AAAR 35th Annual Conference October 17 - October 21, 2016 Oregon Convention Center Portland, Oregon, USA
Abstract View
What All Organic Aerosols Serving as Ice Nuclei Have in Common
SARAH BROOKS, Kristen Collier, Texas A&M University
Abstract Number: 248 Working Group: Aerosols, Clouds, and Climate
Abstract A wide range of organic compounds can act as heterogeneous ice nuclei including polycyclic aromatic compounds, long chain alkenes, alkanes, and even glucose. Mounting experimental evidence suggests that molecular structure has seemingly no impact on the freezing temperatures of these and more work is needed to determine what alternative traits, if any, can be used to predict organic aerosols' ability to act as ice nuclei. In this study, we use an optical ice microscope apparatus equipped with a sealed cooling stage and CCD camera to examine freezing events of droplets in contact with organic ice nucleating particles (INP). Two of the representative compounds studied, squalane and squalene are liquids while the remainder are solids. Samples exposed to ozone to represent atmospheric oxidative aging. Fresh and oxidized samples are characterized using two methods, Fourier Transfer Infrared Spectroscopy with Horizontal Attenuated Total Reflectance (FTIR-HATR) and Raman Microspectroscopy. Two of the representative compounds studied, squalane and squalene are liquids while the remainder are solids. Oxidative aging causes modest improvements in ice nucleation efficiency. Both solids and viscous liquids were observed to nucleate water ice, indicating that not even phase is a strong determinant in determining the ice nucleation ability of SOA type compounds. In the case of viscous liquids, while freezing temperatures are not well correlated with viscosity, it has been shown that increased viscosity is proportional to decreased nucleation rate.