N2O5 Uptake Coefficient Research Articles

Kinetic of NO2 uptake by Phleum pratense pollen: Chemical and allergenic implications

Phleum pratense pollen was exposed to NO2 in a reactor allowing a continuous analysis of NO2 concentration by FTIR. The uptake coefficient of NO2 on pollen was calculated postulating a first order kinetic reaction and a value of (1.1 ± 0.1) × 10−7 was determined. NO2 uptake was faster when the pollen water content was increased and when the pollen was pre-treated with ozone. The effect of NO2 exposure on pollen allergic properties was investigated by quantifying Th2- and Th1-associated chemokines in a model of human dendritic cells. Cellular analysis clearly showed that cells exposed to fumigated pollen favored the production of chemokines known to promote Th2-cell responses. Altogether these data demonstrate that NO2 uptake by pollen directly correlates with increased Th2 response in human cells, and are in favor of the involvement of NO2 pollution in the increase of allergic diseases.

Heterogeneous reaction of NO2 on α-Al2O3 in the dark and simulated sunlight.

Although there have been a number of publications focused on heterogeneous of NO2 on mineral particles, most of these studies were focused on β-Al2O3 and performed in the dark. Less was known about the reaction process of NO2 on α-Al2O3, especially the effect of sunlight factor. The heterogeneous reaction between NO2 and α-Al2O3 was investigated by using diffuse reflectance infrared Fourier transform spectrometry. The effects of NO2 and O2 concentrations as well as simulated sunlight were examined, and the reaction mechanism including the consumption of surface OH groups, oxidation process of nitrites, and the formation of water was also discussed in detail. It was observed that the formation rates of nitrates and nitrites were sensitive to NO2 concentrations and O2 concentrations. Nitrite was identified to be an intermediate production and disappeared very soon as [NO2] was up to 4.035 × 10(15) molecules/cm(3). Light played an important role in the changes of the electronic configuration of mineral dust, such as electronic donating ability, surface OH groups orientation, as well as the conversion efficiency between proton acid and nonproton acid, all of which could significantly enhance the heterogeneous reaction process. The reaction order for NO2 and O2 was determined to be 0.960 ± 0.111 and 0.620 ± 0.028, respectively. The uptake coefficient of NO2, which dominated the first step of the heterogeneous reaction, was calculated by the infrared absorbance with the use of ion chromatography and determined to be 9.9 × 10(-10) in the dark and varied from 2.54 to 3.33 × 10(-9) under simulated sunlight from 0.45 to 1.35 mW/cm(2). It was also found that γNO2 was independent of [NO2] and sunlight increased the uptake coefficient by three times, indicating that the heterogeneous reaction between NO2 and α-Al2O3 was enhanced under sunlight.

Heterogeneous reaction of N<sub>2</sub>O<sub>5</sub> with airborne TiO<sub>2</sub> particles and its implication for stratospheric particle injection

Abstract. Injection of aerosol particles (or their precursors) into the stratosphere to scatter solar radiation back into space has been suggested as a solar-radiation management scheme for the mitigation of global warming. TiO2 has recently been highlighted as a possible candidate particle because of its high refractive index, but its impact on stratospheric chemistry via heterogeneous reactions is as yet unknown. In this work the heterogeneous reaction of airborne sub-micrometre TiO2 particles with N2O5 has been investigated for the first time, at room temperature and different relative humidities (RH), using an atmospheric pressure aerosol flow tube. The uptake coefficient of N2O5 onto TiO2, γ(N2O5), was determined to be ~1.0 × 10−3 at low RH, increasing to ~3 × 10−3 at 60% RH. The uptake of N2O5 onto TiO2 is then included in the UKCA chemistry–climate model to assess the impact of this reaction on stratospheric chemistry. While the impact of TiO2 on the scattering of solar radiation is chosen to be similar to the aerosol from the Mt Pinatubo eruption, the impact of TiO2 injection on stratospheric N2O5 is much smaller.

