O2 Reaction Research Articles

Heterogeneous photochemical uptake of SO2 on typical brown carbon species: A significant sulfate source

The heterogeneous reactions of SO2 on organic aerosols (OA) have been proposed as a significant source of sulfates. The photochemical conversion of SO2 to sulfates on the surface of light-absorbing OA, i.e., brown carbon (BrC), remained slight understanding. Herein, the photochemical uptake of SO2 on typical BrC species, including aromatic carbonyl compounds (ACs), polycyclic aromatic hydrocarbons (PAHs) and phenols (PHs), was systematically investigated by a flow tube reactor. Light can significantly promote the uptake of SO2 on all BrC species used here, especially for ACs. The initial and steady-state uptake coefficients (γi and γss) of SO2 exhibited positive relationships with the light intensity, whereas they negatively correlated with the initial SO2 concentration. Significant sulfate formation was clearly observed with in situ attenuated total internal reflection infrared (ATR-IR) spectrometer, and H2O and O2 had obvious enhancement effects on the sulfate production. Photoinduced •OH, which primarily originated from •O2− that was generated through an electron transfer process on BrC under irradiation, was determined to be a key driver for the oxidation of SO2 to sulfates. Finally, SO2 lifetime and sulfate formation rate were evaluated on the basis of experimental results, highlighting potential contributions of BrC photochemistry to atmospheric SO2 loss and sulfate sources.

Influence of Wind Flows on Surface O3 Variation over a Coastal Province in Southeast China

Surface ozone (O3) is influenced not only by anthropogenic emissions but also by meteorological factors, with wind direction being one of the most overlooked factors. Here, we combine the observational data of both O3 and wind flow to compare the variation in surface O3 with wind direction between coastal and inland regions of Fujian, a province in the southeast coast of China with complicated topography. We further conduct a numerical simulation using a global chemical transport model, GEOS-Chem, to interpret the observational results, explore the linkages between these O3 variations and wind flows, and identify the dominant processes for the occurrence of high O3 that varies with wind flows. The results from the observations over 2015–2021 suggest that, over coastal regions, surface O3 concentrations show a strong dependence on wind flow changes. On average, during the daytime, when southeasterly winds prevail, the mean of O3 concentrations reaches 83.5 μg/m3, which is 5.0 μg/m3 higher than its baseline values (the mean O3 concentrations), while the northwesterly winds tend to reduce surface O3 by 6.4 μg/m3. The positive O3 anomalies with southeasterly wind are higher in the autumn and summer than in the spring and winter. During the nighttime, the onshore northeasterly winds are associated with enhanced O3 levels, likely due to the airmass containing less NO2, alleviating the titration effects. Over inland regions, however, surface O3 variations are less sensitive to wind flow changes. The GEOS-Chem simulations show that the prevailing southeasterly and southwesterly winds lead to the positive anomaly of chemical reactions of O3 over coastal regions, suggesting enhanced photochemical production rates. Furthermore, southeasterly winds also aid in transporting more O3 from the outer regions into the coastal regions of Fujian, which jointly results in elevated surface O3 when southeasterly winds dominates. When affected by wind flows in different directions, the chemical reaction and transport in the inland regions do not exhibit significant differences regarding their impact on O3. This could be one of the reasons for the difference in O3 distribution between coastal and inland regions. This study could help to deepen our understanding of O3 pollution and aid in providing an effective warning of high-O3 episodes.

