Multiphase Chemical Kinetics of NO3

Article pubs.acs.org/est

Multiphase Chemical Kinetics of NO3 Radicals Reacting with Organic Aerosol Components from Biomass Burning Manabu Shiraiwa,†,§ Ulrich Pöschl,† and Daniel A. Knopf*,‡ †

Biogeochemistry Department, Max Planck Institute for Chemistry, P.O. Box 3060, 55128 Mainz, Germany Institute for Terrestrial and Planetary Atmospheres, School of Marine and Atmospheric Sciences, Stony Brook University, Nicolls Road, Stony Brook, New York 11794, United States

‡

S Supporting Information *

ABSTRACT: Multiphase reactions with nitrate radicals are among the most important chemical aging processes of organic aerosol particles in the atmosphere especially at nighttime. Reactive uptake of NO3 by organic compounds has been observed in a number of studies, but the pathways of mass transport and chemical reaction remained unclear. Here we apply kinetic flux models to experimental NO3 exposure studies. The model accounts for gas phase diffusion within a cylindrical flow tube, reversible adsorption of NO3, surface-bulk exchange, bulk diffusion, and chemical reactions from the gas-condensed phase interface to the bulk. We resolve the relative contributions of surface and bulk reactions to the uptake of NO3 by levoglucosan and abietic acid, which serve as surrogates and molecular markers of biomass burning aerosol (BBA). Applying the kinetic flux model, we provide the first estimate of the diffusion coefficient of NO3 in amorphous solid organic matrices (10−8−10−7 cm2 s−1) and show that molecular markers are wellconserved in the bulk of solid BBA particles but undergo rapid degradation upon deliquescence/liquefaction at high relative humidity, indicating that the observed concentrations and subsequent apportionment of the biomass burning source could be significantly underestimated.

1. INTRODUCTION Organic substances are ubiquitous in the environment and are prone to chemical modification by multiphase reactions with atmospheric oxidants such as O3, OH, and NO3.1,2 Reactions at the surface and in the bulk of organic aerosol particles in the atmosphere affect the particles’ chemical and physical properties that are important for air quality, public health and climate (toxicity and allergenicity, aerosol optical parameters, cloud droplet, ice nucleating ability, etc.).3 A major source of organic aerosol is biomass burning which has been observed in remote and urban locations but also in the upper troposphere and lower stratosphere.4,5 Biomass burning aerosol is a major source of particulate matter to the atmosphere with a source strength of similar magnitude to fossil fuel burning.4 Chemical modification during atmospheric transport, also termed chemical aging,2 by multiphase oxidation reactions changes the particle properties but also results in chemical loss of biomarkers applied to trace and apportion biomass burning aerosol6 crucial for policy regulations on air quality and health related issues.7 These particles constitute a complex mixture of organic and inorganic species where cellulose and hemicellulose decomposition products like levoglucosan (1,6-anhydro-b-D-glucopyranose, C6H10O5) and resin acids like abietic acid (1-phenanthrenecarboxylic acid, C20H30O2) represent a major fraction of the identified organic material8 and are often used as biomass burning tracers.6 Degradation of these species by reaction with atmospheric © 2012 American Chemical Society

oxidants would result in significant underestimation of the biomass burning source strength. In particular in urban polluted environments nighttime NO3 concentrations can reach up to 400 ppt9−11 (corresponding to ∼9.9 × 109 cm−3 at 298 K) and recent model studies indicate that particle oxidation by NO3 is the most important aging process.12,13 The reactive uptake coefficients of NO3 by various liquid and solid organic substrates have been experimentally derived ranging from ∼2 × 10−4−1.14−16 So far, however, the relative contributions of surface and bulk reactions to the overall reactivity have not been quantified, and the mass accommodation coefficient, desorption lifetime, and diffusion coefficient of NO3 necessary for a complete description of NO3 uptake by a solid organic surface have not been determined. Here, we apply data obtained from NO3 uptake and exposure experiments involving levoglucosan and abietic acid substrates that serve as surrogates for biomass burning compounds.14 These species include different molecular functionalities such as OH groups and benzene rings with a carboxylic group. Furthermore, previous studies indicate that levoglucosan constitutes a solid or semisolid amorphous phase state for Received: Revised: Accepted: Published: 6630

February 18, 2012 May 16, 2012 May 17, 2012 May 17, 2012 dx.doi.org/10.1021/es300677a | Environ. Sci. Technol. 2012, 46, 6630−6636

