Study of the atmospheric chemistry of 2-formylcinnamaldehyde

Article abstract of DOI:10.1021/jp404994w

2-Formylcinnamaldehyde is a significant product of the reaction of naphthalene with OH radicals, and its photolysis and gas-phase reactions with O₃, NO₃ radicals, and OH radicals have been investigated in this work. 2-Formylcinnamaldehyde was observed to undergo photolysis by black lamps, with a photolysis rate of 0.14 × J(NO₂), where J(NO₂) is the NO₂ photolysis rate. The measured rate constants for the reactions of 2-formylcinnamaldehyde with O₃, NO₃ radicals, and OH radicals (in units of cm³ molecule^-1 s^-1) were 1.8 × 10^-18, 4.3 × 10^-14, and 2.1 × 10^-11, respectively, with those for the O₃ and NO₃ reactions being for the E-isomer. 2-Formylcinnamaldehyde was observed to undergo significant adsorption and desorption from the reaction chamber Teflon film walls, and the photolysis rate and rate constants are subject to significant uncertainties. In the atmosphere, the dominant chemical loss processes for 2-formylcinnamaldehyde will be photolysis during daylight hours and reaction with NO₃ radicals during nighttime. Phthaldialdehyde and glyoxal were observed as products of the OH radical and O₃ reactions, and photolysis of E-2- formylcinnamaldehyde led to formation of Z-2-formylcinnamaldehyde plus two other molecular weight 160 isomers. The present results are compared with previous literature data, and reaction mechanisms are discussed.

Full text of DOI:10.1021/jp404994w

Article
pubs.acs.org/JPCA
Study of the Atmospheric Chemistry of 2‑Formylcinnamaldehyde
,†
Sara M. Aschmann, Janet Arey,* and Roger Atkinson*
Air Pollution Research Center, University of California Riverside, California 92521, United States
*
S Supporting Information
ABSTRACT: 2-Formylcinnamaldehyde is a significant product of the reaction of naphthalene
with OH radicals, and its photolysis and gas-phase reactions with O , NO radicals, and OH
3
3
radicals have been investigated in this work. 2-Formylcinnamaldehyde was observed to undergo
photolysis by black lamps, with a photolysis rate of 0.14 × J(NO ), where J(NO ) is the NO
2
2
2
photolysis rate. The measured rate constants for the reactions of 2-formylcinnamaldehyde with
3
−1 −1
−18
O , NO radicals, and OH radicals (in units of cm molecule s ) were 1.8 × 10 , 4.3 ×
3
3
−
14
−11
10
, and 2.1 × 10 , respectively, with those for the O and NO reactions being for the E-
3 3
isomer. 2-Formylcinnamaldehyde was observed to undergo significant adsorption and desorption from the reaction chamber
Teflon film walls, and the photolysis rate and rate constants are subject to significant uncertainties. In the atmosphere, the
dominant chemical loss processes for 2-formylcinnamaldehyde will be photolysis during daylight hours and reaction with NO3
radicals during nighttime. Phthaldialdehyde and glyoxal were observed as products of the OH radical and O reactions, and
3
photolysis of E-2-formylcinnamaldehyde led to formation of Z-2-formylcinnamaldehyde plus two other molecular weight 160
isomers. The present results are compared with previous literature data, and reaction mechanisms are discussed.
INTRODUCTION
Naphthalene is the most abundant polycyclic aromatic
hydrocarbon in ambient air, being emitted into the atmosphere
were carried out at a light intensity corresponding to an NO
2
■
−
1
photolysis rate of 0.144 min . E-2-FC [11.6−17.9 mg
1
2
−3
(
corresponding to (5.8−9.0) × 10 molecules cm in the
1
−4
chamber if introduced quantitatively)] was flushed into the
primarily from vehicle exhaust.
In the atmosphere,
chamber with a stream of N gas while being gently heated.
naphthalene is chemically removed by daytime reaction with
OH radicals and evening and nighttime reaction with NO3
2
Dark Decays of 2-Formylcinnamaldehyde. Dark decays
of E-2-FC were routinely measured by monitoring the
concentration of E-2-FC, on a relative basis, in the chamber
over periods of up to 6.7 h. In certain dark decay experiments,
5
radicals. The daytime reaction with OH radicals is estimated to
5
be the dominant naphthalene transformation process, with the
reaction proceeding by initial addition to form OH−
naphthalene adducts, which subsequently react with O and
2
cyclohexane or NO was added to simulate the prereaction
2
NO (in air the two reactions are of equal importance for an
conditions in kinetic experiments. 2-FC concentrations were
measured during experiments by gas chromatography with
2
1
2
−3
NO concentration of ∼1.5 × 10 molecules cm (∼60 parts-
2
6
1
4
per-billion mixing ratio)). 2-Formylcinnamaldehyde (meas-
flame ionization detection (GC−FID). Samples were
collected on a 65 μm poly(dimethylsiloxane)/divinylbenzene
solid-phase microextraction (SPME) fiber, by exposing the fiber
to the chamber contents for 20 min with the mixing fan on.
The SPME fibers were thermally desorbed at 270 °C onto a
DB-5 megabore column, initially held at 40 °C and then
ured as a mixture of the E- and Z-isomers) is an important first-
generation product of the OH radical-initiated reaction,
7
−14
with a formation yield which ranges from ∼14% under
conditions where the OH−naphthalene adducts react only
with O to ∼56% for conditions where the OH−naphthalene
2
8
,10,14
adducts react only with NO .
