The gas-phase ozonolysis of 1-penten-3-ol, (Z)-2-penten-1-ol and 1-penten-3-one: Kinetics, products and secondary organic aerosol Formation

Article abstract of DOI:10.1524/zpch.2010.6141

The gas-phase ozonolysis of the biogenic unsaturated compounds 1-penten-3-ol, (Z)-2-penten- 1-ol and 1-penten-3-one has been investigated in two atmospheric simulation chambers. The following rate coefficients (in units of 10^-17 cm³ molecule^-1 s^-1) were determined at atmospheric pressure and 293±2 K using an absolute rate method: 1-penten-3-ol, (1.64±0.15); (Z)-2- penten-1-ol, (11.5±0.66); 1-penten-3-one, (1.17±0.15). Reaction products were identified by in situ FTIR spectroscopy and gas chromatography - mass spectrometry (GC-MS). The major products and their average molar yields in the presence of a radical scavenger at relative humidity < 1% were: formaldehyde (0.49±0.02), 2-hydroxybutanal (0.46±0.03) and propanal (0.15±0.02) from 1-penten-3-ol; propanal (0.39±0.03) and glycolaldehyde (0.43±0.04) from (Z)-2-penten-1-ol; formaldehyde (0.37±0.02) and 2-oxobutanal (0.49±0.03) from 1-penten-3- one. The formation of secondary organic aerosol was also observed with yields ranging from 0.13-0.17 for the unsaturated alcohols. Significantly lower yields of around 0.03 were measured for 1-penten-3-one. The results of this work are used to determine atmospheric lifetimes and reaction mechanisms for the gas-phase ozonolysis of 1-penten-3-ol, (Z)-2-penten-1-ol and 1- penten-3-one. The broader atmospheric implications of this work are also discussed. by Oldenbourg Wissenschaftsverlag.

Full text of DOI:10.1524/zpch.2010.6141

Z. Phys. Chem. 224 (2010) 1059–1080 . DOI 10.1524.zpch.2010.6141
© by Oldenbourg Wissenschaftsverlag, München
The Gas-phase Ozonolysis of 1-Penten-3-ol,
(Z)-2-Penten-1-ol and 1-Penten-3-one: Kinetics,
Products and Secondary Organic Aerosol
Formation
By M. A. O'Dwyer1, T. J. Carey1, R. M. Healy1, J. C. Wenger1,
B. Picquet-Varrault2, and J. F. Doussin2
,
*
1
Department of Chemistry and Environmental Research Institute, University College Cork,
Cork, Ireland.
Laboratoire Interuniversitaire des Systèmes Atmosphériques (LISA), UMR-CNRS 7583,
Universités de Paris 12 et Paris 7, CNRS, Créteil, France
2
Dedicated to Prof. Dr. Reinhard Zellner on the occasion of his 65th birthday
(Received December 23, 2009; accepted March 25, 2010)
Ozonolysis . 1-Penten-3-ol . (Z)-2-Penten-1-ol . 1-Penten-3-one
The gas-phase ozonolysis of the biogenic unsaturated compounds 1-penten-3-ol, (Z)-2-penten-
1-ol and 1-penten-3-one has been investigated in two atmospheric simulation chambers. The
following rate coefficients (in units of 10K17 cm3 moleculeK1 K1) were determined at atmos-
s
pheric pressure and 293 2 K using an absolute rate method: 1-penten-3-ol, (1.64 0.15); (Z)-2-
penten-1-ol, (11.5 0.66); 1-penten-3-one, (1.17 0.15). Reaction products were identified by in
situ FTIR spectroscopy and gas chromatography – mass spectrometry (GC-MS). The major
products and their average molar yields in the presence of a radical scavenger at relative humid-
ity < 1% were: formaldehyde (0.49 0.02), 2-hydroxybutanal (0.46 0.03) and propanal
(0.15 0.02) from 1-penten-3-ol; propanal (0.39 0.03) and glycolaldehyde (0.43 0.04) from
(Z)-2-penten-1-ol; formaldehyde (0.37 0.02) and 2-oxobutanal (0.49 0.03) from 1-penten-3-
one. The formation of secondary organic aerosol was also observed with yields ranging from
0.13–0.17 for the unsaturated alcohols. Significantly lower yields of around 0.03 were measured
for 1-penten-3-one. The results of this work are used to determine atmospheric lifetimes and
reaction mechanisms for the gas-phase ozonolysis of 1-penten-3-ol, (Z)-2-penten-1-ol and 1-
penten-3-one. The broader atmospheric implications of this work are also discussed.
*
Corresponding author. E-mail: j.wenger@ucc.ie
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M. A. O'Dwyer et al.
1. Introduction
The gas-phase reactions of ozone with unsaturated volatile organic compounds
(VOCs) are of major importance in atmospheric chemistry [1, 2]. In addition to
being an atmospheric sink for both ozone and unsaturated VOCs, ozonolysis
reactions are also significant sources of oxygenated hydrocarbons, radicals and
secondary organic aerosol (SOA) in the atmosphere [2]. In order to determine
the atmospheric impact of a specific ozonolysis reaction, detailed information on
the kinetics, products and SOA formation is required.
