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The workshop will explore achievements at and future options for large-scale facilities like the Swiss Light Source (SLS), the Swiss Spallation Neutron Source (SINQ), and the Free Electron Laser (SwissFel) to address questions related to Earth’s atmosphere. Using techniques such as spectroscopy, scattering, and imaging, structures and processes at the molecular and atomic levels are investigated to understand their connection to macroscopic physical properties and chemical reactivity.
This workshop brings together scientists who are developing novel techniques at large-scale facilities with scientists who are active in atmospheric research. The workshop is open to invited speakers, LAC members, and collaborators.
Workshop goals | Overview LAC science | A brief history of atmospheric chemistry at PSI's large facilities
Aerosol particles range typically from a few nanometers to several micrometers in size and have significant impacts on climate, air quality, and health. These particles stem from a wide range of sources and are multicomponent and multiphase in nature. This physicochemical complexity makes it a challenge to assess the particles’ roles in altering atmospheric processes. Scanning transmission X-ray microscopy with near-edge X-ray absorption fine-structure spectroscopy (STXM/NEXAFS) is uniquely suited to resolve particle morphology and composition on the nanoscale. STXM application within a multi-modal instrument approach is showcased to study atmospheric ice nucleation, which is highly selective process, initiated by only a tiny fraction of the aerosol population. Chemical imaging of soil dust particles sheds light on the ice-nucleating agents on a single-particle level. This case study is followed by addressing future challenges in the field and required STXM capabilities. This includes the idea of “bringing the atmosphere into STXM”, multimodal operation, AI/ML assisted analysis, and automated sample loading and analysis.
I will present strategies for highly surface sensitive and chemically sensitive XPS experiments on aerosol samples with atmospherically relevant compositions. I will present results from both inflight and deposited aerosol samples and ambient pressure conditions and discuss atmospheric significance, challenges, and ongoing and planned developments.
The talk will exemplify the unique research opportunities for environmental science using X-ray micro-spectroscopy, scattering and imaging using tender X-ray (2-8~keV). A key challenge for atmospheric research is the sample injection under atmospherically relevant thermodynamic and chemical conditions. The talk will briefly discuss different techniques, their challenges and applicability for atmospheric research. Finally, a method is presented to take XAS spectra directly from a ‘cloud’ of airborne aerosols at tender X-rays to determine the phase state in situ.
Our previous work has demonstrated the feasibility of liquid jet XPS for identifying reactive intermediates at the aqueous solution - air interface for solutions in the mM range of concentrations. This establishes a major concentration or water activity gap to atmospheric aerosol particles existing at ambient relative humidity and thus characterized by highly non-ideal conditions. Aerodynamic focussing of aerosols into a particle beam requires vacuum at the point of measurement, which will lead to departure of particle composition from equilibrium. Therefore, I am suggesting to work towards flow focusing systems that allow maintaining relevant water vapor pressure to allow probing particles at equilibrium. This would offer new opportunities in reaction studies of many relevant aerosol reaction systems.
Cloud formation, atmospheric chemistry, and human health are influenced by multiphase chemistry at the air-substrate interface of atmospheric particles and ground surfaces (Pöschl and Shiraiwa 2015). All of these impacts are affected by acidity (Angle et al. 2021). A conceptional understanding of interfacial acid-base character has not yet been reached (Saykally 2013). Using X-ray photoemission spectroscopy at near ambient pressure, we have suggested that the dissociation of acids adsorbed to ice is governed by the availability and mobility of water molecules to stabilize the dissociated ions and that the degree of dissociation at the air-ice interface differs from that predicted based on dissociation behavior in aqueous bulk solutions (Bartels-Rausch et al. 2017, Kong et al. 2017). Ice and snow host chemistry of relevance for the atmosphere and are of importance in cold regions of the Earth (Thomas et al. 2019). Here, we present additional results of fundamental studies on the structure of the hydrogen bonding network of interfacial water and the dissociation of acidic trace gases upon adsorption. REFERENCES Angle, K. J., D. R. Crocker, R. M. C. Simpson, K. J. Mayer, L. A. Garofalo, A. N. Moore, S. L. Mora Garcia, V. W. Or, S. Srinivasan, M. Farhan, J. S. Sauer, C. Lee, M. A. Pothier, D. K. Farmer, T. R. Martz, T. H. Bertram, C. D. Cappa, K. A. Prather and V. H. Grassian (2021). "Acidity