The absolute rate constant for the reaction Cl + H2CO yields HCl + HCO was determined by the flash-photolysis resonance fluorescence method to be 7.5 plus or minus 0.9 (2 sigma) times 10 to the minus 11th power cu cm/molecule sec at 298 K and to have a negligible temperature dependence. This rate which is more than 2000 times faster than the rate of Cl + CH4 indicates that formaldehyde (H2CO) will compete significantly with methane (CH4) for the conversion of active chlorine in the stratosphere to the inactive reservoir HCl. Chlorine will thus be a less efficient destroyer of stratosphere ozone than previously believed. Ambient stratospheric ozone will depend less on the ambient chlorine amount and the predicted response to chlorine perturbations will be lessened. One-dimensional eddy-diffusion photochemical model calculations indicate a factor of 1.1 less sensitivity to chlorine than recently reported. For a steady-state CFM release at 1975 rates (750,000 tons/year) the eventual ozone depletion is now calculated to be 14%

Butler, D. M.

Michael, J. V.

Nava, D. F.

Payne, W. A.

Stief, L. J.

Stolarski, R. S.

English

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https://ntrs.nasa.gov/search.jsp?R=19780016768 2020-03-22T04:46:34+00:00Z
^ ,f !	 1f
I.
NASA
Technical Memorandum 79552
(!NASA-TM-79552)	 THE REACTION C1 • H2C0 	 N78-24711
YIELDS HC1 • HCO: CECPEASEC SENSITIVITY CF
STRF.TOSPHFFIC OZCNE TIC CELCFINE
PEPTORPATICHS (NASA)	 15 p HC A02/MV A01 	 Unclas
CSCL 04A G3/46 21287
The Reaction
CI + H z CO - HC, + HCO:
Decreased Sensitivity of
Stratospheric Ozone to
Chlorine Perturbations
L. J. Stief, J. V. Michael,
W. A. Payne, D. F. Nava,
D. M. Butler and R. S. Stolarski
MAY 1978
111121 ^^^^
LI N 1978	 N^.
National Aeronautics and
Space Administration	 RF `= F "	 n;1r	 nsS Sil flclL TIGoddard Space Flight Center 	 ^'	 c
Greenbelt. Mdryland 20771	
` 19 5 b z Z ^^,^C,
) ,
13
I	 I	 T ;	 ;
1*11L REACTION Cl + H,W - II0 + HCO: DECREASED
SEiNSITIVITY OF STRATOSPHERIC OZONF TO
CHLORINE: PERTURBATIONS
1	
7f
a '9
L. J. Stief, J. V. Michael, W. A. Payne and D. F. Nava
	
