Henry's Law Research Articles

The pKa of Water and the Fundamental Laws Describing Solution Equilibria: An Appeal for a Consistent Thermodynamic Pedagogy

AbstractA recurring misconception in some textbooks and research papers has led to an abandonment of fundamental physical laws when describing a subset of acid‐base equilibria, especially regarding the role of the solvent. In the specific case of the autoprotolysis of water, experiments and theoretical calculations prove that the Kw of water at 25 °C, 1.00×10−14, is identical to its acid ionization constant, Ka. Nevertheless, several articles have been published erroneously purporting to give theoretical proof that the Ka of water is 10−15.743 (1.81×10−16) and that the Ka of the aqueous proton (hydronium ion) is 55.3 rather than 1.00. Here we argue that using the incorrect numbers has pedagogical implications beyond those of a simple error. Arguments for the incorrect Ka and pKa values require a misapplication of Henry's law and violate long‐standing methods that use Raoult's law and the conservation of matter to describe the behavior of solutions. As a result, chemistry students may be asked to accept one set of physical principles in one course and another set in another course. Here we argue for adherence to fundamental physical laws governing solution equilibria as applied to the autoprotolysis of water and all aqueous acid base equilibria.

Positive Feedback between Partitioning of Carbonyl Compounds and Particulate Sulfur Formation during Haze Episodes.

Carbonyl compounds are important precursors of aqueous aerosols in the atmosphere, while their gas-particle partitioning behaviors and roles in particulate sulfur formation are poorly understood. In this study, we investigate the partitioning of five carbonyl compounds (formaldehyde, acetaldehyde, acetone, glyoxal, and methylglyoxal) during haze episodes in Beijing, China. On haze days, the values of field-derived effective Henry's law coefficients (KHf) on aerosols for these carbonyl compounds are 106-108 M atm-1, which are significantly higher (102-104 times) than those in pure water. Sulfate is observed to have a pronounced "salting-in" effect on these carbonyl compounds, resulting in at least 1-order-of-magnitude increase in their particle-phase concentrations. Parameterization schemes for their partitioning in the ambient aerosols were provided and applied to the multiphase chemical box model (RACM2-CAPRAM). When incorporated into the field-derived parametrization, the model significantly increased hydroxymethanesulfonate (HMS) production by 50-fold compared to using the parameters obtained in pure water, increasing from 2.6 × 10-2 to 1.23 μg m-3 h-1. The formed HMS can facilitate sulfate formation in turn through further oxidation by OH radicals and enhance aerosol hygroscopicity. These findings indicate a positive feedback loop between the partitioning of carbonyl compounds and particulate sulfur formation during haze episodes, providing new insights for controlling particulate pollution and reducing SO2 levels in urban areas.

A QSPR Model for Henry's Law Constants of Organic Compounds in Water and Ethanol for Distilled Spirits.

Henry's law describes the vapor-liquid equilibrium for dilute gases dissolved in a liquid solvent phase. Descriptions of vapor-liquid equilibrium allow the design of improved separations in the food and beverage industry. The consumer experience of taste and odor are greatly affected by the liquid and vapor phase behavior of organic compounds. This study presents a machine learning (ML) based model that allows quick, accurate predictions of Henry's law constants (kH) for many common organic compounds. Users input only a Simplified Molecular-Input Line-Entry System (SMILES) string or a common English name, and the model returns Henry's law estimates for compounds in water and ethanol. Training was performed on 5,690 compounds. Training data were gathered from an existing database and were supplemented with quantum mechanical (QM) calculations. An extra trees regression model was generated that predicts kH with a mean absolute error of 1.3 in log space and an R2 of 0.98. The model is applied to common flavor and odor compounds in bourbon whiskey as a test case for food and beverage applications.

Simulation of lithium hydroxide decomposition using deep potential molecular dynamics.

