Experimental Gas-Phase Removal of OH Radicals in the Presence of NHC(O)H over the 11.7-353 K Range: Implications in the Chemistry of the Interstellar Medium and the Earth's Atmosphere.

Formamide (NHC(O)H) has been observed both in the interstellar medium (ISM), being identified as a potential precursor of prebiotic molecules in space, and in the Earth's atmosphere. In these environments where temperature is very distinct, hydroxyl (OH) radicals may play an important role in the degradation of NHC(O)H. Thus, in this work, we report for the first time the experimental study of the temperature dependence of the gas-phase removal of OH in the presence of NHC(O)H over the 11.

Atmospheric chemistry of CFCHFCFOCH (HFE-356mec3) and CHFCHFOCF (HFE-236ea1) initiated by OH and Cl and their contribution to global warming.

The kinetic study of the gas-phase reactions of hydroxyl (OH) radicals and chlorine (Cl) atoms with CFCHFCFOCH (HFE-356mec3) and CHFCHFOCF (HFE-236ea1) was performed by the pulsed laser photolysis/laser-induced fluorescence technique and a relative method by using Fourier Transform infrared (FTIR) spectroscopy as detection technique. The temperature dependences of the OH-rate coefficients (k(T) in cms) between 263 and 353 K are well described by the following expressions: 9.93 × 10exp{-(988 ± 35)/T}for HFE-356mec3 and 4.

Kinetic and Products Study of the Atmospheric Degradation of -2-Hexenal with Cl Atoms.

The gas-phase reaction between -2-hexenal (T2H) and chlorine atoms (Cl) was studied using three complementary experimental setups at atmospheric pressure and room temperature. In this work, we studied the rate constant for the titled oxidation reaction as well as the formation of the gas-phase products and secondary organic aerosols (SOAs). The rate constant of the T2H + Cl reaction was determined using the relative method in a simulation chamber using proton-transfer reaction time-of-flight mass spectrometry (PTR-ToF-MS) to monitor the loss of T2H and the reference compound.

Kinetics of CFCHOCH (HFE-263fb2), CHFCFCHOCH (HFE-374pcf), and CFCFCHOCH (HFE-365mcf3) with OH radicals, IR absorption cross sections, and global warming potentials.

Hydrofluoroethers (HFEs), such as CFCHOCH (HFE-263fb2), CHFCFCHOCH (HFE-374pcf), and CFCFCHOCH (HFE-365mcf3), have been proposed in the last few decades as the third-generation replacements for perfluorocarbons (PFCs) and hydrofluorocarbons (HFCs) because of their zero stratospheric ozone depletion potentials and relatively low global warming potentials (GWPs). These GWPs depend on the radiative efficiency (RE) and the atmospheric lifetime () of HFEs due to the reaction with hydroxyl (OH) radicals. The temperature and pressure dependencies of the OH-rate coefficient (()) for HFE-263fb2, HFE-374pcf, and HFE-365mcf3 are not known.

The impact of water vapor on the OH reactivity toward CHCHO at ultra-low temperatures (21.7-135.0 K): Experiments and theory.

The role of water vapor (HO) and its hydrogen-bonded complexes in the gas-phase reactivity of organic compounds with hydroxyl (OH) radicals has been the subject of many recent studies. Contradictory effects have been reported at temperatures between 200 and 400 K. For the OH + acetaldehyde reaction, a slight catalytic effect of HO was previously reported at temperatures between 60 and 118 K.

An experimental study of the gas-phase reaction between Cl atoms and trans-2-pentenal: Kinetics, products and SOA formation.

The gas-phase reaction of trans-2-pentenal (T2P) with Cl atoms was studied at atmospheric pressure and room temperature. A rate coefficient of (2.56 ± 0.

Gas-Phase Reaction of -2-Methyl-2-butenal with Cl: Kinetics, Gaseous Products, and SOA Formation.

The gas-phase reaction between -2-methyl-2-butenal and chlorine (Cl) atoms has been studied in a simulation chamber at 298 ± 2 K and 760 ± 5 Torr of air under free-NO conditions. The rate coefficient of this reaction was determined as = (2.45 ± 0.

Experimental and theoretical investigation on the OH + CHC(O)CH reaction at interstellar temperatures (T=11.7-64.4 K).

The rate coefficient, (), for the gas-phase reaction between OH radicals and acetone CHC(O)CH, has been measured using the pulsed CRESU (French acronym for Reaction Kinetics in a Uniform Supersonic Flow) technique ( = 11.7-64.4 K).

Gas-phase reactivity of CHOH toward OH at interstellar temperatures (11.7-177.5 K): experimental and theoretical study.

The reactivity of methanol (CH3OH) toward the hydroxyl (OH) radical was investigated in the temperature range 11.7-177.5 K using the CRESU (French acronym for Reaction Kinetics in a Uniform Supersonic Flow) technique.