Environmental Science & Technology

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applied experimental conditions.17 The experimental data is analyzed in detail applying flux-based kinetic models. The kinetic double-layer model for aerosol chemistry (K2-SURF)13 and the kinetic multilayer model for aerosol surface and bulk chemistry (KM-SUB)18 which account for gas phase diffusion and reversible adsorption of NO3, surface reaction, surface-bulk exchange, bulk diffusion and chemical reactions from the gascondensed phase interface to the bulk, resolving concentration gradients and diffusion throughout the bulk. A novel formalism has been developed to account for gas phase diffusion correction within a cylindrical tube allowing application of the kinetic flux models to reactive uptake experiments using flow tube reactors. This allows in yet not achieved detail to treat the underlying multiphase chemistry. The role of surface and bulk reactions in the overall reactive uptake of NO3 by different organic surfaces is evaluated and physicochemical parameters such as second order surface and bulk reaction rate constants and bulk diffusion coefficients typically inaccessible to experiments are derived. We show that even for a solid organic substrate bulk diffusion and subsequent reaction has to be accounted for to correctly describe the underlying heterogeneous kinetics. The atmospheric implications of these novel findings with respect to particle lifetime and aerosol source apportionment are briefly discussed.

The mean free path is given by the gas phase diffusion coefficient and the mean thermal velocity of Xi: λXi = 3 Dg,Xi/ ωXi.20 eq 1 is based on a flux matching approach analogous to the well-established formalisms for spherical particles,20−23 and it has been validated against commonly used analytical and numerical methods24−26 as detailed in the supplement (Supporting Information Figure S1). In addition to gas phase diffusion and surface processes, KMSUB explicitly treats surface-bulk exchange, bulk diffusion and chemical reactions from the gas-particle interface to the particle core, resolving concentration gradients and diffusion throughout the particle bulk. Surface-bulk transport and bulk diffusion of volatile and nonvolatile reactants are treated as the mass transport from one bulk layer to the next by describing the mass transport fluxes between different layers of the bulk by first-order transport velocities, which are calculated from the bulk diffusion coefficients.18 Bulk reaction rates are calculated assuming that bulk reactions proceed with second-order rate dependencies on the concentrations within each bulk layer. In the numerical simulations presented in this study, the number of the model layers was set to n = 100. Test calculations using smaller or higher values of n gave almost identical results. The temporal evolution of γNO3 and the particle surface and bulk composition were modeled by numerically solving the differential equations for the mass balance of each model compartment. The model input parameters include the surface accommodation coefficient of NO3 (αs,0), desorption lifetime of NO3 (τd), the second-order surface and bulk reaction rate coefficients between NO3 and organics (kSLR, kBR), Henry’s law coefficient for NO3 (Ksol,cc), and the bulk diffusion coefficients of NO3 and organics (DNO3, Dorg). Additional input parameters are the mean thermal velocity of NO3 (ωNO3 = 3.2 × 104 cm s−1) and the effective molecular diameter of NO3 (δNO3 = 0.47 nm), levoglucosan (LG) and abietic acid (AA) (δLG = 0.69 nm, δAA = 0.78 nm). Considering the molecular mass (MLG = 162 g mol−1, MAA = 304 g mol−1), and density (ρLG = 1.6 g cm−3, ρAA = 1.06 g cm−3) of applied organics and assuming that the organics are densely packed with a simple cubic packing fraction of 0.52,27 the initial surface and bulk concentrations of levoglucosan are 2 × 1014 cm−2 and 3 × 1021 cm−3, respectively, and those of abietic acid are 1.6 × 1014 cm−2 and 1 × 1021 cm−3, respectively. Sensitivity studies showed that estimated uncertainties of a factor of 2 in the initial surface and bulk concentrations of the organic reactants lead to ∼20% uncertainty in the derived DNO3. The initial concentrations of NO3 at the surface and in the bulk were set to zero. kBR between NO3 and levoglucosan at 298 K in an organic matrix is unknown but kBR for levoglucosan in an aqueous 3 −1 solution is reported to be 2.7 × 10−14 cm s .28 As a first-order approximation we used this reported value as an initial estimate and as detailed below we found kBR is an insensitive parameter −15 −3 −1 as long as kBR is >5 × 10 cm s . Initial estimates for other required kinetic parameters are based on our previous studies13,29−33 and typical ranges for the interactions between organic surfaces and oxidants: αs,0 = 10−3 − 1, τd = 10−10 − 1, kSLR = 10−18 − 10−9 cm2 s−1, and kBR= 10−18 − 10−12 cm3 s−1 and Ksol,cc= 10−4 − 10−3 mol cm−3 atm−1. These parameters were systematically and iteratively varied using Matlab software to find a best fit solution as summarized in Table 1. Note that the optimized parameter combination given in Table 1 is not a unique solution and other parameter combinations can also