Chemical reactions and vapor-liquid equilibria for molten lithium hydroxide (LiOH) were studied using molecular dynamics simulations and a deep potential (DP) model. The neural network for the model was trained on quantum density functional theory data for a range of conditions. The DP model allows simulations over timescales of hundreds of ns, which provide equilibrium compositions for the systems of interest. Single-phase NPT simulations of the liquid show the decomposition of LiOH into lithium oxide (Li2O) and dissolved water (H2O). These DP results were validated by direct abinitio molecular dynamics simulations that confirmed the accuracy of the model with respect to reaction kinetics and equilibrium properties of the melt. The reactive vapor-liquid behavior of this system was subsequently studied using direct coexistence interfacial DP simulations. Partial pressures of H2O in the vapor are found to be in close agreement with available experimental measurements. By fitting temperature-dependent expressions for the reaction equilibrium and Henry's law constants, the equilibrium composition for any given initial composition and temperature can be quantitatively modeled. For high initial concentrations of Li2O or H2O, mixtures of LiOH + Li2O/H2O are found to undergo phase separation. The present study illustrates how DP-based molecular dynamics simulations can be used for quantitative modeling of multiphase reactive behavior with the accuracy of the underlying abinitio quantum chemical methods.

Prediction of organic sulfur solubility in mixed solvent using feature-based transfer learning and a hybrid Henry's law constant calculation method

Prediction of organic sulfur solubility in mixed solvent using feature-based transfer learning and a hybrid Henry's law constant calculation method

Experimental study of hydrogen sulfide (H2S) behavior in brine/n-decane mixtures under HPHT conditions

This research investigates the dynamic behavior of hydrogen sulfide (H2S) under oil reservoir conditions, focusing on their interplay within both aqueous and organic phases. Surprising findings emerge, notably the heightened solubility of H2S at 250°C compared to 150°C, with values of 19.9 mg to 41.5 and 12.8 mg to 16.4 mg in 100ml of solution, respectively, diverging from conventional expectations, due to organosulfur compounds generated at the water/n-decane interface under high pressure and temperature conditions. Through an examination of Henry's Law and the calculation of Henry's constants across several temperatures, insights into these observations are gained. In the organic phase, temperature is observed to catalyze the formation of organosulfur compounds from n-decane and H2S. Notable compounds identified include aromatic hydrocarbons bearing sulfur substituents. highlighting the presence of 2-Propyldibenzothiophene (2 – 392 mg/mL), which represents between 57 and 95% of the total concentration of organosulfur compounds found in the organic fraction, being more abundant at 250°C. These findings underscore the intricate interplay between temperature, pressure, and phase composition, elucidating the nuanced solubility patterns and reaction dynamics of sulfur and organosulfur compounds.

Interactions between volatile air pollutants and atmospheric water production – Effects of chemical properties, mechanisms, and transfer processes

Regional water scarcity is among the most urgent challenges of global climate change. Atmospheric water harvesting is a promising method to mitigate these challenges, and the atmospheric water generator (AWG) is already an established technology. Although this method can produce over 10,000 L of water per day, the water's quality has not been studied in depth. Air pollutants, especially volatile organic compounds (VOCs), are potential contaminants of water produced from air. We evaluated the chemical and physical parameters of different VOCs that might influence their ability to be transferred from air to AWG water. Our findings strongly suggest that the ability to form hydrogen bonds is a key factor in this transfer. Henry's law constant, polarity, and intrinsic solubility were the main predictors of a VOC's transfer to AWG water. Hence, aliphatic or aromatic compounds (such as benzene or octane) were not found at significant concentrations in AWG water (e.g. above WHO guidelines), whereas ammonia and alcohol compounds were. This should be taken into consideration when analyzing potential contaminants in harvested atmospheric water. The condensation process itself was also found to enhance the transfer of VOCs into water droplets, and higher relative humidity (%RH) also increased VOC transfer. Gas-phase infrared spectrum analysis of VOCs at different %RH revealed possible interactions between water vapor and specific VOCs in the air. However, our main conclusion from this study is that VOC transfer from the air into AWG water occurs predominantly via dissolution in the condensed droplets, and strongly depends on their chemical properties of polarity and hydrogen-bond formation.

Selectivities of Carbon Dioxide over Ethane in Three Methylimidazolium-Based Ionic Liquids: Experimental Data and Modeling.

