FINAL TECHNICAL REPORT 

for 

NASA Grant NAG 2-267 

Photochemical Production of H2S04 Aerosols on Venus 

1 

?. 

Yuk L. Yung 

Principal Investigator 

Division of Geological and Planetary Sciences 

California Institute of Technology 

Pasadena, California 91125 

Grand Period 

October 1, 1983 to October 31, 1986 

(KAS.4-Cii-180256) FBCTCCHEEICAL E EGDUC~.I.CN N07-19327 

CE ii2S04 AEBGSCLS CN BEEUS Einal Technical 

Geprt, 1 Cct, 1SE3 - 31 Cct, 19Eb 

(Calitcrnia Inst- cf Tech.) 21 F CSCL 03~1 Unclas 

G3/91 43872 
FINAL TECHNICAL REPORT 

Evidence for SO injection (by a volcano?) into the upper atmosphere 2 

of Venus 

The quantum yields for producing 02(a 1 A ) and 02(b 7+ ) for reacticn 

g g 

(3) are summarized in Table I which also includes results for other simple 

reactions capable of producing the singlet oxygen states. 

quantum yields are very small, ranging from less than lo-‘ to 4 x 

In general, the 

According to Yung and DeMore (19821, the 02(a1A ) emissions due to (l), 

(2), and (3) could be as high as 0.72, 0.37, and 0.72 MR, respectively, sdciing 

g 

up to a total of 1.8 MR, if the quantum yields for forming O2(a1A ) in the 

g 

reactions were unity. Eowever, using the current values for quantum yields, we 

obtain revised estimates of 02( a’ 4 ) emission (including cascading from 6 

02(b 2 

respectively. The total amounts to 0.05 MF!, considerably less than the 

observed 1.2-7.5 MR. 

1+ )) due to (l), (2), and (3) as 0.029, 0.007, and 0.014 MR, 

g 

We now face a fundamental dilemma. Reaction (1) turns oxygen atoms into 

02. 

oxygen into 02. 

Venus in the Present model is co2 photolysis, which proceeds at a mea rate of 

8 x lo’* cm’2 s”. 

cannot exceed 4 x 10 l2 cmo2 so’. 

the a Ag state is q in each 0-0 bond forming reaction, the airglow would be 

less than 4q MR. 

Or lessReactions (2) and (3) constitute a catalytic cycle for converting odd 

The ultimate source of 0 atoms in the upper atmosphere of 

This implies that the total rate of 0-0 bond formation 

Therefore, if the quantum yield for producing 

1 

The recent laboratory results suggest that q is a few percent 

Hence, the O2(a7A ) emission of Venus cannot arise from 0-0 bord 

g 
forming reactions in which the 0 atoms are derived from C02 dissociation. 

simplicity of the argument outlined here suggests that our conclusion is 

largely independent of the details of the photochemical model. 

The 

? 

One obvious possibility is that there might have been a calibration error 

in the observations. A dibcussion with one of the authors (Traub, 1987, 

private communication) led to a critical reexamination of the data analysis 

procedure used in Comes et al.'s (1979) paper. It was concluded that 

calibration errors could have been at most a factor of 2, since two independent 

methods, based on the terrestrizl airglow and the Venus continuum brightness 

were used, and both methods gave essentially the same result. 

We can speculate on other explanations. The crucial clue is the source 

of 0 atoms. As was first pointed out by Winnick and Stewart (1980), photolysis . 

of SO2 is a major source of 0 atoms in the stratosphere of Venus. Indeed, 

according to the models of Winnick and Stewart (1980), and Yung and DeMore 

(1982), the photolysis rate of SOq on Venus is considerably higher than that of 

C02. 

stratosphere, just above the cloud tops (-60 km). 

this region would be effectively quenched, and could not contribute to the 

However, most of the photolysis of SO2 occurs in the lower part of the 

Any 0 (a'A ) produced in 2 e 

observed emissions under "normalR circumstances. 

