AERONOMICA ACTA

I N S T I T U T D A E . R 0 N 0 M I E S P A T I A L E D E B E L G I Q U E

3 • Avenue Circulaire B - 1180 B R U X E L L E S

AERONOMICA ACTA

A - N° 296 - 1985

CO2 and CO abundances below 130 km altitude from infrared spectra

by

J. VERCHEVAL, C. LIPPENS, C. MULLER, M. A C K E R M A N M-P. LEMAITRE, J. BESSON, A. GIRARD and J. LAURENT

b e l g i s c h i n s t i t u u t v o o r r u i m t e - a e r o n o m i e 3 - Ringlaan

B • 1180 B R U S S E L

F O R E W O R D

T h i s text h a s been p r e s e n t e d at the Fall Meeting of the American Geophysical Union (December 3 - 7 , 1984).

A V A N T - P R O P O S

Ce texte a été p r é s e n t é à la r é u n i o n d'automne de l'American Geophysical Union ( 3 - 7 décembre 1984).

V O O R W O O R D

Deze t e k s t w e r d v o o r g e s t e l d tijdens de h e r f s t v e r g a d e r i n g v a n de American Geophysical Union ( 3 - 7 december 1984).

V O R W O R T

Dieser T e x t w u r d e p r ä s e n t i e r t w ä h r e n d der H e r b s t - t a g u n g der American Geophysical Union ( 3 - 7 Dezember 1984).

C 0² A N D CO A B U N D A N C E S BELOW 130 KM A L T I T U D E FROM I N F R A R E D S P E C T R A

J . V E R C H E V A L * , C . L I P P E N S * , C . M U L L E R * , M. A C K E R M A N * M . - P . L E M A I T R E * * , J . B E S S O N * * , A . G I R A R D * * a n d J . L A U R E N T * *

* B e l g i a n I n s t i t u t e f o r Space A e r o n o m y , B - 1 1 8 0 B r u s s e l s , B e l g i u m

* * O f f i c e N a t i o n a l e d ' E t u d e s et de R e c h e r c h e s A é r o s p a t i a l e s F - C h â t i l l o n , F r a n c e .

A h s t r a r . t

T h e o b s e r v a t i o n o f i n f r a r e d a b s o r p t i o n l i n e s b y means o f a g r i l l s p e c t r o m e t e r on b o a r d S p a c e l a b 1 has a l l o w e d t h e d e t e r m i n a t i o n o f C O ^ a n d CO a b u n d a n c e s in t h e low t h e r m o s p h e r e a n d in t h e m i d d l e a t m o s p h e r e . I t is s h o w n t h a t t h e r e s u l t s c a n be well r e p r e s e n t e d b y t h e o r e t i c a l models b a s e d on t h e i n t e r a c t i o n p r o c e s s e s b e t w e e n s o l a r UV r a d i a t i o n , C O , C O ^ a n d OH m o l e c u l e s .

Résumé

L ' o b s e r v a t i o n d e r a i e s d ' a b s o r p t i o n i n f r a r o u g e au m o y e n d ' u n s p e c t r o m è t r e à g r i l l e a b o r d d e S p a c e l a b 1 a p e r m i s la d é t e r m i n a t i o n des c o n c e n t r a t i o n s d e C 0² et CO d a n s la basse t h e r m o s p h è r e e t d a n s l ' a t m o - s p h è r e m o y e n n e . On m o n t r e q u e les r é s u l t a t s o b t e n u s p e u v e n t ê t r e r e p r é s e n t é s v a l a b l e m e n t p a r des modèles t h é o r i q u e s basés s u r les p r o c e s s u s d ' i n t e r a c t i o n e n t r e la r a d i a t i o n u l t r a v i o l e t t e s o l a i r e , les molécules C O , CO~ et O H .

Samenvatting

De waarneming van i n f r a r o d e absorptielijnen door middel van een rasterspectrometer aan boord van Spacelab 1 h e e f t toegelaten CO^

en CO concentraties te bepalen in de lage thermosfeer en de midden- atmosfeer. Er w o r d t aangetoond dat de resultaten op degelijke wijze

kunnen voorgesteld worden door theoretische modellen gebaseerd op de wisselwerkingsprocessen tussen de u l t r a v i o l e t t e z o n n e s t r a l i n g , C O , CO^

en OH moleculen.

Zusammenfassung

Die Beobachtung von i n f r a r o t e n Absorptionslinien mittels eines Grillespektrometers an Bord Spacelab 1 hat ermöglicht C 02 und CO

Konzentrationen zu bestimmen in der Niederthermosphäre und der M i t t e l - atmosphäre. Man zeigt das die Resultaten auf solider Weise können p r ä s e n t i e r t werden d u r c h theoretische Modellen basiert auf den Wechsel- wirkungsprozessen zwischen der u l t r a v i o l e t t e n S o n n e n s t r a h l u n g , C O , CO„ un OH Molekülen.

