Showing papers by "Paul Scherrer Institute published in 2023"

Commissioning of the novel Continuous Angle Multi-energy Analysis spectrometer at the Paul Scherrer Institut

Abstract: We report on the commissioning results of the cold neutron multiplexing secondary spectrometer CAMEA (\textbf{C}ontinuous \textbf{A}ngle \textbf{M}ulti-\textbf{E}nergy \textbf{A}nalysis) at the Swiss Spallation Neutron Source (SINQ) at the Paul Scherrer Institut, Switzerland. CAMEA is optimized for an efficient data acquisition of scattered neutrons in the horizontal scattering plane, allowing for detailed and rapid mapping of low-energy excitations under extreme sample environment conditions.

Night-time NO emissions strongly suppress chlorine and nitrate radical formation during the winter in Delhi

Abstract: Abstract. Atmospheric pollution in urban regions is highly influenced by oxidants due to their important role in the formation of secondary organic aerosol (SOA) and smog. These include the nitrate radical (NO3), which is typically considered a night-time oxidant, and the chlorine radical (Cl), an extremely potent oxidant that can be released in the morning in chloride-rich environments as a result of nocturnal build-up of nitryl chloride (ClNO2). Chloride makes up a higher percentage of particulate matter in Delhi than has been observed anywhere else in the world, which results in Cl having an unusually strong influence in this city. Here, we present observations and model results revealing that atmospheric chemistry in Delhi exhibits an unusual diel cycle, controlled by high concentrations of NO during the night. As a result of this, the formation of both NO3 and dinitrogen pentoxide (N2O5), a precursor of ClNO2 and thus Cl, are suppressed at night and increase to unusually high levels during the day. Our results indicate that a substantial reduction in night-time NO has the potential to increase both nocturnal oxidation via NO3 and the production of Cl during the day.

Computational models for high-power cyclotrons and FFAs

Abstract: A summary of numerical modeling capabilities regarding high power cyclotrons and fixed field alternating gradient machines is presented. This paper focuses on techniques made available by the OPAL simulation code.

Cover Feature: Bonding in Low‐Coordinated Organoarsenic and Organoantimony Compounds: A Threshold Photoelectron Spectroscopic Investigation (Chem. Eur. J. 35/2023)

Abstract: Biradical formation vs. π-bonding: The low-valent, highly reactive pnictogen compounds PnCH3 (Pn=As, Sb) have been generated in situ by controlled homolysis of Pn(CH3)3 in the gas phase and investigated by photoelectron–photoion coincidence spectroscopy. This allowed us to establish trends in nature's strategy to stabilize low-valent pnictogen species either by tautomerization with concomitant multiple bond formation (HPn=CH2) or by biradical formation (Pn−CH3). The graphic illustrates the energetic steps separating the isomers of these fundamentally important group 15 compounds. More information can be found in the Research Article by C. Lichtenberg, P. Hemberger, I. Fischer and co-workers (DOI: 10.1002/chem.202300637).

Physicochemical Properties of Nascent vs. Aged Sea Spray Aerosols in the Eastern North Atlantic

Abstract: Sea spray aerosols (SSA) represent one of the largest sources of atmospheric particles since over two-thirds of the Earth’s surface is covered by oceans. They play an important role in climate and atmospheric chemistry, however, despite this a series of knowledge gaps hinder us from constraining their relevance. One critical question is why the physicochemical properties of nascent particles generated in the laboratory are so different from those measured in the ambient marine atmosphere. For example, a series of studies have highlighted that SSA generated in the laboratory exhibit essentially the same ability to act as cloud condensation nuclei as inorganic sea salt, regardless of the amounts of organic substances present in the seawater from which they were generated (e.g., Collins et al., 2016). This is in stark contrast to observations of ambient marine aerosols - their ability to act as cloud condensation nuclei is often significantly reduced in comparison (Swietlicki et al., 2000).To address this discrepancy, we prepared a novel experimental setup in which we deployed a chemical ionisation mass spectrometer (CIMS) with an Aim inlet in a setup together with a sea spray simulation chamber, an oxidative flow reactor (OFR), and a differential mobility particle sizer (DMPS) at Graciosa Island, Azores, in the eastern north Atlantic Ocean during summer 2022 as a part of the AGENA campaign.We used freshly-sampled ocean water to generate SSA that were aged in an OFR for an equivalent period of 3 to 3.5 days in the atmosphere. We recorded the gas-phase chemical composition of nascent and aged aerosols using the AIM-CIMS with multiple reagent ions, collected filter samples for offline analysis of the particle-phase chemical composition, and used a DMPS to compare the particle size distribution and concentration.The first results of our study show that the volatile organic compounds released from the sampled ocean water considerably nucleate when they are oxidized in the OFR. Furthermore, the chemical analysis of these gases reveals an increase in the concentration of DMS oxidation products, such as methane sulfonic acid, when the nascent SSAs along with the gases in the tank headspace are exposed to oxidants in the OFR. However, we did not observe any substantial differences in the concentration and size distribution of the accumulation and larger-mode particles for primary and aged SSA. This could be attributed to extensive nucleation taking place in the OFR. It is possible that in the real world, these VOCs would rather condense on the primary SSA than form new particles.In this presentation we will compare the properties of ambient SSA particles in the Eastern North Atlantic and those generated and aged with our experimental setup using real seawater in an attempt to address the discrepancy.Collins, D. B., et al., Geophys. Res. Lett. 2016, 43 (18), 9975-9983.Swietlicki, E., et al., Tellus B: Chemical and Physical Meteorology 2000, 52 (2), 201-227

