Heterogeneous reactions of particulate matter-bound PAHs and NPAHs with NO3/N2O5, OH radicals, and O3 under simulated long-range atmospheric transport conditions: reactivity and mutagenicity.

The heterogeneous reactions of ambient particulate matter (PM)-bound polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs (NPAHs) with NO3/N2O5, OH radicals, and O3 were studied in a laboratory photochemical chamber. Ambient PM2.5 and PM10 samples were collected from Beijing, China, and Riverside, California, and exposed under simulated atmospheric long-range transport conditions for O3 and OH and NO3 radicals. Changes in the masses of 23 PAHs and 20 NPAHs, as well as the direct and indirect-acting mutagenicity of the PM (determined using the Salmonella mutagenicity assay with TA98 strain), were measured prior to and after exposure to NO3/N2O5, OH radicals, and O3. In general, O3 exposure resulted in the highest relative degradation of PM-bound PAHs with more than four rings (benzo[a]pyrene was degraded equally well by O3 and NO3/N2O5). However, NPAHs were most effectively formed during the Beijing PM exposure to NO3/N2O5. In ambient air, 2-nitrofluoranthene (2-NF) is formed from the gas-phase NO3 radical- and OH radical-initiated reactions of fluoranthene, and 2-nitropyrene (2-NP) is formed from the gas-phase OH radical-initiated reaction of pyrene. There was no formation of 2-NF or 2-NP in any of the heterogeneous exposures, suggesting that gas-phase formation of NPAHs did not play an important role during chamber exposures. Exposure of Beijing PM to NO3/N2O5 resulted in an increase in direct-acting mutagenic activity which was associated with the formation of mutagenic NPAHs. No NPAH formation was observed in any of the exposures of the Riverside PM. This was likely due to the accumulation of atmospheric degradation products from gas-phase reactions of volatile species onto the surface of PM collected in Riverside prior to exposure in the chamber, thus decreasing the availability of PAHs for reaction.

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.

Novel nitro-PAH formation from heterogeneous reactions of PAHs with NO2, NO3/N2O5, and OH radicals: prediction, laboratory studies, and mutagenicity.

The heterogeneous reactions of benzo[a]pyrene-d12 (BaP-d12), benzo[k]fluoranthene-d12 (BkF-d12), benzo[ghi]perylene-d12 (BghiP-d12), dibenzo[a,i]pyrene-d14 (DaiP-d14), and dibenzo[a,l]pyrene (DalP) with NO2, NO3/N2O5, and OH radicals were investigated at room temperature and atmospheric pressure in an indoor Teflon chamber and novel mono-NO2-DaiP and mono-NO2-DalP products were identified. Quartz fiber filters (QFF) were used as a reaction surface and the filter extracts were analyzed by GC/MS for nitrated-PAHs (NPAHs) and tested in the Salmonella mutagenicity assay, using Salmonella typhimurium strain TA98 (with and without metabolic activation). In parallel to the laboratory experiments, a theoretical study was conducted to rationalize the formation of NPAH isomers based on the thermodynamic stability of OH-PAH intermediates, formed from OH-radical-initiated reactions. NO2 and NO3/N2O5 were effective oxidizing agents in transforming PAHs to NPAHs, with BaP-d12 being the most readily nitrated. Reaction of BaP-d12, BkF-d12, and BghiP-d12 with NO2 and NO3/N2O5 resulted in the formation of more than one mononitro isomer product, while the reaction of DaiP-d14 and DalP resulted in the formation of only one mononitro isomer product. The direct-acting mutagenicity increased the most after NO3/N2O5 exposure, particularly for BkF-d12 in which di-NO2-BkF-d10 isomers were measured. The deuterium isotope effect study suggested that substitution of deuterium for hydrogen lowered both the direct and indirect acting mutagenicity of NPAHs and may result in an underestimation of the mutagencity of the novel NPAHs identified in this study.

Atmospheric chemistry of methyl and ethyl N,N,N',N'-tetramethylphosphorodiamidate and O,S-dimethyl methylphosphonothioate.

