Ozone in Los Angeles Atmosphere - Advances in Chemistry (ACS

Ozone in Los Angeles Atmosphere N. A. RENZETTI

Downloaded by NORTH CAROLINA STATE UNIV on December 26, 2017 | http://pubs.acs.org Publication Date: January 1, 1959 | doi: 10.1021/ba-1959-0021.ch036

Air Pollution Foundation, 2556 Mission St., San Marino, Calif.

Shortly after W o r l d W a r II the presence of more than the usual amount of oxidant which arises principally from ozone in natural air was suspected of existing in the Los Angeles atmosphere. The cracking of stressed rubber was a n early symptom. Chemical measurements with phenolphthalin a n d potassium iodide reagents confirmed oxidant concentrations up to 100 p.p.h.m., especially on days associated with other manifestations of s m o g — n a m e l y , eye irritation, crop d a m a g e , a n d reduced visibility. Ultraviolet absorption data in 1952 confirmed the suspicion that ozone was a primary component of the total oxidant. Laboratory studies demonstrated that trace amounts of organics a n d nitrogen dioxide produced ozone photochemically in chemical systems closely simulating atmospheric conditions. Theoretical studies have indicated that certain primary photochemical processes in polluted atmospheres can give rise to observed oxidant values.

A A a n ' s i n t e r e s t i n a t m o s p h e r i c ozone b e g a n m o r e t h a n 100 y e a r s ago w h e n C . F . Schônbein, w h o w a s r e s p o n s i b l e f o r i t s d i s c o v e r y , c l a i m e d i t s presence i n t h e n o r m a l e a r t h ' s a t m o s p h e r e (34). Schônbein's o z o n o m e t e r c o n s i s t e d of p a p e r s o a k e d i n potassium iodide a n d s t a r c h ; for years data thus obtained were subject to the criticism t h a t t h e c h e m i c a l r e a c t i o n u s e d w a s n o t specific t o ozone. H o w e v e r , i t w a s n o t u n t i l some 80 y e a r s l a t e r t h a t a n o t h e r o x i d a n t , n i t r o g e n d i o x i d e , w a s i d e n t i f i e d i n t h e a t m o s p h e r e (10, 31). F u r t h e r m o r e , these f i n d i n g s cast d o u b t o n t h e p r e v i o u s l y o b t a i n e d ozone d a t a . P a n e t h u n d e r t o o k t o c l a r i f y t h e s i t u a t i o n (24) since some c h e m i s t s were i n c l i n e d t o d e n y a l t o g e t h e r t h e presence of ozone i n the atmosphere. H e set o u t t o m a k e t h e o l d c h e m i c a l m e t h o d (17, 40) m o r e r e l i a b l e a n d r e p o r t e d ozone a n d n i t r o g e n d i o x i d e v a l u e s v a r y i n g f r o m 0 t o 3 p . p . h . m . (24, 25) by volume. y

T h e first u n d i s p u t e d d e t e r m i n a t i o n s of ozone i n t h e e a r t h ' s a t m o s p h e r e were m a d e b y s p e c t r o s c o p i s t s s t u d y i n g t h e r a d i a t i o n f r o m t h e s u n a n d t h e s t a r s (7, 9). I t was s o o n r e c o g n i z e d t h a t m o s t of t h e ozone t h u s m e a s u r e d w a s c o n c e n t r a t e d i n t h e h i g h e r a t m o s p h e r e (39). S t a r t i n g i n 1931, s e v e r a l i n v e s t i g a t o r s u s i n g t h e c h a r a c t e r i s t i c s t r o n g a b s o r p t i o n of ozone i n t h e u l t r a v i o l e t (2200 t o 3000 A . ) w i t h a r t i f i c i a l l i g h t sources o v e r l o n g o p t i c a l p a t h s m a d e d i r e c t m e a s u r e m e n t s of t h e ozone c o n t e n t n e a r t h e e a r t h (2-4, 6, 11, 12, 38). B y 1941 t h e c h e m i c a l a n d s p e c t r o s c o p i c m e t h o d s a g r e e d t o v a l u e s of 0 t o 3 p . p . h . m . as t h e n o r m a l b u t v a r i a b l e c o n c e n t r a t i o n of ozone i n t h e l o w e r a t m o s 230

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

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RENZETTI—OZONE IN LOS ANGELES ATMOSPHERE

p h e r e . A t t i m e s , a n d i n some areas, t h e r e o c c u r r e d 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 from 0 to 2 p.p.h.m. T h e i d e n t i f i c a t i o n a n d m e a s u r e m e n t of ozone i n t h e L o s A n g e l e s s m o g h a v e h a d a h i s t o r y n o t u n l i k e those of t h e e a r l y d a y s of ozone i n n o r m a l a t m o s p h e r e s . T h e e a r l y clue t o t h e presence of m o r e t h a n o r d i n a r y levels o f ozone o r o x i d a n t w a s g i v e n b y t h e excessive c r a c k i n g of stressed r u b b e r i n t h e L o s A n g e l e s B a s i n as c o m p a r e d t o o t h e r l o c a t i o n s . H a a g e n - S m i t f o l l o w e d t h i s l e a d a n d , u s i n g t h e r u b b e r c r a c k i n g (1) a n d p h e n o l p h t h a l i n reagent (22) m e t h o d s , m a d e e s t i m a t e s of ozone a n d o x i d a n t d u r i n g s m o g a t t a c k s (13). H i s d a t a i n d i c a t e d o x i d a n t c o n c e n t r a t i o n s i n t h e r a n g e of 0 t o 100 p . p . h . m . L i t t m a n , u s i n g a m o d i f i c a t i o n of t h e c l a s s i c a l p o t a s s i u m i o d i d e t e c h n i q u e (19), r e p o r t e d o x i d a n t v a l u e s of 0 t o 6 0 p . p . h . m . H e also u s e d t h e m e t h o d of P a n e t h (24) to d e t e r m i n e t h e ozone i n a s m o g s a m p l e a n d r e c e n t l y r e p o r t e d h i s r e s u l t s (21). R e g e n e r a n d h i s c o w o r k e r s , i n c o l l a b o r a t i o n w i t h L i t t m a n , o b t a i n e d evidence of ozone i n s m o g b y i t s a b s o r p t i o n i n t h e u l t r a v i o l e t (2600 t o 3200 A . ) u s i n g p h o t o g r a p h i c s p e c t r o m e t r y (27). R e n z e t t i , u s i n g p h o t o e l e c t r i c s p e c t r o m e t r y i n t h e u l t r a v i o l e t b a s e d o n t h e same p r i n c i p l e as R e g e n e r ' s i n s t r u m e n t (26), r e p o r t e d v a l u e s f o r ozone u p t o 35 p . p . h . m . (29). T h e s e i n v e s t i g a t i o n s g a v e q u a l i t a t i v e evidence of t h e presence of ozone i n s m o g g y a t m o s p h e r e i n L o s A n g e l e s . T h e c o n c e n t r a t i o n s c e r t a i n l y h a v e exceeded those of n o r m a l c l e a n a i r , a n d m a y a t t i m e s h a v e r e a c h e d 100 p . p . h . m . H o w e v e r , t h e q u a n t i t a t i v e p i c t u r e is s t i l l f a r f r o m c l e a r . T h e different responses of t h e v a r i o u s t e c h n i q u e s suggested t h e n e e d f o r a n i n t e n s i v e i n t e r c o m p a r a t i v e s t u d y of t h e a n a l y t i c a l m e t h o d s , as w e l l as extensive s i m u l t a n e o u s d e t e r m i n a t i o n s o f o x i d a n t i n t h e a t m o s p h e r e w i t h as m a n y of these m e t h o d s as possible. M e t h o d s of

Analysis

T h e p r o b l e m of i d e n t i f y i n g a n d m e a s u r i n g ozone i n t h e c o m p l e x gaseous-aerosol m i x t u r e w h i c h is s m o g is f o r m i d a b l e . T h e r e a r e s u c h gases p r e s e n t as n i t r i c o x i d e , nitrogen dioxide, sulfur dioxide, h y d r o c a r b o n vapors f r o m methane u p to p r o b a b l y x y l e n e , p l u s s u c h p a r t i a l o x i d a t i o n p r o d u c t s as a l d e h y d e s , k e t o n e s , a n d a c i d s . T h e s e a r c h f o r a m e t h o d of h i g h s p e c i f i c i t y has b e e n a n i n t e n s i v e o n e . T h e v e r y clue w h i c h first s t i m u l a t e d t h e s e a r c h f o r o z o n e — n a m e l y , c r a c k i n g of stressed r u b b e r — w a s d e v e l o p e d b y H a a g e n - S m i t i n t o a u s e f u l m e t h o d (1). S p e c i a l l y t r e a t e d r u b b e r is c u t i n t o r e c t a n g u l a r s t r i p s 50 X 8 X 1.5 m m . , w h i c h a r e b e n t i n t o a l o o p , t h e n p l a c e d i n a t u b e 13 m m . i n d i a m e t e r . A flow r a t e of a p p r o x i m a t e l y 1 l i t e r p e r m i n u t e of t h e a i r s a m p l e is m a i n t a i n e d p a s t t h e s t r i p . A c a l i b r a t i o n c u r v e , u s i n g k n o w n a m o u n t s of ozone i n a i r v e r s u s t i m e t o i n i t i a l c r a c k i n g , m u s t be d e v e l o p e d f o r e a c h piece of s t o c k r u b b e r . T h i s t e c h n i q u e is c u r r e n t l y i n use i n L o s A n g e l e s i n m o n i t o r i n g ozone i n s m o g f o r t h e p u r p o s e of c a l l i n g " a l e r t s " w h e n t h e ozone c o n c e n t r a t i o n exceeds 50 p . p . h . m . V a l u e s u p t o 100 p . p . h . m . h a v e b e e n r e p o r t e d b y t h i s m e t h o d w h e n t h e r u b b e r h a s b e e n c a l i b r a t e d w i t h a s t r e a m o f ozone i n a i r , s t a n d a r d ized w i t h a 2 % potassium iodide ( i n distilled water) midget impinger bubbler system. A n a c c u r a c y of ± 1 0 % is c l a i m e d f o r t h i s m e t h o d . F i g u r e 1 shows a p h o t o g r a p h of this apparatus. H a a g e n - S m i t i n t r o d u c e d a m e t h o d (22) f o r m e a s u r i n g o x i d a n t i n t h e a t m o s p h e r e a f t e r h i s l a b o r a t o r y i n v e s t i g a t i o n s suggested t h a t t h e presence o f o x i d a n t s o t h e r t h a n ozone s h o u l d be f o u n d i n s m o g . T h i s m e t h o d is b a s e d o n t h e o x i d a t i o n of p h e n o l p h t h a l i n ( C o H 0 ) to phenolphthalein ( C o H 0 ) a n d subsequent colorimetric deter m i n a t i o n of t h e o x i d a n t i n t h e a i r s a m p l e . F o r c o n c e n t r a t i o n ranges of i n t e r e s t , s a m p l i n g of 1 l i t e r p e r m i n u t e f o r 10 m i n u t e s gives a d e q u a t e c o l o r d e v e l o p m e n t . T h e c a l i b r a t i o n c u r v e i s d e r i v e d b y o b t a i n i n g a b s o r b a n c e v e r s u s k n o w n c o n c e n t r a t i o n s of aqueous h y d r o g e n p e r o x i d e . T h e s e m i a u t o m a t i c i n s t r u m e n t u s i n g t h i s m e t h o d is s h o w n i n F i g u r e 2 . V a l u e s u p t o 110 p . p . h . m . of o x i d a n t a r e r e p o r t e d as h y d r o g e n peroxide. H o w e v e r , w h e n this system is standardized w i t h a n ozone-in-air stream, w h i c h i n t u r n is m o n i t o r e d w i t h 2 % p o t a s s i u m i o d i d e , t h e response t o a t m o s p h e r i c o x i d a n t is c u t d o w n t o 0.33 t o 0.50 of t h e p e r o x i d e d e t e r m i n a t i o n . 2

1 6

4

2

1 4

4



232

A D V A N C E S IN CHEMISTRY SERIES

Figure 1.

O z o n e rubber cracking

apparatus

L i t t m a n (19) d e v e l o p e d a c o n t i n u o u s a u t o m a t i c o x i d a n t r e c o r d e r b a s e d o n t h e use of 2 0 % p o t a s s i u m i o d i d e i n n e u t r a l ( p H = 7 ) b u f f e r e d s o l u t i o n , as s h o w n i n F i g u r e 3. T h e c a l i b r a t i o n i s b a s e d o n t h e a s s u m p t i o n t h a t t h e i o d i n e is released i n s t o i c h i o m e t r i c p r o p o r t i o n t o t h e a m o u n t of ozone a c c o r d i n g t o t h e e q u a t i o n 0

3

+ 2 K I - f H 0 ;=± 0 2

2

+ I + 2KOH 2

(1)

L i t t m a n h a s o b t a i n e d v a l u e s of 0 t o 60 p . p . h . m . of o x i d a n t as ozone, a s s u m i n g t h e above stoichiometry, i n L o s Angeles smog.

Figure 2.

Phenolphthalin oxidant

apparatus




Figure 3 .

233

Potassium iodide oxidant recorder

H e n z e t t i (29) d e v e l o p e d a n a u t o m a t i c c o n t i n u o u s ozone r e c o r d e r b a s e d o n t h e p r e v i o u s w o r k of R e g e n e r a n d of S t a i r (35) ( F i g u r e s 4 a n d 5 ) . T h i s m e t h o d u s e d t h e a b s o r p t i o n data of V i g r o u x (41) f o r t h e w a v e l e n g t h s 2 6 5 , 2 8 0 , a n d 3 1 3 m ^ i n t h e c o m p u t a t i o n of ozone c o n c e n t r a t i o n s a c c o r d i n g t o t h e f o r m u l a

Figure 4.

Optica! system of spectrometer



234


Figure 5.

