# E X E C U TI V E 

# S U M M A R Y

WM O / U N E P

“ S CIE N TI FI C 

# A SS ES S ME N T OF 

# O Z O NE



# D EP L ET IO N 

# : 2 0 0 6 ”

P R EP A R E D B Y T H E

S C I E N T I F I C A S S ES S M EN T P A N EL

O F T H E

M O N T R E A L P R O T O C O L O N S U BS T A N C ES

TH A T D EP L ETE TH E O Z O N E L A Y ER

**************************

C on t e n t s

I nt r oduc t i on

.............................. ............... .......................................... 1

F i gur e 1: O z one

- D e pl e t i ng S ubs t a nc e s

, t he O z one L a ye r

, a n d U V R a di a t i on:

P a s t

, P r e s e nt

, a nd F ut ur e

R e c e nt M a j or F i ndi ngs a nd C ur r e nt S c i e nt i f i c U nde r s t a ndi ng

............................ . 2

O z one

- D e pl e t i ng S ubs t a nc e s

O z one

, U l t r a vi ol e t R a di a t i on

, a n d O t he r R e l a t e d C ha nge s t o D a t e

T he F ut ur e of t he O z one L a ye r a nd S ur f a c e U V R a di a t i on

A ddi t i ona l S c i e nt i f i c E vi de nc e a nd R e l a t e d I nf or m a t i on

...................... . ............. 8

L ong

- L i ve d O z one

- D e pl e t i ng S ubs t a nc e s

H a l oge na t e d V e r y S hor t

- L i ve d S ubs t a nc e s

G l oba l O z one ( 60°S

- 60°N )

P ol a r O z one

I m pa c t of C l i m a t e C ha nge

T he O z one L a ye r i n t he 21 s t C e nt ur y

U V R a di a t i on a nd I t s C ha nge s

O z one D e pl e t i on P ot e nt i a l s a nd G l oba l W a r m i ng P ot e nt i a l s

I m pl i c a t i ons f or P ol i c y F or m ul a t i on

............... ............................................. 20

******************* *******

R e l e as e d by W M O an d U N

E

P on 1 8 A ugus t 2006E x e c u t i v e S u m m a r y R e l e a s e d 1 8 A u g u s t 2 0 0 6

S

c i e n t i f

i c A s s e s s m e n t o f O z o n e D e p l e t i o n : 2 0 0 6

1 

## Exe c u t i v e S u mm ar y

S c i e n t i f

i c As s e s s m e n t of O z on e D e p l e t i on : 2 006

T he pr ovi s i ons of t he 1987 M ont r e a l P r ot oc ol on S ubs t a nc e s t ha t D e pl e t e t he O z one L a ye r

i nc l ude t he r e qui r e m e nt t ha t t he P a r t i e s t o t he P r ot oc ol ba s e t he i r f ut u r e de c i s i ons on t he up da t e d

s c i e nt i f i c

, e nvi r onm e nt a l

, t e c hni c a l

, a nd e c onom i c i nf or m a t i on t ha t i s a s s e s s e d t hr ough P a ne l s

dr a w n f r om t he w o r l dw i de e xpe r t c om m uni t i e s

. T o pr ovi de t ha t i nput t o t he de c i s i on

- m a ki ng

pr oc e s s

, a dva nc e s i n s c i e nt i f i c unde r s t a ndi ng w e r e a s s e s s e d by t he S c i e n t i f i c A s s e s s m e nt P a ne l

i n 1989, 1991, 1994, 1998, a nd 2002

. T hi s i n f or m a t i on he l pe d s uppor t di s c us s i ons a m ong t he

P a r t i e s t ha t l e d t o t he s ubs e que nt A m e ndm e nt s a nd A dj us t m e nt s of t he 1987 P r ot oc ol

. T he 2006

S c i e nt i f i c A s s e s s m e nt s um m a r i z e d he r e i s t he s i xt h i n t ha t s e r i e s

. T he i n f or m a t i on c ont a i ne d i n

t hi s E xe c ut i ve S um m a r y i s ba s e d on t he e i ght de t a i l e d c ha pt e r s of t he f ul l r e por t

.

T he pr e vi ous A s s e s s m e nt pr e s e nt e d e vi de nc e t ha t t he t r opos phe r i c a bunda nc e s of m os t

oz one

- de pl e t i ng s ubs t a nc e s

, a s w e l l a s of s t r a t os phe r i c c hl or i ne

, w e r e s t a bl e or de c r e a s i ng due t o

a c t i ons t a ke n unde r t he M ont r e a l P r ot oc ol ( s e e s c he m a t i c F i gur e 1a

, b)

, w i t h t he s t r a t os phe r i c

a

bunda nc e s s how i ng a t i m e l a g due t o t he t i m e f or s ur f a c e e m i s s i ons t o r e a c h t he s t r a t os phe r e

. B a s e d on t he s e f a c t s

, i t w a s s t a t e d t ha t “ T he M ont r e a l P r ot oc ol i s w o r ki ng, a nd t he oz one

- l a ye r

de pl e t i on f r om t he P r ot oc ol ’ s c ont r o l l e d s ubs t a nc e s i s e xpe c t e d t o be gi n t o a m e l i or a t e w i t h i n t he

ne xt de c a de or s o. ”E x e c u t i v e S u m m a r y R e l e a s e d 1 8 A u g u s t 2 0 0 6

S

c i e n t i f

i c A s s e s s m e n t o f O z o n e D e p l e t i o n : 2 0 0 6

2 A n i m por t a nt ne xt s t e p i s t o a s k w he t he r s t r a t os ph e r i c oz one a nd s ur f a c e ul t r a vi ol e t ( U V )

r a di a t i on a r e r e s pondi ng a s e xpe c t e d t o t he c ont r ol s on oz one

- de pl e t i ng s ubs t a nc e s i m pos e d by

t he P r ot oc ol ( s e e s c he m a t i c F i gur e 1c

, d)

. I n a ddr e s s i ng t hi s que s t i on, i t i s ne c e s s a r y t o c ons i de r

f

a c t or s ot he r t ha n oz one

- de pl e t i ng s ubs t a nc e s t ha t a l s o i nf l ue nc e oz one a nd U V r a di a t i on. T he s e

f

a c t or s i nc l ude na t ur a l dyna m i c a l va r i a bi l i t y

, vol c a ni c e r upt i ons

, s ol a r va r i a t i ons

, a e r os ol s

( a i rbor ne f i ne pa r t i c l e s )

, a nd c l i m a t e c ha nge

.

P r e

- 1980 va l ue s a r e o f t e n us e d a s a be nc hm a r k f or oz one a nd U V r e c ove r y. H ow e ve r

, be c a us e of t he a bove

- m e nt i one d f a c t or s

, i f a nd w h e n oz one a nd U V r a di a t i on r e t u r n t o t he i r pr e

1980 va l ue s w oul d not be a s s oc i a t e d s ol e l y w i t h t h e r e t ur n o f oz one

- de pl e t i ng s ubs t a nc e s t o t he i r

pr e

- 1980 va l ue s ( s e e s c he m a t i c F i gur e 1c

, d )

.

W e a ddr e s s t he be ha vi or of oz one

- de pl e t i ng s ubs t a nc e s

, t he r e s pons e of s t r a t os phe r i c oz one

a nd U V r a di a t i on t o oz one

- de pl e t i ng s ubs t a nc e s a n d ot he r f a c t or s t o da t e

, a nd t he f ut u r e

e vol ut i on of oz one a nd U V r a di a t i on. W e f i r s t p r e s e nt t he m a i n f i ndi ngs

, t he n t he de t a i l e d

s uppor t i ng e vi de nc e

, a nd f i na l l y t he i m pl i c a t i ons f or pol i c y f or m ul a t i on

.

R E C E N T M A J O R F I N D I N G S A N D C U R R E N T S C I E N T I F I C U N D E R S T A N D I N G

S i nc e t he Sc i e nt i f

i c A s s e s s m e nt of O z one D e pl e t i o n: 2002

, num e r ous l a bor a t o r y

i nve s t i ga t i ons

, a t m os phe r i c obs e r va t i ons

, a nd t he o r e t i c a l a nd m ode l i ng s t udi e s ha ve pr oduc e d

ne w ke y f i ndi ngs a nd ha ve s t r e ngt he ne d t he ove r a l l unde r s t a ndi ng of t he oz one l a ye r a nd i t s

e f

f

e c t on U V r a di a t i on. T he s e a dva nc e s a r e hi ghl i ght e d i n t he f ol l ow i ng s um m a r y of t he c ur r e nt

unde r s t a ndi ng of t he i m pa c t of hum a n a c t i vi t i e s a n d na t ur a l phe nom e na on t he oz one l a ye r

, a s

w e l l a s t he c oupl i ng be t w e e n c l i m a t e c ha nge a nd s t r a t os phe r i c oz one de pl e t i on.

O zo n e

- D e p l e t i n g S u b s t a n c e s

T he pr e vi ous A s s e s s m e nt not e d t ha t t he t r opos phe r i c a bunda nc e s of oz one

- de pl e t i ng ga s e s

w e r e de c l i ni ng, w he r e a s t he s t r a t os phe r i c a bunda nc e s w e r e a t or ne a r t he i r pe a k. N ow w e a s k:

A r e t he t r opos phe r i c a nd s t r a t os phe r i c a bunda nc e s of oz one

- de pl e t i ng ga s e s s how i ng f ur t he r

c ha nge s t ha t c a n be l i nke d t o pol i c y a c t i ons

, a nd h ow a r e t he y e xpe c t e d t o e vol ve i n t he f u

t ur e ?

• T h e t ot al c o m b i n e d ab u n d a n c e s of an t h r op oge n i c oz on e

- d e p l e t i n g gas e s i n t h e

t r op os p h e r e c on t i n u e t o d e c l i n e f r om t h e p e ak v al u e s r e ac h e d i n t h e 1992

- 1994 t i m e

p e r i od

.

− T he s hor t e r

- l i ve d ga s e s ( e

. g.

, m e t hyl c hl or o f or m a nd m e t hyl b r om i de ) c ont i nue t o

pr ovi de m uc h o f t he de c l i ne i n t ot a l c om bi ne d e f f

e c t i ve a bunda nc e s of a nt hr opoge ni c

c hl or i ne

- c ont a i ni ng a nd b r om i ne

- c ont a i ni ng oz one

- de pl e t i ng ga s e s i n t he t r opos phe r e

. T he e a r l y r e m ova l of t he s hor t e r

- l i ve d ga s e s m e a ns t ha t l a t e r de c r e a s e s i n oz one

de pl e t i ng s ubs t a nc e s w i l l l i ke l y be dom i na t e d by t he a t m os phe r i c r e m ova l o f t he l onge r

l i ve d ga s e s

.E x e c u t i v e S u m m a r y R e l e a s e d 1 8 A u g u s t 2 0 0 6

S

c i e n t i f

i c A s s e s s m e n t o f O z o n e D e p l e t i o n : 2 0 0 6

3 − B y 2005, t he t ot a l c om bi ne d a bunda nc e of a nt h r op oge ni c oz one

- de pl e t i ng ga s e s i n t he

t r opos phe r e ha d de c r e a s e d by 8

- 9 % f r om t he pe a k va l ue obs e r ve d i n t he 1992

- 1994 t i m e

pe r i od. T he ove r a l l m a gni t ude of t hi s de c r e a s e i s a t t r i but a bl e t o t he e s t i m a t e d c ha nge s i n

e m i s s i ons a nd i s c ons i s t e nt w i t h t he know n a t m os phe r i c l i f e t i m e s a nd ou r unde r s t a ndi ng

of t r a ns por t pr oc e s s e s

.

− T he t r opos phe r i c a bunda nc e s of hydr oc hl or o f l uor o c a rbons H C F C

- 22,

- 141b

, a nd

- 142b

i nc r e a s e d m uc h l e s s t ha n pr oj e c t e d i n t he pr e vi ous A s s e s s m e nt

. T he i m p l i c a t i on i s t ha t

e m i s s i ons ha ve be e n l ow e r t ha n a nt i c i pa t e d.

− T he s um of br om i ne f r om ha l ons a nd m e t hyl br om i de i n t he t r opos phe r e ha s de c r e a s e d by

3

- 5% s i nc e 1998 be c a us e of de c r e a s e s i n m e t hyl br om i de a bunda nc e

. M e t hyl b r om i de

a

bunda nc e ha s de c r e a s e d by 14% be t w e e n 1997 a n d 2004. T h i s de c r e a s e w a s l a r ge r t ha n

e xpe c t e d a nd s ugge s t s t ha t w he n a nt hr opoge ni c e m i s s i ons of m e t hyl br om i de a r e

r e duc e d, i t s a t m os phe r i c a bunda nc e de c r e a s e s m or e t ha n pr e vi ous l y t hought

.

• T h e c om b i n e d s t r at os p h e r i c a b u n d an c e s of t h e oz on e

- d e p l e t i n g gas e s s h ow a d ow n w ar d

t r e n d f r om t h e i r p e ak va l u e s of t h e l a t e 1990s

, w h i c h i s c on s i s t e n t w i t h s u r f ac e

ob s e r vat i on s of t h e s e gas e s an d a t i m e l ag f or t r an s p or t t o t h e s t r at os p h e r e

.

− M e a s ur e m e nt s of hydr oge n c hl o r i de gi ve a c l e a r s i gna t ur e i n t he s t r a t os phe r e of t he

de c r e a s e i n s t r a t os phe r i c oz on e

- de pl e t i ng ga s e s s i n c e r e a c hi ng t he i r pe a k i n t he l a t e

1990s

.

− S t r a t os phe r i c br om i ne ha s i nc r e a s e d i n l i ne w i t h i t s t r opos phe r i c t r e nds i n pr e c e di ng

ye a r s

. A de c r e a s e i n s t r a t os phe r i c br om i ne ha s not ye t be e n i de nt i f i e d. B r om i ne

c ont i nue s t o pl a y a m a j o r r o l e i n s t r a t os phe r i c oz one de pl e t i on.

• O u r q u an t i t at i ve u n d e r s t an d i n g of h ow h al oge n at e d ve r y s h or t

- l i ve d s u b s t an c e s

c on t r i b u t e t o h a l oge n l e ve l s i n t h e s t r at os p h e r e h as i m p r ove d s i gn i f i c an t l y s i n c e t h e

2002 A s s e s s m e n t

, w i t h b r o m i n at e d ve r y s h or t

- l i ve d s u b s t an c e s b e l i e ve d t o m ak e a

s i gn i f i c an t c on t r i b u t i o n t o t o t al s t r at os p h e r i c b r om i n e an d i t s e f f

e c t o n s t r at os p h e r i c

oz on e

.

− B r om i na t e d ve r y s hor t

- l i ve d s ubs t a nc e s

, ( w hi c h a r e m a i nl y of na t ur a l or i gi n) c ont r i but e

~ 5 pa r t s pe r t r i l l i on ( ppt ) o f br o m i ne ( e s t i m a t e s r a n ge f r om 3 t o 8 ppt ) t o c ur r e nt l e ve l s of

t ot a l s t r a t os phe r i c br om i ne ( w hi c h a r e a bout 18 t o 25 ppt )

. T he s e va l ue s a r e de r i ve d f r om

obs e r va t i ons of t r opos phe r i c b r om i ne s our c e ga s e s a nd br om i ne m onoxi de i n t he

s t r a t os phe r e

, ba s e d on our c ur r e nt u nde r s t a ndi ng o f c he m i c a l t r a ns f or

m a t i ons a nd

t r a ns por t of ve r y s hor t

- l i ve d s ubs t a nc e s t o t he s t r a t os phe r e

.

− C hl or i na t e d ve r y s hor t

- l i ve d s our c e ga s e s

, w hi c h a r e m a i nl y o f a nt hr opoge ni c or i gi n

, ha ve now be e n obs e r ve d a t l e ve l s of a bout 50 ppt i n t he t r op i c a l uppe r t r opos phe r e a nd

c ur r e nt l y m a y be a s m a l l s our c e o f c hl or i ne t o t he s t r a t os phe r e

.

− E vi de nc e s ugge s t s t ha t i odi ne i s c ur r e nt l y m uc h l e s s i m por t a nt t ha n br om i ne a nd c hl or i ne

f

or s t r a t os phe r i c oz one de s t r uc t i on

.E x e c u t i v e S u m m a r y R e l e a s e d 1 8 A u g u s t 2 0 0 6

S

c i e n t i f

i c A s s e s s m e n t o f O z o n e D e p l e t i o n : 2 0 0 6

4 O zo n e

, U l t r a v i o l e t R a d i a t i o n

, a n d O t h e r R e l a t e d C h a n g e s t o D a t e

T he pr e vi ous A s s e s s m e nt not e d t ha t s t r a t os phe r i c oz one de pl e t i on w a s e xpe c t e d t o be gi n t o

r e ve r s e w i t hi n t he ne xt de c a de or s o. N ow w e a s k: A r e t he r e a ny s i gns of t hi s be gi nni ng? H a ve

ot he r f a c t or s i n f l ue nc e d t he be ha vi or of oz one dur i ng t hi s pe r i od? H a s s ur f a c e U V r a di a t i on

r e s ponde d a s a nt i c i pa t e d?

• O u r b as i c u n d e r s t an d i n g t h at an t h r op oge n i c oz on e

- d e p l e t i n g s u b s t an c e s h ave b e e n t h e

p r i n c i p al c au s e of t h e oz on e d e p l e t i on ove r t h e p as t f e w d e c ad e s h as b e e n s t r e n gt h e n e d

. D u r i n g t h e r e c e n t p e r i od of n e ar

- c on s t an t ab u n d an c e s of oz on e

- d e p l e t i n g gas e s ,

var i at i on s i n m e t e or ol ogy h ave b e e n p ar t i c u l ar ly i m p or t a n t i n i n f l u e n c i n g t h e b e h avi or

of oz on e ove r m u c h o f t h e p ol ar an d e xt r ap ol ar ( 60°S

- 60°N ) r e gi on s

.

