Glaciers serve as natural archives for reconstructing past changes of atmospheric aerosol concentration and composition. While most ice-core studies have focused on inorganic species, organic compounds, which can constitute up to 90% of the submicrometer aerosol mass, have been largely overlooked. To our knowledge, this study presents the first nontarget screening record of secondary organic aerosol species preserved in a Belukha ice core (Siberia, Russian Federation), ranging from the pre-industrial to the industrial period (1800-1980 CE). We identified a total of 398 molecules, primarily polar and low-volatile compounds. Since the 1950s, the atmospheric aerosol composition has changed, with the appearance of organic molecules, including nitrogen-containing compounds, deriving from enhanced atmospheric reactions with anthropogenic NOx, or direct emissions. In addition, there was a significant increase in the oxygen-to-carbon ratio (+3%) and the average carbon oxidation state (+18%) of the detected molecules compared to the pre-industrial period, suggesting an increased oxidative capacity of the atmosphere.

Organic aerosols make up to 70-90% of the total aerosol mass, yet ice-core studies have predominantly focused on a limited set of compounds or bulk fractions altogether. Previous investigations have centered on biomass burning tracers, marine phytoplankton oxidation products, low molecular weight carboxylic acids and persistent organic pollutants, leaving a large majority of molecules unidentified. Advances in high-resolution mass spectrometry (HRMS) have recently enabled the exploration of a wider chemical space through the development of non-target screening (NTS) workflows.In this work, we present three applications of a novel NTS method. Designed to detect secondary organic aerosol compounds in ice-core and snow samples, the method has contributed to a more comprehensive characterization of past molecular aerosol composition and has supported the development of new molecular proxies. Initially, the method was applied to the Belukha ice core (Siberian Altai, 4072 m. a.s.l.) between 1830 and 1980 CE, providing the first NTS ice-core record that embraces both the pre-industrial and industrial periods. More than 400 compounds were identified, and a clear anthropogenic fingerprint was recognized over the industrial period. Subsequently, the ice core samples from Colle Gnifetti (Switzerland, 4500 m. a.s.l.) covering the period from 1750 to 2000 CE were analyzed. Here, a smaller number of molecules was detected (≈200), consistent with the lower concentrations of dissolved organic carbon observed at this site. In both cores, most of the molecules are composed of carbon (C), hydrogen (H) and oxygen (O) and are associated with atmospheric oxidation of monoterpenes and isoprenes (e.g., succinic acid, pinic acid, azelaic acid). The industrial onset was characterized by an increase in nitrogen and sulfur containing compounds, likely due to the atmospheric reactions with anthropogenic NOx and SO2. The higher occurrence of compounds with higher O/C ratios during the industrial period observed at both locations, suggests an increase in the atmosphere oxidative capacity. Lastly, the method was applied to 56 snow samples collected in springtime close to Ny-Ålesund (Svalbard Archipelago) and covering both pre- and phytoplankton bloom periods. Together with marine observations of algal bloom, the NTS results suggest promising evidence towards new ice-core marine productivity proxies for long-term reconstructions.

Ice cores are environmental archives that are used to reconstruct past changes in the atmospheric aerosol composition. Most ice-core studies have focused mainly on inorganic species and a few dozen organic molecules. However, organic compounds can account for up to 90% of the aerosol composition, meaning that only a fraction of the organic constituents has been studied, limiting our understanding of past atmospheric aerosol chemistry changes. Here, we present the first non-target screening ice-core record investigating the molecular composition of the Belukha ice core (Altai, Russian Federation) over the 1830-1980 CE period. We identified 491 molecules, mainly constituted by aliphatic secondary organic aerosol (SOA) species (e.g., dicarboxylic acids, ketoacids…) consisting of carbon, hydrogen, and oxygen atoms. Since 1955 CE, the ice-core molecular composition has changed with higher occurrence of nitrogen and sulfur-containing compounds, either associated to enhanced atmospheric reactions with anthropogenic-sourced NOx and SO2 or linked to direct emissions. During this period, we also observed an increase in the SOA oxygen-to-carbon ratio and average carbon oxidation state, suggesting an increase in the oxidative capacity of the atmosphere.

