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Ice Nucleation of Model Nano-Micro Plastics: A Novel Synthetic Protocol and the Influence of Particle Capping at Diverse Atmospheric Environments Mainak Ganguly, and Parisa A Ariya ACS Earth Space Chem., Just Accepted Manuscript • DOI: 10.1021/ acsearthspacechem.9b00132 • Publication Date (Web): 12 Aug 2019 Downloaded from pubs.acs.org on August 12, 2019
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ACS Earth and Space Chemistry
Ice Nucleation of Model Nano-Micro Plastics: A Novel Synthetic Protocol and the Influence of Particle Capping at Diverse Atmospheric Environments Mainak Ganguly,1 Parisa A. Ariya*1,2 1Department
of Atmospheric and Oceanic Sciences, McGill University, Montreal, Quebec H3A 0B9, Canada
2Department
of Chemistry, McGill University, Montreal, Quebec H3A 0B8, Canada Corresponding author:
[email protected] Abstract Little is known about airborne atmospheric aerosols containing emerging contaminants such as nano and microplastics. A novel, minimum energy usage, synthetic protocol of plastic micro-nano particles was herein developed. Stable plastic hydrosols were synthesized and characterized using three different types of plastics. The ice nucleation efficiency (INE) was investigated in both normal and synthetic sea-water to mimic environmental ice nucleation. Among the three tested plastic precursors (low density polyethylene, high density polyethylene and polypropylene), polypropylene produced the highest particle density with narrow particle size distribution. The change of size, shape, surface charge, and electronic behaviour of the plastic nano and micro particles accounted for the altered INE. The effects of environmental factors such as particle acidity and temperature on ice nucleation were also examined. An increase in pH increased INE due to an increased particle density (number of particles per unit volume), while increased temperature decreased INE significantly due to aggregation (attaching particles to produce a larger particle). Four types of capping were used on the surfaces of nano and
microplastics to investigate how the plastics act to nucleate ice when mixed with different particles. They include (a) ZnO as an emerging metal contaminant, (b) kaolin as a clay mineral, (c) HgCl2 as a toxic ionic water pollutant and, (d) phenanthrene as a polycyclic aromatic hydrocarbon. Capping by ZnO & HgCl2 decreased INE of plastic nano and microparticles, while kaolin & phenanthrene enhanced INE significantly. The association of contaminants to micro and nanoplastics changes INE likely due to water affinity, surface buckling, and lattice mismatch energy of ice, affecting ice nuclei formation processes. The observed differential physicochemical behaviours of plastic nano and microplastics, with and without cocontaminant cappings provide further insights to understand natural environmental ice nucleation and precipitation events. Our work shows that future emissions of nano and
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microplastics may become important for cloud formation and thus anthropogenic climate change. Keywords: Contaminant; Hydrophobicity; Efficiency; Immersion; Climate. 1. Introduction The International Panel on Climate Change (IPCC) has reported a lack of physicalchemical understanding of airborne particulates or aerosols; their interactions with cloud is the main gap in their knowledge. Aerosol-cloud interactions are highly uncertain in the context of estimation and interpretation of the Earth’s changing energy budget.1,2 The research required to narrow this knowledge gap in aerosols and aerosol-cloud interactions is related to the physicochemical investigation of processes such as size, composition, configuration, contact angle, surface properties, and photochemistry.3,4 Interestingly, similar physical and chemical properties play significant roles in the toxicological evaluation of the adverse health impact of particles. The World Health Organization (WHO) also named aerosols, especially smaller aerosols called nanoparticles (diameters
