Rate coefficients for the OH + pinonaldehyde (C10H 16O2) reaction between 297 and 374 K

Article abstract of DOI:10.1021/es070048d

The rate coefficient for the reaction of OH with pinonaldehyde (C ₁₀H₁₆O₂, 3-acetyl-2,2-dimethyl-cyclobutyl- ethanal), a product of the atmospheric oxidation of α-pinene, was measured under pseudo-first-order conditions in OH at temperatures between 297 and 374 K at 55 and 96 Torr (He). Laser induced fluorescence (LIF) was used to monitor OH in the presence of pinonaldehyde following its production by 248 nm pulsed laser photolysis of H₂O₂. The reaction exhibits a negative temperature dependence with an Arrhenius expression of k₁(T) = (4.5 ± 1.3) × 10^-12 exp((600 ± 100)/7) cm³ molecule^-1 s^-1; K₁(297 K) = (3.46 ± 0.4) × 10^-11 cm³ molecule^-1 s^-1. There was no observed dependence of the rate coefficient on pressure. Our results are compared with previous relative rate determinations of k₁ near 297 K and the discrepancies are discussed. The state of knowledge for the atmospheric processing of pinonaldehyde is reviewed, and its role as a marker for α-pinene (monoterpene) chemistry in the atmosphere is discussed.

Full text of DOI:10.1021/es070048d

Environ. Sci. Technol. 2007, 41, 3959-3965
of R-pinene leads to ring-opening and a variety of stable
end-products that contain carbonyl, alcohol, and carboxylic
functional groups (2). Pinonaldehyde (C10 , 3-acetyl-
,2-dimethyl-cyclobutyl-ethanal) is an end-product formed
in high yield in the OH, O and NO initiated oxidation of
R-pinene. The molecular structure of pinonaldehyde is shown
in the Supporting Information, Figure 1S. A pinonaldehyde
yield of 60% for the OH initiated R-pinene oxidation has
recently been suggested for use in atmospheric model
calculations (3).
Pinonaldehyde is a possible marker for R-pinene (monot-
erpene) chemistry in the atmosphere. At present, measure-
ments of pinonaldehyde in the lower troposphere are limited
to just a few field campaigns in forested areas (4-7). In
addition to direct observations of its atmospheric abundance,
a marker requires a detailed understanding of its atmospheric
formation and loss processes. Our work focuses on the
Rate Coefficients for the OH +
16 2
H O
Pinonaldehyde (C H O ) Reaction
1
0 16 2
2
between 297 and 374 K
3
3
M A X I N E E . D A V I S , †
, ‡
R A N A J I T K . T A L U K D A R , †
, ‡
§
G R E G O R Y N O T T E ,
§
G . B A R N E Y E L L I S O N , A N D
J A M E S . B . B U R K H O L D E R * , †
Earth System Research Laboratory, National Oceanic and
Atmospheric Administration, 325 Broadway, Boulder,
Colorado 80305-3328, Cooperative Institute for Research in
Environmental Sciences, University of Colorado, Boulder,
Colorado 80309, Department of Chemistry and Biochemistry,
University of Colorado, Boulder, Colorado 80309-0215
determination of the rate coefficient, k
1
, for the reaction
OH + Pinonaldehyde f Products
(1)
The rate coefficient for the reaction of OH with pinonaldehyde
which is a significant daytime removal process for pinonal-
dehyde.
Several studies of the rate coefficient for reaction 1 around
room temperature have been reported in the literature.
(
C10H16O2, 3-acetyl-2,2-dimethyl-cyclobutyl-ethanal), a
product of the atmospheric oxidation of R-pinene, was
measured under pseudo-first-order conditions in OH at
temperatures between 297 and 374 K at 55 and 96 Torr (He).
Laser induced fluorescence (LIF) was used to monitor
OH in the presence of pinonaldehyde following its production
by 248 nm pulsed laser photolysis of H2O2. The reaction
exhibits a negative temperature dependence with an Arrhenius
However, discrepancies exist among the reported rate
-11
cm3
coefficients with values ranging from 4.0 × 10
-1 -1
-11
3
-1 -1
molecule
s
to 9.1 × 10 cm molecule
s
(8-11). Each
of these studies used the relative rate technique, and there
is not a clear explanation for the large range in the measured
values. Further rate coefficient measurements are needed to
resolve the existing discrepancies and also to determine the
-
12
expression of k1(T) ) (4.5 ( 1.3) × 10 exp((600 ( 100)/
3
-1 -1
-11
T) cm molecule s ; k1(297 K) ) (3.46 ( 0.4) × 10
3
-1 -1
1
temperature dependence of k .
cm molecule s . There was no observed dependence
of the rate coefficient on pressure. Our results are
compared with previous relative rate determinations of k1
near 297 K and the discrepancies are discussed. The
state of knowledge for the atmospheric processing of
pinonaldehyde is reviewed, and its role as a marker for
R-pinene (monoterpene) chemistry in the atmosphere is
discussed.