This work focused on the solubility of ethane in three promising ionic liquids {1-Hexyl-3-methylimidazolium bis(trifluormethylsulfonyl) imide [HMIM][Tf2N], 1-Butyl-3-methyl-imidazolium dimethyl-phosphate [BMIM][DMP], and 1-Propyl-3-methylimidazolium bis(trifluoromethyl-sulfonyl)-imide [PMIM][Tf2N]}. The solubilities were measured at 303.15 K to 343.15 K and pressures up to 1.4 MPa using a gravimetric microbalance. The overall ranking of ethane solubility in the ionic liquids from highest to lowest is the following: [HMIM][Tf2N] > [PMIM][Tf2N] > [BMIM][DMP]. The Peng-Robinson equation of state was used to model the experimental data using three different mixing rules: van der Waals one, van der Waals two, and Wong-Sandler mixing rules combined with the Non-Random Two-Liquid model. The average absolute deviations for the three mixing rules for the ionic liquids at the three temperatures were 4.39, 2.45, and 2.45%, respectively. Henry's Law constants for ethane in [BMIM] [DMP] were the highest (lowest solubility) amongst other ionic liquids studied in this work. The solubility ranking for the 3 ILs was confirmed by calculating their overall polarity parameter (N) using COSMO-RS. The selectivity of CO2 over C2H6 was estimated at three temperatures, and the overall ranking of the selectivity was in the following order: [PMIM][Tf2N] > [BMIM][DMP] > [HMIM][Tf2N] > Selexol. Selexol is an efficient and widely used physical solvent in gas sweetening. It has lower selectivity than the three ionic liquids studied. [PMIM][Tf2N], a promising solvent, has the highest selectivity among the three ILs studied and would, therefore, be the best choice if, in addition to carbon dioxide capture, ethane co-absorption was to be avoided. The enthalpy and entropy of solvation at infinite dilution were also estimated.

Insights on influence of polymer molecular weight on gas sorption, transport and plasticization in glassy 6FDA-DAM polyimide membranes

It is well-known that spinning of defect-free asymmetric polyimide hollow fibers is promoted by using high polymer molecular weight. On the other hand, effects of polymer molecular weight on microstructure and separation performance of dense film 6FDA-based polyimide membranes relevant to sheath layers of composite membranes are less well-explored. In this work, gas sorption, diffusion and permeation of CO2, N2 and CH4 for 6FDA-DAM dense films are considered for 45 kDa and 176 kDa weight average molecular weights. Such molecular weights are relevant for practical hollow fiber spinning of membranes. Earlier results for polystyrene samples show similar trends in dual mode sorption model results like those noted here for the 6FDA-DAM polyimide case; however, effects on permeation like those considered here were not addressed for the polystyrene case. Here we also address actual pure and mixed gas CO2 and CH4 permeation and show higher free volumes, higher gas permeability but lower 50:50 CO2/CH4 selectivity associated with the higher molecular weight sample. Analysis using the self-consistent dual-mode sorption and transport models help understand the observed trends. Our results suggest denser packing of polymer segments exists in the Henry's law environment of the low molecular weight sample. Moreover, the higher polymer segmental packing in the Henry's law environment suppresses CO2 plasticization with a dual-mode microstructure controlling separation performance and plasticization behavior for this important member of the 6FDA polyimide family. We show evidence of effects of charge transfer complexes as possible main features in these trends. These dense film results help guide future work on dense sheath layers on composite hollow fiber membranes.