Rate constants for the reactions of OH radicals with methyl N,N,N',N'-tetramethylphosphorodiamidate [CH3OP(O)[N(CH3)2]2; MTMPDA], ethyl N,N,N',N'-tetramethylphosphorodiamidate [C2H5OP(O)[N(CH3)2]2; ETMPDA], and O,S-dimethyl methylphosphonothioate [CH3OP(O)(CH3)SCH3; OSDMMP] have been measured over the temperature range 281-349 K at atmospheric pressure of air using a relative rate method. The rate expressions obtained were 4.96 × 10(-12) e((1058±71)/T) cm(3) molecule(-1) s(-1) (1.73 × 10(-10) cm(3) molecule(-1) s(-1) at 298 K) for OH + MTMPDA, 4.46 × 10(-12) e((1144±95)/T) cm(3) molecule(-1) s(-1) (2.07 × 10(-10) cm(3) molecule(-1) s(-1) at 298 K) for OH + ETMPDA, and 1.31 × 10(-13) e((1370±229)/T) cm(3) molecule(-1) s(-1) (1.30 × 10(-11) cm(3) molecule(-1) s(-1) at 298 K) for OH + OSDMMP. The rate constant for OH + OSDMMP was independent of O2 content over the range 2.1-71% O2 at 296 ± 2 K. In addition, rate constants for the reactions of NO3 radicals and O3 with MTMPDA, of (1.4 ± 0.1) × 10(-12) cm(3) molecule(-1) s(-1) and <3.5 × 10(-19) cm(3) molecule(-1) s(-1), respectively, were measured at 297 ± 2 K. Products of the OH radical- and, for MTMPDA, NO3 radical-initiated reactions were investigated using gas chromatography and in situ atmospheric pressure ionization mass spectrometry. A product of molecular weight 180 was observed from the OH and NO3 radical-initiated reactions of MTMPDA, and this is attributed to CH3OP(O)[N(CH3)2]N(CH3)CHO. Similarly, a product of molecular weight 194 was observed from the OH + ETMPDA reaction and attributed to C2H5OP(O)[N(CH3)2]N(CH3)CHO. Possible reaction mechanisms are discussed.

Study of the atmospheric chemistry of 2-formylcinnamaldehyde.

2-Formylcinnamaldehyde is a significant product of the reaction of naphthalene with OH radicals, and its photolysis and gas-phase reactions with O3, NO3 radicals, and OH radicals have been investigated in this work. 2-Formylcinnamaldehyde was observed to undergo photolysis by black lamps, with a photolysis rate of 0.14 × J(NO2), where J(NO2) is the NO2 photolysis rate. The measured rate constants for the reactions of 2-formylcinnamaldehyde with O3, NO3 radicals, and OH radicals (in units of cm(3) molecule(-1) s(-1)) were 1.8 × 10(-18), 4.3 × 10(-14), and 2.1 × 10(-11), respectively, with those for the O3 and NO3 reactions being for the E-isomer. 2-Formylcinnamaldehyde was observed to undergo significant adsorption and desorption from the reaction chamber Teflon film walls, and the photolysis rate and rate constants are subject to significant uncertainties. In the atmosphere, the dominant chemical loss processes for 2-formylcinnamaldehyde will be photolysis during daylight hours and reaction with NO3 radicals during nighttime. Phthaldialdehyde and glyoxal were observed as products of the OH radical and O3 reactions, and photolysis of E-2-formylcinnamaldehyde led to formation of Z-2-formylcinnamaldehyde plus two other molecular weight 160 isomers. The present results are compared with previous literature data, and reaction mechanisms are discussed.

Formation of nitro-PAHs from the heterogeneous reaction of ambient particle-bound PAHs with N2O5/NO3/NO2.

Reactions of ambient particles collected from four sites within the Los Angeles, CA air basin and Beijing, China with a mixture of N2O5, NO2, and NO3 radicals were studied in an environmental chamber at ambient pressure and temperature. Exposures in the chamber system resulted in the degradation of particle-bound PAHs and formation of molecular weight (mw) 247 nitropyrenes (NPYs) and nitrofluoranthenes (NFLs), mw 273 nitrotriphenylenes (NTPs), nitrobenz[a]anthracenes (NBaAs), nitrochrysene (NCHR), and mw 297 nitrobenzo[a]pyrene (NBaP). The distinct isomer distributions resulting from exposure of filter-adsorbed deuterated fluoranthene to N2O5/NO3/NO2 and that collected from the chamber gas-phase suggest that formation of NFLs in ambient particles did not occur by NO3 radical-initiated reaction but from reaction of N2O5, presumably subsequent to its surface adsorption. Accordingly, isomers known to result from gas-phase radical-initiated reactions of parent PAHs, such as 2-NFL and 2- and 4-NPY, were not enhanced from the exposure of ambient particulate matter to N2O5/NO3/NO2. The reactivity of ambient particles toward nitration by N2O5/NO3/NO2, defined by relative 1-NPY formation, varied significantly, with the relative amounts of freshly emitted particles versus aged particles (particles that had undergone atmospheric chemical processing) affecting the reactivity of particle-bound PAHs toward heterogeneous nitration. Analyses of unexposed ambient samples suggested that, in nighttime samples where NO3 radical-initiated chemistry had occurred, heterogeneous formation of 1-NPY on ambient particles may have contributed to the ambient 1-NPY concentrations at downwind receptor sites. These results, together with observations that 2-NFL is consistently the dominant particle-bound nitro-PAH measured in ambient atmospheres, suggest that for PAHs that exist in both the gas- and particle-phase, the heterogeneous formation of particle-bound nitro-PAHs is a minor formation route compared to gas-phase formation.