2
−1
temperature-programmed at 8 °C min . SPME fibers exposed
To date, information concerning photolysis and reaction with
OH radicals of 2-formylcinnamaldehyde (2-FC) has been
obtained from the behavior of 2-FC in irradiated CH ONO−
NO−naphthalene−air mixtures using direct air sampling
to the standard of Z-2-FC introduced into the chamber and to
an irradiated CH ONO−NO−naphthalene−air mixture (which
3
3
8
leads to the formation of Z- and E-2-FC ) were analyzed by
10
combined gas chromatography−mass spectrometry (GC−MS),
using a 60 m DB-5 capillary column in an Agilent 6890N GC
interfaced to an Agilent 5973N mass selective detector operated
in positive chemical ionization (PCI) mode with methane as
the CI gas. These GC−MS analyses provided the retention
times of the E- and Z- isomers of 2-FC and confirmed that the
minor impurity in the E-2-FC sample was the Z-isomer and
atmospheric pressure ionization mass spectrometry. In this
work, we have used a synthesized sample of E-2-formylcinna-
maldehyde (E-2-FC) to investigate its photolysis and reactions
with OH radicals, NO radicals, and O . During our study, it
3
3
became evident that partitioning of 2-FC to the chamber walls
presented significant problems.
EXPERIMENTAL METHODS
■
All experiments were carried out in a ∼7200 L Teflon chamber
equipped with two parallel banks of black lamps for irradiation,
at 298 ± 2 K and ∼735 torr of dry purified air. All irradiations
Received: May 21, 2013
Revised: July 24, 2013
Published: August 7, 2013
©
2013 American Chemical Society
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The Journal of Physical Chemistry A
Article
−
3
allowed the Z-isomer to be identified and quantified in the
GC−FID analyses.
concentrations (in molecules cm ) were the following:
13
13
reference compound, ∼2.4 × 10 ; NO , ∼(4.8−9.6) × 10 ;
and four additions of N O were made to the chamber, with
2
Kinetics of O Reaction. For the O reaction, the decay of
3
3
2
5
1
2
E-2-FC was measured in the presence of O over periods of
each addition of N O corresponding to (4.8−24) × 10
3
2
5
15
−3
6
.6−6.8 h, and in two of the three experiments 2.2 × 10
molecules cm of cyclohexane was present in the chamber to
scavenge any OH radicals formed. Assuming that the only loss
molecules cm
in the chamber, except for the initial
−3
experiment which had only two additions of N O ,
2
5
corresponding to 12 × 1013 and 6.0 × 10 molecules cm
13
−3
process for E-2-FC was by reaction with O3
of N O in the chamber. Dilutions caused by additions of N O
2
5
2
5
to the chamber during the NO radical reactions were minor
3
O + E‐2‐formylcinnamaldehyde → products
(1)
3
(
≤1%) and were taken into account in the data analysis.
2-FC was monitored as described above. The concentrations
then
ln([E‐2‐FC] /[E‐2‐FC] ) = k [O ](t − t )
of the reference compounds were measured during the
to
t
1
3
o
(I)
experiments by GC−FID. For the analysis of 1,3,5-
3
trimethylbenzene and thiophene, gas samples of 100 cm
where [E-2-FC] and [E-2-FC] are the concentrations of E-2-
to
t
FC at times t and t, respectively, and k is the rate constant for
volume were collected from the chamber onto Tenax-TA
adsorbent, with subsequent thermal desorption at ∼205 °C
onto a 30 m DB-1701 megabore column, initially held at −40
°C and then temperature programmed to 250 °C at 8 °C
o
1
reaction 1. O concentrations were measured by ultraviolet
3
absorption using a Thermo Electron Corporation 49i ozone
monitor, and the initial and average O concentrations were
3
1
3
−3
13
−1
(
3.33−5.69) × 10 molecules cm and (3.21−5.40) × 10
molecules cm , respectively. 2-FC was monitored as described
above.
min . For the analysis of 1-butene, gas samples were collected
−3
3
from the chamber into a 100 cm volume all-glass gas-tight
3
syringe and transferred via a 1 cm gas sampling loop onto a 30
Kinetics of OH and NO3 Radical Reactions. Rate
m DB-5 megabore column initially held at −25 °C and then
−1
constants for the reactions of OH radicals and NO radicals
temperature programmed to 200 °C at 8 °C min . Replicate
analyses of the reference compounds showed that their
measurement uncertainties were typically ≤2%.
3
with 2-FC (E-2-FC for the NO radical reaction and, because of
3
E-/Z- interconversion, an E-/Z- mixture for the OH radical
15
reaction) were measured using a relative rate method, in
which the relative disappearance rates of 2-FC and a reference
compound (whose rate constant for reaction with OH radicals
Photolysis. In these experiments, the concentration of 2-FC
(Z- and E-isomers) was monitored in the dark over a period of
1
.0−1.8 h, followed by two sequential 7−20 min irradiation
or NO radicals is reliably known) were measured in the
3
periods with two or three analyses of 2-FC before and after
each irradiation period. Cyclohexane (2.2 × 10 molecules
cm ) was present in the chamber to scavenge any OH radicals
formed during photolysis of 2-FC.
1
5
presence of OH radicals or NO radicals.
3
−3
OH (or NO ) + 2‐formylcinnamaldehyde → products
3
(2)
Product Formation. GC−MS analyses were conducted on
samples collected onto SPME fibers after photolysis of E-2-FC
OH (or NO ) + reference compound → products
(3)
3
and after irradiation of CH ONO−NO−E-2-FC−air mixtures.