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MATERIALS AND METHODS Levoglucosan and abietic substrates were exposed under dry conditions to NO3 in presence of NO2 and atmospheric relevant O2 concentrations using a rotating-wall flow-tube reactor coupled to a chemical ionization mass spectrometer as described in detail previously.14,19 The NO3 exposure experiments were conducted for about 1 h and at about 3 hPa under dry conditions. Note that NO3 concentrations in these experiments were about 7 × 1010 cm−3, which is about a factor of 7 higher than NO3 concentrations in highly polluted urban environments.9−11 The substrate thickness was estimated to be 0.1−0.2 mm. Experiments employing different amounts of substrate and film preparation techniques, i.e. applying an aqueous organic solution or melting of the pure organic compound,14 did not significantly affect the reactive uptake coefficient. The resulting films are assumed to be nonporous. Reported changes in NO3 concentration due to uptake by the organic substrates were derived by detection of NO3− after chemical ionization of NO3 by I−. K2-SURF resolves gas phase diffusion, reversible adsorption and surface reaction of NO3.13 The surface reactions are considered with two different mechanism of an Eley−Rideal (ER) mechanism, where collision of a gas-phase species with the organic surface results in reaction, or a Langmuir− Hinshelwood (LH) mechanism, in which the gas-phase species first adsorb and subsequently react with surface bound compounds.1 The effects of gas phase diffusion are taken into account through a gas phase diffusion correction factor Cg,Xi which is the ratio between the near-surface gas phase concentration [Xi]gs and the average gas phase concentration [Xi]g.20 For a cylindrical flow tube operated under fast flow conditions, Cg,Xi can be expressed as a function of the gas uptake coefficient γXi, the flow tube diameter d and the mean free path of Xi molecules in the gas phase λXi: Cg,Xi =

[X i]gs [X i]g

1

=

1 + γX 14.64λ i

3d 2 X i(d − 2λ X i)

(1) 6631

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hydrogen abstraction from an alkyl group or NO3 addition across the unsaturated carbon−carbon bond.14 The black dashed lines in Figure 1 show K2-SURF modeled γNO3. For levoglucosan (Figure 1a) K2-SURF can reproduce only the magnitude of the initial plateau of γNO3 up to ∼102 s, but then modeled γNO3 decrease quickly due to the depletion of surface reactive sites. The temporal evolution of γNO3 could not be reproduced by neither LH nor ER mechanisms simulated by K2-SURF. However, the temporal evolution of γNO3 can be fully reproduced if bulk diffusion and reaction are resolved by KM-SUB as shown as solid black line in Figure 1A, providing strong evidence of bulk diffusion of NO3. Moreover, the double-logarithmic plot for levoglucosan exhibits a slope of −0.5 after ∼102 s, which is characteristic for diffusion-limited uptake (∂lnγ/∂lnt = −0.5).29,34,35 Figure 1 also displays bulk accommodation coefficients (αb,NO3), the probability for a gas molecule colliding with surface to enter the bulk of the particle. For levoglucosan up to ∼102 s γNO3 is almost as large as bulk accommodation coefficient αb,NO3 ≈ 7 × 10−4, which indicates that probability of uptake and that of entering the bulk is almost same. This shows that the contribution of surface reaction to the total NO3 uptake is relatively minor and rather dominated by transport of NO3 from surface to near-surface bulk where it can readily react with levoglucosan. Indeed sensitivity studies revealed that the kinetic parameters for surface processes of αs,0, τd, and kSLR are not critical for describing the observed γNO3 by levoglucosan over the time scales of the experiments. The uptake of NO3 is also insensitive 3 −1 to kBR as long as it is larger than 5 × 10−15 cm s . The most sensitive parameter is found to be DNO3, confirming that bulk diffusion of NO3 is the rate-limiting step. Note that the different combination of DNO3 and Ksol,cc can match the observed γNO3, but the reported range of Ksol,cc of 10−4 − 10−3 mol cm−3 atm−136 limit the range of DNO3 to 2−20 × 10−8 cm2 s−1. The sensitivity study suggests that the actual value of Dorg is unimportant as long as it is below 10−18 cm2 s−1. The NO3 uptake by abietic acid proceeds differently compared to levoglucosan as shown in Figure 1B. K2-SURF can reproduce the observed γNO3 well up to ∼102 s, but afterward K2-SURF underestimates the experiment. Including bulk diffusion and reaction by KM-SUB results in a much better representation of experimentally derived γNO3. This, again, provides support that significant numbers of NO3 molecules also diffuse into the organic bulk. Up to ∼20 s, γNO3 is by a factor of 10 larger than αb,NO3, indicating that NO3 uptake is dominated by surface reaction. The surface reaction of NO3