Supercritical water gasification (SCWG) is a promising technology to convert wet biomass to renewable natural gas. The present study sheds light on the chemical composition and the formation mechanism of coke deposits on a Ru/CNF catalyst during continuous SCWG of glycerol in a fixed-bed reactor. SCWG experiments were performed using pristine carbon nanofibers (CNF) and 5 wt% Ru/CNF catalysts, which suffered from partial deactivation. Transmission electron microscopy (TEM) indicated a 34-42 % dispersion loss independently of the conditions, only partially explaining the activity loss observed during the test at very high space velocity. When operated under thermodynamic conditions, no deposits could be observed. A nanometric layer of deposits on the catalysts was present under intermediate conditions, while in the kinetic regime (conversion of glycerol down to 4 %), significant carbon deposition was observed. The chemical compositions of aqueous phases and organic deposits extracted from the catalysts and support showed that the presence of Ru enhanced the formation of unsaturated compounds from glycerol. In particular, molecules containing aromatic rings were detected. The space velocity significantly affected the composition of the coke deposits. The number of carbons in the molecules increased from 5-25 to 10-45 when moving away from the thermodynamic regime (full conversion), and the O/C ratio significantly decreased from 0.3-0.6 to 0.05-0.3, maintaining a very broad H/C ratio. The extracted organic deposits contained various aromatic compounds but were mostly represented by unsaturated aliphatic compounds. All these results were used to elucidate a reaction pathway for the formation of organic deposits from glycerol.

Wildfires can influence the earth's radiative forcing through the emission of biomass-burning aerosols. To better constrain the impacts of wildfires on climate and understand their evolution under future climate scenarios, reconstructing their chemical nature, assessing their past variability, and evaluating their influence on the atmospheric composition are essential. Ice cores are unique to perform such reconstructions representing archives not only of past biomass-burning events but also of concurrent climate and environmental changes. Here, we present a novel methodology for the quantification of five biomass-burning proxies (syringic acid, vanillic acid, vanillin, syringaldehyde, and p-hydroxybenzoic acid) and one biogenic emission proxy (pinic acid) using solid phase extraction (SPE) and ultrahigh-performance liquid chromatography coupled with high-resolution mass spectrometry. This method was also optimized for untargeted screening analysis to gain a broader knowledge about the chemical composition of organic aerosols in ice and snow samples. The method provides low detection limits (0.003-0.012 ng g-1), high recoveries (74 ± 10%), and excellent reproducibility, allowing the quantification of the six proxies and the identification of 313 different molecules, mainly constituted by carbon, hydrogen, and oxygen. The effectiveness of two different sample storage strategies, i.e., re-freezing of previously molten ice samples and freezing of previously loaded SPE cartridges, was also assessed, showing that the latter approach provides more reproducible results.

Zirconium-containing metal-organic framework (MOF) with UiO-66 topology is an extremely versatile material, which finds applications beyond gas separation and catalysis. However, after more than 10 years after the first reports introducing this MOF, understanding of the molecular-level mechanism of its nucleation and growth is still lacking. By means of in situ time-resolved high-resolution mass spectrometry, Zr K-edge X-ray absorption spectroscopy, magic-angle spinning nuclear magnetic resonance spectroscopy, and X-ray diffraction it is showed that the nucleation of UiO-66 occurs via a solution-mediated hydrolysis of zirconium chloroterephthalates, whose formation appears to be autocatalytic. Zirconium-oxo nodes form directly and rapidly during the synthesis, the formation of pre-formed clusters and stable non-stoichiometric intermediates are not observed. The nuclei of UiO-66 possess identical to the crystals local environment, however, they lack long-range order, which is gained during the crystallization. Crystal growth is the rate-determining step, while fast nucleation controls the formation of the small crystals of UiO-66 with a narrow size distribution of about 200 nanometers.

