Advanced Placement Environmental Science Teacher Ozone Hole Mark Ewoldsen, Ph.D. Advanced Placement Environmental Science Teacher La Cañada High School

Two Atmosphere Layers Stratosphere is above Troposphere Ozone Layer blocks UV radiation Troposphere is where we live Weather occurs here 72% of all air is below the cruising altitude of commercial airliners (33000 ft)

Stratospheric Ozone vs. Tropospheric Ozone (Good) vs. Tropospheric Ozone (Bad)

Ozone – Two Faces Stratosphere – Good Ozone Troposphere – Bad Ozone Blocks UV radiation Hole caused by depletion due to CFC’s Troposphere – Bad Ozone Pollution Photochemical smog Eye irritant

Harmful effects of UV radiation Skin cancer such as melanoma(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 Cooling of the Earth's stratosphere and possibly some surface climatic effect Degradation of paints and plastic material

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

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Good Ozone

Ozone Formation Ozone forms a layer in the stratosphere, thinnest in the tropics (around the equator) and denser towards the poles. O2 + hv  O + O (1) O + O2 O3 wavelength ~ 240 nm

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Natural Ozone Hole Winter = no sunlight Air in the polar vortex can get very cold -80C Special clouds called Polar Stratospheric Clouds form as nitric acid trihydrate PSCs are crucial for ozone loss to occur Since there is no sunlight, the air within the polar vortex can get very cold

The ozone hole builds up over the winter months, peaking at around September and breaking up again by December, this data set from 2005                                July                           August                                September              October                                November December

Destroying Good Ozone

Destroying Good Ozone Chloroflourocarbons were first created in 1928 as non-toxic, non-flamable refrigerants, and were first produced commercially in the 1930's by DuPont In 1974, a laboratory study demonstrated the ability of CFC's to catalytically breakdown Ozone in the presence of high frequency UV light Cl + O3 -> ClO + O2 ClO + O3 ---> 2 O2 + Cl In a 1985, a study summarized data that had been collected by the British Antartic Survey showing that ozone levels had dropped to 10% below normal January levels for Antarctica. http://www.nas.nasa.gov/About/Education/Ozone/history.html

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

The frozen crystals that make up polar stratospheric clouds provide a surface for the reactions that free chlorine atoms in the Antarctic stratosphere

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

http://www.clas.ufl.edu/users/dlsmith/Lecture_11.html

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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)

Septembe r 21-30, 2006 the average area of the ozone hole was the largest ever observed, at 10.6 million square miles