1. IV/1 Atmospheric transport and chemistry lecture I.Introduction II.Fundamental concepts in atmospheric dynamics: Brewer-Dobson circulation and waves III.Radiative transfer, heating and vertical transport IV.Stratospheric ozone chemistry

2. IV/2 Processes affecting stratospheric O3 3/1997 3/1999

3. IV/3 IV. Stratospheric ozone chemistry 1.Basic concepts of atmospheric chemistry 2.Ozone chemistry and ozone distribution 3.Sources and distribution of ozone-related species 4.Ozone trends 5.The ozone hole

4. IV/4 IV. Stratospheric ozone chemistry 1.Basic concepts of atmospheric chemistry 2.Ozone chemistry and ozone distribution 3.Sources and distribution of ozone-related species 4.Ozone trends 5.The ozone hole

5. IV/5 What goes in ? What goes out ? horizontal / vertical transport What goes on in there ? gas-phase reactions surface reactions ion reactions External forcing ? solar radiation, (solar / magnetospheric particles in polar regions) Chemical-transport „model“: simple scheme Most common reactions in the stratosphere are neutral gas-phase reactions with two reactants, involving at least one radical

6. IV/6 Chemical reactions: second order and higher High order reaction  reactants A and B form products C and D  a,b,c,d: stoechiometric quantities of A, B, C, D Rate R of the reaction: rate of change of A units of R: molecules / cm 3 ·sec

7. IV/7 Chemical reactions: second order and higher High order reaction  Rate R of the reaction:  k rate constant of the reaction  [A] concentration (number density) of A  [B] concentration of B  Order of reaction n=a+b - rate of change of A - rate constant k are measured in laboratory

8. IV/8 Chemical reactions: second order and higher Second order (bimolecular) reaction  Rate constant R:: Simple collision theory:  Assume molecules A and B are hard spheres of radii r A and r B  then rate constant is approximately the product of cross-section of both hard spheres and the molecular velocity

9. IV/9 Chemical reactions: second order Second order (bimolecular) reaction  Rate constant R:: Simple collision theory:  Assume molecules A and B are hard spheres of radii r A and r B  then rate constant is approximately the product of cross-section of both hard spheres and the molecular velocity

10. IV/10 activated complex reactants products Arrhenius-form reaction kinetics E 1 : activation energy E 2 : energy gained by reaction  H: reaction enthalpy (reaction heat) The reaction takes place if the thermal energy of the reactants is larger than E 1 : AC+B

11. IV/11 Summary of gas-phase reactions First order (unimolecular) reaction: photolysis or thermal decomposition Second order (bimolecular) reaction Three-body reaction

12. IV/12 Summary of gas-phase reactions First order (unimolecular) reaction: thermal decomposition  pressure and temperature dependent Second order (bimolecular) reaction  temperature dependent Three-body reaction  Pressure and temperature dependent pressure (air molecules: N2, O2)

13. IV/13 I Photodissociation and decomposition Photodissociation: Thermal decomposition: quantum yield = 0: AB is not dissociated quantum yield = 1: AB is totally dissociated number of photons absorbed quantum yield absorption cross- section actinic flux J AB : photolysis rate

14. IV/14 II First order reaction  : lifetime of A

15. IV/15 III second order reaction Lifetime of A:  A valid if [B] is constant, or, approximately valid if the lifetime of B is larger than the lifetime of A

16. IV/16 Examples Bimolecular reaction:  NO + O 2  NO 3  It involves an intermiediate reactant, the nitrate radical NO 3 NO + O 2  NO 3 NO 3 + NO  2NO 2 2NO + O 2  2NO 2 (net)  reaction rates (second order):  First reaction is of pseudo-first order, since [O2] is constant (air!), e.g. air density Unimolecular reaction:  N 2 O 5  NO 3 +NO 2  thermal decomposition  Reaction rate:  N 2 O 5 +h  NO 3 +NO 2  photodissociation  reaction rate: N 2 O 5 +h  NO 3 +NO 2 NO 3 +h  NO+O 2 N 2 O 5 +h  NO+NO 2 +O 2 (net) night (polar night): NO 2 +O 3  NO 3 +O 2 NO 3 +NO 2 +M  N 2 O 5 +M 2NO 2 + O 3 +M  N 2 O 5 +O 2 +M NOx catalytic cycle O3 loss reservoir species