Reactive uptake of N<sub>2</sub>O<sub>5</sub> to internally mixed inorganic and organic particles: the role of organic carbon oxidation state and inferred organic phase separations

Abstract. We measured N2O5 reactive uptake onto mixed organic/inorganic submicron particles using organic compounds with a variety of oxidation states (using mainly atomic O : C ratios as a proxy) and molecular weights. The organic mass fraction, organic molecular composition, and relative humidity (RH) were varied to assess their effects separately on the N2O5 uptake coefficient, γ(N2O5). At a constant RH, mixtures of organic components having an O : C < 0.5 with ammonium bisulfate significantly suppressed the uptake of N2O5(g) compared to pure ammonium bisulfate, even at small organic mass fractions (e.g., ≤ 15%). The effect of the organic component became less pronounced at higher RH. In general, highly oxygenated organic components (O : C > 0.8) had a smaller or even negligible impact on N2O5(g) uptake at all RHs probed; however, a few exceptions were observed. Notably, γ(N2O5) for mixtures of ammonium bisulfate with polyethylene glycol (PEG), PEG-300 (O : C = 0.56), decreased nearly linearly as the PEG mass fraction increased at constant RH until leveling off at the value measured for pure PEG. The response of γ(N2O5) to increasing PEG mass fraction was similar to that measured on ambient atmospheric particles as a function of organic mass fraction. The effects of the organic mass fraction on γ(N2O5), for mixtures having an O : C < ~0.8, were best described using a standard resistor model of reactive uptake assuming the particles had an RH-dependent inorganic core–organic shell morphology. This model suggests that the N2O5 diffusivity and/or solubility in the organic layer is up to a factor of 20 lower compared to aqueous solution particles, and that the diffusivity, solubility, and reactivity of N2O5 within organic coatings and particles depend upon both RH and the molecular composition of the organic medium. We use these dependencies and ambient measurements of organic aerosol from the global aerosol mass spectrometry (AMS) database to show that the typical impact of organic aerosol components is to both uniformly decrease γ(N2O5), by up to an order of magnitude depending on the RH, organic mass fraction, and O : C ratio, and to induce a stronger dependence of γ(N2O5) upon RH compared to purely inorganic aqueous solutions.

Heterogeneous reaction of N<sub>2</sub>O<sub>5</sub> with illite and Arizona test dust particles

Abstract. The heterogeneous reaction of N2O5 with airborne illite and Arizona test dust (ATD) particles was investigated at room temperature and at different relative humidities using an atmospheric pressure aerosol flow tube. N2O5 at concentrations in the range 8 to 24 × 1012 molecule cm−3 was monitored using thermal-dissociation cavity ring-down spectroscopy at 662 nm. At zero relative humidity a large uptake coefficient of N2O5 to illite was obtained, γ(N2O5) = 0.09, which decreased to 0.04 as relative humidity was increased to 67%. In contrast, the uptake coefficient derived for ATD is much lower (~0.006) and displays a weaker (if any) dependence on relative humidity (0–67%). Potential explanations are given for the significant differences between the uptake behaviour for ATD and illite and the results are compared with uptake coefficients for N2O5 on other mineral surfaces.

N2O5 uptake coefficients and nocturnal NO2 removal rates determined from ambient wintertime measurements

Heterogeneous N2O5 uptake onto aerosol is the primary nocturnal path for removal of NOx (= NO + NO2) from the atmosphere and can also result in halogen activation through production of ClNO2. The N2O5 uptake coefficient has been the subject of numerous laboratory studies; however, only a few studies have determined the uptake coefficient from ambient measurements, and none has been focused on winter conditions, when the portion of NOx removed by N2O5 uptake is the largest. In this work, N2O5 uptake coefficients are determined from ambient wintertime measurements of N2O5 and related species at the Boulder Atmospheric Observatory in Weld County, CO, a location that is highly impacted by urban pollution from Denver, as well as emissions from agricultural activities and oil and gas extraction. A box model is used to analyze the nocturnal nitrate radical chemistry and predict the N2O5 concentration. The uptake coefficient in the model is iterated until the predicted N2O5 concentration matches the measured concentration. The results suggest that during winter, the most important influence that might suppress N2O5 uptake is aerosol nitrate but that this effect does not suppress uptake coefficients enough to limit the rate of NOx loss through N2O5 hydrolysis. N2O5 hydrolysis was found to dominate the nocturnal chemistry during this study consuming ~80% of nocturnal gas phase nitrate radical production. Typically, less than 15% of the total nitrate radical production remained in the form of nocturnal species at sunrise when they are photolyzed and reform NO2.