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I N T R O D U C T I O N

During Spacelab 1 mission, a grille spectrometer operating on the Spacelab pallet has observed trace species in the low thermosphere and in the mesosphere by pointing the Sun at sunrise or sunset.

Preliminary data on C H

, C 0

, C O , H

0 , NO and N 0

molecules have already published (LemaTtre et a l . , 1984; Lippens et a l . , 1985; Laurent at a l . , 1984).

We wish to report here results obtained for the C 0

and CO molecules in order to compare them with those provided by theoretical models.

O B S E R V A T I O N

Several portions of absorption runs were scheduled during the Spacelab 1 mission to observe C 0

at the highest possible altitudes where its mixing ratio has been already shown to depart from its homo- spheric values. As an example, figure 1 shows the spectrum obtained during event 14 when the sunlight was grazing the Earth at an altitude of 117 km. The region of the strongest absorption lines was chosen, that is to say near a wave number of 2360 cm . One can note the v e r y

large resolution of the spectrum. Retrieved number densities for two runs are shown in figure 2. The nearly parallel lines represent constant volume mixing ratios from 310~

to 310"

. Event 13 has been studied in detail and the results from two lines are shown. Up to 100 km altitude,

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the. C 0

volume mixing ratio follows closely the 310 value and drops abruptly above by a factor of 10 over 15 kilometers. These results are in good agreement with the mass spectrometric data and give great confidence in the data used from the instrument.

In addition, two absorption runs provided data on carbon monoxide CO. In the same figure 2,one can see the number density of

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I I

3250

2357 2359 2361

WAVE NUMBER (cm

)

2363

Fig. 1.- CO2 absorption spectrum recorded at sunlight tangent altitude equal to 117 km.

en I I

6 0 - 10

n

(OH)<n

(OH)<n,(OH) (3) (2) (1)

10' 10 ⁸ 10a

® 2357.835 cm"

B 2358.728 cm-' !

V 2358.728 cm-

EVT 14 SPACELAB I

EVT 13

3 s 10

C O

o 2119.681 cm"

EVT 3 3x10"

10 ¹⁰ 10 ^li

NUMBER DENSITY (cm"

)

Fig. 2 . - Number density of C O ^ and C O v e r s u s altitude using two different C O „ absorption lines and the C O line. The nearly parallel lines

2 6 -8 -14

represent constant volume mixing ratios from 3 x 10 to 3 x 10 The c u r v e s ( 1 ) , (2) and (3) are theoretical profiles of C O number density obtained with thé three adopted vertical distributions of n(0H) shown in figure 5. The solid line is the theoretical profile of C Q ^ number density.

CO u s i n g t h e P_ CO l i n e w h i c h is s h o w n i n f i g u r e 3 a t a w a v e n u m b e r - 1

o f 2119.68 cm , t h i s o b s e r v a t i o n c o r r e s p o n d i n g t o a g r a z i n g r a y a t 9 2 . 6 km. T h i s a b s o r p t i o n was o b s e r v e d at s u n s e t i n t h e n o r t h e r n h e m i - s p h e r e . T h e d o t t e d l i n e s i m u l a t e s t h e CO s o l a r l i n e i n s u c h a w a y t h a t t h e d i f f e r e n c e b e t w e e n t h e t w o c u r v e s g i v e s t h e a t m o s p h e r i c a b s o r p t i o n d u e t o C O . T h i s Pg l i n e is c o n t a m i n a t e d b y ozone [ O ^ ] a b s o r p t i o n s below 60 km p r e c l u d i n g CO d e t e r m i n a t i o n s at l o w e r a l t i t u d e s . In f i g u r e 2 , one can o b s e r v e t h e l a r g e i n c r e a s e o f t h e CO m i x i n g r a t i o at a l t i - t u d e s w h e r e t h e CO^ p h o t o d i s s o c i a t i o n b y t h e s o l a r H L y m a n a r a d i a t i o n t a k e s place a n d w h e r e t h e w a t e r v a p o r h ^ O a b u n d a n c e v a n i s h e s a b r u p t -

l y . T h e CO l a r g e s t n u m b e r d e n s i t y is o b s e r v e d n e a r 70 km a l t i t u d e , close t o t h e H L y m a n a p h o t o p r o d u c t i o n p e a k . V e r t i c a l d i s t r i b u t i o n s o f c a r b o n m o n o x i d e i n t h e m e s o s p h e r e a n d i n t h e t h e r m o s p h e r e c o m b i n e d w i t h d i s t r i b u t i o n o f c a r b o n d i o x i d e shows f o r t h e f i r s t t i m e w h e r e t h e s e t w o c o n s t i t u e n t s p r e s e n t equal a b u n d a n c e s . M e a s u r e m e n t s i n d i c a t e an e q u a l a b u n d a n c e a t 115 ± 5 k m .

