Kinetics of heterogeneous reaction of CaCO3 particles with gaseous HNO3 over a wide range of humidity

Article abstract of DOI:10.1021/jp076169h

Heterogeneous reaction kinetics of gaseous nitric acid (HNO₃) with calcium carbonate (CaCO₃) particles was investigated using a particle-on-substrate stagnation flow reactor (PS-SFR). This technique utilizes the exposure of substrate deposited, isolated, and narrowly dispersed particles to a gas mixture of HNO₃/H₂O/N₂, followed by microanalysis of individual reacted particles using computer-controlled scanning electron microscopy with energy-dispersive X-ray analysis (CCSEM/EDX). The first series of experiments were conducted at atmospheric pressure, room temperature and constant relative humidity (40%) with a median dry particle diameter of D_p = 0.85 μm, particle loading densities 2 × 10⁴ ≤ N_s ≤ 6 × 10⁶ cm ^-2 and free stream HNO₃ concentrations of 7, 14, and 25 ppb. The apparent, pseudo first-order rate constant for the reaction was determined from oxygen enrichment in individual particles as a function of particle loading. Quantitative treatment of the data using a diffusion-kinetic model yields a lower limit to the net reaction probability γ_net ≥ 0.06 (x 3/÷-2). In a second series of experiments, HNO₃ uptake on CaCO₃ particles of the same size was examined over a wide range of relative humidity, from 10 to 80%. The net reaction probability was found to increase with increasing relative humidity, from γ_net ≥ 0.003 at RH= 10% to 0.21 at 80%.

Full text of DOI:10.1021/jp076169h

J. Phys. Chem. A 2008, 112, 1561-1571
1561
Kinetics of Heterogeneous Reaction of CaCO3 Particles with Gaseous HNO3 over a Wide
Range of Humidity
†
‡
§
§
,‡
,†
Y. Liu, E.R. Gibson, J.P. Cain, H. Wang, V.H. Grassian,* and A. Laskin*
William R. Wiley EnVironmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory,
P. O. Box 999, MSIN K8-88, Richland, Washington 99352, Department of Chemistry, UniVersity of Iowa,
Iowa City, Iowa 52242, and Department of Aerospace and Mechanical Engineering, UniVersity of Southern
California, Los Angeles, California 90089-1453
ReceiVed: August 2, 2007; In Final Form: October 13, 2007
Heterogeneous reaction kinetics of gaseous nitric acid (HNO
investigated using a particle-on-substrate stagnation flow reactor (PS-SFR). This technique utilizes the exposure
of substrate deposited, isolated, and narrowly dispersed particles to a gas mixture of HNO /H O/N , followed
3 3
) with calcium carbonate (CaCO ) particles was
3
2
2
by microanalysis of individual reacted particles using computer-controlled scanning electron microscopy with
energy-dispersive X-ray analysis (CCSEM/EDX). The first series of experiments were conducted at atmospheric
pressure, room temperature and constant relative humidity (40%) with a median dry particle diameter of Dh
p
4
6
-2
)
0.85 µm, particle loading densities 2 × 10 e N
s
e 6 × 10 cm and free stream HNO
3
concentrations
of 7, 14, and 25 ppb. The apparent, pseudo first-order rate constant for the reaction was determined from
oxygen enrichment in individual particles as a function of particle loading. Quantitative treatment of the data
using a diffusion-kinetic model yields a lower limit to the net reaction probability γnet g 0.06 (×3/÷2). In a
3 3
second series of experiments, HNO uptake on CaCO particles of the same size was examined over a wide
range of relative humidity, from 10 to 80%. The net reaction probability was found to increase with increasing
relative humidity, from γnet g 0.003 at RH ) 10% to 0.21 at 80%.
Introduction
transformation can occur is through heterogeneous reaction with
HNO3:
Mineral dust aerosol comprises one of the largest mass
fractions of the total global aerosol loading. The annual
production of mineral dust is estimated to be 800-2000 Tg.
%
RH
CaCO (s) + 2HNO (g)
8 Ca(NO ) (s,aq) + H CO (aq)
3
3
3 2 2 3
1
,2
As mineral dust aerosol is entrained and transported through
the atmosphere, it can alter the chemical balance of the
atmosphere through heterogeneous reactions with trace atmo-
f Ca(NO ) (s,aq) + CO (g) + H O (1)
3 2 2 2
The formation of Ca(NO3)2 by reaction 1 has been observed
for both pure calcium carbonate and authentic mineral dust in
spheric gases.3 Mineral dust also affects climate through direct
,4
1
7-19
5
-7
previous laboratory studies.
and indirect radiative forcing. Likewise, mineral dust particles
are expected to undergo changes in their chemical composition
and physical properties as a result of heterogeneous processing.
Thus, when quantifying the impact of mineral dust on atmo-
spheric chemistry and climate, it is important to consider
Uptake of HNO3 on mineral dust is one of the most important,
but least certain, parameters in the analysis of the impact of
2
,3,20
dust on tropospheric ozone concentrations.
To assess this
impact, accurate measurements of the heterogeneous uptake
coefficient (γ) under conditions representative of the atmosphere
are critical. Currently, most of the kinetic studies for reaction 1
have been conducted in Knudsen cell reactors under dry
conditions. Under dry conditions, the reaction proceeds until
the carbonate surface is saturated by nitrate, thus preventing
changes in the physicochemical properties of particles as they
are transported and aged in the atmosphere.8,9
The carbonate components of mineral dust, e.g., calcite
(CaCO3) and dolomite (CaMg(CO3)2), can comprise as much
as 30% of the total dust loading and are known to be especially
1
6
10
further HNO3 uptake. For moist air, however, surface passi-
vation is no longer an issue. The nitrate product that forms on
the carbonate surface is aqueous under typical atmospheric
conditions of 20-90% relative humidity (RH), facilitating
continuous reaction until the entire carbonate content of a
particle is consumed. Table 1 summarizes the reaction prob-
reactive with nitrogen oxides. In particular, a strong correla-
tion between Ca2 and NO3 has been reported in a number of
+
-
field and modeling studies.1
1-13
Single-particle analyses of
mineral dust samples have shown that as CaCO3 particles are
transported throughout the troposphere they can be completely
converted to Ca(NO3)2.1
4,15
One pathway through which this
1
6,21-23
abilities reported to date.
As seen, discrepancies in the
uptake coefficient span several orders of magnitude, from
*
Authors to whom correspondence should be addressed. V.H.G.:
2
4
E-mail: vicki-grassian@uiowa.edu. Phone: (319) 335-1392. Fax: (319)
0.00025 to 0.1. With the exception of one study, all of the
uptake coefficients were observed under dry or nearly dry
3
8
35-1270. A.L.: E-mail: Alexander.Laskin@pnl.gov. Phone: (509) 376-
741. Fax: (509) 376-6066.
16
conditions. Based on single particle analyses, Johnson et al.
†
Pacific Northwest National Laboratory.
University of Iowa.
University of Southern California.
‡
§
predicted that under typical atmospheric conditions of
20-90% RH the uptake of HNO3 on CaCO3 could be a factor
1
0.1021/jp076169h CCC: $40.75 © 2008 American Chemical Society
Published on Web 01/31/2008

1562 J. Phys. Chem. A, Vol. 112, No. 7, 2008
Liu et al.
TABLE 1: Reactive Uptake Coefficients Reported for HNO
3
(g) onto CaCO
3
and ATD at Room Temperature
particle
uptake
type of
sample
a
experimental
technique
diameter,
(µm)
[HNO
3
]
RH
(%)
coefficient,
-
12
D
p
(×10 cm-3)
γ
net
ref
b
-2
CaCO
CaCO
CaCO
CaCO
3
3
3
3
KCR-MS
5-100
3.5
0.01-10
1.3
0.065
0.065-1.3
0
0
0
0
(10 ( 2) ×10
21
a
a
a
-4
KCR-MS
KCR-MS
KCR-MS
(2.5 ( 0.1)×10
22
38
23
-5
1.8
<10
1.4 × 10
-2
(10 ( 2.5)×10
-2 c
(
18 ( 4.5)×10
a,d
-3
CaCO
CaCO
ATD
3
KCR-MS
0.2-10
0.01-0.7 (Dh
0.02-0.7 (Dh
19
1
0
33
12
(2 ( 1)×10
16
24
24
d
13
e
e
3
FR-N isotope tracer
p
p
) 0.042)
) 0.21)
0.11
d
13
FR-N isotope tracer
1
0.022 ( 0.007
0.03 ( 0.008
0.034 ( 0.011
0.058 ( 0.009
0.08 ( 0.012
0.072 ( 0.019
0.113 ( 0.017
0.0032
0.014
0.019
0.06
0.07
20
36
47
58
66
73
d
PS-SFR CCSEM/EDXf
CaCO
3
0.85 ( 0.18
0.17-0.73
10
this work
2
3
4
5
6
7
8
0
0
0
0
0
0
0
0.10
0.13
0.21
a
Powder sample. b Knudsen cell reactor - mass spectrometer. Values corresponding to heated and unheated CaCO
c
. d Aerosol or single particle
3
e
13
f
layers samples. Flow reactor - N-labeled nitric acid. Particles-on-substrate stagnation flow reactor - computer-controlled scanning electron
microscopy with energy-dispersed analysis of X-ray (see text).
of 10-100 faster than under dry conditions. This prediction
measurements. The Ca(NO3)2 aerosol was atomized from a 0.5
M calcium nitrate aqueous solution.
appears to be supported by a measurement made at 33% RH,
where γ ) 0.11,24 a value that is several orders of magnitude
Particle Exposure Apparatus. A schematic description of
the Particle-on-Substrate Stagnation Flow Reactor (PS-SFR) is
shown in Figure 2. A detailed description of the apparatus and
greater than those observed under dry conditions.9
,25-27
To date
no systematic studies are available to provide definitive and
quantitative characterization of HNO3 uptake on CaCO3 particles
under a wide range of humidity.