Consider now an unusual event, an episodic injection of SO2 into the 

upper atnosphere of Venus. We shall leave the cause of tfiis.event unspecified, 

although volcanism is a possibility (Esposito, 1984). The presence of large 

quantities of SO 

photolysis and production of oxygen atoms. 

by (1) or the catalytic cycle (2) and (3) would yield a source of 02(z1A ). 

Detailed modeling of this event appears difficult since the O2(a14 ) airglow ' 

observations were carried out in 1975, before there were any quantitative data 

in the upper stratosphere (above 80 km) would lead to rapid 

Recombination of these atoms either 

2 

g 

g 

on SO2 (Pioneer-Venus started collecting data in 1978). 
Table I 

1 1 List of the relevant, reactions that produce 02(a 1 and 02(b E' ) g E 

in the atmosphere of Venus and their quantum yields. 

? Quantum Yield 

Reactions 02(a) 02(b) References 

1 O+O+M --> 0 2+M 4(-2) 2(-2) 

3 (-2) 

4(-5) 

2 c1 + o3 --> c10 + o2 

3 0 + c10 --> c1 + o2 

4 c1 + c102 --> c1 + o2 2 

5 C1 + H02 --> HC1 + O2 

6 H + H02 --> H + O2 2 

<2 (-2) <5(-4) 

<2.5( -2) 4.4 ( -4) 

.1.5(-2) 

2 8 ( -4 ) 

<1(-21 

7 0 + BO2 --> OH + O2 <8 (-3) 

W raight 

Ogryzlo et al. 

Young and Black 

Choo snd Lec 

This work 

Choo and Leu 

Keyser et al. 

Washida et 21. 

Eislop and Heme 

Keyser et al. 

Keyser et al. 

% 

Defined as the rate coefficient for the branch divided by the total rate 

coefficient. 
1 1+ Determinationpf 02(a A i3 ) and 02(b g ) Yields in the 

Reaction 0 + C10 --> C1 + 02: Implications for Photochemistry 

In the Atmosphere of Venus 

Ming-Tam Leu 

Earth and Space Sciences Division 

Jet Propulsion Laboratory 

California Institute of Technology 

Pasadena, California 91109 

and 

Yuk L. Yung 

Division of Geological and Planetary Sciences 

California Institute of Technology 

Pasadena, California 9 1 1 25 

March, 1987 

Contribution number 4465from the Division of Geological and Planetary Sciences, 

California Institute of Technology, Pasadena, California 91125. 
Abstract ? 

A discharge flow apparatus with a chemiluminescence detector has been 

1 

= 02(a Ag) or 

ff used to study the reaction 0 + c10 --> C1 + 0, , where O2 

02(b 2 

producing o2(a A ) and 02(b 

loo2 and (4.4 + 1.1) x lo4, respectively. The observed 02(a P ) airglow of 

Venus cannot be explained in the context of standard photochemistry using our 

L 

ff 1+ ), and the radiative decay of O2 . The measured quantum yields for 

) in the above reaction are less than 2.5 x 

g 

1 1+ 

& g 

1 

- & 

experimental results and those reported in recent literature. 

of an episodic injection of SO2 into the mesosphere of Venus is speculzted. 

The possibility 

2 
Introduction ? 

1 The intense 02(a A ) emission of Venus at 1.27 pm was discovered by g 

Connes et al. (1979), who estimated the dayglow and nightglow brightness to be 

1.5 and 1.2 MR (1 Megarayleigh = 1 x 

aforecited authors also proposed that the 

02(a1A ) on Venus are: 

g 

photons ~rn’~ s-’ ) , respec tivelg . most likely processes for producing The 

0 + 0 + C02 --> 0 + C02 + 498 KJ/EOl (1) 2 

C1 + 0 --> C10 + O2 + 161 KJ/mol (2) 3 

0 + C10 --> C1 + O2 + 236 KJ/mol . (3) 

Detailed modeling by Yung and DeMore (1982) and Krasnopolsky and Parshev (1983) 

showed that, in order to explain the Venus observations, the quantun: yields in 

reactions (1)-(3) must be close to unity. 

