Reaction between CH3O2 and BrO Radicals: A New Source of Upper Troposphere Lower Stratosphere Hydroxyl Radicals

Effect of water on the oxidation of CO by a Criegee intermediate

The present work employs the CCSD(T)/CBS//M06-2X/aug-cc-pVTZ level of theory to investigate the effect of a water monomer and dimer on the oxidation of carbon-monoxide by a Criegee intermediate (CH2OO). The present work suggests that in the presence of a water monomer the energy barrier of the title reaction reduced to ∼3.4 kcal mol-1 from the corresponding uncatalyzed barrier (∼12.4 kcal mol-1), whereas, in the presence of a water dimer it became as low as ∼-3.2 kcal mol-1. It has also been found that, in the presence of catalysts, additional channels become available from which the title reaction can proceed. The estimated values of rate constants suggest that within the temperature range of 210-320 K, the effective bimolecular rate constant for the water monomer catalyzed channel is 10 to 100 times lower than the bimolecular rate constant of the uncatalyzed channel, whereas in the case of the water dimer it is ∼5-10 times higher than that of the uncatalyzed channel.

The atmospheric importance of methylamine additions to Criegee intermediates

The methylamine addition to Criegee intermediates is investigated using high level ab initio methods.

The reaction of hydroxyl and methylperoxy radicals is not a major source of atmospheric methanol

Methanol is a benchmark for understanding tropospheric oxidation, but is underpredicted by up to 100% in atmospheric models. Recent work has suggested this discrepancy can be reconciled by the rapid reaction of hydroxyl and methylperoxy radicals with a methanol branching fraction of 30%. However, for fractions below 15%, methanol underprediction is exacerbated. Theoretical investigations of this reaction are challenging because of intersystem crossing between singlet and triplet surfaces - ∼45% of reaction products are obtained via intersystem crossing of a pre-product complex - which demands experimental determinations of product branching. Here we report direct measurements of methanol from this reaction. A branching fraction below 15% is established, consequently highlighting a large gap in the understanding of global methanol sources. These results support the recent high-level theoretical work and substantially reduce its uncertainties.

Theoretical Investigations on Mechanisms and Pathways of C₂H₅O₂ with BrO Reaction in the Atmosphere

In this work, feasible mechanisms and pathways of the C₂H₅O₂ + BrO reaction in the atmosphere were investigated using quantum chemistry methods, i.e., QCISD(T)/6-311++G(2df,2p)//B3LYP/6-311++G(2df,2p) levels of theory. Our result indicates that the title reaction occurs on both the singlet and triplet potential energy surfaces (PESs). Kinetically, singlet C₂H₅O₃Br and C₂H₅O₂BrO were dominant products under the atmospheric conditions below 300 K. CH₃CHO₂ + HOBr, CH₃CHO + HOBrO, and CH₃CHO + HBrO₂ are feasible to a certain extent thermodynamically. Because of high energy barriers, all products formed on the triplet PES are negligible. Moreover, time-dependent density functional theory (TDDFT) calculation implies that C₂H₅O₃Br and C₂H₅O₂BrO will photolyze under the sunlight.

Criegee intermediates and their impacts on the troposphere

Criegee intermediates (CIs), carbonyl oxides formed in ozonolysis of alkenes, play key roles in the troposphere. The decomposition of CIs can be a significant source of OH to the tropospheric oxidation cycle especially during nighttime and winter months. A variety of model-measurement studies have estimated surface-level stabilized Criegee intermediate (sCI) concentrations on the order of 1 × 10⁴ cm^-3 to 1 × 10⁵ cm^-3, which makes a non-negligible contribution to the oxidising capacity in the terrestrial boundary layer. The reactions of sCI with the water monomer and the water dimer have been found to be the most important bimolecular reactions to the tropospheric sCI loss rate, at least for the smallest carbonyl oxides; the products from these reactions (e.g. hydroxymethyl hydroperoxide, HMHP) are also of importance to the atmospheric oxidation cycle. The sCI can oxidise SO₂ to form SO₃, which can go on to form a significant amount of H₂SO₄ which is a key atmospheric nucleation species and therefore vital to the formation of clouds. The sCI can also react with carboxylic acids, carbonyl compounds, alcohols, peroxy radicals and hydroperoxides, and the products of these reactions are likely to be highly oxygenated species, with low vapour pressures, that can lead to nucleation and SOA formation over terrestrial regions.

Environmental effects of ozone depletion and its interactions with climate change: progress report, 2015

The Environmental Effects Assessment Panel (EEAP) is one of three Panels that regularly informs the Parties (countries) to the Montreal Protocol on the effects of ozone depletion and the consequences of climate change interactions with respect to human health, animals, plants, biogeochemistry, air quality, and materials. The Panels provide a detailed assessment report every four years. The most recent 2014 Quadrennial Assessment by the EEAP was published as a special issue of seven papers in 2015 (Photochem. Photobiol. Sci., 2015, 14, 1-184). The next Quadrennial Assessment will be published in 2018/2019. In the interim, the EEAP generally produces an annual update or progress report of the relevant scientific findings. The present progress report for 2015 assesses some of the highlights and new insights with regard to the interactive nature of the effects of UV radiation, atmospheric processes, and climate change.

A theoretical study of the atmospherically important radical–radical reaction BrO + HO2; the product channel O2(a1Δg) + HOBr is formed with the highest rate

A theoretical study has been made of the BrO + HO₂ reaction, a radical–radical reaction which contributes to ozone depletion in the atmosphere via production of HOBr.