Tai Lieu Chat Luong Fundamentals and Applications in Aerosol Spectroscopy Fundamentals and Applications in Aerosol Spectroscopy Edited by Ruth Signorell ■ Jonathan P Reid MATLAB® is a trademark of The MathWorks, Inc and is used with permission The MathWorks does not warrant the accuracy of the text or exercises in this book This book’s use or discussion of MATLAB® software or related products does not constitute endorsement or sponsorship by The MathWorks of a particular pedagogical approach or particular use of the MATLAB® software CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2011 by Taylor and Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S Government works Printed in the United States of America on acid-free paper 10 International Standard Book Number: 978-1-4200-8561-7 (Hardback) This book contains information obtained from authentic and highly regarded sources Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint Except as permitted under U.S Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers For permission to photocopy or use material electronically from this work, please access www.copyright.com (http:// www.copyright.com/) or contact the Copyright Clearance Center, Inc (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400 CCC is a not-for-profit organization that provides licenses and registration for a variety of users For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com Contents Preface .ix Editors xiii Contributors xv Section I  Infrared Spectroscopy Chapter Infrared Spectroscopy of Aerosol Particles Thomas Leisner and Robert Wagner Chapter Vibrational Excitons: A Molecular Model to Analyze Infrared Spectra of Aerosols 25 George Firanescu, Thomas C Preston, Chia C Wang, and Ruth Signorell Chapter Aerosol Nanocrystals of Water Ice: Structure, Proton Activity, Adsorbate Effects, and H-Bond Chemistry 49 J Paul Devlin Chapter 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 Infrared Spectroscopy of Dust Particles in Aerosols for Astronomical Application 101 Akemi Tamanai and Harald Mutschke Section II  Raman Spectroscopy Chapter Linear and Nonlinear Raman Spectroscopy of Single Aerosol Particles 127 N.-O A Kwamena and Jonathan P Reid Chapter 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 Micro-Raman Spectroscopy for the Analysis of Environmental Particles 193 Sanja Potgieter-Vermaak, Anna Worobiec, Larysa Darchuk, and Rene Van Grieken Chapter 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 vii Contents 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 knowledge 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 planetary 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 spectroscopy and concluding with x-ray and electron beam studies Infrared spectroscopy is one of the most important aerosol characterization methods in laboratory 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 interaction 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 altogether 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 extinction 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 description 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 properties of water ice surfaces Chapters and are devoted to the infrared spectroscopy of dust particles The infrared radiative effects of mineral dust aerosols in the Earth’s atmosphere are investigated by Hudson, Young, Kleiber, and Grassian in Chapter Remote sensing studies using infrared data from satellites provide 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 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 satellitebased telescopes are used for infrared studies of these dust particles Tamanai and Mutschke discuss 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 controlled 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 performed on droplet trains using pulsed laser and continuous-wave laser techniques, on aerosol particles 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 scattering from aerosol particles In particular, Kwamena and Reid highlight the considerable accuracy ( 110% controlled by a Peltier element However, understanding the HIN ability of particles relevant to the processes of ice formation in cirrus clouds requires additional experiments at temperatures measuring −60°C An extension of ESEM studies to lower temperatures requires the design and construction of novel, cryogenically cooled sample holders Proof-of-principle ESEM experiments examined the onset of ice nucleation by imaging relatively large 100 μm (approximately) ice crystals (see Figure 18.9) that also could be successfully imaged by optical microscopes (e.g., Dymarska et al., 2006; Knopf and Koop, 2006) However, visualization of ice nucleation using ESEM requires imaging of nucleation events on the surface of ­submicron 478 Fundamentals and Applications in Aerosol Spectroscopy 200 μm Figure 18.9  ESEM image of ice crystals nucleated on the surface of illite particles from supersaturated water vapors (From Zimmermann et al 2008 Journal of Geophysical Research–Atmospheres 113 Copyright 2008, American Geophysical Union With permission.) 