Noriko Nishino

Formation yields of glyoxal and methylglyoxal from the gas-phase OH radical-initiated reactions of toluene, xylenes, and trimethylbenzenes as a function of NO2 concentration.

Aromatic hydrocarbons comprise 20% of non-methane volatile organic compounds in urban areas and are transformed mainly by atmospheric chemical reactions with OH radicals during daytime. In this work we have measured the formation yields of glyoxal and methylglyoxal from the OH radical-initiated reactions of toluene, xylenes, and trimethylbenzenes over the NO2 concentration range (0.2-10.3) × 1013 molecules cm(-3). For toluene, o-, m-, and p-xylene, and 1,3,5-trimethylbenzene, the yields showed a dependence on NO2, decreasing with increasing NO2 concentration and with no evidence for formation of glyoxal or methylglyoxal from the reactions of the OH-aromatic adducts with NO2. In contrast, for 1,2,3- and 1,2,4-trimethylbenzene the glyoxal and methylglyoxal formation yields were independent of the NO2 concentration within the experimental uncertainties. Extrapolations of our results to NO2 concentrations representative of the ambient atmosphere results in the following glyoxal and methylglyoxal yields, respectively: for toluene, 26.0 ± 2.2% and 21.5 ± 2.9%; for o-xylene, 12.7 ± 1.9% and 33.1 ± 6.1%; for m-xylene, 11.4 ± 0.7% and 51.5 ± 8.5%; for p-xylene, 38.9 ± 4.7% and 18.7 ± 2.2%; for 1,2,3-trimethylbenzene, 4.7 ± 2.4% and 15.1 ± 3.3%; for 1,2,4-trimethylbenzene, 8.7 ± 1.6% and 27.2 ± 8.1%; and for 1,3,5-trimethylbenzene, 58.1 ± 5.3% (methylglyoxal).

Formation of nitro products from the gas-phase OH radical-initiated reactions of toluene, naphthalene, and biphenyl: effect of NO2 concentration.

Aromatic hydrocarbons, including polycyclic aromatic hydrocarbons (PAHs), are released into the atmosphere principally during incomplete combustion and account for approximately 20% of nonmethane organic compounds in urban air. Reaction with OH radicals is the dominant atmospheric chemical loss process for aromatic hydrocarbons, leading mainly to the formation of an OH-aromatic or OH-PAH adduct which then reacts with O2 and/or NO2. For OH-monocyclic aromatic adducts, reaction with O2 dominates under atmospheric conditions; however, no data are available concerning the relative importance of reactions of OH-PAH adducts with O2 and NO2. We have measured formation yields of 3-nitrotoluene, 1- and 2-nitronaphthalene, and 3-nitrobiphenyl from the OH radical-initiated reactions of toluene, naphthalene, and biphenyl as a function of NO2 concentration. Our data showthatthe OH-aromatic adduct reactions with O2 and NO2 are of equal importance in the atmosphere at NO2 mixing ratios of approximately 3.3 ppmV for toluene, approximately 0.06 ppmV for naphthalene, and approximately 0.6 ppmV for biphenyl. Ambient concentrations of toluene, naphthalene, and biphenyl and their nitrated products measured at a site in the Los Angeles air basin are consistent with our laboratory measurements.

Nitrate Ion Photolysis in Thin Water Films in the Presence of Bromide Ions

Nitrate ions commonly coexist with halide ions in aged sea salt particles, as well as in the Arctic snowpack, where NO(3)(-) photochemistry is believed to be an important source of NO(y) (NO + NO(2) + HONO + ...). The effects of bromide ions on nitrate ion photochemistry were investigated at 298 ± 2 K in air using 311 nm photolysis lamps. Reactions were carried out using NaBr/NaNO(3) and KBr/KNO(3) deposited on the walls of a Teflon chamber. Gas phase halogen products and NO(2) were measured as a function of photolysis time using long path FTIR, NO(y) chemiluminescence and atmospheric pressure ionization mass spectrometry (API-MS). Irradiated NaBr/NaNO(3) mixtures show an enhancement in the rates of production of NO(2) and Br(2) as the bromide mole fraction (χ(NaBr)) increased. However, this was not the case for KBr/KNO(3) mixtures where the rates of production of NO(2) and Br(2) remained constant over all values of χ(KBr). Molecular dynamics (MD) simulations show that the presence of bromide in the NaBr solutions pulls sodium toward the solution surface, which in turn attracts nitrate to the interfacial region, allowing for more efficient escape of NO(2) than in the absence of halides. However, in the case of KBr/KNO(3), bromide ions do not appreciably affect the distribution of nitrate ions at the interface. Clustering of Br(-) with NO(3)(-) and H(2)O predicted by MD simulations for sodium salts may facilitate a direct intermolecular reaction, which could also contribute to higher rates of NO(2) production. Enhanced photochemistry in the presence of halide ions may be important for oxides of nitrogen production in field studies such as in polar snowpacks where the use of quantum yields from laboratory studies in the absence of halide ions would lead to a significant underestimate of the photolysis rates of nitrate ions.