Study on the Vertical Distribution and Transport of Aerosols in the Joint Observation of Satellite and Ground-Based LiDAR

The mechanism of aerosol pollution transport remains highly elusive owing to the myriad of influential factors. In this study, ground station data, satellite data, ground-based LiDAR remote sensing data, sounding data, ERA5 reanalysis and a backward trajectory model were combined to investigate the formation process and optical properties of winter aerosol pollution in Beijing and surrounding areas. The analysis of ground station data shows that compared to 2019 and 2021, the pandemic lockdown policy resulted in a decrease in the total number of pollution days and a decrease in the average concentration of particulate matter in the Beijing area in 2020. The terrain characteristics of the Beijing-Tianjin-Hebei (BTH) made it prone to northeast and southwest winds. The highest incidence of aerosol pollution in Beijing occurs in February and March during the spring and winter seasons. Analysis of a typical heavy aerosol pollution process in the Beijing area from 28 February to 5 March 2019 shows that dust and fine particulate matter contributed to the primary pollution; surface air temperature inversion and an average wind speed of less than 3 m/s were conducive to the continuous accumulation of pollutants, which was accompanied by the oxidation reaction of NO2 and O3, forming photochemical pollution. The heavy aerosol pollution was transmitted and diffused towards the southeast, gradually eliminating the pollution. Our results provide relevant research support for the prevention and control of aerosol pollution.

Distinct Site Motifs Activate O2 and H2 on Supported Au Nanoparticles in Liquid Water.

Au nanoparticles catalyze the activation and conversion of small molecules with rates and kinetic barriers that depend on the dimensions of the nanoparticle, composition of the support, and presence of catalytically culpable water molecules that solvate these interfaces. Here, molecular interpretations of steady-state rate measurements, kinetic isotope effects, and structural characterizations reveal how the interface of Au nanoparticles, liquid water, and metal oxide supports mediate the kinetically relevant activation of H2 and sequential reduction of O2-derived intermediates during the formation of H2O2 and H2O. Rates of H2 consumption are 10-100 fold greater on Au nanoparticles supported on metal oxides (e.g., titania) compared to more inert and hydrophobic materials (carbon, boron nitride). Similarly, Au nanoparticles on reducible and Lewis acidic supports (e.g., lanthana) bind dioxygen intermediates more strongly and present lower barriers (<22 kJ mol-1) for O-O bond dissociation than inert interfaces formed with silica (>70 kJ mol-1). Selectivities for H2O2 formation increase significantly as the diameters of the Au nanoparticles increase because differences in nanoparticle size change the relative fractions of exposed sites that exist at Au-support interfaces. In contrast, site-normalized rates and barriers for H2 activation depend weakly on the size of Au nanoparticles and the associated differences in active site motifs. These findings suggest that H2O aids the activation of H2 at sites present across all surface Au atoms when nanoparticles are solvated by water. However, molecular O2 preferentially binds and dissociates at Au-support interfaces, leading to greater structure sensitivity for barriers of O-O dissociation across different support identities and sizes of Au nanoparticles. These insights differ from prior knowledge from studies of gas-phase reactions of H2 and O2 upon Au nanoparticle catalysts within dilute vapor pressures of water (10-4 to 0.1 kPa H2O), in which catalysis occurs at the perimeter of the Au-support interface. In contrast, contacting Au catalysts with liquid water (55.5 M H2O) expands catalysis to all surface Au atoms and enables appreciable H2O2 formation.

Decreased LPS-induced lung injury in pigs treated with a lung surfactant protein A-derived nonapeptide that inhibits peroxiredoxin 6 activity and subsequent NOX1,2 activation.