In this paper, measurements of the OH + pinonaldehyde
reaction rate coefficient including its temperature depen-
dence are reported. Our results are compared with previous
determinations and the discrepancies are discussed. An
overview of the current understanding of the atmospheric
processing of pinonaldehyde is presented and existing gaps
in knowledge are discussed.
Experimental Details. Pulsed laser photolysis production
of OH coupled with its detection by laser induced fluores-
cence (PLP-LIF) was used to determine the gas-phase rate
coefficient for reaction 1 under pseudo-first-order conditions
in OH. Rate coefficient determinations were made at tem-
peratures between 297 and 378 K at 55 and 96 Torr (He). The
experimental setup is similar to that used in previous kinetic
and photolysis quantum yield studies from this laboratory
(12, 13). A schematic of the apparatus is shown in Davis et
al. (12) and described briefly below.
Introduction
Monoterpenes (C10H16) are a class of unsaturated cyclic
Biogenic Volatile Organic Compounds (BVOCs) which are
emitted from coniferous trees and account for approximately
1
0% of the total biogenic hydrocarbons emitted globally (1).
The oxidation of monoterpenes in the lower troposphere
plays an important role in determining the local HO budget,
regional ozone production, and secondary organic aerosol
SOA) formation. The atmospheric oxidation of R-pinene,
the most abundant monoterpene emitted in North America,
is initiated by its gas-phase reaction with OH, O , or NO
The lifetime of R-pinene is on the order of hours for OH and
reactive loss and ∼0.15 h for NO reactive loss for
representative daytime (OH and O ) and nighttime (NO
concentrations in the lower troposphere (2). The oxidation
x
The LIF reactor consisted of a jacketed Pyrex cell ap-
proximately 15 cm in length with an internal volume of ∼150
3
(
cm . The reactor was maintained at a constant temperature
by circulating a temperature-regulated fluid through its jacket.
The temperature of the gas in the reaction zone was directly
measured and was accurate to (1 K.
3
3
.
O
3
3
OH radicals were produced by pulsed laser photolysis of
3
3
)
H
2
O
2
at 248 nm (KrF excimer laser). The initial OH radical
concentration, [OH] , was calculated using
0
*
Corresponding author phone: 303-497-3252; fax: 303-497-5822;
[OH]0 ) σλ Φλ [H2O2] F
(2)
e-mail: James.B.Burkholder@noaa.gov.
†
Earth System Research Laboratory.
Cooperative Institute for Research in Environmental Sciences,
-20
where σ
λ
and Φ
λ
are the absorption cross section (2.0 × 10
‡
2
-1
cm molecule ) and OH quantum yield, respectively, for
at 248 nm (Φ ) 2) (14), and F is the photolysis laser
University of Colorado.
§
2
H O
Department of Chemistry and Biochemistry, University of
Colorado.
2
λ
-
2
-1
fluence (photon cm pulse ), measured with a calibrated
1
0.1021/es070048d CCC: $37.00

2007 American Chemical Society
VOL. 41, NO. 11, 2007 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
3959
Published on Web 04/27/2007

TABLE 1. Summary of Experimental Conditions and Rate Coefficients, k (T), Determined in This Work for the OH + Pinonaldehyde
1
Reaction
temperature pressure
V
laser fluence
[H
2 2
O ]
[OH]
0
[pinonaldehyde]
1
k (T)
(Torr He) (cm s-1) (mJ cm pulse-1) (1014 molecule cm-3) (1011 molecule cm-3) (10 molecule cm
-2
14
-3 a
)
(10 11 cm molecule s-1
)
-
3
-1
(
K)
374
349
325
297
297
297
57
58
58
96
59
49
45
42
31
38
20-38
5.9
5.8
6.4
7.0
7.0
4.3-15.6
0.8
0.6
0.8
0.5
1.0
0.5-1.4
0.76
0.6
0.9
0.6
1.1
0.25-0.94 (5)
0.19-0.98 (5)
0.10-1.15 (6)
0.81-1.24 (3)
0.54-1.2 (4)
0.23-1.28 (15)
2.35 ( 0.04b
2.56 ( 0.04
2.69 ( 0.06
3.31 ( 0.06
3.30 ( 0.08
c
55-57
0.6-3.0
3.48 ( 0.02
d
1
k (297) ) 3.46 ( 0.04
a
at that temperature. b Quoted uncertainties
The value in parenthesis is the number of pinonaldehyde concentrations used in the determination of k
1
are 2σ from the fits of k′ versus [pinonaldehyde] and do not include estimated systematic errors. c 2 Torr O
coefficient obtained by fitting all the T ) 297 K data simultaneously. This value was used as the room-temperature value in the determination
of the Arrhenius parameters.
added. d Room-temperature rate
2
power meter. The H
the measured first-order decay of OH in the absence of
pinonaldehyde using the OH + H rate coefficient (14).
OH] was varied during the course of the study but was <3.0
2
O
2
concentration was estimated from
Torr at 296 K (10)) is the possible loss of the compound to
the walls of the apparatus, particularly at reduced temper-
atures. In this work, pinonaldehyde loss was determined
experimentally to be insignificant for temperatures g297 K.