How well are aerosol-cloud interactions represented in climate models? Part 1: Understanding the sulphate aerosol production from the 2014–15 Holuhraun eruption

Abstract: Abstract. For over 6-months, the 2014–2015 effusive eruption at Holuhraun, Iceland injected considerable amounts of sulphur dioxide (SO2) into the lower troposphere with a daily rate of up to one-third of the global emission rate causing extensive air pollution across Europe. The large injection of SO2, which oxidises to form sulphate aerosol (SO42−), provides a natural experiment offering an ideal opportunity to scrutinise state-of-the-art general circulation models (GCMs) representation of aerosol-cloud interactions (ACIs). Here we present Part 1 of a two-part model inter-comparison using the Holuhraun eruption as a framework to analyse ACIs. We use SO2 retrievals from the Infrared Atmospheric Sounding Interferometer (IASI) instrument and ground-based measurements of SO2 and SO42− mass concentrations across Europe in conjunction with trajectory analysis using the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model to assess the spatial and chemical evolution of the volcanic plume as simulated by 5 GCMs and a chemical transport model (CTM). IASI retrievals of plume altitude and SO2 column load reveal that the volcanic perturbation is largely contained within the lower troposphere and that the spatial evolution and vertical variability of the plume is reasonably well captured by the models, although the models underestimate the mean plume altitude. HYSPLIT trajectories are used to attribute to Holuhraun emissions 184 instances of elevated sulphurous surface mass concentrations recorded at 22 air monitoring stations across Europe. Comparisons with the simulated concentrations show that the models underestimate the elevated SO2 concentrations observed at stations closer to Holuhraun whilst overestimating those observed further away. Using a biexponential function to describe the decay of observed surface mass concentration ratios of SO2-to-SO42− with plume age, in-plume gas-phase and aqueous-phase oxidation rates are estimated as 0.031 ± 0.002 h−1 and 0.22 ± 0.16 h−1 respectively with a near-vent ratio of 31 ± 4 [μgm−3 of SO2 / ugm−3 of SO42−]. The derived gas-phase oxidation rates from the models are all lower than the observed estimate, whilst the majority of the aqueous-phase oxidation rates agree with the observed rate. This suggests that the simulated plumes capture the observed chemical behaviour in the young plume (when aqueous-phase oxidation is dominant), yet not in the mature plume (when gas-phase oxidation is dominant). Overall, despite their coarse resolution, the 6 models show reasonable skill in capturing the spatial and chemical evolution of the Holuhraun plume which is essential when exploring the eruption impact on ACIs in the second part of this study.

Linking aerosol size distribution and hygroscopicity to cloud droplet formation at an Arctic mountain site

Abstract: The regulation of energy transfer by clouds and fog is a key process affecting the climate of the Arctic, a region that exhibits frequent cloud cover and suffers an extreme vulnerability to climate change. Measurements were performed over a whole year at the Zeppelin station, Ny-Ålesund, Svalbard, Norway from October 2019 to October 2020 in the framework of the NASCENT campaign (Ny-Ålesund AeroSol Cloud ExperimeNT). Aiming at a better understanding of the susceptibility of cloud droplet formation, we analyzed particle number size distributions obtained from differential mobility particle sizers and chemical composition derived from filter samples and an aerosol chemical speciation monitor. Combined with updraft velocity information from a wind lidar and an ultrasonic anemometer, the data were used as input parameters for a state-of-the-art cloud droplet formation parameterization to investigate the particle sizes that can activate to cloud droplets, the levels of supersaturation as well as potential cloud droplet formation and its susceptibility to aerosol. We showed that low aerosol levels in fall and early winter led to clouds that are formed under an aerosol-limited regime, while higher particle concentrations centered around the Arctic Haze together with a drop in cloud supersaturation could be linked to periods of updraft velocity-limited cloud formation regime. In the latter case, we observed that the maximum number of cloud droplets forming - also called the limiting droplet number - and the updraft velocity follow a relationship that is universal, as proved by similar studies previously performed in different environments and cloud types. Finally, we successfully performed a droplet closure, proving, for the first time, the ability of our cloud droplet parameterization to predict cloud droplet number not only in liquid clouds but also in mixed-phase clouds with a very high degree of glaciation. This closure suggests that rime splintering may not be significant enough to affect droplet concentrations, which is consistent with previous observations and model simulations.