3
Providing that the only loss processes for 2-FC and the
reference compound were by reaction with OH radicals or NO3
radicals, then
In addition, samples were collected after these reactions for 60
−1
min at 15 L min onto an XAD-coated annular denuder,
further coated with O-(2,3,4,5,6-pentafluorobenzyl)-
hydroxylamine (PFBHA) prior to sampling to derivatize
carbonyls to their oximes, and extracted as described
⎛
ln⎜
⎝
⎞
⎛
⎞
⎟
[
2‐FC]to
k2 [reference compound]to
⎟ = ln⎜
[2‐FC] ⎠
k3 ⎝ [reference compound] ⎠
16
t
t
(II)
previously. The extracts were analyzed by PCI GC−MS
using the instrumentation noted above and by GC−FID using a
where [2-FC]to and [reference compound]to are the concen-
trations of 2-FC and the reference compound, respectively, at
time t , [2-FC] and [reference compound]t are the
3
0 m DB-5 column. Each carbonyl group derivatized to an
oxime adds 195 mass units to the compound’s molecular weight
MW), and methane-PCI gives characteristic protonated
o
t
(
corresponding concentrations at time t, and k and k are the
2
3
+
+
molecules ([M + H] ) and smaller adduct ions at [M + 29]
and [M + 41] .
rate constants for reactions 2 and 3, respectively.
OH radicals were generated from the photolysis of
+
16
Chemicals. The chemicals used, and their stated purity
levels, were the following: cyclohexane (99.9+%), phthaldialde-
hyde [2-formylbenzaldehyde or phthalic dicarboxaldehyde]
CH ONO at wavelengths >300 nm, and NO was included in
3
the reactant mixtures to minimize formation of O and hence of
3
NO radicals. 1,3,5-Trimethylbenzene was used as the reference
3
(
97%), phthalic anhydride (99+%), thiophene (99+%), and
compound for the OH radical kinetics, and the initial
−
3
1,3,5-trimethylbenzene (98%), Aldrich; O-(2,3,4,5,6-
pentafluorobenzyl)hydroxylamine hydrochloride (99+%), Alfa
Aesar; E-2-formylcinnamaldehyde (containing ∼1.2% of the Z-
isomer based on the SPME fiber analyses and assuming equal
collection efficiencies on the SPME fiber for the E- and Z-
isomers), Hestia Laboratories, Inc.; and 1-butene (99%) and
concentrations (in molecules cm ) of CH ONO, NO, and
3
1
4
14
1
1
,3,5-trimethylbenzene were ∼2.4 × 10 , ∼2.4 × 10 (∼1.2 ×
14
13
0
in one experiment), and ∼2.4 × 10 , respectively. Two
irradiation periods were carried out in each experiment, of 10 +
1
0 min or 5 + 5 min. NO radicals were generated from the
3
thermal decomposition of N O , with NO being included in
2
5
2
the reactant mixtures. 1-Butene was used as the reference
compound in the initial two experiments, but because E-2-FC
was found to be significantly more reactive than 1-butene
NO (≥99.0%), Matheson Gas Products. NO
needed by reacting NO with an excess of O
prepared as needed using a Welsbach T-408 ozone generator.
2
was prepared as
, and O was
2
3
17
toward NO radicals, thiophene was used as the reference
Methyl nitrite was prepared as described by Taylor et al. and
stored at 77 K under vacuum.
3
compound in subsequent experiments. The initial reactant
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The Journal of Physical Chemistry A
Article
RESULTS
■
Kinetic Studies. Dark Decays of E-2-Formylcinnamalde-
hyde. After introduction into the chamber in the dark, E-2-FC
Figure 3. Plots of the measured decays rates of E-2-formylcinna-
maldehyde (E-2-FC) against the average O concentrations during the
3
1
5
experiments. ○, Experiments in the presence of 2.2 × 10 molecules
−
3
cm of cyclohexane to scavenge any OH radicals formed; ●,
experiment in the absence of added cyclohexane. The indicated errors
are two least-squares standard deviations of the slopes of the plots
shown in Figure 2.
Figure 1. Plots of the decays of E-2-formylcinnamaldehyde (E-2-FC),
defined as ln([E-2-FC] /[E-2-FC] ), against time from the first
to
t
analysis for the long-duration dark decay experiments. ○, Initial
experiment, MTC-2565; △, MTC-2567; ▽, MTC-2569, with 2.2 ×
1
5
−3
1
×
1
0
molecules cm of cyclohexane present; □, MTC-2571, with 4.8
13
−3
10 molecules cm of NO present; ◇, MTC-2575, with 9.6 ×
2
3
01 molecules cm of NO present. The two solid lines are for
−3
2
illustrative purposes only.
Figure 4. Plot of eq II for the reaction of NO radicals with E-2-
3
formylcinnamaldehyde (E-2-FC). ○, △, ▽, Experiments with
thiophene as the reference compound; ■, ⧫, experiments with 1-
butene as the reference compound. The measured values of ln([1-
butene] /[1-butene] ) have been converted to values of ln-
to
t
(
[thiophene] /[thiophene] ) by multiplication by 3.175 (=1/0.315).
to t
Figure 2. Plot of eq I for the reaction of O3 with E-2-
formylcinnamaldehyde (E-2-FC). The O concentrations are listed
3
−3
in the figure in molecules cm units. △, ▽, Experiments in the
presence of 2.2 × 10 molecules cm of cyclohexane to scavenge any
OH radicals formed; ●, experiment in the absence of added
the chamber walls would, if anything, decrease with increasing
exposure of E-2-FC to the chamber walls; the reasons for the
observed behavior are not obvious.
15
−3
cyclohexane.