Kinetic measurements were not extended below room-
temperature due to limitations imposed by the pinonalde-
hyde vapor pressure.
2
O
2
[
0
11
-3
×
10 molecule cm to minimize secondary radical-radical
chemistry on the time scale of the OH temporal profile
measurements.
OH radicals were excited by pulsed laser excitation near
82 nm (A Σ , ν′ ) 1 r Ì Π, ν′′ ) 0) with the frequency-
doubled output of a Nd:YAG pumped dye laser. The OH
fluorescence signal was detected with a photomultiplier tube
PMT) orthogonal to both the probe and photolysis beams.
Pinonaldehyde was introduced into the gas flow by passing
a large fraction, >15%, of the total He gas flow over the semi-
liquid pinonaldehyde sample held at 297 K. The flow
containing the pinonaldehyde sample was diluted at the exit
2
+
2
2
(
14
of the sample reservoir. The largest [Pin]LIF was ∼1.5 × 10
A 309 nm band-pass filter mounted in front of the PMT was
used to isolate the OH fluorescence. OH temporal profiles
were obtained by varying the delay between the photolysis
and probe lasers over the range 10-3000 µs.
-3
molecule cm which is roughly a factor of 10 lower than its
room-temperature vapor pressure. Infrared absorption spec-
tra were recorded using Fourier transform infrared spec-
troscopy (FTIR) and quantified using literature absorption
OH temporal profiles were measured under pseudo-first-
-1
-19
cm2
cross section data, σ(1725.4 cm ) ) 8.08 × 10
order conditions in OH, [pinonaldehyde] . [OH]
followed the rate law:
0
, and
-1
molecule (base e) (10). Infrared absorption spectra were
recorded in 50 coadded scans between 500 and 4000 cm
at 1 cm resolution. The infrared absorption cell was a small
-1
-
1
3
[
OH]t
St
volume, ∼750 cm , multipass cell mounted in the FTIR sample
ln
) ln
) (k [pinonaldehyde] + k ) t ) k′t
1 d
([OH]
)
( )
compartment. The path length of the cell was calibrated in
S
0
0
separate measurements to be 485 ( 8 cm and the detection
(
3)
1
2
-3
sensitivity for pinonaldehyde was ∼2 × 10 molecule cm
.
It should be noted that if the pinonaldehyde infrared
absorption cross section is revised, the rate coefficient data
presented in this study can be scaled accordingly.
where S
t
is the OH LIF signal at time t and is proportional
, k′ is the pseudo-first-order rate coefficient and k
is the first-order rate coefficient measured in the absence of
pinonaldehyde. k represents the loss of OH radicals due to
reaction with H and buffer gas impurities and diffusion
out of the detection volume. Typical values of k were between
0 and 200 s . k′ was measured for a range of pinonaldehyde
concentrations at each temperature and pressure, and k
was determined from the slope of a plot of k′ versus
to [OH]
t
d
d
UV absorption measurements were made continuously
during the kinetic measurements. The UV measurements
were made at 185 nm using Hg pen-ray lamps and solar
blind photodiodes with 185 nm narrow bandpass filters. The
Pyrex absorption cells used for the kinetic measurements
had 50 cm pathlengths and quartz windows. The pinonal-
dehyde absorption cross section at 185 nm was determined
relative to the infrared cross section reported by Hallquist
et al. (10) as part of this study. In our cross section
determinations, the infrared measurements were performed
using the FTIR spectrometer setup described above. The 185
nm cross section measurements were made using an 84 cm
path length absorption cell. UV absorption measurements
were also made using a diode array spectrometer (210-400
2
O
2
d
-1
5
1
[
pinonaldehyde].
Pinonaldehyde Concentration Determination. The de-
termination of the pinonaldehyde concentration in the LIF
reactor, [Pin]LIF, is an important factor in determining the
1
overall accuracy of k measured in this work. [Pin]LIF was
determined by in situ infrared absorption, before the LIF
reactor, and by 185 nm UV absorption, before and after the
LIF reactor. The two optical absorption methods provide
complimentary measurements of [Pin]LIF and also provide a
test for possible loss of pinonaldehyde in the gas flow. The
IR and UV absorption measurements were made at room
temperature thereby eliminating uncertainties in the pi-
nonaldehyde IR and UV absorption cross section temperature
dependence (discussed below) from contributing to the
nm) with a 30W D
2
light source at a resolution of ∼1 nm. A
He flow passed through the pinonaldehyde sample reservoir,
the FTIR, and then into the UV absorption cell. The total
pressure in the absorption cells was in the range 150-230
Torr and the residence times of the gas mixture in the
absorption cells were ∼5 s (FTIR) and ∼15 s (UV). The
14
1
uncertainty in k . [Pin]LIF was not measured directly but was
pinonaldehyde concentration was varied between 0.7 × 10
-3 14 -3
calculated from the IR and UV absorption measurements
and includes factors to account for differences in pressure
and temperature between the absorption cells and LIF
reactor. A concern when working with low vapor pressure
compounds such as pinonaldehyde (vapor pressure ) 0.03
molecule cm and 3.0 × 10 molecule cm in the diode
13
array/FTIR measurements and between 0.3 × 10 molecule
-
3
13
-3
cm and 1 × 10 molecule cm for the 185 nm/FTIR
measurements. The absorption signals varied linearly with
pinonaldehyde concentration over this range obeying Beer-
3
960
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 41, NO. 11, 2007

Lambert’s law. The shape of the pinonaldehyde absorption
spectrum recorded between 210 and 400 nm was in good
agreement with that reported by Hallquist et al. (10). We
obtained an absorption cross section at 285 nm, the peak of
-
19
2
-1
the spectrum, of (1.35 ( 0.08) × 10
cm molecule in
excellent agreement, within 2%, with the value reported by
Hallquist et al. (10). Measurements made with the gas flow
reversed (UV measurements first) yielded identical infrared
and UV absorption cross sections, i.e., loss of pinonaldehyde
was <5%. The pinonaldehyde cross section at 185 nm was
-
17
2
-1
determined to be (1.38 ( 0.09) × 10 cm molecule (2σ
precision error limit).
