Pristine and Aged Microplastics Can Nucleate Ice through Immersion Freezing

HEIDI L. BUSSE, Devaka Ariyasena, Jessica Orris, Miriam Freedman, The Pennsylvania State University

     Abstract Number: 107
     Working Group: Chemicals of Emerging Concern in Aerosol: Sources, Transformations, and Impacts

Abstract
Microplastics (MP) are ubiquitous in the environment—their atmospheric relevance being increasingly recognized. A recent question is whether MP can act as ice nucleating particles in the atmosphere. This study looks at the immersion freezing activity of lab-prepared MP of four different compositions (low-density polyethylene, polypropylene, poly(vinyl chloride), and polyethylene terephthalate) using droplet freezing assays. The MP are also exposed to ultraviolet light and ozone for environmental equivalents of up to 593 and 99 days, respectively, as well as sulfuric acid and ammonium sulfate to mimic environmental aging of the plastics to elucidate the role that these processes play in the ice nucleating activity of MP. Results show that all studied MP act as immersion nuclei and aging processes can modify this ice nucleating activity, leading to increases or decreases in ice nucleating activity. Chemical changes are monitored with infrared spectroscopy and the growth of a C=O peak is associated with a decrease in ice nucleating activity while a loss of an existing C=O peak is associated with an increase in ice nucleating activity. The MP studied here have ice nucleating activities sufficient to be a non-negligible source of ice nucleating particles in the atmosphere if present in high enough concentrations.