Production of primary marine aerosol at the ocean surface is a major process in the earth?s climate system, with important implications for the physicochemical evolution of the troposphere and feedbacks on upper ocean biogeochemistry. Newly formed marine aerosol are number-dominated by sub-ìm diameter, hygroscopic, organic-rich particles that scatter solar radiation and serve as condensation nuclei. Photolysis of the associated marine-derived organic matter (OM) produces reactive oxygen species and other oxidized species. The nature, magnitude, and consequences of the production and evolution of marine aerosol are highly uncertain, precluding development of a reliable predictive capability for associated influences on tropospheric chemistry, upper ocean biogeochemistry, and climate.
To address some of these uncertainties, an interdisciplinary research team from the SUNY College of Environmental Science and Forestry, the University of Virginia, and the Scripps Institute of Oceanography will participate on a multidisciplinary research cruise from the US to Bermuda in the summer of 2012 to study fluxes of marine aerosols as a function of seawater characteristics. In particular they will characterize size- and composition-resolved marine aerosols by comparison of measurements made with their own custom-designed UVA aerosol generator with parallel measurements with the NOAA SeaSweep aerosol generator and eddy covariance techniques. Comparative studies will be carried out at two or three optically distinct stations with seawater characteristics that are compositionally distinct. These results will also be compared with similar data already in-hand to yield a more thorough synthesis and to serve as the basis for developing numerical models of the aerosol transport system. An important outcome of this project will be a thorough characterization of the aerosol material generated by the UVA instrument for future aerosol work at sea.
Broader Impacts: Results of the proposed research are expected to advance further study of the influences of the surface ocean on the size-resolved organic and inorganic composition and flux of nascent and ambient marine aerosol, and the related influences of these aerosol in the multiphase chemical and physical evolution of the marine boundary layer, surface ocean biogeochemistry, and Earth's radiation balance. The project will also provide for the training and support of one or more graduate and undergraduate students.
The major goal of this project is to evaluate the influences of seawater characteristics on size-resolved production fluxes and physicochemical properties of nascent marine aerosol and to characterize the nature of the associated organic matter (OM). From August 19 to August 26, 2013, a seawater "Bubbler" was operated on board the R/V Ronald H. Brown as part of the Western Atlantic Climate Study (WACS). The Bubbler was run continuously in two different ocean water types during the study. We collected and measured particles generated with the Bubbler in two different seawater types including colder, high chlorophyll water off the coast of the northeastern United States and warmer, low chlorophyll water in the Sargasso Sea. In both seawater types, we did full physical and chemical characterizations for the particles produced from the Bubbler. Different bubble production mechanisms were used including a range of airflow rates through two different sets of sintered glass frits. Simultaneously, another marine aerosol generator (the "Sea Sweep") was deployed alongside the research vessel by collaborators at PMEL. The Sea Sweep consisted of a raft with two stainless steel diffusers (2µm) used to produce bubbles below the ambient seawater surface. We analyzed particles generated from the Sea Sweep using similar techniques and compared them with the particles generated from the Bubbler. For the two seawater types and during the different production configurations, we measured particle size distributions and collected particles on Teflon filters for chemical analysis. We analyzed these filters using Fourier transform infrared (FTIR) spectroscopy to get the infrared absorption spectra of the submicron particles in each production configuration and water type. Particles were also sampled using a MOUDI sampler and analyzed collaboratively at the University of Virginia and the SUNY Syracuse. Our significant results are that submicron particles generated from the Bubbler have organic functional group compositions measured using FTIR spectroscopy that are similar to previously measured marine aerosol particles and to seawater and bubbled seawater. They also have saccharide-like compositions with large fractions of hydroxyl group and smaller fractions of alkane group and some amine functional groups. Four papers led by a graduate student (Amanda Frossard) and a postdoc (Rob Modini) in our group were completed using the results from the WACS cruise funded by this project. Three of these peer-reviewed papers are published, and the last one is submitted, as listed below. Frossard et al. (2014, submitted J. Geophys. Res.) use more than 10 years of ship-based measurements to assess the degree to which ambient atmospheric organic aerosol composition measurements can be attributed to primary marine aerosols and how the similarity of their composition with models for generating primary marine aerosol provides a robust indication of the origin of these particles. Further their chemical identification of organic functional group components suggests subtle differences that vary with the local productivity and seasons. Frossard et al. (2012, Environ. Sci. Technol.) developed the method used to characterize organic functional groups in sea salt mixtures, which is the basis for the findings on marine organic aerosol. In addition, Frossard et al. (2014, Aerosol Sci. Technol.) resolved the apparent discrepancies between spectroscopic and spectrometric measurements of marine organic aerosol, showing that the 650C volatilization used by AMS did not detect the organic components present on refractory salt particles but that those components could be identified by FTIR and NEXAFS-STXM. The importance of this method comparison was highlighted by its publication as an "Aerosol Research Letter." Modini et al. (2013, J. Geophys. Res.) explored the role of small fractions of surfactants in modifying controlled systems of bubbling of particles, showing that bubble film behavior is strongly controlled by even trace surfactant amounts.