O z o n e ultraviolet spectrometer

C - C t

where

0

_^°\313 Υ

=

Λ313

^Xî65_ _

(2)

Co = c o n c e n t r a t i o n of ozone i n a t m o s p h e r e a t n i g h t , w h i c h w a s a l w a y s a p p r o x i m a t e l y zero (say 2 p . p . h . m . ) . s = optical path «λι = 0.123 k m . α

λ 2

I\ I\

2

^

- 1

p.p.h.m.

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w h e r e λι = 265 m u

= 0.00087 k m . " p . p . h . m . " w h e r e λ 1

1

2

= 313 m u

_ r a t i o of r e c e i v e d r a d i a t i o n i n t e n s i t i e s a t reference c o n d i t i o n ~ (Co = 2 p . p . h . m . ) = r a t i o of r e c e i v e d r a d i a t i o n i n t e n s i t i e s a t t i m e t c = c o n c e n t r a t i o n of o z o n e a t t i m e t

A s i m i l a r p r o c e d u r e w a s u s e d f o r o t h e r p a i r s of r a t i o s i n v o l v i n g / λ ι a n d 7λ3 w h e r e λ

= 2 8 0 m/Λ. R e c e n t l y t h e F r a n k l i n I n s t i t u t e h a s set u p a l o n g - p a t h i n f r a r e d s p e c t r o m e t e r ( u p t o 500 m e t e r s ) i n L o s A n g e l e s t o d e t e r m i n e , a m o n g o t h e r s t u d i e s , t h e ozone c o n c e n t r a tions i n smog b y its absorption a t t h e 9.6-micron b a n d . 3

Atmospheric Oxidant

and

Ozone

Data

H a a g e n - S m i t (IS) e s t a b l i s h e d t h e p a t t e r n of t h e d i u r n a l v a r i a t i o n of o x i d a n t s a n d ozone e a r l y i n t h e s m o g h i s t o r y w i t h b o t h t h e r u b b e r c r a c k i n g a n d p h e n o l p h t h a l i n m e a s u r e m e n t s . T h e c h a r a c t e r i s t i c s h a r p rise i n t h e m o r n i n g , a p e a k i n t h e m i d d l e of t h e d a y , a s l o w e r d e c a y i n t h e a f t e r n o o n , a n d a l m o s t zero o x i d a n t a t n i g h t ( a v e r a g e of 2 p.p.h.m.) were t h e essential f e a t u r e s . T h e p h e n o l p h t h a l i n o x i d a n t v a l u e s as h y d r o g e n p e r o x i d e were g e n e r a l l y h i g h e r t h a n t h e c o r r e s p o n d i n g ozone b y r u b b e r c r a c k i n g . T h e p h e n o l p h t h a l i n d a t a since A u g u s t 1953 f o r P a s a d e n a h a v e b e e n p u b -


RENZETTI—OZONE

IN LOS ANGELES

235

ATMOSPHERE

DIURNAL VARIATION

Phenolphtholin Kl Rubber Crock! "9 UVSpcctronw

OF OXIDJINTS AND 0 ZONE PASADENA

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AUGUST 3 0 , 1955 I

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10 10 100 NITROGEN DIOXIDE PARTS PER MILLION

Logarithmic plot of ozone formation

1000

area

1

10.000

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242


10,000 π

1000

f

0

5000 N0 r?r?M. 2

Figure 12.

Linear plot of a r e a of ozone forma tion

A s a r e s u l t of a s u r v e y of o r g a n i c v a p o r s , i t w a s e s t a b l i s h e d t h a t t h e classes of c o m p o u n d s s h o w n i n T a b l e I were m o s t i m p o r t a n t t o ozone f o r m a t i o n i n s m o g . T h e e x p e r i m e n t a l evidence suggests t h a t t h e t o t a l ozone f o r m e d i n t h e p h o t o c h e m i c a l r e a c t i o n is r e l a t e d t o t h e c o n c e n t r a t i o n s of t h e r e a c t a n t s b y t h e r e l a t i o n [OJtotal = ^ [ N 0 ] [ R H ] 2

(3)

Laboratory Investigations of Stanford Research Institute. T h i s work was spon s o r e d b y t h e S m o k e a n d F u m e s C o m m i t t e e of t h e A m e r i c a n P e t r o l e u m I n s t i t u t e . T h e p h i l o s o p h y of e x p e r i m e n t a t i o n of these i n v e s t i g a t o r s was t o use t h e a c t u a l s m o g g y a i r as a s u b s t r a t e f o r l a b o r a t o r y e x p e r i m e n t s (20, 32). T h e d a i l y f l u c t u a t i o n s of o x i d a n t c o n c e n t r a t i o n were f o l l o w e d f o r s e v e r a l y e a r s b y m e a n s of a n a u t o m a t i c o x i d a n t r e c o r d e r a t t h e S t a n f o r d R e s e a r c h I n s t i t u t e ' s P a s a d e n a L a b o r a t o r y (19). T y p i c a l oxidant curves showed a characteristic p a t t e r n : l o w con centrations at night increasing to a m a x i m u m around noon, a n d disappearing again at sunset. M a x i m u m c o n c e n t r a t i o n s v a r i e d g r e a t l y , w i t h v a l u e s as h i g h as 60 p . p . h . m . o c c u r r i n g d u r i n g s m o g g y w e a t h e r . C o n c e n t r a t i o n s a t n i g h t s e l d o m exceeded 5 p . p . h . m . T h e v a r i a t i o n s f r o m d a y t o d a y were g r e a t e r t h a n those f r o m m o n t h t o m o n t h . N e v e r theless, a n a n n u a l c y c l e d i d exist, w i t h h i g h c o n c e n t r a t i o n s o c c u r r i n g m o r e f r e q u e n t l y f r o m M a y t h r o u g h O c t o b e r t h a n d u r i n g t h e rest of t h e y e a r . H o w e v e r , i f a i r w a s i r r a d i a t e d w i t h a r t i f i c i a l s u n l i g h t before e n t e r i n g t h e r e c o r d e r , a t o t a l l y different p a t t e r n r e s u l t e d . T h e a i r w a s passed t h r o u g h a 5 0 - l i t e r flask, i r r a d i a t e d w i t h f o u r H 4 0 0 E - l m e r c u r y v a p o r l i g h t s . T h e a v e r a g e residence t i m e of t h e a i r w a s a b o u t 20 m i n u t e s . S i n c e t h e m e r c u r y arcs gave off n o r a d i a t i o n b e l o w a b o u t 3000 Α . , t h e y were n o t c a p a b l e of f o r m i n g ozone d i r e c t l y b y d i s s o c i a t i o n of o x y g e n . A t y p i c a l o x i d a n t p a t t e r n r e s u l t i n g f r o m t h i s a r r a n g e m e n t is s h o w n i n F i g u r e 13. T h e characteristic d i v i s i o n between d a y t i m e a n d n i g h t t i m e has disappeared a n d oxidant c o n c e n t r a t i o n s of t h e same o r d e r of m a g n i t u d e as those e x i s t i n g i n d a y t i m e r e s u l t e d f r o m i r r a d i a t i o n of n i g h t a i r . C o n t i n u e d m o n i t o r i n g of o u t s i d e a i r s h o w e d t h a t t h e o x i d a n t f o r m e d b y i r r a d i a t i o n of n i g h t a i r f o l l o w e d a d a i l y a n d a n a n n u a l c y c l e . T h e d a i l y c y c l e f r e q u e n t l y s h o w e d t w o m a x i m a , one a r o u n d 7 : 0 0 P . M . , t h e o t h e r a b o u t 8 : 0 0 A . M . H i g h c o n c e n t r a t i o n s of o x i d a n t c o u l d be f o r m e d r e g u l a r l y b y i r r a d i a t i o n of n i g h t a i r d u r i n g f a l l a n d w i n t e r ,



RENZETTI—OZONE

IN LOS ANGELES

Figure 13.

ATMOSPHERE

243

Diurnal variation of ozone formed by constant irradiation of outside air

from September through M a r c h . D u r i n g the summer months little, if a n y , oxidant was f o r m e d a t n i g h t , despite t h e f a c t t h a t h i g h c o n c e n t r a t i o n s o c c u r r e d i n t h e d a y t i m e during that period. I s o l a t i o n of O x i d a n t P r e c u r s o r s . T h e o b s e r v a t i o n t h a t o x i d a n t c o u l d be f o r m e d e x p e r i m e n t a l l y b y t h e a c t i o n of l i g h t o n p o l l u t e d u r b a n a i r l e d t o a n i n v e s t i g a t i o n of those i m p u r i t i e s i n a i r w h i c h , u p o n i r r a d i a t i o n , f o r m e d o x i d a n t . T h e t e r m , " o x i d a n t p r e c u r s o r s , " w a s c o i n e d t o describe these m a t e r i a l s , a n d a series of e x p e r i m e n t s w a s started to determine their physical a n d chemical properties. T h a t light was responsible for the f o r m a t i o n was demonstrated b y using t w o o x i d a n t r e c o r d e r s , one w h i c h i n d i c a t e d t h e o x i d a n t c o n c e n t r a t i o n i n u n t r e a t e d a i r a n d t h e o t h e r , i n i r r a d i a t e d a i r ( F i g u r e 14). A t t e m p t s were m a d e t o d e t e r m i n e t h e r e g i o n of a c t i v e l i g h t b y use of o p t i c a l cutoff f i l t e r s . T h e r e s u l t s , s u m m a r i z e d as f o l l o w s , i n d i c a t e t h a t p r i m a r y l i g h t a c c e p t o r (s) a b s o r b i n a r a t h e r b r o a d r e g i o n , b e g i n n i n g n e a r t h e s h o r t w a v e e n d of t h e v i s i b l e s p e c t r u m a n d e x t e n d i n g t o b e l o w 3600 A . Filter Light envelop and flask walls Window glass, 1/8 inch Solex glass X-ray lead glass Corning glass filter No. 373

Cut Off below 2800 A . 3100 A . 3400 A . 3700 A . 4000 A .

Level of Ozone Formation Maximum No reduction Definite, small reduction 50% reduction Substantially complete reduction

A t t e m p t s w e r e t h e n m a d e t o d e t e r m i n e some of t h e c h e m i c a l p r o p e r t i e s of t h e p r e c u r s o r s b y s u b j e c t i n g t h e a i r ( p r i o r t o i r r a d i a t i o n ) t o t h e a c t i o n of v a r i o u s s c r u b b e r s i n a n effort t o r e m o v e t h e p r e c u r s o r s . T h e s e e x p e r i m e n t s i n d i c a t e d t h a t passage t h r o u g h a b e d of a c t i v a t e d c a r b o n o r t h r o u g h a c o m b u s t i o n f u r n a c e a t 760° C . r e m o v e d or destroyed the precursors. O n the other h a n d , when the incoming a i r was scrubbed

Figure 14.

Diurnal variation of oxidants from natural and artificial irradiation of Pasadena air




244

c o u n t e r c u r r e n t l y t h r o u g h p a c k e d c o l u m n s 4 feet l o n g w i t h 5 % s o d i u m h y d r o x i d e , t h e bulk of the oxidant precursors remained (Figure 15), although the concentration of a c i d gases s u c h as c a r b o n d i o x i d e , s u l f u r d i o x i d e , a n d n i t r o g e n d i o x i d e w a s g r e a t l y r e duced b y this procedure. S i m i l a r l y , a 5 % s o l u t i o n of s e m i c a r b a z i d e b u f f e r e d t o p H 4 w i t h p h o s p h o r i c a c i d h a d n o effect ( F i g u r e 1 6 ) , a l t h o u g h t h i s agent effectively r e m o v e s c a r b o n y l c o m p o u n d s s u c h as a l d e h y d e s a n d k e t o n e s . A p a r t i c l e f i l t e r c a p a b l e of r e m o v i n g p a r t i c u l a t e m a t e r i a l d o w n t o 0.2 m i c r o n i n d i a m e t e r also h a d n o effect. Freezeout t r a p s were used next i n a n a t t e m p t to separate or t r a p the precursors.

Figure 16.

O z o n e formation in irradiated scrubbed Pasadena


air


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A t r a p p a c k e d w i t h stainless steel helices a n d c o o l e d i n d r y i c e - a c e t o n e p r o d u c e d n o s i g n i f i c a n t r e d u c t i o n i n t h e a m o u n t of o x i d a n t f o r m e d u p o n i r r a d i a t i o n of a i r p a s s e d t h r o u g h t h e t r a p . W h e n a l i q u i d o x y g e n - c o o l e d t r a p w a s u s e d i n series w i t h t h e d r y ice t r a p , e s s e n t i a l l y c o m p l e t e r e t e n t i o n of t h e o x i d a n t p r e c u r s o r s r e s u l t e d ( F i g u r e 17). U p o n r e m o v a l of t h e c o o l a n t b a t h , t h e b u l k of t h e p r e c u r s o r s w a s released ( F i g u r e 17). T h u s , t h i s t e c h n i q u e f o r t h e c o l l e c t i o n a n d c o n c e n t r a t i o n of t h e substances w h i c h y i e l d o x i d a n t o n i r r a d i a t i o n p r o m i s e d t o m a k e t h e i r a n a l y s i s feasible a n d g a v e h o p e for t h e i r e v e n t u a l i d e n t i f i c a t i o n . N u m e r o u s freezeout collections w e r e m a d e a n d a n a l y z e d . T h e a i r w a s d r a w n through a semicarbazide c o l u m n a n d a caustic scrubbing column. T h e stream was t h e n s p l i t ; one h a l f passed t h r o u g h a n i r r a d i a t e d flask a n d t h e n i n t o a series o f t r a p s , a n d t h e o t h e r h a l f passed t h r o u g h a d a r k flask o n i t s w a y t o t h e t r a p s . B y e x a m i n i n g

the c o n t e n t s of t h e t r a p s , i t w a s h o p e d t o o b t a i n a d i f f e r e n t i a l a n a l y s i s w h i c h w o u l d be easier t o i n t e r p r e t , because i r r a d i a t i o n s h o u l d i n t r o d u c e a c h a n g e w h i c h c o u l d b e picked out f r o m the general b a c k g r o u n d c o m m o n to the d a r k a n d i r r a d i a t e d samples. V a r i o u s t r a p designs w e r e t r i e d , a n d i t w a s c o n c l u d e d t h a t t r a p s p a c k e d w i t h stainless steel helices gave t h e best r e c o v e r y of p r e c u r s o r s . T h e samples were analyzed using i n f r a r e d , ultraviolet, a n d mass spectrometric methods. A f t e r being collected i n l i q u i d oxygen-cooled traps, t h e samples were k e p t in liquid nitrogen. A f t e r c o n n e c t i o n s w e r e m a d e t o t h e mass s p e c t r o m e t e r , t h e n o n c o n d e n s a b l e f r a c t i o n w a s p u m p e d off a n d t h e r e m a i n i n g s a m p l e w a s i n t r o d u c e d i n t o the inlet system b y gradually w a r m i n g the t r a p to r o o m temperature. Samples for i n f r a r e d a n d u l t r a v i o l e t analyses w e r e h a n d l e d s i m i l a r l y , b u t t h e t r a n s f e r w a s a c c o m plished b y freezing the sample over into the optical cell w h i c h was equipped w i t h a c o l d finger.


