Reactions of hydroxyl radicals and ozone with acenaphthene and acenaphthylene

Article abstract of DOI:10.1021/es025761b

Acenaphthene and acenaphthylene are polycyclic aromatic hydrocarbons (PAHs) emitted into the atmosphere from a variety of incomplete combustion sources such as diesel exhaust. Both PAHs are present in the gas phase under typical atmospheric conditions and

Full text of DOI:10.1021/es025761b

Environ. Sci. Technol. 2002, 36, 4302-4311
Reactions of Hydroxyl Radicals and
Ozone with Acenaphthene and
Acenaphthylene
†
, §
F A B I E N N E R E I S E N
J A N E T A R E Y* , † , ‡ , §
A N D
Air Pollution Research Center, Interdepartmental Program in
Environmental Toxicology, and Department of Environmental
Sciences, University of California, Riverside, California 92521
(
4, 8). Reaction with ozone has also been shown to be an
important loss process for acenaphthylene, due to the
presence of an unsaturated bond in the cyclopentafused ring
(
4). Although both compounds are expected to have lifetimes
in the troposphere of only a few hours, there is some
disagreement concerning the rate constants of the gas-phase
reactions with the OH radical (4-7). Therefore, we used
relative rate techniques to reexamine those rate constants
Acenaphthene and acenaphthylene are polycyclic
aromatic hydrocarbons (PAHs) emitted into the atmosphere
from a variety of incomplete combustion sources such
as diesel exhaust. Both PAHs are present in the gas phase
under typical atmospheric conditions and therefore can
undergo atmospheric gas-phase reactions with the hydroxyl
and that of O
The mechanisms of the gas-phase reactions of acenaph-
thene and acenaphthylene with the OH radical and O have
3
with acenaphthylene.
3
not been fully elucidated and only limited product informa-
tion for these atmospherically important reactions has to
date been reported (5). In this study, we have used in-situ
direct air sampling atmospheric pressure ionization mass
spectrometry (API-MS) as well as gas chromatography
techniques to investigate the products of the gas-phase
reactions of OH radicals with acenaphthene and acenaph-
(
OH) radical and for acenaphthylene with ozone. Using a
relative rate method, rate constants have been measured at
96 ( 2 K for the OH radical reactions with acenaphthene
2
-
11
3
-1
and acenaphthylene of (in units of 10 cm molecule
s
-
1
) 8.0 ( 0.4 and 12.4 ( 0.7, respectively, and for the O3
-
16
reaction with acenaphthylene of (1.6 ( 0.1) × 10
3
-1 -1
thylene and of O
3
with acenaphthylene, including API-MS
cm molecule
s
. The products of the gas-phase reactions
experiments utilizing acenaphthene-d10 and acenaphthylene-
of acenaphthene and acenaphthylene and their fully
deuterated analogues have been investigated using in
situ atmospheric pressure ionization tandem mass
spectrometry (API-MS) and gas chromatography-mass
spectrometry (GC-MS). The major products identified from
the OH radical-initiated reaction of acenaphthene and
acenaphthylene were a 10 carbon ring-opened product
and a dialdehyde, respectively. The major product observed
from the API-MS analysis of the O3 reaction with
acenaphthylene was a secondary ozonide, which was not
observed by GC-MS.
8
d .
Experimental Section
Experiments were carried out in ∼6500-7500 L Teflon
chambers at 296 ( 2 K and at 740 Torr total pressure of
purified air at a relative humidity of ∼5%. The chambers are
equipped with a Teflon-coated fan to ensure mixing of the
reactants during their introduction into the chamber, two
parallel banks of blacklamps for irradiation, and ports for
the introduction of reactants and collection of gas samples
for analysis. Acenaphthene or acenaphthylene was intro-
duced into the chamber by flowing N
tube packed with the solid PAH.
2
gas through a Pyrex
OH radicals were generated by photolysis of methyl nitrite
CH ONO) in air at wavelengths >300 nm (9). To avoid the
formation of O , and hence of NO radicals, NO was added
(
3
Introduction
3
3
Polycyclic aromatic hydrocarbons (PAHs) are released into
the atmosphere during combustion processes. Acenaphthene
to the reactant mixture (9). The initial reactant concentrations
-3
(
×
in molecule cm units) were as follows: CH
3
ONO, NO, ∼2.7
(
I) and acenaphthylene (II) are PAHs emitted into the
14
13
10 ; trans-2-butene, ∼2.6 × 10 (in kinetic experiments);
atmosphere from a variety of sources including diesel exhaust.
Under typical ambient temperatures, both compounds exist
mainly in the gas phase (1, 2) and can thus be removed from
the troposphere by gas-phase reaction with hydroxyl (OH)
radicals, nitrate (NO ) radicals, and ozone (O ) and by
3 3
photolysis (3).
Previous studies have shown that OH radical-initiated
reactions with acenaphthene and acenaphthylene are im-
portant daylight loss processes in the troposphere (4-7).