17. IV/17 General behaviour of molecule A d[A] / dt = (sum of formation reactions) – (sum of loss reactions) d[A] / dt =  k ij [C i ][C j ] -  k j [A][C j ] +  J j [C i ] – J A [A] gas-phase production and loss reactions of A photolysis reactions forming and dissociating A

18. IV/18 IV. Stratospheric ozone chemistry 1.Basic concepts of atmospheric chemistry 2.Ozone chemistry and ozone distribution - oxygen atmosphere - ozone distribution - catalytic cycles 3.Sources and distribution of ozone-related species 4.Ozone trends 5.The ozone hole

19. IV/19 Pure oxygen chemistry (Chapman cycle) lifetime of family (O x ) is long, family members (O3,O) transfer into each other in fast reactions OO3O3 O2O2 J 1 - slow k 2 - fast J 3 - fast k 4 - slow odd oxygen family: O x =O 3 +O <242 nm =240-320 nm

20. IV/20 Ozone vertical distribution Ozone altitude distribution at 8°N, January 28, 2004  model result from the modified Leeds-Bremen model mixing ratio number density ozone maximum ~33km ozone maximum ~25km number density =vmr × air density  the ozone column (= total ozone) is dominated by the lower stratosphere secondary maximum

21. IV/21 ozone vertical distribution Ozone vertical distribution from pole to pole (number density) [O3] 10 12 molec./cm 3 ozone maximum ~18 km (pole) ~25 km (tropics)

22. IV/22 Pure oxygen chemistry (extended Chapman cycle) O( 1 D) cannot deexcite into the electronic ground state O, only by collission with air molecules (k 6a, k 6b, k 6c ) lack of O3 in upper atmosphere

23. IV/23 Pure oxygen chemistry (extended Chapman cycle) odd oxygen family: O x =O 3 +O+O( 1 D) Change in O x : formation of O x loss of O x neglect slow and thermospheric reactions

24. IV/24 Chemical and dynamical lifetime  h<40 km: O x is dominated by transport of ozone  h=40-80 km: O x is dominated by chemistry  h>80 km: O x is dominated by transport of O photochemical lifetimes of O3, O and O x (  Ox,  O3,  O ) compared to time scales of horizontal (u,v) and vertical transport (w)

25. IV/25 dynamical and chemical control of Ox dynamical control of Ox (ozone) in polar night dynamical control throughout the upper mesosphere / lower thermosphere dynamical control in the lower stratosphere Chemical control from mid- stratosphere to mid-mesosphere transition zone of transport/chemistry control

26. IV/26 Partitioning of family members

27. IV/27 Partitioning of family members (continued) from these equations the partitioning of family members can be calculated if photochemical equilibrium is assumed for O and O( 1 D), i.e,

28. IV/28 Partitioning of family members (continued) from these equations the partitioning of family members can be calculated if photochemical equilibrium is assumed for O and O( 1 D), i.e, both O and O(1D) are zero during night-time in the stratosphere:  [O 3 ] >> [O] (O x  O 3 ) in the upper mesosphere:  [O 3 ] < [O] (O x  O)

29. IV/29 Odd oxygen noon daytime: h < 50 km: Ox  O 3 h > 70 km: Ox  O h = 50-70 km: transition zone, O and O 3 O( 1 D) more than five orders of magnitude smaller Ozone altitude distribution at 8°N, January 28, 2004  model result from the modified Leeds-Bremen model

30. IV/30 Odd oxygen Ozone altitude distribution at 8°N, January 28, 2004  model result from the modified Leeds-Bremen model noon night night: Ox  O 3 up to ~ 75 km