Table 1. Kinetic Parameters for the Interaction Between NO3 and Levoglucosan or Abietic Acid at 298 K

αs,0: surface accommodation coefficient of NO3 on adsorbate-free substrate, τd: desorption lifetime of NO3, kSLR: second-order rate coefficients of surface reaction between NO3 and organics, kBR: second-order rate coefficients of bulk reaction between NO3 and organics, Ksol,cc: Henry’s law coefficient of NO3, DNO3 and Dorg: bulk diffusion coefficients of NO3 and organics. a

match the observed uptake coefficients. However, the key results presented in our study remain unchanged. In particular, the available literature data on Henry’s law coefficients of NO3 does limit the range of diffusion coefficients that we extracted by applying KM-SUB to the experimental data observed as a function of time and NO3.

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RESULTS AND DISCUSSION Figure 1 shows the experimental data of NO3 uptake by levoglucosan (A) and abietic acid (B) as a function of NO3 exposure time performed at ∼7 × 1010 cm−3 NO3 and at 298 K.14 The measurement results are uptake coefficient γNO3, which is the probability for a NO3 molecule colliding with surface to be taken up by the film.20 As shown, γNO3 by levoglucosan stays constant at ∼10−3 up to ∼100 s and then decrease slowly. Initial γNO3 by abietic acid is higher than γNO3 by levoglucosan at ∼2.5 × 10−3 and then decreases very fast. The initial reaction step of NO3 with levoglucosan is the abstraction of hydrogen from the carbon of the OH-group leading to nitration, whereas that with abietic acid is either

Figure 1. NO3 uptake coefficient (γNO3) by (A) levoglucosan and (B) abietic acid. Kinetic model results simulated with KM-SUB which includes bulk diffusion and reaction (solid line) and with K2-SURF which includes only surface reaction (dashed line). The bulk accommodation coefficient (αb) is given as green line. 6632



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Figure 2. Kinetic model results for the NO3 uptake by levoglucosan (LG) at 6.9 × 1010 cm−3 NO3 calculated with KM-SUB. (A) Surface concentrations of NO3 (black line) and levoglucosan (red line). Radial profiles of bulk concentrations of (B) NO3 and (C) levoglucosan. (D) Loss rate profile of levoglucosan.

with abietic acid is faster than that with levoglucosan because NO3 addition is generally faster than hydrogen abstraction. After ∼20 s γNO3 decreases swiftly as surface abietic acid is quickly depleted via surface reaction. For abietic acid the sensitivity study suggests αs,0, τd, and kSLR are critical parameters to describe γNO3 up to ∼102 s, showing that the surface process is the rate-limiting step. DNO3 is critical afterward and the reported range of Ksol,cc of 10−4 − 10−3 mol cm−3 atm−136 limit the range of DNO3 to 0.5 − 5 × 10−8 cm2 s−1. The upper limit of the diffusion coefficient of abietic acid is suggested to be 10−17 cm2 s−1. Figure 2 shows the simulation results of surface and bulk composition for NO3 uptake by levoglucosan using kinetic parameters specified in Table 1. As shown in Figure 2A, the surface concentration of NO3 stays at steady-state level of 107 cm−2 determined by the combination of reversible adsorption, surface reaction, and bulk diffusion and reaction. After ∼102 s γNO3 start decreasing below αb,NO3 as the uptake kinetics are limited by diffusion of NO3 into the bulk. NO3 starts diffusing into the bulk after ∼102 s (Figure 2B) exhibiting a steep concentration gradient near the surface, while the underlying bulk remains essentially NO3-free. Accordingly levoglucosan is depleted near the surface and also exhibits a strong concentration gradient (Figure 2C). Figure 2D shows the bulk profile of turnover rate of levoglucosan, indicating the reaction front move from surface to further into the bulk. The simulation results and interpretation of surface and bulk composition for NO3 uptake by abietic acid are very similar to the case of levoglucosan and are given in Figure S2. The dependence of γNO3 on gas phase NO3 concentration for uptake by levoglucosan and abietic acid is given in Figure 3. For both organic substrates γNO3 decrease with increasing of NO3 concentration.14 The dashed and solid lines are modeled by K2SURF and KM-SUB, respectively. For levoglucosan KM-SUB

