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Chemical Kinetics and Photochemical Data for Use in Atmospheric Studies, Evaluation Number 16, Supplement to Evaluation 15: Update of Key Reactions

Authors:
1
JPL Publication 09-31
Chemical Kinetics and Photochemical Data
for Use in Atmospheric Studies
Evaluation Number 16
Supplement to Evaluation 15: Update of Key Reactions
NASA Panel for Data Evaluation:
S. P. Sander
R. R. Friedl
NASA/Jet Propulsion
Laboratory
Pasadena, California
J. Abbatt
University of Toronto
Toronto, Canada
J. R. Barker
University of Michigan
Ann Arbor, Michigan
J. B. Burkholder
NOAA Earth System Research Laboratory
Boulder, Colorado
D. M. Golden
Stanford University
Stanford, California
C. E. Kolb
Aerodyne Research, Inc.
Billerica, Massachusetts
M. J. Kurylo
GEST/UMBC
Greenbelt, Maryland
G. K. Moortgat
Max
-Planck Institute for Chemistry
Mainz, Germany
P. H. Wine
Georgia Institute of Technology
Atlanta,
Georgia
R. E. Huie
V. L. Orkin
Nati
onal Institute of Standards and
Technology
Gaithersburg, Maryland
National Aeronautics and
Space Administration
Jet Propulsion Laboratory
California Institute of Technology
Pasadena, California
2
The research described in this publication was carried out by the Jet Propulsion Laboratory, California
Institute of Technology, under a contract with the National Aeronautics and Space Administration.
Reference herein to any specific commercial product, process, or service by trade name, trademark,
manufacturer, or otherwise, does not constitute or imply its endorsement by the United States
Government or the Jet Propulsion Laboratory, California Institute of Technology
Copyright 2010. All rights reserved.
3
Table 1-1. Rate Constants for Second-Order Reactions
O(1D) Reactions A-Factora
E/R
k(298 K)a
f(298
K
)
b
g
N
ote
1D) + H2O o OH + OH
1.63
x10–10
-60
2.0 x10–10
1.08 45
A6
2
o N2 + O2
o
1.19x10-10
4.63
x10–11
7.25
x10–11
-20
-20
-20
1.27x10-10
4.95
x10–11
7.75
x10–11
1.1
1.1
1.1
25
25
25
A8
4
o CH3 + OH
o CH3O or CH2
o
2
2
1.75x10–10
1.31
x10–10
0.35
x10–10
0.09
x10–10
0
0
0
0
1.75x10–10
1.31
x10–10
0.35
x10–10
0.09
x10–10
1.15
1.15
1.15
1.15
25
25
25
25
A11
ClOx Reactions A-
Factor
E/R
k(298 K
)
f(298 K
)
g
N
ote
→ HCl + O2
7.4×10
–12
6.0×10–13
270
230
1.8×10
–11
1.3×10
–12
1.2
1.7
50
100
F10
o H2O + Cl 1.8x10-12
250
7.8x10-13
1.1 50
F12
2 + Cl → HCl + O2
→ OH + ClO
1.4×10
–11
3.6×10–11
269
375
3.5
×10–11
1.
0×10–11
1.2
1.4
10
0
1
5
0
F45
2 + ClO o HOCl + O2 2.6x10-12 -290
6.9x10-12 1.2
150
F46
BrOx Reactions A-
Factor
E/R
k(298 K
)
f(298 K
)
g
N
ote
3 o BrO + O2 1.6x10-11 780
1.2x0-12
1.15
100
G31
2CO o HBr + HCO 1.7x10-11
800
1.1x10-12
1.2
125
G34
o Br + ClOO
o
2
9.5x10-13
2.3x10-12
4.1x10-13
-550
-260
-290
6.0x10-12
5.5x10-12
1.1x10-12
1.2
1.2
1.2
100
100
100
G41
k(T) = Aexp([-E/R]/T)
a Units are cm3 molecule1 s1.
4
b f(298 K) is the uncertainty factor at 298 K. To calculate the uncertainty at other temperatures, use the
expression:
11
f(T) = f(298 K)exp g T 298
§·
¨¸
©¹
Note that the exponent is the absolute value.
f(T) represents approximately one standard deviation. The 95% confidence limit is obtained by squaring f(T).
Shaded areas indicate changes or additions since JPL 06-2.
A6. The recommended k(298 K) is based on the results of Davidson et al. [31], Amimoto et al.[1], Wine and Ravishankara
[143-144], Gericke and Comes [41], Dunlea and Ravishankara [37], Carl [20], and Takahashi et al. [125], but is weighted
towards the study of Dunlea and Ravishankara because the latter study used several different methods to quantify the water
vapor concentration. The results of Lee and Slanger [65] and Dillon et al. [34] are consistent with the recommended value.
The temperature dependence of this rate coefficient is derived from the data of Streit et al.[123] and Dunlea and
Ravishankara, after normalizing the results from the two studies to the k(298 K) value recommended here. The O2 + H2
product yield was measured by Zellner et al. [147] to be (1 +0.5/1)% and Glinski and Birks [42] to be (0.6 +0.7/0.6)%.
The yield of O(3P) from O(1D) + H2O is reported to be less than (4.9 ± 3.2)% by Wine and Ravishankara [144], (2 ± 1)% by
Takahashi et al. [126], and <0.3% by Carl [20]. The recommended yield of OH in this reaction is 2.0. To calculate the rates
of OH production via O(1D) reactions in the atmosphere, the quantities of interest are the ratios of the rate coefficients for the
reaction of O(1D) with H2O to those with N2 and O2. Ratio data are given in the original references for this reaction. (Table
09-X, Note: 09-X)
A8. O(1D) +N2O. This reaction has two channels, one producing 2NO and the other producing N2 + O2. For atmospheric
calculations of NOx production, the rate coefficient for the channel that produces NO is critical, while the overall rate
coefficient is important for deriving the loss rate of N2O. The recommendation for the overall room temperature rate
coefficient for the removal of O(1D) by N2O was derived from a weighted average of the results from Davidson et al. [30],
Amimoto et al. [1], Wine and Ravishankara [144], Blitz et al. [8], Dunlea and Ravishankara [36], Carl [20], Takahashi et al.
[125], Dillon et al. [34], and Vranckx et al. [139]. The temperature dependence of the rate coefficient was derived from the
results of Davidson et al. (204 359 K), Dunlea and Ravishankara (220 370 K), and Vranckx et al. (227 715 K); only
data at <400 K were considered in the evaluation, after normalization to the k(298 K) value recommended here for the overall
rate coefficient. The recommended rate coefficients for the N2 + O2 and 2NO product channels were evaluated for 298 K, the
only temperature at which such data are available. The branching ratio, R, k(NO + NO)/k(Total) is taken from Cantrell et al.
[19] who reported R = 0.57 as well as an analysis of all measurements from 19571994 that led them to recommend R = 0.61
± 0.06, where the uncertainty is the 95% confidence interval. Their recommended branching ratio agrees well with earlier
measurements of the quantum yield from N2O photolysis (Calvert and Pitts [17]). Dependencies of the branching ratio on
O(1D) translational energy and temperature are at present not clearly resolved. The recommended rate coefficients for the
two channels as a function of temperature were derived assuming that the branching ratio for the two channels is invariant
with temperature.
The yield of O(3P) from O(1D) + N2O (physical quenching or chemical deactivation) has been determined to be <0.04, 0.04 ±
0.02, 0.056 ± 0.009, and 0.005 ± 0.002 by Wine and Ravishankara [144], Nishida et al. [92], Carl [20] and Vranckx et al.
[139] at 298 K, respectively. Vranckx et al. report a slight increase in the O(3P) yield with increasing temperature (248 600
K) and their reported yield supercedes the anomalously high value reported by Carl [20] from the same laboratory. A
recommended O(3P) yield of <0.01 is based on the Vranckx et al. study. A direct measurement of the NO yield from the
O(1D) + N2O reaction in synthetic air by Greenblatt and Ravishankara [44] and the re-analysis by Dunlea and Ravishankara
[36] agrees very well with the value predicted using the recommended O(1D) rate coefficients for N2, O2, and N2O and the
O(1D) + N2O product branching ratio to give NO + NO. Better reactive channel branching ratio measurements at
stratospheric temperatures and/or measurements of the NO yield in this reaction as a function of temperature below 298 K
would be useful. The uncertainty for this reaction includes factors for both the overall rate coefficient and the branching
ratio. (Table 09-X, Note: 09-X)
5
A11. O(1D) + CH4. The recommended overall rate coefficient for the removal of O(1D) by CH4 at room temperature is a
weighted average of the results from Davidson et al. [31], Blitz et al. [8], Dillon et al. [33], and Vranckx et al. [138]. The
temperature dependence of the rate coefficient was derived from the results of Davidson et al. (198 357 K), Dillon et al.