31. IV/31 Ox diurnal variation h=40 km: no diurnal variation of ozone and Ox Ozone O Ox h=40km noon Ozone altitude distribution at 8°N, January 28, 2004  model result from the modified Leeds-Bremen model

32. IV/32 Ox diurnal variation h=40 km: no diurnal variation of ozone and Ox h=50 km: small diurnal variation of O 3, Ox constant Ozone O Ox h=50km noon Ozone altitude distribution at 8°N, January 28, 2004  model result from the modified Leeds-Bremen model

33. IV/33 Ox diurnal variation h=40 km: no diurnal variation of ozone and Ox h=50 km: small diurnal variation of O 3, Ox constant h=60 km  night: O x = O 3  day: O x  O Ozone O Ox h=60km noon midnight Ozone altitude distribution at 8°N, January 28, 2004  model result from the modified Leeds-Bremen model

34. IV/34 Ox diurnal variation h=40 km: no diurnal variation of ozone and Ox h=50 km: small diurnal variation of O 3, Ox constant h=60 km  night: O x = O 3  day: O x  O h=70 km  night: O x = O 3  day: O x = O Ozone O Ox h=70km noon midnight Ozone altitude distribution at 8°N, January 28, 2004  model result from the modified Leeds-Bremen model

35. IV/35 Ox diurnal variation h=40 km: no diurnal variation of ozone and Ox h=50 km: small diurnal variation of O 3, Ox constant h=60 km  night: O x = O 3  day: O x  O h=70 km  night: O x = O 3  day: O x = O h=80 km: Ox  O Ozone O Ox h=80km noon midnight Ozone altitude distribution at 8°N, January 28, 2004  model result from the modified Leeds-Bremen model

36. IV/36 meridional circulation

37. IV/37 Ozone from Ox equilibrium model result from the modified Leeds-Bremen model January (NH winter) ozone in ppm unrealistic high values in polar night (equilibrium model!) ozone production

38. IV/38 Ozone from Ox equilibrium model result from the modified Leeds-Bremen model July (SH winter) ozone in ppm unrealistic high values in polar night (equilibrium model!)

39. IV/39 Annual variation in ozone model result from the modified Leeds-Bremen model, O3 in ppm tropics (0°N) mid-lats (47°N) polar (75°N)

40. IV/40 Seasonal and meridional ozone variation Downward transport during polar winter total O3 [DU] ozone hole (Antarctic winter)

41. IV/41 Ozone variation with tropopause height Variation of total ozone with 200hPa altitude and tropopause altitude (~300 hPa) low tropopause high tropopause low 200hPa altitude high 200hPa altitude high ozone low ozonec

42. IV/42 catalytic cycles the Chapman reactions do a fairly good job of reproducing the shape of the ozone profile, with a 20 – 30 km maximum. the Chapman reactions significantly overestimate stratospheric ozone levels by a factor of 2  Additional catalytical cycles are needed to explain observations Chapman cycle calculated ozone observed ozone

43. IV/43 Catalytic ozone loss cycle: HOx Catalytic cycle: First proposed by Bates and Nicolet (1950) for HOx reactants, i.e. X=OH, H

44. IV/44 Catalytic ozone loss cycle: ClOx Catalytic cycle: Molina and Rowland, 1974: stratospheric sink for chlorofluoromethanes: chlorine atom catalysed destruction of ozone (X=Cl)  Cl catalysed ozone loss was primarily predicted for the upper stratosphere (40-50 km altitude), the ozone hole (mainly 15-20 km, polar region) was linked to stratospheric chlorine not before the 1980s

45. IV/45 Catalytic ozone loss cycle: NOx Catalytic cycle: Crutzen, 1970s: numerous studies about catalytic cycles of HO x and NO x (X=NO)  In analogy to the O x family (fast reactants), NO x is defined as NO+NO 2

46. IV/46 Nobel prize in chemistry 1995 Molina, Crutzen, and Roland received the Nobel prize in chemistry 1995 for achievements in „atmospheric chemistry, particularly concerning the formation and decomposition of ozone“

