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Cryomicroscopy is commonly hampered by frost accumulation, reducing the visual clarity of the specimen. Pulling a vacuum or purging with nitrogen gas can greatly reduce the sample chamber's humidity, but at cryogenic temperatures, even minute concentrations of water vapor can still result in frost deposition. Here, a hygroscopic ice frame was created around the specimen to suppress frost growth during cryomicroscopy. Specifically, fluorescently tagged rat brain vessels were frozen on a silicon nitride window with an ice frame, and the luminescence of the fluorescent tag was improved by a factor of 6 compared to a similar specimen in only a nitrogen purge environment. These findings suggest that the simple implementation of a hygroscopic ice frame surrounding the specimen can substantially improve the visual clarity for cryomicroscopy, beyond that of a vacuum or nitrogen purge system. Center of BioMolecular Structure (CBMS); National Institutes of Health, the National Institute of General Medical Sciences (NIGMS), through a Center Core P30 Grant [P30GM133893]; DOE Office of Biological and Environmental Research (DOE-BER) [KP1607011]; DOE-BER Published version This work was supported by the Center of BioMolecular Structure (CBMS). CBMS is primarily supported by the National Institutes of Health, the National Institute of General Medical Sciences (NIGMS), through a Center Core P30 Grant (P30GM133893), and by the DOE Office of Biological and Environmental Research (DOE-BER) (KP1607011). The BioImaging Core within the CMBS was supported entirely by the DOE-BER.

We have used the COSMOtherm program to estimate activity coefficients and solubilities of mono- and alpha, omega-dicarboxylic acids and water in binary acid-water systems. The deviation from ideality was found to be larger in the systems containing larger acids than in the systems containing smaller acids. COnductor-like Screening MOdel for Real Solvents (COSMO-RS) underestimates experimental monocarboxylic acid activity coefficients by less than a factor of 2, but experimental water activity coefficients are underestimated more especially at high acid mole fractions. We found a better agreement between COSMOtherm-estimated and experimental activity coefficients of monocarboxylic acids when the water clustering with a carboxylic acid and itself was taken into account using the dimerization, aggregation, and reaction extension (COSMO-RS-DARE) of COSMOtherm. COSMO-RS-DARE is not fully predictive, but fit parameters found here for water-water and acid-water clustering interactions can be used to estimate thermodynamic properties of monocarboxylic acids in other aqueous solvents, such as salt solutions. For the dicarboxylic acids, COSMO-RS is sufficient for predicting aqueous solubility and activity coefficients, and no fitting to experimental values is needed. This is highly beneficial for applications to atmospheric systems, as these data are typically not available for a wide range of mixing states realized in the atmosphere, due to a lack of either feasibility of the experiments or sample availability. Based on effective equilibrium constants of different clustering reactions in the binary solutions, acid dimer formation is more dominant in systems containing larger dicarboxylic acids (C-5-C-8), while for monocarboxylic acids (C-1-C-6) and smaller dicarboxylic acids (C-2-C-4), hydrate formation is more favorable, especially in dilute solutions.

Atmospheric autoxidation of volatile organic compounds (VOC) leads to prompt formation of highly oxidized multifunctional compounds (HOM) that have been found crucial in forming ambient secondary organic aerosol (SOA). As a radical chain reaction mediated by oxidized peroxy (RO2) and alkoxy (RO) radical intermediates, the formation pathways can be intercepted by suitable reaction partners, preventing the production of the highest oxidized reaction products, and thus the formation of the most condensable material. Commonly, NO is expected to have a detrimental effect on RO2 chemistry, and thus on autoxidation, whereas the influence of NO2 is mostly neglected. Here it is shown by dedicated flow tube experiments, how high concentration of NO2 suppresses cyclohexene ozonolysis initiated autoxidation chain reaction. Importantly, the addition of NO2 ceases covalently bound dimer production, indicating their production involving acylperoxy radical (RC(O)OO•) intermediates. In related experiments NO was also shown to strongly suppress the highly oxidized product formation, but due to possibility for chain propagating reactions (as with RO2 and HO2 too), the suppression is not as absolute as with NO2. Furthermore, it is shown how NOx reactions with oxidized peroxy radicals lead into indistinguishable product compositions, complicating mass spectral assignments in any RO2 + NOx system. The present work was conducted with atmospheric pressure chemical ionization mass spectrometry (CIMS) as the detection method for the highly oxidized end-products and peroxy radical intermediates, under ambient conditions and at short few second reaction times. Specifically, the insight was gained by addition of a large amount of NO2 (and NO) to the oxidation system, upon which acylperoxy radicals reacted in RC(O)O2 + NO2 → RC(O)O2NO2 reaction to form peroxyacylnitrates, consequently shutting down the oxidation sequence. Keywords: acylperoxy radicals; Autoxidation; dimers; Highly oxidized multifunctional compounds; Highly oxygenated molecules; HOM; nitrogen oxides; peroxyacylnitrate

