The Reaction of CH3O2 Radicals with OH Radicals: A Neglected Sink for CH3O2 in the Remote Atmosphere

Fittschen, Christa; Whalley, Lisa K.; Heard, Dwayne E.

doi:10.1021/es502481q

Cited by 55 publications

(65 citation statements)

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“…Further details regarding the impact of the reaction between OH and CH 3 O 2 on the HO 2 / OH ratio and CH 3 O 2 budget are given in the Supplement. The budget analyses for SOS are consistent with those determined for the RHaMBLe campaign Fittschen et al, 2014;Assaf et al, 2017), reflecting similarities in observed concentrations of long-lived species and the method of the model constraint with observed O 3 concentrations and photolysis rates. The primary source of radicals therefore remains fixed in all simulations, with the primary sinks for these species occurring through radical-radical reactions.…”

Section: Constrained Box Modelsupporting

confidence: 74%

“…In this work we use a chemistry scheme based on a subsection of the hydrocarbons (ethane, propane, iso-butane, n-butane, iso-pentane, n-pentane, hexane, ethene, propene, 1-butene, acetylene, isoprene, toluene, benzene, methanol, acetone, acetaldehyde and DMS) available from the Master Chemical Mechanism version 3.2 (MCM v3.2 http://mcm.leeds.ac.uk/MCM/home.htt) Saunders et al, 2003), with a halogen chemistry scheme described by Saiz-Lopez et al (2006), Whalley et al (2010) and Edwards et al (2011). We also include the reaction between OH and CH 3 O 2 (Bossolasco et al, 2014;Fittschen et al, 2014;Assaf et al, 2016;Yan et al, 2016), with a rate coefficient of 1.6 × 10 −10 cm 3 s −1 (Assaf et al, 2016) and products HO 2 + CH 3 O (Assaf et al, 2017), the impact of which on the HO 2 : OH ratio and CH 3 O 2 budget is described in the Supplement. The total number of species in the model is ∼ 1200, with ∼ 5000 reactions.…”

Section: Constrained Box Modelmentioning

confidence: 99%

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Impacts of bromine and iodine chemistry on tropospheric OH and HO2: comparing observations with box and global model perspectives

et al. 2018

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Abstract. The chemistry of the halogen species bromine and iodine has a range of impacts on tropospheric composition, and can affect oxidising capacity in a number of ways. However, recent studies disagree on the overall sign of the impacts of halogens on the oxidising capacity of the troposphere. We present simulations of OH and HO 2 radicals for comparison with observations made in the remote tropical ocean boundary layer during the Seasonal Oxidant Study at the Cape Verde Atmospheric Observatory in 2009. We use both a constrained box model, using detailed chemistry derived from the Master Chemical Mechanism (v3.2), and the three-dimensional global chemistry transport model GEOSChem. Both model approaches reproduce the diurnal trends in OH and HO 2 . Absolute observed concentrations are well reproduced by the box model but are overpredicted by the global model, potentially owing to incomplete consideration of oceanic sourced radical sinks. The two models, however, differ in the impacts of halogen chemistry. In the box model, halogen chemistry acts to increase OH concentrations (by 9.8 % at midday at the Cape Verde Atmospheric Observatory), while the global model exhibits a small increase in OH at the Cape Verde Atmospheric Observatory (by 0.6 % at midday) but overall shows a decrease in the global annual mass-weighted mean OH of 4.5 %. These differences reflect the variety of timescales through which the halogens impact the chemical system. On short timescales, photolysis of HOBr and HOI, produced by reactions of HO 2 with BrO and IO, respectively, increases the OH concentration. On longer timescales, halogen-catalysed ozone destruction cycles lead to lower primary production of OH radicals through ozone photolysis, and thus to lower OH concentrations. The global model includes more of the longer timescale responses than the constrained box model, and overall the global impact of the longer timescale response (reduced primary production due to lower O 3 concentrations) overwhelms the shorter timescale response (enhanced cycling from HO 2 to OH), and thus the global OH concentration decreases. The Earth system contains many such responses on a large range of timescales. This work highlights the care that needs to be taken to understand the full impact of any one process on the system as a whole.