Oil sands process-affected water composition effect on Henry's law constants for polycyclic aromatic compounds: Theory and experiment

Oil sands process-affected water (OSPW) is a source of atmospheric emission for polycyclic aromatic compounds (PACs), compounds known to have toxic effects on humans. Estimating emissions and assessing the chemical fate of PACs requires measured or predicted physical-chemical properties such as Henry's law constants (H), that can be used to predict chemical transfer into the atmosphere. OSPW is a complex water-based mixture that is highly variable in composition and nature and contains both organic and inorganic ions. This study uses COSMO-RS solvation theory to estimate and compare Henry's law constants for a set of PACs in both water and theoretically modelled OSPW, to assess the expected deviation that occurs from pure water H values due to the ionic content within OSPW. Experimental measurements of Henry's law constants for PACs in pure water and OSPW using EVA-coated passive dosing and sampler beads were also made in support of our theoretical predictions. For the theory work, OSPW composition data for the Athabasca oil sands in Alberta were used to model a simulated OSPW environment with realistic sodium, chloride, fluoride, sulfate, potassium, bicarbonate, and naphthenic acid concentrations. Theory results indicate that the combined presence of these ions at OSPW concentrations has a negligible effect on H values, causing on average a 3% or 0.014 log unit deviation. By comparison, temperature has a much larger influence on H values, with estimations showing an average 0.20 log unit increase for a 5 °C increase in temperature. The experimental results demonstrate that Henry's law constants can be accurately and precisely measured with this technique in pure water but with less precision in OSPW. Nevertheless, the experimental results support the conclusion that Henry's law constants for OSPW can be accurately estimated assuming a pure water phase.

Urban air PCDD/Fs: Dry deposition fluxes and mass transfer coefficients determined using a water surface sampler

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) cause significant environmental concerns. Atmospheric PCDD/Fs permeate water bodies and other ecosystems through wet and dry deposition. In an urban site, dry deposition flux samples of gaseous phase PCDD/Fs were collected by a water surface sampler (WSS) operated between June 2022 and June 2023. There is a conspicuous absence of literature on the direct measurement of dry deposition flux levels in the gaseous phase of PCDD/Fs. In the study, PCDD/Fs in the gas phase reaching the WSS dissolved in the water according to Henry's Law. The PCDD/Fs in the water were transferred to an XAD-2 resin column, sorbing the dissolved PCDD/Fs. The average monthly gas phase dry deposition flux was 34.07 ± 9.35 pg/m2-day (7.35 ± 2.16 pg I-TEQ/m2-day). The highest flux was measured in March (49.53 pg/m2-day), and the lowest was in August (18.64 pg/m2-day). These values indicated the direct flux from air to water. The atmospheric concentration of the gas-phase ranged from 68.38 to 126.88 fg/m3 (13.22–25.01 fg I-TEQ/m3). Dry deposition fluxes and concentrations of atmospheric PCDD/Fs were bigger in the colder months than in the warmer months. This was probably due to a significant increase in residential heating during the colder months, decreased photochemical reactions, and lower mixing heights. Regarding congeners in the dry deposition flux and concentration values in I-TEQ units, 2,3,7,8-TCDD compound predominated with the proportions of 31.61 ± 7.76% and 29.09 ± 12.34%, respectively. Concurrently measured dry deposition flux (Fg) and ambient air concentration (Cg) of PCDD/Fs were considered in the determination of mass transfer coefficient (MTC = Fg/Cg) calculation for each PCDD/F congener. The average MTC for targeted 17 PCDD/Fs was 0.45 ± 0.15 cm/s, and it fluctuated between 0.89 ± 0.30 cm/s for 2,3,7,8-TCDF and 0.2 ± 0.16 cm/s for OCDD.

Efficacy of Aflatoxin B1 and Fumonisin B1 Adsorption by Maize, Wheat, and Oat Bran.

Mycotoxins, especially aflatoxin B1 (AFB1) and fumonisin B1 (FMB1), are common contaminants in cereal-based foods. Instances of contamination are predicted to increase due to the current challenges induced by climate change. Despite the health benefits of whole grains, the presence of mycotoxins in bran remains a concern. Nonetheless, previous research indicates that wheat bran can adsorb mutagens. Therefore, this study investigated the capacity of maize, wheat, and oat brans to adsorb AFB1 and FMB1 under varying in vitro conditions, including pH, binding time, temperature, particle size, and the amount of bran utilized. Maize bran demonstrated a high AFB1 adsorption capacity (>78%) compared to wheat and oat brans. However, FMB1 was not adsorbed by the brans, possibly due to its hydrophilic nature. Lower temperature (≤25 °C) enhanced AFB1 adsorption efficacy in wheat and oat bran, while for maize bran, the highest adsorption occurred at 37 °C. A linear model following Henry's law best explained AFB1 adsorption by the brans. Further studies identified the pericarp layer of bran as the primary site of AFB1 adsorption, with the initial liquid volume being a critical factor. The study concludes that bran could potentially act as an effective bioadsorbent. Further research is essential to confirm the adsorption efficacy and the bioavailability of AFB1 through in vivo experiments.

