Fundamentals and Applications in Aerosol Spectroscopy

495 Pages·2010·32.474 MB·English

by  Ruth Signorell, Jonathan P. Reid

Fundamentals and
Applications in
Aerosol Spectroscopy
Fundamentals and
Applications in
Aerosol Spectroscopy
Edited by
Ruth Signorell Jonathan P. Reid
■
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Contents
Preface...............................................................................................................................................ix
Editors ............................................................................................................................................xiii
Contributors .....................................................................................................................................xv
SectIon I Infrared Spectroscopy
Chapter 1 Infrared Spectroscopy of Aerosol Particles .................................................................3
Thomas Leisner and Robert Wagner
Chapter 2 Vibrational Excitons: A Molecular Model to Analyze Infrared
Spectra of Aerosols ..............................................................................................25
George Firanescu, Thomas C. Preston, Chia C. Wang, and Ruth Signorell
Chapter 3 Aerosol Nanocrystals of Water Ice: Structure, Proton Activity, Adsorbate
Effects, and H-Bond Chemistry .................................................................................49
J. Paul Devlin
Chapter 4 Infrared Extinction and Size Distribution Measurements
of Mineral Dust Aerosol ......................................................................................79
Paula K. Hudson, Mark A. Young, Paul D. Kleiber, and Vicki H. Grassian
Chapter 5 Infrared Spectroscopy of Dust Particles in Aerosols for Astronomical
Application .......................................................................................................101
Akemi Tamanai and Harald Mutschke
SectIon II Raman Spectroscopy
Chapter 6 Linear and Nonlinear Raman Spectroscopy of Single Aerosol Particles ................127
N.-O. A. Kwamena and Jonathan P. Reid
Chapter 7 Raman Spectroscopy of Single Particles Levitated by an Electrodynamic
Balance for Atmospheric Studies .............................................................................155
Alex K. Y. Lee and Chak K. Chan
v
vi Contents
Chapter 8 Micro-Raman Spectroscopy for the Analysis of Environmental Particles ..............193
Sanja Potgieter-Vermaak, Anna Worobiec, Larysa Darchuk,
and Rene Van Grieken
Chapter 9 Raman Lidar for the Characterization of Atmospheric Particulate Pollution .........209
Detlef Müller
SectIon III VIS/UV Spectroscopy, Fluorescence,
and Scattering
Chapter 10 UV and Visible Light Scattering and Absorption Measurements on
Aerosols in the Laboratory .......................................................................................243
Zbigniew Ulanowski and Martin Schnaiter
Chapter 11 Progress in the Investigation of Aerosols’ Optical Properties Using
Cavity Ring-Down Spectroscopy: Theory and Methodology ..................................269
Ali Abo Riziq and Yinon Rudich
Chapter 12 Laser-Induced Fluorescence Spectra and Angular Elastic Scattering Patterns
of Single Atmospheric Aerosol Particles .................................................................297
R. G. Pinnick, Y. L. Pan, S. C. Hill, K. B. Aptowicz, and R. K. Chang
Chapter 13 Femtosecond Spectroscopy and Detection of Bioaerosols .......................................321
Luigi Bonacina and Jean-Pierre Wolf
Chapter 14 Light Scattering by Fractal Aggregates ...................................................................341
C. M. Sorensen
SectIon IV UV, X-ray, and electron Beam Studies
Chapter 15 Aerosol Photoemission .............................................................................................367
Kevin R. Wilson, Hendrik Bluhm, and Musahid Ahmed
Chapter 16 Elastic Scattering of Soft X-rays from Free Size-Selected Nanoparticles ...............401
Harald Bresch, Bernhard Wassermann, Burkhard Langer, Christina Graf, and
Eckart Rühl
Contents vii
Chapter 17 Scanning Transmission X-ray Microscopy: Applications in
Atmospheric Aerosol Research ................................................................................419
Ryan C. Moffet, Alexei V. Tivanski, and Mary K. Gilles
Chapter 18 Electron Beam Analysis and Microscopy of Individual Particles ...........................463
Alexander Laskin
Index ..............................................................................................................................................493
Preface
This book is intended to provide an introduction to aerosol spectroscopy and an overview of the
state-of-the-art of this rapidly developing field. It includes fundamental aspects of aerosol spectro-
scopy as well as applications to atmospherically and astronomically relevant problems. Basic knowl-
edge is the prerequisite for any application. However, in aerosol spectroscopy, as in many other
fields, there remain crucial gaps in our understanding of the fundamental processes. Filling this gap
can only be a first step, with the challenge then remaining to develop instruments and methods
based on those fundamental insights, instruments that can easily be used to study aerosols in plan-
etary atmospheres as well as in space. With this in mind, this book also touches upon some of the
aspects that need further research and development. As a guideline, the chapters in this book are
arranged in the order of decreasing wavelength of light/electrons, starting with infrared spectros-
copy and concluding with x-ray and electron beam studies.
