This animation created from data from the Microwave Limb Sounder instrument on NASA's Aura spacecraft depicts the complex interaction of chemicals involved in the destruction of ozone during the 2005 Arctic winter. Red is high, blue/purple is low for all chemicals, and data are taken at an altitude of about 19 kilometers (12 miles). As temperatures dip, nitric acid levels drop, indicating the presence of polar stratospheric clouds, which destroy ozone. Levels of hydrogen chloride (the primary "safe" form of chlorine) are shown dropping, while levels of chlorine monoxide (the primary "dangerous" form of chlorine that destroys ozone) rise, and ozone is destroyed (ozone levels generally go down after about January 20).
The animation also illustrates how air motions change ozone levels. Prior to about January 20, ozone levels increase as ozone is transported down from higher altitudes. After that, ozone decreases gradually, and appears to move around on the surface as horizontal air motions change the shape of the polar vortex and move air into and out of it. Since the highest ozone is mostly around the edge of the vortex, this can increase the ozone inside it.