P O L A R O Z O N E

• S p r i n gt i m e p o l ar oz on e d e p l e t i on c on t i n u e s t o b e s e ve r e i n c ol d s t r at os p h e r i c w i n t e r s

. M e t e or ol ogi c al var i ab i l i t y h as p l aye d a l ar ge r r ol e i n t h e ob s e r ve d var i ab i l i t y i n oz on e ,

ove r b ot h p ol e s , i n t h e p as t f e w ye ar s

.

− L a r ge A nt a r c t i c oz one hol e s c ont i nue t o oc c ur

. T h e s e ve r i t y of A nt a r c t i c oz one de pl e t i on

ha s not c ont i nue d t o i nc r e a s e s i nc e t he l a t e 1990s a nd, s i nc e 2000, oz one l e ve l s ha ve be e n

hi ghe r t ha n i n s om e pr e c e di ng ye a r s

. T he s e r e c e nt c ha nge s

, s e e n t o di f f

e r e nt de gr e e s i n

di f f

e r e nt di a gnos t i c a na l ys e s

, r e s ul t f r om i nc r e a s e d dyna m i c a l a c t i vi t y a nd not f r om

de c r e a s e s i n oz one

- de pl e t i ng s ubs t a nc e s

.

− T he A nt a r c t i c oz one ho l e now i s no t a s s t r ongl y i n f l ue nc e d by m ode r a t e de c r e a s e s i n

oz one

- de pl e t i ng ga s e s

, a nd t he unus ua l l y s m a l l oz one hol e s i n s om e r e c e nt ye a r s ( e

. g.

, 2002 a nd 2004) a r e a t t r i bu t a bl e t o dyna m i c a l c ha n ge s i n t he A nt a r c t i c vo r t e x.

− T he a nom a l ous A nt a r c t i c oz one hol e of 2002 w a s m a ni f e s t e d i n a s m a l l e r oz one

- ho l e

a r e a a nd m uc h s m a l l e r oz one de pl e t i on t ha n i n t he pr e vi ous de c a de

. T hi s a nom a l y w a s

due t o a n unus ua l m a j o r s t r a t os phe r i c s udde n w a r m i ng.

− A r c t i c oz one de pl e t i on e xhi bi t s l a r ge ye a r

- t o

- ye a r va r i a bi l i t y, dr i ve n by m e t e or ol ogi c a l

c ondi t i ons

. O ve r t he pa s t f our de c a de s

, t he s e c ond i t i ons be c a m e m or e c onduc i ve t o

s e ve r e oz one de pl e t i on be c a us e of i nc r e a s i ngl y w i de s pr e a d c ondi t i ons f or t he f or m a t i on

of pol a r s t r a t os phe r i c c l ouds dur i ng t he c ol de s t A r c t i c w i nt e r s

. T hi s c ha nge i s m uc h

l a r ge r t ha n c a n be e xpe c t e d f r om t he d i r e c t r a di a t i v e e f f

e c t of i nc r e a s i ng gr e e nhous e ga s

c onc e nt r a t i ons

. T he r e a s on f or t he c ha nge i s unc l e a r

, a nd i t c oul d be be c a us e of l ong

t e r m na t ur a l va r i a bi l i t y or a n unknow n dyna m i c a l m e c ha ni s m

. T he c ha nge i n

t e m pe r a t ur e c ondi t i ons ha s c ont r i but e d t o l a r ge A r c t i c oz one l os s e s dur i ng s om e w i nt e r s

s i nc e t he m i d

- 1990s

.

− T he A r c t i c w i nt e r 2004/ 2005 w a s e xc e pt i ona l l y c o l d, a nd c he m i c a l oz one l os s w a s

a m ong t he l a r ge s t e ve r di a gnos e d. T he A r c t i c r e m a i ns s us c e pt i bl e t o l a r ge c he m i c a l

oz one l os s

, a nd a l a c k o f unde r s t a ndi ng o f t he l ong

- t e r m c ha nge s i n t he oc c ur r e nc e of

pol a r s t r a t os phe r i c c l ouds l i m i t s ou r a bi l i t y t o pr e d i c t t he f ut u r e e vol ut i on of A r c t i c oz one

a

bunda nc e a nd t o de t e c t t he e a r l y s i gns of r e c ove r y.E x e c u t i v e S u m m a r y R e l e a s e d 1 8 A u g u s t 2 0 0 6

S

c i e n t i f

i c A s s e s s m e n t o f O z o n e D e p l e t i o n : 2 0 0 6

5 − T he r ol e of c he m i c a l r e a c t i ons of c hl o r i ne a nd b r o m i ne i n t he pol a r s t r a t os phe r e i s be t t e r

qua nt i f i e d. I nc l us i on o f t he s e a dva nc e s r e s ul t s i n i m pr ove d a gr e e m e nt be t w e e n t he or y

a nd obs e r va t i on of t he t i m i ng of bot h A r c t i c a nd A nt a r c t i c pol a r oz one l os s

.

G L O B A L O Z O N E ( 60 ° S

- 60 ° N )

• T h e d e c l i n e i n ab u n d a n c e s of e xt r ap ol ar s t r at os p h e r i c oz on e s e e n i n t h e 1990s h as n ot

c on t i n u e d

.

− O z one a bunda nc e s i n t he e xt r a pol a r r e gi ons

, 60 ° S

- 60°N

, ha ve not f ur t he r de c l i ne d i n

r e c e nt ye a r s

. T he m i d l a t i t ude c ol um n ( i

. e

. , ove r he a d) oz one va l ue s f or t he 2002

- 2005

pe r i od w e r e a ppr oxi m a t e l y 3% be l ow pr e

- 1980 va l ue s i n t he N or t he r n H e m i s phe r e a nd

a

ppr oxi m a t e l y 6% i n t he S out he r n H e m i s phe r e

, e s s e nt i a l l y t he s a m e a s i n t he 1998

- 2001

pe r i od.

− T he c ont r i but i on of pol a r oz one de pl e t i on t o m i dl a t i t ude oz one de pl e t i on i s s ubs t a nt i a l ;

t he e xt e nt of t he c ont r i bu t i on i s e s t i m a t e d t o be a b out one

- t hi r d i n t he N or t he r n

H e m i s phe r e a nd one

- ha l f i n t he S ou t he r n H e m i s ph e r e

. T he l a r ge r c ont r i but i on i n t he

S out he r n H e m i s phe r e i s t o be e xpe c t e d, g i ve n t he l a r ge r pol a r oz one de pl e t i on i n t he

A nt a r c t i c r e l a t i ve t o t he A r c t i c r e gi on

, a nd m a y e x pl a i n t he di f f

e r e nc e s i n m a gni t ud e a nd

s e a s ona l i t y of t he l ong

- t e r m oz one c ha nge s i n m i d l a t i t ude s be t w e e n t he t w o he m i s phe r e s

.

− C ha nge s i n t r opos phe r i c a nd s t r a t os phe r i c m e t e or o l ogy a r e pa r t i a l l y r e s pons i bl e f o r t he

obs e r ve d N or t he r n H e m i s phe r e m i dl a t i t ude w i nt e r oz one de c l i ne f r om 1979 t o t he m i d

1990s a nd t he oz one i nc r e a s e t he r e a f t e r

. Q ua nt i f i c a t i on of t he s e dyna m i c a l e f f

e c t s on

l ong

- t e r m t r e nds r a nge s f r o m ~ 20% t o up t o 50%

, de pe ndi ng on t he s t udy. M os t of t he s e dyna m i c a l l y i nduc e d oz one c ha nge s a ppe a r t o oc c ur i n t he l ow e r m os t s t r a t os phe r e

.

− U ppe r s t r a t os phe r i c oz one de c l i ne d be t w e e n 1979 a nd t he m i d

- 1990s

, w i t h t he l a r ge s t

de c r e a s e of a bout 10

- 15% ne a r 40 km ove r m i d l a t i t ude s

, but ha s be e n r e l a t i ve l y c ons t a nt

dur i ng t he l a s t de c a de

. L ow e r s t r a t os phe r i c ( 20

- 25 km ) oz one ove r m i dl a t i t ude s a l s o

s how e d a de c r e a s e of up t o 10% f r om 1979 t o t he m i d

- 1990s a nd ha s be e n r e l a t i ve l y

c ons t a nt t he r e a f t e r

.

− O z one a bunda nc e s i n t he N or t he r n H e m i s phe r e m i dl a t i t ude l ow e r m os t s t r a t os phe r e ( 12

-

15 km ) s how a s t r ong de c r e a s e be t w e e n 1979 a nd t he m i d

- 19 90s

, f ol l ow e d by a n ove r a l l

i nc r e a s e f r om 1996 t o 2004

, gi vi ng no ne t l ong

- t e r m de c r e a s e a t t hi s l e ve l

. T hi s

l ow e r m os t s t r a t os phe r e oz one c ha nge c ont r i but e d s i gni f i c a nt l y t o t he c ol um n oz one

c ha nge dur i ng t he l a s t de c a de

. S ou t he r n H e m i s ph e r e obs e r va t i ons do not s how a s i m i l a r

i nc r e a s e i n t he 12

- 15 km a l t i t ude r a nge s i nc e t he m i d

- 1990s

.

− T ot a l c ol um n oz one ove r t he t r opi c s ( 25°S

- 25°N ) r e m a i ns e s s e nt i a l l y unc ha nge d. T hi s

f i ndi ng i s c ons i s t e nt w i t h t he f i ndi ngs o f t he pr e vi o us A s s e s s m e nt s

.

• O b s e r vat i on s t oge t h e r w i t h m o d e l s t u d i e s s u gge s t t h at t h e e s s e n t i al l y u n c h an ge d

c ol u m n oz on e ab u n d an c e s ave r age d ove r 60° S

- 60 ° N ove r r ou gh l y t h e p as t d e c ad e ar e

r e l at e d t o t h e n e ar c on s t an c y of s t r at os p h e r i c oz on e

- d e p l e t i n g gas e s d u r i n g t h i s p e r i od

.

− T he s l ow i ng of t he de c l i ne a nd l e ve l i ng o f f o f m i d l a t i t ude uppe r s t r a t os phe r i c ( 35

- 45 k m )

oz one ove r t he pa s t de c a de ha ve ve r y l i ke l y be e n d om i na t e d by t he c o r r e s pondi ng

c ha nge s i n s t r a t os phe r i c oz one

- de pl e t i ng ga s e s

.E x e c u t i v e S u m m a r y R e l e a s e d 1 8 A u g u s t 2 0 0 6

S

c i e n t i f

i c A s s e s s m e n t o f O z o n e D e p l e t i o n : 2 0 0 6

6 − O ve r t he pa s t de c a de

, c ha nge s i n s t r a t os phe r i c oz o ne

- de pl e t i ng ga s e s ha ve l i ke l y

c ont r i but e d t o t he s l ow i ng of t he m i dl a t i t ude t ot a l c ol um n oz one de c l i ne a nd t he ge ne r a l

l e ve l i ng of f of oz one a bunda nc e s

. T r a ns por t ha s a l s o pl a ye d a n i m por t a nt r ol e i n oz one

c ha nge s

, pa r t i c ul a r l y i n t he l ow e r m os t s t r a t os phe r e

, m a ki ng a t t r i but i on of c ol um n oz one

c ha nge s t o c ha nge s i n oz one

- de pl e t i ng ga s e s m or e di f f i c ul t t ha n i n t he uppe r s t r a t os phe r e

.

S T R A T O S P H E R I C T E M P E R A T U R E A N D S U R F A C E U V R A D I A T I O N

• T h e s t r at os p h e r i c c ool i n g ob s e r ve d d u r i n g t h e p as t t w o d e c ad e s h as s l ow e d i n r e c e n t

ye ar s

.

− S a t e l l i t e a nd r a di os onde m e a s ur e m e nt s r e ve a l a n o ve r a l l de c r e a s e i n t he gl oba l

- m e a n

l ow e r s t r a t os phe r i c t e m pe r a t ur e of a pp r oxi m a t e l y 0. 5 K / de c a de ove r t he 1979

- 2004

pe r i od, w i t h a s l ow dow n i n t he t e m pe r a t u r e de c l i n e s i nc e t he l a t e 1990s

. T he ov e r a l l

t e m pe r a t ur e de c r e a s e i s punc t ua t e d by t r a ns i e nt w a r m i ngs of t he s t r a t os phe r e a s s oc i a t e d

w i t h t he m a j or vol c a ni c e r upt i ons i n 1982 a nd 199 1. M ode l c a l c ul a t i ons s ugge s t t ha t t he

obs e r ve d oz one l os s i s t he pr e dom i na nt c a us e of t h e gl oba l

- m e a n c ool i ng o bs e r ve d ove r

t hi s pe r i od.

− T he l ow e r s t r a t os phe r i c c ool i ng i s e vi de nt a t a l l l a t i t ude s

, i n pa r t i c ul a r i n bot h t he A r c t i c

a nd A nt a r c t i c w i nt e r / s pr i ng l ow e r s t r a t os phe r e

, but w i t h c ons i de r a bl e i nt e r a nnua l

va r i a bi l i t y i n t hos e r e gi ons

.

− S a t e l l i t e obs e r va t i ons s how l a r ge r c ool i ng t r e nds i n t he uppe r s t r a t os phe r e

, w i t h va l ue s of

1 t o 2 K / de c a de

, but l i t t l e a ddi t i ona l de c l i ne s i nc e t he m i ddl e 1990s

. M ode l c a l c ul a t i ons

s ugge s t t ha t t he uppe r s t r a t os phe r e t r e nds a r e due

, a bout e qua l l y, t o de c r e a s e s i n oz one

a nd i n c r e a s e s i n w e l l

- m i xe d gr e e nhous e ga s e s

.

− T he l ong

- t e r m c ool i ng r a t e o f t he A nt a r c t i c s t r a t os phe r e ha s l i ke w i s e r e duc e d c om pa r e d

w i t h w ha t w a s s e e n by t he t i m e of t he p r e vi ous a s s e s s m e nt

. T he r e ha s be e n l a r ge

va r i a bi l i t y i n A nt a r c t i c t e m pe r a t u r e s i n r e c e nt ye a r s

.

• M e as u r e m e n t s f r om s om e s t at i o n s i n u n p ol l u t e d l oc at i on s i n d i c at e t h at U V i r r ad i an c e

( r ad i at i on l e ve l s ) h as b e e n d e c r e as i n g s i n c e t h e l at e 1990s

, i n ac c or d an c e w i t h ob s e r ve d

oz on e i n c r e as e s

. H ow e ve r , at s om e N or t h e r n H e m i s p h e r e s t at i on s U V i r r ad i an c e i s s t i l l

i n c r e as i n g, as a c on s e q u e n c e of l on g

- t e r m c h a n g e s i n ot h e r f ac t or s t h a t al s o a f f

e c t U V

r ad i at i on

. O ut s i de pol a r r e gi ons

, oz one de pl e t i on ha s be e n r e l a t i ve l y s m a l l

, he nc e

, i n m a ny pl a c e s

, i nc r e a s e s i n U V due t o t hi s de pl e t i on a r e d i f f i c ul t t o s e pa r a t e f r om t he i nc r e a s e s

c a us e d by ot he r f a c t or s

, s uc h a s c ha nge s i n c l oud a nd a e r os ol

. I n s om e unpol l ut e d l oc a t i ons

,

e s pe c i a l l y i n t he S out he r n H e m i s phe r e

, U V i r r a di a nc e ha s be e n de c r e a s i ng i n r e c e nt ye a r s

, a s

e x pe c t e d f r om t he obs e r ve d i nc r e a s e s i n oz one a t t hos e s i t e s

. M ode l c a l c ul a t i ons

i nc or por a t i ng onl y oz one pr oj e c t i ons s how t ha t c l o ud

- f r e e U V i r r a di a nc e w i l l c ont i nue t o

de c r e a s e

, a l t hough ot he r U V

- i nf l ue nc i ng f a c t or s a r e l i ke l y t o c ha nge a t t he s a m e t i m e

.

• I n p ol ar r e gi on s , h i gh U V i r r ad i an c e s l as t i n g f o r a f e w d ays h ave b e e n ob s e r ve d i n

as s oc i at i on w i t h e p i s od e s of l ow t ot al oz on e

. E r yt he m a l ( i

. e

. , s unbur ni ng) i r r a di a nc e

a ve r a ge d ove r s e ve r a l da ys ha s be e n i nc r e a s e d by

~ 70% ove r s ub

- A nt a r c t i c r e gi ons w he n

oz one

- de pl e t e d a i r f r om t he pol a r r e gi o n pa s s e s ove r

. I n A nt a r c t i c a dur i ng O c t obe r

,E x e c u t i v e S u m m a r y R e l e a s e d 1 8 A u g u s t 2 0 0 6

S

c i e n t i f

i c A s s e s s m e n t o f O z o n e D e p l e t i o n : 2 0 0 6

7 i ns t a nt a ne ous e nha nc e m e nt s t ha t c a n e xc e e d a f a c t or of t hr e e ha ve be e n obs e r ve d. O ve r

nor t h e r n E ur ope a nd A l a s ka

, t he obs e r ve d e nha nc e m e nt s w e r e s m a l l e r

.

T h e F u t u r e o f t h e O z o n e L a y e r a n d S u r f a c e U V R a d i a t i o n

T he pr e vi ous ( 2002 ) A s s e s s m e nt not e d t ha t c l i m a t e c ha nge w oul d i nf l ue nc e t he f ut u r e of t he

oz one l a ye r

. N ow w e a s k: H ow ha s our unde r s t a n di ng of t hi s i s s ue pr ogr e s s e d? H ow ha s our

i nc r e a s e d unde r s t a ndi ng l e d t o a n i m pr ove d e s t i m a t e of t he s t a t e of t he f ut u r e oz one l a ye r ?

