Abstract View
Organic Fraction of the <0.15 µm Diameter Aerosol Particles over the Southern Ocean
GEORGES SALIBA, Kevin Sanchez, Savannah Lewis, Lynn Russell, Cynthia Twohy, Greg Roberts, Scripps Institution of Oceanography
Abstract Number: 261
Working Group: Aerosol Chemistry
Abstract
Aerosol particles smaller than 0.15 µm in diameter can be cloud condensation nuclei (CCN) active at supersaturations typical of marine stratocumulus clouds depending on their chemical composition. However, little is known about the composition and contribution to CCN of organic mass (OM) for particles over the Southern Ocean marine boundary layer. Airborne measurements of aerosol number and mass size distributions, chemical composition using scanning transmission electron microscopy with energy dispersive X-ray spectroscopy (STEM-EDS), and CCN spectra during the Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study (SOCRATES) provide a comparison of organic contributions. Here, we estimate the organic fraction of the <0.15 μm particles indirectly by comparing CCN spectra to particle size distributions. STEM-derived composition of particles smaller than 0.15 μm diameter was consistent with a larger fraction of sulfate and sodium-based sea spray particles with OM components accounting for less than 2% of analyzed particles. Particles <0.15 μm diameter had kappa values of 0.2 – 0.5, indicating the substantial presence of OM at these sizes. These inferred organic components are found mostly at sizes below STEM range. The OM fraction estimated from comparing the size distribution and supersaturation spectra varied from <10% to 70% for particles <0.15 μm in diameter. This variable OM fraction accounted for <0.1 μg/m3 mass concentrations of particles smaller than 0.15 μm diameter but may play a role at cloud supersaturations greater than 0.3%.