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Section: Constrained Box Modelsupporting

confidence: 74%

Section: Constrained Box Modelmentioning

confidence: 99%

Impacts of bromine and iodine chemistry on tropospheric OH and HO2: comparing observations with box and global model perspectives

et al. 2018

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“…Jones et al (2014) proposed SCIs produced from alkyl iodide photolysis as a possible source of surprisingly high formic acid concentrations observed in the marine environment in the European Arctic. Other non-ozonolysis sources of SCIs include dissociation of the DMSO peroxy radical (Asatryan and Bozzelli, 2008;Taatjes et al, 2008) (which could be an important source in the marine environment, where DMSO is an oxidation product of OH + DMS), and potentially from reactions of peroxy radicals with OH in remote atmospheres (Fittschen et al, 2014).…”

Section: Discussion and Atmospheric Implicationsmentioning

confidence: 99%

“…However, the analysis also neglects additional sources of SCIs, e.g. photolysis of alkyl iodides (Gravestock et al, 2010;Stone et al, 2013), dissociation of the DMSO peroxy radical (Asatryan and Bozzelli, 2008;Taatjes et al, 2008), and reactions of peroxy radicals with OH (Fittschen et al, 2014), which are currently poorly constrained and may even dominate SCI production over an ozonolysis source in some environments.…”

Section: Atmospheric Implicationsmentioning

confidence: 99%

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Atmospheric isoprene ozonolysis: impacts of stabilised Criegee intermediate reactions with SO2, H2O and dimethyl sulfide

et al. 2015

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Abstract. Isoprene is the dominant global biogenic volatile organic compound (VOC) emission. Reactions of isoprene with ozone are known to form stabilised Criegee intermediates (SCIs), which have recently been shown to be potentially important oxidants for SO 2 and NO 2 in the atmosphere; however the significance of this chemistry for SO 2 processing (affecting sulfate aerosol) and NO 2 processing (affecting NO x levels) depends critically upon the fate of the SCIs with respect to reaction with water and decomposition. Here, we have investigated the removal of SO 2 in the presence of isoprene and ozone, as a function of humidity, under atmospheric boundary layer conditions. The SO 2 removal displays a clear dependence on relative humidity, confirming a significant reaction for isoprene-derived SCIs with H 2 O. Under excess SO 2 conditions, the total isoprene ozonolysis SCI yield was calculated to be 0.56 (±0.03). The observed SO 2 removal kinetics are consistent with a relative rate constant, k(SCI + H 2 O) / k(SCI + SO 2 ), of 3.1 (±0.5) × 10 −5 for isoprene-derived SCIs. The relative rate constant for k(SCI decomposition) / k(SCI+SO 2 ) is 3.0 (±3.2) × 10 11 cm −3 . Uncertainties are ±2σ and represent combined systematic and precision components. These kinetic parameters are based on the simplification that a single SCI species is formed in isoprene ozonolysis, an approximation which describes the results well across the full range of experimental conditions. Our data indicate that isoprenederived SCIs are unlikely to make a substantial contribution to gas-phase SO 2 oxidation in the troposphere. We also present results from an analogous set of experiments, which show a clear dependence of SO 2 removal in the isopreneozone system as a function of dimethyl sulfide concentration. We propose that this behaviour arises from a rapid reaction between isoprene-derived SCIs and dimethyl sulfide (DMS); the observed SO 2 removal kinetics are consistent with a relative rate constant, k(SCI + DMS) / k(SCI + SO 2 ), of 3.5 (±1.8). This result suggests that SCIs may contribute to the oxidation of DMS in the atmosphere and that this process could therefore influence new particle formation in regions impacted by emissions of unsaturated hydrocarbons and DMS.