29
its operation have been given elsewhere. Briefly, a laminar
flow of premixed N2/H2O/HNO3 gases impinges onto substrate-
deposited particles. In each experiment, a substrate is loaded
with CaCO particles of a known number density (N ) and placed
The objective of the present work was to systematically
investigate the kinetics of the heterogeneous uptake of nitric
acid on calcium carbonate particles over a wide range of relative
humidity. Measurements were made using a recently developed
technique, which was successfully employed to study the
reaction kinetics for the uptake of hydroxyl radicals and nitric
3
s
atop a cylindrical Teflon sample holder 1′′ in diameter. The
particle sample and the holder were placed inside a sealed boro-
silicate glass chamber with a FETFE O-ring quick seal. The
nickel-based grid was fixed in place using a magnet embedded
inside the holder.
28,29
acid on NaCl particles.
In this technique, particle composi-
tion changes are followed by computer-controlled scanning
electron microscopy and energy dispersive X-ray analysis
The reactor and its gas delivery lines were made of glass
and Teflon parts; neither material reacts with the HNO3 vapor.
Nitrogen was used as a carrier gas and allowed to flow through
two bubblers containing a solution of concentrated HNO3 and
distilled water to generate nitric acid and water vapor, respec-
tively. Flow rates of the reactant HNO3/H2O/N2 mixture were
controlled by three mass flow controllers and relative humidity
was monitored by an inline sensor (Honeywell, inc., model
HIH4000). A rotameter was installed downstream of the reactor
to ensure no negative flow (into the apparatus) or leaks. A
chemiluminescence NOy analyzer (Thermo Environmental, Inc.,
model 42C-Y) was used to determine HNO3 concentration
exiting the reactor. Throughout this work, the reactor was
passivated before each experiment for at least 2 h with a flow
of the HNO3/H2O/N2 mixture to ensure there was no significant
loss of HNO3 on the walls of the apparatus and its gas lines.
During the reaction, both the HNO3 concentration and RH were
monitored continuously with fluctuations found to be smaller
than 5 and 1%, respectively.
(
CCSEM/EDX) of individual particles before and after reac-
28,29
tion.
Experimental Section
Materials and Sample Preparation. CaCO3 particles were
generated by atomizing a water suspension of calcium carbonate
powder (Alfa Aesar, 99.95% purity). The particles were dried
in a diffusion drier (TSI, Inc., model 3062) prior to sizing and
substrate deposition using a micro-orifice uniform deposition
impactor (MOUDI; model 110, MSP, Inc.). For this study, we
used the fifth stage of the MOUDI to generate dry particles.
These particles were deposited on filmed substrates (Carbon
Type-B, 400 mesh nickel grids, Electron Microscopy Sciences,
Inc.) mounted on the impaction plate. The size uniformity of
substrate deposited particles was confirmed by CCSEM analysis
of over 3000 particles in several samples. Figure 1 shows an
SEM image of a typical CaCO3 particle sample and its diameter
distribution obtained from equivalent circle diameters of two-
dimensional projected areas. The size distribution is log-normal
with a median diameter Dh p ) 0.85 µm and geometric standard
deviation σ ) 1.45. Similarly, samples of size-selected calcium
nitrate particles were prepared using MOUDI for reference
The gaseous reactant mixture is ejected at a volumetric rate
of 2 L/min (STP) from a 1.25 cm diameter (outer) boro-silicate
glass tube (inside diameter 0.8 cm). The flow impinges upon
particles deposited on a single grid with its center placed along
the flow tube centerline. The distance between the tube exit

Heterogeneous Reaction of CaCO3 Particles
J. Phys. Chem. A, Vol. 112, No. 7, 2008 1563
experiments were conducted at ambient temperature and under
atmospheric pressure.
CCSEM/EDX Single-Particle Analysis. Computer-con-
trolled scanning electron microscopy coupled with energy-
dispersed X-ray spectrometry was used to determine the
elemental composition and loading density of CaCO3 particles.
The instrument used in this study is an FEI XL30 digital field
emission gun environmental SEM. The microscope is equipped
with an EDAX spectrometer (model PV7761/54 ME, EDAX,
2
Inc.) that has an Si(Li) detector of 30 mm in active area and
an ATW2 window. The spectrometer allows X-ray detection
from elements higher than beryllium (Z > 4). The system is
equipped with Genesis hardware and software (EDAX, Inc.)
for CCSEM/EDX single particle analysis. Particles were
recognized by an increase in the detector signal above a
threshold value. The program acquires an X-ray spectrum from
each particle detected. Particle imaging was done by acquiring
a mixed signal of backscattered (BSE) and transmitted (TE)
3
0
electrons. During the X-ray acquisition, the electron beam
scanned over the particle projection area. The spectra were
acquired for 10 s at a beam current of ∼500 pA and an
accelerating voltage of 20 kV. For quantification of the EDX
results, the Genesis software utilizes a standardless microanalysis
method that relates X-ray intensities to elemental concentrations
through theoretically calculated equivalent intensities of corre-
sponding peaks. Details of the quantification method can be
3
1
found elsewhere.
As shown in our previous work,19 the apparent elemental
composition of CaCO3 and Ca(NO3)2 particles in terms of O/Ca
atomic ratios measured by CCSEM/EDX analysis do not match
their stoichiometric values. This instrumental response is due
to a combination of atomic number, absorption and florescence
(ZAF) effects, and beam damage that affect quantitation of X-ray
spectra. As a result, the O/Ca ratio in CaCO3 particles increases
monotonically with decreasing particle size. For example, the
O/C ratio was measured to be 3 and 1.3 for particles ∼0.1 and
∼
1.0 µm in size, respectively. Additionally, the O/Ca ratio
Figure 1. SEM image (top panel) and CCSEM measured particle size
distribution (symbols in the bottom panel) of a typical CaCO sample.
3
The size distribution is fit by a log-normal distribution (solid line).
characteristic of Ca(NO3)2 particles show a rise-then-fall
behavior with respect to particle size. The maximum value is
1
9
∼
3.5 for particles in the 0.8 to 2.0 µm size range. As will be
shown below, two reference values of atomic O/Ca ratios
measured in the standard samples of CaCO3 and Ca(NO3)2
particles are used to calculate the extent of CaCO3-to-Ca(NO3)2
conversion. A larger difference in the two O/Ca reference values
introduces a smaller uncertainty in our analysis. As these two
O/Ca reference values have the maximum difference near 1
1
9
µm, we used only one CaCO3 particle size ( Dh p ) 0.85 µm, σ
)
1.45) over the course of this study.
Experimental Protocol. The change in the O/Ca molar ratio
of reacted particles was taken to quantify the kinetic conversion
of CaCO3 to Ca(NO3)2, according to reaction 1. Unlike a
2
9
previous study, two reference values, corresponding to 0%
and 100% conversion of the initial CaCO3 particles, had to be
used for determining the reaction extent. The CaCO3 reactant
concentration upon a finite exposure time t is given by
EDX
Ca(NO )
EDX
- [O/Ca]t
[
O/Ca]
[
CaCO3]t
3 2
)
(2)
EDX
EDX
[
CaCO3]
t)0
[O/Ca]
- [O/Ca]
Ca(NO3)2 CaCO3
Figure 2. Schematic of the PS-SFR used in these studies for exposure
3
of CaCO to nitric acid vapor.
EDX
CaCO3
Here, [O/Ca]
is the molar ratio of O to Ca measured for
and the grid surface is 0.2 cm. These reactor parameters were
chosen on the basis of computational fluid dynamics (CFD)
modeling to ensure that all particles deposited on and across
pure, unreacted CaCO3 particles. The determination of [O/Ca-
]Ca(NO ) requires special sample preparation due to an enhance-
ment of the O/Ca ratio in the Ca(NO3)2 particles that results
from the following reason. Once deliquesced, Ca(NO3)2 particles
3
2
2
9
the grid are exposed to the same flux of HNO3. The

1564 J. Phys. Chem. A, Vol. 112, No. 7, 2008
Liu et al.
and nitrogen content in the particles after reactive exposure, as
one would expect from the stoichiometry of reaction 1.
As shown in Table 2, three sets of data were obtained for
the first series of experiments (A, B, and C). Each set used a
fixed HNO3 free-stream concentration (A, 7.1 ( 0.4; B, 14.4
(
0.7; and C, 24.5 ( 1.5 ppb) at RH ) 40% over a wide range
of reaction times (t ) 5 to 300 min) and particle loading
4
6
-2
densities (Ns ) 2 × 10 to 6 × 10 cm ). The HNO3
concentrations used in the first set of experiments correspond
to 10 to 20 ppb levels that are found in polluted environments.35
Altogether, over 100 substrates containing CaCO3 particles were
analyzed over the course of this study. A vast majority of the
particles had less than a 0.35 Ca(NO3)2/CaCO3 conversion ratio.
An additional series of experiments (data set labeled D) were
carried out to investigate the effect of relative humidity on the
reactive uptake of HNO3 on CaCO3. These data are given in
Table 3.
The kinetics data were analyzed using a theoretical kinetics-
diffusion model of gaseous reactant transport from the bulk gas
2
8
to the substrate surface. The effects of diffusion arise from
the finite proximity of the reacting particles mounted on the
substrate at high particle loadings, which alter the effective local
concentrations of the gaseous reactant (HNO3) immediately
above the particle surface and hence the apparent kinetics of
the CaCO3-to-Ca(NO3)2 conversion. For series A, B, and C
experiments, the influence of particle loading was eliminated
by fitting the kinetic data as a function of particles density Ns
2
8,29
Figure 3. Top panel: SEM images of CaCO
and after (right) reaction with gaseous HNO of 7 ppb concentration,
0% RH and reaction time of 120 min. Bottom panel: typical EDX
3
particles before (left)
using a diffusion-kinetic analysis,
as will be presented in
3
the Discussion section. Experiments in series D were done using
4
4
-2
a smaller particle loading (Ns < 5 × 10 cm ) to ensure that
3
spectra of CaCO particles before and after reaction.
the measured kinetics are representative of the single particle
2
8,29
interacting with the gas phase.
