Physics of the Atmosphere Physik der Atmosphäre WS 2010 Ulrich Platt Institut f. Umweltphysik R. 424

Last Week Sulfur, Nitrogen and halogens form acids in the atmosphere, can lead to acid rain. Sulfur and Iodine reactions can lead to primary particle formation Primary particles are important in the hydrological cycle Halogen radicals (atoms (X) and halogen oxides (XO)) play a role in certain parts of the troposphere (polar and coastal BL, above salt lakes, etc.) The overall role of halogen radicals is unclear to date.

Contents

The Stratospheric Ozone Layer Altitude (km) Concentration, molecules cm -3

Oxygen Species in the Atmosphere

Stratosphere – The Chapman - Cycle This reaction sequence was discovered in the 1920ties by Sidney Chapman, it qualitatively explains the formation of an ozone layer in the stratosphere, the sequnece encompasses the following five reactions: O 2 + h O( 3 P) + O( 3 P)(J c2 ) O( 3 P) + O 2 + M  O 3 + M (R c2 ) O 3 + h O( 3 P) + O 2 ( 3  )(J c3 ) O( 3 P) + O( 3 P) + M  O 2 + M (R c1 ) O( 3 P) + O 3  O 2 + O 2 (R c3 ) J c2 = see next overhead sheet. k c2 = 6   (300/T) 2.3  [M] k c3 = 8  exp(-2060/T) cm 3 Molek -1 s -1 J c3  5  s -1 (only weakly altitude dependent, see diagram) T = absolute Temperature (K)

The O 2 - and O 3 - Photolysis Frequency (J c2, J c3 ), s -1 Altitude (km) Photolysis Frequency, s -1 

The Lifetimes of the „Odd Oxygen Species“(O Y = O + O 3 )

The Chapman Approach (1) (1) Budget for O (short for O( 3 P)): d/dt[O] = 2  j c2  [O 2 ] + j c3  [O 3 ] - 2  k c1  [O] 2  [M] – k c2  [O]  [O 2 ]  [M] – k c3  [O]  [O 3 ] (2) Budget for O 3 : d/dt[O 3 ] = k c2  [O]  [O 2 ]  [M] – J c3  [O 3 ] - k c3  [O]  [O 3 ] (3) Budget for O Y : d/dt[O Y ] = 2  j c2  [O 2 ] - 2  k c1  [O] 2  [M] – 2  k c3  [O]  [O 3 ]

The Chapman Equation (2)

The Chapman Equation (3) = Chapman Equation Derived by Chapman for the first time

Solar Radiation Flux and Absorption Spectra of O 2 and O 3

Absorption in the Atmosphere

Global Distribution of the O 3 Column Density (Pre-Ozone Hole)

Chapman – Ozon and Measurements

Catalytic Ozone Destruction in the Stratosphere X + O 3  XO + O 2 XO + O  X + O 2 net:O + O 3  2O 2 X/XO: „catalyst“ (e.g. OH/HO 2, NO/NO 2, Cl/ClO, Br/BrO) HO X (Bates and Nicolet, 1950) NO X (Crutzen, 1970) ClO X (Stolarski and Cicerone, 1974; Molina and Rowland, 1974) Catalytic desctruction cycles explain difference between measured and calculated O 3 profiles

Hydrogen Chemistry in the Stratosphere Ozone destruction cycles: Mesosphere:H + O 3  OH + O 2 OH + O  H + O 2  O + O 3  2O 2 Upper Strat.:OH + O 3  HO 2 + O 2 HO 2 + O  OH + O 2  O + O 3  2O 2 Lower Strat.:HO 2 + O 3  OH + 2O 2  O 3 + O 3  3O 2

The Cycles of Oxidised Nitrogen in the Stratosphere

In the Stratosphere “Evening NO 2 “ is higher than “Morning NO 2 “ Zenith Scattered Light DOAS measurements on board RV „Polarstern“, Kreher et al., Geophys. Res. Lett. 22,1217–1220, 1995

Relevant Chlorine Catalysed O 3 -Destruction Cycles a) Cl + O 3  ClO + O 2 ClO + O  Cl + O 2 (2.43) Net:O + O 3  2O 2 b) ClO + HO 2  Cl + HOCl +O 2 (2.44) HOCl + h HO + Cl(2.45) O 3 + OH  O 2 + HO 2 (2.46) Net:2O 3  3O 2 c) ClO + NO  Cl + NO 2 (2.47) Net:O + O 3  2O 2 d) ClO + NO 2 +M  ClONO 2 + M(2.48) O 3 + NO  NO 2 + O 2 (2.49) ClONO 2 + h Cl + NO 3 (2.50) NO 3 + h NO + O 2 (2.51) Net:2O 3  3O 2

Primary Sources of Chlorine for the Stratosphere (1999) From: Scientific Assessment of Ozone Depletion 2002, Fig. Q7-1, D. Fahey

Chlorine Chemistry in the Stratosphere Mid-latitude (unperturbed) stratosphere: ClONO 2 :  20% HCl:  80% ClO  1%

Vertical Profiles of CFC-11 and CFC-12 Altitude profiles of CFC-11 (bottom) and CFC-12 (top) [NASA, 1994].

