Characterization of Sea Surface Microlayer and Marine Aerosol Organic Composition Using STXM-NEXAFS Microscopy and FTIR Spectroscopy

Abstract

Atmospheric submicron particles, generated primary marine aerosol (gPMA), seawater (depth 5 m), and sea surface microlayer (depth ∼0.001 m) samples were collected during the North Atlantic Aerosol and Marine Ecosystem Study (NAAMES) on the R/V Atlantis in September 2017 and March 2018 and analyzed by scanning transmission X-ray microscopy with near-edge X-ray absorption fine structure (STXM-NEXAFS) and Fourier transform infrared (FTIR) spectroscopy. Three organic functional groups (hydroxyl, alkane, and amine) were present in all sample types, with the hydroxyl group typically being 50–90% of the quantified organic mass concentration. Microlayer and atmospheric particle samples both had a larger range of hydroxyl group to alkane group mass ratios than either seawater or gPMA. These measurements suggest that the sea surface microlayer organic composition contributes to the range of submicron atmospheric aerosol organic functional group composition. Atmospheric and microlayer sample alkane/hydroxyl group ratio variations were also associated with tracers of seawater biological activity, including chlorophyll and net primary production. Seawater and gPMA samples had relatively constant organic functional group composition for all of the sampled locations and varying phytoplankton activity conditions, suggesting that they are associated with the more consistent nature of dissolved organic carbon fraction that is ubiquitous in seawater. Eight k-means clusters of STXM-NEXAFS particles were identified from the spectra for all four sample types (atmospheric aerosol particles, gPMA, seawater, and microlayer), which showed that all four sample types had particles in four of the clusters and seven of the eight clusters included a mixture of sample types. These STXM-NEXAFS results support the FTIR measurements by showing consistent organic particle clusters across the four sample types as well as heterogeneity within each type.

Non-volatile marine and non-refractory continental sources of particle-phase amine during the North Atlantic Aerosols and Marine Ecosystems Study (NAAMES)

“…These aerosol types have been associated with biologically derived marine organic com-pounds, as they frequently contain a consistent ratio of primary (C-NH 2 ) amine groups to organic mass across multiple oceans including the Arctic, Atlantic, and Pacific (Frossard et al, 2014a). Similar primary amine group contributions have been identified across four seasons in the North Atlantic in seawater, the sea surface microlayer, generated primary particles, and atmospheric aerosol particles (Lewis et al, 2021(Lewis et al, , 2022.…”

“…Marine amines are estimated to contribute 0.6 TgC yr −1 to aerosol, and the formation of amine salts has been estimated to comprise 21 % of submicron marine secondary organic aerosol (SOA) mass (Myriokefalitakis et al, 2010). Primary marine sources of amines have been identified, showing correlations with sea salt, wind speed, and alcohol groups (Frossard et al, 2014a;Lewis et al, 2022;Russell et al, 2011). Secondary marine sources of amine have been identified for diethylamine, dimethylamine, and monomethylamine, which were correlated with the primary productivity of phytoplankton (Facchini et al, 2008;Müller et al, 2009).…”

Non-volatile marine and non-refractory continental sources of particle-phase amine during the North Atlantic Aerosols and Marine Ecosystems Study (NAAMES)

“…These aerosol types have been associated with biologically-derived marine organic compounds, since they frequently contain a consistent ratio of primary (C-NH2) amine groups to organic mass across multiple oceans including the Arctic, Atlantic, and Pacific (Frossard et al, 2014a). Similar primary amine group contributions have been identified across four seasons in the North Atlantic in seawater, sea surface microlayer, generated primary particles, and atmospheric aerosol particles (Lewis et al, 2021;Lewis et al, 2022).…”

“…FTIR NV amine functional groups have been reported in atmospheric aerosol, generated primary marine aerosols, seawater, and the sea surface microlayer sampled in air masses that were considered clean marine in the North Atlantic, with their presence in both seawater and aerosols supporting that those amines are largely both primary and marine (Lewis et al, 2022;Frossard et al, 2014a). FTIR NV amine groups indicate an association with sea spray (Saliba et al, 2019) because of their positive (0.49 < R < 0.52, Figure 3h) correlations to wind speed during continental periods in Winter and Early Spring, which included the highest wind speeds during NAAMES.…”

“…Marine amines are estimated to contribute 0.6 TgC/yr to aerosol, and the formation of amine salts have been estimated to comprise 21% of submicron marine secondary organic aerosol (SOA) mass (Myriokefalitakis et al, 2010). Primary marine sources of amines have been identified, showing correlations to sea salt, wind speed, and alcohol groups (Frossard et al, 2014a;Lewis et al, 2022;Russell et al, 2011). Secondary marine sources of amine were identified for diethylamine, dimethylamine, and monomethylamine, which were correlated with primary productivity of phytoplankton (Facchini et al, 2008;Muller et al, 2009).…”