Catalytic Atmospheric Ozone Analyzer - Advances in Chemistry (ACS

Catalytic Atmospheric Ozone Analyzer F. J . OLMER

Downloaded by UNIV OF PITTSBURGH on May 4, 2015 | http://pubs.acs.org Publication Date: January 1, 1959 | doi: 10.1021/ba-1959-0021.ch012

Armour Research Foundation, Illinois Institute of Technology, Chicago,

Ill.

With the catalytic ozone analyzer described, ozone concentration can be measured by the temperature differential between two thermistors placed in the gas stream. O n e of the thermistors is coated with a catalyst promoting the decomposition of ozone; the other is uncoated a n d is used as reference to the temperature of the gas. The two thermistors are part of a bridge circuit, the output of which is fed directly to a recorder. The instrument is not affected by the presence of water vapor, carbon monoxide, chlorine, nitrogen dioxide, sulfur dioxide, organic peroxides, hydrocarbon vapors, a n d combustion smokes at their usual concentrations in polluted atmospheres.

T h e p r o b l e m of c o n t r o l l i n g a t m o s p h e r i c p o l l u t i o n i n i n d u s t r i a l areas h a s b e c o m e a c u t e . T h i s p o l l u t i o n is c h a r a c t e r i z e d b y decreased v i s i b i l i t y , eye a n d nose i r r i t a t i o n , d e t e r i o r a t i o n of r u b b e r a r t i c l e s , a n d d a m a g e t o v e g e t a t i o n . I n e x t r e m e cases i t m a y e v e n affect h u m a n l i f e . A t m o s p h e r i c p o l l u t i o n c a n n o t b e c o n t r o l l e d so l o n g as t h e n a t u r e a n d t h e m e c h a n i s m of f o r m a t i o n of i t s deleterious c o n s t i t u e n t s r e m a i n u n k n o w n . W h i l e m a n y c h e m i c a l c o n s t i t u e n t s of p o l l u t e d a t m o s p h e r e s h a v e b e e n i d e n t i f i e d , t h e i r presence o r c o n c e n t r a t i o n does n o t seem t o f o l l o w a r e g u l a r p a t t e r n . O n t h e o t h e r h a n d , ozone is a l w a y s p r e s e n t i n p o l l u t e d o u t d o o r a t m o s p h e r e s . I t s concentration consistently rises f r o m a n o r m a l v a l u e of a f e w p a r t s p e r h u n d r e d m i l l i o n t o m a n y t i m e s t h i s v a l u e d u r i n g p e r i o d s of severe c o n t a m i n a t i o n . W h e t h e r ozone is t h e p r i m a r y cause of p o l l u t i o n o r is a s e c o n d a r y effect of t h e r e a c t i o n of o t h e r substances is n o t e n t i r e l y clear, b u t i t a p p e a r s t o b e a n i m p o r t a n t l i n k i n t h e c h a i n of c h e m i c a l r e a c t i o n s w h i c h p r o d u c e a t m o s p h e r i c p o l l u t i o n . V e r y l i k e l y , a k n o w l e d g e of t h e v a r i a t i o n s of ozone c o n c e n t r a t i o n i n a t m o s p h e r e s w o u l d p e r m i t a s t u d y of t h e influence of t h e v a r i o u s p a r a m e t e r s , a n d t h i s k n o w l e d g e m a y e v e n t u a l l y f u r n i s h a l e a d t o a n e x p l a n a t i o n of t h e m e c h a n i s m of f o r m a t i o n a n d t h e effects of p o l l u t a n t s . R e c e n t l y , a n u m b e r of m u n i c i p a l i t i e s h a v e b e c o m e so c o n c e r n e d w i t h t h e p r o b l e m t h a t t h e y h a v e i n s t a l l e d a u t o m a t i c ozone recorders a t s t r a t e g i c l o c a t i o n s . S o m e of these i n s t r u m e n t s a r e b a s e d o n t h e c h e m i c a l d e t e r m i n a t i o n of ozone b y o x i d a t i o n of p o t a s s i u m i o d i d e , a n d c o l o r i m e t r i c o r e l e c t r o m e t r i c m e a s u r e m e n t of t h e e x t e n t of t h e reaction. Others are spectrophotometric i n s t r u m e n t s ; a few are based o n rubber c r a c k i n g . T h e v a l u e of t h e c h e m i c a l d e t e r m i n a t i o n s of ozone i n t h e presence of t h e o x i d i z i n g o r r e d u c i n g substances p r e s e n t i n p o l l u t e d a t m o s p h e r e s i s q u e s t i o n a b l e . S p e c t r o p h o t o m e t r i c m e t h o d s r e q u i r e a l i g h t p a t h of a f e w h u n d r e d feet a n d c a n n o t be m o v e d e a s i l y f r o m one l o c a t i o n t o a n o t h e r . D e t e r m i n a t i o n b y r u b b e r c r a c k i n g is 87

