Article pubs.acs.org/JPCA
Kinetics of Heterogeneous Reaction of Ozone with Linoleic Acid and its Dependence on Temperature, Physical State, RH, and Ozone Concentration Guang Zeng,†,‡ Sara Holladay,† Danielle Langlois,† Yunhong Zhang,*,‡ and Yong Liu*,† †
Department of Chemistry, University of Colorado Denver, Denver, Colorado 80217, United States The Institute of Chemical Physics, Key Laboratory of Cluster Science, School of Chemistry, Beijing Institute of Technology, Beijing 100081, People’s Republic of China
‡
ABSTRACT: Heterogeneous reaction between ozone and linoleic acid (LA) thin film was investigated by a flow reactor coupled to attenuated total reflection infrared spectroscopy (FR-ATR-IR) over wide ranges of temperature, relative humidity (RH), and ozone concentration under atmospheric pressure condition. Pseudo-first-order rate constants kapp and overall reactive uptake coefficients γ were acquired on the basis of changes in absorbance from peaks located near 1743, 1710, 1172, and 1110 cm−1, which can be assigned to CO in ester, CO in acid, and CC and CO stretching modes, respectively. Results showed that the kapp and γ increased nearly by a factor of 6 with increasing temperatures from 258 to 314 K. It was noted the temperature effect on the reaction kinetics was much more pronounced at lower temperatures. Such behavior can be explained by a change in the physical state of LA at lower temperatures. In addition, kapp and γ were enhanced by 2-fold as the RH increased from 0 to 80%. Moreover, the effect of ozone concentration on the reaction kinetics was reported for the first time. kapp was found to display a Langmuir−Hinshelwood dependence on ozone concentration with KO3 = (1.146 ± 0.017) × 10−15 molecules cm−3 and k[S] = 0.0522 ± 0.0004 s−1, where KO3 is a parameter that describes the partitioning of ozone to the thin film surface, and k[S] is the maximum pseudo-first-order coefficient at high ozone concentration. Furthermore, yields and hygroscopic properties of reaction products were also investigated by FTIR spectroscopy. The intensity ratio of two CO stretching bands, A1743/A1710, which was utilized as an indicator of the product yields, increased sharply with increasing temperatures in the lower temperature region (258−284 K), and then remained nearly constant in the higher temperature region (284−314 K). The product yields showed no significant variation with RH, for the intensity ratio of A1743/A1710 barely changed in the wide RH range 0−80%. Water uptake studies showed that the LA thin film absorbed water with an increasing RH, and the hygroscopicity of the thin film was enhanced after ozone exposure. and uptake probability.4−27 It is generally believed that the reaction undergoes ozonolysis, which proceeds via the addition of ozone to the carbon−carbon double bond to form primary ozonides, followed by the formation of carbonyl oxides, commonly referred to as Criegee intermediates (CI). The CI can further recombine with aldehyde or ketone to form secondary ozonides or react with the carboxylic group, forming α-acyloxyalkyl hydroperoxide and cyclic diperoxides. The carboxylic acid and carbonyl moieties of the products may further react with other intermediates to produce high molecular weight species.17,19,22,27 In addition to the OA, selfassembled monolayers and organic thin films were also used as proxies for atmospheric carbonaceous surfaces in OH-initiated chemical aging studies.28−30 Molina et al. suggested that the heterogeneous oxidation of saturated hydrocarbon by OH radicals proceeds in a mechanism analogous to the one in gas
1. INTRODUCTION Atmospheric aerosols have been widely recognized as key elements in many environmental issues ranging from air quality, sky visibility, public health, to climate change.1,2 One class of atmospheric aerosols is organic matter. Atmospheric organic matter is ubiquitous and abundant and can constitute up to 90% mass fraction of ultrafine particles in some tropospheric environment.3 Once in the particle phase, atmospheric organics can undergo chemical aging throughout their lifetimes via heterogeneous reactions with gaseous oxidants such as hydroxyl radicals, ozone, nitrate radicals, and halogen radicals, and in turn grossly alter their chemical composition and physiochemical and radiative properties of atmospheric aerosols. Lately there has been a surge of interest in the formation mechanism and chemical aging processes of atmospheric organics, and several model systems have emerged as benchmarks for investigating heterogeneous oxidation of atmospheric organics. For example, oleic acid (OA), a proxy for unsaturated organic matter, and its reaction with ozone was extensively studied for determination of reaction mechanism © 2013 American Chemical Society
Received: August 21, 2012 Revised: January 24, 2013 Published: January 24, 2013 1963
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phase.28 When several reaction channels compete with each other, one may dominate under a specific condition controlled by one or more factors, including type of initiators, structure of organic molecules, phase of aerosols, concentration of other species such as O2 and NOx, and ambient conditions (temperature, and relative humidity, RH). Despite overall good agreement in reaction mechanism, currently there are still fairly large discrepancies in reaction kinetics and uptake coefficient measurements. For instance, literature values of the uptake coefficient of ozone onto OA ranges over 1 order of magnitude.4,19,20,23,24,26,31−33 RH and temperature in the atmosphere span wide ranges. As individual reactions may have different RH and temperature dependences, changes in ambient RH and temperature could play pivotal roles in determining an overall reaction pathway. Recently, increasing efforts have been devoted to the effects of RH and temperature on heterogeneous chemistry of atmospheric aerosol,34−46 and most literature work centered on reaction product yield. At present, our knowledge about how ambient RH and temperature may affect the heterogeneous chemistry of atmospheric organics, and in particular the reaction kinetics is still scattered and incomplete. In the past decade, a number of experimental approaches have been advanced to study aerosol chemistry. Suspended aerosol particles in a smog chamber or flow tube coupled to an aerosol mass spectrometer (AMS) or a chemical ionization mass spectrometer (CIMS) has been the most commonly used and has provided the vast majority of data on chemical transformation of atmospheric organics.3,47 In addition, techniques based on samples deposited on chemically inert substrates have been developed to study heterogeneous aerosol reaction. For instance, a particle-on-substrate stagnation flow reactor in combination with computer controlled scanning electron microscopy with energy-dispersive X-ray analysis (CCSEM/EDX) was used to measure the reactive uptake coefficients of nitric acid on sea salt and mineral dust particles.48−50 Recently, a flow reactor coupled to an attenuated total reflection infrared spectrometer (FR-ATR-IR) has been used to investigate ozone initiated heterogeneous oxidation of OA, cypermethrin, and squalene.22,33,51,52 Additionally, FRATR-IR was used to study sorption and desorption, water uptake, phase transition, and hygroscopic growth.8,16,53,54 Though each of the above referenced techniques has its own advantages and disadvantages, results obtained on the basis of the samples deposited on substrates approach, in general, agree with data acquired from experiments using suspended aerosol particles very well, and thus they serve as complementary methods for atmospheric aerosol chemistry study. Similar to OA, linoleic acid (LA) is a fatty acid with an 18carbon chain. It is one of the major components of edible oils and cell membrane lipids and is believed to play important roles in various biologic processes. LA has been observed in atmospheric aerosols and its sources include leaf abrasion and meat cooking.55,56 Because LA has two cis double bonds, as compared to one double bond in OA, LA is expected to be at least as reactive as OA toward ozone. To date, LA has also been used to study ozone initiated heterogeneous oxidation of atmospheric unsaturated organics several times.4,23,24,57 For example, Moise and Rudich,4 Thornberry and Abbatt,23 Hearn and Smith,24 have utilized flow systems to measure ozone reaction uptake at different temperatures and found that the uptake coefficient onto LA was slightly larger than that onto OA and temperature had seemingly very week effect on the
reaction kinetics, similar to that in the case of OA.4 In addition, Thornberry and Abbatt observed that relative humidity did not affect ozone uptake considerably.23 It should be pointed out that all previous studies4,23,24 were conducted under very low pressure conditions, and to the best of our knowledge, there is no reported kinetic study of ozone reaction with LA performed under atmospheric pressure conditions. At present, except for Hung and Tang’s work33 in which temperature and phase dependent reaction kinetics of OA/O3 were investigated, little is known about reaction kinetics, in particular, roles of temperature, RH, gas-phase ozone concentration and physical state of unsaturated fatty acids in the reaction kinetics under atmospherically relevant pressure conditions. Therefore, in this work, we employed LA as a model compound for long chain polyunsaturated fatty acids to investigate its heterogeneous reaction with ozone using the FR-ATR-IR approach. We conducted experiments under atmospheric pressure condition and acquired pseudo-first-order rate constants and uptake coefficients from changes in absorbance of peaks located near 1743, 1710, 1172, and 1110 cm−1, which can be assigned to CO in ester, CO in acid, and CC and CO stretching modes, respectively, over wide ranges of temperature (258−314 K), RH (0−80% RH), and ozone concentration (0.05−50 ppm). We reported how physical state and ozone concentration affect the reactive uptake of ozone on LA for the first time. We also observed fairly different RH dependence of reaction kinetics from the sole literature result.23 In addition, we utilized infrared spectroscopy to determine the effect of temperature and RH on reaction product yield and hygrosocpicity of the reacted LA.