(223 297 K), and Vranckx et al. (227 450 K). The recommended rate coefficients for the product channels (a) CH3 + OH,
(b) CH3O or CH2OH + H and (c) CH2O + H2 were evaluated for 298 K, the only temperature at which such data are
available. Lin and DeMore [72] analyzed the final products of N2O/CH4 photolysis mixtures and concluded that (a)
accounted for about 90% and CH2O and H2 (c) accounted for about 9%. Casavecchia et al. [21] used a molecular beam
experiment to observe H and CH3O (or CH2OH) products. They reported that the yield of H2 was <25% of the yield of H
from channel (b). Satyapal et al. [114] observed the production of H atoms in a pulsed laser experiment and reported an H
atom yield of 25 ± 8%. Matsumi et al. [77] reported the H atom yield in low pressure gas mixtures to be (15±3)%. Chen et
al. [24] used laser infrared kinetic spectroscopy to study product formation and report yields of 67 ± 5%, 30 ± 10%, and 5%
for channels a, b, and c, respectively. The yield of O(3P) via the physical quenching of O(1D) by CH4 has been reported by
several groups. Wine and Ravishankara [144], Matsumi et al. [76], and Takahashi et al. [126] reported O(3P) yields of
<4.3%, <5%, and <1%, respectively. Vranckx et al. [138] reported the most sensitive O(3P) yield measurement to date and
obtained a yield of 0.002 ± 0.003. We recommend the following branching ratios (a) (75 ± 15)%, (b) (20 ± 10)%, (c) (5 ±
5)% and it is assumed that the branching ratio for the three channels is invariant with temperature. The uncertainties are
based on the evaluation of the overall rate coefficient. (Table 09-X, Note: 09-X)
F10. OH + ClO. The reaction has two known product channels under atmospheric conditions: OH + ClO→ Cl + HO2 and OH
+ ClO → HCl + O2. Most studies measure the rate coefficients for the overall reaction (OH + ClO → products) that is
presumably the sum of the two channels. The recommendation for the Cl + HO2 channel is obtained from the equilibrium
constant for this channel combined with the recommended value for the reverse reaction in entry F45. The difference between
a critical assessment of the measurements of the overall reaction and the recommendation for the HCl + O2 channel as
discussed below is in reasonable accord.
The assessment of the overall reaction (OH + ClO → products) is based on a fit to the 219373 K data of Hills and Howard
[51], the 208298 K data of Lipson et al. [74], the 234356 K data of Kegley-Owen et al. [59], the 298 K data of Poulet et al.
[102], measurements by Wang and Keyser (218298 K) [141], and measurements by Bedjanian et al. (230360 K) [6]. Data
reported in the studies of Burrows et al. [16], Ravishankara et al. [105], and Leu and Lin [70] were not used in deriving the
recommended value because ClO was not measured directly in these studies and the concentration of ClO was determined by
an indirect method.
The minor reaction channel forming HCl poses significant experimental difficulties due to the complications associated with
the measurement of the HCl reaction product. Early studies inferred the HCl branching ratio without measuring HCl. These
included the 298 K measurements of the yield of the Cl + HO2 channel by Leu and Lin [70] (>0.65); Burrows et al. [16]
(0.85±0.2) and Hills and Howard [51] (0.86±0.14). Poulet et al. [102] measured the Cl + HO2 product yield to be 0.98±0.12
using mass spectroscopy but their HCl sensitivity was marginal. These studies were not considered in the evaluation. Later
studies of Lipson et al. using mass spectroscopy [74] and diode laser spectroscopy by Wang and Keyser [142] improved the
precision of the HCl product channel measurements. Lipson et al. [73] measured rate constants for the HCl channel over the
temperature range 207298 K and report a branching ratio of (7±3%), while Wang and Keyser [142] measured the HCl yield
between 218298 K, obtaining (9.0±4.8) %, independent of temperature. Their rate constant was computed from this yield
and their overall rate constant [141]. Measurements by Tyndall et al. [134] and Bedjanian et al. [6] were also considered. (It
was noted that although the values for this channel obtained by Lipson et al. by combining the values obtained in [74] and
[73] and Bedjanian et al. [6] are in agreement, their values for the overall reaction differ by 40-70%.) The recommendation
for the HCl channel is unchanged from JPL 06-2 and the error limits have been reduced.
F12. OH + HCl. The recommended value is based on a least squares fit to the data over the temperature range 204300 K
reported in the studies of Molina et al. [85], Keyser [60], Ravishankara et al. [107], Battin-Leclerc et al. [5] and Bryukov et
6
al. [12]. In these studies particular attention was paid to the determination of the absolute concentration of HCl by UV and IR
spectrophotometry. Earlier studies by Takacs and Glass [124], Zahniser et al. [146], Smith and Zellner [118], Ravishankara et
al. [106], Hack et al. [45], Husain et al. [54], Cannon et al. [18], Husain et al. [55], and Smith and Williams [117] had
reported somewhat lower room temperature values. The data of Sharkey and Smith [115] over the temperature range 138
216 K, Battin-Leclerc et al. [5] below 240 K Bryukov et al over the temperature range 298 1015 K, depart from normal
Arrhenius behavior. Quantum chemical and transition state calculations performed by Battin-Leclerc et al. [5], Bryukov et al.
[12] and Steckler et al. [120] generally support the existence of a weakly bound complex, however, a large tunneling effect is
required to explain the low temperature data. Additional work at low temperature is needed to confirm the strong non-
Arrhenius behavior. (Table 09-X, Note: 09-X)
F45. HO2 + Cl. The recommendations for the two reaction channels are based upon the results of Hickson and Keyser [48],
who measured both channels using the discharge flow-resonance fluorescence technique coupled with infrared diode laser
spectroscopy, detecting HO, HO2, Cl and HCl, by Lee and Howard [67] who measured the total rate constant and the OH +
ClO channel, using a discharge flow system with laser magnetic resonance detection of HO2, OH, and ClO, and by Riffault
et al. [109] who measured the total rate constant and the OH + ClO channel using the discharge flow mass spectrometric
technique. The latter two studies suggest that the total rate constant is temperature independent with a value of (4.2±0.7)×10-
11 and (4.4±0.6)×10-11 cm3 molecule1 s1 over the temperature range 250420 K and 230-360 K respectively. The Hickson
and Keyser study concludes that the HCl channel may be represented as (1.4±0.3)×10-11 exp[(269±58)/T] for temperatures
from 256 to 296 K, while the OH channel is given by (12.7±4.1)×10-11 exp[-(801±94)/T] for temperatures of 226-336 K, the
sum of which yields 4.3×10-11 cm3 molecule1 s1 at 298 K with a small temperature dependence.. These values for the total
rate constant are in agreement with the results of indirect studies relative to Cl + H2O2 (Leu and DeMore [68], Poulet et al.
[103], Burrows et al. [14]) or to Cl + H2 (Cox [27]). The contribution of the reaction channel producing OH + ClO (22% at
room temperature) is much higher than the upper limit reported by Burrows et al. (1% of total reaction). Cattell and Cox [22],
using a molecular modulation-UV absorption technique over the pressure range 50760 Torr, report results in good
agreement with those of Lee and Howard both for the overall rate constant and for the relative contribution of the two
reaction channels. A study by Dobis and Benson [35] reports a total rate constant in good agreement with this
recommendation but a much lower contribution (5±3%) of the channel producing OH + ClO. The equilibrium constant for
the channel producing ClO + OH can be calculated with excellent accuracy. The recommended value for this channel comes
from the combination of this equilibrium constant and the rate constant for the reverse reaction found in entry F10.
F46. HO2 + ClO. The recommended value is based on studies by Hickson et al. [49], Nickolaisen et al. [89], Knight et al.