Due largely to the presence of the cyclopentafused ring, both
12
and acenaphthene, acenaphthylene, ∼(1-2) × 10 for
13
reactions with GC analyses; CH
3
ONO, NO, ∼2.7 × 10 ; and
11
acenaphthene, acenaphthylene, ∼(5-10) × 10 for reactions
with API-MS analyses.
Ozone was generated using a Welsbach T-408 ozone
12
generator. Each addition of O
3
corresponded to ∼6 × 10
-3
molecule cm of O
3
in the chamber. The initial reactant
concentrations (in molecule cm units) were as follows:
-3
13
2
-methyl-2-butene, ∼2.6 × 10 (in kinetic experiments);
1
6
1
2
cyclohexane, ∼1.3 × 10 ; and acenaphthylene, ∼1 × 10 for
compounds also react with NO
3
radicals during nighttime
15
reactions with GC analyses; cyclohexane, 8.6 × 10 ; and
1
1
acenaphthylene, ∼5 × 10 for reactions with API-MS
*
Corresponding author phone: (909)787-3502; fax: (909)787-5004;
analyses.
e-mail: janet.arey@ucr.edu. Corresponding address: Air Pollution
Research Center, University of California, Riverside, CA 92521.
Kinetic Studies. Rate constants for the reactions of
acenaphthene and acenaphthylene with OH radicals and, of
†
Interdepartmental Program in Environmental Toxicology.
Department of Environmental Sciences.
Air Pollution Research Center.
‡
§
acenaphthylene with O
3
were measured using relative rate
methods, in which the decay rates of the PAH and a reference
4
3 0 2
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 36, NO. 20, 2002
10.1021/es025761b CCC: $22.00

2002 Am erican Chem ical Society
Published on Web 09/06/2002

compound, whose rate constant is known, were measured
in the presence of OH radicals or O (4, 10). Providing that
acenaphthene, acenaphthylene, and the reference compound
reacted only with OH radicals or O , then
L Teflon chamber directly linked via a Pyrex sampling port
to the PE SCIEX API III MS/ MS mass spectrometer. The
3
-
1
chamber contents were sampled at ∼20 L min directly into
3
the API-MS source (13).
For the OH radical-initiated reactions, the reactants were
[
PAH]t0
k1
k2
[reference organic]t0
[reference organic]t
irradiated at 20% of maximum light intensity for 1 min. For
ln
)
ln
(1)
3
{[
}
{
}
the O
3
reactions, one addition of 50 cm volume of O
3
in O
2
PAH]t
diluent was made to the chamber. The positive ion mode
was used in all the API-MS and API-MS/ MS analyses, as
described in Kwok et al. (13).
Reactions with GC Analysis. While sampling on Tenax
adsorbent was conducted for analysis of the PAH during the
kinetic experiments, sampling both onto Tenax and using
solid-phase microextraction (SPME) (14, 15) was used for
product identification and quantification.
where [PAH]t0 and [reference organic]t0 are the concentrations
of the PAH and the reference compound at t
reference organic] are the concentrations of the PAH and
the reference compound at time t; and k and k are the rate
constants for reactions 2 and 3, respectively (4).
0 t
and [PAH] and
[
t
1
2
SPME Product Identification and Quantification. Pre-
liminary product analyses were conducted using samples
collected during the API-MS experiments for later off-line
GC-MS analyses. Conditions for the separate experiments
carried out for product identification and quantification were
as follows. Irradiations were carried out at 20% of the
maximum light intensity for 3 min (1 experiment) and 7 min
Plots of ln{[PAH]t0/ [PAH]
reference] } should be straight lines with a slope of k
and a zero intercept.
trans-2-Butene was chosen as the reference compound
for the OH radical reactions because its rate constant for
reaction with OH radicals is similar to those reported for
acenaphthene and acenaphthylene (4). Three irradiations of
t
}
versus ln{[reference]t0
/
2
(
2 experiments), resulting in reaction of 52% and 78% of the
[
t
1
/ k
initially present acenaphthene and for 1.5 min (1 experiment)
and 4 min (2 experiments), resulting in 56% and 80% reaction
of the initially present acenaphthylene. For the reactions
with O
chamber, each addition corresponding to ∼6 × 10 molecule
cm of O in the chamber.
3 3 2
, two additions of O / O mixture were made to the
1
2
-
3
3
min each at 20% of maximum light intensity were carried
3
out, resulting in up to 50% reaction of the initially present
acenaphthene and up to 60-65% reaction of the initially
present acenaphthylene. Three replicate experiments were
done for each PAH.