130% Illite 125% RHice (%) 120% 115% 110% 105% 100% RHW = 100% –5 –10 t (°C) –15 –20 –25 Figure 18.10  Supersaturation temperature curves showing the onset conditions of heterogeneous ice nucleation on illite particles reported in ESEM (From Zimmermann et al 2008 Journal of Geophysical Research–Atmospheres 113 Copyright 2008, American Geophysical Union With permission.) particles Such experiments would provide a fundamental understanding of ice nucleation processes specific to individual particles and their surface chemistry 18.3.4 Optical Properties of Individual Particles Scattering and absorption of solar light by atmospheric aerosols, known to directly effect climate, may result in both warming and cooling of the atmosphere The light-scattering particles reflect the  visible solar radiation back to space and have a net cooling effect on climate, whereas the ­light-absorbing aerosol traps this energy in the lower atmosphere and has a warming effect 479 Electron Beam Analysis and Microscopy of Individual Particles Therefore, the magnitude and sign of the direct forcing by aerosols depend on the relative amounts of scattering and absorption, which differ substantially for diverse mixtures of particles Optical properties of particles depend on their size, morphology, and RI of the particle matter In turn, RIs are a function of the chemical composition, phase, and mixing state of particles Physical and chemical properties of large ensembles of particles can be assessed using EM and electron probe analysis Based on this characterization, size-selected particles are classified into particletype groups The average RI of particle mixture (RImix) can be calculated based on estimated (RIi) values for each particle group and a volume approximation for externally mixed particles using Equation 18.1 (Horvath, 1998): ∑ RI V ∑ n V ∑ k V = −i ∑V ∑V ∑V i i RI mix = i i i i i i i i (18.1) i i i i i In this equation, ni, and ki are real and imaginary parts of RI (RIi), and Vi is the total volume of particles in group i This approach oversimplifies particle mixture in many ways, and its accuracy distinctly depends on the nature of particles present in the sample It can be used to provide reasonable estimates of the RImix values for particle mixtures dominated by inorganic and mineral dust particles for which RI values are well tabulated (Horvath, 1998; Sokolik and Toon, 1999) Such estimates were recently employed in several field studies where practical information on the general trends of optical properties of aerosols in rural and urban air masses were reported (Ebert et al., 2002b, 2004) However, the application of this approach to soot and organic particles is largely unfeasible because of ambiguous data and definitions of particle chemical composition, size, morphology, and generally unknown RI values Recently, Alexander et al (2008) presented an elegant application of the HR-TEM and EELS measurements for determination of optical properties of spherical carbon particles The mean RI of spherical carbon particles, RI = 1.67–0.27i at a wavelength of λ = 550 nm, was obtained directly from measured EELS spectra The method used a Kramers–Kronig transformation of EELS spectra of individual particles to obtain corresponding dielectric functions that can be transformed into RI values The dielectric function calculations assume isotropic material of particles and require accurate measurements of particle thickness Because of the amorphous nature of carbon particles and their nearly perfect spherical shape, these calculations were relatively straightforward However, the extension of this method to other types of particles is a recondite process 18.3.5 Laboratory Studies of Gas-Particle Reactions Laboratory studies are essential for a fundamental understanding of the atmospheric chemistry of particles and their possible effects on the environment Over the last decade, EM and microanalysis have been extensively used for chemical characterization of individual particles after their heterogeneous reactions with gas-phase reactants (e.g., Allen et al., 1996; Krueger et al., 2003a, 2003b, 2004; Laskin et  al., 2003b, 2005b; Al-Hosney et  al., 2005) These microscopy studies provided fundamental information of crucial importance for understanding the reaction mechanisms of atmospheric particles, their possible airborne history, and source apportionment An important challenge for laboratory studies of gas-particle heterogeneous chemistry is the ability to capture realistic, atmospherically relevant conditions of RH, temperature, pressure, reaction time, and trace reactive gas concentrations To address this challenge, a Particle-on-Substrate Stagnation Flow Reactor (PS-SFR) approach has been developed (Liu et al., 2007) In this approach, the reactivity of individual particles is examined by exposing them to trace level concentrations of common atmospheric oxidants under carefully controlled conditions Detailed microscopic analysis of particle samples is then used to obtain information on particle composition and morphology 480 Fundamentals and Applications in Aerosol Spectroscopy before and after the reaction This method provides a unique opportunity to study the chemical reactions of particles of various sizes under different conditions of RH and atmospherically relevant reaction times, as well as the trace concentrations of gas reactants and their mixtures To date, this approach has been used in the kinetic studies of heterogeneous gas-particle reactions of NaCl + HNO3, NaCl/MgCl2 + HNO3, and SeaSalt + HNO3 (Liu et  al., 2007); CaCO3 + HNO3 (Liu et  al., 2008); NaCl + OH (Laskin et al., 2006b); and NaCl/CH3SO3Na + HNO3 (Laskin and co-workers, unpublished results) Figure 18.11 shows typical SEM images and EDX spectra of NaCl particles before and after exposure to gaseous HNO3 in the PS-SFR Morphological and chemical changes indicative of reactive transformation are clearly seen The reaction kinetics was followed by quantitative detection of chloride depletion in particles according to the reaction NaCl + HNO3 → NaNO3 + HCl Figure 18.12 shows values of the experimental uptake coefficients (γnet) determined over a range of 20–80% RH for initially deliquesced particles of Dp = 0.9 μm (dry size) composed of NaCl, mixed NaCl/MgCl2, and sea salt, respectively The overall trend of HNO3 uptake is in agreement with previously published data (Saul et  al., 2006) However, the exact values are somewhat different because γnet is particle-size dependent The experimental uptake coefficient initially increases as RH decreases from 80%, reaches its maximum at approximately 55% RH, and then decreases at lower RH This behavior was explained by the variation in chloride concentration in particles and their efflorescence phase transition Over the RH range from 80% to 55%, a decrease in RH results in an increase in the chloride ion concentration in droplets, leading to a larger reactive uptake Below the ERH (45–50%), the reactive uptake drops rapidly However, a sudden “shutoff” in the reactivity was not observed Considerable HNO3 uptake onto all three types of particles (γnet = 0.04–0.10) was measured under quite dry conditions of RH 2.00 μm (black, dark gray, light gray, dashed, and dotted lines, respectively) (From Hopkins et al 2008 Journal of Geophysical Research–Atmospheres 113 Copyright 2008, American Geophysical Union With permission.) 