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

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n o t specific a n d does n o t p r o v i d e c o n t i n u o u s i n d i c a t i o n s , a n d i t s i n t e r p r e t a t i o n is subjective. T h e A r m o u r R e s e a r c h F o u n d a t i o n h a s d e v e l o p e d a n a t m o s p h e r i c ozone a n a l y z e r w h i c h is n o t s u b j e c t t o t h e d r a w b a c k s of t h e different k i n d s of a p p a r a t u s m e n t i o n e d . P r i n c i p l e of

Operation


T h e p r i n c i p l e of t h e i n s t r u m e n t is i l l u s t r a t e d i n F i g u r e 1. T h e gas t o be a n a l y z e d is c i r c u l a t e d t h r o u g h a c h a m b e r c o n t a i n i n g t w o t h e r m i s t o r s . O n e of these is c o a t e d w i t h a c a t a l y s t t o p r o m o t e d e c o m p o s i t i o n of ozone. T h e t w o t h e r m i s t o r s a r e

Figure 1. Principle of the ozone analyzer p a r t of a b r i d g e c i r c u i t , w h i c h is s c h e m a t i c a l l y s h o w n i n F i g u r e 2. A n y increase i n t h e t e m p e r a t u r e of t h e c o a t e d t h e r m i s t o r i s reflected b y a decrease i n i t s resistance. T h e u n b a l a n c e of t h e b r i d g e causes a p o t e n t i a l t o a p p e a r b e t w e e n p o i n t s A a n d B. T h i s is f e d t o t h e c h o p p e r a n d a m p l i f i e r of a B r o w n E l e k t r o n i k r e c o r d e r , a n d causes t h e b a l a n c i n g m o t o r t o r o t a t e . T h e r o t a t i o n of t h i s m o t o r is t r a n s m i t t e d t o t h e c u r s o r of t h e p o t e n t i o m e t e r , P , w h i c h re-establishes t h e b a l a n c e i n t h e c i r c u i t . T h e c u r r e n t f r o m t h e b a t t e r y flows c o n t i n u o u s l y t h r o u g h t h e t h e r m i s t o r s i n s u c h a w a y t h a t t h e i r t e m p e r a t u r e is s l i g h t l y h i g h e r t h a n t h a t of t h e s u r r o u n d i n g gas. I f

