Uptake of Gas Phase Nitrous Acid onto Boundary Layer Soil

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Uptake of Gas Phase Nitrous Acid onto Boundary Layer Soil Surfaces Melissa A. Donaldson, Andrew E. Berke, and Jonathan D. Raff* School of Public and Environmental Affairs and Department of Chemistry, Indiana University, Bloomington, Indiana 47405-2204, United States S Supporting Information *

ABSTRACT: Nitrous acid (HONO) is an important OH radical source that is formed on both ground and aerosol surfaces in the well-mixed boundary layer. Large uncertainties remain in quantifying HONO sinks and determining the mechanism of HONO uptake onto surfaces. We report here the first laboratory determination of HONO uptake coefficients onto actual soil under atmospheric conditions using a coated-wall flow tube coupled to a highly sensitive chemical ionization mass spectrometer (CIMS). Uptake coefficients for HONO decrease with increasing RH from (2.5 ± 0.4) × 10−4 at 0% RH to (1.1 ± 0.4) × 10−5 at 80% RH. A kinetics model of competitive adsorption of HONO and water onto the particle surfaces fits the dependence of the HONO uptake coefficients on the initial HONO concentration and relative humidity. However, a multiphase resistor model based on the physical and chemical processes affecting HONO uptake is more flexible as it accounts for the pH dependence of HONO uptake and bulk diffusion in the soil matrix. Fourier transform infrared (FTIR) spectrometry and cavity-enhanced absorption spectroscopy (CEAS) studies indicate that NO and N2O (16% and 13% yield, respectively) rather than NO2 are the predominant gas phase products, while NO2− and NO3− were detected on the surface postexposure. Results are compared to uptake coefficients inferred from models and field measurements, and the atmospheric implications are discussed.

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trace gases and aerosols.35 The quantification of HONO uptake on soil surfaces is also relevant in light of recent studies suggesting that soil nitrite derived from microbial activity is a source of HONO.36,37 Parameterizing the adsorption of HONO onto the soil surfaces is one of the prerequisites for modeling HONO deposition and would improve our understanding of the partitioning and fate of HONO. Here we present a study of HONO uptake on soil under atmospherically relevant conditions as it transitions from what is predominantly a dry and porous mineral surface to one that is coated with water. Kinetic measurements are performed using a coated-wall flow reactor coupled to a chemical ionization mass spectrometer (CIMS) that enables us to determine the uptake coefficients for HONO adsorption to soil under atmospherically relevant conditions of pressure, HONO mixing ratios, and relative humidity. In addition, we use spectroscopic techniques to investigate the gas-phase products associated with reactive uptake of HONO onto soil. The results are compared to findings from recent laboratory and field studies, and the atmospheric implications are discussed.

INTRODUCTION Nitrous acid (HONO), a trace gas with tropospheric concentrations of 0.01−10 ppb, plays a significant role in regulating the oxidative capacity of the atmosphere. Photolysis of HONO produces nitric oxide (NO) and hydroxyl radical (OH), the latter of which is an important atmospheric oxidant that leads to ozone and secondary aerosol formation.1−5 In some studies, photolysis of HONO in the morning and throughout the daytime accounts for up to 56% of the daytime HOx production, which is greater than or comparable to the amount of HOx generated from ozone and formaldehyde photolysis.5,6 Pathways of HONO formation have been the subject of numerous field and laboratory studies and include homogeneous gas phase reactions,5,7,8 heterogeneous thermal reactions,9−13 and photochemical reactions.14−19 The sinks for HONO in the atmosphere, on the other hand, have received less consideration; this is problematic as it means that HONO is not properly represented in the atmospheric models used for prediction and regulation. In addition to photolysis during daytime hours, the atmospheric fate of HONO is defined by uptake onto boundary layer surfaces composed of inorganic and organic matter and water. Uptake of HONO onto water, 11,20−22 ice,23−26 soot,12,19,27 borosilicate glass,3,7,28,29 several plant species,30,31 and proxies for mineral dusts32−34 has been studied. However, uptake coefficients for HONO adsorption to actual soil surfaces have yet to be measured explicitly. Soil and soil-derived dust coats large areas of both rural and urban areas and, as such, represents an important surface for deposition of atmospheric © 2013 American Chemical Society

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EXPERIMENTAL SECTION Sample Preparation and Characterization. Soil samples were collected from an agricultural field located in BartholoReceived: Revised: Accepted: Published: 375

September 17, 2013 December 3, 2013 December 13, 2013 December 13, 2013 dx.doi.org/10.1021/es404156a | Environ. Sci. Technol. 2014, 48, 375−383

Environmental Science & Technology

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temperature of 293 ± 2 K. All measurements were carried out under strict exclusion of light. All glass surfaces with the exception of the soil-coated tube are coated with a hydrophobic and inert perfluorinated polymer film (Fluoropel PFC 801A, Cytonix Corp.) to reduce interactions of HONO with nonessential surfaces. HONO was generated via the heterogeneous reaction of HCl with solid NaNO2, as described by Febo et al.42 Humidified air was flowed through an HCl permeation device at 296 K followed by a bed of stirred NaNO2 (∼1.0 g) in a fritted glass reactor at 333 K. The HONO stream was free of HCl and NO2 impurities, as verified by long-path FTIR and CEAS. The HONO was diluted to the desired concentrations (0.5−60 ppb) with humidified air and flowed through the moveable piston with a ∼100 cm3 min−1 carrier gas in the rear of the flow tube to obtain a total flow of ∼2100 cm3 min−1. The bath gas was maintained at the desired relative humidity ranging from 0% to 80 ± 2% (Vaisala, HMT 130). Separate experiments were performed to study the effect of the soil coating mass on HONO uptake coefficients. Uptake coefficients increase with surface coverage, as more accessible surface area was added to the tube, but plateaued around 30 mg cm−2, at which point additional soil surface had no influence on the uptake kinetics. This suggests that uptake is limited by bulk diffusion and reaction near the surface of the soil and does not involve the entire volume of soil. The >75 coated tubes used each contained ∼50 mg cm−2 of soil, which was well within this plateau region; this reduced variability related to uneven surface coverage and best represents an infinitely thick layer of soil. Each uptake coefficient listed is derived from replicate measurements using 3−5 freshly coated tubes. Thus, the confidence intervals listed include the error associated with any variations in the surface coating. Product Studies. In addition to the uptake experiments described above, the long-path FTIR cell and a home-built cavity enhanced absorption spectrometer (CEAS) were coupled to the flow tube to quantify gas phase products emitted during HONO uptake on the soil surface. The FTIR was used for the quantification of NO and N2O, while the CEAS was used to detect NO2 and HONO. Experiments using FTIR were carried out for an initial HONO mixing ratio of 130 ± 17 ppb under relatively dry conditions (∼10% RH) to minimize interference of water absorption peaks with those of NO and N2O during quantitation. Infrared absorption cross sections for NO (1900.25 cm−1) and N2O (2232.50 and 2209.60 cm−1) were used for quantitation.43 The CEAS system used is functionally similar to several other published designs,44−48 and specific aspects of its design are described in the Supporting Information. For CEAS experiments, data were collected as soil was exposed to HONO mixing ratios of 21 and 158 ppb at 0% and 40% relative humidity, respectively. To determine soil NO2− and NO3− concentrations following HONO exposure, a sample of dry soil (7.5 g) was exposed to a stream of ∼700 ppb HONO in air for 24 h while being stirred in a batch reactor. This sample and an unexposed control were divided into three ∼3.75 g samples, extracted with 2 M KCl (10 mL), mechanically agitated for 1 h, centrifuged for 20 min, and then the supernatant was decanted and refrigerated until analysis. These samples were then analyzed for combined NO2− and NO3− concentrations using the cadmium reduction method and nitrite alone without the cadmium column on a Lachat QC8500 Flow Injection Autoanalyzer (Lachat Instruments). Nitrite and nitrate levels increased by 1.3 and 0.5 mg N L−1, respectively, relative to what was present in the control