For SPME analysis, a 100 µm poly(dimethylsiloxane)
(PDMS) coated fiber was used. The fiber was exposed to the
analytes for 30 min, 2 h, and ∼16-20 h. Equilibrium of the
reactants was reached after 30 min, but longer equilibrium
times were required for the products. To have sufficient
product signals on the GC-MS and for convenience of
sampling, a 16-20 h sampling time was chosen. The sampling
process was followed by desorption of the concentrated
analytes onto a GC column for analysis. For product
identification, a Varian Saturn 2000 GC/ MS/ MS ion trap was
run under chemical ionization (CI) conditions, with isobutane
as the reagent gas. Additionally an HP 5971A GC-Mass
Selective Detector was run in full scanning mode with electron
impact (EI) ionization. The instruments were equipped with
a 30 m (Varian Saturn) and a 60 m (HP 5971A) DB-1701
column (0.25 µm phase thickness), and the fiber was thermally
desorbed at 250 °C.
In the O
3
-acenaphthylene reactions, 2-methyl-2-butene
was used as the reference compound, and sufficient cyclo-
1
6
-3
hexane (1.3 ×10 molecules cm ) was added to the chamber
to scavenge > 97% of OH radicals formed (11, 12). Four
additions of 50 cm volume of O
3
3
in O
2
diluent were made
during an experiment. After allowing 8 min for reaction to
occur, a sample was collected on a Tenax TA solid adsorbent
cartridge for quantitative analysis of acenaphthylene after
each addition. Again, three replicate experiments were
conducted.
3
For both the OH radical and O reactions, the reactants
were monitored during the experiments by gas chromatog-
raphy with flame ionization detection (GC-FID). For the
analysis of acenaphthene and acenaphthylene, gas samples
For GC-FID quantification with SPME, the fiber was
exposed to the chamber contents for 2 and 16 h, subsequently
desorbed at 250 °C onto a DB-5 megabore column initially
at 40 °C, and then temperature programmed to 280 °C at 8
3
of 100 cm volume were collected from the chamber onto
Tenax TA solid adsorbent cartridges, with subsequent thermal
desorption at ∼250 °C onto a DB-1701 megabore column.
Replicate analyses of acenaphthylene were reproducible,
showing no indication of losses to the chamber walls.
However, initial experiments with acenaphthene showed a
steady drop in concentration over time. Decreasing the initial
acenaphthene concentration gave more reproducible results
with values typically within 5% (the estimated uncertainty
in the GC analyses) over 1.5 h and, therefore, during the less
than 2 h required for the acenaphthene kinetic experiments,
wall losses were negligible. For the analysis of trans-2-butene
and 2-methyl-2-butene, gas samples were collected from the
-
1
°C min . The amount of analyte that is extracted by the fiber
coating when equilibrium has been reached is directly
proportional to the analyte concentration in the sample and
depends on the volume of the fiber coating and the fiber/
sample partition coefficient, as described in ref 16 (refer to
Supporting Information for details on product quantifica-
tion).
Tenax Product Quantification. Product quantification of
the OH radical-initiated reaction with acenaphthene was also
done using 1 L samples collected on Tenax cartridges and
thermally desorbed at 250 °C onto a DB-5 megabore column
3
chamber in a 100 cm all-glass, gastight syringe and injected
3
via a 1-cm stainless steel loop onto a DB-5 megabore column.
3
of a GC-FID. For one experiment with an initial CH ONO
1
4
-3
Product Studies. Product analyses were carried out in
two series of experiments, with analyses by API-MS in one
series and by gas chromatography-mass spectrometry (GC-
MS) and GC-FID in another series of experiments.
Reactions with API-MS Analysis. OH radical-initiated
reactions of acenaphthene, acenaphthene-d10, acenaphth-
concentration of 2.7 × 10 molecule cm , three irradiations
of 3 min each were carried out at 20% of the maximum light
3
intensity, and for a second experiment with the lower CH -
1
3
-3
ONO concentration of 5.5 × 10 molecule cm , three 5 min
irradiations were done. The amount of product formed was
determined from the analyte peak’s area counts based on
GC-FID response factors, which were estimated using the
calculated ECNs (17).
ylene, and acenaphthylene-d
8
and O
3
reactions with acenaph-
thylene and acenaphthylene-d
8
were carried out in a ∼7000
VOL. 36, NO. 20, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
4 3 0 3

SCHEME 1. OH Radical Addition to a Six-Membered Ring of Acenaphthenea
a
See also Schem e S2, Supporting Inform ation, for form ation of additional products by OH radical addition.