NO3 radical oxidation of most monoterpenes is a significant source of secondary organic aerosol (SOA) in many regions influenced by both biogenic and anthropogenic emissions, but there are very few published mechanistic studies of NO3 chemistry beyond simple first generation products. Here, we present a computationally derived mechanism detailing the unimolecular pathways available to the second generation of peroxy radicals following NO3 oxidation of Delta-3-carene, defining generations based on the sequence of peroxy radicals formed rather than number of oxidant attacks. We assess five different types of unimolecular reactions, including peroxy and alkoxy radical (RO2 and RO) hydrogen shifts, RO2 and RO ring closing (e.g., endoperoxide formation), and RO decomposition. Rate constants calculated using quantum chemical methods indicate that this chemical system has significant contribution from both bimolecular and unimolecular pathways. The dominant unimolecular reactions are endoperoxide formation, RO H-shifts, and RO decomposition. However, the complexity of the overall reaction is tempered as only 1 or 2 radical propagation pathways dominate the fate of each radical intermediate. Chemical ionization mass spectrometry (CIMS) measurements using the NO3- reagent ion during Delta-3-carene + NO3 chamber experiments show products consistent with each of the three types of unimolecular reactions predicted to be important from the computational mechanism. Moreover, the SIMPOL group contribution method for predicting vapor pressures suggests that a majority of the closed-shell products inferred from these unimolecular reactions are likely to have low enough vapor pressure to be able to contribute to SOA formation.

We present ambient observations of dimeric monoterpene oxidation products (C16-20HyO6-9) in gas and particle phases in the boreal forest in Finland in spring 2013 and 2014, detected with a chemical ionization mass spectrometer with a filter inlet for gases and aerosols employing acetate and iodide as reagent ions. These are among the first online dual-phase observations of such dimers in the atmosphere. Estimated saturation concentrations of 10(-15) to 10(-6)mu gm(-3) (based on observed thermal desorptions and group-contribution methods) and measured gas-phase concentrations of 10(-3) to 10(-2)mu gm(-3) (similar to 10(6)-10(7)moleculescm(-3)) corroborate a gas-phase formation mechanism. Regular new particle formation (NPF) events allowed insights into the potential role dimers may play for atmospheric NPF and growth. The observationally constrained Model for Acid-Base chemistry in NAnoparticle Growth indicates a contribution of similar to 5% to early stage particle growth from the similar to 60 gaseous dimer compounds. Plain Language Summary Atmospheric aerosol particles influence climate and air quality. We present new insights into how emissions of volatile organic compounds from trees are transformed in the atmosphere to contribute to the formation and growth of aerosol particles. We detected for the first time over a forest, a group of organic molecules, known to grow particles, in the gas phase at levels far higher than expected. Previous measurements had only measured them in the particles. This finding provides guidance on how models of aerosol formation and growth should describe their appearance and fate in the atmosphere.

Particulate phase reactions between organic and inorganic compounds may significantly alter aerosol chemical properties, for example, by suppressing particle volatility. Here, chemical processing upon drying of aerosols comprised of organic (acetic, oxalic, succinic, or citric) acid/monovalent inorganic salt mixtures was assessed by measuring the evaporation of the organic acid molecules from the mixture using a novel approach combining a chemical ionization mass spectrometer coupled with a heated flow tube inlet (TPD-CIMS) with kinetic model calculations. For reference, the volatility, i.e. saturation vapor pressure and vaporization enthalpy, of the pure succinic and oxalic acids was also determined and found to be in agreement with previous literature. Comparison between the kinetic model and experimental data suggests significant particle phase processing forming low-volatility material such as organic salts. The results were similar for both ammonium sulfate and sodium chloride mixtures, and relatively more processing was observed with low initial aerosol organic molar fractions. The magnitude of low-volatility organic material formation at an atmospherically relevant pH range indicates that the observed phenomenon is not only significant in laboratory conditions but is also of direct atmospheric relevance.

