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Gas-phase interactions with aerosol particle surfaces are involved in the physicochemical evolution of our atmosphere as well as those of other planets (e.g., Mars). However, our understanding of interfacial properties remains limited, especially in natural systems with complex structures and chemical compositions. In this study, a surface-sensitive technique, ambient pressure X-ray photoelectron spectroscopy, combined with molecular dynamics simulations, were employed to investigate a Martian salt analogue sampled on Earth, including a comparison with a typical sulfate salt (MgSO4) commonly found on both Earth and Mars. For MgSO4, elemental depth profiles show that there always exists residual water on the salt surface, even at very low relative humidity (RH). When RH rises, water is well mixed with the salt within the probed depth of a few nanometers. The Cl-- and SO42--bearing Martian salt analogue surface is extremely sensitive to water vapor, and the surface layer is already fully solvated at very low RH. Unexpected ion-selective surface behavior are observed as RH rises, where the chloride is depleted, while another major anion, sulfate, is relatively enhanced when the surface becomes solvated. Molecular dynamics simulations suggest that, upon solvation with the formation of an ion-concentrated water layer adsorbed on the crystal substrate, monovalent ions experience a higher degree of dehydration than the divalent ions. Thus, to complete their first solvation shell, monovalent ions are driven away from the surface and move toward the water accumulated at the hydrophilic crystal structure., ACS Earth and Space Chemistry, 7 (2), ISSN:2472-3452

ConspectusLiquids are of overarching importance for the atmosphere, as 72% of the Earth's surface is covered by oceans, a large number of liquid aerosol particles fill the air, and clouds hold a tiny but critical fraction of Earth's water in the air to influence our climate and hydrology, enabling the lives of humans and ecosystems. The surfaces of these liquids provide the interface for the transfer of gases, for nucleation processes, and for catalyzing important chemical reactions. Coupling a range of spectroscopic tools to liquid microjets has become an important approach to better understanding dynamics, structure, and chemistry at liquid interfaces. Liquid microjets offer stability in vacuum and ambient pressure environments, thus also allowing X-ray photoelectron spectroscopy (XPS) with manageable efforts in terms of differential pumping. Liquid microjets are operated at speeds sufficient to allow for a locally equilibrated surface in terms of water dynamics and solute surface partitioning. XPS is based on the emission of core-level electrons, the binding energy of which is selective for the element and its chemical environment. Inelastic scattering of electrons establishes the probing depth of XPS in the nanometer range and thus its surface sensitivity.In this Account, we focus on aqueous solutions relevant to the surface of oceans, aqueous aerosols, or cloudwater. We are interested in understanding solvation and acid dissociation at the interface, interfacial aspects of reactions with gas-phase reactants, and the interplay of ions with organic molecules at the interface. The strategy is to obtain a link between the molecular-level picture and macroscopic properties and reactivity in the atmospheric context.We show consistency between surface tension and XPS for a range of surface-active organic species as an important proof for interrogating an equilibrated liquid surface. Measurements with organic acids and amines offer important insight into the question of apparent acidity or basicity at the interface. Liquid microjet XPS has settled the debate of the surface enhancement of halide ions, shown using the example of bromide and its oxidation products. Despite the absence of a strong enhancement for the bromide ion, its rate of oxidation by ozone is surface catalyzed through the stabilization of the bromide ozonide intermediate at the interface. In another reaction system, the one between Fe

Water is prevalent on all atmospheric particle surfaces, independent of material, phase state or water vapor saturation ratio. Under subsaturated relative humidity conditions, water occurs as reversibly adsorbed layers on solid surfaces or as concentrated aqueous solutions in aqueous particles, exhibiting different composition at the interface than in the bulk. The hydrogen bonding structure at these interfaces is affected by interactions with the substrate on solid surfaces and by ions and ionic or neutral surfactants on aqueous solutions. The water structure and its interplay with hydrated substrate features, hydrated free ions or neutral solutes or surfactant head groups are playing a key role in many chemical and physical processes at these interfaces. We have developed X-ray photoelectron spectroscopy (XPS) and electron yield near edge X-ray absorption fine structure (NEXAFS) spectroscopy to explore the interfacial water structure in situ. We will present examples of the structure of adsorbed water on different Feldspar surfaces, on silver iodide and titanium dioxide. We will also show cases related to the water structure on aqueous solutions containing salts or different surfactant species.

Iodine chemistry is implicated in atmospheric chemistry and can lead to the formation of several oxides such as HOI, I2, IO, OIO, and finally I2O5 or HIO3, which may nucleate as nanoparticles relevant for cloud formation in remote environments (Saiz-Lopez et al., 2012, Finkenzeller et al., 2022). These oxides can be formed through reaction with oxidants or other halogen compounds in the gas phase or the particle phase. Most of the iodide oxidation processes have been suggested to be enhanced at interfaces, similar to those involving other halogen species, either due to the surface propensity of intermediates (Artiglia et al., 2017) or the iodine species itself (Moreno and Beaza-Romero, 2019). However, no data are available about the surface concentration of iodine species other than iodide. After two decades of research into the surface propensity of iodide and bromide, the picture emerges that their surface propensity is not as extreme as initially thought (Jungwirth and Tobias, 2002; Ghosal et al., 2005; Olivieri et al., 2018).Liquid jet X-ray photoelectron spectroscopy (XPS) experiments have been carried out at the SIM beamline at the Swiss Light Source. Acquisition of kinetic energy dependent (thus at different probing depth) I3d, I4d core level and valence level spectra has been done for iodide, iodate and iodic acid. This allows to retrieve the surface propensity of these iodine species at the aqueous solution – air interface. HIO3, HOI and iodide surface propensity has also been investigated by Ab Initio Molecular Dynamics computation at the revPBE-D3/DZVP-SR level using CP2K software (Khüne et al., 2020).Artiglia et al., Nat. Commun., 8, 700 (2017). Finkenzeller et al., Nat. Chem. (2022). Ghosal et al., Science, 307, 563 (2005). Jungwirth and D. Tobias, J. Phys. Chem. B, 106, 25, 6361 (2002). D. Kühne et al., J. Chem. Phys., 152, 194103 (2020). Moreno and M. T. Baeza-Romero, 21, 19835 (2019). Olivieri et al., J. Phys, Chem. B, 122, 2, 910 (2018). Saiz-Lopez et al., Chem. Rev., 112, 1773 (2012).

