Shipborne measurements of Antarctic submicron organic aerosols: an NMR perspective linking multiple sources and bioregions

Abstract

The concentrations of submicron aerosol particles in maritime regions around Antarctica are influenced by the extent of sea ice. This effect is two ways: on one side, sea ice regulates the production of particles by sea spray (primary aerosols); on the other side, it hosts complex communities of organisms emitting precursors for secondary particles. Past studies documenting the chemical composition of fine aerosols in Antarctica indicate various potential primary and secondary sources active in coastal areas, in offshore marine regions, and in the sea ice itself. In particular, beside the well-known sources of organic and sulfur material originating from the oxidation of dimethylsulfide (DMS) produced by microalgae, recent findings obtained during the 2015 PE-GASO cruise suggest that nitrogen-containing organic compounds are also produced by the microbiota colonizing the marginal ice zone. To complement the aerosol source apportionment performed using online mass spectrometric techniques, here we discuss the outcomes of offline spectroscopic analysis performed by nuclear magnetic resonance (NMR) spectroscopy. In this study we (i) present the composition of ambient aerosols over open-ocean waters across bioregions, and compare it to the composition of (ii) seawater samples and (iii) bubble-bursting aerosols produced in a sea-spray chamber onboard the ship. Our results show that the process of aerosolization in the tank enriches primary marine particles with lipids and sugars while depleting them of free amino acids, providing an explanation for why amino acids occurred only at trace concentrations in the marine aerosol samples analyzed. The analysis of water-soluble organic carbon (WSOC) in ambient submicron aerosol samples shows distinct NMR fingerprints for three bioregions: (1) the open Southern Ocean pelagic environments, in which aerosols are enriched with primary marine particles containing lipids and sugars; (2) sympagic areas in the Weddell Sea, where secondary organic compounds, including methanesulfonic acid and semivolatile amines abound in the aerosol composition; and (3) terrestrial coastal areas, traced by sugars such as sucrose, emitted by land vegetation. Finally, a new biogenic chemical marker, creatinine, was identified in the samples from the Weddell Sea, providing another confirmation of the importance of nitrogen-containing metabolites in Antarctic polar aerosols.

Contribution of Water-Soluble Organic Matter from Multiple Marine Geographic Eco-Regions to Aerosols around Antarctica

“…The average concentrations of the PM 1 aerosol water soluble fraction in the OO and SI samples are shown in Figure 1 Weddell Sea were previously attributed to emissions from the marginale ice zone biota 35,36,42 in agreement with the global MSA climatology 43 . In the OO region, average concentration was 0.043±0.012 µg m -3 (n=3; min, max: 0.036-0.057µg m -3 ), representing on average 2% of the aerosol water soluble mass.…”

“…As we have previously showed 35,36,42 , SI samples are influenced by aerosol precursors emitted by the peculiar microbiota thriving in sea ice and sea iceinfluenced waters, while OO samples are representative of the open Ocean biota. This results in distinct chemical compositions, which we will investigate in detail below.…”

“…were assigned to OO, and PE09, PE13 and PE18 were assigned to SI 35 . A detailed characterization of the air mass history, ground type contribution and water soluble organic features of each sample have been presented in Decesari et al 42 , where a map of the sampling locations can also be found.…”

“…represented an important aerosol component. Whilst the speciation of individual organic compounds was treated in a separate paper 42 , the next section discusses two chemicals of interest as markers of secondary aerosol sources.…”

Mediterranean nascent sea spray organic aerosol and relationships with seawater biogeochemistry

“…The ToF-ACSM is based on the same operating principles as the aerosol mass spectrometer (Drewnick et al, 2009). The ToF-ACSM contains a critical orifice, a PM 1 aerodynamic lens to focus submicron particles into a narrow beam that flows into a differentially pumped vacuum chamber, a standard vaporizer heated to 600 • C to vaporize particles, an electron-emitting tungsten filament (70 eV) to ionize the vapor, a compact time-of-flight mass analyzer (ETOF, Tofwerk AG, Thun, Switzerland), and a discrete dynode detector (Fröhlich et al, 2013).…”