Cloud response to co-condensation of water and organic vapors over the boreal forest

Abstract: Abstract. Accounting for the condensation of organic vapors along with water vapor (co-condensation) has been shown in adiabatic cloud parcel model (CPM) simulations to enhance the number of aerosol particles that activate to form cloud droplets. The boreal forest is an important source of biogenic organic vapors, but the role of these vapors in co-condensation has not been systematically investigated. In this work, the environmental conditions under which strong co-condensation -driven cloud droplet number enhancements would be expected over the boreal biome are identified. Recent measurement technology, specifically the Filter Inlet for Gases and AEROsols (FIGAERO) coupled to an iodide-adduct Chemical Ionization Mass Spectrometer (I-CIMS), is utilized to construct a volatility distribution of the boreal atmospheric organics. Then, a suite of CPM simulations initialized with a comprehensive set of concurrent aerosol observations collected in the boreal forest of Finland during Spring 2014 is performed. The degree to which co-condensation impacts droplet formation in the model is shown to be dependent on the initialization of the updraft velocity, aerosol size distribution, organic vapor concentration and the volatility distribution. The predicted median enhancement in cloud droplet number concentration (CDNC) due to accounting for the co-condensation of water and organics is 20 % (interquartile range 29–14 %). This corresponds to activating particles 12–16 nm smaller in dry diameter, that would otherwise remain as interstitial aerosol. The highest CDNC enhancements (ΔCDNC) are predicted in the presence of a nascent ultrafine aerosol mode with a geometric mean diameter of ~40 nm and no clear Hoppel minimum, indicative of pristine environments with a source of ultrafine particles (e.g., via new particle formation processes). Such aerosol size distributions are observed 30–40 % of the time in the studied boreal forest environment in spring and fall when new particle formation frequency is the highest (six years of statistics). Five years of UK Earth System Model (UKESM1) simulations are further used to evaluate the frequencies to which such distributions are experienced by an Earth System Model over the whole boreal biome. The frequencies are substantially lower than those observed at the boreal forest measurement site (< 6 % of the time) and the positive values, peaking in spring, are modeled only over Fennoscandia and western parts of Siberia. For the aerosol size distribution regime simulated by UKESM1, offline simulations with the adiabatic parcel model reveal the ΔCDNC to be sensitive to the concentrations of semi-volatile and some intermediate-volatility organic compounds (SVOCs and IVOCs). The magnitudes of ΔCDNC remain less affected by the more volatile vapors such as formic acid and extremely low and low volatility organic compounds (ELVOCs and LVOCs) in the CPM simulations. The reasons for this are that most volatile organic vapors condense inefficiently due to their high volatility below cloud base and the concentrations of LVOCs and ELVOCs are too low to gain significant concentrations of soluble mass to reduce critical supersaturations needed for droplet activation. Suppression of the critical supersaturation caused by organic condensation is the main driver of the modeled ΔCDNC. The results highlight the potential significance of co-condensation in pristine boreal environments close to sources of fresh ultrafine particles. For accurate predictions of co-condensation effects on CDNC, the representation of the aerosol size distribution is of essence. Further studies targeted at finding observational evidence and constraints for co-condensation in the field are encouraged.

Non-target screening of organic aerosol tracers applied to a high-alpine firn core

Abstract: Ice cores are unique natural archives that provide important information about the past evolution of the Earth&#8217;s atmosphere. Whereas the inorganic atmospheric aerosol fraction is well characterized, the organic composition is less understood. The organic aerosol burden is consistently underestimated in the current state-of-the-art models, thus highlighting major gaps in our understanding of the pathways by which organic aerosols accumulate and evolve in the atmosphere. So far, organic aerosols in ice cores have been primarily reported as either bulk (e.g., water insoluble or dissolved organic carbon) or specific parameters (e.g., biomass burning tracers).To provide a more comprehensive characterization of the organic fraction, we applied a non-target screening approach optimised for determining oxidation products of volatile organic compounds to a firn core collected on the Corbassi&#232;re glacier (Grand Combin, Swiss Alps), in 2020, covering the period 2008-2020. In comparison with a firn core drilled two years earlier (2018), we observe a drastic disturbance of seasonal trends for certain species, such as major ions at depths corresponding to the annual layers from 2008 to 2016, induced by meltwater percolation.As organic tracers are present in low concentrations in the firn core, we performed solid phase extraction. The organic tracers were analysed with high-resolution mass spectrometry based on Orbitrap technology coupled with liquid chromatography. This technique makes it possible to study a wide range of individual compounds at low concentration and to identify them with MS/MS fragmentation. We can attribute molecular formulas to detected compounds by comparing the MS/MS spectra with spectral libraries (e.g., mzCloud) or reference standards. With this approach we will present a unique record of molecular composition of organic aerosol in the Corbassi&#232;re firn core.Furthermore, this firn core presents a unique opportunity to examine the effect of melting on the organic tracers. We found that specific burning tracers (e.g., vanillic acid, vanillin and syringaldehyde) are less affected than other biomass tracers (e.g., pinic acid) by meltwater percolation. In general, we observe a decrease in concentration of the organic tracers in the same firn core section where we also observe a decrease in major ion concentrations.