Figure 2. The bridge circuit


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t h e gas flowing p a s t t h e t h e r m i s t o r s c o n t a i n s ozone, a c e r t a i n n u m b e r of m o l e c u l e s of ozone w i l l s t r i k e t h e c a t a l y s t a n d d e c o m p o s e , g e n e r a t i n g a s m a l l a m o u n t of h e a t . T h e r a t e a t w h i c h t h e heat is l i b e r a t e d m a y be a s s u m e d t o be p r o p o r t i o n a l t o t h e m o l a l ozone c o n c e n t r a t i o n i n t h e gas. B e c a u s e t h e rise i n t e m p e r a t u r e of t h e c o a t e d t h e r m i s t o r is a p p r o x i m a t e l y p r o p o r t i o n a l t o t h e ozone c o n c e n t r a t i o n , t h e t e m p e r a t u r e d i f f e r e n t i a l b e t w e e n t h e t w o t h e r m i s t o r s , a n d , t h e r e f o r e , t h e o u t p u t s i g n a l , is also a p p r o x i m a t e l y p r o p o r t i o n a l t o t h e ozone c o n c e n t r a t i o n . I n t h i s m e t h o d n o a t t e m p t is m a d e t o d e c o m p o s e a l l t h e ozone p r e s e n t i n t h e s a m p l e . T h e cross s e c t i o n of t h e t h e r m i s t o r s is p u r p o s e l y k e p t s m a l l i n r e l a t i o n t o the c h a m b e r i n o r d e r t o m i n i m i z e a d i a b a t i c heat effects d u e t o changes i n v e l o c i t y of t h e gas. T h e t h e r m i s t o r s ( M o d e l 1 0 1 A 1 , V i c t o r y E n g i n e e r i n g C o r p . ) a r e a b o u t V32 i n c h i n d i a m e t e r . T h e y h a v e a n o m i n a l resistance of 1 0 o h m s a t r o o m t e m p e r a t u r e . T h e c a t a l y s t is a p p l i e d b y c o a t i n g t h e t h e r m i s t o r w i t h a n a d h e s i v e a n d d i p p i n g i n t o t h e p u l v e r i z e d c a t a l y s t . I n t h i s s e t u p , t h e o u t p u t of t h e b r i d g e w h e n t h e a i r s t r e a m c o n t a i n s 1 p . p . m . of ozone is a b o u t 0.001 v o l t , w h i c h c o r r e s p o n d s t o a decrease of 5 o h m s i n t h e resistance of t h e c o a t e d t h e r m i s t o r . T h i s , i n t u r n , c o r r e s p o n d s t o a t e m p e r a t u r e d i f f e r e n t i a l of a b o u t 0.001° C . p e r 1 p . p . m . of ozone b e t w e e n t h e t h e r m istors. T h e m e c h a n i c a l i n e r t i a of t h e r e c o r d e r filters o u t a l l t h e noise f r o m t h e c i r c u i t . T h e s p e e d of response is s u c h t h a t t h e r e c o r d e r p e n t r a v e r s e s t h e f u l l w i d t h of t h e scale i n a b o u t 10 t o 20 m i n u t e s w h e n t h e ozone c o n c e n t r a t i o n is v a r i e d f r o m 0 t o 1 p . p . m . o r f r o m 1 t o 0 p . p . m . T h i s s l o w response m a y n o t be o b j e c t i o n a b l e i n f o l l o w i n g t h e v a r i a t i o n s of c o n c e n t r a t i o n i n a t m o s p h e r i c ozone. H o p c a l i t e , m a n u f a c t u r e d b y the M i n e Safety A p p l i a n c e s C o . , has been f o u n d t o be a n excellent c a t a l y s t f o r t h i s p u r p o s e ; i t is a m i x t u r e of s i n t e r e d m e t a l l i c oxides. I n a p r e l i m i n a r y series of e x p e r i m e n t s , t h e c a t a l y s t q u a l i t a t i v e l y d e c o m p o s e d 9 0 p . p . m . of ozone i n a n a i r s t r e a m , a n d i t s a c t i v i t y r e m a i n e d u n c h a n g e d a f t e r 100 h o u r s of operation, when the experiment was discontinued.


5

O p e r a t i o n of A n a l y z e r I f t h e t w o t h e r m i s t o r s w ere p e r f e c t l y m a t c h e d i n respect t o t h e i r resistances, t e m p e r a t u r e coefficients of resistance, a n d h e a t d i s s i p a t i o n c h a r a c t e r i s t i c s , t h e a n a l y z e r c o u l d be o p e r a t e d w i t h o u t r e g a r d t o v a r i a t i o n s i n t h e t e m p e r a t u r e of t h e c h a m b e r o r of t h e gas o r i n t h e r a t e of flow of t h e gas. I n p r a c t i c e , t h e c h a r a c t e r i s t i c s of a p a i r of t h e r m i s t o r s differ a p p r e c i a b l y . T h u s , i f t h e t e m p e r a t u r e of t h e c h a m b e r o r of t h e gas is i n c r e a s e d , t h e o p e r a t i n g t e m p e r a t u r e of b o t h t h e r m i s t o r s also increases, b u t a n u n d e s i r a b l e d i f f e r e n t i a l occurs b e t w e e n t h e t e m p e r a t u r e of t h e t w o t h e r m i s t o r s . T r a n s i e n t effects also a p p e a r w h e n t h e t e m p e r a t u r e o r r a t e of flow is a b r u p t l y changed. T h e s e a r e d u e t o m o m e n t a r y differences b e t w e e n t h e r a t e of h e a t i n g o r c o o l i n g o f t h e t w o t h e r m i s t o r s . S u c h effects c a n be e l i m i n a t e d b y e n c l o s i n g t h e chamber containing the thermistors i n a constant temperature b a t h a n d b y regulating t h e a i r flow. r

