History of Ozone• Discovered in 1840 by Christian Friedrich

Schönbein .

• In the 1920’s Gordon Dobson made the first O3 column measurements.

1 DU = 1x10-3m thick layer of pure ozone at standard temperature and pressure.

• In 1930 Sydney Chapman proposed a mechanism for ozone in the stratosphere.

The Stratosphere

from: http://okfirst.ocs.ou.edu/train/meteorology/graphics/VertTP.gif

Ozone in the Stratosphere• Shields the surface of the Earth from

harmful UV radiation.

From: http://www.atmosphere.mpg.de/enid/208.html

Ozone in the Stratosphere

From: Jacob

The Chapman Mechanism

2k

3

2320nmhJ

3

3k

2

240nmhJ2

O2OO 4.

OOhO 3.

MOOO 2.

OO hO 1.

4

3O

2

2O

M

The Chapman Mechanism

From: Jacob

The Chapman Mechanism

O2 O O3(1)

slow

(4)slow

(2)fast(3)

The Ox Family

• Reaction 1: Production of Ox

• Reaction 4: Loss of Ox

OO hO 240nmh2

23 O2OO

The Chapman Mechanism

]O][O[k]O[J-M]][O][O[k]O[

]O][O[k-M]][O][O[k]O[J]O[J2O][

343O223

34223O2O

3

32

dtd

dtd

M]][[OkJ

][O[O]

M]][O][O[k]O[J

22

O

3

223O

3

3

Assuming steady-state for either O or O3:

The Chapman Mechanism

1M]][[Ok

J][O

[O]

22

O

3

3

Everywhere in the stratosphere

]O[][O][OO][ x33

O3 in the Stratosphere

O][2k]O[J2

][O

0]O][O[2k-]O[J2]O[

4

2O3

342Ox

2

2

dt

d

Derive an expression for the steady-stateof O3 in the stratosphere:

Find steady-state for O

O3 in the Stratosphere

]O[kJ

M][kJ]O[

]O[kJM]][O[k]O[J

]O[

M]][[Ok][OJ

O][

M]][O][O[k]O[J

2

21

4O

2O3

34O

222O3

22

3O

223O

3

2

3

2

3

3

O3 in the Stratosphere

From: Jacob

Catalytic Ozone Destruction

223

2

23

OOOO :net

OXOXO

OXOO X

X is a catalyst and may be:X = H, OH, NO, Cl, or Br

The HOx Family in the Stratosphere

• Source: Water vapor

• Source: methane, H2

z

T

cold trap, T≈190KPH2O≈2.5x10-4 torr at 75mbar (3.5ppmv)

tropopause

stratosphere

troposphere

ppmv5.0 OHO21H

1.7ppmv OH2COO2 CH

222

2224

The HOx Family in the Stratosphere

OH2OHD)O(

D)O(P)O(hO

OD)O(hO

21

13180nm2

21320nm

3

Catalytic Ozone Destruction (HOx)

223

2

23

OOOO :net

OHOOH

OOHO H

223

22

223

OOOO :net

OOHOHO

OHOO OH

2

22

22

2

OOO :net

OOHOHO

MHOMOH

OHO OH

233

2232

223

3OOO :net

OOOHOHO

OHOO OH

Catalytic Ozone Destruction (HOx)

223

2

23

OOOO :net

OXOXO

OXOO X

233

223

23

3OOO :net

OOXOXO

OXOO X

Cycle I Cycle II

•Cycle I: important at higher z and only during the day

•Cycle II: important at lower z and also at night

Catalytic Ozone Destruction (HOx)

• Termination occurs when:

• H2O and HNO3 may mix back to the troposphere and be removed.

• However:

32

222

HNONO OH

OOHHO OH

23

12

NOOHhHNO

OH2 D)O(OH

The NOx Family in the Stratosphere

• Source: N2O

• Source: Direct emissions of NO to the stratosphere

2NOD)O( ON

OND)O( ON

ND)O(h ON

12

221

2

21

2

only about 5%

Catalytic Ozone Destruction (NOx)

223

22

223

OOOO :net

ONOONO

ONOO NO

23

23

2332

223

3O2O :net

ONOhNO

ONOONO

ONOO NO

Active in the daytime-reaction scheme should look familiar?!

Active in the day or night-a little different than cycle II

To complete the catalyticcycle in the daytime

Null Cycles

OOhO :net

ONOhNO

ONOO NO

23

2

223

Ox Ox

‘Null cycles’ do not lead to the formation or destruction of O3.

-ties up reactive species (in this case, NOx) reducing their ability to destroy ozone.

OOhO :net

ONOhNO

OHNONOHO

OHOO OH

23

2

22

223

Catalytic Ozone Destruction

• Cycles may be ‘short-circuited’ through competing reactions:

ONOhNO

ONOONO

2

22

Leads to O3 destruction

Leads to null cycle

Catalytic Ozone Destruction (NOx)

• Termination of catalytic cycles occur when:

• However:

MONMNO NO

MHNOMNO OH

5223

32

3(s)(s)252

3252

23

2HNOOHON

NONOhON

NOOHhHNO

Reservoirs• For NOx:

– HNO3, and N2O5 are reservoirs of NOx

– NOy = NOx + reservoirs

– NOx/NOy gives us an idea of how effective NOx is at destroying ozone.

• For HOx:– H2O and HNO3 are reservoirs of HOx

– HOy = HOx + reservoirs

– HOx/HOy gives us an idea of how effective HOx is at destroying ozone.

Mixed Cycles• The HOx and NOx cycles are coupled:

323

23

32

22

NOOHOHHNO

NOOHhHNO

MHNOMNOOH

OHNONOHO

An increase of stratospheric HOx causes a decreasein the effectiveness of NOx towards destroying O3.

Transport in the Stratosphere

From: http://www-as.harvard.edu/people/faculty/djj/book/powerpoints/

Global Ozone Distribution

From: http:woudc.ec.gc.ca/e/ozone/Curr_allmap_g.htm

Global Ozone Distribution

From: http:woudc.ec.gc.ca/e/ozone/Curr_allmap_g.htm

Tropospheric NOx and HOx

versusStratospheric NOx and HOx

• In the troposphere (ozone production):

• In the stratosphere (ozone destruction):

ONOhNO

NOOONO

OHNONOHO

HCOCOOH

2

223

22

2

HOx

NOx

22

223

232

223

ONOONO

NOOONO

O2OHOHO

OHOOOH

HOx

NOx

The troposphere has extremely low atomic oxygen concentrations.

The stratosphere has high ozone and atomic oxygen concentrations relative to the troposphere.