Impacts of reducing scattering and absorbing aerosols on the temporal extent and intensity of South and East Asian summer monsoon

Abstract: Abstract. The vast majority of reductions in aerosol emissions are projected to take place in the near future; however, associated impacts on the large-scale circulation over the populated Asian monsoon region remain uncertain. Using the state-of-the-art UK Earth System Model version 1 (UKESM1), this study examines the response of the South Asian and East Asian summer monsoon (SASM and EASM) to idealized reductions in anthropogenic emissions of carbonaceous aerosols and SO2. The analysis focuses on changes in the monsoon temporal extent and intensity of precipitation following decreases in either scattering (SCT), absorbing (ABS) aerosols, or decreases in both. For SCT, the combination of the early transition of land-sea thermal contrast and sea level pressure gradient during the pre-monsoon season together with the late transition in the post-monsoon season associated with the tropospheric warming, advances the monsoon onset but delays its withdrawal, which leads to an extension of the summer rainy season across South and East Asia. The northward shift of the upper-tropospheric Asian jet forced by the SCT reduction causes the anomalous convergence of tropospheric moisture and low-level ascent over northern India and eastern China. The intensification of the South Asian High (SAH) due to the warming over land also contributes to the dynamic instability over Asia. These changes enhance the rainy season of these regions in boreal summer. Reductions in absorbing aerosol act in the opposite sense, making the Asia's rainy season shorter and weaker due to the opposite impacts on land-sea contrast, Asian jet displacement and SAH intensity. With reductions in both SCT and ABS aerosol together the monsoon systems intensify, as the overall impact is dominated by aerosol scattering effects and results in the strengthening of monsoon precipitation and 850-hPa circulation. Although aerosol scattering and absorption play quite different roles in the radiation budget, their effects on the monsoon precipitation seem to add almost linearly. Specifically, the patterns of monsoon-related large-scale responses from reducing both SCT and ABS together are similar to the linear summation of separate effect of reducing SCT or ABS alone, despite of the inherent nonlinearity of the atmospheric systems. Our findings suggest that emission controls that target e.g. emissions of black carbon that warm the climate would have a different response to those that target overall aerosol emissions.

Sub-seasonal snowline dynamics of glaciers in Central Asia from multi-sensor satellite observations, 2000-202

Abstract: Glaciers are an important contributor to the freshwater supply in the Central Asian region. Their response to climate change has profound consequences for the land-use applications, and is thus essential to understand. The collapse of the Soviet Union has interrupted the vast majority of the conducted glacier mass balance observations, which began to re-establish in 2010. The existing data gap, limited spatial resolution of glaciological measurements, and the high heterogeneity of the region limits the use of in-situ data. Mass balance models rely on observation-based calibration and validation data, such as transient snowlines (TSLs), a transition between snow and ice-covered surfaces on a glacier at a given point in time. At the end of the ablation season TSL approximates the equilibrium line. From TSL we can calculate the snow-covered area fraction (SCAF), the area on the glacier surface that is snow covered in relation to the total glacier area. The TSL and SCAF can be mapped from satellite imagery due to the distinctive spectral and structural signature of snow over time. Our approach presented in this contribution is based on the MODIS time-series, harnessing the advantage of long and close-to-daily observations records for the period before high-resolution satellites became available. To resolve the issue of MODIS coarse spatial resolution, we retrieved SCAF from multispectral Sentinel-2 and cloud-independent Sentinel-1 SAR imagery using established workflow. The automatic classification and calculation of SCAF is performed using the cloud computing service of the Google Earth Engine, which makes the entire approach easily applicable on a large number of remote glaciers worldwide. We validated the results independently with Landsat data over selected glaciers in Central Asia. From the&#160; SCAF time-series we analysed changes in various parameters indicative for the atmospheric conditions and its changes&#160; (amongst others the length of ablation period, the minimum SCAF, and the seasonal SCAF changes ) as well as their 20-year trends. Our results provide a unique time series of temporally and spatially high-resolved SCAF estimates giving observation-based information on the heterogeneity of the region&#8217;s climatic setting as well as its changes on subseasonal scale.&#160;

Quantifying effects of long-range transport of air pollutants over Delhi using back-trajectories and satellite NO₂ data