I n t h e p r o t o t y p e t h e t h e r m i s t o r s were enclosed i n a m a s s i v e a l u m i n u m b l o c k i m m e r s e d i n a w a t e r b a t h . T h e t e m p e r a t u r e of t h e l a t t e r w a s c o n t r o l l e d t o w i t h i n 0.2° C . b y t h e u s u a l s y s t e m of t h e r m o s t a t a n d h e a t e r s . P o s s i b l e effects of c y c l i c v a r i a t i o n s of t e m p e r a t u r e w i t h i n t h i s r a n g e were n o t o b s e r v a b l e o n t h e records o r were less t h a n those c o r r e s p o n d i n g t o 1 p . p . h . m . of ozone. I t is possible t h a t a t e m p e r a t u r e c o n t r o l as coarse as 1° o r 2 ° C . m i g h t be a d e q u a t e . T h e t e m p e r a t u r e of t h e gas was c o n t r o l l e d b y p a s s i n g i t t h r o u g h 4 o r 5 feet of glass o r a l u m i n u m t u b i n g p l a c e d i n t h e b a t h . F r o m a t h e o r e t i c a l s t a n d p o i n t t h e s e n s i t i v i t y of t h e a n a l y z e r is i n c r e a s e d b y m a i n t a i n i n g the b a t h at a low temperature. P r a c t i c a l l y , the requirements for r e f r i g e r a t i o n , f o r m o r e efficient heat exchange b e t w e e n t h e gas a n d t h e b a t h , a n d f o r p r e v e n t i o n of m o i s t u r e c o n d e n s a t i o n i n t h e c h a m b e r o r o n t h e t h e r m i s t o r s m a k e t h i s s o l u t i o n u n a t t r a c t i v e . I n t h e p r o t o t y p e t h e t e m p e r a t u r e of t h e b a t h w a s m a i n t a i n e d a t 32° C . — t h a t i s , s l i g h t l y a b o v e r o o m t e m p e r a t u r e . W h e n t h e r a t e a t w h i c h t h e gas is passed o v e r t h e c a t a l y s t i s i n c r e a s e d , t h e t e r n -