[61], and Stimpfle et al. [121] that studied the reaction as a function of temperature. Earlier room temperature studies by
Reimann and Kaufman [108]; Leck et al. [64], Burrows and Cox [15], and Cattell and Cox [22] are slightly lower than the
current recommendation. The studies of Cattell and Cox and Nickolaisen et al. were performed over extended pressure
ranges and did not observe a pressure dependence. The most recent studies find the T-dependence to be characterized by
linear Arrhenius behavior over the entire temperature range and do not support the finding of Stimpfle et al. of non-Arrhenius
behavior. The recommended value for E/R is based on an average of individual E/R values for each of the four studies over
their entire temperature ranges. The two most probable pairs of reaction products are, (1) HOCl + O2 and (2) HCl + O3.
Finkbeiner et al. [39], using matrix isolation/ FTIR spectroscopy, studied product formation between 210 and 300 K at 700
Torr. HOCl was observed to be the dominant product (> 95% at all temperatures). Upper limits ranging from 0.3% to 2%
have been determined for the channel (2) room temperature branching ratio by Leu [71], Leck et al., Knight et al., and
Finkbeiner et al. Slightly larger branching ratio (<5%) upper limit values for k2/k were determined at temperatures below
250 K by Finkbeiner et al. and Leck et al. However, no direct evidence of product channels other than channel (1) was
found. Theoretical calculations by Nickolaisen et al. suggest that the reaction to channel (1) proceeds mainly through a ClO-
HO2 complex on the triplet potential surface. However, these calculations also suggest that collisionally stabilized HOOOCl
formed on the singlet surface will possess an appreciable lifetime. Zhu et al. [145], using ab initio molecular orbital methods,
hypothesize that stabilization of the HOOOCl complex should increasingly occur as temperature is decreased below 298 K
for pressures above 1 Torr. Further studies of the possible formation of HOOOCl are warranted. (Table 09-X, Note: 09-X)
7
G31. Br + O3. The results reported for k(298 K) by Clyne and Watson [25], Leu and DeMore [69], Michael et al. [82],
Michael and Payne [83], Toohey et al. [130], Nicovich et al. [90] and Ninomiya et al. [91] are in excellent agreement. The
preferred value at 298 K is derived by taking the mean of these seven values. There is less agreement among reported
temperature dependences, with E/R values ranging from ~900 (Leu and DeMore and Toohey et al.) to ~600 (Michael et al.
and Michael and Payne). The preferred value of E/R represents an average of the E/R’s from the five studies carried out as a
function of temperature (not including Clyne and Watson and Ninomiya et al. which were room temperature only). (Table
09-X, Note: 09-X)
G34. Br + H2CO. There have been two direct studies of this rate constant as a function of temperature: Nava et al. [87], using
the flash photolysisresonance fluorescence technique, and Poulet et al. [101], using the discharge flow-mass spectrometric
technique. These results are in reasonably good agreement. The Arrhenius expression was derived from a least squares fit to
the data reported in these two studies. The higher room temperature value of Le Bras et al. [63], using the discharge flow
EPR technique, has been shown to be in error due to secondary chemistry (Poulet et al.). The relative rate study of Ramacher
et al. [104] is in good agreement with the recommendation. (Table 09-X, Note: 09-X)
G41. BrO + ClO. Friedl and Sander [40], using DF/MS techniques, measured the overall rate constant over the temperature
range 220400 K and also over this temperature range determined directly branching ratios for the reaction channels
producing BrCl and OClO. The same authors in a separate study using flash photolysisultraviolet absorption techniques
(Sander and Friedl [113]) determined the overall rate constant over the temperature range 220400 K and pressure range 50
750 Torr and also determined at 220 K and 298 K the branching ratio for OClO production. The results by these two
independent techniques are in excellent agreement, with the overall rate constant showing a negative temperature
dependence. Toohey and Anderson [129], using DF/RF/LMR techniques, reported room temperature values of the overall
rate constant and the branching ratio for OClO production. They also found evidence for the direct production of BrCl in a
vibrationally excited Ȉstate. Poulet et al. [100], using DF/MS techniques, reported room temperature values of the overall
rate constant and branching ratios for OClO and BrCl production. Overall room temperature rate constant values reported
also include those from the DF/MS study of Clyne and Watson [26] and the very low value derived in the flash photolysis
study of Basco and Dogra [3]. The recommended Arrhenius expressions for the individual reaction channels are taken from
the study of Friedl and Sander [40] and Turnipseed et al. [133]. These studies contain the most comprehensive sets of rate
constant and branching ratio data. The overall rate constants reported in these two studies are in good agreement (20%) at
room temperature and in excellent agreement at stratospheric temperatures. Both studies report that OClO production by
channel (1) accounts for 60% of the overall reaction at 200 K. Both studies report a BrCl yield by channel (3) of about 8%,
relatively independent of temperature. The recommended expressions are consistent with the body of data from all studies
except those of Hills et al. [50] and Basco and Dogra [3]. (Table 09-X, Note: 09-X)
8
Table 2-1. Rate Constants for Termolecular Reactions
Reaction
Low-Pressure Limita
ko(T) = ko
300 (T/300)–n
High-Pressure Limitb
kf(T) = kf300 (T/300)–m
f(298 K)
g
k
o
300
n
k
f
300
m
ClO
x
Reactions
ClO + ClO
M
o
Cl
2
O
2
1.6x10-32 4.5
3.0x10-12 2.0
1.15
0
 
>@

>@



>@


^`
-1
2
0
1+ log k T M /k T
0
0
kTM
k M,T = 0.6
1+ k T M /k T
f
ªº
¬¼
f
§·
¨¸
¨¸
©¹
The values quoted are suitable for air as the third body, M.
a Units are cm6 molecule-2 s-1.
b Units are cm3 molecule-1 s-1.
f(298 K) is the uncertainty factor at 298 K. To calculate the uncertainty at other temperatures, use the expression:
11
f(T) = f(298 K)exp g T 298
§·
¨¸
©¹
Note that the exponent is the absolute value
Shaded areas indicate changes or additions since JPL 06-2.
ClO + ClO. The recommendation is based on a fit to data from Sander et al. (195247 K) [112] as quoted by Nickolaisen et
al. (260390 K) [88], Bloss et al. (183245 K) [9], Trolier et al. (200263 K) [132] and Boakes et al. [10]. The Trolier et al.
data have been corrected for values at the zero pressure intercept as suggested in the Trolier et al. paper. With this
adjustment all the data except the Boakes et al. values are in reasonable agreement. Boakes et al. [10] report higher values.
They found a zero pressure intercept as well, but they suggest disregarding their data at less than 100 Torr and report
preferred parameters of 2.79x10-32; 3.78; 3.44x10-12; 1.73. The Boakes et al [10] values are accommodated in this evaluation
by the change in the values of the high pressure limiting rate constant compared with the evaluation in JPL 06-2 [111]. Error
limits represent an attempt to include all the data within the 95% uncertainty. Golden [43] has performed RRKM and master
equation calculations using the potential energy surface in Zhu and Lin [148] and concluded that while a channel to form
ClOClO might exist, the best representation of the data remains that only a single channel exists. The value of m = 2 is
somewhat high, but attempts to statistically model any and all of the data sets yield even higher values. The ko value for N2 is
not in accord with a simple theory as explained in Patrick and Golden [94] and in some detail in Golden [230]. It has been
suggested [131] that the “radical-complex’ mechanism may apply here, although a study by Liu and Barker [75] suggests
otherwise. Other previous rate constant measurements, such as those of Hayman et al. [47], Cox and Derwent [28], Basco and
Hunt [4], Walker [140], and Johnston et al. [57], range from (15)×1032 cm6 molecule-2s1, with N2 or O2 as third bodies.
