Konradin Weber

Separation of ash and sulfur dioxide during the 2011 Grímsvötn eruption

Modeling the transport of volcanic ash and gases released during volcanic eruptions is crucially dependent on knowledge of the source term of the eruption, that is, the source strength as a function of altitude and time. For the first time, an inversion method is used to estimate the source terms of both volcanic sulfur dioxide (SO2) and ash. It was applied to the explosive volcanic eruption of Grimsvotn, Iceland, in May 2011. The method uses input from the particle dispersion model, FLEXPART (flexible particle dispersion model), a priori source estimates, and satellite observations of SO2 or ash total columns from Infrared Atmospheric Sounding Interferometer to separately obtain the source terms for volcanic SO2 and fine ash. The estimated source terms show that SO2 was emitted mostly to high altitudes (5 to 13 km) during about 18 h (22 May, 00-18 UTC) while fine ash was emitted mostly to low altitudes (below 4 km) during roughly 24 h (22 May 06 UTC to 23 May 06 UTC). FLEXPART simulations using the estimated source terms show a clear separation of SO2 (transported mostly northwestward) and the fine ash (transported mostly southeastward). This corresponds well with independent satellite observations and measured aerosol mass concentrations and lidar measurements at surface stations in Scandinavia. Aircraft measurements above Iceland and Germany confirmed that the ash was located in the lower atmosphere. This demonstrates that the inversion method, in this case, is able to distinguish between emission heights of SO2 and ash and can capture resulting differences in transport patterns. Key Points Ash and SO2 source terms estimated using inverse techniques and satellite data The transport and separation of ash and SO2 are modeled Model simulations correspond well with a range of independent observations ©2014. The Authors.

Coupling of urban street canyon and backyard particle concentrations

Differences in particle mass and number concentrations between a busy urban street canyon (north-south orientation, about 50,000 vehicles 24 h -1 ) and an adjacent backyard were measured with optical particle counters. The influence of meteorological quantities, especially turbulent flow within the urban canopy layer, was also studied. Particle mass concentrations PM 10 and PM 1 were consistently larger within the street canyon due to enhanced emission and resuspension. For the study period this resulted in higher concentrations in the canyon of on average 30 % (PM 10 ) and 22 % (PM 1 ). Although elevated transport of submicrometer particles was related to easterly wind directions, the largest relative concentration differences between both sites were associated to cross-canyon flow from westerly wind directions. This is due to the canyon vortex being able to direct polluted air masses to the measurement site during flow being directed perpendicular to the canyon axis. For less polluted air within the backyard the backyard vortex is of minor influence. We found different influence of thermal and mechanical turbulence on the temporal evolution of concentration differences at both sites. Thermal turbulence was positively correlated with particle concentrations, while the latter was characterised by negative correlation coefficients.

Airborne measurements of the Eyjafjallajökull volcanic ash plume over northwestern Germany with a light aircraft and an optical particle counter: first results

During the eruption phase of the Icelandic volcano Eyjafjallajökull in April/May 2010 the University of Applied Sciences Duesseldorf has performed 14 measurement flights over north-western Germany in the time period of 23 April 2010 to 21 May 2010. Additionally 4 flights have been performed for visual observations, referencing and transfer. The measurement flights have been performed in situations, where the ash plume was present over north-western Germany as well as in situations, when there was no ash plume predicted. For the measurements a light aircraft (Flight Design CTSW Shortwing) was used, which was equipped with an optical particle counter (Grimm 1.107). Additionally the aircraft was equipped for one flight with an UV-DOAS system and a CO2-measurement system. The optical particle counter allowed in-situ measurements of the particle distribution between 250 nm and 32 μm and of PM10, PM2.5 and PM1. The ash plume appeared during the measurements as inhomogeneous in structure. Layers or multilayers of one hundred meters to a few hundred meters vertical depth of ash plume could be identified. Sub-plumes with a horizontal extension of several kilometres to several tenths of kilometres could be found. The layers of the ash plume could be found in altitudes between 2500m and 4500m. The measured concentrations have been compared with the concentration and extension of the ash plume predicted by the Volcanic Ash Advisory Centre (VAAC).

Artificial cloud test confirms volcanic ash detection using infrared spectral imaging

Airborne volcanic ash particles are a known hazard to aviation. Currently, there are no means available to detect ash in flight as the particles are too fine (radii < 30 μm) for on-board radar detection and, even in good visibility, ash clouds are difficult or impossible to detect by eye. The economic cost and societal impact of the April/May 2010 Icelandic eruption of Eyjafjallajökull generated renewed interest in finding ways to identify airborne volcanic ash in order to keep airspace open and avoid aircraft groundings. We have designed and built a bi-spectral, fast-sampling, uncooled infrared camera device (AVOID) to examine its ability to detect volcanic ash from commercial jet aircraft at distances of more than 50 km ahead. Here we report results of an experiment conducted over the Atlantic Ocean, off the coast of France, confirming the ability of the device to detect and quantify volcanic ash in an artificial ash cloud created by dispersal of volcanic ash from a second aircraft. A third aircraft was used to measure the ash in situ using optical particle counters. The cloud was composed of very fine ash (mean radii ~10 μm) collected from Iceland immediately after the Eyjafjallajökull eruption and had a vertical thickness of ~200 m, a width of ~2 km and length of between 2 and 12 km. Concentrations of ~200 μg m−3 were identified by AVOID at distances from ~20 km to ~70 km. For the first time, airborne remote detection of volcanic ash has been successfully demonstrated from a long-range flight test aircraft.

