Changes In Particle Diameter Research Articles

A Combined SAXS and XAS Setup for Operando Electrocatalyst Degradation Studies

The noble metal nanoparticles (NPs, including oxides and/or alloys) customarily used to catalyze the electrochemical reactions at play in low temperature fuel cells and electrolyzers are prone to potential-induced dissolution1 which leads to changes in their composition and morphology. Minimizing the impact of these processes on the devices’ operation requires a better understanding of their mechanism under application-relevant operando conditions. In this regard, small angle X-ray scattering (SAXS) provides information about a sample’s NP size distribution and agglomeration, while X-ray absorption spectroscopy (XAS) is sensitive to the electronic (oxidation state) and geometric (identity and number of coordinating atoms, bond distances) structure of the element of interest. The combination of these two techniques in an operando setup would result in novel insight on the degradation mechanisms affecting noble metal nanoparticles. With this motivation, we have developed a novel setup in which the gas ionization chambers and flight tube plus 2D-detector required for XAS and SAXS acquisition respectively, are mounted in parallel on a movable table that allows to transition among techniques within a couple of minutes. This configuration allows to use both techniques in their optimal configuration, without losing signal quality while compromising on one technique while combining it with the other (as done in the past).2 To validate this approach it was used to study the operando degradation of two carbon-supported Pt-NP (Pt/C) catalysts customarily used in polymer electrolyte fuel cells, which constitute a relatively well understood system owing to the large volume of work that has been devoted to its study.3 Specifically, commercial Pt on Vulcan and Pt on graphitized Black Pearls catalysts (Pt/V and Pt/BP-g, respectively – both with 30 wt. % Pt) were processed into electrodes and electrochemically tested in an operando flow cell developed in-house.4 The degradation protocol consisted of 250 potential cycles between 0.5 and 1.5 V vs. the reversible hydrogen electrode (RHE) at 50 mV∙s-1, using 0.1 M HClO4 at 60 °C as the electrolyte. Complementing results derived from both techniques with respect to changes in particle diameter as well as oxidation state of the catalyst particles are then used to quantifiy NP-growth rates, correlation of particle size with Pt-Pt bond distance as well as NP oxide coverages. In summary, this contribution will introduce a novel, combined SAXS and XAS setup devoted to (electro)catalyst research, and exemplify its potential application based on the results derived for two Pt/C catalysts, which are fully consistent with previous literature on such materials. Cherevko, A. R. Zeradjanin, A. A. Topalov, N. Kulyk, I. Katsounaros, and K. J. J. Mayrhofer, ChemCatChem 6, 2219 (2014).Nikitenko, A. M. Beale, A. M. J. van der Eerden, S. D. M. Jacques, O. Leynaud, and M. G. O‘Brien, J. Synchrotron Rad. 15, 632 (2008).Shao-Horn, W. C. Sheng, S. Chen, P. J. Ferreira, F. Holby, and D. Morgan, Top. Catal. 46, 285 (2007).Binninger, E. Fabbri, A. Patru, M. Garganourakis, J. Han, D. Abbott, O. Sereda, R. Kötz, A. Menzel, M. Nachtegaal, and T. J. Schmidt, J. Electrochem. Soc. 163, H906 (2016).A. Gilbert, N. N. Kariuki, R. Subbaraman, A. J. Kropf, M. C. Smith, E. F. Holby, D. Morgan, and D. J. Myers, J. Am. Chem. Soc. 134, 14823 (2012).Lei, J. Jelic, L. C. Nitsche, R. Meyer, and J. Miller, Top. Catal. 54, 334 (2011).

Non-invasive Detection of Unique Molecular Signatures in Laser-Induced Retinal Injuries.

Unintentional laser exposure is an increasing concern in many operational environments. Determining whether a laser exposure event caused a retinal injury currently requires medical expertise and specialized equipment that are not always readily available. The purpose of this study is to test the feasibility of using dynamic light scattering (DLS) to non-invasively detect laser retinal injuries through interrogation of the vitreous humor (VH). Three grades of retinal laser lesions were studied: mild (minimally visible lesions), moderate (Grade II), and severe (Grade III). A pre-post-treatment design was used to collect DLS measurements in vivo at various time points, using a customized instrument. VH samples were analyzed by liquid chromatography/tandem mass spectrometry (LC-MS/MS) and relative protein abundances were determined by spectral counting. DLS signal analysis revealed significant changes in particle diameter and intensity in laser-treated groups as compared with control. Differences in protein profile in the VH of the laser-treated eyes were noted when compared with control. These results suggest that laser injury to the retina induces upregulation of proteins that diffuse into the VH from the damaged tissue, which can be detected non-invasively using DLS.

