North Atlantic marine organic aerosol characterized by novel offline thermal desorption mass spectrometry: polysaccharides, recalcitrant material, and secondary organics

Abstract

Abstract. The composition of organic compounds in marine aerosols and the relative contributions of primary and secondary organic compounds remain uncertain. We report results from a novel approach to characterize and quantify organic components of the marine aerosol. Size-segregated discrete aerosol filter samples were collected at sea in the North Atlantic from both ambient aerosol and artificially generated primary sea spray over four cruises timed to capture the seasonal phytoplankton bloom dynamics. Samples were analyzed by Fourier transform infrared spectroscopy (FTIR), extracted into water, and analyzed by offline thermal desorption chemical ionization mass spectrometry (TDCIMS) and ion chromatography (IC). A positive matrix factorization (PMF) analysis identified several characteristic aerosol components in the TDCIMS mass spectra. Among these is a polysaccharide factor representing about 10 %–30 % of the submicron organic aerosol mass. Aerosol polysaccharide : sodium mass ratios were consistently higher in ambient air than in the artificially generated sea spray, and we hypothesize that this results from more rapid wet deposition of sodium-rich aerosol. An unquantified recalcitrant factor of highly thermally stable organics showed significant correlation with FTIR-measured alcohol groups, consistently the main organic functional group associated with sea spray aerosol. We hypothesize that this factor represents recalcitrant dissolved organic matter (DOM) in seawater and that by extension alcohol functional groups identified in marine aerosol may more typically represent recalcitrant DOM rather than biogenic saccharide-like material, contrary to inferences made in previous studies. The recalcitrant factor showed little seasonal variability in its contribution to primary marine aerosol. The relative contribution of polysaccharides was highest in late spring and summer in the smallest particle size fraction characterized (<180 nm).

Ocean Aerobiology

“…Microorganisms become embedded and enriched within a gel matrix of polymeric surfactants in the SML (Aller et al, 2005;Thornton et al, 2016), such as transparent exopolymer particles (TEP) (Alldredge et al, 1993) and Coomassie staining particles (CSP) (Long and Azam, 1996). This is consistent with the identification of polysaccharides in marine aerosol from the North Atlantic Ocean (Aller et al, 2017;Lawler et al, 2020). It has been presumed that the SML plays a dominant role in determining the composition of the organic matter is SSA.…”

“…Therefore, it is likely that nascent SSA generally contains a complex mixture of DOM from labile to ultra-recalcitrant. Chemical characterization of samples from the North Atlantic by Lawler et al (2020) supports this hypothesis. Lawler et al (2020) concluded that there was a seasonal signal associated with labile polysaccharides and a relatively constant pool of recalcitrant organic matter associated with alcohol groups.…”

“…Chemical characterization of samples from the North Atlantic by Lawler et al (2020) supports this hypothesis. Lawler et al (2020) concluded that there was a seasonal signal associated with labile polysaccharides and a relatively constant pool of recalcitrant organic matter associated with alcohol groups. Strictly speaking, the thermally stable (i.e., refractory) DOM identified by Lawler et al (2020) is not necessarily equivalent to the recalcitrant pool defined by Hansell (2013).…”

“…Lawler et al (2020) concluded that there was a seasonal signal associated with labile polysaccharides and a relatively constant pool of recalcitrant organic matter associated with alcohol groups. Strictly speaking, the thermally stable (i.e., refractory) DOM identified by Lawler et al (2020) is not necessarily equivalent to the recalcitrant pool defined by Hansell (2013). Current hypotheses explaining the stability of recalcitrant DOM are based on unavailability to microorganisms rather than thermal stability (Hansell, 2013).…”

Editorial: Unraveling Mechanisms Underlying Annual Plankton Blooms in the North Atlantic and Their Implications for Biogenic Aerosol Properties and Cloud Formation

“…The composition of submicron primary marine aerosol varied with season and latitude (Lewis et al). Organic materials in aerosol were linked to ubiquitous recalcitrant dissolved organic matter and transient polysaccharides emitted under bloom conditions (Lawler et al, 2020).…”