The major dimerization product is chlorine peroxide (Birk et al. [7], DeMore and Tschuikow-Roux [32], Slanina and Uhlik
[116], Stanton et al. [119] and Lee et al. [66]). (Table 09-X, Note: 09-X)
9
Table 3-1. Equilibrium Constants
Reaction
A/cm3
molecule–1
B/°K Keq(298 K)
f(298 K)a
g
ClO + ClO o Cl
2
O
2
1.72×10–27
8649
6.9×10–15
1.25
200
K/cm3 molecule1 = A exp (B/T) [200 < T/K < 300]
Shaded areas indicate changes or additions since JPL06-2.
a f(298 K) is the uncertainty factor at 298 K, and g is a measure of the uncertainty in the quantity B. To calculate the
uncertainty at temperatures other than 298 K, use the expression:
 
11
f T f 298 K exp g T 298
ªº
§·
¨¸
«»
©¹
¬¼
ClO + ClO. The values of the equilibrium constant and the thermochemical parameters are from a third-law calculation
based on the data from Cox and Hayman [29] and Nickolaisen et al.[88]. The 95% error limits were chosen to incorporate all
the data points in these two studies. The entropy of ClOOCl, the value of which is 72.0 cal mol1 K1 (301.1 J mol-1 K-1) at
300 K, can be calculated from structures and frequencies calculated by Zhu and Lin [148] (symmetry number corrected by
Golden [43] to account for optical isomers) or by treatment of the torsion as a hindered rotor [62], in which case the
symmetry number correction is not required. The latter has been adopted here, but there is very little difference between the
results. The heat of formation at 0 K is 'f,0 =31.6±0.5 kcal mol1 (132.4±2 kJ mol-1) and at 300 K is 'f,300 =30.8±0.5
kcal mol1 (129.0±2 kJ mol-1). A study of branching ratios of ClO + ClO channels in Cl2/O2/O3 mixtures by Horowitz et al.
[52] also finds the equilibrium constant in O2 at 285 K to be in agreement with the recommendation. Values at single
temperatures are available from Ellermann et al. [38] and Boakes et al. [10], the former agreeing with this recommendation,
while the latter is a bit outside the 95% confidence limit. Broske and Zabel [11] measured the reverse reaction at four
temperatures between 245 and 260 K. They used the parameters for the forward reaction recommended in JPL 02-25 to
suggest van’t Hoff parameters of 5.09×10-26 and 7584. Vant Hoff parameters suggested by Plenge et al. [98], who measured
'Hf,0(ClOOCl) =134.0±2.80 kJ mol-1 by photoionization mass spectrometry and computed the entropy change for the
reaction, are 1.92×10-27 and 8430.
Several studies have derived values of Keq using atmospheric measurements in the nighttime polar stratosphere under
conditions where ClO and ClOOCl should be in equilibrium. These are summarized here but are not used in the derivation of
the recommended equilibrium constants. Avallone and Toohey [2] used Keq = 1.99x10-30×T×exp(8854/T) derived from in situ
aircraft experiments. The Avallone and Toohey [2] expression yields values that are quite close to those from the
recommended expression. Atmospheric measurements from an airborne platform have also been used by von Hobe et al.
[137] to deduce Keq parameters of 3.61×10-27 and 8167, resulting in values which lie outside the 95% confidence limits. A
reanalysis by Salawitch and Canty [110] of ER-2 data between 185 and 200 K, from Stimpfle et al. [122] results in an
expression for Keq which lies within the uncertainty bounds and is quite close to the Avallone and Toohey [2] expression.
(Table 09-X, Note: 09-X)
10
Table 4-1. Photochemical Reactions
ClOOCl. The recommendation for the cross-sections is unchanged from JPL 06-2. However, changes in the recommended
uncertainties have been made. The new note discusses these changes and other recent activities.
F7. ClOOCl + hν → ClO + ClO 17.7 kcal mol-1 1614 nm (1)
→ Cl + ClOO 21.6 kcal mol-1 1323 nm (2)
Absorption Cross Sections: The gas-phase UV absorption spectrum of ClOOCl is continuous with a maximum at 245 nm, a
minimum near 218 nm, and a weak diffuse shoulder in the wavelength region 280 300 nm. There are a number of studies
that have reported UV absorption data for ClOOCl over a range of wavelengths or at specific wavelengths. Table 1
summarizes the currently available studies. The ClOOCl UV absorption spectrum reported by Basco and Hunt [4] and
Molina and Molina [84] have been shown to contain systematic errors and are not considered further in this evaluation. In
laboratory studies, ClOOCl has been produced in the gas-phase at low temperature as a product of the termolecular ClO
radical self-reaction, ClO + ClO + M. Studies, to date, indicate that only one stable isomer of Cl2O2 is produced in the ClO
self-reaction and that this species is dichlorine peroxide, ClOOCl, rather than ClOClO or ClClO2. Using sub-millimeter wave
spectroscopy, Birk et al. [7] have further established the structure of the reaction product to be ClOOCl. This is in general
agreement with the quantum mechanical calculations of McGrath et al. [79-80], Jensen and Odershede [56], and Stanton et al.
[119] although the recent theoretical study by Matus et al. [78] found the ClClO2 isomer to be more stable than ClOOCl by
3.1 kcal mol-1 at 298 K.
Cox and Hayman [29], Burkholder et al. [13], DeMore and Tschuikow-Roux [32], and Bloss et al. [9] report absolute
VO, values. The studies of Permien et al. [95], Vogt and Schindler [135], Huder and DeMore [53],
McKeachie et al. [81] and Pope et al.[99] report absorption spectra normalized to 245 nm. von Hobe et al. [136] report a
solid-phase ClOOCl UV absorption spectrum measured in a Ne matrix at ~10 K with reported cross sections obtained by
normalization using the cross section value recommended in JPL-2006 for the gas-phase spectrum.
Discrepancies in the wavelength dependence of the ClOOCl absorption spectrum at wavelengths >300 nm, the region that is
most critical for atmospheric photolysis rate calculations, exist and most likely originate from uncertainties in corrections for
spectral interferences by reactant precursors (O3, Cl2O, and Cl2) and impurities (OClO, Cl2, and Cl2O3) formed in the ClOOCl
source chemistry. Near the peak, the reported spectra are in reasonable agreement. The studies of Cox and Hayman,
Burkholder et al., DeMore and Tschuikow-Roux, Vogt and Schindler, and McKeachie et al. show systematic deviations that
are possibly consistent with spectral interference due to minor absorption by Cl2O and in the case of Cox and Hayman,
Burkholder et al., and McKeachie et al. possibly Cl2O3. At O >300 nm, the ClOOCl spectrum is weaker and more sensitive to
spectral interferences from impurities, in particular Cl2. The studies of Burkholder et al. and DeMore and Tschiukow-Roux
are the only gas-phase studies to date that report cross section data at O >360 nm. Pope et al. recently developed a method to
isolate bulk samples of ClOOCl in which ClOOCl is produced in the gas-phase and condensed at low temperatures. Pope et
al. measured gas-phase UV spectra that are due mostly to Cl2 and ClOOCl absorption following the warming of the
condensate. The spectra were analyzed using a Gaussian fitting procedure and they report a ClOOCl absorption spectrum
that decreases rapidly at O >320 nm with a cross section at 350 nm that is a factor of 6 lower than recommended in JPL-2006.
The von Hobe et al. matrix study used the Pope et al. method to prepare their ClOOCl samples and Raman spectroscopy to
evaluate the spectral contribution from Cl2 impurities. They report a ClOOCl spectrum with significant absorption at
wavelengths out to 400 nm.
The recommended ClOOCl absorption cross sections for the temperature range 190 250 K are listed in Table 4-85 and are
unchanged from JPL-2006. The peak absorption cross section was obtained from the studies given in Table 1. Cross
sections at other wavelengths are based on the data of DeMore and Tschuikow-Roux for 190-200 nm and the data of Cox and
Hayman [29], DeMore and Tschuikow-Roux [32], and Burkholder et al. [13] for the wavelength range 200-360 nm. Data at
11
O >360 nm are from a log-linear extrapolation and are given by the expression log[σ(λ)] = 7.589 - 0.01915 u λ where λ is in
nm and σ is in units of 10-20 cm2 molecule-1.
Bloss et al. [9] measured a value for V(210 nm) in a pulsed photolysis ClO + ClO + M kinetics study over the temperature
range 183 245 K that is ~25% greater than the current recommendation. Recently, Chen et al. [23] used a new
experimental method involving pulsed laser photolysis of ClOOCl in a molecular beam combined with mass spectrometric
detection to determine VO)O where )O is the ClOOCl photolysis quantum yield, the quantity needed for atmospheric
photolysis rate calculations, at 308 and 351 nm. Their experimental method is not sensitive to spectral interference from Cl2
and the lower-limit for the ClOOCl cross sections, assuming )O = 1, for measurements made at 200 and 250 K are in good
agreement at 308 nm and ~40% greater at 351 nm than the current recommendation. Additional studies of the ClOOCl
absorption spectrum by Papanastasiou et al. [93] and VO)Oby the Anderson group [46] at Harvard are currently in
preparation for publication but were not considered in this evaluation.
