Decreasing wavelength Increasing frequency, energy (& potential damage) UV-C: blocked by ozone UV-B: blocked by ozone UV-A: only blocked

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1 Ozone Shield a natural process that filters radiati on before it reaches the lower atmosphere. In : Concentration of ozone in this layer is While ozone is made primarily at the equator, there is about ozone above the tropics than at higher latitudes

2 Decreasing wavelength Increasing frequency, energy (& potential damage) UV-C: blocked by ozone UV-B: blocked by ozone UV-A: only blocked

3 Ozone Shield Oxygen: Ozone: O 2 O 3 Energy from Sun uv Ultraviolet Energy is absorbed in this process, which keeps most uv radiation from reaching Earth s surface Ozone is not very, and it breaks apart easily to make, which can then make more O 3

4 Ozone Shield

5 Human inputs to Ozone depletion: Chlorofluorocarbons (CFCs): found in sprays, for air conditioners and refrigerators,, house insulation Other stable halogen containing gases (halogens = chlorine, fluorine, & bromine) Supersonic jets which travel in the stratosphere they produce reactive compounds which, when in the stratosphere, can destroy ozone

6 How Does Depletion Occur? CFCs are very molecules, move from troposphere to stratosphere this takes about years Uv breaks off chlorine molecule (Cl) from CFC Cl acts as a catalyst to break down ozone (O 3 ) promotes a chemical reaction without itself in the reaction shifts equilibrium of oxygen / ozone reaction:

7 UV radiation Sun Ultraviolet light hits a chlorofluorocarbon (CFC) molecule, such as CFCl 3, breaking off a chlorine atom and leaving CFCl 2. Cl C Cl Cl F C Cl Cl F Cl Cl The chlorine atom attacks an ozone (O 3 ) molecule, pulling an oxygen atom off it and leaving an oxygen molecule (O 2 ). O O O O Ozone O O Summary of Reactions CFCl 3 + UV Cl + CFCl 2 Cl + O 3 ClO + O 2 Repeated ClO + O Cl + O 2 many times Once free, the chlorine atom is off to attack another ozone molecule and begin the cycle again. O A free oxygen atom pulls the O O O oxygen atom off the chlorine O monoxide molecule to form Cl O 2. O O O The chlorine atom and the oxygen atom join to form a chlorine monoxide molecule (ClO). Cl O O Fig. 19-D, p. 525

8 Ozone Depletion Each Cl atom can destroy ~100,000 O 3 molecules Some CFCs can remain in the atmosphere for up to ( = ) Rowlands and Molina were scientists who discovered link between CFC s and ozone depletion in Received a Nobel Prize in 1995.

9 Ozone hole over Antarctic: Happens during Antarctic and early summer when sunlight returns (Sept-Nov) In winter, steady winds blow in a circular pattern around south pole A is created (mass of very cold air) Water droplets form ice crystals in vortex, which collect CFC molecules on their surfaces, and act as catalysts for reaction that releases Cl atoms to the atmosphere Without, Cl ClO Cl 2 O 2 during winter When sunlight returns, breaks up, releasing large amounts of Cl to start ozone destruction Sunlight melts ice crystals and breaks up polar vortex, eventually ozone hole until the next season Effect is lesser over north pole, because winds don t create as strong a vortex

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12 Antarctic Ozone Hole 1 Dobson Unit (DU) = 0.01 mm thickness of a gas at STP Normal Ozone thickness ~ DU (~1/8 inch) dv/spo_oz/movies/index.html Southern tip of South America, and southernmost part of Australia are the most populated areas affected by the ozone hole These areas get more UV-B radiation (and up to more) in most years during seasonal thinning.

13 Consequences of Ozone Depletion Increase in skin cancer & cataracts, especially in southern hemisphere U-v damage to plants ( ) Damage to marine organisms in the Southern Ocean: phytoplankton and krill, which are at the bottom of the

14 Fig , p. 524

15 Potential Link Between Ozone Depletion and Global Warming Ozone depletion could exacerbate global warming by impairing or destroying which play a key role in removing CO 2 from the atmosphere (primary producers/photosynthesis).

16 This long-wavelength (low-energy) form of UV radiation causes aging of the skin, tanning, and sometimes sunburn. It penetrates deeply and may contribute to skin cancer. This shorter-wavelength (high-energy) form of UV radiation causes sunburn, premature aging, and wrinkling. It is largely responsible for basal and squamous cell carcinomas and plays a role in malignant melanoma. Ultraviolet A Ultraviolet B Thin layer of dead cells Hair Squamous cells Basal layer Melanocyte cells Epidermis Sweat gland Dermis Basal cell Blood vessels Squamous Cell Carcinoma Basal Cell Carcinoma Melanoma Stepped Art Fig. 19-E, p. 526

17 Skin Cancer Over of all new cancers are skin cancers More than 1 million cases of skin cancer will be diagnosed in the US this year About 80% of skin cancers are basal cell carcinoma,16% are squamous cell carcinoma, 4% are melanoma An estimated people will die of skin cancer this year: (7,901 from melanoma)

18 Types of Skin Cancer Squamous Cell Carcinoma Basal Cell Carcinoma Melanoma Arising from cells in the upper layer of the epidermis, this cancer is also caused by exposure to sunlight or tanning lamps. It is usually curable if treated early. It grows faster than basal cell carcinoma and can spread to other parts of the body (metastasize). The most common skin malignancy usually is caused by excessive exposure to sunlight or tanning lamps. It develops slowly, rarely metastasizes and is nearly 100% curable if diagnosed early and treated properly. This deadliest of skin cancers involves melanocyte cells, which produce pigment. It can develop from a mole or on blemished skin, grows quickly, and can spread to other parts of the body (metastasize).

19 There were about 95,880 new cases of melanoma in This is a 4% increase from At current rates, Americans have a lifetime risk of developing melanoma, and one in 65 have a risk of invasive melanoma (older Caucasian males have the highest mortality rates from melanoma The incidence of melanoma more than among Caucasians between 1980 and 2003 Melanoma is more common than any non-skin cancer among women between 25 and 29. Invasive melanoma is the most common cancer in men, the most common in women ABCD s of Melanoma Identification

20 History of Political Action on Ozone Depletion In 1979 US banned containing CFCs, but it was still used in other materials By 1985, demand for CFCs was growing by in 1985: required a plan for phasing out CFC use, and required scientists to summarize latest information on effects of CFCs and other halons was discovered over Antarctica in 1985 causing a large international consensus that something must be done

21 Montreal Protocol In 1987, 36 nations representing the developed world met to form a treaty Decision was made to cut CFCs by between 1989 and nations met in 1990, 1992, and 1997 to adopt a policy to completely phase out key ozone-depleting chemicals CFC production fell by between 1988 and 1998 $250 million fund created to help developing countries make switch away from CFCs 58 developing nations have agreed to phase out CFCs, but India and China were not involved In 2007, 191 nations met in Montreal, and agreed to phase out production of HCFCs by 2020 in developed nations and by 2030 in developing nations

22 Montreal Protocol Despite resolve of international community to protect the ozone layer, due to the long of CFCs in atmosphere, ozone layer will continue to be depleted until or so, but there are already signs that the problem is not getting any worse Models predict that we will return to 1980 levels of ozone within 60 years and pre-1950 levels within. Ozone is projected to be at its lowest levels between.

23 Reasons for success in ozone story: United State Production of CFCs

24 Past and future abundance of ozone depleting gases Present and Future CFC Levels