Detailed chemical characterization of unresolved complex mixtures in atmospheric organics: Insights into emission sources, atmospheric processing, and secondary organic aerosol formation. Issue 12 (25th June 2013)

• Record Type: Journal Article
• Authors: Chan, Arthur W. H.; Isaacman, Gabriel; Wilson, Kevin R.; Worton, David R.; Ruehl, Christopher R.; Nah, Theodora; Gentner, Drew R.; Dallmann, Timothy R.; Kirchstetter, Thomas W.; Harley, Robert A.; Gilman, Jessica B.; Kuster, William C.; de Gouw, Joost A.; Offenberg, John H.; Kleindienst, Tadeusz E.; Lin, Ying H.; Rubitschun, Caitlin L.; Surratt, Jason D.; Hayes, Patrick L.; Jimenez, Jose L.; Goldstein, Allen H.
• Is Part Of: Journal of geophysical research. Volume 118:Issue 12(2013:Dec.)
• Page Start: 6783
• Page End: 6796
• Publication Date: 2013-06-25
• Subjects: semivolatile organic compounds -- secondary organic aerosol -- urban emissions -- unresolved complex mixture -- gas chromatography mass spectrometry; Atmospheric physics -- Periodicals; Geophysics -- Periodicals; 551.5
• DOI: 10.1002/jgrd.50533
• Languages: English
• ISSNs: 2169-897X

Abstract

Abstract : [1] Recent studies suggest that semivolatile organic compounds (SVOCs) are important precursors to secondary organic aerosol (SOA) in urban atmospheres. However, knowledge of the chemical composition of SVOCs is limited by current analytical techniques, which are typically unable to resolve a large number of constitutional isomers. Using a combination of gas chromatography and soft photoionization mass spectrometry, we characterize the unresolved complex mixture (UCM) of semivolatile aliphatic hydrocarbons observed in Pasadena, California (~16 km NE of downtown Los Angeles), and Bakersfield, California, during the California Research at the Nexus of Air Quality and Climate Change 2010. To the authors' knowledge, this work represents the most detailed characterization of the UCM in atmospheric samples to date. Knowledge of molecular structures, including carbon number, alkyl branching, and number of rings, provides important constraints on the rate of atmospheric processing, as the relative amounts of branched and linear alkanes are shown to be a function of integrated exposure to hydroxyl radicals. Emissions of semivolatile branched alkanes from fossil fuel‐related sources are up to an order of magnitude higher than those of linear alkanes, and the gas‐phase OH rate constants of branched alkanes are ~30% higher than their linear isomers. Based on a box model considering gas/particle partitioning, emissions, and reaction rates, semivolatile branched alkanes are expected to play a more important role than linear alkanes in the photooxidation of the UCM and subsequent transformations into SOA. Detailed speciation of semivolatile compounds therefore provides essential understanding of SOA sources and formation processes in urban areas. Key Points: Previously unresolved organics are characterized by molecular structures. Branched alkanes play an important role in oxidation of SVOCs to form SOA. Composition of UCM provides constraints on rate of atmospheric processing.