Infrared spectroscopy is one of the most important aerosol characterization methods in labora-
tory studies, for field measurements, for remote sensing, and in space missions. It provides a wealth
of information about aerosol particles ranging from properties such as particle size and shape to
information on their composition and chemical reactivity. The analysis of spectral information,
however, is still a challenge. In Chapter 1, Leisner and Wagner provide a detailed description of the
most widely used method to analyze infrared extinction spectra, namely classical scattering theory
in combination with continuum models of the optical properties of aerosol particles. The authors
explain how information such as number concentration, size distribution, chemical composition,
and shape can be retrieved from infrared spectra, and outline where pitfalls could occur. Theoretical
considerations are illustrated with experiments performed in the large cloud chamber, aerosol inter-
action and dynamics in the atmosphere (AIDA).
Classical scattering theory and continuum models for optical properties are not always suitable
for a detailed analysis of particle properties. Available optical data are often not accurate enough,
and for small particles, where the molecular structure becomes important, these methods fail alto-
gether. In Chapter 2, Firanescu, Preston, Wang, and Signorell discuss a molecular model that allows
a detailed analysis of particle properties on the basis of the band shapes observed in infrared extinc-
tion spectra. In particular, this approach explains why and when infrared spectra of molecular
aerosols are determined by particle properties such as shape, size, or architecture. After a descrip-
tion of the approach, the authors illustrate its application by means of a variety of examples.
Water and ice are the most important components of aerosols in our Earth’s atmosphere. They
play a crucial role in many atmospheric processes. Water ice is also ubiquitous beyond our planet
and solar system. In Chapter 3, Devlin uses infrared spectroscopy to characterize this important
type of particle and shows how the structural properties of pure and mixed ice nanocrystals can be
unraveled by this technique. Special consideration is given to the nature of the surface of these
particles, the role it plays, and how it is influenced by adsorbates. The formation and transformation
of numerous naturally occurring hydrates are discussed. These studies reveal the exceptional prop-
erties of water ice surfaces.
Chapters 4 and 5 are devoted to the infrared spectroscopy of dust particles. The infrared radia-
tive effects of mineral dust aerosols in the Earth’s atmosphere are investigated by Hudson, Young,
Kleiber, and Grassian in Chapter 4. Remote sensing studies using infrared data from satellites pro-
vide the source of information to determine the radiative effects of these particles. Such data are
commonly analyzed using Mie theory, which treats all particles as spheres. The authors discuss
the errors associated with this assumption and demonstrate that the proper treatment of particle
ix
x Preface
shape is crucial in retrieving reliable information about the radiative effect of mineral dust particles
from remote sensing. The properties of dust grains occurring in astrophysical environments are the
subject of Chapter 5 by Tamanai and Mutschke. Dust grains of different composition with sizes in
the micrometer range are widely distributed throughout space. Ground-based as well as satellite-
based telescopes are used for infrared studies of these dust particles. Tamanai and Mutschke dis-
cuss infrared laboratory studies of astrophysically relevant dust grains and their application to the
interpretation of astronomical spectra. While the wide variety of dust properties makes spectral
analysis a difficult task, the authors demonstrate that important information can be obtained from
such measurements about the conditions under which dust grains exist and evolve in astronomical
environments.
Raman spectroscopy has proved to be a versatile tool for examining aerosol particles in con-
trolled laboratory measurements, allowing the unambiguous identification of chemical species, the
determination of particle composition, and even the determination of particle size and temperature.
Although Raman scattering is inherently a weak process, measurements have been routinely per-
formed on droplet trains using pulsed laser and continuous-wave laser techniques, on aerosol parti-
cles isolated in optical or electrodynamic traps, and on particles deposited on substrates. Section II
begins with a general introduction to the fundamentals of both linear and nonlinear Raman scatter-
ing from aerosol particles. In particular, Kwamena and Reid highlight the considerable accuracy
(<1 nm) that can be achieved in the determination of droplet size from the unique fingerprint of
enhanced Raman scattering that occurs at discrete wavelengths commensurate with whispering gal-
lery modes, also referred to as morphology-dependent resonances. Before reviewing some recent
applications of Raman spectroscopy for characterizing aerosol, they introduce some of the key
experimental considerations that must be remembered when designing a Raman instrument for
aerosol studies. Lee and Chan describe the coupling of Raman spectroscopy with an electrody-
namic balance in Chapter 7, outlining how information gained from Raman measurements can
complement that from other methods, including light scattering for probing particle size and mor-
phology, or tracking evolving particle mass. In particular, they review recent studies of hygroscopic-
ity and heterogeneous chemistry. They demonstrate that resolving Raman line shapes can provide
important insights into intermolecular interactions between solvent and solute molecules within the
condensed aerosol phase, particularly important for understanding the properties of metastable
supersaturated states accessed at high solute concentrations.
Raman analysis can provide an important tool for characterizing particulate matter of atmo-
spheric origin as well as for probing particles in controlled laboratory measurements. Potgieter-
Vermaak, Worobiec, Darchuk, and Van Grieken review the application of micro-Raman spectroscopy
for the analysis of environmental particles in Chapter 8. They begin by reviewing the methods avail-
able for ambient sampling and the importance of choosing suitable substrates, before discussing the
advantages and challenges of utilizing the technique on a stand-alone basis. The practicalities of
coupling micro-Raman measurements with other techniques, such as scanning electron microscopy
coupled with energy-dispersive x-ray spectrometric detection, are also described and assessed.
