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Physics of the Atmosphere Physik der Atmosphäre. WS 2010 Ulrich Platt Institut f. Umweltphysik R. 424 Ulrich.Platt@iup.uni-heidelberg.de. Last Week. Sulfur, Nitrogen and halogens form acids in the atmosphere, can lead to acid rain.

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Physics of the Atmosphere Physik der Atmosphäre

WS 2010

Ulrich Platt

Institut f. Umweltphysik

R. 424

Ulrich.Platt@iup.uni-heidelberg.de

last week
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.

the stratospheric ozone layer

Altitude (km)

Concentration, molecules cm-3

The Stratospheric Ozone Layer
stratosphere the chapman cycle
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)

the chapman approach 1
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]
the chapman equation 3
The Chapman Equation (3)

Derived by Chapman for the first time

= Chapman Equation

catalytic ozone destruction in the stratosphere
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

hydrogen chemistry in the stratosphere
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

in the stratosphere evening no 2 is higher than morning no 2
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

relevant chlorine catalysed o 3 destruction cycles
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

primary sources of chlorine for the stratosphere 1999
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
Chlorine Chemistry in the Stratosphere

Mid-latitude (unperturbed) stratosphere:

ClONO2:  20%HCl:  80%ClO 1%

vertical profiles of cfc 11 and cfc 12
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
Measurement of Chlorine Gases From Space (Nov. 1994, 35o-49oN)

From: Scientific Assessment of Ozone Depletion 2002, Table Q8-2, D. Fahey

slide25

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

atmospheric lifetimes emissions and ozone depletion potentials of halogen source gases
Atmospheric lifetimes, emissions,and Ozone Depletion Potentials of halogensource gases.

From: Scientific Assessment of Ozone Depletion 2002, Table Q7-1, D. Fahey

relevant bromine catalysed o 3 destruction cycles
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)

primary sources of bromine for the stratosphere 1999
Primary Sources of Bromine for the Stratosphere (1999)

From: Scientific Assessment of Ozone Depletion 2002, Fig. Q7-1, D. Fahey

measured stratospheric bro profiles
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.

temporal evolution of daytime clo 1991 1997
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].

stratospheric cl burden 1960 2080
Stratospheric Cl-Burden 1960-2080

Predicted future atmospheric burden of chlorine (adapted from Brasseur [1995]).

evolution of global total ozone
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

evolution of mid latitude 35 o 60 o total ozone
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

the global ozone trend
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

stratospheric aerosol 1976 2000
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

global ozone volcanic eruptions and the solar cycle
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
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
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
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.