Vapor‐liquid interfacial properties of binary mixtures from molecular simulation and density gradient theory

AbstractProperties of the vapor‐liquid interface of 16 binary mixtures were studied using molecular dynamics simulations and density gradient theory in combination with the PCP‐SAFT equation of state. All binary combinations of the heavy‐boiling components (cyclohexane, toluene, acetone, and carbon tetrachloride) with the light‐boiling components (methane, carbon dioxide, hydrogen chloride, and nitrogen) were investigated at 0.7 times the critical temperature of the heavy‐boiling component in the whole composition range. Data on the surface tension, the enrichment, the relative adsorption, and the interfacial thickness, as well as for the vapor‐liquid equilibrium and Henry's law constant are reported. The binary interaction parameters were fitted to experimental data in a consistent way for all systems and both methods. Overall, the results from both methods agree well for all investigated properties. The interfacial properties of the different studied systems differ strongly. We show that these differences are directly related to the underlying phase equilibrium behavior.

Carbon Dioxide Solubility in Three Bis Tri (Fluromethylsulfonyl) Imide-Based Ionic Liquids.

This study delves into the necessity of mitigating carbon dioxide (CO2) emissions, focusing on effective capture methods to combat global warming by investigating the solubility of CO2 in three ionic liquids (ILs), 1-Decyl-3-MethylimidazoliumBis (Trifluromethylsulfonyl Imide) [IL1], 1-Hexadecyl-3-Methyl imidazoliumBis (Trifluromethylsulfonyl Imide) [IL2] and Triethytetradecyl Ammonium Bis (Trifluromethylsulfonyl Imide) [IL3]. Solubility experiments were conducted at (30, 50 and 70) °C with pressures up to 1.5 MPa. The research shows [IL2] as the superior candidate for CO2 capture, with its longer alkyl chain, and is confirmed by its lower Henry's Law constant. Utilizing the Peng Robinson equation of state, the study correlates well with the solubility measurements using three mixing rules. The study reveals promising results for IL1, IL2 and IL3 surpassing all other published ionic liquids including Selexol/Genesorb 1753, except for 1-Methyl-3-octylimidazolium bis(trifluoromethylsulfonyl)imide. Insights into the enthalpy and entropy of absorption underscore the significant impact of IL structure on CO2 solubility, emphasizing the potential of tailored ILs for advanced carbon capture strategies. In summary, this research highlights [IL2] as the optimal choice for CO2 capture, offering valuable contributions to the ongoing efforts in combating climate change.

Understanding shape selectivity effects of hydroisomerization using a reaction equilibrium model.

We study important aspects of shape selectivity effects of zeolites for hydroisomerization of linear alkanes, which produces a myriad of isomers, particularly for long chain hydrocarbons. To investigate the conditions for achieving an optimal yield of branched hydrocarbons, it is important to understand the role of chemical equilibrium in these reversible reactions. We conduct an extensive analysis of shape selectivity effects of different zeolites for the hydroisomerization of C7 and C8 isomers at chemical reaction equilibrium conditions. The reaction ensemble Monte Carlo method, coupled with grand-canonical Monte Carlo simulations, is commonly used for computing reaction equilibrium of heterogeneous reactions. The computational demands become prohibitive for a large number of reactions. We used a faster alternative in which reaction equilibrium is obtained by imposing chemical equilibrium in the gas phase and phase equilibrium between the gas phase components and the adsorbed phase counterparts. This effectively mimics the chemical equilibrium distribution in the adsorbed phase. Using Henry's law at infinite dilution and mixture adsorption isotherm models at elevated pressures, we calculate the adsorbed loadings in the zeolites. This study shows that zeolites with cage or channel-like structures exhibit significant differences in selectivity for alkane isomers. We also observe a minimal impact of pressure on the gas-phase equilibrium of these reactions at typical experimental reaction temperatures 400-700K. This study marks initial strides in understanding the reaction product distribution for long-chain alkanes.

