Probing the Processes that Govern the Direct and Indirect Climate Effects of Nanoplastics

Katrina Betz, Habeeb Al-Mashala, Sithumi Liyanage, Micah Miles, Jace Barton, ELIJAH SCHNITZLER, Oklahoma State University

     Abstract Number: 451
     Working Group: Chemicals of Emerging Concern in Aerosol: Sources, Transformations, and Impacts

Abstract
Plastic particles with dimensions in the nanometer range, or nanoplastics, have been shown to be emitted into the atmosphere over land and the ocean and transported long distances to remote regions. During their atmospheric residence time, nanoplastics may influence climate through the direct and indirect effects, but the combined magnitude and direction of these effects are unknown. Here, we describe a series of experiments designed to probe the processes that govern the direct and indirect climate effects of nanoplastics. Macroscopic plastics, commonly colored with azo dyes, are known to whiten with environmental exposure, and we have demonstrated that azo dyes undergo reactive uptake of ozone, so we expect the direct effect to depend on the rate of whitening in the atmosphere due to oxidants and irradiation. We generated colored nanoplastics using a heated nozzle from a 3D printer, deposited the particles on filters, and monitored the absorbance through the filters as a function of exposure to ozone at 30 ppb and irradiation in a UV-B photo-reactor and solar simulator. In the first 24 h of ozone exposure, the absorbance decreased by about 15%, and the remaining 85% persisted for subsequent exposure over the course of days, suggesting that only dye within a thin layer near the surface of the particles is susceptible to ozone. In contrast, the absorbance decreased rapidly and almost completely through irradiation. We have also investigated the partitioning of secondary organic aerosol from the ozonolysis of α-pinene onto nanoplastics. Results indicate that partitioning under dry conditions can give partially engulfed, rather than core-shell particles, and the coating increases the hygroscopicity of the core nanoplastics, likely enhancing their impact on cloud formation as well as increasing their wet deposition.