2. EXPERIMENTAL SECTION 2.1. Experimental Setup. A schematic diagram of the experimental setup is shown in Figure 1. The heterogeneous
Figure 1. Schematic diagram of FR-ATR-IR.
reactions of LA with ozone under different conditions were monitored in real time by an ATR-FTIR spectrometer (Nicolet 6700) equipped with a liquid-nitrogen cooled MCT detector. A multireflection sampler equipped with a ZnSe ATR crystal (refractive index: 2.4, 5 × 1 cm2) was placed in a customized flow-through stainless steel chamber in which ZnSe crystal was selected for its large penetration depth. The penetration depth is estimated to be 1.1 μm at 1700 cm−1. Reacting gaseous mixtures were composed of O3, H2O, and air, in which air was used to serve as the source of oxygen for O3 generation, the carrier gas for moisture generation and for dilution as well. Makeup of the gas mixture and flow rates through the reactor 1964
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were controlled by two mass controllers installed upstream of the reactor. Readings of the rotameter installed downstream of the reactor ensure no negative leaks present during the experiments. For most experiments, ozone was generated by a small flow of dry air at 50 mL/min through a UV light source (Pen-Ray) and was then diluted by a second flow of air of 950 mL/min. The ozone concentration measured downstream by an ozone monitor (UV-100, Ozone solutions) was about 350 ± 10 ppb. For experiments that required higher concentration of ozone, an ozone generator (600, Jelight) was used. Humidification in the reactor was achieved by switching the dry air flow to a path through a dew point generator (V-gen, Instruquest) and RH was controlled by adjusting the dew point temperature. The setup allowed O 3 and H 2 O concentrations to be varied independently. Temperature control was achieved with a refrigerated circulating bath by circulating heat transfer fluid through stainless steel cooling blocks surrounding the flow reactor. Two thermocouples were placed inside the inlet and outlet of the reactor. The temperature differences between the inlet and outlet were usually very small at room temperature, and became slightly larger at lower temperatures. For example, at 253 K, the difference was about 2 deg. Averaged readings from two thermocouples were used to determine the reaction temperatures. It was noted that it took several minutes to generate an ozone flow with stable concentration after the UV lamp was turned on. To minimize uncertainty resulting from the changes in ozone concentration, an additional ozone bypass line was installed. Ozone flow was kept on throughout the experiments and was switched back and forth between bypass line and reaction line through the flow reactor. 2.2. Experimental Procedure. Before each reaction, the reacting gas flow was initially switched to the bypass line and a background spectrum of the clean ZnSe crystal was taken. LA thin film was prepared by dispensing a 100 μL solution of 3 mM linoeic acid (99% purity, Acros Organics) in carbon tetrachloride (99% purity, Aldrich) directly onto the ATR crystal using a micropipet. The amount of LA and carbon tetrachloride is sufficient to completely cover the whole ATR crystal surface. It usually took less than 3 min for the solvent to evaporate completely, which was confirmed by the disappearance of C−Cl vibration mode in IR spectra. The thickness of the thin film is about 0.2 μm, much less than the penetration depth of evanescent wave to ensure bulk of the film is fully probed by IR beam. The flow reactor was then sealed and spectral measurements were started once the ozone flow was switched to the reaction line. In all experiments, IR spectra were collected automatically using the macro function built in the OMNIC program in the range 650−4000 cm−1 with a resolution of 2 cm−1, and averaged over 64 scans. For each reaction condition, experiments were repeated at least 3 times.
Figure 2. FTIR spectrum of fresh LA thin film at room temperature.
stretching vibration. The −CH2 bending vibration is observed at 1465 and 1413 cm−1, whereas the −CH2 wagging vibration shows peaks at 1285, 1247, and 1224 cm−1. A broad band with medium intensity at about 938 cm−1 is likely due to the carboxylic −COH out-of-plane bending vibration.58 Assignments of infrared vibration mode of fresh LA and ozone treated thin films are listed in Table 1. Table 1. IR Feature Assignments of Fresh Linoleic Acid and Ozone Treated Thin Films wavenumber (cm−1) 3010 2955 2927 2856 1710 1466 1413 1247 1285 1224 938 3430 1743 1710 1170 1110
3. RESULTS AND DISCUSSION 3.1. IR Spectra of Ozone-Processed LA Film. LA is an 18-carbon chain unsaturated carboxylic acid with two double bonds. Figure 2 shows an infrared spectrum of the LA thin film at room temperature before exposed to ozone. Generally, the main absorption features arise from −CH3, −CH2, and CO groups. As shown in Figure 2, there are peaks located at 3010, 2954, 2927, and 2856 cm−1, which can be attributed to CH stretch, −CH3 antisymmetric stretch, −CH2 antisymmetric stretch, and −CH2 symmetric stretch, respectively. The most intense peak at 1710 cm−1 is assigned to the carboxylic CO
assignment Fresh Linoleic Acid Thin Film CH stretch −CH3 antisymmetric stretching −CH2 antisymmetric stretching −CH2 symmetric stretching carboxylic CO stretching −CH2 bending −CH2 bending −CH2 wagging −CH2 wagging −CH2 wagging carboxylic −COH out-of-plane bending Ozone Treated Thin Film −OH stretching ester CO stretching ketones, aldehydes and carboxylic acids CO stretching CC stretching CO stretching
When the LA thin film is exposed to ozone, the initial heterogeneous oxidation is expected to proceed in a similar fashion to OA reaction with ozone. Figure 3 shows spectral evolution of the LA thin film during exposure to ozone over time under room temperature and dry (RH∼0%) conditions. As shown in Figure 3, in the high wavenumber region a band near 3430 cm−1, which is attributed to the −OH stretch, increased whereas the CH stretching vibration at 3010 cm−1 decreased with increasing ozone exposure time, respectively. In 1965
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Figure 3. FTIR spectra of LA thin film at different ozone exposure time during the reaction. Conditions: [O3] ∼ 350 ppb, room temperature, and RH ∼ 0%.