Kinetic experiments in which the dark decay of E-2-FC was
monitored for 2−3 h prior to photolysis or reaction with OH
radicals, NO radicals, or O all showed dark decays similar to
initially decayed rapidly, with the decay rate decreasing until the
3
3
E-2-FC concentration approached a plateau value. Decays of E-
those over the same time period shown in Figure 1 (i.e., they
2
-FC, defined as ln([E-2-FC] /[E-2-FC] ), are plotted against
would fit on the upper curve in Figure 1). This behavior is that
to
t
18
time from the first analysis for those dark decay experiments
extending for ≥4 h in Figure 1. The first experiment involving
E-2-FC (MTC-2565, denoted by the ○ symbol in Figure 1)
had both a slower initial decay rate and a lower plateau overall
decay than subsequent experiments (Figure 1). A priori, it was
anticipated that the rate and extent of partitioning of E-2-FC to
expected for equilibrium partitioning to the Teflon film and
obviously made measurements of the photolysis rate of E-2-FC
and rate constants for its reactions with OH radicals, NO3
radicals, and O more difficult. In the kinetic experiments, the
3
2-FC concentrations were monitored in the dark for ≥141 min
(a time when the initially rapid 2-FC decay rate had slowed
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The Journal of Physical Chemistry A
Article
Figure 5. Plot of eq II for the reaction of NO radicals with E-2-
Figure 7. Plot of the measured signals due to E- and Z-2-FC as a
function of time during OH radical reaction, experiment MTC-2587,
with two irradiation periods of 5 min each (indicated by the vertical
3
formylcinnamaldehyde (E-2-FC) for values of ln([E-2-FC] /[E-2-
to
FC] ) < 2.0. ○, △, ▽, Experiments with thiophene as the reference
t
compound; ■, experiment with 1-butene as the reference compound.
dashed lines). Initial mixture was CH ONO−NO−E-2-FC−1,3,5-
3
The measured values of ln([1-butene] /[1-butene] ) have been
trimethylbenzene−air.
to
t
converted to values of ln([thiophene] /[thiophene] ) by multi-
to
t
plication by 3.175 (=1/0.315).
Figure 8. Plot of ln([2-FC] /[2-FC] ) as a function of time during
to
t
experiment MTC-2587 with two irradiation periods of 5 min each (the
midpoints being indicated by the vertical dashed lines), where [2-FC]
is the sum of E- + Z-2-FC (the isomer-specific data are shown in
Figure 7).
Figure 6. Plot of the measured signals due to E- and Z-2-FC as a
function of time during photolysis experiment MTC-2581, with two
irradiation periods of 15 min each (indicated by the vertical dashed
lines). Initial mixture was E-2-FC and cyclohexane (to scavenge any
OH radicals formed from the photolysis of 2-FC).
against the average O concentrations in Figure 3 (the O
3
3
concentrations decreased by between 8% and 13% over the
.90−3.95 h reaction times). A good straight line plot is
observed, and a least-squares analysis led to a measured rate
constant for the reaction of O with E-2-FC of
down significantly) before initiating photolysis or reaction with
3
OH radicals, NO radicals, or O .
3
3
Reaction with O . As noted above, E-2-FC was introduced
3
1
5
−3
into the chamber (with 2.2 × 10 molecules cm of
cyclohexane present in two of the three experiments), and O3
was introduced 172−193 min after introduction of E-2-FC. The
subsequent E-2-FC concentrations are plotted in accordance
3
−18
3
−1 −1
k (O + E‐2‐FC) = 1.8 × 10 cm molecule s
1
3
While the two least-squares standard deviation uncertainty in
the slope of the plot in Figure 3 is ±14% and the estimated
uncertainty in the average O3 concentrations during the
experiments is ±10%, the likelihood of wall adsorption and/
or desorption of E-2-FC during the experiments means that the
with eq I in Figure 2, with [E-2-FC] being the measured E-2-
to
FC concentration 13−14 min after addition of O (the time
3
being the midpoints of the 20 min SPME sampling periods).
Reasonably good straight line plots are observed, and within
the experimental uncertainties the E-2-FC decay rate is not
dependent on the presence of cyclohexane to scavenge OH
overall uncertainty in our measured rate constant for O + E-2-
3
FC is much larger (see the Discussion section below).
radicals, suggesting that the O + 2-FC reaction does not lead
to significant OH radical formation. The slopes of the plots
shown in Figure 2 (i.e., the E-2-FC decay rates) are plotted
Reaction with NO Radicals. In a similar manner to the O
3
3
3
reactions, mixtures of E-2-FC, NO , and the reference
2
compound were left in the chamber in the dark for 144−187
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The Journal of Physical Chemistry A
Article
Table 2. Products Observed from Photolysis and Reactions
of 2-Formylcinnamaldhyde (2-FC) with O , NO Radicals,
3
3
and OH Radicals
observed from reaction of E-2-FC with
product
O3
yes ,
ab
NO3
OH
ab
photolysis
c
yes ,
phthaldialdehyde (MW 134)
phthalic anhydride (MW 148)
Z-2-FC
yes
a
a
yes
minor
no
no
yes
yes
yes
8
MW 160 #1 in Sasaki et al.
MW 160 #4 in Sasaki et al.
8
b
b
glyoxal
yes
yes
a
Identified by matching retention time and mass spectrum with those
of an authentic standard in GC−MS analysis of a SPME fiber sample.
b
Observed as its oxime from GC-MS analysis of an extract of a
c
PFBHA-coated denuder sample. Identified by matching retention
time with that of an authentic standard in GC−FID analysis of a
SPME fiber sample.