This study addressed the efficacy of a liposome-encapsulated nine amino acid peptide [peroxiredoxin 6 PLA2 inhibitory peptide-2 (PIP-2)] for the prevention or treatment of acute lung injury (ALI) +/- sepsis. PIP-2 inhibits the PLA2 activity of peroxiredoxin 6 (Prdx6), thereby preventing rac release and activation of NADPH oxidases (NOXes), types 1 and 2. Female Yorkshire pigs were infused intravenously with lipopolysaccharide (LPS) + liposomes (untreated) or LPS + PIP-2 encapsulated in liposomes (treated). Pigs were mechanically ventilated and continuously monitored; they were euthanized after 8 h or earlier if preestablished humane endpoints were reached. Control pigs (mechanical ventilation, no LPS) were essentially unchanged over the 8 h study. LPS administration resulted in systemic inflammation with manifestations of clinical sepsis-like syndrome, decreased lung compliance, and a marked decrease in the arterial Po2 with vascular instability leading to early euthanasia of 50% of untreated animals. PIP-2 treatment significantly reduced the requirement for supportive vasopressors and the manifestations of lung injury so that only 25% of animals required early euthanasia. Bronchoalveolar lavage fluid from PIP-2-treated versus untreated pigs showed markedly lower levels of total protein, cytokines (TNF-α, IL-6, IL-1β), and myeloperoxidase. Thus, the porcine LPS-induced sepsis-like model was associated with moderate to severe lung pathophysiology compatible with ALI, whereas treatment with PIP-2 markedly decreased lung injury, cardiovascular instability, and early euthanasia. These results indicate that inhibition of reactive oxygen species (ROS) production via NOX1/2 has a beneficial effect in treating pigs with LPS-induced ALI plus or minus a sepsis-like syndrome, suggesting a potential role for PIP-2 in the treatment of ALI and/or sepsis in humans.NEW & NOTEWORTHY Currently available treatments that can alter lung inflammation have failed to significantly alter mortality of acute lung injury (ALI). Peroxiredoxin 6 PLA2 inhibitory peptide-2 (PIP-2) targets the liberation of reactive O2 species (ROS) that is associated with adverse cell signaling events, thereby decreasing the tissue oxidative injury that occurs early in the ALI syndrome. We propose that treatment with PIP-2 may be effective in preventing progression of early disease into its later stages with irreversible lung damage and relatively high mortality.

The WRF-CMAQ Simulation of a Complex Pollution Episode with High-Level O3 and PM2.5 over the North China Plain: Pollution Characteristics and Causes

The problem of atmospheric complex pollution led by PM2.5 and O3 has become an important factor restricting the improvement of air quality in China. In drawing on observations and Weather Research and Forecasting-Community Multiscale Air Quality (WRF-CMAQ) model simulations, this study analyzed the characteristics and causes of a regional PM2.5-O3 complex pollution episode in North China Plain, in the period from 3 to 5 April 2019. The results showed that in static and stable weather conditions with high temperature and low wind speed, despite photochemical reactions of O3 near the ground being weakened by high PM2.5 concentrations, a large amount of O3 generated through gas-phase chemical reactions at high altitudes was transported downwards and increased the O3 concentrations at the ground level. The high ground-level O3 could facilitate both the conversion of SO2 and NO2 into secondary inorganic salts and volatile organic compounds into secondary organic aerosols, thereby amplifying PM2.5 concentrations and exacerbating air pollution. The contributions of transport from outside sources to PM2.5 (above 60%) and O3 (above 46%) increased significantly during the episode. This study will play an instrumental role in helping researchers to comprehend the factors that contribute to complex pollution in China, and also offers valuable references for air pollution management.

Unveiling the significant promoting effect of SO2 on Ir/SiO2 catalyst for the CO-SCR of NOx in the presence of O2

Selective catalytic reduction of NOx by CO (CO-SCR) in the presence of O2 is challenging because in this process CO is prone to being oxidized by O2, thus inhibiting NOx reduction by CO. Furthermore, SO2 typically leads to the deactivation of the CO-SCR catalyst. Herein, a significant promoting effect of SO2 on Ir/SiO2 catalyst for the CO-SCR of NOx in the presence of O2 is reported. In-situ X-ray Absorption Fine Structure (XAFS) and X-ray photoelectron spectroscopy (XPS) analysis showed that SO2 does not affect the chemical nature of Ir0 under reaction conditions. However, SO2 can be oxidized to sulfate and deposit on the catalyst surface. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis demonstrated that the presence of SO2 can inhibit the CO + O2 reaction, thus leaving more CO available to reduce NOx over the active Ir0 sites. As a result, the reduction of NOx is remarkably promoted even in the presence of O2 and SO2.

