Odd‐hydrogen: An account on electronic structure, kinetics, and role of water in mediating reactions with atmospheric ozone. Just a catalyst or far beyond?

Varandas, A. J. C.

doi:10.1002/qua.24580

Cited by 22 publications

(17 citation statements)

References 317 publications

(584 reference statements)

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“…We explore whether ammonia can accelerate the OH + H 2 SO 4 reaction and a single water molecule can promote the NH 2 + H 2 SO 4 reaction. Some theoretical and experimental investigations have demonstrated that a single water molecule can affect the rate constants of gas‐phase reactions in the atmosphere . In addition, the competition mechanisms between OH + NH 3 and OH + H 2 SO 4 are also considered, which may be of great interest because previous investigations have demonstrated that the similar reaction mechanisms play an important role in the atmospheric oxidation of HNO 3 .…”

Section: Introductionmentioning

confidence: 74%

Theoretical Studies on Reactions of OH with H₂SO₄^…NH₃Complex and NH₂with H₂SO₄in the Presence of Water

et al. 2016

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The OH + H 2 SO 4 … NH 3 , NH 2 + H 2 SO 4 , and NH 2 + H 2 SO 4 … H 2 O reactions have been theoretically investigated using high-accuracy quantum chemical methods and conventional transition state theory. The calculation results reveal that remarkable tunneling effects appear at 200 K in the OH + H 2 SO 4 … NH 3 reaction, compared with obvious tunneling effects below 100 K in the OH + NH 3 reaction. The calculated rate constants predict that the hydrogen atom of the free OH group in M1 (H 2 SO 4 … NH 3 ) abstracted via OH can compete well with the H atom in H 2 SO 4abstracted by OH at 200-240 K. The reaction kinetic results also show that a single water molecule could play an important role in the NH 2 + H 2 SO 4 … H 2 O reaction below 240 K. The present results provide new insights into the atmospheric oxidation of sulfuric acid, which could be of great use in understanding atmospheric nucleation processes. Additionally, the findings are tunneling effects enhanced by sulfuric acid, which may be wide applications in reaction kinetics of gas-phase reactions.

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Section: Introductionmentioning

confidence: 74%

Theoretical Studies on Reactions of OH with H₂SO₄^…NH₃Complex and NH₂with H₂SO₄in the Presence of Water

et al. 2016

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“…In a global chemical-transport-model-based study, the deposition velocity was considered to be similar to formic acid, yielding a HNCO lifetime of 1-3 d (over the ocean) to 1-2 weeks (over vegetation) (Young et al, 2012). The UV absorption for HNCO is only reported at wavelengths < 262 nm, and photolysis is mostly reported for energies at wavelengths below 240 nm by excitation to the first singlet excited states, forming H + NCO or NH + CO (Keller-Rudek et al, 2013;Okabe, 1970;Uno et al, 1990;Vatsa and Volpp, 2001). In the troposphere photolysis occurs only at the UV absorption wavelength band > 290 nm due to filtering of shorter-wavelength radiation (Hofzumahaus et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

Atmospheric chemical loss processes of isocyanic acid (HNCO): a combined theoretical kinetic and global modelling study

Rosanka

Nguyen

et al. 2020

Atmos. Chem. Phys.

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Abstract. Isocyanic acid (HNCO) is a chemical constituent suspected to be harmful to humans if ambient concentrations exceed ∼1 ppbv. HNCO is mainly emitted by combustion processes but is also inadvertently released by NOx mitigation measures in flue gas treatments. With increasing biomass burning and more widespread usage of catalytic converters in car engines, good prediction of HNCO atmospheric levels with global models is desirable. Little is known directly about the chemical loss processes of HNCO, which limits the implementation in global Earth system models. This study aims to close this knowledge gap by combining a theoretical kinetic study on the major oxidants reacting with HNCO with a global modelling study. The potential energy surfaces of the reactions of HNCO with OH and NO3 radicals, Cl atoms, and ozone were studied using high-level CCSD(T)/CBS(DTQ)//M06-2X/aug-cc-pVTZ quantum chemical methodologies, followed by transition state theory (TST) theoretical kinetic predictions of the rate coefficients at temperatures of 200–3000 K. It was found that the reactions are all slow in atmospheric conditions, with k(300K)≤7×10-16 cm3molecule-1s-1, and that product formation occurs predominantly by H abstraction; the predictions are in good agreement with earlier experimental work, where available. The reverse reactions of NCO radicals with H2O, HNO3, and HCl, of importance mostly in combustion, were also examined briefly. The findings are implemented into the atmospheric model EMAC (ECHAM/MESSy Atmospheric Chemistry) to estimate the importance of each chemical loss process on a global scale. The EMAC predictions confirm that the gas-phase chemical loss of HNCO is a negligible process, contributing less than 1 % and leaving heterogeneous losses as the major sinks. The removal of HNCO by clouds and precipitation contributes about 10 % of the total loss, while globally dry deposition is the main sink, accounting for ∼90 %. The global simulation also shows that due to its long chemical lifetime in the free troposphere, HNCO can be efficiently transported into the UTLS by deep convection events. Daily-average mixing ratios of ground-level HNCO are found to regularly exceed 1 ppbv in regions dominated by biomass burning events, but rarely exceed levels above 10 ppt in other areas of the troposphere, though locally instantaneous toxic levels are expected.

