Sunday, April 28, 2013

Yellow sand, black snow

Kōsa: the dust in Japan's skies takes a turn for the worse

Back then, it was just part of the natural scenery. Swathes of dust – we understood it drifted in from China – overlay the spring snow, so that our skis cut white tracks in the tawny slopes as we swung down them. Even on high Tateyama (see photo below), the dust would collect in the gullies and rills, dulling the snow’s brilliance.

Kosa by Alpine Light & Structure
Kosa, a photo by Alpine Light & Structure on Flickr.
In recent years, “kōsa” – the term means ‘yellow sand’ – has taken on a more sinister character. Borne on high-altitude winds from China’s desert regions, it seems to be obscuring Japan’s skies more often, and for longer. And the same winds are bringing in more industrial pollutants too.

In March this year, the Fukuoka local government issued the nation’s first-ever health warning over smog from China; citizens were advised to stay indoors or to wear a mask if they ventured outside. In Korea, where the yellow sand is known as “hwangsa”, far more drastic measures have been taken: bad air days have forced the closure of schools, airports and high-precision factories.

Everyone agrees that breathing dust is bad for you. But the yellow sand’s other effects are disputed. Nobody is quite sure, for example, whether those characteristic milky skies help to warm or cool the earth’s climate. And the dust particles from China’s deserts might actually absorb and neutralise the industrial pollutants that cause acid rain.

Even so, the pollutants are getting through. A professor at Tohoku University has found that metallic precipitates lodged in the soil of Hachimantai – one of the Hyakumeizan – have increased two to fivefold from the levels of the 1950s. At the other end of the archipelago, a rare species of pine is dying off on the slopes of Yakushima, another of the One Hundred Mountains.

Nagafuchi Osamu, a researcher at the University of Shiga Prefecture, believes that industrial pollution is causing this "Waldsterben". He was alerted to the possibility during a hiking trip to the island in 1992, when he noticed black snow. Testing it, he found that the soot contained silicon, aluminium and other byproducts from the burning of coal. Whatever its effects on the trees, this dust was never part of the natural scenery.


Japan Times, No clearing the air over neighbour’s pollution, March 10, 2013

Yoshika Yamamoto, Recent moves to address the KOSA (yellow sand) phenomenon, Science and Technology Trends - Quarterly Review, Japan National Institute of Science and Technology Policy (NISTEP), January 2007

New York Times, Scientist says pollution from China is killing a Japanese island’s trees, April 24, 2013


Iainhw said...

If this pollution is so damaging in Japan after it has travelled x hundred miles, I dread to think what it's like in china.
The jma also publish status and forecasts in the yellow dust:

Peter Skov said...

The footage on the news from China after their New Year's celebrations looked like a city the morning after a massive conflagration: brown smoke covering the buildings like a shroud. Warning bells went off in Japan as Asian winds would carry all that smoke over to the archipelago in the days that followed.

As for the loess from the deserts, I am reminded of something I read a couple of years back concerning dust, loess, and volcanic ash. There is a region of the Pacific Ocean where this particulate matter falls and provides fresh nutrients to the soils of the remote islands. However, islands too far east fall outside of this zone and support plant life on stale soil. Basically, all the nutrients available are inside the living matter of those islands. Thus, once the native vegetation is stripped and burned, there is only but poor soil left for cultivation. Easter Island was the prime example.

While Japan is by far starved for nutritional deposition from desert dust minerals, that dust does provide benefit elsewhere. Yet Japan does suffer in the spring from loess, pollution and pollen, only two parts of which are natural.

Project Hyakumeizan said...

Peter: you make some interesting points. So the "kosa" does have its uses, when it doesn't come mixed with industrial pollution, that is ...