Aerosol formation from the reaction of α-pinene and ozone using a gas- phase kinetics-aerosol partitioning model

Article abstract of DOI:10.1021/es980725r

As a result of new aerosol compositional information, we have implemented an exploratory model for predicting aerosol yields from the reaction of α-pinene with ozone in the atmosphere. This new approach has the ability to embrace a range of different atmospheric chemical conditions, which bring about biogenic aerosol formation. A kinetic mechanism was used to describe the gas-phase reactions of α-pinene with ozone. This reaction scheme produces low vapor pressure reaction products that distribute between gas and particle phases. Some of the products have subcooled liquid vapor pressures which are low enough to initiate self-nucleation. More volatile products such as pinonic acid and pinonaldehyde will not self-nucleate but will partition onto existing particle surfaces. Partitioning was treated as an equilibrium between the rate of particle uptake and rate of particle loss of semivolatile terpene reaction products. Given estimated liquid vapor pressures and activation energies of desorption, it was possible to calculate gas-particle equilibrium constants and aerosol desorption rate constants at different temperatures. This permitted an estimate of the rate of absorption from the gas phase. Gas- and aerosol-phase reactions were linked together in one chemical mechanism, and a chemical kinetics solver was used to predict reactant and product concentrations over time. Aerosol formation from the model was then compared with aerosol production observed from outdoor chamber experiments. Approximately 20-40% of the reacted α-pinene carbon appeared in the aerosol phase. Models vs experimental aerosol yields are shown in Figure 2 and illustrate that reasonable predictions of secondary aerosol formation are possible. The majority of the aerosol mass came from the mass transfer of gas-phase products to the aerosol phase. An important observation from the product data and the model was that as temperatures and aerosol mass changed from experiment to experiment, the composition of the aerosol changed. An exploratory model for predicting aerosol yields from the reaction of α-pinene with ozone in the atmosphere was implemented. A kinetic mechanism was used to describe the gas-phase reactions of α-pinene and ozone. This reaction scheme produces low vapor pressure reaction products that distribute between gas and particle phases. Gas- and aerosol-phase reactions were linked together in one chemical mechanism, and a chemical kinetics solver was used to predict reactant and product concentrations over time. Approximately 20-40% of the reacted α-pinene carbon appeared in the aerosol phase. The majority of the aerosol mass came from the mass transfer of gas-phase products to the aerosol phase.

Full text of DOI:10.1021/es980725r

Environ. Sci. Technol. 1999, 33, 1430-1438
and their high aerosol forming potential. Although the
Aerosol Formation from the
Reaction of r-Pinene and Ozone
Using a Gas-Phase Kinetics-Aerosol
Partitioning Model
potential of aerosol formation from terpenes was noted as
early as 1960 (1), the magnitude of the natural contribution
by biogenics to the particulate burden in the atmosphere is
still not well characterized.
Efforts to represent secondary organic aerosol (SOA)
formation in ambient models have been based primarily on
experimentally determined fractional aerosol yields (2, 3 and
references therein). In general, measured yields for a single
compound have shown a wide degree of variation either
between or within laboratories (4,5). Odum et al. (3,6) have
developed an elegant technique for estimating SOA yields
starting with an absorptive gas-particle (G/ P) partitioning
model (7-9). In this model the overall SOA yield from a single
reactant is given as a function of two hypothetical product
dependent G/ P partitioning coefficients, Kom,i, their associated
individual mass-based stoichiometric reaction coefficients,
R I C H A R D K A M E N S , * M YO S E O N J A N G ,
C H A O - J U N G C H I E N , A N D K E R I L E A C H
Department of Environmental Sciences and
Engineering, University of North Carolina,
Chapel Hill, North Carolina 27599-7400
As a result of new aerosol compositional information, we
have implemented an exploratory model for predicting
aerosol yields from the reaction of R-pinene with ozone
in the atmosphere. This new approach has the ability to
embrace a range of different atmospheric chemical conditions,
which bring about biogenic aerosol formation. A kinetic
mechanism was used to describe the gas-phase reactions
of R-pinene with ozone. This reaction scheme produces
low vapor pressure reaction products that distribute between
gas and particle phases. Some of the products have
subcooled liquid vapor pressures which are low enough
to initiate self-nucleation. More volatile products such as
pinonic acid and pinonaldehyde will not self-nucleate
but will partition onto existing particle surfaces. Partitioning
was treated as an equilibrium between the rate of
particle uptake and rate of particle loss of semivolatile
terpene reaction products. Given estimated liquid vapor
pressures and activation energies of desorption, it
was possible to calculate gas-particle equilibrium constants
and aerosol desorption rate constants at different
temperatures. This permitted an estimate of the rate of
absorption from the gas phase. Gas- and aerosol-phase
reactions were linked together in one chemical mechanism,
and a chemical kinetics solver was used to predict
reactant and product concentrations over time. Aerosol
formation from the model was then compared with aerosol
production observed from outdoor chamber experiments.
Approximately 20-40% of the reacted R-pinene carbon
appeared in the aerosol phase. Models vs experimental
aerosol yields are shown in Figure 2 and illustrate
that reasonable predictions of secondary aerosol formation
are possible. The majority of the aerosol mass came
from the mass transfer of gas-phase products to the aerosol
phase. An important observation from the product data
and the model was that as temperatures and aerosol mass
changed from experiment to experiment, the composition
of the aerosol changed.
R
i
, and the absorbing organic mass concentration, M
). While this is a very useful advance, it does not address
o
(µg
-
3
m
the fundamental atmospheric reactions that bring about
secondary aerosol formation. In this paper, we will describe
the feasibility of a predictive technique for the formation of
secondary aerosols from biogenic hydrocarbons. An advan-
tage of this approach is that it has the ability to embrace the
range of different atmospheric chemical and physical condi-
tions that bring about secondary aerosol formation.
Experimental Section
Gas-particle samples for this study were generated in a large
outdoor 190 m Teflon film chamber (10,11). All experiments
were carried out in darkness to exclude photochemical effects.
Rural background air was used to charge the chamber without
any additional injections of oxides of nitrogen. Secondary
aerosols were created by the reaction of R-pinene with O
the chamber. O from an electric discharge ozone generator
was added to the chamber over the course of at least an hour
with initial concentrations ranging, depending on the
experiment, from 0.25 to 0.65 ppm. It was measured using
a Bendix chemiluminescent O
cerverte,WV) and calibrated via gas-phase titration using a
NIST traceable NO tank. O addition to the chamber was
followed by volatilizing, depending on the experiment, 0.4-1
mL of liquid R-pinene into the chamber atmosphere. The
gas-phase concentration of R-pinene was monitored with
an online gas chromatograph (Shimadzu Model 8A, column:
3
3
in
3
3
meter (model 8002, Ron-
3
1
.5 m, 3.2 mm stainless steel packed with Supelco 5%
Bentanone 34) using a flame ionization detector and
calibrated with a known concentration of a mixture of toluene
and propylene.