Reaction (1) has been studied by a number of workers (see recent review 

by Wayne, 1985). The quantum yields for singlet oxygen (both a and b ststes), 

as summarized in Table 111, are low. Reaction (2) was studied by Choo and Leu 

(1985), who found no evidence for the production of excited O2 (see Table 111). 

In this article we shall report new experhental results on the quantum yields 

of singlet oxygen produced by reaction (3). 

producing 02(a 

modeled and observed airglow brightness of Venus. 

discussed. 

Using the known efficiencies for 

1 ) in (1)-(3), we can make a quantitative comparison of the 

g 

The results will be briefly 

3 
Experiment I 

The experimental technique used in this study has been described in 

detail in previous publications (Leu, 1984; Choo and Leu, 1985). 

production and detection of the single oxygen molecules, O2(a1Ag) ad 

o2(b 2 g), were carried out in a discharge flow apparatus with a 

chemiluminescence detector. 

The 

1+ 

Oxygen atoms were produced in the side arm of the flow tube via the fast 

reaction 

(4) 2' N + NO --> 0 + ET 

where the nitrogen atoms were generated in a microwave discharge by passing 

nitrogen gas through a quartz tube. Since the N atoms were slightly in excess, 

the final 0 atom concentration would be equal to that of NO, which was aeasured 

with a mass flowmeter. 

. C10 radicals were generated as follows: First, C1 atoms in the 

concentration range (5-10) x 1013 cm-3 were produced by passing a small amount 

of c12 in a helium carrier through a microwave discharge tube. Then, C1 atoms, 

in slight excess, were allowed to react with C120 in a fast reacticn leading to 

the production of C10 

c1 + Cl20 --> C12 + c10 . (5) 

The Cl20 molecules used in this work were prepared as described in Leu (1984). 

The absolute concentration of C120 was monitored by an optical absorption 

technique. 

strong line at 253.7 nm, and the adopted cross section for C120 at this 

wavelength is 2.01 x 

The light source was a low pressure mercury lamp, which emits a 

cm2. The detector was a photomultiplier equipped 

4 
with an interference filter. By virtue of the stoicheiometry of reaction (5), 

the final concentration of C10 must equal the initial concentration C120. 

Having prepared the C10 molecules in this manner, they were then introduced 

I 

into the reaction cell via a movable Pyrex injector. 

The observation of the singlet oxygen emissions was carried out using the 

chemiluminescence detection system. 

nrn was resolved with a l/4 m McPherson monochromator (Model 275) and registered 

by a Haamatsu cooled photomultiplier tube (Model P.943-02) in conjunction with 

a Keithley picoammeter (Model 480). 

Radiation in the wavelength range 600-9CC 

Radiation in the wavelength range 900-17GO 

nm was resolved with an Oriel grating monochromator (Model 7240) and detected 

with a liquid nitrogen cooled germanium detector (Applied Detector Corp. Model 

40%). The signals were nodulated with a 100 Hz chopper (Bulova) and a lock-in 

amplifier (EG h G Model 5804) was used for the phase sensitive detection. 

Detection of emissions from both singlet oxygen states were simultaneously 

recorded on a two-channel recorder. 

Figure 1 shows the chemiluminescence data taken under the following 

conditions: 

species x); total pressure = 1.25 Torr; flow velocity = 3620 cm sol; and 

reaction time = 4.8 ms. 

nm was clearly detected. 

Of O2 in the blx+g state, derived from reaction (3). 02(a 4 ) emission at 

1270 nm was not detectable in the same experiment. The experimental data 8re 

summarized in Table I. 

