National Oceanic and
Atmospheric Administration
United States Department of Commerce


FY 2022

Characterization of sea surface microlayer and marine aerosol organic composition using STXM-NEXAFS microscopy and FTIR spectroscopy

Lewis, S.L., L.M. Russell, G. Saliba, P.K. Quinn, T.S. Bates, C.A. Carlson, N. Baetge, L.I. Aluwihare, E. Boss, A.A. Frossard, T.G. Bell, and M.J. Behrenfeld

ACS Earth Space Chem., 6(7), 1899–1913, doi: 10.1021/acsearthspacechem.2c00119, View online (2022)

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.

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