Gas- and particle-phase R-pinene products were simul-
taneously collected with a sampling train that consisted of
an upstream five-channel annular denuder, followed by a 47
mm Teflon glass fiber filter (type T60A20, Pallflex Products
Corp., Putnam, CT) and another denuder. In one of the
experiments, a parallel sampling system consisting of a filter,
followed by a denuder, was also used. The details of the
sample workup procedure and quantitative analysis have
been reported in previous manuscripts (10,11). Carbonyl
products of R-pinene-O
3
aerosols were derivatized by
Introduction
O-(2,3,4,5,6-pentafluorobenzyl)hydroxyl-amine hydrochlo-
ride (PFBHA) as described by Yu et al. (12), and carboxylic
acids, using pentafluorobenzyl bromide (PFBBr) as a de-
rivatizing agent as described by Chien et al. (13). (()-R-Pinene,
O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine hydrochlo-
ride (PFBHA), pentafluorobenzylbromide (PFBBr), deca-
fluorobiphenyl (internal standard for derivatization), cis-
The atmospheric chemistry of nonmethane biogenic hy-
drocarbons has received much attention because of their
significant global emissions, high photochemical reactivity,
*
Corresponding author phone: (919) 966-5452; fax: (919) 966-
7
911; e-mail: kamens@unc.edu.
1
4 3 0
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 33, NO. 9, 1999
10.1021/es980725r CCC: $18.00

1999 Am erican Chem ical Society
Published on Web 03/26/1999

SCHEME 1
Possible mechanisms for the overall R-pinene-O
recently been presented by Jang and Kamens and Yu et al.
17, 18). Reaction pathways were constructed from experi-
3
have
(
mentally measured products which include pinonaldehyde,
norpinonaldehyde, pinonic acid, norpinonic acid, pinic acid,
2
,2-dimethylcyclobutane-1,3-dicarboxylic acid (norpinic acid),
and hydroxy and aldehyde substituted pionaldehydes and
hydroxy pinonic acids. To simplify the mechanism in this
study, six generalized semivolatile products were defined:
1
. “pinald” to represent pinonaldehyde and norpinonalde-
hyde, 2. “pinacid” to represent pinonic and norpinonic acids,
. “diacid” for pinic acid and norpinic acid, 4. “oxy-pinald”
3
for hydroxy and aldehyde substituted pinonaldehydes (called
oxo-substituted), 5. “P3” for 2,2-dimethylcyclobutane-3-
acetylcarboxylic acid, (a pinic acid precursor), and 6. “oxy-
pinacid” for hydroxy and aldehyde substituted pinonic acids.
A last group, frag, was employed to account for volatile
oxygenated products.
Model Representation of Criegee1 Reactions. In the
reaction of ozone with alkenes, alkyl substitution on the
carbon atoms participating in the carbon double bond
stabilizes the formation of the resulting Criegee biradicals
pinonic acid, n-hexanoic acid, n-octanoic acid, hexane-1,6-
dionic acid, and heptane-1,7-dionic acid were all purchased
from Aldrich (Milwaukee, WI).
In one of the experiments the particle size distribution
and aerosol concentration for particles ranging from 0.018
to 1.0 µm were monitored by an Electrical Aerosol Analyzer
(
EAA) (Thermo Systems, Inc., Model 3030, Minneapolis, MN).
3
(28,29). For the R-pinene-O system, a bias toward the
Total aerosol number concentration was also measured by
a Condensation Nuclei Counter (CNC, Model Rich 100,
Environment One Corp., Schenectady, NY).
formation of the methyl substituted biradical was assumed
with a split ratio of 60:40. A temperature-dependent Arrhenius
rate constant for the reaction of O
3
with R-pinene of 1.01 ×
1
5
-732/ T
cm3 molecule
-1 -1
1
0
× e
s
was used (29), where T is
Results and Discussion
in degrees Kelvin. The initial reaction of R-pinene with O
3
is thus represented in eq 1 as
Overview. Conceptually, we began with the development of
a kinetic mechanism to describe gas-phase reactions of
R-pinene with ozone. This reaction scheme produces low
vapor pressure reaction products that distribute between
gas and particle phases. Some of the products may have
R-pinene + O f 0.4Criegee1 + 0.6Criegee2
(1)
3
In Scheme 1, 12.5% ((4) of the high energy R-pinene
Criegee biradicals are collisionally stabilized (29, 30). We
assumed a value of 15%. These stable biradicals (called
stabcrieg1 in the mechanism) can react with aldehydes, nitric
oxide, nitrogen dioxide, water, sulfur dioxide, and oxygen
(29, 31). The reaction of Criegee biradicals with water
dominates (29) and in this case yields pinonic acid (pinacid).
A rate constant for the reaction of water with a stabilized
-
6
subcooled liquid vapor pressures of ∼10 Torr or lower.
These are low enough so that if surfaces are not available for
sorption from that gas phase, self-nucleation may occur. Once
surfaces and their corresponding liquid volumes exist, G/ P
partitioning becomes the dominant process, and compounds
partition from the gas phase onto existing particles. Parti-
tioning can be represented as an equilibrium between the
rate of oxidized terpene product uptake and the rate of
terpene product loss from the aerosol system. Kinetically,
this is represented as forward and backward reactions. The
sum of the product mass in the condensed phase equals the
aerosol concentration. This was then compared with aerosol
-
18
3
-1
Criegee radical is on the order of 4 × 10
cm molecule
-1
s
(31). The high-energy Criegee1 biradical can also undergo
rearrangement and stabilize to directly form pinonic acid.
Given the recent observation that pinonic acids can account
for 20-40% of the aerosol mass (32), 30% of the Criegee1
mass was shunted into the formation of pinacid. Recent
studies have suggested similar yields of pinonic and nor-
pinonic acids (17, 32). We have therefore assumed that the
group pinacid represents approximately equal portions of
pinonic and norpinonic acids.
As shown in Scheme 1, the rearrangement of Criegee1
also leads to the formation of norpinonaldehyde (17, 18).
The reported ratio of norpinonaldehyde to pinonaldehyde
varies from almost zero to 50% (17, 19). A ratio of ∼20% was
assumed and given the model yields of pinonaldehyde via
OH attack on R-pinene in our mechanism, this translated
into ∼30% of the Criegee1 decomposition. Norpinaldehyde
(represented as pinald in the mechanism) can then react
with OH and in the presence of oxygen form a peroxyacyl
radical (pinald-oo). The peroxyacyl radical then reacts with
3
concentrations obtained by reacting R-pinene with O in an
outdoor chamber.
An r-Pinene-Ozone Gas-Phase Reaction Mechanism .
During darkness, the reaction of R-pinene with O is one of
3
the dominant atmospheric loss mechanisms for R-pinene.
The electrophilic addition of ozone to the unsaturated
carbon-carbon bond of terpenes leads to the formation of
an ozonide that rapidly decomposes to energy-rich biradicals
often called Criegee biradicals (14). As shown in Scheme 1,
the ozonide intermediate generated from the reaction of
3
R-pinene with O will undergo ring opening and yield two
species that contain a high energy biradical at one end and
an aldehyde or ketone group at the other. One of these
biradicals, which will be called Criegee1, quickly reacts to
form pinonic acid, norpinonaldehyde, and norpinonic acid
(
15-19). As will be discussed later, the other biradical,
2 3 3
HO (33) to form norpinonic acid and O . O formation from
this reaction, however, was not included in the mechanism,
Criegee2, can rearrange to form 2,2-dimethyl,3-carboxylic-
cyclobutaneethanoic acid (pinic acid), which has recently
since it is implicitly represented in the rate constant of
3
been reported as an R-pinene-O
0, 21). The reactions of the energetic Criegee biradicals also
lead to the formation of carbon monoxide (CO), carbon
dioxide, (CO ), formaldehyde (HCHO), hydroxyl radicals
OH), and hydroperoxyl radicals (HO ) (16,22-26). The
3
reaction product (17, 18,
R-pinene with O
3
. Given the low yields of the O( P) atom
2
from the Criegge decomposition (29), its reaction with
R-pinene was not included.
