07Jun Oz NASC5120

O3zone A story in three acts : O3zone A story in three acts Introducing three oxygen atoms in one molecule - O3zone - our hero Narrator - Terry Deshler


Can you answer the ozone quiz? If not stay tuned. : Can you answer the ozone quiz? If not stay tuned. How does ozone form? Why is ozone important? Is ozone being lost over Antarctica? If so, why Antarctica and not over Laramie? Is ozone loss caused by human activity? Does ozone loss occur above the Arctic? Will ozone recover soon? Is ozone loss related to global warming?


Ozone Formation : Ozone Formation O2 + h  O + O Then, O + O + M  O2 + M or O + O2 + M  O3 + M (Ozone created) Where will this primarily occur? Also, O3 + h ( > 310 nm)  O2 + O and O3 + h ( < 310 nm)  O2* + O* (UV absorption) O2* + O2  2O2 + thermal energy (Excess energy dumped O2*  O2 + h ( = 1.3 m) in ozone layer)


Slide4 : Our setting - the atmosphere


Slide5 : Our setting - the atmosphere


Slide6 : Our setting - the atmosphere


Slide7 : Our setting - the atmosphere


Importance of ozone : Importance of ozone Absorbs DNA damaging UV radiation This UV affects both animals and plants SH/NH differences - In summer UV radiation is 50% more intense in SH than NH. Australia - world leader in skin cancer Reasons 10% - Earth is closer to sun in SH summer than NH summer 20% - Antarctic ozone loss/clearer atmosphere 20% - Unknown


Is ozone being lost over Antarctica? (data time) : Is ozone being lost over Antarctica? (data time) YES! So let us introduce our vocabulary / cast of characters


Polar ozone loss (act I)cast in order of appearance : Polar ozone loss (act I) cast in order of appearance Chlorofluorocarbons (CFCs) - Truck drivers, good for cool places Ultraviolet (UV) light - Truck breakers Chlorine - Useful guys, but can be bad - “hit molecules” Reservoir molecules - Foster homes


Food Preservation : Food Preservation 100 BC - 1700s, Early methods: Drying, Salting, Cool cellars/Spring houses, Pickling, Fermenting, Canning. Cooking -> could eat spoiled food - spices to hide the flavor. 1803 Ice Boxes - Thomas Moore invented the insulated box, with ice was in a separate container above the food storage area. Relied on stores of natural ice from frozen lakes and rivers. 1850s - Methods to artificially produce ice were developed. 1890 - Warm weather/rain lead to a shortage of natural ice. Spurred the development of mechanical refrigeration.


Refrigeration : Refrigeration 1918 - Kelvinator, First refrigerator introduced to American market. 1920s - Refrigerators used ammonia (NH4), sulfur dioxide (SO2), (toxic, odorous), and methyl chloride (CH3Cl), (toxic, no odor) - silent killer. 1928 - Thomas Midgley, Fridgidaire, dichlorodifluoromethane (CCl2F2) 1929 - Fridgidaire and DuPont joined to produce CCl2F2, and CFCl3 as Freon.


CFCs - Truck drivers : CFCs - Truck drivers 1928 - First totally safe molecule for mechanical refridgerators - Thomas Midgley, dichlorodifluoromethane (CCl2F2), Fridgidaire and DuPont joined to produce CCl2F2, and CCl3F as Freon (F12, F11). 1941 - Automobile air conditioning - Packard 1943 - Bug bomb used in WWII  CFCs became propellants for aerosol spray cans. 1940 - 1960 - Uses of Freon boomed. 1970s - CFC production 600,000 tons annually growing 10% per year. Uses with immediate releases to the atmosphere - 66%, refrigeration - 20%


The Awakening : The Awakening 1971 - Lovelock - Electron Capture Device coupled with Gas Chromatography -> First capability to detect molecule concentrations on the order of ppt (parts per trillion = 10-12). 1974 - Molina and Rowland - simple question - What happens to CFCs released into the atmosphere?


