Ash Mass Concentration Research Articles

Physical and optical properties of 2010 Eyjafjallajökull volcanic eruption aerosol: ground-based, Lidar and airborne measurements in France

Abstract. During the Eyjafjallajökull eruption (14 April to 24 May 2010), the volcanic aerosol cloud was observed across Europe by several airborne in situ and ground-based remote-sensing instruments. On 18 and 19 May, layers of depolarizing particles (i.e. non-spherical particles) were detected in the free troposphere above the Puy de Dôme station, (PdD, France) with a Rayleigh-Mie LIDAR emitting at a wavelength of 355 nm, with parallel and crossed polarization channels. These layers in the free troposphere (FT) were also well captured by simulations with the Lagrangian particle dispersion model FLEXPART, which furthermore showed that the ash was eventually entrained into the planetary boundary layer (PBL). Indeed, the ash cloud was then detected and characterized with a comprehensive set of in situ instruments at the Puy de Dôme station (PdD). In agreement with the FLEXPART simulation, up to 65 μg m−3 of particle mass and 2.2 ppb of SO2 were measured at PdD, corresponding to concentrations higher than the 95 percentile of 2 yr of measurements at PdD. Moreover, the number concentration of particles increased to 24 000 cm−3, mainly in the submicronic mode, but a supermicronic mode was also detected with a modal diameter of 2 μm. The resulting optical properties of the ash aerosol were characterized by a low scattering Ångström exponent (0.98), showing the presence of supermicronic particles. For the first time to our knowledge, the combination of in situ optical and physical characterization of the volcanic ash allowed the calculation of the mass-to-extinction ratio (η) with no assumptions on the aerosol density. The mass-to-extinction ratio was found to be significantly different from the background boundary layer aerosol (max: 1.57 g m−2 as opposed to 0.33 ± 0.03 g m−2). Using this ratio, ash mass concentration in the volcanic plume derived from LIDAR measurements was found to be 655 ± 23 μg m−3 when the plume was located in the FT (3000 m above the sea level – a.s.l.). This ratio could also be used to retrieve an aerosol mass concentration of 579 ± 60 μg m−3 on 19 April, when LIDAR observations detected the ash cloud at 3000 m a.s.l. in correspondence with model simulations (FLEXPART). On 22 April, another ash plume entered the BL, and although it was more diluted than during the May episode, the French research aircraft ATR42 that passed over Clermont-Ferrand in the PBL confirmed the presence of particles with a supermicronic mode, again with a modal diameter at 2 μm. This data set combining airborne, ground-based and remote sensing observations with dispersion model simulations shows an overall very good coherence during the volcanic eruption period, which allows a good confidence in the characteristics of the ash particles that can be derived from this unique data set.

A case study of observations of volcanic ash from the Eyjafjallajökull eruption: 1. In situ airborne observations

On 17 May 2010, the FAAM BAe‐146 aircraft made remote and in situ measurements of the volcanic ash cloud from Eyjafjallajökull over the southern North Sea. The Falcon 20E aircraft operated by Deutsches Zentrum für Luft‐ und Raumfahrt (DLR) also sampled the ash cloud on the same day. While no “wingtip‐to‐wingtip” co‐ordination was performed, the proximity of the two aircraft allows worthwhile comparisons. Despite the high degree of inhomogeneity (e.g., column ash loadings varied by a factor of three over ∼100 km) the range of ash mass concentrations and the ratios between volcanic ash mass and concentrations of SO2, O3 and CO were consistent between the two aircraft and within expected instrumental uncertainties. The data show strong correlations between ash mass, SO2concentration and aerosol scattering with the FAAM BAe‐146 data providing a specific extinction coefficient of 0.6–0.8 m2 g−1. There were significant differences in the observed ash size distribution with FAAM BAe‐146 data showing a peak in the mass at ∼3.5μm (volume‐equivalent diameter) and DLR data peaking at ∼10μm. Differences could not be accounted for by refractive index and shape assumptions alone. The aircraft in situ and lidar data suggest peak ash concentrations of 500–800 μg m−3with a factor of two uncertainty. Comparing the location of ash observations with the ash dispersion model output highlights differences that demonstrate the difficulties in forecasting such events and the essential nature of validating models using high quality observational data from platforms such as the FAAM BAe‐146 and the DLR Falcon.

