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Analysis concepts of aerosols by on-line aerosol mass spectrometry [Elektronische Ressource] / Stéphane Gallavardin

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Published 01 January 2006
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Technische Universität München
Fakultät Wissenschaftszentrum Weihenstephan
für Ernährung, Landnutzung und Umwelt
Lehrstuhl für Ökologische Chemie und Umweltanalytik
Analysis Concepts Of Aerosols by On-Line Aerosol Mass Spectrometry
Stéphane Gallavardin
Vollständiger Abdruck der von der
Fakültät Wissenschaftszentrum Weihenstephan
für Ernährung, Landnutzung und Umwelt
der Technischen Universität München
zur Erlangung des akademischen Grades eines
Doktors der Naturwissenschaften
genehmigten Dissertation.
Vorsitzender: Univ.-Prof. Dr.-Ing. Roland Meyer-Pitroff
Prüfer der Dissertation:
1. Univ.-Prof. Dr.rer.nat., Dr.h.c.(RO) Antonius Kettrup, em.
2. Univ.-Prof. Dr.rer.nat., Dr.agr.habil., Dr.h.c.(Zonguldak Univ/Turkei) Harun Parlar
3. Univ.-Prof. Dr.rer.nat. Ralf Zimmermann (Universität Augsburg)
Die Dissertation wurde am 27.4.2006 bei der Technischen Universität München
eingereicht und durch die Fakultät Wissenschaftszentrum Weihenstephan für
Ernährung, Landnutzung und Umwelt am 17.06.2006 angenommen.Results? Why, man, I have gotten lots of results! If I find 10,000 ways something won't work, I
haven't failed. I am not discouraged, because every wrong attempt discarded is often a step
forward....
Thomas Edison
Why the best solution is always the last one to come ?
Daniel JacobAcknowledgments
Acknowledgments
The work conducted over the last 3 years and half was for me the occasion of being involved in a
nice “pioneer” project: the design, birth, growth, care and use of an aerosol mass spectrometer. This
project made me discover the exciting field that is aerosol science and technology: a
multidisciplinary field were mechanic, thermodynamic, optic, electricity and chemistry are involved.
The outcome of this project was for me a real motivation in contributing in making this technique
more mature and a very good start for a carrier in aerosol sciences and atmospheric sciences.
The success of this work was possible due to the excellent technical equipment facilities in Prof.
Zimmermann's group at the GSF-Forschungszentrum and the wide library resources of the GSF-
Forschungszentrum.
I first thank Prof. Kettrup and Prof. Zimmermann for offering me a PhD student position with this
research topic which satisfied my interests in miscellaneous science and technology topics and made
me participate to the birth, growth and operation of a high-tech aerosol mass spectrometer. This
position gave me the opportunity to get a solid experience with all the necessary techniques that are
involved in analytical chemistry instrumentation such as vacuum engineering, optic, electronics and
data processing engineering.
I wish to special thank Dr. Fabian Mühlberger for its availability and patience to help me fixing my
technical problems, Stefan Mitschke for his help in computer problems, Jürgen Maguhn for his
support in GSF-administrative questions, Mr. Dietz and his collaborators of the GSF-workshop for
their availability and their diligence in producing the mechanical parts needed for the project, Mr.
Jungbauer for his patience and electronic lectures, Mr. Karg for aerosol generation questions, Mr.
Reznikov and Dr. Wenzel for the PIXE analysis and finally Dr. T. Ferge for his early help in my
first year in making me stepping efficiently in this project and for choosing/ordering/assembling the
first elements of the instrument and Matthias Bente for his help during his training on this project.
Finally I warmly thank my other collaborators in the group for their punctual help and their
availability.
I would like to address also warm thanks to my friends in Munich, in particular those of the group
“Compagnie de Munich”, from the “CRFM – Club de Rhétorique Francophone de Munich” and my
two roommates of our “Auberge Espagnole” of the years 2004-2005 who support my much too
usual litany “my instrument does not want to work ...”. They all support me as they could, motivated
me efficiently writing-up this work, helped me understanding in depth my scientific work by their
simple novice questions and made my stay in Munich a very nice time by many hikes in the
Bavarian mountains, dinners and endless discussions in “Biergartens”.
As special thank goes to my parents for the education they provided me and their occasional
financial support and my sisters and brothers for their moral support.