Cross-Section Uncertainties: The uncertainties in the ClOOCl absorption cross section have been re-evaluated from JPL-
2006. Over the wavelength range 200 300 nm, we estimate the uncertainty in VO to be ±35%. The estimated uncertainty
increases towards longer wavelengths and the upper and lower limits for VO>300 nm) are given by: VO+ = 1.35 x V(300
nm) x exp[-0.038(O - 300)] and VO = (1/1.35) x V(300 nm) x exp[-0.0525(O - 300)]. The estimated error limits cover a
range in VO that includes the values reported by Burkholder et al. (upper limit) and the extrapolated values of Huder and
DeMore (lower limit). The results reported in the Pope et al. study fall outside the currently estimated range of uncertainty
for VO. Further studies of the peak cross section and spectrum at O >300 nm that reduce uncertainties in the calculated
atmospheric photolysis rate of ClOOCl are desired.
Photolysis Quantum Yields and Product Studies: Molina et al. ^Molina, 1990 #939`reported a quantum yield, ), of
approximately unity (1.03 ± 0.12) for the Cl + ClOO pathway from a flash photolysis study at 308 nm, in which the yield of
Cl atoms was measured using time-resolved atomic resonance fluorescence. These results are in agreement with the steady-
state photolysis study of Cox and Hayman [29]. In a molecular beam/flash-photolysis study Moore et al.[86] measured the
relative Cl:ClO product yields from which the branching ratio for both photolysis channels ClOO + Cl and ClO + ClO was
derived. At 248 nm, they obtained 0.88 ± 0.07 and 0.12 ± 0.07 respectively, and at 308 nm, 0.90 ± 0.1 and 0.10 ± 0.01.
Plenge et al. [97] measured the primary products from ClOOCl photolysis at 250 and 308 nm using photoionization mass
spectrometry. At both wavelengths 2Cl + O2 was observed as the exclusive products corresponding to a primary Cl quantum
yield near unity at 250 nm )Cl ≥0.98 and at 308 nm )Cl ≥0.90. At both photolysis wavelengths the pathway leading to ClO
was not observed corresponding to )ClO ≤0.02 at 250 nm and )ClO ≤0.10 at 308 nm.
A quantum yield of )Cl = 1.0 (± 0.1) is recommended for λ <300 nm while )Cl = 0.9 (± 0.1) is recommended for λ >300 nm.
The determination of photolysis quantum yields and product branching ratios at wavelengths >300 nm are desired.
Theoretical Studies: Toniolo et al.[128], Peterson and Francisco [96], and Matus et al. [78] report theoretical calculations for
the electronic transitions of the ClOOCl UV absorption spectrum that include transitions to excited singlet and triplet states.
Peterson and Francisco report that the strongest triplet transition is dissociative to Cl + ClOO, centered near 385 nm, and is
three orders of magnitude weaker than the strongest singlet transition at shorter wavelengths. Kalekin and Morokuma [58]
studied the ClOOCl photodissociation dynamics and predict the synchronous and sequential formation of 2Cl + O2 at 308
nm, and three possible fragmentation routes at 248 nm: 2Cl + O2, Cl + O(3P) + ClO, and 2Cl + 2O(3P). Similar theoretical
calculations performed by Toniolo et al. [127] for excitation at 264, 325 and 406 nm found that 2Cl + O2 was produced at all
wavelengths with only a small yield of 2ClO at the shortest wavelength.
12
Table 4.xx Summary of ClOOCl UV absorption spectrum studies
Reference
Year
Temperature(K)
O (nm)
1020 VO)(cm2)
Cox and Hayman [29]
1988
200 300
220 360
640 ± 60*
Permien et al. [95]
1988
235
211 290
$
Burkholder et al. [13]
1990
205 250
212 410
650 +80/-50*
DeMore and Tschuikow-Roux [32]
1990
206
190 400
680 ± 80*
Vogt and Schindler [135]
1990
230
204 350
$
Huder and DeMore [53]
1995
195
200 310
$,@
Bloss et al. [9]
2001
183 245
210
294 ± 86
McKeachie et al. [81]
2004
223
235 400
$
Pope et al. [99]
2008
193
226 355
$
von Hobe et al. [136]
2009
10
220 400
$,#
Chen et al. [23]
2009
200
250
200
250
308
308
351
351
49&
50.9
11.2
12.6
* Absorption cross section values at the peak of the spectrum, 245 nm. Cross section data also given over the reported range
of wavelengths. $ Reported ClOOCl absorption spectrum without absolute cross section determination. # Solid-phase
ClOOCl absorption spectrum measured in a Ne matrix. @ ClOOCl absorption spectrum at wavelengths reported at >310
obtained using a log-linear extrapolation. & ClOOCl cross section obtained assuming a unit photolysis quantum yield.
13
Table 4-85. Absorption Cross Sections of ClOOCl
λ (nm)
1020 σ (cm2)
λ (nm)
1020 σ (cm2)
λ (nm)
1020 σ (cm2)
λ (nm)
1020 σ (cm2)
190
565.0
256
505.4
322
23.4
388
1.4
192
526.0
258
463.1
324
21.4
390
1.3
194
489.0
260
422.0
326
19.2
392
1.2
196
450.0
262
381.4
328
17.8
394
1.1
198
413.0
264
344.6
330
16.7
396
1.0
200
383.5
266
311.6
332
15.6
398
0.92
202
352.9
268
283.3
334
14.4
400
0.85
204
325.3
270
258.4
336
13.3
402
0.78
206
298.6
272
237.3
338
13.1
404
0.71
208
274.6
274
218.3
340
12.1
406
0.65
210
251.3
276
201.6
342
11.5
408
0.60
212
231.7
278
186.4
344
10.9
410
0.54
214
217.0
280
172.5
346
10.1
412
0.50
216
207.6
282
159.6
348
9.0
414
0.46
218
206.1
284
147.3
350
8.2
416
0.42
220
212.1
286
136.1
352
7.9
418
0.38
222
227.1
288
125.2
354
6.8
420
0.35
224
249.4
290
114.6
356
6.1
422
0.32
226
280.2
292
104.6
358
5.8
424
0.29
228
319.5
294
95.4
360
5.5
426
0.27
230
365.0
296
87.1
362
4.5
428
0.25
232
415.4
298
79.0
364
4.1
430
0.23
234
467.5
300
72.2
366
3.8
432
0.21
236
517.5
302
65.8
368
3.5
434
0.19
238
563.0
304
59.9
370
3.2
436
0.17
240
600.3
306
54.1
372
2.9
438
0.16
242
625.7
308
48.6
374
2.7
440
0.15
244
639.4
310
43.3
376
2.4
442
0.13
246
642.6
312
38.5
378
2.2
444
0.12
248
631.5
314
34.6
380
2.1
446
0.11
250
609.3
316
30.7
382
1.9
448
0.10
252
580.1
318
28.0
384
1.7
450
0.09
254
544.5
320
25.6
386
1.6
Note: 190-200nm, DeMore and Tschuikow-Roux [32], 200-360 nm, mean of Cox and Hayman [29], Burkholder et al. [13],
Permien et al. [95], and DeMore and Tschuikow-Roux [32], 362-450 nm, log[σ(λ)] = 7.589 - 0.01915 u λ extrapolation
where λ is in nm and σ is in units of 10-20 cm2 molecule-1.
14
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... The gas-phase iodine chemistry is shown in Table 2 (Atkinson et al., 2007) Further, the model includes all the iodine reactions presented by the IUPAC (Atkinson et al., 2007(Atkinson et al., , 2008 and JPL 10-6 (Sander et al., 2011) relevant to the troposphere. ...
... Seven wavelength bin cross-sections are processed, which are used by FAST-J (Bian and Prather, 2002). For most cross-sections, JPL 10-6 (Sander et al., 2011) values were used. In the mode, for I2OX, where X = 2, 3, 4, the same cross-sections as INO3 are assumed to be right, as done in previous work (Bloss et al., 2010). ...