II^
Laboratory for Extraterrestrial Physics
	
1
NASA/Goddard Space Flight Center
Greenbelt-, Maryland 20771
and
l). M. Butler and R. S. Stolarski
Laboratory for Planetary Atmospheres
i	 NASA/Goddard Space Flight Center
Greenbelt, Maryland 0771
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1
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I
The absolute rate constant for the reaction Cl + H 2CO _, HCl + HCO i,
has been deternink,by the flash-photolysis-resonance fluorescence method
to be 7.5 + O^Q (2e)^x 10-11 Cm3 molecule
_1 
sec_
1
 at 29h	 and to have
a negligible temperature dependence. 	 This rate which is'more than 2000
times faster than the rate of Cl + CH 	 indicates that formaldehyde
I	 u
(II 2 CO) will compete significantly with methane (CH 4)for the conversion
of active chlorine Q tho stratosphole to the inactive 	 ^Sservoir HC1.
a'
Chlorine will thus be L less efficient destroyer of stratospheric ozone
than breviously„uel'ev^ad.	 Ambient stratospheric ozone will depend less l^;
OD the ambient chlorine amount and the predicted response to chlorine y,)
perturbations will be lessened. 	 One-dimensional eddy-diffusion photo-
chemical model calculations indicate a factor of 1.1 less sensitivity to
se
_	 chlorine than recently re ported.	 For a stead	 state , §FM relea	 at 1975'	 y	 I	 Y-'
_^
rates (750,000 tons/year) the eventual ozone del ^^lction is nod calculated
to be 14%.
^	 4 i
p 6
C4	 I
a^
II. Niki (personal communication) has recortly measured the rate
constant of Cl atoms with formaldehyde (112CO) relativo-to that of Cl
atoms with ethane (C,Ii6).	 Since the rate constant for the ethane reac-
tion is well characterized by direct methods (Manning and Kurylo, 1977),
i
Niki's inferred room temperature value for the reaction
Cl
	 + 11XO _^ IIC1 + IICO
	 (1)
y
• is k l = 7.8 + 0.6 (20) x 10' 11 cm 	 molocule -1 sec -i
 at T=298]9.	 rurther-
r'
o	 more, by comparison with Cl a• C 2 1IG , reaction (1) should have a nogligi-
Ule temperature
	 1
The specific purpose of this letter is to:
	 (a) report on ;> direct
measurement of the rate of reaction (1);
	 (U) confirm, also through
CjlreCt measurement, that (1) has negligible temperature dependence;
and (c) show that stratospheric model calculations including (1) yield
-significantly lower sensitivity to Chlorine perturbati ons,
--
The .kinetic experiments were performed as, described previously
(Whytock of al b, 1977 and Lee ct al., 1977).b') , the flash-photolysis-
resonance-f-1116 escence method.	 The results of 42 experiments at 1'=298K give
k1 = 7.5 + 0. '9 (20) x 10"11 cnt
	 molecule- 1 see -1 .	 To date a partial
study at T = 20oK of 15 experiments g:ive,s a preliminary value of k l =
7.5	 1.2 (20) xZO -ll cm° Molecule . l !sec -1 .	 To within the experimental
{ I.111COrtalillty.these rOSUts indicate no evidence for it temperature depen-
dence.
	 Thus., for stratospheric model calculations these results plus
thos
	
of Nihi indicate that a value of
`of,temlorature	
ti7.$ x 1011 ctl3 molecule
-l sec
-1
Independent^s appropriate.
i
{I
n
Implications for Stratospheric Chemistry
The role of (1) is- to remove catalytically active chlorine (Cl + C10)
to the temporary inactive reservoir HC1. The primary reactions by
which this transformation is accomplished in present stratospheric
models are
Cl + CH  4 HC1 + CH 
	 (2a)
Cl + HO  -> HCl + 0 2 	(2b)
which have recommended rate constants of 7.3 x 10 -12 e- 1260/T cm  molecule-1
sec-
1
 and 3 x 10 -11 cm3 molecule -1 sec -1 respectively (see Hudson,
1977). At T = 250K, appropriate to r 40 km in the stratosphere where
ozone is most sensitive to chlorine, k 
2a ^: 
is 4.7 x 10-14 ^cm3 molecule-1
sec l or almost 2000 times slower than k 1 while k2b is about a factor of
2 slower. Thus H2C0 concentrations of the order of 10
-3
 of the CH 
I
concentration will have a significant effect on the chlorine chemistry
of the stratosphere. Since CH4 concentrations in the 40 kin 	 are a
few tenths of a part per million U volume	 my Chhalt et al. 1972P	 P	 Y	 (PP ) ('	 ,
Ackerman, et al., 1977), H 2CO concentrations of only-'a few tenths of a
part per billion by volume (ppUv) would be significant. At 40 kin this
.
1	 corresponds o about 2 x 10 7	 -3moleculescm
	
The H2C0 concentration has
I	 never been measured in the stratosphere but several model calculations
hale yie,:ded-,-oncentrations well within the above significant range.
V^
Using values of some key parameters from the Goddard Space Plight
Center one -dimensional - steady-state photochemical model the effect of
reaction (1) on the chlorine cycle can be demonstrated by some simple
algebraic manipulations. These estimates will then be compared with a
complete numerical model calculation.
r,
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it
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--
	