The oxygenated pentene derivatives, 1-penten-3-ol, (Z)-2-penten-1-ol and 1-
penten-3-one, are part of a family of compounds known as the green leaf vola-
tiles which are emitted by plants following leaf damage caused by cutting, drying
etc. [3]. In particular, it has been shown that these oxygenated pentene deriva-
tives are emitted as a result of freeze-thaw cycles [4] and total mixing ratios of
up to 5 ppbv were observed in air following a freezing spell in the Austrian Alps
[5]. The subsequent atmospheric degradation of 1-penten-3-ol, (Z)-2-penten-1-ol
and 1-penten-3-one can be initiated via gas-phase reaction with hydroxyl (OH)
radicals, nitrate (NO3) radicals and ozone. A number of laboratory studies have
been performed to date. Orlando et al. [6] determined rate coefficients and pro-
ducts for the reaction of OH with 1-penten-3-ol and (Z)-2-penten-1-ol, whilst
Jiménez et al. [7] recently reported temperature-dependent kinetic data for the
photooxidation of 1-penten-3-ol and 1-penten-3-one. The rate coefficients for
reaction of the three compounds with NO3 have been determined by Pfrang et
al. [8, 9], whilst Grosjean et al. investigated the kinetics and products of the
ozonolysis reactions [10–13]. Apart from the reaction of 1-penten-3-ol with OH,
each of the atmospherically relevant reactions has only been studied once. Fur-
ther experimental work is therefore required in order to verify kinetic and mecha-
nistic parameters and also to ascertain the SOA formation potential of these
biogenic compounds.
In this work the gas-phase ozonolysis of 1-penten-3-ol, (Z)-2-penten-1-ol and
1-penten-3-one has been performed in two atmospheric simulation chambers.
Absolute rate coefficients have been determined and the reaction products identi-
fied by in situ FTIR spectroscopy and gas chromatography – mass spectrometry
(GC-MS). The formation of secondary organic aerosol during these reactions
was also investigated.
2. Experimental
Experiments were performed in the 3910 L atmospheric simulation chamber at
University College Cork (UCC) and in the 977 L reactor at the Laboratoire
Interuniversitaire des Systèmes Atmosphériques (LISA) in Paris.
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The Gas-phase Ozonolysis
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2.1 3910 L chamber at UCC
The chamber consists of a cylinder (4 m long, 1.2 m diameter) made of chemi-
cally inert FEP Teflon foil sealed at the ends by two aluminium endplates coated
with FEP foil. A detailed description is provided elsewhere [14, 15]. The cham-
ber design has been modified to include fans, located at both ends of the cylinder,
in order to promote rapid mixing of reactants. The chamber was operated at
293 2 K using purified dry air (relative humidity < 0.4%) at 0.1–1 mbar above
atmospheric pressure. The chamber was equipped with a multiple reflection opti-
cal arrangement coupled to an FTIR spectrometer (BioRad Excalibur) for chemi-
cal analysis by in situ FTIR spectroscopy using a path length of (229.6 0.6) m.
Infrared spectra were obtained throughout the reactions at a resolution of 1 cmK1
using a narrow-band mercury cadmium telluride (MCT) detector and derived
from the co-addition of 300 scans collected over 5 min. The oxygenated alkenes
were added to the chamber using an inlet system in which known amounts of
the substances were heated in a small flow of purified air. Ozone was produced
by flowing oxygen through an ozone generator (Yanco Ozone Services GE60.
FM5000) and into the chamber. Between experiments the chamber was cleaned
by flushing with purified air at a flow rate of 150 L minK1 for a minimum of
four hours and usually overnight. The humidity and temperature in the chamber
was measured using a dew point hygrometer and temperature meter (DM70 Vais-
ala).
Kinetics experiments were performed by measuring the rate of ozone decay
in the presence of known excess concentrations of the oxygenated alkene [16,
17]. Ozone was added to the chamber and after a period of 20–30 minutes, the
alkene was rapidly added. The initial reactant concentrations were varied as fol-
lows; [O3] = (0.1–6.5)!1013 molecule cmK3 and [oxygenated alkene] = (0.2–
7.4)!1014 molecule cmK3. The estimated uncertainty in the concentration of the
oxygenated alkenes is 1%. In all experiments, the initial alkene concentration
was in excess by a factor of 10 or more to ensure that pseudo-first-order condi-
tions prevailed. The concentration of ozone was measured at 10 second intervals
throughout the reactions using an ozone analyser (Thermo Electron Corporation,
model 49i) connected to the chamber via a Teflon tube. The ozone analyser
works on the principle of UV absorption at 254 nm and although some of the
reaction products (e.g. carbonyls, hydroperoxides) can absorb light at this wave-
length, they were not generated in sufficient amounts to cause any interference
with the ozone measurements. The loss of ozone to the walls of the chamber
was measured periodically by performing control experiments where no alkene
was present in the chamber. The loss of ozone was found to be negligible over
the time scale of the kinetic experiments (typically of the order of minutes and
seldom exceeding 15 minutes), confirming that reaction with the oxygenated
alkenes was the only important removal process for ozone. Dilution of the reac-
tant mixture due to sampling was also negligible.