Figure 9. Plots of {2-FC decay rate/J(NO )} against [OH]/J(NO )
2
2
for the photolysis of 2-formylcinnamaldehyde (2-FC) and its reaction
with OH radicals, from irradiation of 2-FC−air (with cyclohexane to
scavenge any OH radicals formed) and CH ONO−NO−E-2-FC−
3
1
,3,5-trimethylbenzene−air mixtures. ○, Present work, using a sample
10
of E-2-FC; △, Nishino et al., with a Z- + E-2-FC mixture formed in
situ from OH + naphthalene.
min before the first addition of N O was made, and the first
2
5
postreaction analysis midpoint was 23−55 min later. 1-Butene
was used as the reference compound in the first two
experiments but was found to be significantly less reactive
than E-2-FC. Thiophene was used as the reference compound
in an additional three experiments. The E-2-FC and thiophene
data are plotted in accordance with eq II in Figure 4, with [E-2-
FC] being the E-2-FC concentration in the analysis prior to
to
addition of N O . The data with 1-butene as the reference
2
5
compound are also included in Figure 4, using a rate constant
Figure 10. Plot of phthaldialdehyde formed (uncorrected for any
reactive losses) against the amount of 2-FC photolyzed or reacted with
O , NO radicals, and OH radicals.
19−21
ratio of k(NO + 1-butene)/k(NO + thiophene) = 0.315
3
3
to scale the values of ln([reference compound] /[reference
to
3
3
compound] for 1-butene to those for thiophene.
t
Table 1. Rate Constants for Reaction of O , NO Radicals, and OH Radicals with 2-Formylcinnamaldehyde (2-FC) and
3
3
Photolysis Rate of 2-Formylcinnamaldehyde for Irradiation by Black Lamps, Together with Literature Data for Benzaldehyde
and E-Cinnamaldehyde
room temperature rate constant (cm molecule s−1) or {photolysis rate/J(NO )}
3
−1
2
2
-FC
a
b
c
d
reaction with
this work
Nishino et al.
benzaldehyde
E-cinnamaldehyde
1.8 × 10−
4.3 × 10−
2.1 × 10−
18
<10−20
(2.2 ± 1.8) × 10
(1.9 ± 0.7) × 10
(4.8 ± 1.4) × 10
−18
−14
−11
O3
NO3
OH
14
11
2.4 × 10−15
(7.7 ± 2.7) × 10−11
(0.66 ± 0.45) × J(NO2)
1.26 × 10
−11
e
f
photolysis
0.14 × J(NO2)
(0.14 ± 0.03) × J(NO2)
a
The rate constants for the O reaction and the NO radical reaction are for E-2-FC. The measured Z- and E-2-FC isomer distributions during the
3
3
photolysis and OH radical reactions are shown in Figures 6, 7, and S1−S6, with an E-/Z-isomer ratio of typically >1. In view of the significant
uncertainties in the measured rate constants due to the occurrence of wall adsorption/desorption of 2-FC to the chamber walls during the
experiments (see Figure 1 and associated text and the Discussion), no error limits on the cited rate constants are given. As noted in the Discussion, it
b
is likely that these cited rate constants are actually lower limits because of 2-FC desorption from the walls as the reactions progressed. From a least-
1
0
squares analysis of the data of Nishino et al. for the Z- + E-FC isomer distribution present in irradiated CH ONO−NO−naphthalene−air mixtures
3
(
Figure 9). A SPME fiber measurement in this work of an OH + naphthalene reaction showed an E-/Z-isomer ratio of 36:64 for conditions similar to
those employed by Nishino et al. The rate constants for the O reaction (estimated based on data for other aldehydes and aromatic compounds)
and the NO radical reaction are from Atkinson and Arey. The rate constant for reaction with OH radicals is from the IUPAC evaluation. From
Smith et al. Relative to the NO photolysis rate J(NO ); all irradiations were with black lamps. Photolysis rate refers to loss of E-cinnamaldehyde,
10 c
3
2
3
25 d
3
2
6
e
f
2
2
2
6
with formation of the Z-isomer accounting for 57 ± 7% of the E-cinnamaldehyde photolyzed. The photolysis rate leading to loss of Z- + E-
cinnamaldehyde would be 0.06 ± 0.02 × J(NO2).
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1
0
Figure 4 shows that as the reactions proceed, the slope of the
plot decreases with increasing extent of reaction, and hence that
E-2-FC must be desorbing back from the chamber walls into
the gas phase as the reaction proceeds in order to re-establish
the gas−wall equilibrium. Figure 5 shows the experimental data
at relatively low extents of reaction (ln([E-2-FC] /[E-2-FC] <
low concentrations of Z-2-FC (∼(7−11) × 10 molecules
−3
cm from its minor presence in the E-2-FC sample).
Since E-2-FC clearly undergoes photoisomerization to form
Z-2-FC, the sum of Z- + E-2-FC was used to obtain an average
photolysis rate and OH radical reaction rate constant. No dark
losses of 1,3,5-trimethylbenzene were observed, and values of
ln([1,3,5-trimethylbenzene] /[1,3,5-trimethylbenzene] ) were
to
t
2.0). While the plot may still exhibit curvature, especially during
to
t
the periods up to the first data point for each experiment, this
could be due to E-2-FC initially undergoing wall adsorption/
absorption just after the N O addition or E-2-FC desorbing
back from the walls as the reaction proceeds. A least-squares
analysis of the data shown in Figure 5 leads to a rate constant
ratio of
therefore readily determined in the OH radical reactions. For
quantifying 2-FC, extrapolation of the Z- and E-2-FC
concentration data to the midpoints of the irradiation periods
was carried out, using the dark decay behavior shown in Figure
1 as a guide to the preirradiation portion of the experiments. By
summing the concentrations of Z- and E-2-FC (this assumes
that the SPME fiber collection efficiencies for Z- and E-2-FC
are identical), values of ln([2-FC] /[2-FC] ) were obtained for
2
5
k (NO + E‐2‐FC)/k (NO + thiophene) = 1.11 ± 0.19
2
3
3
3
to
t
each irradiation period. In a second approach, values of Z- + E-
where the indicated error is two least-squares standard
2
-FC were used and extrapolated to the midpoints of the
deviations. Combined with k (NO + thiophene) = 3.93 ×
3
3
−14
3
−1 −1
22
irradiation periods assuming exponential decays (or increases)
in their concentrations. An example of this approach is shown
in Figure 8 for MTC-2587 (the same data as shown in the
isomer-specific form in Figure 7).
