 Many atmospheric chemicals occur in the gas phase as well as in liquid cloud droplets and aerosol particles Therefore, it is necessary to understand the distribution between the phases According to Henry's law, the equilibrium ratio between the abundances in the gas phase and in the aqueous phase is constant for a dilute solution Henry's law constants of trace gases of potential importance in environmental chemistry have been collected and converted into a uniform format The compilation contains 17 350 values of Henry's law constants for 4632 species, collected from 689 references It is also available at http://wwwhenrys-laworg 

/pdf/compilation-of-henry-s-law-constants-version-4-0-for-water-58il9q0ogv.pdf

Compilation of Henry's law constants (version 4.0) for water as solvent

. Kinetic and mechanistic data relevant to the tropospheric degradation of volatile organic compounds (VOC), and the production of secondary pollutants, have previously been used to define a protocol which underpinned the construction of a near-explicit Master Chemical Mechanism. In this paper, an update to the previous protocol is presented, which has been used to define degradation schemes for 107 non-aromatic VOC as part of version 3 of the Master Chemical Mechanism (MCM v3). The treatment of 18 aromatic VOC is described in a companion paper. The protocol is divided into a series of subsections describing initiation reactions, the reactions of the radical intermediates and the further degradation of first and subsequent generation products. Emphasis is placed on updating the previous information, and outlining the methodology which is specifically applicable to VOC not considered previously (e.g. a - and b -pinene). The present protocol aims to take into consideration work available in the open literature up to the beginning of 2001, and some other studies known by the authors which were under review at the time. Application of MCM v3 in appropriate box models indicates that the representation of isoprene degradation provides a good description of the speciated distribution of oxygenated organic products observed in reported field studies where isoprene was the dominant emitted hydrocarbon, and that the a -pinene degradation chemistry provides a good description of the time dependence of key gas phase species in a -pinene/NOX photo-oxidation experiments carried out in the European Photoreactor (EUPHORE). Photochemical Ozone Creation Potentials (POCP) have been calculated for the 106 non-aromatic non-methane VOC in MCM v3 for idealised conditions appropriate to north-west Europe, using a photochemical trajectory model. The POCP values provide a measure of the relative ozone forming abilities of the VOC. Where applicable, the values are compared with those calculated with previous versions of the MCM.

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Protocol for the development of the Master Chemical Mechanism, MCM v3 (Part A): tropospheric degradation of non-aromatic volatile organic compounds

A new gas-phase chemical mechanism for the modeling of regional atmospheric chemistry, the “Regional Atmospheric Chemistry Mechanism” (RACM) is presented. The mechanism is intended to be valid for remote to polluted conditions and from the Earth's surface through the upper troposphere. The RACM mechanism is based upon the earlier Regional Acid Deposition Model, version 2 (RADM2) mechanism [Stockwell et al., 1990] and the more detailed Euro-RADM mechanism [Stockwell and Kley, 1994]. The RACM mechanism includes rate constants and product yields from the most recent laboratory measurements, and it has been tested against environmental chamber data. A new condensed reaction mechanism is included for biogenic compounds: isoprene, α-pinene, and d-limonene. The branching ratios for alkane decay were reevaluated, and in the revised mechanism the aldehyde to ketone ratios were significantly reduced. The relatively large amounts of nitrates resulting from the reactions of unbranched alkenes with NO3 are now included, and the production of HO from the ozonolysis of alkenes has a much greater yield. The aromatic chemistry has been revised through the use of new laboratory data. The yield of cresol production from aromatics was reduced, while the reactions of HO, NO3, and O3 with unsaturated dicarbonyl species and unsaturated peroxynitrate are now included in the RACM mechanism. The peroxyacetyl nitrate chemistry and the organic peroxy radical-peroxy radical reactions were revised, and organic peroxy radical +NO3 reactions were added.

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A new mechanism for regional atmospheric chemistry modeling

The tropospheric degradation of volatile organic compounds: a protocol for mechanism development

An updated H2/O2 kinetic model based on that of Li et al. (Int J Chem Kinet 36, 2004, 566–575) is presented and tested against a wide range of combustion targets. The primary motivations of the model revision are to incorporate recent improvements in rate constant treatment and resolve discrepancies between experimental data and predictions using recently published kinetic models in dilute, high-pressure flames.