Secondary organic aerosol (SOA) can undergo atmospheric aging processes that alter their impact on climate, air quality and human health. Transition metals, such as iron, can age SOA particles through catalytic chemical reactions within the condensed phase. Iron-containing particles originating from e.g., mineral dust, often become internally mixed with SOA, forming iron-containing SOA particles through various atmospheric processes, such as coagulation, condensation or cloud processing. When acidic organic vapors condense on iron-containing mineral dust particles, they can cause dissolution of minerals followed by iron-organic complex formation. Iron-organic complexes are common in atmospheric particles and can generate reactive oxygen species within a particle through dark peroxide and photochemical reactions (i.e., Fenton chemistry), leading to further aging of the particles by functionalization or fragmentation of organic species. Such particle-phase aging processes can considerably change the particle chemical composition. However, detailed understanding of these compositional changes is lacking to date, and hence considerable uncertainties still exist regarding the impact aged particles have on air quality and climate.Here, we present detailed information on the chemical composition of iron-containing SOA particles and how it evolves over time. Particles were produced by forming SOA via α-pinene ozonolysis on both ammonium sulfate or iron-containing seed particles in an atmospheric simulation chamber under dark conditions. This allowed us to probe the impacts of iron on dark e.g., peroxide reactions and aerosol aging in the absence of photochemical driven Fenton chemistry, i.e., simulating nocturnal aging processes. Experiments were also conducted under both wet (relative humidity (RH) >80%) and dry (RH

Recent studies have suggested that injection of solid particles such as alumina (Al2O3) and calcite (CaCO3) instead of SO2 for stratospheric aerosol intervention could reduce some of the adverse side effects of SAI such as ozone depletion, stratospheric heating, and changes in diffuse radiation. However, the expected improvements from alteration of stratospheric chemistry are subject to large uncertainties. We constrain some of these uncertainties by experimental work on calcite particles using elastic recoil detection analysis (ERDA) and in-situ experiments using X-ray photoelectron spectroscopy (XPS). Subsequently, we use a global aerosol-chemistry climate model that, for the first time, interactively couples microphysical and chemical processes of solid calcite and alumina particles as well as liquid sulfuric acid aerosols with model radiation and transport. Notably, SAI by solid particles only leads to more effective radiative forcing per aerosol burden compared to sulfuric acid aerosols, not per injected mass. However, reduced stratospheric warming remains a major advantage of solid particles. Furthermore, different assumptions on the heterogeneous chemistry of solid particles, based on the available experimental data, result in drastically different impacts on stratospheric composition, in particular, ozone. For alumina particles, which are thought to not undergo chemical aging during their stratospheric residence time we present a sensitivity analysis for heterogenous reactions to quantify uncertainty. For the alkaline calcite particles, which are thought to undergo chemical aging in the stratosphere via reaction with acids (e.g., HCl, HNO3, H2SO4) we find even larger uncertainties due to unknown reaction pathways and highly uncertain rates under stratospheric conditions. The large uncertainty in predicted stratospheric ozone changes can only be reduced via substantial additional laboratory experiments under stratospheric conditions, i.e., partial pressures of relevant gases (e.g., HCl, HNO3, H2SO4), temperatures < 220 K, relative humidity < 1% and realistic UV irradiance. From the present perspective, sulfur-based SAI has significantly lower uncertainty than injection of solid particles, which have significantly reduced stratospheric heating but very large uncertainties in impacts on stratospheric composition.

Atmospheric aerosol particles play an important role for air quality and climate. Secondary organic aerosol (SOA) make up a significant mass fraction of these particles. SOA particles mostly forms from oxidation of gases, followed by gas-particle conversion of the oxidation products. Due to the variety of precursors and oxidation pathways involved in SOA formation, atmospheric SOA rank among the least understood aerosol types. To assess the impacts of SOA particles on air pollution and climate, knowledge of the number of phases in internal mixtures of different SOA types is critical. For example, gas-particle partitioning of organic species, and thus ultimately ambient SOA mass concentration, strongly depend on the number of phases in SOA particles. Atmospheric models traditionally assumed that different SOA types form a single condensed organic phase when internally mixed in individual particles. In case of mixed SOA particles with a single condensed phase uptake of semi-volatile vapors are enhanced, due to a lowering of the activities in the organic aerosol phase, and hence a lowering of the equilibrium partial pressure. By contrast, the equilibrium partial pressure is greater if the different SOA types form separate phases due to repulsive intermolecular forces between immiscible organic molecules. Consequently, enhancement of vapor uptake and ambient SOA mass concentrations will be smaller or absent in the case of phase-separated SOA particles.Here, using fluorescence microscopy, we directly observed the number of phase in individual particles containing mixtures of different SOA types. A total of 6 different SOA types were generated in environmental chambers from oxidation of single precursors. This included both biogenic and anthropogenic SOA types, having elemental oxygen-to-carbon (O/C) ratios between 0.34 and 1.05, covering values characteristic for aged and fresh atmospheric SOA. The number of phases of all possible internal mixtures of two different SOA types, termed SOA+SOA particles, was investigated as a function of humidity between 90% and 0% relative humidity (RH). We found that the number of phases was independent of RH within the range investigated and that 6 out of 15 SOA+SOA mixtures resulted in particles with two condensed organic phases. The observation of phase separated SOA+SOA particles challenges the approach of assuming a single condensed organic phase when representing SOA formation in atmospheric models. Specifically, we demonstrate that the difference in the average O/C ratio between the two SOA types of a mixture (ΔO/C) is a good predictor of the number of phases in particles that are internal mixtures of different SOA types: two-phase SOA+SOA particles formed for ΔO/C ≥ 0.47, while one-phase SOA+SOA particles formed for ΔO/C < 0.47. This threshold ΔO/C provides a simple, yet powerful parameter to predict whether mixtures of fresh and aged SOA particles form one- or two-phase particles in models.