A molecular model for urea to be used in conjunction with the simple point charge (SPC) model for liquid water in protein denaturation studies is validated by comparison of molecular dynamics (MD) simulation results to experimental data at 298 K as a function of urea mole fraction. The density, enthalpy of mixing, free enthalpy of urea hydration, and urea diffusion show very good agreement with the experimental values. The experimental error in the free enthalpy of hydration, which is dominated by the inaccuracy of the vapor pressure of solid urea, is larger than the simulation error. This limited accuracy does not allow a check of the nonideality of the solution. Free enthalpies have been obtained by thermodynamic integration. The importance of a correct use of the combinatorial factor in the partition function when interpreting simulation results obtained by thermodynamic integration is discussed. The tested, GROMOS96 compatible, force field parameters form a good basis for biomolecular simulations using urea-water mixtures.

Ultrafast hole dynamics created in molecular systems as a result of sudden ionisation is the focus of much attention in the field of attosecond science. Using the molecule glycine we show through ab initio simulations that the dynamics of a hole, arising from ionisation in the inner valence region, evolves with a timescale appropriate to be measured using X-ray pulses from the current generation of SASE free electron lasers. The examined pump–probe scheme uses X-rays with photon energy below the K edge of carbon (275–280 eV) that will ionise from the inner valence region. A second probe X-ray at the same energy can excite an electron from the core to fill the vacancy in the inner-valence region. The dynamics of the inner valence hole can be tracked by measuring the Auger electrons produced by the subsequent refilling of the core hole as a function of pump–probe delay. We consider the feasibility of the experiment and include numerical simulation to support this analysis. We discuss the potential for all X-ray pump-X-ray probe Auger spectroscopy measurements for tracking hole migration.

A single horizontally-propagating zeroth order Bessel laser beam with a counter-propagating gas flow was used to confine single fine-mode aerosol particles over extended periods of time, during which process measurements were performed. Particle sizes were measured by the analysis of the angular variation of light scattered at 532 nm by a particle in the Bessel beam, using either a probe beam at 405 nm or 633 nm. The vapour pressures of glycerol and 1,2,6-hexanetriol particles were determined to be 7.5 +/- 2.6 mPa and 0.20 +/- 0.02 mPa respectively. The lower volatility of hexanetriol allowed better definition of the trapping environment relative humidity profile over the measurement time period, thus higher precision measurements were obtained compared to those for glycerol. The size evolution of a hexanetriol particle, as well as its refractive index at wavelengths 532 nm and 405 nm, were determined by modelling its position along the Bessel beam propagation length while collecting phase functions with the 405 nm probe beam. Measurements of the hygroscopic growth of sodium chloride and ammonium sulfate have been performed on particles as small as 350 nm in radius, with growth curves well described by widely used equilibrium state models. These are the smallest particles for which single-particle hygroscopicity has been measured and represent the first measurements of hygroscopicity on fine mode and near-accumulation mode aerosols, the size regimes bearing the most atmospheric relevance in terms of loading, light extinction and scattering. Finally, the technique is contrasted with other single particle and ensemble methods, and limitations are assessed.

The vaporization behaviour and thermodynamics of the ionic liquid 1-butyl-3-methylimidazolium bis(trifluoromethyl) sulfonylimide (BMImNTf(2)) were studied by combining the Knudsen Effusion Mass Loss (KEML) and Knudsen Effusion Mass Spectrometry (KEMS) techniques. KEML studies were carried out in a large temperature range (398-567) K by using effusion orifices with 0.3, 1, and 3 mm diameters. The vapor pressures so measured revealed no kinetically hindered vaporization effects and provided second-law vaporization enthalpies at the mean experimental temperatures in close agreement with literature. By exploiting the large temperature range covered, the heat capacity change associated with vaporization was estimated, resulting in a value of -66.8 J K-1 mol(-1), much lower than that predicted from calorimetric measurements on the liquid phase and theoretical calculations on the gas phase. The conversion of the high temperature vaporization enthalpy to 298 K was discussed and the value Delta H-g(l)m(298 K) = (128.6 +/- 1.3) kJ mol(-1) assessed on the basis of data from literature and present work. Vapor pressure data were also processed by the third-law procedure using different estimations for the auxiliary thermal functions, and a Delta H-g(l)m(298 K) consistent with the assessed value was obtained, although the overall agreement is sensitive to the accuracy of heat capacity data. KEMS measurements were carried out in the lower temperature range (393-467) K and showed that the largely prevailing ion species is BMIm(+), supporting the common view of BMImNTf(2) vaporizing as individual, neutral ion pairs also under equilibrium conditions. By monitoring the mass spectrometric signal of this ion as a function of temperature, a second-law Delta H-g(l)m(298 K) of 129.4 +/- 7.3 kJ mol(-1) was obtained, well consistent with KEML and literature results. Finally, by combining KEML and KEMS measurements, the electron impact ionization cross section of BMIm(+) was estimated.