Figure 4. Proposed pathway for LA (a) reaction with ozone. Ozone attack on double bond leads to formation of Criege intermediate (b), followed by its recombination with carboxyl group to yield α-acyloxyalkyl hydroperoxide (c).
the CO stretching region, the peak at 1710 cm−1, which is reportedly attributable to ketones, aldehydes, and carboxylic acids CO stretching vibration,22 decreased gradually as the heterogeneous reaction progressed. It is noted that because the oscillator strength of carboxylic acid CO groups is 100-fold greater than those of ketones and aldehydes,59,60 as long as carboxylic acids are present, they are likely to dominate absorption behaviors in the CO stretching band (1710 cm−1). In addition to the decrease in absorption at 1710 cm−1, once the reaction started off, a new peak located at about 1743 cm−1 began to appear and increased accordingly as the reaction proceeded. The band was characteristic of ester CO absorption and has been observed in the study of ozone initiated oxidation of OA.22 In the meantime, along with the increase in absorption at 1743 cm−1, in the low wavenumber region two additional bands at about 1110 and 1170 cm−1, which are attributed to the CO and CC stretching vibrations,22 increased with increasing ozone exposure time. Moreover, there is an isosbestic point near 1725 cm−1, indicating that there is a transformation between two components (acid to ester). All these spectral changes have demonstrated that LA readily reacted with ozone and as the ozone exposure time increased, LA was gradually consumed and converted to some products containing hydroxyl and ester groups. In previous study of heterogeneous oxidation of OA by ozone using the FR-ATR-IR,22 α-acyloxyalkyl hydroperoxide was identified in the reaction products by an offline LC-MS analysis. The spectral evidence obtained in the present work revealed that the oxidation of LA may have led to the formation of α-acyloxyalkyl hydroperoxide. Figure 4 illustrates the most probably reaction pathway occurring in this study.
As discussed below, the spectral changes in the two CO stretching bands (1710 and 1743 cm−1) as well as the CO and CC stretching bands (1110 and 1170 cm−1) were utilized in this work to derive kinetics of the heterogeneous oxidative reaction of LA. 3.2. Temperature Effect. 3.2.1. Phase Transition. To better understand the influence of temperature on the reaction kinetics, we first looked into phase transition of the LA thin film as a function of temperature. As the temperature of the sample cell was gradually lowered from 314 to 258 K, corresponding infrared spectra were recorded simultaneously, as shown in Figure 5. Note that as temperature decreased from 314 to 266 K, the spectrum of LA remained nearly unchanged; a slight red shift of about 1 cm−1 in the CO stretching region at ∼1710
Figure 5. FTIR spectra of LA thin film at various temperatures. 1966
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Figure 6. Temporal changes in the infrared spectra shown in Figure 3 focusing on several spectral bands: (a) CO in esters; (b) CO in acids, aldehyde, and ketones; (c) CO and (d) CC stretching bands. The absorbance difference data (hollow squares) in each band was exponentially fit (black solid lines) to derive the kapp.
cm−1 was observed. As the temperature further decreased from 266 to 265 K, a new peak at ∼1690 cm−1, which is characteristic of solid carboxyl CO stretching vibration, appeared. In the meantime, a red shift of the absorption band in the C−H stretching region near 2927 cm−1 as well as sharpness of several bands in the low wavenumber region were also observed, indicative of crystallization of the LA thin film. Such a shift during the phase transition has been previously observed in the studies of unsaturated fatty acids such as OA, LA, and linolenic acid.61,62 For example, Sinclair et al.61 investigated infrared absorption spectra of LA at room temperature and when cooled with liquid nitrogen, they observed the carbonyl peak shifted from 1708 to 1682 cm−1 on solidification and there was no peak at 1708 cm−1 for the solid LA. When the temperature continued to drop, the peak at ∼1710 cm−1 gradually decreased, whereas the peak at ∼1690 cm−1 increased. At present, there are still some discrepancies in the measurements of LA melting point and literature values were reported to be 261 and 268 K.63,64 Regardless, our infrared spectrum showed that the peak at 1710 cm−1 did not disappear even at 258 K. To find out whether the peak may change over time, the sample was placed at 258 K for extended period of time (up to 12 h), and no noticeable change in infrared spectra was observed. This indicated that at this temperature a small portion of LA was present in likely a supercooled liquid form and coexisted with the solid phase. 3.2.2. Rate Constant and Uptake Coefficient. The method for deriving reaction rate constant and overall reactive uptake coefficient employed in the present work is similar to the method used in previous studies of ozone reaction with OA, cypermethrin, and squalene.22,33,51,52 Details regarding the approach have been well discussed elsewhere.22,33,51,52 In brief,
for a given second order reaction: A + B → P (P = product), when reactant A is present in great excess over reactant B, the rate equation can be written as d[B] = kapp[B], where kapp[B] = k[A] dt
(1)
Here kapp is the pseudo-first-order rate constant, also commonly referred to as the apparent first-order rate constant, and k is the second-order rate constant. Under the pseudo-first-order condition, concentrations of the reactant B or the product P would change exponentially with reaction time. On the basis of Beer’s law, absorbance of CO stretching band at ∼1710 cm−1, is linearly proportional to the concentration of LA. Meanwhile, absorbance values of CO, CO, and CC stretching bands that are assigned to the reaction products and located at ∼1743, 1110, and 1170 cm−1, respectively, can be assumed to be linearly proportional to product concentrations. In the present study, ozone was kept with a molar ratio of ozone to LA over 1 order of magnitude at any given moment throughout the reaction to ensure the pseudo-first-order condition is met. As a result, the absorbance values of CO, CO, and CC stretching bands are expected to follow an exponential pattern with reaction time. Figure 6 presents the time dependent absorbance profiles of CO (1743 and 1710 cm−1), CO (1110 cm−1), and CC (1170 cm−1) stretching bands as the LA thin film was exposed to ozone at ∼350 ppb under room temperature and dry conditions for different times. The hollow squares are absorbance data and solid lines are from exponential curve-fitting using the fitting function ΔA = A∞e−kappt,22,33 where ΔA = At − A∞ (At and A∞ are the integrated absorbance values at time t and time infinite). For simplicity, the integrated absorbance value of the infrared 1967
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⎛ PO c ̅ ⎞ S d[LA] = −γ ⎜ 3 ⎟ A dt ⎝ 4RT ⎠ V
spectrum recorded at the end of the experiment was utilized as the A∞ in this work. As seen in Figure 7, the exponential
(2) −3
where d[LA]/dt = −kapp[LA], and [LA] [molecules cm ] is the initial concentration of LA; c ̅ [cm s−1] is the mean speed of ozone molecules in gas phase; and SA/V [cm−1] is the surface area-to-volume ratio of the LA thin film. In the present study, the surface area of the LA thin film was estimated to be 5 cm2, which is the geometric surface area of the ZnSe crystal. The rate constants derived from different bands and the corresponding γ under various reaction conditions are summarized in Table 2. All these data are averaged over at least three independent measurements. To avoid duplication, when temperature, physical state, RH, and ozone concentration dependent data are reported below, only data derived from the apparent firstorder rate constants acquired at 1743 cm−1 are included. The temperature dependent experiments were carried out under the condition of [O3] = ∼350 ppb and RH = ∼0% and temperature ranged from 314 to 258 K. Figure 7a shows curvefitting for the absorbance of ester CO band near 1743 cm−1 at different temperatures. The kapp derived from Figure 7a and the corresponding γ versus temperature are shown in Figure 7b. Literature values of γ are also included in Figure 7b.4 As seen, both the kapp and the γ were found to increase with increasing temperatures. Within the temperature range studied here the kapp was increased by 6-fold from 1.1 × 10−4 s−1 at 258 K to 6.6 × 10−4 s−1 at 314 K, and the γ was increased by 1 order of magnitude from 7.6 × 10−5 to 4.1 × 10−4. It is noticeable that such a temperature effect on the reaction kinetics was much more pronounced at lower temperatures. This may be explained by the change in physical state of LA at lower temperatures. As discussed in the previous section, LA is present as a mixture of both solid and supercooled liquid at lower temperatures and the amount of solid phase increases with decreasing temperature. When the liquid LA layer freezes, diffusion of ozone to the bulk of LA was expected to considerably slow down, resulting in a marked decrease in the rate coefficients. For this reason, temperature effects on reaction kinetics became more appreciable at lower temperature. Moreover, this may indicate the participation of subsurface layers in the observed ozone reactive uptake and imply that the overall reaction rate is limited by diffusion in bulk phase. This is consistent with the conclusion drawn from studies of O3 reaction with OA and LA film.4 The slight deviation in absorbance profile from exponential behavior at 258 K shown in Figure 7a may result from the slower diffusion in the solid phase. As seen in Figure 7b, the γ value for liquid LA (∼(3.5 ± 0.2) × 10−4) at room temperature obtained in this work is within a factor of 3 of the uptake coefficients reported previously (∼1.2 × 10−3).4,23,24 The slight disagreement may be due to pressure differences in reaction systems. Unlike previous experiments, which were operated under typical pressures of several Torrs, much lower than realistic atmospheric condition, our study under ambient pressure condition likely resulted in an ozone concentration gradient above the film surface due to diffusion in the gas. Because ozone concentration in the bulk gas phase was used in eq 2, it was not unexpected to observe slightly lower results. For liquid LA over the temperature range from 274 to 314 K, we observed little temperature dependence, in good agreement with previous results.4,23 In contrast, literature data4 for the lower temperature region (258−274 K) presented different behavior from ours. Despite γ values from Moise and Rudich’s study overall in agreement with our
Figure 7. Exponential curve-fitting results of the absorbance difference in CO stretching band (1743 cm−1) at different reaction temperatures at RH = 0% (a), and the temperature dependence of kapp and γ in the reaction of LA and ozone (b).