Abstract: Abstract. Exposure to air pollution is a leading public health risk factor in India, especially over densely populated Delhi and the surrounding Indo-Gangetic Plain. During the post-monsoon months, the prevailing north-westerly winds are known to influence aerosol pollution events in Delhi, by advecting pollutants from agricultural fires as well as from local sources. Here we investigate the year-round impact of meteorology on gaseous nitrogen oxides (NOx = NO + NO2), a hazardous primary air pollutant for health, which can lead to the formation of secondary aerosols and ozone. We use bottom-up NOx emission inventories (anthropogenic and fire) and high-resolution satellite measurement based tropospheric column NO2 (TCNO2) data, from S5P on-board TROPOMI, alongside a back-trajectory model (ROTRAJ) to investigate the balance of local and external sources influencing air pollution changes in Delhi, with a focus on different emission sectors. Our analysis shows that accumulated emissions (i.e. integrated along the trajectory path, allowing for chemical loss) are highest under westerly, north-westerly and northerly flow during pre- (February–March) and post- (October–January) monsoon periods. During the pre-monsoon period, the residential and transport sectors together account for more than 50 % of the total accumulated emissions, which are dominated by local sources (90 %) under easterly winds and by non-local sources (> 70 %) under north-westerly winds. The high accumulated emissions estimated during the pre-monsoon season under north-westerly wind directions are likely to be driven by high NOx emissions locally and in nearby regions (since NOx lifetime is reduced and the boundary layer is relatively deeper in this period). During the post-monsoon period non-local (60 %) transport emissions are the largest contributor to the total accumulated emissions as high emissions, coupled with a relatively long NOx atmospheric lifetime and shallow boundary-layer aid the build-up of emissions along the trajectory path. Analysis of surface daily NO2 observations indicates that high pollution episodes (> 90th percentile) occur predominantly in the post-monsoon and more than 75 % of high pollution events are primarily caused by non-local sources. Overall, we find that in the post-monsoon period, there is a substantial import of NOx pollution into Delhi with a large contribution from the transport sector. This work indicates that the advection of highly polluted air originating from outside Delhi is of concern for the population and air quality mitigation strategies need to be adopted not only in Delhi but in the surrounding regions to successfully control this issue. In addition, our analysis suggests that the largest benefits to Delhi NOx air quality would be seen with targeted reductions in emissions from the transport sector, particularly during post-monsoon months.

Protein Oligomer Engineering: A New Frontier for Studying Protein Structure, Function, and Toxicity

Abstract: Prevalent in nature, protein oligomers play critical roles both physiologically and pathologically. The multimeric nature and conformational transiency of protein oligomers greatly complicate a more detailed glimpse into the molecular structure as well as function. In this minireview, the oligomers are classified and described on the basis of biological function, toxicity, and application. We also define the bottlenecks in recent oligomer studies and further review numerous frontier methods for engineering protein oligomers. Progress is being made on many fronts for a wide variety of applications, and protein grafting is highlighted as a promising and robust method for oligomer engineering. These advances collectively allow the engineering and design of stabilized oligomers that bring us one step closer to understanding their biological functions, toxicity, and a wide range of applications.

Profiles of δ18O and δ2H in porewater of a Mesozoic rock sequence: Regional variability and relation to large-scale transport regimes

Abstract: Clay-rich rocks have very low hydraulic permeability and they also have good chemical retention properties for cationic contaminants. This makes them ideal as host rocks for the underground disposal of radioactive waste. In Switzerland, the Opalinus Clay Formation, Jurassic sediments deposited ~174 Ma ago, is envisaged as potential host rock. A large drilling campaign has recently been run in three potential siting regions in northern Switzerland. Drill core samples from a ~400 m thick Mesozoic low permeability zone were obtained at high spatial resolution in one slanted and eight vertical boreholes. Data including various natural tracers were obtained from these core samples. Here we report on the profiles of the stable isotopes &#948;18O and &#948;2H in porewater and groundwater in the eight vertical boreholes. The distribution of the tracers results from hydrogeological and transport processes acting in the past, and the profiles can be interpreted as results of &#8216;experiments performed by nature&#8217;. Hydrogeochemical investigations of groundwater and veins mineralisations help to constrain the temporal evolution of the system and to assess the system&#8217;s large-scale transport properties. The comparably large number of boreholes allows us comparing the observed depth distributions of the two tracers not only vertically, but also laterally in the three regions (~15-20 kilometers apart), and in the 2 to 4 boreholes in each region (a few kilometers apart). The isotope profiles from the different boreholes show many similarities, but also distinct features that are mainly related to the lateral variation in aquifer properties. The regional aquifers in the Malm (one locality Hauptrogenstein) and Muschelkalk typically build the upper and lower boundary, respectively, of the &#948;18O and &#948;2H profiles. In some, but not in all tracer profiles, there are indications of a local Keuper aquifer in the lower part. The variability reflects the lithological heterogeneity of this rock unit in the lateral dimension. The maximum isotope values plot to the right of the GMWL, are often similar and are found in the central part of the profiles in the Opalinus Clay Formation. Towards the Keuper aquifer (if present), the values decrease and approach the GMWL, and often some gentle decrease is also observed towards the upper aquifer, without reaching the GMWL. Towards the Muschelkalk aquifer, the values decrease sharply and reach the GMWL. The shapes of the profiles hint to the importance of diffusive transport processes over large spatial and geologic time scales. With transport simulations, we try to narrow down the timing of any changes in the aquifer signatures in the more recent past (10 ka to few Ma ago), as well as to assess the importance of various transport mechanisms in the development of the profiles. The interpretation of such tracer profiles is a key element with respect to the assessment of the large-scale transport properties of a host rock.