Materials. Pinonaldehyde was synthesized and purified
for this study. The pinonaldehyde synthesis used the oxida-
tion of R-pinene method as reported by Hallquist et al. (10).
R-pinene (4 g or 29.4 mmol) was dissolved in dichlo-
romethane (CH
solution was purged with N
from an ozonizer (∼1% O in O
of N and bubbled through the reaction mixture until a blue
color persisted. Purging with N was continued until the blue
color disappeared. Dimethylsulfide (DMS) was added by
syringe and the solution warmed to room temperature and
stirred overnight.
2
Cl
2
)/methanol and NaHCO
and cooled to -78 C. Ozone
) was mixed with a stream
3
added. The
2
3
2
2
FIGURE 1. Summary of all the OH + pinonaldehyde rate coefficient
data measured at 297 K. The symbols highlight sets of data measured
under different experimental conditions. The error bars shown are
the 2σ (95% confidence limit) uncertainties obtained from the
weighted linear least-squares fit of the OH decay profile to eq 3.
2
The solution was diluted with dichloromethane and
3
washed with 40 mL of saturated NaHCO . The aqueous layer
was extracted three times with 20 mL dichloromethane and
the combined organic layers were washed with saturated
NaCl (3 × 20 mL). Organics were dried over MgSO
4
, filtered,
and concentrated to a clear oil. The expected yield of
pinonaldehyde was (0.0294 × 168.24 g) or 4.9 g; the recovered
organic sample weighed 4.9 g. The initial oil appeared by
NMR to be largely pinonaldehyde with small contaminations.
The oily product was subjected to flash chromatography in
7:1 hexane/ethylacetate on silica gel. A very clear product
was recovered (2.8 g) that was a low-melting solid. The NMR
analysis was in prefect agreement with the literature indicat-
ing a pure sample with no detected impurities (15).
UHP He (>99.9995%) was used as the buffer gas. O
99.99%) and N (99.99%) were used as supplied. Concen-
trated hydrogen peroxide (>95%) was prepared by bubbling
through a H sample initially at 60% concentration for
several days prior to use. H was introduced into the main
2
(
2
N
2
2 2
O
2
O
2
gas flow just prior to entering the LIF reactor by passing a
small flow of He through a bubbler containing the concen-
trated sample. Gas flow rates were measured using calibrated
electronic mass flow transducers. Pressures were measured
using 100 and 1000 Torr capacitance manometers.
FIGURE 2. Arrhenius plot for the OH + pinonaldehyde reaction.
Results from this work are shown as the solid circles. The solid
Results
line is a weighted linear least-squares fit to our data yielding k
1
(T)
Table 1 summarizes the experimental conditions used in the
kinetic measurements and the rate coefficients obtained for
reaction 1. The OH temporal profiles measured with different
pinonaldehyde concentrations were of high quality and
obeyed eq 3 under all variations in the experimental
conditions. Figure 2S in the Supporting Information shows
a representative set of OH temporal profiles measured at
-12
3
-1 -1
)
(4.5 ( 1.3) × 10 exp((600 ( 100)/T) cm molecule
s
(see
text for error analysis). The dashed lines represent the uncertainty
limits in the rate coefficient in the format used in data evaluations
(14) where the error, f(T), is given by f(T) ) f(298 K) exp|g(1/T -
1/298)| and f(298 K) ) 1.15 and g ) 50 (1σ level). The values reported
in the previous relative rate studies are included for comparison;
Glasius et al. (9) (]), Hallquist et al. (10) (4), Alvarado et al. (8) (0),
Nozi e` re et al. (16) (O).
297 K.
The first-order rate coefficient, k′, data obtained at 297
K, including all variations in experimental conditions, are
shown in Figure 1. The error bars on the data points are the
obtained from the individual determinations at room tem-
perature, as summarized in Table 1, and was used for the
2σ values from the precision of the weighted linear least-
squares fits to the OH temporal profiles using eq 3. The
precision of the kinetic data shown in Figure 1 is representa-
tive of that obtained at 325, 349, and 374 K, although fewer
variations in the experimental conditions were made in those
measurements. Analyzing all room-temperature data to-
1
determination of the temperature dependence of k .
