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The eruption of the Grimsvötn volcano in May 2010 posed with its ash plume a thread to the aviation in northern Europe. Because of ash plume forecasts of the VAAC London the airport of Keflavik in Iceland as well as airports in England, Scotland and Scandinavia were closed for some time, which caused the cancellation or change of about 500 flights in Europe. Even in Germany the airports of Bremen, Hamburg and Berlin were closed for several hours on 25 May 2011.
During this eruption period in May 2011, a team of the Duesseldorf University of Applied Sciences, the University of Iceland, the University of Reykjavik and the IMO has performed airborne in-situ measurements over Iceland and Germany as well as ground based measurements in the south of Iceland. The ground based measurements were performed continuously during the whole eruption period at two significant positions (Skogar and Hvollsvöllur) with optical particle counters (OPCs). The measurement method was based on measuring the airborne concentrations of the classic aerosol components (PM10, PM2.5 and PM1) and TSP (total suspended particles) every 6 seconds.
Additional measurement flights on Iceland were started already one day after the beginning of the eruption (twelve in-situ measurement flights) and marked the spatial and temporal spread of volcanic ash in the atmosphere. For the flights light slow flying piston engine powered airplanes where used.
The flights over Iceland focused on the western part of Iceland in the region of Reykjavik and Keflavik and over the international airport in Keflavik and were mostly coordinated by ISAVIA. The measurement flights helped to keep Keflavik International Airport open for many additional hours despite of adverse predictions by the London VAAC model, because it was possible to observe the particle concentration on-line during the flights.
In Germany a measurement flight was performed on 25 May 2012 over the northern part of Germany where the volcanic ash cloud was forecasted from the dispersion model of the London VAAC. This flight was performed on the behalf of the German Weather Service (DWD).
The measurement flights revealed most time relative low airborne ash concentrations over western Iceland, although the groundbased measured ash concentrations in the south of Iceland nearer to the Grimsvötn were very high.
In Germany the measured concentrations during the flight were low enough to be consistent with the re-opening of the airports Bremen, Hamburg and Berlin, which were closed by the authorities for several hours on 25 May 2011 because of high concentration predictions by the VAAC-model.
The measurement flights clearly proved that OPCs, based on slow flying piston-motor driven aircrafts, are very suitable for the determination of airborne ash particles during volcanic eruptions. This is an important issue for air traffic safety.
The science of measuring airborne volcanic ash concentrations supports research in such fields as atmospheric environmental science and the modeling of atmospheric pollution from volcanoes, and is thus very valuable to the aviation industry. These measurements show large scatter directly traceable to turbulent fluctuations responsible for diffusing volcanic dust. Before semistationary components in observations can be compared to each other or to simulation results, they must be separated from fluctuations. In the design of the separation process, however, neither seasonal or diurnal periodicity nor random disturbance with known properties exists to serve as a guideline. It has been suggested that fluctuations could be eliminated through repeated convolutions of a simple 3-point filter enough times. The number of convolutions is chosen from the change in the rate of increase of a special variability parameter. When semistationary concentrations are separated from fluctuations, their statistics are compared to turbulence parameters and the autocorrelation of the series. The method is demonstrated using three measurement series from Sakurajima, Japan measured in 2013. It is concluded that this new method is simple and trustworthy where knowledge and experience of the environmental parameters can be utilized to support the results. They indicate a variability of 40% in the relative fluctuations of the PM10 and around 20% of the PM2.5. The relative fluctuations may be considered completely random, but normally distributed rather than a white noise with an evenly distributed variance spectrum.
Airborne Investigations and WRF - Model Calculations of the Bardarbunga-Holuhraun Eruption Plume
(2015)
The eruption in Holuhraun is the largest producer of lava and gas in Iceland since 1783. The Volcanic Ash Research (VAR) group organized an airborne measurement campaign including 10 flights, where emissions of SO2 and ash concentrations were measured at the source and at the far plume. The highest SO2 concentration at the source was nearly up to 100 mg/m3. This is an extremely high value, compared to other airborne campaigns and a contamination considered to cause serious illness by the Icelandic Directorate of Health. Volcanic ash consisted of very fine particles, but the concentration was low when compared to other recent eruptions. Measurements of the far plume showed that scavenging is very active. The dispersion was successfully modeled with the Weather Research and Foreast (WRF-chem) model and analysis using the model showed that a large amount of the sulphur was precipitated in the Icelandic highlands.
