EC-10. Gobal-scale size-resolved measurements of sea salt aerosol organic content

Abstract
Primary seawater organic compounds can influence the hygroscopic behavior and the number flux of sea salt aerosols formed at the ocean surface, possibly significantly impacting cloud properties and radiative balance over at least some ocean regions. Results from ambient observations, laboratory mesocosm studies, and measurements of the composition of artificially generated sea spray aerosol yield widely varying results for the organic content of sea spray particles. We present results from the ATom series of missions of airborne observations of size-resolved sea salt organic mass fractions (SSOMF) from about 0.2-1 µm particle diameter, made using Particle Analysis by Laser Mass Spectrometry (PALMS). SSOMF was generally low in the marine boundary layer (MBL), typically below 15%, and smaller particles had larger values, as expected. Atmospheric aging appears to be able to drive SSOMF to much higher values in the free troposphere (medians up to about 70%). These results imply that any influence seawater organics may have on MBL cloud condensation nucleus concentrations would most likely result from changes to sea spray number flux, not changes to hygroscopicity.