Probing the dynamics and bottleneck of the key atmospheric SO2 oxidation reaction by the hydroxyl radical

SO2 (Sulfur dioxide) is the major precursor to the production of sulfuric acid (H2SO4), contributing to acid rain and atmospheric aerosols. Sulfuric acid formed from SO2 generates light-reflecting sulfate aerosol particles in the atmosphere. This property has prompted recent geoengineering proposals to inject sulfuric acid or its precursors into the Earth's atmosphere to increase the planetary albedo to counteract global warming. SO2 oxidation in the atmosphere by the hydroxyl radical HO to form HOSO2 is a key rate-limiting step in the mechanism for forming acid rain. However, the dynamics of the HO + SO2 → HOSO2 reaction and its slow rate in the atmosphere are poorly understood to date. Herein, we use photoelectron spectroscopy of cryogenically cooled HOSO2- anion to access the neutral HOSO2 radical near the transition state of the HO + SO2 reaction. Spectroscopic and dynamic calculations are conducted on the first ab initio-based full-dimensional potential energy surface to interpret the photoelectron spectra of HOSO2- and to probe the dynamics of the HO + SO2 reaction. In addition to the finding of a unique pre-reaction complex (HO⋯SO2) directly connected to the transition state, dynamic calculations reveal that the accessible phase space for the HO + SO2 → HOSO2 reaction is extremely narrow, forming a key reaction bottleneck and slowing the reaction rate in the atmosphere, despite the low reaction barrier. This study underlines the importance of understanding the full multidimensional potential energy surface to elucidate the dynamics of complex bimolecular reactions involving polyatomic reactants.

Structure, variability, and origin of the low-latitude nightglow continuum between 300 and 1800 nm: evidence for HO2 emission in the near-infrared

Abstract. The Earth's mesopause region between about 75 and 105 km is characterised by chemiluminescent emission from various lines of different molecules and atoms. This emission was and is important for the study of the chemistry and dynamics in this altitude region at nighttime. However, our understanding is still very limited with respect to molecular emissions with low intensities and high line densities that are challenging to resolve. Based on 10 years of data from the astronomical X-shooter echelle spectrograph at Cerro Paranal in Chile, we have characterised in detail this nightglow (pseudo-)continuum in the wavelength range from 300 to 1800 nm. We studied the spectral features, derived continuum components with similar variability, calculated climatologies, studied the response to solar activity, and even estimated the effective emission heights. The results indicate that the nightglow continuum at Cerro Paranal essentially consists of only two components, which exhibit very different properties. The main structures of these components peak at 595 and 1510 nm. While the former was previously identified as the main peak of the FeO “orange arc” bands, the latter is a new discovery. Laboratory data and theory indicate that this feature and other structures between about 800 and at least 1800 nm are caused by emission from the low-lying A′′ and A′ states of HO2. In order to test this assumption, we performed runs with the Whole Atmosphere Community Climate Model (WACCM) with modified chemistry and found that the total intensity, layer profile, and variability indeed support this interpretation, where the excited HO2 radicals are mostly produced from the termolecular recombination of H and O2. The WACCM results for the continuum component that dominates at visual wavelengths show good agreement for FeO from the reaction of Fe and O3. However, the simulated total emission appears to be too low, which would require additional mechanisms where the variability is dominated by O3. A possible (but nevertheless insufficient) process could be the production of excited OFeOH by the reaction of FeOH and O3.

Quantum cascade laser absorption sensor for in-situ, real-time and sensitive measurement of high-temperature SO2 and SO3

We report a mid-infrared quantum cascade laser absorption sensor capable of measuring SO2 and SO3 simultaneously and sensitively at elevated temperatures. In the sensor development, the intense transitions of SO2 and SO3 in the mid-infrared region of 1129 cm−1 and 1398 cm−1 were exploited by two quantum cascade lasers. A high-temperature multipass cell was adopted to increase the absorption path length to 10 m. The quantitative concentrations of SOx were directly obtained from the calibration-free wavelength modulation spectroscopic method, which was validated at varied temperature and pressure conditions. From Allan deviation analysis, we achieved a minimum detection limit of 8 parts per billion (ppb) for SO2 and 3 ppb for SO3, with an average time of 100 s. Lastly, we successfully demonstrated the real-time and sensitive measurement of SO2 and SO3 during the oxidation reaction of SO2 by O3 at 460 K. Our laser sensor shows great potential for in-situ and real-time monitoring of SOx from combustion emissions.

