The Facts

• 90% of ozone in the atmosphere is in the ozone layer, between 6-10 and 31 miles from Earth’s surface. The remaining 10% is in the troposphere, which is from ground level to 6-10 miles above the surface. (Q1)*
• Ozone absorbs ultraviolet radiation from the sun. Without the ozone layer, there would be widespread problems with skin cancer and eye cataracts, as well as plant and animal damage in ecosystems. (Q3)*
• Ozone is a very sparse gas in the atmosphere, even at normal levels. The amount of ozone in the atmosphere, if it were concentrated at Earth’s surface, would make a layer of pure gas just 2-5 millimeters deep. This emphasizes the fragility of the ozone layer. (Q4)*
• A “hole” has formed in the ozone layer above Antarctica, which is at its most extreme in October. (During the rest of the year it is filled in.) This is due to special chemical reactions resulting from the extreme cold. (Q10)*
•  Ozone content in the atmosphere is often expressed in Dobson units (DU), which typically range from 200-500. The measurement takes into account the ozone in all layers of the atmosphere (including the troposphere and the stratosphere), so it does increase marginally in urban areas where there is smog. In an area of 500 DU, the total ozone over that area could be concentrated to a depth of just 5 millimeters on Earth's surface. (Q4)*

*Source: http://ozone.unep.org/Assessment_Panels/SAP/Scientific_Assessment_2010/SAP-2010-FAQs-update.pdf

20 Questions and Answers about the Ozone Layer: 2010 Update