An Arrhenius plot of the rate coefficient data is shown in
Figure 2. The results of a weighted least-squares fit of the
data given in Table 1 (weighted by the number of measure-
ments made at each temperature) to a linearized Arrhenius
expression are given in Table 2.
-11
3
-1
gether yields k
1
(297 K) ) (3.46 ( 0.04) × 10 cm molecule
where the quoted uncertainty is at the 2σ level (fit
precision). This value is in good agreement with the values
-
1
s
Error Analysis. A source of uncertainty in the determi-
nation of k (T) using the PLP-LIF method is the systematic
1
VOL. 41, NO. 11, 2007 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
3961

TABLE 2. Summary of OH + Pinonaldehyde Rate Coefficient Data
pressure
(Torr)
k1(297 K) ( 2σa
Ab
E/R (K)
T (K)
techniquej
reference
c
-12
3
4
4
9
8
2
3
.46 ( 0.4
(4.5 ( 1.3) × 10
600 ( 100 297-374 PLP-LIF
55-96
760
this work
.0 (1.0d
293
296
300
298
298
298
RR
RR
RR
RR
f
Nozi e` re et al., 1999 (16)
e
g
h
i
.8 ( 0.8
740
Alvarado et al., 1998 (8)
Glasius et al., 1997 (9)
Hallquist et al., 1997 (10)
Kwok and Atkinson, 1995 (17)
Vereecken and Peeters, 2003 (18)
.1 ( 1.8d
.72 ( 1.14
740
760
d
.4
.5
SAR estimation
DFT calculation
a
-
1
1
3
-
1
-
1
b
3
-
1
-
1
I
n
u
n
i
t
s
o
f
1
0
c
m
m
o
l
e
c
u
l
e
s
,
l
i
t
e
r
a
t
u
r
e
v
a
l
u
e
s
a
r
e
f
o
r
t
e
m
p
e
r
a
t
u
r
e
s
n
e
a
r
2
9
7
K
a
s
l
i
s
t
e
d
i
n
t
h
e
t
a
b
l
e
.
I
n
u
n
i
t
s
o
f
c
m
m
o
l
e
c
u
l
e
s
.
c
d
The quoted errors from this work are at the 2σ level (95% confidence) and include estimated systematic errors. The errors quoted are twice the
standard deviation of the weighted fit. The error given is twice the standard deviation of the weighted fit combined with the estimated overall
uncertainty in the rate coefficient of the reference compound. Cyclohexane, 1,2-butadiene and isoprene reference compounds. Propene, 1-butene,
and m-xylene reference compounds. Isoprene and 1,3-butadiene reference compounds. Propene reference compound. PLP-LIF: pulsed laser
photolysis-laser induced fluorescence, RR: relative rate, SAR: structure activity relationship, DFT: density functional theory.
e
f
g
h
i
j
errors associated with the determination of [Pin]LIF. The
determination of the pseudo-first-order OH decays was very
precise and makes a small contribution to the overall
1
uncertainty, typically <2%. The precision of the k deter-
minations, as shown in Figure 1, was also on the order of a
few percent.
Discussion
There are four OH + pinonaldehyde rate coefficient mea-
surements around room-temperature currently available in
the literature (8-10, 16) to compare with our results. There
is no temperature-dependent data available in the literature.
The results from the previous studies are included in Figure
Systematic errors in the kinetic measurements were
evaluated experimentally by varying the experimental con-
2
for comparison with our work and are also summarized in
Table 2. The previous rate coefficient values fall into two
groups with Glasius et al. (9) and Hallquist et al. (10) reporting
ditions and by using multiple methods to determine [Pin]LIF
(T) was found to be independent of [OH] (varied by a
factor of 5); the photolysis laser fluence (varied by a factor
of 4); total He pressure; H concentration; and gas flow
.
k
1
0
-11
3
-1 -1
values near 8.9 × 10 cm molecule
s
and Nozi e` re et al.
(
1
16) and Alvarado et al. (8) reporting values around 4.4 ×
2
O
2
-11
3
-1 -1
0
cm molecule
1
s . Our k (297 K) value is closest to the
velocity through the LIF reactor. The range of experimental
conditions used in the measurements is summarized in Table
values reported by Nozi e` re et al. (16) and Alvarado et al. (8)
although somewhat smaller. The rate coefficients reported
by Glasius et al. (9) and Hallquist et al. (10) fall outside of the
combined uncertainty ranges of our study and theirs.
