Physics of the Atmosphere Physik der Atmosphäre

1. Physics of the Atmosphere Physik der Atmosphäre WS 2010 Ulrich Platt Institut f. Umweltphysik R. 424 Ulrich.Platt@iup.uni-heidelberg.de

2. 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.

3. Contents

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

5. Oxygen Species in the Atmosphere

6. 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: O2 + h O(3P) + O(3P) (Jc2) O(3P) + O2 + M  O3 + M (Rc2) O3 + h O(3P) + O2 (3) (Jc3) O(3P) + O(3P) + M  O2 + M (Rc1) O(3P) + O3 O2 + O2 (Rc3) Jc2 = see next overhead sheet. kc2 = 6  10-34 (300/T)2.3 [M] kc3 = 8  10-12 exp(-2060/T) cm3Molek-1s-1 Jc3 5  10-4 s-1 (only weakly altitude dependent, see diagram) T = absolute Temperature (K)

7. Altitude (km) Photolysis Frequency, s-1  The O2- and O3- Photolysis Frequency (Jc2,Jc3), s-1

8. The Lifetimes of the „Odd Oxygen Species“(OY = O + O3)

9. The Chapman Approach (1) • (1) Budget for O (short for O(3P)): • d/dt[O] = 2jc2[O2] + jc3[O3] - 2kc1[O]2[M] – kc2[O][O2][M] – kc3[O][O3] • (2) Budget for O3: • d/dt[O3] = kc2[O][O2][M] – Jc3[O3] - kc3[O][O3] • (3) Budget forOY: • d/dt[OY] = 2jc2[O2] - 2kc1[O]2[M] – 2kc3[O][O3]

10. The Chapman Equation (2)

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

12. Solar Radiation Flux and Absorption Spectra of O2 and O3

13. Absorption in the Atmosphere

14. Global Distribution of the O3 Column Density (Pre-Ozone Hole)

15. Chapman – Ozon and Measurements

16. Catalytic Ozone Destruction in the Stratosphere X + O3 XO + O2 XO + O  X + O2 net: O + O3 2O2 X/XO: „catalyst“ (e.g. OH/HO2, NO/NO2, Cl/ClO, Br/BrO) HOX (Bates and Nicolet, 1950) NOX (Crutzen, 1970) ClOX (Stolarski and Cicerone, 1974; Molina and Rowland, 1974) Catalytic desctruction cyclesexplain difference between measured and calculated O3 profiles

17. Hydrogen Chemistry in the Stratosphere Ozone destruction cycles: Mesosphere: H + O3 OH + O2 OH + O  H + O2  O + O3  2O2 Upper Strat.:OH + O3 HO2 + O2 HO2 + O  OH + O2 O + O3  2O2 Lower Strat.: HO2 + O3  OH + 2O2 O3 + O3  3O2

18. The Cycles of Oxidised Nitrogen in the Stratosphere

19. In the Stratosphere “Evening NO2“ is higher than “Morning NO2“ Zenith Scattered Light DOAS measurements on board RV „Polarstern“, Kreher et al., Geophys. Res. Lett. 22,1217–1220, 1995

20. Relevant Chlorine Catalysed O3-Destruction Cycles a) Cl + O3 ClO + O2 ClO + O  Cl + O2 (2.43) Net: O + O3 2O2 b) ClO + HO2 Cl + HOCl +O2 (2.44) HOCl + h HO + Cl (2.45)  O3 + OH  O2 + HO2 (2.46) Net: 2O3 3O2 c) ClO + NO  Cl + NO2 (2.47) Net: O + O3 2O2 d) ClO + NO2 +M  ClONO2 + M (2.48) O3 + NO  NO2 + O2 (2.49) ClONO2 + h Cl + NO3 (2.50) NO3 + h NO + O2 (2.51) Net: 2O3 3O2

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

22. Chlorine Chemistry in the Stratosphere Mid-latitude (unperturbed) stratosphere: ClONO2:  20%HCl:  80%ClO 1%

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

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

25. Vertical Profiles of Chlorine Source Gases (CFC's), Reservoir Species (HCl, ClONO2), and Reactive Species (Cl, ClO, …) in the Stratosphere

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

27. Relevant Bromine Catalysed O3-Destruction Cycles a) BrO + O  Br + O2 (2.52) Br + O3 BrO + O2Net: O + O3 2O2 b) BrO + BrO  Br + Br + O2 (2.53) 2(Br + O3 BrO + O2) (2.54)Net: 2O3 3O2 The BrO-BrO self reaction leads also to the products Br2 + O2. Br2 can be photolysed to 2Br which also closes the cycle. c) BrO + ClO  Br + ClOO (2.55) ClOO + M  Cl + M + O2 (2.56) Cl + O3 ClO + O2 (2.57)Net: 2O3 3O2 The BrO-ClO reaction (McElroy mechanism) also leads to the products:  Br + OClO (30%) (2.55b) BrCl + O2 (10%) (2.55c)

28. Bromine Chemistry in the Stratosphere

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

30. 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. 1996 and at Kiruna (North-Sweden) in Feb. 1997. From: Pfeilsticker et al.

31. Temporal evolution of daytime ClO 1991-1997 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].

32. Stratospheric Cl-Burden 1960-2080 Predicted future atmospheric burden of chlorine (adapted from Brasseur [1995]).

33. 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 1979-1987, and deviations are expressed as percentages of the ground-based time average for the period 1964-1980. 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 1979-2001, and the ground-based data extend back to 1964. 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

34. Evolution of Mid-Latitude (35o-60o) 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

35. The Global Ozone Trend Meridional cross section of ozone profile trends derived from the combined SAGE I (1979-1981) and SAGE II (1984-2000) 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

36. Stratospheric Aerosol 1976-2000 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

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

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

39. 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].

40. 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 O3 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 HOX, NOX, CLOX ,and BrOX chemistry catalyse the O+O3  2O2reaction and thus bring theory and observation in agreement.