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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.
High ambient air concentrations of fine particulate matter are a problem in many European cities, especially in traffic loaded street canyons. Therefore, the introduction of traffic restricted or traffic reduced areas is discussed as a countermeasure in several towns. However, at that point it is not always clear, in what extent the restriction of traffic in presently overloaded streets causes the exceeding of limit values in other areas of the town after the redirection of the traffic. Presently this cannot be recorded appropriately, when the concentrations of fine particulate matter are monitored only at rarely distributed single points by the official measurement systems of the environmental state agencies.
On the other hand, meanwhile there are low cost and mid cost sensors for the measurement of fine particulate matter available, which enable the parallel monitoring with many measurement systems in an extended area of the town. By this way, the effect of traffic restrictions on the distribution of fine particulate matter in the city can potentially be observed. However, at this point the question arises, how reliable the results are, which are delivered by the low and mid cost sensors for fine particulate matter. For this reason different low cost and mid cost sensors have been evaluated for this study and intercompared with certified reference measurement systems for fine particulate matter. The study comprised the sensors SDS011 (Nova Fitness), which is in use already for several citizen science projects in Germany, SPS30 (Sensirion), OPC-R1 (Alphasense), OPC-N2 (Alphasense) and OPC-N3 (Alphasense).
This study was performed at urban sites in Düsseldorf (Germany) for several weeks and covered different traffic loads and different meteorological situations, in order to get representative results. As atmospheric humidity can influence the measurement results, the humidity was measured in parallel to the fine particulate matter. It could be shown that the validity of the measurement results of fine particulate matter could be improved, when the parallel readings of the humidity were taken into account.
It is well known from medical studies that fine particulate matter has adverse effects to human health. However, exceeding of limit values for fine particulate matter PM10 and PM2.5 is still a problem in major German cities. Therefore, fine particulate matter is monitored in Germany by environmental state agencies at fixed stations with certified instruments. These certified instruments are able to deliver reliable and high quality results. However, because of the costs of these certified instruments and the maintenance efforts, only few measurements stations are placed in the cities at places, which are regarded as representative for the air pollution. On the other hand, it is of interest to know the concentration of fine particulate matter in areas and at places, which are not covered by the fixed measurement stations of the environmental state agencies.
In this situation citizen science projects started in Germany using low cost sensors for fine particulate matter. In principle, with these low cost sensors citizens could measure fine particulate matter at places and in situations of their interests.
However, at that point the question of reliability of the low cost sensor data arises. Therefore the Duesseldorf University of Applied Sciences (HSD) in Germany started a project for the testing and evaluation of low-cost sensors. For this reason 20 low-cost sensor units have been built up based on the SDS 011 sensor of Nova Fitness Inc. within the Laboratory for Environmental Measurement Techniques at HSD. The sensor measurement data can be transferred into a network and can be visualized on a digital map.
This testing and evaluation at HSD of the low-cost sensors comprised:
• Short term and long term comparison studies within the laboratory and at different urban sites with a certifiedwide range aerosol measurement system (Grimm WRAS).
• Short term and long term comparison studies within the laboratory and at different urban sites with mid-cost sensors (Alphasense AN2).
• Intercomparison testing and evaluation of sensors of the same production charge.
• Intercomparison testing and evaluation of sensors of different production charges.
• Testing and evaluation of the sensors at different meteorological conditions.
The results of this testing and evaluation will be presented at the conference. Moreover, the potential of additional applications for low-cost sensors, e.g. for mobile measurements (multicopter UAS, bicycles, pedestrians) or for the validation of air pollution models, will be discussed
Detailed mobile measurement of gases and fine particulate matter has been reported in the literature to be suitable to exhibit the air pollutants concentration in populated areas. This concentration is linked to the increase of number of cars, construction areas, industries and other emission sources. However, fixed measurement stations, mostly operated by environmental agencies, are limited in numbers and cannot cover a large area in monitoring. For this reason, to overcome this drawback, mobile measurements of the variability of gases (such as O3, NO, NO2) and particulate matter concentration were carried out during this study using an instrumented car. This car was able to deliver measurement results of all these compounds in a large area. The experimental results in this work demonstrate a large spatial variability of gases and fine particulate matters mainly depended on the traffic density and the location. These effects are especially obvious in the city core and the high traffic roads. In terms of fine particulate matter, this becomes evident for PM 10 and PM 2.5, where the mass and number concentration increases with arriving these zones.