1
×
. Several measurements were also made with O
2
added (7.4
10 molecule cm ) to the reaction mixture. The measured
implying that the
16
-3
rate coefficient was independent of O
2
Although the experimental techniques used in the relative
rate studies were not identical, the discrepancy among the
secondary chemistry of the organic radical products from
the OH + pinonaldehyde reaction did not influence the
1
determination of k .
k
1
values is rather surprising. These studies used different
measurement techniques to monitor pinonaldehyde loss
FTIR (9, 10, 16), gas chromatography (8), and derivatization/
The pinonaldehyde concentration determined from the
infrared and UV absorption measurements made before the
LIF reactor were in excellent agreement, within 2%. The
pinonaldehyde concentration measured after the LIF reactor
was typically within 5% of the concentration measured before
the reactor and was independent of the gas flow velocity
through the LIF reactor, i.e., no measurable pinonaldehyde
loss. The pinonaldehyde concentration was also stable, within
(
high-pressure liquid chromatography (16)) and different
methods to produce OH radicals (methyl nitrite/NO pho-
tolysis (8-10, 16), H
2 2
O photolysis (9, 11, 16), and the reaction
of O with 2,3-dimethyl-2-butene (16)). Nozi e` re et al. even
3
used pinonaldehyde samples prepared by Hallquist and co-
workers for their measurements. Alvarado et al. have sug-
gested that either the high pinonaldehyde concentrations or
the small volume of the reactors (larger surface to volume
ratios) used by Glasius et al. and Hallquist et al. may have
contributed to the higher rate coefficient values. Nozi e` re et
al. conducted several experiments with high pinonaldehyde
concentrations and observed no dependence of the rate
coefficient on concentration.
2%, during a pseudo-first-order rate coefficient measurement.
[Pin]LIF determined from the IR measurements (using lit-
erature IR cross sections) was used in the final data analysis.
Impurities in the pinonaldehyde sample could influence
the determination of k (T) if present and highly reactive with
1
OH. NMR analysis of the pinonaldehyde sample did not
indicate the presence of any impurities, <1%. The infrared
and UV absorption spectra were also free of detectable
impurities and no change in the sample during the course
of the study was observed. The high reactivity of pinonal-
dehyde precludes a substantial uncertainty in k due to trace
1
impurities. Based on the spectroscopic and NMR measure-
ments of the pinonaldehyde sample, we estimate the
Structure activity relationships (SAR) (17) yield k
1
(298 K)
. This estimated rate
coefficient is ∼30% less than our direct measurement of k
297 K) but should be considered good agreement for the
SAR method. The “adjusted” SAR approach of Vereecken
-11
cm3 molecule
-1
-1
)
2.4 × 10
s
1
-
(
1
and Peeters (18) yields a slightly larger k (298 K) value, 3.5
-11
3
-1
-1, which agrees with our measured
×
10 cm molecule
s
contribution of reactive impurities to our measured k
to be <5% at all temperatures.
1
value
value very well. The enhanced pinonaldehyde reactivity in
the “adjusted” SAR value is due to enhanced H abstraction
from the carbon adjacent to the aldehydic group and the two
tertiary H atoms from the carbons in the four-member ring.
Vereecken and Peeters predict a 59:23:14 branching ratio for
abstraction of the aldehydic, R, and tertiary H atoms,
respectively. This enhanced pinonaldehyde reactivity at the
non-aldehydic sites is important in determining the yields
of stable end-products in the atmospheric oxidation of
pinonaldehyde and needs to be verified experimentally.
Other possible systematic uncertainties include the gas
flow (1%), pressure (0.5%) and temperature (0.3%) measure-
ments. Hallquist et al. (10) report a statistical 2σ uncertainty
of 4% in the pinonaldehyde IR absorption cross section. The
total estimated systematic uncertainty in the rate coefficient
at each temperature is ∼10% yielding an overall uncertainty
in the measured rate coefficients of 15% which is included
as the error bars for the data shown in Figure 2.
3
962
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 41, NO. 11, 2007

We observed a negative temperature dependence for the
OH + pinonaldehyde reaction rate coefficient, E/R ) -600
K. This value is in agreement with E/R values measured for
aldehydes of similar size and structure to pinonaldehyde
deposition, gas-phase reaction with OH, NO
UV photolysis.
3
, and O
3
, and
pinonaldehyde f deposition
(4)
(5)
(
19) (and references cited within) and is consistent with the
dominant reaction channel being H abstraction from the
aldehydic group.
pinonaldehyde + O f products
3
In conclusion, the rate coefficient data measured in
this work, using the PLP-LIF technique, helps resolve the
discrepancies in the previously reported room-tempera-
ture relative rate studies. This study has improved the
pinonaldehyde + NO3 f products
pinonaldehyde + hν f products
(6)
(7)
overall accuracy in k
dependent measurements of k
1
and provides the first temperature
. Reaction 1 was also found
1
Under typical atmospheric conditions, the uptake loss of
pinonaldehyde is small compared to gas-phase loss processes
25). However, uptake on acidic aerosol may be important
in the formation of biogenic secondary organic aerosol (25,
6). A summary of the literature kinetic and photochemical
to be independent of pressure over the range of con-
ditions used in this study. We suggest that the rate coefficient
data reported in this work be used in air quality model
calculations.
(
2
data for reactions 5, 6, and 7 is given in the Supporting
Information, Table 3S.