2
Yu et al. (18) have recently suggested that a hydroxypi-
nonaldehyde (oxy-pinald) can also form from Criegee1. Using
the above Criegee1 yields for pinonic acid and norpinonal-
dehyde leaves 25% of the Criegee1 carbon, and this was
(
2
reaction of R-pinene with OH radicals then leads to the
formation of pinonaldehyde and other reaction products (27).
VOL. 33, NO. 9, 1999 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
1 4 3 1

SCHEME 2
Criegee2 to be represented as
Criegee2 f 0.15stabcrieg + 0.3crgprod2 + 0.3HCHO +
0
.55oxy-pinald + 0.8OH + 0.5HO2 (6)
crgprod2 + HO f diacid + HCHO
(7)
(8)
(9)
2
stabcrieg1 + H O f P3 + CH OH
2
3
oxy-pinald + OH f oxy-prepinacid
OH Attack on r-Pinene. OH radicals from the above
Criegee radical reactions will attack the double bond of
R-pinene and ultimately form pinonaldehyde (pinald in the
kinetic mechanism) (27). A yield of pinonaldehyde from
R-pinene reaction with OH in the presence of oxides of
nitrogen (NOx) of approximately 60% has been reported (16).
A small amount of mass was added to the oxy-pinald category
and the remainder to the volatile fragmentation products
category called frag. The combined reaction has a rate
-
12 444/ T
cm3 molecule
-1 -1
constant (29) of 12.1 × 10
e
s
and
shunted into the formation of oxy-pinald. It is proposed (17)
that all of these aldehyde compounds undergo OH abstraction
is represented as
of an aldehyde hydrogen and form, via O
oxidation, hydroxypinonic acids (oxy-pinacid).
Dark OH yields from the rearrangements of the Criegee
biradicals from O + R-pinene range from 0.76 to 0.85 (34,
5). We used a value of 0.8. HO yields were set slightly higher
0.5) than those used in the Carbon Bond IV mechanism of
.44 (36), and here it is expected to include other similar RO
peroxy radical reactions. Fast first-order rate constants were
assigned to the rearrangements of both Criegee biradicals.
The above choices led to the following overall reaction
sequence of the Criegee1 biradical:
2 2
addition and HO
R-pinene + OH f
0.6pinald + 0.1oxy-pinald + 0.3frag (10)
3
3
(
0
2
As with the other aldehydes mentioned above, pinald
will undergo OH abstraction of its aldehyde hydrogen to form
a peroxyacyl species, pinald-oo. This forms pinonic acid,
which appears in the mechanism as pinacid. Literature values
for OH attack on pinonaldehyde range from 2.4 to 9.1 ×
2
-
11
3
-1 -1
10 cm molecule
s
(38, 39). To fit our R-pinene and O
3
decay data, it was necessary to use a value toward the lower
end of this range. The Moortgat et al. (33) rate constant of
-
13 1040/ T
3
-1 -1
Criegee1 f 0.3pinacid + 0.15stabcrieg1 + 0.3pinald +
4.3 ×10
e
cm molecule
s
2
was used for HO reaction
0
.25oxy-pinald + 0.8OH + 0.5HO + 0.3CO (2)
with the peroxyacyl to form pinonic acid from pinonaldehyde
and was also used for the oxidation of other peroxyacyl
radicals to carboxylic acids.
2
stabcrieg + H O f pinacid
(3)
2
All of the above reactions were linked using a kinetics
solver (40) and by convention, rate constant units of min
pinald + OH f pinald-oo
(4)
(5)
-
1
pinald-oo + HO f pinacid
-1
-1
2
or ppm min for first and second order reactions were
3
-1 -1
used with this package. Units of cm molecule
s
were
-
1
-1
-16
Criegee2 Reactions. Possible mechanisms for the Criegee2
biradical have recently been presented (17, 18). To simulate
this chemistry, Criegee2 was assumed to collisionally stabilize
or rearrange and react via the hydroperoxide channel (C) as
shown in Scheme 2 (22, 29, 37). Intermediate A illustrates a
stabilization via the ester channel, which leads to the
converted to ppm min by dividing by 6.77 × 10 (at 298
K). These reactions were then added to the inorganic
chemistry reactions of the Carbon Bond IV photochemical
mechanism (36). A temperature table describing the experi-
mental temperature change over time was used by the kinetic
solver to calculate the pre-exponential and exponential terms
of the rate constant at each time step of a given kinetic
simulation.
formation of methanol (CH
) in Scheme 2. P3 then reacts to form pinic acid via
OH abstraction on the aldehyde hydrogen or continues to
react to form the C diacid, 2,2-dimethycyclobutane-1,3-
dicarboxylic acid. The C diacid represented about 10% of
3
OH) and a compound called P3
9 14 3
(C H O
Particle Nucleation. When R-pinene is vaporized into
the chamber, it exits the injection manifold as a very high
concentration gas cloud and is mixed into the chamber
atmosphere that already contains ozone. Although chamber
mixing takes about one minute, the condensation nuclei
counter responded as the R-pinene was injected, indicating
an immediate formation of condensation nuclei. In the
absence of these particle seeds, the system would have to
wait for gas-phase concentrations of the least volatile
products to reach sufficient supersaturation levels for self-
nucleation to occur. The formation rate of these nuclei is
dependent on the supersaturation level and the number of
molecules needed to form critical clusters (41). The rate of
formation can easily span 50 orders of magnitude as the
supersaturation level increases from 2 to 7 (41). In our systems
we tended to reach supersaturation levels of pinic acid in
less than one minute. At this point supersaturation in our
systems would rapidly increase to values greater than 50 if
gas-phase mass transfer to the particle phase did not occur.
To model our data it was only necessary to initiate the
migration to the aerosol phase with a small amount of initial
8
8
the observed pinic acid (17). We have assumed that the
hydroperoxide channel leads directly to a peroxyacyl com-
pound D, which is then oxidized by HO to also form pinic
2
acid. This assumption was made because of the need in the
particle portion of the model to rapidly produce low volatility
aerosol phase products. This channel also leads (17) to a
hydroxypinonaldehyde and an oxopinonaldehyde (oxy-
pinald), which can be further oxidized via OH, O
to oxopinonic and hydroxypinonic acids (oxy-pinacid).
For modeling purposes, two generalized intermediate
products, called stabcrieg2 and crgprod2, were defined.
Stabcrieg2 represents the reactions of A and crgprod2 the
peroxyacyl compound D in Scheme 2. As with stabcrieg1, we
assumed a 15% split to stabcrieg2. Given the recent observa-
tion of substantial pinic acid formation (17) and the
uncertainty associated with the yields of oxy-pinald, we
assumed an almost even split between products leading to
the diacid and oxy-pinald. This permitted the chemistry of
2 2
, and HO
1
4 3 2
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 33, NO. 9, 1999

i
9
i
o
L
nuclei resulting from the R-pinene injection. This mass was
K ) 7.501RT/ (10 Mw
p )
(14)
p
om
3
equivalent to ∼8 µg/ m of particulate matter.