UV - Truck breakers : UV - Truck breakers 1974 - Molina and Rowland - simple question - What happens to CFCs released into the atmosphere? (awarded Nobel prize Chemistry 1995) CCl3 F (F-11) + h ( < 240 nm, z > O3 layer)  CCl2F + Cl CCl2F2 (F-12) + h ( < 240 nm, z > O3 layer)  CClF2 + Cl Then Cl + O3  ClO + O2 ClO + O  Cl + O2 Net: O3 + O  O2 + O2 This would occur above ozone layer altitudes above 30 km


Reservoir molecules - Foster homes for bad guys : Reservoir molecules - Foster homes for bad guys 1975 - 1980 – Predicted ozone losses above 30 km were not observed. Reservoir molecules discovered. Cl + CH4  HCl + CH3 ClO + NO2  ClONO2 HCl and ClONO2 are reservoir species. 1984 – Models predict 10% ozone loss in 100 years for current CFC production rates.


Ozone loss (Act II) - Cast : Ozone loss (Act II) - Cast Polar stratospheric clouds (nitric acid clouds) - Natural and beautiful, but home wreckers Return of the Sun - A rebirth, but not for everything Catalytic cycle - Steal and keep stealing (making a second appearance) Stratospheric polar vortex - Isolation cell to keep the bad guys in, and the pacifists out The Arctic - Lady in waiting or ?


Ozone Loss Polar Regions - the subtle act : Ozone Loss Polar Regions - the subtle act Polar ozone loss requires the release of Cl from the reservoir molecules, HCl, ClONO2 Based on ozone profiles the Cl release must occur at relatively low altitudes. Gas phase chemistry cannot do it.  Something new Heterogeneous chemistry


Slide25 : Happens during dark winter The photolysis has to wait for the return of light in late winter


Catalytic Cycle Polar Stratosphere : Catalytic Cycle Polar Stratosphere PSC particle + HCl + ClONO2  Cl2 Cl2 + h  Cl + Cl 2 [ Cl + O3  ClO + O] ClO + ClO + M  ClOOCl + M (M=N2 or O2) ClOOCl + h  Cl + ClOO ClOO + M  Cl + O2 + M h = Sun’s return Net 2O3 + h  3O2 A single Cl atom can destroy more than100,000 ozone molecules. This cycle will continue until the NO2 and OH lost in the form of HNO3 in polar stratospheric clouds is replenished by mid latitude air, thus converting Cl back to its reservoir species.


Slide34 : Nitric acid/water Ice Nitric acid/water Ice


Ozone loss (Act III) - Cast : Ozone loss (Act III) - Cast Montreal Protocal and amendments - Laws to limit the formation of new radicals Trend of stratospheric chlorine - Together we can defeat the bad guys Global warming - It is the same atmosphere, but is there any other connection?


Slide36 : Molina & Rowland, 1974 Reservoir Molecules Discovered Montreal Protocol, and amendments Antarctic ozone hole discovered


Measurements continue at McMurdo: : Measurements continue at McMurdo: To maintain good records in anticipation of ozone recovery. To test quantitative models of ozone loss. This last aspect is focus of current measurements.


McMurdo Antarctica78S - 1989 : McMurdo Antarctica 78S - 1989


The End? : The End? No, we have to limit the release of CFCs into the atmosphere from now on. The good news - the atmosphere will cleanse itself of present atmospheric chlorine. The bad news - it will take another 50 years to see the ozone hole above Antarctica disappear.


Postscript : Postscript The ozone loss story is a positive one A global problem created by local human activities was identified, and reasonable solutions adopted by the worlds leading countries to reduce and eventually eliminate the problem. Is there a relation to global warming? Physically - minimal. Politically - the actions on ozone loss may serve as a model to direct future decisions by world leaders


Slide51 : Tropospheric Chlorine