Rate constants for the reactions of OH radicals with 1,2,4,5-tetramethylbenzene, pentamethylbenzene, 2,4,5-trimethylbenzaldehyde, 2,4,5-trimethylphenol, and 3-methyl-3-hexene-2,5-dione and products of OH + 1,2,4,5-tetramethylbenzene.

Using a relative rate method, rate constants have been measured for the reactions of OH radicals with 1,2,4,5-tetramethylbenzene, pentamethylbenzene, 2,4,5-trimethylbenzaldehyde, 2,4,5-trimethylphenol and 3-methyl-3-hexene-2,5-dione at 298 ± 2 K and atmospheric pressure of air. The rate constants obtained (in units of 10(-11) cm(3) molecule(-1) s(-1)) were: 1,2,4,5-tetramethylbenzene, 5.55 ± 0.34; pentamethylbenzene, 10.3 ± 0.8; 2,4,5-trimethylbenzaldehyde, 4.27 ± 0.39; 2,4,5-trimethylphenol, 9.75 ± 0.98; and 3-methyl-3-hexene-2,5-dione, 9.4 ± 1.1. The following first-generation products were identified from the OH + 1,2,4,5-tetramethylbenzene reaction in the presence of NO: biacetyl, methylglyoxal, 3-methyl-3-hexene-2,5-dione, and 2,4,5-trimethylbenzaldehyde. The measured molar formation yields for 3-methyl-3-hexene-2,5-dione and 2,4,5-trimethylbenzaldehyde were 45 ± 9% and 3.3 ± 0.7%, with that for 3-methyl-3-hexene-2,5-dione being extrapolated to low NO2 concentrations where the OH-1,2,4,5-tetramethylbenzene adducts react only with O2. Biacetyl appeared to be formed as both a first- and second-generation product, and a first-generation formation yield of 9 ± 3% was derived. The relative formation yield of methylglyoxal was ~0.8 of that for 3-methyl-3-hexene-2,5-dione, indicating that methylglyoxal and 3-methyl-3-hexene-2,5-dione are coproducts. H-atom abstraction from OH + 1,2,4,5-tetramethylbenzene is estimated to account for 3.7 ± 0.8% of the overall OH radical reaction. On the basis of the current understanding of the mechanism of the OH-aromatic adduct + O2 reaction, the observed formation of biacetyl indicates that some ipso addition of OH occurs for OH + 1,2,4,5-tetramethylbenzene.

Formation yields of C8 1,4-hydroxycarbonyls from OH + n-octane in the presence of NO.

1,4-Hydroxycarbonyls are major products of the OH radical-initiated reactions of ≥ C5 n-alkanes in the presence of NO. However, because of a lack of commercially available standards of 1,4-hydroxycarbonyls and difficulties in using gas chromatography for their analysis without prior derivatization, quantification of 1,4-hydroxycarbonyls in OH + alkane reactions has proven difficult. We have used an annular denuder coated with XAD resin and further coated with O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine for in situ derivatization of the 1,4-hydroxycarbonyls formed from the OH + n-octane reaction in the presence of NO. Quantification was achieved by using 2,5-hexanedione as an internal standard. Formation yields for (7-hydroxy-4-octanone + 6-hydroxy-3-octanone + 5-hydroxy-2-octanone) and of 4-hydroxyoctanal of 61 ± 11% and 2.1 ± 0.5%, respectively, were obtained. When combined with previously measured or estimated formation yields for octyl nitrates and hydroxyoctyl nitrates, 93 ± 15% of the overall reaction products are accounted for, indicating that no additional reaction pathways remain to be identified.

Kinetics, products, and mechanisms of secondary organic aerosol formation.