Detachment Characteristics of Deposited Particles in Porous Medium: Experimentation and Modeling

This paper presents an experimental study of particle transport in porous medium using a self-developed sand layer transportation–deposition testing system, aiming at delineating the detachment characteristics of deposited particles in porous medium. Two experimental modes, increase flow velocity and change flow direction, were adopted in this study. The tests were conducted using quartz powder as the particles and quartz sand as the porous media to study the response of detachment characteristics to changes in particle diameter ( $$d_{s}$$ , with median diameter 18 and 41 $$\upmu $$ m) and grain diameter ( $$d_{p}$$ , with median diameter 0.36 and 1.25 mm). Breakthrough curves after the second peak were well described by a double exponential model with parameters of weight coefficient and detachment coefficient. This study shows that both modes can change the detach rate of deposited particles observably, and detach rate is affected by the value of flow velocity greatly.

Fluorescence Spectroscopy as a Tool to Unravel the Dynamics of Protein Nanoparticle Formation by Liquid Antisolvent Precipitation

Protein-based particles are very promising colloidal systems for protection and controlled release applications in the food, cosmetics and pharmaceutical sector. One technique to produce these protein colloidal particles is liquid antisolvent precipitation (LAS). Despite the simplicity and versatility of LAS, not much is known about the protein conformational changes and interactions that are at the basis of the particle formation process. In this study, steady state fluorescence experiments using intrinsic fluorophores were evaluated as a tool to unravel the dynamics of the protein nanoparticle formation. Colloidal whey protein isolate and gliadin particles were produced by LAS. Changes in particle diameter (distribution), polydispersity index and photophysical properties of intrinsic fluorophores were monitored as a function of antisolvent concentration. By combining dynamic light scattering with photophysical data, a model of the changes occurring during particle formation and disintegration could be proposed. The results suggest that particle formation and disintegration are fully reversible processes during which the main changes in protein conformation (around the fluorescent probes) occur at the same antisolvent concentrations. In principle, steady state fluorescence measurements using intrinsic probes can indeed be used to effectively report on (part of the) conformational changes for both protein systems under study.

Experimental investigation of suspended particles transport through porous media: particle and grain size effect

ABSTRACTParticle and grain size may influence the transportation and deposition characteristics of particles within pollutant transport and within granular filters that are typically used in wastewater treatment. We conducted two-dimensional sandbox experiments using quartz powder as the particles and quartz sand as the porous medium to study the response of transportation and deposition formation to changes in particle diameter (ds, with median diameter 18, 41, and 82 μm) and grain diameter (dp, with median diameter 0.36, 1.25, and 2.82 mm) considering a wide range of diameter ratios (ds/dp) from 0.0064 to 0.228. Particles were suspended in deionized water, and quartz sand was used as the porous medium, which was meticulously cleaned to minimize any physicochemical and impurities effects that could result in indeterminate results. After the experiments, the particle concentration of the effluent and particle mass per gram of dry sands were measured to explore changes in transportation and deposition characteristics under different conditions. In addition, a micro-analysis was conducted to better analyse the results on a mesoscopic scale. The experimental observation analyses indicate that different diameter ratios (ds/dp) may lead to different deposit formations. As ds/dp increased, the deposit formation changed from ‘Random Deposition Type’ to ‘Gradient Deposition Type’, and eventually became ‘Inlet Deposition Type’.

Laser diagnostics of pulverized coal combustion in O2/N2 and O2/CO2 conditions: velocity and scalar field measurements

Optical diagnostic techniques are applied to a 21 kW laboratory-scale pulverized coal–methane burner to map the reaction zone during combustion, in mixtures with varying fractions of O2, N2 and CO2. Simultaneous Mie scatter and OH planar laser-induced fluorescence (PLIF) measurements have been carried out to study the effect of the oxidizer/diluent concentrations as well as the coal-loading rate. The spatial distribution of soot is captured using laser-induced incandescence (LII). Additionally, velocity profiles at selected axial locations are measured using the pairwise two-dimensional laser Doppler velocimetry technique. The OH PLIF images capture the reaction zones of pilot methane–air flames and the variation of the coal flame structure under various O2/CO2 compositions. Coal particles devolatilize immediately upon crossing the flame interface, so that the Mie scatter signal almost vanishes. Increasing coal-loading rates leads to higher reaction rates and shorter flames. LII measurements show that soot is formed primarily in the wake of remaining coal particles in the product regions. Finally, differences in the mean and RMS velocity field are explained by the combined action of thermal expansion and the changes in particle diameter between reacting and non-reacting flows.