For this study an octocopter UAV was used for carrying an ultrafine (UFP) particle monitor, an optical particle counter (OPC) and a micro aethalometer. The UFP-monitor, based on electrical charging of UFPs, was able to count the number of UFPs and give an estimated mean diameter of the measured particles. The OPC, based on the particle induced light scattering of a laser beam, was able to detect aerosols in a size range of about 250 nm to 32 μm in 31 bins. The micro aethalometer measured the soot by optical attenuation of a light beam which is caused by carbon particulate matter. The octocopter with a lift off weight by 10.5 kg was especially designed and constructed at the University of Applied Sciences, Duesseldorf, for the measurement of air pollutants. It was equipped with eight 900 W electric engines and a pixhawk flight control. Technically this octocopter was able to climb up to altitudes of up to 2 km AGL. However, during this study an altitude range of several 10 meters was used. During this study about 60 octocopter flights were performed. The flights clearly revealed a plume of UFPs coming from the traffic on the bridge. This result was confirmed by various upwind and downwind measurements with the octocopter in the region of the bridge.
Fine particulate matter is well known for its adverse health effects for the population. It is still one of the major problems of air pollution in Germany. The limit values of fine particulate matter PM10 are often exceeded in bigger German cities. Therefore the level of fine particulate matter and other air pollutants are routinely monitored at single hot spots in the cities by measurement stations of the environmental state agencies. However, it is of high interest, what levels of concentrations of fine particulate matter are to be found in those areas, where no measurement stations are placed. Moreover, it is important to know, how strong exceedings of fine particulate matter concentrations can be influenced by meteorological conditions. In this paper fine particulate matter concentrations are measured with a car, which was equipped with measurement systems for fine particulate matter and which was driving through industrial and rural areas of the state North Rhine Westphalia in Germany. By this means it was possible to measure coarse and fine fractions of particulate matter continuously during driving. In this way the horizontal variation of fine particulate matter could be investigated throughout the state. The measurements comprised dust concentrations of the fractions PM10 (coarse), PM2.5 (more fine) and PM1(very fine), which are addressed within the European environmental legislation. Moreover, every second during driving the full size distribution of particles between 250 nm and 32 μm diameter was measured. Therefore it could be investigated, at what places more bigger or more smaller particles were present under specific meteorological conditions. The mobile car measurements were performed as a case study in a situation with a strong meteorological inversion layer. The mobile measurements of the horizontal variation of fine particulate matter in industrial and rural areas are compared with model prediction calculations. Moreover, using backward trajectories a source appointment of the fine particulate matter could be performed.
Aircraft measurements compared with ceilometer measurements during a sahara dust period in Germany
(2015)
A significant Sahara dust event took place at the beginning of April 2014 over large areas of Germany and Europe. The German Weather Service (DWD) detected and monitored the expansion and propagation of this dust cloud with a ceilometer network of more than 50 ceilometers. Moreover, these ceilometers were also able to track the altitude of the dust cloud at the positions of the ceilometers.
Additionally, aircraft measurements over Germany and France were performed with two aircraft by the Duesseldorf University of Applied Sciences. These aircraft were equipped with optical particle counters (OPC) and were able to measure the particle size distribution within the Sahara dust cloud and as a result of this to calculate the particle mass concentration of the dust. The ceilometer measurements and the aircraft measurements complemented each other: whereas the ceilometers gave continuous information about the Sahara dust cloud at the ceilometer positions, the aircraft measurements delivered interpolating results between the ceilometer positions.
Moreover, at several ceilometer positions intercomparison flights were performed by spiraling with the aircraft up or down around the ceilometer laser beam. This gave the unique possibility for comparing the remote sensing results of the ceilometers with the in-situ measurements of the aircraft.
This study shows that a significant high amount of Saharan dust particles was transported over Germany during a several days long episode. Furthermore, the intercomparison study between the German ceilometer network and aircraft measurements results shows a good agreement. A combination of these techniques could help to detect the vertical and horizontal distribution of the dust cloud and additionally the particle mass concentration.