... In the mode, for I2OX, where X = 2, 3, 4, the same cross-sections as INO3 are assumed to be right, as done in previous work (Bloss et al., 2010). For most species like I2, HOI, IO, OIO, INO, INO2, I2O2, CH3I, CH2I2, CH2IBr, and CH2ICl, the quantum yield is assumed to be 1, and for INO3, quantum yield is assumed to be 0.21 (Sander et al., 2011). ...
Thesis
Full-text available
This thesis presents MAX-DOAS observation of iodine oxide (IO) in the Indian Ocean and Southern Ocean marine boundary layer (MBL). This study addresses whether the existing parameterisation tools for inorganic iodine oceanic fluxes are sufficient to explain the detected IO in the remote open ocean MBL. A lack of understanding of the vertical distribution of IO in the atmosphere is evident; thus, vertical profile retrievals of IO from observations are included in this study. Finally, this study quantifies the impact of reactive iodine species on the atmospheric chemistry of the tropical troposphere of the Indian Ocean region. A regional chemistry model extended to include iodine chemistry is used to simulate active iodine gas-phase reactions in a tropical atmosphere comprising photolytic reactions, depositions and heterogeneous pathways.
... The recommended quantum yields at wavelengths above 300 nm, being most important in the lower stratosphere, are 0.85 and 0.15, respectively. While in Sander et al. (2011) a combined uncertainty in cross sections and quantum yields of 1.4 is provided, the most recent evaluations (Burkholder et al., 2015(Burkholder et al., , 2019 assign one wavelength-independent uncertainty factor of 1.2 (2σ ) to the cross sections. Further loss of BrONO 2 is due to atomic oxygen (Soller et al., 2001): ...
... Harder et al., 2000;Pundt, 2002;Dorf et al., 2006aDorf et al., , 2008Stachnik et al., 2013;Kreycy et al., 2013), and from satellites (e.g. Sinnhuber et al., 2005;Livesey et al., 2006;Kovalenko et al., 2007;McLinden et al., 2010;Rozanov et al., 2011;Millán et al., 2012;Parrella et al., 2013). In contrast, BrONO 2 , the most important night-time reservoir of bromine, was detected in infrared limb-emission observations by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) instrument on board the Envisat satellite only a decade ago (Höpfner et al., 2009). ...
... We have applied a comprehensive chemistry set-up from the troposphere to the lower mesosphere with more than 100 species involved in gas-phase, photolysis, and heterogeneous reactions on liquid sulfate aerosols, nitric acid trihydrate (NAT), and ice particles. Rate constants for gas-phase reactions have been taken mainly from Atkinson et al. (2007) and the Jet Propulsion Laboratory (JPL) compilation (Sander et al., 2011). Photochemical reactions of short-lived bromine-containing organic compounds CHBr 3 , CH 2 Br 2 , CH 2 ClBr, CHClBr 2 , and CHCl 2 Br are included in the model set-up (Jöckel et al., 2016). ...
Article
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We present the first observational dataset of vertically resolved global stratospheric BrONO2 distributions from July 2002 until April 2012 and compare them to results of the atmospheric chemical climate model ECHAM/MESSy Atmospheric Chemistry (EMAC). The retrieved distributions are based on space-borne measurements of infrared limb-emission spectra recorded by the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) on Envisat. The derived vertical profiles of BrONO2 volume mixing ratios represent 10∘ latitude bins and 3 d means, separated into sunlit observations and observations in the dark. The estimated uncertainties are around 1–4 pptv, caused by spectral noise for single profiles as well as for further parameter and systematic errors which may not improve by averaging. Vertical resolutions range from 3 to 8 km between 15 and 35 km altitude. All leading modes of spatial and temporal variability of stratospheric BrONO2 in the observations are well replicated by the model simulations: the large diurnal variability, the low values during polar winter as well as the maximum values at mid and high latitudes during summer. Three major differences between observations and model results are observed: (1) a model underestimation of enhanced BrONO2 in the polar winter stratosphere above about 30 km of up to 15 pptv, (2) up to 8 pptv higher modelled values than observed globally in the lower stratosphere up to 25 km, most obvious during night, and (3) up to 5 pptv lower modelled concentrations at tropical latitudes between 27 and 32 km during sunlit conditions. (1) is explained by the model missing enhanced NOx produced in the mesosphere and lower thermosphere subsiding at high latitudes in winter. This is the first time that observational evidence for enhancement of BrONO2 caused by mesospheric NOx production is reported. The other major inconsistencies (2, 3) between EMAC model results and observations are studied by sensitivity runs with a 1D model. These tentatively hint at a model underestimation of heterogeneous loss of BrONO2 in the lower stratosphere, a simulated production of BrONO2 that is too low during the day as well as strongly underestimated BrONO2 volume mixing ratios when loss via reaction with O(3P) is considered in addition to photolysis. However, considering the uncertainty ranges of model parameters and of measurements, an unambiguous identification of the causes of the differences remains difficult. The observations have also been used to derive the total stratospheric bromine content relative to years of stratospheric entry between 1997 and 2007. With an average value of 21.2±1.4 pptv of Bry at mid latitudes where the modelled adjustment from BrONO2 to Bry is smallest, the MIPAS data agree with estimates of Bry derived from observations of BrO as well as from MIPAS-Balloon measurements of BrONO2.
... 12 The observed production of H atoms is due to subsequent photodissociation of the corresponding CHCl2 radical, which can also serve as a hydrogen source to form HCl under high-pressure conditions. 13 With a C−Cl bond strength of ~3.25 eV, 14 a 200 nm photon is sufficient to dissociate CHCl3, 40 which happens with a quantum efficiency Φ=1. 12 We here report the photodissociation dynamics of CHCl3 in a molecular beam using the velocity map imaging technique (VMI) 15 with the aim to extract angularly resolved kinetic energy distributions of chlorine atoms in both spin-orbit states, Cl( 2 P3/2) 45 and Cl*( 2 P1/2), and to determine the [Cl*]/[Cl] branching ratio. ...
Article
Energy- and angle-resolved photofragment distributions for ground-state Cl (²P₃/₂) and spin–orbit excited Cl* (²P₁/₂) have been recorded using the velocity map imaging technique after photodissociation of chloroform at wavelengths of 193 and ∼235 nm. Translational energy distributions are rather broad and peak between 0.6 and 1.0 eV. The spin–orbit branching ratios [Cl*]/[Cl] are 1 and 0.3 at 193 and 235 nm, respectively, indicating the involvement of two or more excited state surfaces. Considering the anisotropy parameters and branching ratios collectively, we conclude that the reaction at 193 nm takes place predominantly on the ¹Q₁ surface, while the ³Q₁ surface gains importance at lower dissociation energies around 235 nm.
... Previous studies suggested that N 2 O 5 uptake in aerosols and clouds was the dominant nitrate production pathway during intense haze events under low temperatures and minimal sunlight conditions 20,21 . Some laboratory studies suggested that the hydrolysis of NO 2 and NO 3 was not important for HNO 3 formation because of its low reaction probability [22][23][24] . A recent model simulation found that NO 2 hydrolysis was a neglected source of nitrate formation on haze days in Beijing winter 11 20 found that nocturnal reactions (including NO 3 + HC and N 2 O 5 uptake) dominated nitrate formation along with high ambient humidity and weak sunlight during polluted days in Beijing. ...
Article
Full-text available
Inorganic nitrate production is critical in atmospheric chemistry that reflects the oxidation capacity and the acidity of the atmosphere. Here we use the oxygen anomaly of nitrate (Δ17O(NO3−)) in high-time-resolved (3 h) aerosols to explore the chemical mechanisms of nitrate evolution in fine particles during the winter in Nanjing, a megacity of China. The continuous Δ17O(NO3−) observation suggested the dominance of nocturnal chemistry (NO3 + HC/H2O and N2O5 + H2O/Cl−) in nitrate formation in the wintertime. Significant diurnal variations of nitrate formation pathways were found. The contribution of nocturnal chemistry increased at night and peaked (72%) at midnight. Particularly, nocturnal pathways became more important for the formation of nitrate in the process of air pollution aggravation. In contrast, the contribution of daytime chemistry (NO2 + OH/H2O) increased with the sunrise and showed a highest fraction (48%) around noon. The hydrolysis of N2O5 on particle surfaces played an important role in the daytime nitrate production on haze days. In addition, the reaction of NO2 with OH radicals was found to dominate the nitrate production after nitrate chemistry was reset by the precipitation events. These results suggest the importance of high-time-resolved observations of Δ17O(NO3−) for exploring dynamic variations in reactive nitrogen chemistry.