across the interface from the ocean surface to sea spray aerosol." Proc Natl Acad Sci U S A 118(2). Bartels-Rausch, T., F. Orlando, X. Kong, L. Artiglia and M. Ammann (2017). "Experimental evidence for the formation of solvation shells by soluble species at a nonuniform air-ice interface." ACS Earth and Space Chemistry 1(9): 572-579. Kong, X., A. Waldner, F. Orlando, L. Artiglia, T. Huthwelker, M. Ammann and T. Bartels-Rausch (2017). "Coexistence of physisorbed and solvated HCl at warm ice surfaces." Journal of Physical Chemistry Letters 8(19): 4757-4762. Pöschl, U. and M. Shiraiwa (2015). "Multiphase chemistry at the atmosphere–biosphere interface influencing climate and public health in the anthropocene." Chemical Reviews 115(10): 4440-4475. Saykally, R. J. (2013). "Air/water interface: Two sides of the acid-base story." Nature Chemistry 5(2): 82-84. Thomas, J. L., J. Stutz, M. M. Frey, T. Bartels-Rausch, K. Altieri, F. Baladima, J. Browse, M. Dall'Osto, L. Marelle, J. Mouginot, G. M. Jennifer, D. Nomura, K. A. Pratt, M. D. Willis, P. Zieger, J. Abbatt, T. A. Douglas, M. C. Facchini, J. France, A. E. Jones, K. Kim, P. A. Matrai, V. F. McNeill, A. Saiz-Lopez, P. Shepson, N. Steiner, K. S. Law, S. R. Arnold, B. Delille, J. Schmale, J. E. Sonke, A. Dommergue, D. Voisin, M. L. Melamed and J. Gier (2019). "Fostering multidisciplinary research on interactions between chemistry, biology, and physics within the coupled cryosphere-atmosphere system." Elementa 7.
I'll present some atmospheric chemistry science cases and options to answer key questions with X-ray excited electron spectroscopy. This talk focuses very much on sample development that mimic atmospheric surfaces and allow systematic studies.
Interfaces have a fundamental role in chemistry because they are the place where most reactions take place. Over the last 20 years, in situ X-ray photoelectron spectroscopy (XPS) has known a huge technological development and now offers the possibility to routinely characterize solid-gas, solid-vapor and solid-liquid interfaces. In situ XPS has joined the surface sensitivity of the technique with the possibility to measure in the mbar range, thus partially filling the well-known pressure gap between surface science studies and many applications. As an example, it is possible to investigate the interaction of trace gases with inorganic salts, used as probes for atmospheric particles, with the opportunity to tune important parameters like the relative humidity. At the same time, several efforts have been spent to develop suitable methods to investigate buried interfaces. By creating thin liquid layers on solid substrates, it is possible to investigate ions dissolution and their local structure at the solid-liquid interface. I will focus on recent developments and state-of-the-art setups available worldwide. I will describe how such setups can be and have been used to address fundamental questions related to the field of environmental science. Finally, I will propose an outlook on the impact of future technical developments.
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"Alkali feldspar is an important constituent of airborne mineral dust, the major source of primary ice nucleating particles (INPs) in the atmosphere. Some alkali feldspars have particularly high ice nucleation (IN) activity. This phenomenon has been recently ascribed to the ability of (100) planes of alkali feldspar to nucleate ice. However, the structure of feldspar-ice interface is not known and therefore the molecular level understanding of ice nucleation on feldspar is lacking.
Recently, we have initiated an interdisciplinary project combining expertise in atomistic modelling, mineralogy, crystallography, atmospheric IN research, electron microscopy and synchrotron X-Ray scattering methods with the goal to achieve molecular characterization of the water-feldspar interface prior and during the nucleation of ice crystals. In this contribution, we focus on the application of synchrotron X-Ray scattering methods for in-situ measurements of ice formation on cleaved planes of microcline feldspar in a custom-designed environmental cell. The preliminary results obtained at P08 beamline at DESY support our previous hypothesis of the epitaxial relationship between the prismatic plane of ice and the (100) crystal plane in feldspar, initially formulated from the electron microscope observations. We discuss the potential development of this method and the implications of these findings for the future atmospheric IN research.
We also briefly discuss the results of a recent XPS-NEXAFS study probing the hydrogen bonding structure of interfacial water in the presence of ions, removed from the sub-surface mineral framework by cation exchange. We show that the presence of foreign ions apparently inhibits the formation of tetrahedrally coordinated water upon adsorption on the sample surface, making water structure more “liquid-like”. The interpretation of both X-Ray diffraction and spectroscopic results is supported by direct measurements of the IN efficacy of feldspar specimens performed in a droplet freezing array setup.