7
ORIUINA â. i
Ilk
^r POOR°QJALII a
l
Formaldehyde is likely to-be£ ed in,a one-to-one correspondence
with every molecule of methane that is oxidized (see e.g. Levy, 19;'2;
Crutzen, 1973; Wofsy et al., 1973). Thus, its production rate can be
estimated by knowing the methane destruction rate. The dominant methane
destruction reactions in the stratosphere are
Cl + CH  -)- 11cl + CH 	 (2a)
OH + CH  + CH  + 11 20	 (3)
0( 1 D) + CH  - C113 + 011	 (4)
12 -1710/T	 3	 -1	 -1	 11'
where k3 ' = 2.3 x 10	 a	 cm molecule	 sec	 and k4 = 1.3 x 10
-	
-	
-
cm3 molecule -1' sec 1 . At 40 kin the volume methane destruction rate
and hence the formaldehyde production rate is k 2a [Cl] [CH 41+ k3 [0H]
[C14 41 + k4 [01 D] [C11 
41 
which is approximately (3 x 10 S. 4.7 x 10 -14 +
1.7 x 107. 2:5 x 10
-15 
+ 2 x 10 2. 1.3 x 10-10 ) • ^ x1010 or 1600 molecules
cm
-3 
see
	
at  A,40 kin. Formaldehyde is destroyed in the stratosphere by
4 major processes; reaction (1'O plus
by +^112CO + Products	 (5)
1
01-1 + H2CO } H2O + HCO	 (6)
0 + H2CO } OH + HCO	 (7)
At 40 kin, J 5 ti 10-5 sec-1 , k6 ti 1 x 10
-11 
cm3 molecule
-1
 see-1,
k7 ti 6 x 10-14 cm  molecule -1 sec -1 and k 1 = 7.5 x 10
-11 
cm  molecule-1
sec -1 . Approximate diurnal average concentrations in molecules cm
-3 
at
,40 kin are [OH] = 1.7 x 10 7 , [0]- )) 7.5 x 10 8 and [Cl] = 3 x 10 5 :' Thus
the loss frequencies for these-reactions are:
(1) 3 x_10. 5 x 7.5 x 10-11 ro 2.3 x 10-5
(5)	 1 x 10-5
i
I	 t III
k	 I^	 0	
^'	 a 4
	