... Most of the VOC species of MOM are available for initialization in simulations with MAFOR. Diurnal variation of photolysis rates are based on Landgraf and Crutzen (1998) with the updates included in the JVAL photolysis module (Sander et al., 2014), such as updated UV/VIS cross sections 20 as recommended by the Jet Propulsion Laboratory (JPL), Evaluation no. 17 (Sander et al., 2011). The chemistry mechanism of MECCA was extended by a comprehensive reaction scheme for dimethyl sulphide (DMS) adopted from Karl et al. (2007) and oxidation schemes of several amines: methylamine, dimethylamine, trimethylamine (Nielsen et al., 2011), 2-aminoethanol (Karl et al., 2012b), amino methyl propanol, diethanolamine, and triethanolamine (Karl et al., 2012c). ...
Article
Full-text available
Numerical models are needed for evaluating aerosol processes in the atmosphere in state-of-the-art chemical transport models, urban-scale dispersion models, and climatic models. This article describes a publicly available aerosol dynamics model, MAFOR (Multicomponent Aerosol FORmation model; version 2.0); we address the main structure of the model, including the types of operation and the treatments of the aerosol processes. The model simultaneously solves the time evolution of both the particle number and the mass concentrations of aerosol components in each size section. In this way, the model can also allow for changes in the average density of particles. An evaluation of the model is also presented against a high-resolution observational dataset in a street canyon located in the centre of Helsinki (Finland) during afternoon traffic rush hour on 13 December 2010. The experimental data included measurements at different locations in the street canyon of ultrafine particles, black carbon, and fine particulate mass PM1. This evaluation has also included an intercomparison with the corresponding predictions of two other prominent aerosol dynamics models, AEROFOR and SALSA. All three models simulated the decrease in the measured total particle number concentrations fairly well with increasing distance from the vehicular emission source. The MAFOR model reproduced the evolution of the observed particle number size distributions more accurately than the other two models. The MAFOR model also predicted the variation of the concentration of PM1 better than the SALSA model. We also analysed the relative importance of various aerosol processes based on the predictions of the three models. As expected, atmospheric dilution dominated over other processes; dry deposition was the second most significant process. Numerical sensitivity tests with the MAFOR model revealed that the uncertainties associated with the properties of the condensing organic vapours affected only the size range of particles smaller than 10 nm in diameter. These uncertainties therefore do not significantly affect the predictions of the whole of the number size distribution and the total number concentration. The MAFOR model version 2 is well documented and versatile to use, providing a range of alternative parameterizations for various aerosol processes. The model includes an efficient numerical integration of particle number and mass concentrations, an operator splitting of processes, and the use of a fixed sectional method. The model could be used as a module in various atmospheric and climatic models.
... H 2 O cross sections from Ranjan et al. 2020). The updated cross section and quantum yield data were sourced from Hébrard et al. (2006), Lincowski et al. (2018), the JPL Publication 19-5 recommendations (Burkholder et al. 2019) and the MPI-Mainz UV/VIS Spectral Atlas (Keller-Rudek et al. 2013); and references therein. ...
Preprint
Full-text available
The upcoming deployment of JWST will dramatically advance our ability to characterize exoplanet atmospheres, both in terms of precision and sensitivity to smaller and cooler planets. Disequilibrium chemical processes dominate these cooler atmospheres, requiring accurate photochemical modeling of such environments. The host star's UV spectrum is a critical input to these models, but most exoplanet hosts lack UV observations. For cases in which the host UV spectrum is unavailable, a reconstructed or proxy spectrum will need to be used in its place. In this study, we use the MUSCLES catalog and UV line scaling relations to understand how well reconstructed host star spectra reproduce photochemically modeled atmospheres using real UV observations. We focus on two cases; a modern Earth-like atmosphere and an Archean Earth-like atmosphere that forms copious hydrocarbon hazes. We find that modern Earth-like environments are well-reproduced with UV reconstructions, whereas hazy (Archean Earth) atmospheres suffer from changes at the observable level. Specifically, both the stellar UV emission lines and the UV continuum significantly influence the chemical state and haze production in our modeled Archean atmospheres, resulting in observable differences in their transmission spectra. Our modeling results indicate that UV observations of individual exoplanet host stars are needed to accurately characterize and predict the transmission spectra of hazy terrestrial atmospheres. In the absence of UV data, reconstructed spectra that account for both UV emission lines and continuum are the next best option, albeit at the cost of modeling accuracy.
... Most of the VOC species of MOM are available for initialization in simulations with MAFOR. Diurnal variation of photolysis rates are based on Landgraf and Crutzen (1998) with the updates included in the JVAL photolysis module (Sander et al., 2014), such as updated UV/VIS cross sections 20 as recommended by the Jet Propulsion Laboratory (JPL), Evaluation no. 17 (Sander et al., 2011). The chemistry mechanism of MECCA was extended by a comprehensive reaction scheme for dimethyl sulphide (DMS) adopted from Karl et al. (2007) and oxidation schemes of several amines: methylamine, dimethylamine, trimethylamine (Nielsen et al., 2011), 2-aminoethanol (Karl et al., 2012b), amino methyl propanol, diethanolamine, and triethanolamine (Karl et al., 2012c). ...
Preprint
Full-text available
Numerical models are needed for evaluating aerosol processes in the atmosphere in state-of-the-art chemical transport models, urban-scale dispersion models and climatic models. This article describes a publicly available aerosol dynamics model MAFOR (Multicomponent Aerosol FORmation model; version 2.0); we address the main structure of the model, including the types of operation and the treatments of the aerosol processes. The main advantage of MAFOR v2.0 is the consistent treatment of both the mass- and number-based concentrations of particulate matter. An evaluation of the model is also presented, against a high-resolution observational dataset in a street canyon located in the centre of Helsinki (Finland) during an afternoon traffic rush hour on 13 December 2010. The experimental data included measurements at different locations in the street canyon of ultrafine particles, black carbon, and fine particulate mass PM1. This evaluation has also included an intercomparison with the corresponding predictions of two other prominent aerosol dynamics models, AEROFOR and SALSA. All three models fairly well simulated the decrease of the measured total particle number concentrations with increasing distance from the vehicular emission source. The MAFOR model reproduced the evolution of the observed particle number size distributions more accurately than the other two models. The MAFOR model also predicted the variation of the concentration of PM1 better than the SALSA model. We also analysed the relative importance of various aerosol processes based on the predictions of the three models. As expected, atmospheric dilution dominated over other processes; dry deposition was the second most significant process. Numerical sensitivity tests with the MAFOR model revealed that the uncertainties associated with the properties of the condensing organic vapours affected only the size range of particles smaller than 10 nm in diameter. These uncertainties do not therefore affect significantly the predictions of the whole of the number size distribution and the total number concentration. The MAFOR model version 2 is well documented and versatile to use, providing a range of alternative parametrizations for various aerosol processes. The model includes an efficient numerical integration of particle number and mass concentrations, an operator-splitting of processes, and the use of a fixed sectional method. The model could be used as a module in various atmospheric and climatic models.
Article
Methyl vinyl ketone oxide (MVKO) and methacrolein oxide (MACRO) are resonance-stabilized Criegee intermediates which are formed in the ozonolysis reaction of isoprene, the most abundant unsaturated hydrocarbon in the atmosphere. The absolute photodissociation cross sections of MVKO and MACRO were determined by measuring their laser depletion fraction at 352 nm, which was deduced from their time-resolved UV-visible absorption spectra. After calibrating the 352 nm laser fluence with the photodissociation of NO2, for which the absorption cross section and photodissociation quantum yield are well known, the photodissociation cross sections of thermalized (299 K) MVKO and MACRO at 352 nm were determined to be (3.02 ± 0.60) × 10-17 cm2 and (1.53 ± 0.29) × 10-17 cm2, respectively. Using their reported spectra and photodissociation quantum yields, their peak absorption cross sections were deduced to be (3.70 ± 0.74) × 10-17 cm2 (at 371 nm, MVKO) and (3.04 ± 0.58) × 10-17 cm2 (at 397 nm, MACRO). These values agree fairly with our theoretical predictions and are substantially larger than those of smaller, alkyl-substituted Criegee intermediates (CH2OO, syn-CH3CHOO, (CH3)2COO), revealing the effect of extended conjugation. With their cross sections, we also quantified the synthesis yields of MVKO and MACRO in the present experiment to be 0.22 ± 0.10 (at 299 K and 30-700 torr) and 0.043 ± 0.019 (at 299 K and 500 torr), respectively, relative to their photolyzed precursors. The lower yield of MACRO can be related to the high endothermicity of its formation channel.