Secondary organic aerosol (SOA) is formed in the atmosphere when volatile organic compounds (VOCs) emitted from anthropogenic and biogenic sources are oxidized by reactions with OH radicals, O(3), NO(3) radicals, or Cl atoms to form less volatile products that subsequently partition into aerosol particles. Once in particles, these organic compounds can undergo heterogenous/multiphase reactions to form more highly oxidized or oligomeric products. SOA comprises a large fraction of atmospheric aerosol mass and can have significant effects on atmospheric chemistry, visibility, human health, and climate. Previous articles have reviewed the kinetics, products, and mechanisms of atmospheric VOC reactions and the general chemistry and physics involved in SOA formation. In this article we present a detailed review of VOC and heterogeneous/multiphase chemistry as they apply to SOA formation, with a focus on the effects of VOC molecular structure on the kinetics of initial reactions with the major atmospheric oxidants, the subsequent reactions of alkyl, alkyl peroxy, and alkoxy radical intermediates, and the composition of the resulting products. Structural features of reactants and products discussed include compound carbon number; linear, branched, and cyclic configurations; the presence of C[double bond, length as m-dash]C bonds and aromatic rings; and functional groups such as carbonyl, hydroxyl, ester, hydroxperoxy, carboxyl, peroxycarboxyl, nitrate, and peroxynitrate. The intention of this review is to provide atmospheric chemists with sufficient information to understand the dominant pathways by which the major classes of atmospheric VOCs react to form SOA products, and the further reactions of these products in particles. This will allow reasonable predictions to be made, based on molecular structure, about the kinetics, products, and mechanisms of VOC and heterogeneous/multiphase reactions, including the effects of important variables such as VOC, oxidant, and NO(x) concentrations as well as temperature, humidity, and particle acidity. Such knowledge should be useful for interpreting the results of laboratory and field studies and for developing atmospheric chemistry models. A number of recommendations for future research are also presented.

Kinetics and products of the reactions of OH radicals with cyclohexene, 1-methyl-1-cyclohexene, cis-cyclooctene, and cis-cyclodecene.

Rate constants for the reactions of OH radicals with four C(6)-C(10) cycloalkenes have been measured at 297 ± 2 K using a relative rate technique. The rate constants (in units of 10(-11) cm(3) molecule(-1) s(-1)) were cyclohexene, 6.35 ± 0.12; cis-cyclooctene, 5.16 ± 0.15; cis-cyclodecene, 4.18 ± 0.06; and 1-methyl-1-cyclohexene, 9.81 ± 0.18, where the indicated errors are two least-squares standard deviations and do not include uncertainties in the rate constant for the reference compound 1,3,5-trimethylbenzene. In addition, a rate constant of (4.8 ± 1.3) × 10(-11) cm(3) molecule(-1) s(-1) was derived for the reaction of OH radicals with 1,6-hexanedial, relative to our measured rate constant for OH + cyclohexene. Analyses of products of the OH + cyclohexene, 1-methyl-1-cyclohexene, and cis-cyclooctene reactions by direct air sampling atmospheric pressure ionization mass spectrometry and/or by combined gas chromatography-mass spectrometry showed the presence of products attributed to cyclic 1,2-hydroxynitrates and the dicarbonyls 1,6-hexanedial, 6-oxo-heptanal, and 1,8-octanedial, respectively. These dicarbonyl products, which are those formed after decomposition of the intermediate cyclic 1,2-hydroxyalkoxy radicals, were quantified as their dioximes, with molar formation yields of 76 ± 10%, 82 ± 12%, and 84 ± 18% from the cyclohexene, 1-methyl-1-cyclohexene, and cis-cyclooctene reactions, respectively. Combined with literature data concerning 1,2-hydroxynitrate formation from OH + alkenes and the estimated fractions of the overall reactions proceeding by H-atom abstraction, 90 ± 12%, 95 ± 13% and 108 ± 20% of the products or reaction pathways from the OH radical-initiated reactions of cyclohexene, 1-methyl-1-cyclohexene, and cis-cyclooctene in the presence of NO are accounted for.

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.

Effect of NO2 concentration on dimethylnitronaphthalene yields and isomer distribution patterns from the gas-phase OH radical-initiated reactions of selected dimethylnaphthalenes.