Figure 3. NO3 uptake coefficient (γNO3) on levoglucosan (black) and abietic acid (red) as a function of gas phase NO3 concentration. The data points and error bars represent experimental data and standard deviations.14 The lines are kinetic model results simulated with KMSUB which includes bulk diffusion and reaction (solid line) and with K2-SURF which includes only surface reaction (dashed line).

reproduces well the moderate decreasing trend of γNO3 as NO3 concentration increases, but K2-SURF results in much steeper decrease due to rapid consumption of surface reactants, which again emphasize the importance of bulk diffusion of NO3. For abietic acid the concentration dependence can be reproduced fairly well by both K2-SURF and KM-SUB, as the uptake is initially dominated by the surface process. This is the first study that estimates the bulk diffusion coefficient of NO3 into organics, resulting in the range of 10−8 − 10−7 cm2 s−1. Typically bulk diffusion coefficients of photooxidants such as ozone are ∼10−10 cm2 s−1 in solid, 10−9 − 10−6 cm2 s−1 in semisolid (rubbery, gel-like, or ultraviscous), and 10−5 cm2 s−1 in liquid,29,37−39 depending on molecular size of oxidant and substrate. Levoglucosan is reported to exhibit amorphous phases with glassy or semisolid states17 and DNO3 6633



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particle is activated and becomes a water droplet (cloud processing). To account for this effect, t1/2 is calculated to represent different humid conditions with high DNO3 = 10−6 cm2 s−1 and cloud processing with DNO3 = 10−5 cm2 s−1. As shown in Figure 4B a change in DNO3 exerts a significant effect on t1/2. t1/2 decreases by a factor of ∼10 for humid conditions and thus levoglucosan and abietic acid can be oxidized in less than a week at polluted conditions. In case of cloud processing t1/2 is less than one day even in presence of low NO3 concentrations of ∼50 ppt, indicating that biomass burning aerosol particles can be degraded very efficiently in aqueous droplets.28 In source apportionment studies levoglucosan and abietic acid are typically used as biomarker tracers of biomass burning with an assumption that these traces are stable up to one week during transport in the atmosphere.6,7,43 We estimate the fraction of degraded levoglucosan for a 200 and 500 nm diameter particle exposed to NO3 for one week shown in Figure 5. At 50 ppt NO3, ∼5 and 15% of levoglucosan can be

obtained in this study is consistent with typical diffusion coefficients of oxidants interacting with organic material in a semisolid state. Here we estimate the chemical half-life (t1/2) of levoglucosan and abietic acid exposed to NO3 to explore and characterize the effects of bulk diffusion on the chemical aging of organic biomass organic aerosol. t1/2 is defined as the time after which the number of organic molecules in the condensed phase has decreased to half of its initial value. The particle diameter is set to be 200 nm and the NO3 concentration is varied in the range of few ppt to 250 ppt, covering clean and polluted conditions in the atmosphere.10,11,40 The kinetic parameters used in the simulation are same as in Table 1. t1/2 of levoglucosan and abietic acid at 298 K and dry condition are shown in Figure 4A. t1/2 is lower for levoglucosan

Figure 4. Chemical half-life (t1/2) of biomass burning organic aerosol surrogate in a 200 nm diameter particle exposed to NO3. (A) t1/2 (days) of levoglucosan (solid line) and abietic acid (dotted line) at 25 °C and dry condition. (B) t1/2 (days) of levoglucosan with different scenarios of dry (DNO3 = 8 × 10−8 cm2 s−1; solid line), humid (DNO3 = 10−6 cm2 s−1; dashed line), and cloud processing (DNO3 = 10−5 cm2 s−1; dotted line).