mew County, Indiana (39.17, −85.89) at a depth of 0−5 cm in May 2013. The soil was autoclaved for 1 h at 394 K for three successive days and sieved with a 120 mesh soil sieve. The soil is classified as Genesee, a fine loamy alluvium comprised of silica, aluminosilicates, and less than 3% organic matter.38 The soil pH [1:2 soil/water (v/v), Thermo Scientific, OrionStar A211 pH meter]39 was 6.48. A slurry of soil and deionized water (18.2 MΩ·cm, Milli-Q Integral) was dripped onto the inner walls of cylindrical glass tube inserts and dried overnight in an oven at 393 K, yielding a dry weight of soil of 1.5 ± 0.2 g over the length of the tube. Scanning electron microscopy was used to characterize the soil−glass interface and soil surface (Figure 1); the coating covered the entire inner surface of the tube and was uniform to the eye.

Figure 1. Scanning electron micrographs of (A) the soil layer coating a Pyrex substrate demonstrating the relatively uniform coating achieved; the in-focus region shown by the vertical bar indicates the thickness of the soil layer (∼90 μm); the arrow denotes the soil-glass interface. (B) The soil coating viewed from above shows the inherent porosity of the soil surface.

Coated-Wall Flow Tube System. The uptake measurements were performed in a laminar flow reactor coupled to a chemical ionization mass spectrometer (CIMS), as previously described.40,41 A 5-cm section of Pyrex tube (17 mm i.d.) was coated with soil and placed in a 50-cm long Pyrex reactor with a central, moveable injector to introduce the HONO/humidified air mixture and a conical exit port to the CIMS. Additional details are provided in the Supporting Information. The entire length of the flow reactor was jacketed to maintain a 376

dx.doi.org/10.1021/es404156a | Environ. Sci. Technol. 2014, 48, 375−383


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where NO2− was below the detection limit and NO3− was 0.8 mg N L−1. Quantifying Water Adsorption onto Soil Surfaces. The gravimetric experiments were performed using a MettlerToledo UMT2 microbalance with an accuracy of ±0.1 μg. The weight of the soil sample (322.308 mg dry weight) was measured after the relative humidity was allowed to stabilize for a minimum of 3 h with flows of 20−50 cm3 min−1 of humidified air. Measurements were taken between 0% and 80% relative humidity at room temperature. The experiment was repeated without the sample present to verify that water adsorption to the sample holder was negligible. The gravimetric data, in conjunction with the soil surface area, were used to estimate the transition points from bare mineral surfaces to monolayer and multilayer water coverage of the soil. The specific surface area of the soil was 22.9 ± 0.6 m2 g−1, as determined from ethylene glycol monoethyl ether (EGME) vapor sorption experiments.49,50 The advantage of the EGME method is that it provides information on the total surface area including the surface area available to vapors within the interior of clay minerals. This method provides a more representative description of surface area available for water adsorption than available from the analysis of N2-adsorption isotherms with the widely used Brunauer−Emmett−Teller (BET) method; the BET method yields only the external surface area since N2 does not enter the clay interlayers. For example, the external surface area determined by the BET method (Micromeritics, ASAP 2020 Physisorption Analyzer) represents only 7.8% of the total surface area of the sample. The EGME-derived surface area was divided by the approximate area of an adsorbed water molecule (14.3 Å2), and the result was converted into a mass that constitutes monolayer coverage.51 This was then used with the results from the gravimetric experiments to determine the number of water monolayers adsorbed to the soil surface at a given relative humidity. Determination of Uptake Coefficients. Uptake of HONO onto the soil-coated surface was initiated by retracting the moveable injector to a position upstream of the coated section, exposing the soil layer to a well-mixed and laminar flow of HONO/humidified air. The section of tubing used for mixing the concentrated HONO and dilution streams was greater than that required to ensure complete mixing via diffusion. The Reynolds number was calculated to be 89, well within the laminar region. Each background and exposure was selectively monitored for 1 min using the [NO2]− signal at m/z 46 to derive the HONO steady state, [HONO]ss, and background, [HONO]0, signals. The Cooney−Kim−Davis (CKD) method was used to derive values of γHONO from [HONO]ss/[HONO]0 that are corrected for axial and lateral diffusion in a cylindrical tube under laminar flow conditions.40,50,52,53 Uptake coefficients reported are derived from the steady-state portion of the signal vs time and based on the geometric surface area of the sample. This allows the γHONO values to be implemented in atmospheric models that typically do not account for soil microstructure. The use of the BET or EGME surface areas would decrease the uptake coefficients by a factor of 103 or 104, respectively. Each uptake coefficient has been corrected for uptake of HONO onto the uncoated portions of the flow tube, which was measured in separate experiments before and after the insertion of each soil sample. The diffusion-corrected uptake coefficients for all experiments described are listed in Table 1, where the error represents the

Table 1. HONO Uptake onto Soil as a Function of Initial HONO Concentration, Relative Humidity, and Temperature [HONO]0 (ppb) relative humidity (%) 10 10 10 10 10 10 10 10 10 4 20 31 46 0.8 4 20 30 43 60 20 20 20 a b

0 10 20 30 40 50 60 70 80 0 0 0 0 30 30 30 30 30 30 0 0 0

uptake coefficienta γHONO × 10−5 25 15 9 2.8 2.1 2.0 1.6 1.9 1.1 25 23 31 21 5.1 4.8 3.1 3.4 3.5 3.0 23 25 18

± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ±

4 4 2 0.6 0.7 0.6 0.4 0.4 0.4 5 4 4 3 0.6 0.4 0.5 0.3 0.5 0.5 6b 6c 3d

Indicated error represents the 95% confidence interval of the mean. 286 K. c306 K. d316 K.

