Stratospheric Ozone Depletion Research

Stratospheric Ozone Depletion Research A) Effects of Ozone on the Lower Atmosphere The lower atmosphere (Troposphere) includes 75% by mass of the atmosphere (concentrated). Natural sources of Ozone in the troposphere includes lightning. Approximately 10% of all atmospheric ozone is present in the troposphere. If ozone levels reach 20ppm, they are very poisonous to humans, animals and plants. It oxidises organic tissue which disrupts the normal biochemical reactions in the body, irritates the eyes and causes breathing difficulties. It can be detrimental to plants and agriculture, as it oxidises much more readily then oxygen, killing/spoiling the agriculture and destroying it. Sources of ozone in the troposphere include diffusion from the stratosphere, internal combustion engines, petrochemical smog, naturally from lightning and photochemically when nitrogen dioxide in polluted air is decomposed by sunlight. NO2(g) NO(g) + O(g) O2(g) + O(g) O3(g) Positive effects of ozone include that it can kill bacteria and viruses in water and thus is useful in purifying water supplies. B) Effects of Ozone in the Stratosphere Contrastingly to ozone in the troposphere, Ozone in the stratosphere is essential to life on earth, as it absorbs ultraviolet (UV) radiation which can be harmful to living cells on earth as they can damage living tissues and cause skin cancers. Ozone in the stratosphere is commonly referenced to as â€Å"the ozone shield† as it protects living organisms on earth from UV rays. Ozone Reactions in the Stratosphere and their Beneficial Effects on Living Organisms Formation of Ozone in the Stratosphere O2(g) O(g) + O(g) O(g) + O2(g) → O3(g) Stratospheric oxygen absorbs UV light to form free oxygen radicals The oxygen radicals are highly reactive and combine with oxygen molecules to form an energized ozone molecule. Decomposition of Ozone in the Stratosphere O3(g) O2(g) + O(g) Due to the absorption of UV radiation, the Ozone layer acts as a radiation shield by absorbing medium and high energy UV rays. This protects living organisms as UV radiation can have very harmful effects on them including: Can cause sunburn on skin which can lead to skin cancer caused by a mutation in DNA Can form cataracts on eyes It can kill cells due to DNA readily reacting with UV rays It can impair photosynthesis in plants Many more†¦ Thus without the ozone shield in the stratosphere, life in the biosphere would be dramatically impaired and destroyed by harmful UV rays. A) Functional Groups and General Structure of Compounds Classified as CFC’s CFC’s – Chlorofluorocarbons are haloalkanes in which the hydrogen atoms have been replaced by fluorine or chlorine atoms. Haloalkanes are the products when alkanes react with halogens (members of group 7 of the periodic table). CFC’s generally contain â€Å"chloro† and â€Å"flouro† functional groups and no hydrogen atoms. The general structure of compounds classified as CFCs are haloalkanes whose hydrogens have been replaced by chlorine or fluorine atoms. E.g. B) Main Uses of CFC’s CFC’s were used as refrigerants and as propellants in aerosol spray cans. They have a variety of uses as demonstrated below. However due to the harmful effects of CFC to the environment and the ozone shield, CFCs are not used for these uses anymore. C) Reactions between CFC’s and Ozone that Result in the Destruction of Ozone in the Stratosphere. Effects of Small Concentrations of CFC’s that can Damage Large amounts of Ozone Reactions between CFCs and Ozone Synthetic CFCs are responsible for the destruction of the ozone shield, natural CFCs such as CH3Cl and HCl rarely reach the stratosphere as they readily oxidise in the troposphere. However, synthetic CFCs slowly diffuse from the troposphere into the stratosphere, where they undergo photodissociation (due to UV rays) to produce chlorine and bromine radicals that attack and destroy ozone molecules. e.g. CFC-11 Trichloroflouromethane (CFCl3) (Lifetime of 70 years) 1. In the stratosphere, the CFC comes into contact with short wavelength UV CFCl3(g) + UV → CFCl2 ·(g) + Cl ·(g) 2. The chlorine free radical then reacts with the ozone molecule Cl + O3 → ClO + O2 3. The ClO molecule reacts with free oxygen atoms which exist naturally from UV breakdown of O2 ClO + O → O2 + Cl This Cl Is then regenerated and able to attack more Ozone (Step 2) thus further demonstrating the harmful effects of even one CFC This reaction causes destruction of ozone in the stratosphere, due to the (previously used) synthetic CFCs for refrigeration, dry cleaning etc. Small Amounts of CFCs can still do harm: Evidence has shown that even small amounts of CFCs can damage large amounts of ozone. Firstly, CFCs generally have a long lifespan, ranging from approximately 57 (CFC-11) years to 333 years (CFC-12), and due to the fact that each Chlorine radical can be