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Biological and Chemical Constraints on the Viscosity of Sea Spray Aerosol
Speaker Name
Dr Jonathan Slade, Assistant Professor of Chemistry, University of California San Diego
Online Platform via Zoom
Meeting ID: 948 3471 8888
Password: 968935

Airborne particulate matter of biological origin play an important role in public health and climate. This is evidenced most recently by the global pandemic, whereby transmission of the coronavirus via aerosol and droplets during exhalation is thought to be the dominant exposure pathway. Moreover, studies show that airborne bacteria can influence cloud formation and precipitation by acting as cloud condensation and ice nuclei. The world’s oceans serve as a significant source of biological and particulate organic matter, which become airborne (sea spray aerosol, SSA) from wind shear and bubble bursting mechanisms at the ocean surface, most notably during periods of phytoplankton growth and decay. SSA consists of salts, organic carbon (long- and short-chained fatty acids, and saccharides), and biological matter, including viruses, bacteria, and toxins. Previous studies have shown that the lifetimes of organic and toxic substances in atmospheric aerosol can be influenced by particle viscosity. At present, however, the viscosity of SSA, the most abundant aerosol by mass in the atmosphere, is not well characterized. In this presentation, I will discuss our most recent work investigating SSA viscosity as a function of relative humidity and its connections to aerosol molecular composition and biological processes during a controlled phytoplankton bloom. Our findings indicate SSA viscosity is most significantly affected by the biological activity in the water. Based on online measurements of aerosol molecular composition (e.g., molar mass, O:C, and organic/inorganic ratios) using extractive electrospray ionization high-resolution time-of-flight mass spectrometry, we find that the observed changes to SSA phase state during the bloom can be reconciled by changes in the glass transition temperatures of the particles due to specific biological mechanisms. These results indicate a biological constraint on the viscosity of sea spray aerosol, which may have important implications for coastal ocean-atmosphere interactions, including impacts on ice nucleation activity and multiphase processes such as oxidative aging and secondary organic aerosol formation and growth.

About the Speaker

I am an Assistant Professor of Chemistry in the Department of Chemistry and Biochemistry at the University of California San Diego (UCSD). My relevant background is in atmospheric chemistry, analytical chemistry, and chemical kinetics. I received my B.Sc. in Chemistry from Winthrop University in 2007, a M.Sc. in Analytical Chemistry from Purdue University in 2009, and a Ph.D. in Atmospheric Science from Stony Brook University in 2015. I pursued postdoctoral work in the lab of Prof. Paul B. Shepson at Purdue University from 2015 to 2018. My research group at UCSD focuses on analytical atmospheric chemistry – we do method development and applied analytical chemistry in mass spectrometry, chromatography, and aerosol instrumentation to study aerosols and multiphase chemistry on the nano and molecular level. Our current focus includes understanding fundamental connections between aerosol molecular composition and physical properties, mechanisms involved in new particle formation and growth, and photochemical and oxidative degradation kinetics of persistent organic pollutants in atmospheric aerosol. I am also a father of three beautiful girls.