95% confidence interval of the mean of ∼20 measurements. The effect of temperature on the uptake coefficient of HONO on soil was measured between 286 and 316 K under dry conditions and at a [HONO]0 of 20 ppb. The results demonstrate no statistically significant trend in the uptake kinetics over this temperature range (see Table 1).

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RESULTS AND DISCUSSION HONO Uptake onto Soil. Figure 2 shows the temporal profile of the HONO signal measured by the CIMS as soil is exposed to a humidified stream of HONO (10 ppb at 10% RH). The HONO signal decreases to a steady-state level

Figure 2. Signal due to [NO2]− (m/z 46) measured by chemical ionization mass spectrometry as 10 ppb of HONO is exposed to soil in 1 atm of air at 10% RH and 296 K. Uptake is reproducible over all five 1-min exposures with no sign of surface site saturation or fatigue. Periods of time when soil was exposed to HONO (injector retracted) are indicated by the gray-shaded bars above. The speed of injector withdrawal is faster than its return to the initial point, leading to the slower recovery of the HONO signal at the end of each exposure. 377



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immediately upon exposure of HONO to soil. Occasionally, exposure of soil to HONO is accompanied by a sharp drop in signal just prior to the signal reaching steady state, which stems from instantaneous uptake of HONO to the portions of the flow tube wall that are not coated with soil. From Figure 2, it is evident that the soil surface does not exhibit fatigue after repeated exposures to HONO under the conditions of the experiment, which suggests that the surface is not being irreversibly saturated. In conjunction with the lack of a HONO desorption peak when the injector is returned to the front of the flow tube, this indicates that HONO adsorption proceeds via reactive uptake whereby HONO reacts upon collision with the surface and rapidly reaches equilibrium. Concentration Dependence. Figure 3A shows that γHONO is invariant for initial HONO mixing ratios between 4 and 50

Figure 4. (A) Effect of adsorbed water on HONO uptake onto the soil surface as the relative humidity is increased from 0% to 80% while the mixing ratio of HONO is held constant at 10 ppb. Green dotted lines represent fit of the data to eq 11. Blue solid line is the fit from eq 13. (B) Water adsorption isotherm for the soil based on gravimetric analysis of water uptake and soil surface area determined by the EMGE method.

γHONO were in the low relative humidity regime where HONO is able to interact with the exposed soil surface. As the RH increases and more water adsorbs to the soil, the γHONO values drop precipitously, approaching a plateau at ∼30% RH. To further investigate the role of water in controlling HONO uptake, we measured a water adsorption isotherm for the soil. Figure 4B shows how the number of water monolayers on the soil surface varies as the relative humidity of the surrounding air changed. Full monolayer coverage of the surface occurs at 20− 30% and remains fairly constant until around 40% RH, where it begins a rapid transition to multilayer coverage, similar to what has been observed on other environmentally relevant surfaces.2,35,54,55 Interestingly, 20% RH corresponds to the humidity level where the γHONO values approach a minimum. This trend was observed in studies of HONO decomposition on borosilicate glass28 and subsequently by others studying HONO uptake on homogeneous metal oxide surfaces.32,34 In those studies, it was suggested that saturation of surface sites with water is responsible for the transition from high γHONO values under dry conditions to the lower uptake coefficients seen under humid conditions. This is somewhat counterintuitive since previous measurements of HONO uptake onto pure water surfaces at room temperature find high γHONO values (10−2−10−4).20,56 As described below, this behavior may also be explained by considering bulk diffusion, reaction equilibria, and mass accommodation in the HONO-soil system. Product Studies. We obtained spectroscopic evidence that HONO adsorption on soil surfaces is accompanied by evolution of oxides of nitrogen into the gas phase. Experiments were carried out by retracting the flow tube injector to expose a section of soil to HONO and determining the amount of NO and N2O formed with FTIR; CEAS was used to measure HONO and NO2. As shown in Figure 5, although the soil was

Figure 3. Dependence of the uptake coefficient on initial HONO concentration at (A) 0% and (B) 30% relative humidity in air at 1 atm and 296 K. Green dotted lines represent fit of the data to eqs 11 and 12. Blue solid lines are fits to eq 13.

ppb under dry conditions. This concentration-independence provides further evidence that under dry conditions reactive uptake of HONO onto the mineral surface is quite efficient and there is no surface site saturation. This behavior has been observed by others for HONO adsorption to homogeneous metal oxide surfaces.32,34 Previous studies investigating HONO uptake onto borosilicate glass surfaces suggested that two molecules of HONO react on the surface to release gas phase NOx, thereby allowing more HONO to adsorb.28 Considering the low concentrations used in this study, it is also possible that reactions with surface sites also play a role in HONO decomposition. As seen in Figure 3B, HONO uptake kinetics are no longer concentration-independent when the carrier gas is humidified. At 30% RH, the γHONO values decrease as [HONO]0 increases from 1 to 65 ppb. This prompted a more comprehensive study of the influence of adsorbed water on HONO uptake kinetics. Relative Humidity Dependence. The dependence of HONO uptake on relative humidity when [HONO]0 is held constant at 10 ppb is shown in Figure 4A. The highest values of 378



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−

d[HONO(g)] = v = k 2[HONO(ads)] dt

(4)

Including the concentration of HONO adsorption sites on the soil surface, this becomes

v = k 2[ST]θHONO

(5)

where [ST] is the total number of active sites on the soil surface and θHONO is the fraction of sites occupied by HONO as defined by: θHONO = =

Figure 5. Cavity-enhanced absorption spectroscopy measurement of the flow tube output after soil was exposed to HONO (158 ppb in 1 atm air at 40% RH) shows a distinct absence of NO2 as a product. The raw spectrum from the measurement (red spectrum at the top) is superimposed with its spectral fit (green line). The HONO and NO2 reference spectra are shown by the blue and orange lines, respectively. The residual spectrum of the fitted line to the raw spectrum is shown at the bottom.

v=

k2

HONO(ads) → products k −3

K1k 2[ST][HONO(g)] 1 + K1[HONO(g)] + K3[H 2O(g)]

v = k′[HONO(g)]

(7)