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“…In addition to the traditional cycloaddition channels, three further channels were found, corresponding to Habstraction, forming HO 3 + NCO, oxygen transfer to the N-atom, forming ON(H)CO + 1 O 2 , and addition on the C-and N-atom, forming HN(OO)C(O)O. The HO 3 product radical is known to be only weakly bonded by 2.94 kcal mol -1 , falling apart to OH + O 2 (Bartlett et al, 2019;Le Picard et al, 2010;Varandas, 2014).…”

Section: Hnco + Omentioning

confidence: 99%

Chemical loss processes of isocyanic acid, HNCO, in the atmosphere

Rosanka

Nguyen

et al. 2020

Preprint

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Abstract. The impact of chemical loss processes of isocyanic acid was studied by a combined theoretical and modeling study. The potential energy surfaces of the reactions of HNCO with OH and NO3 radicals, Cl atoms, and ozone, were studied using high-level CCSD(T)/CBS(DTQ)//M06-2X/aug-cc-pVTZ quantum chemical methodologies, followed by TST theoretical kinetic predictions of the rate coefficients at temperatures of 200–3000 K. It was found that the reactions are all slow in atmospheric conditions, with k(300 K) ≤ 7 × 10−16 cm3 molecule−1 s−1; the predictions are in good agreement with earlier experimental work, where available. The reverse reactions of NCO radicals, of importance mostly in combustion, were also examined briefly. The global model confirms that gas phase chemical loss of HNCO is a negligible process, contributing less than 1 %. Removal of HNCO by clouds and precipitation is a larger sink, contributing for about 10 % of the total loss, while globally dry deposition is the main sink, accounting for ~ 90 %. The global simulation also shows that due to its long chemical lifetime in the free troposphere, HNCO can be efficiently transported into the UTLS by deep convection events. Average daily concentrations of HNCO are found to rarely exceed levels considered potentially toxic, though locally instantaneous toxic levels are expected.the free troposphere, HNCO can be efficiently transported into the UTLS by deep convection events. Average daily concentrations of HNCO are found to rarely exceed levels considered potentially toxic, though locally instantaneous toxic levels are expected.

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Odd‐hydrogen: An account on electronic structure, kinetics, and role of water in mediating reactions with atmospheric ozone. Just a catalyst or far beyond?

Cited by 22 publications

References 317 publications

Theoretical Studies on Reactions of OH with H₂SO₄^…NH₃Complex and NH₂with H₂SO₄in the Presence of Water

Theoretical Studies on Reactions of OH with H₂SO₄^…NH₃Complex and NH₂with H₂SO₄in the Presence of Water

Atmospheric chemical loss processes of isocyanic acid (HNCO): a combined theoretical kinetic and global modelling study

Chemical loss processes of isocyanic acid, HNCO, in the atmosphere

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Odd‐hydrogen: An account on electronic structure, kinetics, and role of water in mediating reactions with atmospheric ozone. Just a catalyst or far beyond?

Cited by 22 publications

References 317 publications

Theoretical Studies on Reactions of OH with H2SO4…NH3Complex and NH2with H2SO4in the Presence of Water

Theoretical Studies on Reactions of OH with H2SO4…NH3Complex and NH2with H2SO4in the Presence of Water

Atmospheric chemical loss processes of isocyanic acid (HNCO): a combined theoretical kinetic and global modelling study

Chemical loss processes of isocyanic acid, HNCO, in the atmosphere

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Theoretical Studies on Reactions of OH with H₂SO₄^…NH₃Complex and NH₂with H₂SO₄in the Presence of Water

Theoretical Studies on Reactions of OH with H₂SO₄^…NH₃Complex and NH₂with H₂SO₄in the Presence of Water