Computational approaches for efficiently modelling of small atmospheric clusters

Elm, Jonas; Mikkelsen, Kurt V.

doi:10.1016/j.cplett.2014.09.060

Cited by 84 publications

(94 citation statements)

References 34 publications

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“…Ref. 70 has shown how reducing the basis set from the largest Pople basis set available (6- 311++G(3df,3pd)) to the basis set used in this work (6-31+G(d)) leads to differences in the calculated formation free energies below 1 kcal mol…”

Section: Letter Researchmentioning

confidence: 98%

Ion-induced nucleation of pure biogenic particles

Kirkby

Duplissy

Sengupta

et al. 2016

Nature

592

603

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Atmospheric aerosols and their effect on clouds are thought to be important for anthropogenic radiative forcing of the climate, yet remain poorly understood 1 . Globally, around half of cloud condensation nuclei originate from nucleation of atmospheric vapours 2 . It is thought that sulfuric acid is essential to initiate most particle formation in the atmosphere 3,4 , and that ions have a relatively minor role 5 . Some laboratory studies, however, have reported organic particle formation without the intentional addition of sulfuric acid, although contamination could not be excluded 6,7 . Here we present evidence for the formation of aerosol particles from highly oxidized biogenic vapours in the absence of sulfuric acid in a large chamber under atmospheric conditions. The highly oxygenated molecules (HOMs) are produced by ozonolysis of α-pinene. We find that ions from Galactic cosmic rays increase the nucleation rate by one to two orders of magnitude compared with neutral nucleation. Our experimental findings are supported by quantum chemical calculations of the cluster binding energies of representative HOMs. Ion-induced nucleation of pure organic particles constitutes a potentially widespread source of aerosol particles in terrestrial environments with low sulfuric acid pollution.It is thought that aerosol particles rarely form in the atmosphere without sulfuric acid 3,4 , except in certain coastal regions where iodine oxides are involved 8 . Furthermore, ions are thought to be relatively unimportant in the continental boundary layer, accounting for only around 10% of particle formation 5 . Sulfuric acid derives from anthropogenic and volcanic sulfur dioxide emissions as well as dimethyl sulfide from marine biota. However, typical daytime sulfuric acid concentrations (10 5 -10 7 cm −3, or 0.004-0.4 parts per trillion by volume (p.p.t.v.) at standard conditions) are too low for sulfuric acid and water alone to account for the particle formation rates observed in the lower atmosphere 9 , so additional vapours are required to stabilize any embryonic sulfuric acid clusters against evaporation. Base species such as amines can do this and can explain part of atmospheric particle nucleation 10 . It is well established that oxidation products of volatile organic compounds (VOCs) are important for particle growth 11, but whether their role in the smallest particles is in nucleation or growth alone has remained ambiguous 4,12,13 . Recently, however, it has been shown that oxidized organic compounds do indeed help to stabilize sulfuric acid clusters and probably play a major role in atmospheric particle nucleation 6,14,15 . We refer to these compounds as HOMs (highly oxygenated molecules) rather than ELVOCs (extremely low-volatility organic compounds) 16 because the measured compounds span a wide range of low volatilities.Here we report atmospheric particle formation solely from biogenic vapours. The data were obtained at the CERN CLOUD chamber (Cosmics Leaving OUtdoor Droplets; see Methods for experimental details) betw...

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Section: Letter Researchmentioning

confidence: 98%

Ion-induced nucleation of pure biogenic particles

Kirkby

Duplissy

Sengupta

et al. 2016

Nature

592

603

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“…This is relatively consistent with previous results using local coupled cluster (DF-LCCSD(T)-F12/VDZ-F12), where a scaling factor of 1.07 was identified over a test set of 38 atmospherically relevant clusters. 37 This implies that the DLPNO-CCSD(T)/def2-QZVPP calculations presented herein can be used as lower bound for the binding energy values.…”