47. IV/47 Chain length in catalytic cycles chain length N: number of times the cycle is executed before the chain center is destroyed: Chain effectiveness e:   : rate of propagation (i.e., the rate of the slowest reaction involved, the rate-limiting step)   : rate of termination (rate of destruction of the chain center) chain center

48. IV/48 Summary catalytic cycles Chemical families that destroy ozone catalytically HOx  H, OH, HO 2, 2xH 2 O 2 NOx  N, NO, NO 2, NO 3 ClOx  Cl, ClO, HOCl, OClO, 2xCl 2 O 2 BrOx  Br, BrO, OBrO, HOBr

49. IV/49 Coupling between families: Hox, BrOx The HO2/BrO cycle: The OH / HO2 cycle:

50. IV/50 Coupling between families: Hox, BrOx HOx cycles:  H >40 km: H/HO2 and OH/HO2 cycle dominant  H < 30 km: BrO/HO2  H < 20 km: OH/HO2

51. IV/51 ClOx cycle  Cl/ClO: above 30 km  ClO/ClO: ~20 km altitude  ClO/NOx: ~20-30 km altitude The Cl / ClO cycle:

52. IV/52 Bromine cycle Bromine cycle:  Br/BrO: above 40 km  BrO/ClO: below 30 km  BrO/NO2: below 40 km  Cl/ClO: above 30 km  ClO/ClO: ~20 km altitude  ClO/NOx: ~20-30 km altitude

53. IV/53 NOx cycle NOx cycle:  NO/NO2: 30-50 km  Cl/NO2: 30-35 km

54. IV/54 Summary of catalytic cycles II Summary II:  upper stratosphere / lower mesosphere (> 45 km) ozone destruction by HOx cycles  mid-to upper stratosphere (30-50km): chlorine cycles Cl / ClOx/NOx cycles  lower stratosphere (20-30 km): BrOx cycles (BrO / HO2 and BrO / ClO)  lowermost stratosphere (< 20km): OH / HO2, BrO / HO2  bromine cycles are important for ozone loss in the lower stratosphere: important for total ozone !

55. IV/55 IV. Stratospheric ozone chemistry 1.Basic concepts of atmospheric chemistry 2.Ozone chemistry and ozone distribution 3.Sources and distribution of ozone-related species 4.Ozone trends 5.The ozone hole

56. IV/56 Middle atmosphere lifetime Mean age of air calculated by the Bremen 3-dimensional chemistry transport model WinterSummer On average, tropospheric air takes more than 6 years to reach the polar mesosphere this is much longer than the middle-atmosphere life-times of most species

57. IV/57 Middle atmosphere lifetime Mean age of air calculated by the Bremen 3-dimensional chemistry transport model WinterSummer thermospheric source ? release of radicals and stable reservoirs tropospheric source stable reservoirs enter troposphere

58. IV/58 stratospheric nitrogen compounds total inorganic nitrogen:  NOy = (HNO 3 + 2xN 2 O 5 + ClNO 3 + BrNO 3 + HNO 4 + NOx) reactive inorganic nitrogen: NOx = N + NO + NO 2 + NO 3 tropospheric source: N 2 O (anthropogenic, biosphere) thermospheric source: NO (from dissociation of N 2 ) reservoir species: HNO 3 (night-time reservoir N 2 O 5 )

59. IV/59 NOy in the middle atmosphere Mean age of air calculated by the Bremen 3-dimensional chemistry transport model WinterSummer thermospheric source: NO release of NOx formation of HNO3 tropospheric source: N 2 O HNO 3 enters troposphere: precipitation

60. IV/60 Modelling NOy 2 D model results January N 2 O (ppb) N2O long-lived tacer Release of NOx: N 2 O + O( 1 D)  2 NO N 2 O + O( 1 D)  N 2 + O 2 no thermospheric NOx included N + NO  N 2 + O 2 D model results January NOx (ppb)