^uu
	 c	 i'	 ^	 '	 , iI
,9
(6) 1.7x107 xIx lo - 11ti17x10-5x>	 i
(7) 7.5x108x6x10-14ti4.5,x1050 i
The total loss frequency is about 25 x 10 -5 yielding a formaldehyde
concentration of about 1600/(25 x 10 -5 )' = 6.4 x 106molecules	 cm-3.
' This is somewhat smaller than would have been obtained ignoring reaction
^ (1) and represents a smaller feedbackon the wirect effect on chlorine
chemistry. This concentration is about 1/2000 of CH 	 and reaction (1)
can thus be expected to compete effectively with reactions (2).
The effect on the ratio of active chlorine to HCl can now be
6
#
examined.	 The loss frequency of Cl atoms for reaction (2a) is 2 x 1010
4.7 x 10-14 = 9.4 x 10-4 sec -1 while that for (2b) Iis 3.2 x 107. 3 x-10-11
= 9.6 x	 10-4 sac -l .	 For reaction (1) the loss frequency is 6.4 x 106
x 7.5 x 10 -11 = 4.8 x 10': sec -1 .	 Thus ignoring reaction (1),
W [C1 + C10]/[]-IC1]	 is proportional to 11(19 x 10 -4 ) while inclusion of (1)
` gives	 [Cl + C10]/[I-IC1] proportional to 1/(23.8 x 10 4 ) a decrease of a
factor of 1;,25. 	 The corresponding decrease in [C10]/[C1X] is a factor
of 1.13.	 This approximate analysis is borne out by the complete model4.
calculations,which include methane oxidation chemistr y using the,-Goddard
All
Iz, Space Flight Center 1D - Steady-state model. 	 The calculations show
a decrease in the predicted steady-state CFR; effect on the ozone column
' by a factor.,of 1.12, i.e. from 15.9% to 14.0%.
Figure 1 `bows results from the model for column ozone changes
(above ground level) due to injections of chlorine by CFM's as a function
of the asymptotic value of the added C1X. 	 The model behaves in essen-
tially the same fashion with or without the inclusion of reaction (1)
" except that the sensitivity to added C1X is reduced by an amount depending
on the value of the reaction rate.	 All of these deductions depend on
,
' .—.^z _->. .xt^r..E."-al:^"^=1"^"TiI'- 	 °l•-^'^wr^rRSWliaawrno^el^fYas..^+s•
..	
I J)
h
r ^	 ,
the accuracy with which formaldehyde concentrations .can be calculated.
Sensitivity studies (Butler, 1978) can be used to calculate the uncer-
tainty bounds clue to the imprecision in the measurement of the known
atmospheric processes upon which formaldehyde concentrations depend.
Figure 2 shows resultant 2e bounds on H,CO concentration where most of
the uncertainty comes from the production and destruction processes for
112 CO and the reactions which detcrmine < OH concentrations. Because of
the dependence on the very uncertain 110`
 chemistry, significa„t uncer-
tainties are found to exist in 11,CO, about a factor of 3 on either side.
Thus the impact of reaction (1) on the sensitivity of a stratospheric
model to ClX ,perturbations may be either greater or lesser than showm
above.
Discussion and Conclusion
The most important implicatioQ-1 gf^the fast rate for (1) is the
reduction in model predictions of chlo.ine pev.,urbations of strato
%%spheric ozone. Since Molina and Rowland (197,9, first pointed out the
potential effect of continued chlorofluoromethane (CFNI) release, ntuw,vous
studies have been made including a National Research Council Panel (1(RC, (4^
1976) and a NASA workshop (Hudson, --11977), The standard measure of the
magnitude of the effect that has developed is the model-predicted global
average column ozone change when the 1973 release rates (or 1975 which
,;mare about the same) are continued indefinitely. "Phis number has fluctu-
ated with new cro g-s section measurements, reaction rate measurements
and model improvem+;nts but has generally remained within the b,Ainds of
7 00, to 16U'. Before the NAS report the steady-state ozone change.w+as
40
'r
,I
generally agreed to be around 13%.	 The inclusion of chlorino_n Irate
(see Rowland et a1., 1976) in the NAS report reduced tho:_number_to
around 7%.	 Just before the NA5klreport, Howard and Evenson (1977)
hreported a much faster rate for NO + HO 	 -)- NO 2 + OH which along with
many other minor changes raised the predicted ozone depletion to as high
J/I as 160 in many models.	 The inclusion of reaction (1) in our model is
now found to reduce this number from 16% down to about 14%.	 If uncer-
tainties are resolved such that HZ CO concentrations are significantly
larger than presently calculated, then a larger reduction in the CPDI
perturbation will be deduced.
	
