Bistable effect of organic enrichment on sea spray radiative properties

Abstract

Primary-produced sea spray aerosol, typically comprising sea-salt, but also enriched with organic matter (OM) in biologically active oceanic regions, impacts the global radiative budget through contributions to aerosol optical depth. We show that sea spray light-scattering enhancement, f(RH), as a function of relative humidity (RH) is suppressed when enriched with OM. A new hygroscopic growth factor parameterization reveals a dual hygroscopicity state, flipping from high hygroscopicity and high f(RH) to low hygroscopicity and low f(RH) as the OM mixing volume percentage exceeds ∼ 55% in sea spray. Under elevated wind speeds, this affects the Top-of-atmosphere direct radiative forcing (ΔF) by reducing the cooling contribution of sea spray by ∼ 5.5 times compared to pure sea-salt spray. These results suggest a positive feedback coupling between the marine biosphere, sea spray aerosol, and the direct radiative budget. ©2013. American Geophysical Union. All Rights Reserved.