Role of Organic Carbon in Heterogeneous Reaction of NO2 with Soot

A large uncertainty among the reported uptake coefficients of NO2 on soot highlights the importance of the composition of soot in this reaction. Soot samples with different fractions of organic carbon (OC) were prepared by combusting n-hexane under controlled conditions. The heterogeneous reaction of NO2 on soot was investigated using a flow tube reactor at ambient pressure. The soot with the highest fuel/oxygen ratio showed the largest uptake coefficient (γ(initial)) of NO2 and yield of HONO (yHONO). Compared to fresh soot samples, preheated samples exhibited a great decrease in uptake coefficient of NO2 and HONO yield due to the removal of OC from soot. Ozonized soot also showed a lower reactivity toward NO2 than fresh soot, which can be ascribed to the consumption of OC with a reduced state (OCR). A linear dependence of the NO2 uptake coefficient and yields of HONO and NO on the OCR content of the soot was established, with γ(initial)(NO2) = (1.54 ± 1.39) × 10(-6) + (1.96 ± 0.35) × 10(-7) × OCR, yHONO = (11.6 ± 16.1) + (1.3 ± 0.40) × OCR, and yNO = (13.1 ± 1.9) - (0.2 ± 0.05) × OCR, respectively.

Simulation of nitrate, sulfate, and ammonium aerosols over the United States

Abstract. Atmospheric concentrations of inorganic gases and aerosols (nitrate, sulfate, and ammonium) are simulated for 2009 over the United States using the chemical transport model GEOS-Chem. Predicted aerosol concentrations are compared with surface-level measurement data from the Interagency Monitoring of Protected Visual Environments (IMPROVE), the Clean Air Status and Trends Network (CASTNET), and the California Air Resources Board (CARB). Sulfate predictions nationwide are in reasonably good agreement with observations, while nitrate and ammonium are over-predicted in the East and Midwest, but under-predicted in California, where observed concentrations are the highest in the country. Over-prediction of nitrate in the East and Midwest is consistent with results of recent studies, which suggest that nighttime nitric acid formation by heterogeneous hydrolysis of N2O5 is over-predicted based on current values of the N2O5 uptake coefficient, γ, onto aerosols. After reducing the value of γ by a factor of 10, predicted nitrate levels in the US Midwest and East still remain higher than those measured, and over-prediction of nitrate in this region remains unexplained. Comparison of model predictions with satellite measurements of ammonia from the Tropospheric Emissions Spectrometer (TES) indicates that ammonia emissions in GEOS-Chem are underestimated in California and that the nationwide seasonality applied to ammonia emissions in GEOS-Chem does not represent California very well, particularly underestimating winter emissions. An ammonia sensitivity study indicates that GEOS-Chem simulation of nitrate is ammonia-limited in southern California and much of the state, suggesting that an underestimate of ammonia emissions is likely the main cause for the under-prediction of nitrate aerosol in many areas of California. An approximate doubling of ammonia emissions is needed to reproduce observed nitrate concentrations in southern California and in other ammonia sensitive areas of California. However, even a tenfold increase in ammonia emissions yields predicted nitrate concentrations that are still biased low in the central valley of California. The under-prediction of nitrate aerosol in the central valley of California may arise in part from an under-prediction of both ammonia and nitric acid in this region. Since nitrate aerosols are particularly sensitive to mixed layer depths, owing to the gas-particle equilibrium, the nitrate under-prediction could also arise in part from a potential regional overestimate of GEOS-5 mixed layer depths in the central valley due to unresolved topography in this region.