A review of volcanic ash aggregation

Most volcanic ash particles with diameters<63μm settle from eruption clouds as particle aggregates that cumulatively have larger sizes, lower densities, and higher terminal fall velocities than individual constituent particles. Particle aggregation reduces the atmospheric residence time of fine ash, which results in a proportional increase in fine ash fallout within 10–100skm from the volcano and a reduction in airborne fine ash mass concentrations 1000skm from the volcano. Aggregate characteristics vary with distance from the volcano: proximal aggregates are typically larger (up to cm size) with concentric structures, while distal aggregates are typically smaller (sub-millimetre size). Particles comprising ash aggregates are bound through hydro-bonds (liquid and ice water) and electrostatic forces, and the rate of particle aggregation correlates with cloud liquid water availability. Eruption source parameters (including initial particle size distribution, erupted mass, eruption column height, cloud water content and temperature) and the eruption plume temperature lapse rate, coupled with the environmental parameters, determines the type and spatiotemporal distribution of aggregates. Field studies, lab experiments and modelling investigations have already provided important insights on the process of particle aggregation. However, new integrated observations that combine remote sensing studies of ash clouds with field measurement and sampling, and lab experiments are required to fill current gaps in knowledge surrounding the theory of ash aggregate formation.

Remote sensing measurements of the volcanic ash plume over Poland in April 2010

This work provides information on selected optical parameters related to volcanic ash produced during the eruption of the Eyjafjoll volcano in Iceland in 2010. The observations were made between 16 and 18 April 2010 at four stations representative for northern (Sopot), central (Warsaw, Belsk) and south-eastern (Strzyzow) regions of Poland. The largest ash plume (in terms of aerosol optical thickness) over Poland was observed at night of 16/17 April 2010 in the layer between 4 and 5.5 km a.s.l. The highest values of the aerosol extinction coefficient reached 0.06e0.08 km � 1 at 532 nm (based on lidar observations in Warsaw) and 0.02e0.04 km � 1 at 1064 nm (based on ceilometer observations in Warsaw). The corresponding optical thickness due to volcanic ash reached values of about 0.05 at 532 nm and about 0.03 at 1064 nm. These values are similar to those reported for the Belsk station based on lidar observations. The ash mass concentration estimated based on the maximum aerosol extinction coefficient reached 0.22 � 0.11 mg m � 3 . This value is significantly lower than the limit (2 mg m � 3 ) for the aircraft operation.

Validation of the FALL3D ash dispersion model using observations of the 2010 Eyjafjallajökull volcanic ash clouds

During April–May 2010 volcanic ash clouds from the Icelandic Eyjafjallajökull volcano reached Europe causing an unprecedented disruption of the EUR/NAT region airspace. Civil aviation authorities banned all flight operations because of the threat posed by volcanic ash to modern turbine aircraft. New quantitative airborne ash mass concentration thresholds, still under discussion, were adopted for discerning regions contaminated by ash. This has implications for ash dispersal models routinely used to forecast the evolution of ash clouds. In this new context, quantitative model validation and assessment of the accuracies of current state-of-the-art models is of paramount importance. The passage of volcanic ash clouds over central Europe, a territory hosting a dense network of meteorological and air quality observatories, generated a quantity of observations unusual for volcanic clouds. From the ground, the cloud was observed by aerosol lidars, lidar ceilometers, sun photometers, other remote-sensing instruments and in-situ collectors. From the air, sondes and multiple aircraft measurements also took extremely valuable in-situ and remote-sensing measurements. These measurements constitute an excellent database for model validation. Here we validate the FALL3D ash dispersal model by comparing model results with ground and airplane-based measurements obtained during the initial 14–23 April 2010 Eyjafjallajökull explosive phase. We run the model at high spatial resolution using as input hourly-averaged observed heights of the eruption column and the total grain size distribution reconstructed from field observations. Model results are then compared against remote ground-based and in-situ aircraft-based measurements, including lidar ceilometers from the German Meteorological Service, aerosol lidars and sun photometers from EARLINET and AERONET networks, and flight missions of the German DLR Falcon aircraft. We find good quantitative agreement, with an error similar to the spread in the observations (however depending on the method used to estimate mass eruption rate) for both airborne and ground mass concentration. Such verification results help us understand and constrain the accuracy and reliability of ash transport models and it is of enormous relevance for designing future operational mitigation strategies at Volcanic Ash Advisory Centers. ► We perform high-resolution numerical simulations of the Eyafjallajökull volcanic ash clouds. ► Source term is assessed hourly using different models and plume heights from radar. ► We perform quantitative model validations versus in situ and remote ground-based observations. ► Results are crucial for knowing volcanic ash dispersion model limitations.