(8)

where the pseudo-first-order rate constant k′ is k′ =

K1k 2[ST] 1 + K1[HONO(g)] + K3[H 2O(g)]

(9)

From kinetic gas theory, k′ can be related to the reaction probability γHONO, which is the fraction of collisions between HONO and the surface that result in reactive loss of HONO from the gas phase: γ ωHONO k′ = HONO (10) 2r In this equation, ω is the mean thermal velocity of HONO from ωHONO = (8RT/πM)1/2, where R, T, and M are the gas constant, absolute temperature, and the molecular weight of HONO, respectively. Equating eqs 9 and 10 yields an expression for γHONO that describes the dependence of the reaction probability on the initial HONO concentration and relative humidity: γHONO =

k′ads 1 + K1[HONO(g)] + K3[H 2O(g)]

(11)

where k′ads = (2r/ωHONO)K1k2[ST]. This equation is used to fit the data in Figures 3B and 4A. In the absence of water, K3[H2O(g)] → 0 and eq 11 becomes

(1)

γHONO =

(2)

k′ads 1 + K1[HONO(g)]

(12)

which is of the form used to fit the data in Figure 3A. An alternative interpretation of the γHONO trends shown in Figures 3 and 4 is provided by a resistor model that accounts for the factors affecting HONO uptake, including reactive uptake onto exposed mineral surface, bulk accommodation into the thin layer of water present at higher RH, Henry’s law solubility, and diffusion and reactivity in the aqueous bulk phase.60−63 We assume that reactive uptake of HONO on the

k3

H 2O + S XooY H 2O(ads)

(6)

This provides the rate expression describing the reactive uptake of HONO to soil surfaces and can be further simplified to the following pseudo-first-order rate law:

k1

k −1

K1[HONO(g)] 1 + K1[HONO(g)] + K3[H 2O(g)]

In eq 6, K1 and K3 are the equilibrium constants for reactions 1 and 3, respectively. Substituting eq 6 into eq 5 yields

exposed to nitrous acid, NO2 was not detectable by the CEAS (detection limit of 1.5 ppb). This is seen in the residual spectrum derived from a fit of the HONO reference spectrum to the spectrum taken from the output of the flow tube when soil was exposed to 158 ppb of HONO. Comparison to the NO2 reference spectrum demonstrates that the residual spectrum does not exhibit structure that would be due to NO2. However, both NO and N2O at 7.2 ± 0.5 and 6 ± 3 ppb, respectively, were detected by long-path FTIR. The sum of the contributions of NO and N2O (16% and 13%, respectively, relative to the amount of HONO adsorbed) indicate that the majority of the products are likely retained on the soil surface. Some of these adsorbed products are nitrite and nitrate, which we found present (in a 5:2 ratio) in aqueous extracts of the soil following exposure to 700 ppb of HONO. The N2O observed in our study may stem from secondary reactions of HONO on acidic surfaces11,57 to form hyponitrous acid (HONNOH) or HON, followed by decomposition to N2O, as proposed in previous studies of heterogeneous reactive nitrogen oxide chemistry.9,58 Mechanism of HONO Uptake. The kinetics of HONO uptake onto surfaces in the presence of water have been previously described by a mechanism consisting of a rapid initial equilibrium between gas phase and adsorbed HONO, followed by a slower reaction of HONO on the surface.28,32,59 The model assumes that H2O acts as a competitive inhibitor to HONO uptake, with the overall mechanism described by eqs 1−3: HONO(g) + S XooY HONO(ads)

[HONO(ads)] [ST]

(3)

where S is a reactive surface site, HONO(ads) is an adsorbed nitrous acid molecule, and the products are likely gas phase oxides of nitrogen. Assuming that eq 2 is the rate-determining step, a first-order rate law is written as 379



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Atmospheric Implications. A comprehensive understanding of the HONO vertical gradients and the processes that constitute its sources and sinks in the atmospheric boundary layer is important to quantify the atmospheric HONO budget.15,7,68 Recently, it has been proposed that deposition of HONO to surfaces may be reversible and serve as an additional source of daytime HONO.7,36,69 The work here provides insights into the fate of HONO on soil surfaces under conditions found in the field and lends itself to parametrization of HONO uptake for use in predictive models. Atmospheric models overpredict HONO levels observed during the nighttime, suggesting that HONO uptake onto boundary layer surfaces is not adequately treated.15,68 Uptake of HONO onto boundary layer surfaces was first reported by Trick, who derived a value for γHONO of ∼10−4 at 40% RH from chamber experiments.70 However, in a study of vertical profiles of HONO during the SHARP campaign in Houston, TX, Wong et al. found that this uptake coefficient led to an underestimation of [HONO]/[NO2] ratios measured at ground level;15,68 better agreement between observations and the one-dimensional chemistry transport model they employed was achieved when γHONO was reduced to 2 × 10−5. We note that the ambient relative humidity ranged from 25% to 70% during the SHARP field campaign, which corresponds to our measured range of uptake coefficients of (2.3 ± 0.4) × 10−5 at 30% RH to (1.9 ± 0.4) × 10−5 at 70% RH. Considering the uncertainties of both the model and our laboratory measurements, the agreement is excellent. We can also compare our data to HONO deposition velocities (νd) reported previously. Converting our γHONO values to deposition velocities using νd = γω/4,71 we estimate νd to be between 0.10 and 2.3 cm s−1; this falls in the range of measured gaseous dry deposition velocities reported for HONO (i.e., 0.077−3 cm s−1).4,13,14,31,72 Nitrous acid deposition rates were also considered by Vandenboer et al. in their analysis of results from the 2011 NACHTT-11 campaign at the Boulder Atmospheric Observatory.7 From measurements of nocturnal vertical HONO concentration profiles, they inferred ground-surface uptake coefficients of between 2 × 10−5 and 2 × 10−4, which is in excellent agreement with our experimentally determined uptake coefficients that range from a maximum of (2.5 ± 0.4) × 10−4 under dry conditions to (1.1 ± 0.4) × 10−5 at 80% RH. Again, the excellent correlation between our results and the field studies suggest that deposition to soil surfaces is a sink for HONO, especially in the nocturnal boundary layer. The mechanism of HONO uptake described here helps explain the dependence of ambient [HONO]/[NO2] on relative humidity documented by Stutz et al.73 and others.72In In the former study, it was shown that [HONO]/[NO2] under pseudo-steady-state (PSS) conditions is equal to the ratio of the heterogeneous NO 2 →HONO conversion efficiency (γNO2→HONO) and γHONO according to

bare mineral surface occurs in parallel to its accommodation and reaction in the bulk aqueous layer, and the relative importance of the processes depends the fractional coverage of the soil surface with water, θH2O, according to −1 ⎡1 1⎤ γHONO = (1 − θH2O)γS + θH2O⎢ + ⎥ Γb ⎦ ⎣α

