These data maps from Aura's Microwave Limb Sounder depict levels of hydrogen chloride (top), chlorine monoxide (centre), and ozone (bottom) at an altitude of approximately 19 kilometres (490,000 feet) on selected days during the 2004-05 Arctic winter. White contours demark the boundary of the winter polar vortex. The maps from December 23, 2004, illustrate vortex conditions shortly before significant chemical ozone destruction began. Photo via Newscom