Even under this condition,
always retain some water and do not dry out completely even
under vacuum conditions.32,33 A recent study showed that the
amount of HNO3 uptake was greater than that expected for
known nitrate solubility suggesting Ca(NO3)2 itself could
irreversibly take up HNO3.34 These considerations led us to
determine the reference value for [O/Ca]Ca(NO ) by exposing
the reaction rate may be inherently limited by gas diffusion
because the particle size is larger than the mean free path of
the gas.
Results and Discussion
3
2
Ca(NO3)2 particles to a stream of HNO3/H2O/N2 identical to
the actual kinetic experiments for several hours. The resulting
particles were taken for [O/Ca]Ca(NO ) determination by EDX.
Indeed, Ca(NO3)2 particles treated in this manner displayed O/Ca
ratios nearly a factor of 1.2 higher than that of untreated Ca-
Rate Constant and Net Uptake Coefficient. As shown in
eq 2, the change in the O/Ca ratio in reacted particles was taken
to measure the extent of CaCO3-to-Ca(NO3)2 conversion. It is
important to note that carbonic acid (H2CO3), an intermediate
of reaction 1, is unstable and decomposes to water and carbon
dioxide, both of which for the most part degas as reacted
particles are subject to vacuum condition during microscopy
analysis. Because of the stoichiometry of reaction 1, the change
in the O/Ca ratio determined for vacuum-dried, reacted particles
is equal to the reaction extent given by eq 2, and the reaction
kinetics may be expressed accordingly,
3
2
3
6
(NO3)2 particles. We assume that the O/Ca ratio varies linearly
between the two reference values as the reaction proceeds. This
assumption is supported by the fact that the interaction volume
of the 20 kV electron beam applied in the CaCO3/Ca(NO3)2
3
media is much larger than 1 µm , i.e., the volume of particles
studied in this work. Therefore, the corresponding X-ray spectra
reflect an averaged composition of all the particles.
d[CaCO3]
In principle, measurements made for the N/Ca ratio could
29
-
) k
I
[CaCO
3
]
(3)
be also used to determine the reaction extent. However, the
quantitative detection of nitrogen is typically less accurate
because of complications due to a deep gap in the transmission
characteristic of the ATW2 window that overlaps the KR line
of nitrogen. This results in very low intensities of the nitrogen
peak measured by EDX, and consequently, in difficulties in its
accurate deconvolution.
dt
where [CaCO3] represents the concentration of CaCO3 in the
particles, and kI is the apparent, pseudo first-order rate constant.
If kI is a constant during the course of the reaction, its value
may be calculated from
The top panel of Figure 3 shows typical SEM images of
CaCO3 particles before and after exposure to gaseous HNO3.
The change observed in the morphology of individual particles
is consistent with previous observations,18 indicating the reactive
transformation from crystalline CaCO3 to amorphous Ca(NO3)2
particles. A comparison of the accompanying EDX spectra (the
bottom panel of Figure 3) reveals an enhancement of oxygen
[
CaCO3]t
1
t
k ) - ln
)
I
(
[CaCO3]t)0
)
EDX
Ca(NO )
EDX
- [O/Ca]t
3 2
[
O/Ca]
1
t
-
ln
(4)
EDX
EDX
(
)
[
O/Ca]
- [O/Ca]
Ca(NO3)2 CaCO3

Heterogeneous Reaction of CaCO3 Particles
J. Phys. Chem. A, Vol. 112, No. 7, 2008 1565
TABLE 2: Summary of Experimental Conditions and Pseudo First-Order Rate Constantsa
-
5
EDX
CaCO3,t
EDX
CaCO ,t ) 0
EDX
Ca(NO3)2
× 10 (s-1)
4
[
HNO
3
]
∞
(ppb)
N
s
× 10 (cm-2
)
Time, t (min)
[O/Ca]
[O/Ca]
[O/Ca]
k
I
3
Series A: RH ) 40%; Dh
p
3 ∞
) 0.85 ( 0.18 µm; [HNO ] ) 24.5 ( 1.5 ppb
2
7.0
7.0
2.0
2.0
1.0
1.0
1.0
1.0
3.0
3.0
6.5
6.5
6.0
6.0
5.1
5.1
5.2
5.2
4.7
4.7
4.2
4.2
4.0
5.0
5.0
3.8
3.9
3.9
4.2
4.2
6.5
6.5
6.1
5.0
7.0
7.0
4.2
4.2
2.4 ( 0.6
4.0 ( 1.0
2.7 ( 0.7
2.4 ( 0.6
3.8 ( 1.0
3.6 ( 0.9
0.6 ( 0.1
0.4 ( 0.1
0.6 ( 0.1
0.6 ( 0.1
4.9 ( 1.0
4.5 ( 1.1
8.7 ( 2.2
7.7 ( 1.9
6.3 ( 1.6
9.6 ( 2.4
3.8 ( 0.9
3.1 ( 0.8
2.4 ( 0.6
2.1 ( 0.5
2.6 ( 0.7
2.2 ( 0.6
0.3 ( 0.1
0.3 ( 0.1
0.5 ( 0.1
0.2 ( 0.1
0.9 ( 0.2
1.4 ( 0.3
1.5 ( 0.4
1.3 ( 0.3
1.4 ( 0.4
1.4 ( 0.4
1.7 ( 0.4
30.3 ( 7.6
27.8 ( 6.9
35.7 ( 8.9
1.0 ( 0.3
0.8 ( 0.2
10
10
10
10
10
10
5
2.92 ( 0.86
2.98 ( 0.90
2.67 ( 0.83
2.71 ( 0.75
2.51 ( 0.79
2.60 ( 0.94
2.58 ( 1.24
2.57 ( 0.92
2.70 ( 0.95
2.86 ( 1.17
2.85 ( 1.23
3.06 ( 1.26
2.73 ( 0.87
2.88 ( 1.14
2.68 ( 0.93
2.90 ( 1.21
3.35 ( 1.31
3.23 ( 1.23
3.27 ( 1.25
3.20 ( 1.29
2.69 ( 0.88
2.97 ( 1.10
3.23 ( 1.24
3.62 ( 1.26
3.67 ( 1.27
3.35 ( 1.39
2.54 ( 0.57
2.48 ( 0.74
3.15 ( 1.37
2.84 ( 0.93
2.53 ( 0.57
2.53 ( 0.69
2.96 ( 1.02
2.53 ( 0.85
2.75 ( 1.12
2.67 ( 1.24
2.96 ( 1.28
3.34 ( 1.58
2.04 ( 0.49
2.04 ( 0.49
2.04 ( 0.49
2.04 ( 0.49
2.04 ( 0.49
2.04 ( 0.49
2.04 ( 0.49
2.04 ( 0.49
2.04 ( 0.49
2.04 ( 0.49
2.36 ( 0.56
2.36 ( 0.56
2.36 ( 0.56
2.36 ( 0.56
2.36 ( 0.56
2.36 ( 0.56
2.36 ( 0.56
2.36 ( 0.56
2.36 ( 0.56
2.36 ( 0.56
2.36 ( 0.56
2.36 ( 0.56
2.36 ( 0.56
2.36 ( 0.56
2.36 ( 0.56
2.36 ( 0.56
2.14 ( 0.38
2.14 ( 0.38
2.14 ( 0.38
2.14 ( 0.38
2.14 ( 0.38
2.14 ( 0.38
2.14 ( 0.38
2.27 ( 0.72
2.27 ( 0.72
2.27 ( 0.72
2.36 ( 0.56
2.36 ( 0.56
4.58 ( 0.90
4.58 ( 0.90
4.58 ( 0.90
4.58 ( 0.90
4.58 ( 0.90
4.58 ( 0.90
4.58 ( 0.90
4.58 ( 0.90
4.58 ( 0.90
4.58 ( 0.90
5.67 ( 1.00
5.67 ( 1.00
5.67 ( 1.00
5.67 ( 1.00
5.67 ( 1.00
5.67 ( 1.00
5.67 ( 1.00
5.67 ( 1.00
5.67 ( 1.00
5.67 ( 1.00
5.67 ( 1.00
5.67 ( 1.00
5.67 ( 1.00
5.67 ( 1.00
5.67 ( 1.00
5.67 ( 1.00
5.67 ( 1.00
5.67 ( 1.00
5.67 ( 1.00
5.67 ( 1.00
5.67 ( 1.00
5.67 ( 1.00
5.67 ( 1.00
5.67 ( 1.00
5.67 ( 1.00
5.67 ( 1.00
5.67 ( 1.00
5.67 ( 1.00
7.1 (×2.2/÷2.2)
7.7 (×2.3/÷2.3)
4.7 (×2.5/÷2.0)
5.1 (×2.3/÷2.1)
3.4 (×2.8/÷2.0)
