Kinetics of Photolysis of Low Concentrations of Nitrogen Dioxide in Air

Kinetics of Photolysis of Low Concentrations of Nitrogen Dioxide in Air H. W. FORD, G. J . DOYLE, and NOBORU

ENDOW

Downloaded by UNIV LAVAL on July 13, 2016 | http://pubs.acs.org Publication Date: January 1, 1959 | doi: 10.1021/ba-1959-0021.ch055

Stanford Research Institute, Palo Alto, Calif.

Rate constants obtained at high concentrations are valid for estimating the rates of reaction at low partial pressures of atmospheric contaminants. Kinetic studies may be carried out at trace concentrations. Results are given for determining the rate of reaction of nitrogen dioxide with ozone.

Photochemical s t u d i e s u s i n g t r a c e r e a c t a n t c o n c e n t r a t i o n s h a v e b e e n r e p o r t e d w i t h i n c r e a s i n g f r e q u e n c y i n recent y e a r s , l a r g e l y because of a r a p i d l y d e v e l o p i n g i n t e r e s t i n t h e c h e m i s t r y of p o l l u t e d a t m o s p h e r e s . T h e s e studies h a v e b e e n i l l u m i n a t i n g , b u t t h e e x a c t i n g p r o c e d u r e s of c h e m i c a l k i n e t i c s n e c e s s a r y t o o b t a i n r a t e c o n s t a n t s {1) w e r e not followed. P h o t o c h e m i c a l reactions t h a t occur i n p o l l u t e d atmospheres have been studied. B e c a u s e n i t r o g e n d i o x i d e s h o u l d b e i m p o r t a n t i n these r e a c t i o n s , i n v e s t i g a t i o n w a s d i r e c t e d t o r e a c t i o n s of t h i s c o m p o u n d ; i t s p h o t o l y s i s a t t r a c e c o n c e n t r a t i o n s w a s carried out i n highly purified a i r . T h e purpose was to determine whether the per t i n e n t r a t e c o n s t a n t s m e a s u r e d i n t h e u s u a l p r e s s u r e ranges w e r e v a l i d a t t h e v e r y l o w p a r t i a l pressures o f a t m o s p h e r i c c o n t a m i n a n t s a n d t o d e t e r m i n e t h e f e a s i b i l i t y of c a r r y i n g o u t k i n e t i c studies a t trace concentrations. D e t a i l e d kinetic studies a t c o n centrations below 5 p . p . m . i n purified a i r show t h a t rate constants have been v a l i d i n this range.

Instruments

and

Apparatus

I n s t r u m e n t a t i o n f o r t h e research was developed p r i o r t o f o r m u l a t i o n of the p r o b l e m . T h i s f o r t u n a t e s i t u a t i o n arose because t h e i n s t r u m e n t s w e r e d e v e l o p e d f o r m o n i t o r i n g t h e l o w e r a t m o s p h e r e f o r ozone, n i t r i c o x i d e , a n d n i t r o g e n d i o x i d e ; these c o m pounds are usually present i n polluted atmospheres a t concentrations below 1 p.p.m. b y v o l u m e . O n h a n d w e r e a n a u t o m a t i c r e c o r d i n g n i t r o g e n d i o x i d e a n a l y z e r (11), a n e u t r a l p o t a s s i u m i o d i d e o x i d a n t r e c o r d e r (8), a n d a n ozone p h o t o m e t e r ( M o d e l 53 u l t r a v i o l e t , H a r o l d K r u g e r I n s t r u m e n t s , S a n G a b r i e l , C a l i f . ) . E a c h of these i n s t r u m e n t s h a s a s e n s i t i v i t y o f 1 t o 2 p . p . h . m . p a r t s of c a r r i e r gas a t a t m o s p h e r i c p r e s s u r e . W i t h o u t t h e i r p r i o r d e v e l o p m e n t , t h e p h o t o c h e m i c a l s t u d y w o u l d have b e e n i m p o s s i b l e . T h e flow sheet f o r t h e a p p a r a t u s i s s h o w n i n F i g u r e 1. A carrier gas, u s u a l l y a i r , is b l o w n t h r o u g h t h e a p p a r a t u s w i t h a s m a l l d i a p h r a g m p u m p . F r o m t h e p u m p , t h e a i r passes t h r o u g h a p u r i f i c a t i o n t r a i n , a m i x i n g m a n i f o l d , a r e a c t i o n vessel, a n d a n a n a l y s i s m a n i f o l d . I n t h e p u r i f i c a t i o n t r a i n , t h e a i r passes t h r o u g h a glass w o o l p l u g , a L e c t r o d r y e r ( P i t t s b u r g h L e c t r o d r y e r C o . , 500 32nd S t . , P i t t s b u r g h , P a . ) , a D r i e r i t e t o w e r , a n A s c a r i t e t o w e r , a n d a s e c o n d D r i e r i t e t o w e r . I t t h e n passes t h r o u g h a M i l l i p o r e filter, a p l a t i n u m catalyst furnace, a n d t w o traps cooled b y l i q u i d oxygen, 410