Finally I would like finally to thank particularly here Prof. Lohmann for offering me the very
interesting post-doc position at the ETH Zürich before the PhD defense and Dr. Cziczo for his
encouragements, suggestions and partial corrections.
- 5 -Summary (English)
Summary (English)
The work presented here was carried out by Stéphane Gallavardin at the Institute for Ecological
Chemistry at the GSF-National Research Center for Health and Environment (GSF-
Forschungszentrum für Umwelt und Gesundheit) in Neuherberg near Munich in Germany for the
obtention of the title, Dr. rer nat., at the Technical University of Munich under the supervision of
Prof. Kettrup and Prof. Zimmermann. The work has been carried out from December 2001 to June
2005 and written-up in January 2006. The work consisted in assisting and continuing the initial
work of T. Ferge in the design and building-up of an aerosol mass spectrometer, hereafter
denominated SPALMS, dedicated to the analysis of the organic fraction of aerosol single particles
and to form M. Bente on the instrument.
The Single Particle Aerosol Laser Mass Spectrometer (SPALMS) developed in this study appears to
be a powerful instrument that permits the physical and chemical analysis of aerosol particles. This
instrument was designed based on the critical analysis of a bibliographic review of the current state
of the technique. The SPALMS instrument samples the aerosol particles with a nozzle inlet unit,
detects and sizes them respectively optically and aerodynamically. After the particle sizing step, the
chemical analysis is operated by vaporizing and ionizing its chemical constituents by laser either in
one or two steps before the resulting ions are transmitted to a bipolar mass spectrometer. The ion
mass analysis provides then the chemical composition of the particle. The SPALMS instrument
offers many data acquisition points (up to 12 channels) in order to record information at each
measurement step and to merge them together. This should lead to additional properties of the
single particle in comparison to the current usual use in aerosol mass spectrometry.
The nozzle inlet unit shows two interesting features that compensate the low chemical analysis rate
of 7 Hz in the instrument current state. It permits first the sampling of particles by impaction on the
last skimmer of the inlet and secondly, due to its higher carrier gas velocity, a better aerodynamic
differentiation of the particles than can do an APS instrument or an aerodynamic lens inlet unit. The
combination of the detection/sizing unit and the inlet unit permits the measurement of the aerosol
particle size distribution in a reliable manner between 0,5 μm to 4 μm at a concentration of up to
3800 particles per cm . The detection/sizing unit permits in particular the measurement of the amount
of scattered light as the particle crosses each sizing laser by four photomultipliers . With an adapted
data analysis procedure, particles can not only be aerodynamically sized but also optically
differentiated. Indeed, a data analysis method makes the interpretation of the scattered light possible
by limiting the trajectory ambiguity effects. With a lower noise photomultiplier signal, one can
potentially access to a shape index, defined as the deviation from sphericity, of the particle and to a
method to treat coincidence events.
With a good quality particle detection signal, it is possible to evaluate how representative of the
whole aerosol is the observed single particle chemical composition by comparing the aerodynamic-
optical data set of the whole particle population to the similar data set of the only chemically
analyzed particles. This permits in particular the evaluation of measurement errors due to the
desorption/ionization laser trigger scheme or due to the size/composition of the particles.
Indeed, the desorption/ionization process that provides a “fingerprint” of the chemical composition
of the particle does not always permit its detection if the laser power density is not high enough, the
chemicals are difficult to ionize or chemical reactions proceed in the desorption plume. This is in
particular illustrated by the case of the usual low occurrence of positive carbon clusters in mass
- 7-Summary (English)
spectra or by the apparent impossibility to detect ions from silica particles. This justifies the need of
different desorption/ionization methods and their related trigger schemes and the need of a bipolar
mass spectrometer.
Soot particles from Palas GmbH were extensively studied in this work since they are very
convenient to test the SPALMS instrument. These soot particles were easily detected and the
speciation of the carbon as elemental carbon was established in negative mass spectra. Similarly,
negative mass spectra showed the presence of organic hydrogenated molecules in soot particles
from wood combustion by the presence of hydrogenated carbon clusters C H ions. Positive massn m
spectra were found however to bring less chemical information since the relative high content of
sodium or potassium in the particle masks the signal due to other positive ions probably by either
saturating the detector or by dramatically depleting the amount of positive ions by charge-transfer
reactions because of the low ionization potential of sodium and potassium. The advantage of one-
step desorption/ionization with a bipolar mass spectrometer is also fully demonstrated by the
analysis of ash from the incineration in private fireplace of wood waste material. It suggests that the
negative mass spectrometer brings a wealth of information about the speciation of some elements in
the particle. Indeed, negative mass spectra indicate that iron, sodium, potassium, calcium and silicon
are present in the ash particles respectively as oxides, sulfates and aluminosilicates. Moreover
analyses confirmed that particles are to be considered individually.