The research was performed to study the simultaneous detection of a homologous series ofα,ω-dicarboxylic acids (C2–C10), oxalic, malonic, succinic, glutaric, adipic, pimelic, suberic, azelaic, and sebacic acids, with capillary electrophoresis using indirect UV detection. Good separation efficiency in 2,6-pyridinedicarboxylic acid as background electrolyte modified with myristyl trimethyl ammonium bromide was obtained. The dicarboxylic acids were ionised and separated within five minutes. For the study, authentic samples were collected onto dry cellulose membrane filters of a cascade impactor (12 stages) from outdoor spring aerosols in an urban area. Hot water and ultrasonication extraction methods were used to isolate the acids from membrane filters. Due to the low concentrations of acids in the aerosols, the extracts were concentrated with solid-phase extraction (SPE) before determination. The enrichment of the carboxylic acids was between 86 and 134% with sample pretreatment followed by 100-time increase by preparation of the sample to 50 μL. Inaccuracy was optimised for all the sample processing steps. The aerosols contained dicarboxylic acids C2–C10. Then, mostly they contained C2, C5, and C10. Only one sample contained succinic acid. In the study, the concentrations of the acids in aerosols were lower than 10 ng/m3.

International audience; This paper presents new experimental results for Normafluid ISO 4113. Vapor pressures of Normafluid were measured from 0.001 kPa to 27 kPa and from 273 to 463 K, using a static apparatus. The experimental vapor pressures were smoothed using the Antoine equation. Air solubility in the fuel at 288 K, 298 K and 308 K and up to 0.8 MPa was also determined. Isobaric thermal expansivitites of Normafluid were determined over the temperature range from 273.15 K to 423.15 K at pressures up to 200 MPa using scanning transitiometry; therefrom thermodynamic relations were used to obtain the isobaric specific heat capacities, specific volumes, isothermal compressibilities, isentropic compressibilities and isentropic bulk modulus over wide pressure and temperature ranges.

Thermochemical data of dibenzofuran, a compound of considerable industrial and environmental significance, obtained from experimental calorimetric and computational techniques are reported in this work. The enthalpy of fusion, (19.4 +/- 1.0) kJ mol(-1), at the temperature of fusion, (355.52 +/- 0.02) K, was determined by differential scanning calorimetry measurements of dibenzofuran. From the standard (p degrees = 0.1 MPa) molar enthalpies of formation of crystalline dibenzofuran, (-29.2 +/- 3.8) kJ mol(-1), and of sublimation, (84.5 +/- 1.0) kJ mol(-1), determined at T = 298.15 K by static bomb combustion calorimetry and by vacuum drop microcalorimetry, respectively, it was possible to calculate the enthalpy of formation of the gaseous compound, (55.0 +/- 3.9) kJ mol(-1), at the same temperature. The enthalpy of formation in the gaseous phase was also determined from G3(MP2)//B3LYP calculations. The same computational strategy was employed in the calculation of the standard molar enthalpies of formation, at T = 298.15 K, in the gas-phase, of single methylated derivatives of benzofuran and dibenzofuran.

Enhancement of number concentrations of particles with sizes less than 25 nm diameter has been frequently observed in the boundary layer over the central Arctic Ocean during summer. The sectional aerosol dynamics model for Marine Aerosol Formation (MAFOR) was applied to evaluate the capability of different nucleation mechanisms to reproduce nucleation events observed during three expeditions (1996, 2001 and 2008) onboard the Swedish icebreaker Oden. Model calculations suggest that a source rate of a condensable organic vapour (OV) of about 2x105 cm -3 s -1 is required to reproduce observed growth of nucleation mode particles. Nucleation rates predicted by the newly proposed combined sulphuric acid nucleation mechanism, which best described new particle formation in the Arctic, ranged from 0.04 to 0.1 cm -3 s -1 . This mechanism additively combines ion-mediated nucleation and cluster activation, and treats condensation of OV without correction of the Kelvin effect. In several events, the simultaneous number enhancement of particles in the 20-50 nm size range remained unexplained by the nucleation mechanisms. This lends support to alternative theories such as the fragmentation of marine gels (≈200-500 nm diameter in size) by physical or chemical processes. Keywords: nucleation, aerosol model, biological particles, secondary organic aerosols, arctic environment (Published: 9 February 2012) Citation: Tellus B 2012, 64 , 17158, DOI: 10.3402/tellusb.v64i0.17158