We compare the unimolecular decay mechanism of vanillin in four charge states. The unimolecular thermal decomposition of the neutral and dissociative ionization reactions in the cation have already been addressed in synchrotron-based photoionization studies. The picture is completed here by studying the collision-induced dissociation mechanism of protonated vanillin cations and deprotonated vanillin anions in the 5-30 eV collision energy range. The mass spectrometric observations /\ are rationalized by ab initio calculations, which reveal the mechanism and the energetics of dissociation pathways. In the positive ion mode, the aldehyde oxygen is protonated, after which CO is lost. In contrast to previous results, CO loss is found to be the sole primary fragmentation pathway of protonated vanillin. Two hydrogen migration steps to the benzene ring open sequential CH3OH and CH3 loss channels to yield C6H5O+ and C6H6O2+, respectively. The former fragment ion can continue to lose CO, associated with ring contraction and producing the cyclopentadiene cation, C5H5+. In the negative ion mode, the proton is removed from the hydroxyl group. The primary dissociation channel of deprotonated vanillin corresponds to ( C-)O-CH3 bond breaking in the methoxy group to form C7H4O3 � at m/ z 136. This species goes on to produce C6H4O2 � and C6H4O- anions via CO and CO2 loss, respectively, in sequential dissociation processes at higher collision energies. We compare the protonated and deprotonated vanillin fragmentation pathways with those observed in the decomposition of neutral vanillin and with the dissociation pathways of the vanillin cation. The initial decomposition step for neutral, cationic, and deprotonated vanillin is methyl loss by direct C-O bond breaking, often followed by loss of CO. In contrast, protonated vanillin first loses CO after isomerization.

Ice cores are unique natural archives that provide important information about the past evolution of the Earth’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 Corbassière 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 Corbassière 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.

The present study evaluates the ionization efficiency (IE) of linear and branched C2???C14 dicarboxylic acids (DCAs) by electrospray ionization (ESI) under different conditions. The influence of the concentration of organic modifier (MeOH); mobile phase additive; and its concentration, pH, and DCA structure on IE values is studied using flow injection analysis. The IE values of DCAs increase with the increase of MeOH concentration but also decrease with an increase of pH. The former is due to the increase in solvent evaporation rates; the latter is caused by an ion-pairing between the diacid and the cation (ammonium), which is confirmed by the study with different amines. The investigation of DCA ionization in the presence of different acidic mobile phase additives showed that a significant improvement in the (-)ESI responses of analytes was achieved in the presence of weak hydrophobic carboxylic acids, such as butyric or propanoic acid. Conversely, the use of strong carboxylic acids, such as trichloroacetic acid, was found to cause signal suppression. The results of the IE studies were used to develop the liquid chromatography-high-resolution mass spectrometry (LC-HRMS) method that provided instrumental limits of detection in the range from 6 to 180 pg. Furthermore, upon applying the nonparametric Gaussian process, a model for the prediction of IE values was developed, which contains the number of carbons in the molecule and MeOH concentration as model parameters. As a case study, dicarboxylic acids are quantified in salt-rich effluent and blood serum samples using the developed LC-HRMS method.

Wildfires have an important role in affecting the Earth’s radiative balance. Biomass burning aerosols can scatter or absorb the incoming solar radiation, alter the ice and snow albedo and act as cloud condensation nuclei. Overall, their net contribution to the Earth’s radiative forcing is negative, however this estimate has large uncertainties. To better assess the impact of wildfires on climate (and vice versa), it is crucial to reconstruct their past regional and temporal variability on decadal and centennial timescales. Ice cores are excellent archives to perform such palaeofire reconstructions. Previous studies have reconstructed the occurrence of wildfires in ice cores using both inorganic (ammonium, potassium and black carbon) and organic proxies (levoglucosan, vanillic acid and p-hydroxybenzoic acid). However, a more comprehensive view that involved a broader suite of wildfire proxies was missing. Here, we present a new SPE-UHPLC-HRMS method for the determination of five organic biomass burning tracers (syringic acid, vanillic acid, vanillin, syringaldehyde and p-hydroxybenzoic acid) and pinic acid, as biogenic emission proxy, in ice core samples. This method showed average recoveries of 76% (58-88% range), excellent inter-day reproducibility, no significant matrix effects and fast analysis time (13 min per sample). Comparing the published concentration ranges of the selected species from different ice core regions (i.e. Alps, Greenland, Kamchatka, China and Svalbard Archipelago) with the procedural detection limits of this new methodology, we conclude that four of the six targeted compounds can be successfully detected in real ice and snow samples. Only for vanillin and syringaldehyde, no ice-core measurements have been reported in the scientific literature so far. The method development also involved the evaluation of common laboratory practices such as the melting and refreezing of ice samples before the analysis. We found that the melting and refreezing of the samples resulted in a mass loss for the majority of the investigated compounds, which was more evident at lower concentrations. We hypothesize that the reason of this phenomenon is the adsorption of the compounds on the walls of the glass vials used for this study. In light of this, we propose alternative sample storage strategies that can also be extended for the analysis of other compounds. The method was successfully tested on nine ice core samples from the Colle Gnifetti (European Alps) and it will be applied on ice cores from the Alps and the Russian Altai, contributing to the better understanding of wildfire temporal evolution and their relations with climate.

