Department Seminar: Mike Lawler

Title: Sea spray organics: how much and how important?

Abstract: Sea spray is an important aerosol source over the global oceans. It is responsible for some fraction of marine cloud condensation nucleus (CCN) concentrations and therefore plays a role in marine cloud properties and the surface radiative budget. Organic compounds are enriched in sea spray aerosol relative to the bulk composition of seawater, with greater enrichment at smaller particle diameters. Surface ocean organics may significantly affect sea spray aerosol production fluxes and hygroscopicity, and the amount of these organics may be controlled by recent biological productivity. However, measured values for the organic content of fresh sea spray span an extremely wide range, with some studies finding strong biological controls and others finding little to no influence from surface ocean biological activity. This has made it difficult to draw broad conclusions or identify representative values for inclusion in global models.

I will present results from recent in situ observations of the organic mass fraction of sea spray aerosol from a four-season, global-scale airborne study (ATom), based on single-particle measurements from Particle Analysis by Laser Mass Spectrometry (PALMS). The measurements show that sea spray over the remote oceans has quite low organic content on average, implying that these primary organics are probably not very important in most settings for aerosol-cloud interactions. These results will be discussed in the context of previous measurements to try to interpret the wide range of results and inferences in the literature, and to highlight regions where conditions may be different than the average.