Dimethylnitronaphthalene (DMNN) formation yields from the reactions of 1,7- and 2,7- dimethylnaphthalene (DMN) with OH radicals were measured over the NO(2) concentration range 0.04-1.4 ppmv. The measured DMNN formation yields under conditions that the OH-DMN adducts reacted solely with NO(2) were 0.252 ± 0.094% for Σ1,7-DMNNs and 0.010 ± 0.005% for Σ2,7-DMNNs. 1,7-DM-5-NN was the major isomer formed, with a limiting high-NO(2) concentration yield of 0.212 ± 0.080% and with equal reactions of the adduct with NO(2) and O(2) occurring in air at 60 ± 39 ppbv of NO(2). The reactions of the OH-DMN adducts with NO(2) must therefore result in products other than DMNNs. Although the yields of the DMNNs are low, ≤0.3%, the DMNN (and ethylnitronaphthalene) profiles from chamber experiments match well with those observed in polluted urban areas under conditions where OH radical-initiated chemistry is dominant. Daytime OH radical and nighttime NO(3) radical reactions appear to account for the alkylnitronaphthalenes formed and their observed profiles under most urban atmospheric conditions, with profiles reflecting daytime OH chemistry modified by contributions from isomers formed by any NO(3) radical chemistry that had occurred. Since the formation yields and NO(2) dependencies for the formation of a number of alkylnitronaphthalenes have now been measured, the effect of NO(x) emissions control strategies on their atmospheric formation can be quantitatively assessed, and the decrease in formation of these genotoxic species may provide a previously unrecognized health benefit of NO(x) control.

Reactions of OH radicals with C6-C10 cycloalkanes in the presence of NO: isomerization of C7-C10 cycloalkoxy radicals.

Rate constants have been measured for the reactions of OH radicals with a series of C(6)-C(10) cycloalkanes and cycloketones at 298 ± 2 K, by a relative rate technique. The measured rate constants (in units of 10(-12) cm(3) molecule(-1) s(-1)) were cycloheptane, 11.0 ± 0.4; cyclooctane, 13.5 ± 0.4; cyclodecane, 15.9 ± 0.5; cyclohexanone, 5.35 ± 0.10; cycloheptanone, 9.57 ± 0.41; cyclooctanone, 15.4 ± 0.7; and cyclodecanone, 20.4 ± 0.8, where the indicated errors are two least-squares standard deviations and do not include uncertainties in the rate constant for the reference compound n-octane. Formation yields of cycloheptanone from cycloheptane (4.2 ± 0.4%), cyclooctanone from cyclooctane (0.85 ± 0.2%), and cyclodecanone from cyclodecane (4.9 ± 0.5%) were also determined by gas chromatography, where the molar yields are in parentheses. Analyses of products by direct air sampling atmospheric pressure ionization mass spectrometry and by combined gas chromatography-mass spectrometry showed, in addition to the cycloketones, the presence of cycloalkyl nitrates, cyclic hydroxyketones, hydroxydicarbonyls, hydroxycarbonyl nitrates, and products attributed to carbonyl nitrates and/or cyclic hydroxynitrates. The observed formation of cyclic hydroxyketones from the cycloheptane, cyclooctane and cyclodecane reactions, with estimated molar yields of 46%, 28%, and 15%, respectively, indicates the occurrence of cycloalkoxy radical isomerization. Potential reaction mechanisms are presented, and rate constants for the various alkoxy radical reactions are derived.

Kinetics and products of the reaction of OH radicals with 3-methoxy-3-methyl-1-butanol.

3-Methoxy-3-methyl-1-butanol [CH(3)OC(CH(3))(2)CH(2)CH(2)OH] is used as a solvent for paints, inks, and fragrances and as a raw material for the production of industrial detergents. A rate constant of (1.64 ± 0.18) × 10(-11) cm(3) molecule(-1) s(-1) for the reaction of 3-methoxy-3-methyl-1-butanol with OH radicals has been measured at 296 ± 2 K using a relative rate method, where the indicated error is the estimated overall uncertainty. Acetone, methyl acetate, glycolaldehyde, and 3-methoxy-3-methylbutanal were identified as products of the OH radical-initiated reaction, with molar formation yields of 3 ± 1%, 35 ± 9%, 13 ± 3%, and 33 ± 7%, respectively, at an average NO concentration of 1.3 × 10(14) molecules cm(-3). Using a 12-h average daytime OH radical concentration of 2 × 10(6) molecules cm(-3), the calculated lifetime of 3-methoxy-3-methyl-1-butanol with respect to reaction with OH radicals is 8.5 h. Potential reaction mechanisms are discussed.

Atmospheric chemistry of dichlorvos.