Impact of gas dry deposition parameterization on secondary particle formation in an urban canyon

This study investigates the impact of the parameterization of dry deposition on the local gas-particle partitioning between ammonium nitrate NH4NO3 and its precursor gases (ammonia, NH3 and nitric acid, HNO3) through chemistry-coupled large-eddy simulations on the dispersion of reactive gaseous and particulate pollutant in an idealized street canyon. A key factor in the parameterization of dry deposition is the effective Henry's Law constant H*. Three distinct characterizations of H* are compared: two drawn from existing literature (referred to as Model 1 and Model 2) and one typical of low pH conditions (referred to as Model 3), which could be more representative of urban areas. Model 3 shows contrasting gas-particle partitioning results between NH3, HNO3, and NH4NO3 with Model 1 and Model 2. In detail, the NH4NO3 concentrations in the street of Model 1 and Model 2 are smaller than the background NH4NO3 concentration. However, Model 3 shows higher NH4NO3 concentration in the street than the background NH4NO3 concentration. This is because the dry deposition fluxes of NH3 and HNO3 are higher in Model 1 and Model 2 than in Model 3, resulting in less available NH3 and HNO3 for NH4NO3 formation. These findings highlight the importance of selecting an appropriate H* characterization that is tailored to the specific environmental conditions under investigation.

Evaluation of the vacuum effect on headspace solid-phase microextraction of volatile organic compounds from aqueous samples using finite element analysis modeling

Headspace solid-phase microextraction (HSSPME) of volatile organic compounds (VOCs) from aqueous samples under vacuum conditions (Vac-HSSPME) allows increasing extraction rates and decreasing detection limits compared to HSSPME under atmospheric pressure. The positive effect of the vacuum on HSSPME of an analyte can be quickly estimated using its Henry's law constant (HLC). According to the two-layer model of evaporation, substantial positive effect of the vacuum can be expected for analytes with HLC lower than 1.6·10−4 atm m3 mol−1 (0.0065 at 25 °C), but the model does not consider possible effects of other important extraction parameters. This research was aimed at the evaluation of the possible effect of vacuum on the equilibration time and extracted amounts of analytes with various HLC and fiber coating-headspace distribution constants (Kfh) using the computational model recently developed in COMSOL Multiphysics® software. It has been proven that HSSPME under vacuum provides faster equilibration of VOCs with all studied Kfh and HLC. The largest vacuum effect on the extracted analyte amount was 3.9–4.0 times at logKfh = 6 and HLC = 10−6–10−3. The substantial (≥1.5 times) vacuum impact should not be expected for analytes with logKfh < 5 for 15-min extraction and logKfh < 5.5 for 30-min extraction. The vacuum impact should be more pronounced when using fiber coatings with a stronger affinity to analytes. The obtained results will be useful for the development of new methods based on Vac-HSSPME and evaluation whether HSSPME is reasonable to conduct under vacuum conditions for faster equilibration and/or lower detection limits.

PACMAN: A Robust Partial Atomic Charge Predicter for Nanoporous Materials Based on Crystal Graph Convolution Networks.

We report a fast and easy method (PACMAN) to assign partial atomic charges on metal-organic framework (MOF) and covalent-organic framework (COF) crystal structures based on graph convolution networks (GCNs) trained on >1.8 million high-fidelity partial atomic charge data obtained from the Quantum Metal-Organic Framework (QMOF) database. The developed model shows outstanding performance, achieving a mean absolute error (MAE) of 0.0055 e (test set performance) while maintaining consistency with DDEC6, Bader, and CM5 charges across diverse chemistry and topologies of MOFs and COFs. We find that the new method accurately assigns partial atomic charges for ion-containing nanoporous materials, which has not been possible in previous machine learning (ML) models. Grand canonical Monte Carlo (GCMC) simulation results for CO2 and N2 uptakes and the Widom particle insertion calculation for Henry's law constant of water results based on PACMAN and the original DDEC6 charges show excellent agreements compared to other ML models reported in the literature. The runtime analysis of the new method demonstrates that the partial atomic charges of MOF and COF structures with up to 500 atoms can be obtained in less than 10 s. An easy-to-use web interface has been developed to facilitate the adoption of the developed model.