Attempts are made to identify major remaining sources of uncertainties, in both the reaction rate parameters and the assumptions of the kinetic model, affecting predictions of relevant combustion behavior. With regard to model parameters, present uncertainties in the temperature and pressure dependence of rate constants for HO2 formation and consumption reactions are demonstrated to substantially affect predictive capabilities at high-pressure, low-temperature conditions. With regard to model assumptions, calculations are performed to investigate several reactions/processes that have not received much attention previously. Results from ab initio calculations and modeling studies imply that inclusion of H + HO2 = H2O + O in the kinetic model might be warranted, though further studies are necessary to ascertain its role in combustion modeling. In addition, it appears that characterization of nonlinear bath-gas mixture rule behavior for H + O2(+ M) = HO2(+ M) in multicomponent bath gases might be necessary to predict high-pressure flame speeds within ∼15%.

The updated model is tested against all of the previous validation targets considered by Li et al. as well as new targets from a number of recent studies. Special attention is devoted to establishing a context for evaluating model performance against experimental data by careful consideration of uncertainties in measurements, initial conditions, and physical model assumptions. For example, ignition delay times in shock tubes are shown to be sensitive to potential impurity effects, which have been suggested to accelerate early radical pool growth in shock tube speciation studies. In addition, speciation predictions in burner-stabilized flames are found to be more sensitive to uncertainties in experimental boundary conditions than to uncertainties in kinetics and transport. Predictions using the present model adequately reproduce previous validation targets and show substantially improved agreement against recent high-pressure flame speed and shock tube speciation measurements. Comparisons of predictions of several other kinetic models with the experimental data for nearly the entire validation set used here are also provided in the Supporting Information. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 44: 444–474, 2012

Comprehensive H2/O2 kinetic model for high-pressure combustion

The impact of new laboratory data for the reaction BrO + HO2 → HOBr + O2 has been estimated in a one-dimensional photochemical modelling of bromine/ozone stratospheric chemistry. The reported 6 fold increase in the measured value for the rate constant of this reaction significantly increases both the HOBr mixing ratio and the global ozone depletion due to bromine compounds (the calculated ozone loss increases from 1.14% to 1.45% for a 20 ppt total bromine content). The higher rate constant makes the bromine partitioning and the ozone depletion very sensitive to the branching ratio of the potential channel forming HBr in the BrO + HO2 reaction. The influence of the existing uncertainty in the photolysis rate of HOBr is also analysed.

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Role of the BRO + HO2 reaction in the stratospheric chemistry of bromine

Using the discharge flow method with detection of species by mass spectrometry and laser-induced fluorescence, the kinetics of the reaction BrO + CH 3 O 2 → products has been studied at 298 K. The rate constant obtained is (5.7 ± 0.6)x10 -2 cm3 molecules -1 s -1 . The mechanism of the reaction has been also investigated. These laboratory data are used to discuss the possible impact of this reaction on the ozone budget in different parts of the atmosphere. The reaction is likely to be negligible in the stratosphere, but is potentially significant in the remote marine boundary layer. The BrO + CH 3 O 2 reaction, together with other BrO + RO 2 reactions, may also significantly contribute to the ozone loss events observed in the Arctic troposphere in spring.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/97GL02686

The BrO + Ch3O2 reaction: Kinetics and role in the atmospheric ozone budget

The kinetics of the disproportionation reactions of OH and OD radicals, OH + OH → O + H2O (1), OD + OD → O + D2O (3), have been studied by the mass spectrometric discharge-flow method at temperatures between 233 and 360 K and at total pressure of 1 Torr of helium. The following Arrhenius expressions were obtained:  k1 = (7.1 ± 1.0) × 10-13exp[(210 ± 40)/T] and k3 = (2.5 ± 0.5) × 10-13exp[(170 ± 60)/T] cm3 molecule-1 s-1. Reaction 4 between OH and OD radicals was also investigated and the same rate constant as for reaction 1 was measured. Both the observed temperature dependence of k1 and the measured kinetic isotopic effect (k1/k3) are compatible with the mechanism proposed in a previous theoretical study (Harding, L. B.; Wagner, A. F. 22nd International Symposium on Combustion, 1988). In addition, a temperature-independent rate coefficient of (1.20 ± 0.25) × 10-10 cm3 molecule-1 s-1 was measured for the reaction D + NO2 → OD + NO in the temperature range 230−365 K.

Gilles Poulet

Papers

Role of the BRO + HO2 reaction in the stratospheric chemistry of bromine

The BrO + Ch3O2 reaction: Kinetics and role in the atmospheric ozone budget

Kinetic Study of OH + OH and OD + OD Reactions

Kinetics of halogen oxide radicals in the stratosphere.

Kinetic study of the Br + IO, I + BrO and Br + I2 reactions. Heat of formation of the BrO radical