Plastic particles smaller than 5 mm in size are referred to as "microplastics."
These tiny particles of plastic are frequently discovered in industrial effluents or form as a result of the breakdown of larger plastic debris. Microplastics have been found in numerous organs, including the lungs, heart, blood, placenta, and faeces, and have been swallowed or inhaled by people and animals alike.
Ten million tonnes of these plastic fragments end up in the ocean, where they are released as ocean spray and find their way into the atmosphere.
This suggested that microplastics have become an important component of clouds, polluting practically everything we eat and drink through "plastic rainfall."
While much research on microplastics has concentrated on aquatic environments, few have investigated their impact on cloud formation and climate change as "airborne particles."
A group of Japanese researchers led by Hiroshi Okochi, a Professor at Waseda University, investigated the path of airborne microplastics (AMPs) as they circulate in the biosphere, negatively harming human health and the climate.
Their research was recently published in the journal Environmental Chemistry Letters, with co-authors Yize Wang from Waseda University and Yasuhiro Niida from PerkinElmer Japan Co. Ltd. contributing.
“Microplastics in the free troposphere are transported and contribute to global pollution. If the issue of 'plastic air pollution' is not addressed proactively, climate change and ecological risks may become a reality, causing irreversible and serious environmental damage in the future,” explained Okochi.
To investigate the role of these tiny plastic particles in the troposphere and the atmospheric boundary layer, the team collected cloud water from the summit of Mount Fuji, the south-eastern foothills of Mt. Fuji (Tarobo), and the summit of Mt. Oyama – regions at altitudes ranging between 1300-3776 meters.
Using advanced imaging techniques like attenuated total reflection imaging and micro-Fourier transform infrared spectroscopy (µFTIR ATR imaging), the researchers determined the presence of microplastics in the cloud water and examined their physical and chemical properties.
They identified nine different types of polymers and one type of rubber in the AMPs detected. Notably, most of the polypropylene that was detected in the samples was degraded and had carbonyl (C=O) and/or hydroxyl (OH) groups. The Feret diameters of these AMPs ranged between 7.1 – 94.6 µm, the smallest seen in the free troposphere. Moreover, the presence of hydrophilic (water-loving) polymers in the cloud water was abundant, suggesting that they were removed as “cloud condensation nuclei.” These findings confirm that AMPs play a key role in rapid cloud formation, which may eventually affect the overall climate.
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