Exploring the transport of pollution with a high altitude research aircraft

Climate researcher Thomas Röckmann investigates air at altitudes up to 20 km

StratoClim project - research aircraft M55 Geophysica
The research aircraft M55 Geophysica can fly up to twice as high as normal aircraft

The Asian Monsoon System is one of the Earth’s largest and most energetic weather systems, and monsoon rainfall is critical to feeding over a billion people in Asia. Utrecht researcher Thomas Röckmann is part of an international team of scientists who are now conducting the first-ever scientific mission to the upper levels of the monsoon system, using a high-altitude research aircraft flying out of Nepal. The results will help to better understand how this important weather system affects global climate and how it may change in the future.

Research Asian Monsoon System - Kathmandu
The research aircraft M55 Geophysica at Kathmandu airport

On 27 July, the Russian research aircraft M55 Geophysica took off from Kathmandu (Nepal) to carry out its first scientific mission at altitudes above 20 km – about twice as high as normal aircraft can fly. Thomas Röckmann developed the sampler that will be used on these flights to take air samples from the stratosphere. “The air pressure at an altitude of 20 km is very low, about one fifteenth of the air pressure on the ground,” he explains. “We use two special compressors to compress the air into steel canisters, reaching a pressure of 4.5 times the standard atmospheric pressure.” Back on the ground, Röckmann’s group will perform measurements on the air samples, studying the isotope composition of greenhouse gases. “That allows us to study how pollution is transported from the ground to greater altitudes, and hopefully to identify the sources of this pollution.”

We study how pollution is transported from the ground to greater altitudes

Asian Monsoon

During summer, the Asian Monsoon is not only important for Asia but affects weather patterns over the entire northern hemisphere. The Monsoon also acts like an enormous elevator, pumping vast amounts of air and pollutants from the surface up to levels above 16km altitude. These altitudes are so high that monsoon air then ascends into the stratosphere, the layer that contains the Earth’s protective ozone layer. Once in the stratosphere, monsoon air spreads globally and persists for years. Satellite images show a large cloud of aerosols – small droplets or dust particles – directly above the monsoon and extending from the Arabian Peninsula to the eastern coast of China.

StratClim project - Thomas Röckmann
Thomas Röckmann (right) and technician Michel Bolder inspect the sampler before it is deployed on board the M55 Geophysica

The formation and properties of the aerosol cloud that sits above the monsoon are a major unknown in climate science, and their potential future changes represent one of the largest uncertainties in climate predictions. Aerosols may either warm or cool the Earth’s surface, depending on their composition and how they interact with cloud formation processes. It is also unclear how monsoon rainfall will respond to changes in emissions of pollutants or to climate change.


An international team of scientists led by the Alfred Wegener Institute is now setting out to close this gap of knowledge. The StratoClim project involves teams from 37 research institutions from 11 European countries, the United States, Bangladesh, India, and Nepal, and marks an important milestone in international research cooperation in the region. The Institute for Marine and Atmospheric Research Utrecht (IMAU) is one of the institutes involved. The StratoClim observations will provide the first close-up view of the upper reaches of the monsoon, as no prior research flights have ever sampled this critical part of the Earth’s atmosphere.

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