The product compounds that actually participate in the
self-nucleation process are as yet unknown. One possibility
is that the stabilized Criegee radical (stabcrieg1 and stabcrieg2)
reacts with the carbonyl portion of product compounds to
produce an extremely low-pressure secondary ozonide
product. These types of products have been observed from
The average molecular weight of the liquid particle
includes any water absorbed from the atmosphere. It is
possible to estimate the water uptake for these aerosols (46)
and this tends not to exceed 5% of the particle mass. On a
molecular basis, however, water can make up 30-50% of the
mole fraction. This suggests that compounds such as pinic
acid may exhibit liquid-like properties when dissolved in the
aerosol bound water.
An implicit assumption in the use of the above equilibrium
model is that partitioning from the gas phase takes place
into the particle liquid volume. It is this available and
accumulating liquid volume, and the mass of products
produced in the gas phase, that “drives” the equilibrium
between the gas and particle phases. Although surface is not
explicitly represented in the model, it is expected that total
particle surface changes after the onset of particle formation.
Particle size measurements taken with an Electrical Aerosol
Analyzer (EAA) show that 4-5 min after the injection of
R-pinene (for particles ranging from 0.018 to 1.0 µm in
diameter), the chamber aerosol count, surface, and volume
geometric mean diameters were 0.054, 0.095, and 0.151 µm,
respectively. These diameters increased to 0.096, 0.158, and
3
an O -propylene system by Niki and co-workers and more
recently by others for larger molecules (42, 43). It is also
possible to form an anhydride from the reaction of the Criegee
with a dicarboxylic acid (44). In the R-pinene case, these
products would have molecular weights of ∼350 and be of
extremely low volatility. By techniques described later in this
-
15
paper, vapor pressures lower than 10 Torr are estimated
and ∼1 s after the start of the experiments in this study would
exceed supersaturation by ∼1000-fold. This suggests these
compounds would most certainly self-nucleate. In our
mechanism these are called “seed1” particles. We assumed
that stabilized Criegees would react with all carbonyl
-
14
3
-1
products, with a rate constant of 2 × 10
cm molecule
-
1
s
(31). For example,
stabcrieg1 + pinald f seed1
(11)
0
.214 µm over the next 30 min and then increased very slowly
This process was not very important for the experiments
over the next 3 h. The EAA total particle surface to total volume
ratio after 5 min of reaction was 51 µm and declined to 33
µm in 30 min; it then decreased slowly to 26 µm over the
next 3 h. This less than dramatic change in the EAA surface-
to-volume ratio with time and the fact that most of the
particle mass was in the measured EAA range suggest that
not including surface directly in the model is not a significant
in this study, given the background nucleation levels that
resulted during the injection of R-pinene into the chamber.
Predictions, using the model developed here, however,
suggest a strong influence of these seeds on particle formation
when R-pinene has concentrations of ∼5 ppb.
-
1
-
1
-1
A Gas-Particle Model. For a kinetics-based model, it is
necessary to calculate the rate constants for sorption and
problem.
desorption of R-pinene-O
3
products on and off the growing
i
Estim ating K
p
. To estimate K
p
it is necessary to have
aerosol mass. The ratio of the rate constants for the forward
i
o
i
i
knowledge of p
diacid products of the R-pinine-O system, p information
. For the aldehyde, acid-carbonyl, and
L
and backward reactions kon/ koff is equal to the equilibrium
i
o
L
i
3
constant, K
p
, for the gas-particle equilibrium of a given
is scarce. There are some vapor pressure data, however, for
nonandionic acid, a linear alkanoic diacid with the same
carbon number as pinic acid (47). At 560 K it has a vapor
pressure of 100 Torr, and at 498 K, 10 Torr. Using the simple
form of the Clausius-Clapeyron equation at 295 and 270 K,
vapor pressures of 6.0 × 10 and 2.3 × 10 Torr can be
estimated for nonandionic acid. An expanded form of the
Clausius-Clapeyron (48) equation can also be used to
estimate vapor pressures at ambient Kelvin temperatures
partitioning compound.
i
i
i
K ) k / k
off
(12)
p
on
Previous investigations by our group (45) show that
aerosols can be treated using an absorptive
-6
-7
R-pinene-O
3
i
(
gas-liquid) partitioning model (7). K
p
can be calculated
from
(
T), from boiling point (T
b
) and entropy of vaporization
i
i
o
L
i
log K ) - log p - log γ
+
(∆SvapTb) information.
p
om
9
log[(7.501RTfom)/ (10 Mwom)] (13)
∆
SvapTb
Tb
Tb
i
o
L
ln p )
1.8 1 -
[
+ 0.8 ln
(15)
i
3
(
)
(
)
]
where K
p
has units of m / µg, T is the temperature (K), fom
R
T
T
is the mass fraction of organic material in particulate matter,
Mwom is the average molecular weight of a given liquid
medium (g/ mol), and γom is the activity coefficient of a given
Entropies of vaporization can be estimated from the
boiling points for organic compounds and boiling points
from chemical structural semiempirical additive techniques
(49). For nonandionic acid, a boiling point of 696 K at 760
Torr and an entropy of vaporization of 91 J/ mol were
computed. When these values were used in eq 14, estimated
subcooled liquid vapor pressures for nonandionic acid at
i
organic compound i, in a given organic mixture, om. When
i
o
L
p
(the subcooled liquid vapor pressure for a pure com-
pound i) is in Torr and R, the gas constant, has units of 8.31
-
1
-1
JK mol , a conversion factor of 7.501 is necessary. The
activity coefficient thermodynamically represents the non-
ideality of the semivolatile organic compound (SOC) dissolved
in the liquid layer of the particle. The activity coefficients of
a given SOC vary with the composition of the organic layer
associated with the particulate matter. It is reasonable,
however, to assume that the activity coefficients of R-pinene
products partitioning into particles composed of R-pinene
products will be nearly ideal and fairly close to one. This was
actually observed for these compounds using a combinatorial
calculation technique (46). The fractional mass of organic
-
6
ambient temperatures of 295 K and 270 were 3.3 × 10 and
-
8
9.6 × 10 Torr. These results are remarkably close to the
-
6
-7
vapor pressures (6.0 × 10 and 2.3 × 10 Torr) estimated
above from the experimental data in ref 47. Similar results
9
were also obtained for the C monoacid, only in this case the
vapor pressure was 2 orders of magnitude lower than the
diacid, nonandionic acid. Given this agreement, Fishtine
correction factors for molecular polarity were not included
as a multiplier on the entropy term in eq 13 (50). For the
R-pinene product pinic acid, a boiling point of 698 K and
entropy of vaporization of 91.0 J/ mol were estimated. This
material in these particles is also close to one. Hence the
partitioning expression for K
i
p
can be simplified to
VOL. 33, NO. 9, 1999 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
1 4 3 3

3
TABLE 1. Experimental Outdoor Chamber Conditions Used To Produce r-Pinene-O Aerosols
r-pinene
(ppmV)
TSP (µg/m3)
(max concn)
run ID
date
temp (K)
RH (%)
O3 (ppm)
MWom
A
B
C
Aug. 5, 1996
J uly 15, 1996
Mar. 11, 1997
296-294
296-295
288-279
55-66
90-100
62-92
0.60
0.25
0.65
0.82
0.35
0.60
2190
504
1860
142
106
114
a
a
Using the com position for the Aug. 5, 1996 experim ent (see ref 17).
