Atmospheric Oxidation Reactions Research Articles

The chemical composition of secondary organic aerosols regulates transcriptomic and metabolomic signaling in an epithelial-endothelial in vitro coculture

BackgroundThe formation of secondary organic aerosols (SOA) by atmospheric oxidation reactions substantially contributes to the burden of fine particulate matter (PM2.5), which has been associated with adverse health effects (e.g., cardiovascular diseases). However, the molecular and cellular effects of atmospheric aging on aerosol toxicity have not been fully elucidated, especially in model systems that enable cell-to-cell signaling.MethodsIn this study, we aimed to elucidate the complexity of atmospheric aerosol toxicology by exposing a coculture model system consisting of an alveolar (A549) and an endothelial (EA.hy926) cell line seeded in a 3D orientation at the air‒liquid interface for 4 h to model aerosols. Simulation of atmospheric aging was performed on volatile biogenic (β-pinene) or anthropogenic (naphthalene) precursors of SOA condensing on soot particles. The similar physical properties for both SOA, but distinct differences in chemical composition (e.g., aromatic compounds, oxidation state, unsaturated carbonyls) enabled to determine specifically induced toxic effects of SOA.ResultsIn A549 cells, exposure to naphthalene-derived SOA induced stress-related airway remodeling and an early type I immune response to a greater extent. Transcriptomic analysis of EA.hy926 cells not directly exposed to aerosol and integration with metabolome data indicated generalized systemic effects resulting from the activation of early response genes and the involvement of cardiovascular disease (CVD) -related pathways, such as the intracellular signal transduction pathway (PI3K/AKT) and pathways associated with endothelial dysfunction (iNOS; PDGF). Greater induction following anthropogenic SOA exposure might be causative for the observed secondary genotoxicity.ConclusionOur findings revealed that the specific effects of SOA on directly exposed epithelial cells are highly dependent on the chemical identity, whereas non directly exposed endothelial cells exhibit more generalized systemic effects with the activation of early stress response genes and the involvement of CVD-related pathways. However, a greater correlation was made between the exposure to the anthropogenic SOA compared to the biogenic SOA. In summary, our study highlights the importance of chemical aerosol composition and the use of cell systems with cell-to-cell interplay on toxicological outcomes.Graphical

Theoretical kinetic investigation of the multichannel mechanism of O(3P) atmospheric oxidation reaction of but-3-enal

Several levels of theory such as Møller-Plesset MP2, G3, and CBS-QB3, have been used in order to investigate the complex and multichannel potential energy surface of the reaction of but-3-enal with the triplet oxygen atom. The results show that the O-addition channel is dominant. The different possible pathways of oxygen atom attack are thoroughly studied to better understand and explain the reaction mechanism. Regarding the oxidation of but-3-enal by triplet oxygen O(3P), it is shown that the major thermodynamic product is H3CC(O)CH2C(O)H (P3) being the most stable for the whole reaction. However, the most favored product kinetically is H2CC(OH)CH2C(O)H (P2). For the H-abstraction second possible pathway, the most favored product both kinetically and thermodynamically is found to be P8. The activation energy and calculated rate constants are consistent with the proposed addition mechanism.

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.

Understanding the importance of atmospheric transformation in assessing the hazards of liquid crystal monomers.

Liquid crystal monomers (LCMs), a group of synthetic chemicals released from liquid crystal devices such as televisions and smartphones, have recently been recognized as emerging contaminants due to their widespread occurrence in the environment and potential negative impacts on human health. Airborne LCMs can undergo atmospheric oxidation reactions to form various transformation products. Despite the certainty of atmospheric transformation chemistry, the knowledge about the hazard properties of transformation products remains largely unknown. Here, we perform an in silico model-based evaluation of the persistence, bioaccumulation potential, mobility, and toxicity of two representative LCMs, namely, 1-ethyl-4-(4-(4-propylcyclohexyl)phenyl)benzene and 4''-ethyl-2'-fluoro-4-propyl-1,1':4',1''-terphenyl, and their transformation products. We found that, among the investigated transformation products, 38% have overall persistence greater than the minimum of 331 days among the persistent organic pollutants regulated by the Stockholm Convention, 62% meet the bioaccumulation threshold of 1000 L kg-1 used by the United States Environmental Protection Agency, 44% are classified "mobile" according to the criterion used by the German Environmental Agency, and 58% have the potential to induce unacceptable toxic effects in aquatic organisms. Furthermore, we identified several transformation products with increased persistence, bioaccumulation potential, and mobility compared to their parent compounds. These findings not only offer insights for prioritizing LCM transformation products for future risk assessment, but also underscore the significance of considering atmospheric transformation in the evaluation of environmental risks posed by emerging contaminants, including LCMs.