Beverage emulsions: Comparison among nanoparticle stabilized emulsion with starch and surfactant stabilized emulsions

Emulsions are widely used in beverages to impart desired appearance and flavor to the products. Ring formation in beverages with emulsions during thermal processing and storage is one of the key challenges. This study was aimed at comparing the relative effectiveness of silica nanoparticle based emulsifiers with surfactant and biopolymer based emulsifier (modified starch) in influencing physical stability of emulsions in a model juice. The stability of emulsions was measured by characterizing changes in emulsion droplet size, zeta potential, UV–vis absorbance and visual evaluation of phase separation or ring formation in both primary emulsions and beverage emulsions as a function of storage time. The influence of thermal processing on stability of emulsions both immediately after processing and upon storage was evaluated. The thermal processing conditions simulated both high temperature short time and low temperature long time pasteurization conditions. The results demonstrate that the mean droplet diameter of primary emulsions stabilized by selected emulsifiers was stable during storage for 21days with and without pasteurization. Based on measurements of mean droplet diameter and visible ring formation, polyoxyethylene sorbitan monolaurate (tween-20) stabilized emulsion was not stable in a model juice and the stability of this emulsion was further reduced with thermal processing. In contrast, starch and silica stabilized emulsions in a model juice did not show significant changes in particle diameter or visible ring formation during storage with and without prior thermal processing, although starch stabilized emulsion did show a decrease in absorbance during storage. Zeta potential measurements in a model juice indicate that the surface properties of emulsions were significantly distinct from those of primary emulsion, indicating interaction of juice components with the emulsion interface influencing the surface charge at the interface. These changes in zeta potential of emulsion droplets did not correlate with reduced stability of the emulsions. Overall, the results demonstrate that nanoparticle stabilized emulsions can improve stability of emulsion in beverages as compared to surfactant and biopolymer stabilized emulsions and provides a comprehensive matrix to evaluate stability of emulsions in beverages.

Monitoring inverse-phase emulsion polymerization using electrical impedance spectroscopy

Inverse-phase emulsion polymerization (IEP) is a widely used technique for synthesizing polyacrylamide, a product in demand for water treatment and in food industries. Despite its extensive application, challenges exist in controlling and monitoring IEP due to the relatively high polymerization rate and high viscosity of polyacrylamide. We investigated IEP of acrylamide with an industrial solvent, D80, as the oil phase, azobisisobutyronitrile as an oil-soluble initiator, and a mixture of sorbitan monooleate (Span 80) and poly(oxyethylene sorbitan trioleate) (Tween 85) as emulsifier. Our study showed that electrical impedance spectroscopy (EIS) is an efficient tool for monitoring the progress and characteristics of IEP in real time. The results revealed that the monomer conversion and polymerization rate correlate well with on-line capacitance measurements using EIS at an appropriate frequency, while changes in conductance correlate well with changes in particle diameter which was validated using an off-line dynamic light scattering method. © 2014 Society of Chemical Industry

Oriented attachment explains cobalt ferrite nanoparticle growth in bioinspired syntheses

Oriented attachment has created a great debate about the description of crystal growth throughout the last decade. This aggregation-based model has successfully described biomineralization processes as well as forms of inorganic crystal growth, which could not be explained by classical crystal growth theory. Understanding the nanoparticle growth is essential since physical properties, such as the magnetic behavior, are highly dependent on the microstructure, morphology and composition of the inorganic crystals. In this work, the underlying nanoparticle growth of cobalt ferrite nanoparticles in a bioinspired synthesis was studied. Bioinspired syntheses have sparked great interest in recent years due to their ability to influence and alter inorganic crystal growth and therefore tailor properties of nanoparticles. In this synthesis, a short synthetic version of the protein MMS6, involved in nanoparticle formation within magnetotactic bacteria, was used to alter the growth of cobalt ferrite. We demonstrate that the bioinspired nanoparticle growth can be described by the oriented attachment model. The intermediate stages proposed in the theoretical model, including primary-building-block-like substructures as well as mesocrystal-like structures, were observed in HRTEM measurements. These structures display regions of substantial orientation and possess the same shape and size as the resulting discs. An increase in orientation with time was observed in electron diffraction measurements. The change of particle diameter with time agrees with the recently proposed kinetic model for oriented attachment.