-
6
gave subcooled liquid vapor pressures of 3.0 × 10 Torr at
values, then very crude estimates of E
a
values can be made
-
8
2
95 K and 8.9 × 10 Torr at 270 K.
for example, for pinic acid, pinonic acid, and cis-pinonal-
dehyde from their estimated vapor pressures. These were
calculated as 84.4, 79.2, and 71.4 kJ/ mol, respectively, for
these three compounds. As will be discussed later the model
is not very sensitive to these choices within ( 5 kJ/ mol.
From eq 18, the preexponential factor, â, in eq 17 is equal
Computed vapor pressures were then used in eq 14 to
calculate Kp. Based on our measurement of R-pinene-O
aerosol particle composition and water uptake as a function
of humidity (46), average molecular weights of the particles
were calculated for each experiment and are shown in Table
i
3
1
2
-1
1
(
. To simplify calculations, an average molecular weight
Mwom) of 120 was used. Using the experiment specific Mwom
to k
b
T/h, and at 298 K is 6.21 × 10
s . It is also of interest
to note that for solids, a parameter similar to â is equal to
the inverse of the molecular vibrational frequency (54,55)
and has an approximate value of 10 -10 s. If an average
values did not have any impact on the modeling results
discussed later in this manuscript. As mentioned previously,
units of ppmV (40) were used in the kinetics solver for gas-
-
12
-13
-
13
value of 5 × 10 is used for the solid vibrational frequency,
3
i
12 -1
phase compounds, and thus units of m / µg for K
p
were
its reciprocal equals 2 × 10
s , and this is within a factor
converted to their equivalent 1/ ppmV units. When the
average Mwom was combined with estimated vapor pressures
of 3 of the â values calculated above for liquids. From the
i
computed E
a
values for the R-pinene products, koff can now
i
-2
3
i
in eq 14, K
p
values for pinic acid of 5.1 × 10 m / µg (or 390
be obtained from eq 17, and given estimated K
p
values from
eq 14, kon can be computed from eq 12. As indicated above,
on does not significantly change with temperature, and an
average value computed from K and koff over a temperature
range of 285-305 K was used.
3
4
i
L/ ppmV) at 295 K and 1.6 m / µg (or 1.3 × 10 L/ ppmV) at
2
70 K were obtained.
k
Estim ating Rates of Particle Sorption and Desorption.
It is expected that the gas-phase uptake by the particles will
not be overly temperature sensitive, since the rate constant,
on, for the gas-phase uptake by particles varies with
p
At this point it is useful, for illustrative purposes, to
describe the partitioning of the product, pinonic acid (pincid).
The initial aerosol surfaces available for partitioning come
from background aerosols called seed or from self-nucleating
particles called seed1. Newly formed low vapor pressure
products such as gas-phase pinic acid (diacidgas) migrate to
these nuclei and contribute their mass to the particle phase
k
temperature to the 1/ 2 power
i
1/ 2
kon R (RT/ 2πMWi)
(16)
i
where MW is the molecular weight of the partitioning gas
(
diacidpart). This creates more mass for additional partitioning.
phase compound. The rate of loss from a particle, however,
will be strongly temperature dependent, where the rate
constant, koff, for loss of a compound from the liquid particle
phase has the form
To conserve mass and distinguish between seed and newly
formed diacid particle mass, seed appears on both sides of
the equation.
i
-Ea/ RT
diacidgas + seed f diacidpart + seed
(19)
koff ) âe
(17)
The migration of gas-phase pinonic acid (pinacidgas) to the
diacid particle phase (diacidpart) can thus be represented as
Here, E
for desorption from the particles and â is a preexponential
factor. E can be calculated from the following general
expression by Glasstone (51) for evaporation from a pure
liquid surface
a
is the activation energy or energy barrier required
a
pinacidgas + diacidpart f pinacidpart + diacidpart
-
1
kon ) 29.7 min
(20)
kbT
To maintain equilibrium, pinacidpart back reacts or “off-gases”
from the particle to give back gas-phase pinonic acid.
-∆φ
kbT
jevap ) ηκ
exp
t ηκevap
(18)
h
pinacidpart f pinacidgas
where jevap is the molecular flux across the surface (molecules
1
4
-1
-
2
-1
cm
Boltzmann’s constant (1.381 × 10 Joules/ K); h is Planck’s
constant (6.626 × 10 Joules s); ∆φ is the energy barrier a
single molecule must overcome to evaporate from the surface
Joules); and η is the number of molecules exposed on the
s
); κ is a transmission coefficient (assumed ≈1); k
b
is
koff ) 3.73 × 10 exp (-9525/ T) min
(21)
-
23
-
34
Similarly, when gas-phase pinonaldehyde partitions to the
particle phase, it will “see”, in this example, particles
composed of seed, diacidpart, and pinacidpart, and it will
partition onto all three of these. A similar set of reactions can
be written for all of the partitioning products. The rate
(
2
liquid surface (number/ cm ). By dividing eq 18 by the particle
radius, kevap becomes koff in eq 17. Using recent koff data (52)
for fluorene and phenanthrene for diesel soot particles (0.51
and 0.37 s ) and koff for fluoranthene (0.03 s ) calculated
for this study from this same data set, E values of 73.9, 74.6,
-
1
-1
constants are given in ppm
min
for second-order
-
1
-1
-1
processes and min for first-order reactions (Table 2). All
the reactions and rate constants used to demonstrate the
feasibility of this approach are reproduced in Table 2. By
keeping track of the amount of mass that appears in the
particle phase from each of the products, an estimate of the
overall particle mass yield can be made over a range of
temperature conditions.