Heterogeneous uptake of NO2 on soils under variable temperature and relative humidity conditions

Heterogeneous reactions of nitrogen dioxide (NO2) on soils collected from Dalian (S1) and Changsha (S2) were investigated over the relative humidity (RH) range of 5%–80% and temperature range of 278–328 K using a horizontal coated-wall flow tube. The initial uptake coefficients of NO2 on S2 exhibited a decreasing trend from (10 ± 1.3) × 10−8 to (3.1 ± 0.5) × 10−8 with the relative humidity increasing from 5% to 80%. In the temperature effect studies, the initial uptake coefficients of S1 and S2 decreased from (10 ± 1.2) × 10−8 to (3.8 ± 0.5) × 10−8 and from (16 ± 2.2) × 10−8 to (3.8 ± 0.4) × 10−8 when temperature increased from 278 to 288 K for S1 and from 278 to 308 K for S2, respectively. As the temperature continued to increase, the initial uptake coefficients of S1 and S2 returned to (7.9 ± 1.1) × 10−8 and (20 ± 3.1) × 10−8 at 313 and 328 K, respectively. This study shows that relative humidity could influence the uptake kinetics of NO2 on soil and temperature would impact the heterogeneous chemistry of NO2.

Interaction of NO<sub>2</sub> with TiO<sub>2</sub> surface under UV irradiation: measurements of the uptake coefficient

Abstract. The interaction of NO2 with TiO2 solid films was studied under UV irradiation using a low pressure flow reactor (1–10 Torr) combined with a modulated molecular beam mass spectrometer for monitoring of the gaseous species involved. The NO2 to TiO2 reactive uptake coefficient was measured from the kinetics of NO2 loss on TiO2 coated Pyrex rods as a function of NO2 concentration, irradiance intensity (JNO2 = 0.002–0.012 s−1), relative humidity (RH = 0.06–69 %), temperature (T = 275–320 K) and partial pressure of oxygen (0.001–3 Torr). TiO2 surface deactivation upon exposure to NO2 was observed. The initial uptake coefficient of NO2 on illuminated TiO2 surface (with 90 ppb of NO2 and JNO2≅0.006 s−1) was found to be γ0 = (1.2±0.4) ×10−4 (calculated using BET surface area) under dry conditions at T = 300 K. The steady state uptake, γ, was several tens of times lower than the initial one, independent of relative humidity, and was found to decrease in the presence of molecular oxygen. In addition, it was shown that γ is not linearly dependent on the photon flux and seems to level off under atmospheric conditions. Finally, the following expression for γ was derived, γ = 2.3×10−3 exp(−1910/T)/(1 + P0.36) (where P is O2 pressure in Torr), and recommended for atmospheric applications (for any RH, near 90 ppb of NO2 and JNO2 = 0.006 s−1).

Radicals in the marine boundary layer during NEAQS 2004: a model study of day-time and night-time sources and sinks

Abstract. This paper describes a modelling study of several HOx and NOx species (OH, HO2, organic peroxy radicals, NO3 and N2O5) in the marine boundary layer. A model based upon the Master Chemical Mechanism (MCM) was constrained to observations of chemical and physical parameters made onboard the NOAA ship R/V Brown as part of the New England Air Quality Study (NEAQS) in the summer of 2004. The model was used to calculate [OH] and to determine the composition of the peroxy radical pool. Modelled [NO3] and [N2O5] were compared to in-situ measurements by Cavity Ring-Down Spectroscopy. The comparison showed that the model generally overestimated the measurements by 30–50%, on average. The model results were analyzed with respect to several chemical and physical parameters, including uptake of NO3 and N2O5 on fog droplets and on aerosol, dry deposition of NO3 and N2O5, gas-phase hydrolysis of N2O5 and reactions of NO3 with NMHCs and peroxy radicals. The results suggest that fog, when present, is an important sink for N2O5 via rapid heterogeneous uptake. The comparison between the model and the measurements were consistent with values of the heterogeneous uptake coefficient of N2O5 (γN2O5)>1×10−2, independent of aerosol composition in this marine environment. The analysis of the different loss processes of the nitrate radical showed the important role of the organic peroxy radicals, which accounted for a significant fraction (median: 15%) of NO3 gas-phase removal, particularly in the presence of high concentrations of dimethyl sulphide (DMS).