P r e vi ous A s s e s s m e nt s ha ve r e l i e d he a vi l y on t w o

- di m e ns i ona l m ode l s f or p r oj e c t i ons of

f ut ur e oz one

, a nd t he s e m ode l s a r e us e d a ga i n he r e

. T he 2002 A s s e s s m e nt not e d t he e m e r gi ng

us e of t hr e e

- di m e ns i ona l C he m i s t r y

- C l i m a t e M ode l s ; w e ha ve now us e d t he s e m ode l s

e xt e ns i ve l y i n t hi s c ur r e nt 2006 A s s e s s m e nt

.

• I t i s u n l i k e l y t h a t t ot al oz on e ave r age d ove r t h e r e gi on 60 ° S

- 60°N w i l l d e c r e as e

s i gn i f i c an t l y b e l ow t h e l ow val u e s of t h e 1990s

, b e c au s e t h e ab u n d an c e s of oz on e

d e p l e t i n g s u b s t an c e s h ave p e ak e d an d ar e i n d e c l i n e

. T w o

- di m e ns i ona l m ode l s a nd t hr e e

di m e ns i ona l C he m i s t r y

- C l i m a t e M ode l s s ugge s t t ha t t he m i ni m um t ot a l c ol um n oz one va l ue s

i n t hi s r e gi on ha ve a l r e a dy oc c ur r e d. T hi s c onc l us i on i s c ons i s t e nt w i t h t he obs e r va t i on t ha t

ove r t hi s r e gi on

, oz one ha s not de c l i ne d f u

r t he r i n t he 2002

- 2005 pe r i od

.

• T h e d e c r e as e i n oz on e

- d e p l e t i n g s u b s t an c e s i s t h e d om i n a n t f ac t or i n t h e e xp e c t e d

r e t u r n of oz on e l e ve l s t o p r e

- 1980 val u e s

. C h an ge s i n c l i m at e w i l l i n f l u e n c e i f

, w h e n ,

an d t o w h at e xt e n t oz on e w i l l r e t u r n t o p r e

- 198 0 val u e s i n d i f f

e r e n t r e gi on s

.

− T he c ur r e nt be s t e s t i m a t e i s t ha t gl oba l ( 60°S

- 60 ° N ) oz one w i l l r e t ur n t o p r e

- 1980 l e ve l s

a r ound t he m i ddl e of t he 21s t c e nt ur y

, a t or be f or e t he t i m e w he n s t r a t os phe r i c

a

bunda nc e s of oz one

- de pl e t i ng ga s e s r e t ur n t o pr e

- 1980 l e ve l s

.

− M ode l s i m ul a t i ons s ugge s t t ha t c ha nge s i n c l i m a t e

, s pe c i f i c a l l y t he c ool i ng of t he

s t r a t os phe r e a s s oc i a t e d w i t h i nc r e a s e s i n t he a bund a nc e of c a r bon di oxi de

, m a y ha s t e n t he

r e t ur n of gl oba l c ol um n oz one t o pr e

- 1980 va l ue s by up t o 15 ye a r s

, de pe ndi ng on t he

c l i m a t e

- ga s s c e na r i o us e d. H ow e ve r

, t hi s w oul d n ot be c ons i de r e d a “ r e c ove r y” o f

s t r a t os phe r i c oz one f r om oz one

- de pl e t i ng ga s e s

, b e c a us e pe r c e pt i bl e de pl e t i on due t o

a nt hr opoge ni c oz one

- de pl e t i ng s ubs t a nc e s w i l l s t i l l b e c ont r i but i ng t o t he oz one l e ve l s

.

• T h e A n t ar c t i c oz on e h ol e i s e xp e c t e d t o c on t i n u e f or d e c ad e s

. A n t ar c t i c oz on e

ab u n d an c e s ar e p r oj e c t e d t o r e t u r n t o p r e

- 1980 l e ve l s ar ou n d 2060

- 2075

, r ou gh l y 10

- 25

ye ar s l at e r t h an e s t i m at e d i n t h e 2002 A s s e s s m e n t

. T h e pr oj e c t i on of t hi s l a t e r r e t ur n i s

pr i m a r i l y due t o a be t t e r r e pr e s e nt a t i on of t he t i m e e vol ut i on of oz one

- de pl e t i ng ga s e s i n t he

pol a r r e gi ons

. I n t he ne xt t w o de c a de s

, t he A nt a r c t i c oz one hol e i s not e xpe c t e d t o i m p r ove

s i gni f i c a nt l y.

• L ar ge oz on e l os s e s w i l l l i k e l y c on t i n u e t o oc c u r i n c ol d A r c t i c w i n t e r s d u r i n g t h e n e xt 15

ye ar s

. T he h i gh va r i a bi l i t y i n t he vol um e of pol a r s t r a t os phe r i c c l ouds i n t he s e c ol d w i nt e r s

l i m i t s our a bi l i t y t o pr e di c t t he i r f ut ur e oc c ur r e nc e s

. A c c or di ng t o C he m i s t r y

- C l i m a t e

M ode l s

, A r c t i c oz one l e ve l s a r e e xpe c t e d, on a ve r a ge

, t o r e t ur n t o p r e

- 1980 l e ve l s be f o r e

2050.E x e c u t i v e S u m m a r y R e l e a s e d 1 8 A u g u s t 2 0 0 6

S

c i e n t i f

i c A s s e s s m e n t o f O z o n e D e p l e t i o n : 2 0 0 6

8 • C l i m at e c h an ge w i l l al s o i n f l u e n c e s u r f ac e U V r ad i at i on t h r ou gh c h an ge s i n d u c e d

m ai n l y t o c l ou d s an d t h e ab i l i t y of t h e E ar t h ’ s s u r f ac e t o r e f l e c t l i gh t

. A e r os ol s a nd a i r

pol l ut a nt s a r e a l s o e xpe c t e d t o c ha nge i n t he f ut ur e

. T he s e f a c t or s m a y r e s ul t i n e i t he r

i nc r e a s e s or de c r e a s e s of s ur f a c e U V i r r a di a nc e

, t h r ough a bs or pt i on o r s c a t t e r i ng. A s oz one

de pl e t i on be c om e s s m a l l e r

, t he s e f a c t or s a r e l i ke l y t o do m i na t e f u

t ur e U V r a di a t i on l e ve l s

.

A D D I T I O N A L S C I E N T I F I C E V I D E N C E A N D R E L A T E D I N F O R M A T I O N

F or t he pu r pos e of t hi s r e por t

, oz one

- de pl e t i ng s ubs t a nc e s a r e c ons i de r e d a s be i ng e i t he r

l ong

- l i ve d ( m o r e t ha n 6 m ont hs i n t he a t m os phe r e ) or ve r y s hor t

- l i ve d ( l e s s t ha n 6 m ont hs i n t he

a t m os phe r e )

, a nd t he s e a r e c ons i de r e d i n t he ne xt t w o s e c t i ons

. T he a t m os phe r i c l i f e t i m e

de t e r m i ne s t he l i ke l i hood o f ha l oge ns e m i t t e d i n t h e t r opos phe r e r e a c hi ng t he s t r a t os phe r e a nd s o

be i ng a bl e t o de pl e t e s t r a t os phe r i c oz one

. T he c u m ul a t i ve e f f

e c t i ve a bunda nc e of ha l oge ns i n t he

s t r a t os phe r e i s qua nt i f i e d a s e qui va l e nt e f f

e c t i ve s t r a t os phe r i c c hl or i ne ( E E S C ) 1

.

L o n g

- L i v e d O z o n e

- D e p l e t i n g S u b s t a n c e s

A T M O S P H E R I C T R E N D S

• T h e d e c l i n e i n t h e a b u n d an c e of m e t h yl c h l or of or m an d m e t h yl b r om i d e , w h i c h ar e

s h or t e r l i ve d t h a n c h l or of l u or oc ar b on s ( C F C s )

, c on t r i b u t e d t h e m os t t o t h e d e c l i n e i n

e f

f

e c t i ve e q u i val e n t t r op os p h e r i c c h l or i n e l e ve l s

. B y 2005, t he a bunda nc e s of t he t ot a l

c om bi ne d a nt hr opoge ni c oz one

- de pl e t i ng ga s e s i n t he t r opos p he r e ha d de c r e a s e d by 8

- 9%

f r om t he pe a k va l ue obs e r ve d i n t he 1992

- 1994 t i m e pe r i od. T he t ot a l de c l i ne w a s ~ 120

pa r t s pe r t r i l l i on ( ppt ) be t w e e n 2000 a nd 2004, of w hi c h

~ 60 ppt w a s due t o t he de c l i ne of

m e t hyl c hl or of o r m a nd

~ 45 ppt due t o m e t hyl b r o m i de

. T he C F C s t oge t he r a c c ount e d f or

l e s s t ha n 23 ppt of t he de c l i ne

. T he c ont r i but i on o f hydr oc hl or of l uor oc a r bons ( H C F C s ) w a s

t o a dd 12 pp t

.

• T ot al t r op os p h e r i c c h l or i n e

- c on t ai n i n g c h e m i c a l s ( ap p r oxi m a t e l y 3

. 44 p ar t s p e r b i l l i o n

( p p b ) i n 2004) c on t i n u e d t o d e c r e as e

. R e c e nt de c r e a s e s ( 20 ppt / ye a r or 0. 59% i n

2003

- 2004) ha ve be e n a t a s l i ght l y s l ow e r r a t e t ha n de c r e a s e s i n e a r l i e r ye a r s ( 23 ppt / ye a r or

0. 64% i n 1999

- 2000 ) p r i m a r i l y be c a us e of t he r e duc e d c ont r i but i on f r om m e t hyl c hl o r of or m

. T he de c l i ne s i n t ot a l c hl or i ne ( C l ) du r i ng 2000

- 200 4 w e r e s l i ght l y f a s t e r t ha n p r oj e c t e d f or

t he s e ye a r s i n t he A b s c e na r i o o f t he p r e vi ous ( 200 2) oz one a s s e s s m e nt r e por t ( ba s e l i ne

s c e na r i o f ol l ow i ng t he 1999 B e i j i ng A m e ndm e nt s )

.

− C h l or of l u or oc ar b on s , c on s i s t i n g p r i m ar i l y o f C F C

- 11,

- 12

, an d

- 113

, ac c ou n t e d f or

2. 13 p p b ( ~62 %) o f t ot al C l i n 2004 a n d ac c ou n t e d f or a d e c l i n e o f 9 p p t of C l f r om

1 E q u i v al en t eff ect i v e s t rat o s p h eri c ch l o ri n e ( E E S C)

, a met ri c n o t ed i n t h e p r ev i o u s as s es s m en t

, h as fo u n d

w i d es p re ad u s e

. E E S C i s a g au g e o f t h e o v er al l s t rat o s p h eri c b u rd en o f o zo n e

- d ep l et i n g h al o g en

. It i s

d eri v ed fro m g ro u n d

- b as ed me as u re men t s o f o zo n e

- d e p l et i n g s u b s t an ces

, w i t h co n s i d erat i o n g i v en t o t h e

n u mb er o f ch l o ri n e an d b ro mi n e at o ms i n o zo n e

- d ep l et i n g s u b s t an ces

, t h e rat es at w h i ch d i ffer en t o zo n e

d ep l et i n g s u b s t an ces rel ea s e t h ei r h al o g en o n c e t h ey re ach t h e s t r at o s p h ere, an d t h e h i g h er p er

- at o m

effi ci en cy fo r b ro mi n e rel at i v e t o ch l o ri n e i n d es t ro y i n g o zo n e.E x e c u t i v e S u m m a r y R e l e a s e d 1 8 A u g u s t 2 0 0 6

S

c i e n t i f

i c A s s e s s m e n t o f O z o n e D e p l e t i o n : 2 0 0 6

9 2003

- 2004 ( or n e ar l y h al f o f t h e t o t al C l d e c l i n e i n t h e t r op os p h e r e ove r t h i s p e r i od )

. A t m os phe r i c m i xi ng r a t i os of C F C

- 12

, w hi c h a c c ount f or a bout one

- t hi r d o f t he c ur r e nt

a t m os phe r i c c hl or i ne l oa di ng, ha ve be e n c ons t a nt w i t hi n 1% ( 5 pp t ) s i nc e 2000

, a nd s om e

i n s i t u a nd N or t he r n H e m i s phe r e c ol um n ( i

. e

. , ove r he a d) m e a s ur e m e nt s s how t ha t pe a k

va l ue s w e r e a t t a i ne d i n 2003

. C F C

- 11 m i xi ng r a t i os a r e de c r e a s i ng a t a ppr oxi m a t e l y

0. 8% / ye a r ( 1. 9 ppt / ye a r ) a nd C F C

- 113 m i xi ng r a t i os a r e de c r e a s i ng a t a ppr oxi m a t e l y

1% / ye a r ( 0

. 8 ppt / ye a r )

, w hi c h i s t w i c e a s f a s t a s i n 1999

- 2000.

− H yd r oc h l or of l u or oc ar b on s ( H C F C s )

, w h i c h ar e s u b s t i t u t e s f or C F C s , c on t i n u e t o

i n c r e as e i n t h e a t m os p h e r e

. H C F C s ac c ou n t e d f or 214 p p t

, or 6%

, o f t ot al

t r op os p h e r i c c h l or i n e i n 2004 ve r s u s 180 p p t ( 5 %) of t ot a l C l i n 2000

. H C F C

- 22 i s

t he m os t a bunda nt of t he H C F C s a nd i s c ur r e nt l y ( 2000

- 2004) i nc r e a s i ng a t a r a t e of 4

. 9

ppt / ye a r ( 3

. 2% / ye a r )

. H C F C

- 141b a nd H C F C

- 142 b m i xi ng r a t i os i nc r e a s e d by 1

. 1

ppt / ye a r ( 7

. 6% / ye a r ) a nd 0

. 6 ppt / ye a r ( 4

. 5% / ye a r ) ove r t hi s s a m e pe r i od

, or a t a bout ha l f

t he r a t e s f ound f or t he s e t w o ga s e s i n 1996

- 2000

. T he r a t e s of i nc r e a s e f or a l l t h r e e of

t he s e H C F C c om pounds a r e s i gni f i c a nt l y s l ow e r t h a n pr oj e c t e d i n t he 2002 O z one

A s s e s s m e nt ( 6. 6, 2

. 6, a nd 1

. 6 ppt / ye a r f o r H C F C

- 2 2, H C F C

- 141b, a nd H C F C

- 142b,

r e s pe c t i ve l y)

.

− M e t h yl c h l or of or m h as c on t i n u e d t o d e c r e as e a n d c on t r i b u t e d 13

. 5 p p t ( or m or e

t h an h a l f ) of t h e ove r al l d e c l i n e o b s e r ve d f or t o t al t r op os p h e r i c C l i n 2003

- 2004. I t i s

c ur r e nt l y s t i l l t he l a r ge s t c ont r i but or t o t he de c l i ne i n t r opos phe r i c c hl o r i ne

.

• T h e s t r at os p h e r i c c h l or i n e b u r d e n d e r i ve d f r o m gr ou n d

- b as e d t ot al c ol u m n an d s p ac e

b as e d m e as u r e m e n t s of i n or gan i c c h l or i n e i s n o w i n d e c l i n e

. T hi s i s c ons i s t e nt w i t h t he

de c l i ne i n t r opos phe r i c c hl o r i ne f r om l ong

- l i ve d ha l oc a rbons

. T he bur de n of t ot a l

s t r a t os phe r i c c hl or i ne de r i ve d f r om s a t e l l i t e m e a s ur e m e nt s a gr e e s

, w i t hi n ± 0. 3 ppb ( a bout

12% )

, w i t h t he a m ount s e xpe c t e d f r o m s ur f a c e da t a w he n t he de l a y due t o t r a ns por t i s

c ons i de r e d. T he unc e r t a i nt y i n t hi s bu r de n i s l a r ge r e l a t i ve t o t he e xpe c t e d c hl or i ne

c ont r i but i on f r om s hor t e r

- l i ve d ga s e s

.

• T ot al or gan i c t r op os p h e r i c b r om i n e f r o m h al on s an d m e t h yl b r o m i d e p e ak e d i n ab ou t

1998 at 16

. 5 t o 17 p p t an d h as s i n c e d e c l i n e d b y 0. 6

- 0. 9 p p t ( 3

- 5%)

. T hi s obs e r ve d

de c r e a s e w a s s ol e l y a r e s ul t of de c l i ne s obs e r ve d f or m e t hyl br om i de

. B r o m i ne f r om ha l ons

c ont i nue s t o i nc r e a s e

, but a t s l ow e r r a t e s i n r e c e nt ye a r s ( 0. 1 pp t B r / ye a r i n 2003

- 2004)

.

− A t m os p h e r i c am ou n t s of m e t h yl b r om i d e d e c l i n e d b e gi n n i n g i n 1999, w h e n

i n d u s t r i al p r od u c t i on w as r e d u c e d

. B y m i d

- 200 4, m i xi ng r a t i os ha d de c l i ne d 1. 3 ppt

( 14% ) f r om t he pe a k o f 9

. 2 ppt m e a s ur e d be f o r e 1 999. R e por t e d pr oduc t i on of m e t hyl

br om i de f o r e m i s s i ve us e s de c r e a s e d by 50% dur i n g t hi s s a m e pe r i od.