4.1 (×2.8/÷2.0)
8.1 (×3.5/÷2.0)
7.9 (×2.9/÷2.0)
5.0 (×2.6/÷2.0)
6.5 (×2.8/÷2.0)
2.7 (×3.5/÷2.0)
3.9 (×2.9/÷2.0)
1.6 (×3.3/÷2.0)
2.3 (×3.2/÷2.0)
1.3 (×3.8/÷2.0)
2.3 (×3.2/÷2.0)
6.6 (×2.5/÷2.0)
5.6 (×2.6/÷2.0)
6.7 (×2.5/÷2.0)
6.1 (×2.7/÷2.0)
2.7 (×3.6/÷2.0)
5.2 (×2.8/÷2.0)
10.1 (×2.6/÷2.0)
15.9 (×2.3/÷2.3)
16.7 (×2.6/÷2.0)
11.8 (×2.6/÷2.0)
4.0 (×2.3/÷2.0)
3.4 (×2.9/÷2.0)
9.4 (×2.5/÷2.0)
6.1 (×2.3/÷2.0)
3.5 (×2.4/÷2.0)
3.5 (×2.6/÷2.0)
6.8 (×2.2/÷2.1)
0.5 (×4.4/÷2.0)
0.8 (×3.4/÷2.0)
0.7 (×4.1/÷2.0)
6.7 (×3.1/÷2.0)
11.6 (×2.9/÷2.0)
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
2
5
10
10
10
10
12
12
13
13
9
9
8
8
6.5
6.5
5
5
5
5
5
5
6
6
5.5
5.5
6.5
25
30
30
5
5
Series B: RH ) 40%; Dh
p
3 ∞
) 0.85 ( 0.18 µm; [HNO ] )14.4 ( 0.7 ppb
15.5
15.5
13.7
13.7
15.0
15.0
14.5
14.0
14.0
13.8
14.1
14.9
14.9
14.4
14.7
14.7
14.7
14.2
14.2
13.2
13.2
13.1
15.3
15.3
1.1 ( 0.3
1.0 ( 0.3
0.8 ( 0.2
0.9 ( 0.2
5.8 ( 1.5
2.3 ( 0.6
10.8 ( 2.7
3.8 ( 0.9
1.8 ( 0.5
0.2 ( 0.1
0.4 ( 0.1
55.1 ( 13.8
51.8 ( 13.0
42.9 ( 10.7
7.8 ( 2.0
6.1 ( 1.5
5.1 ( 1.3
0.3 ( 0.1
0.3 ( 0.1
0.5 ( 0.1
0.6 ( 0.1
0.3 ( 0.1
0.3 ( 0.1
0.2 ( 0.1
14
14
14.5
14.5
45
45
45
46
46
14.5
16
67
67
85
60
60
60
12
12
12
12
9
2.97 ( 1.70
2.97 ( 1.55
3.39 ( 1.68
3.51 ( 1.49
3.23 ( 1.49
3.19 ( 1.18
2.58 ( 1.29
3.24 ( 1.55
3.15 ( 1.60
3.38 ( 2.02
3.26 ( 1.02
2.49 ( 1.24
2.48 ( 1.03
2.54 ( 1.23
2.74 ( 1.23
2.83 ( 1.25
3.10 ( 1.43
3.08 ( 1.01
3.09 ( 1.35
2.77 ( 1.13
3.28 ( 1.56
2.97 ( 1.23
2.88 ( 1.23
3.08 ( 0.68
2.22 ( 0.91
2.22 ( 0.91
2.22 ( 0.91
2.22 ( 0.91
2.24 ( 0.99
2.24 ( 0.99
2.24 ( 0.99
2.24 ( 0.99
2.24 ( 0.99
2.22 ( 0.91
2.22 ( 0.91
2.24 ( 0.96
2.24 ( 0.96
2.24 ( 0.96
2.24 ( 0.99
2.24 ( 0.99
2.24 ( 0.99
2.22 ( 0.91
2.22 ( 0.91
2.22 ( 0.91
2.22 ( 0.91
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 0.97
5.51 ( 0.97
5.51 ( 0.97
3.1 (×3.8/÷2.0)
3.1 (×3.5/÷2.0)
5.1 (×3.1/÷2.0)
5.7 (×2.7/÷2.1)
1.3 (×3.0/÷2.0)
1.3 (×2.6/÷2.0)
0.4 (×5.2/÷2.0)
1.3 (×3.1/÷2.0)
1.2 (×3.3/÷2.0)
5.0 (×3.8/÷2.0)
4.0 (×2.3/÷2.2)
0.2 (×6.4/÷2.0)
0.2 (×5.0/÷2.0)
0.2 (×5.5/÷2.0)
0.5 (×3.8/÷2.0)
0.6 (×3.4/÷2.0)
0.9 (×3.1/÷2.0)
4.2 (×2.5/÷2.0)
4.3 (×2.9/÷2.0)
2.5 (×3.3/÷2.0)
5.4 (×3.0/÷2.0)
6.1 (×2.3/÷2.1)
4.1 (×2.4/÷2.0)
5.2 (×1.7/÷2.9)
12
12
Series C: RH ) 40%; Dh
p
3 ∞
) 0.85 ( 0.18 µm; [HNO ] )7.1 ( 0.4 ppb
6.5
6.5
7.0
7.1
7.1
7.3
7.3
7.2
2.6 ( 0.6
1.6 ( 0.4
1.8 ( 0.5
1.8 ( 0.4
2.0 ( 0.5
1.9 ( 0.5
2.6 ( 0.7
2.4 ( 0.6
25
25
28
23
23
20
20
23
2.88 ( 1.4
2.30 ( 0.9
2.90 ( 1.4
2.65 ( 1.2
2.68 ( 1.3
2.63 ( 1.0
2.55 ( 1.1
2.32 ( 1.1
2.04 ( 0.49
2.04 ( 0.49
2.04 ( 0.49
2.04 ( 0.49
2.04 ( 0.49
2.04 ( 0.49
2.04 ( 0.49
2.04 ( 0.49
4.58 ( 0.90
4.58 ( 0.90
4.58 ( 0.90
4.58 ( 0.90
4.58 ( 0.90
4.58 ( 0.90
4.58 ( 0.90
4.58 ( 0.90
2.7 (×3.3/÷2.0)
0.7 (×4.4/÷2.0)
2.5 (×3.3/÷2.0)
2.0 (×3.1/÷2.0)
2.1 (×3.3/÷2.0)
2.2 (×2.9/÷2.0)
1.9 (×3.3/÷2.0)
0.9 (×4.8/÷2.0)

1566 J. Phys. Chem. A, Vol. 112, No. 7, 2008
Liu et al.
TABLE 2. (Continued)
× 10 (cm-2
-
5
)
Time, t (min)
[O/Ca]
EDX
CaCO3,t
[O/Ca]
EDX
CaCO ,t ) 0
[O/Ca]
EDX
Ca(NO3)2
k
I
× 10 (s-1)
4
[
HNO
3
]
∞
(ppb)
N
s
3
7
7
6
6
6
6
7
7
7
7
6
6
7
7
7
6
6
6
6
7
7
6
6
7
7
6
6
7
7
7
7
7
7
7
7
7
7
7
7
7
7
7
.0
4.2 ( 1.1
2.8 ( 0.7
0.7 ( 0.2
0.8 ( 0.2
0.5 ( 0.1
0.6 ( 0.2
1.5 ( 0.4
1.4 ( 0.3
1.2 ( 0.3
1.1 ( 0.3
0.8 ( 0.2
0.8 ( 0.2
0.2 ( 0.1
0.2 ( 0.1
0.2 ( 0.0
0.2 ( 0.0
0.2 ( 0.0
0.1 ( 0.0
0.1 ( 0.0
0.5 ( 0.1
0.4 ( 0.1
0.5 ( 0.1
0.5 ( 0.1
7.6 ( 1.9
16.6 ( 4.2
6.2 ( 1.6
14.3 ( 3.6
0.4 ( 0.1
0.5 ( 0.1
7.0 ( 1.7
7.3 ( 1.8
4.4 ( 1.1
1.7 ( 0.4
27.8 ( 6.9
28.6 ( 7.2
26.2 ( 6.6
32.1 ( 8.0
0.4 ( 0.1
0.4 ( 0.1
0.2 ( 0.1
0.3 ( 0.1
0.3 ( 0.1
30
30
2.67 ( 1.2
2.48 ( 0.9
2.32 ( 1.0
2.43 ( 1.1
2.32 ( 1.0
2.50 ( 1.3
3.12 ( 2.0
2.60 ( 1.6
2.46 ( 1.5
2.90 ( 1.8
3.02 ( 2.0
2.56 ( 1.5
2.69 ( 1.7
2.52 ( 1.1
2.45 ( 1.8
2.39 ( 0.8
2.30 ( 0.4
2.66 ( 1.5
2.71 ( 1.6
2.28 ( 1.0
2.46 ( 1.2
2.51 ( 1.2
2.28 ( 1.2
2.76 ( 1.3
2.86 ( 1.4
2.91 ( 1.4
2.82 ( 1.5
2.48 ( 0.9
2.93 ( 1.3
3.12 ( 1.5
3.22 ( 1.5
3.04 ( 1.5
3.12 ( 1.4
3.11 ( 1.6
2.56 ( 1.1
2.64 ( 1.1
2.61 ( 1.1
2.51 ( 0.9
2.44 ( 1.7
3.21 ( 1.1
2.85 ( 1.0
2.72 ( 1.2
2.04 ( 0.49
2.04 ( 0.49
2.04 ( 0.49
2.04 ( 0.49
2.04 ( 0.49
2.04 ( 0.49
2.22 ( 0.91
2.22 ( 0.91
2.22 ( 0.91
2.22 ( 0.91
2.22 ( 0.91
2.22 ( 0.91
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
1.98 ( 0.42
4.58 ( 0.90
4.58 ( 0.90
4.58 ( 0.90
4.58 ( 0.90
4.58 ( 0.90
4.58 ( 0.90
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.51 ( 1.03
5.5 ( 0.97
5.5 ( 0.97
5.5 ( 0.97
5.5 ( 0.97
5.5 ( 0.97
5.5 ( 0.97
5.5 ( 0.97
5.5 ( 0.97
1.6 (×3.2/÷2.0)
1.0 (×3.1/÷2.0)
0.6 (×4.7/÷2.0)
0.9 (×3.8/÷2.0)
1.0 (×4.0/÷2.0)
2.3 (×4.0/÷2.0)
2.3 (×4.1/÷2.0)
0.9 (×5.5/÷2.0)
0.6 (×4.8/÷2.0)
1.8 (×4.3/÷2.0)
2.0 (×4.2/÷2.0)
0.9 (×5.7/÷2.0)
3.7 (×3.4/÷2.0)
2.8 (×2.9/÷2.0)
2.4 (×4.8/÷2.0)
2.1 (×2.9/÷2.0)
1.6 (×2.3/÷2.0)
3.0 (×3.3/÷2.0)
3.2 (×3.2/÷2.0)
1.0 (×3.8/÷2.0)
1.6 (×3.4/÷2.0)
2.3 (×3.1/÷2.0)
1.2 (×4.5/÷2.0)
0.2 (×2.7/÷2.0)
0.3 (×2.7/÷2.0)
0.3 (×2.7/÷2.0)
0.3 (×2.8/÷2.0)
1.7 (×2.7/÷2.0)
3.5 (×2.4/÷2.0)
0.4 (×2.5/÷2.1)
0.4 (×2.5/÷2.1)
1.2 (×2.5/÷2.0)
1.3 (×2.4/÷2.1)
0.2 (×2.6/÷2.0)
0.1 (×2.7/÷2.0)
0.1 (×2.5/÷2.0)
0.1 (×2.6/÷2.0)
2.3 (×2.6/÷2.0)
1.9 (×4.5/÷2.0)
4.5 (×2.0/÷2.4)
2.9 (×2.1/÷2.2)
2.5 (×2.6/÷2.0)
.0
.4
.4
.3
.3
.0
.0
.5
.5
.7
.7
.0
.0
.0
.5
.5
.2
.2
.5
.5
.8
.8
.1
.1
.9
.9
.8
.8
.5
.5
.9
.9
.4
.4
.4
.4
.2
.0
.8
.8
.8
30
30
35
35
23
23
21
21
23
23
10
10
10
10
10
12
12
15
15
12
12
180
180
150
150
15
15
180
180
50
50
300
300
300
300
12
12
16
16
16
a
Uncertainty values represent one-standard deviation. k
I
is the apparent, pseudo first-order rate constant determined from eq 4, and the uncertainty
EDX
EDX
EDX
factors in the parentheses correspond to one standard deviation in [O/Ca]
, [O/Ca]
and [O/Ca]
.
