While atmospheric pollution over rapidly developing China, including Beijing, has captured scientific and media attention because of the 2008 Summer Olympics, metropolitan areas in all countries are producers of atmospheric haze. Images of haze over the northeastern United States are shown for November 2006 (upper image) and April 1990 (lower image). The upper image is a southeast-looking view of the Long Island Sound and New Jersey coast, with the lower Hudson River and New York Bay in the area of brightest sunglint. On the far right, gray haze streams out to sea offshore of New Jersey, where it becomes harder to see. In fact, haze covers most of the visible area offshore, partly obscuring the sea surface.
By contrast, clouds look quite different from haze in these astronaut images. Clouds usually have sharp margins and are pure white, as clouds at the bottom of both images show. Industrial haze is grayer and more diffuse, and is typical of the air over the Northeast. Flow lines in the upper image show that winds are transporting the haze in a clockwise fashion—bending south. This motion indicates that a high-pressure system was operating on that day, centered roughly over the coast. High-pressure weather systems are notorious for promoting smog events because they bring clear skies, and sunlight promotes smog formation. High pressure also concentrates polluted air near the ground.
Confidence that the haze is indeed human-made stems from prior research, conducted under similar weather conditions, based on a Space Shuttle photograph taken in April 1990 (lower image). This 1990 view looks northwards up the East Coast, with the Florida Peninsula in the foreground. A mass of haze stretches across the top of the entire view. Weather, visibility, and sulfate-content data showed that the haze was indeed industrial smog haze, rather than cloud. The air mass was transported west to east (left to right in this view) around the north edge of a high-pressure system (indicated by an “H”). It moved offshore for at least 1,500 kilometers (932 miles), reaching the Atlantic islands of Bermuda. The leading edge of the haze is visible far to the south, near the Bahamas—indicating that aerosols from the industrial Northeast flowed clockwise around the high and headed directly back toward the large population centers of Florida. (This image has been enhanced to accentuate the haze slightly.)
The upper astronaut photograph was acquired November 10, 2006, with a Kodak 760C digital camera using an 80 mm lens. The lower image was acquired April 26, 1990, with a Linhof camera using a 90 mm lens. The images are provided by the ISS Crew Earth Observations experiment and the Image Science & Analysis Laboratory, Johnson Space Center. The images in this article have been cropped and enhanced to improve contrast. The International Space Station Program supports the laboratory to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth.