Since the implementation of the Montreal protocol, developed countries have decreased the amount of ozone destroying substances they used tremendously. Alink to the Montreal protocol can be found on the course Webliography. Reduction by the United States has been 97%. View the following two animations. The first shows the ozone concentrations as they varied fro July to December 2008; the second animation shows average concentrations of ozone over Antarctica during October during the Southern Hemisphere spring when the ozone hole typically is at its maximum extent. The areas of least ozone are shown by blue and purple.