Concept, absolute calibration and validation of a new, bench-top laser imaging polar nephelometer

Abstract: Abstract. Polar nephelometers provide in situ measurements of aerosol angular light scattering and play an essential role in validating numerically calculated phase functions or inversion algorithms used in space-borne and land-based aerosol remote sensing. In this study, we present a prototype of a new polar nephelometer called uNeph. The instrument is designed to measure the phase function, F11, and polarized phase function, –F12/F11 over the scattering range of around 5° to 175° with an angular resolution of 1° at a wavelength of 532 nm. In this work, we present details of the data processing procedures and instrument calibration approaches. The uNeph was validated in a laboratory setting using mono-disperse polystyrene latex (PSL) and Di-Ethyl-Hexyl-Sebacate (DEHS) aerosol particles over a variety of sizes, ranging from 200 nm to 800 nm. An error model was developed and the level of agreement between uNeph measurements and Mie theory was found to be consistent within the uncertainties of the measurements and the uncertainties of the input parameters for the theoretical calculations. The estimated measurement errors were between 5 % to 10 % (relative) for F11 and smaller than ~0.1 (absolute) for –F12/F11. Additionally, by applying the Generalized Retrieval of Aerosol and Surface Properties (GRASP) inversion algorithm to the measurements conducted with broad unimodal DEHS aerosol particles, the volume concentration, size distribution and refractive index of the ensemble of aerosol particles were accurately retrieved. This paper demonstrates that the uNeph prototype can be used to conduct accurate measurements of aerosol phase function and polarized phase function and to retrieve aerosol properties through inversion algorithms.

Effect of plant mucilage on retention and flow of water in soils with different textures

Abstract: Previous studies showed that mucilage extracted from chia seed enhanced retention and flow of water in dry conditions due to the intrinsic features of mucilage (increasing viscosity, water-holding capacity, and decreasing surface tension of the liquid phase). To date, there is limited information about the effect of mucilage from plant roots on the hydraulic properties of soils of different textures.In this contribution, we aimed to evaluate the effect of plant mucilage in different contents (mucilage extracted from maize roots) on the retention and flow of water in soils with contrasting textures (coarse and fine-textured soils). To this end, soils were mixed with mucilage at different contents (0, 2.5, 5, 7.5 mg dry mucilage per gr dry soil) and were packed in aluminum containers (diameters of 1 cm and height of 8 cm) as follows: the control sandy soil (the content of zero) was packed in the first 4 cm of containers followed by a 1 cm layer of treated soils with mucilage. These containers were equipped with porous plates at the bottom allowing us to drain soil from the bottom by applying suction. In the case of fine-textured soils, a 1 cm layer of treated soils with varying mucilage contents was first saturated with water and then placed on top of a 4 cm layer of dry soil inducing a big suction to dry treated soils. During soil drying, we used a time series neutron radiography technique to monitor soil water content redistribution. We used the profiles of water contents during soil drying with a combination of modeling of water flow within soils (the Richard equation) to inversely estimate the hydraulic properties of soils treated with different mucilage contents.Our data showed that maize mucilage affects the soil&#8217;s hydraulic properties. On the one hand, mucilage exuded by maize roots increased the water-holding capacity of both soils. Mucilage also impacted the hydraulic conductivity of both soils. In general, it decreased soil hydraulic conductivity of soils at the near saturation range, but it prevented a big drop in soil hydraulic conductivity as the soil dried compared to a sharper decrease observed in the control soils. Our findings showed that both effects are mucilage content dependent and the magnitude of the effects is soil texture dependent.

Origin of the Activity Trend in the Oxidative Dehydrogenation of Ethanol over VO _<i>x</i> /CeO ₂ **

Abstract: Supported vanadia (VOx) is a versatile catalyst for various redox processes where ceria-supported VOx have shown to be particularly active in the oxidative dehydrogenation (ODH) of alcohols. In this work, we clarify the origin of the volcano-shaped ethanol ODH activity trend for VOx/CeOx catalysts using operando quick V K- and Ce L3- edge XAS experiments performed under transient conditions. We quantitatively demonstrate that both vanadium and cerium are synergistically involved in alcohol ODH. The concentration of reversible Ce4+/Ce3+ species was identified as the main descriptor of the alcohol ODH activity. The activity drop in the volcano plot, observed at above ca. 3 V nm−2 surface loading (ca. 30 % of VOx monolayer coverage), is related to the formation of spectator V4+ and Ce3+ species, which were identified here for the first time. These results might prove to be helpful for the rational optimization of VOx/CeO2 catalysts and the refinement of the theoretical models.

