New evidence has been found of the long distances that airborne pollution can be transported, and of its potential impacts far from its point of origin.
Researchers from the UK and Malaysia have detected a human fingerprint deep in the Borneo rainforest in south-east Asia − and it has implications for air quality in the region, and for the ozone layer.
The research, published in European Geosciences Union journal Atmospheric Chemistry and Physics, shows that cold winds from the north carry industrial pollutants from East Asia towards the equator. The air quality in Borneo depends very much 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 in the School of Biosciences at the University of Nottingham’s Malaysia campus, and formerly of the University of Cambridge.
Prof Ashfold and his colleagues show that these “cold surges” can very quickly carry polluted air southwards. “The pollution travels about 1,000 km (620 miles) per day, crossing the South China Sea in just a couple of days,” he says.
We aren’t arguing that our measurements indicate that there is a major climate impact, but they do nicely show that what is happening at the surface in industrialised middle latitudes can have an important impact elsewhere, with potential for important feedbacks to the surface.
They were originally looking for natural chemical compounds, to test whether the oceans around Borneo were a source of bromine and chlorine, but they also detected another gas called perchloroethene, or perc, in the air samples they collected from two sites in the Borneo forest.
“This gas is a common ‘marker’ for pollution because it does not have natural sources,” Prof Ashfold explains.
The team found evidence suggesting that the high levels of perc in the samples were influenced by East Asian pollution.
Perc is produced in industrial and commercial activities, such as dry cleaning and metal degreasing, and exposure to large amounts (above about 100 parts per million) can affect human health.
Global emissions have declined in the last 20 years or so, but it is not clear whether this applies to East Asia, where air pollution has increased over that period.
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 − are present, and levels of all three gases fluctuate at similar rates.
Ozone in high concentrations can damage forests by reducing plant growth, and is also a human health risk.
Poorer air quality in the remote rainforest is not the only consequence of the pollution. Prof Ashfold says: “The atmosphere over south-east Asia and the western Pacific is home to unusually strong and deep thunderstorms during the northern hemisphere winter. Because of this, the region is an important source of air for the stratosphere.”
There is a potentially two-way interaction between atmospheric composition and the climate.
One of the study’s co-authors, Professor John Pyle, from the Department of Chemistry at the University of Cambridge and director of the UK’s National Centre for Atmospheric Science, told the Climate News Network: “This study certainly exemplifies part of that feedback cycle.
“The mosaic of islands in Southeast Asia − our measurements are in Sabah, Malaysian Borneo − is a preferred region for very rapid lifting, sometimes within hours, of atmospheric compounds to higher levels.
“Some of these compounds − the industrially-produced halocarbons, and the halocarbons naturally emitted from the ocean, both of which we measure − are ozone-depleting substances.”
Both types of halocarbons and the ozone itself are greenhouse gases.
Professor Pyle says: “We aren’t arguing that our measurements indicate that there is a major climate impact, but they do nicely show that what is happening at the surface in industrialised middle latitudes can have an important impact elsewhere, with potential for important feedbacks to the surface.”