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PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Unit IX. The Ozone Hole(s)A.Discovery: Antarctic Ozone HoleSatellites have been monitoring the totalamount of ozone (mostly in the stratosphere)since the late 1970s. Satellites accurately recorded the suddendisappearance of at least half of all the ozone,but the computer rejected the results for many years.B. What is Ozone? 1. Ozone: A gaseous molecule that contains three oxygen atoms (O3), rather than the normal two atoms (O2).This is NASTY stuff: Extremely reactiveStrongly oxidizingFormation and destruction of ozone is going on all the time in a natural cycle.This natural cycle is also being impacted by human activity.Unit IX. The Ozone Hole(s)A. Discovery: Antarctic Ozone HoleB. What is Ozone? 1. Ozone: A gaseous molecule (O3).2. Where does it come from?O2 + UV photon O + O O + O2 + M O3 + MO3 + photon O2 + OO + O32 O2slowfastfastslowO2 + UV photon O + O O + O2 + M O3 + MO3 + photon O2 + OO+ O32 O2slowfastfastslowProductionDestructionO2 + UV photon O + O O + O2 + M O3 + MO3 + photon O2 + OO+ O32 O2slowfastfastslowRecyclingDestructionO2 + UV photon O + O O + O2 + M O3 + MO3 + photon O2 + OO+ O32 O2slowfastfastslowProductionDestructionRecyclingPhotodissociation of O3 both heats the stratosphere, and consumes (blocks) most of the shorter UV energy from the Sun: hence, the “ozone shield”Most O3 production is in the tropical stratosphere, because the solar flux is highest there (perpendicular to Sun’s energy). Stratospheric winds move O3 to higher latitudes.3. Why is it mostly in the stratosphere?The small amount of very short wave energy(<200 nm) required to split O2 molecules is consumed in the stratosphere and is not foundbelow 20 km.C. UV RadiationUV radiation is between 200 and 400 nmWe divide the UV portion into 3 segments:UVA: longer ans youUVB: middle  Burns you; skin cancersBCC (most will get), melanoma, squamousUVC: shortest Destroys DNATropopause90% of O3 is in the stratosphereWe can repair minor (UVB) damage; not UVCDNAO3 absorbs very efficiently at UVC, and moderately well at UVB, but not at UVA.Consequently, at Earth surface, UVA and UVBMore ozone in the stratosphere means less UVB at Earth’s surface.D. Measuring ozone concentrationsDobson Units (DU): 1 DU = layer of pureozone 0.001 cm thick at 1 atmosphere.Typical concentration is 300 DUTropospheric ozone: 10% of all ozone is in the troposphere from both natural and industrial sources. Its reactive nature cleans the troposphere of pollutants, but at ground level it is a major eye and lung irritant and kills plants. LA and Denver photochemical smog….Unit IX. The Ozone Hole(s)E. Other ozone depletion mechanisms.1. Total amount of ozone is always 30% less than predicted if photodissociation is the only loss.There are other trace gases in the stratosphere…. Can these interact with ozone?2. Chlorine catalytic cycleChlorine as a catalyst. Catalyst: A substance that increases the rate of a reaction, but is itself unchanged by the reaction.Cl + O3 ClO +O2ClO + O Cl + O2 fastfastCl + O3 ClO +O2fastAs a catalyst, Chlorine is now free to repeat the cycle of ozone destructionUnit IX. The Ozone Hole(s)E. Other ozone depletion mechanisms.1. 30% less ozone than predicted2. Chlorine catalytic cycle3. Other catalytic radicalsNitrogen (NO + O3 = NO2 + O2)(NO2 + O = NO + O2)N2O + O = 2 NOUnit IX. The Ozone Hole(s)E. Other ozone depletion mechanisms.1. 30% less ozone than predicted2. Chlorine catalytic cycle3. Other catalytic radicalsNitrogen (NO + O3 = NO2 + O2)(NO2 + O = NO + O2)Sources of N2O in the stratosphere…• Natural from microbial activity in soils• Soil microbials enhanced by fertilizers• Also from jet exhaust (NO)……particularly if they fly in the stratosphere (SST)Unit IX. The Ozone Hole(s)E. Other ozone depletion mechanisms.4. CFCs and the chlorine catalytic cycleWhat are CFCs?Chloro-Fluoro-Carbon compounds: compounds containing chlorine, fluorine and carbon.A simple CFC: CCl3FCarbon tetrachloride: CCl4Unit IX. The Ozone Hole(s)E. Other ozone depletion mechanisms.4. CFCs and the chlorine catalytic cyclea) sources: leaky fridges/AC/spraysb) fate of CFCs.Because they are an inert gas, CFCs have a long residence time in the troposphere.But how do they then get through the tropopauseinto the stratosphere? Through rare large convective storms in the tropics. Mixed slowly(1 to 2 yr) by stratospheric winds.Unit IX. The Ozone Hole(s)4. CFCs and the chlorine catalytic cyclea) sources: leaky fridges/AC/spraysb) fate of CFCs. c) solar radiation and CFCs. Short-wave UV radiation breaks CFC bonds,releasing atomic Cl, which is then free to participate in the chlorine catalytic cycle, whereeach Cl atom destroys tens of thousands of O3 molecules. The chlorine cycle is eventually broken when Cl combines with CH4 or H2 toform HCl, which is scrubbed out by rain.solar radiationDestruction of CFCs in the stratosphereUVCd) Natural sources of Cl in the stratosphere:• HCl (from mild volcanic eruptions)• Methyl chloride (CH3Cl) from marine biota.But CFCs supply a larger portion of stratospheric Cl.Unit IX. The Ozone Hole(s)F. The Antarctic Ozone Hole1. Only occurs in the Antarctic spring (September, October [strongest]). 2. Was not present in the early 1970s…. only after ~1976.Global ozone distribution in OctoberUnit IX. The Ozone Hole(s)F. The Antarctic Ozone Hole1. Only occurs in the Antarctic spring (September, October [strongest]). 2. Was not present in the early 1970s…. only after ~1976.3. In 2003, the Antarctic ozone hole was the second largest on record.Unit IX. The Ozone Hole(s)F. The Antarctic Ozone Hole1. Only occurs in the Antarctic spring (September, October [strongest]). 2. Was not present in the early 1970s…. only after ~1976.3. In 2003, the Antarctic ozone hole was the second largest on record.4. Is ozone depletion restricted to the Antarctic?Unit IX. The Ozone Hole(s)F. The Antarctic Ozone Hole1. Only occurs in the Antarctic spring (September, October [strongest]). 2. Was not present in the early 1970s…. only after ~1976.3. In 2003,


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CU-Boulder GEOL 1060 - The Ozone Hole

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