The sky north of Ellesmere Island had just cleared when Matevz Lenarcic, flying alone in a Pipistrel Virus airplane at around 3,600m (10,000ft), got a call on his satellite phone. His friend following the weather on a computer in Slovenia had spotted heavy clouds and snow closing in on Lenarcic’s destination, an airfield near Resolute Bay, in the Canadian Arctic.
Lenarcic, a Slovenian pilot and adventurer, had departed Longyearbyen, Norway, early that morning. When he reached the North Pole, he tipped the ultralight plane's wings over and circled the Pole in a whimsical, if brief, round-the-world flight. Two hours later, shivering despite the immersion suit he wore, Lenarcic faced a more serious decision: race the storm to Resolute Bay or divert to Eureka, a nearby weather station with no facilities for protecting his plane after landing.
On the passenger seat beside him, he carried precious cargo – an experimental Aethalometer, a device that measures black carbon, or soot, in the air. Black carbon is a common contaminant, found in emissions from diesel engines and burning farm fields. Researchers say it is the second largest human contribution to climate change after carbon dioxide.
Flying above the Arctic Ocean may seem an unlikely way to look for humanity's footprints. But soot travels thousands of miles on winds, and the hundreds of cargo ships that ply the Arctic Ocean every year also inject it straight into the atmosphere. Soot has a stronger effect in the Arctic than in more temperate regions.
Clean Arctic sea ice can reflect as much as 90% of the sunlight that hits it. But a thin layer of soot makes the surface darker and less reflective. The Arctic has been losing sea ice since Nasa began tracking it in 1978, and it has been doing so much faster than climate models predict. Last year Arctic ice shrank by 18% compared to the previous record low of 2007, according to the official US monitoring organisation, the National Snow and Ice Data Center in Boulder, Colorado. Climate scientists have believed for some time that soot is accelerating Arctic sea ice melt.
Most soot monitoring is done from ground stations in populated areas and aerial data on polar soot are rare and scientifically valuable. “In the Arctic in particular the role of black carbon is potentially very, very important," says atmospheric scientist Drew Shindell of Nasa's Goddard Institute for Space Studies in New York, “What’s really important is understanding how the black carbon interacts with clouds in the Arctic.”
To address the data gap, Nasa launched a sensor-laden Gulfstream jet on a handful of soot-collecting missions. But these missions cost almost $500,000 a year. As a result, some researchers are now dabbling with aerosol-monitoring drones. Then there is Lenarcic’s no-fuss, experimental approach in a small private aircraft. “I would like to show how useful they are and that we could get huge benefits from them for just a fraction of the cost this kind of project normally requires,” he says.
The black, brick-sized Aethalometer by his side feeds on air from a tube outside the airplane. Incoming particles pass through a filter under the steady gaze of an optical beam, which measures the colour of the filter, revealing the size, colour and density of the captured particles. The analysis can even distinguish between particles from forest fires, diesel engines, wood stoves and cargo ships. By repeating the process around the world, Lenarcic hopes to collect a global overview of the story of soot.
The work lends scientific meaning to Lenarcic’s regular routine. He makes a living doing more mundane aerial surveys in Slovenia, punctuated with far-flung adventures in his plane. In 2011, he was planning a solo, round-the-world flight in pursuit of material for a photography book, when atmospheric scientist Grisa Mocnik asked him to test a prototype of the airborne Aethalometer. It was a good opportunity to show how small-time inventors and pilots can help to tackle a global problem.