Published on July 24, 2014
Ozone Layer in Atmosphere: Ozone Layer in Atmosphere Ozone-oxygen cycle in the ozone layer [2010-01-27 20:56 ] PowerPoint Presentation: The photochemical mechanisms that give rise to the ozone layer were discovered by the British physicist Sidney Chapman in 1930. Ozone in the Earth's stratosphere is created by ultraviolet light striking oxygen molecules containing two oxygen atoms (O 2 ), splitting them into individual oxygen atoms (atomic oxygen). The atomic oxygen then combines with unbroken O 2 to create ozone, O 3 . The ground state oxygen atoms O(2 3 P) combine with oxygen molecules O 2 (X 3 g - ) to yield ozone in a vibrationally excited state which must get stabilized by a third body M in a number of steps: Formation of ozone: -: Formation of ozone: - Formation and dissociation of ozone has been one of the important mechanisms. Although the steady state concentration of ozone in the upper atmosphere is very small, it absorbs so strongly in the near ultraviolet region. In these way it screens the earth’s surface from the light of wavelength 290 nm which is dangerous to life. Without this shield, the life would not have been possible on earth. PowerPoint Presentation: Thus, origin of life is thought to have originated under water. Ozone is having weak and diffuse absorption throughout the visible region and even in the near infrared region. Absorption in the visible region decomposes ozone into oxygen atoms and molecules in the ground state. But at = 264 nm, excited O-atoms are produced. Mechanism of decomposition: - PowerPoint Presentation: The maximum quantum yield for decomposition of ozone at low pressures has been 4. Though most of the oxygen in the atmosphere gets formed by photosynthesis in plants, some gets produced by photolysis of water vapour in the vacuum uv -region = 200 nm. How halogen radicals destroy ozone? Chlorine ozone reaction. Dots indicate, that the reaction partners are radicals. Full size: 35 K The development of the ozone hole 2001. : The development of the ozone hole 2001. PowerPoint Presentation: The ozone molecule is also unstable (although, in the stratosphere, long-lived) and when ultraviolet light hits ozone it splits into a molecule of O 2 and an atom of atomic oxygen, a continuing process called the ozone-oxygen cycle , thus creating an ozone layer in the stratosphere , the region from about 10 to 50 km (32,000 to 164,000 feet) above Earth's surface. About 90% of the ozone in our atmosphere is contained in the stratosphere. Ozone concentrations are greatest between about 20 and 40 km, where they range from about 2 to 8 parts per million. If all of the ozone were compressed to the pressure of the air at sea level, it would be only a few millimeters thick. PowerPoint Presentation: Ultraviolet light and ozone Level of ozone at various altitudes and blocking of ultraviolet radiation .[ 15:38, 4 May 2006 . PowerPoint Presentation: Although the concentration of the ozone in the ozone layer is very small, it is vitally important to life because it absorbs biologically harmful ultraviolet (UV) radiation coming from the Sun. UV radiation is divided into three categories, based on its wavelength; these are referred to as UV-A (400–315 nm), UV-B (315–280 nm), and UV-C (280–100 nm). UV-C, which would be very harmful to all living things, is entirely screened out by ozone at around 35 km altitude. PowerPoint Presentation: UV-B radiation can be harmful to the skin and is the main cause of sunburn ; excessive exposure can also cause genetic damage, resulting in problems such as skin cancer . The ozone layer is very effective at screening out UV-B; for radiation with a wavelength of 290 nm, the intensity at the top of the atmosphere is 350 million times stronger than at the Earth's surface. Nevertheless, some UV-B reaches the surface. Most UV-A reaches the surface; this radiation is significantly less harmful, although it can potentially cause genetic damage PowerPoint Presentation: During winter, the ozone layer actually increases in depth. This puzzle is explained by the prevailing stratospheric wind patterns, known as the Brewer-Dobson circulation . While most of the ozone is indeed created over the tropics, the stratospheric circulation then transports it pole ward and down ward to the lower stratosphere of the high latitudes. However, in the southern hemisphere, owing to the ozone hole phenomenon, the lowest amounts of column ozone found anywhere in the world are over the Antarctic in the southern spring period of September and October. PowerPoint Presentation: Brewer-Dobson circulation in the ozone layer [ 08:52, 24 May 2007 ]. PowerPoint Presentation: NASA projections of stratospheric ozone concentrations if chlorofluorocarbons had not been banned (2009-05-21) .