During summertime ozone near the Earths surface forms in most major U.S. cities when sunlight and heat mix with car exhaust and other pollution, causing health officials to issue "ozone alerts." But in other parts of the world, such as the tropical Atlantic, this low level ozone appears to originate naturally in ways that have left scientists puzzled. Now, NASA-funded scientists using four satellites can tell where low level ozone pollution comes from and whether it was manmade or natural.
This image shows the vertical column of carbon monoxide (CO) for January, 2001, measured by NASA’s Terra satellite. The reds are the highest levels and blues show the lowest levels. The white areas have no data due to clouds. Pollution plumes from agricultural fires over northwestern Africa extend westward over the Atlantic Ocean. High pollution levels are seen in the green area from Asia out over the Pacific Ocean. Pollution over China is mostly from industrial emissions, and this plume sometimes reaches the U.S. west coast. Image and Caption Credit: David Edwards
Ozone is a gas that forms in the atmosphere when 3 atoms of oxygen combine. At ground level ozone is created by a chemical reaction between sunlight, oxides of nitrogen, and volatile organic compounds. Ozone has the same chemical structure whether "good" or "bad," depending on its location in the atmosphere. Image and Caption Credit: U.S. EPA
Atmospheric scientist David Edwards and his colleagues from the National Center for Atmospheric Research (NCAR) and collaborators in Canada and Europe have studied this problem using satellite data from three NASA spacecraft, one from the European Space Agency (ESA), and a computer model from NCAR. They were surprised to find that a greater amount of near-surface ozone over the tropical Atlantic develops as a result of lightning instead of agricultural and fossil fuel burning.
Their findings appeared in a recent issue of the American Geophysical Unions Journal of Geophysical Research Atmospheres. The formation of ozone involves several factors, such as lightning and pollution from agricultural and fossil fuel burning, which is why it was helpful to use NASAs multiple satellites to look at each in turn.
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