(468d) The Hygroscopicity of Nano-Plastic Particles and Implications for Cloud Formation and Climate

Nano-plastics have been found in snow and evidence shows that they can act as nuclei. The aerosol water-uptake ability is an important property that will determine wet deposition, a potential main route for nano-plastics to fall to the ground. In this work, we measure the hygroscopicity of three nano-plastics - low-density polyethylene (LDPE), polyethylene terephthalate (PET) and polyvinyl chloride (PVC), and a fourth compound, cellulose, with in- situ aerosol techniques via a cloud condensation nuclei counter (CCNC). Cellulose is a high- molecular weight compound and a main component of commonly used paper products. Ultrafine nano-plastic particles in the range of 20 to 200 nm are explored. Nano-plastic materials LDPE, PET, and PVC form droplets more readily than cellulose nanoparticles. The high hygroscopicity of nano-plastics indicates that the nano-plastics are either oligomers or polymer with properties for water adsorption. Furthermore, a single parameter hygroscopicity, κ, derived from different droplet activation models (Flory Huggins Köhler and Frenkel-Halsey-Hill adsorption theory) are reported. Moreover, the molecular weights of the leeched oligomers are predicted by Flory Huggins Köhler theory assuming ideal polymer mixing. Thus nano-plastics can be incorporated into clouds, transported globally, and may also be removed from the atmosphere via wet deposition processes. The observed intrinsic hygroscopicity is size-dependent and the adsorption-based hygroscopicity model could be applied to estimate the lifetime and transport of nano-plastic particles in the atmosphere.