Fine natural (mineral) and anthropogenic particles suspended in the atmosphere have a large, still poorly known, impact on climate. Human health is also affected by particles. Our methodology is based on sampling with impactors or electrostatic sampler and analysis with electron microscopy based single particle analysis.
Together with the Trinational aerosol research network and with the start-up company Particle Vision we are also involved in projects dealing with the emission, dispersion and the toxicity of natural and anthropogenic nanoparticles.
Iron oxide particle sampled adjacent to a rail way track. The shape and morphology suggests, that it was emitted as a liquid droplet formed by the friction between wheel and rail.
Volcanic particulate matter
Fine particles emitted by volcanoes may have a major impact on climate and human health. Volcanic aerosols contain finest silicate particles called ash and particles, which where formed by condensation or resublimation of gaseous emission products i.e. solid sulphate and halogenide particles.
We are interested in the formation and evolution of such particles for volcanoes with fumarolic and mildly eruptive activity and to determine what importance these particles have in the overall sulphur budget. Our main field area is the Aeolian archipelago (Italy) i.e. Stromboli and Vulcano.
TEM image (top right), EDS spectrum (left) and electron diffraction pattern (bottom right) of a particle collected on Stromboli. EDS and ED patterns are compatible with the mineral aphtitalite (Cu-peak: sample grid)
A second project deals with eruptive mechanisms and the long range transport of volcanic particles. In collaboration with FH Düsseldorf, we analysed particles from Eyjafjallajökull sampled during a airborne campaign over Iceland and Germany.
Eruptive mechanisms are in the center of a third project together with Prof. Schminke, Magmatic and hydrothermal system group GEOMAR. The samples are volcanic ash deposits in the Eifel volcanic area. In collaboration with Dr. P. Vonlanthen (Uni Lausanne) we undertook a fractal shape analysis of tephra particles using microtomographic imaging and put the fractal dimensions in relation with possible eruption mechanisms.
Weber, K, Eliasson, J., Vogel, A., Fischer, C., Pohl, T., Grobéty, B., Meier, M., Van Haren, G, Dahmann, D. (2010) : Airborne in-situ investigations of the Eyjafjallajokull volcanic ash plume on Iceland and over north-western Germany with light aircrafts and optical particle counters. Atmospheric Environment, 48, 9 – 21.
Grobéty B, Meier MF, Fierz M and C. Botter (2010) Single particle analysis of aerosols from El Chichon and Stromboli. Geochimica and Cosmochimica Acta, 74 Suppl. 1 A355.
Emission-dispersion and toxicity of natural and anthropogenic (nano-) particles
Nanoparticles are present in our working environment not only since the advent of nanotechnology. “Conventional” processes and materials may also lead to the formation and emission of (nano)particles. Typical examples are soot particles from the combustion of fossil fuels, toner emission from copying machines, or particles in the fumes produced during welding.
We use SEM and TEM based single particle analysis to establish size and composition resolved emission profiles and together with the Trinational aerosol research network and the Department of Environmental Health Sciences of the University of Freiburg im Breisgau we are involved in projects analyzing the toxicity of (nano)particles in In-vitro experiments on lung cells.
A frequent contributor to the particle load in the central European atmosphere is desert dust, transported by northerly winds from the Sahara. Together with Swiss Meteo we sampled Saharan dust at Junfrau Joch, in order to understand the impact of the dust on optical parameters of the atmosphere.
TEM picture of particles sampled at Junfrau Joch. The dark particles consist meinly of carbon (= soot). The grey and spotted haloes consist of phases precipitated when wet particles dried on the substrate.
Marris, H., Deboudt, K., Flament, P., Grobety, B., and Giere, R. (2013) Fe and Mn Oxidation States by TEM-EELS in Fine-Particle Emissions from a Fe-Mn Alloy Making Plant. Environmental Science & Technology, 47(19), 10832-10840Lorenzo, R., Kaegi, R., Gehrig, R., and Grobéty, B. (2006) Particle emissions of a railway line determined by detailed single particle analysis. Atmospheric Environment, 40, 7831-7841.
Konczol M., Ebeling, S., Goldenberg E., Treude F. , Gminski R., Giere R., Grobety B., Rothen-Rutishauser B., Merfort I., Mersch-Sundermann V. (2012) Cytotoxicity and Genotoxicity of Size-Fractionated Iron Oxide (Magnetite) in A549 Human Lung Epithelial Cells: Role of ROS, JNK, and NF-kappa B. Chemical Research in Toxicology, 24, 1460-1475.
Gminski, R., Decker, K., Heinz, C, Seidel, A., Konczol,, M., Goldenberg E., Treude F., Ebner, W., Giere, R., Grobety, B., Mersch-Sundermann V. (2011) Genotoxic Effects of Three Selected Black Toner Powders and Their Dimethyl Sulfoxide Extracts in Cultured Human Epithelial A549 Lung Cells In Vitro. Environmental and Molecular Mutagenesis, 52, 296-309.