function fit the time dependent absorbance profiles of all four vibration bands markedly well and the apparent first-order rate constants kapp acquired on the basis of curve-fitting of the time dependent absorbance profiles of CO (1743 and 1710 cm−1), CO (1110 cm−1), and CC (1170 cm−1) stretching bands are 5.5 × 10−4, 6.0 × 10−4, 3.3 × 10−4, and 5.6 × 10−4 s−1, respectively. Such agreement among these data confirms that the reaction in this study is under pseudo-first-order conditions. With the apparent first-order rate constants kapp, overall uptake coefficient γ could be estimated by the following equation22,23 1968
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Table 2. Summary of Pseudo-First-Order Rate Constants, kapp, Derived from Different Bands, and Corresponding Calculated Uptake Coefficients, γ kapp × 10−4 (s−1) T (K), physical state
RH (%)
[O3] (ppb)
314, 293, 288, 284, 273, 265, 258, 293, 293, 293, 293,
0 0 0 0 0 0 0 0 30 55 80
350 350 350 350 350 350 350 250 250 250 250
liquid liquid liquid liquid liquid solid/liquid solid/liquid liquid liquid liquid liquid
1743 cm−1 6.56 5.34 5.62 5.31 5.20 3.06 1.10 5.24 5.98 9.83 11.20
± ± ± ± ± ± ± ± ± ± ±
0.86 0.27 0.37 0.26 0.39 0.81 0.27 0.46 0.95 1.26 1.24
1710 cm−1
γ × 10−4
1172 cm−1
1110 cm−1
6.30 5.76 6.07 5.14 5.02
± ± ± ± ±
1.66 0.30 0.46 0.58 0.60
7.51 5.31 5.53 5.12 4.93
± ± ± ± ±
1.28 0.40 0.19 0.21 0.26
5.97 3.16 3.52 3.29 3.28
± ± ± ± ±
1.17 0.23 0.12 0.26 0.28
4.04 6.92 5.42 12.20
± ± ± ±
1.01 1.22 2.17 2.35
5.88 6.04 3.43 8.49
± ± ± ±
0.27 1.30 0.81 0.30
3.81 4.04 4.04 6.67
± ± ± ±
0.40 0.26 0.18 0.32
data, they observed nearly no temperature dependence for temperatures lower than 265 K and then a big jump from 265 to 267 K, different from our gradual increase in γ values with increasing temperatures. The discrepancy may arise from differences in experimental method, which led to different physical states of LA. In Moise and Rudich’s work, a cylindrical rotating wall flow reactor was used and first-order loss of gasphase ozone on the frozen LA was monitored by a mass spectrometer under low pressure condition.4 Whereas, in the present work, the mixture of solid and supercooled liquid was found on the ATR crystal under atmospheric pressure condition. It is noted that Hung and Tang33 observed similar dependences of kapp and γ on temperature to ours in their OA/ ozone study based on the same FR-ATR-IR approach. 3.3. RH Effect. The RH effect on kinetics was studied at 0, 30, 55, and 80% with ozone concentration of ∼250 ppb and temperature of 293 K. Figure 8a shows the exponential curvefitting for the absorbance of 1743 cm−1 CO stretching band at different RHs. The kapp and γ versus RH are illustrated in Figure 8b. Figure 8b shows that both the kapp and the γ increased more than 2-fold as the RH increased from 0% to 80%, indicating that water vapor promoted the heterogeneous reaction of ozone and LA. Unlike our results, however, SegalRosenheimer et al. reported that the reaction kinetics of heterogeneous oxidation of cypermethrin thin film by ozone was insensitive to RH.51 Petrick et al. also obtained a similar result when they studied the RH influence on kinetics of ozone and squalene thin film.52 The disagreement of our result with those of previous studies may originate from the differing physiochemical properties of the organic compounds. In the present work, it was observed that the LA thin film could absorb a certain quantity of water both before and after ozone exposure (see section 3.5.2). This is likely due to the nature of carboxylic acids, which have a tendency to trap water molecules via hydrogen-bond formation. As the RH increased, multiple layers of water molecules were formed at the surface, which was confirmed by IR spectra. Ozone molecules show increased solubility in water (109 mg/L at 25 °C), nearly 13 times more soluble than oxygen molecules.65 When ozone molecules collided with the LA thin film, some molecules might be captured and dissolved into the water layers. This would considerably augment the residence time of ozone molecules at the surface and lead to a greater uptake probability. It should be pointed out that Thornberry and Abbatt23 measured the O3 reaction probability for ozone loss on LA up to 55% RH at 263
1743 cm−1 4.12 3.48 3.69 3.51 3.50 2.09 0.76 5.08 5.79 9.52 10.80
± ± ± ± ± ± ± ± ± ± ±
0.53 0.18 0.24 0.18 0.27 0.55 0.18 0.44 0.92 1.21 1.20
1710 cm−1
1172 cm−1
1110 cm−1
3.96 3.75 3.97 3.39 3.38
± ± ± ± ±
1.03 0.19 0.30 0.38 0.41
4.72 3.45 3.63 3.38 3.32
± ± ± ± ±
0.80 0.26 0.12 0.14 0.18
3.75 2.06 2.30 2.18 2.21
± ± ± ± ±
0.73 0.15 0.08 0.17 0.20
3.91 6.69 5.25 11.90
± ± ± ±
0.99 1.18 2.10 2.27
5.70 5.84 3.32 8.22
± ± ± ±
0.26 1.27 0.78 0.30
3.69 3.91 3.91 6.45
± ± ± ±
0.39 0.25 0.17 0.30
Figure 8. Exponential curve-fitting results of the absorbance difference in CO stretching band (1743 cm−1) at different reaction RHs at 293 K (a), and the RH dependence of kapp and γ in the reaction of LA and ozone (b).
