Airborne nanoplastics: surface chemistry and cloud-crystallisation properties

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The amount of micro and sub-micro-sized plastic particles polluting the environment is, unfortunately, increasing due to human activity. It has been shown that microplastics have an adverse effect on the environment, but little is known about their influence on the formation of ice in clouds (which alters the radiative properties of the Earth). Moreover, our theoretical understanding of the phenomenon of ice formation is fairly poor. As a result, models cannot be used accurately to predict whether a substrate will promote the formation of an ice nucleus within a body of liquid water. Therefore, experimental investigations are needed to assess whether a plastic species will promote the formation of ice crystals in clouds. For this purpose, microplastics are synthesized using cryogenic ball milling and separated in size by sieving. Their sizes and surface functionalities were investigated using characterization techniques such as XPS, optical microscopy, and IR spectroscopy. The ice nucleating properties of the laboratory-made microplastics are investigated by performing droplet freezing experiments with suspensions of the plastic samples in ultrapure water. For this, the IceBox, a novel open droplet system, was used to cool suspension droplets at a constant rate in an atmosphere with controlled humidity. Depending on the plastic's chemical and physical characteristics, the micro and nano plastics could have a notable effect on the temperature of freezing of the droplets. This research will be of importance to both the field of atmospheric science and ice physics.