Multiphase Chemistry Group
Head of the group: Markus Ammann
The Surface Chemistry group performs laboratory studies related to the chemistry, photochemistry and kinetics of atmospheric multiphase processes involving organic, halogen, nitrogen oxide and odd oxygen species on substrates relevant for aerosol particles, cirrus ice, ocean surface, soil surfaces, snow and sea ice. Understanding these processes is relevant for the assessment of the human impact on atmospheric composition, climate, human and ecosystem health.
We use a combination of in-situ spectroscopy, flow tube and chamber techniques to cover scales from molecular level world of interfaces to the microstructure in aerosol particles and to the mesosopic medium of snow.
We educate young scientists in laboratory atmospheric chemistry within the frame of the Institute of Atmospheric and Climate Sciences (IAC) at ETH Zürich (Department of Environmental Systems Sciences, D-USYS).
Environmental micro-reactor for atmospheric chemistry and physics
Organic particles can be highly viscous in air that is dry and cold. Therefore, it is important to quantify limitations of gases through organic materials as a function of temperature and relative humidity to better understand chemical and physical process involving atmospheric aerosol particles. Using state of the art spectro-microscopic techniques at the Swiss Light Source with the development of a new environmental micro-reactor, I investigate molecular diffusion of water vapor, ozone and other reactive gasses through organic particles less than 1 micrometer in diameter. At cold temperatures and low humidity, I expect that chemical reactions are limited to particle surfaces and microphysical processes such as ice nucleation and water condensation are altered.
Uptake kinetics of trace gases to aerosol particles
Loss of dinitrogen pentoxide (N2O5) and hydroperoxy (HO2) radicals to aerosol particles are amongst the most important but still least well understood processes to affect the gas phase composition of the troposphere. In collaboration with University of Leeds and the Max Planck Institute for Chemistry in Mainz we are interested in the impact of changing viscosity in secondary organic aerosol particle proxies on the uptake kinetics of these two species. The results suggest drastic changes in kinetic regime between dry and humid conditions.
Laboratory data evaluation for atmospheric chemistry
Emissions from human activities have led to important changes in the composition of the atmosphere. Computational models are used to understand the impacts of emissions on air quality on local, regional, and global scales and the global climate system. An accurate representation of atmospheric chemistry is of critical importance in these models. The mission of the IUPAC Task Group on Atmospheric Chemical Kinetic Data Evaluation is to provide evaluated kinetic data for gas-phase, heterogeneous, and aqueous-phase reactions. The data are published periodically in a special issue of Atmospheric Chemistry and Physics .
Near Ambient Pressure Photoemission (NAPP) applied to catalysis and surface chemistry.
My interest is in the NAPP endstation covering several topics such as the characterization of catalysts under steady and transient state, ice nucleation and growth, adsorption of organic and inorganic molecules on ice, the phase diagrams of binary solutions, titanium dioxide photochemistry and the surface propensity of selected compounds and mixtures in aqueous solutions. The core of the NAPP endstation is a Scienta R4000 HiPP-2 electron analyzer. It can operate from ultra high vacuum up to 20 mbar in pressure. Two experimental chambers can be connected to the analyser which are a solid chamber allowing for the analysis of solid samples and/or the growth in-situ of ice sample, and the liquid jet chamber that hosts a liquid microjet assembly (diameter of the liquid delivery nozzle in the 15-50 µm range) for the analysis of solutions. My current research project is about Fenton’s chemistry at interfaces. I will investigate both liquid solutions of Fe2+ and Cu2+ and heterogeneous catalysts (iron- and copper-exchanged zeolites). Thanks to the surface sensitivity of XPS, active species both at the liquid/gas and solid/gas interface will be identified and characterized.
Hunting liquid micro-pockets in snow and ice by core level spectroscopy
We use electron- and fluorescence yield near-edge X-ray absorption fine structure (NEXAFS) spectroscopy to probe the local environment of chlorine ions in frozen NaCl-water binary systems. NEXAFS spectra reflect the binding environment of the probe and thus reveal phase changes in aqueous solutions. Switching between electron and fluorescence detection allows to either probe barely the air-ice interface or the bulk of the sample. The goal is to describe frapant differences in the phases of NaCl - water mixtures at temperatures blow the freezing point for the surface of the ice vs. its bulk. This has significant impact on modelling chemical reactions in snow or ice and it’s environmental consequences.
Radical production and aerosol aging in the atmosphere by photocatalyzers
Pablo Corral Arroyo
Our goal is to understand radical production, aging and changes in physical properties of atmospheric aerosols arising from photocatalytic reactions. Absorption of near ultra-violet light can trigger triplet state excitation and radical production followed by addition radical chemical reaction. The techniques used are coated wall flow tube experiments, scanning transmission X-ray microspectrocopy, aerosol flow tube experiments, electrodynamic balance and proton transfer reaction mass spectrometer. The systems on which our work is focused are organic or organometallic compounds which include photosensitizers and donors which are photocatalyzer and reactive species, respectively. We expect to quantify and parameterize the magnitude of these processes to improve understanding of these atmospheric processes.
We focus on the chemical reactivity of ozone with halide salts in snow. These reactions are of significant environmental interest because they have been linked to vast ozone depletion events regularly observed in the Polar Regions and mid-latitudes. With the application of coated wall flow-tube experiments, the aim of this study is to investigate the reactivity of halide salts when temperatures decrease. Our hypothesis is that viscosity and phase changes with temperature influence heterogeneous reaction rates and products beyond a purely temperature effect.
Heterogeneous photochemistry of atmospheric mineral dust
Our research focuses on photocatalytic processes on metal oxides, which are a major component of natural mineral dust and represent important reactive atmospheric aerosols that influence the ozone budget and the climate. The goal is to shed light on the impact of heterogeneous photochemistry on mineral dust aerosol in the atmosphere. Major open research topics include the role of water adsorption and surface hydroxylation on heterogeneous photochemistry. Specifically, we investigate the surface chemical evolution of nitrogenated species and organic compounds on metal oxides surfaces, like TiO2 or FexOy, under UV irradiation by means of near ambient pressure electron spectroscopies (XPS and NEXAFS) performed at relevant atmospheric conditions of humidity.