Key uncertainties remain in the direct and indirect impact of aerosols on climate, and coordi-
nated monitoring of the temporal variability of global aerosol distribution is a basic requirement
of climate research. In Chapter 9, Müller describes the application of Raman LIDAR (light detec-
tion and ranging) in the characterization of atmospheric pollution. After a description of the basic
principles of Raman LIDAR, methods for deriving the optical and microphysical properties of
particulate pollution are introduced. This is followed by an illustration of the potential of modern
Raman LIDARs, particularly when measurements are made with a network of systems on a con-
tinental scale.
Elastic light scattering by particles in the visible and UV parts of the electromagnetic spectrum
provides the basis for many conventional and routine techniques for determining particle size and
concentration. More recently, it has been shown that resolving the light scattering from single
particles may lead to the development of new instruments for assessing particle size and shape.
Preface xi
In addition, fluorescence spectroscopy is becoming an increasingly applied technique for identify-
ing particle composition. Ulanowski and Schnaiter begin Section III with a discussion of light scat-
tering and absorption measurements on aerosols in the laboratory. Following an introduction to key
parameters that must be typically measured, they review some of the common methods for perform-
ing extinction spectroscopy, using an optical extinction cell, and absorption spectroscopy, specifi-
cally photoacoustic spectroscopy, and applications of these instruments in laboratory and chamber
measurements. Resolving the angular dependence of light scattering has a long history in the field
of particle analysis, and recent developments have concentrated on the measurement and analysis of
complex morphologies recorded at the single-particle level, allowing the categorization of sampled
particles into distinct classes.
In Chapter 11, Riziq and Rudich describe the information that can be gained by measuring light
extinction from ensembles of accumulation mode aerosol particles using cavity ring-down spectros-
copy (CRD-S). CRD-S is widely used for performing highly sensitive measurements of gas-phase
composition and is now becoming more extensively used in both field and laboratory-based aerosol
measurements. The authors introduce the underlying principles of CRD-S, before describing pulsed
and continuous-wave implementations of the technique, and the sensitivity that can be achieved.
The chapter concludes with a review of recent applications, particularly focusing on the retrieval of
aerosol optical properties.
The application of laser-induced fluorescence (LIF) spectroscopy for identifying and classifying
biological aerosol particles is described by Pinnick, Pan, Hill, Aptowicz, and Chang in Chapter 12.
Although many compounds have similar fluorescence spectra with relatively broad and indistin-
guishable features, unlike those that occur in Raman or IR spectra, single-particle LIF measure-
ments can provide clear and distinguishable signatures for different classes of biological and
anthropogenic aerosol. Further classification of particle type/morphology can be achieved by two-
dimensional angular optical scattering (TAOS), complementing and expanding on the discussion of
this technique provided by Ulanowski and Schnaiter in Chapter 10. Bonacina and Wolf describe the
improved specificity of bioaerosol detection that can be achieved using ultrafast laser techniques,
including time-resolved pump–probe fluorescence spectroscopy, femtosecond laser-induced break
down spectroscopy, and coherent optimal control in Chapter 13. In particular, they show that the
application of an ultrafast double-pulse excitation scheme can induce strong fluorescence depletion
from biological samples such as bacteria-containing droplets, allowing discrimination from possi-
ble interferents, such as polycyclic aromatic compounds, which otherwise have similar spectro-
scopic properties.
In many optical studies of aerosols, particles can be assumed to be spherical in shape, allowing
the application of Mie scattering theory. In many cases, this only provides an approximate picture
and the application of more rigorous treatments that describe the nonspherical morphology of a
particle must be considered. Sorensen explores the complexity apparent in scattering measurements
from fractal aggregates in Chapter 14, concentrating on diffusion-limited cluster aggregates. The
theoretical treatment of such particles is based on the Rayleigh–Debye–Gans (RDG) approxima-
tion, which assumes that the monomeric units forming the aggregate scatter light independently.
Once the fundamental concepts describing scattering in such complex systems have been intro-
duced, the absolute scattering and differential cross-sections are defined, and the methods used in
the analysis of data recorded from polydisperse systems are described.
Section IV deals with VUV, x-ray, and electron beam studies of aerosols. All these techniques
constitute fairly new ways of characterizing aerosols, many aspects of which have been developed
in recent years by the authors of these chapters. This book contains a unique overview of the differ-
ent aspects and prospects of these methods. Photoelectron spectroscopy as applied to aerosol sci-
ence is the subject of Chapter 15 by Wilson, Bluhm, and Ahmed, who provide a comprehensive
overview of the techniques, the history, and the literature in the field. The use of photoelectric
charging to probe surface composition and chemical as well as physical properties of aerosols is
demonstrated by various examples in the second part of their chapter. The third part demonstrates,