Microplastics are plastic particles smaller than 5 millimetres. They are increasingly found not only in oceans and soil, but also in the air we breathe. Microplastics released in the air in urban environments can be transported by wind and air currents, and as a result be found in remote locations far from urban sources. Recent studies have highlighted the presence of microplastics in human lungs, blood, and even breast milk. These particles can carry hazardous chemicals and potentially pose a threat to human health and the environment, making their presence in the air a growing concern.

Sampling was conducted from July to August 2024 through a harmonised wet-dry deposition method using funnels with glass bottles. Sample collection was conducted in parallel during a week-long exposure period in diverse urban environments including Melbourne (AU), Budapest (HU), Bergen (NO), Gijón (ES), Rovaniemi (FI), Aabybro (DK), Barneveld (NL), Northampton (UK), Sacramento and South Bend (USA). Rural reference sites in Pelkosenniemi (FI) and Alta (NO) were also included for comparison.

Samples were filtered, prepared, and analysed at various Eurofins Environment Testing state-of-the-art microplastics testing laboratories using a suite of complementary detection technologies, including vibrational spectroscopy (FTIR, LDIR, Raman) and thermoanalytical methods (Pyrolysis-GC/MS, TED-GC/MS). Stringent QA/QC protocols were applied throughout the entire process.

Results revealed varying deposition rates depending on site and detection technology, ranging from 1,250 particles per square metre per day (with a median value of 143 particles per square metre per day) to 3,110 μg per square metre per day (with a median value of 19 μg per square metre per day), using vibrational spectroscopy and thermoanalytical technologies respectively. The most frequently identified polymers were polyethylene (PE) and polypropylene (PP), reflecting global plastic production trends. In addition to plastics, tire wear particles (rubbers) were identified, with levels reaching up to 304 μg per square metre per day (median value of 2.4 μg per square metre per day), highlighting road traffic as an additional significant source of microplastics. Most particles identified via vibrational spectroscopy were smaller than 100 μm which is in the breathable fraction. Results demonstrated notable variations in deposition rates between adjacent sample collection points which were analysed by the same detection technology, highlighting the heterogeneity of microplastics in air, and underscoring the complexity of accurately measuring airborne microplastics.

This research adds critical data to a growing body of evidence showing that microplastic pollution is not just a marine or terrestrial issue, but also a global air quality concern that demands internationally coordinated action.

• Deposition rates: up to 1,300 particles/m² per day (spectroscopy) and 3.1 mg/m² per day (spectrometry), depending on site and detection technology.
• Polymer composition: polymer types varied depending on location, with PE and PP being the most prevalent.
• Size: the majority of particles analysed were less than 100 μm large, meaning they can be inhaled by humans.
• Analytical methods: no single analytical technique is universally applicable; method selection must align with specific research objectives.
• Global standardisation needed: this study underscores the urgent need for standardised global monitoring protocols for airborne microplastics.

• Results revealed varying deposition rates depending on site and detection technology, ranging from 1,250 particles per square metre per day in Barneveld, NL (with a median value of 143 particles per square metre per day) to 3,110 µg per square metre per day in Bergen, NO (with a median value of 19 µg per square metre per day), using vibrational spectroscopy and thermoanalytical technologies respectively.
• The most frequently identified polymers were polyethylene (PE) and polypropylene (PP), reflecting global plastic production trends. But they are also amongst the less dense polymers they will be more likely to be airborne and able to be distributed by the wind.
• In addition to plastics, tire wear particles (rubbers as PIP, SBR, PBD) were identified, with levels reaching up to 304 µg per square metre per day (median value of 2.4 µg per square metre per day), highlighting road traffic as an additional significant source of microplastics.
• 91% of the particles identified by vibrational spectroscopy were smaller than 100 µm which is in the breathable fraction.
• The analysis of the morphology data shows that 85 % of the particles detected are fragments and 10% fibres and 5% spheres.
• The analysis of the colour data across Raman and LDIR shows that 97% of the particles detected are white, 2% black and 0.6% brown. Other colours detected are brown, pink and blue, but at very low numbers.
• But overall, the results demonstrated notable variations in deposition rates between adjacent sample collection points which were analysed by the same detection technology, highlighting the heterogeneity of microplastics in air, and underscoring the complexity of accurately sampling airborne microplastics.
• Further work is required to further to improve the sampling efficiency specifically for microplastics.

This research adds critical data to a growing body of evidence showing that microplastic pollution is not just a marine or terrestrial issue, but also a global air quality concern that demands internationally coordinated action.