The reaction of ozone with sea-salt derived bromide is relevant for marine boundary layer atmospheric chemistry. The oxidation of bromide by ozone is enhanced at aqueous interfaces. Ocean surface water and sea spray aerosol are enriched in organic compounds, which may also have a significant effect on this reaction at the interface. Here, we assess the surface propensity of cationic tetrabutylammonium at the aqueous liquid-vapor interface by liquid microjet X-ray photoelectron spectroscopy (XPS) and the effect of this surfactant on ozone uptake to aqueous bromide solutions. The results clearly indicate that the positively charged nitrogen group in tetrabutylammonium (TBA), along with its surface activity, leads to an enhanced interfacial concentration of both bromide and the bromide ozonide reaction intermediate. In parallel, off-line kinetic experiments for the same system demonstrate a strongly enhanced ozone loss rate in the presence of TBA, which is attributed to an enhanced surface reaction rate. We used liquid jet XPS to obtain detailed chemical composition information from the aqueous-solution-vapor interface of mixed aqueous solutions containing bromide or bromide and chloride with and without TBA surfactant. Core level spectra of Br 3d, C 1s, Cl 2p, N 1s, and O 1s were used for this comparison. A model was developed to account for the attenuation of photoelectrons by the carbon-rich layer established by the TBA surfactant. We observed that the interfacial density of bromide is increased by an order of magnitude in solutions with TBA. The salting-out of TBA in the presence of 0.55 M sodium chloride is apparent. The increased interfacial bromide density can be rationalized by the association constants for bromide and chloride to form ion-pairs with TBA. Still, the interfacial reactivity is not increasing simply proportionally with the increasing interfacial bromide concentration in response to the presence of TBA. The steady state concentration of the bromide ozonide intermediate increases by a smaller degree, and the lifetime of the intermediate is 1 order of magnitude longer in the presence of TBA. Thus, the influence of cationic surfactants on the reactivity of bromide depends on the details of the complex environment at the interface. ISSN:2472-3452

A Viewpoint regarding our recently published Letter in this Journal (Gladich et al.

This article, the eighth in the series, presents kinetic and photochemical data sheets evaluated by the IUPAC Task Group on Atmospheric Chemical Kinetic Data Evaluation. It covers the gas-phase thermal and photochemical reactions of organic species with four, or more, carbon atoms (≥ C4) available on the IUPAC website in 2021, including thermal reactions of closed-shell organic species with HO and NO3 radicals and their photolysis. The present work is a continuation of volume II (Atkinson et al., 2006), with new reactions and updated data sheets for reactions of HO (77 reactions) and NO3 (36 reactions) with ≥ C4 organics, including alkanes, alkenes, dienes, aromatics, oxygenated, organic nitrates and nitro compounds in addition to photochemical processes for nine species. The article consists of a summary table (Table 1), containing the recommended kinetic parameters for the evaluated reactions, and a supplement containing the data sheets, which provide information upon which recommendations are made.

Earth's snow cover is very dynamic on diurnal timescales. The changes to the snow structure during this metamorphism have wide-ranging impacts on processes such as avalanche formation and on the capacity of surface snow to exchange trace gases with the atmosphere. Here, we investigate the influence of dry metamorphism, which involves fluxes of water vapour, on the chemical reactivity of bromide in the snow. To this end, the heterogeneous reactive loss of ozone in the dark at a concentration of 5×1012-6× 1012 molec. cm-3 is investigated in artificial, shock-frozen snow samples doped with 6.2μM sodium bromide and with varying metamorphism history. The oxidation of bromide in snow is one reaction initiating polar bromine releases and ozone depletion. We find that the heterogeneous reactivity of bromide is completely absent from the air-ice interface in snow after 12 d of temperature gradient metamorphism, and we suggest that the burial of non-volatile bromide salts occurs when the snow matrix is restructuring during metamorphism. Impacts on polar atmospheric chemistry are discussed. © Author(s) 2020., Atmospheric Chemistry and Physics, 20 (21), ISSN:1680-7375, ISSN:1680-7367

Since implementation of the laparoscopic approach for removal of the gallbladder in the early 90s, a shift in numbers from open cholecystectomy (OC) to laparoscopic cholecystectomy (LC) has been observed. Despite initial reservations, LC has become the most favoured technique in the past 3 decades. Consecutive technical improvements support this trend. Considering this development, the question regarding the relevance of OC nowadays inevitably arises. This study represents a literature review performed in PubMed. Laparoscopic cholecystectomy has evolved to be the leading technique for cholecystectomy. This technique has become well established in elective as well as in acute indications. However, concomitant to increasing numbers of performed LC, the proportion of performed OC is declining, leading to a decreasing expertise and a lack in training in OC nowadays. However, in complex situations, when the operation strategy has to be changed to maintain patient safety, conversion to OC is the most common strategy. Owing to past and current developments, open cholecystectomy can hardly be assumed to be common surgical knowledge anymore. Hence, OC as bail-out strategy in cases of intraoperative difficulties must be critically evaluated. From this point of view, alternative patient management and treatment concepts should be considered to maintain patient safety.