02(b 2 ), it is necessary to employ a computer simulztion. 

relevant chemical reactions is listed in Table 11. The rate of loss of 

02(b 

[O] = [ClO] z 1.7 x 1013 (1x1 denotes the concentration of 

02(b'x+ ) emission at 762 nm with a bandwidth of 10 

g 

9 This result suggests that there were 3.8 x 10 

1 

g 

1 In order to derive the quantum yields of 02(a A ) and 

8 

1+ The set of 

g 

1+ ) on the walls of the reaction cell and quenching by N2 has been 

g 

5 
measured using the sanie technique as reported here. The rate of loss of 

0 (ala ) by quenching on ihe walls and by collisions with N2, C1, 0, and C1G 

2 g 

can be shown to be negligible. The experiments1 conditions have been chosen so 

as to minimize interference from the reactions (1) and C1 + C102 --> c1 

The results of our analysis can be summarized as: 

kb = (1.6 2 0.4) x 

produce 02(a ) and 02(b 2 1, respectively. The uncertainty represents one 

+ 02. 2 

ka < g x cmj s”, and 

cm3 s-l for the absolute rate constants for (3) to 

1 1+ 

g g 

standard deviation error. 

6 
Discussion 

I 

1 1+ The quantum yields for producing 02(a A ) and 02(b ) for reacticn 

g g 

(3) are summarized in Table 111, which also includes results for other simple 

reactions capable of producing the singlet oxygen states. 

quantum yields are very small, ranging from less than 

In general, the 

to 4 x 

According 1 to Yung and DeMore (19821, the 02(a A ) emissions due to (l), 

(2), and (3) could be as high as 0.72, 0.37, and 0.72 MR, respectively, sdding 

up to a total of 1.8 MR, if the quantum yields for forming 0 (alA ) in the 

reactions were unity. 

g 

2 g 

However, using the current values for quantum yields, we 

obtain revised estimates of 02(a14 ) emission (including cascading from 

g 

respectively. The total amounts to 0.05 MI?, considerably less than the 

observed 1.2-1.5 MR. 

We now face a fundamental dilemma. Reaction (1) turns oxygen atoms into 

02. 

oxygen into 02. 

Venus in the Present model is co2 photolysis, which proceeds at a mean rste of 

8 x 

cannot exceed 4 x cm s . Therefore, if the quantum yield for producir?.g 

the a 

less than 4q MR. 

or less. 

forming reactions in which the 0 atoms are derived from CO dissociation. 

simplicity of the argument outlined here suggests that our conclusion is 

largely independent of the details of the photochemical model. 

Reactions (2) and (3) constitute a catalytic cycle for converting odd 

The ultimate source of 0 atoms in the upper atmosphere of 

cmo2 s’l. This implies that the total rate of 0-0 bond formation 

-2 -1 

1 state is q in each 0-0 bond forming reaction, the airglow would be 

g 

The recent laboratory results suggest that q is a few percent 

1 Hence, the 02(a 4,) emission of Venus cannot arise from 0-0 bond 

The 2 

7 
;. 

One obvious possibility is that there might have been a calibration error 

in the observations. 

private communication) led to a critical re-examination of the data analysis 

procedure used in Connes et al.'s (1979) paper. 

calibration errors could have been at most a factor of 2, since two independent 

methods, based on the terrestrial airglow and the Venus continuum brightness 

were used, and both methods gave essentially the same result. 

A dibcussion with one of the authors (Traub, 1987, 

It was concluded that 

We can speculate on other explanations. The crucial clue is the source 

of 0 atoms. As was first pointed out by Winnick and Stewart (19801, photolysis 

of SO2 is a major source of 0 atoms in the stratosphere of Venus. Indeed, 

according to the models of Winnick and Stewart (1980), and Yung and DeMore 

(19821, the photolysis rate of SO2 on Venus is considerably higher than that of 

C02. 

stratosphere, just above the cloud tops (-60 km). 

this region would be effectively quenched, and could not contribute to the 

However, most of the photolysis of SO2 occurs in the lower part of the 

Any G2(a1A 1 produced in e 

observed emissions under "normalR circumstances. 