Product studies were performed with initial mixing ratios of 0.5–2.0 ppmV
for ozone and the oxygenated alkenes in the presence of carbon monoxide (7000–
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1062
M. A. O'Dwyer et al.
7500 ppmV) which acts as a scavenger for any OH radicals produced during the
reactions. The reactants and products were quantified using calibrated reference
infrared spectra obtained by introducing known quantities of pure materials into
the chamber. The formation and evolution of SOA was monitored using a scan-
ning mobility particle sizer (TSI model 3936). During these experiments, O-
(pentafluorobenzyl)-hydroxyl amine (PFBHA) derivatisation [18] was employed
to identify the carbonyl compounds formed. At the end of each experiment the
contents of the chamber were bubbled for 30 minutes at a flow rate of
0.5 L minK1 through two 10 mL glass impingers connected in series and filled
with a solution of PFBHA dissolved in acetonitrile (10 mg LK1). A column filled
with KI crystals was inserted between the chamber and the impingers to prevent
ozone from entering the solutions. The impingers were immersed in a water-ice
bath during sampling to increase the efficiency of the trapping process. A blank
sample was also taken before the addition of O3 to the chamber to determine
background levels. Samples were kept in the dark for approximately 48 hours at
room temperature to ensure complete conversion of the carbonyls to their oxime
derivatives. One microlitre of the solution was analysed by GC-MS (Varian CP-
3800 GC coupled to Saturn 2000 MS) using a CP-Sil8 fused silica capillary
column (Varian, 30 m, 0.25 mm i.d., 0.5μm film thickness). The injector temper-
ature was held at 200°C throughout the analysis. The oven temperature was
programmed to maintain a temperature of 60°C for 1 min, then increased to
100°C at a rate of 5°C minK1, then to 280°C at a rate of 10°C minK1, and finally
to 310°C at 30°C minK1 and held at this temperature for 5 min. The MS was
operated in electron impact (EI) or chemical ionisation (CI) mode, using methane
as the CI reagent gas, over the mass range 40 to 650.
2.2 977 L chamber at LISA
Product studies were also carried out at 295 2 K and atmospheric pressure in
the 977 L reaction chamber at the LISA in Paris. The chamber is a pyrex tube,
6 m in length, equipped with a FTIR spectrometer (Bomem DA8-ME) coupled
to a multiple reflection White cell for in-situ analysis of gaseous species. Details
concerning the chamber and the experimental procedures are provided elsewhere
[19, 20]. Before each experiment the chamber was evacuated to a pressure of
1!10K2 mbar to ensure the walls of the chamber were free of any residual
compounds from previous experiments. The chamber was then filled to atmos-
pheric pressure with a gaseous mixture comprising 80% N2 and 20% O2 and the
mixing fans were started. The relative humidity was < 1%. The oxygenated
alkenes were added to the chamber by flowing N2 through known amounts of
the reactant in a 0.55 litre bulb and into the chamber. Initial mixing ratios were
in the range 0.9–6.0 ppmV. Carbon monoxide (7000–8000 ppmV), used as a
radical scavenger, was flowed into the chamber at a rate of 2 L minK1. After a
mixing period of around one hour, ozone (1.0–6.0 ppmV), generated by passing
oxygen through a silent discharge ozoniser (Kaufmann Umwelttechnik, GmbH),
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The Gas-phase Ozonolysis
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was then flowed into the chamber. Chemical analysis was performed throughout
the experiments using in-situ FTIR spectroscopy using a pathlength of 156 m.
Once the chamber was filled with the N2.O2 mixture a background FTIR spec-
trum was recorded by co-adding 600 interferograms. Infrared spectra in the 500–
4000 cmK1 range, with a resolution of 0.5 cmK1, were obtained for the duration
of the experiment by co-adding 200 scans collected over approximately six mi-
nutes. The reactants and products were quantified using calibrated reference in-
frared spectra obtained by introducing known quantities of pure materials into
the chamber.
2.3 Materials
The following compounds, with stated purities in brackets, were obtained from
Sigma Aldrich Chemical Company; 1-penten-3-ol (99%), (Z)-2-penten-1-ol
(95%), 1-penten-3-one (99%), formaldehyde (99%), ethanal (99%), n-propanal
(97%), n-butanal (99%), formic acid (99%), glycolaldehyde (99%), PFBHA
(≥98%) and acetonitrile (99.9%). Carbon monoxide (99.99%) and methane
(99.995%) were obtained from BOC gases and Air Liquide respectively.
3. Results and discussion
3.1 Kinetics studies
Reactions of ozone with the oxygenated pentene derivatives were performed
under pseudo first-order conditions;
d
K ln[O3] = k'[oxygenated alkene]
dt
where k# is the pseudo-first-order rate coefficient, given by k# = k[O3]. A plot
of ln[O3] versus time was obtained for each experiment and used to obtain the
slope k#. The plots exhibited a strong linear decay with time over a broad range
of concentrations during all experiments. Five or six experiments were performed
on each oxygenated alkene. Plots of k# versus starting alkene concentration are
shown in Figure 1, yielding straight lines with gradient k, the bimolecular rate
coefficient for ozonolysis. A summary of the rate coefficients obtained in this
work is presented in Table 1. The indicated errors associated with k are twice
the standard deviation arising from the least squares fit of the second-order data.
The available literature data are also listed in Table 1. Although the rate coeffi-
cient obtained for 1-penten-3-ol is in very good agreement with that reported by
Grosjean et al. [11] the values for (Z)-2-Penten-1-ol and 1-penten-3-one differ
by factors of around 1.5 and 2.0 respectively. Grosjean et al. [10, 11] also ob-
tained the rate coefficients by measuring the decay of ozone by UV photometry
in the presence of excess oxygenated alkene. However, a smaller number of
experiments were performed on each compound (typically 3) and there was little
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1064
M. A. O'Dwyer et al.
Fig. 1. Plots of the pseudo-first-order rate coefficients (k#) versus initial alkene concentration
for the reaction of ozone with 1-penten-3-ol, (Z)-2-penten-1-ol and 1-penten-3-one at 293 2 K.