Acknowledgement: we acknowledge FWF and DFG for financial support (project number 515700978) and support by PETRA III P08 beamline stuff scientists Florian Bertram and Chen Shen (DESY). David Heuser, Elena Petrishcheva, and Prof. Rainer Abart (University of Vienna) are greatly acknowledged for sample preparation and characterization, and for general guidance."
Aerosol particles, in particular mineral dust, play an important role in the condensation of cloud droplets and formation of ice crystals. Airborne mineral dust consists mainly of clay minerals (~60%), quartz (~25%), and feldspar (~12 %). The comparatively low fraction of feldspar dominates the ice nucleation. Recently, A. Kiselev et al. revealed oriented ice growth on several feldspar surfaces. The ice nucleation seems to be affected by specific nucleation sites (steps, cracks, dissolution lamellae). Thus, ice nucleation on solid surfaces becomes a classical surface-science question and can be tackled with established synchrotron methods such as grazing-incidence scattering techniques (GID, XRR, CTR-Measurements…). These techniques have significantly evolved with the developments of synchrotron sources, beamline optics, and detectors, opening new opportunities for atmospheric research. In this presentation, the possibilities and the complexity of surface science experiments during water condensation and ice nucleation on natural crystals will be discussed. Some aspects will be demonstrated using in situ data obtained with a newly developed environmental cell at the KIT light source (MPI-beamline) and Petra III (P08).
Small-angle scattering (SAS), including neutron (SANS) and X-ray scattering (SAXS) techniques, enables in-depth examination of particle structure and composition at the nanometer scale, making it highly applicable for atmospheric research. This presentation will introduce the fundamentals of SANS, with a focus on its distinctive advantage of contrast variation, which allows selective visualization of specific particle components. By manipulating contrast agents such as D2O and H2O, SANS enables precise isolation of layers within complex particles, facilitating analysis of internal structures. A key example will feature core-shell particles, where contrast variation distinctly reveals core and shell regions, supporting quantification of water content and composition. SANS also allows for the analysis of surface properties and material porosity, offering insights into pore accessibility to solvents, particularly when a Porod regime - dominated by surface scattering - can be observed. Furthermore, SANS sheds light on the collective structures of nanoparticles, characterizing fractal geometries common in particles formed through aggregation. Beyond structural insights, SANS characterization enhances our understanding of the processes that govern aggregate formation, offering implications for atmospheric particulate growth and behavior.
The presentation with give an overview of our recent work at X-ray and neutron facilities focussing mainly on droplets and thin films of atmospheric importance including ageing processes and phase changes.
I will present results of highly surface sensitive and chemically sensitive XPS experiments on liquid microjet aqueous samples as models for atmospheric aqueous aerosols and cloud droplets. I will present examples of further application of the results from XPS experiments to atmospheric modeling. I will discuss prospects for similar experiments on micro-droplets.
Neutron reflectometry was used to study the interaction of gaseous SO2 and organic films at the air-water interface to determine whether a reaction occurred, resulting in a product film, or, removal of the film from the interface. Three different organic films extracted from particulate matter sampled from different atmospheric environments (woodland, urban, and wood smoke) and two pure proxy chemical films were studied. Exposure of SO2 to the proxy films confirmed that gaseous SO2 reacts with unsaturated material at the air-water interface. No reaction was observed between SO2 and organic films extracted from particulate matter sampled from woodland and urban environments. However, a change in the film properties was observed on exposure of gaseous SO2 to organic films extracted from wood smoke aerosol. Additionally, the fitting of the thick wood smoke film data suggested a possible three-layer structure at the interface consistent with a surfactant-rich layer in contact with the air-water interface, a middle layer rich in PAHs, and a third layer consistent with an aliphatic region. These findings indicate that gaseous SO2 does not remove organic films from the air-aqueous interface of atmospheric aerosol, but can impact film chemical composition with consequences for further reactivity and optical properties. Preliminary results also suggest that thick wood smoke films can form multi-layer structures at the air-water interface.
The intense X-ray pulses from free-electron laser sources (XFEL) allow imaging of single nanometer sized samples with single shots. In my talk I will briefly introduce XFELs and the single-shot imaging capabilities of free-flying particles at SwissFEL. I will then present a few showcase examples for studying the (static) morphology of nanoparticles and following light-induced processes on the nanoscale. I will finish with first applications of single-shot imaging to atmospherically relevant systems.