SCHEME 2. OH Radical Addition to the Unsaturated
Cyclopentafused Ring of Acenaphthylene
1 2 1
TABLE 1. Rate Constant Ratios k /k and Rate Constants k
for the Gas-Phase Reactions of the OH Radical with
Acenaphthene and Acenaphthylene at 296 ( 2 K and
Atmospheric Pressure of Air
1
011 × k
cm molecule s-1
3
-1
)
(
PAH
k1/k2a
this worka,b
literaturec
ref
acenaphthene
1.23 ( 0.06
8.0 ( 0.4
5.8c
(7)
(4)
(6)
(5)
(4)
(5)
c
1
0.2 ( 1.2
c,d
6
6
.0 ( 0.8
e
.4
c
acenaphthylene 1.92 ( 0.11 12.4 ( 0.7 10.9 ( 1.1
e
1
2.8
a
Indicated errors are two least-squares standard deviations. b Placed
on an absolute basis using a rate constant for the reaction of the OH
-
11
cm 3 m olecule
-1 -1
radical with trans-2-butene of k
2
) 6.48 × 10
s
at
2
96 K(12). Uncertainties in the rate constant k
2
are not taken into account.
c
Updated using the m ost recent recom m endations for the rate constants
of the reference com pounds (12). d Rate constant m easured over the
tem perature ranges 325-366 K (6). Within the experim ental uncertain-
ties, the rate constant is independent of tem perature, with the average
value cited. e Relative to the rate constant for the reaction of the OH
radical with naphthalene of 2.2 × 10 cm 3 m olecule
-11
-1 -1
s
at 295 K (5).
Particle Form ation. Three additional experiments without
reference compounds were carried out to investigate the
formation of organic aerosols following the oxidation of
acenaphthene and acenaphthylene in the presence of OH
the SMPS were inverted to obtain particle size distributions.
The procedure included corrections for particle charging,
the DMA function, and the CPC counting efficiency. Details
of the general inversion procedure are described in the
literature (20). The size distributions were used to calculate
the total aerosol volume concentration and then multiplied
by an assumed particle density of 1 g cm to obtain the
aerosol mass concentration. The reactant loss was monitored
by GC-FID.
radicals and the reaction of acenaphthylene with O
3
. The
particle size distributions were measured using a Scanning
2
10
Mobility Particle Sizer (SMPS), consisting of a Po bipolar
charger, a conventional differential mobility analyzer (DMA)
(
18, 19) similar in design to the TSI Model 3934, and a TSI
-
3
Model 3010 condensation particle counter (CPC). The aerosol
-
1
flow rate was 1 L min and the sheath air flow rate was 3
-
1
L min . The particle mobility distributions measured with
4
3 0 4
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 36, NO. 20, 2002

The rate of the OH radical reaction with acenaphthene
has been studied previously (4-7), but as evident from Table
1
, the results of these studies are not in agreement. The
reference compound chosen by Kl o¨ pffer et al. (7) (ethene)
was not ideal, as it reacts significantly more slowly than
acenaphthene and no uncertainty was cited for their
measurement. The Banceu et al. (5) study was done relative
to naphthalene and used SPME for analysis. Again, no error
estimates were reported, and they also reported data for 1,3-
and 2,3-dimethylnaphthalenes which are in poor agreement
with literature values (21, 22), including a recent study of 14
alkylnaphthalenes (22). Although outside the stated error
limits, the value obtained in this study falls between the rate
coefficients determined by Brubaker and Hites (6) and by
Atkinson and Aschmann (4). Brubaker and Hites (6) carried
out their experiments at elevated temperatures (325-366 K)
and extrapolated the data to room temperature. The earlier
rate constant measurements from this laboratory (4) em-
ployed packed column GC techniques, and it is anticipated
that our present study using capillary GC columns is more
accurate as well as more precise. The rate coefficient obtained
in this study is in good agreement with the estimated value
-
11
cm3 molecule
-1 -1
of Klamt (23) of 8.6 × 10
s , which was
based on molecular orbital calculations.
The rate coefficient obtained for the OH reaction with
acenaphthylene is in agreement with the previous values of
Atkinson and Aschmann (4) and Banceu et al. (5). Acenaph-
thylene reacts faster with the OH radical than does acenaph-
thene, presumably due to the higher reactivity of the
unsaturated cyclopentafused ring of acenaphthylene.
PAHs react with the OH radical by two reaction path-
ways: (1) OH radical interaction with the substituent groups,
either through H-atom abstraction from a substituent alkyl
group, if present, or for those PAHs containing unsaturated
cyclopentafused rings, OH radical addition to the >CdC<
bond; (2) OH-addition to the aromatic ring to form an initially
energy-rich hydroxycyclohexadienyl-type radical (4).
Acenaphthene and acenaphthylene can each undergo two
distinct reaction pathways (see Schemes 1 and 2 and Schemes
S1-S3, Supporting Information). As indicated by the products
discussed below, addition to the six-membered aromatic rings
seems to be the dominant pathway for acenaphthene
FIGURE 1. API-MS spectra of the gas-phase OH radical-initiated
reactions of acenaphthene (A) and acenaphthene-d10 (B). See Table
(
Scheme 1), while the faster reaction rate for acenaphthylene
suggests that reaction also occurs at the unsaturated bond
of the cyclopentafused ring (Scheme 2). Both PAHs react
quite rapidly with the OH radical, leading to atmospheric
lifetimes with respect to OH radical reactions of 1.8 h for
acenaphthene and 1.1 h for acenaphthylene, assuming an
average ambient 12-h daytime OH radical concentration of
2
for identification of ion peaks.