− B ot h t h e r e c e n t l y ob s e r ve d d e c l i n e a n d t h e 20 t h c e n t u r y i n c r e as e i n f e r r e d f or

at m os p h e r i c m e t h y l b r om i d e w e r e l ar ge r t h a n e xp e c t e d

. A l t hough i ndus t r i a l

e m i s s i ons of m e t hyl br om i de w e r e t hought t o a c c o unt f or 20% ( r a nge 10

- 40% ) of

a t m os phe r i c m e t hyl br om i de dur i ng 1992

- 1998 ( i

. e

. , be f o r e pr oduc t i on w a s r e duc e d)

, obs e r ve d c onc e nt r a t i ons a r e c ons i s t e nt w i t h t hi s f r a c t i on ha vi ng be e n 30% ( r a nge 20

-

40% )

. T hi s s ugge s t s t ha t f um i ga t i on

- r e l a t e d e m i s s i ons c oul d ha ve a s t r onge r i nf l ue nc e

on a t m os phe r i c m e t hyl b r om i de m i x i ng r a t i os t ha n e s t i m a t e d i n pa s t A s s e s s m e nt s

, t houghE x e c u t i v e S u m m a r y R e l e a s e d 1 8 A u g u s t 2 0 0 6

S

c i e n t i f

i c A s s e s s m e n t o f O z o n e D e p l e t i o n : 2 0 0 6

10 unc e r t a i nt i e s i n t he va r i a bi l i t y o f na t ur a l e m i s s i on r a t e s a nd l os s

, a nd i n t he m a gni t ud e of

m e t hyl br om i de ba nke d i n r e c e nt ye a r s

, l i m i t ou r u nde r s t a ndi ng of t hi s s e ns i t i vi t y.

− M i xi n g r at i os c al c u l a t e d f r o m u p d at e d e m i s s i on e s t i m at e s ar e i n good agr e e m e n t

w i t h t h e m e as u r e m e n t s f or H al on

- 1211, b u t t h e y e xc e e d al l t h e H al o n

- 1301

m e as u r e m e n t s s i n c e 1980 b y m or e t h an 10%

. A t m os phe r i c i nc r e a s e s i n H a l on

- 1211

( 0. 06 ppt / ye a r ) i n 2000

- 2004 w e r e a bout ha l f t hos e i n 1996

- 200 0. I t i s c ur r e nt l y unc l e a r

w he t he r H a l on

- 1301 c ont i nue s t o i nc r e a s e

.

E M I S S I O N E S T I M A T E S

• G l ob al e m i s s i on s of C F C

- 11 ( 88 G g/ yr , w h e r e 1 G g = 10 9 gr a m s )

, C F C

- 12 ( 114 G g/ yr )

,

an d C F C

- 113 ( 6 G g/ yr ) i n 2003 w e r e ap p r oxi m a t e l y 25%, 25%, an d 3% o f t h e i r

m axi m u m val u e s ar ou n d 1986

. E m i s s i ons of C F C

- 11, C F C

- 12, a nd C F C

- 113 ha ve a l l

c ont i nue d t o de c r e a s e s i nc e 2000.

• R e gi on al e m i s s i on e s t i m at e s f or C F C s , m e t h y l c h l or of or m , an d c ar b on t e t r ac h l or i d e

h ave b e e n r e p or t e d f or t h e f i r s t t i m e

. D i f f

e r e nc e s be t w e e n de ve l ope d a nd de ve l opi ng

r e gi ons a r e i ndi c a t i ve o f t he d i f f

e r i ng s c he dul e s of pha s e

- out

. H ow e ve r

, t he pa t c hi ne s s i n t he

pr e s e nt c ove r a ge ( e s pe c i a l l y i n de ve l opi ng r e gi ons s uc h a s S out he a s t A s i a ) a nd t he

unc e r t a i nt i e s i n t he r e gi ona l e s t i m a t e s m e a n t ha t us e f ul c om pa r i s ons be t w e e n s um m e d

r e gi ona l e m i s s i ons a nd gl oba l e m i s s i ons de r i ve d f r om t r e nds c a nnot c ur r e nt l y be m a de

. R e gi ona l e m i s s i o n e s t i m a t e s of m e t hyl c hl or of o r m i ndi c a t e t ha t gl oba l e m i s s i ons a f t e r 2000

m a y ha ve be e n r oughl y 22 G g/ ye a r

, w hi c h i s not s t a t i s t i c a l l y di f f

e r e nt f r om t he e s t i m a t e of

12. 9 G g/ ye a r ( f o r 2002) obt a i ne d f r om i ndus t r y/ U n i t e d N a t i ons E nvi r on m e nt P r ogr a m m e

da t a

.

• Wh i l e e m i s s i on s of H C F C

- 22 h ave r e m ai n e d n e ar l y c on s t an t f r om 2000 t o 2004,

e m i s s i on s of H C F C

- 141 b an d H C F C

- 142b d e c r e as e d b y ap p r oxi m a t e l y 15% ove r t h e

s am e p e r i od

.

• H yd r of l u or oc ar b on

- 23 ( H F C

- 23) e m i s s i on s e s t i m at e d f r om a t m os p h e r i c m e as u r e m e n t s

h ave i n c r e as e d f r om a b ou t 6 G g/ yr i n 1990 t o a b ou t 13 G g/ yr i n 2001 ( an i n c r e as e of

ap p r oxi m at e l y 120%)

. T he s e e m i s s i ons a r e a by pr oduc t of H C F C

- 22 pr oduc t i on

. H F C

- 23

m i xi ng r a t i os ( 18 ppt i n 2004 ) ha ve c ont i nue d t o i n c r e a s e

, a t a ppr oxi m a t e l y 0

. 7 ppt / yr ( 4% / yr )

, i n 2001

- 2004.

H a l o g e n a t e d V e r y S h o r t

- L i v e d S u b s t a n c e s

• O b s e r vat i on s s h ow t h at t h e t ot al i n or gan i c b r o m i n e ( B r y ) i n t h e s t r at os p h e r e i s m or e

ab u n d an t t h a n c an b e ac c ou n t e d f or b y t h e s u m of b r om i n e d e l i ve r e d t o t h i s r e gi on b y

“l on g

- l i ve d ” b r om i n at e d s ou r c e gas e s

. V e r y s hor t

- l i ve d s ubs t a nc e s ( V S L S ) a r e de f i ne d a s

t r a c e ga s e s w hos e l oc a l t r opos phe r i c l i f e t i m e s a r e c om pa r a bl e t o or s hor t e r t ha n t r opos phe r i c

t r a ns por t t i m e s c a l e s

, s uc h t ha t t he i r t r opos phe r i c d i s t r i but i ons a r e non

- uni f or m

. H e r e

, V S L S

a r e c o ns i de r e d t o ha ve a t m os phe r i c l i f e t i m e s of l e s s t ha n 6 m ont hs

.E x e c u t i v e S u m m a r y R e l e a s e d 1 8 A u g u s t 2 0 0 6

S

c i e n t i f

i c A s s e s s m e n t o f O z o n e D e p l e t i o n : 2 0 0 6

11 • V ar i ou s l i n e s of e vi d e n c e s h ow t h at b r om i n at e d V S L S c on t r i b u t e ab ou t 5 p p t ( w i t h

e s t i m at e s r an gi n g f r om 3 t o 8 p p t ) t o t ot al s t r at os p h e r i c B r y :

− T he e s t i m a t e of t ot a l s t r a t os phe r i c B r y a bunda nc e e xi s t i ng i n t he l a t e 1990s i s a bout 18

- 25

ppt

. T hi s va l ue i s de r i ve d f r om di f f

e r e nt obs e r va t i ons of br om i ne m onoxi de ( B r O )

. T hi s

i s gr e a t e r t ha n t he 16

- 17 ppt o f br o m i ne de l i ve r e d t o t he s t r a t os phe r e by “ l ong

- l i ve d”

br om i na t e d s our c e ga s e s ( i

. e

. , t he ha l ons a nd m e t h yl br om i de

, C H 3 B r ) dur i ng t hi s pe r i od

.

− M e a s ur e m e nt s of or ga ni c b r om i na t e d ve r y s hor t

- l i ve d s our c e ga s e s i n t he t r opi c a l uppe r

t r opos phe r e a m ount t o a bout 3

. 5 ppt

. C om pounds r e s ul t i ng f r om s our c e ga s de gr a da t i on

a nd ot he r s our c e s of t r opos phe r i c i no r ga ni c br om i ne m a y c ont r i but e c om pa r a bl e

a m ount s

.

• L e ve l s of t ot al s t r at os p h e r i c b r om i n e c on t i n u e t o s h ow e vi d e n c e f or a t r e n d t h a t i s

c on s i s t e n t w i t h t h at of t r op os p h e r i c t o t al b r om i n e

. F ur t he r s t udi e s a r e r e qui r e d t o

de t e r m i ne i f t he r e c e nt de c l i ne i n t r opos phe r i c br o m i ne w i l l be r e f l e c t e d i n s t r a t os phe r i c

br om i ne a bunda nc e

.

• I t i s u n l i k e l y t h a t i o d i n e i s i m p or t an t f or s t r at os p h e r i c oz on e l os s i n t h e p r e s e n t

- d ay

at m os p h e r e

. T he r e i s l i t t l e e vi de nc e f or m e a s ur a bl e i odi ne i n t he f o r m o f i odi ne oxi d e ( I O )

i n t he l ow e r s t r a t os phe r e ( i

. e

. , a bout 0

. 1 pp t )

. T hi s di f f

e r e nc e i n be ha vi or c om pa r e d w i t h

br om i ne m a y be pa r t l y a t t r i but e d t o t he s hor t phot o c he m i c a l l i f e t i m e a nd l ow e r a bunda nc e s

of i odi ne s our c e ga s e s

, a nd a e r os ol upt a ke of i odi n e i n t he s t r a t os phe r e

.

• T h e s u m of t h e c h l or i n e c on t e n t f r om ve r y s h or t

- l i ve d s ou r c e gas e s i n t h e t r op i c al u p p e r

t r op os p h e r e i s n ow e s t i m a t e d t o b e a b ou t 50 p p t

. W hi l e 50 ppt of i nor ga ni c c hl or i ne ( C l

y )

f r om V S L S w oul d r e p r e s e nt onl y 1

- 2 % o f C l

y f r o m l ong

- l i ve d s our c e ga s e s (

~ 3500 ppt )

, i t

w oul d r e pr e s e nt a s i gni f i c a nt c ont r i but i on t o ba c kg r ound C l

y due onl y t o na t ur a l l y oc c ur r i ng

m e t hyl c hl or i de ( 550 ppt )

. T he va l ue o f 100 ppt f o r C l

y f r om s hor t

- l i ve d s pe c i e s i n t he

pr e vi ous A s s e s s m e nt a l s o i nc l ude d a c ont r i but i on of 50 ppt f r om phos ge ne

.

• T h e m aj or i t y of k n ow n b r om i n a t e d an d i od i n at e d ve r y s h or t

- l i ve d s ou r c e gas e s ar e

p r e d om i n an t l y of n at u r al or i gi n an d ar e n e ar l y u n c h an ge d i n t h e p as t f e w d e c ad e s , a s

i ndi c a t e d by f i r n a i r s t udi e s

. S om e ha ve s m a l l a nt hr opoge ni c s our c e s a nd ha ve i nc r e a s e d

s l i ght l y i n t he N or t he r n H e m i s phe r e ( e

. g

. , c e r t a i n b r om i na t e d t r i ha l om e t ha ne s ) a nd a f e w a r e

a l m os t e xc l us i ve l y a nt hr opoge ni c ( not a bl y n

- pr opy l br om i de ( n

- P B ) )

.

• C h l or i n at e d ve r y s h or t

- l i ve d s ou r c e gas e s or i gi n at e l ar ge l y f r o m an t h r op o ge n i c

e m i s s i on s , a l t hough na t ur a l s our c e s a l s o c ont r i bu t e

. T he r e i s e vi de nc e f or s i gni f i c a nt r e c e nt

de c l i ne s i n c onc e nt r a t i ons of s om e c hl or i na t e d ve r y s hor t

- l i ve d s our c e ga s e s

, not a bl y

c hl or of or m

, di c hl or o m e t ha ne

, a nd t e t r a c hl or oe t he n e

.

• T h e r ou t e b y w h i c h V S L S ar e m os t l i k e l y t o r e a c h t h e s t r at os p h e r e i s t r an s p or t ou t o f

t h e b ou n d ar y l aye r b y d e e p c on ve c t i on i n t r op i c al r e gi on s ( p ar t i c u l ar l y i f c o

- l oc at e d

w i t h r e gi on s of h i gh e m i s s i on s ove r t r op i c al oc e an s ) f ol l ow e d b y q u as i

- h or i z on t al

t r an s p or t i n t o t h e l ow e r s t r at os p h e r e

. T he f r a c t i on of s our c e ga s a nd pr oduc t ga s

t r a ns por t e d i nt o t he s t r a t os phe r e a l s o de pe nds on t he l oc a l c he m i c a l l i f e t i m e

, w he r e s our c eE x e c u t i v e S u m m a r y R e l e a s e d 1 8 A u g u s t 2 0 0 6

S

c i e n t i f

i c A s s e s s m e n t o f O z o n e D e p l e t i o n : 2 0 0 6

12 ga s e s de c om pos e

, a nd t he l os s of pr oduc t ga s e s by he t e r oge ne ous pr oc e s s e s i nvol vi ng

a e r os ol s a nd c l ouds

.

G l o b a l O zo n e ( 6 0 °S

- 6 0 °N )

T O T A L C O L U M N O Z O N E

• G l ob al m e an t o t al c ol u m n ( i

. e

. , ove r he a d) oz on e val u e s f or 2002

- 2005 w e r e 3. 5% b e l ow

1964

- 1980 ave r age val u e s

. T he 2002

- 2005 va l ue s a r e s i m i l a r t o t he 1998

- 2001 va l ue s

. T hi s

be ha vi or i s e vi de nt i n a l l a va i l a bl e gl oba l da t a s e t s

, a l t hough di f f

e r e nc e s of up t o 1 % be t w e e n

a nnua l a ve r a ge s e xi s t be t w e e n s om e i ndi vi dua l s e t s

.

• T h e r e ar e d i f f

e r e n c e s b e t w e e n t h e t w o h e m i s p h e r e s i n t h e e vol u t i on o f t ot al c ol u m n

oz on e at m i d l at i t u d e s :

− A ve r a ge d f or t he pe r i od 20 02

- 2005, t ot a l c ol um n o z one f or t he N or t he r n H e m i s phe r e ( N H ) a nd S out he r n H e m i s phe r e ( S H ) m i dl a t i t ude s ( 35 °

- 60 ° ) a r e a bout 3% a nd 5. 5 %

,

r e s pe c t i ve l y, be l ow t he i r 1964

- 1980 a ve r a ge va l ue s a nd a r e s i m i l a r t o t he i r 1998

- 2001

va l ue s

. T he N H s how s a m i ni m um a r ound 1993 f ol l ow e d by a n i nc r e a s e

. T he S H s how s

a n ongoi ng de c r e a s e t hr ough t he l a t e 1990s f ol l ow e d by t he r e c e nt l e ve l i ng of f

.

− T he r e a r e s e a s ona l di f f

e r e nc e s be t w e e n t he N H a nd t he S H i n oz one c ha nge s ove r

m i dl a t i t ude s

. C ha nge s s i nc e t he pr e

- 1980 pe r i od o ve r nor t he r n m i dl a t i t ude s ( 35 ° N

- 60 ° N )

a r e l a r ge r i n s pr i ng

, w he r e a s t hos e ove r s out he r n m i dl a t i t ude s ( 35 ° S

- 60 ° S ) a r e ne a r l y t he

s a m e t hr oughout t he ye a r

.

• T ot al c ol u m n oz on e ove r t h e t r op i c s ( 25 ° S

- 25 ° N ) r e m ai n s e s s e n t i al l y u n c h an ge d

. T he s e

f i ndi ngs a r e c ons i s t e nt w i t h t he f i ndi ngs o f t he pr e vi ous A s s e s s m e nt s

.

V E R T I C A L O Z O N E D I S T R I B U T I O N

• U p p e r s t r at os p h e r i c oz on e d e c l i n e d d u r i n g 1979

- 1995, b u t h as b e e n r e l at i ve l y c on s t an t

d u r i n g t h e l as t d e c ad e

. M e a s ur e m e nt s f r om S t r a t os phe r i c A e r os ol a nd G a s E xpe r i m e n t

( S A G E I + I I ) a nd S ol a r B a c ks c a t t e r U l t r a vi ol e t s pe c t r om e t e r ( S B U V ( / 2) ) s a t e l l i t e i ns t r um e nt s

s how s i gni f i c a nt de c l i ne s t hr ough 1995 w he n a ve r a ge d ove r 60°N

- 60°S a nd a l t i t ude s o f 35 t o

50 km

. T he ne t oz one de c r e a s e w a s ~ 10

- 15% ove r m i dl a t i t ude s w i t h s m a l l e r

, but s i gni f i c a nt

c ha nge s ove r t he t r opi c s

. A va i l a bl e i nde pe nde nt U m ke hr

, l i da r

, a nd m i c r ow a ve oz one

m e a s ur e m e nt s c onf i r m t he s e f i ndi ngs

.

• L ow e r s t r at os p h e r i c oz on e d e c l i n e d ove r t h e p e r i od 1979

- 1995

, b u t h as b e e n r e l at i ve l y

c on s t an t w i t h s i gn i f i c an t va r i ab i l i t y ove r t h e l as t d e c ad e

. A t m i dl a t i t ude s of bot h t he

nor t he r n a nd s out he r n he m i s phe r e s

, m e a s ur e m e nt s by t he S A G E I + I I a nd S B U V ( / 2 ) s a t e l l i t e

i ns t r um e nt s s how e d de c l i ne s of up t o 10% by 1995 be t w e e n 20 a nd 25 km a l t i t ude

. T he s e

de c r e a s e s di d not c o nt i nue i n t he l a s t de c a de

.