Theoretical analysis of the OH-initiated atmospheric oxidation reactions of imidazole.

Imidazoles are present in Earth's atmosphere in both the gas-phase and in aerosol particles, and have been implicated in the formation of brown carbon aerosols. The gas-phase oxidation of imidazole (C3N2H4) by hydroxyl radicals has been shown to be preferentially initiated via OH-addition to position C5, producing the 5-hydroxyimidazolyl radical adduct. However, the fate of this adduct upon reaction with O2 in the atmospheric gas-phase is currently unknown. We employed an automated approach to investigate the reaction mechanism and kinetics of imidazole's OH-initiated gas-phase oxidation, in the presence of O2 and NOx. The explored mechanism included reactions available to first-generation RO2 radicals, as well as alkoxyl radicals produced from RO2 + NO reactions. Product distributions were obtained by assembling and solving a master equation, under conditions relevant to the Earth's atmosphere. Our calculations show a complex, branched reaction mechanism, which nevertheless converges to yield two major closed-shell products: 4H-imidazol-4-ol (4H-4ol) and N,N'-diformylformamidine (FMF). At 298 K and 1 atm, we estimate the yields of 4H-4ol and FMF from imidazole oxidation initiated via OH-addition to position C5 to be 34 : 66, 12 : 85 and 2 : 95 under 10 ppt, 100 ppt and 1 ppb of NO respectively. This work also revealed O2-migration pathways between the α-N-imino peroxyl radical isomers. This reaction channel is fast for the first-generation RO2 radicals, and may be important during the atmospheric oxidation of other unsaturated organic nitrogen compounds as well.

Year-round measurement of atmospheric volatile organic compounds using sequential sampling in Dronning Maud Land, East-Antarctica

Antarctica is considered the most pristine environment on Earth but is also characterized by its unique conditions such as the strong polar vortex and extreme cold. A detailed understanding of volatile organic compounds (VOCs) and the atmospheric oxidation reactions they undergo is essential to document biogeochemical cycles and to better understand their impact on radiative forcing. This research aims to provide a unique dataset of oxygenated (O)VOCs occurring in the Antarctic troposphere and provide insights into their temporal behavior. A home-made sequential sorbent tube auto sampler was deployed at the atmospheric observatory of the Princess Elisabeth station (71.95° S, 23.35° E, 1390 m asl) to collect 20 samples during the period from December 2019 to October 2020. The samples were analyzed consecutively by TD-GC-MS followed by direct thermal desorption of samples in a high-resolution PTR-Qi-TOFMS.Concentrations of 70 VOCs allocated to 4 different chemical groups (halogenated compounds, non-aromatic hydrocarbons, sulfur-containing compounds, and oxygenated aromatic and non-aromatic compounds) were determined. The results show temporal patterns for compounds such as bromoform (14 ± 6 ng/m3) and OVOCs such as furaldehyde (24 ± 9 ng/m³), amongst others, which are attributed to the seasonality of atmospheric conditions. Products of the atmospheric oxidation process show linear correlation indicating their mutual relationship and association with a common parent compound.The usage of an autonomous autosampler in the extreme conditions of Antarctica was demonstrated and proved to be a powerful tool in the sampling of air in such a remote location. The novel approach of using two analytical techniques boasts increased sensitivity and a broad range of compounds that can be detected, yielding the first dataset of its kind for Antarctica.