10
cm molecule
s
at 298 K, this results in
k (NO + E‐2‐FC)
2
3
14
3
−1 −1
=
4.3 × 10− cm molecule
s
at 298 ± 2K
Since photolysis also occurs in the OH radical reactions, the
10
data analysis approach of Nishino et al. was used to obtain the
-FC photolysis rate and OH radical reaction rate constant. For
the reactions
While the two least-squares standard deviation uncertainty in
2
the slope of the plot in Figure 5 is ±17%, wall desorption of E-
2-FC, even during the initial stages of the experiments used for
the plot in Figure 5, means that the overall uncertainty in our
measured rate constant ratio, and hence rate constant for NO3
2
‐FC + hν → products other than 2‐FC
(4)
(2)
+
E-2-FC, is much larger and our cited rate constant may well
OH + 2‐FC → products
be a lower limit (see the Discussion section below).
then
Photolysis and Reaction with OH Radicals. In a similar
manner to the O and NO radical reactions, mixtures of E-2-
FC and cyclohexane (to scavenge any OH radicals formed in
3
3
2‐FC decay rate = d ln[2‐FC]/dt = kphot + kOH[OH]
(III)
the photolysis experiments) or E-2-FC, CH ONO, NO, and
the reference compound 1,3,5-trimethylbenzene (in the OH
3
and
radical reactions) were left in the chamber in the dark for 141−
2
‐FC decay rate/J(NO ) = (k
+ kOH[OH])/J(NO2)
2
phot
194 min prior to the first irradiation. Two irradiations were
(
IV)
carried out in each experiment, with two or three analyses of 2-
FC and, when present, 1,3,5-trimethylbenzene before the initial
irradiation and after each of the two irradiation periods. In
these experiments, formation of Z-2-FC was observed, and
hence both Z- and E-2-FC were measured from the SPME fiber
analyses. Typical plots of the concentrations of Z- and E-2-FC
as a function of time during these experiments are shown in
Figure 6 (photolysis, experiment MTC-2581) and Figure 7
where J(NO ) is the light intensity in terms of the NO
photolysis rate. Hence a plot of {2-FC decay rate/J(NO )}
against [OH]/J(NO ) should have a slope of k
intercept of kphot/J(NO ). While the use of eq IV, involving
2
2
2
and an
2
OH
2
J(NO ), is not necessary for the data analysis from the present
2
study (which was carried out at a constant light intensity, and
hence a plot of 2-FC decay rate versus [OH] would have a
slope of kOH and an intercept of kphot), it is needed for
comparison with the previous study of Nishino et al. carried
out at various light intensities. The average OH radical
concentrations during each irradiation period in the irradiated
(
OH radical reaction, MTC-2587, which of course also includes
10
photolysis). Corresponding plots for the other three photolysis
experiments and the other three OH radical reactions are
shown in the Supporting Information (Figures S1−S6). The
photolysis and OH radical reactions were similar in behavior,
involving (a) preirradiation loss of E-2-FC to the walls, with the
decay rate decreasing with time as observed in the dark decay
experiments (Figure 1) and a concurrent slight increase in the
gas-phase Z-2-FC due to desorption from the walls (in the first
of these experiments, the Z-2-FC concentration remained very
low, as shown in Figure S1); (b) a marked decrease in the gas-
phase E-2-FC concentration and a marked increase in the gas-
phase Z-2-FC concentration upon irradiation, (c) a decrease in
the Z-2-FC gas-phase concentration with time after the
irradiation, and often a concurrent increase in the E-2-FC, re-
establishing the gas−wall equilibria. In the first two experi-
ments, a very rapid decrease in the Z-2-FC concentration after
the irradiations was observed (Figures S1 and S2), presumably
because the chamber walls had previously been exposed to only
CH ONO−NO−2-FC−1,3,5-trimethylbenzene−air mixtures
3
were determined from the 1,3,5-trimethylbenzene decays, with
[
OH] = ln([1, 3, 5‐trimethylbenzene]to
/
[1, 3, 5‐trimethylbenzene] )/k (t − t )
(V)
t
3
o
by use of k = 5.67 × 10− cm molecule s . As noted
11
3
−1 −1 23
3
above, the concentrations of 1,3,5-trimethylbenzene before and
after each irradiation period could be precisely measured, with
two or three replicate analyses before the first irradiation
period, between the first and second irradiation periods, and
after the second irradiation period agreeing to within 1.6%. For
example, for MTC-2587, the two replicate preirradiation
analyses agreed to within 1.5%, and the values of ln([1,3,5-
trimethylbenzene] /[1,3,5-trimethylbenzene] ) after the first
to
t
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Scheme 1
Scheme 2
2
4
and second irradiation periods were 1.4749, 1.4806, and 1.4861
and 2.6101 and 2.5971, respectively, using the average of the
the rate constant for OH + 1,3,5-trimethylbenzene, wall
desorption and adsorption of E- and Z-2-FC means that the
overall uncertainties in our measured photolysis rate and rate
constant for reaction with OH radicals are much larger and our
cited photolysis rate and OH radical reaction rate constant are
likely to be lower limits (see the Discussion section below).
Table 1 summarizes the kinetic data obtained in this study.
Products of the Reactions of 2-Formylcinnamaldehyde.
Phthaldialdehyde (2-formylbenzaldehyde) and phthalic anhy-
dride were identified by matching retention times and mass
spectra in GC−MS analyses of SPME fiber samples with those
of authentic standards introduced into the chamber and
similarly sampled. Glyoxal was identified by GC−MS analyses
two preirradiation analyses for [1,3,5-trimethylbenzene] . The
to
uncertainty in the rate constant for OH + 1,3,5-trimethylben-
24
zene is estimated to be ∼± 10%.