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p e r a t u r e o f t h e t h e r m i s t o r s is l o w e r e d , a n d i f t h e t w o t h e r m i s t o r s a r e n o t m a t c h e d , a s i g n a l a p p e a r s across t h e b r i d g e . T h i s d i f f i c u l t y w a s e l i m i n a t e d b y c i r c u l a t i n g t h e gas b y m e a n s of a s m a l l m e c h a n i c a l v a c u u m p u m p p l a c e d o n t h e o u t l e t of t h e c h a m b e r a n d b y c o n t r o l l i n g t h e flow b y m e a n s of a c r i t i c a l orifice b e t w e e n p u m p a n d chamber. T h e s e n s i t i v i t y of t h e a n a l y z e r is a c o m p l e x f u n c t i o n of t h e flow r a t e of t h e gas. I n a l o w flow r a t e a s m a l l n u m b e r of ozone m o l e c u l e s s t r i k e t h e c a t a l y s t p e r u n i t t i m e . A t a h i g h flow r a t e t h e r a t e o f h e a t d i s s i p a t i o n f r o m t h e t h e r m i s t o r s is h i g h . T h u s , a t b o t h l o w a n d h i g h flow rates t h e s e n s i t i v i t y is l o w . I t is m a x i m u m f o r a flow r a t e c o r r e s p o n d i n g t o a b o u t 100 c c . p e r m i n u t e ; t h i s o p t i m u m flow r a t e is o b t a i n e d b y a d j u s t i n g t h e c r i t i c a l orifice. T h e s e n s i t i v i t y of t h e a n a l y z e r w a s d e t e r m i n e d b y c i r c u l a t i n g s y n t h e t i c m i x t u r e s of a i r a n d ozone p r e p a r e d f r o m 100% ozone w i t h successive d i l u t i o n s w i t h a i r ; these m i x t u r e s were p r e p a r e d b y m e m b e r s of t h e O z o n e T e c h n o l o g y G r o u p . A n a n a l y z e r w i t h a r a n g e of 0.1 t o 10 p . p . m . of ozone i s b e i n g used i n t h e B i o c h e m i s t r y R e s e a r c h S e c t i o n of t h e f o u n d a t i o n . A n o t h e r p r o t o t y p e w i t h a range of 0.01 t o 1 p.p.m. was found to be subject to drift. T h e drift was traced to temperature dif f e r e n t i a l s b e t w e e n t h e v a r i o u s elements of t h e b r i d g e c i r c u i t a n d leakages d u e t o s u p e r f i c i a l c o n d e n s a t i o n of a t m o s p h e r i c m o i s t u r e . A n i m p r o v e d i n s t r u m e n t i s b e i n g a s s e m b l e d i n w h i c h a l l t h e elements of t h e c i r c u i t , e x c e p t t h e b a l a n c i n g p o t e n t i o m e t e r , a r e enclosed i n t h e t h e r m o s t a t i c a l l y c o n t r o l l e d b a t h . T h e v a l u e of a n a t m o s p h e r i c ozone a n a l y z e r i s d e t e r m i n e d a l m o s t e n t i r e l y b y i t s s p e c i f i c i t y t o w a r d ozone. C h e m i c a l a n a l y t i c a l m e t h o d s a r e i n f l u e n c e d b y t h e presence of s u c h r e d u c i n g o r o x i d i z i n g agents as c h l o r i n e , s u l f u r d i o x i d e , n i t r o g e n d i o x i d e , a n d peroxides, w h i c h are a l l present i n polluted atmospheres. T h e influence of these agents o n t h e c a t a l y t i c a n a l y z e r w a s i n v e s t i g a t e d b y i n t r o d u c i n g m e a s u r e d c o n c e n t r a t i o n s of t h e m i n t o t h e a i r s t r e a m p a s s i n g o v e r t h e t h e r m i s t o r s . T h e d i l u t i o n a p p a r a t u s i s r e p r e s e n t e d i n F i g u r e 3. T h e i n f l u e n c e of t h e p o l l u t a n t w a s o b s e r v e d w h e n a i r alone o r o z o n e - a i r m i x t u r e s were passed over the thermistors. T h i s procedure was repeated several times over a p e r i o d o f s e v e r a l h o u r s i n o r d e r n o t o n l y t o o b s e r v e t h e i n f l u e n c e of t h e p o l l u t a n t o n t h e zero p o s i t i o n of t h e r e c o r d e r p o i n t e r b u t also t o ensure t h a t t h e presence of

OZONIZER J L

AIR

AIR

-•-MIXING

CHAMBER

Λ SATURATOR

Figure 3. Diagram of the dilution apparatus


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t h e i m p u r i t y h a d n o effect o n t h e s e n s i t i v i t y

of

t h e c a t a l y s t t o w a r d ozone.

This

effect w o u l d h a v e b e e n s h o w n b y a p r o g r e s s i v e c h a n g e i n m a g n i t u d e of t h e d e f l e c t i o n