"Intense X-ray free-electron laser pulses allow to obtain ""snapshots"" of individual nanoparticles in free flight. The accessible size regime roughly ranges from tens of nanometers up to a few micrometers with a spatial resolution of few nanometers and a temporal resolution of 50 femtoseconds or better. Thus, the approach called single-shot single-particle Coherent Diffractive Imaging (CDI) opens up ample opportunities for atmospheric research, such as structure determination of aerosols from combustion or the study of freezing in supercooled water droplets. Basically all processes in aerosols that are influenced or disturbed by a substrate or surrounding medium may be good candidates.
I will introduce the CDI method and novel approaches for time-resolved studies and discuss our recent findings on nanoparticle shapes and dynamics."
Topics and Themes for Discussion
"Unravelling the fundamental properties of water and water´s phase diagram is highly relevant for our understanding of water in our environment. Moreover, amorphous ice was predicted to occur under summer mesospheric conditions, prior to crystallising into hexagonal ice. Since the discovery of two distinct amorphous states of ice with different density (high- and low-density amorphous ice, HDA and LDA) it has been discussed whether and how this phenomenon of polyamorphism at high pressures is connected to the occurrence of two distinct liquid phases (HDL and LDL). An important question in this context is if and how these different states of water are related to the anomalous bulk properties of water.
Our studies give insight to the structural and dynamical properties of different amorphous ices, their glass transition and subsequent crystallization. In my talk I will present recent X-ray experiments on supercooled water derived from amorphous ices, including XFEL based experiments as well as X-ray photon correlation spectroscopy."
I will discuss the experimental electrodynamics, electrical conductivity, and dielectric properties of water confined between clay nanocrystals within nanometer-scale slit channels. I will highlight how ionic and molecular transport are influenced by clay type, humidity, pressure, and electrolyte concentration. These findings have significant implications for natural phenomena such as electrification, lightning, soil swelling, and freezing. Finally, I will demonstrate how these insights can be applied to develop efficient, low-cost electricity storage solutions.
Be it in heterogeneous catalysis, combustion, the atmosphere or in the interstellar medium, reactive and elusive intermediates are the key players responsible for the branching of chemical reaction pathways. This makes radicals, carbenes or ketenes in control of the selectivity of industrial processes. However, catching elusive intermediates is challenging but essential for unveiling the reaction mechanism. In this short talk, I will introduce Photoelectron Photoion Coincidence (PEPICO) spectroscopy with vacuum ultraviolet (VUV) synchrotron radiation as a multiplexed, rapid, and sensitive detection tool for reaction intermediates, developed at the Swiss Light Source. PEPICO combines the sensitivity of mass spectrometry (1st analytical dimension), the isomer-specifity of (threshold) photoelectron spectroscopy (2nd) and the performance of ion velocity map imaging (VMI, 3rd) to trace complex reaction mixtures. I will give a few examples from heterogeneous catalysis, atmospheric as well as interstellar chemistry.
In this presentation, I will discuss advanced experimental techniques available at the Swiss Free Electron Laser (SwissFEL) for probing time-resolved chemical dynamics with femtosecond temporal resolution. My talk will focus on two key areas. First, I will explore time-resolved X-ray photoemission spectroscopy on gaseous targets, potentially extending the method to aerosol systems. Second, I will present time-resolved X-ray absorption spectroscopy, emphasizing its applicability to liquid-phase samples using soft X-rays. A nanometer-thin liquid sheet, developed and characterized for these studies, enables experiments in transmission geometry, covering a wide energy range from Vacuum UV to soft X-rays.
Multi-color X-ray pulses with adjustable delay allow to follow ultrafast charge and energy transfer in time and space due to the state selectivity of X-ray photoabsorption. With two freely tunable X-ray pump-probe energies from the Athos line, we can excite at one atomic site and monitor subsequent relaxation processes throughout a system at another site. In this talk, I will show results from our first two-color experiment on small gas-phase molecules. We employed transient absorption and ion-time-of-flight spectroscopy to track the core-excitation induced dynamics in nitrous oxide by exciting the molecules with a pump pulse tuned to the nitrogen K-edge and probing with a pulse tuned to the oxygen K-edge. Pushing the pulse duration into the few to sub-fs regime will give access to study X-ray induced dynamics on sub-Auger lifetimes. This is crucial to understand processes like charge migration or the initial steps of radiation damage, and to implement non-linear X-ray spectroscopy techniques.