La1–xSrxCoO3-δ perovskites are potential catalysts for the anodic reaction of alkaline water electrolyzers, i.e., the oxygen evolution reaction (OER). It is well-known that La1–xSrxCoO3−δ perovskit...

The ongoing COVID-19 pandemic has revealed that developing effective therapeutics against viruses might be outpaced by emerging variants,1–5 waning immunity,6–9 vaccine skepticism/hesitancy,10–12 lack of resources,13–16 and the time needed to develop virus-specific therapeutics,17,18 emphasizing the importance of non-pharmaceutical interventions as the first line of defense against virus outbreaks and pandemics.19–23 However, fighting the spread of airborne viruses has proven extremely challenging,23–28 much more if this needs to be achieved on a global scale and in an environmentally-friendly manner.29,30 Here, we introduce an aerosol filter made of granular material based on whey protein nanofibrils and iron oxyhydroxides nanoparticles. The material is environmentally-friendly, biodegradable, and composed mainly of a dairy industry byproduct.31 It features remarkable filtration efficiencies between 95.91% and 99.99% for both enveloped and non-enveloped viruses, including SARS-CoV-2, the influenza A virus strain H1N1, enterovirus 71, bacteriophage Φ6, and bacteriophage MS2. The developed material is safe to handle and recycle, with a simple baking step sufficient to inactivate trapped viruses. The high filtration efficiency, virtually-zero environmental impact, and low cost of the material illuminate a viable role in fighting current and future pandemics on a global scale.

Secondary organic aerosol (SOA) constitutes a large fraction of atmospheric aerosol. To assess its impacts on cli-mate and air pollution, knowledge of the number of phases in internal mixtures of different SOA types is required. Atmospheric models often assumed that different SOA types form a single phase when mixed. Here, we present visual observations of the number of phases formed after mixing different anthropogenic and biogenic SOA types. Mixing SOA types generated in environmental chambers with oxygen-to-carbon (O / C) ratios between 0.34 to 1.05, we found six out of fifteen mixtures of two SOA types to result in two phase particles. We demonstrate that the number of phases depends on the difference in the average O / C ratio between the two SOA types (Δ(O / C)). Using a threshold Δ(O / C) of 0.47, we can predict the phase behavior of over 90 % of our mixtures, with one- and two-phase particles predicted for Δ(O / C) < 0.47 and Δ(O / C) ≥ 0.47, respectively. This Δ(O / C) threshold further allows to predict if mixtures of fresh and aged SOA form one- or two-phase particles in the atmos-phere. In addition, we show that phase separated SOA particles form when mixtures of volatile organic compounds emitted from real trees are oxidized.

Fenton chemistry, involving the reaction between Fe

Precipitation is mostly formed via the ice phase in mixed phase clouds, and ice clouds are very relevant for Earths’ climate. Freezing or prevention of freezing is common to everyday life, e.g. for food and drug storage, icing and de-icing, etc. However, the ice nucleation process is not well understood, since it occurs on the size scale of clusters of molecules and time scales of molecular fluctuations. In this study, we have taken a step toward nanoscale observation of particles that nucleate ice by developing a new ice nucleation instrument, referred as the INXcell, which couples an ice nucleation environmental cell to the scanning transmission X-ray microscope (STXM) at the Swiss Light Source. We employ near-edge X-ray absorption fine-structure spectroscopy (NEXAFS) to map in situ chemical composition of ice nucleating particles with 35 × 35 nm2 spatial resolution. The main technical challenge was control of temperature, T, and thus relative humidity, RH, while maintaining X-ray transparency. In the INXcell, X-rays are focused onto a sample through a temperature-controlled aperture, which was modified to host a jet of nitrogen cooled down to 170 K. The cold jet impinges on the back surface of a sample exposed to water vapor to control sample temperature and thus RH. We used our unique spectroscopic and ice nucleation capability and investigated the heterogeneous freezing ability of ferrihydrite particles with and without coatings of citric acid. Ferrihydrite is an amorphous or poorly crystalline iron oxyhydroxide abundant in mineral dust and is difficult to identify with conventional XRD analysis. We confirmed that ferrihydrite could nucleate ice via immersion freezing and deposition ice nucleation, depending on whether or not the particles first take up water, respectively. When coating ferrihydrite with citric acid, mimicking organic coatings that aerosol particles obtain throughout their atmospheric lifetime, we observed a reduction in the efficiency to nucleate ice following freezing point depression. Spectroscopic identification of the coated ferrihydrite structure emplyed the iron and carbon X-ray absorption L-edges and K-edge, respectively. We also investigated feldspar particles coated with xanthan gum, a surrogate for a highly ice active mineral with a highly viscous organic coating. We observed that deposition ice nucleation occurred only below the RH dependent glass transition of xanthan gum. Using a newly developed stochastic freezing model (SFM) based on solution water activity, we reproduced average conditions and data scatter of the RH and T at which ice formed. Additionally, we ran our model with atmospheric idealized air parcel trajectories and found overall that deposition ice nucleation was the dominant heterogeneous freezing mechanism. Homogeneous ice nucleation subsequent to water uptake out-performed immersion freezing.