Theoretical Study on the Mechanisms, Kinetics, and Toxicity Evaluation of OH-Initiated Atmospheric Oxidation Reactions of Coniferyl Alcohol

In this paper, we investigated the mechanisms, kinetics, and toxicity evaluation of the OH-initiated reaction of coniferyl alcohol (4-(3-hydroxy-1-propenyl)-2-methoxyphenol) in the atmosphere using theoretical calculations. The initial reaction of coniferyl alcohol with OH radicals had two pathways, H-abstraction and OH-addition reactions. The total reaction rate constants were 2.32 × 10−9 cm3 molecule−1 s−1 (in gas-phase) and 9.44 × 109 s−1 M−1 (in liquid-phase) for the preliminary reactions of coniferyl alcohol with OH radicals at 298 K, respectively, and the half-lives of the total reaction (including all initial H-abstraction and OH-addition reactions) of coniferyl alcohol with OH radical in the atmosphere, urban and remote clouds were 8.3 × 10−2 h, 5.83 × 103 h and 9.27 × 102 h, respectively. The temperature had a strong and positive influence on the initial reaction rate constant. The branching ratios of H-abstraction and OH-addition reactions were 3.68% and 97.69%, respectively, making the OH-addition reactions become dominant reactions. The ecotoxicity evaluation revealed that the toxicity levels of coniferyl alcohol and its products were similar and non-toxic. However, all these products have developmental toxicity, with most of them having no mutagenicity. Therefore, further attention should be paid to the oxidation process and product toxicity evaluation of coniferyl alcohol in the atmosphere.

Spectroscopic signatures and oxidation characteristics of nanosecond laser-induced cerium plasmas

Improving technologies related to the wide area environmental sampling of nuclear materials supports the nuclear nonproliferation mission of preventing the proliferation of nuclear weapons by monitoring nuclear weapons tests and detecting undeclared nuclear fuel cycle activities. Standoff, laser-based detection techniques such as laser-induced breakdown spectroscopy have the potential to offer robust, field-deployable methods that provide rapid element-specific and phase identifiable measurements over a wide range of materials. This work aims to elucidate the effects of atmospheric conditions and oxidation reactions on the highly complex and transient spectroscopic signatures of laser-induced plutonium surrogate plasmas. Time-resolved spectra of nanosecond laser ablation cerium plasmas were measured using laser-induced breakdown spectroscopy in a range of atmospheres containing low to high concentrations of oxygen. The growth of strong CeO molecular emission bands was observed in the visible spectrum, where it was shown that the persistence of CeO is reduced from around 60 μs to 50 μs in oxygen rich atmospheric environments. To further investigate the growth and depletion of CeO in the laser-produced plasma, ratios of CeO-to-Ce emission were generated using integrated intensities corresponding to the Q-branch of the CeO D1-X1 transitions and numerous strong atomic Ce peaks. It was determined that the fastest rate of formation of CeO in argon occurred for moderate oxygen mass fractions between 0.10 and 0.15 while the ratios were reduced at higher oxygen mass fractions (i.e., YO2=0.20) due to competing oxidation reactions and lower plasma temperatures.

Oxidation and degradation of (epi)gallocatechin gallate (EGCG/GCG) and (epi)catechin gallate (ECG/CG) in alkali solution

The oxidative decomposition/degradation of two main tea flavanols, EGCG/GCG and ECG/CG, was studied in alkaline solution under ultrasonic-assisted thermal conditions. The study employed HPLC–ESI-ToF-MS to identify the products generated by atmospheric oxygen oxidation and various base-catalyzed reactions. Strong basic condition led to accelerated hydrolysis and oxidation of EGCG/GCG and ECG/CG and yielded gallic acid, de-galloyl flavanols and corresponding o-quinone derivatives. Meanwhile, peroxidation or base-catalyzed cleavage and rearrangement occurred extensively on C- and B-rings of flavanol and generated various simpler aldehydes or acids. Besides, a number of dimers/trimers were produced. This contribution provides empirical proof of oxidative degradation of flavanols under strong alkaline condition. Meanwhile, detailed reaction mechanisms of C-/B-ring degradation and dimerization/polymerization phenomena are proposed to help understand the structural changes of flavanols under strong alkaline conditions.