(13)

In this equation, θH2O ranges from 0 under dry conditions with maximum porosity to 1 at RH > 30%, where we know from Figure 4B the equivalent of a monolayer of water covers the soil surface. The other terms are defined as follows: γS is the reactive uptake of HONO to exposed mineral surface at 0% RH, α is the accommodation coefficient describing the probability that a HONO molecule striking water-coated soil enters into the bulk liquid phase, and Γb is the term describing the solubility of HONO in the bulk water present in the soil at higher RH: Γb =

4Heff RT ωHONO

Dapp πτ

(14)

The term Dapp is the apparent diffusion coefficient of HONO in the soil−water matrix, and τ is the exposure time. The effective Henry’s law constant, Heff, is defined as ⎛ K a1 [H]+ ⎞ Heff = H ⎜1 + + ⎟ [H+] K a2 ⎠ ⎝

(15)

where H is the absolute Henry’s law constant for HONO and Ka1 and Ka2 are the acid dissociation constants for HONO and H2NO2+ ion, respectively. At 0% RH, θH2O → 0 and γS = γHONO. Under these conditions, γHONO is insensitive to the gas phase HONO concentration, in accordance with the data in Figure 3A. At RH > 30%, the mineral surfaces are covered by adsorbed water and uptake of HONO is dominated by mass transport into this water layer [i.e., (1 − θH2O)γS = 0 in eq 13]. Uptake into the bulk liquid layer depends on diffusion through the soil−water matrix and the bulk soil pH. While the initial soil pH was measured at 6.48, this is expected to drop as [HONO]g increases.26 Based on charge balance calculations under equilibrium conditions we find the pH drops to 4.3 at 60 ppb of HONO; see Figure S1. As the pH approaches the pKa1 of HONO, net uptake of HONO is expected to decrease as the equilibrium shifts from favoring NO2− to HONO; this is in accord with the data shown in Figure 3B. A good fit to the data in Figure 3 and 4A is obtained when α is 5.8 × 10−5 and Dapp is 6.5 × 10−10 cm2 s−1. This Dapp value is ∼5 orders of magnitude lower than diffusion of HONO in pure water and may explain why uptake onto a pure water surface is more efficient.20,56 Numerous studies have measured diffusion coefficients of sorbates in soil that are between 10−7 and 10−17 cm2 s−1 and depend on factors such as soil pore tortuosity and constrictivity, sorbate-pore wall affinity, soil organic matter viscosity, and the highly structured nature of water present in interlayer pores of a few Å that greatly restricts solute diffusion.64 Similarly, recent work shows that uptake of gases onto aerosol particles is kinetically limited by bulk diffusion in particles comprised of highly viscous organic matrices.65−67 While the two models described above fit the data in Figure 3 and 4, the resistor model based on eq 13 is preferred since it accounts for pH and diffusion in the soil−water matrix.

γNO → HONO(RH) ⎛ [HONO] ⎞ 2 ⎟ = ⎜ γHONO(RH) ⎝ NO2 ⎠PSS

(16)

where γNO2→HONO and γHONO are functions of relative humidity. Stutz et al. demonstrated that maximum [HONO]/[NO2] ratios increase linearly with relative humidity, a trend that was observed at several different locations across the U.S.73 At that time, there were questions as to whether the RH dependence of γNO2→HONO or γHONO were responsible for the trend in 380



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[HONO]/[NO2]. Our work clearly shows that on soil d(γHONO)/d(RH) is negative and plays an important role in controlling the RH dependence of ambient [HONO]/[NO2] ratios. A similar conclusion was arrived at from determinations of γHONO on homogeneous metal oxide surfaces.32 Comparison of our results to other laboratory measurements of HONO uptake onto homogeneous metal oxide surfaces highlights some important similarities and differences. In general, values of γHONO measured for the substrates TiO2 and Al2O3 are in the range 3 × 10−3 to 0.5 × 10−5 between 0% and 100% RH, respectively.32,34 A study of HONO adsorption to Fe2O3 and Arizona test dust yielded γHONO values between 5 × 10−4 and 0.03 × 10−5 in the range of 0% to 100% RH, respectively.33 The agreement with our γHONO values measured on soil is satisfactory considering differences in experimental methods used, although uptake coefficients on soil tend to be lower than those reported by El Zein et al. in the low RH regime.33 This may be due to residual water present in our samples; it is impossible to heat our soil samples to high temperatures to drive off water since this would denature the surface. Significant differences exist between the type and amount of gaseous products detected in our study and previous reports. For example, on TiO2, Al2O3, Fe2O3, and Arizona test dust it was reported that HONO adsorption afforded NO and NO2 in yields of 60% and 40%, respectively, regardless of RH.32−34 In contrast, we did not detect NO2 but rather found NO and N2O are the main gas-phase products stemming from reactive uptake of HONO on soil. Our FTIR and CEAS measurements are robust since these methods provide unambiguous identification of the described products. The reason for this discrepancy may stem from differences in the reactivity of homogeneous metal oxides and the heterogeneous soil surfaces used here. Syomin and Finlayson-Pitts were able to explore the products associated with HONO adsorption at high relative humidity on borosilicate glass using an FTIR technique.28 They saw a transition from a product distribution with equal amounts of NO and NO2 under dry conditions to more than 90% NO at 50% RH. They attribute the predominance of NO at high RH to a reaction between HONO and surface adsorbed NO2+ to form H+, NO, and O2. Our results support this mechanism, although it is possible that other components present in the soil matrix contribute to its reactivity. While we focus here on quantifying HONO uptake kinetics, our results show that atmospheric deposition of HONO will leave behind appreciable amounts of nitrite in the soil−water matrix. This will add to stocks of soil NO2− that accumulate due to microbial nitrification36,37 and thermal and photochemical reactions of NO2.8,9,18,74 If HONO uptake is kinetically limited by bulk diffusion, diffusion constraints in the soil matrix will also play a role in HONO desorption processes, leading to prolonged outgassing of HONO from soil NO2−. Thus, nitrite deposited on soil surfaces at night could contribute to the flux of HONO from ground surfaces observed during the next day7,36,68,74 and will depend on soil properties.