Humidity induced burning rate degradation of an iron oxide catalyzed ammonium perchlorate/HTPB composite propellant

Burn rate degradation of ammonium perchlorate based solid propellants can occur when moisture diffuses in and out of the material while exposed to fluctuating ambient humidity conditions. For high burn rate propellants with significant mass fractions of ammonium perchlorate particles less than 10μm, small changes in particle diameter can significantly alter the total oxidizer surface area resulting in propellant burning rate reductions. Ammonium perchlorate propellant samples are aged at various relative humidity and constant temperature. The samples are subsequently dried to equal moisture content and examined by SEM and optical microscopy. The propellant samples are combusted in a closed combustion bomb to measure the burning rate of the aged samples. The results show a clear correlation of the burning rate degradation and the level of humidity exposure. Evidence indicates that the degradation is a result of ammonium perchlorate crystal size growth and surface morphology changes reducing the available surface area. The changes are shown to be correlated with the moisture content of the aging environment.

Microfluidic device for trapping and monitoring three dimensional multicell spheroids using electrical impedance spectroscopy

In this paper, we report the design, fabrication, and testing of a lab-on-a-chip based microfluidic device for application of trapping and measuring the dielectric properties of microtumors over time using electrical impedance spectroscopy (EIS). Microelectromechanical system (MEMS) techniques were used to embed opposing electrodes onto the top and bottom surfaces of a microfluidic channel fabricated using Pyrex substrate, chrome gold, SU-8, and polydimethylsiloxane. Differing concentrations of cell culture medium, differing sized polystyrene beads, and MCF-7 microtumor spheroids were used to validate the designs ability to detect background conductivity changes and dielectric particle diameter changes between electrodes. The observed changes in cell medium concentrations demonstrated a linear relation to extracted solution resistance (Rs), while polystyrene beads and multicell spheroids induced changes in magnitude consistent with diameter increase. This design permits optical correlation between electrical measurements and EIS spectra.

Lipid Encapsulated Phenolic Compounds by Fluidization

Phenolic compounds exhibit antioxidant and antimicrobial activities with applications as functional food and feed additives. Ferulic acid, a phenolic compound present in grain crops and lignocellulose biomass, was encapsulated with saturated triglycerides using a laboratory fluidizer. Stability of the encapsulated ferulic acid particles was evaluated over a 3 month storage period. Laser light scattering and fluorescence spectroscopy were used to characterize particles. Loss of ferulic acid from particles was measured by emission spectra. Results showed no significant changes in particle diameter, 717.6 nm ± 28.4 nm, or loss of ferulic acid from lipid particles during storage. This combination of renewable materials, physical processing techniques, and nondestructive analytical methods promotes sustainable agriculture.

Fixed bed property changes during scCO2 extraction of natural materials – Experiments and modeling

Properties of the fixed bed of plant material during the extraction with scCO2 from rapeseed were investigated for the two types of mechanical pretreatments: flaking and impact milling. Obtained results indicated that particle density, bulk density of the bed and consequently the bed porosity changed during the extraction. In the case of flaked rapeseed, the change of particle diameter was also detected and quantified. On the basis of experimental data linear relationships between the particle density/bed porosity/mean particle diameter and oil content in solid were established. Mathematical model based on the mass balances for the supercritical and solid phase which took into account particle density, bed porosity and particle diameter (for flaked plant material) as variables was derived. The proposed model described experimental data with high accuracy. Possible error due to neglecting the change of the fixed bed properties was presented as well.