Table 1. Rate coefficients for the reaction of ozone with 1-penten-3-ol, (Z)-2-penten-1-ol and
1-penten-3-one.
Compound
k (10−17 cm3 molecule s−1
)
T (K)
Reference
1-penten-3-ol
1.64 0.15
1.79 0.18
293 2
289 1
This work
[11]
(Z)-2-penten-1-ol
11.5 0.66
16.9 2.50
293 2
288 1
This work
[11]
1-penten-3-one
1.17 0.15
0.60 0.04
293 2
285 1
This work
[10]
or no variation in the starting concentration of the oxygenated alkene. As a result,
the rate coefficients reported here could possibly be more reliable. Nevertheless,
further experiments using a different technique, e.g., the relative rate method
might help to resolve the discrepancies.
Reaction of ozone with the oxygenated alkenes proceeds via electrophilic
addition of ozone to the carbon-carbon double bond. Thus reactivity will be
affected by the nature, number and position of the substituents on the >C=C<
bond. Compounds with internal carbon-carbon double bonds have a higher react-
ivity than those with terminal >C=C< bonds because the electron-donating alkyl
substituents promote the electrophilic addition of ozone. Thus, (Z)-2-penten-1-
ol, has a considerably higher reactivity than both 1-penten-3-ol and 1-penten-3-
one. The parent alkenes, (Z)-2-pentene (k(O3) = 20.9!10K17 cm3 mole-
culeK1 sK1 [1]) and 1-pentene (k(O3) = 1.1!10K17 cm3 molecule sK1 [1]) also
exhibit the same reactivity pattern. There are two other observations of note.
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The Gas-phase Ozonolysis
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Firstly, 1-penten-3-ol and 1-penten-3-one exhibit a similar reactivity to their par-
ent alkene, indicating that the functional group does not significantly affect the
rate coefficient. Secondly, 1-penten-3-ol is slightly more reactive than its parent
alkene, while (Z)-2-penten-1-ol is slightly less reactive. As indicated by Grosjean
et al. [11], these differences in reactivity may reflect a specific influence of the –
OH group, such as electronic and steric effects during the addition step, stability
of the primary ozonide, or stability of the hydroxyalkyl-substituted Criegee inter-
mediate. Theoretical calculations based on transition state theory, such as those
performed by Sato et al. [21], may help to provide further information on the
factors affecting the reactivity of the oxygenated alkenes towards ozone.
3.2 Product studies
FTIR spectroscopy was used to identify and quantify products of the reaction of
O3 with 1-penten-3-ol, (Z)-2-penten-1-ol and 1-penten-3-one. FTIR spectra ob-
tained for the ozonolysis of (Z)-2-penten-1-ol are shown in Figure 2. The data
obtained from the spectral analysis were used to produce concentration-time pro-
files and product yield plots by subtraction of calibrated reference spectra. Wall
loss rates were measured for reactants and all commercially available products,
but were found to be negligible over the timescale of the experiments. Typical
product yield plots are shown in Figures 3–5 and a summary of the products
identified and quantified by FTIR spectroscopy is shown in Table 2. As shown
in Figure 2, subtraction of the absorption features of reactants and known pro-
ducts results in a residual spectrum. For (Z)-2-penten-1-ol, the residual spectrum
only contains weak absorption features, indicating that the majority of reaction
products have been identified. In contrast, the residual spectra for the 1-penten-
3-ol and 1-penten-3-one reactions exhibit strong absorption bands in the carbonyl
region, 1650–1850 cmK1, Figure 6. Since 2-hydroxybutanal and 2-oxobutanal
are major products of the reaction of ozone with 1-penten-3-ol and 1-penten-3-
one respectively [12, 13], then it is highly probable that their absorption bands
contribute to the residual spectra. Unfortunately, neither of these compounds is
commercially available and calibrated reference spectra could not be obtained.
However, the position of the main carbonyl peak is very similar to that observed
in butanal, Figure 6, and an estimate of the yields of these products was obtained
by careful subtraction of this carbonyl absorption feature from the residual spec-
tra.
The identification of 2-hydroxybutanal and 2-oxobutanal as major products
of the reaction of ozone with 1-penten-3-ol and 1-penten-3-one respectively was
confirmed by PFBHA derivatisation followed by GC-MS analysis. Carbonyl
compounds were distinguished by their oxime derivatives, which showed the
characteristic peak at m.z = 181 [18] due to the C6F5CH2+ ion and were identified
by their molecular ion. Using chemical ionisation (CI), the oxime derivatives
also produce a strong protonated molecular ion (M+1) and hydroxycarbonyls
exhibit a noticeable peak at (M-17) due to the loss of OH. Additional peaks that
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M. A. O'Dwyer et al.
Fig. 2. FTIR spectra in the range 3500–500 cmK1 obtained from the reaction of ozone with
(Z)-2-penten-1-ol in the 977 L chamber: 1. (Z)-2-penten-1-ol before ozone addition; 2. 90 min
after the addition of ozone; 3. Propanal reference spectrum; 4. Glycolaldehyde reference spec-
trum; 5) Residual spectrum after subtraction of (Z)-2-penten-1-ol, propanal and glycolaldehyde.
Note that the CO and CO2 (2390–1890 cmK1) region has been removed for reasons of clarity.