• I n t h e l ow e r m os t s t r a t os p h e r e of t h e N or t h e r n H e m i s p h e r e , b e t w e e n 12 an d 15 k m , a

s t r on g d e c r e as e i n oz on e w as ob s e r ve d b e t w e e n 1979 an d 1995

, f ol l ow e d b y an ove r al l

i n c r e as e f r om 1996 t o 2004 l e ad i n g t o n o n e t l on g

- t e r m d e c r e as e at t h i s l e ve l

. T he s e

c ha nge s i n t he l ow e r m os t s t r a t os phe r e ha ve a s ubs t a nt i a l i nf l ue nc e on t he c ol um n. T heE x e c u t i v e S u m m a r y R e l e a s e d 1 8 A u g u s t 2 0 0 6

S

c i e n t i f

i c A s s e s s m e n t o f O z o n e D e p l e t i o n : 2 0 0 6

13 S out he r n H e m i s phe r e m i dl a t i t ude da t a do not s ho w s i m i l a r i nc r e a s e s s i nc e 1995 a t t he s e

a l t i t ude s

.

U N D E R S T A N D I N G P A S T C H A N G E S I N G L O B A L O Z O N E

• T h e r e i s good ove r al l agr e e m e n t b e t w e e n ob s e rve d l on g

- t e r m c h an ge s i n e xt r ap ol ar

oz on e an d m od e l s i m u l at i on s t h at i n c l u d e t h e e f f

e c t s of i n c r e as i n g h al oge n s

. T he m ode l s

ge ne r a l l y r e pr oduc e t he obs e r ve d oz one c ha nge s a s a f unc t i on o f a l t i t ude

, l a t i t ude

, a n d

s e a s on, c onf i r m i ng our unde r s t a ndi ng t ha t ha l oge n c ha nge s a r e t he m a i n d r i ve r of g l oba l

oz one c ha nge s

. T hi s l i nk i s s uppor t e d by t he s t a t i s t i c a l f i t of gl oba l l y a ve r a ge d oz one

obs e r va t i ons w i t h e qui va l e nt e f f

e c t i ve s t r a t os phe r i c c hl or i ne ( E E S C ; s e e f oot not e a t t he

be gi nni ng of t hi s s e c t i on of t he E xe c ut i ve S um m a r y)

. H ow e ve r

, t he r e a r e di s c r e pa nc i e s

be t w e e n t he m ode l e d a nd obs e r ve d c ha nge s

. N ot a bl y, t he m ode l s t e nd t o pe r f o r m l e s s w e l l

i n s i m ul a t i ng c ha nge s i n t he S H c om pa r e d w i t h t he N H

.

• E m p i r i c al an d m od e l s t u d i e s h ave s h ow n t h a t c h an ge s i n t r op os p h e r i c a n d

s t r at os p h e r i c d yn am i c s h ave b e e n p ar t i al l y r e s p on s i b l e f or t h e ob s e r ve d N H

m i d l at i t u d e w i n t e r oz on e d e c l i n e f r om 1979 t o t h e m i d

- 1990s an d t h e oz on e i n c r e as e

t h e r e af t e r

. W he t he r t hi s i s due t o dyn a m i c a l va r i a bi l i t y or r e s ul t s f r o m a l ong

- t e r m t r e nd i n

s t r a t os phe r i c c i r c ul a t i on i s not ye t c l e a r

. E s t i m a t e s of t he s e dyna m i c a l e f f

e c t s on l ong

- t e r m

t r e nds r a nge f r o m ~ 20% up t o 50% f o r t he w i nt e r pe r i od.

• T h e i n c l u s i on of ad d i t i on al i n or gan i c b r om i n e ( B r y ) f r om ve r y s h or t

- l i ve d s u b s t an c e s

( V S L S ) i n m od e l s y i e l d s s i m u l at i on s w i t h l ar ge r oz on e d e s t r u c t i on at m i d l a t i t u d e s an d

p ol ar r e gi on s , c om p ar e d w i t h s t u d i e s i n c l u d i n g on l y l on g

- l i ve d b r o m i n e s ou r c e gas e s

. I n bot h r e gi ons

, t he e nha nc e d oz one l os s oc c ur s i n t he l ow e r s t r a t os phe r e vi a i nt e r a c t i ons of

t hi s br om i ne w i t h a nt hr opoge ni c c hl o r i ne

. M i dl a t i t ude oz one l os s i s m os t e nha nc e d dur i ng

pe r i ods of hi gh a e r os ol l oa di ng. O z one l os s t hr oug h c he m i c a l r e a c t i ons i nvol vi ng br om i ne

a nd odd

- hydr oge n ( H O

x ) i s a l s o e nha nc e d a t m i dl a t i t ude s unde r a l l c ondi t i ons

. T he i m pa c t

on l ong

- t e r m m i dl a t i t ude oz one t r e nds ( 1 980

- 2004 )

, a s s um i ng c ons t a nt V S L S B r y , i s

c a l c ul a t e d t o be s m a l l be c a us e a e r os ol l oa di ng w a s l ow a t t he s t a r t a nd e nd of t hi s t i m e

pe r i od.

• S e ve r al i n d e p e n d e n t m od e l i n g s t u d i e s c on f i r m t h at d i l u t i on of oz on e

- d e p l e t e d p ol ar a i r

m ak e s a s u b s t an t i a l c on t r i b u t i on t o m i d l at i t u d e oz on e d e p l e t i o n , e s p e c i al l y i n t h e

S ou t h e r n H e m i s p h e r e , w h e r e p ol ar oz on e l os s i s m u c h l ar ge r

. L ong

- t e r m a nnua l l y

a ve r a ge d m ode l

- ba s e d e s t i m a t e s i ndi c a t e t ha t a bout one

- t hi r d of t he de pl e t i on i n t he N or t he r n

H e m i s phe r e ( w i t h l a r ge i nt e r a nnua l va r i a t i on ) a nd a bout one

- ha l f i n t he S out he r n

H e m i s phe r e

, r e s ul t s f r om pol a r l os s

. T hi s i s s uppo r t e d by t he obs e r va t i on t ha t pol a r oz one

de pl e t i on i n t he A nt a r c t i c s pr i ng i s s t r ongl y c o r r e l a t e d w i t h s out he r n s um m e r m i dl a t i t ude

oz one de pl e t i on.

• I d e n t i f i c at i on of t h e s ol ar c yc l e s i gn al i n ob s e r ve d oz on e h as b e e n i m p r ove d b e c au s e of

t h e ab s e n c e of m aj or vol c an i c e r u p t i on s ove r t h e p as t 15 ye ar s

. T he de duc e d s ol a r c yc l eE x e c u t i v e S u m m a r y R e l e a s e d 1 8 A u g u s t 2 0 0 6

S

c i e n t i f

i c A s s e s s m e n t o f O z o n e D e p l e t i o n : 2 0 0 6

1 4 va r i a t i on i n c ol um n oz one ha s a m e a n a m pl i t ude o f 2

- 3 % ( f r om m i ni m um t o m a xi m um ) i n

l ow t o m i dl a t i t ude s f r om t he e xt e nde d da t a s e r i e s

.

P o l a r O zo n e

A R C T I C

• A r c t i c s p r i n g t ot al oz on e val u e s ove r t h e l as t d e c ad e ar e l ow e r t h an val u e s ob s e r ve d i n

t h e 1980s

, b u t s om e w h at l ar ge r t h an t h os e i n t h e 1990s ; t h e y ar e h i gh l y var i ab l e

d e p e n d i n g on d yn a m i c al c on d i t i on s

. F o r c ur r e nt ha l oge n l e ve l s

, a nt hr opoge ni c c he m i c a l

l os s a nd va r i a bi l i t y i n oz one t r a ns por t a r e a bout e qua l l y i m por t a nt f or ye a r

- t o

- ye a r A r c t i c

oz one va r i a bi l i t y. L ow e r

- t ha n

- a ve r a ge A r c t i c vor t e x t e m pe r a t ur e s r e s ul t i n l a r ge r ha l oge n

dr i ve n c he m i c a l oz one l os s e s

.

• F or t h e “c ol d e s t ” A r c t i c w i n t e r s , t h e vol u m e of ai r w i t h t e m p e r at u r e s l ow e n ou gh t o

s u p p or t p ol ar s t r at os p h e r i c c l ou d s ( c al l e d “V P S C ”) h as i n c r e as e d s i gn i f i c an t l y s i n c e t h e

l at e 1960s

. T hi s c ha nge i s m uc h l a r ge r t ha n e xpe c t e d f r om t he di r e c t r a di a t i ve e f f

e c t o f

i nc r e a s i ng gr e e nhous e ga s c onc e nt r a t i ons

. T he r e a s on f or t he c ha nge i s not c l e a r

, a nd i t

c oul d be due t o l on g

- t e r m na t ur a l va r i a bi l i t y or a n unknow n dyna m i c a l m e c ha ni s m

.

• C ol u m n oz on e c h e m i c al l os s i n t h e 2004/ 2005 A r c t i c w i n t e r w as am o n g t h e l ar ge s t e ve r

d i agn os e d

. T he 2004/ 2005 A r c t i c s t r a t os phe r e w a s e xc e pt i ona l l y c ol d, pa r t i c ul a r l y a t

a l t i t ude s be l ow 18 km

, l e a di ng t o a va l ue of V P S C 2 5% l a r ge r t ha n t he pr e vi ous r e c or d va l ue

. V a r i ous i nde pe nde nt s t udi e s a nd m e t hods s ugge s t t ha t t he c he m i c a l c ol um n oz one l os s i n

2004/ 2005 w a s a m ong t he l a r ge s t e ve r obs e r ve d.

• T h e c h e m i c al l os s of c ol u m n oz on e f or A r c t i c w i n t e r s e xh i b i t s a n e ar

- l i n e ar r e l at i on

w i t h V P S C d u r i n g e ac h w i n t e r

. A s i m i l a r r e l a t i on be t w e e n oz one l os s a nd V P S C i s now s e e n

f

or t w o i nde pe nde nt a na l ys e s of c he m i c a l oz one l o s s

, i nc r e a s i ng our c onf i de nc e i n t he

r obus t ne s s of t hi s r e l a t i on. O bs e r va t i ons of t he l a r ge A r c t i c oz one l os s i n 2004/ 2005 a r e i n

l i ne w i t h t he r e l a t i ons hi p e s t a bl i s he d f or pr i or w i nt e r s

.

A N T A R C T I C

• L ar ge A n t ar c t i c oz on e h ol e s c on t i n u e t o oc c u r

. T h e s e ve r i t y of A n t ar c t i c oz on e

d e p l e t i on h as n ot c on t i n u e d t o i n c r e as e s i n c e t h e l at e 1990s an d

, s i n c e 2000, oz on e l e ve l s

h ave b e e n h i g h e r i n s om e ye ar s

. T he s e r e c e nt c h a nge s

, e vi de nt t o di f f

e r e nt de gr e e s i n

di f f

e r e nt di a gnos t i c m e a s ur e s

, r e s ul t f r o m i nc r e a s e d dyna m i c a l w a ve a c t i vi t y a nd not f r om

de c r e a s e s i n oz one

- de pl e t i ng s ubs t a nc e s

.

• I n S e p t e m b e r 2002

, t h e f i r s t

- e ve r ob s e r ve d m aj or s t r at os p h e r i c s u d d e n w ar m i n g

oc c u r r e d i n t h e S o u t h e r n H e m i s p h e r e

. T h i s e ar l y s p r i n g w ar m i n g c au s e d a d r as t i c

r e d u c t i on of t h e oz on e h ol e ar e a an d r e s u l t e d i n a l e s s s e ve r e oz on e h ol e

. T hi s w a r m i ng

r e s ul t e d f r om a nom a l ous l y s t r ong dyna m i c a l w a ve a c t i vi t y i n t he S out he r n H e m i s phe r e

. T he

A nt a r c t i c w i nt e r o f 2004 w a s a l s o dyna m i c a l l y ve r y a c t i ve a nd ha d hi ghe r oz one l e ve l s t ha n

i n pr e vi ous ye a r s

.E x e c u t i v e S u m m a r y R e l e a s e d 1 8 A u g u s t 2 0 0 6

S

c i e n t i f

i c A s s e s s m e n t o f O z o n e D e p l e t i o n : 2 0 0 6

15 G E N E R A L

• L ar ge i n t e r an n u al var i ab i l i t y i n p ol ar s t r at os p h e r i c t e m p e r at u r e s c om p l i c at e s t h e

i n t e r p r e t at i on of t e m p e r at u r e t r e n d s

. P r e vi ous l y r e por t e d e s t i m a t e s of t e m pe r a t ur e t r e nds

i n pol a r r e gi ons ha ve di f f

e r e d f r om a s s e s s m e nt t o a s s e s s m e nt

. I n r e t r os pe c t

, i t i s e vi de nt t ha t

t e m pe r a t ur e t r e nds de r i ve d ove r t i m e s c a l e s of 1

- 2 de c a de s

, t hough t he y m a y a ppe a r

s t a t i s t i c a l l y s i gni f i c a nt

, a r e not r obus t be c a us e of l a r ge i nt e r a nnua l a nd de c a da l va r i a bi l i t y i n

obs e r ve d t e m pe r a t ur e s

. T he r e f o r e

, c ha nge s i n r e p or t e d t e m pe r a t ur e t r e nds do no t ne c e s s a r i l y

i ndi c a t e s ys t e m a t i c c ha nge s i n phys i c a l or c he m i c a l pr oc e s s e s

.

• C al c u l at e d c h e m i c al l os s r at e s of p o l ar oz on e s u b s t an t i al l y i n c r e as e i n m od e l s t h at

as s u m e : 1) m or e e f f i c i e n t oz on e d e s t r u c t i on b y r e ac t i on s i n vol vi n g t w o c h l or i n e

m on oxi d e ( C l O ) m ol e c u l e s ( r e f e r r e d t o as t h e C l O d i m e r c yc l e ) an d 2) h i gh e r

c on c e n t r at i on s of b r om i n e

. T he hi ghe r c onc e nt r a t i ons of br o m i ne a r e a s s um e d be c a us e of

ne w e vi de nc e t ha t na t ur a l b r om oc a r bons pl a y a c ons i de r a bl e r ol e i n t he s t r a t os phe r i c br om i ne budge t

. M or e e f f i c i e nt oz one de s t r uc t i on by t he C l O di m e r c yc l e i s s uppor t e d by a na l ys e s of

t he f i r s t s t r a t os phe r i c obs e r va t i ons o f t he C l O di m e r

. T he s e t w o c ha nge s t o m ode l s i m pr ove

t he c om pa r i s on be t w e e n m e a s ur e d a nd m ode l e d A r c t i c oz one l os s r a t e s t ha t w a s not e d i n t he

pa s t A s s e s s m e nt

. T he s e c ha ng e s a l s o i m pr ove c o m pa r i s on be t w e e n t he or y a nd obs e r va t i on

of t he t i m i ng o f oz one l os s ove r A nt a r c t i c a

.

• F or t h e f i r s t t i m e , m e as u r e m e n t s s h ow u n am b i g u ou s l y t h at n i t r i c ac i d t r i h yd r at e ( N A T )

P S C p ar t i c l e s c an n u c l e at e ab ove t h e i c e f r os t p oi n t

, an d t h e r e i s ad d i t i on al e vi d e n c e o f

t h e i r w i d e s p r e ad oc c u r r e n c e

. W i de s pr e a d, l ow

- num be r

- de ns i t y N A T c l ouds c a n l e a d t o

de ni t r i f i c a t i on a nd e nha nc e d oz one l os s

. I nc or por a t i ng N A T nuc l e a t i on a bove t he i c e f r os t

poi nt i nt o c he m i c a l t r a ns por t m ode l s ha s i m pr ove d de ni t r i f i c a t i on s i m ul a t i ons

, but

di s c r e pa nc i e s i n i nt e r a nnua l va r i a bi l i t y r e m a i n, pr o ba bl y be c a us e t he N A T nuc l e a t i on

m e c ha ni s m s a r e not f ul l y unde r s t ood.

I m p a c t o f C l i m a t e C h a n g e

• T h e s t r at os p h e r i c c ool i n g ob s e r ve d d u r i n g t h e p as t t w o d e c ad e s h as s l ow e d i n r e c e n t

ye ar s

.

− S a t e l l i t e a nd r a di os onde m e a s ur e m e nt s r e ve a l a n o ve r a l l de c r e a s e i n t he gl oba l

- m e a n

l ow e r s t r a t os phe r i c t e m pe r a t ur e of a pp r oxi m a t e l y 0. 5 K / de c a de ove r t he 1979

- 2004

pe r i od, w i t h a s l ow dow n i n t he t e m pe r a t u r e de c l i n e s i nc e t he l a t e 1990s

. T he ove r a l l

t e m pe r a t ur e de c r e a s e i s punc t ua t e d by t r a ns i e nt w a r m i ngs of t he s t r a t os phe r e a s s oc i a t e d

w i t h t he m a j or vol c a ni c e r upt i ons i n 1982 a nd 199 1. C ons i s t e nt w i t h t he pr e vi ous

A s s e s s m e nt

, m ode l c a l c ul a t i ons i ndi c a t e t ha t t he o bs e r ve d oz one l os s i s t he pr e do m i na nt

c a us e of t he gl oba l

- m e a n l ow e r s t r a t os phe r i c c oo l i ng obs e r ve d ove r t hi s pe r i od.

