Acid-catalyzed reactions of hexanal on sulfuric acid particles: Identification of reaction products

Title:
Acid-catalyzed reactions of hexanal on sulfuric acid particles: Identification of reaction products
Authors:
Garland, Rebecca M.; Elrod, Matthew J.; Kincaid, Kristi; Beaver, Melinda R.; Jimenez, Jose L.; Tolbert, Margaret A.
Abstract:
While it is well established that organics compose a large fraction of the atmospheric aerosol mass, the mechanisms through which organics are incorporated into atmospheric aerosols are not well understood. Acid-catalyzed reactions of compounds with carbonyl groups have recently been suggested as important pathways for transfer of volatile organics into acidic aerosols. In the present study, we use the aerodyne aerosol mass spectrometer (AMS) to probe the uptake of gas-phase hexanal into ammonium sulfate and sulfuric acid aerosols. While both deliquesced and dry non-acidic ammonium sulfate aerosols showed no organic uptake, the acidic aerosols took up substantial amounts of organic material when exposed to hexanal vapor. Further, we used 1H-NMR, Fourier transform infrared (FTIR) spectroscopy and GC-MS to identify the products of the acid-catalyzed reaction of hexanal in acidic aerosols. Both aldol condensation and hemiacetal products were identified, with the dominant reaction products dependent upon the initial acid concentration of the aerosol. The aldol condensation product was formed only at initial concentrations of 75-96wt% sulfuric acid in water. The hemiacetal was produced at all sulfuric acid concentrations studied, 30-96wt% sulfuric acid in water. Aerosols up to 88.4wt% organic/11.1wt% H2SO4/0.5wt% water were produced via these two dimerization reaction pathways. The UV-VIS spectrum of the isolated aldol condensation product, 2-butyl 2-octenal, extends into the visible region, suggesting these reactions may impact aerosol optical properties as well as aerosol composition. In contrast to previous suggestions, no polymerization of hexanal or its products was observed at any sulfuric acid concentration studied, from 30 to 96wt% in water.
Citation:
Garland, R.M., M.J. Elrod, K. Kincaid, M.R. Beaver, J.L. Jimenez, and M.A. Tolbert. 2006. "Acid-Catalyzed Reactions of Hexanal on Sulfuric Acid Particles: Identification of Reaction Products." Atmospheric Environment 40: 6863.
Publisher:
Elsevier
DATE ISSUED:
2006-11
Department:
Chemistry
Type:
article
PUBLISHED VERSION:
10.1016/j.atmosenv.2006.07.009
PERMANENT LINK:
http://hdl.handle.net/11282/309752

Full metadata record

DC FieldValue Language
dc.contributor.authorGarland, Rebecca M.en_US
dc.contributor.authorElrod, Matthew J.en_US
dc.contributor.authorKincaid, Kristien_US
dc.contributor.authorBeaver, Melinda R.en_US
dc.contributor.authorJimenez, Jose L.en_US
dc.contributor.authorTolbert, Margaret A.en_US
dc.date.accessioned2013-12-23T16:17:06Zen
dc.date.available2013-12-23T16:17:06Zen
dc.date.issued2006-11en
dc.identifier.citationGarland, R.M., M.J. Elrod, K. Kincaid, M.R. Beaver, J.L. Jimenez, and M.A. Tolbert. 2006. "Acid-Catalyzed Reactions of Hexanal on Sulfuric Acid Particles: Identification of Reaction Products." Atmospheric Environment 40: 6863.en_US
dc.identifier.issn1352-2310en_US
dc.identifier.urihttp://hdl.handle.net/11282/309752en
dc.description.abstractWhile it is well established that organics compose a large fraction of the atmospheric aerosol mass, the mechanisms through which organics are incorporated into atmospheric aerosols are not well understood. Acid-catalyzed reactions of compounds with carbonyl groups have recently been suggested as important pathways for transfer of volatile organics into acidic aerosols. In the present study, we use the aerodyne aerosol mass spectrometer (AMS) to probe the uptake of gas-phase hexanal into ammonium sulfate and sulfuric acid aerosols. While both deliquesced and dry non-acidic ammonium sulfate aerosols showed no organic uptake, the acidic aerosols took up substantial amounts of organic material when exposed to hexanal vapor. Further, we used 1H-NMR, Fourier transform infrared (FTIR) spectroscopy and GC-MS to identify the products of the acid-catalyzed reaction of hexanal in acidic aerosols. Both aldol condensation and hemiacetal products were identified, with the dominant reaction products dependent upon the initial acid concentration of the aerosol. The aldol condensation product was formed only at initial concentrations of 75-96wt% sulfuric acid in water. The hemiacetal was produced at all sulfuric acid concentrations studied, 30-96wt% sulfuric acid in water. Aerosols up to 88.4wt% organic/11.1wt% H2SO4/0.5wt% water were produced via these two dimerization reaction pathways. The UV-VIS spectrum of the isolated aldol condensation product, 2-butyl 2-octenal, extends into the visible region, suggesting these reactions may impact aerosol optical properties as well as aerosol composition. In contrast to previous suggestions, no polymerization of hexanal or its products was observed at any sulfuric acid concentration studied, from 30 to 96wt% in water.en_US
dc.language.isoen_USen_US
dc.publisherElsevieren_US
dc.identifier.doi10.1016/j.atmosenv.2006.07.009en_US
dc.subject.departmentChemistryen_US
dc.titleAcid-catalyzed reactions of hexanal on sulfuric acid particles: Identification of reaction productsen_US
dc.typearticleen_US
dc.identifier.journalAtmospheric Environmenten_US
dc.subject.keywordTroposphereen_US
dc.subject.keywordOrganic aerosolsen_US
dc.subject.keywordAcid-catalyzed reactionsen_US
dc.subject.keywordProduct identificationen_US
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