Kinetic study of isoprene hydroxy hydroperoxide radicals reacting with sulphur dioxide and their global-scale impact on sulphate formation.

Isoprene is the most relevant volatile organic compound emitted during the biosynthesis of metabolism processes. The oxidation of isoprene by a hydroxy radical (OH) is one of the main consumption schemes that generate six isomers of isoprene hydroxy hydroperoxide radicals (ISOPOOs). In this study, the rate constants of ISOPOOs + sulphur dioxide (SO2) reactions that eventually generate sulphur trioxide (SO3), the precursor of sulphate aerosol (SO42-(p)), are determined using microcanonical kinetic theories coupled with molecular structures and energies estimated by quantum chemical calculations. The results show that the reaction rates range from 10-27 to 10-20 cm3 molecule-1 s-1, depending on the atmospheric temperature and structure of the six ISOPOO isomers. The effect of SO3 formation from SO2 oxidation by ISOPOOs on the atmosphere is evaluated by a global chemical transport model, along with the rate constants obtained from microcanonical kinetic theories. The results show that SO3 formation is enhanced in regions with high SO2 or low nitrogen oxide (NO), such as China, the Middle East, and Amazon rainforests. However, the production rates of SO3 formation by ISOPOOs + SO2 reactions are eight orders of magnitude lower than that from the OH + SO2 reaction. This is indicative of SO42-(p) formation from the direct oxidation of SO2 by ISOPOOs, which is almost negligible in the atmosphere. The results of this study entail a detailed analysis of SO3 formation from gas-phase reactions of isoprene-derived products.

Quantitative analysis of air-oxidation reactions of thiolate-protected gold nanoclusters.

The interaction of dioxygen (O2) with inorganic nanomaterials is one of the most essential steps to understanding the reaction mechanism of O2-related reactions. However, quantitative analyses for O2-binding processes and subsequent oxidation reactions on the surface are still elusive, whereas the reaction of O2 with molecules such as transition metal complexes has been widely explored. Herein, we have quantitatively evaluated reaction processes of air-oxidation reactions of atomically precise thiolate-protected Au25 nanoclusters ([Au25(SR)18]-) as a model of O2 activation by inorganic nanomaterials. Kinetic analyses on the air-oxidation reaction of [Au25(SR)18]- revealed a controlling factor for O2-activation processes, which could be finely tunable by the protecting thiolate ligands.

Unveiling the chemical kinetics of aminomethanol (NH2CH2OH): insights into H and O2 photo-oxidation reactions and formamide dominance.

Aminomethanol is released into the atmosphere through various sources, including biomass burning. In this study, we have expounded the chemical kinetics of aminomethanol in the reaction pathways initiated by the hydroxyl radical ( H) with the aid of ab initio//density functional theory (DFT) i.e., coupled-cluster theory (CCSD(T))//hybrid-DFT (M06-2X/6-311++G (3df, 3pd). We have explored various possible directions of the H radical on aminomethanol, as well as the formation of distinct pre-reactive complexes. Our computational findings reveal that the H transfer necessitates activation energies ranging from 4.1 to 6.5kcal/mol from the -CH2 group, 3.5-6.5kcal/mol from the -NH2 group and 7-9.3kcal/mol from the -OH group of three rotational conformers. The H transfer from -CH2, -NH2 and -OH exhibits an estimated total rate constant (k OH) of approximately 1.97 × 10-11cm3 molecule-1s-1 at 300K. The branching fraction analysis indicates a pronounced dominance of C-centered NH2 HOH radicals with a favorability of 77%, surpassing the N-centered HCH2OH (20%) and O-centered NH2CH2 (3%) radicals. Moreover, our investigation delves into the oxidation of the prominently favored carbon-centered NH2 HOH radical through its interaction with atmospheric oxygen molecules. Intriguingly, our findings reveal that formamide (NH2CHO) emerges as the predominant product in the NH2 HOH + 3O2 reaction, eclipsing alternative outcomes such as amino formic acid (NH2COOH) and formimidic acid (HN = C(H)-OH). At atmospheric conditions pertinent to the troposphere, the branching fraction value for the formation of formamide is about 99%, coupled with a rate constant of 5.5 × 10-12cm3 molecule-1 s-1. Finally, we have scrutinized the detrimental impact of formamide on the atmosphere. Interaction of formamide with atmospheric hydroxyl radicals could give rise to the production of potentially perilous compounds such as HNCO. Further, unreacted HCH2OH radicals may initiate the formation of carcinogenic nitrosamines when reacting with trace N-oxides (namely, NO and NO2). This, in turn, escalates the environmental risk factors.

