OZONE LAYER DEPLETION: OZONE LAYER DEPLETION Why the hole in the atmospheric ozone layer above us? What has been done about this? Why should I worry ourselves about the Ozone Layer Depletion? What is Ozone? Ozone Layer?: What is Ozone? Ozone Layer? Ozone (O3) is a highly-reactive from of oxygen. Unlike oxygen (O2), ozone has a strong scent and is blue in color. Ozone exists within both the tropospheric and stratospheric zones of the Earth’s atmosphere In the troposphere , ground level ozone is a major air pollutant and primary constituent of photochemical smog In the stratosphere, the ozone layer is an essential protector of life on earth as it absorbs harmful UV radiation before it reaches the earth. CFC’s and ozone depletion: CFC’s and ozone depletion Chlorofluorocarbons are created and used in refrigerators and air conditioners. These chlorofluorocarbons are not harmful to humans and have been a benefit to us. Once released into the atmosphere, chlorofluorocarbons are bombarded and destroyed by ultraviolet rays. In the process chlorine is released to destroy the ozone molecules Destruction of ozone by chlorine: Destruction of ozone by chlorine Molecular oxygen is broken down in the stratosphere by solar radiation to yield atomic oxygen, which then combines with molecular oxygen to produce ozone. The ozone is then destroyed by chlorine atoms. Ozone destruction by UV rays: Ozone destruction by UV rays UV radiation from the sun releases the radicals Cl and ClO. Ozone is a highly unstable molecule so it readily donates its extra oxygen molecule to free radical species such as hydrogen, bromine, and chlorine. These compound species act as catalysts in the breakdown of ozone molecules. The ozone depletion process: The ozone depletion process Responsibility for ozone damage each year: Responsibility for ozone damage each year Global CFC production: Global CFC production Ozone hole in Southern hemisphere October 1979 & 1998: Ozone hole in Southern hemisphere October 1979 & 1998 Monthly means of total ozone in the Southern Hemisphere observed with TOMS Images for October of 1979 (left) and 1998 (right). Ozone hole: size by month: Ozone hole: size by month Ozone hole measurements over the Antarctic region 1980-98: Ozone hole measurements over the Antarctic region 1980-98 Ozone concentration at the center of ozone hole: Ozone concentration at the center of ozone hole Ozone hole over continents: comparison 1996: Ozone hole over continents: comparison 1996 Image of the ozone hole over the South pole: July 10 2003: Image of the ozone hole over the South pole: July 10 2003 PowerPoint Presentation: Image of the ozone hole over the North pole: July 10 2003 Ozone status: full day global image, July 9th 2003: Ozone status: full day global image, July 9 th 2003 Effects of UV rays on Aquatic Ecosystems: Effects of UV rays on Aquatic Ecosystems Ozone depletion causes increases in UV rays’s effects on aquatic ecosystems by: 1. decreasing the abundance of phytoplankton – affects the food stock for fishes and the absorption of CO2 2. decreasing the diversity of aquatic organisms – reduces food stock and also destroys several fish and amphibians. Effects of UV rays on Terrestrial Ecosystems: Effects of UV rays on Terrestrial Ecosystems Damage to plant cell DNA molecules - makes plants more susceptible to pathogens and pests Reductions in photosynthetic capacity in the plant - results in slower growth and smaller leaves Causes mutations in mammalian cells and destroys membranes Harmful effects of UV rays on people: Harmful effects of UV rays on people Skin cancer Premature aging (photoaging) of the skin (different from normal chronological aging) Cataracts and eye disorders (corneal sunburn and blindness) Immune system damage Correlation between Ozone depletion and skin diseases: Correlation between Ozone depletion and skin diseases The Ultraviolet Exposure Index: The Ultraviolet Exposure Index INDEX VALUES EXPOSURE 0 – 2 = Minimal 3 - 4 = Low 5 - 6 = Moderate 7 - 9 = High 10 + = Very High Factors affecting UV exposure : Factors affecting UV exposure Clouds cover - partly cloudy days do little to reduce UV exposure but rainy or substantially overcast days reduce UV exposures The time of day – peak exposure time is 12:00 noon - 1:00 p.m. UV intensity is reduced by about half at three hours before and three hours after the peak exposure time. Factors affecting UV exposure..2 : Factors affecting UV exposure..2 The time of year - more UV is received in the late spring and early summer and much less is received in the late fall and early winter. Life style – determines a person’s risk to UV exposure. Skiing, sunbathing, or swimming can lead to extremely high exposures. Use of tanning parlors also increase risk. Policy responses to Ozone depletion: Policy responses to Ozone depletion Mario Molina and Sherwood Rowland showed in 1974 that CFC gases destroy ozone Coordinating committee on Ozone Layer (CCOL) established by UNEP in the 1970’s Vienna Convention for the protection of the ozone layer held in 1985 Montreal Protocol to ban substances that deplete the ozone layer held in 1987 Amendments to the Montreal Protocol : London - 1990, Copenhagen - 1992 and Montreal - 1997.