People living in cities may be inhaling far higher levels of microplastics than previously understood, simply by breathing the air around them, according to new research from Xi’an, China. Scientists found that airborne microplastic levels in the city tripled over the course of their study, highlighting how everyday pollution and human activity are quietly adding plastic particles to the air people breathe.
The study, led by aerosol scientist Fobang Liu of Xi’an Jiaotong University, examined fine air pollution known as PM2.5, tiny particles small enough to penetrate deep into the lungs. By analysing air filters collected in both summer and winter, before and after the COVID-19 pandemic, the researchers were able to track how microplastic concentrations and types changed over time. Their findings show that the pandemic marked a clear turning point in the makeup of airborne plastics.
Before 2020, air samples from Xi’an contained a wide range of plastic types and colours, suggesting many everyday sources such as synthetic clothing, packaging, and road wear. This variety provided a baseline, indicating that microplastics were already a regular part of city air. However, after disposable face masks became a daily necessity during the pandemic, the composition of airborne plastics shifted sharply.
The researchers found that transparent and white fibres dominated air samples during and after the pandemic, closely matching materials used in disposable masks. Most of these fibres were made of polypropylene and polyethylene terephthalate, plastics commonly found in mask fabrics, drink bottles, and synthetic textiles. The team linked this change to discarded masks that degrade as they rub against roads, soil, and other surfaces, releasing tiny fibres that are easily carried by the wind.
Chemical analysis also revealed that airborne microplastics often increased alongside ozone levels, a reactive gas that forms in sunlight. Ozone and ultraviolet radiation can weaken plastic surfaces, making them crack and shed fibres more easily. In busy cities, where sunlight, heat, foot traffic, and vehicle movement all accelerate plastic wear, lightweight fragments can be lifted into the air during dry conditions and transported over long distances.
Breathing these particles adds a new dimension to plastic exposure. Unlike plastics consumed through food or water, airborne microplastics can enter the respiratory system directly. Using particle deposition models, the researchers estimated where inhaled fibres are likely to settle in the body. Many are trapped in the nose and throat, but some reach the branching airways of the lungs and even deeper pulmonary regions.
The study suggests that children and teenagers may be more vulnerable than adults, as they breathe more air relative to their body weight. Modelling showed higher particle deposition in the lower airways of younger people, raising concerns even though direct links to disease are not yet proven. Scientists caution that microplastics vary widely in size, shape, and chemistry, making it difficult to predict their exact health effects.
Indoor environments may further increase exposure. Carpets, furniture, and clothing shed fibres into enclosed spaces, and outdoor pollution often flows indoors through doors and windows. While the Xi’an study focused on outdoor air, researchers note that indoor air quality and ventilation play a major role in daily exposure.
The findings also highlight broader waste management challenges. During the pandemic, the surge in disposable protective equipment strained waste systems worldwide. When collection and disposal fail, plastic debris escapes into streets and waterways, where it continues to break down and re-enter the environment as airborne particles.
Researchers say reducing microplastics in city air will require cleaner streets, improved waste collection, and better handling of disposable plastics. Some cities are encouraging reusable masks where appropriate and strengthening medical waste tracking systems. Scientists also argue that routine air quality monitoring should begin including microplastics as a public health indicator.
The study, published in the journal of Geophysical Research, underscores how everyday habits can shape the invisible pollution around us. As urban populations grow, researchers stress the need for long-term monitoring, stronger toxicology studies, and smarter waste policies to reduce the plastic particles people inhale with every breath.