Metabolic Disorder Enhances Oxidative Stress after Exposure to Aromatic Components of Fine Particulate Matter

Metabolic disorder can exacerbate oxidative damage following exposure to fine particulate matter (PM2.5), but the role of chemical composition in this process remains unclear. This study comprehensively assessed the oxidative stress effect from the synergy of metabolic disorder and the organic components in PM2.5 as well as their molecular features. We high-throughput characterized 942 PM2.5 chemicals from an elderly urban population exposure and found the association between oxidative stress markers of exhaled nitric oxide (eNO) and urinary malondialdehyde (MDA) and 330 and 32 compounds, respectively, was enhanced by metabolic disorder. Most of these compounds were aromatics, including PAHs and their functionalized and oxidized products. The integrated explanatory random forest approach incorporating source tracers showed that primary aromatics arising from combustion with a high unsaturation degree, high logKOW, and low volatility were responsible for the increased eNO levels in participants with metabolic disorder, while compounds formed through atmospheric oxidation reactions with high numbers of carbonyl groups and oxygen atoms and relatively low logKOW were associated with elevated MDA in disordered individuals. This study provides the first evidence that metabolic disorder exacerbates oxidative stress after exposure to specific PM2.5 components, which could in turn exacerbate chronic diseases in the elderly population.

Review of technologies and their applications for the speciated detection of RO2 radicals

Peroxy radicals (RO2), which are formed during the oxidation of volatile organic compounds, play an important role in atmospheric oxidation reactions. Therefore, the measurement of RO2, especially distinct species of RO2 radicals, is important and greatly helps the exploration of atmospheric chemistry mechanisms. Although the speciated detection of RO2 radicals remains challenging, various methods have been developed to study them in detail. These methods can be divided into spectroscopy and mass spectrometry technologies. The spectroscopy methods contain laser-induced fluorescence (LIF), UV-absorption spectroscopy, cavity ring-down spectroscopy (CRDS) and matrix isolation and electron spin resonance (MIESR). The mass spectrometry methods contain chemical ionization atmospheric pressure interface time-of-flight mass spectrometry (CI-APi-TOF), chemical ionization mass spectrometry (CIMS), CI-Orbitrap-MS and the third-generation proton transfer reaction–time-of-flight mass spectrometer (PTR3). This article reviews technologies for the speciated detection of RO2 radicals and the applications of these methods. In addition, a comparison of these techniques and the reaction mechanisms of some key species are discussed. Finally, possible gaps are proposed that could be filled by future research into speciated RO2 radicals.

Thermochemistry and Kinetics of the Atmospheric Oxidation Reactions of Propanesulfinyl Chloride Initiated by OH Radicals: A Computational Approach.

The thermochemistry and kinetics of the atmospheric oxidation mechanism for propanesulfinyl chloride (CH3-CH2-CH2-S(═O)Cl; PSICl) initiated by the hydroxyl (OH) radical were investigated with high level quantum chemistry calculations and the Master equation solver for multi-energy well reaction (Mesmer) kinetic code. The mechanism for the oxidation of PSICl in the presence of OH radical can proceed via H-abstraction and substitution pathways. The CCSD(T)/aug-cc-pV(T+d)Z//MP2/aug-cc-pV(T+d)Z level calculated energies revealed addition of the OH radical to the S-atom of the sulfinyl (-S(═O)) moiety, followed by cleavage of the Cl-S(═O) single bond, leading to formation of propanesulfinic acid (PSIA) and the Cl radical to be the major pathway when compared to all other possible channels. The transition state barrier height for this reaction was found to be -3.0 kcal mol-1 relative to the energy of the starting PSICl + OH radical reactants. The rate coefficients were calculated for all possible paths in the atmospherically relevant temperature range of 200-320 K and at 1 atm. The rate coefficient for the formation of the PSIA + Cl radical from the PSICl + OH radical reaction was found to be 8.2 × 10-12 cm3 molecule-1 s-1 at 298 K and a pressure of 1 atm. From branching ratio calculations, it was revealed that the reaction resulting in the formation of the PSIA + Cl radical contributed ∼52% to the total reaction. The overall rate coefficient for the PSICl + OH reaction was also calculated and found to be 1.6 × 10-11 cm3 molecule-1 s-1 at 298 K and a pressure of 1 atm. In the aggregate, the results indicate the atmospheric lifetime of PSICl to be ∼12-20 h in the temperature range between 200 and 320 K, which suggests that its contribution to global warming is negligible. However, the degradation products revealed to be formed in its interactions with the OH radical, which include that SO2, Cl radical, HO2 radical, and propylene have significant effects on the formation of acid rain, secondary organic aerosols, the ozone layer, and global warming.