− T he c ool i ng o f t he l ow e r s t r a t os phe r e i s e vi de nt a t a l l l a t i t ude s

. T he a nnua l

- m e a n

t e m pe r a t ur e i n t he A r c t i c l ow e r s t r a t os phe r e ha s de c r e a s e d by a ppr oxi m a t e l y 1 K ove r t he

1979

- 2004 pe r i od

. T he r e c ont i nue s t o be a l a r ge i nt e r a nnua l va r i a bi l i t y i n t he w i nt e r a nd

s pr i ngt i m e

, w hi c h m a ke s i t di f f i c ul t t o de t e r m i ne r e l i a bl e t r e nds i n t he A r c t i c l ow e r

s t r a t os phe r e

.E x e c u t i v e S u m m a r y R e l e a s e d 1 8 A u g u s t 2 0 0 6

S

c i e n t i f

i c A s s e s s m e n t o f O z o n e D e p l e t i o n : 2 0 0 6

16 − A c ons i de r a bl e i nt e r a nnua l va r i a bi l i t y i n t he t e m pe r a t ur e o f t he A nt a r c t i c l ow e r

s t r a t os phe r e ha s be c om e e vi de nt i n r e c e nt ye a r s ; t h i s ha s r e duc e d t he e s t i m a t e of t he

de c a da l

- s c a l e c ool i ng t r e nd i n t ha t r e gi on f r om t ha t i n t he pr e vi ous A s s e s s m e nt

.

− S a t e l l i t e obs e r va t i ons s how l a r ge gl oba l

- m e a n c ool i ng t r e nds i n t h e uppe r s t r a t os phe r e ( 1

t o 2 K / de c a de ove r 1979

- 2004)

, but t he r e i s l i t t l e a ddi t i ona l de c l i ne s i nc e t he m i ddl e

1990s

. T he c onc l us i on of t he pr e vi ous A s s e s s m e n t

, t ha t t he obs e r ve d uppe r s t r a t os phe r e

t r e nds a r e due t o a ppr oxi m a t e l y s i m i l a r c ont r i but i o ns f r o m de c r e a s e s i n oz one a nd

i nc r e a s e s i n w e l l

- m i xe d gr e e nhous e ga s e s

, i s r e a f f i r m e d.

• F u t u r e i n c r e as e s of gr e e n h ou s e gas c on c e n t r at i o n s w i l l c on t r i b u t e t o t h e ave r age c ool i n g

i n t h e s t r at os p h e r e

. E s t i m a t e s de r i ve d f r om c l i m a t e m ode l s ( A O G C M s

, c oupl e d oc e a n

a t m os phe r e ge ne r a l c i r c ul a t i on m ode l s ) a nd C he m i s t r y

- C l i m a t e M ode l s ( C C M s ) w i t h

i nt e r a c t i ve oz one c ons i s t e nt l y pr e di c t c ont i nue d c o ol i ng of t he gl oba l a ve r a ge s t r a t os phe r e

. T he pr e di c t e d c ool i ng r a t e w i t hi n t he ne xt t w o de c a de s i s de pe nde nt on t he pr e s c r i b e d

s c e na r i o a nd t he t ype of m ode l us e d f or t he A s s e s s m e nt

. A t 50 hP a ( a n a l t i t ude of a bout 20

km )

, a n a ve r a ge of a l l A O G C M s gi ve s a ppr oxi m a t e l y 0. 1 K / de c a de

, w hi l e C C M s pr e di c t a

l a r ge r c ool i ng o f a bout 0. 25 K / de c a de c a us e d by t h e i nt e r a c t i ve c ons i de r a t i on of oz one

c ha nge s

. A l l m ode l s c a l c ul a t e a s t r onge r c ool i ng a t 10 hP a ( a bout 30 km )

, a ve r a gi ng

a

ppr oxi m a t e l y 0. 5 K / de c a de

. S i m ul a t i ons of pol a r t e m pe r a t ur e s i n t he f ut ur e a r e l e s s c e r t a i n

t ha n gl oba l m e a n t e m pe r a t u r e s be c a us e of gr e a t e r i nt e r a nnua l va r i a bi l i t y

.

• C h e m i c al r e ac t i on r a t e s i n t h e at m os p h e r e ar e d e p e n d e n t on t e m p e r at u r e , a n d t h u s t h e

c on c e n t r at i on o f oz on e i s s e n s i t i ve t o t e m p e r at u r e c h an ge s

. D e c r e a s e s i n uppe r

s t r a t os phe r i c t e m pe r a t ur e s l ow t he r a t e of phot oc h e m i c a l oz one de s t r uc t i on i n t hi s r e gi on.

H e nc e t he c onc e nt r a t i on of uppe r s t r a t os phe r i c oz o ne i nc r e a s e s i n r e s pons e t o c ool i ng.

C ool i ng of t he pol a r l ow e r s t r a t os phe r e w oul d l e a d t o m o r e e f f i c i e nt c hl or i ne a c t i va t i on on

a e r os ol s a nd pol a r s t r a t os phe r i c c l ouds

, a nd e nha nc e d oz one de s t r uc t i on. T he r e f o r e

, t he

c onc e nt r a t i on of oz one i n t he s pr i ng t i m e pol a r l ow e r s t r a t os phe r e w oul d de c r e a s e i n r e s pons e

t o c ool i ng.

I N T E R A C T I O N S B E T W E E N S T R A T O S P H E R E A N D T R O P O S P H E R E

• C h an ge s t o t h e t e m p e r at u r e an d c i r c u l at i on of t h e s t r at os p h e r e af f

e c t c l i m at e an d

w e at h e r i n t h e t r op os p h e r e

. C ons i s t e nt e vi de nc e f or t hi s c oupl i ng c om e s f r om bot h

obs e r va t i ona l a na l ys e s a nd m ode l s

, but t he m e c ha n i s m s r e s pons i bl e a r e not w e l l unde r s t ood.

T he dom i na nt t r opos phe r i c r e s pons e c om pr i s e s c ha nge s i n t he s t r e ngt h of t he m i dl a t i t ude

w e s t e r l i e s ( t he pr e va i l i ng w i nds f r om t he w e s t )

. O bs e r va t i ons a nd m ode l s s ugge s t t ha t

A nt a r c t i c oz one de pl e t i on, t hr ough i t s e f f

e c t s on t h e l ow e r s t r a t os phe r i c vor t e x, ha s

c ont r i but e d t o t he obs e r ve d s t r e ngt he ni ng o f t r opos phe r i c w i nds a nd A nt a r c t i c s ur f a c e

c ool i ng dur i ng D e c e m be r

- F e br ua r y

.

• U p d at e d d a t as e t s of s t r at os p h e r i c w a t e r vap or c on c e n t r at i on s n ow s h ow d i f f

e r e n c e s i n

l on g

- t e r m b e h avi or

. R e c e nt t r e nd a na l ys e s

, w hi c h a r e ba s e d on onl y t w o a va i l a bl e

m ul t i ye a r da t a s e t s

, c a s t doubt on t he po s i t i ve s t r a t o s phe r i c w a t e r va por t r e nd t ha t w a s not e d

i n t he pr e vi ous A s s e s s m e nt

. B a l l oon

- bor ne w a t e r va por m e a s ur e m e nt s a t B oul de r

, C ol or a do,

f

or t he pe r i od 1980

- 2005 s how a s i gni f i c a nt i nc r e a s e of 5

- 10% pe r de c a de ove r a l t i t ude s of

15

- 28 km

. G l oba l w a t e r va po r m e a s ur e m e nt s f r o m t he H a l oge n O c c ul t a t i on E xpe r i m e ntE x e c u t i v e S u m m a r y R e l e a s e d 1 8 A u g u s t 2 0 0 6

S

c i e n t i f

i c A s s e s s m e n t o f O z o n e D e p l e t i o n : 2 0 0 6

17 ( H A L O E ) s a t e l l i t e i ns t r um e nt f or 1991

- 2005 do no t s how a c or r e s pondi ng pos i t i ve l ow e r

s t r a t os phe r i c t r e nd. I nt e r a nnua l w a t e r va por c ha ng e s de r i ve d f r om H A L O E da t a e xhi bi t

qua nt i t a t i ve a gr e e m e nt w i t h t e m pe r a t ur e va r i a t i ons ne a r t he t r opi c a l t r opopa us e

. I n c ont r a s t

,

t he l ong

- t e r m i nc r e a s e s i nf e r r e d f r om t he B oul de r da t a a r e l a r ge r t ha n c a n be e xpl a i ne d by

obs e r ve d t r opopa us e t e m pe r a t ur e c ha nge s or pa s t i nc r e a s e s i n t r opos phe r i c m e t ha ne

.

T h e O zo n e L a y e r i n t h e 2 1 s t C e n t u r y

• T h e s l ow i n g of t h e d e c l i n e an d l e ve l i n g o f f of m i d l at i t u d e u p p e r s t r at os p h e r i c ( 35

- 45

k m ) oz on e ove r t h e p as t 10 ye ar s h as ve r y l i k e l y b e e n d o m i n at e d b y c h a n ge s i n

e q u i val e n t e f f

e c t i ve s t r at os p h e r i c c h l or i n e ( E E S C )

. G a s

- pha s e c he m i s t r y, m odul a t e d by

c ha nge s i n t e m pe r a t ur e a nd ot he r ga s e s s uc h a s m e t ha ne

, di r e c t l y c ont r ol s oz one i n t hi s

r e gi on, a nd obs e r ve d oz one i nc r e a s e s a r e s i m i l a r t o t hos e m ode l e d f r om E E S C de c r e a s e s

.

• O ve r t h e p as t 10 ye ar s , c h a n ge s i n E E S C h ave l i k e l y c on t r i b u t e d t o t h e s l ow i n g o f

m i d l at i t u d e t ot al c ol u m n oz on e d e c l i n e an d t h e l e ve l i n g of f of c ol u m n oz on e

. T r a ns por t

a l s o ha s pl a ye d a n i m por t a nt r ol e

, pa r t i c ul a r l y i n t h e l ow e r m os t s t r a t os phe r e

, m a ki ng

a t t r i but i on o f oz one c ha nge s t o s ol e l y E E S C di f f i c ul t

. F or nor t he r n m i dl a t i t ude s

, i nc r e a s e s i n

oz one ha ve be e n gr e a t e r t ha n e xpe c t e d f r om E E S C de c r e a s e s a l one ; w he r e a s ove r s out he r n

m i dl a t i t ude s

, oz one c ha nge s a r e m or e c ons i s t e nt w i t h t he r a nge e xpe c t e d f r om E E S C

d e c r e a s e s

.

• T h e d e c l i n e i n E E S C h as n ot c au s e d t h e l ar ge a n n u al var i at i on s ob s e r ve d i n A r c t i c

oz on e d e p l e t i on

. I nde e d, t he ons e t of oz one r e c ov e r y i n t he A r c t i c ha s not be e n de t e c t e d.

T he l a r ge i n t e r a nnua l va r i a t i ons d r i ve n by c ha nge s i n m e t e or ol ogy a r e l i ke l y t o pr e c l ude t he

de t e c t i on of t he f i r s t s t a ge o f r e c ove r y

.

M O D E L P R O J E C T I O N S

T w o

- di m e ns i ona l m ode l s a nd t h r e e

- di m e ns i ona l c oupl e d C he m i s t r y

- C l i m a t e M ode l s ( C C M s )

, bot h of w hi c h i nc or po r a t e m a ny o f t he f a c t or s t ha t a f f

e c t oz one a s w e l l a s t he i r

f

e e dba c ks

, ha ve be e n us e d i n t hi s A s s e s s m e nt t o m a ke pr oj e c t i ons of t he e vol ut i on o f oz one

t hr oughout t he 21s t c e nt ur y. T he m ode l pr oj e c t i on s gui di ng t he c onc l us i ons be l ow w e r e ba s e d

on t he s ur f a c e t i m e s e r i e s of ha l o c a r bons f r om t he “ A b” s c e na r i o ( ba s e l i ne s c e na r i o f ol l ow i ng t he

B e i j i ng A m e ndm e nt s ) f r om t he 2002 oz one a s s e s s m e nt

, a s w e l l a s t he w e l l

- m i xe d g r e e nhous e

ga s c onc e nt r a t i ons f r om t he T hi r d A s s e s s m e nt R e p or t of t he I nt e r gove r nm e nt a l P a ne l on C l i m a t e

C ha nge

, C l i m at e C hange 2001: T he Sc i e nt i f

i c B as i s

. T o f oc us on l ong

- t e r m c ha nge s

, t he

pr oj e c t e d oz one a nom a l i e s ha ve be e n de c a da l l y s m oot he d.

• T h e C C M s u s e d t o p r oj e c t f u t u r e oz on e a b u n d a n c e s h ave b e e n c r i t i c al l y e val u at e d an d

m or e e m p h as i s h as b e e n gi ve n t o t h os e m od e l s t h at b e s t r e p r e s e n t t h e p r oc e s s e s k n ow n

t o s t r on gl y a f f

e c t c ol u m n oz on e ab u n d an c e s

. T he C C M s va r y i n t he i r s ki l l i n r e pr e s e nt i ng

di f f

e r e nt p r oc e s s e s a nd c ha r a c t e r i s t i c s of t he a t m os phe r e

. H ow e ve r

, t he r e i s s uf f i c i e nt

a gr e e m e nt be t w e e n t he m a j or i t y of t he C C M s a nd t he obs e r va t i ons

, s o t ha t s om e c onf i de nc e

c a n be pl a c e d i n t he i r pr oj e c t i ons

.E x e c u t i v e S u m m a r y R e l e a s e d 1 8 A u g u s t 2 0 0 6

S

c i e n t i f

i c A s s e s s m e n t o f O z o n e D e p l e t i o n : 2 0 0 6

18 • A ve r age d ove r 60°S t o 60°N

, t ot al c ol u m n oz on e i s p r oj e c t e d t o i n c r e as e b y 1% t o 2

. 5%

b e t w e e n 2000 an d 2020, r e ac h i n g 1980 val u e s at t h e s am e t i m e or b e f or e E E S C i n t h at

r e gi on d e c l i n e s t o 1980 val u e s ( 2040

- 2050)

. B y 2 100, oz on e s h ou l d b e u p t o 5 % ab ove

1980 val u e s

. B ot h t w o

- di m e ns i ona l m ode l s a nd C C M s s ugge s t t ha t m i ni m um t ot a l c ol um n

oz one va l ue s ha ve a l r e a dy oc c ur r e d i n t hi s r e gi on

. O z one e xc e e ds pr e

- 1980 va l ue s a t t he

t i m e E E S C r e t u r ns t o 1980 va l ue s i n ne a r l y a l l m o de l s t ha t i nc l ude c oupl i n g be t w e e n w e l l

m i xe d gr e e nhous e ga s e s a nd t e m pe r a t ur e ( i nt e r a c t i ve t w o

- di m e ns i ona l m ode l s a nd t he

C C M s )

. S i m i l a r l y t he e l e va t e d oz one l e ve l s i n 210 0 a r e obs e r ve d i n a l l i nt e r a c t i ve t w o

di m e ns i ona l m ode l s a nd i n t he one C C M t ha t e xt e nde d t o 2100.

• A n t ar c t i c s p r i n gt i m e oz on e i s p r oj e c t e d t o i n c r e as e b y 5% t o 10% b e t w e e n 2000 an d

2020, r e ac h i n g 1980 val u e s c l os e t o w h e n A n t ar c t i c E E S C d e c r e as e s t o 1980 val u e s

( 2060

- 2075)

, an d c h an gi n g l i t t l e t h e r e af t e r

. D i f f e r e nt di a gnos t i c i ndi c a t or s of oz one

de pl e t i on s h ow di f f

e r e nt s e ns i t i vi t i e s t o E E S C

. T h e m os t r a pi d c ha nge ( de c r e a s e ) oc c ur s i n

t he oz one m a s s de f i c i t a nd t he s l ow e s t c ha nge ( i nc r e a s e ) oc c ur s i n oz one m i ni m u m va l ue s

a nd O c t obe r oz one a nom a l i e s

. M i ni m um oz one va l ue s r e m a i n r oughl y c ons t a nt be t w e e n

2000 a nd 2010 i n m a ny m ode l s

. T he p r oj e c t e d on s e t of de c r e a s e s i n t he oz one m a s s de f i c i t

oc c ur s be t w e e n 2000 a nd 2005, w he r e a s t he pr oj e c t e d ons e t of i nc r e a s e s i n m i ni m um

A nt a r c t i c oz one doe s not oc c ur unt i l a f t e r 2010 i n m a ny m ode l s

.

• A r c t i c s p r i n gt i m e oz on e i s p r oj e c t e d t o i n c r e as e b y 0% t o 10% b e t w e e n 2000 an d 2020

,

r e ac h i n g 1980 val u e s m u c h e ar l i e r t h an w h e n A r c t i c E E S C d e c r e as e s t o 1980 val u e s

( 2060

- 2070)

. B y 2100, A r c t i c oz on e i s p r oj e c t e d t o b e s u b s t an t i al l y ab ove 1980 val u e s

. W hi l e t he l a r ge i n t e r a nn ua l va r i a bi l i t y i n pr oj e c t e d A r c t i c oz one obs c ur e s t he da t e w he n t he

oz one t ur na r ound due t o de c r e a s i ng E E S C oc c ur s

, t hi s i s pr oj e c t e d t o oc c ur be f o r e 2020.

T he i nc r e a s e i n A r c t i c oz one doe s not f ol l ow E E S C a s c l os e l y a s i n t he A nt a r c t i c

, a nd i n t he

m a j or i t y of C C M s

, A r c t i c oz one e xc e e ds 1980 va l ue s be f or e t he A nt a r c t i c

. T he r e i s no

i ndi c a t i on of f ut ur e l a r ge de c r e a s e s i n A r c t i c c ol u m n oz one i n a ny of t he m ode l s i m ul a t i ons

. T he r e i s l a r ge unc e r t a i nt y i n pr e di c t i ons o f A r c t i c oz one be c a us e of t he s m a l l e r oz one

de pl e t i on a nd t he l a r ge r i nt e r a nnua l va r i a bi l i t y i n t he A r c t i c s t r a t os phe r e

.

