The Jet Stream & Pollutants

It has long been known that the bands of strong winds that encircle the globe at the troposphere-stratosphere boundary, collectively known as the jet stream, significantly affect aviation and the weather. Perhaps it is less well known that the jet stream is also a high-speed pathway for moving pollutants, man-made as well as nature-made, across and between continents. Thanks to the jet stream, Europe exports its pollution to Asia, China to the United States, and South Africa to Australia and so on.

The Jet Stream

• The air currents of the jet stream move at up to 275 miles per hour from west to east at about 10 miles above ground level at latitudes of about 30 degrees (the subtropical jet) and 50 to 60 degrees (the polar jet). The jet stream rises and dips in altitude as well latitude, it thickens and thins, and it splits, disappears and reappears. The juxtaposition of warm and cold air masses and the Earth’s rotation provide the energy that drives the jet stream.

From the Smokestack to the Jet Stream

• Local weather systems, called warm conveyor belts by meteorologists, push pollutants released near ground level to the altitude of the jet stream. When the movement of lighter warm air is blocked by a mass of dense cold air, it tends to climb over the cold-air barrier and thus gain altitude. Also, air gains height when heated by any means such as the sun hitting the ground or human activities. This process is known as convective heating and transport.

From Asia to the United States

• The jet stream carries pollution from China to North America.

  Extensive use of coal and lax environmental standards in heavily industrialized eastern China, make it a prime source of pollutants, carried to the U.S. Pacific Northwest by the jet stream. Research models have shown that ozone and carbon monoxide in North America is mostly imported from China. Pollutants from India and Indonesia also reach the jet stream at the western Pacific Rim, from which point they hitch a ride to North America. The transit time of pollutants from China to the U.S. can be as low as three days under the right weather conditions.

From Europe to the Arctic

• Partly because of colder temperatures, warm conveyor belts are not as prominent in Europe as in eastern Asia. Consequently, the jet stream is not the only means of pollutant transport out of Europe. Much of Europe’s industrial pollution drifts north of the Arctic Circle, where it forms what is known as the Arctic haze. However, central Asia does receive some European pollution via the jet stream.

Nature-Made Pollutants

• The jet stream moves volcanic dust between continents.

  The jet stream carries volcanic ash, desert dust and forest-fire ash between continents.

  In the spring of 2010 the jet stream transported ash from an Icelandic volcano into the airspace over Western Europe’s major airports. Dust from Africa’s Sahara

  Desert has been detected in northern South America and the Caribbean, and China’s Gobi desert has exported dust to Korea. In 1998, forest fires in Canada’s boreal forest caused a dense haze over Germany.