For millions of people, flying is routine, a commute between cities, a holiday ritual, or a business necessity. But a new scientific study suggests that while passengers fasten their seatbelts and settle into their seats, they may also be breathing in something far less visible: extremely high levels of ultrafine air pollution.

According to the research, airline passengers can be exposed to concentrations of ultrafine particles far higher than previously recognised, particularly during boarding, taxiing on runways, and landing the very moments when aircraft are closest to airport operations and jet exhaust.

Ultrafine particles are among the smallest pollutants known, thousands of times thinner than a human hair. Because of their size, they can penetrate deep into the lungs and even enter the bloodstream. While they are not yet regulated under most global air-quality standards, growing scientific evidence links them to inflammation, cardiovascular disease and long-term respiratory harm.

Researchers monitored air quality inside aircraft cabins on short-haul European flights using specialised instruments designed to detect ultrafine particles and black carbon, a sooty pollutant associated with fossil-fuel combustion.

What they found was striking. Pollution levels inside the cabin remained relatively low once aircraft reached cruising altitude. But before take-off and after landing, particle concentrations surged, in some cases reaching levels more than double what health experts would consider high in other environments.

The spikes are believed to occur as aircraft draw in outside air while operating close to the ground where emissions from jet engines, ground vehicles and airport infrastructure are most concentrated.

“Passengers may assume that the most polluted part of flying is the time spent in the air,” the researchers noted. “In reality, the highest exposure appears to happen while the plane is still on the ground or approaching it.”

Unlike road traffic or industrial emissions, aviation particle pollution remains lightly regulated, particularly when it comes to ultrafine particles. Most existing air-quality rules focus on larger particles that are easier to measure, leaving the smallest and potentially most dangerous largely unmonitored.

This matters at a time when global air travel is booming. More than five billion passengers are expected to fly this year, passing repeatedly through environments where pollution levels can quietly spike.

The concern extends beyond passengers. Airport staff from ground crews to baggage handlers and communities living near major airports may face chronic exposure, with studies detecting elevated particle levels several kilometres away from busy runways.

The researchers stress that flying remains safe in terms of aviation security, and they are not calling for people to stop travelling. Instead, they argue that the findings highlight an urgent need for better monitoring, cleaner airport operations and updated regulations that reflect modern scientific understanding of air pollution.

Potential solutions could include cleaner ground vehicles, improved aircraft filtration systems, and stricter controls on emissions during taxiing and idle periods.

For now, the study adds a new dimension to how we think about air travel not just as a climate challenge, but as a public health issue unfolding inside the cabin itself.

As aviation continues to connect the world, the invisible air we breathe along the way may soon demand as much attention as the journey’s destination.