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Ozone levels in many U.S. national parks are similar to those in large cities

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Even in the awe-inspiring canyons of Yellowstone and mountains of Yosemite, the fresh air may not be so fresh: Concentrations of ozone in many U.S. national parks are similar to levels in America’s largest metropolitan areas, according to a new study in Science Advances by researchers at Iowa State University and Cornell University. Learn More...