246

A D V A N C E S IN

CHEMISTRY SERIES


T h e results of these a n a l y s e s i n d i c a t e d t h a t t h e b u l k of t h e m a t e r i a l r e t a i n e d i n t h e l i q u i d o x y g e n t r a p s c o n s i s t e d of c a r b o n d i o x i d e a n d w a t e r . T h e b a l a n c e of t h e s a m p l e was m a d e u p of o r g a n i c s . T h e g e n e r a l d i s t r i b u t i o n of t h e mass p e a k s r e s e m b l e d a gasoline m a s s s p e c t r u m w i t h t h e h i g h m o l e c u l a r e n d a t t e n u a t e d . C o m p a r i s o n of s p e c t r a of i r r a d i a t e d a n d n o n i r r a d i a t e d s a m p l e s s h o w e d a c o n s i s t e n t decrease of olefin a n d d i o l e f i n m a s s p e a k s o n i r r a d i a t i o n ( p a r t i c u l a r l y m/e 39, 4 3 , a n d 6 7 ) , b u t i n g e n e r a l , l a r g e differences i n c o m p o s i t i o n of t h e s a m p l e s m a d e m e a n i n g f u l c o m p a r i s o n difficult. T h e i n f r a r e d a n a l y s e s s h o w e d a b s o r p t i o n b a n d s i n t h e r e g i o n of 3.4, 6.9, a n d 7.3 m i c r o n s c a u s e d b y c a r b o n - h y d r o g e n b o n d s ; b a n d s of 5.8 a n d 8.3 m i c r o n s i n d i c a t i v e of a c e t o n e ; c a r b o n d i o x i d e b a n d s of 4.3, 13.9, a n d 15 m i c r o n s ; a n d a d o u b l e t a t 6.3 m i c r o n s , c a u s e d p o s s i b l y b y o r g a n i c n i t r a t e s . S e v e r a l m i n o r u n i d e n t i f i e d b a n d s were also p r e s e n t . T h e u l t r a v i o l e t s p e c t r a s h o w e d no s i g n i f i c a n t a b s o r p t i o n b a n d s . C h e m i c a l a n a l y s e s were p e r f o r m e d o n s e v e r a l s a m p l e s t o detect n i t r o g e n oxides n o t f o u n d b y s p e c t r a l a n a l y s e s . A m o d i f i e d G r i e s s reagent w a s u s e d , a n d t h e c o n t e n t s of s e v e r a l freezeout t r a p s were e x a m i n e d b y v e n t i n g t h e m t h r o u g h a n i r r a d i a t e d flask i n t o a scrubber containing the reagent. A l t e r n a t i v e l y , ozone w a s a d d e d t o t h e flask a n d p e r m i t t e d t o react w i t h i t s c o n t e n t s , as G r i e s s reagent r e s p o n d s t o n i t r o g e n d i o x i d e b u t n o t t o n i t r i c o x i d e . R e l a t i v e l y l a r g e a m o u n t s of n i t r o g e n d i o x i d e were f o u n d i n these cases ( m o r e t h a n c o u l d be a c c o u n t e d f o r b y t h e n i t r o g e n d i o x i d e p r e s e n t a t t h e t i m e of c o l l e c t i o n ) . T h u s , n i t r o g e n d i o x i d e was a p p a r e n t l y f o r m e d d u r i n g t h e c o l l e c t i o n a n d / o r i r r a d i a t i o n of t h e a i r s a m p l e . T h i s p o i n t e d a w a y t o w a r d a possible m e c h a n i s m of o x i d a n t f o r m a t i o n . T h e f o r m a t i o n of ozone f r o m m i x t u r e s of n i t r o g e n d i o x i d e a n d h y d r o c a r b o n s has b e e n d e s c r i b e d b y o t h e r i n v e s t i g a t o r s (13). I n t h i s l a b o r a t o r y a series of e x p e r i m e n t s was r u n u s i n g o x i d a n t r e c o r d e r s a n d i r r a d i a t e d flasks. A m i x t u r e of c a r b o n - f i l t e r e d a i r a n d 40 p . p . h . m . of n i t r o g e n d i o x i d e was r u n i n t o t h e r e c o r d e r u n t i l a n e q u i l i b r i u m l e v e l w a s e s t a b l i s h e d . A s m a l l q u a n t i t y of h y d r o c a r b o n was t h e n a d d e d t o t h e flask f r o m a s y r i n g e a n d p e r m i t t e d t o flush i n t o t h e r e c o r d e r . T h e r e s u l t i n g o x i d a n t c u r v e s i n d i c a t e t h a t r e l a t i v e l y l a r g e a m o u n t s of a n o x i d a n t c a n be f o r m e d b y i r r a d i a t i n g s y n t h e t i c m i x t u r e s of a v a r i e t y of h y d r o c a r b o n s a n d n i t r o g e n d i o x i d e . P h o t o l y s i s of N i t r o g e n O x i d e i n O u t s i d e A i r . S i n c e h y d r o c a r b o n s exist i n o u t s i d e a i r , i t seemed i m p o r t a n t t o d e t e r m i n e w h e t h e r t h e y were c a p a b l e of p r o d u c i n g s i m i l a r results. W h e n n i t r o g e n d i o x i d e was a d d e d t o a s t r e a m of c a r b o n - f i l t e r e d n i g h t a i r at a t i m e w h e n n o p r e c u r s o r s were p r e s e n t a n d t h e a i r was p a s s e d t h r o u g h a n i r r a d i a t e d flask i n t o a n o x i d a n t r e c o r d e r , a l e v e l of o x i d a n t w a s e s t a b l i s h e d because t h e r e c o r d e r is s o m e w h a t s e n s i t i v e t o n i t r o g e n d i o x i d e . W h e n t h e c a r b o n filter was r e m o v e d so t h a t t h e m i x t u r e c o n s i s t e d of u n t r e a t e d o u t s i d e a i r a n d n i t r o g e n d i o x i d e , t h e r e c o r d e r r a p i d l y c l i m b e d t o a h i g h e r l e v e l , i n d i c a t i n g t h a t a n a d d i t i o n a l a m o u n t of o x i d a n t h a d b e e n f o r m e d . T h u s , substances n o r m a l l y p r e s e n t i n o u t s i d e a i r r e a c t e d d u r i n g p h o t o l y sis of n i t r o g e n d i o x i d e to p r o d u c e o x i d a n t a b o v e t h a t due t o n i t r o g e n d i o x i d e i t s e l f . A s i t h a d b e e n p r e v i o u s l y d e m o n s t r a t e d ( b y m e a n s of c a u s t i c s c r u b b e r s ) t h a t e v e n a s u b s t a n t i a l r e d u c t i o n of t h e n i t r o g e n d i o x i d e p r e s e n t i n o u t s i d e a i r d i d n o t h a v e a gross effect o n i t s o x i d a n t - f o r m i n g a b i l i t y , these e x p e r i m e n t s a p p e a r e d t o be l a r g e l y of a c a d e m i c i n t e r e s t . A possible c o n n e c t i n g l i n k was n i t r i c o x i d e , b u t i t s k n o w n r a t e of o x i d a t i o n t o n i t r o g e n d i o x i d e is s l o w a n d i t s presence i n o u t s i d e a i r h a d n o t been established. T h i s l i n e of r e s e a r c h r e c e i v e d f u r t h e r i m p e t u s w h e n a n i t r o g e n d i o x i d e a n d n i t r i c oxide r e c o r d e r was d e v e l o p e d b y t h e i n s t i t u t e . T h i s i n s t r u m e n t was b a s e d o n t h e a b s o r p t i o n of n i t r o g e n d i o x i d e i n a m o d i f i e d G r i e s s reagent a n d s u b s e q u e n t c o l o r i m e t r i c d e t e r m i n a t i o n of its a m o u n t . I n i t s s i m p l e s t f o r m t h e i n s t r u m e n t r e s p o n d e d o n l y t o n i t r i t e i n s o l u t i o n ( w h i c h m a y o r i g i n a t e f r o m n i t r o g e n d i o x i d e or o r g a n i c a n d i n o r g a n i c n i t r i t e s ) , b u t a m o d i f i c a t i o n d e t e r m i n e d n i t r i c oxide as w e l l . T h i s was a c h i e v e d b y filtering t h e i n c o m i n g a i r t h r o u g h a c t i v a t e d c h a r c o a l , w h i c h passes n i t r i c


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oxide b u t r e t a i n s n i t r o g e n d i o x i d e a n d n i t r i t e s , f o l l o w e d b y a g a s - p h a s e o x i d a t i o n of n i t r i c oxide t o n i t r o g e n d i o x i d e u s i n g ozone. T h e r e s u l t i n g n i t r o g e n d i o x i d e w a s t h e n determined colorimetrically. M o n i t o r i n g of t h e a t m o s p h e r e a t P a s a d e n a i n d i c a t e d t h a t n i t r i c oxide is n o r m a l l y present i n q u a n t i t i e s w e l l i n excess of those of n i t r o g e n d i o x i d e . I t s c o n c e n t r a t i o n s r a n g e d f r o m 2 t o 30 p . p . h . m . T h e o x i d a t i o n r a t e of n i t r i c o x i d e ( b y o x y g e n ) i n these c o n c e n t r a t i o n s is s l o w . B u t u n d e r t h e c o n d i t i o n s of these e x p e r i m e n t s , u s i n g i r r a d i a t e d 5 0 - l i t e r flasks a n d m i x t u r e s c o n t a i n i n g 1 t o 10 p . p . m . of h y d r o c a r b o n s a n d 0.1 t o 1.0 p . p . m . of n i t r i c oxide, a r a p i d o x i d a t i o n t o n i t r o g e n d i o x i d e a p p e a r e d t o t a k e p l a c e , a c c o m p a n i e d b y t h e f o r m a t i o n of some ozone. T h e l o w b o i l i n g p o i n t of n i t r i c oxide (—156° C . ) m a d e i t s r e t e n t i o n i n freezout t r a p s c o o l e d w i t h l i q u i d o x y g e n u n l i k e l y , a t least o n t h e basis of i t s p a r t i a l p r e s s u r e . N e v e r t h e l e s s , e x p e r i m e n t s set u p t o c h e c k t h i s p o i n t s h o w e d t h a t n i t r i c o x i d e w a s q u a n t i t a t i v e l y r e t a i n e d . O n r e v a p o r i z a t i o n , a t least p a r t of t h e n i t r i c o x i d e a p p e a r e d i n t h e f o r m of n i t r o g e n d i o x i d e . O t h e r s , t o o , h a v e o b s e r v e d t h i s p h e n o m e n o n . T h e effect of i r r a d i a t i o n o n t h e o x i d a n t a n d n i t r o g e n d i o x i d e c o n c e n t r a t i o n s of n i g h t a i r a p p a r e n t l y p r o d u c e d a s i g n i f i c a n t increase of n i t r o g e n d i o x i d e c o n c e n t r a t i o n , b u t n o t e n o u g h t o a c c o u n t f o r a l l of t h e o x i d a n t f o r m e d . T h u s , e x p e r i m e n t a l o b s e r v a t i o n s r e l a t i n g t o f o r m a t i o n of o x i d a n t i n t h e L o s A n g e l e s a t m o s p h e r e c a n be e x p l a i n e d b y t h e b a s i c a s s u m p t i o n t h a t ozone is f o r m e d b y 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 , a i d e d b y a r a p i d c o n v e r s i o n of n i t r i c o x i d e t o n i t r o g e n d i o x i d e i n t h e presence of certain hydrocarbons. R i c h a r d s ' a n d L i t t m a n ' s r e s u l t s c a n be s u m m a r i z e d as f o l l o w s : T h e i m p o r t a n t w a v e l e n g t h r a n g e of r a d i a t i o n w a s 3000 t o 4000 A . f o r t h e p h o t o c h e m i c a l p r o d u c t i o n of ozone i n s m o g . T h e photochemical hypotheses was furthered b y the demonstration t h a t i r r a d i a t e d night air formed oxidant. I t w a s c o n f i r m e d t h a t ozone is f o r m e d f r o m 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 a n d organic v a p o r . I t w a s suggested t h a t n i t r i c oxide w a s a n i m p o r t a n t p r e c u r s o r t o ozone f o r m a t i o n . Experimental Studies of A r m o u r Research sponsored b y the A i r P o l l u t i o n F o u n d a t i o n .

Foundation.