Development of a multiphase chemical mechanism to improve secondary organic aerosol formation in CAABA/MECCA (version 4.7.0)

Abstract. During the last few decades, the impact of multiphase chemistry on secondary organic aerosols (SOAs) has been demonstrated to be the key to explaining laboratory experiments and field measurements. However, global atmospheric models still show large biases when simulating atmospheric observations of organic aerosols (OAs). Major reasons for the model errors are the use of simplified chemistry schemes of the gas-phase oxidation of vapours and the parameterization of heterogeneous surface reactions. The photochemical oxidation of anthropogenic and biogenic volatile organic compounds (VOCs) leads to products that either produce new SOA or are taken up by existing aqueous media like cloud droplets and deliquescent aerosols. After partitioning, aqueous-phase processing results in polyols, organosulfates, and other products with a high molar mass and oxygen content. In this work, we introduce the formation of new low-volatility organic compounds (LVOCs) to the multiphase chemistry box model CAABA/MECCA. Most notable are the additions of the SOA precursors, limonene and n-alkanes (5 to 8 C atoms), and a semi-explicit chemical mechanism for the formation of LVOCs from isoprene oxidation in the gas and aqueous phases. Moreover, Henry's law solubility constants and their temperature dependences are estimated for the partitioning of organic molecules to the aqueous phase. Box model simulations indicate that the new chemical scheme predicts the enhanced formation of LVOCs, which are known for being precursor species to SOAs. As expected, the model predicts that LVOCs are positively correlated to temperature but negatively correlated to NOx levels. However, the aqueous-phase processing of isoprene epoxydiols (IEPOX) displays a more complex dependence on these two key variables. Semi-quantitative comparison with observations from the SOAS campaign suggests that the model may overestimate methylbutane-1,2,3,4-tetrol (MeBuTETROL) from IEPOX. Further application of the mechanism in the modelling of two chamber experiments, one in which limonene is consumed by ozone and one in which isoprene is consumed by NO3 shows a sufficient agreement with experimental results within model limitations. The extensions in CAABA/MECCA are transferred to the 3D atmospheric model MESSy for a comprehensive evaluation of the impact of aqueous- and/or aerosol-phase chemistry on SOA at a global scale in a follow-up study.

Ammonia permeation and plasticization of glassy polymeric membranes

Ammonia (NH3) is a vital industrial chemical and a potential clean fuel, whose production is increasing globally. The permeation of ammonia through glassy polymeric membranes demonstrates considerable variability, due to hydrogen bonding with both the polymer and residual water. This study reveals the underlying mechanisms for ammonia permeability within membranes, which is strongly correlated with the presence of water and the polymer's chemistry. Three polymers with varying water/ammonia affinity were studied: poly (vinyl alcohol) (PVA), polysulfone (PSU), and Teflon AF 1600. Ammonia was found to readily plasticize PVA, with sorption isotherms that follow Henry's law at conditions below the nominal glass transition temperature. Residual water within the PVA membranes increased ammonia permeability by an order of magnitude greater than that observed for well-dried PVA, due to water-induced swelling. PSU, being hydrophobic, was unaffected by residual water, though ammonia permeability was clearly time-dependent with a 50 % reduction over 4 days. This was attributed to ammonia clustering within the ammonia phobic PSU, which resulted in pore-blocking. The superhydrophobic Teflon AF 1600 membrane demonstrated the same time dependent permeability behaviour, but at a much faster timescale of minutes rather than days. It is suggested that this relates to the rate of formation of ammonia clusters, which is dependent on the degree of ammonia sorption within the polymer.