Chem icals. The chemicals used and their stated purities
were as follows: acenaphthene (99%, impurities included
acenaphthylene), acenaphthylene (95%, impurities included
acenaphthene), 2-methyl-2-butene (99+%) (from Aldrich
Chemical Co., St. Louis, MO); acenaphthene-d10 (98.7%),
6
-3
2
× 10 molecule cm (24, 25).
Reaction Rate Constant. The experimental data from
a series of O -cyclohexane-air-2-methyl-2-butene-acenaph-
thylene experiments were plotted in accordance with eq 1
Figure S2, Supporting Information). The rate constant
ratio k / k obtained by least-squares analyses of the data is
.395 ( 0.017. This rate constant ratio can be placed on an
absolute basis by use of a rate constant k for the reaction
O
3
3
acenaphthylene-d
8
(99.7%) (from C/ D/ N Isotopes Inc.); trans-
2
-butene (95%), NO (>99%), Matheson Gas Products; cyclo-
(
hexane (HPLC grade) (from Fisher Scientific, Pittsburgh, PA).
Methyl nitrite was prepared and stored as described previ-
ously (9).
1
2
0
2
-
16
3
of 2-methyl-2-butene with O
3
of k
2
) 3.96 × 10
cm
Results and Discussion
-1 -1
molecule
for the O
s
at 296 K (12), and the resulting rate constant
reaction with acenaphthylene is (1.6 ( 0.1) × 10
-
16
OH Radical Reaction Rate Constants. The experimental data
3
cm3 molecule
-1
s .
-1
obtained from irradiated CH
3
ONO-NO-PAH-trans-2-butene-
air mixtures were plotted in accordance with eq 1 (Figure S1,
Supporting Information). Reasonable straight-line plots were
The significant reactivity of acenaphthylene toward O
ascribed to the reaction of O with the unsaturated cyclo-
pentafused ring, since O does not react to any observable
3
is
3
observed, and the rate constant ratios k
squares analyses of the data are given in Table 1. These ratios
are placed on an absolute basis by use of a rate constant k
for the OH radical reaction with trans-2-butene of k
1
/ k
2
obtained by least-
3
extent with aromatic hydrocarbons containing only six-
membered rings or with saturated side chains or, as is the
case for acenaphthene, saturated cyclopentafused rings (4).
The rate coefficient determined here is lower than that of
Atkinson and Aschmann (4), where an approximate rate
2
2
)
-
11
3
-1 -1
6
.48 × 10 cm molecule
s
at 296 K (12). The resulting
rate constants are also given in Table 1 together with the
available literature data.
-16
3
-1 -1
constant of k )5.5 ×10 cm molecule
s
was determined
VOL. 36, NO. 20, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
4 3 0 5

TABLE 2. Products Observed by API-MS and GC-MS and Their Formation Yields from the Gas-Phase OH Radical-Initiated Reactions
of Acenaphthene and Acenaphthene-d10
a
The form ation yield has been determ ined for the MW 160 product, with quantification by Tenax therm al desorption and by SPME (see
b
Supporting Inform ation). GC-MS analysis showed the presence of three isom ers of the dialdehyde, which is form ed by OH-addition to the
arom atic ring. c The 205 ion seen in Figure 1A is a water cluster of the 187 ion. d Potential artifacts, see text.
under second-order kinetic conditions, with an estimated
overall uncertainty of a factor of 2. The present study is the
first to use a relative rate method with an OH radical scavenger
in the acenaphthene-d10 reaction, is suggested to be an
epoxide rather than a hydroxy-derivative, since there are 10
nonexchangeable D atoms. Rapid -OD to -OH exchange in
the chamber for hydroxy-substituted compounds has been
for the determination of the rate constant of the O
with acenaphthylene.
3
reaction
observed (13), and, therefore, if the C12
10 3
H O compound
1
1
contained an -OH group, only nine nonexchangeable D
atoms would be expected, either from -OD/ -OH exchange
or initial addition of the reactant OH (and not OD) radical.
The products seen by API-MS are consistent with those
expected from OH radical addition to a six-membered ring
of acenaphthene (Scheme 1). The formation of the MW 202
product, shown in the lower pathway in Scheme 1, follows
Assuming an ambient O
3
concentration of 7 × 10
-
3
molecules cm (30 parts-per-billion, ppbv), which is rep-
resentative of global lower tropospheric levels (26), the rate
constant determined in this study results in an atmospheric
3
lifetime of acenaphthylene with respect to O reaction of 2.5
h. This atmospheric lifetime would drop in polluted atmo-
spheres, for example, to 22 min during a California Stage 1
Ozone Episode (O
3
concentration of 200 ppbv).
the reaction mechanism proposed by Bartolotti and Edney
+
(
27). The lack of a significant ion peak at m/ z 185, [M + H]
Products of the Reactions of OH Radicals with Acenaph-
thene and Acenaphthene-d10. API-MS Analysis. Reactions
of acenaphthene and acenaphthene-d10 with OH radicals in
of naphthalene-1,8-dicarbaldehyde, principal product ex-
pected from H-atom abstraction (see Scheme S1, Supporting
Information), suggests that H-atom abstraction from the
cyclopentafused ring is not important.
x
the presence of NO were carried out, and the chamber
contents were directly sampled and analyzed by API-MS.
