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Detailed chemical characterization of unresolved complex mixtures in atmospheric organics: Insights into emission sources, atmospheric processing, and secondary organic aerosol formation
Author(s) -
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.,
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.
Publication year - 2013
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1002/jgrd.50533
Subject(s) - aerosol , chemistry , environmental chemistry , atmospheric chemistry , branching (polymer chemistry) , radical , photoionization , organic chemistry , ozone , ionization , ion
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.