The Global Sweep of Pollution: Satellite Snapshots Capture Long-Distance Movement

Towering smokestacks were a popular mid-twentieth-century “remedy” for industrial emissions. Pump the stuff high enough into the air, went the thinking, and the problem would go away. But evidence collected since then has strongly suggested that tall smokestacks are not sufficient to mitigate the effects of pollution—those pollutants eventually came down somewhere, dozens or thousands of miles away. In the November 2006 issue of EHP, for example, Morton Lippmann of the New York University School of Medicine and colleagues reported a strong link between nickel emitted from a very tall smokestack at a smelter in Sudbury, Canada, and acute heart rate changes in mice some 500 miles away. At the same time, we also now know that tall stacks are not necessary for pollutant emissions to waft great distances, as verified by scores of individual studies showing that one pollutant or another—such as ozone, particulate matter (PM), and sulfur dioxide (SO2)—can blow from country to country, and continent to continent. Beginning in the 1980s and accelerating since about 2000, satellite surveillance with increasingly sophisticated instruments has enabled us to better visualize the complex fluctuations of several important pollutants as they ebb and flow around the planet. This new capability is partly serendipitous. “Most of these satellites weren’t designed to have an air quality focus,” says Terry Keating, an environmental scientist with the U.S. Environmental Protection Agency (EPA) and co-chair of the Task Force on Hemispheric Transport of Air Pollution, which was created in 2004 by the United Nations Economic Commission for Europe’s Convention on Long-Range Transboundary Air Pollution. “But we find ourselves with this stream of data, and we are figuring out how to use it,” he says. One use has been a handful of pilot projects directly linking satellite-observed column-wise concentrations of atmospheric pollutants—that is, the concentration from the Earth’s surface to the top of the atmosphere—with concentrations at the ground level. “Only in the past ten years have we been able to advance epidemiological science with satellites,” says John Haynes, program manager for public health and aviation applications at the National Aeronautics and Space Administration (NASA). “This is truly a leap forward into the twenty-first-century science of epidemiology.”