Airborne Measurement in the Ash Plume from Mount Sakurajima: Analysis of Gravitational Effects on Dispersion and Fallout

Volcanic ash concentrations in the plume from Sakurajima volcano in Japan are observed from airplanes equipped with optical particle counters and GPS tracking devices. The volcano emits several puffs a day. The puffs are also recorded by the Sakurajima Volcanological Observatory. High concentrations are observed in the puffs and fallout driven by vertical air current, called streak fallout. Puffs dispersion is analyzed by the classical diffusion-advection method and a new gravitational dispersion method. The fluid mechanic of the gravitational dispersion, streak fallout, and classical diffusion-advection theory is described in three separate appendices together with methods to find the time gravitational dispersion constant and the diffusion coefficient from satellite photos. The diffusion-advection equation may be used to scale volcanic eruptions so the same eruption plumes can be scaled to constant flux and wind conditions or two eruptions can be scaled to each other. The dispersion analyses show that dispersion of volcanic plumes does not follow either theories completely. It is most likely diffusion in the interface of the plume and the ambient air, together with gravitational flattening of the plumes core. This means larger boundary concentration gradients and smaller diffusion coefficients than state of the art methods can predict.

First results of ambient air measurements with different remote sensing systems over a lake in Germany

In summer 1998 a measurement campaign was performed at the lake Baldeney See in the south of the city of Essen in Germany. Two major goals should be achieved: First the intercomparison of several different remote sensing systems in real field measurements and second the determination of the ozone levels during summer with respect to the complex orographic and climatological situation of the lake Baldeney See which is intensely used as a recreational area. This paper only refers to the first results of the intercomparison of the remote sensing systems open-path FTIR, DOAS, and TDL and some interesting features of the ozone concentration results like secondary ozone peak concentration during night time.

Summer air quality over an artificial lake

In the summer of 1998, the air quality (indicators: CO, NO, NO2 ,O 3) above the water surface of the Lake Balderey (Essen, Ruhr area, North Rhine-Westphalia, Germany), an artificial lake used for recreation purposes, was measured using the Fourier transform infrared spectroscopy (FTIR) and differential optical absorption spectroscopy (DOAS) remote measurement methods. The lake, with an area of 3 km 2 was created by damming the Ruhr and is surrounded by higher ground. In calm, bright weather conditions, this location results in a low-exchange situation (formation of temperature inversions, cold air dynamics) with a sustained impact on pollutant concentrations over the lake. The results of trace substance measurements (1/2 h mean values) were compared with values from comparison stations (suburban, high traffic and forest) located outside the area of the lake. In general, it was found that mean CO and NO concentrations over the lake were very low (0.3 ppm and 7.5 ppb, respectively). NO2 values (B15 ppb) were some 3.5 times higher than those recorded at the forest station and O3 values, at 27 ppb, almost reached the same level as at the forest station (30 ppb). Mass flow densities as a function of wind direction, diurnal courses, differences between weekdays and weekends and comparisons with air quality standards are presented for the lake station. r 2002 Elsevier Science Ltd. All rights reserved.

Quality-assurance procedures and measurements for open-path FTIR spectroscopy

Infrared Fourier transform open-path spectroscopy becomes a more and more well-known method to monitor air pollution. Several companies are even selling instruments especially devoted to this application. Numerous campaigns have delivered interesting information and proved the usefulness of the technique. However the results still suffer from a certain mistrust. Reliability, reproducibility, stability are for instance not yet well defined. In order to fill this lack, we have performed a set of test measurements which could be carried out on any FTIR long-path system. This quality assurance protocol includes the determination of noise, return signal stability, detection limits, precision and accuracy. The procedure to estimate each of these parameters is described. The feasibility and relevance of these measurements have been tested on both monostatic and bistatic set-ups. Both instruments have been studied over a period of several months. Many of the parameters can be calculated without doing extra measurements and were evaluated whenever the instruments were in use. To determine parameters such accuracy and precision, series of spectra were especially acquired. This shows the possibility to better quantify the performance of open-path FTIR spectrometers. Further improvements are also suggested.

Stand-Off Detection of Explosives of Suicide Bombers by Means of Open-Path FTIR Spectroscopy

In view of potential terroristic attacks on public areas like airports, metro stations, stadiums etc. it is important to detect suspect persons like suicide bombers before they can bring the explosive to detonation. This detection of the explosives must not be recognized by the suspect persons. It should deliver online results and should be performed in a stand-off way without direct contact to the suspect person (remote sensing). The open-path FTIR spectroscopy is a promising tool for that specific task. In this paper several applications are described and first measurement results for the online detection of TATP are presented. Moreover a short glance on further planned research items is given.

Use of quality assurance procedures for FTIR field measurement data

The OP-FTIR measurement technique and other remote sensing systems (for example UV-DOAS and TDL) become more and more established methods to monitor the ambient air quality. Some quality assurance procedures have to be done on the field measurement data to get more reliable results. Both the German and US-EPA standardization documents for the OP-FTIR technique prescribe such procedures to check the data. To assess the applicability of these procedures, OP-FTIR field measurement data of a three month continuous measurement campaign were evaluated concerning the signal strength, the influence of stray light, water vapor concentration, baseline noise, wave number shifts and the detection limits. In addition the long time signal stability of the OP-FTIR systems and the UV-DOAS systems are intercompared. The results of the several quality assurance procedures will be presented in this paper.