Grobéty, B. (2010) Airborne Particles in the Urban Environment . Elements, 6, 229-234.
Vernooij, M., Mohr, M., Tzvetkov, G., Zelenay, V., Huthwelker, T., Kaegi, R., Gehrig, R., and Grobéty, B. (2009) On source identification and alteration of single diesel and wood smoke soot particles in the atmosphere; an x-ray microspectroscopy study. Environmental Science and Technology, Environmental Science & Technology, 43, 5339-5344.
Lorenzo, R., Kaegi, R., Gehrig, R., Scherrer, L., Grobéty, B. , Burtscher, H.(2007) A thermophoretic precipitator for the representative collection of atmospheric ultrafine particles for microscopic analysis. Aerosol Science and Technology, Aerosol Science and Technology, 41, 934-943.
Aerosol analysis equipment
Our laboratory is equipped with the infrastructure necessary to do single particle analyses of aerosol samples:
The PM10 samplers are home built prototypes (C. Neururer, Dep. of Geosciences). As basis served a robust and high-powered vacuum pump (KNF membrane pump, model N 828 KNE). To regulate the flow rate without electronics, a critical orifice with a diameter of 0.72 mm was integrated into the Swagelok fitting at the inlet of the pump. To be able to verify the flow rate during operation, a rotameter (Vögtlin V100) was integrated into the waterproofed aluminum casing. The pump is operated at a flow rate of 4l/min.
The sampler can be powered either from an external 220V electrical source or via a pack of Li-batteries with autonomy of 8hours. The pump inlet is connected via plastic tubing to the sample head composed of a PM10 impactor and the filter holder. As sampling substrate Nuclepore® filters with different pore diameters are used (0.1 – 0.4 microns). There are 5 samplers operating. On the same basis, a 5 sample PM 10 collector has been built. The sampling schedules of each of the samples can be set individually (starting time, duration).
The electrostatic sampler is a prototype build by the group of Prof. Burtscher at the Fachhochschule Nordwestschweiz, Windisch, Switzerland. The particle flow is first guided through a PM1 impactor and than charged by a corona discharger. The pump is operated at 4l/min. The amount of deposited material is measured via an electrometer. The total charge corresponding to the ideal particle concentration on the grid has been calibrated. The sampler is corrosion resistant and can be operated in harsh environments.
The portable Mini Diffusion Size Classifier (MiniDISC) allows to measure on-line the particle number concentration for particles < 400 nm and their mean diameter. For particles > 400 nm a TSI optical particle sizer OPS3330 is at disposal. The measuring range is between 0.3 and 10 micron distributed over 16 channels with adjustable size.
Computer controlled scanning electron microscopy
The size, morphology and chemical composition of individual particles is analyzed by Scanning Electron Microscopy and Energy Dispersive Spectroscopy (EDS) performed on a FEI XL30 Sirion FEG equipped with an EDAX Pegasus EDS system.
The particle analysis software allows automatic recognition of the particles based on the contrast on back scatter (BSE) images. A BSE image as well as morphological parameters (different diameters) and the chemical composition are acquired for each particle and stored.
To obtain an unbiased selection of particles, five sampling fields (stubs, size depends on particle coverage) are selected randomly. The particle analysis software divides the so defined stubs into five columns with five images each, totalling in 125 images per filter. The data are either treated by the EDAX software or by a MATHLAB code developped in-house.
Computer-based single particle analysis
a) “Stubs” (= rectangular regions which will be analyzed) are selected by random process on a nucleopore
filters taken from a PM10-sampler. Stubs have sizes which are multiples of the size of a SEM image
for a chosen magnification, in the above example the stub consist of 25 images.
b) Backscatter images are taken, and contrast/brightness tresholds are set in order to delimit the
background from the particles
c) Particle are recognized according to the thresholds set.Particles crossing the image boundary
are discarded. Size ranges can be set. In the present example the smallest particles are not considered.
d) Backscatter images of the individual particles are taken and morphological parameters are determined.
e) EDS analysis are taken with the beam scanning across the internal part of the particle (red dots in d) are taken.
f) Classification of the result according to chemical composition.
Ternary plot for particles sampled in at crater rim of the El Chichon, Chiapas, Mexico. Three classes can be distinguished: sulfur dominated particles (red): sulfates, sulfuric acid particles, aluminum dominated particles (green): aluminum hydroxides from soil, and aluminum – silicon particles(blue): clay minerals.
Although there are a large amount of sulfuric acid particles in this sample (checked by TEM analysis), there are not many analysis points in the sulfur apex, where they should be. Cause for the aluminum and silicon content: improper background subtraction leaves some intensity in the region of the aluminum and the silicon peak. The presence of composite particles is the second cause.
- Chemical and mineralogical composition of a aerosol are determined
- Chemistry resolved particle size distribution can be obtained
- Morphological (shape) parameters of individual grains can be obtained
- Tresholding problems. Uneven background grey-scale can lead to difficulties in recognizing grains and in separating close lying grains.
- Time-consuming. Approximately 100 per hour a possible