Paul Scherrer Institute

About: Paul Scherrer Institute is a facility organization based out in Villigen, Switzerland. It is known for research contribution in the topics: Neutron & Large Hadron Collider. The organization has 9248 authors who have published 23984 publications receiving 890129 citations. The organization is also known as: PSI.

Source apportionment of submicron organic aerosols at an urban site by factor analytical modelling of aerosol mass spectra

Abstract: Submicron ambient aerosol was characterized in summer 2005 at an urban background site in Zurich, Switzer- land, during a three-week measurement campaign Highly time-resolved samples of non-refractory aerosol components were analyzed with an Aerodyne aerosol mass spectrometer (AMS) Positive matrix factorization (PMF) was used for the first time for aerosol mass spectra to identify the main com- ponents of the total organic aerosol and their sources The PMF retrieved factors were compared to measured reference mass spectra and were correlated with tracer species of the aerosol and gas phase measurements from collocated instru- ments Six factors were found to explain virtually all vari- ance in the data and could be assigned either to sources or to aerosol components such as oxygenated organic aerosol (OOA) Our analysis suggests that at the measurement site only a small (<10%) fraction of organic PM1 originates from freshly emitted fossil fuel combustion Other primary sources identified to be of similar or even higher importance are charbroiling (10-15%) and wood burning ( 10%) The fraction of all identified primary sources is considered as pri- mary organic aerosol (POA) This interpretation is supported by calculated ratios of the modelled POA and measured pri- mary pollutants such as elemental carbon (EC), NOx, and CO, which are in good agreement to literature values A high fraction (60-69%) of the measured organic aerosol mass is OOA which is interpreted mostly as secondary organic aerosol (SOA) This oxygenated organic aerosol can be sepa- rated into a highly aged fraction, OOA I, (40-50%) with low volatility and a mass spectrum similar to fulvic acid, and a more volatile and probably less processed fraction, OOA II (on average 20%) This is the first publication of a multiple component analysis technique to AMS organic spectral data and also the first report of the OOA II component

GEM-Selektor geochemical modeling package: revised algorithm and GEMS3K numerical kernel for coupled simulation codes

Abstract: Reactive mass transport (RMT) simulation is a powerful numerical tool to advance our understanding of complex geochemical processes and their feedbacks in relevant subsurface systems. Thermodynamic equilibrium defines the baseline for solubility, chemical kinetics, and RMT in general. Efficient RMT simulations can be based on the operator-splitting approach, where the solver of chemical equilibria is called by the mass transport part for each control volume whose composition, temperature, or pressure has changed. Modeling of complex natural systems requires consideration of multiphase–multicomponent geochemical models that include nonideal solutions (aqueous electrolytes, fluids, gases, solid solutions, and melts). Direct Gibbs energy minimization (GEM) methods have numerous advantages for the realistic geochemical modeling of such fluid–rock systems. Substantial improvements and extensions to the revised GEM interior point method algorithm based on Karpov’s convex programming approach are described, as implemented in the GEMS3K C/C+ + code, which is also the numerical kernel of GEM-Selektor v.3 package (http://gems.web.psi.ch). GEMS3K is presented in the context of the essential criteria of chemical plausibility, robustness of results, mass balance accuracy, numerical stability, speed, and portability to high-performance computing systems. The stand-alone GEMS3K code can treat very complex chemical systems with many nonideal solution phases accurately. It is fast, delivering chemically plausible and accurate results with the same or better mass balance precision as that of conventional speciation codes. GEMS3K is already used in several coupled RMT codes (e.g., OpenGeoSys-GEMS) capable of high-performance computing.

Visualization of O-O peroxo-like dimers in high-capacity layered oxides for Li-ion batteries

Abstract: Lithium-ion (Li-ion) batteries that rely on cationic redox reactions are the primary energy source for portable electronics. One pathway toward greater energy density is through the use of Li-rich layered oxides. The capacity of this class of materials (>270 milliampere hours per gram) has been shown to be nested in anionic redox reactions, which are thought to form peroxo-like species. However, the oxygen-oxygen (O-O) bonding pattern has not been observed in previous studies, nor has there been a satisfactory explanation for the irreversible changes that occur during first delithiation. By using Li2IrO3 as a model compound, we visualize the O-O dimers via transmission electron microscopy and neutron diffraction. Our findings establish the fundamental relation between the anionic redox process and the evolution of the O-O bonding in layered oxides.