Ca(NO3)2
CaCO3,t
CaCO ,t)0
3
EDX
Ca(NO3)2
EDX
EDX
CaCO3
Table 2 lists the [O/Ca]
, [O/Ca]t , [O/Ca]
and kI
where k* is the lower limit of the apparent first-order rate
I
values for the first series of experiments. The uncertainty of kI
was calculated from the standard deviations in the measurements
of the O/Ca ratios and is expressed in Table 2 as the
multiplication and division factor (i.e., the uncertainty factor)
because of the logarithmic function of eq 4. To examine the
validity of the pseudo first-order rates, we analyzed the
constant in the limit of Ns f 0, i.e., that of a single particle, ks
is the rate constant of the HNO3 reaction with the substrate
surface and δ is a parameter equal to l/DHNO -N , where l is the
3
2
boundary layer thickness above the substrate and DHNO -N is
3
2
the HNO3-N2 binary diffusion coefficient. In eq 5, parameter
b is related to particle volume and the characteristic diffusion
[
HNO3]∞/kI values taken at several averaged particle loadings
but over a range of reaction times (6 e t e 300 min). Here,
HNO3]∞ is the gaseous HNO3 concentration in the free stream.
The analysis shows no discernible, systematic variation of
HNO3]∞/kI as a function of time, as shown in Figure 4. That
length of HNO . Its value is approximately constant during
3
28
reaction. A plot of [HNO ] /k data versus N and extrapolating
3
∞
I
s
[
the data to zero N yields the value for k* , as shown in Figure
s
I
5. The solid line in Figure 5 represents the fit, and the dashed
lines represent the scatter of the data. As seen, the data cluster
around the fitted line within a degree of scatter, but no
systematic variation is observed as a function of the free-stream
HNO3 concentration, which again verifies the assumption of
pseudo first-order reaction kinetics. The value of [HNO3]∞/kI
[
is, kI is time invariant over the range of reaction times
investigated.
Because of the finite density and thus spatial separation of
the particles on the substrate, the measured pseudo first-order
rate constant is influenced by diffusive competition of the
gaseous reactant, and as such its value is dependent on the
particle loading density. As shown in a previous diffusion-kinetic
analysis,28 kI may be related to Ns by the following equation:
14
-3
is found to be 4.8 × 10 (×3/÷2) cm ‚s in the limit of Ns f
0
. The uncertainty of the data and their extrapolation are
represented by the dashed lines in Figure 5
An underlying assumption of the data analysis28,29 is that the
substrate is unreative, i.e., HNO3 consumption by the substrate
does not affect kinetics of the HNO3-to-CaCO3 reaction (δks
, 1 in eq 5). If some of the reactive gas molecules are removed
[
HNO3]∞ [HNO3]∞
)
(1 + δk ) + bNS
(5)
s
kI
k*I

Heterogeneous Reaction of CaCO3 Particles
J. Phys. Chem. A, Vol. 112, No. 7, 2008 1567
TABLE 3: Summary of Experimental Conditions and Pseudo First-Order Rate Constants in Relative Humidity Dependency
a
Study (Series D)
-
4
4
-4
4
[
HNO
3
]
∞
N
(cm
s
× 10
time
(min)
k
I
× 10
[HNO
(ppb)
3
]
∞
N
(cm
s
× 10
time
(min)
k
I
× 10
-
2
EDX
CaCO3,t
-1
-2
EDX
CaCO3,t
-1
(ppb)
)
[O/Ca]
(s
)
)
[O/Ca]
(s )
RH ) 10%
2.0
2.2 ( 0.5
2.4 ( 0.6
3.3 ( 0.8
1.9 ( 0.5
3.2 ( 0.8
25.0
50.0
50.0
40.0
40.0
2.44 ( 1.17
2.36 ( 1.14
2.26 ( 0.76
3.07 ( 1.76
2.39 ( 1.00
0.9 (×3.2/÷2.0)
0.4 (×3.9/÷2.0)
0.3 (×4.7/÷2.0)
1.5 (×2.1/÷1.8)
0.5 (×3.6/÷2.0)
22.2
21.6
34.5
34.5
2.3 ( 0.6
2.4 ( 0.6
3.3 ( 0.8
2.5 ( 0.6
50.0
50.0
40.0
40.0
2.35 ( 1.00
2.27 ( 1.11
2.57 ( 1.26
2.53 ( 1.33
0.4 (×3.8/÷2.0)
0.3 (×5.1/÷2.0)
0.8 (×2.7/÷2.0)
0.7 (×3.0/÷2.0)
RH ) 20%
16.2
16.2
19.5
19.5
19.5
21.0
2.2 ( 0.5
1.7 ( 0.4
2.5 ( 0.6
2.2 ( 0.5
3.5 ( 0.9
3.2 ( 0.8
16.0
16.0
16.0
16.0
16.0
16.0
2.35 ( 1.76
2.53 ( 1.51
2.61 ( 1.17
2.72 ( 1.15
2.40 ( 0.85
2.50 ( 1.42
1.2 (×4.5/÷2.0)
1.8 (×3.0/÷2.0)
2.1 (×2.5/÷2.0)
2.5 (×2.2/÷2.0)
1.3 (×3.3/÷2.0)
1.7 (×3.1/÷2.0)
20.0
20.0
20.0
20.8
20.8
3.5 ( 0.9
4.8 ( 1.2
3.2 ( 0.8
2.3 ( 0.6
2.1 ( 0.5
16
16
16
16
16
3.11 ( 1.80
2.61 ( 1.10
2.37 ( 0.88
2.38 ( 1.39
2.85 ( 1.57
4.0 (×2.0/÷1.8)
2.1 (×2.5/÷2.0)
1.2 (×3.4/÷2.0)
1.3 (×4.1/÷2.0)
3.0 (×2.2/÷1.9)
RH ) 30%
8.8
8.7
8.9
8.8
8.5
8.5
3.1 ( 0.8
3.3 ( 0.8
2.1 ( 0.5
2.5 ( 0.6
4.2 ( 1.0
4.4 ( 1.1
15.0
15.0
30.0
30.0
35.0
35.0
2.43 ( 1.19
2.47 ( 0.99
2.37 ( 1.15
2.39 ( 1.19
2.67 ( 1.27
2.52 ( 1.09
1.5 (×3.4/÷2.0)
1.7 (×3.2/÷2.0)
0.7 (×3.9/÷2.0)
0.7 (×3.8/÷2.0)
1.0 (×2.5/÷2.0)
0.8 (×2.8/÷2.0)
8.2
8.0
8.0
8.2
8.2
3.7 ( 0.9
1.7 ( 0.4
3.7 ( 0.9
4.4 ( 1.1
2.2 ( 0.5
35.0
40.0
40.0
40.0
40.0
2.85 ( 1.40
3.19 ( 0.82
2.64 ( 1.30
2.79 ( 1.25
2.87 ( 0.56
1.4 (×2.2/÷1.9)
1.8 (×1.9/÷1.7)
0.9 (×2.5/÷2.0)
1.1 (×2.2/÷1.9)
1.2 (×2.0/÷1.8)
RH ) 40%
1
1
1
1
7
7
7
6
3.8
4.1
4.2
4.2
.0
.0
.0
.5
2.2 ( 0.5
3.7 ( 0.9
2.7 ( 0.7
2.8 ( 0.7
2.0 ( 0.5
2.1 ( 0.5
1.7 ( 0.4
1.5 ( 0.4
14.5
16.0
12.0
12.0
10.0
10.0
10.0
10.0
3.38 ( 2.02
3.26 ( 1.02
3.08 ( 1.01
3.09 ( 1.35
2.69 ( 1.69
2.52 ( 1.12
2.45 ( 1.82
2.39 ( 0.84
5.0 (×2.0/÷1.8)
4.0 (×2.0/÷1.8)
4.2 (×2.2/÷1.9)
4.3 (×2.2/÷1.9)
3.7 (×2.6/÷2.0)
2.8 (×2.9/÷2.0)
2.4 (×3.8/÷2.0)
2.1 (×3.4/÷2.0)