Even if the one-step desorption/ionization is rich in information, the processes occurring in this step
are complex and render difficult the mass spectra analysis because of the chemical ionization and
fragmentation processes that take place. Indeed the two-step laser desorption/ionization analysis
permitted the detection of PAHs in wood sample particles that were not detected before with a one-
step approach. It points out that the better management and control of both the desorption and
ionization steps lead to (i) limit the fragmentation of the molecules and (ii) to better resolve
chemical mixtures. The chemical analyses presented here suggest that the comparison of mass
spectra obtained in both conditions permits a better evaluation of the particle chemical composition
by a better understanding the ionization processes.
These analyses lead particularly to develop other desorption/ionization schemes that should enhance
the analytical potential of the SPALMS instrument. This is made possible by the unique feature of
the mass spectrometer to perform either a simultaneous bipolar ion analysis or two successive cation
mass analyses delayed by some microseconds. In this configuration, the same particle can be
analyzed twice with different ionization methods and information about the radial composition can
be accessible. In this case, each mass spectrometer tube is operated in pulse mode one after the other
that permits the operation of a given ionization method for each mass analysis. For instance,
possible schemes can address the analysis of initially present native cations in the particle and/or a
better molecule identification capacity by first operating a soft photoionization followed by electron
impact ionization to fragment the molecules. In addition, it exists the possibility to operate bipolar
mass analysis with soft ionization methods producing cations (SPI, Single Photo Ionization) and
anions (PERCI, Photo-Electron Resonance Capture Ionization).
Since the two or many steps laser desorption/ionization schemes are complex to operate, it is also
important to better qualify the one-step approach. Indeed due to its simplicity, it should be in a next
future commonly implemented in field instruments. The careful examination of the mass spectra
signal obtained with a sufficiently good mass resolution should permit the evaluation of the extent
of the particle ablation in certain circumstances by looking at the shape of the mass peaks at given
low masses for usual ions observed in mass spectra such as the C , C H and C H negatively2 2 2 2
charged carbon clusters.
- 8-Summary (English)
The operation of the SPALMS can be completed with the off-line analysis of particles sampled by
impaction within the instrument in the inlet unit or after the desorption/ionization unit. Their
analysis can address any low-volatile chemicals, confirm and lead to extrapolate the observed
chemical composition of the single particles to the whole aerosol. In this work, an off-line analysis
has been performed with PIXE (Proton Induced X-ray Emission) which gives the elemental
composition even if it can also be easily operated by LMMS (Laser Microprobe Mass Spectrometry)
or any conventional chromatographic methods. An Aerodynamic Particle Sizer (APS3321, TSI.,
Inc) was operated simultaneously in parallel to confirm the SPALMS measurements of the particle
size distribution.
As a result, the SPALMS instrument design permits the analysis of single particle aerosol by
providing the usual aerosol mass spectrometry information, “size and chemical fingerprint”, and
offering additional data that complete the analysis. Indeed, its modular and flexible
desorption/ionization methods and trigger scheme permit the adaptation of particle analysis to
different aerosol types and to specific laboratory studies aimed at better understanding the
desorption/ionization processes. These laboratory works would serve the aerosol mass spectrometry
community by permitting a re-interpretation of the data and a better determination of the “real”
chemical composition of the single particles.
As a result, from this study it appears that aerosol mass spectrometers will evolve to simple, robust,
small and cheap instruments for their use in field measurement campaign and observation networks
since their current basic features are well tested, rather mature, technically more reliable and
sensitive than they were some years ago. On the other hand, these instruments will be further
developed in a modular manner with the same inlet unit, detection/sizing unit but with different
chemical analyzers that range from different mass spectrometers and different ionization methods to
infrared, Raman spectroscopy and UV fluorescence. Finally various modules measuring, for
example, the particle light scattering patterns or light depolarization should be inserted between the
inlet unit and the chemical analyzer to complete the physical description of the single particle.
- 9-