61. IV/61 Modelling NOy 2 D model results January HNO3 (ppb) HNO3 reservoir gas no thermospheric NOx included N + NO  N 2 + O 2 D model results January NOx (ppb)

62. IV/62 stratospheric hydrogen compounds reactive inorganic hydrogen: HOx = H + OH + HO 2 + H 2 O 2 tropospheric source: CH 4, H 2 O thermospheric source: H reservoir species: H 2 O

63. IV/63 startospheric hydrogen compounds: methane oxidation 2 D model results January CH4 (ppm) methane is a long-lived tracer in the lowermost stratosphere Methane oxidation:  CH 4 + OH  CH 3 + H 2 O

64. IV/64 stratospheric hydrogen compounds: methane oxidation Net reaction:  CH 4 + 2 O 2  CO 2 + 2 H 2 O CH 4 +2H 2 O  const, is conserved during transport (dynamical tracer) Methane is a mesopheric source of CO 2 (IR cooling in a changing climate!) CH 4 CH 2 O HCO CO CO 2 CH 3 CH 3 O 2 CH 3 OOH CH 3 O OH, O( 1 D), Cl O( 1 D) O2O2 OH O, OH OH NO,CH 3 O 2 O2O2 Release of H 2 O formaldehyde methyl radical

65. IV/65 stratospheric hydrogen compounds: total water 2 D model results January CH4 (ppm) 2 D model results January H2O (ppm) Total water: CH 4 +2H 2 O  const overestimated due to model restrictions

66. IV/66 Total water: ascent in the tropics HALOE observations of total water (CH 4 +2H 2 O)  ascent in the tropics White contours: Vertical wind shear (2 m/s /km contour, dashed: negative, solid: positive  Changing wind direction (QBO), descent(!) of wind anomalies upwelling velocity: w* [mm/s] 17 km 30 km Niwano 2003

67. IV/67 HOx partitioning Partitioning of HOx  Bremen 2D model January HOx H OH HO 2 H2O2H2O2

68. IV/68 stratospheric chlorine Total inorganic chlorine: Cly = HCl + ClONO 2 + ClOx Reactive inorganic chlorine: ClOx = Cl + ClO + HOCl + OClO + 2xCl 2 O 2 Reservoirs: HCl, ClONO 2 Sources:  CFCs, HCFCs, CCl 4 (anthropogenic)  CFC-11: CCl 3 F  CFC-12: CCl 2 F 2  HCFC-22: CHClF 2  CH 3 Cl (mainly from the biosphere)

69. IV/69 CFCs: release of Cly CFCs are stable in the lowermost stratosphere, increasing photolysis with height  releasing Cly 2 D model results January CFC-11 (10 -1 ppb) CFC-12 (10 -1 ppb)

70. IV/70 chlorine reservoirs main chlorine reservoirs:  HCl: upper stratosphere and mesosphere  ClONO 2 : lowermost stratosphere 2 D model results January HCl (ppb) ClONO2 (ppb)

71. IV/71 chlorine reservoir and active chlorine active chlorine (gas phase):  near 40 km  mesosphere in polar night 2 D model results January HCl (ppb) ClO (ppb)

72. IV/72 Summary: stratospheric chlorine CFCs, HCFCs HCl, Cl, ClO HCl, ClONO 2 HCl, ClONO 2 HCl, ClO HCl Cl

73. IV/73 stratospheric bromine Total inorganic bromine: Bry = BrONO 2 + HOBr + HBr + BrOx Reactive inorganic bromine: BrOx = BrO + Br Reservoirs: BrONO 2 Sources: CH 3 Br (biosphere), Halons, short-lived bromine compounds  Halon-1211: CBrClF 2  Halon-1301: CBrF 3

74. IV/74 Bromine sources bromine release  halon-1211: ~20 km  halon-1301: ~25 km 2 D model results January halon-1211 (ppt) halon-1301 (ppt)

75. IV/75 bromine compounds HBrHOBr BrOBrONO 2 units: ppt