The Hygroscopicity Parameter of Marine Organics in Sea Spray Aerosols

Abstract

Atmospheric aerosols have important implications on Earth’s radiation budget by scattering and absorbing incoming solar radiation either directly or indirectly through cloud processes. Aerosols have a net cooling effect on climate, which opposes the warming caused by greenhouse gases. The magnitude of cooling, however, is poorly constrained due to large uncertainties associated with natural aerosol sources and their interactions with clouds. As oceans cover 70% of the earth’s surface, sea spray aerosols (SSA), which act efficiently as cloud condensation nuclei (CCN), are an important source of natural aerosol emissions. Surface active organic compounds readily accumulate in the sea surface microlayer (SML) and transfer onto SSA during bubble bursting; however, the resulting effects of organic content on CCN activation remains unresolved. Consequently, the work in this thesis proposes and tests a desalting method for quantifying the cloud nucleating properties of the organic components in surface seawater using κ-Köhler theory.

CCN measurements were used to infer the hygroscopicity parameter (κ) of atomized particles generated from ambient SML and bulk seawater samples. Using analyses of seawater chemistry, the concentration of organic and inorganic components in the particles were quantified. Even after desalting, inorganic constituents dominate the particle composition (>97%). Comparisons of hygroscopicity measurements in the samples before and after desalting show a significant reduction in κ (47 – 62%), which is inconsistent with κ-Köhler theory predictions. The project is still a work in progress; additional experiments are necessary to provide conclusive results on the mechanism contributing to the discrepancy between the observations and theoretical predictions.