Fig. 3. Typical product yield plot obtained for the ozonolysis of 1-penten-3-ol in the 977 L
chamber.
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The Gas-phase Ozonolysis
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Fig. 4. Typical product yield plot obtained for the ozonolysis of (Z)-2-penten-1-ol in the 3910 L
chamber.
Fig. 5. Typical product yield plot obtained for the ozonolysis of 1-penten-3-one in the 977 L
chamber.
were used to identify the carbonyl compounds include m.z = M-30 and M+181,
resulting from loss of NO from the neutral molecule, or from the coupling of a
C6F5CH2+ ion with the neutral molecule. It should be noted that some of the
derivatives exist as geometric isomers consisting of Z and E forms due to re-
stricted rotation of the carbon-nitrogen double bond. In addition, dicarbonyl com-
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M. A. O'Dwyer et al.
Fig. 6. FTIR spectra in the range 3500–500 cmK1 (obtained in the 977 L chamber): 1. Residual
spectrum for reaction of 1-penten-3-ol with ozone; 2. Residual spectrum for reaction of 1-
penten-3-one with ozone; 3. Butanal reference spectrum.
pounds such as 2-oxobutanal can exist in both the single and double derivative
forms. However, the long derivatisation times employed in this study ensured
complete conversion of the dicarbonyls to their double derivatives [22]. A list of
the carbonyl products detected using this method and the associated diagnostic
ions is provided in Table 3.
In general, there is very good agreement between the product yields obtained
in both chambers. The slight variation in the yields observed for formaldehyde
may be due to small differences in the reaction conditions during experiments
performed in the chambers. For example, variations in the amount of scavenger
or reactants present may influence the extent to which secondary reactions can
occur. Another possibility is that the slightly different amounts of water vapour
present in the chambers could affect the reaction pathways of the Criegee inter-
mediates and thus alter product distributions.
The results obtained in this work are also compared to those reported by
Grosjean and Grosjean [12, 13], who performed the reactions at a relative humid-
ity of ca. 55% and used the 2,4-dinitrophenylhydrazine (DNPH) derivatisation
method coupled with liquid chromatography, for the identification of carbonyl
compounds. Although there is a reasonable level of agreement between the yields
measured in the two studies, it seems probable that the variations in product
distributions may be due, at least in part, to the large difference in water vapour
present during the experiments.
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The Gas-phase Ozonolysis
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Table 2. Products resulting from the gas-phase ozonolysis of 1-penten-3-ol, (Z)-2-penten-1-ol
and 1-penten-3-one.
Compound
Product
Average Product Yielda
Previous studies
[12,13]
UCC
LISA
1-penten-3-ol
Formaldehyde
0.42 0.02
0.56 0.02
0.47 0.03b
0.34 0.04
0.30 0.05
0.12 0.01
-
2-Hydroxybutanal 0.44 0.03b
Propanal
0.15 0.02
c
0.15 0.02
c
Formic acid
(Z)-2-penten-1-ol Propanal
Glycolaldehyde
0.38 0.03
0.44 0.04
0.39 0.02
0.51 0.02
0.53 0.04
0.07 0.02
0.08 0.01
0.04 0.01
0.55 0.07
0.44 0.03
-
0.42 0.03
Formaldehyde
Ethanal
-
d
-
-
Methylglyoxal
Formaldehyde
2-Oxobutanal
Formic acid
-
-
1-penten-3-one
0.41 0.02
0.33 0.02
0.51 0.03b
0.46 0.03b
c
b
aAverage yields are based on 3–4 experiments on each reaction system at UCC and 2–3 ex-
periments at LISA. Errors are twice the standard deviation arising from the least squares fit
of the data and represent precision only.
bEstimated yield based on subtraction of butanal carbonyl peak in FTIR spectra.
cSecondary product, not quantified.
dIdentified by GC-MS but not quantified.
3.3 Reaction mechanisms
The ozonolysis of unsaturated hydrocarbons proceeds via electrophilic addition
of the O3 molecule across the >C=C< bond forming an ozonide which then
cleaves to yield two primary carbonyls and the corresponding Criegee intermedi-
ates [1, 2]. The mechanisms for the reaction of ozone with 1-penten-3-ol, (Z)-2-
penten-1-ol and 1-penten-3-one are presented in Figures 7–9. Assuming that the
primary carbonyls are only produced from direct cleavage of the ozonide, the
sum of their respective yields should be unity. The average of the product yields
obtained in this work give total primary carbonyl yields of (0.96 0.05) for 1-
penten-3-ol, (0.82 0.07) for (Z)-2-penten-1-ol and (0.86 0.05) for 1-penten-3-
one. The small deviations from a yield of unity are likely to be a result of a
combination of factors including: (i) uncertainties in quantification of the pro-
ducts, especially 2-hydroxybutanal and 2-oxobutanal; (ii) secondary reactions of
the aldehydes; (iii) possible incorporation of the aldehydes into the aerosol phase,
as outlined below.
The relative yields of the primary carbonyls can also be used to determine the
branching ratio between the two decomposition channels of the ozonide. Inspection
of the data in Table 2 indicates that there is no significant preference for the forma-
tion of any particular primary carbonyl, with branching ratios of around 50:50. This
observation is in line with results obtained for the corresponding alkenes [1] and
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M. A. O'Dwyer et al.
Table 3. Carbonyl products identified using PFBHA derivatisation and GC-MS analysis.