of t h e p o i n t e r w h e n i d e n t i c a l a m o u n t s of ozone w e r e i n t r o d u c e d i n t h e gas s t r e a m . Carbon Monoxide. It was found that 20 p.p.m. of carbon monoxide do not interfere with the operation or sensitivity of the analyzer. This result is surprising, because the catalyst used in this study (Hopcalite) is also used to detect carbon monoxide in a device manufactured by the Mine Safety Appliances C o . However, the catalyst must be carefully dried prior to use in order to decompose any carbon monoxide present. The inertness of the ozone detector to carbon monoxide in these experiments may be attributed to the poisoning of the catalyst by the water vapor normally present in the atmosphere. Chlorine and Nitrogen Dioxide. Chlorine in concentrations to 20 p.p.m. does not affect the ozone analyzer. Concentrations of nitrogen dioxide up to 10 p.p.m. have no perceptible effect. With 10 to 20 p.p.m. of nitrogen dioxide some slight irregularities were observed on the recorded trace. These irregularities are not reproducible and cannot be unambiguously attributed to nitrogen dioxide. As the atmospheric concentration of nitrogen dioxide in air seldom exceeds 3 p.p.m., the effect of this gas is probably negligible, even in measuring very low concentrations of ozone. Water. A switch from substantially dry air to air of about 90% relative humidity does not perceptibly affect the analyzer. However, if liquid water collects over a thermistor, the bridge is thrown out of balance. The thermistor must then be dried by circulation of dry air for considerable periods of time before the operation of the bridge returns to normal. Hydrocarbons and Smokes. Illuminating gas, benzene vapors, and cigar smoke did not appreciably affect the operation of the analyzer. N o effort was made to measure the concentrations of these pollutants ; however, the concentrations must have been much larger than those occurring in normal atmospheres. In particular, some of the transient effects observed with illuminating gas are believed to be due to excessive concentrations of this gas and to drastic changes in the heat transfer coefficient of the atmosphere surrounding the thermistors. Peroxides. E v e n rather small concentrations of some peroxides affect the operation of the analyzer noticeably ; the magnitude of the possible error in apparent ozone concentration due to peroxide contamination depends upon the particular peroxide or peroxides present. The analyzer differs widely in its response toward the various peroxides; the variations may be due either to the differences between the heats of decomposition of the compounds or to differences between rates of decomposition upon the catalyst. Uncertainty as to the chemical decomposition mechanism of the peroxides makes it difficult to calculate the heats of decomposition, so at the present time it has not been possible to determine exactly what causes the variations. For instance, ieri-butyl hydroperoxide at a concentration of 14 p.p.m. produces a deflection of 20 divisions on the recorder, or 1.4 divisions per 1 p.p.m. of peroxide. A t volume concentrations equal to that of the ozone present, ieri-butyl peroxide thus introduces an error of slightly over 2%. A t a concentration of 3.6 p.p.m. of cumene peroxide, the deflection is 3 divisions; the error is 1.2%. A t a concentration of 120 p.p.m. of di-ieri-butyl peroxide, the deflection is only 14 divisions, corresponding to an error of 0.18%. Equal volumetric concentrations of ozone and some common peroxides produce the following relative deflections on the galvanometer: Ozone Hydrogen peroxide tert-Butyl hydroperoxide Cumene hydroperoxide Di-ieri-butyl peroxide

100 7 2 1.2 0.2

T h e d a t a p r e s e n t e d i n t h e T e c h n i c a l R e p o r t s of 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 i n d i c a t e t h a t t h e c o n c e n t r a t i o n of p e r o x i d e s o r p r e c u r s o r s i n t h e a t m o s p h e r e does n o t exceed one t h i r d o r one h a l f t h a t of o z o n e . I f o n l y h a l f of these p e r o x i d e s a r e i n t h e f o r m of h y d r o p e r o x i d e s of l o w m o l e c u l a r w e i g h t , s i m i l a r t o t e r i - b u t y l h y d r o p e r o x i d e , t h e e r r o r d u e t o t h e presence of these i n t e r f e r i n g agents s h o u l d n o t exceed 1% of t h e r e a d i n g s due t o t h e presence of ozone a l o n e . I n o r d e r t o d e t e r m i n e w h e t h e r t h e a c t i v i t y of t h e c a t a l y s t m i g h t be affected b y p r o l o n g e d e x p o s u r e t o a n y one o r a c o m b i n a t i o n of some of t h e m a n y c o m p o u n d s p r e s e n t i n p o l l u t e d a t m o s p h e r e , s o m e of t h e c a t a l y s t w a s s h i p p e d t o t h e S t a n f o r d L a b o r a t o r i e s a n d e x p o s e d t o L o s A n g e l e s a t m o s p h e r e f o r 100 h o u r s d u r i n g a p e r i o d of s m o g . N o s i g n i f i c a n t difference w a s o b s e r v e d i n t h e p e r f o r m a n c e of t h e e x p o s e d


92

A D V A N C E S IN CHEMISTRY SERIES

catalyst as compared to that of fresh material. Thus, it appears that the normal atmospheric constituents of polluted atmospheres do not affect the sensitivity of Hopcalite toward decomposing ozone. Admittedly, this experiment might not be conclusive; longer field trials i n various polluted atmospheres will be required to measure the resistance of the catalyst to poisoning. E v e n i n an unfavorable case, however, the catalyst-coated thermistor could be replaced i n a few minutes.


RECEIVED f o r r e v i e w April 19, 1957. A c c e p t e d J u n e 19, 1957. P r o g r a m sponsored b y t h e American Petroleum Institute.


Catalytic Atmospheric Ozone Analyzer - Advances in Chemistry (ACS

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