Microplastics as Ice Nucleating Particles in the Atmosphere

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

     Abstract Number: 383
     Working Group: Aerosols, Clouds and Climate

Abstract
The role that microplastics act as ice nucleating particles in the atmosphere is unknown. Studies have indicated that microplastics have sufficient atmospheric lifetimes and transport to warrant studies into their impact on these climate systems. Aerosol particles, including microplastics, can impact the global radiation balance through direct or indirect pathways of interaction with incoming and outgoing radiation. One indirect pathway is ice nucleation, by which aerosol particles impact the properties of clouds. Here, drop freezing assays performed in an environmental chamber were used to investigate the immersion freezing of microplastics. Microplastics studied included three compositions (i.e., polypropylene, polyethylene, and poly(vinyl chloride)) and ranged in size from 25 to 150 µm. The immersion freezing across size ranges of the plastics found no size dependence on the ice nucleation of the samples. Additionally, microplastics were exposed to ozone, ultraviolet light, ammonium sulfate, and sulfuric acid to mimic aging of the plastics in the environment. Investigation into immersion freezing of unaged and aged microplastics found that exposure to ultraviolet light and ozone led to a general decrease in the freezing temperature while aging via ammonium sulfate and sulfuric generally increased the freezing temperature. Overall, a better understanding of the ways in which microplastics may act as ice nucleating particles and what factors may contribute to an enhancement or suppression of this ice nucleating ability allows for the improvement of atmospheric models and a better understanding of our complex atmospheric system.