Assessment statements 5.6.2-5.6.6 Depletion of Stratospheric Ozone Ozone Depletion Assessment statements 5.6.2-5.6.6 Depletion of Stratospheric Ozone

5.6.2 - The Role of Ozone Stratospheric ozone shields earth against biologically harmful Ultroviolet radiation (up to 99%). UV rays are absorbed during the formation and destruction of ozone (O3) from oxygen (O2).

How is ozone formed? Ozone, under natural conditions, is constantly being consumed and created by a cyclic photolytic reaction. What does this mean? Oxygen (O2) is continuously being converted to ozone (O3) and back again to O2. Reaction is driven by UV rays Net Reaction: 2O3 + UV  3O2 It is in steady state equilibrium

5.6.3 Depletion of Ozone The natural process of ozone formation is slowing down due to gasses that we are putting into the atmosphere! Halogenated organic gases like Chlorofluorocarbons (CFCs) and molecules with chlorine, flourine and bromine, and nitrous oxide (N2O). CFCs were used as aerosol propellants, for gas blown plastics like Styrofoam and plastic bottle shapes, and as a refrigerant. These gasses cause ozone in the stratosphere to be destroyed faster than it is formed.

http://www.epa.gov/ozone/science

How Does Depletion Occur? CFCs are stable in the troposphere and were thought to be heavy enough to stay in there, however, they move from troposphere into stratosphere UV breaks off chlorine molecule (Cl) from CFC Cl acts as a catalyst to break down ozone (O3) catalyst – promotes a chemical reaction without itself being used up in the reaction. shifts equilibrium of oxygen / ozone reaction. more O3 destroyed than made.

5.6.4 - Effects of UV radiation Damage DNA, causes many problems, including cancer. Increase in skin cancer & cataracts. Lower crop yield Decline in forest productivity Reduction of surface dwelling phytoplankton, which would therefore affect who? Damage & degrade materials paints & plastics More ozone near earth’s surface, produced in photochemical smog – lung problems, suppressed immune response, cancer.

                                              

5.6.5- 3 Methods of reducing the manufacture and release of ozone depleting substances. 1. Use of CFC Alternatives: Replace CFCs with: HFCs (hydrofluorocarbons) - alternative to CFCs don’t contain chlorine. Contain fluorine (1000 times less efficient in UV Reactions) HCFC - replace a Cl atom with H atom which enables it to be broken down in troposphere. Problem: if it gets to stratosphere it will deplete ozone **The problem with most of these replacements is that they are greenhouse gases!** 2. Recycle old refrigerators

5.6.6 - Role of national & world organizations in reducing the emissions of ozone depleting substances December 1995 - 100 countries signed an agreement to phase out the use of methyl bromide, a pesticide accredited with causing 15% of ozone depletion EPA made amendments to 1967 clean air act and is responsible for monitoring air quality standards for hazardous substances. A 1990 United Nations agreement called the “Montreal Protocol” outlined the phasing out of certain chlorocarbons by 1996 and provides aid for developing countries in order to do so.

Montreal Protocol “Perhaps the single most successful international agreement to date has been the Montreal Protocol.” -Kofi Annan, Former Secretary General of the United Nations Treaty originally signed in 1987 & amended in 1990 & 1992. The treaty provided a timetable on which the production of ozone depleting substances must be phased out and eventually eliminated. If international agreement is adhered to, ozone layer expected to recover by 2050. IMPACTS: Atmospheric concentration of CFCs has leveled off and/or decreased. Concentration of HFCs (an alternative) has increased substantially. Currently there are plans for a complete worldwide phase out by 2030.

Pollution Management for Ozone Depletion Replace = Regulate = Restore = ?