The old chestnut about the Great Wall of China being visible from space is just a legend, but something man-made is visible to orbiting satellites: Chinese smog.
NASA’s Terra satellite recently captured an image of the eastern coast of China swathed in a mixture of natural fog and unnatural smog, with the pollution clearly discernible as streaks of white and gray. On the day the image was captured, Dec. 7, pollution monitors operated by the U.S. embassy in Beijing and the U.S. consulate in Shanghai respectively recorded PM 2.5 readings of 480 and355 micrograms per cubic meter of air in the two cities. According to the World Health Organization, PM 2.5 levels below 25 are regarded as safe.
Courtesy Jeff Schmaltz/Lance Modis Rapid Response/NASANASA Earth Observatory posted the satellite image with explanatory text on its website yesterday. Rudolf Husar, director of the Center for Air Pollution Impact and Trend Analysis at Washington University, explains why satellites can visually differentiate among fog, smog, and ordinary cloud cover: “The fog has a smooth surface on the top, which distinguishes it from mid- and high-level clouds that are more textured and have distinct shadows on their edge. If there is a significant haze layer on top of the fog, it appears brownish,” he said. “In this case, most of the fog over eastern China is free of elevated haze, and most of the pollution is trapped in the shallow winter boundary layer of a few hundred meters.”
Shanghai experienced one of its worst bouts of air pollution in recent memory earlier this month, leading to road and school closures as well as canceled and delayed flights. “This is a shock,” Robert Theleen, chairman of the American Chamber of Commerce in Shanghai, told Bloomberg News. “There was a perception that Shanghai was doing a better job in controlling pollution than Beijing.” That’s no longer the view from low-earth orbit, it seems.