K and did not observe a discernible effect of RH on the reaction kinetics. The source of the disagreement may result from the temperature difference. The saturated vapor pressures at 263 and 293 K are 2.15 and 31.8 mmHg, respectively. Under our experimental conditions, formation of water molecular layers was expected to be much more facile. 3.4. Ozone Concentration Effect. The observed kapp values and the corresponding calculated γ values at various 1969
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ozone concentrations (1012−1015 molecules/cm3) are plotted in Figure 9a,b. The kapp values were determined for LA thin film
This indicates that the reaction of ozone and LA likely involves two processes: ozone molecules are first adsorbed on the surface of the LA thin film and quickly reach equilibrium with the gas phase; then the adsorbed ozone molecules react with the LA on the surface at a relatively slower rate. Surface kinetics have shown a high dependence on chemical and physical properties of the substrate,42,66,67 and the KO3 values for different systems may range over several orders of magnitude.68 In the present work, the parameters of k[S] and KO3 derived from the curve fitting in Figure 9a are 0.0522 ± 0.0004 s−1 and (1.146 ± 0.017) × 10−15 molecules cm−3, respectively. The obtained KO3 value is on the same order of magnitude as those reported previously in heterogeneous ozonolysis studies of anthracene film at the air−water interface,69 benzo[a]pyrene on solid organic aerosols,41 and squalene thin film on ZeSn crystal.52 In addition, a nonlinear function (eq 4) based on the eqs 2 and 3 was used to fit the calculated γ vs ozone concentrations. γ=
under the following conditions, temperature 293 K and dry state. The nonlinear plot in Figure 9a shows a shape in accordance with the Langmuir−Hinshelwood surface reaction mechanism. Equation 3 was used to fit the observed kapp data in Figure 9a k[S]K O3[O3]gas 1 + K O3[O3]gas
(4)
The uptake coefficient γ is the ratio of the number of collisions which lead to a reaction to the total number of collisions between a gas-phase molecule and the surface. As the heterogeneous reaction between ozone and LA follows the Langmuir−Hinshelwood mechanism, with an increase in the ozone concentration, reactive surface sites would gradually become saturated and ozone surface coverage would eventually reach a plateau. Because the number of collisions leading to a reaction would remain unchanged after saturation, further increasing ozone concentration would just increase the total number of collisions. Therefore, γ was expected to decrease with increasing ozone concentrations. As shown in Figure 9b, it is indeed the case that γ decreased from 4.4 × 10−4 to 1.4 × 10−4 with increasing ozone concentration. This observed trend in γ also confirms the Langmuir−Hinshelwood surface reaction mechanism in the ozone/LA system. 3.5. Yields and Hygroscopicities of Products. 3.5.1. Product Yields. Product yields may change with reaction conditions.22 In the study of the reaction of ozone and OA, Hung and Tang employed the absorbance ratio of two CO stretching bands, A1743/A1710, presumably due to the formed αacyloxyalkyl hydroperoxide-related products and carboxylic acids, as an indicator to investigate how ambient temperature affected the product yields.33 In this work, the absorbance ratio of A1743/A1710 was also used to investigate how RH and temperature affected the product yields in the reaction of ozone and LA. The absorbance ratios of A1743/A1710 obtained at the end of each reaction under different temperatures and RH conditions are illustrated in Figure 10a,b. As seen in Figure 10a, the absorbance ratio vs temperature plot has a trend analogous to those of rate constants and uptake coefficients vs temperature; i.e., they increase relatively sharply with temperature in the lower temperature region (258−284 K) and then change slightly in the higher temperature region (284−314 K). The large increase in the absorbance ratios between 265 and 273 K is probably due to the disappearance of solid phase. Such a temperature effect on the product yield is also observed in the study of ozone initiated oxidation of OA.33 This may indicate that the product yield of unsaturated fatty acids reaction with ozone is not highly sensitive to temperature in nature but
Figure 9. Plots of kapp (a) and γ (b) versus gas-phase ozone concentration for the reaction of LA thin film with ozone. The black solid lines in (a) and (b) show a fit of the data to the Langmuir− Hinshelwood mechanism using eqs 3 and 4, respectively.
kapp =
k[S]K O3 4[LA] × c ̅SA /V 1 + K O3[O3]gas
(3)
where kapp [s−1] is the pseudo-first-order reaction rate constant, k [cm2 s−1 molecule−1] is the second-order reaction rate constant, [S] [molecules cm−2] is the total surface density of O3 adsorption sites, KO3 [cm3 molecule−1] is the ratio between O3 adsorption and desorption rate coefficients, and [O3]gas is the gas-phase O3 concentration [molecules cm−3]. As illustrated in Figure 9a, the curve (solid black line) based on the Langmuir− Hinshelwood mechanism fit well with the observed data of kapp. 1970
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absorbed water content. Because other groups, such as −CH2 and −OH of carboxylic acids, also contribute to the absorbance intensity in the region of 2750−3660 cm−1, the spectrum recorded at RH = 0% for each film was subtracted from those recorded at higher RHs. Figure 11 shows the water absorbance
Figure 11. Changes in water absorbance of 5 different thin films with RH.
values of the five different thin films at different RHs. As mentioned before, the thin film absorbed water not only after but also before the exposure to ozone with increasing RH. Comparing water uptake behaviors of the thin films before and after ozone treatment under RH = 0% and T = 293 K condition, it is evident that the hygroscopicity of chemically transformed thin films was considerably enhanced even after exposure to ozone for 1 h. This is probably due to the formation of more oxygenated compounds with higher water uptake capacity. The amount of water adsorbed on the oxidized thin film at RH = 80% was more than quadrupled as compared to that on the LA thin film without prior exposure to ozone. With an increase in exposure time from 1 to 2 h, the hygroscopicity of the thin film was slightly improved. This indicates that reaction products may not undergo significant change in composition at the end of 2 h exposure and the overall reaction may have been already complete. As illustrated in Figure 8, the reaction rate can be greatly boosted by higher RH. Indeed, the hygroscopic behavior of thin film after exposure to ozone for 1 h at RH = 80% showed larger water uptake as compared to counterpart at RH = 0%. The coincidental overlapping of the hygroscopic growth curves for thin films after exposure to ozone for 2 h at RH = 0% and for 1 h at RH = 80% supported our speculation that the reaction may have gone to completion and no considerable compositional change occurred. In addition, hygroscopicity of the thin film acquired at lower temperature (258 K) only presented a slight increase compared with the thin film without the prior exposure, whereas the hygroscopicity of the thin film obtained at higher temperature (293 K) increased significantly. Again, it was probably because of the change in physical state at lower temperature, which markedly slowed the reaction rate and led to the formation of less hygroscopic compounds. All these results have indicated that temperature can affect the physical state of atmospheric organics, which, in turn, influence their reaction kinetics and properties of reaction products; on the other hand, RH showed an influence on the kinetics, but no
Figure 10. Absorbance ratios of A1743/A1710 as a function of temperature (a) and RH (b).