Consider now an unusual event, an episodic injection of SO2 into the 

upper atmosphere of Venus. We shall leave the cause of this event unspecified, 

although volcanism is a possibility (Esposito, 1984). 

quantities of SO 

photolysis and production of oxygen atoms. 

The presence of large 

in the upper stratosphere (above 80 km) would lead to rapid 

Recombination of these atons either 

2 

by (1) or the catalytic cycle (2) and (3) would yield a source of 02(a1A ) . 

Detailed modeling of this event appears difficult since the 02(a14 ) airglow 

g 

g 

observations were carried out in 1975, before there were any quantitative data 

on SO2 (Pioneer-Venus started collecting data in 1978). 

8 
Conclusion 

I 

d discharge flow apparatus with a chemiluminescence detector has been 

1 1+ used to determine the quantum yields of 02(a L\ ) and 02(b g Q 

reaction 0 + C10 -> C1 + 02. The results are summarized in Tables I1 and 111. 

Application of these results to explain the airglow brightness of Venus reveals 

) in the 

a fundamental difficulty with a "normal" photochemical 

atmosphere of Venus might have been strongly perturbed 

of SO2 in 1975. 

model. The upper 

by a nassive injection 

It is important that our laboratory kinetics-chemiluminescence results be 

1 confirmed using an independent experimental technique. 

from Venus have been observed only once. 

to establish the magnitude and nature of possible variations, along with the 

simultaneous observation of other chemical species such as CO, B20, EC1, HF, 

02, and SO2. 

The 02(a A ) emission 

These observations should be repeated 

9 
Acknowledgements 

I 

We thank W.A. Traub, W.B. DeMore, M. Allen, J.P. Pinto, L.W. Esposito, 

and L.D. Travis for helpful discussions. This research was perfomed at the 

Jet Propulsion Laboratory, California Institute of Technology, under contract 

with NASA. YLY was supported as a guest investigator on the Pioneer-Venus 

Project under contract NAG 2267 to the California Institute of Technology. 

10 
Table 1. 

1+ SWarY of O2(b g) Measurements+ 

Number of [o2(b) 1 kb [Ol c c10 1 Reaction Time 

(cm-3) (cm-3) (m) (cm-3) (cm3 S'l) Experhents 

1 *6( 13) 1-7(13) 4.8 3. a(?) 14-14) 6 

1*6(13) 1-9(13) 4.8 5*2(9) 2.1(-14) 1 

Average Value (1.6 - + 0.4) x (-14)" 

+ The numbers a(b) should be read as a x in this table and Tables 11 and 

111. 

1+ &st fit of the 02(b-2 

One standard deviation. 

+ 

) measurenent. 

g ++ 

11 
Table 11. 

Chemical scheme for computer simulation of the production of 

02(a1A ) and 02(b 1+ 2 1in the reacticn 0 + C10 --> C1 + O2 

g g 

Reactions References 

2 0 + c10 --> c1 + 0 

C1 + 02(a) 

c1 + O2(b) 

02(a) + wall --> O2 

02(a) + N2 --> 0 + N 22 

O,(a) + C1 --> 0 + C1 2 

02(a) + 0 --> O2 + 0 

02(a) + C10 --> O2 + C10 

O2(b) + wall --> 0 2 

02(b) + N2 --> O2 + N2 

02(b) + C1 --> O2 + C1 

02(b) + 0 --> O2 + O 

O2(b) + C10 --> O2 + c10 

Leu 

This work 

?I 

Choo and Leu 

n 

* 

4 

Choo and Leu 

n 

* 

a 

4 

Estimated based on analogous reactions; see the review by Wayne (1985). 

12 
Table 111 

1 List of the relevant, reactions that produce 02(a A 1 and @,(b’r+ g ein the atmosphere of Venus and their quantum yields. 