This

research was

M i l l e r a n d c o w o r k e r s used a 2 - l i t e r V y c o r p h o t o l y s i s flask w r a p p e d i n a l u m i n u m foil except for a n opening to a d m i t t h e collimated r a d i a t i o n f r o m a H a n o v i a T y p e A m e r c u r y a r c t h a t w a s filtered w i t h a b o r o s i l i c a t e glass filter t o c u t o u t r a d i a t i o n s a t w a v e l e n g t h s b e l o w 3000 A . (23). T h e use of t h e reflective l i n i n g o n t h e flask t o f o r m a m u l t i p l e r e f l e c t i o n s y s t e m w a s necessary t o a c h i e v e sufficient l i g h t i n t e n s i t y w i t h t h i s s y s t e m . A r e l a t i v e l y u n i f o r m r a d i a t i o n flux w a s t h e r e b y o b t a i n e d . T h e r a d i a t i o n i n t e n s i t y , as d e t e r m i n e d w i t h a p h o t o e l e c t r i c p r o b e , w a s a p p r o x i m a t e l y t h e s a m e as t h a t of n o o n s u n l i g h t i n t h e u l t r a v i o l e t r e g i o n b u t c o n s i d e r a b l y less i n t h e v i s i b l e r e g i o n . A t t h e c o n c l u s i o n of p h o t o l y s i s , t h e r e a c t i o n m i x t u r e w a s p a s s e d t h r o u g h l i q u i d o x y g e n - c o o l e d t r a p s p a c k e d w i t h glass beads a n d t h e n t h r o u g h a t r a i n of t h r e e b u b b l e r s c o n t a i n i n g a l k a l i n e p h e n o l p h t h a l i n r e a g e n t . O x i d a n t v a l u e s were o b t a i n e d b y s p e c t r o p h o t o m e t r i c m e a s u r e m e n t of t h e p a r t i a l l y o x i d i z e d reagent m i x t u r e . C o n t r o l l e d e x p e r i m e n t s r e v e a l e d t h a t n i t r o g e n d i o x i d e w a s efficiently t r a p p e d i n t h e freezeout t r a p s a n d d i d n o t c o n t r i b u t e t o o x i d a t i o n of t h e reagent. P r e s u m a b l y , o x i d a n t s less v o l a t i l e t h a n n i t r o g e n d i o x i d e ( p e r o x i d e s , etc.) w o u l d also be t r a p p e d . T h e p h y s i c a l e v i d e n c e , t h e r e f o r e , p o i n t s s t r o n g l y t o ozone as t h e p r i n c i p a l o x i d a n t p r o d u c t of t h e p h o t o c h e m ical reaction. T y p i c a l r e s u l t s of i r r a d i a t i o n of n i t r o g e n d i o x i d e a n d 3 - m e t h y l h e p t a n e i n o x y g e n are g i v e n b e l o w . N o ozone w a s o b t a i n e d w h e n e i t h e r t h e n i t r o g e n d i o x i d e o r t h e h y d r o c a r b o n w a s o m i t t e d . R e c o v e r y of n i t r o g e n d i o x i d e f r o m t h e freezeout t r a p s was checked b y analysis w i t h a modified Griess reagent. A tendency t o w a r d h i g h recovery b y this m e t h o d has n o t been completely resolved, b u t t h e results consistently

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

248


s h o w l o w r e c o v e r y ( o r n o n e ) i n p h o t o l y s e s i n w h i c h a n a p p r e c i a b l e q u a n t i t y of ozone was f o u n d .


Concentration, P . P . M . s, Hours 3 1 1 3 17 3 3 5 3 3 3 3 3

3-Methylheptane 13.2 14.7 8.9 20.4 10.0 3.5 0.97 0.00 3.9 2.3 1.35 0.04 3.3

NO2, initial 1.36 1.47 0.76 0.93 0.48 0.65 0.50 1.11 0.72 0.72 0.48 0.50 0.00

Ozone 0.89 0.33 0.38 0.86 0.53 0.97 0.59 0.0 0.2» 0.44 0.39 0.0 0.00

NO2, recovered 0.08 1.44 1.07 0.24 0.18 0.05 0.20 1.47 0.51

—

0.51 0.76 0.00

Corning-7380 glass filter, 2 mm. thick, cut out 3130-A. radiation but passed 60% of 3660 A . a

M i l l e r ' s f i n d i n g s c a n be s u m m a r i z e d as c o n f i r m i n g t h e f o l l o w i n g : O z o n e is f o r m e d f r o m 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 a n d o r g a n i c v a p o r f o r reactant concentrations below 1 p.p.m. 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 alone p r o d u c e s ozone of t h e o r d e r of 0.1 p . p . m . ; w h e n o r g a n i c v a p o r c o n c e n t r a t i o n s a b o v e 0.2 p . p . m . a r e a d d e d , t h e r e is a n e n h a n c e m e n t of ozone p r o d u c t i o n . N i t r o g e n d i o x i d e i s c o n s u m e d i n t h e r e a c t i o n , p r o b a b l y as a r e s u l t of t h e r e a c t i o n of n i t r i c oxide a n d t h e o r g a n i c v a p o r , i n d i c a t i n g t h a t n i t r o g e n d i o x i d e is m o r e t h a n t h e radiation absorber. Infrared Studies of F r a n k l i n Institute. I n this work, sponsored b y the A m e r i c a n Institute, the decision to s t u d y t h e smog reactions w i t h i n f r a r e d spectrometry was b a s e d o n h a v i n g a n a n a l y t i c a l m e t h o d as u n e q u i v o c a l as possible i n i d e n t i f y i n g p a r t i c u l a r c o m p o u n d s i n t h e presence o f a n u n k n o w n m i x t u r e . I n f r a r e d a b s o r p t i o n c a n p r o v i d e n e c e s s a r y s e l e c t i v i t y , b u t o r d i n a r y e q u i p m e n t does n o t h a v e n e a r l y e n o u g h s e n s i t i v i t y t o d e t e c t s u b s t a n c e s a t l o w c o n c e n t r a t i o n s of s m o g . A c c o r d i n g l y , first e x p e r i m e n t s w e r e d o n e w i t h c o n c e n t r a t i o n s of r e a c t a n t s m a n y t i m e s h i g h e r than are found i n polluted a i r . I n these e x p e r i m e n t s e i t h e r n i t r o g e n d i o x i d e o r ozone w a s m i x e d w i t h a n o r g a n i c c o m p o u n d a t c o n c e n t r a t i o n s of a b o u t 1 p . p . t . i n a i r o r o x y g e n a n d a l l o w e d t o r e a c t w i t h o r w i t h o u t a r t i f i c i a l s u n l i g h t ; t h e p r o d u c t s were a n a l y z e d b y m e a n s of s t a n d a r d i n f r a r e d t e c h n i q u e s . A l k y l n i t r a t e , a l k y l n i t r i t e , a l d e h y d e , a n d p e r o x y a c i d were t y p i c a l products of t h e nitrogen dioxide-organic c o m p o u n d reaction. O z o n e , w h i c h h a s p l a y e d a c e n t r a l role i n studies of t h e L o s A n g e l e s s m o g , w a s n o t d e t e c t e d as a p r o d u c t i n t h i s first s t u d y . O z o n e w a s f o u n d t o r e a c t s l o w l y w i t h s a t u r a t e d h y d r o c a r b o n s b u t r a p i d l y w i t h olefins. P e r o x y a c i d s were i d e n t i f i e d a m o n g t h e p r o d u c t s w h e n ozone w a s r e a c t e d w i t h a l d e h y d e s . D u r i n g these first studies i t b e c a m e o b v i o u s t h a t i t w o u l d be d e s i r a b l e t o s t u d y these r e a c t i o n s a t c o n c e n t r a t i o n s n e a r e r t o those e n c o u n t e r e d i n p o l l u t e d a i r . T h i s r e q u i r e d d e s i g n a n d c o n s t r u c t i o n of a s p e c i a l r e a c t i o n vessel a n d i n f r a r e d a b s o r p t i o n c e l l . T h i s c e l l u t i l i z e d a m u l t i p l e r e f l e c t i o n s y s t e m of t h e W h i t e t y p e . B y a d j u s t m e n t of t h e t w o m i r r o r s a t t h e r i g h t - h a n d e n d of t h e c e l l s h o w n i n F i g u r e 18, i t i s possible t o o b t a i n a n y i n t e g r a l m u l t i p l e of f o u r passes t h r o u g h t h e c e l l . I n a s m u c h as t h e m i r r o r s a t t h e r i g h t e n d a r e 3 m e t e r s f r o m t h e s m a l l e r m i r r o r a t t h e left e n d , 144 passes t h r o u g h t h e c e l l gives a t o t a l p a t h l e n g t h of 4 3 2 m e t e r s . S i n c e i n f r a r e d p a t h s of a p p r o x i m a t e l y 5 0 0 m e t e r s c o u l d be o b t a i n e d , i t w a s possible t o d e t e c t r e a c t i o n p r o d u c t s a t c o n c e n t r a t i o n s of a f e w t e n t h s of 1 p . p . m . I n t h e first e x p e r i m e n t a l p r o g r a m c a r r i e d o u t w i t h t h i s c e l l {36), ozone as a p r o d u c t w a s f o u n d i n c o n c e n t r a t i o n s o f 1 t o 2 p . ρ . m . a n d less w h e n n i t r o g e n d i o x i d e a n d


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v a r i o u s o r g a n i c c o m p o u n d s were r e a c t e d . I n these e x p e r i m e n t s r e a c t a n t s a t a f e w p a r t s p e r m i l l i o n i n o x y g e n o r a i r w e r e i r r a d i a t e d w i t h a n A H - 6 a r c enclosed i n b o r o s i l i c a t e glass as s h o w n i n F i g u r e 18. T h e v a r i a t i o n of ozone c o n c e n t r a t i o n w i t h t i m e of i r r a d i a t i o n w a s f o u n d t o d e p e n d , i n a c o m p l e x w a y , o n t h e s t r u c t u r e of t h e o r g a n i c c o m p o u n d a n d o n t h e c o n c e n t r a t i o n of b o t h r e a c t a n t s ( F i g u r e 19). T h e t r a n s i t o r y f o r m a t i o n of o z o n e b y 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 o x y g e n w a s d e m o n s t r a t e d ; i t was s h o w n t h a t , i f t h e fast b a c k r e a c t i o n b e t w e e n ozone a n d n i t r i c o x i d e i s s u p p r e s s e d b y t h e a d d i t i o n of n i t r o g e n p e n t o x i d e t o r e a c t w i t h t h e n i t r i c o x i d e , t h e o z o n e w i l l q u i c k l y a c c u m u l a t e i n t h e s y s t e m ( F i g u r e 20) (36).

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7

(min)

Figure 20. Effect of nitro gen pentoxide on photolysis of nitrogen dioxide in oxy gen O t h e r p r o d u c t s o b s e r v e d i n t h i s first s t u d y w i t h t h e l o n g - p a t h c e l l were a l d e h y d e , a l k y l nitrate, formic acid, carbon monoxide, carbon dioxide, a n d water. Several p r o m i n e n t a b s o r p t i o n s w h i c h a p p a r e n t l y a l l b e l o n g t o one c o m p o u n d c o u l d n o t b e i d e n t i f i e d . T h i s i n t e r e s t i n g p r o d u c t , r e f e r r e d t o as c o m p o u n d X , h a s b e e n s u b j e c t e d t o considerable s t u d y i n a n a t t e m p t t o determine i t s structure a n d physical properties. A s i d e f r o m ozone, i t is p r o b a b l y t h e m o s t i m p o r t a n t p r o d u c t of these r e a c t i o n s {37). C o m p o u n d X . O b t a i n i n g s a m p l e s of c o m p o u n d X f o r s t u d y p r e s e n t e d some d i f f i culty. W h e n organic compounds a n d nitrogen dioxide are photolyzed at h i g h concen t r a t i o n s ( o n t h e o r d e r of m i l l i m e t e r s of m e r c u r y ) , a l k y l n i t r a t e i s t h e chief n i t r o g e n c o n t a i n i n g p r o d u c t a n d c o m p o u n d X is n o t f o r m e d . T h e o n l y successful t e c h n i q u e of p r e p a r a t i o n of c o m p o u n d X is a c t u a l p h o t o l y s i s of m i x t u r e s of o r g a n i c c o m p o u n d s a n d n i t r o g e n d i o x i d e a t l o w pressures i n t h e presence of o x y g e n . Diacetyl was found t o g i v e t h e best r e s u l t s — i . e . , i t g a v e t h e least a m o u n t of side p r o d u c t s . W i t h 100 p . p . m . e a c h of d i a c e t y l a n d n i t r o g e n d i o x i d e i n 1 a t m . of o x y g e n , a b o u t 2 h o u r s of A H - 6 a r c i r r a d i a t i o n w e r e necessary f o r m o s t of t h e r e a c t a n t s t o b e c o n v e r t e d t o p r o d u c t s . A t these l o w pressures of r e a c t a n t s a l a r g e v o l u m e of g a s w a s required i n order to give enough c o m p o u n d X f o r a l i q u i d sample t o be collected. Therefore, t h e reaction was conducted i n t h e 500-meter, l o n g - p a t h absorption cell. A t t h e e n d of t h e r e a c t i o n , p r o d u c t s were s l o w l y p u l l e d t h r o u g h a t r a p c o o l e d b y a d r y i c e - i s o p r o p y l a l c o h o l m i x t u r e . T h i s t r a p passed some of t h e p r o d u c t s , s u c h as a c e t a l d e h y d e , c a r b o n d i o x i d e , a n d c a r b o n m o n o x i d e , b u t t r a p p e d c o m p o u n d X , o r a t least p a r t of i t . I t also t r a p p e d w a t e r v a p o r a n d some u n r e a c t e d d i a c e t y l . H o w e v e r , a n i n f r a r e d s p e c t r u m , a mass s p e c t r u m , a n d a n u c l e a r m a g n e t i c resonance s p e c t r u m of t h e c o m p o u n d were o b t a i n e d a n d i t w a s possible t o p e r f o r m q u a n t i t a t i v e tests of i t s c h e m i c a l properties. T h e i n f r a r e d s p e c t r u m of t h e c o m p o u n d X f r o m d i a c e t y l i s s h o w n i n F i g u r e 2 1 . I t shows t h e f o l l o w i n g f e a t u r e s : T h e C H a b s o r p t i o n is w e a k c o m p a r e d t o o t h e r s t r o n g b a n d s i n t h e s p e c t r u m , indicating a methyl compound. T h e r e is a s t r o n g single c a r b o n y l b a n d a t 5.75 m i c r o n s s i m i l a r i n s h a p e a n d w a v e l e n g t h t o t h e c a r b o n y l b a n d s of a l d e h y d e s , k e t o n e s , p e r o x y a c i d s , a n d esters, a n d d i f f e r e n t f r o m t h e d o u b l e c a r b o n y l b a n d s of a c i d s , a c i d a n h y d r i d e s , a n d d i a c y l p e r o x i d e s . T h e r e i s a n e i g h b o r i n g , w e a k e r b a n d a t 5.4 m i c r o n s w h i c h m i g h t b e c o n s i d e r e d a p a r t of a d o u b l e c a r b o n y l b a n d , b u t t h i s seems d o u b t f u l because t h e t w o b r a n c h e s of a d o u b l e c a r b o n y l b a n d a r e u s u a l l y of a p p r o x i m a t e l y e q u a l i n t e n s i t y a n d a r e u s u a l l y closer t o g e t h e r . T h e i n d i c a t i o n s a r e t h a t c o m p o u n d X f r o m d i a c e t y l is a n a c e t y l c o m p o u n d — a logical product. T h e b a n d s a t 5.4, 7.7, a n d 12.6 m i c r o n s i n d i c a t e t h e presence of n i t r o g e n i n t h e molecule f o r the following reasons:


RENZETTI—OZONE

IN LOS ANGELES

251

ATMOSPHERE

WAVE L E N G T H 2

3

4

5

6

7

8

9

(micron) 10

ll

12

13

14

15

16

τ—τ

Z

Q1

1

1

I

l^LJ

I

I

I

I

I

ι

ι

I


ο

Figure 21. Products of reaction of 10 p.p.m. of 1-pentene a n d 5 p.p.m. of nitrogen dioxide in 1 atm. of dry oxygen Path length, 240 meters A. Before irradiation B. Irradiated by AH-6 mercury arc

a. b a n d s n e a r 5.4 m i c r o n s arise f r o m t h e n i t r i c o x i d e s t r e t c h i n g v i b r a t i o n i n n i t r i c oxide, n i t r o s y l c h l o r i d e , a n d n i t r o g e n t e t r o x i d e ; f e w o t h e r c o m p o u n d s h a v e b a n d s here. 6. A l k y l n i t r a t e s , n i t r o s o c o m p o u n d s , a n d n i t r o g e n t e t r o x i d e a b s o r b n e a r 7.7 m i c r o n s . c. A l k y l n i t r i t e s h a v e a s t r o n g b a n d n e a r 12.6 m i c r o n s w h i c h is s u p posed to originate i n the n i t r i c oxide group. T h e r e is a p a r t i c u l a r l y s t r o n g b a n d i n t h e s p e c t r u m w h i c h h a d n o t p r e v i o u s l y been assigned t o c o m p o u n d X . T h i s is t h e b a n d a t 8.6 m i c r o n s . I d e n t i f i c a t i o n of t h i s b a n d was i m p o r t a n t because i t w a s t h e o n l y m a j o r u n i d e n t i f i e d b a n d i n t h e s p e c t r a of t h e reaction products f r o m organic compounds a n d nitrogen dioxide, other t h a n the bands w h i c h were o b v i o u s l y d u e t o c o m p o u n d X . T h i s b a n d , u n l i k e t h e b a n d s a t 5.4, 5.74, 7.7, a n d 12.6 m i c r o n s , a p p e a r s i n t h e s p e c t r u m of t h e s a m p l e of c o m p o u n d X p r e p a r e d f r o m diacetyl b u t n o t i n a sample p r e p a r e d f r o m d i b u t y r y l . T h u s , c o m p o u n d X is p r o b a b l y r e a l l y a h o m o l o g o u s series of c o m p o u n d s , of w h i c h o n l y t h e lowest m e m b e r possesses a b a n d a t 8.6 m i c r o n s . T h e p r o d u c t s of t h e r e a c t i o n of n i t r o g e n d i o x i d e w i t h 2 - p e n t e n e o r w i t h m e t h y l e t h y l k e t o n e also s h o w e d t h i s b a n d . T h e s a m p l e p r e p a r e d f r o m d i b u t y r y l also h a s a m o d e r a t e s t r e n g t h b a n d a t 9.6 m i c r o n s w h i c h h a d been o b s e r v e d i n t h e s p e c t r a of r e a c t i o n p r o d u c t s . T h e d e c o m p o s i t i o n p r o d u c t s of c o m p o u n d X were e x a m i n e d f o r clues t o i t s s t r u c t u r e . I n one e x p e r i m e n t a s a m p l e w a s a l l o w e d t o d e c o m p o s e f o r o v e r a week a t r o o m temperature i n oxygen. T h e i n f r a r e d s p e c t r u m of t h e p r o d u c t s s h o w e d c a r b o n d i o x i d e a n d a s m a l l a m o u n t of o r g a n i c n i t r a t e . I t is clear f r o m t h i s t h a t t h e o r i g i n a l m o l e c u l e c o n t a i n e d n i t r o g e n . T h e s u r p r i s i n g weakness of t h e p r o d u c t s p e c t r u m l e d t o t h e suggestion t h a t a d s o r p t i o n o n t h e c e l l w a l l s w a s o c c u r r i n g r a t h e r t h a n d e c o m p o s i t i o n . B u t t h e m a r k e d increase i n c a r b o n d i o x i d e c o n c e n t r a t i o n argues a g a i n s t t h i s . There was n o n i t r o u s oxide, n i t r i c oxide, n i t r o g e n d i o x i d e , n i t r o g e n p e n t o x i d e , n i t r o u s a c i d , nitric acid, nitrite, or nitro compound evident. I n another experiment compound X was decomposed b y heating i n nitrogen at 185° C . f o r 2 h o u r s . T h e s p e c t r u m of t h e p r o d u c t s of t h i s r e a c t i o n s h o w e d s m a l l


A D V A N C E S IN

252

amounts

of

carbon

dioxide,

carbon

nitromethane, and m e t h y l nitrite.

monoxide,

formaldehyde,

CHEMISTRY SERIES

methanol,

probably

T h e r e was n o n i t r o u s o x i d e , n i t r i c o x i d e , n i t r o g e n d i

oxide, nitrogen pentoxide, nitrous acid, nitric acid, or nitrate evident.

Unfortunately,

i t has n o t been possible t o d r a w m a n y c o n c l u s i o n s f r o m these p r o d u c t s , a l t h o u g h t h e y do i n d i c a t e a g a i n t h a t n i t r o g e n is p r e s e n t i n t h e m o l e c u l e .

O n one o c c a s i o n a

2-drop

s a m p l e of c o m p o u n d X e x p l o d e d w i t h e x t r e m e v i o l e n c e , a g a i n s h o w i n g t h i s c o m p o u n d ' s instability. Compound X

dissolves i n w a t e r , p r o b a b l y h y d r o l y z i n g , t o f o r m a s t r o n g l y a c i d

s o l u t i o n w h i c h c a n a c t as e i t h e r a n o x i d i z i n g agent o r a r e d u c i n g a g e n t — i . e . , i t l i b e r a t e s i o d i n e f r o m p o t a s s i u m i o d i d e s o l u t i o n , a n d i t decolorizes p o t a s s i u m p e r m a n g a n a t e .


s o l u t i o n gives t h e b r o w n r i n g test f o r n i t r i t e a n d n i t r a t e .

The

W h e n a f e w d r o p s of

com

p o u n d X w e r e m i x e d w i t h a f e w d r o p s of w a t e r a n d t h e m i x t u r e w a s e v a p o r a t e d

back

into the l o n g - p a t h cell, the s p e c t r u m showed t h a t nitric acid h a d been An

i m p o r t a n t p r o p e r t y of c o m p o u n d

photolyzed i n oxygen.

X

is i t s r a p i d p r o d u c t i o n of

T h e only other compounds

photolysis are the nitrites.

formed.

I n its ozone-producing

ozone w h e n

f o u n d to produce ozone r e a d i l y o n properties, compound

X

behaves

like a nitrite. T a k e n a l l together, evidence indicates t h a t c o m p o u n d X

is a c o m p o u n d of one

of

these t y p e s : O

O

11

O

O

II

R—C—NO (Ό

R—C—ONO (Π)

Ο

II R—C—N0 (III)

II 2

R—C—0N0 (IV)

II 2

R—C—OONO (V)

F o r m u l a V , w h i c h c o u l d be c a l l e d p e r o x y a c y l n i t r i t e , a p p e a r s t o be t h e m o s t l i k e l y . S u c h a c o m p o u n d seems l i k e l y t o h a v e a l l t h e o b s e r v e d p h y s i c a l a n d c h e m i c a l p r o p e r t i e s of c o m p o u n d X , a n d a m e c h a n i s m f o r i t s f o r m a t i o n c a n e a s i l y be w r i t t e n as f o l l o w s : A c y l r a d i c a l s are p r d u c e d i n p h o t o l y s i s of d i a c e t y l , w h e n h y d r o g e n i s a b s t r a c t e d f r o m a l d e h y d e , o r w h e n a n o x v g e n a t o m or a n o z o n e m o l e c u l e r e a c t s w i t h o l e f i n . 0 T h e a c y l radicals add oxygen to give the peroxyacyl radical, R — C — 0 — 0 . T h i s r e a c t i o n seems p r o b a b l e because, a t t h e c o n c e n t r a t i o n s a t w h i c h c o m p o u n d X i s f o r m e d , the a c y l radical collides w i t h oxygen several thousand times more frequently t h a n w i t h a n y of t h e o t h e r p o s s i b l e r e a c t a n t s . T h e l i k e l i h o o d of t h e r e a c t i o n i s also i n d i c a t e d b y t h e f a c t t h a t t h e l o w t e m p e r a t u r e o x i d a t i o n of a l d e h y d e i n p u r e o x y g e n p r o d u c e s p e r o x y a c i d s . 0 T h e p e r o x y a c y l r a d i c a l a d d s n i t r i c o x i d e to p r o d u c e R — C — 0 — 0 — N O . T h i s i s c o n s i s t e n t w i t h t h e f a c t t h a t n i t r i c o x i d e is i t s e l f a free r a d i c a l w i t h a n u n p a i r e d e l e c t r o n a n d i s c o m m o n l y u s e d as a n i n h i b i t o r of free r a d i c a l r e a c t i o n s . W h a t e v e r t h e e x a c t f o r m u l a of c o m p o u n d X , i t o b v i o u s l y c o n t a i n s n i t r o g e n , a n d i t is l i k e l y t h a t i t is f o r m e d i n t h e r e a c t i o n b e t w e e n a free r a d i c a l a n d n i t r i c o x i d e . I t a p p e a r s t o b e t h e k e y t o t h e u n d e r s t a n d i n g of m a n y of t h e o b s e r v e d f a c t s , as pointed out below.

Mechanism

of

Ozone

Formation

T h e i d e n t i f i c a t i o n of c o m p o u n d X as a n a c y l n i t r o g e n c o m p o u n d fits i n w i t h o b s e r v e d f a c t s of o z o n e f o r m a t i o n i n n i t r o g e n d i o x i d e - o r g a n i c c o m p o u n d p h o t o c h e m i c a l r e a c t i o n s . A s u m m a r y of t h e m e c h a n i s m f o l l o w s . F i r s t , p h o t o l y s i s i n t h e absence of o r g a n i c m a t e r i a l is c o n s i d e r e d , b a s e d o n d a t a p r e s e n t e d i n a p r e v i o u s p a p e r (36). N i t r o g e n d i o x i d e is p h o t o l y z e d b y t h e u l t r a v i o l e t radiation present i n s u n l i g h t : N0

2

-> N O + Ο


253


T h e o x y g e n a t o m so p r o d u c e d reacts w i t h a n o x y g e n m o l e c u l e : Ο + 0 —» 0 , 2

I n t h e absence of a n o r g a n i c m a t e r i a l t h i s ozone reacts q u i c k l y w i t h t h e n i t r i c o x i d e produced b y the photodissociation, NO + 0 - » N 0 + 0


3

2

2

p r e v e n t i n g a c c u m u l a t i o n of a s i g n i f i c a n t a m o u n t of ozone. T h e s e t h r e e r e a c t i o n s p r e d i c t t h a t e q u a l 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 of ozone a n d n i t r i c o x i d e w i l l b e f o r m e d w h e n n i t r o g e n d i o x i d e i n o x y g e n is i r r a d i a t e d w i t h u l t r a v i o l e t r a d i a t i o n ( a s s u m i n g 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 of a t o m i c o x y g e n is i n s i g n i f i c a n t ) . A c t u a l l y , t h e ozone f o r m e d u n d e r these c i r c u m s t a n c e s is o b s e r v e d t o d i s a p p e a r u n d e r c o n t i n u e d i r r a d i a t i o n , a n d nitric oxide appears to accumulate i n the system. T h i s is ascribed t o t h e occurrence of a s l o w e r side r e a c t i o n w h i c h e i t h e r p r o d u c e s n i t r i c o x i d e o r consumes o z o n e . A good possibility is Ο + N 0 —> N O + 0 2

