In situ observations of volcanic ash clouds from the FAAM aircraft during the eruption of Eyjafjallajökull in 2010

Abstract

During April–May 2010 the UK Facility for Airborne Atmospheric Measurements (FAAM) BAe‐146 aircraft flew 12 flights targeting volcanic ash clouds around the UK. The aircraft observed ash layers between altitudes of 2–8 km with peak mass concentrations typically between 200–2000μg/m3, as estimated from a Cloud and Aerosol Spectrometer (CAS). A peak value of 2000–5000 μg/m3 was observed over Scotland on 14 May 2010, although with considerable uncertainty due to the possible contamination by ice. Aerosol size distributions within ash clouds showed a fine mode (0.1–0.6 μm) associated with sulphuric acid and/or sulphate, and a coarse mode (0.6–35 μm) associated with ash. The ash mass was dominated by particles in the size range 1–10 μm (volume‐equivalent diameter), with a peak typically around 3–5μm. Electron‐microscope images and scattering patterns from the SID‐2H (Small Ice Detector) probe showed the highly irregular shape of the ash particles. Ash clouds were also accompanied by elevated levels of SO2 (10–100 ppbv), strong aerosol scattering (50–500 × 10−6 m−1), and low Ångstrom exponents (−0.5 to 0.4) from the 3‐wavelength nephelometer. Coarse‐mode mass specific aerosol extinction coefficients (kext), based on the CAS size distribution varied from 0.45–1.06 m2/g. A representative value of 0.6 m2/g is suggested for distal ash clouds (∼1000 km downwind) from this eruption.

Lidar observation and model simulation of a volcanic-ash-induced cirrus cloud during the Eyjafjallajökull eruption

“…For volcanic ash particles we use a mono modal log-normal distribution with a width of 1.7 σ , minimal radius of 0.1 µm and maximum radius of 5 µm. This values are similar to the outcome of inverted lidar and photometer data from Gasteiger et al (2011) or aircraft in-situ measurements (Johnson et al, 2012;Schumann et al, 2011).…”

“…Ansmann et al, 2010;Gross et al, 2012;Seifert et al, 2011) and aircraft (e.g. Johnson et al, 2012;Schumann et al, 2011) and is well documented in several special issues (ACP, JGR, and Atmospheric Environment). Two days after the first large eruption on 14 April, we detected the ash cloud with a backscatter lidar system over Jülich,western Germany (50 • 54 N,6 • 24 E).…”

Anthropogenic radionuclides in atmospheric air over Switzerland during the last few decades

“…In the atmosphere, sulphur-bearing gases such as SO 2 transformed into tiny sulphuric acid particles 2,44 . Aerosol size distributions within ash clouds showed a fine mode (0.1-0.6 mm) associated with sulphuric acid and/or sulphate, and a coarse mode (0.6-35 mm) associated with ash 45 . Numerous studies showed that the Eyjafjallajökull ash particles were strongly depolarizing 46 and that particles were electrically charged 47,48 .…”

Uncertainty in two-channel infrared remote sensing retrievals of a well-characterised volcanic ash cloud

“…A lognormal distribution has been justified for volcanic ash PSDs for the 2010 Eyjafjallajökull eruption from aircraft measurement (Schumann et al 2011;Johnson et al 2012;Turnbull et al 2012). Although all flights where the ash PSD was measured were during the same eruptive phase, discrepancies exist between PSD parameter measurements, perhaps due to the difference in assumed ash properties and sampling methods used (see Turnbull et al (2012) for full discussion).…”

“…The PSD of the volcanic ash was observed to be lognormal during in situ sampling at various dates throughout April and May by the FAAM ) and DLR (Schumann et al 2011) aircrafts, and therefore, a lognormal PSD is used. The average value for the geometric standard deviation given by Johnson et al 2012 (σ g =1.85±0.5, dependent on assumed single scattering properties) is here considered the best approximation to use. Variations in atmospheric water vapour, surface emissivity and plume geometry are not discussed, but this work is well covered by Corradini et al (2008).…”