Compound Product
m/z (EI)
m/z (CI)
1-penten-3-ol Formaldehyde
225 (M); 406 (M + 181);
195 (M-30); 181
226(M + 1); 406 (M + 181)
195 (M-30); 181
Propanal
253 (M); 434 (M + 181)
223 (M-30); 181
254 (M + 1); 434 (M + 181)
223 (M-30); 181
2-Hydroxy-
butanal
283 (M); 253 (M-30)
181
284 (M + 1); 464 (M + 181)
253 (M-30); 266 (M-17);
181
(Z)-2-penten- Ethanal
1-ol
239 (M); 420 (M + 181)
209 (M-30); 181
Propanal
253 (M); 434 (M + 181)
223 (M-30); 181
254 (M + 1); 434 (M + 181)
223 (M-30); 181
Glycolaldehyde 255 (M); 436 (M + 181)
225 (M-30); 181
256 (M + 1); 436 (M + 181)
225 (M-30); 238 (M-17);
181
1-penten-3-
one
Formaldehyde
2-Oxobutanal a
225 (M); 406 (M + 181)
195 (M-30); 181
226(M + 1); 406 (M + 181)
195 (M-30); 181
476 (M); 279 (M-197)
446 (M-30); 181
477 (M + 1); 279 (M-197)
446 (M-30); 181
a
2-Oxobutanal was only detected as a double derivative
suggests that the presence of the oxygenated functional group, which is not directly
linked to the >C=C< bond, does notgreatly affect the reactivity of the ozonide. How-
ever, it is interesting to note that a 75:25 branching ratio is observed in the reaction
of ozone with methyl vinyl ether [23], with the formation of the longer carbonyl and
shorter Criegee intermediate preferred. In this case, the methoxy substituent is
linked directly to the >C=C< bond and may therefore exert a stronger influence on
the reactivity of the ozonide.
The Criegee intermediates contain excess energy (denoted by *) and can un-
dergo collisional stabilisation and follow a variety of decomposition pathways in-
cluding; (i) O-atom channel; (ii) ester or ‘hot’ acid channel and (iii) hydroperoxide
channel. Although, in general, there is evidence for the existence of all three decom-
position pathways, the hydroperoxide channel appears to be the principal decompo-
sition route for the majority of Criegee intermediates, since the two former channels
typically only account for < 5% of the reaction products [1, 2]. The branching ratio
for the hydroperoxide channel can often be estimated from the yield of OH radicals
produced during the reaction, which varies with the structure of the alkene, but is
generally in the range 30–70% [1].
The simplest Criegee intermediate, (CH2OO)*, is a product of the ozonolysis
of both 1-penten-3-ol and 1-penten-3-one. The major products arising from de-
composition of (CH2OO)* are CO, OH, H2O, CO2, H2 and the stabilised Criegee
species [1, 2]. The determination of product yields for H2O and CO2 was not
attempted due to interference from background levels of these compounds in the
reaction chambers and in the housing for the optical components. The yield of
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The Gas-phase Ozonolysis
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Fig. 7. Mechanism for the gas-phase reaction of ozone with 1-penten-3-ol.
CO could also not be determined because it was used as the OH scavenger. The
stabilised Criegee, CH2OO, is believed to undergo a variety of reactions includ-
ing; (i) reaction with water to form HCHO and H2O2; (ii) reaction with HCHO
to produce formic acid, HCOOH; (iii) reaction with HCOOH to produce hydrop-
eroxymethyl formate, HC(O)OCH2OOH; and (iv) reaction with water to produce
hydroxymethyl hydroperoxide, HOCH2OOH [1, 2]. Whilst formic acid was posi-
tively identified as a reaction product using FTIR spectroscopy, its concentration-
time profile is indicative of a secondary product, suggesting that it may originate
from the reaction of the stabilised Criegee with formaldehyde;
CH2OO + HCHO / HCOOH + HCHO
Note that formaldehyde is effectively a catalyst during this reaction. Hy-
droxymethyl hydroperoxide and hydroperoxymethyl formate may also be present
in the reaction chambers and could thus be responsible for some of the absorption
features in the residual infrared spectra. However, this cannot be confirmed due
to the lack of reference spectra for these compounds.
The ozonolysis of 1-penten-3-ol produces the Criegee intermediates
(CH2OO)* and (CH3CH2CHOHCHOO)*. Assuming that, like other substituted
Criegee intermediates, the major fate of (CH3CH2CHOHCHOO)* is decomposi-
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1072
M. A. O'Dwyer et al.
Fig. 8. Mechanism for the gas-phase reaction of ozone with (Z)-2-penten-1-ol.
tion via the hydroperoxide channel, the expected organic products are propanoic
acid and 2-oxobutanal, Figure 10. However, neither of these products was de-
tected by FTIR spectroscopy or GC-MS. Furthermore, the three decomposition
reactions (hydroperoxide channel, O-atom channel and ester.hot acid channel)
do not account for the formation of propanal, which was identified by GC-MS
and FTIR spectroscopy with a molar yield of 0.15. This strongly suggests that
(CH3CH2CHOHCHOO)* is involved in at least one other reaction pathway. The
formation of propanal was also observed by Grosjean and Grosjean [12], who
proposed that it may be produced from direct unimolecular decomposition of the
excited Criegee, as shown in Figure 10.