2-Formylcinnamaldehyde formation yield from the OH radical-initiated reaction of naphthalene: effect of NO(2) concentration.

Naphthalene, typically the most abundant polycyclic aromatic hydrocarbon in the atmosphere, reacts with OH radicals by addition to form OH-naphthalene adducts. These OH-naphthalene adducts react with O(2) and NO(2), with the two reactions being of equal importance in air at an NO(2) mixing ratio of ∼60 ppbv. 2-Formylcinnamaldehyde [o-HC(O)C(6)H(4)CH═CHCHO] is a major product of the OH radical-initiated reaction of naphthalene, with a yield from the reaction of OH-naphthalene adducts with NO(2) of ∼56%. We have measured, on a relative basis, the formation yield of 2-formylcinnamaldehyde from the OH radical-initiated reaction of naphthalene in air at average NO(2) concentrations of 1.2 × 10(11), 1.44 × 10(12), and 1.44 × 10(13) molecules cm(-3) (mixing ratios of 0.005, 0.06, and 0.6 ppmv, respectively). These NO(2) concentrations cover the range of conditions corresponding to the OH-naphthalene adducts reacting ∼90% of the time with O(2) to ∼90% of the time with NO(2). The 2-formylcinnamaldehyde formation yield decreased with decreasing NO(2) concentration, and a yield from the OH-naphthalene adducts + O(2) reaction of 14% is obtained based on a 56% yield from the OH-naphthalene adducts + NO(2) reaction. Based on previous measurements of glyoxal and phthaldialdehyde from the naphthalene + OH reaction and literature data for the OH radical-initiated reactions of monocyclic aromatic hydrocarbons, the reactions of OH-naphthalene adducts with O(2) appear to differ significantly from the OH-monocyclic adduct + O(2) reactions.

Yields of glyoxal and ring-cleavage co-products from the OH radical-initiated reactions of naphthalene and selected alkylnaphthalenes.

Naphthalene and alkylnaphthalenes are the most abundant polycyclic aromatic hydrocarbons present in ambient air and are transformed mainly by chemical reaction with hydroxyl (OH) radicals during daylight hours. To better understand the reaction mechanisms, we have quantified glyoxal from the OH radical-initiated reactions of naphthalene, 1-methylnaphthalene, 1,4-dimethylnaphthalene, acenaphthene, and acenaphthylene as a function of the NO(2) concentration and, for the naphthalene reaction, also in the absence of NO(2). Glyoxal was formed as a first-generation product from the naphthalene, 1-methylnaphthalene, 1,4-dimethylnaphthalene, and acenaphthene reactions, and its yields were independent of the NO(2) concentration over the ranges employed, being 5% in the presence of NO(2) and 3% in the absence of NO(2) from naphthalene; approximately 3% from 1-methylnaphthalene; approximately 2% from 1,4-dimethylnaphthalene; approximately 10-15% from acenaphthene; and <2% from acenaphthylene. Second-generation formation of glyoxal was evident in the 1-methylnaphthalene, 1,4-dimethylnaphthalene, and acenaphthene reactions. For the naphthalene reaction, our results suggest that the reactions of the OH-naphthalene adducts with NO(2) and O(2) both lead to glyoxal formation in similar yield. Simultaneous measurements of phthaldialdehyde from naphthalene, 2-acetylbenzaldehyde from 1-methylnaphthalene, and 1,2-diacetylbenzene from 1,4-dimethylnaphthalene suggest that these C(n-2)-dicarbonyls are coproducts to glyoxal.

Rate constants for the gas-phase reactions of OH radicals with a series of C6-C14 alkenes at 299 +/- 2 K.