Atmospheric Processing of Pinonaldehyde
-
20
In this section, an overview of the current state of know-
ledge of the atmospheric processing of pinonaldehyde is
presented. We highlight areas where further studies are
desired to reduce uncertainties in the atmospheric processing
of pinonaldehyde.
The reaction of pinonaldehyde with O is slow, <2 × 10
3
3
-1 -1
cm molecule
s
(8) and, therefore, represents a minor
loss process for pinonaldehyde. The loss rate due to OH
reaction is well characterized from this work; a daytime
6
-3
lifetime of ∼2 h for [OH] ) 5 × 10 molecule cm . Nighttime
OH chemistry may also play a role in determining the
pinonaldehyde abundance and its diurnal cycle.
Formation Processes of Pinonaldehyde in the Atmo-
sphere. Pinonaldehyde is formed as an end-product in the
oxidation of R-pinene. The rate coefficients for the R-
Three rate coefficient studies of reaction 6 have been
reported to date. The rate coefficients from these rela-
tive rate studies differ by as much as a factor of ∼3. The
pinene + OH, O
and are summarized in the Supporting Information (Table
S). The atmospheric lifetime of R-pinene with respect to
3 3
, and NO reactions are well established
-
14
3
1
IUPAC (27) recommended value of 2.0 × 10
cm mole-
-
1
-1 -1
reactive losses, defined as τ ) (k(297 K) [Reactant]) , are
cule
s
is based on the study by Alvarado et al. (8). There
1
×
, 3, and 45 h for OH, O
3
, and NO
3
for concentrations of 5
is currently no recommendation for the temperature de-
pendence of the NO3 reaction. Reaction 6 represents a
nighttime loss for pinonaldehyde only under conditions of
6
-3
12
-3
6
10 molecule cm , 1 × 10 molecule cm , and 1 × 10
-3
molecule cm , respectively. At night, when the NO
3
9
concentration is usually the highest, the R-pinene life-
highly elevated [NO ], lifetime of ∼1 day for [NO ] ) 1 × 10
3
3
-
3
time with respect to NO
minutes.
3
reaction could be as short as
molecule cm , and is a minor loss process under daylight
conditions.
The oxidation mechanisms for R-pinene are complex and
are an area of experimental and theoretical research. Several
studies have suggested mechanisms for the OH initiated
oxidation of R-pinene (20-22) (and references cited within)
including pathways leading to the formation of pinonalde-
hyde. A detailed literature survey of pinonaldehyde yield,
UV photolysis has been shown to be an important loss
process for pinonaldehyde. Hallquist et al. (10) calculated an
upper limit for the pinonaldehyde photolysis rate, assuming
-
5 -1
a photolysis quantum yield of unity, of 8.4 × 10
s
at noon
in July at 50 °N. Jaoui and Kamens (28) report an effective
pinonaldehyde solar photolysis quantum yield of 0.4. Al-
though UV photolysis is a slower loss process than OH
reaction, it needs to be included in model calculations. Direct
measurements of the pinonaldehyde photolysis quantum
yield and radical production, as a function of wavelength
and pressure, are needed to provide a more quantitative
characterization of its UV photolysis.
3 3
Φ(Pin), studies for the OH, O , and NO initiated oxidation
of R-pinene, which all have significant yields, is included in
the Supporting Information (Table 2S). Φ(Pin) from studies
of the OH initiated reaction show the largest variability with
molar yields in the range 28-87% reported. The lower range
of Φ(Pin) values are currently believed to be the most reliable
but further studies are desired.
Another consideration in any discussion of the atmo-
spheric processing of pinonaldehyde is its degradation end-
products. The pinonaldehyde molecule is a dauntingly
complex VOC. In addition to two different carbonyl groups
for this aldehyde/ketone there are nine different C-H reactive
sites, Figure 1S. SAR (17) and theoretical calculations (18, 29)
have been used to quantify the site specific reactivities,
proposed reaction mechanisms, and possible end-product
yields. These methods predict H abstraction from the
aldehydic group to be the dominant reaction channel in the
OH reaction. However, in the theoretical treatment, there is
an additional factor that does not seem to have been
considered in OH/VOC oxidations. This is the role of
hydrogen-bonded intermediates in the bimolecular reactions
of the hydroxyl radical (30). The OH radical is initially tethered
to the polar carbonyl groups leading to two possible
hydrogen-bonded OH-pinonaldehyde complexes, structures
shown in Figure 3S (Supporting Information). The formation
of OH complexes would enhance abstraction from the
aldehydic group and from the C-H group in the ring adjacent
to the ketone group.
Φ(Pin) values for the O
are in good agreement with most values in the range 14-
0%. In the most recent study, Berndt et al. (23) reported a
dependence of Φ(Pin) on relative humidity (RH) and the
extent of the O + R-pinene reaction. Warscheid and
Hoffmann (24) also report a RH dependence to Φ(Pin)
although opposite to that of Berndt et al. Baker et al. (22)
report Φ(Pin) to be independent of RH. A dependence of
Φ(Pin) on RH would have a direct impact on modeled
pinonaldehyde production, and therefore, these discrepan-
cies need to be resolved.
