An unwelcome Chinese import: transcontinental air pollution

  Photo courtesty of Flickr.

China seems like such a long way away, doesn’t it? It’s halfway around the globe from the United States.

Yet on some days, up to one third of the air over San Francisco and Los Angeles can be directly traced back to Asia. And that one third of air is responsible for three quarters of the black carbon particulate pollution that reaches the West Coast, according to today’s Wall Street Journal.

Asia is the world’s largest source of aerosols, man-made and natural. Every spring and summer, storms whip up silt from the Gobi desert of Mongolia and the hardpan of the Taklamakan desert of western China, where, for centuries, dust has shaped a way of life. From the dunes of Dunhuang, where vendors hawk gauze face masks alongside braided leather camel whips, to the oasis of Kashgar at the feet of the Tian Shan Mountains 1,500 miles to the west, there is no escaping it.

The Taklamakan is a natural engine of evaporation and erosion. Rare among the world’s continental basins, no river that enters the Taklamakan ever reaches the sea. Fed by melting highland glaciers and gorged with silt, these freshwater torrents all vanish in the arid desert heat, like so many Silk Road caravans.

Only the dust escapes.

In an instant, billows of grit can envelope the landscape in a mist so fine that it never completely settles. Moving east, the dust sweeps up pollutants from heavily industrialized regions that turn the yellow plumes a bruised brown. In Beijing, where authorities estimate a million tons of this dust settles every year, the level of microscopic aerosols is seven times the public-health standard set by the World Health Organization.

Once aloft, the plumes can circle the world in three weeks. “In a very real and immediate sense, you can look at a dust event you are breathing in China and look at this same dust as it tracks across the Pacific and reaches the United States,” said climate analyst Jeff Stith at the National Center for Atmospheric Research in Colorado. “It is a remarkable mix of natural and man-made particles.”

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