K-O2 electrochemistry at the Au/DMSO interface probed by in situ spectroscopy and theoretical calculations.

The reaction mechanism underpinning the operation of K-O2 batteries, particularly the O2 reactions at the positive electrode, is still not completely understood. In this work, by combining in situ Raman spectroelectrochemistry and density functional theory calculations, we report on a fundamental study of K-O2 electrochemistry at a model interface of Au electrode/DMSO electrolyte. The key products and intermediates (O2-, KO2 and K2O2) are identified and their dependency on the electrode potential is revealed. At high potentials, the first reduction intermediate of O2-* radical anions (* denotes the adsorbed state) can desorb from the Au electrode surface and combine with K+ cations in the electrolyte producing KO2via a solution-mediated pathway. At low potentials, O2 can be directly reduced to on the Au electrode surface, which can be further reduced to at extremely low potentials. The fact that K2O2 has only been detected in the very high overpotential regime indicates a lack of KO2 disproportionation reaction both on the Au electrode surface and in the electrolyte solution. This work addresses the fundamental mechanism and origin of the high reversibility of the aprotic K-O2 batteries.

Time-resolved quantification of key species and mechanistic insights in low-temperature tetrahydrofuran oxidation.

We investigate the kinetics and report the time-resolved concentrations of key chemical species in the oxidation of tetrahydrofuran (THF) at 7500 torr and 450-675 K. Experiments are carried out using high-pressure multiplexed photoionization mass spectrometry (MPIMS) combined with tunable vacuum ultraviolet radiation from the Berkely Lab Advanced Light Source. Intermediates and products are quantified using reference photoionization (PI) cross sections, when available, and constrained by a global carbon balance tracking approach at all experimental temperatures simultaneously for the species without reference cross sections. From carbon balancing, we determine time-resolved concentrations for the ROO˙ and ˙OOQOOH radical intermediates, butanedial, and the combined concentration of ketohydroperoxide (KHP) and unsaturated hydroperoxide (UHP) products stemming from the ˙QOOH + O2 reaction. Furthermore, we quantify a product that we tentatively assign as fumaraldehyde, which arises from UHP decomposition via H2O or ˙OH + H loss. The experimentally derived species concentrations are compared with model predictions using the most recent literature THF oxidation mechanism of Fenard et al., (Combust. Flame, 2018, 191, 252-269). Our results indicate that the literature mechanism significantly overestimates THF consumption and the UHP + KHP concentration at our conditions. The model predictions are sensitive to the rate coefficient for the ROO˙ isomerization to ˙QOOH, which is the gateway for radical chain propagating and branching pathways. Comparisons with our recent results for cyclopentane (Demireva et al., Combust. Flame, 2023, 257, 112506) provide insights into the effect of the ether group on reactivity and highlight the need to determine accurate rate coefficients of ROO˙ isomerization and subsequent reactions.