responsible for the breakdown of tens of thousands of ozone molecules, and due to their lifespan once released, even a small amount, will be around for many decades to come. In addition, most CFCs will almost definitely make their way up to the stratosphere as they cannot be destroyed at low altitudes as they are unreactive and they are insoluble in water and therefore cannot be washed out of the atmosphere by rain. Alternative Compounds for CFCs. A) Ozone Monitoring Instruments Ozone Concentrations in the Stratosphere Source: Earth System Research Laboratory, 2012, Viewed 07.06.14, http://www.esrl.noaa.gov/gmd/dv/spo_oz/spototal.html A) Analysis of Trends There are a variety of trends that can be interpreted from the above diagram. Based on the data above, before the 1980’s, the total ozone concentration was VERY high, at approximately 194 DU (Dobson Units), however there was a very rapid decrease in this concentration from 1980 – 1999, whereby in this 19 year period sees a 56% decrease in the amount of total ozone, a remarkably concerning figure. On a year round basis globally, total ozone concentration have caused a 3-8% decrease in the amount of ozone, this increased in the years between 1995-200, where there was a low of total ozone concentration. However, in more recent years, 2010 to 2014 there has been a general increase in total ozone concentration, which can be inferred from the replacement of CFCs finally starting to impact (slightly) on the total concentration of ozone, this increase based on the data is 31%. The general pattern is that the total column ozone decreases during spring time, it can be inferred that the overall concentration of ozone decreases during this time of the year. This is because in an Antarctic winter, there is no U.V light to convert the chlorine molecule Cl2 into a Cl radical, which then destroy ozone molecules, and thus the concentration of ozone is higher in winter. In spring, the U.V light converts the Cl2 into Cl which then destroys ozone in a chain reaction, thus decreasing the total ozone concentration There are various peaks in the graph, in the years of 1988, 2003, 2011 and 2013, which may be due to limitation so of the instruments used. B) Montreal Protocol Effectiveness The Montreal protocol occurred in 1987, which the main aim was to control the production of ozone depleting substances (CFCs) worldwide. A number of amendments have been adopted to further ride ozone depleting substances. The protocol is applied in 193 countries. The main aims of the original agreement is as follow: Halt the use of Halons by late 1994 By the early 21st century, phase out the use of HCFCs Stop manufacture of CFCs by 1996 Allow for leeway with less developed countries but still get them to rid the use of these substances The Montreal Protocol (and amendments) has been effective as by 2006, the consumption of ozone depleting substances has been reduced globally by 96%. However, due to the long lives of the previously used ozone depleting substances, the total concentration will take hundreds of years to be completely down. However, the total concentration in the troposphere has generally been declining since the mid-1990s. Bibliography Thickett, G 2006, Chemistry 2 HSC course, John Wiley and Sons, Queensland, Australia. Role of Ozone, 2013, viewed 05.06.14, http://www.easychem.com.au/monitoring-and-management/the-atmosphere/roles-of-ozone Allen, J, 2001, Ultraviolet Radiation – How it Affects life on Earth, viewed 05.06.14, http://earthobservatory.nasa.gov/Features/UVB/ Environmental Protection Agency, 2010, The Process of Ozone Depletion, Viewed 07.06.14, http://www.epa.gov/ozone/science/process.html Clean Air Strategic Alliance, 2013, Chlorofluorocarbons (CFCs) and Halons, Viewed 07.06.13, http://dwb.unl.edu/teacher/nsf/c09/c09links/www.casahome.org/chlorofl.htm Welch, C 2014, The Ozone Hole, Viewed 07.06.14, http://www.theozonehole.com/cfc.htm Cracknell, A 2012, Remote Sensing and Atmospheric Ozone, Viewed 07.06.14, http://books.google.com.au/books?id=YZzGFPnaEv0Cpg=PA94lpg=PA94dq=nimbus+4+satellite+ozonesource=blots=k3Ixvnqeupsig=Z_jW0D4jdcvG8hpjbb7d4QeUzBMhl=ensa=Xei=DpCSU-qHMsLtkQWJsIHQDQved=0CF8Q6AEwCg#v=onepageq=nimbus%204%20satellite%20ozonef=false ESA, 2013, Eathnet Online, Viewed 07.06.14, https://earth.esa.int/handbooks/gomos/CNTR1-2-2.htm The Canadian Ozone and Ultraviolet Measurement Program, 2010, Viewed 07.06.14 http://es-ee.tor.ec.gc.ca/e/ozone/ozonecanada.htm Earth System Research Laboratory, 2012, Viewed 07.06.14, http://www.esrl.noaa.gov/gmd/dv/spo_oz/spototal.html EPA, 2013, Ozone Layer Protection Glossary, Viewed 14.06.14, http://www.epa.gov/ozone/defns.html Bureau of Meteorology 2013, Ozone Frequently Asked Questions, Viewed 14.06.14, http://www.bom.gov.au/uv/faq.shtml Smith, R 2008, Conquering Chemistry Fourth Edition, The McGraw-Hill Companies, NSW, Australia 1 | Page