The effect of structure and isomerism on the vapor pressures of organic molecules and its potential atmospheric relevance

Caroline Dang, Thomas Bannan, Petroc Shelley, Michael Priestley, Stephen D Worrall, John Waters, Hugh Coe, Carl J. Percival, David Topping

Research output: Contribution to journalArticle

Abstract

Knudsen Effusion Mass Spectrometry (KEMS) was used to find the solid state vapor pressures of a range of atmospherically relevant organic molecules from 298 K to 333 K. The selection of species analyzed allowed for the effect of structural isomerism, specifically positional isomerism, and stereoisomerism, specifically geometric isomerism, on solid state vapor pressure to be investigated. In addition, the effect of varying the number of carboxylic acid groups present within a molecule’s structure and of varying alkyl chain length was assessed. The solid state vapor pressures were converted to subcooled liquid vapor pressures using experimental heat of fusion and melting point values. The resulting subcooled liquid vapor pressures were found to be up to 7 orders of magnitude lower than the vapor pressures estimated from models. Some of this variation between experimentally determined subcooled liquid vapor pressures and predicted vapor pressures, which use group contribution methods, can be attributed to the effects of isomerism which are largely not taken into account in models. Whilst these techniques might have both structural and parametric uncertainties, of the compound classes tested, a general inverse relationship between melting point and solid state vapor pressure was observed. Within each compound class the variations in vapor pressure can be attributed to the number and size of functional groups present and the relative positions of those functional groups to each other both positionally and geometrically. These two factors impact upon both the molecules’ dipole moments and upon their ability to interact both intramolecularly and intermolecularly via hydrogen bonding, thus explaining the differences in observed vapor pressure. Partitioning calculations using a range of condensed mass loadings show that whilst using vapor pressure values derived from models would put most of the compounds in the vapor phase, using the experimental values obtained here would mean a significant fraction of the organic molecules would be in the condensed phase. This could have a significant impact upon the formation and nature of atmospheric aerosol, and comparisons with ambient data obtained from other mass spectrometry techniques during bonfire night in Manchester in 2016 are made in an attempt to assess this potential atmospheric importance.

Original languageEnglish
Pages (from-to)1040-1055
Number of pages16
JournalAerosol Science and Technology
Volume53
Issue number9
Early online date24 Jun 2019
DOIs
Publication statusE-pub ahead of print - 24 Jun 2019

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Vapor pressure
vapor pressure
Molecules
Functional groups
functional group
liquid
Mass spectrometry
Melting point
effect
Liquids
mass spectrometry
melting
Atmospheric aerosols
Stereoisomerism
Dipole moment
carboxylic acid
Carboxylic Acids
Carboxylic acids
Chain length
Hydrogen bonds

Cite this

Dang, C., Bannan, T., Shelley, P., Priestley, M., Worrall, S. D., Waters, J., ... Topping, D. (2019). The effect of structure and isomerism on the vapor pressures of organic molecules and its potential atmospheric relevance. Aerosol Science and Technology, 53(9), 1040-1055 . https://doi.org/10.1080/02786826.2019.1628177
Dang, Caroline ; Bannan, Thomas ; Shelley, Petroc ; Priestley, Michael ; Worrall, Stephen D ; Waters, John ; Coe, Hugh ; Percival, Carl J. ; Topping, David. / The effect of structure and isomerism on the vapor pressures of organic molecules and its potential atmospheric relevance. In: Aerosol Science and Technology. 2019 ; Vol. 53, No. 9. pp. 1040-1055 .
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Dang, C, Bannan, T, Shelley, P, Priestley, M, Worrall, SD, Waters, J, Coe, H, Percival, CJ & Topping, D 2019, 'The effect of structure and isomerism on the vapor pressures of organic molecules and its potential atmospheric relevance', Aerosol Science and Technology, vol. 53, no. 9, pp. 1040-1055 . https://doi.org/10.1080/02786826.2019.1628177

The effect of structure and isomerism on the vapor pressures of organic molecules and its potential atmospheric relevance. / Dang, Caroline; Bannan, Thomas; Shelley, Petroc; Priestley, Michael; Worrall, Stephen D; Waters, John; Coe, Hugh; Percival, Carl J.; Topping, David.

In: Aerosol Science and Technology, Vol. 53, No. 9, 24.06.2019, p. 1040-1055 .

Research output: Contribution to journalArticle

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AU - Dang, Caroline

AU - Bannan, Thomas

AU - Shelley, Petroc

AU - Priestley, Michael

AU - Worrall, Stephen D

AU - Waters, John

AU - Coe, Hugh

AU - Percival, Carl J.

AU - Topping, David

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AB - Knudsen Effusion Mass Spectrometry (KEMS) was used to find the solid state vapor pressures of a range of atmospherically relevant organic molecules from 298 K to 333 K. The selection of species analyzed allowed for the effect of structural isomerism, specifically positional isomerism, and stereoisomerism, specifically geometric isomerism, on solid state vapor pressure to be investigated. In addition, the effect of varying the number of carboxylic acid groups present within a molecule’s structure and of varying alkyl chain length was assessed. The solid state vapor pressures were converted to subcooled liquid vapor pressures using experimental heat of fusion and melting point values. The resulting subcooled liquid vapor pressures were found to be up to 7 orders of magnitude lower than the vapor pressures estimated from models. Some of this variation between experimentally determined subcooled liquid vapor pressures and predicted vapor pressures, which use group contribution methods, can be attributed to the effects of isomerism which are largely not taken into account in models. Whilst these techniques might have both structural and parametric uncertainties, of the compound classes tested, a general inverse relationship between melting point and solid state vapor pressure was observed. Within each compound class the variations in vapor pressure can be attributed to the number and size of functional groups present and the relative positions of those functional groups to each other both positionally and geometrically. These two factors impact upon both the molecules’ dipole moments and upon their ability to interact both intramolecularly and intermolecularly via hydrogen bonding, thus explaining the differences in observed vapor pressure. Partitioning calculations using a range of condensed mass loadings show that whilst using vapor pressure values derived from models would put most of the compounds in the vapor phase, using the experimental values obtained here would mean a significant fraction of the organic molecules would be in the condensed phase. This could have a significant impact upon the formation and nature of atmospheric aerosol, and comparisons with ambient data obtained from other mass spectrometry techniques during bonfire night in Manchester in 2016 are made in an attempt to assess this potential atmospheric importance.

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Dang C, Bannan T, Shelley P, Priestley M, Worrall SD, Waters J et al. The effect of structure and isomerism on the vapor pressures of organic molecules and its potential atmospheric relevance. Aerosol Science and Technology. 2019 Jun 24;53(9):1040-1055 . https://doi.org/10.1080/02786826.2019.1628177