Probing O2-dependence of cyclopentyl reactions via isomer-resolved speciation

Modeling chemical kinetics relevant to low-temperature combustion requires complete description of reactions involving critical species such as hydroperoxyalkyl radicals, Q˙OOH, which undergo competing unimolecular reactions and bimolecular reactions with O2. The balance of flux across the two pathways affects rates of chain-branching and depends on temperature, pressure, and oxygen concentration. Accordingly, the influence of [O2] on product formation from alkyl + O2 reactions and the subsequent fate of Q˙OOH and related products is central to the development of an accurate chemical kinetics mechanism. However, chemical reactions consuming Q˙OOH-mediated species are often simplified to such a degree that mechanism truncation error (uncertainty derived from incomplete reaction networks) becomes significant.For the specific purpose of determining the extent to which expanded sub-mechanisms ameliorate inaccuracies in model predictions resulting from mechanism truncation error, the present work integrates speciation measurements from jet-stirred reactor experiments on cyclopentane oxidation with modeling using an expanded detailed chemical kinetics mechanism. The experiments utilize vacuum ultraviolet-absorption spectroscopy and mass spectrometry for isomer-resolved speciation of intermediates produced from cyclopentane oxidation at 835 Torr from 500 – 1000 K. [O2]-dependent experiments were also conducted from 0.12 – 3.66 · 1018 molecules cm–3 at 825 K to examine the influence on species profiles. The expanded mechanism is produced by merging detailed sub-mechanisms for Q˙OOH-mediated species (cyclopentene and 1,2-epoxycyclopentane) produced using Reaction Mechanism Generator (RMG) with an existing detailed mechanism for cyclopentane.Model predictions using the expanded mechanism yielded improvements in species mole fractions for both temperature- and O2-dependence. Ignition delay time simulations were also conducted and show appreciable sensitivity in the negative-temperature coefficient region due to incorporation of the detailed sub-mechanisms due to influence on O˙H radical populations. Sensitivity analysis revealed reactions that merit theoretical rate calculations for additional improvements and include species such as H2O2 and species related to R˙ + O2 reactions of cyclopentene and 1,2-epoxycyclopentane.

Iodide oxidation by ozone at the surface of aqueous microdroplets.

The oxidation of iodide by ozone occurs at the sea-surface and within sea spray aerosol, influencing the overall ozone budget in the marine boundary layer and leading to the emission of reactive halogen gases. A detailed account of the surface mechanism has proven elusive, however, due to the difficulty in quantifying multiphase kinetics. To obtain a clearer understanding of this reaction mechanism at the air-water interface, we report pH-dependent oxidation kinetics of I- in single levitated microdroplets as a function of [O3] using a quadrupole electrodynamic trap and an open port sampling interface for mass spectrometry. A kinetic model, constrained by molecular simulations of O3 dynamics at the air-water interface, is used to understand the coupled diffusive, reactive, and evaporative pathways at the microdroplet surface, which exhibit a strong dependence on bulk solution pH. Under acidic conditions, the surface reaction is limited by O3 diffusion in the gas phase, whereas under basic conditions the reaction becomes rate limited on the surface. The pH dependence also suggests the existence of a reactive intermediate IOOO- as has previously been observed in the Br- + O3 reaction. Expressions for steady-state surface concentrations of reactants are derived and utilized to directly compute uptake coefficients for this system, allowing for an exploration of uptake dependence on reactant concentration. In the present experiments, reactive uptake coefficients of O3 scale weakly with bulk solution pH, increasing from 4 × 10-4 to 2 × 10-3 with decreasing solution pH from pH 13 to pH 3.

Dry desulphurisation of gas streams using KCC-1 mesoporous silica functionalised with deep eutectic solvents.