6.2
6.2
7.2
7.0
7.8
7.8
7.8
1.3 ( 0.3
1.2 ( 0.3
4.2 ( 1.1
4.0 ( 1.0
2.4 ( 0.6
2.9 ( 0.7
3.3 ( 0.8
12.0
12.0
12.0
12.0
16.0
16.0
16.0
2.66 ( 1.54
2.71 ( 1.61
2.51 ( 0.94
2.44 ( 1.69
3.21 ( 1.10
2.85 ( 0.99
2.72 ( 1.23
3.0 (×2.6/÷2.0)
3.2 (×2.4/÷2.0)
2.3 (×2.6/÷2.0)
1.9 (×3.6/×f72.0)
4.5 (×1.9/÷1.7)
2.9 (×2.1/÷1.8)
2.5 (×2.2/÷1.9)
RH ) 50%
7
7
7
7
7
.6
.6
.2
.2
.2
1.9 ( 0.5
2.1 ( 0.5
1.7 ( 0.4
2.3 ( 0.6
2.7 ( 0.7
9.5
9.5
9.5
10.0
10.0
2.64 (0.92
2.76 ( 0.96
2.90 ( 1.14
2.57 ( 0.71
2.40 ( 0.76
3.6 (×2.3/÷2.0)
4.4 (×2.2/÷1.9)
5.3 (×2.1/÷1.9)
3.0 (×2.4/÷2.0)
2.1 (×3.1/÷2.0)
7.0
7.0
6.9
7.3
7.3
3.9 ( 1.0
2.7 ( 0.7
1.3 ( 0.3
1.9 ( 0.5
3.7 ( 0.9
10.0
10.0
10.0
10.0
10.0
2.43 ( 0.89
2.59 ( 0.96
2.82 ( 1.60
2.93 ( 1.43
2.43 ( 1.19
2.3 (×3.3/÷2.0)
3.2 (×2.5/÷2.0)
4.5 (×2.2/÷1.9)
5.2 (×2.1/÷1.8)
2.3 (×3.4/÷2.0)
RH ) 60%
7.5
7.5
7.5
7.5
7.6
7.6
1.9 ( 0.5
1.3 ( 0.3
1.9 ( 0.5
2.1 ( 0.5
1.7 ( 0.4
2.0 ( 0.5
8.0
8.0
8.0
8.0
9.0
9.0
2.62 ( 0.73
2.58 ( 1.10
2.70 ( 0.69
2.60 ( 0.61
2.86 ( 0.87
3.02 ( 0.97
4.2 (×2.3/÷2.0)
3.9 (×2.6/÷2.0)
4.8 (×2.2/÷1.9)
4.0 (×2.2/÷2.0)
5.3 (×2.1/÷1.8)
6.5 (×2.0/÷1.8)
7.6
7.6
7.8
7.8
7.8
7.8
1.7 ( 0.4
1.7 ( 0.4
2.3 ( 0.6
2.5 ( 0.6
2.1 ( 0.5
2.3 ( 0.6
9.0
9.0
8.5
8.5
8.5
8.5
3.39 ( 1.05
3.31 ( 0.91
3.10 ( 1.12
3.04 ( 0.84
2.93 ( 0.95
2.63 ( 0.83
9.4 (×1.9/÷1.7)
8.8 (×1.8/÷1.7)
7.5 (×1.9/÷1.8)
7.0 (×2.0/÷1.8)
6.1 (×2.0/÷1.8)
4.0 (×2.3/÷2.0)
RH ) 70%
8.0
8.0
7.9
7.9
7.5
3.9 ( 1.0
2.3 ( 0.6
2.7 ( 0.7
2.5 ( 0.6
2.3 ( 0.6
8.5
8.5
8.5
8.5
8.0
3.12 ( 0.94
3.14 ( 0.92
2.72 ( 0.76
3.34 ( 0.96
3.32 ( 1.07
7.6 (×1.9/÷1.8)
7.8 (×1.9/÷1.8)
4.6 (×2.2/÷1.9)
9.5 (×1.8/÷1.7)
9.9 (×1.9/÷1.7)
7.5
7.4
6.7
7.1
7.1
2.4 ( 0.6
2.4 ( 0.6
1.9 ( 0.5
1.6 ( 0.4
2.3 ( 0.6
8.0
8.0
8.0
8.0
8.0
2.79 ( 0.91
3.26 ( 0.97
2.46 ( 0.52
2.98 ( 0.78
3.15 ( 0.91
5.4 (×2.1/÷1.9)
9.4 (×1.9/÷1.7)
3.0 (×2.7/÷2.0)
6.9 (×2.0/÷1.8)
8.4 (×2.2/÷1.7)
RH ) 80%
7
7
7
7
8
8
.8
.8
.9
.9
.0
.0
3.9 ( 1.0
3.6 ( 0.9
3.0 ( 0.8
2.4 ( 0.6
2.1 ( 0.5
2.4 ( 0.6
5.0
5.0
5.0
5.0
5.0
5.0
3.22 ( 0.91
3.32 ( 1.08
3.17 ( 1.05
3.29 ( 1.08
3.01 ( 1.02
3.15 ( 1.13
14.4 (×1.9/÷1.7)
15.9 (×1.9/÷1.7)
13.7 (×1.9/÷1.7)
15.5 (×1.9/÷1.7)
11.5 (×2.0/÷1.8)
13.4 (×2.0/÷1.8)
8.0
8.0
7.5
7.5
7.5
7.5
2.1 ( 0.5
2.3 ( 0.6
2.6 ( 0.7
3.0 ( 0.8
3.5 ( 0.9
3.8 ( 1.0
5.0
5.0
5.0
5.0
5.0
5.0
3.29 ( 1.16
3.22 ( 0.89
2.79 ( 0.84
2.42 ( 0.73
3.31 ( 0.86
2.79 ( 0.80
15.5 (×1.9/÷1.7)
14.4 (×1.9/÷1.7)
8.7 (×2.1/÷1.9)
4.4 (×3.1/÷2.0)
15.8 (×1.8/÷1.7)
8.7 (×2.1/÷1.9)
a
EDX
CaCO ,t)0
EDX
All of the experiments were conducted under conditions of Dh
Uncertainty values represent one-standard deviation. k
factors in the parentheses correspond to one standard deviation in [O/Ca]CaCO3,t, [O/Ca]
p
) 0.85 ( 0.18 µm, [O/Ca]
) 2.0 ( 0.5 and [O/Ca]
) 5.5 ( 1.0.
Ca(NO3)2
3
I
is the apparent, pseudo first-order rate constant determined from eq 4, and the uncertainty
EDX
EDX
CaCO ,t)0
EDX
and [O/Ca]
.
Ca(NO3)2
3
by the substrate, values of kI and thus γnet would be underes-
where [CaCO3]0 ) 27.1 M is a formal volume concentration of
calcite particle, V /S is the particle volume-to-surface area ratio,
2
8,29
timated. Hence, as discussed in our earlier publications,
a
d
d
4
rigorous view is that the uptake coefficient reported here
represents the lower limit.
cj HNO3 ) 3.18 × 10 cm/s is the mean molecular speed of HNO
3
and Dh is the wet particle diameter at RH ) 40%. The above
d
The net uptake coefficient (γnet) can be calculated by
equation is used in all subsequent analysis to obtain γnet values.
The determination of the droplet diameter required some special
considerations. During the reaction, CaCO3 is partially converted
to hydrated Ca(NO3)2. At RH ) 40%, CaCO3 particles remain
solid while Ca(NO3)2, a highly hygroscopic substance, rapidly
*
I
*
4
k [CaCO ] Vd 2[CaCO ] Dd
kI
[HNO3]∞
3 t)0
3 t)0
γnet
)
)
(6)
cj HNO3[HNO ] Sd
3 cj HNO3
3 ∞

1
568 J. Phys. Chem. A, Vol. 112, No. 7, 2008
Liu et al.
Figure 6. Simplified core-shell model for estimating the size of
reacted CaCO .
3
that upon reaction a uniform coating of Ca(NO3) forms over a
spherical CaCO3 core, as illustrated in Figure 6. The volumes
of the CaCO3 core and the Ca(NO3)2 coating are given by eqs
7
and 8 as a function of reaction time, respectively
1
6
3
p
V
(t) ) π Dh [1 - ø(t)]
(7)
(8)
CaCO ,core
3
3FCaCO3MWCa(NO3)2
4
3
3
p
V
(t) ) π( Dh g
)
ø(t)
Ca(NO3)2
Ca(NO ) ,RH
3 2
FCa(NO3)2MWCaCO3
where ø(t) is the extent of reaction, gCa(NO ) ,RH the hygroscopic
3
2
growth factor for Ca(NO3)2 at a specific relative humidity, and
F and MW the mass density and molecular weight, respectively.
If volume additivity is assumed, the largest diameter of a
reacting CaCO3 particle at the end of the experiment ( Dh d,max )
may be estimated by
Figure 4. Variations of [HNO
Symbol are experimental data (∆, 7.1 ( 0.4 ppb HNO
0.7 ppb; 0, 24 ( 1.5 ppb). The dashed line indicates the average of
the measured data; the error bars at the left- and rightmost of the line
indicate one standard deviation of the [HNO /k data.
3
]
∞
/k
I
as a function of reaction time.