2

I f some o t h e r r e a c t a n t w a s i n t r o d u c e d i n t o t h e s y s t e m t o r e m o v e n i t r i c o x i d e i n c o m p e t i t i o n w i t h t h e o z o n e - n i t r i c oxide r e a c t i o n , i t w a s p r e d i c t e d t h a t t h e ozone w o u l d a c c u m u l a t e . N i t r o g e n p e n t o x i d e w a s f o u n d t o p r o d u c e t h e p r e d i c t e d effect; p h o t o l y s i s 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 p e n t o x i d e - o x y g e n s y s t e m y i e l d e d s u b s t a n t i a l q u a n t i t i e s of ozone. W h e n n i t r o g e n d i o x i d e is p h o t o l y z e d i n t h e presence of a n o r g a n i c s u b s t a n c e ( i n o x y g e n ) , free r a d i c a l s a r i s i n g d u r i n g t h e o x i d a t i o n of t h e o r g a n i c m a t e r i a l a r e b e l i e v e d to p l a y a p a r t s i m i l a r t o t h e n i t r o g e n p e n t o x i d e — t h a t i s , t h e y r e a c t w i t h t h e n i t r i c oxide t o f o r m c o m p o u n d X , a l l o w i n g ozone t o a c c u m u l a t e i n t h e s y s t e m . T h i s m e c h a n i s m r e a d i l y a c c o u n t s f o r t h e p a r a l l e l i s m b e t w e e n t h e r a t e of c o m p o u n d X f o r m a t i o n , t h e r a t e of ozone f o r m a t i o n , a n d t h e r a t e of n i t r o g e n d i o x i d e d i s a p p e a r a n c e w h i c h w a s r e p o r t e d p r e v i o u s l y (36). T h e m e c h a n i s m also e x p l a i n s t h e f a c t t h a t 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 - o r g a n i c c o m p o u n d - a i r m i x t u r e s s o m e t i m e s p r o d u c e s ozone c o n c e n t r a t i o n s i n excess of t h e i n i t i a l n i t r o g e n d i o x i d e c o n c e n t r a t i o n . T h e r e a s o n f o r t h i s is t h a t c o m p o u n d X is p h o t o l y z e d i n a i r t o p r o d u c e ozone (discussed b e l o w ) . I n this r e a c t i o n n i t r o g e n d i o x i d e is p r o b a b l y first f o r m e d a n d is t h e n q u i c k l y p h o t o l y z e d , l e a d i n g t o ozone a n d p r o b a b l y t o r e g e n e r a t i o n of c o m p o u n d X . T h e c h a i n o x i d a t i o n of t h e o r g a n i c m a t e r i a l p r e s u m a b l y is i n i t i a t e d b y t h e a t t a c k of a n o x y g e n a t o m o n a n o r g a n i c m o l e c u l e . T h e r e a r e a n u m b e r o f w a y s e a c h o x y g e n a t o m used i n t h i s i n i t i a l a t t a c k m a y l e a d t o t h e f o r m a t i o n of m a n y free r a d i c a l s c a p a b l e of r e a c t i n g w i t h n i t r i c o x i d e . T h e s e a r e c h a i n b r a n c h i n g d u r i n g o x i d a t i o n ; p h o t o l y s i s of i n t e r m e d i a t e s f o r m e d d u r i n g o x i d a t i o n , s u c h as a l d e h y d e s ; a n d p h o t o l y s i s of c o m p o u n d X itself. F o r t h i s r e a s o n o n l y a f r a c t i o n of t h e o x y g e n a t o m s p r o d u c e d b y 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 a r e c o n s u m e d i n i n i t i a t i o n r e a c t i o n s , w h i l e t h e m a j o r i t y react w i t h m o l e c u l a r o x y g e n t o f o r m ozone. T h e observation made b y H a a g e n - S m i t a n d F o x a n d confirmed b y l o n g - p a t h cell s t u d i e s — t h a t t h e r e is a n u p p e r l i m i t c o n c e n t r a t i o n of n i t r o g e n d i o x i d e a b o v e w h i c h ozone is n o t p r o d u c e d w i t h i n a l i m i t e d i r r a d i a t i o n t i m e — i s r e a d i l y e x p l a i n e d . W i t h a h i g h i n i t i a l c o n c e n t r a t i o n of n i t r o g e n d i o x i d e , p h o t o l y s i s p r o d u c e s n i t r i c o x i d e m o r e r a p i d l y t h a n i t c a n b e c o n s u m e d b y free r a d i c a l s p r o d u c e d f r o m t h e o r g a n i c m a t e r i a l . W i t h c o n t i n u e d i r r a d i a t i o n , t h e r a t e of f o r m a t i o n of n i t r i c o x i d e i s s l o w e d d o w n b e cause n i t r o g e n d i o x i d e is d e p l e t e d . T h e free r a d i c a l s t h e n s l o w l y c o n s u m e n i t r i c o x i d e to f o r m c o m p o u n d X , eventually reducing the n i t r i c oxide concentration sufficiently t o a l l o w ozone t o a c c u m u l a t e . T h i s d e l a y i n f o r m a t i o n of ozone w a s o b s e r v e d i n s t u d i e s w i t h t h e l o n g - p a t h c e l l . I t w a s also o b s e r v e d t h a t t h e l i m i t i n g c o n c e n t r a t i o n o f n i t r o g e n dioxide is reduced b y increasing the initial h y d r o c a r b o n concentration. T h i s is ex plained b y the fact t h a t , w i t h greater h y d r o c a r b o n concentration, capacity to consume n i t r i c o x i d e b y t h e free r a d i c a l m e c h a n i s m is i n c r e a s e d .



254


Photolysis of C o m p o u n d X , B u t y l Nitrite, and D i a c e t y l . A relatively pure s a m p l e of c o m p o u n d X w a s p r e p a r e d f r o m d i a c e t y l a n d n i t r o g e n d i o x i d e b y m e a n s of the photolysis a n d cold t r a p collection technique described previously. T h i s sample was t h e n v a p o r i z e d b a c k i n t o t h e l o n g - p a t h c e l l , m i x e d w i t h 1 a t m . of o x y g e n , a n d p h o t o l y z e d w i t h t h e A H - 6 a r c . T h e exact p a r t i a l p r e s s u r e of c o m p o u n d X c o u l d n o t be m e a s u r e d because of t h e presence of a n u n k n o w n p e r c e n t a g e of w a t e r v a p o r . H o w e v e r , i f t h e c o m p o u n d X i n f r a r e d b a n d s are c o m p a r a b l e i n s t r e n g t h t o those of n i t r i t e s a n d n i t r a t e s , i t s p a r t i a l pressure w a s i n t h e p a r t p e r m i l l i o n r a n g e . O z o n e w a s q u i c k l y f o r m e d i n t h e p h o t o l y s i s . T h i s is s h o w n i n F i g u r e 22. W h e n p h o t o l y z e d i n o x y g e n , η - b u t y l n i t r i t e w a s f o u n d t o p r o d u c e ozone r e a d i l y . T h e r a t e of ozone p r o d u c t i o n a n d t h e a m o u n t of ozone p r o d u c e d were c o m p a r a b l e t o t h e r a t e a n d a m o u n t o b s e r v e d i n t h e p h o t o l y s i s of c o m p o u n d X . P u r e d i a c e t y l , d i b u t y r y l , a n d p y r u v i c a c i d h a v e a l l been r e p o r t e d t o p r o d u c e ozone on photolysis i n oxygen. F i r s t a t t e m p t s t o v e r i f y t h i s r e s u l t w i t h use of t h e l o n g - p a t h i n f r a r e d t e c h n i q u e were f r u s t r a t e d b y a p p e a r a n c e i n t h e s p e c t r u m of a b a n d of m e t h a n o l w h i c h m a s k e d t h e a b s o r p t i o n r e s u l t i n g f r o m ozone. T h i s d i f f i c u l t y w a s o v e r c o m e b y t h e use of t h e f o l l o w i n g t e c h n i q u e :

î Ο.·

*

ο

3

/

Ζ

ο

I £

Ul

2

υ ζ ο υ ζ' * ο

Ν Ο

Ο

/

f /

0

1

2

ΤΙΜΕ

3

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(HOURS)

Figure 22. O z o n e forma tion from compound X T h e diacetyl was photolyzed, a n d the spectrum was recorded i n the ozonem e t h a n o l r e g i o n (9 t o 10 m i c r o n s ) . T h e ozone w a s r e m o v e d b y t h e a d d i t i o n of a r e l a t i v e l y l a r g e a m o u n t of n i t r o g e n d i o x i d e , a n d t h e s p e c t r u m w a s a g a i n r e c o r d e d . T h e s e c o n d s p e c t r u m w a s t h e n s u b t r a c t e d f r o m t h e first. T h e r e s u l t i n g difference s p e c t r u m w a s a g o o d ozone s p e c t r u m . T h r e e different c o n c e n t r a t i o n s of d i a c e t y l were u s e d , e a c h i n 1 a t m . of d r y o x y g e n . T h e y were p h o t o l y z e d 20 m i n u t e s w i t h t h e A H - 6 a r c , a n d t h e n t h e s p e c t r a w e r e r e c o r d e d . T h e a m o u n t of w a t e r v a p o r present w a s f o u n d t o h a v e n o i m p o r t a n t effect o n t h e a m o u n t of o z o n e p r o d u c e d . T h e d r y a t m o s p h e r e s i n w h i c h t h e d i a c e t y l w a s p h o t o l y z e d u n d o u b t e d l y c o n t a i n e d traces of w a t e r v a p o r . A n a t t e m p t w a s m a d e t o detect ozone as a p r o d u c t of t h e p h o t o l y s i s of 20 p . p . m . of p y r u v i c a c i d i n 1 a t m . of o x y g e n . N o n e w a s d e t e c t e d , t h o u g h a f e w t e n t h s of 1 p . p . m . of ozone w o u l d h a v e p r o d u c e d a n i d e n t i f i a b l e a b s o r p t i o n b a n d . T h e a m o u n t of ozone f o r m e d i n t h e p h o t o l y s i s of d i a c e t y l is s m a l l c o m p a r e d t o a m o u n t s f o r m e d b y p h o t o l y s i s f r o m c o m p o u n d X o r η - b u t y l n i t r i t e . I t is also s m a l l c o m p a r e d to amounts formed i n reactions i n v o l v i n g organic compounds a n d nitrogen d i o x i d e . T h e ozone f o r m a t i o n f r o m d i a c e t y l m u s t be t h e r e s u l t of r e a c t i o n s i n v o l v i n g free r a d i c a l s a n d o x y g e n . P e r h a p s t h e p h o t o l y s i s of t h e n i t r o g e n - c o n t a i n i n g c o m p o u n d X o r η - b u t y l n i t r i t e also p r o d u c e s ozone t h r o u g h a free r a d i c a l m e c h a n i s m , a n d t h e


255



X

3- METHYLHEPTANE

A

I-PENTENE

ϋ

2-PENTENE

ο

METHYL

I

n-BUTYRALDEHYDE

V

n- BUTYRIC ACID

•

n- BUTYL

I

ETHYL

ALCOHOL

2 IRRADIATION

KETONE |

3 TIME (hr)

igure 23. O z o n e formation with vari ous organics a n d nitrogen dioxide g r e a t e r a m o u n t of ozone i s f o r m e d because of t h e g r e a t e r r e a c t i v i t y o f t h e r a d i c a l s . H o w e v e r , i t is b e l i e v e d t h a t these c o m p o u n d s first y i e l d n i t r o g e n d i o x i d e , w h i c h t h e n i s p h o t o l y z e d t o y i e l d ozone. T h e s e r e s u l t s c a n b e s u m m a r i z e d as follows : O z o n e , as o b s e r v e d b y i t s i n f r a r e d a b s o r p t i o n b a n d , i s f o r m e d i n t h e p h o t o l y s i s of nitrogen dioxide a n d organic vapors (Figure 2 3 ) . A n e w a c y l n i t r o g e n c o m p o u n d i s f o r m e d s i m u l t a n e o u s l y w i t h t h e ozone i n these same e x p e r i m e n t s . M o r e o v e r , t h i s c o m p o u n d , t e n t a t i v e l y i d e n t i f i e d as p e r o x y a c y l n i t r i t e , also f o r m s ozone u p o n i r r a d i a t i o n . I t w a s e s t a b l i s h e d t h a t n i t r o g e n d i o x i d e i s c o n s u m e d i n these r e a c t i o n s ( F i g u r e 2 4 ) . I t w a s e s t a b l i s h e d t h a t 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 alone i n o x y g e n p r o d u c e s a s t e a d y - s t a t e c o n c e n t r a t i o n of ozone ( F i g u r e 2 4 ) .

X

3-METHYLHEPTANE

5

IRRADIATION TIME (hr.)