3
initiated oxidation of R-pinene
2
3
The NO
Nighttime NO
3
reaction has the largest measured Φ(Pin), ∼60%.
3
chemistry can, therefore, represent a
significant source of pinonaldehyde under certain condi-
tions. It is also worth pointing out that while the daytime
loss of R-pinene by reaction with NO is small it could
3
contribute to daytime pinonaldehyde production under
certain conditions.
Loss Processes of Pinonaldehyde in the Atmosphere.
Atmospheric loss processes for pinonaldehyde include
VOL. 41, NO. 11, 2007 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
3963

Experimentally, Nozi e` re and co-workers (11, 31) reported
CH O and CH C(O)CH product yields following reaction 1
in the presence of NO (11) and the yield of R-pinonyl
peroxynitrate following reactions 1 and 6 in the presence of
(9) Glasius, M.; Calogirou, A.; Jensen, N. R.; Hjorth, J.; Nielsen, C.
J. Kinetic study of gas-phase reactions of pinonaldehyde and
structurally related compounds. Int. J. Chem. Kinet. 1997, 29,
2
3
3
5
27-533.
(
10) Hallquist, M.; W a¨ ngberg, I.; Ljungstr o¨ m, E. Atmospheric
NO
products are in qualitative agreement. Jaoui and Kamens
28) have identified a number of stable photolysis end-
2
(31). The measured and predicted (3) yields for these
fate of carbonyl oxidation products originating from R-
3
pinene and ∆ -carene: Determination of rate of reaction
(
with OH and NO
vapor pressures. Environ. Sci. Technol. 1997, 31, 3166-
172.
3
radicals, UV absorption cross sections, and
products and have proposed reaction mechanisms to
account for their formation. Further studies are desired
for a more complete understanding of the pinonal-
dehyde oxidation mechanism, product yields, and the
possible impact on tropospheric ozone formation and
SOA.
In conclusion, pinonaldehyde is a reasonably well-defined
marker for the atmospheric chemistry of R-pinene (monot-
erpenes). Refinements in the pinonaldehyde yield from the
3
(
(
(
11) Nozi e` re, B.; Barnes, I.; Becker, K. H. Product study and
mechanisms of the reactions of R-pinene and of pinonalde-
hyde with OH radicals. J. Geophys. Res. 1999, 104, 23645-
2
3656.
12) Davis, M. E.; Gilles, M. K.; Ravishankara, A. R.; Burkholder, J.
B. Rate coefficients for the reaction of OH with (E)-2-pentenal,
(E)-2-hexenal, and (E)-2-heptenal. Phys. Chem. Chem. Phys.
2
007, doi: 10.1039/b700235a.
13) Jim e´ nez, E.; Gierczak, T.; Stark, H.; Burkholder, J. B.;
Ravishankara, A. R. Reaction of OH with HO NO (peroxy-
OH + R-pinene reaction, the NO + pinonaldehyde rate
3
2
2
coefficient, and the pinonaldehyde photolysis quantum yields
are, however, desired.
nitric acid): Rate coefficients between 218 and 335 K and
product yields at 298 K. J. Phys. Chem. A 2004, 108, 1139-
1
149.
Acknowledgments
(14) Sander, S. P.; Friedl, R. R.; Golden, D. M.; Kurylo, M. J.;
Moortgat, G. K.; Keller-Rudek, H.; Wine, P. H.; Ravishankara, A.
R.; Kolb, C. E.; Molina, M. J.; Finlayson-Pitts, B. J.; Huie, R. E.;
Orkin, V. L. Chemical Kinetics and Photochemical Data
for Use in Atmospheric Studies, JPL Pub. 06-2; Jet Propul-
sion Laboratory: Pasadena, 2006; Vol. Evaluation Num-
ber 15.
We thank M. Trainer and M. Hallquist for helpful discussions.
This work was funded in part by NOAA’s Air Quality and
Health of the Atmosphere programs. The work at the
University of Colorado was supported by the National Science
Foundation (CHE-0310674).
(
(
(
(
15) Hakola, H.; Arey, J.; Aschmann, S.; Atkinson, R. Product for-
mation from the gas-phase reactions of OH radicals and O
with a series of monoterpenes. J. Atmos. Chem. 1994, 18, 75-
02.
16) Nozi e` re, B.; Spittler, M.; Ruppert, L.; Barnes, I.; Becker, K. H.;
Pons, M.; Wirtz, K. Kinetics of the reactions of pinonaldehyde
with OH radicals and with Cl atoms. Int. J. Chem. Kinet. 1999,
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Supporting Information Available
3
Diagrams of the experimental apparatus, molecular structures
for R-pinene, pinonaldehyde, and OH-pinonaldehyde ad-
ducts, representative measured OH temporal profiles, and
a detailed summary of literature data for R-pinene kinetics,
pinonaldehyde yield studies, and pinonaldehyde loss pro-
cesses are available in the Supporting Information. This
material is available free of charge via the Internet at http://
pubs.acs.org.
1
17) Kwok, E. S. C.; Atkinson, R. Estimation of hydroxyl radical
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