The sampling artifacts for C(2)-C(5) dicarboxylic acids (DCAs) were studied by collecting high-volume PM(2.5) samples using front and back quartz-fibre filters. The filters were analysed for carbonaceous components, and for inorganic cationic and anionic and organic anionic species. Back/front filter ratios were determined for the C(2)-C(5) DCAs, but also for methanesulphonate (MSA(-)), the various inorganic species, and the carbonaceous components. The sampling artifacts for the inorganic species were small (< 5%) with the exception of those for nitrate. The median back/front filter ratios for MSA(-) and the C(2)-C(5)DCAs increased in the following order: oxalate (1.5%)-succinate (3%)-MSA(-) (4%)-malonate (2%-9%)-glutarate (7%-26%). Most of these ratios are smaller than those that were obtained for organic carbon, total carbon, and especially water-soluble organic carbon. Our back/front ratios for the C(2)-C(5) DCAs are lower to much lower than those found in other studies.

Gibbs free energies of formation for gas, subcooled liquid, and aqueous solution phases were estimated for all 209 polychlorinated biphenyl (PCB) congeners at 298.15 K and 100 000 Pa. A literature search was conducted to locate experimental data or predicted data for PCBs. Where other data were not available, the standard-state enthalpies of formation of the gas and absolute standard-state entropies of the gas were estimated using the NIST Structures and Properties Database and Estimation Program based on Benson's group additivity method. Resultant Gibbs free energies of formation in aqueous solution, as well as all intermediate quantities used in their calculation, are tabulated. Implications of the data relative to dechlorination are briefly discussed.

International audience; Active materials that can solubilize in different compartments of a sample show release properties which might be of interest in some applications where a delayed release of solutes for instance is required. We studied perfume solutes in compartments of Pluronic block copolymers of different compositions and molecular weights over a range of ethanol-water mixtures. Phase diagrams were constructed to identify and map micellar phases, then dynamic light scattering was used to characterize the solute-swollen micelles; NMR provided with the partition of solutes between solvent and micelles, and equilibrium constants K(c) were estimated using headspace analysis. Finally solute-evaporation rates were measured by thermogravimetry. We focused on two typical behaviors: when solubilization in a micellar compartment occurs, delayed release increased with K(c) When solubilization was limited or absent, either because no micelles form or, in the presence of micelles, because solubilization was minor or absent, delayed release was correspondingly absent.

Gibbs free energies of formation for gas, subcooled liquid, and aqueous solution phases were estimated for all 209 polychlorinated biphenyl (PCB) congeners at 298.15 K and 100 000 Pa. A literature search was conducted to locate experimental data or predicted data for PCBs. Where other data were not available, the standard-state enthalpies of formation of the gas and absolute standard-state entropies of the gas were estimated using the NIST Structures and Properties Database and Estimation Program based on Benson's group additivity method. Resultant Gibbs free energies of formation in aqueous solution, as well as all intermediate quantities used in their calculation, are tabulated. Implications of the data relative to dechlorination are briefly discussed.

A modified Kay-type apparatus has been used for the measurement of the critical temperature Tc and critical pressure Pe of thermally stable or slightly unstable alkanols. Since some oxygen-containing compounds decompose at their critical temperature, thermal decomposition was reduced by heating the sample rapidly to the critical temperature in the present apparatus. The critical temperatures and critical pressures were determined by the standard method of visual observation of the disappearance and reappearance of the meniscus between the liquid and vapour phases. Temperatures and pressures were measured with an accuracy of ±0.1 K and of ±0.001 MPa with a calibrated mineral-coated chromel-to-alumel thermocouple, and a transducer assembly, respectively. The critical temperatures and critical pressures of seven esters, three ketones, and two ethers are reported. The results have been compared with the predicted values using the methods of Ambrose and of Somayajulu.