Diurnal evolutions and sources of water-soluble chromophoric aerosols over Xi'an during haze event, in Northwest China

Atmospheric brown carbon and their chemical behavior potentially impacts the climate and air quality. Due to lack of researches on the atmospheric chromophores by using online experimental instrument, so using the offline EEM approaches to study their types, sources and chemical processes. In this study, PILS-EEM-TOC system (Particle into liquid sampler coupled with excitation-emission matrix and total organic carbon) was developed in order to distinguish the hourly evolutions and sources of water-soluble chromophoric organic matters in atmospheric fine particles. The results suggested that the sources of atmospheric chromophores in winter were primary combustion (~90%) and coal burning, followed by biomass burning and cooking emissions in Xi'an (Northwest China). These atmospheric chromophores decay under the combined action of solar radiation and atmospheric oxidants. Meanwhile, the secondary chromophores were mainly highly-oxygenated humic-like substance (HULIS), produced by atmospheric oxidation reactions with the highest peak in the afternoon. The partly secondary chromophores can also be generated through the Maillard-like reaction in the morning, which depends on the relative humidity of the atmosphere. These findings made a deeper understanding of the sources and transformation of atmospheric brown carbon aerosols.

Atmospheric Oxidation Reactions of Methyl Salicylate as Green Leaf Volatiles by OH Radical: Theoretical Kinetics and Mechanism

AbstractGreen leaf volatile (GLV) organic compounds, released from vegetation, act as plants’ multifunctional weapon and are known to be a source of secondary organic aerosols (SOAs). In the present study, the mechanism of oxidation reaction of methyl salicylate (MeSa), a known GLV, by OH radical has been investigated by means of density functional theory (DFT). Canonical transition state (CTST) and Rice‐Ramsperger‐Kassel‐Marcus theories (RRKM) with Wigner and Eckart tunneling correction were applied to calculate the transition pressure, the total rate constant, and the individual rate constants for every channel of this oxidation reaction of MeSa with OH radical. The calculated overall bimolecular rate constant with Eckart tunneling correction for the title reaction is 1.18×109 and 1.01×109 L mol−1s−1 at Mn15‐L/aug‐cc‐pVTZ and MN15‐L/MG3S levels of theory in the gas phase at 298 K which is comparable to the experimental reported value of 6.66×109 L mol−1s−1, indicating that the results of MN15‐L/aug‐cc‐pVTZ level of theory is more accurate. Investigation of transition pressure and fall‐off curve of unimolecular channels at proposed mechanism for oxidation reaction of MeSa revealed that the TST breaks down slightly to estimate the high pressure limit of reaction rate and the reaction become second order (bimolecular reaction). Furthermore, the atmospheric lifetime of MeSa is about 2.95 and 3.44 days calculated at those two levels of theory, respectively, which indicates that MeSa can be considered as a medium‐lifetime organic volatile compound.