Sulphur dioxide, a toxic gas pollutant, is mainly generated by the combustion of fossil fuels and the smelting of sulphur-bearing mineral ores. Removal of SO2 gas or desulphurisation can be accomplished in industries using a variety of processes; the most efficient is wet flue gas desulphurisation (FGD). However, wet FGD has challenges, such as the requirement for wastewater treatment, excessive water usage, and the necessity for chloride protective coating. Despite having a lesser adsorption capacity than wet FGD, dry FGD can efficiently remove SO2 from the effluent gas stream and avoid the issues associated with wet FGD, provided that the sorbents are modified and regenerable. An alternative dry desulphurisation strategy by using fibrous mesoporous silica (KCC-1) modified with deep eutectic solvents (DES), choline chloride-glycerol (DES1) and choline chloride-ethylene glycol (DES2) is studied in this paper. KCC-1 modified with DES1 is found to increase SO2 adsorption capacity to 4.83 mg g-1, which is 1.73 times greater than unmodified KCC-1 and twice higher than KCC-1 modified with DES2 attributed to the sorbent's high porosity. Increasing reaction temperature and SO2 concentration reduce the adsorption capacity to 1.73 mg g-1 and 2.73 mg g-1, respectively. The Avrami kinetic model and the Toth isotherm model best reflect SO2 adsorption on the modified KCC-1, indicating that SO2 molecules are adsorbed exothermically in multilayer adsorption on a heterogeneous surface through a combination of physical and chemical processes. The higher SO2 adsorption capacity of the modified KCC-1 suggests that choline chloride-glycerol can provide additional sites for SO2 adsorption in dry FGD technology.

Preparation of HMn2O4 lithium-ion sieves with low manganese dissolution loss for improved cycling stability.

Manganese-based lithium-ion sieves have become some of the promising adsorbents for extracting Li+ from brines. However, manganese dissolution loss (MDL) severely impairs the stability and cyclicity of ion sieves. A novel ozone eluent was first developed to extract Li+ from lithium manganese oxides, which decreased MDL decreased from 5.89% to 0.11%, and after ten regeneration cycles, the adsorption capacity retained 85.39% of the initial value, which was better than 55.15% when only hydrochloric acid (HCl) was used as the eluent. Based on these phenomena, the mechanism for the O3 lowering of MDL was investigated. First, the catalytic decomposition reaction of O3 competed with the disproportionation reaction, and the involvement of O3 inhibited the occurrence of the disproportionation reaction. Additionally, the presence of O3 and reactive oxygen species provided a preferential electron acceptor compared to Mn3+ during the migration of electrons from the bulk phase to the surface. In this study, MDL was greatly reduced with a very simple strategy, and the cycling stability of the adsorbent was improved.

The reaction mechanism of SO3 with the multifunctional compound ethanolamine and its atmospheric implications.

SO3 is an important reactive species in sulfur cycle and sulfuric acid formation processes and its reactions with some functional group substances, such as H2O, NH3, CH3OH, and organic and inorganic acids, have been extensively studied. However, its loss mechanism with multifunctional species is still lacking in detail. Herein, the reaction mechanism between SO3 and monoethanolamide (MEA) was investigated in the gas phase and on water droplets. The quantum chemical calculations indicate that the gas-phase reactions of SO3 with the OH and NH2 moieties of MEA hardly occur as their reaction energy barriers are up to 21.9-29.4 kcal mol-1. When a single water molecule is added into the SO3 + MEA reaction, it not only decreases the reaction barrier by at least 15.0 kcal mol-1 and thus enhances the rate obviously, but can also lead to the main product changing from HOCH2CH2NHSO3H to NH2CH2CH2OSO3H. The Born Oppenheimer molecular dynamics simulations on a water droplet show that the routes of the NH2CH2CH2OSO3-⋯H3O+ ion pair, HSO4- and HOCH2CH2NH3+ ions and zwitterionic formations of HOCH2CH2NH2+-SO3- and SO3--OCH2CH2NH3+ occur through a loop-structure route or chain reaction process, and can be finished within several picoseconds. Interestingly, the nucleation simulations show that the products of HOCH2CH2NHSO3H and NH2CH2CH2OSO3H have a potential ability to participate in the formation of new particles as they can form larger clusters with H2SO4, NH3 and H2O molecules within 20 ns. Thus, the present study will not only give new insight into the reaction between SO3 and multifunctional compounds, but also provide a new potential formation mechanism for particles resulting from the loss of SO3.