486 Fundamentals and Applications in Aerosol Spectroscopy Equations 18.2 and 18.3 contain the same two unknowns The equations were then solved to determine values for both [CH 3SO3− ]/[ Na ] and [ nss-SO2− ]/[ Na ] This analysis was applied to CC SEM/EDX and STXM/NEXAFS data sets and yielded plots presented in the panels (c) and (d) of Figure 18.16 For the first time, size-resolved nss-S/Na and CH 3SO3− /nss-SO24− ratios were reported for marine particles (Hopkins et al 2008) Characteristic ratios of nss-S/Na > 0.10 were obtained for sea-salt particles, with higher values observed for smaller particles indicating more extensive formation of sulfur-containing salts Characteristic ratios of CH 3SO3− /nss-SO24− > 0.60 were reported for sea-salt particles of all sizes, with higher values for large particles This indicates that CH 3SO3− salts were likely the dominant form of nss-sulfur in large particles, while SO2− was more common in smaller particles These results were in qualitative agreement with the schematic of the sulfur–aerosol–climate links in the marine boundary layer mediated by atmospheric oxidation of dimethyl sulfide (DMS)—the major source of sulfur over the oceans The presence of CH 3SO3− in sea-salt particles indicates substantial formation and fast uptake of CH3SO3H (reaction r5) presumably resulting from the oxygen addition channel in the DMS oxidation mechanism (von Glasow and Crutzen, 2004) The presence of nss-SO2− in sea-salt particles is attributed to reaction r4 with H2SO4 formed via the H abstraction channel of DMS oxidation (von Glasow and Crutzen, 2004) The quantitative assessment of the partitioning between the two different forms of sulfur, that is, CH 3SO3− and nss-SO2− , is important for kinetic modeling Ratios of [CH 3SO3− ]/[ Na] and [nss-SO24 − ]/[ Na ] provide information on the pathways of DMS oxidation in the environment at a given geographic location The partitioning between these reaction ­products is important for climate modeling, because it impacts the number and size of CCN produced in the marine atmosphere (von Glasow and Crutzen, 2004) 18.5 Summary As discussed throughout this chapter, electron beam microscopy and microspectroscopy methods of particle analysis offer unique analytical tools to study the composition and chemistry of environmental particles collected in both field and laboratory experiments Over the last decade, numerous advances in the instrumentation and analytical methodologies of electron beam techniques have resulted in the development of novel approaches for the fundamental studies of particle physical chemistry The information obtained in these studies is crucial for evaluating the chemistry and physical properties of particles related to climate change, as well as understanding particle aging and reactivity in the atmosphere Therefore, microscopy and microspectroscopy studies of individual particles will continue to be a subject of many environmental research projects for years to come Obtaining comprehensive information on the chemical composition, physical properties, and atmospheric reactivity of particles is challenging, because no single method of analytical chemistry is capable of providing all the requisite information For instance, the methods of EM and microanalysis discussed in this chapter can be employed to visualize particle morphology and internal structure at the nanometer scale However, the analytical power of these techniques in terms of a comprehensive chemical characterization of atmospheric particles is limited to the elemental analysis, which is not informative enough for complex organic particles A comprehensive characterization of atmospheric particles can only be obtained using a complementary combination of different analytical methods, ranging from microscopic properties of individual particles to an advanced chemical characterization of complex molecules comprising particulate matter The development of analytical methodologies for comprehensive studies and their applications presents both challenging and exciting opportunities for future research Acknowledgments The author acknowledges financial support from the Atmospheric Science Program, Office of Biological and Environmental Research (OBER) of the U.S Department of Energy (DOE); the Electron Beam Analysis and Microscopy of Individual Particles 487 Tropospheric Chemistry and the Radiation Sciences programs at the National Aeronautics and Space Administration (NASA); the Laboratory Directed Research and Development funds of Pacific Northwest National Laboratory (PNNL); and operational budget of the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the OBER DOE and located at PNNL PNNL is operated by Battelle Memorial Institute for the DOE under contract no. DE-AC05-76RL01830 The author also acknowledges his colleagues and collaborators who profoundly influenced the research projects described in this chapter: C M Berkowitz, J P Cain, J P Cowin, Y Desyaterik, M J Ezell, B J Finlayson-Pitts, D J Gaspar, E R Gibson, M K Gilles, V H Grassian, E R Graber, J L Hand, R C Hoffman, R J Hopkins, S W Hunt, M J Iedema, K S Johnson, B J Krueger, Y Liu, W C Malm, R C Moffet, L T Molina, M J Molina, K A Prather, Y Rudich, V. Shutthanandan, A V Tivanski, T W Wietsma, C Wang, H Wang, R A Zaveri, and B Zuberi 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