Biomass burning organic aerosols significantly influence the light absorption properties of polarity-dependent organic compounds in the Pearl River Delta Region, China

Atmospheric brown carbon (BrC) is an important constituent of light-absorbing organic aerosols with many unclear issues. Here, the light-absorption properties of BrC with different polarity characteristics at a regional site of Pearl River Delta Region during 2016–2017, influenced by sources and molecular compositions, were revealed using radiocarbon analysis and Fourier transform ion cyclotron resonance mass spectrometry. Humic-like substance (HULIS), middle polar (MP), and low polar (LP) carbon fractions constitute 46 ± 17%, 30 ± 7%, and 7 ± 3% of total absorption coefficient from bulk extracts, respectively. Our results show that the absorption proportions of HULIS and MP to the total BrC absorption are higher than their mass proportions to organic carbon mass, indicating that HULIS and MP are the main light-absorbing components in water-soluble and water-insoluble organic carbon fractions, respectively. With decreases in non-fossil HULIS, MP, and LP carbon fractions (66 ± 2%, 52 ± 2%, and 36 ± 3%, respectively), the abundances of unsaturated compounds and mass absorption efficiency at 365 nm of three fractions decreased synchronously. Increases in both non-fossil carbon and levoglucosan in winter imply that the enhanced light-absorption could be attributed to elevated levels of biomass burning organic aerosols (BBOA), which increases the number of light-absorbing nitrogen-containing compounds. Moreover, the major type of potential BrC in HULIS and MP carbon fractions are oxidized BBOA, but the potential BrC chromophores in LP are mainly associated with primary BBOA. This study reveals that biomass burning has adverse effects on radiative forcing and air quality, and probably indicates the significant influences of atmospheric oxidation reactions on the forms of chromophores.

Mechanism of the atmospheric chemical transformation of acetylacetone and its implications in night-time second organic aerosol formation

Recently, a high concentration of acetylacetone (AcAc) has been measured in China, and its day-time chemistry with OH reaction has been evaluated. The phenomenon has profound implications in air pollution, human health and climate change. To systematically understand the atmospheric chemistry of AcAc and its role in the atmosphere, the night-time chemistry of AcAc with O3 and NO3 radical were investigated in this work in detail using density functional theory. The results show that for O3- and NO3-initiated atmospheric oxidation reactions of AcAc, the barrier energies of O3/NO3-addition are found to be much lower than those of H-abstraction, suggesting that O3/NO3-addition to AcAc is a major contributing pathway in the atmospheric chemical transformation reactions. The total degradation rate constants were calculated to be 2.36 × 10−17 and 1.92 × 10−17 cm3 molecule−1 s−1 for the O3- and NO3-initiated oxidation of AcAc at 298 K, respectively. The half-life of AcAc+O3 in some polluted areas (such as, Pearl River Delta and Yangtze River Delta) is close to 3 h under typical tropospheric conditions. Due to its short half-life, the ozonolysis of AcAc plays a more significant role in the night-time hours, leading to fast transformations to form primary ozonides (POZs). A prompt, thermal decomposition of POZs occurred to yield methylglyoxal, acetic acid and Criegee intermediates, which mainly contributed to the formation of secondary organic aerosol (SOA). Subsequently, using the high-resolution time-of-flight chemical ionization mass spectrometer (HR-ToF-CIMS), a non-negligible concentration of AcAc was measured in the field observation during the night-time in Nanjing, China. The obtained results reveal that the atmospheric oxidation of AcAc can successively contribute to the formation of SOA under polluted environments regardless of the time (day-time or night-time). This is due to its high reactivity to tropospheric oxidant species (such as, O3 and NO3 radicals at night-time).

Computational Study on the Atmospheric Oxidation Mechanism of 6-Chlorobenzo[a]pyrene Initiated by OH Radicals

Density functional theory (DFT) calculations at the MPWB1K/ 6-311+G(3df,2p) level were performed to study OH-initiated atmospheric oxidation reactions of 6-chlorobenzo[a]pyrene (6-ClBaP). The rate constants for key elementary reactions were estimated by means of transition state theory. The computed results demonstrate that only four of the twelve possible intermediates (INT1, INT3, INT4, and INT12) can be generated kinetically. The principal atmospheric oxidation products of 6-ClBaP, benzo[a]pyrenols, can be produced by subsequent reactions of INT1, INT3, INT4, and INT12, although their hydrogen abstraction mechanism is not exactly the same. For peroxy radical intermediates formed by O2 addition toward INT4 intramolecular hydrogen transfer from −OH to −OO was found to be a highly non-spontaneous process and hence difficult to proceed. The rate-controlling steps for subsequent reactions of INT1, INT3, INT4, and INT12 involving NO2 or NO were found to be very slow kinetically.