• T h e p r oj e c t e d oz on e i n 2100 i s s e n s i t i ve t o f u t u r e l e ve l s of t h e w e l l

- m i xe d gr e e n h ou s e

gas e s

. F or e xa m pl e

, e xpe c t e d f u t u r e i nc r e a s e s i n n i t r ous oxi de ( N 2 O ) w i l l i nc r e a s e

s t r a t os phe r i c ni t r oge n oxi de s ( N O

x )

, w hi c h m a y e xa c e r ba t e oz one de pl e t i on. H ow e ve r

, t he

e xpe c t e d s t r a t os phe r i c c ool i ng i nduc e d by i nc r e a s i ng c onc e nt r a t i ons of g r e e nhous e ga s e s

,

pr i m a r i l y c a r bon di oxi de ( C O 2 )

, i s e xpe c t e d t o s l ow ga s

- pha s e oz one de pl e t i on r e a c t i ons a nd,

t he r e by, i n c r e a s e oz one

. T he ne t e f f

e c t on oz one a m ount s w i l l de pe nd on f ut ur e l e ve l s of t he

di f f

e r e nt w e l l

- m i xe d g r e e nhous e ga s e s

. T he i m po r t a nc e of t hi s t e m pe r a t u r e f e e dba c k i s

de m ons t r a t e d by t he non

- i nt e r a c t i ve t w o

- d i m e ns i ona l m ode l s

, w hi c h p r e di c t t ha t e xt r a pol a r

c ol um n oz one w i l l be l e s s t ha n or ne a r 1980 va l ue s t hr ough t he l a t t e r ha l f o f t he c e nt ur y.

• H u m an ac t i vi t i e s ar e e xp e c t e d t o af f

e c t s t r at os p h e r i c oz on e t h r ou gh c h an ge s i n

t r op os p h e r i c e m i s s i on s of t r ac e gas e s

. E nha nc e d m e t ha ne ( C H 4 ) e m i s s i on ( f r om w e t t e r a nd

w a r m e r s oi l s ) i s e xpe c t e d t o e nha nc e oz one pr oduc t i on i n t he l ow e r s t r a t os phe r e

, w he r e a s a n

i nc r e a s e i n ni t r ous oxi de ( N 2 O ) e m i s s i on ( f r om e xt e nde d us e of a r t i f i c i a l f e r

t i l i z e r ) i s

e xpe c t e d t o r e duc e oz one i n t he m i ddl e a nd hi gh s t r a t os phe r e

. A l s o, c ha nge s i n non

- m e t ha neE x e c u t i v e S u m m a r y R e l e a s e d 1 8 A u g u s t 2 0 0 6

S

c i e n t i f

i c A s s e s s m e n t o f O z o n e D e p l e t i o n : 2 0 0 6

19 hydr oc a rbons a nd ni t r oge n oxi de ( N O

x ) e m i s s i ons a r e e xpe c t e d t o a f f

e c t t he t r opos phe r i c

c onc e nt r a t i ons of hydr oxyl r a di c a l ( O H ) a nd

, he nc e

, i m pa c t t he l i f e t i m e a nd c onc e nt r a t i on o f

s t r a t os phe r i c t r a c e ga s e s s uc h a s C H 4 a nd or ga ni c ha l oge n s pe c i e s

.

• F u t u r e c h a n ge s of s t r at os p h e r i c w a t e r vap or c o n c e n t r at i on s ar e u n c e r t ai n

. I f w a t e r

va por c onc e nt r a t i ons i nc r e a s e i n t he f ut ur e

, t he r e w i l l be bot h a r a di a t i ve a nd a c he m i c a l

e f

f

e c t

. M ode l i ng s t udi e s s ugge s t i nc r e a s e d w a t e r va por c onc e nt r a t i ons w i l l e nha nc e odd

hydr oge n ( H O

x ) i n t he s t r a t os phe r e a nd s ubs e que nt l y i nf l ue nc e oz one de pl e t i on

. I nc r e a s e s i n

w a t e r va por i n t he pol a r r e gi ons w oul d r a i s e t he t e m pe r a t ur e t hr e s hol d f or t he f o r m a t i on o f

pol a r s t r a t os phe r i c c l ouds

, pot e nt i a l l y i nc r e a s i ng s pr i ngt i m e oz one de pl e t i on

.

U V R a d i a t i o n a n d I t s C h a n g e s

• S om e u n p o l l u t e d s i t e s s h ow t h a t U V r ad i at i on h as b e e n d e c r e as i n g s i n c e t h e l a t e 1990s

. H ow e ve r , at s om e m i d l a t i t u d e s t at i on s i n t h e N o r t h e r n H e m i s p h e r e , s u r f ac e U V

i r r ad i an c e c on t i n u e d t o i n c r e as e at r at e s of a f e w p e r c e n t p e r d e c ad e

. T he obs e r ve d

i nc r e a s e s a nd t he i r s i gni f i c a nc e de pe nd on l oc a t i on

, w a ve l e ngt h r a nge

, a nd t he pe r i od of

m e a s ur e m e nt s

. T he s e i nc r e a s e s c a nnot be e xpl a i ne d s ol e l y by oz one de pl e t i on a nd c ou l d be

a t t r i but e d t o a de c r e a s i ng t e nde nc y i n a e r os ol op t i c a l e xt i nc t i on a nd a i r pol l ut i on s i nc e t he

be gi nni ng of t he 1990s a nd pa r t l y t o de c r e a s i ng c l oudi ne s s

, a s e s t i m a t e d f r om s a t e l l i t e s

.

• T r op os p h e r i c ae r os ol s ar e r e s p on s i b l e f or t h e o ve r e s t i m at i on of U V i r r ad i an c e f r om

s at e l l i t e i n s t r u m e n t s ( e

. g

. , T O M S

, t h e T ot al O z o n e M ap p i n g S p e c t r om e t e r ) t h a t u s e

s ol ar b ac k s c at t e r e d u l t r avi ol e t r ad i at i o n t o d e r i ve s u r f ac e U V i r r ad i an c e

. A t c l e a n s i t e s

t he a gr e e m e nt w i t h g r ound

- ba s e d m e a s ur e m e nt s i s good. H ow e ve r

, o ve r m or e pol l u t e d

l oc a t i ons t he bi a s c a n be a s l a r ge a s 40 % be c a us e t he l ow e r m os t a t m os phe r e c ont a i ni ng t he

a

bs orbi ng a e r os ol s i s not a de qua t e l y pr obe d by t he m e a s ur e m e nt s

. T he pr e s e nc e of c l ouds

a nd s now or i c e c ove r c a n a l s o l e a d t o s i gni f i c a nt b i a s e s

. N e w a l gor i t hm s ha ve be e n

de ve l ope d t o i m pr ove t he pa r a m e t e r i z a t i on of a e r o s ol

, s now

, a nd i c e e f f

e c t s on s a t e l l i t e

de r i ve d s ur f a c e U V i r r a di a nc e

, a s w e l l a s of c l oud e f f

e c t s us i ng A dva nc e d V e r y H i gh

R e s ol ut i on R a di om e t e r ( A V H R R ) a nd M e t e os a t i m a ge s

, s how i n g on a ve r a ge good

a gr e e m e nt w i t h gr ound

- ba s e d U V obs e r va t i ons

. A l t hough t he T O M S i ns t r um e nt i s no l onge r

a va i l a bl e

, t he c ont i nui t y of s a t e l l i t e

- de r i ve d gl oba l U V da t a i s m a i nt a i ne d w i t h t he ne w

O z one M oni t or i ng I ns t r um e nt ( O M I ) onboa r d t he A ur a s a t e l l i t e

.

• C l ou d s ar e t h e m aj or f ac t or l i m i t i n g t h e d e t e c t a b i l i t y o f l o n g

- t e r m c h an ge s i n U V

r ad i at i on d u e t o oz on e c h an ge s or ot h e r f ac t or s

. E ve n i f oz one t r e nds w e r e l i ne a r

, a t l e a s t

10

- 15 ye a r s of m e a s ur e m e nt s w oul d be ne e de d f o r de t e c t i ng a t r e nd i n U V r a di a t i on. A t

m os t e xt r a pol a r l oc a t i ons

, t he e f f

e c t s on U V

- B r a di a t i on f r om oz one de pl e t i on a r e r e l a t i ve l y

s m a l l

, a nd t he i nf l ue nc e of c l ouds i s dom i na nt

.

• A i r p ol l u t an t s m ay c ou n t e r b al an c e t h e U V r ad i at i on i n c r e as e s r e s u l t i n g f r om oz on e

d e p l e t i on

. O bs e r va t i ons c onf i r m t ha t U V

- a bs or bi ng a i r pol l ut a nt s i n t he l ow e r t r opos phe r e

,

s uc h a s oz one

, ni t r oge n di oxi de ( N O 2 ) a nd s ul f u

r d i oxi de ( S O 2 )

, a t t e nua t e s ur f a c e U V

i r r a di a nc e by up t o ~ 20 %

. T hi s e f f

e c t i s obs e r ve d a t l oc a t i ons ne a r t he e m i s s i on s our c e s

. A i r

pol l ut i on e xe r t s s t r onge r a t t e nua t i on i n U V c om pa r e d w i t h a t t e nua t i on i n t ot a l s ol a r

i r r a di a nc e

.E x e c u t i v e S u m m a r y R e l e a s e d 1 8 A u g u s t 2 0 0 6

S

c i e n t i f

i c A s s e s s m e n t o f O z o n e D e p l e t i o n : 2 0 0 6

20 O zo n e D e p l e t i o n P o t e n t i a l s a n d G l o b a l W a r m i n g P o t e n t i a l s

• T h e e f f

e c t i ve n e s s of b r om i n e c om p ar e d w i t h c h l or i n e f or gl ob a l oz on e d e p l e t i on ( on a

p e r

- at om b as i s )

, t yp i c al l y r e f e r r e d t o as α

, h as b e e n r e

- e val u at e d u p w ar d f r om 45 t o a

val u e of 60

. T he c a l c ul a t e d va l ue s f r om t hr e e i nde pe nde nt t w o

- di m e ns i ona l m ode l s r a nge

be t w e e n 57 a nd 73, de pe ndi ng on t he m ode l us e d a nd de pe ndi ng on t he a s s um e d a m ount of

a ddi t i ona l br om i n e a dde d t o t he s t r a t os phe r e by ve r y s hor t

- l i ve d s ubs t a nc e s

.

• O z on e D e p l e t i on P ot e n t i al s ( O D P s ) h ave b e e n r e

- e val u at e d

, w i t h t h e m os t s i gn i f i c an t

c h an ge b e i n g a 33% i n c r e as e f or b r om oc ar b on s d u e t o t h e u p d at e i n t h e e s t i m at e f or

t h e val u e o f α

. A c a l c ul a t i on e r r o r i n t he p r e vi ous oz one a s s e s s m e nt l e a di ng t o a 13 %

ove r e s t i m a t e f or t he O D P o f H a l on

- 1211 ha s be e n c or r e c t e d.

• D i r e c t an d i n d i r e c t G l o b al War m i n g P ot e n t i a l s ( G WP s ) h ave b e e n u p d at e d

. T h e d i r e c t

G WP s w e r e r e vi s e d f or c h an ge s i n r ad i at i ve e f f i c i e n c i e s of H F C

- 134a

, c ar b on

t e t r af l u or i d e ( C F 4 )

, H F C

- 23, H F C

- 3 2, H F C

- 227 e a, an d n i t r oge n t r i f l u or i d e ( N F 3 )

, as

w e l l as c h an ge s i n t h e l i f e t i m e s o f t r i f l u or om e t h yl s u l f u r p e n t af l u or i d e ( S F 5 C F 3 ) an d

m e t h yl c h l or i d e ( C H 3 C l )

. I n a ddi t i on

, t he di r e c t G W P s f or a l l c om pounds a r e a f f

e c t e d by

s l i ght de c r e a s e s i n t he C O 2 a bs ol ut e G l oba l W a r m i ng P ot e nt i a l s f o r va r i ous t i m e hor i z ons

. I ndi r e c t G W P s ha ve be e n upda t e d pr i m a r i l y t o r e f l e c t t he l a t e r r e t ur n o f oz one

- de pl e t i ng

s ubs t a nc e s t o 1980 l e ve l s e s t i m a t e d i n t hi s A s s e s s m e nt c om pa r e d w i t h t he e a r l i e r A s s e s s m e nt

a nd t o a c c ount f o r t he i nc r e a s e d br om i ne e f f i c i e nc y f a c t or

.

I M P L I C A T I O N S F O R P O L I C Y F O R M U L A T I O N

T he r e s ul t s f r o m ove r t hr e e de c a de s of r e s e a r c h ha ve pr ovi de d a p r ogr e s s i ve l y be t t e r

unde r s t a ndi ng of t he i nt e r a c t i on o f hum a n a c t i vi t y a nd t he oz one l a ye r

. N e w pol i c y

- r e l e va nt

i ns i ght s i nt o t he r o l e s of oz one

- de pl e t i ng ga s e s ha ve be e n c onve ye d t o de c i s i on

- m a ke r s t hr ough

a s e r i e s of i nt e r na t i ona l s t a t e

- of

- unde r s t a ndi ng a s s e s s m e nt r e por t s

. T he r e s e a r c h f i ndi ngs i n t he

Sc i e nt i f

i c A s s e s s m e nt of O z one D e pl e t i on: 2006 t h a t a r e gi ve n a bove a nd a r e s um m a r i z e d he r e

pr ovi de di r e c t c u r r e nt s c i e nt i f i c i nput t o gove r nm e nt a l

, i ndus t r i a l

, a nd ot he r pol i c y de c i s i ons

a s s oc i a t e d w i t h pr ot e c t i on of t he oz one l a ye r :

• O u r b as i c u n d e r s t an d i n g t h at an t h r op oge n i c oz on e

- d e p l e t i n g s u b s t an c e s h ave b e e n t h e

p r i n c i p al c au s e of t h e oz on e d e p l e t i on ove r t h e p as t d e c ad e s h as b e e n s t r e n gt h e n e d

.

• T h e M on t r e al P r ot oc ol i s w or k i n g : T h e r e i s c l e a r e vi d e n c e of a d e c r e as e i n t h e

at m os p h e r i c b u r d e n of oz on e

- d e p l e t i n g s u b s t an c e s an d s om e e ar l y s i gn s of s t r at os p h e r i c

oz on e r e c ove r y. A s n ot e d e ar l i e r i n t h i s E xe c u t i ve S u m m ar y :

− A bunda nc e s of oz one

- de pl e t i ng s ubs t a nc e s

, t a ke n t oge t he r

, a r e c l e a r l y de c r e a s i ng i n t he

l ow e r a t m os phe r e

. N e a r l y a l l t he a bunda nc e s of i n di vi dua l oz one

- de pl e t i ng s ubs t a nc e s

a r e a l s o de c r e a s i ng.E x e c u t i v e S u m m a r y R e l e a s e d 1 8 A u g u s t 2 0 0 6

S

c i e n t i f

i c A s s e s s m e n t o f O z o n e D e p l e t i o n : 2 0 0 6

21 − T he r e a r e c l e a r i ndi c a t i ons t ha t t he e qui va l e nt e f f

e c t i ve s t r a t os phe r i c c hl or i ne ( w hi c h i s a

s t a nda r di z e d m e a s ur e of oz one

- de pl e t i ng c a pa c i t y of br om i ne a nd c hl or i ne i n t he

s t r a t os phe r e ; s e e f oot n ot e i n t he pr e vi ous s e c t i on o f t hi s E xe c ut i ve S um m a r y ) ha s a l s o

s t a r t e d t o de c r e a s e

.

− I n t he l a s t de c a de

, t he de pl e t i on of t he gl oba l oz on e l a ye r ha s not w o r s e ne d.

− M e a s ur e m e nt s f r om s om e unpol l u t e d l oc a t i ons s how t ha t U V r a di a t i on ha s de c r e a s e d

s i nc e t he l a t e 1990s

, i n a c c or da nc e w i t h obs e r ve d oz one i nc r e a s e s a t t hos e s i t e s

.

• T h e u n u s u al l y s m al l 2002 A n t ar c t i c oz on e h ol e w as c h ar ac t e r i z e d b y a s m al l e r ar e a an d

h i gh e r oz on e l e ve l s t h a n ob s e r ve d d u r i n g t h e p a s t d e c ad e

. T hi s w a s due t o a n unus ua l l y

s t r ong m e t e or ol ogi c a l e ve nt ( a " m a j or s t r a t os phe r i c s udde n w a r m i ng" ) a nd w a s not due t o

c ha nge s i n oz one

- de pl e t i ng ga s e s

. T he 2003 a nd 2 005 oz one hol e s e xhi bi t e d s e ve r e

de pl e t i ons a s obs e r ve d s i nc e t he e a r l y 1990s

. S e ve r e A nt a r c t i c oz one l os s e s w i l l ve r y l i ke l y

c on t i nue t o be obs e r ve d f or a t l e a s t t he ne xt 10

- 20 ye a r s be c a us e of t he e xpe c t e d s l ow de c l i ne

of t he l ong

- l i ve d oz one

- de pl e t i ng ga s e s

.

• B r om i n e i s n ow e s t i m a t e d t o b e ap p r oxi m a t e l y 60 t i m e s as e f f

e c t i ve as c h l or i n e i n gl ob al

oz on e d e p l e t i on , on a p e r

- at om b a s i s

. T hi s va l ue i s l a r ge r t ha n t he e f f

e c t i ve ne s s of 45 us e d

i n t he 2002 A s s e s s m e nt

. T h i s i nc r e a s e i n t he e f f

e c t i ve ne s s of br om i ne i nc r e a s e s t he O z one

D e pl e t i on P ot e nt i a l of br om i ne

- c ont a i ni ng c om pou nds

, e va l ua t e d us i ng t he s e m i

- e m pi r i c a l

m e t hod t ha t ha s be e n us e d i n pr e vi ous A s s e s s m e nt s

.