F i g u r e 4 s h o w s , b y t h e c o n t i n u o u s c u r v e , t h e p r o f i l e o f CO f r o m t h e w e a k e r F ^ l i n e f o r an o b s e r v a t i o n w h i c h t o o k place a t s u n r i s e 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 e R? l i n e p r o v i d e d d a t a d o w n t o

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t h e low s t r a t o s p h e r e w h e r e a m i x i n g r a t i o v a l u e e q u a l t o 10 is r e a c h e d a t 30 km a l t i t u d e in a g r e e m e n t w i t h b a l l o o n b o r n e m e a s u r e m e n t s . T h e d o t t e d l i n e r e p r e s e n t s t h e p r o f i l e s h o w n i n f i g u r e 2 . T h e c o m p a r i s o n b e t w e e n t h e t w o o b s e r v e d d i s t r i b u t i o n s i n d i c a t e s a l a r g e v a r i a b i l i t y o f t h e m e s o s p h e r i c c a r b o n m o n o x i d e , i n d i c a t i n g t h e need f o r more m e a s u r e - m e n t s .

COMPARISON W I T H MODELS

T h e o b s e r v a t i o n s o f CO a n d CO^ h a v e been c o m p a r e d w i t h model r e s u l t s . Models h a v e been c o n s t r u c t e d f o r t h e a l t i t u d e i n t e r v a l f r o m 60 u p t o 120 km a l t i t u d e b y c o n s i d e r i n g f i r s t t h e p h o t o d i s s o c i a t i o n o f C O?

1900

O >

â, 1700

UJ o

a. < 1500

C O E V T 3

Q ? ft It m fc • »«lit

t]

u

i . . • • ^{— . — . — . — • —}

2119 2120 WAVE NUMBER (cm"

)

2121

Fig. 3.- CO absorption spectrum recorded at sunlight tangent altitude equal to 92.6 km. P6 line appears at a wave number of 2119.68 cm . The - 1

dotted line simulates the CO solar line.

\

Fig. 4 . - Carbon monoxide number density v e r s u s altitude retrieved from two solar occultation r u n s , one in the southern hemisphere at sunrise and the other one in the northern hemisphere at sunset. The geographic coordinates of the solar rays tangent points at 50 km altitude are indicated. Two different absorption lines were used of which the wavenumbers are indicated. The nearly parallel lines represent

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constant volume mixing ratios from 10 to 10 . The dates of data capture are also g i v e n . The dashed line ( 1 ) is the theoretical profile of C O number density obtained with the vertical distribution n^COH)

shown in figure 5.

second, t h e d e s t r u c t i o n reaction of CO by OH molecules leading to reformation of C 02 ( C O + OH C 02 + H ) . We have considered s t e a d y - state conditions, solar conditions corresponding to solar z e n i t h angle of 75° and atmospheric parameters t a k e n from the s t a n d a r d atmosphere due to Nicolet ( N i c o l e t , 1980). In these models, two parameters play a major role : t h e eddy diffusion coefficient and the v e r t i c a l profile of t h e OH molecule abundance.

We have adopted t h e 3 v e r t i c a l profiles of n ( O H ) shown in f i g u r e 5 . T h e f i r s t one one called n ^ O H ) is c h a r a c t e r i z e d b y number densities which are generally the g r e a t e s t given in t h e l i t t e r a t u r e with

7 7 - 3

values between 10 and 210 cm below 80 km a l t i t u d e . T h e second p r o f i l e , called n £ ( O H ) , is similar to the f i r s t one b u t with values n e a r l y two times smaller. F i n a l l y , one consider a t h i r d profile n^COH) with a v e r y a b r u p t decrease already above 70 km; this t h i r d profile can be related with t h e rapid decrease, at t h e same a l t i t u d e , of t h e water vapor abundance which was also observed in t h e n o r t h e r n hemisphere d u r i n g sunset and which has been described elsewhere ( L i p p e n s et a l . , 1984).

Theoretical profiles were obtained by solving t r a n s p o r t and continuity equations and by adopting a vertical profile f o r t h e eddy diffusion coefficient which provides the best agreement with the o b s e r - vations of CO and CO^/ g i v i n g especially a maximum of n ( C O ) at about 70 km altitude and a v a l u e , at 60 km, which n e a r l y corresponds to t h e photochemical equilibrium between CO and C 02.