Ash and fine-mode particle mass profiles from EARLINET-AERONET observations over central Europe after the eruptions of the Eyjafjallajökull volcano in 2010

[1] A combined lidar-photometer method that permits the retrieval of vertical profiles of ash and non-ash (fine-mode) particle mass concentrations is presented. By using a polarization lidar, the contributions of non-ash and ash particles to total particle backscattering and extinction are separated. Sun photometer measurements of the ratio of particle volume concentration to particle optical thickness (AOT) for fine and coarse mode are then used to convert the non-ash and ash extinction coefficients into respective fine-mode and ash particle mass concentrations. The method is applied to European Aerosol Research Lidar Network (EARLINET) and Aerosol Robotic Network (AERONET) Sun photometer observations of volcanic aerosol layers at Cabauw, Netherlands, and Hamburg, Munich, and Leipzig, Germany, after the strong eruptions of the Icelandic Eyjafjallajokull volcano in April and May 2010. A consistent picture in terms of photometer-derived fine- and coarse-mode AOTs and lidar-derived non-ash and ash extinction profiles is found. The good agreement between the fine- to coarse-mode AOT ratio and non-ash to ash AOT ratio ( 15 μm.

Volcanic aerosol optical properties and phase partitioning behavior after long-range advection characterized by UV-Lidar measurements

Abstract In this paper, an UV-polarization Lidar is used to study the optical properties of volcanic aerosol in the troposphere. The particles were released by the mid-April 2010 eruption of the Eyjafjallajokull volcano (63.63°N, 19.62°W, Iceland) and passed in the troposphere above Lyon (45.76°N, 4.83°E, France) after advection over 2600 km. The FLEXPART particle dispersion model was applied to simulate the volcanic ash transport from Iceland to South West Europe, at the border of the air traffic closure area. Time-altitude plots of FLEXPART ash concentrations as well as of aerosol backscattering are presented, showing the arrival of volcanic particles in the troposphere above Lyon and their mixing into the planetary boundary layer. The particle UV-backscattering coefficient was typically 4 Mm−1 sr−1 and highly sensitive and accurate particle UV-depolarization measurements were performed, with depolarization ranging from a few to 44%. After few days long-range transport, observed ash particles are still non spherical. The observed variations of the backscattering and depolarization coefficients can be attributed to variations in the volcanic particles content. Ash mass concentrations are then retrieved. Moreover, a partitioning into spherical and non spherical particles is evaluated from number concentration ratios between solid ash particles and spherical hydrated sulfate particles. The microphysical properties of volcanic particles can thus be studied by associating an UV-polarization remote sensing instrument with a numerical volcanic ash dispersion model.

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

Abstract. Airborne lidar and in-situ measurements of aerosols and trace gases were performed in volcanic ash plumes over Europe between Southern Germany and Iceland with the Falcon aircraft during the eruption period of the Eyjafjalla 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, and up to 120 h plume ages. 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 concentrations were derived from optical particle spectrometers for a particle density of 2.6 g cm−3 and various values of the refractive index (RI, real part: 1.59; 3 values for the imaginary part: 0, 0.004 and 0.008). The mass concentrations, effective diameters and related optical properties were compared with ground-based lidar observations. Theoretical considerations of particle sedimentation constrain the particle diameters to those obtained for the lower RI values. The ash mass concentration results have an uncertainty of a factor of two. The maximum ash mass concentration encountered during the 17 flights with 34 ash plume penetrations was below 1 mg m−3. The Falcon flew in ash clouds up to about 0.8 mg m−3 for a few minutes and in an ash cloud with approximately 0.2 mg m−3 mean-concentration for about one hour without engine damage. The ash plumes were rather dry and correlated with considerable CO and SO2 increases and O3 decreases. To first order, ash concentration and SO2 mixing ratio in the plumes decreased by a factor of two within less than a day. In fresh plumes, the SO2 and CO concentration increases were correlated with the ash mass concentration. The ash plumes were often visible slantwise as faint dark layers, even for concentrations below 0.1 mg m−3. The large abundance of volatile Aitken mode particles suggests previous nucleation of sulfuric acid droplets. The effective diameters range between 0.2 and 3 μm with considerable surface and volume contributions from the Aitken and coarse mode aerosol, respectively. The distal ash mass flux on 2 May was of the order of 500 (240–1600) kg s−1. The volcano induced about 10 (2.5–50) Tg of distal ash mass and about 3 (0.6–23) Tg of SO2 during the whole eruption period. The results of the Falcon flights were used to support the responsible agencies in their decisions concerning air traffic in the presence of volcanic ash.