instead is more sensitive to physical state of the organics. As discussed previously, high RH promotes the reaction rate; however, Figure 10b reveals no significant variations in the absorbance ratios with RH. This is because the absorbance ratios were obtained at the end of each reaction. It also indicates that the product yields are not very sensitive to RH. 3.5.2. Hygroscopic Properties of Products. Chemical aging of organic surfaces may enhance their hygroscopic properties.29 To understand how the ozone initiated oxidation affects interaction between water molecules and LA, five sets of water uptake experiments were carried out on unreacted and reacted LA thin films using the identical FR-ATR-IR setup for heterogeneous reaction kinetics study. The only difference between the two studies is whether ozone flow is on or off. Using the same setup in both studies allows us to stop the heterogeneous reaction at any age and quickly switch to water uptake investigation. For the ozone treated LA samples, reactions were conducted under four different conditions, i.e., (1) T = 293 K, RH = 0%, 1 h, (2) T = 293 K, RH = 0%, 2 h, (3) T = 293 K, RH = 80%, 1 h, and (4) T = 258 K, RH = 0%, 1 h, with the same ozone concentration of ∼250 ppb. The method for the hygroscopictiy study is similar to previously reported ones.53,70,71 Absorbance of the −OH stretching band in the 2750−3660 cm−1 region was employed to represent the 1971
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(6) Shiraiwa, M.; Pfrang, C.; Poschl, U. Kinetic Multi-layer Model of Aerosol Surface and Bulk Chemistry (KM-SUB): the Influence of Interfacial Transport and Bulk Diffusion on the Oxidation of Oleic Acid by Ozone. Atmos. Chem. Phys. 2010, 10 (8), 3673−3691. (7) McIntire, T. M.; Ryder, O. S.; Gassman, P. L.; Zhu, Z.; Ghosal, S.; Finlayson-Pitts, B. J. Why Ozonolysis May Not Increase the Hydrophilicity of Particles. Atmos. Environ. 2010, 44 (7), 939−944. (8) Last, D. J.; Najera, J. J.; Percival, C. J.; Horn, A. B. A Comparison of Infrared Spectroscopic Methods for the Study of Heterogeneous Reactions Occurring on Atmospheric Aerosol Proxies. Phys. Chem. Chem. Phys. 2009, 11 (37), 8214−8225. (9) Stokes, G. Y.; Chen, E. H.; Buchbinder, A. M.; Paxton, W. F.; Keeley, A.; Geiger, F. M. Atmospheric Heterogeneous Stereochemistry. J. Am. Chem. Soc. 2009, 131 (38), 13733−13737. (10) King, M. D.; Rennie, A. R.; Thompson, K. C.; Fisher, F. N.; Dong, C. C.; Thomas, R. K.; Pfrang, C.; Hughes, A. V. Oxidation of Oleic Acid at the Air-water Interface and its Potential Effects on Cloud Critical Supersaturations. Phys. Chem. Chem. Phys. 2009, 11 (35), 7699−7707. (11) Last, D. J.; Najera, J. J.; Wamsley, R.; Hilton, G.; McGillen, M.; Percival, C. J.; Horn, A. B. Ozonolysis of Organic Compounds and Mixtures in Solution. Part I: Oleic, Maleic, Nonanoic and Benzoic acids. Phys. Chem. Chem. Phys. 2009, 11 (9), 1427−1440. (12) Rosen, E. P.; Garland, E. R.; Baer, T. Ozonolysis of Oleic Acid Adsorbed to Polar and Nonpolar Aerosol Particles. J. Phys. Chem. A 2008, 112 (41), 10315−10324. (13) Vesna, O.; Sjogren, S.; Weingartner, E.; Samburova, V.; Kalberer, M.; Gaggeler, H. W.; Ammann, M. Changes of fatty acid aerosol hygroscopicity induced by ozonolysis under humid conditions. Atmos. Chem. Phys. 2008, 8 (16), 4683−4690. (14) Hearn, J. D.; Smith, G. A. Ozonolysis of Mixed oleic acid/Ndocosane particles: The Roles of Phase, Morphology, and Metastable states. J. Phys. Chem. A 2007, 111 (43), 11059−11065. (15) Voss, L. F.; Bazerbashi, M. F.; Beekman, C. P.; Hadad, C. M.; Allen, H. C. Oxidation of Oleic Acid at Air/Liquid Interfaces. J. Geophys. Res. Atmos. 2007, 112 (D6), 9. (16) Hung, H. M.; Ariya, P. Oxidation of Oleic Acid and Oleic Acid/ Sodium Chloride(aq) Mixture Droplets with Ozone: Changes of Hygroscopicity and Role of Secondary Reactions. J. Phys. Chem. A 2007, 111 (4), 620−632. (17) Reynolds, J. C.; Last, D. J.; McGillen, M.; Nijs, A.; Horn, A. B.; Percival, C.; Carpenter, L. J.; Lewis, A. C. Structural Analysis of Oligomeric Molecules Formed From the Reaction Products of Oleic Acid Ozonolysis. Environ. Sci. Technol. 2006, 40 (21), 6674−6681. (18) Mochida, M.; Katrib, Y.; Jayne, J. T.; Worsnop, D. R.; Martin, S. T. The Relative Importance of Competing Pathways for the Formation of High-Molecular-Weight Peroxides in the Ozonolysis of Organic Aerosol Particles. Atmos. Chem. Phys. 2006, 6, 4851−4866. (19) Ziemann, P. J. Aerosol Products, Mechanisms, and Kinetics of Heterogeneous Reactions of Ozone with Oleic Acid in Pure and Mixed Particles. Faraday Discus. 2005, 130, 469−490. (20) Hearn, J. D.; Lovett, A. J.; Smith, G. D. Ozonolysis of Oleic Acid Particles: Evidence for a Surface Reaction and Secondary Reactions Involving Criegee Intermediates. Phys. Chem. Chem. Phys. 2005, 7 (3), 501−511. (21) Katrib, Y.; Biskos, G.; Buseck, P. R.; Davidovits, P.; Jayne, J. T.; Mochida, M.; Wise, M. E.; Worsnop, D. R.; Martin, S. T. Ozonolysis of Mixed Oleic-Acid/Stearic-Acid Particles: Reaction Kinetics and Chemical Morphology. J. Phys. Chem. A 2005, 109 (48), 10910− 10919. (22) Hung, H. M.; Katrib, Y.; Martin, S. T. Products and Mechanisms of the Reaction of Oleic Acid with Ozone and Nitrate Radical. J. Phys. Chem. A 2005, 109 (20), 4517−4530. (23) Thornberry, T.; Abbatt, J. P. D. Heterogeneous Reaction of Ozone with Liquid Unsaturated Fatty Acids: Detailed Kinetics and Gas-phase Product Studies. Phys. Chem. Chem. Phys. 2004, 6 (1), 84− 93.
obvious effect on the hygroscopic property of reaction products.
4. CONCLUSIONS In this study, FR-ATR-IR was utilized to study the heterogeneous reaction of LA thin film with gas-phase ozone under atmospheric pressure conditions. The kinetics of LA thin film oxidization by ozone was found to be dependent on temperature and RH. Specifically, the pseudo-first-order rate constant kapp and the overall uptake coefficient γ were observed to increase with rising temperature and RH. The kapp and γ were increased by 6-fold as temperature rose from 258 to 314 K, and were enhanced by 2-fold as RH increased from 0 to 80%. The temperature dependent reaction kinetics was in agreement with those reported previously, whereas the enhancement effect of RH on kinetics was only observed in the present work. It was found that the temperature effect on the reaction kinetics was much more pronounced at lower temperatures, which was likely due to the change in physical state of LA at lower temperatures. Furthermore, the kapp was found to display a Langmuir−Hinshelwood dependence on gasphase ozone concentration with KO3 = (1.146 ± 0.017) × 10−15 molecules cm−3 and k[S] = 0.0522 ± 0.0004 s−1. In addition, the yields and hygroscopic properties of the ozonized products were also investigated by FTIR spectroscopy. The intensity ratio of the two CO stretching bands, A1743/A1710, which was utilized as an indicator of the product yields, increased sharply with increasing temperature in the lower temperature region (258−284 K), and then remained fairly constant in the higher temperature region (284−314 K). The product yields showed no significant variation with RH over the range of 0−80%. Water uptake studies showed that the LA thin film absorbed water with increasing RH, and the hygroscopicity of the thin film was enhanced after ozone exposure.