a
and 80.7 kJ/ mol were estimated from eq 18 for these three
compounds. Interestingly, the values for phenanthrene and
fluoranthene are close to the pure liquid enthalpy values as
reported by Pankow (53). If one assumes a direct relationship
i
o
L
between PAH activation energies and their respective log p
1
4 3 4
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 33, NO. 9, 1999

TABLE 2. Gas and Particle Phase Reactions Used To Simulate Secondary Aerosol Formationa-c
min- or ppm-1 min-1
1
reference
gas phase reactions
1
2
. R-pinene + O3 f 0.4 Criegee1 + 0.6 Criegee2
1.492 exp-732/T
1 × 10
(29)
6
. Criegee1 f 0.3pinacidgas + 0.15stabcrieg1 + 0.8OH +
0
.5HO2 + 0.3pinaldgas + 0.25oxy-pinaldgas + 0.3CO
6
3
. Criegee2 f 0.3 crgprod2 + 0.55oxy-pinaldgas +
0
1 × 10 ,
.35HCHO + 0.15stabcrieg2 + 0.8OH + 0.5HO2
-
-
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
. stabcrieg1 + H2O f pinacidgas
. stabcrieg2 + H2O f P3gas + CH3OH
. P3gas + OH f predi-oo
. oxy-pinald + OH f oxy-prepinacid
. predi-oo + HO2 f diacidgas
. crgprod2 + HO2 f diacidgas
0.oxy-prepinacid +HO2 f oxy-pinacid
1. OH + R-pinene f 0.6pinaldgas + 0.1oxy-pinald + 0.3frag
2. pinald + OH f pinald-oo
3. pinald-oo + HO2 f pinacidgas
4. diacidgas {walls} f
5. oxy-pinacidgas {walls} f
6. pinacidgas {walls} f
7. oxy-pinaldgas {walls} f
8. pinaldgas {walls} f
6 × 10
6 × 10
35450
35450
(31)
(31)
(38)
(38)
(38)
(33,38)
(33)
(29)
(38)
3
677 exp1040/T
677 exp1040/T
677 exp1040/T
17873 exp444/T
35450
677 exp1040/T
(33)
-
7
6 × 10 exp2445/T
(10,56)
(10,56)
(10,56)
(10,56)
(10,56)
-
7
6 × 10 exp2445/T
-7
4 × 10 exp2445/T
-7
4 × 10 exp2445/T
-7
2.5 × 10 exp2445/T
min- or ppm -1 m in-1
1
partitioning reactions
reference
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
2. stabcrieg1 + pinaldgas f seed1
29.5
29.5
29.5
29.7
29.7
29.7
29.7
29.7
29.7
29.7
29.7
(42)
(42)
(42)
3. stabcrieg2 + oxy-pinaldgas f seed1
4. stabcrieg2 + HCHO f oxy-pinald
5. pinacidgas + seed1 f seed1 + pinacidpart
6. pinacidgas + diacidpart f diacidpart + pinacidpart
7. pinacidgas + seed f seed + pinacidpart
8. pinacidgas + pinacidpart f pinacidpart + pinacidpart
9. pinacidgas + pinacidpart f pinacidpart + pinacidpart
0. pinacidgas + oxy-pinaldpart f oxy-pinaldpart + pinacidpart
1. pinacidgas + P3part f P3part + pinacidpart
2. pinacidgas + oxy-pinacidpart f oxy-pinacidpart + pinacidpart
3. pinacidpart f pinacidgas
4. diacidgas + pinacidpart f pinacidpart + diacidpart
5. diacidpart f diacidgas
6. pinaldgas + oxy-pinacidpart f oxy-pinacidpart + pinaldpart
7. pinaldpart f pinaldgas
8. oxy-pinaldgas + P3part f P3part + oxy-pinaldpart
9. oxy-pinaldpart f oxy-pinaldgas
0. p3gas + oxy-pinacidpart f oxy-pinacidpart + p3part
1. p3part f p3gas
2. oxy-pinacidgas + seed1 f seed1 + oxy-pinacidpart
3 oxy-pinaldpart f oxy-pinacidgas
4. diacidpart {walls} f
5. O3 {walls)} f
1
4
3.73 × 10 exp-9525/T
106
1
4
3.73 × 10 exp-10285/T
5.94
1
4
3.73 × 10 exp-8598/T
21.7
1
4
3.73 × 10 exp-9341/T
19.9
1
4
3.73 × 10 exp-9282/T
116
1
4
3.73 × 10 exp-10353/T
0.0008
0.0005
a
Rate constants are at 298 K. To convert the second-order rate constant in cm m olecule-1 s-1 in the text to ppm -1 m in-1 divide the rate constant
3
in cm 3 m olecule
gas constant R is im bedded in A so that A ) E
the pinacid but, to save space, are only given for koff and one particle species. stabcrieg1 and stabcrieg2 reactions are illustrated for pinacidgas
-1
s
-1
by 6.77 × 10
-16
.
b
Exp in the tem perature-dependent reactions is the natural base e, in the rate equation, k ) Be
-A/T
. The
/R. c The partitioning reactions for pinald, oxy-pinald, diacid, and oxy-pinacid are the sam e as for
a
,
and oxy-pinacidgas and HCHO but are the sam e for the other carbonyls. Loss of product gases to the cham ber walls were estim ated from observed
pyrene loss at 297 and 271 K (10, 56). Reactions not referenced were determ ined in this study. All reactants were diluted from the cham ber at
1
a rate determ ined with an SF
product to the walls were adjusted for the SF
6
tracer. A typical loss was 0.0005 m in- . Other specific m easured or estim ated losses such as O
3
, particles and R-pinene
6
loss rate.
Experiential Data and Model Fits. Three experiments
1, reasonable fits to the experimental data for the reaction
(
A, B, and C in Table 1) were conducted under different
3
of gas-phase R-pinene with O with the mechanism shown
temperatures and spanned a total temperature range of 279-
96 K. The individual temperature profiles for each experi-
in Table 2 were observed.
2
Our experimental data show that 20-40% of the reacted
R-pinene carbon appeared in the aerosol phase. Approxi-
mately 30% of the aerosol mass was generated via the Criegee1
pathway. This pathway produces higher volatility products
than Criegee2. OH attack on R-pinene generates pinonal-
dehyde and ultimately pinonic acid. This channel accounts
for ∼10% of the model aerosol. Model simulations of the
measured particle concentration in mg/ m3 are shown in
Figure 2. The experimentally measured aerosol concentra-
tions with the denuder-filter-denuder system ranged from
ment were used as inputs to the individual simulations. It
was not possible to obtain an R-pinene concentration at the
instant of injection. This is because there is a need for
chamber mixing on the order of ∼1 min, and sampling (2-8
min), during which time reaction takes place. Hence the initial
R-pinene concentration was based on the mass of R-pinene
injected into the chamber. This was not an issue with the
initial O
chamber prior to R-pinene, and O
as R-pinene was injected. In Figure 1, it can be seen that
R-pinene reacts faster than O , and this is due to the additional
reaction of R-pinene with the OH radical. As shown in Figure
3
concentration data, since O
3
was injected into the
3
measurements were taken
3
350 to 2700 µg/ m . The parallel filter-denuder sampling
3
system gave particle concentrations that were within 5% of
the denuder-filter denuder system. Again, reasonable model
VOL. 33, NO. 9, 1999 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
1 4 3 5

FIGURE 2. Comparison of experimental (squares) and model aerosol
concentrations (lines) with model reacted r-pinene concentrations
FIGURE 1. Reaction of r-pinene (triangles) with O
3
(squares) in 190
outdoor chamber; symbols are data and lines are model
(
triangles). Experimental conditions listed in Table 1. The total
3
m
electrical aerosol (EAA) volumes in graph C (solid circles) were
scaled to approximate the experimental concentrations.
simulations. Letters correspond to experiments in Table 1.
fits to the experimental secondary aerosol data for all three
experiments (A-C) were possible, even though R-pinene and
O from these experiments exhibited very different time-
3
concentration behaviors (Figure 1). Electrical aerosol analyzer
data (EAA) were available for run B in Figure 2, and the initial
rate of mass flow to the particle phase in the model seems
to follow the total EAA volume (mass) build up. This suggests
that it is only necessary to “seed” the model with condensa-
tion nuclei, after which almost all of the resulting aerosol
mass will come from gas-phase mass transfer to the particle
phase. An initial aerosol concentration resulting from the
3
initial mixing of R-pinene and O
the experiments.
