AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
Alteration of the Ice Nucleating Properties of Biological and Biomass Burning Particles
Michael Polen, Hassan Beydoun, Emily Lawlis, Leif Jahn, Lydia Jahl, RYAN SULLIVAN, Carnegie Mellon University
Abstract Number: 580 Working Group: Aerosols, Clouds, and Climate
Abstract Particles can experience extensive chemical and physical evolution during atmospheric transport, and this can significantly alter the particles’ ice nucleation properties. We found that photochemical oxidation in a smog chamber enhanced the ice nucleation ability of authentic biomass burning aerosol. The droplet freezing temperature spectrum was observed to increase by more than 5 C following photochemical aging. We suspect this is caused by the oxidation of soot particle surfaces and have investigated this using online particle mass spectrometry and offline electron and x-ray spectromicroscopy.
We have found the immersion freezing properties of Snomax bacterial particles to be substantially unstable, observing a loss of ice nucleation ability over months of repeated droplet freezing measurements of the same batch of Snomax stored in a freezer. This reflects the fragility of the most ice active large protein aggregates. The easy loss of the most efficient ice nucleating proteins presents issues for the use of Snomax as an INP standard, and has implications for the evolution of ice nucleation properties of biological particles during atmospheric transport. Using an oil-immersion droplet freezing technique, repeated freezes of Snomax droplets resulted in a decrease in ice nucleation ability after successive refreezes. We attribute this to the disruption or displacement of the most ice active protein aggregates that are thought to contain the ice nucleants. Caution therefore is warranted in the use of oil-immersion droplet freezing methods to determine immersion freezing properties of biological or other hydrophobic particle types.