Dynamic neutron and X-ray three-dimensional imaging of fluid flow and mixing during mineral precipitation in porous rocks

Abstract: Flow and mixing processes in porous media control many natural and industrial systems, such as microbial clogging, oil extraction, and effluent disposal. In many systems, the porosity may evolve during mineral precipitation, such as in rocks, and control fluid mixing and fluid transport properties. Here, we use three-dimensional in situ dynamic neutron and X-ray micro-tomography imaging to explore fluid transport into Berea sandstone core samples during in-situ carbonate precipitation. Neutron imaging can track fluid flow inside the rock, whereas X-ray imaging illuminates the regions where mineral precipitation occurs. We control the precipitation of calcium carbonate in the rock through reactive-mixing between solutions containing CaCl2 and Na2CO3. By solving the advection-diffusion equation using the contrast in neutron attenuation from time-lapse images, we derive the 3D velocity field of the injected fluids and characterize the evolution of the permeability field into the rock during mineral precipitation. We also investigate the mixing between heavy water and a cadmium solution under the influence of mineral precipitation. Results show that, under the effect of mineral precipitation, a wide range of local flow velocities develop in the sample, under the same fluid injection rate, and we quantify the distribution of flow velocities in the sample. Moreover, we observe more efficient mixing between heavy water and a cadmium solution after mineral precipitation. The finding of this experimental study is useful in progressing the knowledge in the domain of reactive solute and contaminant transport in the subsurface.

Microplastic Interaction with Soil Water - Visualization and Quantification with Neutron and X-ray Imaging

Abstract: Soil is considered the largest sink of microplastics (MP) in terrestrial ecosystems. Among the expected effects of MP as hydrophobic surface addition is the likelihood that MP enhances soil water repellency. So, crucial for MP fate in soils is the interaction between MP and water. If MP is translocated by water flow and, vice versa, MP impacts water flow, to what extent? Water flow on the pore scale will be impacted with feedbacks on transport and retention of MP. However, we don&#8217;t know the extent of and conditions under which MP are transported through porous media and, if deposited, how they interplay with soil water dynamics. We hypothesize that: (i) isolated MP are displaced and translocated by air-water interfaces and (ii) local accumulation of MP is facilitated by bypassing water flow. To approach this question, neutron and x-ray imaging of MP and water in soils was utilized.Dual neutron and x-ray imaging at the beamlines ICON (Paul-Scherrer-Institute) during repeated wetting-drying cycles was applied to trace MP-water interactions in aluminum cylinders filled with sand (0.7-1.2 mm) and MP (PET, 20-75 &#181;m) in gravimetric contents of 0.35, 1.05 and 2.10%. The contents refer to static contact angle estimations of the mixtures resembling < 90&#176;, 90&#176; and > 90&#176;. First, simultaneous neutron and x-ray tomography captured the initial dry MP configuration in samples. Subsequently, neutron radiographies of deuterated water flow through the sample of 1 ml min-1 were recorded for 200s. After drying, repeated tomography gave insights into MP translocation.Neutron and x-ray imaging results showed that regions of major MP content are water repellent. Water flow bypasses and MP is mainly retained. Resultant air entrapments lead to reduced water contents. In regions of minor MP content water can infiltrate. Here, the air-water interface collects isolated MP and shifts their distribution towards an enhanced accumulation.Extrapolation of these results to natural soil systems suggests that vertical transport of MP can be limited especially at hotspots of high MP contents. Water bypasses here. This might limit the water dependent degradation processes of MP due to reductions in hydrolysis, coating and colonization by microorganisms even elongating the process of natural attenuation.

Not all types of secondary organic aerosol mix: two phases observed when mixing different secondary organic aerosol types

Abstract: 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 (&#916;O/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 &#916;O/C &#8805; 0.47, while one-phase SOA+SOA particles formed for &#916;O/C < 0.47. This threshold &#916;O/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.

Surface propensity of atmospheric iodine oxides: AIMD and LJ-XPS investigation

Abstract: 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 &#8211; 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 (Kh&#252;ne 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. K&#252;hne 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). &#160;

Molecular composition and volatility of secondary organic compounds from nitrate radical oxidation of biogenic volatile organic compounds – from lab to field