3
of 8 µg/ m was used for all
Quantitative product data to guide the development and
testing of the mechanism for the reaction of R-pinene + O
are very scarce. Our experimental product measurements
17) from the combined samples of each experiment ac-
3
(
counted for ∼50% ((15%) of the observed aerosol yields
where pinic acid, pinonaldehyde, and pinonic acid were the
major aerosol phase products. Although hydroxypinonal-
dehydes and hydroxypinonic acids were detected in trace
amounts, it is expected, based on the Criegee fragmentation
scheme, that these would also contribute substantially to
the aerosol mass.
An important observation from the product data was that
as temperatures decreased from experiment A to experiment
C, the contribution of the pinic acid mole fraction of measured
aerosol products decreased from 77 to 61%, while the
importance of the pinonaldehyde mole fraction increased
from 13 to 30% (17). Although not as much pinald compared
to diacid was predicted in this study for the particle phase,
the general trend is supported by the model product
distributions (Figure 3). The model predictions also suggest
FIGURE 3. Simulated particle phase products for a warm and cool
r-pinene + O
3
experiment: diacid ) large 9, pinald ) 2, pinacid
)
1, oxy-pinald ) b, oxy-pinacid ) Q, P3 ) small 9.
that the composition of the secondary aerosol changes with
temperature and particle concentration. This is because
higher volatility compounds tend to partition to the aerosol
1
4 3 6
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 33, NO. 9, 1999

phase more under cool conditions and high particle con-
centrations than under warm conditions and lower particle
concentrations.
As with pinonaldehyde, it was expected that as experi-
mental conditions cooled, much more pinonic acid would
be observed on the particle phase than under warm
experimental conditions. Measured pinonic acid compounds,
however, only constituted 4% of the mole fraction products
however, that the feasibility of a new secondary aerosol
modeling approach has been demonstrated, and in doing
so, it highlights significant areas of research which should
be undertaken.
Acknowledgments
This work was supported by a Grant from the National Science
Foundation (ATM 9708533) to the University of North
Carolina at Chapel Hill, and Fulbright fellowship support to
R. Kamens in Thailand. We also acknowledge the gift of a
GC/ FTIR system (HP 5890 GC & HP 5965B Infrared Detector)
from the Hewlett-Packard Corporation to the Department
of Environmental Sciences & Engineering at UNC-CH. The
authors would like to thank Dana Coe for the activation energy
calculations, Michael Strommen for helping with the chamber
experiments, and the helpful suggestions of Jian Yu, Harvey
Jeffries, and Bharadwaj Chandramouli. Jay Odum’s recent
breakthrough in this area was an inspiration to us all and he
will be deeply missed.
(
17), and this did not change dramatically between experi-
ments A and C. It is possible, although yet unknown, that
storage of the samples before analysis resulted in a loss of
pinacid compounds. That more pinonic and norpinonic acid
should have been observed in our experiments is cor-
roborated by the recent observations of Kavouras et al. (32).
These authors show that ∼20-40 of the aerosol mass over
a Eucalyptus forest in Portugal was composed of pinonic
and norpinonic acids.
Im pact of Model Inputs and Choices. Many of the choices
made in this manuscript will influence the amount of aerosol
generated and the timing of model events compared to
outdoor data. The choice of a 60:40 split for the formation
of Criegee2 over Criegee1 is reasonable based on the
observations of Grosgean et al. (28). At 295 K increasing or
decreasing the split to 70:30 or 50:50 changed the model
particle yield by ∼ (10%. At 285 K there was less of an effect.
The splits used to obtain norpinonic acid, diacid, and oxy-
pinald product yields are speculative and must await further
product verification. In addition, we assumed that the rate
constant for the OH attack on pinonaldehyde (38) was
applicable to the oxidation of P3 and oxy-pinald and that the
Literature Cited
(
(
1) Went, F. W. Nature 1960, 187, 641-643.
2) Pandis, S. N.; Wexler, A. S.; Seinfeld, J. H. Atmos. Environ. 1993,
2
7A, 2403-2416.
(
3) Odum, J. R.; Hoffmann, T.; Bowman, F.; Collins, D.; Flagan, R.
C.; Seinfeld, J. H. Environ. Sci. Technol. 1996, 30, 2580-2585.
(4) Grosjean, D.; Seinfeld, J. H. Atmos. Environ. 1989, 23, 1733-
1747.
(5) Zhang, S. H.; Shaw, M.; Seinfeld, J. H.; Flagan, R. C. J. Geophys.
Res. 1992, 97, 20717-20729.
(
6) Odum, J. R.; Jungkamp, T. P. W.; Seinfeld, J. H. Science 1997,
76, 96-102.
2
Moortgat rate (33) used for HO oxidation of small aldehydes
2
to carboxylic acids was also applicable to larger radicals.
Vapor pressure estimates are at best within an order of
magnitude. When vapor pressures were lowered for all
product compounds by ∼1 order of magnitude, aerosol yields
were overestimated by 40-100%; when vapor pressures were
increased by a factor of 10, aerosol yields were underestimated
by a factor of 2. It is also possible that vapor pressures were
not uniformly under- or overestimated. For example, an
alcohol group can increase Fishtine correction factors to 1.3
(
7) Pankow, J. F. Atmos. Environ. 1994, 28, 185-188.
(8) Pankow, J. F.; Isabelle, L. M.; Bucholz, D. A.; Luo, W.; Reeves,
B. D. Environ. Sci. Technol. 1994, 28, 363-365.
9) Pankow, J. F.; Storey, J. M. E.; Yamasaki, H. Environ. Sci. Technol.
(
1
994, 27, 2220-2226.
10) Kamens, R. M.; Odum, J.; Fan, Z. Environ. Sci. Technol. 1995,
9, 43-50.
11) Fan, Z.; Kamens, R. M.; Hu, J.; Zhang, J. Environ. Sci. Technol.
1996, 30, 1359-1364.
(
(
2
(12) Yu, J.; Jeffries, H. E.; Le Lacheur, R. M. Environ. Sci. Technol.
995, 100, 1923-1932.
1
(
50). This would lower vapor pressure calculations in eq 15.
(
13) Chien, C. J.; Charles, M. J.; Sexton, K. G.; Jeffries, H. E. Environ.
Sci. Technol. 1998, 32, 299-309.
14) Finlayson-Pitts, B. J.; Pitts, J. N. Atmospheric Chemistry: Fun-
damentals and experimental techniques; John Wiley & Sons:
New York, New York, 1986.
If this were the case, it would suggest that hydroxy pinon-
aldehyde products would partition to the particle phase to
a greater extent than suggested by our model.
(
Estimates for activation energies (E
completely different class of compounds (PAHs) than the
products used in this study. The effect of changing E values
by ( 5 kJ/ mol, and adjusting kon and koff accordingly, was
explored. Uniformly increasing E for all partitioning com-
a
) are based on a
(15) Hatakeyama, S.; Bandow, H.; Okuda, M.; Akimoto, H. J. Phys.
Chem. 1981, 85, 2249-2254.
a
(
16) Hatakeyama S.; Izumi, K.; Fukuyama, T.; Akimoto, H. J. Geophys.
Res. 1989, 94, 13013-13024.
a
(
(
17) Jang, M.; Kamens R. M. Atmos. Environ. 1999, 33, 459-474.
