Ozone layer depletion ppt


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Ozone layer depletion ppt

  1. 1.  The ozone layer refers to a region of Earth's stratosphere that absorbs most of the Sun's UV radiation.  It contains high concentrations of ozone (O3) relative to other parts of the atmosphere.  The ozone layer is mainly found in the lower portion of the stratosphere.  The ozone layer was discovered in 1913 by the French physicists Charles Fabry and Henri Buisson.
  2. 2.  Ozone depletion describes two phenomena : a steady decline of about 4% per decade in the total volume of ozone in Earth's stratosphere,the ozone hole.  catalytic destruction of ozone is by atomic halogens. The main source of these halogen atoms is halocarbon refrigerants, solvents, propellants, and foam-blowing agents (HCFCs, freons, halons).  CFCs and other contributory substances are referred to as ozone- depleting substances (ODS).
  3. 3.  Three forms of oxygen are involved in the ozone-oxygen cycle: oxygen atoms, oxygen gas, and ozone gas.  chlorine ion (Cl·) and atomic bromine ion (Br·) are the ions which are most harmful for the ozone layer. These elements are found in certain stable organic compounds, especially chlorofluorocarbons, which may find their way to the stratosphere without being destroyed in the troposphere due to their low reactivity.
  4. 4.  The most pronounced decrease in ozone has been in the lower stratosphere.  Marked decreases in column ozone have been observed using instruments such as the Total Ozone Mapping Spectrometer (TOMS)  polar stratospheric clouds (PSCs) form more readily in the extreme cold of the Arctic and Antarctic stratosphere. So , ozone holes first formed, and are deeper, over Antarctica.
  5. 5. Chlorofluorocarbons (CFCs) and other halogenated ozone depleting substances (ODS) are mainly responsible for man-made chemical ozone depletion. The total amount of effective halogens (chlorine and bromine) in the stratosphere can be calculated and are known as the equivalent effective stratospheric chlorine (EESC)
  6. 6. Scientists have been increasingly able to attribute the observed ozone depletion to the increase of man-made halogen compounds from CFCs by the use of complex chemistry transport models and their validation against observational data
  7. 7.  The primary cause of ozone depletion is the presence of chlorine-containing source gases (primarily CFCs and related halocarbons).  Most of the ozone that is destroyed is in the lower stratosphere, in contrast to the much smaller ozone depletion through homogeneous gas phase reactions, which occurs primarily in the upper stratosphere.
  8. 8. The decrease in the ozone layer was predicted in the early 1980s to be roughly 7% over a 60-year period. The sudden recognition in 1985 that there was a substantial "hole" was widely reported in the press. Many of those unsure about what the ozone hole was and what caused it were worried that ozone holes might start appearing over other areas of the globe.
  9. 9. If the conditions become more severe global ozone may decrease at a much greater pace When the Antarctic ozone hole breaks up, the ozone depleted air drifts out into nearby areas.
  10. 10. Increased UV Effect on human health Effects on non human animals Crop production is affected
  11. 11.  Five areas of linkage between ozone layer and global warming The same CO2 radiative forcing that produces global warming is expected to cool the stratosphere. This cooling, in turn, is expected to produce a relative increase in ozone (O3) depletion in polar area and the frequency of ozone holes. Conversely, There are two opposing effects: Reduced ozone causes the stratosphere to absorb less solar radiation, the resulting colder stratosphere emits less long-wave radiation downward, thus cooling the troposphere. Overall, the cooling dominates
  12. 12. One of the strongest predictions of the greenhouse effect is that the stratosphere will cool. Although this cooling has been observed, it is not trivial to separate the effects of changes in the concentration of greenhouse gases and ozone depletion since both lead to cooling. ozone depleting chemicals are also often greenhouse gases. The increases in these chemicals have produced 14% of the total radiative forcing from increases in the concentrations of well-mixed greenhouse gases. The long term modeling of the process, its measurement, study, design of theories and testing take decades to document, gain wide acceptance, and ultimately become the dominant paradigm.
  13. 13.  In 1994, the United Nations General Assembly voted to designate September 16 as "World Ozone Day", to commemorate the signing of the Montreal Protocol on that date in 1987.