For acenaphthene, as shown in Figure 1A, three main
products were observed by API-MS. The observed products
and their suggested structures are listed in Table 2. The major
product was tentatively identified as a C10 ring-opened
GC-MS Analysis. Since the ions that are mass-analyzed
are mainly protonated molecular ions, the peaks obtained
by API-MS can be matched with the peaks obtained by GC-
MS with the CI analyses confirming the molecular ions and
EI analyses providing spectra with additional structural
information. Figure 2A shows a GC-MS EI total ion chro-
matogram of an overnight sample collected on a 100 µm
PDMS fiber from the gas-phase OH radical-initiated reaction
of acenaphthene (78% reaction of the initially present
acenaphthene). Single peaks corresponding to the MW 160
and 202 products seen in the API-MS analysis were observed,
while three isomers of MW 186 were found (see Scheme 1
+
product of [M + H] ) 161. The structure shown in Table 2
+
is consistent with the [M + H] ) 169 observed in the ace-
naphthene-d10 reaction (Figure 1B). The second product seen
+
+
as [M + H] ) 187 with a water cluster at [M + H + H
2
O]
)
205 is tentatively identified as a dialdehyde, consistent
with the presence of 10 nonexchangeable deuteriums in the
acenaphthene-d10 reaction product. The structure of the third
+
+
product observed at [M + H] ) 203, and at [M + H] ) 213
4
3 0 6
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 36, NO. 20, 2002

FIGURE 2. GC-MS total ion chromatogram of overnight samples collected on PDMS 100 µm fiber from the gas-phase OH radical-initiated
reactions of acenaphthene (A) (7 min irradiation, 78% reaction of initially present acenaphthene) and acenaphthylene (B) (1.5 min irradiation;
56% reaction of initially present acenaphthylene).
for suggested formation pathways). Possible structures of
these products are shown in Figure 2A and include cis- and
trans-isomers of a ring-opened dialdehyde analogous to cis-
and trans-2-formylcinnamaldehyde, which were identified
from the reaction of naphthalene with the OH radical (28,
of MW 182 attributed to 1,2-acenaphthylenedione (molecular
ion has successive losses of CdO) is believed to be a sampling
artifact formed from naphthalene-1,8-dicarbaldehyde during
the desorption process (see discussion of acenaphthylene
reaction products below). Naphthalene-1,8-dicarbaldehyde
could have been present as the reaction product from a small
acenaphthylene impurity present in the acenaphthene
reactions or, since it would be formed by H-atom abstraction
from acenaphthene (see Scheme S1, Supporting Informa-
tion), it could indicate that this pathway occurred. However,
as noted above, naphthalene-1,8-dicarbaldehyde was not
observed in the API-MS analyses of the acenaphthene-OH
reactions, indicating that H-atom abstraction can be only a
very minor pathway.
Product Quantification. Because the MW 160 product was
the most prominent in the GC-MS analyses of the SPME
samples and of the Tenax samples as well as in the API-MS
analyses, an attempt was made to quantify its yield. The
amounts of the reactants and products were determined from
the peak area counts based on GC-FID response factors.
Taking into account secondary reactions, a formation yield
of the MW 160 product of ∼14% was derived from the
experiments where the product was sampled onto Tenax
(see Figure S4 and discussion in Supporting Information).
For the quantification with SPME, a maximum yield at
37% was obtained for the 3 min irradiation with a 2 h sampling
time after correcting for secondary reactions. The higher yield
2
9). The formation of the cis-isomer is shown in Scheme 1,
with the trans-isomer potentially formed from photolysis of
the cis-isomer (29). The EI mass spectra of the suggested
dialdehyde products from acenaphthene are consistent with
the proposed structures with prominent losses of 29 (CHO)
from the molecular ion.
Three additional peaks (see Figure 2A) were observed by
GC-MS analysis: a small nitroacenaphthene peak (see
Scheme S2, Supporting Information), a peak of MW 182
attributed to 1,2-acenaphthylenedione, and a peak due to
1
,8-naphthalic anhydride. From the OH radical-initiated
reaction of acenaphthene under similar experimental condi-
tions, low yields (∼0.2%) of nitroacenaphthenes have been
reported from this laboratory (8). Note that hydroxy-
acenaphthene, a potential product shown in Scheme S2,
Supporting Information, was not observed either by GC-MS
or API-MS. 1,8-Naphthalic anhydride was found in the GC-
MS analyses from reactions of both acenaphthene and
acenaphthylene with OH as well as acenaphthylene with O
3
and did not appear in the API-MS analyses of any of these
reactions. It is suggested that this stable product forms from
more labile products during sampling and analysis. The peak
VOL. 36, NO. 20, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
4 3 0 7

)
185 suggested to be a dialdehyde and consistent with the
+
[
M + H] ) 193 in the acenaphthylene-d
8
reaction (Figure
3
B).
