10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Biogenic Macromolecules from Terrestrial and Marine Biospheres Acting as Ice Nucleating Particles
DANIEL KNOPF, Joseph Charnawskas, Peter Aaron Alpert, Josephine Aller, Swarup China, Daniel Veghte, Daniel Bonanno, Alexander Laskin, Ryan Moffet, Mary Gilles, Jian Wang, Stony Brook University
Abstract Number: 976 Working Group: Unraveling the Many Facets of Ice Nucleating Particles and Their Interactions with Clouds
Abstract The terrestrial and marine biospheres are sources of ice nucleating particles (INPs) active in the immersion freezing and deposition ice nucleation modes. In regions where mineral dust is scarce, biogenic INPs may control cold cloud formation. Atmospheric particles collected i) in the marine environment including surf zones and Pacific and Atlantic oceans in addition to laboratory mesocosm experiments with natural seawater, ii) above and below the forest canopy in the Amazonian region during the Green Ocean Amazon campaign, and iii) at the ground site of Graciosa Island during the Aerosol and Cloud Experiments in Eastern North Atlantic campaign are examined for their ice nucleation ability. Particles were collected on various substrates for micro-spectroscopic single particle chemical analyses using size-resolved impaction. Ice nucleation experiments were conducted covering temperature and humidity conditions for mixed-phase and cirrus clouds. Experiments were accompanied by scanning electron microscopy with energy dispersive X-ray spectroscopy SEM/EDX for elemental and morphology analyses of particles including INPs, and scanning transmission X-ray microscopy with near edge X-ray absorption spectroscopy (STXM/NEXAFS) for particle mixing state analysis. Additionally, sea spray aerosol (SSA) particles were photospectroscopically examined for the presence of polysaccharidic and proteinaceous matter following chemical analyses.
Analyses of ambient particles including INPs by STXM/NEXAFS show that the organic matter, often present as a coating, is very similar among biogenic particles from different sources. The widespread presence of polymeric carbohydrate molecules is corroborated, in the case of SSA particles, by staining and photospectroscopic analyses. Corresponding ice nucleation experiments with collected particles find that deposition ice nucleation and immersion freezing are initiated under very similar conditions of temperature and humidity. The observations of similar chemical composition and ice nucleation propensity for particles from both the marine and terrestrial biospheres suggest that naturally occurring biogenic polysaccharidic macromolecules from photosynthetic-active plants and phytoplankton form amorphous polymers that may play a role in cloud glaciation under atmospheric conditions. These findings support previous studies showing that ice nucleating macromolecules (INMs), which can be polysaccharides, demonstrate freezing temperatures that correlate with the size of the INMs according to classical nucleation theory.