3
; O, at ∼14.4
(
Dh d,max
)
3
]
∞
I
1
/3
3
3FCaCO3MWCa(NO3)2
Dh [1 - ø(t)] + (g
Dh p)
Ca(NO ) ,RH
3 2
ø(t)
(9)
p
{
FCa(NO3)2MWCaCO3
}
Here the extent of reaction is given by
[
CaCO3]t
ø(t) ) 1 -
(10)
[
CaCO3]t)0
At a relative humidity of 40%, the hygroscopic growth factor
3
3
for Ca(NO3)2 is gCa(NO ) ,RH ) 40% ) 1.4. The mass densities
3
2
of pure CaCO3 and Ca(NO3)2 were taken to be FCaCO ) 2.71
g/cm and FCa(NO ) ) 2.50 g/cm . It was found that under the
3
3
3 37
3
2
current experimental conditions Dh d,max e1.2 Dh p for RH ) 40%.
Toward higher RH values, the approximation yields larger
differences in Dh d,max values, i.e., Dh d,max e1.6 Dh p at RH ) 80%.
Considering that these differences are notably smaller than the
Figure 5. Experimental values of [HNO
3
]
∞
/k
I
, measured for ∼0.85
scatter in the data and that the k* value represents the lower
µm CaCO
3
particles under 40% RH as a function of particle number
on the substrate surface. Symbols: experimental data for
I
28,29
density N
s
limit of reaction rates,
we used the Dh d,min ) Dh p approxima-
different concentrations of HNO
0.7 ppb; 0, 24 ( 1.5 ppb), solid line: fit to data; dashed lines: the
uncertainty of the fit.
3
(∆, 7.1 ( 0.4 ppb HNO
3
; O, at ∼14.4
tion to calculate the uptake coefficients reported in this work,
as tabulated in Table 1.
(
RH Dependence. To date, there is only one systematic
investigation reported for nitric acid uptake onto a mineral dust
surrogate, ATD, as a function of relative humidity.24 Here we
report the uptake coefficients of HNO3 on CaCO3 over a broad
range of relative humidity. Experimental conditions and kinetic
data for this series of the study are listed in Table 3. The uptake
coefficients are summarized in Table 1.
takes up water, deliquesces, and undergoes hygroscopic growth.
Under our experimental conditions, reacted particles are com-
posed of a solid CaCO3 core and a coating of concentrated
aqueous solution of Ca(NO3)2 product. As the reaction proceeds
and more of the Ca(NO3)2 product is formed, the particles
undergo continuous growth, and as such the droplet diameter
is expected to be larger than the dry particle diameter, Dh d g
Dh p.
Therefore, the smallest size of the reacting particle can be
approximated assuming Dh d,min ) Dh p) 0.85 µm. Using this
diameter value, we obtain γnet ) 0.06 (×3/÷2) for RH ) 40%,
which is somewhat lower than γnet ) 0.11 at RH ) 33%
reported for CaCO3 particles by Vlasenko et al.24 The largest
size of the reacting particle ( Dh d,max ) can be estimated using a
simplified core-shell model as described below. We assume
Figure 7 shows uptake coefficients measured as a function
of RH for CaCO3 particles with a dry diameter of 0.85 µm. For
2
4
comparison, data from Vlasenko et al. and other previous
16,21-23,38
measurements
are included in the figure. Additionally,
the water adsorption isotherm measured on CaCO3 particles at
3
9
296 K using a quartz crystal microbalance and the water-to-
4
0
solute ratios (WSR) measured for dehydrating Ca(NO3)2
particles are also shown in the plot. The water uptake and WSR
data are scaled to match the range of the γnet values reported.
As can be seen, the reactive uptake coefficient (γnet) exhibits a

Heterogeneous Reaction of CaCO3 Particles
J. Phys. Chem. A, Vol. 112, No. 7, 2008 1569
deliquesces at 8-10% RH19 and then undergoes subsequent
hygroscopic growth at higher RH, similarly to the hygroscopic
4
0
behavior of pure Ca(NO3)2 particles. The presence of a large
quantity of water at increasing RH facilitates hydrolysis reactions
12-14, but dissolution and a liquid layer also causes continued
reactivity the carbonate surface, making more of the core of
the particle available for the reaction. Eventually, these processes
lead to the consumption of carbonate core. Although, Prince et
3
4
al. estimated that the viscosity of a metastable supersaturated
5
nitrate product at low RH would be about 10 time larger than
in pure water. Diffusion coefficients for dissolved species would
substantially increase at higher RH; and characteristic diffusion
times would be significantly shorter, which would have
significant ramifications for the subsequent gas-to-particle
chemistry. To conclude, all of the factors presented above
enhance the reaction extent and may contribute to the observed
increase in the uptake coefficient at higher RH.
Figure 7. Experimentally determined uptake coefficient, γnet, as a
3 3
function of the relative humidity for HNO reaction with CaCO . For
comparison, literature data are also included. The green line indicates
characteristic water uptake measured on CaCO particles (ref 39). The
blue line indicates characteristic water-to-solute ratio (WSR) measured
in hydration experiments with levitated Ca(NO particles (ref 40).
3
3 2
)
The measured reactive uptake coefficients are in reasonable
agreement with data reported for ATD, considering that our
approach measures the lower limit for HNO3 uptake on CaCO3
particles. Additionally, the reactive uptake at low relative
humidity determined here is consistent with the literature value
The water uptake and WSR data are scaled to match the reactive uptake
coefficient (γnet) values.
monotonic increase with increasing relative humidity from 0.032
at 10% RH to 0.21 at 80% RH, somewhat proportionally to the
increase in the reported water uptake of CaCO3 and Ca(NO3)2.
Qualitatively, a similar effect of relative humidity has been
reported for other heterogeneous reactions on solid surfaces
including those of CaCO3, ATD, borosilicate glass and some
-3
-3
of (2 ( 1) × 10 and 2.7 × 10 at RH ) 0% reported by
16
52
Johnson et al. and Santschi and Rossi, respectively. The
current results reported here at low relative humidity are,
however, about a factor of 30 lower than values reported by
2
2,26,34,41-43
others.
The reaction enhancement observed under
23
21
Hanisch et al. and Fenter et al. The discrepancy is ascribed
to the use of geometric surface area in the Knudsen cell
humid conditions is likely a combined result of several processes
which play important roles in determining the overall reactivity
of HNO3 with CaCO3, as discussed below.
16
experiments that contained many particle layers.
In a previous NaCl study, we investigated the effect of
29
It is generally understood that in the atmospheric environment
the surface of calcium carbonate is terminated by hydroxyl (OH)
and bicarbonate (CO3H) groups (Ca(OH)(CO3H)) due to the
dissociative adsorption of water.34 These terminal groups can
particle size on heterogeneous HNO3 reactive uptake. A
29
combined consideration of uptake coefficients reported in that
53,54
29
and previous works,
indicated that the experimentally measured uptake coefficient
γnet) of the HNO3(gas)-to-NaCl(particle) reaction follows a
along with our modeling results,
be spectroscopically detected even under vacuum condi-
(
tions.3
6,44-47
The reaction between calcite and nitric acid is then
characteristic rise-then-fall behavior with respect to particle size
with the peak value of γnet ≈ 0.2, which occurs for 0.7 µm wet
particles. The results showed that finite rate reaction kinetics is
the major contributor to reactive uptake of HNO3 onto small
NaCl particles ( Dh d , 0.7 µm) and gaseous diffusion of HNO3
becomes a factor that limits its uptake onto larger NaCl particles
initiated by exchange of bicarbonate ligand with nitrate to yield
3
6,45
carbonic acid
Ca(OH)(CO H) + HNO T Ca(OH)(NO ) + H CO
3
(11)
3
3
3
2
Under dry conditions, the particle surface could be saturated
with a layer of adsorbed carbonic acid, thus preventing further
HNO3 uptake. Surface saturation, however, is not an issue when
RH is greater than 0%, as H2CO3 is unstable and rapidly
( Dh d . 0.7 µm). Similarly, it is likely that the uptake of HNO3
on 0.85 µm CaCO3 particles might be also controlled by gas-
phase HNO3 diffusion. In this case, the experimentally measured
reactive uptake coefficient (γnet) cannot exceed the fundamental
diffusion limit, which may be calculated as
3
4,36
dissociates into CO2 and H2O in the presence of water.
Additionally, the trace amount of water initially adsorbed at
surface sites promotes the overall reaction by facilitating the
dissociation of HNO3 and enhancing ionic mobility for segrega-
tion or crystallization of nitrate at the surface and replenishment
of CaCO3 surface.48 Similar water effects have also been
observed in the studies of the heterogeneous reaction of dry
NaCl crystals with nitric acid.4
8
D
HNO -N
3
2
γnet eΓ )
(15)
g
Dh d cj HNO3
Applying a size of the reacting particle in the range of Dh p < Dh d
< 1.6 Dh p and a diffusion coefficient of DHNO3-N2 ) 0.118
1,49-51
2
29
As the amount of surface absorbed water increases at higher
RH, acid assisted hydrolysis of the CaCO3 surface is activated,
which further facilitates the overall reaction34
cm /s, we obtain γnet eΓg ) 0.22 to 0.35. As seen in Figure
7, with the increase of RH our experimentally measured γnet
approaches this limit only at ∼80% RH, while at lower RH the
HNO3-to-CaCO3 reaction becomes increasingly kinetically
controlled.