The ozonolysis of (Z)-2-penten-1-ol produces the Criegee intermediates
(CH2OHCHOO)* and (CH3CH2CHOO)*. The latter species can produce methyl-
glyoxal, formic acid, CO and OH radicals via the hydroperoxide channel. Meth-
ylglyoxal was not observed as a product in this work, although, Grosjean and
Grosjean [12] did detect a small amount of methylglyoxal during the ozonolysis
of (Z)-2-penten-1-ol and attributed this to decomposition of the hydroperoxide
originating from (CH3CH2CHOO)*. For the other Criegee intermediate,
(CH2OHCHOO)*, the hydroperoxide channel results in the formation of glyoxal
and formic acid, Figure 11. However, glyoxal was not detected as a product,
both in this work and by Grosjean and Grosjean [12], indicating that the hydrop-
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The Gas-phase Ozonolysis
1073
Fig. 9. Mechanism for the gas-phase reaction of ozone with 1-penten-3-one.
eroxide channel is not an important pathway for this species. Direct unimolecular
decomposition of (CH2OHCHOO)* and (CH3CH2CHOO)* may possibly ac-
count for the observed formation of formaldehyde and ethanal respectively [12].
The ozonolysis of 1-penten-3-one produces the Criegee intermediates
(CH2OO)* and (CH3CH2C(O)CHOO)*. It is of interest to note that the hydroper-
oxide channel is not possible for (CH3CH2C(O)CHOO)* since there is no hydro-
gen atom on the ꢀ-carbon. Thus it appears that unimolecular decomposition may
dominate. This pathway, shown in Figure 12, results in the formation of the
propionyl radical, CH3CH2CO, which rapidly reacts with oxygen to produce
the corresponding peroxy propionyl radical. Under the experimental conditions
employed in this study, this latter species can undergo reaction with other peroxy
radicals to ultimately produce ethanal and CO2 or react with HO2 to yield a
hydroperoxide or propanoic acid. Ethanal was not detected as a product in the
experiments performed in this work and was also not detected by Grosjean and
Grosjean [13]. It is possible that the hydroperoxide species, CH3CH2C(O)OOH,
may be present in the reaction chambers and could thus be responsible for some
of the absorption features in the residual spectra shown in Figure 6. However,
this cannot be confirmed due to the lack of a reference spectrum.
The results obtained in this work indicate that the hydroperoxide channel,
which is usually the major reaction pathway for alkyl substituted Criegee inter-
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1074
M. A. O'Dwyer et al.
Fig. 10. Proposed reaction pathways for the (CH3CH2CHOHCHOO)* Criegee intermediate
produced from the reaction of ozone with 1-penten-3-ol.
mediates, is not as important for oxygenated Criegee intermediates. These spe-
cies appear to undergo direct unimolecular decomposition more readily to yield
so-called secondary carbonyls, as described by Grosjean and Grosjean [12]. It is
also possible that the collisional stabilisation channel may be significant for these
oxygenated Criegee intermediates [1, 2]. Although no information on the yields
and possible reactions of the stabilized Criegee species can be obtained from the
experiments performed in this study, it seems likely that they could react with
HCHO, HCOOH and H2O, in an analogous manner to CH2OO, to produce acids
and hydroperoxides.
Another possibility worth considering is that the hydroperoxide channel is
still important for the oxygenated Criegee intermediates, but that the resulting
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The Gas-phase Ozonolysis
1075
Fig. 11. Proposed reaction pathways for the (CH2OHCHOO)* Criegee intermediate produced
from the reaction of ozone with (Z)-2-penten-1-ol.
hydroxylated hydroperoxides undergo different reaction pathways compared to
their alkyl counterparts. For example, the hydroxylated hydroperoxides shown
in Figures 10 and 11 may possibly undergo keto-enol tautomerism to produce
CH3CH2C(O)CH2OOH and HC(O)CH2OOH respectively. However, such reac-
tions remain speculative until further information becomes available on the react-
ivity of oxygenated Criegee intermediates.
3.4 Secondary organic aerosol formation
The formation of secondary organic aerosol during the ozonolysis of the oxygen-
ated pentene derivatives was observed in the 3910 L simulation chamber. The
experiments were performed in the absence of seed aerosol and under dry condi-
tions, which favoured the formation of new particles by nucleation. The temporal
evolution of the aerosol size and number distributions were similar in all experi-
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1076
M. A. O'Dwyer et al.
Fig. 12. Proposed reaction pathway for the (CH3CH2C(O)CHOO)* Criegee intermediate pro-
duced from the reaction of ozone with 1-penten-3-one.
Fig. 13. Number and size distribution of particles formed during the ozonolysis of 1-penten-3-
ol in the 3910 L reaction chamber. The numbers in the legend refer to the time (in sec) elapsed
since ozone was added to the chamber.
ments. Typical data for 1-penten-3-ol are shown in Figure 13. A ‘burst’ of parti-
cles with diameters in the range 30–50 nm was observed immediately after the
introduction of ozone. The subsequent growth of these particles via coagulation
and condensation of gas-phase species was rapid and caused a drop in particle
number. Towards the end of the experiments mean diameters in the range 130–
150 nm were measured.
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The Gas-phase Ozonolysis
1077
Table 4. Yields of secondary organic aerosol produced during the ozonolysis of 1-penten-3-ol,
(Z)-2-penten-1-ol and 1-penten-3-one.
Compound
Initial
Conc.