Article
Atmospheric nitrous oxide (N2O) contributes to global warming and stratospheric ozone depletion, so reducing uncertainty in estimates of emissions from different sources is important for climate policy. Here, we simulate atmospheric N2O using an atmospheric chemistry-transport model (ACTM), and the results are first compared with the in situ measurements. Five combinations of known (a priori) N2O emissions due to natural soil, agricultural land, other human activities and sea-air exchange are used. The N2O lifetime is 127.6 ± 4.0 yr in the control ACTM simulation (range indicate interannual variability). Regional N2O emissions are optimised by Bayesian inverse modelling for 84 partitions of the globe at monthly intervals, using measurements at 42 sites around the world covering 1997-2019. The best estimate global land and ocean emissions are 12.99 ± 0.22 and 2.74 ± 0.27 TgN yr⁻¹, respectively, for 2000-2009, and 14.30 ± 0.20 and 2.91 ± 0.27 TgN yr⁻¹, respectively, for 2010-2019. On regional scales, we find that the most recent ocean emission estimation, with lower emissions in the Southern Ocean regions, fits better with that predicted by the inversions. Marginally higher (lower) emissions than the inventory/model for the tropical (extra-tropical) land regions is estimated and validated using independent aircraft observations. Global land and ocean emission variabilities show statistically significant correlation with El Niño Southern Oscillation (ENSO). Analysis of regional land emissions shows increases over America (Temperate North, Central, Tropical), Central Africa, and Asia (South, East and Southeast) between the 2000s and 2010s. Only Europe as a whole recorded a slight decrease in N2O emissions due to chemical industry. Our inversions suggest revisions to seasonal emission variations for 3 of the 15 land regions (East Asia, Temperate North America and Central Africa), and the Southern Ocean region. The terrestrial ecosystem model (VISIT) is able to simulate annual total emissions in agreement with the observed N2O growth rate since 1978, but the lag-time scales of N2O emissions from nitrogen fertiliser application may need to be revised.
Article
The temperature dependent kinetics for the reactions between (E)/(Z)- CHF=CHCl and OH radicals were studied using CCSD(T)/cc-pVTZ//M06-2X/6-31+G(d,p) level of theory. The rate coefficients of the studied reaction paths were calculated by Canonical Variational Transition state theory followed by small curvature tunnelling corrections from 200 to 400 K. Various reaction pathways involved in both the reactions were exothermic and spontaneous. The Arrhenius expressions for the title reactions were obtained as k(E)-CHF=CHCl = 5.73 × 10⁻¹⁹ T2.44 exp (622.1/T) and k(Z)-CHF=CHCl = 2.22 × 10⁻¹⁸ T2.17 exp (803.6/T) cm³molecule⁻¹s⁻¹ respectively.
Article
Full-text available
Photodissociation of the ClO dimer (ClOOCl) is studied in the ultraviolet regime (250 and 308 nm) under collision-free conditions. The primary photolysis products are probed by photoionization mass spectrometry. At both photolysis wavelengths, exclusively the formation of 2Cl + O 2 is observed, corresponding to a primary quantum yield γ Cl near unity. Considering the error limit of the experimental results one obtains γ Cl g 0.98 at 250 nm and γ Cl g 0.90 at 308 nm, respectively. At both photolysis wavelengths the pathway yielding ClO is not observed, corresponding to γ ClO e 0.02 at 250 nm and γ ClO e 0.10 at 308 nm. Sensitivity studies of these results with respect to ozone depletion in the stratosphere regarding photochemically induced ozone loss are discussed using model simulations. These simulations suggest that a change of γ Cl from 1.0 to 0.9 leads to a reduction of polar ozone loss of ∼5%.
Article
1] The first measurements of ClOOCl in the stratosphere have been acquired from a NASA ER-2 aircraft, deployed from Kiruna, Sweden (68°N, 21°E), during the joint SOLVE/THESEO-2000 mission of the winter of 1999/2000. ClOOCl is detected by thermal dissociation into two ClO fragments that are measured by the well-known technique of chemical conversion, vacuum ultraviolet resonance fluorescence. Ambient ClO is detected simultaneously. Observations of the ratio [ClOOCl]/[ClO] 2 (estimated uncertainty of ±25%, 1 s) are used with a time-dependent photochemical model, to test the model representation of the ratios of kinetic parameters J/k Prod and k Loss /k Prod for day and nighttime observations, respectively. Here, k Prod and k Loss are the rate constants for ClOOCl production and loss, respectively, and J is the photolysis rate of ClOOCl. The observations are in good agreement with J based upon the 2002 JPL recommended cross sections for ClOOCl [Sander et al., 2003], if the true value of k Prod is given by either the 2000 JPL recommendation [Sander et al., 2000] or the work of Trolier et al. [1990]. The larger values of k Prod given by Bloss et al. [2001] and the 2002 JPL recommendation are consistent with the observations only if J is increased by a significant amount. This is accomplished if J is calculated with the larger ClOOCl cross sections measured by Burkholder et al. [1990]. The J values for ClOOCl based on the Huder and DeMore [1995] cross sections are too small, by factors of $1.6 to 2.5 for all values of k Prod , based on the observations. Nighttime results suggest that, for 190 < T < 200 K, the values for K Eq (the equilibrium constant, equal to the ratio of k Prod /k Loss) of Cox and Hayman [1988] and Avallone and Toohey [2001] are in best agreement with the observations.
Article
The bond strength of chlorine peroxide (ClOOCl) is studied by photoionization mass spectrometry. The experimental results are obtained from the fragmentation threshold yielding ClO+, which is observed at 11.52 +/- 0.025 eV. The O-O bond strength D(o) is derived from this value in comparison to the first ionization energy of ClO, yielding D(o)298 = 72.39 +/- 2.8 kJ mol(-1). The present work provides a new and independent method to examine the equilibrium constant K(eq) for chlorine peroxide formation via dimerization of ClO in the stratosphere. This yields an approximation for the equilibrium constant in the stratospheric temperature regime between 190 and 230 K of the form K(eq) = 1.92 x 10(-27) cm3 molecules(-1) x exp(8430 K/T). This value of K(eq) is lower than current reference data and agrees well with high altitude aircraft measurements within their scattering range. Considering the error limits of the present experimental results and the resulting equilibrium constant, there is agreement with previous works, but the upper limit of current reference values appears to be too high. This result is discussed along with possible atmospheric implications.
Article
The photolysis of chlorine peroxide (ClOOCl) is understood to be a key step in the destruction of polar stratospheric ozone. This study generated and purified ClOOCl in a novel fashion, which resulted in spectra with low impurity levels and high peak absorbances. The ClOOCl was generated by laser photolysis of Cl2 in the presence of ozone, or by photolysis of ozone in the presence of CF2Cl2. The product ClOOCl was collected, along with small amounts of impurities, in a trap at about -125 degrees C. Gas-phase ultraviolet spectra were recorded using a long path cell and spectrograph/diode array detector as the trap was slowly warmed. The spectrum of ClOOCl could be fit with two Gaussian-like expressions, corresponding to two different electronic transitions, having similar energies but different widths. The energies and band strengths of these two transitions compare favorably with previous ab initio calculations. The cross sections of ClOOCl at wavelengths longer than 300 nm are significantly lower than all previous measurements or estimates. These low cross sections in the photolytically active region of the solar spectrum result in a rate of photolysis of ClOOCl in the stratosphere that is much lower than currently recommended. For conditions representative of the polar vortex (solar zenith angle of 86 degrees, 20 km altitude, and O3 and temperature profiles measured in March 2000) calculated photolysis rates are a factor of 6 lower than the current JPL/NASA recommendation. This large discrepancy calls into question the completeness of present atmospheric models of polar ozone depletion.
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