+
-
HNO T H + NO
(12)
(13)
(14)
3
3
+
2+
-
Conclusions and Atmospheric Implications
H + CaCO T Ca + HCO3
3
Heterogeneous reaction kinetics of gaseous nitric acid uptake
on calcium carbonate particles were investigated experimentally
using the PS-SFR approach. Two series of experiments were
conducted at a fixed dry particle diameter Dh p ) 0.85 µm with
varying particle loading, HNO3 concentration, and relative
HCO3- + H T CO v + H O
+
2
2
As the reaction proceeds, the highly hygroscopic Ca(NO3)2
product is formed on the surface of CaCO3 particles, which

1570 J. Phys. Chem. A, Vol. 112, No. 7, 2008
Liu et al.
humidity. The first series of experiments was performed for
particles under 40% relative humidity. The results show that
the variation of the apparent, pseudo first-order rate constant
with particle loading and HNO3 concentration is consistent with
the pseudo first-order reaction assumption and a diffusion-kinetic
analysis. Analysis yields the net reaction uptake coefficient γnet
g 0.06(×3/÷2) at 40% RH.
(4) Tang, Y. H.; Carmichael, G. R.; Uno, I.; Woo, J. H.; Kurata, G.;
Lefer, B.; Shetter, R. E.; Huang, H.; Anderson, B. E.; Avery, M. A.; Clarke,
A. D.; Blake, D. R. J. Geophys. Res.-Atmos. 2003, 108, Art. No. 8824,
doi:10.1029/2002JD003100.
(5) DeMott, P. J.; Cziczo, D. J.; Prenni, A. J.; Murphy, D. M.;
Kreidenweis, S. M.; Thomson, D. S.; Borys, R.; Rogers, D. C. Proc. Natl.
Acad. Sci. U.S.A. 2003, 100, 14655.
(
6) Rudich, Y.; Khersonsky, O.; Rosenfeld, D. Geophys. Res. Lett.
002, 29, Art. No. 4478, doi:10.1029/2002GL016055.
7) Sokolik, I. N.; Toon, O. B. J. Geophys. Res.-Atmos. 1999, 104,
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(8) Garrett, T. J.; Russell, L. M.; Ramaswamy, V.; Maria, S. F.;
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11) Dentener, F. J.; Carmichael, G. R.; Zhang, Y.; Lelieveld, J.; Crutzen,
2
The second series of experiments examined the influence of
relative humidity on the kinetics of HNO3 uptake on CaCO3
particles. The uptake was found to increase monotonically with
an increase in relative humidity due to initial water absorption
at the surface and subsequent Ca(NO3)2 hygroscopic growth.
The reactive uptake coefficient is observed to jump between
(
(
(
1
1
0 and 20% RH, which is consistent with deliquescence of an
(
amorphous Ca(NO3)2 hydrate in that RH range.
P. J. J. Geophys. Res.-Atmos. 1996, 101, 22869.
Mineral dusts have the largest atmospheric aerosol loading
in terms of total mass, and their carbonate component is
(12) Song, C. H.; Carmichael, G. R. J. Atmos. Chem. 2001, 40, 1.
(
13) Sullivan, R. C.; Guazzotti, S. A.; Sodeman, D. A.; Prather, K. A.
Atmos. Chem. Phys. 2007, 7, 1213.
14) Laskin, A.; Iedema, M. J.; Ichkovich, A.; Graber, E. R.; Taraniuk,
I.; Rudich, Y. Faraday Discuss. 2005, 130, 453.
15) Matsuki, A.; Iwasaka, Y.; Shi, G. Y.; Zhang, D. Z.; Trochkine, D.;
19
substantially reactive with gas-phase HNO3, leading to forma-
tion of hygroscopic Ca(NO3)2 containing particles in the
(
1
4
atmosphere. Under typical atmospheric conditions of RH >
0%, the Ca(NO3)2 reaction product, once formed, would remain
(
2
Yamada, M.; Kim, Y. S.; Chen, B.; Nagatani, T.; Miyazawa, T.; Nagatani,
M.; Nakata, H. Geophys. Res. Lett. 2005, 32, Art. No. L22806, doi:10.1029/
005GL024176.
in the aqueous phase throughout its atmospheric lifetime. This
will significantly alter the physicochemical properties of the
original aerosol particle in terms of light scattering and CCN
2
(16) Johnson, E. R.; Sciegienka, J.; Carlos-Cuellar, S.; Grassian, V. H.
J. Phys. Chem. A 2005, 109, 6901.
55,56
activity.
In addition, heterogeneous reactions between HNO3
(17) Krueger, B. J.; Grassian, V. H.; Cowin, J. P.; Laskin, A. Atmos.
EnViron. 2004, 38, 6253. Erratum published in Atmos. EnViron. 2005, 39,
95.
and aerosol particles, such as CaCO3 and NaCl, serve as major
sinks for gaseous HNO3 and nitrogen oxides, which impacts
the overall chemical balance of the troposphere. Results from
this work show that CaCO3 has a similar reactive HNO3 uptake
to NaCl at RH ) 40% but exhibits a very different humidity
dependence. The uptake of HNO3 onto NaCl was found to
increase with the decreasing RH and peak around a relative
humidity of 55%, and then below the efflorescence relative
3
(
18) Krueger, B. J.; Grassian, V. H.; Laskin, A.; Cowin, J. P. Geophys.
Res. Lett. 2003, 30, Art. No. 1148, doi:10.1029/2002GL016563.
19) Laskin, A.; Wietsma, T. W.; Krueger, B. J.; Grassian, V. H.
J. Geophys. Res.-Atmos. 2005, 110, Art. No. D10208, doi:10.1029/
004JD005206.
20) Liao, H.; Adams, P. J.; Chung, S. H.; Seinfeld, J. H.; Mickley, L.
J.; Jacob, D. J. J. Geophys. Res.-Atmos. 2003, 108, Art. No. 4001, doi:
0.1029/2001JD001260.
21) Fenter, F. F.; Caloz, F.; Rossi, M. J. Atmos. EnViron. 1995, 29,
3365.
(22) Goodman, A. L.; Underwood, G. M.; Grassian, V. H. J. Geophys.
Res.-Atmos. 2000, 105, 29053.
(
2
(
1
2
9
humidity (∼45% RH) the uptake coefficient decreases rapidly.
(
As a result, if CaCO3 and NaCl aerosol particles are present in
the same HNO3 polluted air mass, both heterogeneous reaction
channels could occur.13 They may take place equivalently or
(23) Hanisch, F.; Crowley, J. N. J. Phys. Chem. A 2001, 105, 3096.
competitively depending on specific conditions.
(24) Vlasenko, A.; Sjogren, S.; Weingartner, E.; Stemmler, K.; Gaggeler,
H. W.; Ammann, M. Atmos. Chem. Phys. 2006, 6, 2147.
Acknowledgment. The PNNL and the USC research groups
acknowledge support provided by Tropospheric Chemistry and
Radiation Sciences programs at the National Aeronautics and
Space Administration (Grants NNG06GE89G and NNG06-
GI51G). The UI research group acknowledges support provided
by the National Science Foundation (Grant No. CHE-0503854).
E.R.G. thanks the Department of Energy Global Change
Education Program for support through a Graduate Research
Environmental Fellowship. This work was performed at the
William R. Wiley Environmental Molecular Sciences Labora-
tory, a national scientific user facility sponsored by the
Department of Energy’s Office of Biological and Environmental
Research and located at Pacific Northwest National Laboratory
(25) Goodman, A. L.; Bernard, E. T.; Grassian, V. H. J. Phys. Chem. A
2001, 105, 6443.
(26) Maxwell-Meier, K.; Weber, R.; Song, C.; Orsini, D.; Ma, Y.;
Carmichael, G. R.; Streets, D. G. J. Geophys. Res.-Atmos. 2004, 109, Art.
No. D19S07, doi:10.1029/2003JD004464.
(27) Underwood, G. M.; Li, P.; Al-Abadleh, H.; Grassian, V. H. J. Phys.
Chem. A 2001, 105, 6609.
(28) Laskin, A.; Wang, H.; Robertson, W. H.; Cowin, J. P.; Ezell, M.
J.; Finlayson-Pitts, B. J. J. Phys. Chem. A 2006, 110, 10619.
(
29) Liu, Y.; Cain, J. P.; Wang, H.; Laskin, A. J. Phys. Chem. A 2007,
11, 10026.
30) Laskin, A.; Cowin, J. P.; Iedema, M. J. J. Electron Spectrosc. Relat.
1
(
Phenom. 2006, 150, 260.
(31) Hua, Y. N. J. Trace Microprobe Tech. 2003, 21, 25.
(32) Hoffman, R. C.; Laskin, A.; Finlayson-Pitts, B. J. J. Aerosol Sci.
2
004, 35, 869.
33) Gibson, E. R.; Hudson, P. K.; Grassian, V. H. J. Phys. Chem. A
006, 110, 11783.
34) Prince, A. P.; Grassian, V. H.; Kleiber, P.; Young, M. A. Phys.
(
PNNL). PNNL is operated by the US Department of Energy
by Battelle Memorial Institute under Contract No. DE-AC06-
6RL0 1830. Finally, we thank Jennifer Schuttlefield of the
(
2
7
(
University of Iowa for the quartz crystal microbalance water
uptake measurements on CaCO3.
Chem. Chem. Phys. 2007, 9, 622.
(35) Hering, S. V.; Lawson, D. R.; Allegrini, I.; Febo, A.; Perrino, C.;
Possanzini, M.; Sickles, J. E.; Anlauf, K. G.; Wiebe, A.; Appel, B. R.;
John, W.; Ondo, J.; Wall, S.; Braman, R. S.; Sutton, R.; Cass, G. R.;
Solomon, P. A.; Eatough, D. J.; Eatough, N. L.; Ellis, E. C.; Grosjean, D.;
Hicks, B. B.; Womack, J. D.; Horrocks, J.; Knapp, K. T.; Ellestad, T. G.;
Paur, R. J.; Mitchell, W. J.; Pleasant, M.; Peake, E.; Maclean, A.; Pierson,
W. R.; Brachaczek, W.; Schiff, H. I.; Mackay, G. I.; Spicer, C. W.; Stedman,
D. H.; Winer, A. M.; Biermann, H. W.; Tuazon, E. C. Atmos. EnViron.
1988, 22, 1519.
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