Mass
Mass of
Aerosol
Formeda
Aerosol Yieldb
Reacted
(μg m−3
)
(μg m−3
)
(μg m−3
466
)
1-Penten-3-ol
5250
5057
2891
5316
6215
7189
8140
3424
1970
2329
3566
3114
5038
8140
0.136
0.166
0.169
0.156
0.164
0.034
0.028
327
393
(Z)-2-penten-1-ol
556
510
1-Penten-3-one
169
225
a
Assuming a density of 1.0 g cmK3
Calculated from (mass of aerosol formed).(mass of compound reacted)
.
b
The yield of SOA produced in each experiment was determined from the
ratio of the aerosol mass formed to the amount of hydrocarbon reacted at the
point where the maximum particle concentration was observed. The aerosol mass
was obtained from the measured volume concentration using a density of
1 g cmK3 and was not corrected for possible wall loss. The calculated yields are
listed in Table 4. Yields of 0.13–0.17 were obtained for the alcohols, which
compares with yields of ca. 0.10 and 0.09 reported for the ozonolysis of (Z)-3-
hexen-1-ol and (Z)-3-hexenyl acetate respectively, under similar reaction condi-
tions [24, 25]. It should be noted that in the experiments performed here and
elsewhere [24–26], the initial mixing ratios of reactants are considerably higher
than those observed in the ambient atmosphere. This is a general feature of
simulation chamber experiments and arises from the requirement to generate
sufficient aerosol mass for reliable measurements to be made. The extrapolation
of SOA yields obtained from chamber experiments to realistic atmospheric con-
ditions is subject to a high degree of uncertainty and remains a topical issue [26].
The large difference in aerosol yields observed for 1-penten-3-ol and 1-
penten-3-one indicates that there are significant differences in the chemistry of
the species produced during the ozonolysis reactions. As outlined above, the
major difference appears to be the absence of the hydroperoxide channel for
(CH3CH2C(O)CHOO)*. Thus it may be speculated that the hydroperoxide chan-
nel plays an important role in aerosol formation. However, recent work by Sad-
ezky et al. [27] suggests that the stabilized Criegee intermediates may in fact
combine or react with the parent alkene to produce oligomeric structures which
can condense to form aerosol. At present, the reactions influencing SOA forma-
tion during the ozonolysis of unsaturated hydrocarbons are the subject of much
uncertainty and speculation [26]. It seems that water plays an important role by
acting as a scavenger for Criegee intermediates. Variations in the relative humid-
ity can thus affect product distributions and SOA yields. Further work over a
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1078
M. A. O'Dwyer et al.
Table 5. Atmospheric lifetimes for 1-penten-3-ol, (Z)-2-penten-1-ol and 1-penten-3-one calcu-
lated using; 12 hour daytime average [OH] = 1.6!106 molecule cmK3, 24 hour average [O3] =
7!1011 molecule cmK3, 12 hour night-time average [NO3] = 5!108 molecule cmK3 [27].
Compound
1-penten-3-ol
τOH
τO3
τNO3
40 hd
3.6 hd
5910 he
2.6 ha
1.6 ha
7.4 hb
23.5 hc
3.7 hc
29.2 hc
(Z)-2-penten-1-ol
1-penten-3-one
a
b
c
d
e
Using the rate coefficient determined by Orlando et al. [6].
Using the rate coefficient determined by Jiménez et al. [7].
Using the rate coefficient determined in this work.
Using the rate coefficient determined by Pfrang et al. [9].
Using the rate coefficient determined by Pfrang et al. [8].
range of experimental conditions is clearly required to determine the key species
and mechanisms responsible for aerosol production and growth.
3.5 Atmospheric implications
The atmospheric lifetime of a compound with respect to reaction with a species
X can be calculated by using the general equation (τx) = 1.kx[X], where kx is
the bimolecular rate coefficient and [X] is the tropospheric concentration of the
reactive species. The kinetic data obtained in this work have been used to deter-
mine the atmospheric lifetimes of the oxygenated pentene derivatives with re-
spect to reaction with ozone. The data, along with the calculated lifetimes for
reaction with the other important oxidising species, OH and NO3 radicals, is
presented in Table 5. The results indicate that reaction with OH radicals is the
dominant atmospheric loss process for each compound. For (Z)-2-penten-1-ol,
reaction with O3 and NO3 are also significant, while ozonolysis is only of minor
importance for 1-penten-3-ol and 1-penten-3-one. Jiménez et al. [7] have also
shown that direct photolysis by sunlight is not an important atmospheric degrada-
tion pathway for these compounds.
Whether initiated by OH [6] or ozone [12, 13], atmospheric degradation of
the oxygenated pentene derivatives results in the formation of aldehydes, which
can react with OH and NO3 radicals, and also undergo photolysis by sunlight,
with lifetimes typically less than 1 day [28]. The high reactivity of the oxygen-
ated pentene derivatives and their oxidation products implies that large emissions
of these biogenic species will contribute to the formation of ozone and SOA in
the atmospheric boundary layer and therefore impact on human health and cli-
mate. In addition, the observed formation of SOA from the oxygenated pentene
derivatives may have interesting implications for the chemistry of the tropo-
sphere, since it gives further strength to the belief that smaller molecular weight
biogenic compounds can give rise to aerosols [26], suggesting that the chemistry
of the rural troposphere is more complicated than first thought.
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The Gas-phase Ozonolysis
1079
Acknowledgement
This work was funded by the European Commission (project EUROCHAMP,
contract number RII3-CT-2004–505968) and the European Science Foundation
(INTROP programme).
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