Recently, Koenig et al. [1] measured both gas phase iodine species and particulate iodine (iodate and iodide) in the lower stratosphere indicating that tropospheric multiphase redox reactions prevent poorly soluble gaseous iodine species from removal by wet deposition leading to injections of inorganic iodine into the lower stratosphere. This may influence stratospheric ozone depletion both indirectly through activation of iodide (I-) to molecular halogens and directly through the aqueous phase reaction of ozone (O3) with iodide. Also in the troposphere, measurements indicate higher than expected iodide to iodate ratios in the aerosol phase [2], suggesting the reaction of O3 with I- to be part of iodine cycling throughout the troposphere. The reaction of O3 with I- in the aqueous phase, leading to IO- and to I2 through the secondary reaction of IO- with I-, is rather well established and one of the main iodine source from oceans [3]. However, for the reaction in the aerosol phase, uncertainties exist with respect to the temperature dependence, effects of pH and ionic strength, and also the extent of a surface reaction pathway [4,5]. In addition, Sakamoto et al. [4] have suggested that from this reaction IO(g) may be released. The objectives of this work has been to determine the temperature dependence of the oxidation of I- by O3 as well as to have a better understanding of the parameters that lead to IO radical and I2 formation. We used a trough reactor [5] coupled to Cavity Enhanced – Differential Optical Absorption Spectroscopy (CE-DOAS) [6] to study the reactivity in dilute aqueous solution (273 – 291 K) and in concentrated ammonium sulfate solutions (255 – 291 K). Measurements at varying O3 mixing ratios indicate a substantial surface reaction component, especially at lower temperature. The IO/I2 ratio is in the range of 10-3 – 10-2. IO formation seems to result predominantly from a surface process. The experiments are also compared with results from theory.References[1] T. K. Koenig et al., PNAS, 117, 4 (2020).[2] Baker, A. R., and Yodle, C.: Atmos. Chem. Phys., 21, 13067-13076, 2021.[3] L. J. Carpenter et al., Nat. Geosci., 6 (2013).[4] Y. Sakamoto et al., J. Phys. Chem. A, 113, 27 (2009).[5] C. Moreno et al., Phys. Chem. Chem. Phys., 22 (2020)[6] L. Artiglia et al., Nat. Commun., 8 (2017).[7] M. Wang et al., Atmos. Meas. Tech., 14, (2021).

Aerosols and clouds are complex systems containing organic and inorganic species, which play central roles in atmospheric chemistry and physics, climate, air pollution and public health. Particularly chemical reactions which occur in the aqueous phase can change the composition and oxidizing capacity of the troposphere via the production and release of trace gas species. Iron(III)-carboxylate complexes impact the chemistry of the atmospheric aqueous phase due to their photochemistry which can trigger free radical chemistry generating reactive oxygen species (ROS), such as HO2 and H2O2. Several studies have highlighted the importance of iodine chemistry due to its capability to influence both oxidative capacity and radiative balance of the atmosphere. A previous work of this group demonstrated a direct link between carbonyl compounds, ROS and iodine chemistry [1]. Furthermore, observed ratios of iodide to iodate in aerosol particles and cloud droplets of the troposphere are much higher than expected [2, 3]. This is indicative of active chemical recycling of iodine between the gas and particle phases, which may be driven by not well understood reductive processes involving iodate, which is thermodynamically the most favored iodine form in the aqueous phase under oxidizing conditions.We performed coated wall flow tube experiments (CWFT) with aqueous films containing iodate and Iron(III)-citrate (fe-cit) using citric acid (CA) as a matrix since it is an established proxy for oxygenated atmospheric organic matter and with well characterized microphysical properties. The CWFT was coupled with a CE-DOAS instrument in order to detect I2 [4] resulting from iodate reduction. The results suggest that photochemistry promotes efficient iodate reduction, linked to the photochemical turnover of the iron(III)-carboxylate complex and to the depletion of the iodine reservoir. We speculate that reduction of iodate is driven by H2O2 according to the Bray-Liebhafsky mechanism, where H2O2 is provided by fe-cit photochemistry. 1. P. Corral Arroyo, et al., Atmospheric Chemistry and Physics, (2019)2. A.R. Baker and C. Yodle, Atmos. Chem. Phys. Discuss., 2021, 1 (2021)3. T.K. Koenig, et al., Sci Adv, 7, eabj6544 (2021)4. R. Thalman, et al., Journal of Quantitative Spectroscopy and Radiative Transfer, 147, 171 (2014)

Recently, Koenig et al. [1] measured both gas phase iodine species and particulate iodine (iodate and iodide) in the lower stratosphere indicating that tropospheric multiphase redox reactions prevent poorly soluble gaseous iodine species from removal by wet deposition leading to injections of inorganic iodine into the lower stratosphere. This may influence stratospheric ozone depletion both indirectly through activation of iodide to molecular halogens and directly through the aqueous phase reaction of ozone (O3) with iodide [2]. The product of this reaction, IO-, is reacting with I- to I2(g) under most circumstances. Sakamoto et al. [3] have suggested that in addition IO(g) may be formed. The primary reaction of iodide with O3 depends on pH. Solute strength effects and the extent of a surface reaction have not been sufficiently established [3,4].An hybrid ONIOM QM/MM method [5] has been used to investigate the reactivity of ozone on a iodide-containing slab of water. The reaction pathway has been determined both at the interface and in the bulk aqueous phase. Both singlet and triplet state surfaces are investigated as the triplet state can be reached through photoexcitation of ozone or by spin state change along the reaction coordinate. These theoretical calculations provide insight into the uptake process at the molecular scale. Comparisons with experimental measurements performed using a trough reactor [6] coupled to Cavity Enhanced – Differential Optical Absorption Spectroscopy (CE-DOAS) [7,8] are also discussed. References[1] T. K. Koenig et al., PNAS, 117, 4 (2020). [2] L. J. Carpenter et al., Nat. Geosci., 6 (2013).[3] Y. Sakamoto et al., J. Phys. Chem. A, 113, 27 (2009).[4] C. Moreno et al., Phys. Chem. Chem. Phys., 22 (2020)[5] L. W. Chung et al., Chem. Rev., 115, 12 (2015)[6] L. Artiglia et al., Nat. Commun., 8 (2017)[7] M. Wang et al., Atmos. Meas. Tech., 14, (2021).[8] R. Thalman and R. Volkamer, Atmos. Meas. Tech., 3, (2010).