Figure 5. Estimated fraction of degraded levoglucosan exposed to NO3 for one week, a typical transport time of biomass burning plume for particles (A) 200 nm and (B) 500 nm in diameter. The different humidity cases correspond to different NO3 bulk diffusivities (DNO3) with dry conditions (8 × 10−8 cm2 s−1), humid conditions (10−6 cm2 s−1), and cloud processing (10−5 cm2 s−1).

compared to abietic acid since bulk diffusion of NO3 is faster in levoglucosan. As expected, t1/2 decreases with increasing NO3 concentration. t1/2 is more than ∼100 days at low NO3 concentrations of 10 ppt in clean condition and ∼20 days even at 200 ppt NO3 in polluted air masses. Long chemical halflife indicates that these organic species are well protected by oxidants when present in (semi)solid matrices due to the slow mass transport as a result of low diffusion coefficients. The organic material on the surface and near-surface bulk can be degraded by oxidants in the time scale of hours or less,14 but the inner bulk material will not be chemically aged. Efficient oxidation of surface and near-surface bulk organic species may result in significant changes in surface hygroscopicity due to addition of oxygenated functional groups with subsequent effects on cloud formation and health related issues. Biomass burning aerosol can consist of a complex mixture of organic and inorganic compounds6,8 that can affect particle reactivity14,41,42 and may also influence the degradation of the biomarker tracers by NO3. If additional compounds on the surface and in the bulk of multicomponent particles were to reduce the uptake and diffusivity of NO3, the lifetimes derived here for a single component particle should be regarded as lower limits. Under humid conditions these organic species can undergo hygroscopic growth and moisture-induced phase transition. For example the phase of levoglucosan can change from (semi)solid to liquid as relative humidity increases.17 In response to the phase transition bulk diffusion coefficients of NO3 can also increase over 10−6 cm2 s−1 in a viscous matrix under humid condition (>∼80% RH) and even up to ∼10−5 cm2 s−1 if the

degraded for dry conditions, ∼20 and 40% at humid conditions, and up to 60 and 100% for cloud processing, for particles 200 and 500 nm in diameter, respectively. These calculations strongly indicate the observed levoglucosan concentrations can be underestimated and subsequent apportionment of the biomass burning source could be also underestimated. Thus, knowledge of the air mass history with respect to humidity is crucial to accurately assess degradation of biomarker tracers and source strength. Moreover, biomass burning aerosol can be also oxidized by other oxidants such as ozone, OH, NO2, and N2O5,14,28,44,45 yielding even more rapid chemical aging of biomass burning aerosol.28,46 Chemical aging can lead to the changes of the optical properties of particles and especially potential nitration can enhance the light absorption of particles by formation of brown carbon47 which can exert a significant effect on climate.48,49 In summary we have shown that chemical aging by NO3 via multiphase oxidation reactions can result in significant degradation of typical tracers for biomass burning aerosol with important implications for source apportionment studies. We have further shown that the level of degradation of these tracers depends strongly on particle viscosity and as such on environmental conditions such as temperature and relative humidity. 6634