Reactive uptake studies of NO3 and N2O5 on alkenoic acid, alkanoate, and polyalcohol substrates to probe nighttime aerosol chemistry

Heterogeneous reactions between NO3 and N2O5 and diethyl sebacate (DES), glycerol, oleic acid (OA), linoleic acid (LA), and conjugated linoleic acid (CLA) were studied to understand better nighttime aerosol chemistry. The reactive uptake coefficient of NO3 on the liquid alkenoic acids (OA, LA, and CLA) was found to be >0.07, which is higher than previous results for unsaturated organics, including alkenoic acids. This reaction could potentially be an important loss process of particle-phase unsaturated organic compounds in the atmosphere and in laboratory secondary organic aerosol studies. The reactive uptake coefficient of N2O5 on liquid glycerol was also found to be relatively large with a value of (3.2-8.5)x10(-4), suggesting that N2O5 heterogeneous reactions with alcohols may also be atmospherically relevant. For all measurements with OA, CLA, and DES, the reactive uptake coefficients decreased significantly upon freezing. One possible explanation is that the liquid reaction is due to both a surface reaction and a bulk reaction and that the freezing process significantly decreases the importance of any bulk reactions. NO3 reactive uptake coefficients for liquid-phase compounds decreased in magnitude in the order: alkenoic acids>DES>glycerol. This is different compared to previous gas-phase studies and the difference may be due to the large viscosity of glycerol compared to the other organic compounds studied. N2O5 reactive uptake coefficients for liquid-phase compounds decreased in magnitude in the order: glycerol>LA>DES congruent with OA congruent with CLA.

A Novel Flow Reactor for Studying Reactions on Liquid Surfaces Coated by Organic Monolayers: Methods, Validation, and Initial Results

A new flow reactor has been developed that allows the study of heterogeneous kinetics on an aqueous surface coated by an organic monolayer. Computational fluid dynamics simulations have been used to determine the flow characteristics for various experimental conditions. In addition a mathematical framework has been developed to derive the true first-order wall loss rate coefficient, k(1st)(w), from the experimentally observed wall loss rate, k(obs). Validation of the new flow reactor is performed by measuring the uptake of O(3) by canola oil as a function of pressure and flow velocity and the reactive uptake coefficients of N(2)O(5) by aqueous 60 wt % and 80 wt % H(2)SO(4). Using this new flow reactor, we also determined the reactive uptake coefficient of N(2)O(5) on aqueous 80 wt % H(2)SO(4) solution coated with an 1-octadecanol (C(18)H(37)OH) monolayer. The uptake coefficient was determined as (8.1 +/- 3.2) x 10-4, which is about 2 orders of magnitude lower compared to the reactive uptake coefficient on a pure aqueous 80 wt % H(2)SO(4) solution. Our measured reactive uptake coefficient can be considered as a lower limit for the reactive uptake coefficient of aqueous aerosols coated with organic monolayers in the atmosphere, because in the atmosphere organic monolayers will likely also consist of surfactants with shorter lengths and branched structures which will have a smaller overall effect.

Variability in Nocturnal Nitrogen Oxide Processing and Its Role in Regional Air Quality

Nitrogen oxides in the lower troposphere catalyze the photochemical production of ozone (O3) pollution during the day but react to form nitric acid, oxidize hydrocarbons, and remove O3 at night. A key nocturnal reaction is the heterogeneous hydrolysis of dinitrogen pentoxide, N2O5. We report aircraft measurements of NO3 and N2O5, which show that the N2O5 uptake coefficient, g(N2O5), on aerosol particles is highly variable and depends strongly on aerosol composition, particularly sulfate content. The results have implications for the quantification of regional-scale O3 production and suggest a stronger interaction between anthropogenic sulfur and nitrogen oxide emissions than previously recognized.

Nitrogen dioxide multiphase chemistry: Uptake kinetics on aqueous solutions containing phenolic compounds

The uptake coefficients of NO2 on aqueous solutions containing guaiacol, syringol and catechol were determined over the pH range from 1 to 13 using the wetted wall flowtube technique. The measured uptake coefficients were used to determine the rate coefficients for the reaction of the physically dissolved NO2 with the neutral and deprotonated forms of phenolic compounds listed above. These organic compounds are ubiquitous not only in biomass burning plumes but also in soils, where they form part of the building blocks of humic acids. The NO2 uptake kinetics on solutions containing guaiacol, syringol or catechol were observed to be strongly pH dependent with uptake coefficients increasing from below 10(-7), under acidic conditions, to more than 10(-5) at pH values above 10. This behaviour illustrates the difference of reactivity between the neutral phenolic species and the phenoxide ions. The corresponding second order rate coefficients were typically observed to increase from 10(5) M(-1) s(-1) for the neutral compounds to a minimum of 10(8) M(-1) s(-1) for the phenoxide ions.

