Article pubs.acs.org/est
Analysis of Organic Anionic Surfactants in Fine and Coarse Fractions of Freshly Emitted Sea Spray Aerosol Richard E. Cochran,† Olga Laskina,† Thilina Jayarathne,† Alexander Laskin,‡ Julia Laskin,§ Peng Lin,‡ Camille Sultana,∥ Christopher Lee,∥ Kathryn A. Moore,∥ Christopher D. Cappa,⊥ Timothy H. Bertram,# Kimberly A. Prather,∥,⊗ Vicki H. Grassian,*,∥,⊗ and Elizabeth A. Stone*,† †
Department of Chemistry, University of Iowa, Iowa City, Iowa 52242, United States William R. Wiley Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99354, United States § Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99354, United States ∥ Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, United States ⊥ Department of Civil and Environmental Engineering, University of California, Davis, Davis, California 95616, United States # Department of Chemistry, University of Wisconsin−Madison, Madison, Wisconsin 53706, United States ⊗ Scripps Institution of Oceanography, University of California, San Diego, La Jolla, California 92093, United States ‡
S Supporting Information *
ABSTRACT: The inclusion of organic compounds in freshly emitted sea spray aerosol (SSA) has been shown to be size-dependent, with an increasing organic fraction in smaller particles. Here we have used electrospray ionization-high resolution mass spectrometry in negative ion mode to identify organic compounds in nascent sea spray collected throughout a 25 day mesocosm experiment. Over 280 organic compounds from ten major homologous series were tentatively identified, including saturated (C8−C24) and unsaturated (C12−C22) fatty acids, fatty acid derivatives (including saturated oxo-fatty acids (C5− C18) and saturated hydroxy-fatty acids (C5−C18), organosulfates (C2− C7, C12−C17) and sulfonates (C16−C22). During the mesocosm, the distributions of molecules within some homologous series responded to variations among the levels of phytoplankton and bacteria in the seawater. The average molecular weight and carbon preference index of saturated fatty acids significantly decreased within fine SSA during the progression of the mesocosm, which was not observed in coarse SSA, sea-surface microlayer or in fresh seawater. This study helps to define the molecular composition of nascent SSA and biological processes in the ocean relate to SSA composition.
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INTRODUCTION Aerosols in the marine boundary layer are derived from both oceanic and continental sources. Aerosols emitted from the ocean are commonly referred to as sea spray aerosol (SSA). SSA particles are a major contributor to the global radiation budget, interacting both directly and indirectly with incoming solar radiation.1 The ability of SSA to either absorb or reflect solar radiation depends on particle size and chemical composition. Although the composition of aerosols in the marine environment has been extensively studied, large uncertainties in the composition of nascent SSA still exists due to significant influences of terrestrial aerosol sources and secondary atmospheric processing.2−4 Organic material (OM), either dissolved or in the form of particulates, present in seawater has been shown to be scavenged by bubbles entrained in the water through the action of breaking waves.3−7 Upon bursting, OM as well as © 2016 American Chemical Society
inorganic salts are released in the form of SSA. The chemical composition of individual particles and their mixing state have been observed to be highly variant and size-dependent and can be broken down into four major classes: sea salt (SS), sea salt with organic carbon (SS-OC), organic carbon (OC), and biological (Bio).8−11 Larger SSA (those with diameters greater than 1 μm) are typically dominated by the SS type, with minor fractions of SS-OC and Bio particle types. In the submicrometer size range, the fraction of SSA particle types enriched in OC becomes more prominent, with decreasing SSA size resulting in a greater number fraction of both SS-OC and OC SSA types. While the chemical mixing state of SSA has Received: Revised: Accepted: Published: 2477
October 15, 2015 January 26, 2016 February 1, 2016 February 1, 2016 DOI: 10.1021/acs.est.5b04053 Environ. Sci. Technol. 2016, 50, 2477−2486
Article
Environmental Science & Technology
activity of various bacterial enzymes in the seawater were measured.14 Collection of SSA, SSML and Seawater Samples for Offline Analysis. Aerosol samples were collected onto precleaned 37 mm quartz fiber filters (PALL, Port Washington, NY) using a dichotomous sampler (Andersen Instruments, Inc., Thermo Scientific, Waltham, MA). SSA larger than 10 μm in diameter were removed from the sampled air using a PM10 cutoff sampling inlet (Model 246b, Andersen Instruments, Inc., Thermo Scientific). SSA were separated within the dichotomous sampler into two size bins based on wet diameters: 2.5− 10 μm (coarse) and