Thermodynamics and kinetics of 1-fluoro-2-methoxypropane vs Bromine monoxide radical (BrO): A computational view

CFCs containing volatile compounds are detrimental to atmospheric environment and to all living organisms. These compounds are frequently reported to be chemically stable/inert. Also their photodissociation reaction results to reasonable amount of Chlorine atoms formation in the stratospheric part of atmosphere. This eventually bring out depletion of Ozone (lives and properties protecting compound) in the stratosphere. In order to cope this environmental havoc, there is need to find substitutable compounds for CFCs and possibly predict their atmospheric effects. Ethers when fluorinated can serve as CFCs substitute. Therefore, in this work, an Insilco investigation was conducted on the thermochemistry, mechanism and kinetics of the Hydrogen abstraction reactions of partially fluorinated isopropyl methyl ether (1-fluoro-2-methoxypropane i.e. (CH2FCH(OCH3)CH3)) with Bromine monoxide radical (BrO.) using the Density Functional Theory (DFT) based M06-2X/6-311++G** strategy. To computationally refine/improve the energy data, the single-point calculations (DFT/M06-2X/6-311++G(2df,2p) were immediately executed on the reacting species involved. The Monte Carlo search on the investigating CH2FCH(OCH3)CH3 showed nine conformers with the lowest global minimum configuration being studied. The results of this investigation showed that the atmospheric oxidation reaction of CH2FCH(OCH3)CH3 with the BrO radical proceeded in four (4) plausible reaction routes. The computed total theoretical rate of 7.95*〖10〗^(-11) M-1 sec-1, the first of its kind with BrO radical was recorded. The atmospheric lifetime/global warming potential of 1.35*10-2 days/72.8 were also reported. The potential energy surface (PES) for each reaction route with the BrO radical was constructed at absolute temperature of 298.15 K.

AN INSILCO STUDY OF 1,1-DIFLUORO-2-METHOXYPROPANE REACTION MECHANISM WITH THE BROMINE MONOXIDE (BrO) RADICAL

An Insilco study was carried out on the thermochemistry, mechanism and kinetics of the Hydrogen abstraction reaction of 1,1-difluoro-2-methoxypropane (CH 3 CH(OCH 3 )CHF 2 ) with the Bromine monoxide radical (BrO) using the Density Functional Theory (DFT) based M06-2X/ 6-311++G ** method. The energy values were immediately improved via optimization at DFT/M06-2X/6-311++G(2df,2p) level ( single-point calculations) of the reacting species involved. The Monte Carlo search on the investigating hydrofluoroether (HFE) showed nine conformers with the lowest global minimum conformer being predicted and considered for this work. The results of this study showed that the atmospheric oxidation reaction of CH 3 CH(OCH 3 )CHF 2 with the BrO radical proceeded in four (4) plausible reaction routes. The total experimental rate of 4.34*10 -06 cm -3 molecule -1 sec -1 for HFE + BrO reaction was estimated with atmospheric lifetime (ALT)/global warming potential (GWP) of 1.80 years and 165.30 respectively. The 3D potential energy surfaces (PES) for the reaction was however constructed at absolute temperature of 298.15 K.

Theoretical study on the atmospheric oxidation reaction of 2-furanaldehyde initiated by NO3 radicals

Abstract Furanaldehydes have raised environmental attention due to their large emission and high potential to generate secondary organic aerosol. In this study, the removal process of 2-furanaldehyde initiated by NO3 in gas phase was investigated by quantum chemical calculations. The overall rate constant for trans-2-furanaldehyde initiated by NO3 is 1.04 × 10−12 cm3 molecule−1 s−1 at 298 K and 1 atm. The atmospheric lifetime of 2-furanaldehyde with NO3 is estimated to be 0.53 h. This study indicates that the night-time reactions of 2-furanaldehyde with NO3 could contribute to the oxidative capacity of the atmosphere, secondary organic aerosol formation and new particle formation.