Apolipoprotein A-II-mediated Conformational Changes of Apolipoprotein A-I in Discoidal High Density Lipoproteins

It is well accepted that HDL has the ability to reduce risks for several chronic diseases. To gain insights into the functional properties of HDL, it is critical to understand the HDL structure in detail. To understand interactions between the two major apolipoproteins (apos), apoA-I and apoA-II in HDL, we generated highly defined benchmark discoidal HDL particles. These particles were reconstituted using a physiologically relevant phospholipid, 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) incorporating two molecules of apoA-I and one homodimer of apoA-II per particle. We utilized two independent mass spectrometry techniques to study these particles. The techniques are both sensitive to protein conformation and interactions and are namely: 1) hydrogen deuterium exchange combined with mass spectrometry and 2) partial acetylation of lysine residues combined with MS. Comparison of mixed particles with apoA-I only particles of similar diameter revealed that the changes in apoA-I conformation in the presence of apoA-II are confined to apoA-I helices 3-4 and 7-9. We discuss these findings with respect to the relative reactivity of these two particle types toward a major plasma enzyme, lecithin:cholesterol acyltransferase responsible for the HDL maturation process.

Aging induced changes on NEXAFS fingerprints in individual combustion particles

Abstract. Soot particles can significantly influence the Earth's climate by absorbing and scattering solar radiation as well as by acting as cloud condensation nuclei. However, despite their environmental (as well as economic and political) importance, the way these properties are affected by atmospheric processing of the combustion exhaust gases is still a subject of discussion. In this work, individual soot particles emitted from two different vehicles, a EURO 2 transporter, a EURO 3 passenger car, and a wood stove were investigated on a single-particle basis. The emitted exhaust, including the particulate and the gas phase, was processed in a smog chamber with artificial solar radiation. Single particle specimens of both unprocessed and aged soot were characterized using near edge X-ray absorption fine structure spectroscopy (NEXAFS) and scanning electron microscopy. Comparison of NEXAFS spectra from the unprocessed particles and those resulting from exhaust photooxidation in the chamber revealed changes in the carbon functional group content. For the wood stove emissions, these changes were minor, related to the relatively mild oxidation conditions. For the EURO 2 transporter emissions, the most apparent change was that of carboxylic carbon from oxidized organic compounds condensing on the primary soot particles. For the EURO 3 car emissions oxidation of primary soot particles upon photochemical aging has likely contributed as well. Overall, the changes in the NEXAFS fingerprints were in qualitative agreement with data from an aerosol mass spectrometer. Furthermore, by taking full advantage of our in situ microreactor concept, we show that the soot particles from all three combustion sources changed their ability to take up water under humid conditions upon photochemical aging of the exhaust. Due to the selectivity and sensitivity of the NEXAFS technique for the water mass, also small amounts of water taken up into the internal voids of agglomerated particles could be detected. Because such small amounts of water uptake do not lead to measurable changes in particle diameter, it may remain beyond the limits of volume growth measurements, especially for larger agglomerated particles.

Screening of a Model for the Distribution of Dye in Dye-Encapsulated Silica Through the Gradual Etching of the Outermost Silica Layer Using Hydrofluoric Acid

Monodispersed spherical silica particles emitting blue light were prepared by incorporating 2,5-bis(5-tert-butyl-2-benzoxazolyl)thiophene (BBOT) into a silica matrix. The morphological and photoluminescent properties were investigated to confirm the proper incorporation of BBOT into the silica matrix, using an electron microscope and a fluorescence spectrometer. Four possible models representing the distribution of the dye molecules in a dye-encapsulated silica particle were proposed. To analyze the distribution of the BBOT dye in the BBOT-encapsulated silica, the fluorescent emission intensity was measured while reducing the particle diameter by etching the outermost silica layer with hydrofluoric acid with 0-0.5 wt.% concentrations. The distribution of BBOT in a silica particle was investigated based on the relationship between the changes in particle diameter and the changes in emission intensity. The emission intensity of the BBOT-encapsulated silica particle oscillated with the decreasing particle diameter. This result supported the multilayered model. Information regarding the distribution of the dye in the silica matrix will provide valuable information for understanding the formation mechanism of dye-encapsulated silica.

Determination of Agglomeration Kinetics in Nanoparticle Dispersions

The direct application of nanoparticles as nonsupported adsorbents and catalysts is of high interest since they offer high surface areas with reduced mass transfer limitations. However, the natural tendency of these materials to aggregate, even faster when at high temperatures, makes the agglomeration process an important phenomenon to be studied, understood and, eventually controlled. A method to obtain the kinetics of nanoparticle agglomeration processes is presented in this paper. This analysis was based on the change of particle diameter during aggregation. The kinetic expression was validated with a series of experiments where the growth of Fe2O3 nanoparticles immersed in base oil was followed at different times, temperatures, and particle concentrations. Results revealed the nature of the particle agglomeration process in the ranges of the experimental conditions; they indicated that physical adhesion, more than chemical binding, is the determining mechanism for agglomeration of Fe2O3 nanoparticles immersed in base oil.