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AUTHOR INFORMATION
Corresponding Author
*E-mail: Y.Z.,
[email protected]; Y.L.,
[email protected]. Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS This work is supported by Research Corporation for Science Advancement (Grant # 20192), and NSFC (20933001) and 111 project B07012.
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REFERENCES
(1) Finlayson-Pitts, B. J.; Pitts, J. N., Jr. Chemistry of the Upper and Lower Atmosphere: Theory, Experiments and Applications; Academic Press: San Diego, 2000. (2) Seinfeld, J. H.; Pandis, S. N. Atmospheric Chemistry and Physics: From Air Pollution to Climate Change; John Wiley & Sons, Inc.: New York, 2006. (3) Rudich, Y.; Donahue, N. M.; Mentel, T. F. Aging of Organic Aerosol: Bridging the Gap Between Laboratory and Field Studies. Annu. Rev. Phys. Chem. 2007, 58, 321−352. (4) Moise, T.; Rudich, Y. Reactive Uptake of Ozone by Aerosol Associated Unsaturated Fatty Acids: Kinetics, Mechanism, and Products. J. Phys. Chem. A 2002, 106 (27), 6469−6476. (5) Pfrang, C.; Shiraiwa, M.; Poschl, U. Coupling Aerosol Surface and Bulk Chemistry with a Kinetic Double Layer Model (K2-SUB): Oxidation of Oleic Acid by Ozone. Atmos. Chem. Phys. 2010, 10 (10), 4537−4557. 1972
dx.doi.org/10.1021/jp308304n | J. Phys. Chem. A 2013, 117, 1963−1974
The Journal of Physical Chemistry A
Article
(24) Hearn, J. D.; Smith, G. D. Kinetics and Product Studies for Ozonolysis Reactions of Organic Particles Using Aerosol CIMS. J. Phys. Chem. A 2004, 108 (45), 10019−10029. (25) Smith, G. D.; Woods, E.; DeForest, C. L.; Baer, T.; Miller, R. E. Reactive Uptake of Ozone by Oleic Acid Aerosol Particles: Application of Single-particle Mass Spectrometry to Heterogeneous Reaction Kinetics. J. Phys. Chem. A 2002, 106 (35), 8085−8095. (26) Morris, J. W.; Davidovits, P.; Jayne, J. T.; Jimenez, J. L.; Shi, Q.; Kolb, C. E.; Worsnop, D. R.; Barney, W. S.; Cass, G. Kinetics of Submicron Oleic Acid Aerosols with Ozone: A Novel Aerosol Mass Spectrometric Technique. Geophys. Res. Lett. 2002, 29 (9), 71.1−71.4. (27) Zahardis, J.; Petrucci, G. A. The Oleic Acid-ozone Heterogeneous Reaction System: Products, Kinetics, Secondary Chemistry, and Atmospheric Implications of a Model System - a Review. Atmos. Chem. Phys. 2007, 7, 1237−1274. (28) Molina, M. J.; Ivanov, A. V.; Trakhtenberg, S.; Molina, L. T. Atmospheric Evolution of Organic Aerosol. Geophys. Res. Lett. 2004, 31, L22104. (29) Bertram, A. K.; Ivanov, A. V.; Hunter, M.; Molina, L. T.; Molina, M. J. The Reaction Probability of OH on Organic Surfaces of Tropospheric Interest. J. Phys. Chem. A 2001, 105 (41), 9415−9421. (30) Liu, Y.; Ivanov, A. V.; Zelenov, V. V.; Molina, M. J. Temperature Dependence of OH Uptake By Carbonaceous Surfaces of Atmospheric Importance. Russ. J. Phys. Chem. B 2012, 6 (2), 327−332. (31) Knopf, D. A.; Anthony, L. M.; Bertram, A. K. Does Atmospheric Processing of Saturated Hydrocarbon Surfaces by NO3 Lead to Volatilization? J. Phys. Chem. A 2005, 109, 5579−5589. (32) Nash, D. G.; Tolocka, M. P.; Baer, T. The Uptake of O3 by Myristic Acid-Oleic Acid Mixed Particle: Evidence for Solid Surface Layer. Phys. Chem. Chem. Phys. 2006, 8, 4468−4475. (33) Hung, H. M.; Tang, C. W. Effects of Temperature and Physical State on Heterogeneous Oxidation of Oleic Acid Droplets with Ozone. J. Phys. Chem. A 2010, 114 (50), 13104−13112. (34) Du, S.; Francisco, J. S.; Kais, S. Study of Electronic Structure and Dynamics of Interacting Free Radicals Influenced by Water. J. Chem. Phys. 2009, 130 (12), 124312. (35) Zhang, H.; Surratt, J. D.; Lin, Y. H.; Bapat, J.; Kamens, R. M. Effect of Relative Humidity on SOA Formation From Isoprene/NO Photooxidation: Role of Particle-phase Esterification Under Dry Conditions. Atmos. Chem. Phys. Discuss. 2011, 11, 5407−5433. (36) Walser, M. L.; Park, J.; Gomez, A. L.; Russell, A. R.; Nizkorodov, S. A. Photochemical Aging of Secondary Organic Aerosol Particles Generated from the Oxidation of D-limonene. J. Phys. Chem. A 2007, 111 (10), 1907−1913. (37) Nguyen, T. B.; Roach, P. J.; Laskin, J.; Laskin, A.; Nizkorodov, S. A. Effect of Humidigy on the Composition of Isoprene Photooxidation Secondary Organic Aerosol. Atmos. Chem. Phys. 2011, 11 (14), 6931− 6944. (38) Zelenay, V.; Monge, M. E.; D’Anna, B.; George, C.; Styler, S. A.; Huthwelker, T.; Ammann, M. Increased Steady State Uptake of Ozone on Soot Due to UV/Vis Radiation. J. Geophys. Res. Atmos. 2011, 116, D11301. (39) Gallimore, P. J.; Achakulwisut, P.; Pope, F. D.; Davies, J. F.; Spring, D. R.; Kalberer, M. Importance of Relative Humidity in the Oxidative Ageing of Organic Aerosols: Case Study of the Ozonolysis of Maleci Acid Aerosol. Atoms. Chem. Phys. 2011, 11 (23), 12181− 12195. (40) Baduel, C.; Monge, M. E.; Voisin, D.; Jaffrezo, J. L.; George, C.; Haddad, I. E.; Marchand, N.; D’Anna, B. Oxidation of Atmospheric Humic Like Substances by Ozone: A Kinetic and Structural Analysis Approach. Environ. Sci. Technol. 2011, 45 (12), 5238−5244. (41) Kwamena, N. O. A.; Thornton, J. A.; Abbatt, J. P. D. Kinetics of Surface-bound Benzo-a-pyrene and Ozone on Solid Organic and Salt aerosols. J. Phys. Chem. A 2004, 108 (52), 11626−11634. (42) Poschl, U.; Letzel, T.; Schauer, C.; Niessner, R. Interaction of Ozone and Water Vapor with Spark Discharge Soot Aerosol Particles Coated with Benzo-a-pyrene: O3 and H2O Adsorption, Benzo-apyrene Degradation, and Atmospheric implications. J. Phys. Chem. A 2001, 105 (16), 4029−4041.