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Formaldehyde in the Tropical Western Pacific: Chemical Sources and Sinks, Convective Transport, and Representation in CAM‐Chem and the CCMI Models

et al. 2017

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Formaldehyde (HCHO) directly affects the atmospheric oxidative capacity through its effects on HOx. In remote marine environments, such as the tropical western Pacific (TWP), it is particularly important to understand the processes controlling the abundance of HCHO because model output from these regions is used to correct satellite retrievals of HCHO. Here we have used observations from the Convective Transport of Active Species in the Tropics (CONTRAST) field campaign, conducted during January and February 2014, to evaluate our understanding of the processes controlling the distribution of HCHO in the TWP as well as its representation in chemical transport/climate models. Observed HCHO mixing ratios varied from ~500 parts per trillion by volume (pptv) near the surface to ~75 pptv in the upper troposphere. Recent convective transport of near surface HCHO and its precursors, acetaldehyde and possibly methyl hydroperoxide, increased upper tropospheric HCHO mixing ratios by ~33% (22 pptv); this air contained roughly 60% less NO than more aged air. Output from the CAM‐Chem chemistry transport model (2014 meteorology) as well as nine chemistry climate models from the Chemistry‐Climate Model Initiative (free‐running meteorology) are found to uniformly underestimate HCHO columns derived from in situ observations by between 4 and 50%. This underestimate of HCHO likely results from a near factor of two underestimate of NO in most models, which strongly suggests errors in NOx emissions inventories and/or in the model chemical mechanisms. Likewise, the lack of oceanic acetaldehyde emissions and potential errors in the model acetaldehyde chemistry lead to additional underestimates in modeled HCHO of up to 75 pptv (~15%) in the lower troposphere.

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The Reaction of CH₃O₂ Radicals with OH Radicals: A Neglected Sink for CH₃O₂ in the Remote Atmosphere

Cited by 55 publications

References 6 publications

Impacts of bromine and iodine chemistry on tropospheric OH and HO<sub>2</sub>: comparing observations with box and global model perspectives

Impacts of bromine and iodine chemistry on tropospheric OH and HO<sub>2</sub>: comparing observations with box and global model perspectives

Atmospheric isoprene ozonolysis: impacts of stabilised Criegee intermediate reactions with SO<sub>2</sub>, H<sub>2</sub>O and dimethyl sulfide

Formaldehyde in the Tropical Western Pacific: Chemical Sources and Sinks, Convective Transport, and Representation in CAM‐Chem and the CCMI Models

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The Reaction of CH3O2 Radicals with OH Radicals: A Neglected Sink for CH3O2 in the Remote Atmosphere

Cited by 55 publications

References 6 publications

Impacts of bromine and iodine chemistry on tropospheric OH and HO&lt;sub&gt;2&lt;/sub&gt;: comparing observations with box and global model perspectives

Impacts of bromine and iodine chemistry on tropospheric OH and HO&lt;sub&gt;2&lt;/sub&gt;: comparing observations with box and global model perspectives

Atmospheric isoprene ozonolysis: impacts of stabilised Criegee intermediate reactions with SO&lt;sub&gt;2&lt;/sub&gt;, H&lt;sub&gt;2&lt;/sub&gt;O and dimethyl sulfide

Formaldehyde in the Tropical Western Pacific: Chemical Sources and Sinks, Convective Transport, and Representation in CAM‐Chem and the CCMI Models

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The Reaction of CH₃O₂ Radicals with OH Radicals: A Neglected Sink for CH₃O₂ in the Remote Atmosphere

Impacts of bromine and iodine chemistry on tropospheric OH and HO<sub>2</sub>: comparing observations with box and global model perspectives

Impacts of bromine and iodine chemistry on tropospheric OH and HO<sub>2</sub>: comparing observations with box and global model perspectives

Atmospheric isoprene ozonolysis: impacts of stabilised Criegee intermediate reactions with SO<sub>2</sub>, H<sub>2</sub>O and dimethyl sulfide