OZONE CHEMISTRY AND TECHNOLOGY Advances in Chemistry; American Chemical Society: Washington, DC, 1959.

411

FORD, DOYLE, A N D ENDOW-KINETICS OF PHOTOLYSIS

t h e s e c o n d of w h i c h i s p a c k e d w i t h a c t i v a t e d c h a r c o a l . T h e a i r t h e n passes t h r o u g h a m i x i n g m a n i f o l d c o n s i s t i n g of t h r e e V e n t u r i - t y p e m i x e r s . A t t h e t h r o a t of e a c h m i x e r is a side t u b e f o r i n t r o d u c i n g t h e gases t o b e s t u d i e d . ( A D r i e r i t e c o l u m n i s s h o w n i n F i g u r e 1, b u t t h i s w a s r e p l a c e d b y t h e L e c t r o d r y e r . ) BALL ANO SOCKET JOINT


INLET

u

ANNULAR TRAP

FLOWMETER

Figure 1.

Schematic flow sheet of air-purification train, mixing manifold, a n d re action vessel

N i t r o g e n d i o x i d e , f o r e x a m p l e , i s a d d e d b y m e a n s of a b l e e d e r b u l b t o t h e t h r o a t of one of t h e m i x e r s . T h e a i r c o n t a i n i n g n i t r o g e n d i o x i d e enters t h e 5 0 - l i t e r r e a c t i o n flask t h r o u g h t h e t h r o a t of a n a l l - g l a s s b l o w e r . T h e b l o w e r c i r c u l a t e s a i r i n t h e flask a n d t h r o u g h a b y p a s s t o a K r u g e r ozone p h o t o m e t e r . T h e a i r t h e n passes t o t h e a n a l y t i c a l s e c t i o n . T h i s s e c t i o n consists of a c o n t i n u o u s n i t r o g e n d i o x i d e a n a l y z e r , a n e u t r a l p o t a s s i u m i o d i d e o x i d a n t r e c o r d e r , a n d , w h e n necessary, a s e c o n d K r u g e r p h o t o m e t e r .

