with enhanced coarse mode particle concentration but without SO<sub>2</sub> enhancements occurred. To first order, ash concentration and SO<sub>2</sub> mixing ratio in the plumes decreased by a factor of two within less than a day. The ash plumes were often visible as faint dark layers even for concentrations below 0.1 mg m<sup>−3</sup>. The ozone concentrations and the humidity inside the plumes were often reduced compared to ambient values. The large abundance of volatile Aitken mode particles suggests nucleation of sulfuric acid droplets. Ammonium sulfate particles were also found on the impactors. The effective diameters decreased from about 5 μm in the fresh plume to about 1 μm for plume ...

A High-Sensitivity Low-Cost Optical Particle Counter Design

“…Our proposed instrument is ideal for in situ volcanic-ash measurements. Since the ash mass is concentrated at large sizes (∼10 µm; Schumann et al 2011), a PMT is not necessary, leading to a significant reduction in cost.…”

Development and application of a backscatter lidar forward operator for quantitative validation of aerosol dispersion models and future data assimilation

“…According to Schumann et al (2011), the real part of the refractive index was between 1.53 and 1.60 at a wavelength of λ = 630 nm and between 1.50 and 1.56 at a wavelength of λ = 2000 nm. The respective imaginary part was ranging from −0.001 to −0.004 i at a wavelength of λ = 630 nm and from −2.0 × 10 −6 to −40.0 × 10 −6 i at a wavelength of λ = 2000 nm.…”

“…A detailed analysis of the emitted ash was performed by Schumann et al (2011) who compared measurements from the DLR Falcon 20 aircraft with data of research lidar systems in Germany. Eyjafjallajökull ash samples were taken in situ, analyzed using a scanning electron microscope, and assigned to matter groups.…”

A review of volcanic ash aggregation

“…Observations during the 18 May 1980 eruption of Mount St. Helens, USA, indicate a close association between the formation of volcanogenic hydrometeors (rain, graupel/hailstones and snow) and fine ash fallout within ~20-30 km of the volcano (Waitt and Dzurisin, 1981;Rosenbaum and Waitt, 1981). The timescales of aggregate formation are short: for example, AP1 aggregates were deposited within five minutes of the onset of the 1990 eruption of Sakurajima volcano, Japan (Gilbert and Lane, 1994) In long-lived ash clouds (>1 day), cloud water concentrations fall close to background levels due to mixing and sedimentation (e.g., Schumann et al, 2011), and electrostatic forces may then play an important role in particle binding (James et al, 2003). Aggregation played an important role in the settling of ash from eruption clouds generated during the 2010 eruption of Eyjafjallajökull volcano, Iceland (Taddeucci et al, 2011).…”