Professor Borrmann is an atmospheric physicist from Johannes Gutenberg University and the Max Planck Institute for Chemistry in Mainz, Germany. He is interested in the complex cloud and aerosol system that forms over much of South Asia as part of the monsoon. The Himalayas force the air upward in a huge mass of swirling clouds. This acts “like a vacuum cleaner,” says Professor Borrmann, sucking up air pollution from all over Asia. In 2009, satellites detected that a layer of aerosol, a suspension of tiny particles, accumulated just above the clouds at an altitude of about 14-18 km. But no one knew what it was made of.
Professor Borrmann and his team wanted to know more because it seemed likely that this layer, known as the Asian Tropospheric Aerosol Layer (ATAL), could have a major and undiagnosed effect on our planet’s climate. Aerosols generally reflect sunlight and are also known to be important seeds for clouds. Therefore, it was expected that ATAL could provide some regional cooling effects, but it was not clear how important they would be.
There was also another aspect of the mystery. The air at this altitude, above the raging monsoon system, is very stable, giving aerosol particles plenty of time to act as surfaces on which unusual chemical reactions can take place. This could create a variety of pollutants that could spread widely through the atmosphere. But no one had any idea what that chemistry would be like.
This is what led Professor Borrmann and his team to Kathmandu airport in July 2017: to find out what was going on in this mysterious ATAL as part of their EXCATRO project. They arrived at around 6:30 am at a back entrance manned by some soldiers who checked their names against a handwritten list. Then they were led into a huge hangar. Inside were a special research plane and a series of benches containing scientific instruments, not only those of Professor Borrmann’s team, but also those of 15 other teams from around the world. “It’s chaos,” said Professor Borrmann. “Cables and tools everywhere”.
Kathmandu
Prof. Borrmann and his team prepare and calibrate about 11 different instruments. But its most precious pieces are two uniquely sensitive mass spectrometers, instruments that separate and measure trace gases based on their mass. It takes a couple of hours to check and calibrate the instruments and attach them to the outside of the plane, even under the wings, to get the air flowing. Then, because there is not enough space for tractors near the hangar, about 20 researchers push the plane out where the Russian pilot, the only person to get on, can start its engines.
There are few aircraft that can fly as high as this one, a Russian M-55 Geophysica. Commercial flights sail at an altitude of about 11 km, but this aircraft can reach more than 20 km. Pilots must wear a pressurized suit on single-seat aircraft. Organizing flights was difficult in a region with political tensions. Professor Borrmann says it took four years of high-level diplomacy to reach an agreement to fly the plane in Nepalese and Indian airspace.
Once it’s there, the instruments should work automatically and there’s not much that Professor Borrmann or anyone else can do other than worry. He says the temperature up there is -85 ° C and the instruments are under incredible stress. Flying through clouds can also get very turbulent. “There are a million little things that could cause failure,” he said.
A satellite phone on the plane sends SMS messages to the ground with readings on the status of the instruments. The researchers sit in the hangar and watch the updates on a big screen. Everything is mostly quiet. On some occasions, says Professor Borrmann, the instruments failed, so he sent an SMS telling them to turn off and on again. Fortunately, it worked.
In the late afternoon, the plane lands and the pilot gives a 20-minute report in Russian (which Professor Borrmann speaks, a little). It is important to understand the exact flight path that the instruments obtained their data so that the chemistry of the aerosol layer can be understood in spatial terms. Then there is a struggle to download the instruments and download the data.
It was at this point one day that Professor Borrmann had a moment that he says he will never forget. “From the traces of time, I could see the blue line that represents nitrate going up and up,” he said. It was pretty obvious to him at the time that ATAL was composed primarily of nitrate salts, and the team later confirmed it as ammonium nitrate. “For a few minutes, I was the only scientist in the world who knew the answer to this enormous mystery.”
Ammonia contamination
It was not entirely a surprise that ammonia was the main culprit at ATAL. The northern Indian subcontinent is known to be one of the world’s hot spots for ammonia pollution, because a large amount of fertilizers is produced and used there. These activities release ammonia into the air, which can then react with nitrogen oxides and sulfur oxides to form aerosols. A couple of research balloon flights had already provided preliminary clues that it was there in 2018. Professor Borrmann and his colleagues have proven this and provided great details on the distribution and concentrations of nitrate aerosols.
Shortly after the start of the measurement flight campaign, Professor Borrmann says he received some memorable messages. “After two or three flights, we received emails from colleagues at NASA,” he said. And essentially they said, ‘We’re seeing your plane fly on our radar. What the hell are you doing?”‘
Perhaps it should come as no surprise that NASA took note of a high-altitude Russian plane.
However, this exchange has led to the next phase of Professor Borrmann’s work. The plan, in collaboration with NASA, is to find out what kind of chemistry occurs in the aerosol layer below and how this could affect our climate. A few weeks after the end of the summer monsoon, the spray layer should have had time to undergo the chemistry and begin to disperse and drift away. Professor Borrmann and the team were planning a flight campaign using an American research aircraft over Japan at the right time of year in 2020 to take some more measurements. That has been canceled as a result of the coronavirus pandemic and similar flights from South Korea are now scheduled for 2021. “We want to see what happens to these particles as they age,” said Professor Borrmann.
Original article
This article was originally published in Horizon, the EU Research and Innovation Magazine