Figure 24. Disappearance of nitrogen dioxide upon irradiation Primary

Photochemical

Processes

T h i s s e c t i o n is d e v o t e d t o t h e r e s u l t s of some t h e o r e t i c a l studies o n solar r a d i a t i o n , a b s o r p t i o n r a t e s , a n d p r i m a r y p h o t o c h e m i c a l processes i n s m o g , u n d e r t a k e n b y L e i g h t o n (18). I n w o r k s p o n s o r e d b y t h e A i r P o l l u t i o n F o u n d a t i o n , L e i g h t o n m a d e a c r i t i c a l a n a l y s i s of t h e c h e m i c a l effects t h a t s u n l i g h t a n d s k y r a d i a t i o n m a y h a v e o n smog formation i n u r b a n atmospheres. T h e radiant energy available for photochemical


256



processes w a s e s t i m a t e d b y t a k i n g i n t o c o n s i d e r a t i o n f a c t o r s s u c h as a t m o s p h e r i c transmissions, p a t h lengths i n contaminated layers, scattering b y particulate matter, a n d s u r f a c e reflections. F r o m p u b l i s h e d a b s o r p t i o n s p e c t r a , e s t i m a t e s w e r e m a d e of the m a x i m u m rates of a b s o r p t i o n w h i c h c o u l d o c c u r u n d e r r e a l i s t i c a t m o s p h e r i c c o n d i t i o n s b y a l l of t h e k n o w n a n d p r o b a b l e m o l e c u l a r species p r e s e n t i n p o l l u t e d a i r . S i n c e o n l y a b s o r b e d r a d i a t i o n c a n b e effective i n p h o t o c h e m i c a l processes, these e s t i m a t i o n s s e r v e d t o e l i m i n a t e some p o s t u l a t e d r e a c t i o n s a n d t o focus a t t e n t i o n o n others w h i c h , fortunately, are relatively few i n n u m b e r . S o l a r R a d i a t i o n . O f a l l t h e factors w h i c h collectively determine t h e amount a n d s p e c t r a l d i s t r i b u t i o n of t h e r a d i a t i o n e n t e r i n g a s u r f a c e l a y e r of t h e a t m o s p h e r e , t h e best e s t a b l i s h e d a p p e a r t o b e t h e s p e c t r a l i r r a d i a n c e o u t s i d e t h e a t m o s p h e r e a n d t h e a t t e n u a t i o n b y m o l e c u l a r s c a t t e r i n g . T h e a b s o r p t i o n coefficients of ozone a r e w e l l e s t a b l i s h e d , b u t n o easy m e t h o d exists f o r d e t e r m i n i n g t h e a m o u n t o f ozone i n a v e r t i c a l p r o f i l e of t h e a t m o s p h e r e a t a g i v e n t i m e . T h e m e a s u r e m e n t of t h e p a r t i c u l a t e c o n t e n t of t h e a t m o s p h e r e a n d i t s c o r r e l a t i o n w i t h a t m o s p h e r i c t r a n s m i s s i o n i s a field i n w h i c h m u c h remains to be accomplished. S u r p r i s i n g l y f e w d a t a exist o n t h e s p e c t r a l d i s t r i b u t i o n of s k y r a d i a t i o n a n d i t s v a r i a t i o n w i t h s o l a r e l e v a t i o n a n d a t m o s p h e r i c c o n d i t i o n s . T h e effect of clouds is of s e c o n d a r y i m p o r t a n c e , as intense s m o g g e n e r a l l y o c c u r s u n d e r a clear s k y . W i t h i n t h e l a y e r u n c e r t a i n t i e s exist as t o w h a t a b s o r b i n g species a r e p r e s e n t , w h a t a m o u n t of e a c h is p r e s e n t , h o w t h e c o n c e n t r a t i o n v a r i e s w i t h h e i g h t , a n d h o w t h e r a t e of a b s o r p t i o n is affected b y p a r t i c u l a t e d i f f u s i o n . S o m e of these f a c t o r s a r e so v a r i a b l e a n d so d i f f i c u l t t o d e t e r m i n e t h a t one m a y e x p e c t a t best o n l y a p p r o x i m a t e estimates of a b s o r p t i o n r a t e s . F o r t h i s p u r p o s e t h e following equation was developed: k

a

where

= Zo^-Vx

( ) 4

k = fraction of absorbing substance receiving photons per unit time a

a\ = decadic absorption coefficient of substance under study 7

- 1

= conversion factor

J\ = function of the transmission coefficients involving scattering, absorption by standard components of the atmosphere, and the solar zenith angle Values of J\

T a b l e II. (Given in photons c m .

λ,Α. 2900 3000 3100 3200 3300 3400 3500 3600 3700 3800 3900 4000 4100 4200 4400 4600 4800 5000 5250 5500 5750 6000 6250 6500 6750 7000 7500 8000

0° 1.2 X 1.53 X 1.32 X 2.59 X 4.18 X 4.31 X 4.75 X 4.84 X 5.71 X 5.43 X 5.07 X 7.15 X 9.24 X 9.34 X 10.4 X 11.5 X 12.0 X 11.4 X 11.9 X 12.2 X 12.2 X 12.2 X 12.2 X 12.1 X 11.9 X 11.7 X 11.1 X 10.5 X

10» 10" 10" 10" 10" 10" 10" 10" 10" 10" 10" 10" 10" 10" 10" 10" 10" 10" 10" 10" 10" 10" 10" 10" 10" 10" 10" 10"

20° 6 X 10i° 1.23 X 10" 1.21 X 10" 2.39 X 10" 4.00 X 10" 4.14 X 10" 4.56 X 10" 4.67 X 10" 5.53 X 10" 5.26 X 10" 4.93 X 10" 6.95 X 10" 8.99 X 10" 9.10 X 10" 10.1 X 10" 11.3 X 10" 11.8 X 10" 11.2 X 10" 11.7 X 10" 12.0 X 10" 12.0 X 10" 12.0 X 10" 12.0 X 10" 11.9 X 10" 11.7 X 10" 11.6 X 10" 11.0 X 10" 10.4 X 10"

- 2

second

-1

100 A . ) - 1

40° 5 X 10» 5.5 X 10» 8.6 X 10" 2.0 X 10" 3.39 X 10" 3.70 X 10" 3.97 X 10" 4.09 X 10" 4.87 X 10" 4.67 X 10" 4.40 X 10" 6.25 X 10" 8.12 X 10" 8.25 X 10" 9.25 X 10" 10.4 X 10" 10.9 X 10" 10.5 X 10" 11.0 X 10" 11.3 X 10" 11.3 X 10" 11.3 X 10" 11.4 X 10" 11.4 X 10" 11.3 X 10" 11.2 X 10" 10.6 X 10" 10.1 X 10"

60° 4 X 10· 6.0 X 10» 3.4 X 10" 1.2 X 10" 2.21 X 10" 2.43 X 10" 2.74 X 10" 2.89 X 10" 3.48 X 10" 3.38 X 10" 3.24 X 10" 4.67 X 10" 6.12 X 10" 6.29 X 10" 7.22 X 10" 8.26 X 10" 8.84 X 10" 8.54 X 10" 9.11 X 10" 9.42 X 10" 9.48 X 10" 9.57 X 10" 9.82 X 10" 9.96 X 10" 10.0 X 10" 10.0 X 10" 9.57 X 10" 9.18 X 10"


80° 1.5 X 8.2 X 0.18 X 0.58 X 0.71 X 0.83 X 0.88 X 1.12 X 1.07 X 1.01 X 1.46 X 1.93 X 2.01 X 2.42 X 2.93 X 3.29 X 3.27 X 3.68 X 3.88 X 3.98 X 4.13 X 4.60 X 5.14 X 5.59 X 5.63 X 5.67 X 5.71 X

10» 10» 10» 10» 10» 10» 10» 10» 10» 10» 10» 10» 10» 10» 10» 10» ΙΟΙ* 10» 10» 10» 10» 10» 10» 10» 10» 10» 10»

257


T a b l e I I gives v a l u e s of J f o r a n i n t e r m e d i a t e set of c o n d i t i o n s ; d e t a i l s a r e i n L e i g h t o n ' s r e p o r t (18). T h i s e q u a t i o n uses t h e w e a k a b s o r p t i o n a p p r o x i m a t i o n ; i t neglects s u r f a c e r e f l e c t i o n , a n d i t t a k e s n o a c c o u n t of t h e effects of d i f f u s i o n w i t h i n the absorbing layer. T h e weak absorption approximation will m a k e the calculated rates t o o h i g h , a n d n e g l e c t i n g t h e s u r f a c e r e f l e c t i o n w i l l m a k e t h e m t o o l o w ; as a r e s u l t these t w o e r r o r s p a r t i a l l y c a n c e l e a c h o t h e r . A n y a c c o u n t i n g of i n t e r n a l d i f f u s i o n o n a b s o r p t i o n rates w i l l d e p e n d o n t h e d i r e c t i o n a l d i s t r i b u t i o n of t h e diffused r a d i a t i o n a n d o n w h e t h e r t h e r a t e n e a r t h e s u r f a c e o n t h e a v e r a g e r a t e t h r o u g h o u t t h e l a y e r is t h e m o r e i m p o r t a n t . U n t i l m o r e i s k n o w n of these f a c t o r s , t h e effects of d i f f u s i o n w i t h i n t h e l a y e r m u s t b e r e g a r d e d as i n d e t e r m i n a t e .


x

Absorption Rates a n d P r i m a r y Photochemical Processes. L e i g h t o n developed a b s o r p t i o n rates f o r a l a r g e n u m b e r of s m o g c o m p o n e n t s f r o m t h e a b o v e e q u a t i o n . I n e a c h case, k i s expressed i n s e c o n d s and k C i n p.p.h.m. h o u r for concentra t i o n ( C ) of 10 p . p . h . m . f o r e a c h a b s o r b e r , e x c e p t i n t h e case of o x y g e n ( C s 2 1 % ) . - 1

a

- 1

a

0 2

A b s o r p t i o n rates a n d e s t i m a t e d u p p e r l i m i t s f o r t h e rates of p r i m a r y p h o t o c h e m i c a l processes i n u r b a n a i r a r e s u m m a r i z e d i n F i g u r e 25 a n d T a b l e I I I . A t o t h e r c o n c e n -

80·

Figure 25.

Comparison of absorption rates

Summary of absorption rates in p.p.h.m. h o u r as function of solar zenith angle, under radiation conditions of Table II. Rates are for absorber concentrations of 10 p.p.h.m. except for oxygen, which is at 0.2 atm. -1


258

ADVANCES

T a b l e III.

IN CHEMISTRY SERIES

Summary of Primary Photochemical Processes in U r b a n Air Estd. Upper Limit for Primary Photochemical Rate in Urban Air, P . P . H . M . Hour"**

Absorber N 0 , < 3850 A .

Primary Photochemical Process N ( V -> N O + Ο R C H O + Η NO

Organic nitrites

RCH ONO'' \

2

ζ = 60° 105

ζ = 20° 250

2

70

40

60

40

30 ~10b 9 ~10" 4.5

20 ~10b 7 ~10~ 1.5

RCH2O + NO R CO + CO 2


Diketones (glyoxal, biacetyl)

(Rcoy' \

2RCO ( R c o y + χ -+ ? 0 + e -> 0 org. + (MO)+ + M O 0 ' + Β -» ? 0 ' —> 0 + Ο 0 ' + Β -> ? C»' —> 0 + Ο

Particulate metal oxides (10 7 ) O2 (0.2 atm.) Os, 4500 to 7000 A .

2

3

O3, 2900 to 3500 A . Olefinic aldehydes (acrolein, crotonaldehyde) Aliphatic aldehydes N 0 , A3850 A . H 0 Aliphatic ketones Nitric acid Organic peroxides SO2 b

2

3

3

2

2

2

2

2

2

2

b

4b

3

Absorber concentration (except metallic oxides and 0 ) Highly uncertain, even as upper limits.

1 0.2 to 0.7 l 0.5 0.15 0.06 0.02 ~10~

2 0.5 to 1.8 lb 1 0.4 0.15 0.1 ~10~

RCH = CHCHO' + 0 — < RCHO' R + CHO Ν 0 ' + Β -> ? HaOj' 2ÔH R R C O ' —> R + R C O ΗΝΟ»' -> ÔH + Ν 0 ? ROOR' RÔ + O R S0 ' + s o S0 + so

2

a

b

b

3

2

2

2

2

10 p.p.h.m.

4b

Oxygen = 0.2 atm.

trations the rates will be proportional to the concentration.

T h e p r i m a r y processes

considered are only those resulting from absorption by the absorber indicated. Because the

actual

example,

of variations in both

absorption

rates

radiation conditions and absorber

in an urban

atmosphere

will

be

Figure 26 shows the effect of concentration changes

concentrations,

highly variable.

For

on the absorption

rate


RENZETTI—OZONE

IN LOS ANGELES

259

ATMOSPHERE

of n i t r o g e n d i o x i d e b e l o w 3850 Α . , a n d t h e u p p e r l i m i t of t h e a b s o r p t i o n r a t e of ozone ( a s s u m i n g t h e o x i d a n t is a l l ozone) r e s u l t i n g f r o m t h e o b s e r v e d 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 o x i d a n t a t P a s a d e n a , C a l i f . , o n S e p t . 13, 1955 (8). I f t h e c o n c e n t r a t i o n s were c o n s t a n t , t h e a b s o r p t i o n r a t e c u r v e s i n F i g u r e 26 w o u l d b e s y m m e t r i c a l w i t h the curve for J . T h e effects of s h o r t t e r m changes i n r a d i a t i o n c o n d i t i o n s m a y b e of t h e same m a g n i t u d e as those of c o n c e n t r a t i o n changes, b u t u n t i l m o r e i n f o r m a t i o n is a v a i l a b l e o n m o n o c h r o m a t i c i r r a d i a n c e , p a r t i c u l a r l y diffuse i r r a d i a n c e , i t i s n o t possible t o t a k e s i m i l a r a c c o u n t of t h e m i n u r b a n a i r . x

T h e o b s e r v e d rates of increase i n o x i d a n t c o n c e n t r a t i o n o n t h e m o r n i n g s of s m o g g y d a y s i n t h e L o s A n g e l e s B a s i n a r e f o r t h e m o s t p a r t b e t w e e n 1 a n d 15 p . p . h . m . h o u r , a l t h o u g h o c c a s i o n a l v e r y s h a r p increases m a y r u n u p t o 100 p . p . h . m . h o u r or more. T h e s e s u d d e n s h a r p increases i n o x i d a n t c o n c e n t r a t i o n m a y b e d u e t o p h o t o c h e m i c a l r e a c t i o n s , o r t h e y m a y b e d u e t o m e t e o r o l o g i c a l changes—e.g., w i n d t r a j e c t o r y . F o r i n s t a n c e , t h e c u r v e of o x i d a n t c o n c e n t r a t i o n i n F i g u r e 27 shows a n a v e r a g e r a t e of - 1


- 1

0800

0400

Figure 27.