Other product ion peaks were observed at 169 and 198
acenaphthylene) and 177 and 205 (acenaphthylene-d ). The
(
8
ion peaks at 169 and 177 u, respectively, indicate the presence
of eight nonexchangeable H atoms, and, therefore this
compound is attributed to an epoxide rather than a hydroxy-
+
derivative. The third product at [M + H] ) 198 was identified
as a nitro-derivative, consistent with the seven deuteriums
in the acenaphthylene-d
-nitroacenaphthylene from the reaction of OH with acenaph-
thylene has previously been reported from this laboratory
8).
GC-MS Analysis. Figure 2B shows a GC-MS total ion
8
reaction (Figure 3B). A 2% yield of
4
(
chromatogram of an overnight sample collected on a 100
µm PDMS fiber from the gas-phase OH radical-initiated
reaction of acenaphthylene (56% reaction of the initially
present acenaphthylene). Possible structures for five products
suggested by their MS EI spectra are shown next to the GC
peaks. Consistent GC-MS analysis results for the acenaph-
thylene products were not obtained. The 1,2-acenaphthyl-
enedione peak (with distinctive successive losses of 28 and
2
8 from the molecular ion) was the largest peak observed in
the analysis shown in Figure 2B. At other times, the 1,2-
acenaphthylenedione peak was small, and two molecular
weight 184 dialdehydes were observed. The relative propor-
tions of the peaks found for the two MW 184 products and
the MW 182 peak suggest that one of the MW 184 products
decomposed to the dione. OH radical addition to the
unsaturated cyclopentafused ring is expected to yield naph-
thalene-1,8-dicarbaldehyde (see Scheme 2), consistent with
the API-MS analyses. It is proposed, therefore, that naph-
thalene-1,8-dicarbaldehyde is susceptible to degradation to
1
,2-acenaphthylenedione during GC analysis, perhaps during
the analyte desorption in the heated inlet. Consistent with
the API-MS analyses, an epoxide of MW 168 and nitro-
acenaphthylene were observed. As noted previously, 1,8-
naphthalic anhydride was again observed, while no corre-
sponding molecular ion peak was seen in the API-MS
analyses.
The reactivity, and double-bond character, of the unsat-
urated cyclopentafused ring of acenaphthylene is demon-
strated by its reaction with O . Therefore the presence of two
3
different MW 184 products suggests that both OH addition
to the cyclopentafused ring (Scheme 2) and to the aromatic
rings of acenaphthylene (see Scheme S3, Supporting Infor-
mation) must occur.
FIGURE 3. API-MS spectra of the gas-phase OH radical-initiated
reactions of acenaphthylene (A) and acenaphthylene-d
8
(B). See
Table 3 for identification of ion peaks.
determined by SPME suggests the yield measured by Tenax
sampling may be an underestimate, but clearly a standard
of this product is required to verify quantitative collection
and desorption from the Tenax as well as to calibrate the
SPME partition coefficient. (Refer to Supporting Information
for details on quantification and estimation of the product
partition coefficient).
Products of the Reactions of O with Acenaphthylene
3
and Acenaphthylene-d . API-MS Analysis. API-MS positive
8
ion analyses of O with acenaphthylene and acenaphthylene-
3
d8 were carried out, and the spectra of these reactions showed
the presence of a single dominant product ion peak [M +
+
H] at 201 and 209 u, respectively (see Figure S3, Supporting
Information for the API-MS/ MS CAD spectra of these ion
peaks). The CAD spectra of both compounds show losses of
OH, CO, and 2CO. Additionally, the acenaphthylene reaction
Products of the Reactions of OH Radicals with Acenaph-
thylene and Acenaphthylene-d
of acenaphthylene and acenaphthylene-d
in the presence of NO were carried out, and the chamber
8
. API-MS Analysis. Reactions
with OH radicals
product peak shows losses of CO + H
2
O, while the acenaph-
thylene-d product peak shows corresponding losses of
8
x
8
contents were directly sampled and analyzed by API-MS.
For acenaphthylene, as shown in Figure 3A, one product
dominated. The products observed by API-MS and their
suggested structures are shown in Table 3. Unlike acenaph-
thene, where addition to the ring and H-atom abstraction
are predicted to give different molecular weight dialdehyde
products, both OH addition to the cyclopentafused ring and
to the aromatic rings of acenaphthylene are predicted to
give dialdehydes of MW 184 (see Scheme 2 and Scheme S3,
Supporting Information). As shown in Figure 3A, the API-MS
analysis is indeed dominated by a product peak at [M + H]+
CO + HDO. Thus, as evidenced by eight nonexchangeable
hydrogens and the addition of 48 mass units in the product
peak, in-situ API-MS analysis allowed identification of the
secondary ozonide (see Table 4 for structure).