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Article

AUTHOR INFORMATION

Corresponding Author

*E-mail: jdraff@indiana.edu. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was funded by Indiana University. We are grateful to Jeffrey White for helpful discussions; Steven Brown, Rebecca Washenfelder, and Rainer Volkamer for discussions of CEAS design; and the Indiana University Nanoscale Characterization Facility for access to the scanning electron microscope. A.E.B. thanks the School of Public and Environmental Affair’s Dean’s Postdoctoral Fellowship Program for financial support. We also thank Abhy Kadakia and David Bish for use of the EGME surface area apparatus and Todd Royer for use of the Lachat system.

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REFERENCES

(1) Lammel, G.; Cape, J. N. Nitrous acid and nitrite in the atmosphere. Chem. Soc. Rev. 1996, 25, 361−370. (2) Lammel, G. Formation of Nitrous Acid: Parameterization and Comparison with Observations; Max Planck Institut für Meteorologie: Hamburg, 1999. (3) Jenkin, M. E.; Cox, R. A.; Williams, D. J. Laboratory studies of the kinetics of formation of nitrous acid from the thermal reaction of nitrogen dioxide and water vapor. Atmos. Environ. 1988, 22, 487−498. (4) Harrison, R. M.; Peak, J. D.; Collins, G. M. Tropospheric cycle of nitrous acid. J. Geophys. Res. Atmos. 1996, 101, 14429−14439. (5) Alicke, B.; Platt, U.; Stutz, J. Impact of nitrous acid photolysis on the total hydroxyl radical budget during the Limitation of Oxidant Production/Pianura Padana Produzione di Ozono study in Milan. J. Geophys. Res. 2002, 107, LOP 9-1−LOP 9-17. (6) Alicke, B.; Geyer, A.; Hofzumahaus, A.; Holland, F.; Konrad, S.; Pätz, H. W.; Schäfer, J.; Stutz, J.; Volz-Thomas, A.; Platt, U. OH formation by HONO photolysis during the BERLIOZ experiment. J. Geophys. Res. Atmos. 2003, 108, 8247. (7) VandenBoer, T. C.; Brown, S. S.; Murphy, J. G.; Keene, W. C.; Young, C. J.; Pszenny, A. A. P.; Kim, S.; Warneke, C.; de Gouw, J. A.; Maben, J. R.; Wagner, N. L.; Riedel, T. P.; Thornton, J. A.; Wolfe, D. E.; Dubé, W. P.; Ö ztürk, F.; Brock, C. A.; Grossberg, N.; Lefer, B.; Lerner, B.; Middlebrook, A. M.; Roberts, J. M. Understanding the role of the ground surface in HONO vertical structure: High resolution vertical profiles during NACHTT-11. J. Geophys. Res. Atmos. 2013, 118, 1−17. (8) Finlayson-Pitts, B. J.; Pitts, J. N., Jr. Chemistry of the Upper and Lower Atmosphere - Theory, Experiments, and Applications; Academic Press: San Diego, 2000; p 969. (9) Finlayson-Pitts, B. J.; Wingen, L. M.; Sumner, A. L.; Syomin, D.; Ramazan, K. A. The heterogeneous hydrolysis of NO2 in laboratory systems and in outdoor and indoor atmospheres: an integrated mechanism. Phys. Chem. Chem. Phys. 2003, 5, 223−242. (10) Svensson, R.; Ljungstrom, E.; Lindqvist, O. Kinetics of the reaction between nitrogen dioxide and water vapor. Atmos. Environ. 1987, 21, 1529−1539. (11) Kleffmann, J.; Becker, K. H.; Wiesen, P. Heterogeneous NO2 conversion processes on acid surfaces: possible atmospheric implications. Atmos. Environ. 1998, 32, 2721−2729. (12) Ammann, M.; Kalberer, M.; Jost, D. T.; Tobler, L.; Rossler, E.; Piguet, D.; Gaggeler, H. W.; Baltensperger, U. Heterogeneous production of nitrous acid on soot in polluted air masses. Nature 1998, 395, 157−160. (13) Spindler, G.; Brüggemann, E.; Herrmann, H. Nitrous acid concentration measurements and estimation of dry deposition over grasslands in eastern Germany. Proc. EUROTRAC Symp. 1998, 98, 218−222.

ASSOCIATED CONTENT

S Supporting Information *

Details of microscopy and mass spectrometry measurements and a description of the cavity-enhanced absorption spectrometer system. This material is available free of charge via the Internet at http://pubs.acs.org. 381