Abstract: Night-time reactions of biogenic volatile organic compounds (BVOCs) and nitrate radicals (NO3) can lead to the formation of secondary organic aerosol (BSOANO3). Here we firstly present the chemical composition and volatility of BSOANO3 formed in the dark from three precursors (isoprene, &#945;-pinene, and &#946;-caryophyllene) in atmospheric simulation chamber experiments (Wu et al., 2021; Bell et al., 2022; Graham et al., 2022). The chemical composition of particle-phase compounds was measured with a chemical ionization mass spectrometer with a filter inlet for gases and aerosols (FIGAERO-CIMS) and an extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF). The volatility information of BSOANO3 was derived from isothermal evaporation chambers, temperature-dependent evaporation in a volatility tandem differential mobility analyzer (VTDMA), and thermal desorption in the FIGAERO-CIMS. In addition, the molecular composition of particulate compounds was used in volatility parametrizations to calculate the compounds&#8217; saturation vapor pressures and to establish volatility basis sets (VBS, Donahue et al., 2011) for the bulk aerosol. Four different parametrizations were tested for reproducing the observed evaporation in a kinetic modeling framework (Riipinen et al., 2010). Here, we compare the different methods for particle volatility determination and discuss the limitation of the parameterizations.Our results suggest the BSOANO3 from &#945;-pinene and isoprene be dominated by low-volatility organic compounds (LVOC) and semi-volatile organic compounds (SVOC), while the corresponding BSOANO3 from &#946;-caryophyllene consists primarily of extremely low-volatility organic compounds (ELVOC) and LVOC. The parameterizations yielded variable results in terms of reproducing the observed evaporation, and generally the comparisons pointed to a need for re-evaluating the treatment of the nitrate group in such parameterizations.Furthermore, we link the lab experiments to field observations of secondary organic aerosols and organic nitrates from a boreal forest (ICOS Norunda, Sweden), which is dominated by monoterpene emissions and includes also isoprene and sesquiterpene emissions. We will show the chemical composition and volatility of the particles detected with a FIGAERO-CIMS, compare them to the lab results, and discuss how nitrate-initiated nighttime oxidation of different precursors contribute to the total particle formation and growth.&#160;References:Wu, C. et al., Atmos. Chem. Phys., 21, 14907&#8211;14925, 2021Bell, D. et al., Atmos. Chem. Phys., 22, 13167&#8211;13182, 2022Graham, E. and Wu, C. et al, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2022-1043, 2022Donahue, N. M. et al., Atmos. Chem. Phys., 11, 3303&#8211;3318, 2011Riipinen, I. et al., Atmos. Environ., 44-5, 597-607, 2010&#160;

Analysis of atmospheric particle growth based on vapor concentrations measured at the high-altitude GAW station Chacaltaya in the Bolivian Andes

Abstract: Abstract. Early growth of atmospheric particles is essential for their survival and ability to participate in cloud formation. Many different atmospheric vapors contribute to the growth, but even the main contributors still remain poorly identified in many environments, such as high-altitude sites. Based on measured organic vapor and sulfuric acid concentrations under ambient conditions, particle growth during new particle formation events was simulated and compared with the measured particle size distribution at Chacaltaya Global Atmosphere Watch station in Bolivia (5240 m a.s.l.) during April and May 2018, as a part of the SALTENA (Southern Hemisphere high-ALTitude Experiment on particle Nucleation and growth) campaign . The simulations showed that the detected vapors were sufficient to explain the observed particle growth, although some discrepancies were found between modelled and measured particle growth rates. This study gives an insight on the key factors affecting the particle growth on the site. Low volatile organic compounds were found to be the main contributor to the particle growth, covering on average 65 % of simulated particle mass in particle with diameter of 40 nm In addition, sulfuric acid had a major contribution to the particle growth, covering at maximum 39 % of simulated particle mass in 40 nm particle during periods when volcanic activity was detected on the area, suggesting that volcanic emissions can greatly enhance the particle growth.

Climate change is rapidly deteriorating the climatic signal in Svalbard glaciers

Abstract: Abstract. The Svalbard archipelago is particularly sensitive to climate change due to the relatively low altitude of its main ice fields and its geographical location in the higher North Atlantic, where the effect of the Arctic Amplification is more significant. The largest temperature increases have been observed during winter, but increasing summer temperatures, above the melting point, have led to increased glacier melt. Here, we evaluate the impact of this increased melt on the preservation of the oxygen isotope signal (δ18O) in firn records. δ18O is commonly used as proxy for past atmospheric temperature reconstructions and, when preserved, it is a crucial parameter to date and align ice cores. By comparing four different firn cores collected in 2012, 2015, 2017 and 2019 at the top of the Holtedahlfonna ice field (1100 m. a.s.l.), we show a progressive deterioration of the isotope signal and we link its degradation to the increased occurrence and intensity of melt events. Although the δ18O signal still reflects the interannual temperature trend, more frequent melting events may in the future affect the interpretation of the isotopic signal, compromising the use of Svalbard ice cores. Our findings highlight the impact and the speed at which Arctic Amplification is affecting Svalbard's cryosphere.

Cryo-Electron Tomography

Abstract: Electron tomography in biology is a technique to reconstruct the three-dimensional structure of macro-molecular, sub-cellular or cellular objects by transmission electron microscopy (TEM). In this technique, micrographs of the sample are recorded from various orientations by tilting the specimen, which are then computationally merged into a 3D structure. Combined with recent developments of cryo-electron microscopy, cryo-electron tomography (cryo-ET) have allowed us to visualize detailed 3D structures of biological macromolecules in vivo at sub-atomic resolution, filling the gap between X-ray crystallography or NMR and light microscopy. In this section, we overview this technique and application to biology and discuss future challenge.