Combined X-ray and Raman Spectroscopic Techniques Linking Sea Spray Aerosol to Surface Water Characteristics

Sea spray aerosol along with mineral dust dominates the global mass flux of particles to the atmosphere. Marine aerosol particles are of particular interest because of their continual impact on cloud formation, precipitation, atmospheric chemical processes, and thus global climate. Here we report on the physical/chemical characteristics of the sub-surface water, aerosolized sea spray particles, and particles/organic species present in surface microlayer (SML) samples collected during oceanic field campaigns and generated during laboratory experiments, revealing the source of the organic fraction of airborne particles. A rotating drum was used to collect SML samples during the JR288 2013 Arctic Ocean aboard the RSS James Clark Ross as part of the ACCACIA (Aerosol-Cloud Coupling and Climate Interactions in the Arctic) project, at coastal locations off British Columbia, Canada as part of the NETCARE (NETwork on Climate and in North Atlantic waters during the Western Atlantic Climate Study II (WACS II) aboard the R/V Knorr. A 13-stage MOUDI cascade impactor with a flow rate of 30 L/min and cut-point inlet stage sizes ranging from 0.018 to 18 μm was used to collect size-fractionated particle samples. Laboratory ice nucleation experiments with SML and aerosolized particles collected during the WACS II cruise and with laboratory generated exudate material from diatom cultures find them equally capable of acting as ice nuclei. Enhanced freezing of micrometer-sized droplets generated from SML water and phytoplankton exudates compared to homogeneous ice nucleation was observed with potential to impact cirrus and mixed phase clouds. Physicochemical analyses using a multi-modal approach which included Scanning Transmission X-ray Microscopy coupled with Near-Edge Absorption Fine Structure Spectroscopy (STXM/NEXAFS) and Raman spectroscopy confirm the presence and chemical similarity of polysaccharide-rich transparent exopolymer (TEP) material and proteins in both SML and sea spray aerosol regardless of the extent of biological activity in surface waters. Our results demonstrate a direct relationship between the marine environment and composition of marine aerosol through primary particle emission.