18) Yu, J.; Flagan, R. C.; Seinfeld J. H. Envrion. Sci. Technol. 1998,
32, 2357-2370.
pounds by 5 kJ/ mol tended to slow the onset of aerosol
formation and only slightly decrease aerosol yields. This was
almost unnoticeable in the high concentration experiments
A and C but delayed aerosol formation by ∼7 min in the
(19) Hull, L. A. Terpene Ozonalysis Products. In Atmospheric Biogenic
Hydrocarbons; Bufalini, J. J., Arnts, R. R., Eds.; Ann Arbor
Science: Michigan, 1981; Vol. 2, pp 161-186.
a
warm July experiment. Decreasing E by 5 kJ/ mol did not
(
20) Christoffersen, T. S.; Hjorth, J.; Horie, O.; Jensen, N. R.; Kotzias,
D. Molander, L. L.; Neeb, P.; Ruppert, L.; Winterhalter, R.;
Virkkula, A.; Wirts, K.; Larsen, B. R. Atmos. Environ. 1998, 32,
1657-1661.
seem to have any effect on aerosol fits. The high concentration
experiments A and C were not sensitive to the choice of initial
3
seed concentrations over the range of 5-40 µg/ m . Effects
were greatest with the low concentration experiment B, where
(21) Kavouras, I. G.; Mihalopoulos, N.; Stephanou, E. G. Geo. Phys.
Res Lett. 1999, 26, 55-586.
3
lower seed values (1-5 µg/ m ) tended to delay the onset of
(
22) Grosjean, D.; Willams II, E. L.; Grosjean, E. Environ. Sci. Technol.
993, 27, 830-840.
particle production. Last, under warm conditions (295 K),
the impact of increasing the temperature by 10 degrees K
was to decrease particle yields by ∼30%. This effect may be
even greater in systems that generate lower aerosol levels.
Decreasing the temperature by 10 degrees from 295 K
increased the aerosol yield by 25-50%, with the greatest effect
observed for the low concentration experiment B. At ∼285
K in experiment C, these kinds of temperature changes caused
a 20-25% change in aerosol formation. In closing there are
many uncertainties in this proposed approach that will
probably require a number of years to sort out. We feel,
1
(
(
23) Dodge, M. C.; Arnts, R. R. Int. J. Chem Kinet. 1979, 11, 399-410.
24) Martinez, R. I.; Herron, J. T.;. Huie, R. E., J. Am. Chem. Soc. 1981,
103, 3807-3820.
(25) Kamens, R. M.; Gery, M. W.; Jeffries, H. E.; Jackson, M.; Cole,
E. I. Int. J. Chem Kinet. 1982, 14, 995-975.
(
(
26) Shu, Y.; Atkinson, R. Int. J. Chem. Kinet. 1994, 26, 1193-1205.
27) Hatakeyama, S.; Izumi, K.; Fukuyama, T.; Akimoto, H. J. Geophys.
Res. 1991, 96, 947-958.
(
28) Grosean, D.; Grosjean, E.; Williams III, E. L. Environ. Sci. Technol.
1994, 28, 186-196.
(29) Atkinson, R. J. Phys. Chem. Ref. Data 1997, 26, 215-290.
1 4 3 7
VOL. 33, NO. 9, 1999 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9

(
(
(
(
(
(
(
30) Hatakeyama, S.; Kobayashi, H.; Akimoto, H. J. Phys Chem. 1984,
8, 4736-4737.
31) Atkinson, R.; Loyd, A. C. J. Phys. Chem. Ref. Data 1984, 13, 315-
44.
32) Kavouras, I. G.; Mihalopoulos, N.; Stephanou, E. G. Nature 1998,
95, 683-686.
33) Moortgat, G. K.; Veyret, B.; Lesclaux, R. Chem. Phys. Lett. 1989,
60, 443-447.
34) Chew, A. A.; Atkinson, R. J. Grophys. Res. 1996, 101, 28649-
8653.
35) Atkinson, R.; Aschmann, S. M.; Arey, J.; Shorees, B. J. Geophys.
Res. 1992, 97, 6065-6073.
36) Gery, M. W.; Whitten, G. Z.; Killus, J. P.; Dodge, M. C. J. Geophys.
Res. 1989, 94, 12925-12956.
(46) Jang, M.; Kamens, R. M. Environ. Sci. Technol. 1998, 32, 1237-
8
1243.
(
(
47) Lide, D. R. Handbook of Chemistry and Physics, 71st ed.; CRC
4
Press: Boston, MA, 1990.
48) Schwarzenbach, R. P.; Gschwend, P. M.; Imboden, D. M.
Environmental Organic Chemistry; John Wiley & Sons Inc.: New
York, 1993.
3
1
(49) Reid, R. C.; Prausnitz, J. M.; Poling, B. E. The Properties of Gases
and Liquids, 4th ed.; McGraw-Hill Co.: New York, 1987.
2
(
50) Lyman, W. J.; Reehl, W. F.; Rosenblatt, D. H. Handbook of
Chemical Property Estimation Methods, Environmental Behavior
of Organic Compounds, American Chemical Society: Wash-
ington, DC, 1990.
(
(
(
37) Martinez, R. I.; Herron, J. T. J. Phys. Chem. 1987, 91, 946-953.
38) Kwok, E.; Atkinson, R. Atmos. Environ, 1995, 29, 1685-1695.
39) Glasius, M.; Calogirou, A.; Jensen, N. R.; Hjorth, J.; Nielsen, C.
J. Int. J. Chem Kinet. 1997, 29, 527-533.
(
51) Glasstone, S.; Laidler, K. J.; Eyring, H. The Theory of Rate Processes;
New York: McGraw-Hill, 1941.
(52) Kamens, R. M.; Coe, D. L. Environ. Sci. Technol. 1997, 31, 1830-
(
40) Jeffries, H. E. PC-Photochemical Kinetics Simulation System
1833.
(
PC-PKSS), Software Version 3.0; Department of Environmental
(
53) Pankow, J. F. Atmos. Environ. 1991, 25A, 2229-2239.
Sciences and Engineering, School of Public Health: University
of North Carolina, Chapel Hill, NC 27599, 1991.
(54) Adamson, A. W.; Gast, A. P. Physical Chemistry of Surfaces, 6th
(
(
(
(
(
41) Seinfeld, J. Atmospheric Chemistry and Physics of Air Pollution;
John Wiley and Sons: New York, 1986.
42) Niki, H.; Maker, P. D.; Savage, C. M.; Breitenbach, L. P. Chem.
Phys. Lett. 1977, 46, 327-330.
43) Neeb, P.; Horie, O.; Moorgot, G. K. Tetrahedron Lett. 1996, 37,
ed.; John Wiley & Sons: New York, 1997.
(
(
55) Pankow, J. F. Atmos. Environ. 1987, 21, 2275-2283.
56) Kamens, R. M.; Fan, Z.; Yao, Y.; Chen, D.; Chen, S.; Vartiainen,
M. Chemosphere 1994, 28, 1623-1632.
9
297-9300.
44) Neeb, P.; Horie, O.; Mortgot. G. K. Chem. Phys Lett. 1995, 150-
56.
Received for review July 17, 1998. Revised manuscript re-
ceived February 10, 1999. Accepted February 18, 1999.
1
45) Jang, M.; Kamens, R. M.; Leach, K.; Strommen, M. R. Environ.
Sci. Technol. 1997, 31, 2805-2811.
ES980725R
1
4 3 8
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 33, NO. 9, 1999