The data from the eight experiments (four photolysis
experiments with cyclohexane to scavenge OH radicals and
hence with an assumed [OH] of zero, four experiments with
CH ONO present to generate OH radicals, and with two
3
irradiation periods per experiment (each treated as an
independent experiment) and with two methods of deriving
the 2-FC decay rate) are plotted in Figure 9 in accordance with
eq IV. A least-squares analysis leads to values of
of extracts of PFBHA-coated denuder samples from the O and
kphot/J(NO ) = 0.14
3
2
OH radical reactions. The products observed are listed in Table
2. GC−MS analyses of SPME fiber samples showed that
photolysis of E-2-FC led to formation of Z-2-FC plus two other
molecular weight 160 products. These two additional molecular
weight 160 products are presumably those observed in low
and
kOH = 2.1 × 10−11 cm3 molecule
−1 −1
s
While the two least-squares standard deviation uncertainties in
8
the intercept (kphot/J(NO )) and slope (kOH) of the plot in
yield by Sasaki et al. from the OH radical-initiated reaction of
2
Figure 9 are ±15% and ±7%, respectively, and do not take into
naphthalene. In an irradiated CH ONO−NO−E-2-FC−air
3
account the estimated ∼± 10% uncertainties in J(NO ) and in
mixture, in addition to formation of Z-2-FC and the other
2
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two molecular weight 160 products, phthaldialdehyde, glyoxal,
and phthalic anhydride were observed. The formation of Z-2-
FC and the other two molecular weight 160 products is
attributed to photolysis of E-2-FC, and hence the OH + 2-FC
reaction forms glyoxal and phthaldialdehyde, with phthalic
anhydride likely being formed as a second-generation product
Scheme 4
27
from OH + phthaldialdehyde. GC−FID analyses of extracts
of PFBHA-coated denuder samples showed that, after
correction for the differing GC−FID responses of the dioximes
of glyoxal and phthaldialdehyde using their effective carbon
2
8,29
numbers (ECNs) of 18.34 and 24.34, respectively,
relative
to the amount of phthaldialdehyde present the amounts of
glyoxal present in an irradiated CH ONO−NO−E-2-FC−air
3
mixture and in an O reaction were ∼0.5 and 1.3, respectively.
3
Figure 10 shows a plot of the phthaldialdehyde signal against
the loss of E-2-FC (both being in area counts), with the initial
E-2-FC being that defined above in the kinetic section and with
only the first irradiation period being used for the OH radical
reactions. The phthaldialdehyde data have been corrected for
any present prereaction or prephotolysis but not for wall losses
or reaction with OH or NO3 radicals (photolysis of
27
phthaldialdehyde could be neglected, and no reaction with
2
3
O is expected ). Assuming that the derived values of (△2-
3
FC) reflect the actual amounts of 2-FC which had reacted, the
NO3 radical and O3 reactions). As evident from the
experimental data presented above, the wall adsorption (or
absorption)/desorption behavior of 2-FC in the chamber
complicated quantitative measurements of its photolysis rate
and reaction rate constants. For example, assuming that the
phthaldialdehyde formation yield from O3 + E-2-FC was
constant during the reactions, then the data shown in Figure 10
suggest that E-2-FC was being adsorbed (or absorbed) to the
chamber walls during the initial stages of the reaction, with the
adsorption/absorption rate of E-2-FC decreasing, or reversing,
during the later stages of the reactions.
relative phthaldialdehyde yields are O reaction ≥ OH radical
3
reaction > NO3 radical reaction > photolysis. Since the
increases in the phthaldialdehyde concentration upon photol-
ysis were of a similar magnitude to the preirradiation
phthaldialdehyde levels, it is likely that these increases in
phthaldialdehyde during the photolysis experiments were due
to desorption from the chamber walls as a result of photolysis
27
(
and hence the slight heating of the chamber walls).
DISCUSSION
■
Our data suggest that 2-FC ultimately attains equilibrium
between gas-phase 2-FC and wall-adsorbed (or absorbed) 2-
FC, with near-equilibrium being attained in ∼5−7 h, and with
These are the first direct measurements of the rate of photolysis
and reaction rate constants of 2-FC (E-2-FC in the case of the
∼
50% of the plateau loss being attained after ∼1 h. In the case
Scheme 3
of Z-2-FC in the first photolysis experiment (MTC-2579; see
Figure S1), after the first irradiation period the Z-2-FC
concentration decreased in the dark by a factor of 5 over a
4
2 min time period (note that the SPME fiber samples were
collected over 20 min time periods, so some averaging would
occur due to the sampling time periods). This indicates that, at
least in some cases, the rates of the 2-FC adsorption/
desorption processes were rapid, with time scales on the
order of 30 min or less. In the O reaction, after the initial
3
addition of O3 the reactions proceeded with no further
additions to the chamber. However, in the NO reactions,
3
additions of N O were made at various intervals during the
2
5
reaction, and these additions could well have affected the gas−
wall behavior of 2-FC (for example, N O is removed from the
2
5
gas phase to the chamber walls with a lifetime of ∼3 h in
30
relatively dry air in a ∼2500 L Teflon chamber, and this could
affect the 2-FC on/in the wall material). Similarly, the
irradiation periods in the photolysis and OH radical reactions
would lead to some slight heating of the Teflon film, and this
could well perturb the gas−wall partitioning of 2-FC during and
after the irradiation periods. It is therefore likely (and was
observed in the NO radical reaction and the photolysis and
3
OH radical reactions) that 2-FC desorption from the walls into
the gas phase as the reactions proceeded means that the
measured reaction rates are lower limits. Unfortunately, how
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Scheme 5
large an effect 2-FC desorption (or adsorption in the case of Z-
those for benzaldehyde (a −CHO substituent) and cinnamal-
dehyde (a −CHCHCHO substituent). Hence it would be
expected that the room temperature rate constants for the
reactions of 2-FC with O , NO radicals, and OH radicals
2
-FC in the photolysis and OH radical reactions) had on the
measured reaction rates cannot be assessed.