Heterogeneous conversion of NO<sub>2</sub> on secondary organic aerosol surfaces: A possible source of nitrous acid (HONO) in the atmosphere?

Abstract. The heterogeneous conversion of NO2 on different secondary organic aerosols (SOA) was investigated with the focus on a possible formation of nitrous acid (HONO). In one set of experiments different organic aerosols were produced in the reactions of O3 with alpha-pinene, limonene or catechol and OH radicals with toluene or limonene, respectively. The aerosols were sampled on filters and exposed to humidified NO2 mixtures under atmospheric conditions. The estimated upper limits for the uptake coefficients of NO2 and the reactive uptake coefficients NO2 -> HONO are in the range of 10-6 and 10-7, respectively. The integrated HONO formation for 1 h reaction time was <1013 cm-2 geometrical surface and <1017 g-1 particle mass. In a second set of experiments the conversion of NO2 into HONO in the presence of organic particles was carried out in an aerosol flow tube under atmospheric conditions. In this case the aerosols were produced in the reaction of O3 with beta-pinene, limonene or catechol, respectively. The upper limits for the reactive uptake coefficients NO2 -> HONO were in the range of 7 x 10-7 - 9 x 10-6. The results from the present study show that heterogeneous formation of nitrous acid on secondary organic aerosols (SOA) is unimportant for the atmosphere.

Reaction Kinetics of NO2 with Resorcinol and 2,7-Naphthalenediol in the Aqueous Phase at Different pH

The uptake coefficients of NO2 on buffered solutions containing m-dihydroxy benzene (resorcinol) or 2,7-dihydroxynaphthalene (Np(OH)2) were determined over the pH range from 3 to 11 using the wetted wall flow tube technique. The nominal reactant concentration was also varied by several orders of magnitude. Taking into account gas phase as well as liquid-phase diffusion, the uptake coefficients were interpreted using a simple model of stepwise deprotonation of these two weak bivalent acids. This model yields the rate constants for the reaction of NO2 with the neutral, singly, and doubly deprotonated forms of both compounds. While the reaction of NO2 with the neutral form is very slow (i.e., with rate constants of a few times 102 M-1 s-1), the reaction of NO2 with the deprotonated species is much faster (rate constants are reaching levels of several 106 M-1 s-1). The rate constant of 3.8 × 108 M-1 s-1 for NO2 with the doubly deprotonated resorcinol ion is in good agreement with the one found by Alfassi, the only reported literature value (Alfassi, Z. B.; Huie, R. E.; Neta, P. J. Phys. Chem. 1986, 90, 4156).

The heterogeneous reaction of N2O5 with HBr on Ice comparison with N2O5+HCl

AbstractThe heterogeneous reactions of N2O5 with HCl and HBr on ice have been studied in the temperature range 180 to 200 K using a Knudsen flow reactor.The uptake of N2O5 on ice in the presence of HBr was found to be strongly dependent on the HBr concentration. For the highest HBr concentrations used a maximum uptake coefficient of N2O5 of γ=0.11 has been determined. We observed Br2 and HONO in 80% yield as products with respect to N2O5 taken up. The uptake coefficient of N2O5 on ice in the presence of HCl was found to be 3.2·10−2 and increased with increasing HCl concentration. CINO2 was detected as the sole reaction product with a maximum yield of 63% with respect to N2O5 consumed.Hydrolysis of N2O5 resulting in HNO3 was found to be competitive with the title reaction. For the case of the HBr reaction the branching ratio between Br2 and HONO formation, on the one hand, and hydrolysis of N2O5, on the other hand, has been determined. Mechanistic aspects of the heterogeneous reaction of N2O5 with HX have been discussed.