Resorcinol and orcinol are simple members of the family of phenolic compounds present in particulate matter in the atmosphere; they are amphiphilic in nature and thus surface active in aqueous solution. Here, we used X-ray photoelectron spectroscopy to probe the concentration of resorcinol (benzene-1,3-diol) and orcinol (5-methylbenzene-1,3-diol) at the liquid-vapor interface of aqueous solutions. Qualitatively consistent surface propensity and preferential orientation was obtained by molecular dynamics simulations. Auger electron yield near-edge X-ray absorption fine structure (NEXAFS) spectroscopy was used to probe the hydrogen bonding (HB) structure, indicating that the local structure of water molecules near the surface of the resorcinol and orcinol solutions tends towards a larger fraction of tetrahedrally coordinated molecules than observed at the liquid-vapor interface of pure water. The order parameter obtained from the molecular dynamics simulations confirm these observations. This effect is being discussed in terms of the formation of an ordered structure of these molecules at the surface leading to patterns of hydrated OH groups with distances among them that are relatively close to those in ice. These results suggest that the self-assembly of phenolic species at the aqueous solution-air interface could induce freezing similar to the case of fatty alcohol monolayers and, thus, be of relevance for ice nucleation in the atmosphere. We also attempted at looking at the changes of the O 1b

Ice nucleation is one of the most uncertain microphysical processes, as it occurs in various ways and on many types of particles. To overcome this challenge, we present a heterogeneous ice nucleation study on deposition ice nucleation and immersion freezing in a novel cryogenic X-ray experiment with the capability to spectroscopically probe individual ice nucleating and non-ice nucleating particles. Mineral dust type particles composed of either ferrihydrite or feldspar were used and mixed with organic matter of either citric acid or xanthan gum. We observed in situ ice nucleation using scanning transmission X-ray microscopy (STXM) and identified unique organic carbon functionalities and iron oxidation state using near-edge X-ray absorption fine structure (NEXAFS) spectroscopy in the new in situ environmental ice cell, termed the ice nucleation X-ray cell (INXCell). Deposition ice nucleation of ferrihydrite occurred at a relative humidity with respect to ice, RHi, between ∼120–138% and temperatures, T ∼ 232 K. However, we also observed water uptake on ferrihydrite at the same T when deposition ice nucleation did not occur. Although, immersion freezing of ferrihydrite both in pure water droplets and in aqueous citric acid occurred at or slightly below conditions for homogeneous freezing, i.e. the effect of ferrihydrite particles acting as a heterogeneous ice nucleus for immersion freezing was small. Microcline K-rich feldspar mixed with xanthan gum was also used in INXCell experiments. Deposition ice nucleation occurred at conditions when xanthan gum was expected to be highly viscous (glassy). At less viscous conditions, immersion freezing was observed. We extended a model for heterogeneous and homogeneous ice nucleation, named the stochastic freezing model (SFM). It was used to quantify heterogeneous ice nucleation rate coefficients, mimic the competition between homogeneous ice nucleation; water uptake; deposition ice nucleation and immersion freezing, and predict the T and RHi at which ice was observed. The importance of ferrihydrite to act as a heterogeneous ice nucleating particle in the atmosphere using the SFM is discussed., Environmental Science: Atmospheres, 2 (3), ISSN:2634-3606

The phase behavior, the number and type of phases, in atmospheric particles containing mixtures of hydrocarbon-like organic aerosol (HOA) and secondary organic aerosol (SOA) is important for predicting their impacts on air pollution, human health, and climate. Using a solvatochromic dye and fluorescence microscopy, we determined the phase behavior of 11 HOA proxies (O/C = 0-0.29) each mixed with 7 different SOA materials generated in environmental chambers (O/C 0.4-1.08), where O/C represents the average oxygen-to-carbon atomic ratio. Out of the 77 different HOA + SOA mixtures studied, we observed two phases in 88% of the cases. The phase behavior was independent of relative humidity over the range between 90% and5%. A clear trend was observed between the number of phases and the difference between the average O/C ratios of the HOA and SOA components (ΔO/C). Using a threshold ΔO/C of 0.265, we were able to predict the phase behavior of 92% of the HOA + SOA mixtures studied here, with one-phase particles predicted for ΔO/C0.265 and two-phase particles predicted for ΔO/C ≥ 0.265. The threshold ΔO/C value provides a relatively simple and computationally inexpensive framework for predicting the number of phases in internal SOA and HOA mixtures in atmospheric models.