Measurement of the stratospheric concen-
tration of 11 CO would contribute significantly to the resolution of this
uncertainty.
Other relatively stable members of the hydrocarbon oxidation chains
should also be examined for their reaction with Cl atoms and their
possible reduction in the sensitivity of column ozone to C1X injections,.
{
k	 '-
9 ',N
Y
.i
i
,r
a
1.
In	 ORIGINAL PAGE IS
OF POOR QUALITY
MIT- L•'NCLS
Ackerman, M., D. hrimont, ap-1 C. Muller, Stratospheric CHaj HCl tntd CIO7
eland the chlorine-ozone cycle, Mature 269, 226, 1977.
/i
Butler, I), M., Input sensitivity study of a stratospheric photochemistry
model, presented at IAGA-IAMAP Joint Assembly at Seattle, W hington,
1977 and s0nitted to Pure and Applied-Gcophys., 1975.
Crutzen, P., A 1 snussion of the chemistry of some minor constituents
•I
in the stratosphere and troposphere, PAG40PH 106-1113, 1355-1359
1973.
T ^` J
`^
lhhalt, ll. 11., L. G. Heidt and G. A. Martell, The concentration of
l
--	
it
m
e thane
 77
"
 2193-2196,
	 and 62
1972.	
-	 l.iloi ^y^ '	 altitude,
	
P l ., -m te.rs altitude. J. Geo
	
	 s. Res.,th^
_  
Howard, Carleton, J-- and K. M. Cvensin, Kinetics of the reaction of
110 2 with NO, Geophys, Res_ Lett._, 4, 437-440, 1977.
Hudson, - It. 0., ed., Chlorofluoromethanes-and the Stratosphere, NASA RP-1010
1977.	 ri
-	
Leo, J. B., J. V. Michael, W. A. Paine, t,. J. Sticf, and U. A. Whytock,
Absolute rate of the reaction of C1( 7 P) with molecular hydrogen
i
`% •1	
from 200-SOOK, J. Chem. Soc. Faraday I 73, 1530-1536, 1977.
Levy, H.,-Rhotochemistry of the lower troposphere, Planet. Space
p
I 	 Sci., 20, 919-93S, 1972.
g ,	 yi,,,	 photolysis r1tonahn fluorescenceManning, R. =G. and M. J. Kur'lo Flash rl	 '
investigation of the-temperature dependencies of the reactions of
Cl( - P	 CII	 CI13C1, C11 F CH 3 F r and C2 H 6 J. Phys
Chem., Sl, 91-2g	 '
atoms with
•	 2	 G, 1J77.
^	 I r^
-^	 G	 ^	 ^	 ^	 4	 1	
I	 ^	 ^	 9	 ^`	 ^	 '	 ^	 ^	 ^	 1
,1,1
	 ^^	 'I	 ^• ,,	 ^	
'	 '	 i^	 ^	 (	 1!b
	 ^	
a	 ^^	 I	 ^^^
44
r	 ,
i
1	 III
D	 A±
Molina, M. J. and P. S. Rowland, Stratospheric Rink for chlorofluoromethanes:	 {
chlorine atom catalysed destruction of ozone, Nature, 249, 810, 1974•
National_ Research Council, Committee on Impacts ofStratospheric Change,
if
	
Nalo,carbons:	 Environmental Effects of Chlorofluormethane Release,
National Academy of Sciences, Washington, DC 1976."
v^
J 1	 Rowland, P. S., J. E. Spencer, and \ M. J. Molina, Stratospheric formation
and photolysis of chlorine nitrate, J. Phys. -Chem, (;0, `2711-2713,-	 ? ,
III	
1976.-
Whytock,	 D. A., J.	 N.	 Lee, J. V. Michael, W. A. 	 Payne,	 and L. J. Stief, 	 ^c
Absolute rate of the reaction of Cl( -2P) with Methane from 200-SOOR,	 h '
J.	 Chem. Jh ys., 6G,	 2690-2695,	 1977.
Wofsv	
S
p °
	 ,,	 C. McConnell and M..,;IkcElroy, Atmospheric CN4 , CO
2	 p	 —
ant CO
	
