Ozone descends to Earth’s surface with consequences for air quality.
At high altitudes, ozone—a chemical made up of three oxygen atoms—naturally forms a protective layer around the planet that helps shield Earth from the sun’s harmful ultraviolet rays. But near the surface, the same chemical is a man-made pollutant that can cause respiratory distress. Sometimes air from the upper atmosphere descends to lower altitudes, transporting ozone with it. Such events, known as stratospheric ozone intrusions, may lead to unexpected spikes in ozone levels within populated areas. The mysterious events often take place over elevated terrain in mountainous states like Colorado, Nevada and California. In April 2012, curtains of ozone plunged from the upper atmosphere and covered parts of the western United States. Using a high-resolution model, NASA scientists simulated the event, showing where high concentrations of ozone made contact with the ground. Watch the video to see the event unfold.