Spontaneous chemistry on aerosol surface Interfacial redox chemistry plays an important role in the formation of gas molecules and aerosol particles. However, the characterization of such heterogeneous processes is challenging, and they are often omitted in chemical kinetics models. Using ambient-pressure x-ray photoelectron spectroscopy combined with molecular dynamics simulations, Kong et al . discovered spontaneous redox chemistry promoted by the surface at the first stages of the solvation process on a typical inorganic aerosol surface of ammonium sulfate (see the Perspective by Ruiz-Lopez). Several unexpected species have been identified as being possible products of a sulfate-reducing ammonium oxidation reaction, and this may help to resolve some of the enduring conundrums of atmospheric chemistry. The present results could also be useful for the development of wastewater treatments and other industrial technologies. —YS

The particle–gas interface in aerosol systems is of essential importance because it is here that many key atmospheric processes occur. In this study, we employ ambient pressure X-ray photoelectron spectroscopy (APXPS) to investigate the surface properties and processes of an atmospherically relevant carboxylic salt, sodium acetate, at subdeliquescence conditions. From the depth profiles of the elemental ratios of sodium, oxygen, and carbon, we find that after deliquescence–efflorescence cycles the salt surface is sodium-depleted. The mechanism of the observed depletion is proposed to be (i) the formation of neutral acetic acid in the solution due to the nature of the basic salt; (ii) the selective surface enhancement of neutral molecules under aqueous condition; and (iii) a hypothetical kinetic barrier to re-homogenization due to spatial separation and special local conditions on the surface, resulting in varied local surface composition. When the relative humidity gradually increases and approaches the d...

The interaction of water with TiO2 is of substantial scientific and technological interest as it determines the activity of TiO2 in photocatalytic and environmental applications in nanoparticle sus...

Die Autonomisierung im Schulwesen hat die Aufgaben und das Handlungsfeld von Schulleitungen in den letzten Jahren verandert. Einerseits ist fur sie das gezielte Wahrnehmen von Fuhrung notwendig geworden, andererseits erfordert die Qualitatssorge uber die Rechenschaftspflicht verstarkte Aufmerksamkeit. Im Zuge dieser Entwicklung setzt sich die Schulleitungsforschung starker mit der Frage nach dem Einfluss von Fuhrung auf den Unterricht und dessen Ergebnisse auseinander. Im vorgestellten Forschungsprojekt wird das Handeln von Schulleitungen an lernwirksamen Schulen in Deutschland untersucht, deren Erfolge uber die sechs Qualitatsbereiche des Deutschen Schulpreises evaluiert worden sind. Uber einen mehrperspektivischen Zugang qualitativer Forschungsmethoden wurde in mehrtagigen Feldphasen erkundet, wie sich Schulleitungshandeln im alltaglichen Schulgeschehen zeigt. Der phanomenologische Zugang bringt als Antwort ein vielschichtiges Geflecht von Facetten zutage, die in Form eines Registers zusammengefasst werden. An einer Beispielfacette wird aufgezeigt, wie sich deren Eigenschaften in unterschiedlichen Auspragungen konkretisieren. Die Untersuchung mochte einen Beitrag zur Frage nach erfolgreichem Fuhrungshandeln im deutschsprachigen Raum leisten und jene Aspekte der Schulentwicklung aufgreifen, die fur die Qualifizierung und Professionalisierung von schulischen Fuhrungspersonen im deutschen Sprachraum und daruber hinaus bedeutsam sind.

Adsorption and desorption represent the initial processes of the interaction of gas species with the condensed phase. It has important implications for evaluating heterogeneous (gas-to-solid) and multiphase chemical kinetics involved in catalysis, environmental interfaces, and, in particular, aerosol particles. When describing gas uptake, gas-to-particle partitioning, and the chemical transformation of aerosol particles the desorption lifetime is a crucial parameter to assess the underlying chemical kinetics such as surface reaction and surface-to-bulk transfer. The desorption lifetime, in turn, depends on the desorption free energy which is affected by the chosen adsorbate model and standard states. To assess the impact of those conditions on desorption energy and, thus, desorption lifetime, we provide a complete classical and statistical thermodynamic treatment of the adsorption and desorption process considering transition state theory for two typically applied adsorbate models, the 2D ideal gas and the 2D ideal lattice gas, the latter being equivalent to Langmuir adsorption. Both models apply to solid and liquid substrate surfaces. We derive the thermodynamic and microscopic relationships for adsorption and desorption equilibrium constants, adsorption and desorption rates, first-order adsorption and desorption rate coefficients, and the corresponding pre-exponential factors. Although, some of these derivations can be found in the literature, this study aims to bring all derivations into one place to facilitate the interpretation and analysis of desorption energies for their application in multiphase chemical kinetics. This exercise allows for a microscopic interpretation of the underlying processes including the surface accommodation coefficient and highlights the importance of the choice of adsorbate model and standard states when analyzing and interpreting adsorption and desorption processes. We demonstrate how the choice of adsorbate model choice affects equilibrium surface concentrations and coverages, desorption rates, and decay of the adsorbate species with time. In addition, we show how those results differ when applying a concentration- or activity-based description. Our treatment demonstrates that the pre-exponential factor can differ by orders of magnitude depending on the choice of adsorbate model with similar effects on the desorption lifetime, yielding significant uncertainties in the desorption energy. Furthermore, uncertainties in surface coverage and assumptions in standard surface coverage can lead to significant changes in desorption energies derived from measured desorption rates. Providing a comprehensive thermodynamic and microscopic representation aims to guide theoretical and experimental assessments of desorption energies and estimate potential uncertainties in applied desorption energies and corresponding desorption lifetimes important for improving our understanding of multiphase chemical kinetics.

Understanding the mechanism of oxygen evolution reaction (OER) on perovskite materials is of great interest to tailor the synthesis of better catalyst materials. Despite the huge amount of literature reports, the complexity of catalytic systems and scarce in situ and operando surface sensitive spectroscopic tools render the detection of active sites and the understanding of the reaction mechanisms challenging. Here, we carried out and compared in situ and ex situ ambient pressure X-ray photoelectron spectroscopy experimental procedures on a La0.2Sr0.8CoO3 perovskite OER catalyst. Experimental results show that segregated surface strontium, which is present in the as prepared sample, is leached into the electrolyte after immersion, leading to surface cobalt active sites enrichment. Such cobalt-enriched oxide surface evolves into a new phase, whose spectral feature is detected in situ, during/after OER. With the help of theoretical simulations, such species is assigned to cobalt oxyhydroxide, providing a direct evidence of its crucial role in the reaction.