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(14) Stutz, J.; Alicke, B.; Neftel, A. Nitrous acid formation in the urban atmosphere: Gradient measurements of NO2 and HONO over grass in Milan, Italy. J. Geophys. Res. 2002, 107, LOP 5−1−LOP 5−15. (15) Wong, K. W.; Oh, H.-J.; Lefer, B. L.; Rappenglück, B.; Stutz, J. Vertical profiles of nitrous acid formation in the nocturnal urban atmosphere of Houston, TX. Atmos. Chem. Phys. 2011, 11, 3595− 3609. (16) Amedro, D.; Parker, A. E.; Schoemaecker, C.; Fittschen, C. Direct observation of OH radicals after 565 nm multi-photon excitation of NO2 in the presence of H2O. Chem. Phys. Lett. 2011, 513, 12−16. (17) Sörgel, M.; Regelin, E.; Bozem, H.; Diesch, J. M.; Drewnick, F.; Fischer, H.; Harder, H.; Held, A.; Hosaynali-Beygi, Z.; Martinez, M.; Zetzsch, C. Quantification of the unknown HONO daytime source and its relation to NO2. Atmos. Chem. Phys. 2011, 11, 10433−10447. (18) Stemmler, K.; Ammann, M.; Donders, C.; Kleffmann, J.; George, C. Photosensitized reduction of nitrogen dioxide on humic acid as a source of nitrous acid. Nature 2006, 440, 195−198. (19) Monge, M. E.; D’Anna, B.; Mazri, L.; Giroir-Fendler, A.; Ammann, M.; Donaldson, D. J.; George, C. Light changes the atmospheric reactivity of soot. Proc. Natl. Acad. Sci. U.S.A. 2010, 107, 6605−6609. (20) Bongartz, A.; Kames, J.; Schurath, U.; George, C.; Mirabel, P.; Ponche, J. L. Experimental determination of HONO mass accommodation coefficients using two different techniques. J. Atmos. Chem. 1994, 18, 149−169. (21) Mertes, S.; Wahner, A. Uptake of nitrogen-dioxide and nitrousacid on aqueous surfaces. J. Phys. Chem. 1995, 99, 14000−14006. (22) Cape, J. N.; Hargreaves, K. J.; Storetonwest, R.; Fowler, D.; Colvile, R. N.; Choularton, T. W.; Gallagher, M. W. Nitrite in orographic cloud as an indicator of nitrous-acid in rural air. Atmos. Environ. 1992, 26, 2301−2307. (23) Fenter, F. F.; Rossi, M. J. Heterogeneous kinetics of HONO on H2SO4 solutions and on ice: Activation of HCl. J. Phys. Chem. 1996, 100, 13765−13775. (24) Chu, L.; Diao, G.; Chu, L. T. Heterogeneous interaction and reaction of HONO on ice films between 173 and 230 K. J. Phys. Chem. A 2000, 104, 3150−3158. (25) Kerbrat, M.; Huthwelker, T.; Bartels-Rausch, T.; Gäggeler, H. W.; Ammann, M. Co-adsorption of acetic acid and nitrous acid on ice. Phys. Chem. Chem. Phys. 2010, 12, 7194−7202. (26) Kerbrat, M.; Huthwelker, T.; Gäggeler, H. W.; Ammann, M. Interaction of nitrous acid with polycrystalline ice: Adsorption on the surface and diffusion into the bulk. J. Phys. Chem. C 2010, 114, 2208-− 2219.. (27) Stadler, D.; Rossi, M. J. The reactivity of NO2 and HONO on flame soot at ambient temperature: The influence of combustion conditions. Phys. Chem. Chem. Phys. 2000, 2, 5420−5429. (28) Syomin, D. A.; Finlayson-Pitts, B. J. HONO decomposition on borosilicate glass surfaces: Implications for environmental chamber studies and field experiments. Phys. Chem. Chem. Phys. 2003, 5, 5236− 5242. (29) Ten Brink, H. M.; Spoelstra, H. The dark decay of HONO in environmental (SMOG) chambers. Atmos. Environ. 1998, 32, 247− 251. (30) Schimang, R.; Folkers, A.; Kleffmann, J.; Kleist, E.; Miebach, M.; Wildt, J. Uptake of gaseous nitrous acid (HONO) by several plant species. Atmos. Environ. 2006, 40, 1324−1335. (31) Harrison, R. M.; Kitto, A.-M. N. Evidence for a surface source of atmospheric nitrous acid. Atmos. Environ. 1994, 28, 1089−1094. (32) El Zein, A.; Bedjanian, Y. Reactive uptake of HONO to TiO2 surface: ″Dark″ reaction. J. Phys. Chem. A 2012, 116, 3665−3672. (33) El Zein, A.; Romanias, M. N.; Bedjanian, Y. Kinetics and products of heterogeneous reaction of HONO with Fe2O3 and Arizona test dust. Environ. Sci. Technol. 2013, 47, 6325−6331. (34) Romanias, M. N.; El Zein, A.; Bedjanian, Y. Reactive uptake of HONO on aluminium oxide surface. J. Photochem. Photobiol. A 2012, 250, 50−57.

(35) Usher, C. R.; Michel, A. E.; Grassian, V. H. Reactions on mineral dust. Chem. Rev. 2003, 103, 4883−4940. (36) Su, H.; Cheng, Y.; Oswald, R.; Behrendt, T.; Trebs, I.; Meixner, F. X.; Andreae, M. O.; Cheng, P.; Zhang, Y.; Pöschl, U. Soil nitrite as a source of atmospheric HONO and OH radicals. Science 2011, 333, 1616−1618. (37) Oswald, R.; Behrendt, T.; Ermel, M.; Wu, D.; Su, H.; Cheng, Y.; Breuninger, C.; Moravek, A.; Mougin, E.; Delon, C.; Loubet, B.; Pommerening-Röser, A.; Sörgel, M.; Pöschl, U.; Hoffmann, T.; Andreae, M. O.; Meixner, F. X.; Trebs, I. HONO emissions from soil bacteria as a major source of atmospheric reactive nitrogen. Science 2013, 341, 1233−1235. (38) Staff, Web Soil Survey. Natural Resources Conservation Service, United States Department of Agriculture: Washington, DC, 2013. (39) Hendershot, W. H.; Lalande, H.; Duquette, M. Soil reaction and exchangeable acidity. In Soil Sampling and Methods of Analysis, 2nd ed.;Carter, M. R., Gregorich, E. G., Eds.; Canadian Society of Soil Science: Pinawa, Canada, 2008; pp 173−178. (40) Kebede, M. A.; Varner, M. E.; Scharko, N. K.; Gerber, R. B.; Raff, J. D. Photooxidation of ammonia on TiO2 as a source of NO and NO2 under atmospheric conditions. J. Am. Chem. Soc. 2013, 135, 8606−8615. (41) Kebede, M. A.; Scharko, N. K.; Appelt, L. E.; Raff, J. D. Formation of nitrous acid during ammonia photooxidation on TiO2 under atmospherically relevant conditions. J. Chem. Phys. Lett. 2013, 4, 2618−2623. (42) Febo, A.; Perrino, C.; Gherardi, M.; Sparapani, R. Evaluation of a high-purity and high-stability continuous generation system for nitrous acid. Environ. Sci. Technol. 1995, 29, 2390−2395. (43) U.S. Environmental Protection Agency, AEDC Calculated Spectra. http://www.epa.gov/ttnemc01/ftir/aedcdat1.html (accessed 14 September 2013). (44) Ball, S. M.; Langridge, J. M.; Jones, R. L. Broadband cavity enhanced absorption spectroscopy using light emitting diodes. Chem. Phys. Lett. 2004, 398, 68−74. (45) Gherman, T.; Venables, D. S.; Vaughan, S.; Orphal, J.; Ruth, A. A. Incoherent broadband cavity-enhanced absorption spectroscopy in the near-ultraviolet: Application to HONO and NO2. Environ. Sci. Technol. 2008, 42, 890−895. (46) Washenfelder, R. A.; Langford, A. O.; Fuchs, H.; Brown, S. S. Measurement of glyoxal using an incoherent broadband cavity enhanced absorption spectrometer. Atmos. Chem. Phys. 2008, 8, 7779−7793. (47) Thalman, R. M.; Volkamer, R. M. Light emitting diode cavity enhanced differential optical absorption spectroscopy (LED-CEDOAS): a novel technique for monitoring atmospheric trace gases. Proc. SPIE 2009, 7462, 74620H/74621−74620H/74610. (48) Wu, T.; Zhao, W.; Chen, W.; Zhang, W.; Gao, X. Incoherent broadband cavity enhanced absorption spectroscopy for in situ measurements of NO2 with a blue light emitting diode. Appl. Phys. B: Lasers Opt. 2009, 94, 85−94. (49) Chiou, C. T.; Rutherford, D. W.; Manes, M. Sorption of nitrogen and ethylene glycol monoethyl ether (EGME) vapors on some soils, clays, and mineral oxides and determination of sample surface areas by use of sorption data. Environ. Sci. Technol. 1993, 27, 1587−1594. (50) deJonge, H.; MittelmeijerHazeleger, M. C. Adsorption of CO2 and N2 on soil organic matter: Nature of porosity, surface area, and diffusion mechanisms. Environ. Sci. Technol. 1996, 30, 408−413. (51) Gustafsson, R. J.; Orlov, A.; Badger, C. L.; Griffiths, P. T.; Cox, R. A.; Lambert, R. M. A comprehensive evaluation of water uptake on atmospherically relevant mineral surfaces: DRIFT spectroscopy, thermogravimetric analysis and aerosol growth measurements. Atmos. Chem. Phys. 2005, 5, 3415−3421. (52) 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, 2753−2759. (53) Behnke, W.; George, C.; Scheer, V.; Zetzsch, C. Production and decay of ClNO2 from the reaction of gaseous N2O5 with NaCl 382