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(12) Kaiser, J. C.; Riemer, N.; Knopf, D. A. Detailed heterogeneous oxidation of soot surfaces in a particle-resolved aerosol model. Atmos. Chem. Phys. 2011, 11 (9), 4505−4520. (13) Shiraiwa, M.; Garland, R. M.; Pöschl, U. Kinetic double-layer model of aerosol surface chemistry and gas-particle interactions (K2SURF): Degradation of polycyclic aromatic hydrocarbons exposed to O3, NO2, H2O, OH and NO3. Atmos. Chem. Phys. 2009, 9 (24), 9571− 9586. (14) Knopf, D. A.; Forrester, S. M.; Slade, J. H. Heterogeneous oxidation kinetics of organic biomass burning aerosol surrogates by O3, NO2, N2O5, and NO3. Phys. Chem. Chem. Phys. 2011, 13 (47), 21050− 21062. (15) Gross, S.; Iannone, R.; Xiao, S.; Bertram, A. K. Reactive uptake studies of NO3 and N2O5 on alkenoic acid, alkanoate, and polyalcohol substrates to probe nighttime aerosol chemistry. Phys. Chem. Chem. Phys. 2009, 11 (36), 7792−803. (16) Moise, T.; Talukdar, R. K.; Frost, G. J.; Fox, R. W.; Rudich, Y. Reactive uptake of NO3 by liquid and frozen organics. J. Geophys. Res., [Atmos.] 2002, 107 (D1-D2), 4014. (17) Mikhailov, E.; Vlasenko, S.; Martin, S. T.; Koop, T.; Pöschl, U. Amorphous and crystalline aerosol particles interacting with water vapor: conceptual framework and experimental evidence for restructuring, phase transitions and kinetic limitations. Atmos. Chem. Phys. 2009, 9 (2), 9491−9522. (18) Shiraiwa, M.; Pfrang, C.; Pöschl, 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. (19) Knopf, D. A.; Mak, J.; Gross, S.; Bertram, A. K. Does atmospheric processing of saturated hydrocarbon surfaces by NO3 lead to volatilization? Geophys. Res. Lett. 2006, 33 (17), L17816. (20) Pöschl, U.; Rudich, Y.; Ammann, M. Kinetic model framework for aerosol and cloud surface chemistry and gas-particle interactions Part 1: General equations, parameters, and terminology. Atmos. Chem. Phys. 2007, 7 (23), 5989−6023. (21) Jayne, J. T.; Pöschl, U.; Chen, Y. M.; Dai, D.; Molina, L. T.; Worsnop, D. R.; Kolb, C. E.; Molina, M. J. Pressure and temperature dependence of the gas-phase reaction of SO3 with H2O and the heterogeneous reaction of SO3 with H2O/H2SO4 surfaces. J. Phys. Chem. A 1997, 101 (51), 10000−10011. (22) Pöschl, U.; Canagaratna, M.; Jayne, J. T.; Molina, L. T.; Worsnop, D. R.; Kolb, C. E.; Molina, M. J. Mass accommodation coefficient of H2SO4 vapor on aqueous sulfuric acid surfaces and gaseous diffusion coefficient of H2SO4 in N2/H2O. J. Phys. Chem. A 1998, 102 (49), 10082−10089. (23) Ferguson, E. E.; Fehsenfeld, F. C.; Schmeltekopf, A. L., Flowing afterglow measurements of ion-neutral reactions. In Advances in Atomic and Molecular Physics, Bates, D. R., Immanuel, E., Eds.; Academic Press: New York, 1969; Vol. 5, pp 1−56. (24) Brown, R. L. Tubular flow reactors with 1st-order kinetics. J. Res. Natl. Bur. Stand. 1978, 83 (1), 1−8. (25) Cooney, D. O.; Kim, S. S.; Davis, E. J. Analyses of mass-transfer in hemodialyzers for laminar blood-flow and homogeneous dialysate. Chem. Eng. Sci. 1974, 29 (8), 1731−1738. (26) Murphy, D. M.; Fahey, D. W. Mathematical treatment of the wall loss of a trace species in denuder and catalytic-converter tubes. Anal. Chem. 1987, 59 (23), 2753−2759. (27) Atkins, P. W., Physical Chemistry; Oxford University Press: Oxford, 1998. (28) Hoffmann, D.; Tilgner, A.; Iinuma, Y.; Herrmann, H. Atmospheric stability of levoglucosan: A detailed laboratory and modeling study. Environ. Sci. Technol. 2010, 44 (2), 694−699. (29) Shiraiwa, M.; Ammann, M.; Koop, T.; Pöschl, U. Gas uptake and chemical aging of semisolid organic aerosol particles. Proc. Natl. Acad. Sci. U.S.A. 2011, 108 (27), 11003−11008. (30) Shiraiwa, M.; Sosedova, Y.; Rouviere, A.; Yang, H.; Zhang, Y.; Abbatt, J. P. D.; Ammann, M.; Pöschl, U. The role of long-lived reactive oxygen intermediates in the reaction of ozone with aerosol particles. Nat. Chem. 2011, 3 (4), 291−295.

ASSOCIATED CONTENT

S Supporting Information *

Additional material as noted in the text. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Present Address §

Department of Chemical Engineering, California Institute of Technology, 1200E. California Boulevard., Pasadena, California 91125, United States Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS M.S. and U.P. thank Max Planck Society and the Pan-European Gas-AeroSOls-climate interaction Study (No. 265148, PEGASOS). D.K. acknowledges support by the National Science Foundation, Grant AGS-0846255. MS thanks the Japan Society for the Promotion of Science (JSPS) for Postdoctoral fellowships for Research Abroad.

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Multiphase Chemical Kinetics of NO3

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