Measurement of Chlorine Gases From Space (Nov. 1994, 35 o -49 o N) From: Scientific Assessment of Ozone Depletion 2002, Table Q8-2, D. Fahey

Vertical Profiles of Chlorine Source Gases (CFC's), Reservoir Species (HCl, ClONO 2 ), and Reactive Species (Cl, ClO, …) in the Stratosphere

Atmospheric lifetimes, emissions, and Ozone Depletion Potentials of halogen source gases. From: Scientific Assessment of Ozone Depletion 2002, Table Q7-1, D. Fahey

Relevant Bromine Catalysed O 3 -Destruction Cycles a)BrO + O  Br + O 2 (2.52) Br + O 3  BrO + O 2 Net:O + O 3  2O 2 b) BrO + BrO  Br + Br + O 2 (2.53) 2(Br + O 3  BrO + O 2 ) (2.54) Net:2O 3  3O 2 The BrO-BrO self reaction leads also to the products Br 2 + O 2. Br 2 can be photolysed to 2Br which also closes the cycle. c) BrO + ClO  Br + ClOO (2.55) ClOO + M  Cl + M + O 2 (2.56) Cl + O 3  ClO + O 2 (2.57) Net:2O 3  3O 2 The BrO-ClO reaction (McElroy mechanism) also leads to the products:  Br + OClO (  30%) (2.55b)  BrCl + O 2 (  10%) (2.55c)

Bromine Chemistry in the Stratosphere

Primary Sources of Bromine for the Stratosphere (1999) From: Scientific Assessment of Ozone Depletion 2002, Fig. Q7-1, D. Fahey

Measured Stratospheric BrO Profiles Comparison of measured BrO profiles by different measurement techniques retrieved under different geophysical conditions at different times [Harder et al. 1998]. Also two model profiles [Chipperfield, 1999] are shown for the balloon-borne DOAS measurement flights at León (Spain) in Nov and at Kiruna (North-Sweden) in Feb From: Pfeilsticker et al.

Temporal evolution of daytime ClO Temporal evolution of daytime ClO as measured by MLS (triangles) and modelled by SLIMCAT (solid line) at 4.6 hPa (  36 km). The straight lines represent the linear trend fitted to the two data sets [Ricaud et al., 1997].

Stratospheric Cl-Burden Predicted future atmospheric burden of chlorine (adapted from Brasseur [1995]).

Evolution of Global, Total Ozone Deseasonalized, area-weighted seasonal (3-month average) total ozone deviations, estimated from five different global datasets. Each dataset was deseasonalized with respect to the period , and deviations are expressed as percentages of the ground-based time average for the period Results are shown for the region 60°S-60°N (top) and the entire globe (90°S- 90°N) (bottom). The different satellite datasets cover , and the ground-based data extend back to TOMS, Total Ozone Mapping Spectrometer; SBUV, Solar Backscatter Ultraviolet; NIWA, National Institute of Water and Atmospheric Research (New Zealand). Adapted from Fioletov et al. (2002). From: Scientific Assessment of Ozone Depletion 2002, Figure 4-2

Evolution of Mid- Latitude (35 o -60 o ) Total Ozone Deseasonalized, area-weighted total ozone deviations for the midlatitude regions of 35°N-60°N (top) and 35°S- 60°S (bottom) (as in Figure 4-6), but smoothed by four passes of a 13- point running mean. Adapted from Fioletov et al. (2002). From: Scientific Assessment of Ozone Depletion 2002, Figure 4-7

The Global Ozone Trend Meridional cross section of ozone profile trends derived from the combined SAGE I ( ) and SAGE II ( ) datasets. Trends were calculated in percent per decade, relative to the overall time average. Shading indicates that the trends are statistically insignificant at the 2s (95%) level. Updated from H.J. Wang et al. (2002). From: Scientific Assessment of Ozone Depletion 2002, Fig. 4-9

Stratospheric Aerosol Multiyear time series of stratospheric aerosols measured by lidar (694.3 nm) at Garmisch (47.5°N, 11.1°E) in Southern Germany (red curve) and zonally averaged SAGE II stratospheric aerosol optical depth (1020 nm) in the latitude band 40°N-50°N (black curve). Vertical arrows show major volcanic eruptions. Lidar data are given as particle backscatter integrated from 1 km above the tropopause to the top of the aerosol layer. The curve referring to SAGE II data was calculated as optical depth divided by 40. For reference, the 1979 level is shown as a dashed line. Data from Garmisch provided courtesy of H. Jäger (IFU, Germany). From: Scientific Assessment of Ozone Depletion 2002, Fig. 4-18

Global Ozone, Volcanic Eruptions, and the Solar Cycle From: Scientific Assessment of Ozone Depletion 2002, Fig. Q14-1, D. Fahey

One of the first observations of the Ozone Hole Observations of total ozone at Halley, Antarctica [Farman et al., 1986; Jones and Shanklin, 1995].

The Antarctic Ozone Hole in 1986 and 1997 Comparison of Ozone profiles at the South Pole for the month of October in different years. The ozone concentrations of the late 1960s and early 1970 are much higher than those of 1986 and 1997 [Solomon, 1998].

Summary The „oxygen only“ chemistry of the „Chapman Cycle“ gives a good semi-quantitative explanation of the ozone layer (and an analytical expression of the O 3 concentration as a function of altitude) A closer look reveals that actually strat. ozone levels are about a factor of 3 smaller than predicted by Chapman chemistry A series of reactions involving HO X, NO X, CLO X, and BrO X chemistry catalyse the O+O 3  2O 2 reaction and thus bring theory and observation in agreement.