Article

solution: Bulk and aerosol experiments. J. Geophys. Res. 1997, 102, 3795−3804. (54) Goodman, A. L.; Bernard, E. T.; Grassian, V. H. Spectroscopic study of nitric acid and water adsorption on oxide particles: Enhanced nitric acid uptake kinetics in the presence of adsorbed water. J. Phys. Chem. A 2001, 105, 6443−6457. (55) Sumner, A. L.; Menke, E. J.; Dubowski, Y.; Newberg, J. T.; Penner, R. M.; Hemminger, J. C.; Wingen, L. M.; Brauers, T.; Finlayson-Pitts, B. J. The nature of water on surfaces of laboratory systems and implications for heterogeneous chemistry in the troposphere. Phys. Chem. Chem. Phys. 2004, 6, 604−613. (56) Hirokawa, J.; Kato, T.; Mafuné, F. Uptake of gas-phase nitrous acid by pH-controlled aqueous solution studied by a wetted wall flow tube. J. Phys. Chem. A 2008, 112, 12143−12150. (57) Kleffmann, J.; Becker, K. H.; Wiesen, P. Investigation of the heterogeneous NO2 conversion on perchloric acid surfaces. J. Chem. Soc., Faraday Trans. 1998, 94, 3289−3292. (58) Rubasinghege, G.; Grassian, V. H. Surface-catalyzed chlorine and nitrogen activation: Mechanisms for the heterogeneous formation of ClNO, NO, NO2, HONO, and N2O from HNO3 and HCl on aluminum oxide particle surfaces. J. Phys. Chem. A 2012, 116, 5180− 5192. (59) Bedjanian, Y.; El Zein, A. Interaction of NO2 with TiO2 surface under UV irradiation: Products study. J. Phys. Chem. A 2012, 116, 1758−1764. (60) Schwartz, S. E.; Freiberg, J. E. Mass-transport limitation to the rate of reaction of gases in liquid droplets: Application to oxidation of SO2 in aqueous solutions. Atmos. Environ. 1981, 15, 1129−1144. (61) Hu, J. H.; Shorter, J. A.; Davidovits, P.; Worsnop, D. R.; Zahniser, M. S.; Kolb, C. E. Uptake of gas-phase halogenated acetic acid molecules by water surfaces. J. Phys. Chem. 1993, 97, 11037− 11042. (62) 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, 5989−6023. (63) Hanson, D. R. Surface-specific reactions on liquids. J. Phys. Chem. B 1997, 101, 4998−5001. (64) Pignatello, J. J.; Xing, B. Mechanisms of slow sorption of organic chemicals to natural particles. Environ. Sci. Technol. 1995, 30, 1−11. (65) 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, 11003−11008. (66) Renbaum-Wolff, L.; Grayson, J. W.; Bateman, A. P.; Kuwata, M.; Sellier, M.; Murray, B. J.; Shilling, J. E.; Martin, S. T.; Bertram, A. K. Viscosity of alpha-pinene secondary organic material and implications for particle growth and reactivity. Proc. Natl. Acad. Sci. U.S.A. 2013, 110, 8014−8019. (67) Berkemeier, T.; Huisman, A. J.; Ammann, M.; Shiraiwa, M.; Koop, T.; Pöschl, U. Kinetic regimes and limiting cases of gas uptake and heterogeneous reactions in atmospheric aerosols and clouds: a general classification scheme. Atmos. Chem. Phys. 2013, 13, 6663− 6686. (68) Wong, K. W.; Tsai, C.; Lefer, B.; Haman, C.; Grossberg, N.; Brune, W. H.; Ren, X.; Luke, W.; Stutz, J. Daytime HONO vertical gradients during SHARP 2009 in Houston, TX. Atmos. Chem. Phys. 2012, 12, 635−652. (69) Wojtal, P.; Halla, J. D.; McLaren, R. Pseudo steady states of HONO measured in the nocturnal marine boundary layer: a conceptual model for HONO formation on aqueous surfaces. Atmos. Chem. Phys. 2011, 11, 3243−3261. (70) Trick, S. Formation of Nitrous Acid on Urban Surfaces - A Physical-Chemical Perspective. Ph.D. Thesis, University of Heidelberg, Heidelberg, Germany, 2004. (71) Dentener, F. J.; Carmichael, G. R.; Zhang, Y.; Lelieveld, J.; Crutzen, P. J. Role of mineral aerosol as a reactive surface in the global troposphere. J. Geophys. Res. 1996, 101, 22869−22889. (72) Li, X.; Brauers, T.; Haseler, R.; Bohn, B.; Fuchs, H.; Hofzumahaus, A.; Holland, F.; Lou, S.; Lu, K. D.; Rohrer, F.; Hu,

M.; Zeng, L. M.; Zhang, Y. H.; Garland, R. M.; Su, H.; Nowak, A.; Wiedensohler, A.; Takegawa, N.; Shao, M.; Wahner, A. Exploring the atmospheric chemistry of nitrous acid (HONO) at a rural site in Southern China. Atmos. Chem. Phys. 2012, 12, 1497−1513. (73) Stutz, J.; Alicke, B.; Ackermann, R.; Geyer, A.; Wang, S. H.; White, A. B.; Williams, E. J.; Spicer, C. W.; Fast, J. D. Relative humidity dependence of HONO chemistry in urban areas. J. Geophys. Res 2004, 109, D03307. (74) Kleffmann, J. Daytime sources of nitrous acid (HONO) in the atmospheric boundary layer. ChemPhysChem 2007, 8, 1137−1144.

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Uptake of Gas Phase Nitrous Acid onto Boundary Layer Soil

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