Researchers have detected a human fingerprint deep in the pristine Borneo rainforest in Southeast Asia.
Cold winds blowing from the north carry industrial pollutants from East Asia to the equator, with implications for air quality in the region.
The research is published in Atmospheric Chemistry and Physics, the journal of the European Geosciences Union (EGU).
Rainforests are often associated with pure, unpolluted air, but in Borneo air quality is dependent on which way the wind blows.
“On several occasions during northern-hemisphere winter, pockets of cold air can move quickly southwards across Asia towards south China and onward into the South China Sea,” says Matthew Ashfold, Assistant Professor at the University of Nottingham Malaysia Campus.
Ashfold and his team show these cold surges can very quickly transport polluted air from countries such as China to remote parts of equatorial Southeast Asia.
“The pollution travels about 1000 km per day, crossing the South China Sea in just a couple of days,” says Ashfold.
The researchers were initially looking for chemical compounds of natural origin. They wanted to test whether the oceans around Borneo were a source of bromine and chlorine.
But they also found a gas called perchloroethene, or perc, in the air samples they collected from two locations in the rainforest.
“This gas is a common ‘marker’ for pollution because it does not have natural sources,” says Ashfold.
The researchers say the levels of perc measured in Borneo are low, at a few parts per trillion. But because the gas does not occur naturally, even small concentrations are a sign that other more common pollutants, such as carbon monoxide and ozone, could be present.
Once in the deep tropics, the polluted air is lifted towards the upper atmosphere.
“This can introduce a range of industrial chemicals with atmospheric lifetimes of just a few months to the stratosphere, which could have a potentially negative impact on the ozone layer.”
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