Characterizing the Organic Composition of Marine Aerosol from the North Atlantic to the Oceano Dunes

Atmospheric aerosol particles in the marine environment play an important role in the Earth’s radiative budget which are affected by the sources and compositions of the aerosol particles. Atmospheric aerosol particles were collected over four cruises in the remote regions of the North Atlantic Ocean and one field experiment from a stationary platform in the Oceano Dunes and were quantified using Fourier Transform Infrared (FTIR) spectroscopy and Scanning Transmission X-Ray Microscopy with Near-Edge Absorption Fine Structure (STXM-NEXAFS) for organic functional groups. X-ray fluorescence (XRF) analyses were used to understand the elemental composition of the Oceano Dunes samples. The four cruises’ atmospheric primary marine aerosol (aPMA) organic functional group composition was compared to see whether seasonal and biological changes had an effect. The average composition was 78% hydroxyl, 10% alkane, 6% amine, and 7% carboxylic acid groups, which was consistent with previous marine studies with sources including marine saccharides and amino sugars. The standard deviation within each season was greater than the differences between seasons, showing a limited seasonal response in the organic fraction. Generated primary marine aerosol particles (gPMA), atmospheric aerosol particles, sea-surface microlayer samples, and seawater samples were collected to compare the particle and bulk organic compositional differences as organics rise through the water column and are ejected into the marine boundary layer. The bulk organic composition consisted of the same three organic functional groups (hydroxyl, alkane, and amine groups) that comprised 50-90% of the quantified organic mass, though STXM-NEXAFS did illuminate the particle-to-particle diversity in all sample sources. The sea-surface microlayer and atmospheric aerosol particles were found to have far more variability in composition than generated primary marine aerosol and seawater, which could be attributed to a closer linkage between the organic sources and greater secondary processing within these sample sources than either generated primary marine aerosol or seawater. Coastal aerosol from Oceano Dunes showed a mixture of sources, with the dominant sources being wind-driven dust from the Oceano Dunes, sea salt from sea spray, and marine-derived organics. While this coastal location has recorded PM10 exceedances, the natural sources are unlikely to be a health-risk because they have not been shown to include toxic components