Nevertheless, the present study shows that 2-FC undergoes
photolysis by black lamps (by both E- to Z-FC photo-
isomerization and photolytic removal of Z- + E-2-FC) and
reacts with O , NO radicals, and OH radicals. The only
3
3
−18
−14
−11
3
would be ∼2 × 10 , ∼2 × 10 , and ∼6 × 10
cm
molecule− s , respectively. Our measured rate constant for
1
−1
the reaction of E-2-FC with O is in agreement with this
3
3
3
10
previous kinetic study of 2-FC was that of Nishino et al., who
monitored the relative 2-FC concentrations during irradiated
expectation, and that for reaction with NO radicals is a factor
3
of ∼2 higher than expected, both reasonable, noting that the
estimation method is subject to significant uncertainties (of at
least a factor of 2) for the NO radical and O reactions for
CH ONO−NO−naphthalene−air mixtures by direct air
3
sampling atmospheric pressure ionization mass spectrometry
3
3
23
(
API-MS) and derived 2-FC loss rates at varying OH radical
which reaction rate constants span many orders of magnitude.
10
concentrations and light intensities. The data of Nishino et al.
Our rate constant for reaction of 2-FC with OH radicals is a
factor of ∼3 lower than that expected based on the
benzaldehyde and E-cinnamaldehyde rate constants, and a
factor of 2.6 lower than that predicted using the Kwok and
are included in Figure 9, and it is apparent that the two sets of
data disagree by a factor of ∼4. It should be noted that in this
work the E-/Z- isomer distribution was >1 and in the work of
1
0
31
Nishino et al. the ratio was <1 (Table 1). Additionally, the
time scales of the experiments in the two studies were quite
Atkinson estimation method. Clearly, the present photolysis
rate and rate constant for reaction with OH radicals are likely to
be lower limits due to wall adsorption/desorption, and as noted
above our present photolysis rate and OH radical reaction rate
constant are a factor of ∼4 lower than those reported by
10
different; Nishino et al. monitored 2-FC by direct air
sampling atmospheric pressure ionization mass spectrometry
during and after the 19−39 min CH ONO−naphthalene−air
3
10
irradiations, time periods comparable with the sampling time
for a single analysis in the present work. Table 1 lists the rate
constants obtained here together with the 2-FC photolysis rate
and OH radical reaction rate constant reported by Nishino et
Nishino et al. Under atmospheric conditions, using a 12 h
6
daytime average OH radical concentration of 2 × 10 molecules
−
3
cm , a 12 h nighttime average NO radical concentration of 5
3
8
−3
× 10 molecules cm , a 24 h average O concentration of 7 ×
3
1
0
11
−3
al. Also listed are the literature rate constants for the reactions
10 molecules cm , and a 12 h daytime average NO
2
−1
of benzaldehyde [C H CHO] and E-cinnamaldehyde
photolysis rate of 0.312 min , the calculated lifetimes of 2-
FC are 9 days for reaction with O , 13 h for reaction with NO
3
6
5
[
C H CHCHCHO] with O , NO radicals, and OH
6
5
3
3
3
2
3,25,26
radicals.
It is expected, by analogy with benzaldehyde and E-
cinnamaldehyde,
radicals, 7 h for reaction with OH radicals, and 23 min for
10
photolysis; use of the Nishino et al. data would decrease the
OH radical and photolysis lifetimes to 2 h and 5 min,
respectively. Clearly, in the atmosphere the dominant chemical
loss processes will be photolysis during daylight hours and
2
5,26
that the reactions of 2-FC with O , NO3
3
radicals, and OH radicals will proceed almost entirely at the
−
CHO and −CHCHCHO substituent groups and that to a
good approximation the rate constants for the reactions of 2-
FC with O , NO radicals, and OH radicals will be the sum of
reaction with NO radicals during nighttime. In addition, it is
3
possible that 2-FC will partition between the gas and particle
3
3
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Article
phases in the atmosphere, and it is likely that such a
partitioning occurred in the chamber experiments of Kautzman
ACKNOWLEDGMENTS
The authors thank the U.S. Environmental Protection Agency
Grant R833752) for supporting this research. While this work
has been supported by this Agency, the results and content of
this publication do not necessarily reflect the views and opinion
of the Agency. J.A. thanks the University of California
Agricultural Experiment Station for partial salary support.
■
1
3
et al. in which particles were added to the chamber and that
this partitioning led to indications that photolysis of 2-FC was
(
1
3
slow.
3
The reactions of 2-FC with O and with OH and NO3
radicals are expected to proceed by initial addition to the CC3
bond in the −CHCHCHO moiety, and for the OH and NO
radical reactions by H-atom abstraction from the two −CHO
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AUTHOR INFORMATION
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(14) Nishino, N.; Arey, J.; Atkinson, R. 2-Formylcinnamaldehyde
Corresponding Author
Formation Yield from the OH Radical-Initiated Reaction of
Naphthalene: Effect of NO2 Concentration. Environ. Sci. Technol.
*
E-mail janet.arey@ucr.edu, telephone (951) 827-3502 (J.A.);
e-mail ratkins@mail.ucr.edu, telephone (951) 827-4191 (R.A.).
2
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Present Address
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†
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Notes
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The authors declare no competing financial interest.
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