The Eyjafjallajokull 2010 and Grimsvotn 2011 eruptions created great problems for commercial aviation in Western Europe and in the North Atlantic region. Comparison of satellite images of the visible and predicted ash clouds showed the VAAC prediction to be much larger than the actual ash clouds. No official explanation of this discrepancy exists apart from the definition of the ash cloud boundary. Papers on simulation of the Eyjafjallajökull ash cloud in peer reviewed journals, typically attempted to simulate the VAAC predictions rather than focusing on the satellite pictures. Sporadic measurements made in-situ showed much lower ash concentrations over Europe than the predicted values. Two of the weak points in ash cloud prediction have been studied in airborne measurements of volcanic ash by the Universities in Kyoto Japan, Iceland and Düsseldorf Germany of eruptions in Sakurajima, Japan. It turns out that gravitational deformation of the plume and a streak fallout process make estimated ash content of clouds larger than the actual, both features are not included in the simulation model. Tropospheric plumes tend to ride in stable inversions this causes gravitational flattening (pancaking) of the volcanic plume, while diffusion in the mixing layer is insignificant. New rules from ICAO, effective from November 2014, reiterate that jetliners should avoid visible ash, this makes information on visible ash important. A procedure developed by JMA′s Tokyo VAAC uses satellite images of visible ash to correct the prediction. This and the fact that meteorological data necessary to model gravitational dispersion and streak fallout do not exist in the international database available to the VAAC′s. This shows that close monitoring by airborne measurements and satellite and other photographic surveillance is necessary.
The Volcanic Ash Research (VAR) group is focused on airborne measurement of ash contamination to support safe air travel. In relations to the recent eruption, the group measured ash and several gaseous species in the plume 10-300 km from the volcano. The eruption emitted ash turned out to be mostly in the fine aerosol range (much less than 10 micrometers in diameter). Our highest measured concentrations were lower than 1 mg/m3 indicating
that commercial air traffic was not threatened (greater than 2 mg/m3) by the ash contamination. But we measured sulfur dioxide (SO2 ) up to 90 mg/m3, which presented a potentially dangerous pollution problem. However, airborne measurements indicate that the sulfur concentration decays (probably due to scavenging) as the plume is carried by the wind from the volcano, which limits the area of immediate danger to the public.
Here we present size distribution for particulate matter collected during flights, near and far from the crater at various times. The particle data is then compared with simultaneously collected sulfur dioxide data and the rate of decay of is estimated. Sulfur and particle concentration variations with height in the far plume are presented. Some airborne measurements for H2S, NO, NO2 and CO2 will also be presented. This includes correlation matrices for simultaneous measurements of these gases and comparison to National Air Quality Standards and background
values.
The fissure eruption in Holuhraun in central Iceland is the country’s largest lava and gas eruption since 1783 but has produced very little volcanic ash. The eruption started in late August 2014 and is still ongoing as of January 2015. The main threat from this event has been atmospheric pollution of SO2 that is carried by wind to all parts of the country and produces elevated concentrations of SO2 that have frequently violated National Air Quality Standards (NAQS) in many population centers.
The Volcanic Ash Research (VAR) group in Iceland is focused on airborne measurement of ash contamination to support safe air travel, as well as various gas concentrations. In relation to the Holuhraun eruption the VAR group has organized an investigation campaign including 10 measurement flights and performed measurements of both the source emissions and the plume distribution. SO2 concentrations measured at the source showed clear potential for creating pollution events in the toxic range and contamination of surface waters.
The data obtained in the measurement campaign was used for calibration of the WRF-chem model of the dispersion of SO2 and volcanic ash concentration. The model has both been run in operational forecast mode (since mid October) as well as in a dynamical downscaling mode, to estimate the dispersion and fallout of SO2 from the plume. The model results indicate that a large part of the sulphur was precipitated in the Icelandic highlands. The first melt waters during the spring thaw are likely to contain acid sulphur compounds that can be harmful for vegetation, with the highland vegetation being the most vulnerable.
These results will be helpful to estimate the pollution load on farmlands and pastures of farmers.