Tuning of the fluorescence wavelength of CdTe quantum dots with 2 nm resolution bysize-selective photoetching

Photoetching of CdTe nanocrystals was applied to thiol-capped CdTe quantum dots (QDs)to control their fluorescence wavelength. CdTe QDs with a high quantum yield (49%) weresynthesized in aqueous solution, and they were successfully photoetched in strong alkaline (pH = 13.5) conditions. When monochromatic light was used, size-selective photoetching could beconducted; the photoetching proceeded until the band gap energy of the CdTe QDsincreased to the energy corresponding to the wavelength of the irradiating light.As a result, a good linear relationship was obtained between the wavelength ofthe irradiating light and that of the fluorescence peak. The resulting CdTe QDsexhibited a fluorescence peak with an FWHM value as small as 23.5 nm, indicatingpreparation of highly monodispersed nanocrystals. The high quantum yield (ca.45%) was maintained after the photoetching. Very fine tuning of the fluorescencewavelength with 2 nm resolution was achieved by changing the wavelength ofthe irradiating light by 2 nm. Theoretical calculation of the quantum size effects(effective mass approximation) predicts that a difference in the band gap fluorescencewavelength of 2 nm corresponds to a change in particle diameter of ca. 0.02 nm.

On the physical interpretation of the initial bending of a Shapiro–Konopicky–Heckel compression profile

The relationship between the natural logarithm of the tablet porosity and the applied pressure is used to describe the compression behavior of a powder. Such a relationship, here referred to as a Shapiro–Konopicky–Heckel ( SKH) profile, is usually divided into three regions, of which the first often is non-linear. The objective of this work was to address the question of the mechanisms controlling the compression and the bending of the first region of a SKH profile for dense particles. In this paper, the first region was described by the Shapiro General Compression Equation, from which a compression parameter was derived as a measure of the bending. The results indicate that for powders undergoing significant particle rearrangement at low applied pressures, the particle rearrangement is the major cause for the initial bending of the SKH profile. For powders showing limited particle rearrangement, the initial bending is mainly caused by the change in particle diameter due to particle fragmentation. It is concluded that the evaluation of the first region of a SKH profile in terms of bending may be used to assess particle fragmentation. The SKH profile could hence be a useful tool to describe powder compression behavior in terms of particle fragmentation and particle deformation from one single compression analysis.

Hygroscopicity of the submicrometer aerosol at the high-alpine site Jungfraujoch, 3580 m a.s.l., Switzerland

Abstract. Data from measurements of hygroscopic growth of submicrometer aerosol with a hygroscopicity tandem differential mobility analyzer (HTDMA) during four campaigns at the high alpine research station Jungfraujoch, Switzerland, are presented. The campaigns took place during the years 2000, 2002, 2004 and 2005, each lasting approximately one month. Hygroscopic growth factors (GF, i.e. the relative change in particle diameter from dry diameter, D0, to diameter measured at higher relative humidity, RH) are presented for three distinct air mass types, namely for: 1) free tropospheric winter conditions, 2) planetary boundary layer influenced air masses (during a summer period) and 3) Saharan dust events (SDE). The GF values at 85% RH (D0=100 nm) were 1.40±0.11 and 1.29±0.08 for the first two situations while for SDE a bimodal GF distribution was often found. No phase changes were observed when the RH was varied between 10–90%, and the continuous water uptake could be well described with a single-parameter empirical model. The frequency distributions of the average hygroscopic growth factors and the width of the retrieved growth factor distributions (indicating whether the aerosol is internally or externally mixed) are presented, which can be used for modeling purposes. Measurements of size resolved chemical composition were performed with an aerosol mass spectrometer in parallel to the GF measurements. This made it possible to estimate the apparent ensemble mean GF of the organics (GForg) using inverse ZSR (Zdanovskii-Stokes-Robinson) modeling. GForg was found to be ~1.20 at aw=0.85, which is at the upper end of previous laboratory and field data though still in agreement with the highly aged and oxidized nature of the Jungfraujoch aerosol.