Determining How Composition Changes in the Sea Surface Microlayer Affect Cloud Formation

• Main Author: Hendrickson, Brianna Nicole
• Other Authors: Brooks, Sarah D, Thornton, Daniel C.O., Zhang, Renyi, Moore, Richard
• Format: Thesis
• Language: English
• Published: 2022
• Subjects: microlayer; aerosols; CCN; cloud formation; desalination; organics; North Atlantic
• Online Access: https://hdl.handle.net/1969.1/195922

The potential influence of marine phytoplankton on cloud formation has been debated for more than forty years and remains unresolved due to uncertainty in the relative contribution of marine organic matter to cloud droplet formation. In this study, cloud condensation nuclei (CCN) measurements were conducted on aerosolized sea surface microlayer (SML) samples collected during the National Aeronautics and Space Administration (NASA) North Atlantic Aerosols and Marine Ecosystems Study (NAAMES) field campaigns. To determine the contribution of organics in marine sea spray to cloud formation, SML samples were desalinated to remove all salts. The CCN activity of the raw SML and desalinated samples were measured using a CCN counter (Droplet Measurement Technologies, Inc.). Sample composition was characterized using a wideband integrated bioaerosol sensor (WIBS), ion chromatography (IC), and a Shimadzu TOC-V. The analysis from the WIBS showed that aerosols produced from all SML samples and desalinated SML samples contained fluorescing material indicative of marine biological source matter. The CCN activity of SML samples was slightly reduced compared to pure salt and artificial seawater, as indicated by a mean hygroscopicity parameter, κ, of 0.96 ± 0.120 compared to a mean κ value of 1.34 ± 0.004 for NaCl and a mean κ value of 1.28 ± 0.004 for artificial seawater. Desalination of the SML samples decreased κ to a mean value of 0.36 ± 0.050. To provide further insight on specific organic groups present in the samples, κ values were predicted based on the size and chemical composition of the aerosols. The chemical composition of the aerosols was assumed to be salts plus a specific organic compound. The organic concentration was determined assuming the total organic carbon (TOC) in the sample was entirely composed of that specific organic compound. Assuming seven different representative organic components of marine aerosol including humic acid, fulvic acid, glucose, 6-glucose, Ribulose-1,5-bisphosphate ...