(43) Jimenez, J. L.; Canagaratna, M. R.; Donahue, N. M.; Prevot, A. S. H.; Zhang, Q.; Kroll, J. H.; DeCarlo, P. F.; Allan, J. D.; Coe, H.; Ng, N. L.; et al. Evolution of Organic Aerosols in the Atmosphere. Science 2009, 326 (5959), 1525−1529. (44) Hildebrandt, L.; Donahue, N. M.; Pandis, S. N. High Formation of Secondary Organic Aerosol from the Photo-oxidation of Toluene. Atmos. Chem. Phys. 2009, 9 (9), 2973−2986. (45) Muller, L.; Reinnig, M. C.; Naumann, K. H.; Saathoff, H.; Mentel, T. F.; Donahue, N. M.; Hoffmann, T. Formation of 3-methyl1,2,3-butanetricarboxylic Acid via Gas Phase oxidation of Pinonic Acid − a Mass Spectrometric Study of SOA Aging. Atmos. Chem. Phys. 2012, 12, 1483−1496. (46) Renbaum, L. H.; Smith, G. D. Organic Nitrate Formation in the Radica-initiated Oxidation of Model Aerosol Particles in the Presences of NOx. Phys. Chem. Chem. Phys. 2009, 11 (36), 8040−8047. (47) Rudich, Y. Laboratory Perspectives on the Chemical Transformations of Organic Matter in Atmospheric Particles. Chem. Rev. 2003, 103 (12), 5097−5124. (48) Liu, Y.; Cain, J. P.; Wang, H.; Laskin, A. Kinetic Study of Heterogeneous Reaction of Deliquesced NaCl Particles with Gaseous HNO3 Using Particle-on-substrate Stagnation Flow Reactor Approach. J. Phys. Chem. A 2007, 111 (40), 10026−10043. (49) Liu, Y.; Gibson, E. R.; Cain, J. P.; Wang, H.; Grassian, V. H.; Laskin, A. Kinetics of Heterogeneous Reaction of CaCO3 Particles with Gaseous HNO3 Over a Wide Range of Humidity. J. Phys. Chem. A 2008, 112 (7), 1561−1571. (50) Liu, Y.; Minofar, B.; Desyaterik, Y.; Dames, E.; Zhu, Z.; Cain, J. P.; Hopkins, R. J.; Gilles, M. K.; Wang, H.; Jungwirth, P.; et al. Internal Structure, Hygroscopic and Reactive Properties of Mixed Sodium Methanesulfonate-Sodium Chloride particles. Phys. Chem. Chem. Phys. 2011, 13, 11846−11857. (51) Segal-Rosenheimer, M.; Dubowski, Y. Heterogeneous Ozonolysis of Cypermethrin Using Real-time Monitoring FTIR Techniques. J. Phys. Chem. C 2007, 111 (31), 11682−11691. (52) Petrick, L.; Dubowski, Y. Heterogeneous Oxidation of Squalene Film by Ozone Under Various indoor Conditions. Indoor Air 2009, 19 (5), 381−391. (53) Schuttlefield, J.; Al-Hosney, H.; Zachariah, A.; Grassian, V. H. Attenuated Total Reflection Fourier Transform Infrared Spectroscopy to Investigate Water Uptake and Phase Transitions in Atmospherically Relevant Particles. Appl. Spectrosc. 2007, 61 (3), 283−292. (54) Sayer, R. M.; Horn, A. B. Simultaneous Spectroscopic Detection of Adsorbed and Gas-phase Species During Atmospherically Relevant Heterogeneous Reactions. Phys. Chem. Chem. Phys. 2003, 5 (23), 5229−5235. (55) Senkan, S.; Castaldi, M. Combustion in Ullmann’s Encyclopedia of Industrial Chemistry; Wiley-VCH: Weinheim, 2003. (56) Sempere, R.; Kawamura, K. Comparative Distributions of Dicarboxylic-Acid and Related Polar Compounds in Snow Rain and Aerosols from Urban Atmosphere. Atmos. Environ. 1994, 28 (3), 449− 459. (57) Lee, A. K. Y.; Chan, C. K. Heterogeneous Reactions of Linoleic Acid and Linolenic Acid Particles with Ozone: Reaction Pathways and Changes in Particle Mass, Hygroscopicity, and Morphology. J. Phys. Chem. A 2007, 111 (28), 6285−6295. (58) Socrates, G. Infrared and Raman Characteristic Group Frequencies: Tables and Charts; John Wiley & Sons: New York, 2001. (59) Palen, E. J.; Allen, D. T.; Pandis, S. N.; Paulson, S. E.; Seinfeld, J. H.; Flagan, R. C. Atmos. Environ. 1992, 26, 1239−1251. (60) Palen, E. J.; Allen, D. T.; Pandis, S. N.; Paulson, S.; Seinfeld, J. H.; Flagan, R. C. FTIR Analysis of Aerosol Formed in the Photooxidation of 1 Octene. Atmos. Environ. 1993, 27, 1471−1477. (61) Sinclair, R. G.; McKay, A. F.; Myers, G. S.; Norman, J. R. The Infrared Absorption Spectra of Unsaturated Fatty Acids and Esters. J. Am. Chem. Soc. 1952, 74, 2578−2585. (62) Kobayashi, M.; Kaneko, F. Vibrational Spectroscopic Study on Polymorphism and Order-Disorder Phase Transition in Oleic Acid. J. Phys. Chem. 1986, 90, 6371−6378. 1973
dx.doi.org/10.1021/jp308304n | J. Phys. Chem. A 2013, 117, 1963−1974
The Journal of Physical Chemistry A
Article
(63) The Merck Index, 11th ed.; Merck & Co: Whitehouse Station, NJ, 1989. (64) GESTIS Substance Database from the Institute for Occupational Safety and Health of the German Social Accident Insurance, http://gestis-en.itrust.de/ (65) Battino, R.; Rettich, T. R.; Tominaga, T. The Solubility of oxygen and Ozone in Liquids. J. Phys. Chem. Ref. Data. 1983, 12 (2), 163−178. (66) Kwamena, N. O. A.; Staikova, M. G.; Donaldson, D. J.; George, I. J.; Abbatt, J. P. D. Role of the Aerosol Substrate in The Heterogeneous Ozonation Reactions of Surface-bound PAHs. J. Phys. Chem. A 2007, 111, 11050−11058. (67) Kahan, T. F.; Kwamena, N. O. A.; Donaldson, D. J. Heterogeneous Ozonation Kinetics of Polycyclic Aromatic Hydrocarbons on Organic Films. Atmos. Environ. 2006, 40, 3448−3459. (68) Najera, J. J.; Percival, C. J.; Horn, A. B. Infrared Spectroscopic Studies of the Heterogeneous Reaction of Ozone with Dry Maleic and Fumaric Acid Aerosol Particles. Phys. Chem. Chem. Phys. 2009, 11, 9093−9103. (69) Mmereki, B. T.; Donaldson, D. J.; Gilman, J. B.; Eliason, T. L.; Vaida, V. Atmos. Environ. 2004, 38, 6091−6103. (70) Liu, Y.; Laskin, A. Hygroscopic Properties of CH3SO3Na, CH3SO3NH4, (CH3SO3)2Mg and (CH3SO3)2Ca Particles Studied by micro-FTIR Spectroscopy. J. Phys. Chem. A 2009, 113 (8), 1531− 1538. (71) Liu, Y.; Yang, Z.; Desyaterik, Y.; Gassman, P. L.; Wang, H.; Laskin, A. Hygroscopic Behavior of Substrate Deposited Particles Studied by Micro-FTIR Spectroscopy and Complementary Methods of Particle Analysis. Anal. Chem. 2008, 80, 633−642.
1974
dx.doi.org/10.1021/jp308304n | J. Phys. Chem. A 2013, 117, 1963−1974