React ions 

0 Quantum Yield 

02(a) 02(b) References 

O+O+M --> 02+M 4(-2) 2(-2) Wraight 

3 (-2) Ogryzlo et al. 

4(-5) Young and Black 

c1 + o3 --> c10 + o2 <2(-2) <5(-4) Choo and Leu 

c1 + c102 --> C12 + 0 

<2.5( -2) 4.4 (-4 1 This work 

1.4(-2) 6(-3) Choo and Leu 

C1 + H02 --> HC1 + O2 <5(-4) Keyser et al. 

1.5(-2) Washida et al. 

2 0 + c10 --> c1 + 0 

2 

2 H + H02 --> H2 + 0 

2.8 (-4) Eislop and liayne 

<1(-2) Keyser et al. 

0 + HO2 --> OH + 02 <8(-3) Keyser et al. 

Defined as the rate coefficient for the branch divided by the total rate 

coefficient. 

13 
References 

Choo, K.Y. and Leu, M.T. ‘(1985). Rate constants for the quenching of 

netastable 02(’A+ ) molecules. _I_ntern. J. Chem. Kin. n, 1155-1167. 

g 

1 Choo, K.Y. and Leu, M.T. (1985). Determination of 0 (’ + g> and 02( Ag) 

yields in C1 + O2 and C1 + 0 reactions. J. Phys. Chem. a, 4832-4837. 3 

Connes, P., Noxon, J.F., Traub, W.A., and Carleton, N.P. (1979). O,(’hg) 

emission in the day and night airglow of Venus. Astrophys. J. z3, L29- 

32 

Esposito, L.W. (1984). Surface dioxide: Episodic injection shows evidence 

for active Venus volcanisIli. Science 3, 1072-1074. 

1+ 

2 Bislop, J.R. and Wayne, R.P. (1985). Production of 02( ) in the I! + 0 

g 

system. J,_C_h_em. SOC. Faraday-.TTans. 11, JJ, 506-516. 

1+ Keyser, L.F., Choo, K.Y., and Leu, M.T. (1985). Yields of O2 (b g) from 

reactions of BO2. Intern. J. Chem. Kinet. lJ, 1169-1185. 

Krasnopolsky, V.A. and Parshev, V.A. (1983). Photochemistry of the Venus 

atmosphere. In Venus, The University of Arizona Press, 431-458. 

Leu, M.T. (1984). Kinetics of the reaction 0 + C10 --> C1 + 02. 3. Phys. 

-- Chem. 88, 1394-1398. 

Ogryzlo, E.A., Shen, Y.A., and Wassel, P.T. (1984). The yields of O2 (blz+ ) 

g 

in oxygen atom recombination. J. Photochem. 3, 389-398. 

Washida, N., Ahimoto, H., and Okuda, M. (1978). Fornation of singlet state 

molecular oxygen in the reaction of E + 02. J. Phvs. Chen. 82, 18-21. 

Wayne, R.P. (1985). Reactions of singlet molecular oxygen in the gas phase. 

CRC Press, Volume I, Physical-Chemical Aspects, 81-175. 

Winick, J.R. and Stewart, A.I.F. (1980). Photochemistry of SO2 in Venus’ 

upper cloud layers. J. Geophys . Res. &j, 7849-7860. 

14 
. 

Wraight, P.C. (1982). Association of atomic oxygen and airglow excitation 

mechanisms. Planet, SDace Sci. 3, 251-259. 

Young, R.A. and G. Black. (1966). Excited-state formation and destruction in 

mixtures of atomic oxygen and nitrogen. J. Chem. Phys. 3, 3741-3751. 

Yung, Y.L. and DeMore, W.B. (1982). Photochemistry of the stratosphere of 

Venus: Implications for atmospheric evclution. Icarus 2, 199-247. 

15 
. 

Figure Caption 

Figure 1. Chemiluminescenbe spectra taken from the reaction of atomic oxygen 

with C10 radical (see text for detail). 

16