GC-MS Analysis. As shown in Table 4, the GC-MS analysis
3
of the acenaphthylene reaction with O showed six apparent
products: 1-naphthaldehyde, oxaacenaphthylen-2-one, 2-hy-
droxy-1-naphthaldehyde, two dialdehydes of MW 184, and
1,8-naphthalic anhydride. The secondary ozonide was not
observed by GC-MS, and the products observed are, therefore,
attributed to breakdown products of the secondary ozonide.
4
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9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 36, NO. 20, 2002

TABLE 3. Products Observed by API-MS and GC-MS from the Gas-Phase OH Radical-Initiated Reactions of Acenaphthylene and
Acenaphthylene-d
8
a
Naphthalene-1,8-dicarbaldehyde is form ed by OH addition to the unsaturated bond at the cyclopentafused ring. Dialdehydes of MW 184 can
also be form ed by OH addition to the arom atic ring. b Potential artifacts, see text.
Overall Reactions, Product Mass Balances, and Particle
Form ation. As a result of the short atmospheric lifetimes for
both acenaphthene and acenaphthylene, their products are
likely to be present in ambient air and therefore the toxicity
of these products is of concern. Carbonyl compounds were
the major products observed here, and unsaturated aldehydes
and dicarbonyl compounds have been shown to react with
DNA (30, 31). Muconaldehyde, a six-carbon diene dialdehyde,
has been shown to be genotoxic (32). Additionally, epoxides
have been identified from the OH radical reactions of both
acenaphthene and acenaphthylene, and epoxy functional
groups have been shown to act as electrophiles and react
with DNA (33-35).
sampling and analysis must explain the low mass balances
obtained.
The products observed from the OH reaction of acenaph-
thene suggest that addition to the aromatic ring dominates
over H-atom abstraction from the cyclopentafused ring. This
is consistent with expectations that ∼60% of reactivity for
acenaphthene arises from the 4 and 5 positions (23) but
inconsistent with the study of Banceu et al. (5), in which a
high proportion of the proposed products are formed by
reaction at the saturated cyclopentafused ring. For acenaph-
thylene, Klamt (23) estimated that reaction at the unsaturated
bond of the cyclopentafused ring accounts for the majority
of reactivity. Again this is consistent with the products
observed here from the OH reaction with acenaphthylene.
Although API-MS analysis cannot distinguish isomers, a
dialdehyde peak totally dominated the spectrum, and GC
analyses suggested that mainly naphthalene-1,8-dicarbal-
dehye was formed (observed as the dialdehyde or as 1,2-
acenaphthylenedione). The formation of naphthalene-1,8-
dicarbaldehyde would result from addition to the cyclopenta-
fused ring (Scheme 2), while the presence of a second less
abundant dialdehyde suggests some reaction with the
aromatic ring also occurred (see Scheme S3, Supporting
Information).
For the OH radical-initiated reactions of acenaphthene
and acenaphthylene, product mass balances were not
obtained. Quantification by API-MS was not possible due
to the lack of standards for the products and this lack
necessitated using GC-FID, where the detector response
can be predicted (17), for quantification. However, no
assessment of quantitative recovery during sampling and
GC analysis could be made. The major product from
acenaphthene (MW 160) accounted for ∼14-37% of the OH
radical reaction products, whereas the dialdehyde product
of the OH reaction with acenaphthylene accounted for even
less. The experiments that were carried out indicate that
organic aerosol formation following the OH radical-initiated
reaction of acenaphthene and acenaphthylene was not
significant, being <1%. Since aerosol formation has proven
to be insignificant and it is believed that the API-MS will
respond to all reaction products (though with varying
sensitivities), wall losses and/ or difficulties in quantitative
The formation of organic aerosol following the reaction
of O with acenaphthylene accounted for ∼13% of the product
3
mass balance. The secondary ozonide, the only product
observed in the API-MS analyses, presumably accounts for
a large fraction of the overall reaction products. The secondary
ozonide was clearly unstable in our off-line GC analyses,
and it is not known what the fate of the secondary ozonide
would be under ambient conditions.
VOL. 36, NO. 20, 2002 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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3 8
TABLE 4. Products Observed by API-MS and GC-MS from the Gas-Phase O Reactions of Acenaphthylene and Acenaphthylene-d
Acknowledgments
Literature Cited
The authors thank Dr. Roger Atkinson for many helpful
discussions and Dr. Paul Ziemann for loaning us the
equipment and providing us with the expertise required to
measure particle formation. The authors gratefully thank the
U.S. Environmental Protection Agency through Grant No.
R826371-01-0 “Ozone and Fine Particle Formation in Cali-
fornia and in the Northeastern United States” to the California
Institute of Technology for support of this research. One of
the authors (F.R.) has been partially supported by a grant
from the University of California Toxic Substances Research
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ES025761B
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