The Quasi-Liquid Layer on ice observed with NEXAFSGabathuler, Y. Manoharan, H. Yang, A. Boucly, A. Luca, M. Ammann, T. Bartels-RauschPaul Scherrer Institute, Villigen, Switzerland As temperature approaches the melting point of ice from below, the hydrogen-bonding network at the air – ice interface evolves from a well-defined hexagonal structure towards more randomly spatialized interactions. The general agreement is that a Quasi-Liquid-Layer (QLL) exists at the surface of the ice, and reports on the thickness of this disordered interfacial layer range from 2 nm to 25 nm at 271 K, depending on the probing technique (atomic force microscopy (AFM), ellipsometry, optical reflectivity, sum-frequency generation (SFG)) [1]. These large differences partly arise from the fact that the different techniques are probing different properties of the interface, and the delicate calibration into the thickness of the QLL contributes greatly to the uncertainty. We investigate the QLL using Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy, as Bluhm and his group did in 2002 [2]. The technique probes Auger electrons emitted upon X-ray absorption, thus, NEXAFS becomes inherently sensitive to the upper few nm of the air-ice interfacial region. This work focuses on the probing depth associated with this method and proposes a comprehensive treatment of the data, to help resolve the discrepancy of current thickness data. The importance of the QLL’s thickness comes from its contribution to environmental science as a reservoir for chemical impurities and as a host of chemical reactions with an impact on atmospheric and cryospheric composition. We will present a first data set of NEXAFS from neat ice between – 40 °C and 0°C acquired at the ISS endstation at the Swiss Light Source of the Paul Scherrer Institute. Results including error bars will be compared to earlier studies. The preliminary analysis suggests that the interfacial disorder seems to be less pronounced than reported in many earlier studies, very much in agreement with recent SFG [3] and AFM data [4]. Literature References: Acknowledgment:We thank A. Laso for technical help, SNF for funding (grant 178962)

Iodine in the atmosphere results from emissions of precursors from the oceans [1, 2] and undergoes continuous multiphase cycling. This cycling also prevents poorly soluble gaseous iodine species from removal by wet deposition. Thus, tropical convective outflow can even inject inorganic iodine into the lower stratosphere [3]. In the troposphere [1] and in the stratosphere [4], iodine appears in the gas- and particulate phase. In both compartments, particulate iodine exists not only in oxidized (as iodate) but also in reduced (as iodide) form [1, 4]. As iodide reacts with ozone in the aqueous phase [2] (which is also a major process related to iodine emission from the oceans), the reaction of ozone with iodide is one wheel of the cycles in the troposphere and may even represent a direct ozone sink in the stratosphere. However, only few kinetic data exist for this reaction. The temperature dependence of the reaction rate coefficient between 275 and 293 K was determined once and extrapolation of its value below 275 K rely on an activation energy estimate with an error of about 40 % [5]. Therefore, we performed laboratory experiments to extend the temperature range of the rate coefficient determination. We used a trough flow reactor [6] for our measurements and analyzed the data with a quasi steady state resistance model [7] to determine the essential physical parameters describing the reaction kinetics and their temperature dependence. Our results help to increase the understanding of atmospheric iodine chemistry and to better assess iodine’s impact on ozone in both, the troposphere and the stratosphere.Bibliography[1] A. Saiz-Lopez et al., Chem. Rev., 112, 3 (2012)[2] L. J. Carpenter et al., Nat. Geosci., 6 (2013)[3] A. Saiz-Lopez et al., Geophys. Res. Lett., 42, 16 (2015)[4] T. K. Koenig et al., PNAS, 117, 4 (2020)[5] L. Magi et al., J. Phys. Chem. A, 101 (1997)[6] L. Artiglia et al., Nat. Commun., 8 (2017)[7] M. Ammann et al., Atmos. Chem. Phys., 13 (2013)

Laboratory experiments are presented on the phase change at the surface of sodium chloride – water mixtures at temperatures between 259 K and 240 K. Chloride is a ubiquitous component of polar coastal surface snow. The chloride embedded in snow is involved in reactions that modify the chemical composition of snow as well as ultimately impact the budget of trace gases and the oxidative capacity of the overlying atmosphere. Multiphase reactions at the snow – air interface have found particular interest in atmospheric science. Undoubtedly, chemical reactions proceed faster in liquids than in solids; but it is currently unclear when such phase changes occur at the interface of snow with air.In the experiments reported here, a high selectivity to the upper few nanometres of the frozen solution – air interface is achieved by using electron yield near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. We find that sodium chloride at the interface of frozen solutions, which mimic sea-salt deposits in snow, remain as supercooled liquid down to 240 K, which is about 10 K lower than the freezing temperature of sodium chloride solutions. Below this temperature, hydrohalite exclusively precipitates, anhydrous sodium chloride is not detected. In this work, we present the first NEXAFS spectrum of hydrohalite. The hydrohalite is found to be stable while increasing the temperature towards the eutectic temperature of 253 K. Taken together, this study reveals no differences in the phase changes of sodium chloride at the interface as compared to the bulk. That sodium chloride remains liquid at the interface upon cooling down to 240 K, which spans the most common temperature range in Polar marine environments, has consequences for interfacial chemistry involving chlorine as well as for any other reactant for which the sodium chloride provides a liquid reservoir at the interface of environmental snow. Implications for the role of surface snow on atmospheric chemistry are discussed.