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OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan The good, the bad & the ugly.

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Presentation on theme: "OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan The good, the bad & the ugly."— Presentation transcript:

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2 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan The good, the bad & the ugly

3 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Driving Questions 1.Why is ozone important? 2.How is it formed? 3.How is it destroyed? 4.How is it different in the stratosphere vs. the troposphere? 5.If stratospheric ozone is decreasing and tropospheric ozone is increasing, why not just build a REALLY big chimney? Issues to be Considered:

4 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Greenhouse Gases 1.Carbon Dioxide (CO 2 ) 2.Nitrous Oxide (N 2 O) 3.Methane (CH 4 ) 4.Ozone (O 3 ) 5.Chlorofluorocarbons (CCFs) and Water Vapor Click me

5 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Ultraviolet Radiation uv-b.280 µm uv-a.315 µm.400 µm uv-c

6 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Ozone Formation

7 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Ozone Maxima

8 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Why the Stratosphere?

9 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Ozone Formation When an oxygen molecule absorbs a photon of light with a wavelength shorter than 0.2 µm the energy splits the molecule into two oxygen atoms. O 2 + h —> O + O One of these atoms can react with another oxygen molecule to form an ozone molecule. O + O 2 + M —> O 3 + M Up to 98% of the sun's high-energy ultraviolet light (UV-B and UV-C) are absorbed by the destruction and formation of atmospheric ozone.

10 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Ozone Formation O 2 + h —> O + O 2 (O + O 2 + M —> O 3 + M) 3O 2 —> 2O 3 Net production

11 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Ozone Destruction Ozone, on the other hand, absorbs photons of light with a wavelength between µm that splits the molecule into an oxygen atom and an oxygen molecule. O 3 + h —> O 2 + O The oxygen atom react with another ozone molecule to form two oxygen molecules. O + O 3 —> O 2 + O 2 2 O 3 —> 3O 2

12 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Catalytic Reactions The term catalytic means that X can react with and remove ozone while X itself is regenerated in the process O 3 + X —> XO + O 2 XO + O 3 —> X + 2O 2 2 O 3 —> 3 O 2 O 3 + X —> XO + O 2 XO + O —> X + O 2 O + O 3 —> 3 O 2 and

13 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Ozone Formation Ozone has a natural photochemical balance between formation and destruction as other gases participate. Example: Nitrogen oxides NO 2 —> NO + O O + O 2 —> O 3 NO + O —> NO 2 O + O 2 —> 2O 2

14 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Ozone Formation But chlorofluorocarbons shift this balance: Cl 2 CF 2 + UV light —> ClCF 2 + Cl Then there is a catalytic destruction of ozone: Cl + O 3 —> ClO + O 2 ClO + O 3 —> Cl + O 2 The net effect of this pair of fast reactions is to turn two ozone molecules into three normal molecules of oxygen. The (catalyst) atomic chlorine is recovered in the second reaction, making it available to start over. In fact, each chlorine atom can destroy hundreds of thousands of ozone molecules!

15 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Lifetime of CFC 1.Emitted into atmosphere as gas. 2.Disperses rapidly throughout Northern hemisphere in ~1 year 3.After a few years is uniformly mixes throughout whole troposphere. 4.Movement into stratosphere is slow. Some leaks upwards to region where sufficient UV light is available to break bonds and release Cl. 5.Each atom of Cl participates in thousands of catalytic reactions, destroying hundreds of thousands of ozone molecules. 6.Ultimately each Cl atom reacts with methane to produce HCl. 7.Some of the HCl is transported back into the troposphere and gets rained out, the rest gets broken apart and the Cl cycle begins again.

16 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Ozone Depletion Potential The Ozone Depletion Potential (ODP) is the ratio of the impact on ozone of a chemical compared to the impact of a similar mass of CFC-11. oThus, the ODP of CFC-11 is defined to be 1.0. oOther CFCs and Hydrochlorofluorocarbon s (HCFC’s) have ODPs that range from 0.01 to 1.0. o Halons have ODPs ranging up to 10. o Carbon tetrachloride (CCl 4 ) has an ODP of 1.2, and methyl chloroform's ODP is o Hydrofluorocarbons ( HFCs) have zero ODP because they do not contain chlorine.

17 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Ozone Column Measure

18 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Problems with Ozone Depletion More than 90% of non-melanoma skin cancers are related to UV-B exposure. 1% ozone decrease produces a ~2% increase in UV-B. Each 2% increase in UV-B is epidemiological linked with a 2%-5% increase in basal- cell cancer cases and a 4-10% increase in squamous cell cancer.

19 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Problems with Ozone Depletion

20 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Problems with Ozone Depletion A national UV Index is issued daily to advise the public on the strength of the sun's UV rays. The chart to the right shows the levels of the UV Index, your time to burn in the sun without sunscreen, and what you can do to protect yourself.

21 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Problems with Ozone Depletion

22 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Problems with Ozone Depletion

23 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan

24 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan

25 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Ozone Hole Discovery In 1985 Farmen et al. published a paper containing this figure. It showed a dramatic decrease in total ozone abundance during October over the Antarctic station at Halley Bay.

26 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Ozone Hole Discovery Moreover the amount of ozone column has decreased steadily.

27 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan

28 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Changing Ozone Concentrations

29 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Changing Ozone Concentrations

30 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Changing Ozone Concentrations The ozone hole is defined geographically as the area wherein the total ozone amount is less than 220 Dobson Units.

31 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Last Updated: May 6, 2015

32 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan

33 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Last Updated: May 6, 2015

34 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan So Why an Ozone “Hole”?

35 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan

36 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Role of Polar Stratospheric Clouds Source: Turco, Earth Under Siege

37 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Last Updated: May 6, 2015 Ozone depletion depends on altitude

38 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Last Updated: May 6, 2015 Ozone depletion depends on altitude and is highly influenced by temperature.

39 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Changing Ozone Concentrations Last Updated: May 6, 2015

40 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Last Updated: May 6, 2015

41 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Last Updated: May 6, 2015 UV radiation is weaker and the photolysis of O 2 is less important. Near the surface the production of ozone is still initiated by sunlight, but the reactors are volatile organic compounds (VOCs) and nitrogen oxides (NO x = NO + NO 2 ) Meanwhile, down near the surface

42 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Last Updated: May 6, 2015 NO 2 —> NO + O O + O 2 + M —> O 3 + M NO + O 3 —> NO 2 + O 2 Meanwhile, down near the surface Net result, no ozone buildup.

43 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Last Updated: May 6, 2015 VOCs produce “radical organics” (RO 2 ) that interfere with the NO chemistry, basically producing extra atomic oxygen RO 2 + NO —> NO 2 + RO NO 2 —> NO + O O + O 2 + M —> O 3 + M Meanwhile, down near the surface Net result, ozone buildup.

44 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Last Updated: May 6, 2015 Meanwhile, down near the surface

45 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Last Updated: May 6, 2015 Meanwhile, down near the surface

46 OZONE Stratospheric Tropospheric Summary Basics Issues ©2003, Perry Samson, University of Michigan Last Updated: May 6, 2015 Ozone Control


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