The vast structural and chemical diversity of metal−organic frameworks (MOFs) provides the exciting possibility of material’s design with tailored properties for gas separation, storage and catalysis. However, after more than twenty years after first reports introducing MOFs, the discovery and control of their synthesis remains extremely challenging due to the lack of understanding of mechanisms of their nucleation and growth. Progress in deciphering crystallization pathways depends on the possibility to follow conversion of initial reagents to products at the molecular level, which is a particular challenge under solvothermal conditions. The present work introduces a detailed molecular-level mechanism of the formation of MIL-53(Al), unraveled by combining in situ time-resolved high-resolution mass-spectrometry, magic angle spinning nuclear magnetic resonance spectroscopy and X-ray diffraction. In contrast to the general belief, the crystallization of MIL-53 occurs via a solid-solid transformation mechanism, associated with the spontaneous release of monomeric aluminum. The role of DMF hydrolysis products, formate and dimethylamine, is established. Our study emphasizes the complexity of MOF crystallization chemistry, which requires case-by-case investigation using a combination of advanced in situ methods for following the induction period, the nucleation and growth across the time domain.

Hydrothermal processesare promising technologies for an efficientvalorization of wet biomass feedstocks or wastes. Their performancestrongly depends on the composition of the feedstock, and methodsto analyze such complex mixtures along with the produced effluentsare in constant progress. Herein, catalytic hydrothermal gasification(cHTG) was used to valorize process water produced from the hydrothermalliquefaction of pine wood. A detailed analysis of the effluents andstreams at various points of the process was performed. About 54%of the feed's chemical energy could be transferred to syntheticnatural gas while an excellent extraction of minerals (98%) into aconcentrated brine (27 wt % dry matter) could be achieved. The lowgasification efficiency observed and the origin of the 41% and 44%loss of chemical energy and carbon in the brine, respectively, wereinvestigated by high-pressure liquid chromatography-high-resolutionmass spectrometry (HPLC-HRMS) analysis of the feed and theeffluents from the salt separator. This allowed for identifying mono-and polycarboxylates accounting for 71% of the carbon in the brine.Increasing temperature in the salt separator to favor decarboxylationreaction was identified as pivotal to improve synthetic natural gasyields, with a 20-fold decrease of carboxylate concentration beingreached with a temperature rise from 723 to 768 K. The use of twonew approaches to estimate the high heating value (HHV) of this feedrich in volatile organic compounds is also reported.

Aerosols still present the largest uncertainty in estimating anthropogenic radiative forcing. Cloud processing is potentially important for secondary organic aerosol (SOA) formation, a major aerosol component: however, laboratory experiments fail to mimic this process under atmospherically relevant conditions. We developed a wetted-wall flow reactor to simulate aqueous-phase processing of isoprene oxidation products (iOP) in cloud droplets. We find that 50 to 70% (in moles) of iOP partition into the aqueous cloud phase, where they rapidly react with OH radicals, producing SOA with a molar yield of 0.45 after cloud droplet evaporation. Integrating our experimental results into a global model, we show that clouds effectively boost the amount of SOA. We conclude that, on a global scale, cloud processing of iOP produces 6.9 Tg of SOA per year or approximately 20% of the total biogenic SOA burden and is the main source of SOA in the mid-troposphere (4 to 6 km).