• L on g

- t e r m r e c ove r y of t h e oz on e l aye r f r om t h e e f f

e c t s of oz on e

- d e p l e t i n g s u b s t an c e s i s

e xp e c t e d t o s p an m u c h of t h e 21 s t c e n t u r y an d i s e s t i m at e d t o oc c u r l at e r t h an p r oj e c t e d

i n t h e p r e vi ou s as s e s s m e n t ( 2002)

. A n i m po r t a nt m i l e s t one i n t he r e c ove r y p r oc e s s i s t he

t i m e w he n c om bi ne d c hl o r i ne a nd b r om i ne a m ount s ( e qui va l e nt e f f

e c t i ve s t r a t os phe r i c

c hl or i ne

, E E S C ) de c l i ne t o pr e

- 1980 va l ue s

.

− T he da t e w he n e qui va l e nt e f f

e c t i ve s t r a t os phe r i c c hl or i ne a t m i dl a t i t ude s r e t ur ns t o pr e

1980 l e ve l s i s now c a l c ul a t e d t o be 2049, f o r t he c a s e of gl oba l c om pl i a nc e w i t h t he

M ont r e a l P r ot oc ol w i t h no s i gni f i c a nt e xc e pt i ons ( S c e na r i o A 1)

. T hi s da t e i s a bout 5

ye a r s l a t e r t ha n p r oj e c t e d i n t he pr e vi ous ( 2002 ) a s s e s s m e nt

. T h i s pr oj e c t e d l a t e r da t e

pr i m a r i l y r e s ul t s f r om ( i ) a n i nc r e a s e i n C F C

- 11 a n d C F C

- 12 e m i s s i ons due t o t he l a r ge r

r e c e nt e s t i m a t e s of a m ount s c ur r e nt l y c ont a i ne d i n e qui pm e nt a nd pr oduc t s ( ba nks ) a nd

( i i ) a n i nc r e a s e i n H C F C

- 22 e m i s s i ons due t o l a r ge r e s t i m a t e d f ut u r e p r oduc t i on

, a s

r e por t e d i n t he 2005 I nt e r gove r nm e nt a l P a ne l on C l i m a t e C ha nge / T e c hnol ogy a nd

E c onom i c A s s e s s m e nt P a ne l ( I P C C / T E A P ) S pe c i a l R e por t on Saf e

guar di ng t he O z one

L ay e r and t he G l obal C l i m at e Sy s t e m : I s s ue s R e l at e d t o H y dr of l uor oc ar bons and

P e r f

l uo r oc ar bons

.

− T he r e t ur n t o pr e

- 1980 c ondi t i ons of e qui va l e nt e f f e c t i ve s t r a t os phe r i c c hl or i ne f o r t he

A nt a r c t i c vor t e x i s p r oj e c t e d t o oc c ur a r ound 2065, m or e t ha n 15 ye a r s l a t e r t ha n t he

r e t ur n of m i dl a t i t ude e qui va l e nt e f f

e c t i ve s t r a t os phe r i c c hl or i ne t o p r e

- 1980 l e ve l s

. T hi s

pr oj e c t e d l a t e r r e c ove r y i s be c a us e

, unl i ke i n pr e vi ous A s s e s s m e nt s

, w e now r e c ogni z e

t ha t t he a ge of a i r i s gr e a t e r i n t he A nt a r c t i c l ow e r s t r a t os phe r e

, w hi c h a f f

e c t s t he a m oun t

of oz one

- de pl e t i ng ga s e s a va i l a bl e f or oz one de pl e t i on. T he e qui va l e nt e f f

e c t i veE x e c u t i v e S u m m a r y R e l e a s e d 1 8 A u g u s t 2 0 0 6

S

c i e n t i f

i c A s s e s s m e n t o f O z o n e D e p l e t i o n : 2 0 0 6

22 s t r a t os phe r i c c hl or i ne e va l ua t i on f o r t he A nt a r c t i c vor t e x ha s not be e n p r e s e nt e d i n

pr e vi ous O z one A s s e s s m e nt s

.

• P ot e n t i al op t i on s f or ac c e l e r at i n g t h e r e c ove r y of t h e oz on e l aye r h ave b e e n e val u a t e d

.

T he t a bl e pr ov i de d be l ow s how s hypot he t i c a l e s t i m a t e s of t he uppe r l i m i t s o f i m p r ove m e nt s

t ha t c oul d be a c hi e ve d i f gl oba l a nt hr opoge ni c pr o duc t i on of oz one

- de pl e t i ng s ubs t a nc e s

w e r e t o s t op a f t e r 2006

, i f e m i s s i ons w e r e e l i m i na t e d f r om e xi s t i ng ba nks a t t he e nd of 2006,

or i f gl ob a l a nt h r opoge ni c e m is s i ons of oz one

- de pl e t i ng s ubs t a nc e s w e r e t o s t op a f t e r 2006

. S om e opt i ons s how gr e a t e r e f f

e c t i ve ne s s f or a c c e l e r a t i ng r e c ove r y o f t he oz one l a ye r t ha n i n

pr e vi ous A s s e s s m e nt s

, f or r e a s ons not e d be l ow

.

T a b l e 1

. P e r c e n t a g e r e d u c t i o n s i n i n t e g r a t e d e q u i v a l e n t e f f e c t i v e s t r a t o s p h e r i c c h l o r i n e r e l a t i v e t o t h e

b a s e l i n e ( A 1 ) s c e n a r i o t h a t c a n b e a c h i e v e d i n t h e h y p o t h e t i c a l c a s e s

. 1

C o m p o u n d o r C o m p o u n d

G r o u p C o l u m n A :

A l l E m i s s i o n s

E l i m i n a t e d f r o m

P r o d u c t i o n a f t e r

2 0 0 6 C o l u m n B :

A l l E m i s s i o n s

E l i m i n a t e d f r o m

E x i s t i n g B a n k s a t

E n d o f 2 0 0 6 C o l u m n C :

A l l E m i s s i o n s

E l i m i n a t e d a f t e r

2 0 0 6

C h l o r o f l u o r o c a r b o n s

( C F C s ) 0

. 3 1 1 1 1

H a l o n s 0

. 5 1 4 1 4

C a r b o n t e t r a c h l o r i d e

( C C l 4 ) 3 ( a ) 3

M e t h y l c h l o r o f o r m

( C H 3 C C l 3 ) 0

. 2 ( a ) 0

. 2

H y d r o c h l o r o f l u o r o c a r b o n s

( H C F C s ) 1 2 4 1 6

M e t h y l b r o m i d e ( C H 3 B r )

( a n t h r o p o g e n i c ) 5 ( a ) 5

1 C o l u m n A c o r r e s p o n d s t o a h y p o t h e t i c a l e l i m i n a t i o n o f a l l e m i s s i o n s f r o m p r o d u c t i o n a f t e r 2 0 0 6

. C o l u m n B c o r r e s p o n d s t o a h y p o t h e t i c a l e l i m i n a t i o n o f a l l e m i s s i o n s f r o m b a n k s e x i s t i n g a t t h e e n d o f

2 0 0 6 ( f o r e x a m p l e

, c a p t u r e a n d d e s t r u c t i o n )

. C o l u m n C c o r r e s p o n d s t o a h y p o t h e t i c a l e l i m i n a t i o n o f

a l l e m i s s i o n s a f t e r 2 0 0 6 a n d i s a p p r o x i m a t e l y e q u a l t o t h e s u m o f c o l u m n s A a n d B

. ( a ) F o r t h e s e c o m p o u n d s

, b a n k s a r e u n c e r t a i n a n d t h e r e f o r e e m i s s i o n s a r e e q u a t e d t o p r o d u c t i o n i n

t h e s e c a l c u l a t i o n s

.

− T he pe r c e nt a ge c um ul a t i ve ( i nt e gr a t e d) r e duc t i ons i n e qui va l e nt e f f

e c t i ve s t r a t os phe r i c

c hl or i ne f or ha l ons a nd C F C s

, i nt e g r a t e d f r om 200 7 unt i l t he 1980 l e ve l i s r e a t t a i ne d

( s how n i n C ol um n B )

, a r e l a r ge r t ha n p r e vi ous l y r e por t e d. T hi s i s be c a us e r e c e nt ba nk

e s t i m a t e s f r om t he 2005 I nt e r gove r nm e nt a l P a ne l on C l i m a t e C ha nge / T e c hnol ogy a nd

E c onom i c A s s e s s m e nt P a ne l ( I P C C / T E A P ) S pe c i a l R e por t on Saf e

guar di ng t he O z one

L ay e r and t he G l obal C l i m at e Sy s t e m : I s s ue s R e l at e d t o H y dr of l uor oc ar bons and

P e r f

l uor oc ar bons a r e s i gni f i c a nt l y l a r ge r a nd l i ke l y m or e r e l i a bl e t ha n va l ue s pr e s e nt e d

i n pr e vi ous A s s e s s m e nt s f or C F C

- 11, C F C

- 12, a nd H a l on

- 1211.

− T he pe r c e nt a ge r e duc t i on i n i nt e g r a t e d e qui va l e nt e f f

e c t i ve s t r a t os phe r i c c hl or i ne f or

H C F C s s how n i n C ol um n A i s l a r ge r t ha n p r e vi ou s l y r e por t e d. T hi s i s be c a us e of

s i gni f i c a nt l y l a r ge r e s t i m a t e s of f ut u r e H C F C

- 22 p r oduc t i on i n A r t i c l e

- 5 c ount r i e s

.E x e c u t i v e S u m m a r y R e l e a s e d 1 8 A u g u s t 2 0 0 6

S

c i e n t i f

i c A s s e s s m e n t o f O z o n e D e p l e t i o n : 2 0 0 6

23 − T he pe r c e nt a ge r e duc t i on i n i nt e g r a t e d e qui va l e nt e f f

e c t i ve s t r a t os p he r i c c hl or i ne f or

m e t hyl br om i de i n C ol um n A i s l a r ge r t ha n pr e vi o us l y r e por t e d. T hi s i s be c a us e of t he

upw a r d r e vi s i on of t he f r a c t i on o f a nt hr opoge ni c e m i s s i ons r e l a t i ve t o t ot a l m e t hy l

br om i de e m i s s i ons

, a s w e l l a s be i ng due t o t he up w a r d r e vi s i on i n t he oz one

- de pl e t i on

e f

f

e c t i ve ne s s of br om i ne a t om s c om pa r e d w i t h c hl or i ne a t om s m e nt i one d e a r l i e r

.

− I n a ddi t i on t o t he pe r c e nt a ge r e duc t i ons i n i nt e gr a t e d e qui va l e nt e f f

e c t i ve s t r a t os phe r i c

c hl or i ne

, t he s e s c e na r i os c a n r e duc e t he t i m e f o r e q ui va l e nt e f f

e c t i ve s t r a t os phe r i c

c hl or i ne t o d r op be l ow 1980 va l ue s

. A hypot he t i c a l e l i m i na t i on o f a l l e m i s s i ons of

oz one

- de pl e t i ng s ubs t a nc e s a f t e r 2006 ( C ol um n C ) w oul d a dva nc e t hi s t i m e by a bout 15

ye a r s

, f r om 2049 t o 2034. A hypot he t i c a l e l i m i na t i on of a l l e m i s s i on s f r om pr oduc t i on o f

oz one

- de pl e t i ng s ubs t a nc e s a f t e r 2006 ( C ol um n A ) w oul d a dva nc e i t by a bout 6 ye a r s

, t o

2043.

− A m e t hyl br o m i de pha s e

- out ha s be e n i n e f f

e c t s i n c e 2005 i n de ve l ope d c ount r i e s

, w i t h

c r i t i c a l

- us e e xe m pt i ons gr a nt e d i n 2005 a nd 2006 a t l e ve l s t ha t a r e 30

- 40% of t he 2003

-

2004 pr oduc t i on l e ve l s

. T w o a ddi t i ona l hypot he t i c a l c a s e s of c r i t i c a l a nd qua r a nt i ne a nd

pr e

- s hi pm e nt ( Q P S ) e xe m pt e d us e s of m e t hyl b r o m i de w e r e c ons i de r e d. I n t he a na l ys i s

of bot h c a s e s

, e qui va l e nt e f f

e c t i ve s t r a t os phe r i c c hl or i ne i s i nt e gr a t e d a bove t he 1980

l e ve l f r om 2007 unt i l i t r e t ur ns t o t he 1980 l e ve l

. T he s i z e of t he c r i t i c a l us e e xe m pt i ons

i s s i m i l a r t o t he e s t i m a t e d us e of m e t hyl br om i de f or Q P S us e

.

> I f c r i t i c a l

- us e m e t hyl b r om i de e xe m pt i ons c ont i nu e i nde f i ni t e l y a t t he 2006 l e ve l

c om pa r e d t o a c e s s a t i on of t he s e e xe m pt i ons i n 20 10 or 2015

, m i dl a t i t ude i nt e g r a t e d

e qui va l e nt e f f

e c t i ve s t r a t os phe r i c c hl or i ne w oul d i nc r e a s e by 4. 7% or 4

. 0%

,

r e s pe c t i ve l y.

> I f p r oduc t i on of m e t hyl br om i de f or Q P S us e w e r e t o c ont i nue a t p r e s e nt l e ve l s a nd

c e a s e i n 2015, m i dl a t i t ude i nt e gr a t e d e qui va l e nt e f f

e c t i ve s t r a t os phe r i c c hl or i ne

w oul d de c r e a s e by 3. 2% c om pa r e d w i t h t he c a s e o f c ont i nue d p r oduc t i on a t pr e s e nt

l e ve l s

.

• F ai l u r e t o c om p l y w i t h t h e M on t r e al P r ot oc ol w ou l d d e l ay , or c o u l d e ve n p r e ve n t

,

r e c ove r y of t h e oz on e l aye r

. E m i s s i ons a s s oc i a t e d w i t h c ont i nue d o r e xpa nde d e xe m pt i ons

, Q P S

, p r oc e s s a ge nt s

, a nd f e e ds t oc ks m a y a l s o de l a y r e c ove r y.

• T h e r ol e of ve r y s h or t

- l i ve d h al oge n at e d s u b s t an c e s i n s t r at os p h e r i c oz on e d e p l e t i on i s

n ow b e l i e ve d t o b e of gr e at e r i m p or t an c e t h an p r e vi ou s l y as s e s s e d

. T hi s s ugge s t s t ha t

s i gni f i c a nt a nt hr opoge ni c pr oduc t i on of s uc h s ubs t a nc e s c oul d e nha nc e oz one de pl e t i on.

C ur r e nt unde r s t a ndi ng of t he O z one D e pl e t i on P ot e nt i a l s of t he s e c l a s s e s of s ubs t a nc e s i s :

− T he O z one D e pl e t i on P ot e nt i a l s of n

- pr opyl br om i de a r e 0. 1 f or t r op i c a l e m i s s i ons a nd

0. 02

- 0. 03 f o r e m i s s i ons r e s t r i c t e d t o n or t he r n m i dl a t i t ude s

. T he s e a r e unc ha nge d f r om

t he pr e vi ous a s s e s s m e nt

.

− N e w a na l ys e s s ugge s t uppe r

- l i m i t O z one D e pl e t i o n P ot e nt i a l s f o r C F 3 I of 0. 018 f o r

t r opi c a l e m i s s i ons a nd 0. 011 f or m i dl a t i t ude e m i s s i ons

. T he pr e vi ous A s s e s s m e nt ha d a n

uppe r l i m i t of 0. 008

.E x e c u t i v e S u m m a r y R e l e a s e d 1 8 A u g u s t 2 0 0 6

S

c i e n t i f

i c A s s e s s m e n t o f O z o n e D e p l e t i o n : 2 0 0 6

24 − A ny c hl or i na t e d ve r y s hor t

- l i ve d s our c e ga s w i t h a l i f e t i m e of

~ 25 da ys

, one c hl o r i ne

a t om

, a nd a s i m i l a r m o l e c ul a r w e i ght t o C F C

- 11, h a s a n O z one D e pl e t i on P ot e nt i a l o f

a

bout 0. 003.

• U n d e r s t an d i n g t h e i n t e r c on n e c t i on s b e t w e e n oz on e d e p l e t i on an d c l i m at e c h an ge i s

c r u c i al f or p r oj e c t i o n s of f u t u r e oz on e ab u n d an c e s

. T he oz one

- de pl e t i ng s ubs t a nc e s a nd

m a ny of t he i r s ubs t i t ut e s a r e a l s o gr e e nhous e ga s e s ; c ha nge s i n oz one a f f

e c t c l i m a t e ; a nd

c ha nge s i n c l i m a t e a f f

e c t oz one

. T he s e i s s ue s w e r e r e c e nt l y t he s ubj e c t of t he I P C C / T E A P

2005 S pe c i a l R e por t on Saf e

guar di ng t he O z one L ay e r and t he G l obal C l i m at e Sy s t e m :

I

s s ue s R e l at e d t o H y dr of l uor oc ar bons and P e r f

l uor oc ar bon s

, a nd s om e a s pe c t s of t he

c oupl i ng be t w e e n oz one de pl e t i on a nd c l i m a t e c ha nge ha ve be e n c ons i de r e d i n t hi s 2006

oz one a s s e s s m e nt

. A n i m por t a nt de ve l opm e nt ha s be e n t he e m e r gi ng us e of t hr e e

di m e ns i ona l m ode l s t ha t i nc or por a t e t he i nt e r a c t i o n be t w e e n c he m i s t r y a nd c l i m a t e

.