Volcanic ash from Iceland over Munich: mass concentration retrieved from ground-based remote sensing measurements

Abstract. Volcanic ash plumes, emitted by the Eyjafjallajökull volcano (Iceland) in spring 2010, were observed by the lidar systems MULIS and POLIS in Maisach (near Munich, Germany), and by a CIMEL Sun photometer and a JenOptik ceilometer in Munich. We retrieve mass concentrations of volcanic ash from the lidar measurements; spectral optical properties, i.e. extinction coefficients, backscatter coefficients, and linear depolarization ratios, are used as input for an inversion. The inversion algorithm searches for model aerosol ensembles with optical properties that agree with the measured values within their uncertainty ranges. The non-sphericity of ash particles is considered by assuming spheroids. Optical particle properties are calculated using the T-matrix method supplemented by the geometric optics approach. The lidar inversion is applied to observations of the pure volcanic ash plume in the morning of 17 April 2010. We find 1.45 g m−2 for the ratio between the mass concentration and the extinction coefficient at λ = 532 nm, assuming an ash density of 2.6 g cm−3. The uncertainty range for this ratio is from 0.87 g m−2 to 2.32 g m−2. At the peak of the ash concentration over Maisach the extinction coefficient at λ = 532 nm was 0.75 km−1 (1-h-average), which corresponds to a maximum mass concentration of 1.1 mg m−3 (0.65 to 1.8 mg m−3). Model calculations show that particle backscatter at our lidar wavelengths (λ ≤ 1064 nm), and thus the lidar retrieval, is hardly sensitive to large particles (r ≳ 3 μm); large particles, however, may contain significant amounts of mass. Therefore, as an independent cross check of the lidar retrieval and to investigate the presence of large particles in more detail, we model ratios of sky radiances in the aureole of the Sun and compare them to measurements of the CIMEL. These ratios are sensitive to particles up to r ≈ 10 μm. This approach confirms the mass concentrations from the lidar retrieval. We conclude that synergistic utilization of high quality lidar and Sun photometer data, in combination with realistic aerosol models, is recommended for improving ash mass concentration retrievals.

The 16 April 2010 major volcanic ash plume over central Europe: EARLINET lidar and AERONET photometer observations at Leipzig and Munich, Germany

The optically thickest volcanic ash plume ever measured over Germany was monitored with multiwavelength Raman lidars and Sun photometer at Leipzig and Munich. When this ash layer, originating from the Eyjafjoll eruptions in southern Iceland, crossed Leipzig between 2.5 and 6 km height on 16 April 2010, the total 500 nm aerosol optical depth reached 1.0, and the ash–related optical depth was about 0.7. Volume light–extinction coefficients (40–75–minute mean values) measured over Leipzig and Munich at 355 and 532 nm reached values of 400–600 Mm−1 and ash mass concentrations were on the order of 1000 ± 350 μg/m3 in the center of the main ash layer. Extinction–to–backscatter ratios ranged from 55 ± 5 sr (Munich) to 60 ± 5 sr (Leipzig) in the main ash layer, and the particle linear depolarization ratio was close to 0.35 at both wavelengths. Rather low photometer–derived Ångström exponents (500–1640 nm wavelength range) indicated the presence of a significant amount of large ash particles with diameters &gt;20 μm.

Fine particle and trace element emissions from waste combustion — Comparison of fluidized bed and grate firing

Waste-to-energy applications are increasingly being used to simultaneously reduce the amount of waste and produce electricity and heat. As waste materials typically contain high concentrations of impurities that are transformed during combustion, the flue gases need to be cleaned efficiently in order to avoid harmful emissions to the environment. In this investigation, we determined experimentally fly ash particle characteristics – particle size, composition and concentration – as well as particle and trace element emissions during waste combustion in two full-scale plants using different combustion technologies but similar gas cleaning technology. The two combustion plants were a grate-fired boiler, and a circulating fluidized bed (CFB) boiler. Both boilers used selective non-catalytic reduction (SNCR) for NO x control together with novel integrated flue gas desulfurization (NID) for flue gas cleaning. The trace elements included in the investigation were As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb, Sb, Tl, and V. Fine fly ash particles were formed from the gas phase ash-forming species by nucleation and condensation. Concentration of particles smaller than 1.0 μm by diameter (PM1.0) at grate-fired plant was 1.0–1.4 g/Nm 3, approximately four times the PM1.0 concentration at CFB combustion, 0.25–0.31 g/Nm 3, as determined upstream of the flue gas cleaning system NID. The average total fly ash mass concentration was higher at CFB combustion than at grate firing with 4.6 g/m 3 and 1.4 g/m 3, respectively. Particle and trace element emissions were very low from both grate-fired and fluidized bed plants. Fabric filter particle collection efficiency was 99.99% by mass at both plants. All the measured emissions were clearly below the limit values set by European Waste Incineration Directive (WID).