Is the gas-phase OH+HCO reaction a source of HCO in interstellar cold dark clouds? A kinetic, dynamic and modelling study.

Chemical kinetics of neutral-neutral gas-phase reactions at ultralow temperatures is a fascinating research subject with important implications on the chemistry of complex organic molecules in the interstellar medium (T∼10-100K). Scarce kinetic information is currently available for this kind of reactions at T<200 K. In this work we use the CRESU (, which means Reaction Kinetics in a Uniform Supersonic Flow) technique to measure for the first time the rate coefficients () of the gas-phase OH+HCO reaction between 22 and 107 K.

Exploring Conditions for Ultrafine Particle Formation from Oxidation of Cigarette Smoke in Indoor Environments.

Cigarette smoke is an important source of particles and gases in the indoor environment. In this work, aging of side-stream cigarette smoke was studied in an environmental chamber via exposure to ozone (O), hydroxyl radicals (OH) and indoor fluorescent lights. Aerosol mass concentrations increased by 13-18% upon exposure to 15 ppb O and by 8-42% upon exposure to 0.

Kinetic and mechanistic study of the gas-phase reaction of CFCHCH (x=1, 2, 3, 4 and 6) with O under atmospheric conditions.

The relative-rate technique has been used to determine the rate coefficient for the reaction of CFCHCH (x = 1, 2, 3, 4 and 6) with ozone at (298 ± 2) K and (720 ± 5) Torr of air by FTIR (Fourier Transform Infrared Spectroscopy) and by GC-MS/SPME (Gas Chromatography-Mass Spectroscopy with Solid Phase Micro Extraction) in two different atmospheric simulation chambers. The following rate coefficients, in units of 10 cm molecule s, were obtained: (3.01 ± 0.

Comment on "Methanol dimer formation drastically enhances hydrogen abstraction from methanol by OH at low temperature" by W. Siebrand, Z. Smedarchina, E. Martínez-Núñez and A. Fernández-Ramos, Phys. Chem. Chem. Phys., 2016, 18, 22712.

The article "Methanol dimer formation drastically enhances hydrogen abstraction from methanol by OH at low temperature" proposes a dimer mediated mechanism in order to explain the large low temperature rate coefficients for the OH + methanol reaction measured by several groups. It is demonstrated here theoretically that under the conditions of these low temperature experiments, there are insufficient dimers formed for the proposed new mechanism to apply. Experimental evidence is also presented to show that dimerization of the methanol reagent does not influence the rate coefficients reported under the conditions of methanol concentration used for the kinetics studies.

Gas phase kinetics of the OH + CHCHOH reaction at temperatures of the interstellar medium (T = 21-107 K).

Ethanol, CHCHOH, has been unveiled in the interstellar medium (ISM) by radioastronomy and it is thought to be released into the gas phase after the warm-up phase of the grain surface, where it is formed. Once in the gas phase, it can be destroyed by different reactions with atomic and radical species, such as hydroxyl (OH) radicals. The knowledge of the rate coefficients of all these processes at temperatures of the ISM is essential in the accurate interpretation of the observed abundances.

Atmospheric Chemistry of E- and Z-CFCH═CHF (HFO-1234ze): OH Reaction Kinetics as a Function of Temperature and UV and IR Absorption Cross Sections.

We report here the rate coefficients for the OH reactions (k) with E-CFCH═CHF and Z-CFCH═CHF, potential substitutes of HFC-134a, as a function of temperature (263-358 K) and pressure (45-300 Torr) by pulsed laser photolysis coupled to laser-induced fluorescence techniques. For the E-isomer, the existing discrepancy among previous results on the T dependence of k needs to be elucidated. For the Z-isomer, this work constitutes the first absolute determination of k.

Atmospheric degradation of 2-chloroethyl vinyl ether, allyl ether and allyl ethyl ether: Kinetics with OH radicals and UV photochemistry.

Unsaturated ethers are oxygenated volatile organic compounds (OVOCs) emitted by anthropogenic sources. Potential removal processes in the troposphere are initiated by hydroxyl (OH) radicals and photochemistry. In this work, we report for the first time the rate coefficients of the gas-phase reaction with OH radicals (k) of 2-chloroethyl vinyl ether (2ClEVE), allyl ether (AE), and allyl ethyl ether (AEE) as a function of temperature in the 263-358 K range, measured by the pulsed laser photolysis-laser induced fluorescence technique.

Atmospheric fate of hydrofluoroolefins, CFCHCH (x = 1,2,3,4 and 6): Kinetics with Cl atoms and products.

Rate coefficients for the gas-phase reactions of CFCHCH (x = 1, 2, 3, 4 and 6) with Cl atoms were determined at (298 ± 2) K and (710 ± 5) Torr of air using a relative rate technique. Two experimental setups with simulation chambers were employed with Fourier Transform Infrared (FTIR) spectroscopy and Gas Chromatography coupled to Mass Spectrometry (GC-MS) as detection techniques. The Cl-rate coefficients obtained were (in 10 cm molecule s): (0.