Experimental T h e l i g h t i n t e n s i t y , s t u d i e d i n t h e r e a c t i o n flask u s i n g u r a n y l o x a l a t e as a n a c t i nometer, was determined w i t h considerable accuracy. R e l a t i v e light intensities are s h o w n i n F i g u r e 2 i n a p p r o x i m a t e l y t h e c o r r e c t p o s i t i o n s i n t h e flask cross sections. T h e l i g h t i n t e n s i t y i n t h e c e n t e r of t h e flask is set e q u a l t o 1.00. T h e a b s o r p t i o n coefficient of n i t r o g e n d i o x i d e w a s m e a s u r e d f o r s e v e r a l m e r c u r y lines b y H o l m e s a n d D a n i e l s (5). T h e r e s o l v e d s p e c t r a of t h e n i t r o g e n d i o x i d e n i t r o g e n t e t r o x i d e s y s t e m were s e p a r a t e d b y H a l l a n d B l a c e t (4). T h e value they f o u n d f o r t h e a b s o r p t i o n coefficient a t 3660 A . w a s i n e s s e n t i a l a g r e e m e n t w i t h t h a t o b t a i n e d b y H o l m e s a n d D a n i e l s . T h e a b s o r p t i o n cross s e c t i o n o f 5.8 Χ 1 0 sq. cm. f o r n i t r o g e n d i o x i d e a t 3660 A . w a s c a l c u l a t e d f r o m t h e d a t a of H o l m e s a n d D a n i e l s . T h e p h o t o l y s i s o f n i t r o g e n d i o x i d e h a s b e e n s t u d i e d b y N o r r i s h (9), B a x t e r a n d D i c k i n s o n (#), H o l m e s a n d D a n i e l s (5), a n d H a l l (3). A recent s t u d y w a s m a d e b y N o r r i s h a n d T h r u s h (10). -


1

9

412

A D V A N C E S IN

CHEMISTRY SERIES


/

Figure 2.

Relative light intensities in 50-liter flask

S t a r t i n g n e a r 3660 A . a n d g o i n g t o s h o r t e r w a v e l e n g t h s (3130 Α . ) , t h e p h o t o l y s i s proceeds b y

Λ* + ΝΟ*-*ΝΟ + 0 w i t h a q u a n t u m y i e l d near unity.

(1)

F o l l o w i n g R e a c t i o n 1,

0 + 0 + M-»0 + M

(2)

0 + NO-> 0 + N0

(3)

2

3

3

2

2

w h e r e M = N a n d / o r 0 , m a y be p r e s u m e d t o o c c u r . A l l q u a n t i t i e s are k n o w n f o r c a l c u l a t i n g t h e r a t e of p r o d u c t i o n of o x y g e n a t o m s , because R e a c t i o n 2 is f a s t , t h e rates of p r o d u c i n g o x y g e n a n d ozone are e q u a l . F r o m t h e r a t e of f o r m a t i o n of ozone a n d t h e s t e a d y - s t a t e ozone c o n c e n t r a t i o n , t h e r a t e of R e a c t i o n 3 c a n be c a l c u l a t e d . A p l o t of t h e ozone levels o b t a i n e d i n t h e p h o t o l y s i s of n i t r o g e n d i o x i d e is s h o w n i n F i g u r e 3 t o g e t h e r w i t h t h e t h e o r e t i c a l c u r v e a n d least squares fit of t h e d a t a . F r o m t h i s , k w a s 3.0 Χ 1 0 l i t e r m o l e s e c . , c o m p a r e d w i t h a v a l u e of 1 Χ 1 0 o b t a i n e d b y e x t r a p o l a t i n g t h e d a t a of J o h n s t o n a n d C r o s b y (6) f r o m —42° C . t o r o o m t e m p e r a t u r e . T h e o b s e r v e d s t e a d y - s t a t e ozone levels are i n a g r e e m e n t w i t h t h e rise a n d d e c a y t i m e s of t h e ozone levels u p o n o p e n i n g a n d c l o s i n g t h e s h u t t e r s . A l t h o u g h R e a c t i o n 3 is a m o n g t h e fastest m e a s u r e d b y d i r e c t o b s e r v a t i o n , t h e d e c a y of ozone u p o n s h u t t e r i n g t h e arcs r e q u i r e s s e v e r a l m i n u t e s . T h i s d e m o n s t r a t e s t h e effectiveness of s t u d y i n g fast r e a c t i o n s u s i n g t r a c e c o n c e n t r a t i o n s of r e a c t a n t s . W h e n c o n c e n t r a t i o n s of n i t r o g e n d i o x i d e a b o v e 1 p . p . m . a r e p h o t o l y z e d i n a i r a t 2