Section: Cluster Formationmentioning

confidence: 99%

Computational Study of the Clustering of a Cyclohexene Autoxidation Product C₆H₈O₇ with Itself and Sulfuric Acid

et al. 2015

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We investigate the molecular interactions between sulfuric acid and a recently reported C6H8O7 ketodiperoxy acid formed through autoxidation from cyclohexene and ozone. Structurally similar but larger ELVOC (extremely low volatility organic compound) products formed from autoxidation of monoterpenes are believed to play a major role in the formation and early growth of atmospheric aerosol particles. Utilizing density functional theory geometries, with a DLPNO-CCSD(T)/def2-QZVPP single point energy correction, the stepwise Gibbs free energies of formation have been calculated, and the stabilities of the molecular clusters have been evaluated. C6H8O7 interacts weakly with both itself and sulfuric acid, with standard free energies of formation (ΔG at 298 K and 1 atm) around or above 0 kcal/mol. This is due to the presence of strong intramolecular hydrogen bonds in the peroxyacid groups of C6H8O7. These stabilize the isolated molecule with respect to its clusters, and lead to unfavorable interaction energies. The addition of sulfuric acid to clusters containing C6H8O7 is somewhat more favorable, but the formed clusters are still far more likely to evaporate than to grow further in atmospheric conditions. These findings indicate that the O/C ratio cannot exclusively be used as a proxy for volatility in atmospheric new particle formation involving organic compounds. The specific molecular structure, and especially the number of strong hydrogen binding moieties, are equally important. The interaction between the C6H8O7 compound and aqueous phase sulfate ions indicates that ELVOC-type compounds can contribute to aerosol mass by effectively partitioning into the condensed phase.

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“…56 Furthermore, it has been demonstrated that the reduction from the larger 6-311++G(3df,3pd) basis set to 6-31++G(d,p) have little effect on the thermal contribution to the Gibbs free energy using a large test set of 107 atmospherically relevant clusters. 57 To identify the lowest free energy structure of the organic compounds, each monomer was initially scanned using a systematic rotor approach with a MMFF94 force field as implemented in Avogadro. 58 Subsequently, the amount of conformers were narrowed down using M06-2X/6-31++G(d,p) yielding 1-6 conformations depending on the compound.…”

Section: Computational Detailsmentioning

confidence: 99%

What Is Required for Highly Oxidized Molecules To Form Clusters with Sulfuric Acid?

2017

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We have studied the specific requirements of a given neutral organic molecule to act as a stabilizer in sulfuric acid induced new particle formation. Based on an analysis of the reaction Gibbs free energies between simple functional groups and sulfuric acid, carboxylic acid groups are identified to show the strongest hydrogen bonding interaction with sulfuric acid. The free energy associated with the hydrogen bonding between sulfuric acid and 14 different carboxylic acids of atmospheric relevance reveal that the binding strength is very dependent on the ability of sulfuric acid to form an additional hydrogen bond via its vacant S-OH group to a γ-carbonyl group in the organic molecule. Extending the analysis to monoterpene oxidation products and further to large dimer esters, we identify the following necessary criteria for a given organic oxidation product to efficiently stabilize sulfuric acid clustering: (1) weak or no intramolecular hydrogen bonds in the isolated monomer; (2) more than two carboxylic acid groups. As a proof of concept we show that these requirements correspond to the docking of a sulfuric acid molecule between two non-interacting carboxylic acid groups in the organic molecule. These findings suggests that, for a given organic oxidation product to participate in the initial steps in new particle formation involving sulfuric acid, very distinct molecular features are required.

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Computational approaches for efficiently modelling of small atmospheric clusters

Cited by 84 publications

References 34 publications

Ion-induced nucleation of pure biogenic particles

Ion-induced nucleation of pure biogenic particles

Computational Study of the Clustering of a Cyclohexene Autoxidation Product C₆H₈O₇ with Itself and Sulfuric Acid

What Is Required for Highly Oxidized Molecules To Form Clusters with Sulfuric Acid?

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Computational approaches for efficiently modelling of small atmospheric clusters

Cited by 84 publications

References 34 publications

Ion-induced nucleation of pure biogenic particles

Ion-induced nucleation of pure biogenic particles

Computational Study of the Clustering of a Cyclohexene Autoxidation Product C6H8O7 with Itself and Sulfuric Acid

What Is Required for Highly Oxidized Molecules To Form Clusters with Sulfuric Acid?

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Computational Study of the Clustering of a Cyclohexene Autoxidation Product C₆H₈O₇ with Itself and Sulfuric Acid