Ice Nucleating Abilities of UV and Ozone Aged Microplastics

Aerosols are an integral aspect of the atmospheric energy budget, however there are many uncertainties regarding the magnitude of their impact as ice nucleating particles. The introduction of particles that are able to nucleate ice allows for heterogenous freezing to occur at warmer temperatures compared to water without ice nucleating particles. Although there have been few studies on the topic, microplastics (MP) have been shown to have the ability to nucleate ice. Treating low density polyethylene (LDPE), polyvinyl chloride (PVC), polypropylene (PP), and polyethylene terephthalate (PET) with ultraviolet light (UV) and ozone simultaneously allows for an atmospherically relevant analysis of their ice nucleation abilities. In addition, infrared spectroscopy (IR) was used to determine chemical changes in the aged MPs. The IR analysis showed that MP with a growth of a peak near 1650-1800 cm-1 had a decrease in ice nucleation after aging, while MP that had the peak decrease or disappear had an increase in ice nucleation after aging. This data was compared to the background data, unaged MP, and MP that were aged with UV and ozone separately. Pristine and all types of aged MPs have been shown to be viable ice nucleating particles, as compared to background data. PVC treated with UV and ozone simultaneously showed more efficient ice nucleation, while PP and LDPE showed little to no change in ice nucleation after the aging process.