UC San Diego
Investigation of the sources and composition of submicron organic aerosol particles in marine environments through artificial generation and atmospheric measurements /
- Author(s): Frossard, Amanda A.
- et al.
Atmospheric aerosol particles in the marine boundary layer (MBL) play an important role in the Earth's radiative balance, and recent studies have proposed a variety of interpretations of their sources and compositions. This dissertation improves the characterization of the sources and organic composition of aerosol particles in the MBL. Atmospheric aerosol particles were collected in the MBL of five ocean regions and analyzed using Fourier transform infrared (FTIR) spectroscopy, high resolution time of flight aerosol mass spectrometry (HR-ToF-AMS), HR-ToF-AMS with a light scattering module HR-ToF-AMS (LS-ToF-AMS), and scanning transmission X-ray microscopy with near-edge X-ray absorption fine structure (STXM-NEXAFS) to determine their organic functional group and mass fragment composition. Model ocean systems were used to generate ocean-derived primary marine aerosol particles (gPMA), which include particles resulting from seawater bubble bursting. The methods for measuring the organic composition of gPMA are compared, and the discrepancy between high resolution time of flight aerosol mass spectrometry (HR-ToF-AMS) and Fourier transform infrared (FTIR) spectroscopy measurements is attributed to the refractory nature of organics on sea salt in the HR-ToF- AMS. A method for dehydrating samples prior to analysis by FTIR spectroscopy is also presented. Both ocean-derived and anthropogenic emissions contribute to the organic mass (OM) in the MBL. Primary marine aerosol particles (PMA) were found to have similar compositions to marine saccharides and amino sugars, with 65% hydroxyl, 21% alkane, 6% amine, and 7% carboxylic acid functional groups. Contributions from photochemical reactions add carboxylic acid groups (15%-25%) to the PMA OM. Non-ocean- derived sources include shipping and other anthropogenic combustion emissions that together contribute more than half of the OM in the MBL. Seawater and gPMA have very similar compositions to the ocean-derived marine aerosol (mainly PMA). But there is a slightly larger fraction of alkane functional groups in gPMA from biologically productive seawater (35%) compared to oligotrophic seawater (16%). Surfactants in productive seawater may stabilize bubbles at the sea surface, enhancing drainage of soluble organics from their films before bursting and emitting particles. gPMA has a hydroxyl group absorption peak location characteristic of monosaccharides and disaccharides, while the seawater hydroxyl group peak location is more consistent with polysaccharides. This may result from the polysaccharides preferentially remaining in the seawater during PMA production