3

2

7

- 1

- 1


7

FORD, DOYLE, A N D EN D O W - K I N E T I C S OF 1,000

Ί — (NO ) t

o

1

M

413

PHOTOLYSIS

Ί

" i i |

I I I I I J

1—I

"I—I

I 1 I 1 LI

IS THE CONCENTRATION OF NITROGEN 0IOXI0E IN THE INFLUENT AIR STREAM


(0,)cer. IS THE OZONE LEVEL CORRECTED FOR THE OZONE DECAY OCCURRING DURING TRANSIT FROM FLASK TO PHOTOMETER

' [](NO )o -(O,)cor] t

Figure 3.

ι

ι ι I I I. ipoo

(pphm)

Calculated a n d observed ozone levels in photolysis of nitrogen dioxide in purified dry air

atmospheric pressure, a transient ozone peak results. the reaction O

+

N O 2 - »

0

2

+

This effect has been ascribed to

N0

(4)

A t least two additional reactions must be taken into account : Μ + 0 + Ν 0 - > NO3 + M 2

N0

3

+ NO-> 2N0

2

(5) (6)

assuming Reaction 6 to be fast and Reaction 5 to be rate-determining. T o separate the rate constant for Reaction 4 from that of Reaction 5, nitrogen dioxide was photolyzed at concentrations below 5 p.p.m. in nitrogen at atmospheric pressure and at a nitric oxide-nitrogen dioxide ratio sufficiently low to keep the reaction. M + 0 + NO-» N 0 + M 2

from competing. Under these conditions, the quantum yield of nitrogen disappearance had a value of 0.5. F r o m this

(7) dioxide

and the net effect of Reactions 4, 5, and 6 is to lead to the transient ozone peak. A s the nitric oxide-nitrogen dioxide ratio increases i n the photolysis of nitrogen dioxide i n nitrogen, the quantum yield of nitrogen dioxide disappearance approaches zero. T h e ratio of the rate of Reaction 7 to Reaction 4 plus 5 can be obtained from the relation-


A D V A N C E S IN CHEMISTRY SERIES

414

s h i p of t h e q u a n t u m y i e l d t o t h i s r a t i o . I f l o w c o n c e n t r a t i o n s o f o x y g e n a r e s u b s t i t u t e d f o r n i t r i c o x i d e a n d t h e q u a n t u m y i e l d is m e a s u r e d as a f u n c t i o n o f t h e o x y g e n n i t r o g e n d i o x i d e r a t i o , t h e r a t i o of t h e r a t e of R e a c t i o n 8 t o t h e rates o f R e a c t i o n 4 plus 5 0 + 0 + M-*0 2

+ M

3

(8)

c a n also b e o b t a i n e d . B e c a u s e t h e r a t e of R e a c t i o n 8 i s k n o w n , t h e rates o f R e a c t i o n s 4, 5, a n d 7 c a n b e o b t a i n e d . W i t h t h i s i n f o r m a t i o n , t h e t r a n s i e n t ozone p e a k m a y b e described qualitatively a n d a quantitative mechanism p r o v i d e d for i t s description. Therefore, several systems are available f o r measuring t h e rates of oxygen a t o m reac t i o n s . F o r e x a m p l e , i n t h e p h o t o l y s i s of n i t r o g e n d i o x i d e i n n i t r o g e n a t h i g h r a t i o s of n i t r i c oxide t o nitrogen dioxide, t h e o n l y significant reactions are 1 a n d 7 :


N0

+ ^ ^ 0 + N0

2

(1,7)

T h i s s y s t e m i s b e i n g u s e d i n a s t u d y of t h e r a t e s o f r e a c t i o n o f a t o m i c o x y g e n w i t h various materials. A s e c o n d r a t e o f a r e a c t i o n s t u d i e d a t h i g h p a r t i a l pressures w a s m e a s u r e d a t l o w c o n c e n t r a t i o n s : I n t h e r e a c t i o n o f ozone w i t h n i t r o g e n d i o x i d e , 0