Reactivity of OH and CHOH Between 22 and 64 K: Modelling the Gas Phase Production of CHO in Barnard 1B.

In the last years, ultra-low temperature chemical kinetic experiments have demonstrated that some gas-phase reactions are much faster than previously thought. One example is the reaction between OH and CHOH, which has been recently found to be accelerated at low temperatures yielding CHO as main product. This finding opened the question of whether the CHO observed in the dense core Barnard 1b could be formed by the gas-phase reaction of CHOH and OH.

First evidence of the dramatic enhancement of the reactivity of methyl formate (HC(O)OCH3) with OH at temperatures of the interstellar medium: a gas-phase kinetic study between 22 K and 64 K.

The gas phase chemistry of neutral-neutral reactions of interest in the interstellar medium (ISM) is poorly understood. The rate coefficients (kOH) for the majority of the reactions of hydroxyl (OH) radicals with interstellar oxygenated species are unknown at the temperatures of the ISM. In this study, we present the first determination of kOH for HC(O)OCH3 between 22.

Connecting the oxidation of soot to its redox cycling abilities.

Although it is known that soot particles are emitted in large quantities to the atmosphere, our understanding of their environmental effects is limited by our knowledge of how their composition is subsequently altered through atmospheric processing. Here we present an on-line mass spectrometric study of the changing chemical composition of hydrocarbon soot particles as they are oxidized by gas-phase ozone, and we show that the surface-mediated loss rates of adsorbed polycyclic aromatic hydrocarbons in soot are directly connected to a significant increase in the particle redox cycling abilities. With redox cycling implicated as an oxidative stress mechanism that arises after inhalation of atmospheric particles, this work draws a quantitative connection between the detailed heterogeneous chemistry occurring on atmospheric particles and a potential toxic mechanism attributable to that aerosol.

Chemical and toxicological evolution of carbon nanotubes during atmospherically relevant aging processes.

The toxicity of carbon nanotubes (CNTs) has received significant attention due to their usage in a wide range of commercial applications. While numerous studies exist on their impacts in water and soil ecosystems, there is a lack of information on the exposure to CNTs from the atmosphere. The transformation of CNTs in the atmosphere, resulting in their functionalization, may significantly alter their toxicity.

Atmospheric chemistry of CF3CF2CHO: absorption cross sections in the UV and IR regions, photolysis at 308 nm, and gas-phase reaction with OH radicals (T = 263-358 K).

The relative importance in the atmosphere of UV photolysis of perfluoropropionaldehyde, CF3CF2CHO, and reaction with hydroxyl (OH) radicals has been investigated in this work. First, the forbidden n → π* transition of the carbonyl chromophore was characterized between 230 and 380 nm as a function of temperature (269–298 K) and UV absorption cross sections, σλ, were determined in those ranges. In addition, IR absorption cross sections were determined between 4000 and 500 cm–1.

Photolysis of CF3CH2CHO in the presence of O2 at 248 and 266 nm: quantum yields, products, and mechanism.

Three different detection techniques, coupled to pulsed laser photolysis (PLP), have been employed to determine the quantum yields of CF3CH2CHO at 248 and 266 nm: CF3CH2CHO + hν → CF3CH2 + HCO (R1a), CF3CH2CHO + hν → CF3CH3 + CO (R1b), and CF3CH2CHO + hν → CF3CH2O + H (R1c). (a) In the presence of air, Fourier transform infrared (FTIR) spectroscopy was employed at a total pressure of 760 Torr to monitor and quantify the loss of CF3CH2CHO at both wavelengths as well as the build-up of formed products (CO, CF3CH3, CF3CHO, and CF3CH2OH) after various laser pulses. Cyclohexane was added as OH-scavenger in most experiments.

Laboratory studies of CHF2CF2CH2OH and CF3CF2CH2OH: UV and IR absorption cross sections and OH rate coefficients between 263 and 358 K.

Fluorinated alcohols, such as 2,2,3,3-tetrafluoropropanol (TFPO, CHF(2)CF(2)CH(2)OH) and 2,2,3,3,3-pentafluoropropanol (PFPO, CF(3)CF(2)CH(2)OH), can be potential replacements of hydrofluorocarbons with large global warming potentials, GWPs. IR absorption cross sections for TFPO and PFPO were determined between 4000 and 500 cm(-1) at 298 K. Integrated absorption cross sections (S(int), base e) in the 4000-600 cm(-1) range are (1.

UV absorption cross sections between 230 and 350 nm and pressure dependence of the photolysis quantum yield at 308 nm of CF3CH2CHO.

Ultraviolet (UV) absorption cross sections of CF(3)CH(2)CHO were determined between 230 and 350 nm by gas-phase UV spectroscopy. The forbidden n → π* transition was characterized as a function of temperature (269-323 K). In addition, the photochemical degradation of CF(3)CH(2)CHO was investigated at 308 nm.