In f i g u r e 2 , we show t h e model c u r v e s obtained with t h e 3 adopted vertical profiles of n ( O H ) . As it can be e x p e c t e d , t h e CO number density is decreasing when n ( O H ) is increasing. For instance, at 75 km, t h e r e is a variation of the CO number density by a factor of 5 between the two extreme c u r v e s ( 1 ) and ( 3 ) , t h a t is to say when t h e OH abundance varies by a factor of 10 at the same a l t i t u d e . It can be seen t h a t the d i s t r i b u t i o n n _ ( O H ) , with t h e smallest values of n ( O H ) , is

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NUMBER DENSITY n(OH) (cm"

)

Fig. 5 . - Vertical distributions of OH number density used in calculations of

theoretical profiles of CO abundance.

the best one to lead to an agreement with the observations. This conclusion gives some guaranty to the measurements of H^O already mentioned.

For the CC>² molecule, the solid line shows that the agreement is perfect up to 100 km and relatively good at higher altitudes.

On the other hand, as shown in figure 4, the agreement with the observations of CO in the southern hemisphere, is obtained with the n^(OH) distribution, that is to say with the greatest values of n ( O H ) . So, two v e r y different vertical profiles of n ( O H ) must be considered to get an agreement with the observations in the two hemispheres. This is probably due to the v e r y large difference in solar conditions in the two hemispheres :. summer in the southern hemisphere and winter in the northern hemisphere. As we can see in figure 6, in the southern hemi- sphere, the sun was almost always above the horizon during the day whereas .in the northern hemisphere, daylight had only a duration of about 10 hours. So, water vapor abundances and therefore OH abundances must be v e r y different during the two series of observa- tions with higher values in the southern hemisphere.

Finally, figure 7 shows the best f i t eddy diffusion profiles corresponding to the three adopted values of OH number density.

D ( C 0 2 > is the diffusion coefficient for CO^ which plays the leading role above 100 km. Concerning the eddy diffusion coefficient, we can see that there is a satisfactory agreement with the values obtained by (Allen et a l . , 1981).

CONCLUSION

The results obtained from the grille spectrometer experiment, on the CO and CO^ molecules, are in good agreement with spectrometric data in the thermosphere, and balloon borne instruments in the strato-

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GMT

F i g . 6 . - Solar elevation v e r s u s time in h o u r s ( G M T ) f o r December 3, 1983 in the s o u t h e r n hemisphere (68 S ) and f o r November 29, 1983 in the n o r t h e r n hemisphere (44 N ) .

EDDY DIFFUSION COEFFICIENT (cm

s"

)

F i g . 7 . - T h e b e s t f i t e d d y d i f f u s i o n c o e f f i c i e n t d e r i v e d i n t h i s p a p e r c o r r e s p o n d i n g t o t h e t h r e e a d o p t e d v e r t i c a l p r o f i l e s o f OH n u m b e r d e n s i t y . T h e s o l i d , l i n e is t h e e d d y , d i f f u s i o n c o e f f i c i e n t d e r i v e d b y A l l e n et a l . ( 1 9 8 1 ) . T h e d a s h e d c u r v e i n d i c a t e s t h e d i f f u s i o n c o e f f i c i e n t f o r C O , u s e d i n t h i s p a p e r .

sphere; they can also be well represented by theoretical models based on the interaction processes between solar UV radiation, CO, C O a n d OH molecules.

ACKNOWLEDGEMENTS

We wish to thank Prof. M. NICOLET for several profitable discussions.

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REFERENCES

A L L E N , M . , Y . L. Y U N G and J . W . W A T E R S , V e r t i c a l T r a n s p o r t and Photochemistry in t h e T e r r e s t r i a l Mesosphere and Lower T h e r m o - sphere ( 5 0 - 1 2 0 k m ) , J. Geophys. R e s . , 86, 3617-3627 ( 1 9 8 1 ) . L A U R E N T , J . , M . - P . L E M A I T R E , J. BESSON, A . G I R A R D , C . LIPPENS

C . M U L L E R , J. V E R C H E V A L and M. A C K E R M A N , Middle atmo- spheric NO and N 0² observed by means of t h e Spacelab one g r i l l e spectrometer, Aeronomica Acta A n ° 293, 19 p p . ( 1 9 8 4 ) .

L E M A I T R E , M . - P . , J. L A U R E N T , J. BESSON, A . G I R A R D , C . LIPPENS C . M U L L E R , J. V E R C H E V A L and M. A C K E R M A N , Sample p e r f o r - mance of t h e g r i l l e spectrometer, Science, 225, 171-172 ( 1 9 8 4 ) . LIPPENS, C . , C . M U L L E R , J. V E R C H E V A L , M. A C K E R M A N , J.

L A U R E N T , M . - P . L E M A I T R E , J. BESSON and A . G I R A R D , T r a c e constituents measurements deduced from spectrometric observations on board Spacelab, Advances in Space Research, in press ( 1 9 8 5 ) . N I C O L E T , M . , Etude des réactions chimiques de l'ozone dans la s t r a t o -

s p h è r e , Edt. I n s t i t u t Royal Météorologique de Belgique, 536 p p . ( 1 9 8 0 ) .

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