1200 TIUE(PST)

1600

2000

Comparison of rate of oxygen atom production with oxi dant concentration on single d a y

increase f r o m sunrise u n t i l 1 1 : 0 0 A . M . of 2.8 p . p . h . m . h o u r , w h i l e b e t w e e n 1 1 : 0 0 a n d 1 1 : 4 5 A . M . t h e r a t e of increase is 36 p . p . h . m . h o u r - . O n t h e c o m p o s i t e a v e r a g e c u r v e i n F i g u r e 2 8 , t h e r a t e of increase i n o x i d a n t c o n c e n t r a t i o n f r o m 7 : 0 0 t o 1 1 : 0 0 A . M . (Z = 8 0 ° t o ζ = 4 4 ° ) averages a b o u t 2 p . p . h . m . h o u r . T h e a v e r a g e r a t e of increase i n o x i d a n t c o n c e n t r a t i o n a t 10 s t a t i o n s i n t h e L o s A n g e l e s B a s i n (28) f o r t h e p e r i o d of A u g u s t t h r o u g h N o v e m b e r 1954 w a s 1.8 p.p.h.m. h o u r a t ζ — 6 0 ° , w h i l e t h e r a t e of increase o n t h e d a y of greatest o x i d a n t v a l u e a t e a c h s t a t i o n d u r i n g t h i s p e r i o d a v e r a g e d 7.6 p . p . h . m . h o u r at ζ = 60°. A d d i t i o n a l w o r k a l o n g these lines is d e v e l o p e d b y R o g e r s (33). R e f e r r i n g t o T a b l e I I I , i t is seen t h a t a t c o n c e n t r a t i o n s of t h e o r d e r of 10 p . p . h . m . t h e o n l y a b s o r b e r s c a p a b l e of i n i t i a t i n g p r i m a r y p h o t o c h e m i c a l processes a t rates exceeding t h e o b s e r v e d a v e r a g e rates of increase i n o x i d a n t c o n c e n t r a t i o n a r e n i t r o g e n d i o x i d e , o r g a n i c n i t r i t e s , d i k e t o n e s , a n d p o s s i b l y p a r t i c u l a t e m e t a l l i c oxides ( a t 10 γ ) and oxygen. N o s a t i s f a c t o r y e v i d e n c e exists o n t h e c o n c e n t r a t i o n of o r g a n i c n i t r i t e s a n d diketones, a n d i t is not y e t k n o w n whether absorption b y particulate metallic - 1

1

- 1

- 1

- 1




260

0400

0800

1200

1600

2000

TIME(PST)

Figure 28.

Comparison

of averaged rates of oxygen oxidant concentration

atom

production a n d

oxides o r b y o x y g e n w i l l l e a d t o a n y r e a c t i o n i n u r b a n a t m o s p h e r e s . A b s o r p t i o n b y ozone w i l l b e i m p o r t a n t o n l y i f i t leads t o d i s s o c i a t i o n , a n d w i l l i n t h i s case s i m p l y s u p p l e m e n t 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 b y p h o t o d i s s o c i a t i o n o f n i t r o g e n dioxide. A b s o r p t i o n b y the aldehydes m a y contribute to smog formation, p a r t i c u l a r l y i n v i e w of t h e f a c t t h a t t h e y h a v e b e e n o b s e r v e d a t c o n c e n t r a t i o n s u p t o 3 0 p . p . h . m . i n the atmosphere, b u t secondary c h a i n reactions w o u l d be r e q u i r e d f o r aldehyde a b s o r p t i o n alone t o lead t o oxidant f o r m a t i o n a t t h e observed rates, a n d there is n o evidence t h a t such c h a i n reactions occur i n t h e atmosphere. T h e r e is n o evidence t h a t h y d r o g e n p e r o x i d e exists i n c o n c e n t r a t i o n s sufficient t o b e a n i m p o r t a n t c o n t r i b u t o r . R e a c t i o n s initiated b y absorption b y nitric acid, organic peroxides, a n d sulfur dioxide are p r o b a b l y too slow to contribute significantly t o smog f o r m a t i o n . I t seems t o b e i m p o r t a n t t o o b t a i n i n f o r m a t i o n o n t h e f o l l o w i n g p o i n t s : T h e c o n c e n t r a t i o n s of o r g a n i c n i t r i t e s a n d d i k e t o n e s i n u r b a n a t m o s p h e r e s . P o s s i b l e r e a c t i o n s f o l l o w i n g a b s o r p t i o n b y m e t a l l i c oxides. Possible reactions following absorption b y oxygen. Possible reactions following absorption b y nitrogen dioxide i n t h e visible region. Reactions following absorption b y aldehydes a n d ketones, i n c l u d i n g diketones, i n urban air. T h e i m p o r t a n c e i n u r b a n a t m o s p h e r e s of a b s o r b e r s s u c h as n i t r o u s a c i d a n d o r g a n i c c o m p o u n d s o t h e r t h a n those c o n s i d e r e d h e r e . P e n d i n g t h i s i n f o r m a t i o n a n d c o n s i d e r a t i o n of s e c o n d a r y r e a c t i o n s , t h e f o r e g o i n g analysis supports the conclusion already reached b y other investigators that, although o t h e r p r i m a r y processes u n d o u b t e d l y c o n t r i b u t e , t h e p h o t o d i s s o c i a t i o n of n i t r o g e n d i o x i d e i n t o n i t r i c o x i d e a n d o x y g e n a t o m s i s of m a j o r i m p o r t a n c e i n s m o g f o r m a t i o n . T h e oxygen atoms resulting f r o m absorption b y nitrogen dioxide w i l l be supple m e n t e d b y those f r o m t h e p h o t o d i s s o c i a t i o n o f ozone, a n d as these a r e t h e o n l y p r i m a r y processes k n o w n t o p r o d u c e o x y g e n a t o m s i n u r b a n a i r , t h e s u m of t h e a b s o r p t i o n rates of n i t r o g e n d i o x i d e a n d ozone sets a n u p p e r l i m i t t o t h e r a t e of o x y g e n a t o m p r o d u c t i o n . I n F i g u r e 27 t h i s s u m is c o m p a r e d w i t h t h e o b s e r v e d o x i d a n t c o n c e n t r a t i o n o n a single d a y , w h i l e i n F i g u r e 28 t h e same c o m p a r i s o n i s m a d e o n t h e basis of a c o m p o s i t e a v e r a g e of o b s e r v a t i o n s a t a n u m b e r of s t a t i o n s o v e r a p e r i o d of one m o n t h . T h e p e a k i n r a t e of o x y g e n a t o m p r o d u c t i o n , a t 7 : 3 0 A . M . i n F i g u r e 27 a n d a t 1 0 : 0 0



RENZETTI—OZONE

IN LOS ANGELES

261

ATMOSPHERE

TiMe(PST)

Figure 29.

Comparison of solar irradiance with diurnal variations in oxidant concentration

A . M . i n F i g u r e 28, is d u e t o t h e m o r n i n g p e a k i n n i t r o g e n d i o x i d e c o n c e n t r a t i o n . How e v e r , t h e t i m e d i s p l a c e m e n t of t h e a v e r a g e d o x i d a n t c o n c e n t r a t i o n c u r v e r e l a t i v e t o t h e r a t e c u r v e i n F i g u r e 28 is n o t e n t i r e l y d u e t o changes i n n i t r o g e n d i o x i d e c o n c e n t r a t i o n . T h i s i s s h o w n i n F i g u r e 2 9 , w h e r e c u r v e s of t h e a v e r a g e o x i d a n t c o n c e n t r a t i o n v e r s u s t i m e o v e r a 4 - m o n t h p e r i o d a t e a c h of five s t a t i o n s i n t h e L o s A n g e l e s B a s i n (28) a r e c o m p a r e d w i t h a r e p r e s e n t a t i v e c u r v e of J\. S i n c e J i n c l u d e s a l l of t h e f a c t o r s i n f l u e n c i n g a b s o r p t i o n r a t e w h i c h a r e d i r e c t l y d e p e n d e n t o n s o l a r z e n i t h angle, p l o t s of a b s o r p t i o n r a t e a t c o n s t a n t a b s o r b e r c o n c e n t r a t i o n s w i l l be s y m m e t r i c a l w i t h t h i s curve. x

T h e s h a p e of t h e a v e r a g e d o x i d a n t c o n c e n t r a t i o n c u r v e s a n d t h e i r t i m e d i s p l a c e m e n t r e l a t i v e t o t h e a b s o r p t i o n r a t e c u r v e s ( F i g u r e s 28 a n d 2 9 ) i n d i c a t e t h a t t h e o x i d a n t i s p r o d u c e d b y a p h o t o c h e m i c a l process a n d c o n t i n u o u s l y r e m o v e d b y a d a r k process. T h i s d a r k process m a y b e e i t h e r c h e m i c a l o r p h y s i c a l , o r b o t h . I f t h i s i s t h e case, t h e o b s e r v e d r a t e of c h a n g e i n o x i d a n t c o n c e n t r a t i o n i s e q u a l t o t h e difference b e t w e e n t h e rates of p r o d u c t i o n a n d r e m o v a l , a n d d u r i n g t h e m o r n i n g h o u r s t h e a c t u a l rate of oxidant p r o d u c t i o n m a y be s u b s t a n t i a l l y greater t h a n t h e observed average r a t e of i n c r e a s e i n c o n c e n t r a t i o n . I f t r u e , t h i s w i l l i m p o s e a f u r t h e r l i m i t a t i o n o n t h e n u m b e r of p r i m a r y p h o t o c h e m i c a l processes w h i c h m a y be of s i g n i f i c a n c e . Acknowledgment T h e a u t h o r h a s b o r r o w e d f r e e l y f r o m t h e w r i t i n g s of m a n y i n v e s t i g a t o r s i n o r d e r to p u t t h i s r e v i e w t o g e t h e r , a n d he i s i n d e b t e d to t h e m f o r t h e i r r e s u l t s . I n a d d i t i o n t o t h e i r p u b l i s h e d r e s u l t s these w o r k e r s h a v e g i v e n f r e e l y of t h e i r t i m e f o r h e l p f u l conversations.



262

Literature C i t e d (1) (2) (3) (4) (5)


(6) (7) (8) (9) (10) (11) (12) (13) (14) (15) (16) (17) (18) (19) (20) (21) (22) (23) (24) (25) (26) (27) (28) (29) (30) (31) (32) (33) (34) (35) (36) (37) (38) (39) (40) (41)

Bradley, C. E., Haagen-Smit, A. J., Rubber Chem. and Technol. 24, 750 (1951). Chalonge, D., Vassy, E., J. phys. radium 5, 309 (1934). Dauvillier, Α., Compt. rend. 201, 679 (1935). Dauvillier, Α., J. phys. radium 5, 455 (1934). Ehmert, Α., Ehmert, H., "Uber die chemische Bestimung des Ozongehaltes der L u f t , " Berichte des Deutschen Wetterdienstes in der U. S. Zone, No. 11, pp. 67-71, Bad Kissengen, Deutscher Wetterdiest in der U. S. Zone, 1949. Fabry, C., Buisson, H., Compt. rend. 192, 457 (1931). Fabry, C., Buisson, H., J. phys. radium 2, 197 (1921). Faith, W. L., Hitchcock, L. B., Neiburger, M., Renzetti, Ν. Α., Rogers, L. H., Air Pollution Foundation (Los Angeles) Second Tech. Progr. Rept., 12 (Novem ber 1955). Fowler, Α., Strutt, R. G., Proc. Roy. Soc. (London) 93A, 577 (1917). Francis, A. G., Parsons, A. T., Analyst 50, 262 (1925). Goetz, F. W. P., Ladenburg, Α., Naturwissenschaften 19, 373 (1931). Goetz, F. W. P., Schein, M., Stoll, B., Gerlands Beitr. Geophys. 45, 237 (1935). Haagen-Smit, A. J., Ind. Eng. Chem. 44, 1342 (1952). Haagen-Smit, A. J., Bradley, C. E., Fox, M. M., Ibid., 45, 2086 (1953). Haagen-Smit, A. J., Fox, M. M., Ibid., 48, 1484 (1956). Inn, E. C. Y., Tanaka, Y., J. Opt. Soc. Am. 43, 870 (1953). Ladenburg, Α., Quasig, R., Naturwissenschaften 19, 373 (1901). Leighton, P. Α., Perkins, W. Α., Air Pollution Foundation (Los Angeles) Rept. 14 (March 1956). Littman, F. E., Benoliel, R. W., Anal. Chem. 25, 1480 (1953). Littman, F. E., Ford, H. W., Endow, N., Ind. Eng. Chem. 48, 1492 (1956). Littman, F. E., Marynowski, C. W., Anal. Chem. 28, 819 (1956). McCabe, L. C., Ind. Eng. Chem. 45, 111A (September 1953). Miller, Α., Brown, C., Franson, K. D., Science 123, 934 (1956). Paneth, F. Α., Edgar, J. L., J. Chem. Soc. 1941, 519. Paneth, F. Α., Edgar, J. L., Nature 142, 112 (1938). Regener, V. H., Univ. New Mexico Sci. Rept. 1, Contract AF 19(122)-381 (June 1954). Ibid., 2 (July 1954). Renzetti, Ν. Α., ed., Air Pollution Foundation (Los Angeles) Rept. 9 (June 1955). Renzetti, Ν. Α., J. Chem. Phys. 24, 909 (1956). Renzetti, Ν. Α., Romanovsky, J. C., A.M.A. Arch. Ind. Health 14, 458 (1956). Reynolds, W. C., J. Soc. Chem. Ind. 49, 168 (1930). Richards, L. M., J. Air Pollution Control Assoc. 5, 216 (1956). Rogers, L. H., ed., Air Pollution Foundation (Los Angeles) Rept. 15 (November 1956). Schönbein, C. F., Ann. Phys. u. Chem. 65, 69, 161 (1845). Stair, R., Bagg, T. C., Johnston, R. G., J. Research Natl. Bur. Standards 52, 133 (1954). Stephens, E. R., Hanst, P. L., Doerr, R. C., Scott, W. E., Ind. Eng. Chem. 48, 1498 (1956). Stephens, E. R., Scott, W. E., Hanst, P. L., Doerr, R. C., J. Air Pollution Control Assoc. 6, 159 (1956). Stoll, B., Helv. Phys. Acta 8, 3 (1935). Strutt, R. G., Proc. Roy. Soc. (London) 94A, 260 (1918). Treadwell, F. P., Anneler, Ε., Z. anorg. Chem. 48, 86 (1905). Vigroux, E., Compt. rend. 234, 2529 (1952). RECEIVED for review M a y 27, 1957.

Accepted June 19, 1957.


Ozone in Los Angeles Atmosphere - Advances in Chemistry (ACS

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