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Fractal morphology, imaging and mass spectrometry of single aerosol particles in flight

An Erratum to this article was published on 08 August 2012


The morphology of micrometre-size particulate matter is of critical importance in fields ranging from toxicology1 to climate science2, yet these properties are surprisingly difficult to measure in the particles’ native environment. Electron microscopy requires collection of particles on a substrate3; visible light scattering provides insufficient resolution4; and X-ray synchrotron studies have been limited to ensembles of particles5. Here we demonstrate an in situ method for imaging individual sub-micrometre particles to nanometre resolution in their native environment, using intense, coherent X-ray pulses from the Linac Coherent Light Source6 free-electron laser. We introduced individual aerosol particles into the pulsed X-ray beam, which is sufficiently intense that diffraction from individual particles can be measured for morphological analysis. At the same time, ion fragments ejected from the beam were analysed using mass spectrometry, to determine the composition of single aerosol particles. Our results show the extent of internal dilation symmetry of individual soot particles subject to non-equilibrium aggregation, and the surprisingly large variability in their fractal dimensions. More broadly, our methods can be extended to resolve both static and dynamic morphology of general ensembles of disordered particles. Such general morphology has implications in topics such as solvent accessibilities in proteins7, vibrational energy transfer by the hydrodynamic interaction of amino acids8, and large-scale production of nanoscale structures by flame synthesis9.

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Figure 1: Schematic of concurrent imaging, morphology and spectroscopy of single soot particles in flight.
Figure 2: Diffraction patterns of self-assemblies of particles in flight, and reconstructions of their electron densities.
Figure 3: Fractal morphology of micrometre-sized soot aggregates.
Figure 4: Time-of-flight mass spectrometry concurrent with diffraction imaging.

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Experiments were carried out at the Linac Coherent Light Source, a national user facility operated by Stanford University on behalf of the US Department of Energy (DOE), Office of Basic Energy Sciences. N.D.L., C.Y.H., R.G.S., P.B. and M.J.B. were supported by the AMOS program within the Chemical Sciences, Geosciences, and Biosciences Division of the Office of Basic Energy Sciences, Office of Science, US Department of Energy. M.J.B. acknowledges support by the SLAC Laboratory Directed Research and Development Program. We acknowledge support from the Max Planck Society for funding the development and operation of the CAMP instrument within the ASG at CFEL, the Hamburg Ministry of Science and Research and Joachim Herz Stiftung as part of the Hamburg Initiative for Excellence in Research (LEXI) and the Hamburg School for Structure and Dynamics in Infection, CBST at UC under Cooperative Agreement number PHY 0120999. Lawrence Livermore National Laboratory (LLNL) is operated by Lawrence Livermore National Security, LLC, for the US Department of Energy, National Nuclear Security Administration under Contract DE-AC52-07NA27344. Work by LLNL has been supported, in part, by University of California Laboratory Fee grant 09-LR-05-118036-BARA. We also acknowledge support from the Swedish Research Council, the European Research Council, Knut och Alice Wallenbergs Stiftelse, and the DFG Cluster of Excellence at the Munich Centre for Advanced Photonics. We acknowledge the staff of the LCLS for their support in carrying out these experiments. The Max Planck Advanced Study Group at CFEL acknowledges technical support by R. Andritschke, K. Gärtner, O. Hälker, S. Herrmann, A. Hömke, Ch. Kaiser, K.-U. Kühnel, W. Leitenberger, D. Miessner, D. Pietschner, M. Porro, R. Richter, G. Schaller, C. Schmidt, F. Schopper, C.-D. Schröter, Ch. Thamm, A. Walenta, A. Ziegler and H. Gorke. N.D.L. thanks M. J. Berg, G. Simpson, G. Williams and J. Hajdu for their critique, and G. M. Stewart for rendering the experiment’s schematic.

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Authors and Affiliations



M.J.B. conceived the soot and soot/salt imaging experiments. M.J.B., C.Y.H., D.S., H.N.C., I.S., A.B., W.H.B., S.P.H.-R., S.M., S.B. and M.F. conceived the sphere/nanoparticle imaging experiments. D.S., N.D.L. and M.J.B conceived the fractal dimension determination. C.B. and J.B. built and managed the AMO beamline at LCLS, where the experiments were performed. C.Y.H., A.V.M., D.S., R.G.S., A.B., A.A., J.S., L.L., R.L.S., S.K., S.W.E., B.E., R.H., D.R., A.R., B.R., L.F., N.K., G.W., G.H., P.H., E.P., M.L., M.S.H., L.G., N.C., C.W., H.G., H.F., H.H., K.N., H.J.T., G.R.F., S.B., M.B., L.S., J.U., P.B. and K.O.H. were responsible for critical preparation leading up to and immediately after the experiment. C.Y.H., L.L., R.L.S., R.G.S., M.L., E.P., H.J.T. and M.J.B. were responsible for sample delivery. A.R., B.R., D.R. and L.F. developed and operated the mass spectrometer. M.L. took the electron micrographs (Supplementary Figs 2 and 3). M.J.B. and R.G.S. characterized and operated the MOUDI particle filter. The CAMP instrument was the responsibility of S.W.E., R.H., D.R., A.R., L.F., N.K., P.H., B.R., B.E., A.H., C.R., G.W., G.H., H.H., C.W., H.G., H.S., J.U., I.S. and L.S., who jointly designed and set up the instrument and/or developed and operated the pnCCD detectors. Efforts to calibrate, align the imaging apparatus and collect data were shared among C.Y.H., D.S., R.G.S., A.B., A.A., J.S., L.L., R.L.S., S.K., C.B., J.B., S.W.E., B.E., R.H., D.R., A.R., B.R., L.F., E.P., M.L., L.G., N.C., H.H., K.N., H.J.T., J.U., M.F., I.S., H.N.C. and M.J.B.. S.K., A.B., K.N. and A.V.M. provided crucial preliminary analysis of the data during the experiment. A.B., A.V.M., A.A. and S.K. processed and analysed the raw data, using software developed by L.F., S.K., A.B., T.A.W. and F.R.N.C.M.; M.J.B., N.D.L., D.S., C.Y.H., A.V.M., A.B., A.A., L.L., J.S., F.R.N.C.M., T.E. and M.H. developed the ideas for analyses. A.V.M. did the phase retrieval reconstructions. N.D.L. and D.S. contributed equally to the fractal morphology and calibration. N.D.L., M.J.B., D.S., A.B., A.V.M., D.R. and I.S. wrote the paper, with input from all co-authors.

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Correspondence to N. D. Loh or M. J. Bogan.

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Loh, N., Hampton, C., Martin, A. et al. Fractal morphology, imaging and mass spectrometry of single aerosol particles in flight. Nature 486, 513–517 (2012).

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