Furan and alkylfurans are present in the atmosphere from direct emissions and in situ formation from other volatile organic compounds. The OH radical-initiated reactions of furan and alkylfurans have been proposed as relatively clean in situ sources of unsaturated 1,4-dicarbonyls, some of which are otherwise not readily available. Using a relative rate method, rate constants at 296 ± 2 K for the gas-phase reactions of OH radicals with 2- and 3-methylfuran, 2,3- and 2,5-dimethylfuran, and Z- and E-3-hexene-2,5-dione have been measured, of (in units of 10(-11) cm(3) molecule(-1) s(-1)): 2-methylfuran, 7.31 ± 0.35; 3-methylfuran, 8.73 ± 0.18; 2,3-dimethylfuran, 12.6 ± 0.4; 2,5-dimethylfuran, 12.5 ± 0.4; Z-3-hexene-2,5-dione, 5.90 ± 0.57; and E-3-hexene-2,5-dione, 4.14 ± 0.02. Products of the OH radical-initiated reaction of 2,5-dimethylfuran were investigated, with 3-hexene-2,5-dione being formed with molar yields of 24 ± 3% in the presence of NO and 34 ± 3% in the absence of NO. Direct air sampling atmospheric pressure ionization mass spectrometry showed the formation of additional products of molecular weight 114, attributed to CH(3)C(O)CH ═ CHC(O)OH and/or 5-hydroxy-5-methyl-2-furanone, and 128, attributed to CH(3)C(O)OC(CH(3)) = CHCHO.

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.

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).

Products of the gas-phase reactions of OH radicals with furan, furan-d 4, 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.

2-Formylcinnamaldehyde [O-HC(O)C6H4CH=CHCHO] is a major product of the OH radical-initiated reaction of naphthalene, the atmospherically most abundant polycyclic aromatic hydrocarbon. Previous studies indicate that 2-formylcinnamaldehyde undergoes photolysis as well as reaction with OH radicals. We have used direct air sampling atmospheric pressure ionization mass spectrometry (API-MS) to monitor 2-formylcinnamaldehyde as its protonated molecular ion during OH radical-initiated reactions of naphthalene. From the time-dependent behavior of the 2-formylcinnamaldehyde signal, ratios of (2-formylcinnamaldehyde removal rate/naphthalene reaction rate) were determined over a range of approximately 3 in (OH radical concentration/ light intensity). With an estimated rate constant for the reaction of OH radicals with 2-formylcinnamaldehyde of 5.3 x 10(-11) cm3 molecule(-1) s(-1), the photolysis rate of 2-formylcinnamaldhyde by blacklamps was determined to be approximately equal to that of NO2. Photolysis of 2-formylcinnamaldehyde will be the dominant loss process in the atmosphere, with an estimated lifetime of 2-formylcinnamaldehyde of approximately 120 s at a solar zenith angle of 30 degrees. Our data were used to re-evaluate the previous 2-formylcinnamaldehyde measurements of Sasaki et al. (Environ. Sci. Technol. 1997, 31, 3173-3179) and derive a 2-formylcinnamaldehyde formation yield from the OH radical reaction of naphthalene in the presence of NO of 56(-10)(+15)%.

We previously studied formation of 3-nitrotoluene (3NT), 1-and 2-nitronaphthalene (1NN and 2NN), and 3-nitrobiphenyl (3NBiPh) from the OH radical-initiated reactions of toluene, naphthalene, and biphenyl over the range 0.014-4.2 ppmV of NO 2 (1). Nitroaromatic formation was interpreted using the following reactions:

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).

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.