+ N0 -> N 0 + 0

3

2

N0

3

+ N0 ->N 0

3

2

2

5

2

(10)

5

N 0 + H 0-*2HN0 2

(9)

2

(11)

3

B e c a u s e t h e 5 0 - l i t e r flask s e r v e d as a c o n t i n u o u s flow s t i r r e d t a n k r e a c t o r , t h e r a t e c o n stant, k was easily obtained b y t w o semi-independent methods. Q

= -2k, ( Ν 0 ) ( 0 ) 2

^

= -k

β

3

β

= Q/V [ ( N 0 ) 2

( N 0 ) (0 ) = Q/V [(0 ) -

9

2

8

3

3

3

-

s

(N0 ) ] 2

0

(0 ) ]

s

3

0

I n these e q u a t i o n s , ( N 0 ) a n d ( 0 ) a r e t h e s t e a d y - s t a t e c o n c e n t r a t i o n s o f n i t r o g e n d i o x i d e a n d ozone, r e s p e c t i v e l y , w h i l e ( N 0 ) a n d ( 0 ) are t h e i r c o n c e n t r a t i o n s i n t h e i n f l u e n t s t r e a m . Q i s t h e a i r flow r a t e t h r o u g h t h e r e a c t o r , a n d V is t h e r e a c t i o n v o l u m e . T h e results of this s t u d y are given i n T a b l e I . 2

s

3

s

2

Table I.

0

3

0

Determination of Rate of Reaction of Nitrogen Dioxide with O z o n e k , P.P.H.M.-i Min.-i 9

Q/V,M'mri 0.052 0.053 0.053 0.087 0.052 0.053

(Ν0 ) , P.P.H.M. 22 37 95 44 67 53 2

(0 )o, P . P . H . M . 52 60 60 36 80 26

β

3

From 0 ... 2.2 X 10"« 5.7 3.0 8.7 7.5 3

From NO2 3.0 X 10~« 5.2 6.4 3.5 4.5 3.4

T h e m e a n value of k is 48 Χ 1 0 p.p.h.m. min. as c o m p a r e d w i t h a v a l u e of 110 Χ 1 0 calculated f r o m the data of Johnston a n d Y o s t ( 7 ) . Q

-

Literature

-

5

- 1

- 1

5

Cited

(1) Air Pollution Foundation (Los Angeles), "Proceedings of the Conference on Chemical Reactions in Urban Atmospheres," Rept. 15 (1956). (2) Baxter, W. P., Dickinson, R. G., J. Am. Chem. Soc. 50, 774 (1928). (3) Hall, T. C., Jr., "Photochemical Studies of Nitrogen Dioxide and Sulfur Dioxide," dissertation, University of California, October 1953. (4) Hall, T. C., Jr., Blacet, F. E., J. Chem. Phys. 20, 1745-9 (1952). (5) Holmes, Η. H., Daniels, F., J. Am. Chem. Soc. 56, 630 (1934).


FORD, DOYLE, A N D E N D O W - K I N E T I C S OF PHOTOLYSIS

(6) (7) (8) (9) (10) (11)

415

Johnston, H. S., Crosby, H. J., J. Chem. Phys. 19, 799 (1951). Johnston, H. S., Yost, D. M., Ibid., 17, 386 (1949). Littman, F. E., Benoliel, R. W., Anal. Chem. 25, 1480 (1953). Norrish, R. G. W., J. Chem. Soc. 1929, 1611. Norrish, R. G. W., Thrush, Β. Α., Quart. Revs. (London) 10, 149 (1956). Thomas, M. D., MacLeod, J. Α., Robbins, R. C., Goettelman, R. C., Eldridge, R. W., Rogers, L. H., Anal. Chem. 28, 1810 (1956).


RECEIVED for review June 19, 1957. Accepted June 19, 1957. Work supported by American Petroleum Institute and Stanford Research Institute.


Kinetics of Photolysis of Low Concentrations of Nitrogen Dioxide in Air

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