Microplastic pollution is occurring in most ecosystem, yet their presence in high altitude clouds and their influence on cloud formation and climate change are poorly known. Here we analyzed microplastics in cloud water sampled at the summits of Japan mountains at 1300–3776 m altitude by attenuated total reflection imaging and micro-Fourier transform infrared spectroscopy. We observed nine microplastics including polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyamide 6, polycarbonate, ethylene–propylene copolymer or polyethylene–polypropylene alloy, polyurethane, and epoxy resin. Microplastic were fragmented, with mean concentrations ranging from 6.7 to 13.9 pieces per liter, and with Feret diameters ranging from 7.1 to 94.6 μm. Microplastics bearing hydrophilic groups such as carbonyl and/or hydroxyl groups were abundant, suggesting that they might have acted as condensation nuclei of cloud ice and water. Overall, our finding suggest that high-altitude microplastics cloud influence cloud formation and, in turn, might modify the climate.

The concentrations of polycyclic aromatic hydrocarbons (PAHs) in aerosol were measured in Shinjuku, which is central Tokyo, Japan, for 10 years from 2007 to 2016. The effects of changes in emission sources and their degradation by reaction with ozone were assessed in this study. There was no significant increasing or decreasing trend of the PAH concentrations during 10 years (P > 0.05). The average selected seven the PAH concentrations (0.88 ng m⁻³) during 10 years was lower than those in New York and Paris. However, the trend of ozone concentrations is increasing in central Tokyo. This inconsistency raises a question. Did the fact that the ozone concentration was higher than the PAH concentrations promote PAH degradation? To apportion the PAH sources, we used PAH concentration profiles and positive matrix factorization analysis. The contribution of vehicle emissions to the PAHs ranged from 40 to 80%. Ozone concentrations increased by 3.70%/year during 10 years. The theoretical degradation rates of PAHs by ozone, which were calculated using a pseudo-first-order rate equation, suggested that the lifetimes of benzo[a]pyrene (BaP) decreased by 1 min from 2007 to 2016. We investigated the aging of BaP using the profile of the isomer ratios. We found that the aging of BaP at the urban and roadside sites were nearly identical indicating aging regardless of the season. Although the decomposition of BaP is promoted by the photochemical oxidation reaction, this result suggests that a certain threshold value exists as the degree of the decomposition. This degradation of PAH can improve chemical loss processes in air quality model.

Microplastics (MPs < 5 mm) have become a growing concern in indoor environments, where their concentrations often exceed those outdoors. Familiar indoor sources include textiles, furniture, paints, and cleaning products, while factors such as ventilation type, occupancy level, and cleaning practices influence their abundance. This review synthesizes current findings on the occurrence, characterization, and risk factors of airborne and dust-borne MPs indoors in various indoor settings, and also based on continent and country income from high to low-income countries. Overall, airborne MP concentrations tend to be higher in lower-middle-income countries, particularly in Southeast Asia and South America, and are generally higher than in high-income regions. Advances in sampling and analytical techniques (including microscopy, FTIR, Raman spectroscopy, and pyrolysis-GC–MS) are discussed alongside the particles' physical and chemical properties. Evidence from toxicological studies demonstrates that inhalation, ingestion, and dermal exposure to MPs are linked to oxidative stress, inflammation, endocrine disruption, and organ-specific effects on the respiratory, digestive, reproductive, immune systems, and nervous systems. This review highlights the urgent need for harmonized monitoring protocols, comprehensive risk assessment, and effective mitigation strategies, such as improved cleaning, ventilation, and material substitution, to reduce exposure and safeguard human health in indoor environments.

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