J.	 Geo hys.	 Res., 77, 4477-4493, 1972.-
_	 _	 I
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	^^	 a
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Figure Capi%ns I,
1. -Column ozone change due to steady-state injection of stratospheric
CiX as a function of the asymptotic value of C1X added. Curves shown
include results neglo,cting reaction (1) as well as inc usion o£-reaction
Dy ut its measured value and at a larger and a smaller value.
2. Calculated formaldehyde concentration versus altitude indicating)	 F f
2a uncertaintiesderived from sensitivity studies.
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BIBLIOGRAPHIC DATA SHEET
1111411111, 	 •or,	 I dwommosiMl-,rtaiA
r 1	 Repxtrt No.
	 2. Govemin •nt Accewon No
1'N	 79552	 1
3. Reclprem's Catalog No.
4. Title and Subtitle
_ __
5. Report Oate
I'he	 React ion C1	 + If ) p a l	 Ht,I	 + 11CO:	 Decreased Mar	 11178
Setts it lvity of	 St ratosphcr is Ozone to Chlor ine 6. Performing Organization Code
Pert Itrhat ions
7. Authorial
	 l..	 J.	 tit i e f ,	 J.V.	 Michael ► 	 W.	 A.	 1 1 .tyne , B. Performing Organization Repot, No
11. F.	 Nave,	 1).M.	 But Ior	 6	 K. S.	 Stol..rskI
9. Performing Organization Name and Address 1 J. Work Unit No.
Goddard Space Flight Center
11. Contract or Grant No.t:reenhel t ,	 Marvland	 20771
13. Type of Repitrt and Period Covered
17 Sponsoring Agency Name and Address
I'ecl u ► ical	 Mcnatr . ln,lum
14. Sponsoring Ayency Code
15. Supplement,ry Notes
1 6. Abstract
The absolute rate constant	 1'"
	
the reaction C1 + H2C0 	 ► H(:I	 + IWO has
l,cen determined by the	 f lash-phut o i ys i r<- resonance	 fluorescence met hod	 to be
7.5 + 0.9
	 (2o)	 x	 10-11	 cm l molecule -1 	sec -1 	at	 198K and
	
to have a	 nef;ll);iblc
t emperature dependence. 	 This rate which	 is more than 2000 t inics	 faster	 t h.it,
the	 rat e 	of
	 Cl	 + ( '11 4 	indica tes 	 t hat	 forma ldchyde	 (H•)CO)	 w ( l l	 comlu-t e
siKniiicantly with methane	 (CH4 )	 for the conversion of 	 active chlorine	 in
the	 stratosphere	 to	 the	 inactive	 reservoir HC1.	 ('ItIorltit , will	 thus be . ►
ef ficient
	
destroyer of	 stratospheric ozone	 than prev iot tsI v tit , lIoved.
	
Ambi ent
st ratospheric ozone will	 aepen,l	 less on	 the mullient	 chlorine .(mount
	
and	 the
predicted	 response to chlorIne port 111- hat ions w i I I	 Iw	 I essened.	 Otte-
dImensional
	
eddv-diffusion	 111totovhemicaI
	
modt , I	 ca I, ul.1t Conti	 indicate	 a
tactor
	 of	 1.1	 less	 sensitivity
	 to	 chlorine	 than	 recent l y 	 r • e lit, r'ted.	 For	 a
-cteadv-state ('F'M release at
	
1975 rates	 ( 7 50 ► 000 tons /li• ear)	 i he eventual	 ozouc
depletion
	
is now calculated
	 to be	 14,x.
17. Key Words iSelecte , l by Author (s))
	
16. Distribution Statement
141.	 Security Classif. (ot this report) ?0. Security Classif. (of this page) 21. No. of Pages 72. Price"
11 11 1	 1i
I	 a
...r..
Y	 r
^J	 I m %,11r by the Notional 14-1 hniraI Ili I c,nrllnnal %, , I l, " r, tit),, ngn,• Id. Vnynu.1 7i Il,1	 Gsri	 •1.1 ( 10/77)


The reaction Cl + H2CO yields HCl + HCO: Decreased sensitivity of stratospheric ozone to chlorine perturbations

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