Rate constants for the gas-phase reactions of OH radicals with the C(6)-C(14) 2-methyl-1-alkenes and the C(6)-C(10) trans-2-alkenes have been measured at 299 +/- 2 K and atmospheric pressure of air using a relative rate technique. The rate constants obtained (in units of 10(-11) cm(3) molecule(-1) s(-1)) were as follows: 2-methyl-1-pentene, 5.67 +/- 0.21; 2-methyl-1-hexene, 6.50 +/- 0.11; 2-methyl-1-heptene, 6.71 +/- 0.21; 2-methyl-1-octene, 7.02 +/- 0.16; 2-methyl-1-nonene, 7.28 +/- 0.21; 2-methyl-1-decene, 7.85 +/- 0.26; 2-methyl-1-undecene, 7.85 +/- 0.21; 2-methyl-1-dodecene, 7.96 +/- 0.26; 2-methyl-1-tridecene, 8.06 +/- 0.37; trans-2-hexene, 6.08 +/- 0.26; trans-2-heptene, 6.76 +/- 0.32; trans-2-octene, 7.23 +/- 0.21; trans-2-nonene, 7.54 +/- 0.16; and trans-2-decene, 7.80 +/- 0.26, where the indicated errors are two least-squares standard deviations and do not include the uncertainty associated with the rate constant for the reference compound alpha-pinene. Our data show that the rate constants for the reactions of OH radicals with 2-methyl-1-alkenes and trans-2-alkenes increase with increasing carbon number, suggesting that this is in part due to H-atom abstraction from the C-H bonds of the alkyl substituent groups. Combined with previous literature data for the reactions of OH radicals with a series of 1-alkenes, we propose that the increase in rate constant with increasing carbon number is due to H-atom abstraction from the C-H bonds of the alkyl substituent groups and to enhancement of the rate constant for OH radical addition to the C=C bond, which increases with carbon number of a C(n)-alkyl substituent group up to a maximum at approximately C(8).

Products of the OH radical-initiated reactions of furan, 2- and 3-methylfuran, and 2,3- and 2,5-dimethylfuran in the presence of NO.

Products of the gas-phase reactions of OH radicals with furan, furan-d4, 2- and 3-methylfuran, and 2,3- and 2,5-dimethylfuran have been investigated in the presence of NO using direct air sampling atmospheric pressure ionization tandem mass spectrometry (API-MS and API-MS/MS), and gas chromatography with flame ionization and mass spectrometric detectors (GC-FID and GC-MS) to analyze samples collected onto annular denuders coated with XAD solid adsorbent and further coated with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine for derivatization of carbonyl-containing compounds to their oximes. The products observed were unsaturated 1,4-dicarbonyls, unsaturated carbonyl-acids and/or hydroxy-furanones, and from 2,5-dimethylfuran, an unsaturated carbonyl-ester. Quantification of the unsaturated 1,4-dicarbonyls was carried out by GC-FID using 2,5-hexanedione as an internal standard, and the measured molar formation yields were: HC(O)CH═CHCHO (dominantly the E-isomer) from OH + furan, 75 ± 5%; CH3C(O)CH═CHCHO (dominantly the E-isomer) from OH + 2-methylfuran, 31 ± 5%; HC(O)C(CH3)═CHCHO (a E-/Z-mixture) from OH + 3-methylfuran, 38 ± 2%; and CH3C(O)C(CH3)═CHCHO from OH + 2,3-dimethylfuran, 8 ± 2%. In addition, a formation yield of 3-hexene-2,5-dione from OH + 2,5-dimethylfuran of 27% was obtained from a single experiment, in good agreement with a previous value of 24 ± 3% from GC-FID analyses of samples collected onto Tenax solid adsorbent without derivatization.

Production of gas phase NO2 and halogens from the photolysis of thin water films containing nitrate, chloride and bromide ions at room temperature

