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

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

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

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

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

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

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

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

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

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

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

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)

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

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

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

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

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

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

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 = nm

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

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

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

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

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)

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

IV/26 Partitioning of family members

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,

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)

IV/29 Odd oxygen noon daytime: h < 50 km: Ox  O 3 h > 70 km: Ox  O h = 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

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

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

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

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

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

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

IV/36 meridional circulation

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

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!)

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)

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

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

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

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

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 km, polar region) was linked to stratospheric chlorine not before the 1980s

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

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“

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

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

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

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

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

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

IV/53 NOx cycle NOx cycle:  NO/NO2: km  Cl/NO2: km

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 !

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

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

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

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 )

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

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)

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)

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

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

IV/64 stratospheric hydrogen compounds: methane oxidation Net reaction:  CH O 2  CO 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

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

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

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

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)

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)

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)

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)

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

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

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)

IV/75 bromine compounds HBrHOBr BrOBrONO 2 units: ppt