OZONE LAYER & CFC’S

Understanding Stratospheric Ozone Discovered in 1839 by Christian Schonbein Pale blue, unstable, made up of 3 oxygen atoms Found in stratosphere naturally If found in troposphere considered a pollutant & major contributing factor to photochemical smog Important b/c it screens out harmful UV rays from sun A 1 % loss in ozone = 2% increase in UV reaching earth’s surface

How is Ozone Formed & Maintained? UV light splits O2 into two free O atoms. One of these free O atoms bonds with another O2 to make O3. More UV light can split O3 to make O and O2 and the process repeats

The Ozone Hole First discovered in 1985 over Antarctica Why Antarctica? Exceptionally cold air during long, dark winter months due to strong circumpolar vortex isolating Antarctic air. Allows ice crystals to form at high altitudes Chlorine containing cmpds (CFC’s) that destroy ozone are attached to ice crystals When sun returns in spring, chlorine atoms are liberated & work quickly to destroy ozone

(Key Learning Figure) Many students (and the public) have the perception that the ozone hole (and ozone in general) is getting much worse. This is likely due to press reports that usually say, ‘the ozone hole reached it’s largest size…’ The reality is that in the last decade, the size and severity of the ozone hole have stayed about the same, compared to rapid changes seen in the middle 1980’s. Year to year variations in the depth and severity of the ozone hole is really a function of the atmospheric weather conditions (I.e. the colder the winter, the more greater the ozone loss). In addition, the ozone hole is about as bad as it can get. Between 16-22 km, all the ozone is essentially destroyed during spring over Antarctica, so it couldn’t get much worse. Thus, we don’t expect the size and depth of the ozone hole to change dramatically in the future. Rather, it is expected that the size of the ozone hole is about as big as it’s going to get, and with time (10 or more years) and reduced chlorine levels, we should start to see the size of the ozone hole get smaller. Thus, this graphic is intended to illustrate how in the 80’s, the size of the ozone hole increased rapidly, while in the 90’s and 2000, things stabilized.

science.widener.edu/svb/ atmo_chem/oct15.html

Latest Data from NASA http://ozonewatch.gsfc.nasa.gov/ October 9, 2010

Chlorofluorocarbons (CFC’s) and halon gases First used in 1928 by General Motors as refrigerant Widely used in 1940’s & 50’s By 1988, 320,000 metric tons of CFC’s have been released Used as propellants in aerosol cans Refrigerants in air conditioning units Making of Styrofoam Fire retardants Last for 10-100 years becuz very stable CFC’s are broken by UV radiation to release chlorine atom which is mostly responsible for breaking ozone molecules O3 +Cl  ClO+ O2 ClO+O  Cl+O2

Ultraviolet light hits a chlorofluorocarbon (CFC) molecule, such as CFCl3, breaking off a chlorine atom and leaving CFCl2. Sun Cl Cl Once free, the chlorine atom is off to attack another ozone molecule and begin the cycle again. C Cl F UV radiation Cl Cl O O A free oxygen atom pulls the oxygen atom off the chlorine monoxide molecule to form O2. The chlorine atom attacks an ozone (O3) molecule, pulling an oxygen atom off it and leaving an oxygen molecule (O2). Cl Cl O O O O O The chlorine atom and the oxygen atom join to form a chlorine monoxide molecule (ClO) Cl O O O

A single chlorine atom removes about 100,000 ozone molecules before it is taken out of operation by other substances

Harmful effects of UV radiation. Skin cancer (ultraviolet radiation can destroy acids in DNA) Cataracts and sun burning Suppression of immune systems Adverse impact on crops and animals Reduction in the growth of ocean phytoplankton Degradation of paints and plastic material

matrix.ucdavis.edu/tumors/tradition/ gallery-ssmm.html

www.snec.com.sg/clinical_services/ cataract.asp

Ozone Legislation 1978- US, Canada, and some of Europe banned nonessential use of CFC’s Montreal Protocol An international treaty designed to protect the ozone layer phasing out production of number of substances believed to be responsible for ozone depletion Effective January 1, 1989 Five revisions 1990 (London) 1992 (Copenhagen) 1995 (Vienna) 1997 (Montreal) 1999 (Beijing) Sherwood Rowland, Mario Molina, and Paul Crutzen shared a Nobel Prize for their work on ozone. First Nobel Prize awarded for an environmental issue.