Nitrate and halide ions coexist in particles generated in marine regions, around alkaline dry lakes, and in the Arctic snowpack. Although the photochemistry of nitrate ions in bulk aqueous solution is well known, there is recent evidence that it may be more efficient at liquid-gas interfaces, and that the presence of other ions in solution may enhance interfacial reactivity. This study examines the 311 nm photolysis of thin aqueous films of ternary halide-nitrate salt mixtures (NaCl-NaBr-NaNO3) deposited on the walls of a Teflon chamber at 298 K. The films were generated by nebulizing aqueous 0.25 M NaNO3 solutions which had NaCl and NaBr added to vary the mole fraction of halide ions. Molar ratios of chloride to bromide ions were chosen to be 0.25, 1.0, or 4.0. The subsequent generation of gas phase NO2 and reactive halogen gases (Br2, BrCl and Cl2) were monitored with time. The rate of gas phase NO2 formation was shown to be enhanced by the addition of the halide ions to thin films containing only aqueous NaNO3. At [Cl(-)]/[Br(-)] ≤ 1.0, the NO2 enhancement was similar to that observed for binary NaBr-NaNO3 mixtures, while with excess chloride NO2 enhancement was similar to that observed for binary NaCl-NaNO3 mixtures. Molecular dynamics simulations predict that the halide ions draw nitrate ions closer to the interface where a less complete solvent shell allows more efficient escape of NO2 to the gas phase, and that bromide ions are more effective in bringing nitrate ions closer to the surface. The combination of theory and experiments suggests that under atmospheric conditions where nitrate ion photochemistry plays a role, the impact of other species such as halide ions should be taken into account in predicting the impacts of nitrate ion photochemistry.

Infrared Studies of the Reaction of Methanesulfonic Acid with Trimethylamine on Surfaces

Organosulfur compounds generated from a variety of biological as well as anthropogenic sources are oxidized in air to form sulfuric acid and methanesulfonic acid (MSA). Both of these acids formed initially in the gas phase react with ammonia and amines in air to form and grow new particles, which is important for visibility, human health and climate. A competing sink is deposition on surfaces in the boundary layer. However, relatively little is known about reactions after they deposit on surfaces. We report here diffuse reflectance infrared Fourier transform spectrometry (DRIFTS) studies of the reaction of MSA with trimethylamine (TMA) on a silicon powder at atmospheric pressure in synthetic air and at room temperature, either in the absence or in the presence of water vapor. In both cases, DRIFTS spectra of the product surface species are essentially the same as the transmission spectrum obtained for trimethylaminium methanesulfonate, indicating the formation of the salt on the surface with a lower limit to the reaction probability of γ > 10(-6). To the best of our knowledge, this is the first infrared study to demonstrate this chemistry from the heterogeneous reaction of MSA with an amine on a surface. This heterogeneous chemistry appears to be sufficiently fast that it could impact measurements of gas-phase amines through reactions with surface-adsorbed acids on sampling lines and inlets. It could also represent an additional sink for amines in the boundary layer, especially at night when the gas-phase reactions of amines with OH radical and ozone are minimized.

Thermal and photochemical reactions of NO2 on chromium(III) oxide surfaces at atmospheric pressure

While many studies of heterogeneous chemistry on Cr(2)O(3) surfaces have focused on its catalytic activity, less is known about chemistry on this surface under atmospheric conditions. We report here studies of the thermal and photochemical reactions of NO(2) on Cr(2)O(3) at one atm in air. In order to follow surface species, the interaction of 16-120 ppm NO(2) with a 15 nm Cr(2)O(3) thin film deposited on a germanium crystal was monitored in a flow system using attenuated total reflectance (ATR) coupled to a Fourier transform infrared (FTIR) spectrometer. Gas phase products were monitored in the effluent of an ~285 ppm NO(2)-air mixture that had passed over Cr(2)O(3) powder in a flow system. A chemiluminescence NO(y) analyzer, a photometric O(3) analyzer and a long-path FTIR spectrometer were used to probe the gaseous products. In the absence of added water vapor, NO(2) formed nitrate (NO(3)(-)) ions coordinated to Cr(3+). These surface coordinated NO(3)(-) were reversibly solvated by water under humid conditions. In both dry and humid cases, nitrate ions decreased during irradiation of the surface at 302 nm, and NO and NO(2) were generated in the gas phase. Under dry conditions, NO was the major gaseous product while NO(2) was the dominant species in the presence of water vapor. Heating of the surface after exposure to NO(2) led to the generation of both NO(2) and NO under dry conditions, but only NO(2) in the presence of water vapor. Elemental chromium incorporated into metal alloys such as stainless steel is readily oxidized in contact with ambient air, forming a chromium-rich metal oxide surface layer. The results of these studies suggest that active photo- and thermal chemistry will occur when boundary layer materials containing chromium(III) or chromium oxide such as stainless steel, roofs, automobile bumpers etc. are exposed to NO(2) under tropospheric conditions.