Dichlorvos [2,2-dichlorovinyl dimethyl phosphate, (CH(3)O)(2)P(O)OCH═CCl(2)] is a relatively volatile in-use insecticide. Rate constants for its reaction with OH radicals have been measured over the temperature range 296-348 K and atmospheric pressure of air using a relative rate method. The rate expression obtained was 3.53 × 10(-13) e((1367±239)/T) cm(3) molecule(-1) s(-1), with a 298 K rate constant of (3.5 ± 0.7) × 10(-11) cm(3) molecule(-1) s(-1), where the error in the 298 K rate constant is the estimated overall uncertainty. In addition, rate constants for the reactions of NO(3) radicals and O(3) with dichlorvos, of (2.5 ± 0.5) × 10(-13) cm(3) molecule(-1) s(-1) and (1.7 ± 1.0) × 10(-19) cm(3) molecule(-1) s(-1), respectively, were measured at 296 ± 2 K. Products of the OH and NO(3) radical-initiated reactions were investigated using in situ atmospheric pressure ionization mass spectrometry (API-MS) and (OH radical reaction only) in situ Fourier transform infrared (FT-IR) spectroscopy. For the OH radical reaction, the major initial products were CO, phosgene [C(O)Cl(2)] and dimethyl phosphate [(CH(3)O)(2)P(O)OH], with equal (to within ±10%) formation yields of CO and C(O)Cl(2). The API-MS analyses were consistent with formation of (CH(3)O)(2)P(O)OH from both the OH and NO(3) radical-initiated reactions. In the atmosphere, the dominant chemical loss processes for dichlorvos will be daytime reaction with OH radicals and nighttime reaction with NO(3) radicals, with an estimated lifetime of a few hours.

Effect of structure on the rate constants for reaction of NO3 radicals with a series of linear and branched C5-C7 1-alkenes at 296 ± 2 K.

Rate constants for the gas-phase reactions of NO3 radicals with 13 linear and branched C5-C7 1-alkenes, CH2═CHR, where R = alkyl, have been measured at 296 ± 2 K and atmospheric pressure of air by a relative rate method. 1-Butene was used as the reference compound, and the rate constants obtained (in units of 10(-14) cm(3) molecule(-1) s(-1)) were as follows: 1-pentene, 1.50 ± 0.07; 1-hexene, 1.80 ± 0.08; 1-heptene, 2.06 ± 0.14; 3-methyl-1-butene, 1.39 ± 0.04; 3-methyl-1-pentene, 1.39 ± 0.03; 4-methyl-1-pentene, 1.52 ± 0.04; 3,3-dimethyl-1-butene, 1.54 ± 0.03; 3-methyl-1-hexene, 1.65 ± 0.08; 4-methyl-1-hexene, 1.86 ± 0.08; 5-methyl-1-hexene, 2.14 ± 0.08; 3,3-dimethyl-1-pentene, 1.44 ± 0.07; 3,4-dimethyl-1-pentene, 1.49 ± 0.10; and 4,4-dimethyl-1-pentene, 1.37 ± 0.06; where the indicated errors are two least-squares standard deviations and do not include uncertainties in the rate constant for the reference compound 1-butene. These rate constants increase along the series 1-butene < 1-pentene < 1-hexene < 1-heptene, and this is attributed to inductive effects. For a given carbon number, the rate constants depend on the position and degree of branching, and the observed trend of measured rate constants with position and degree of branching in the alkyl substituent group R correlates well with steric hindrance as calculated by McGillen et al. ( Phys. Chem. Chem. Phys. 2008 , 10 , 1757 ).

Kinetics of the reactions of OH radicals with 2- and 3-methylfuran, 2,3- and 2,5-dimethylfuran, and E- and Z-3-hexene-2,5-dione, and products of OH + 2,5-dimethylfuran.

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.

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).

Kinetics and products of the reactions of oh radicals with 4,4-dimethyl-1-pentene and 3,3-dimethylbutanal at 296 +/- 2 K.

Using a relative rate method, rate constants have been measured for the reactions of OH radicals with 4,4-dimethyl-1-pentene [(CH(3))(3)CCH(2)CH=CH(2)] and its major reaction product, 3,3-dimethylbutanal [(CH(3))(3)CCH(2)CHO], at 296 +/- 2 K and atmospheric pressure of air. The rate constants obtained were 2.41 x 10(-11) and 2.73 x 10(-11) cm(3) molecule(-1) s(-1), respectively, with estimated uncertainties of +/-10%. The products identified and quantified by gas chromatography with mass spectrometry and/or flame ionization detection from the 4,4-dimethyl-1-pentene reaction were acrolein [CH(2)=CHCHO], 3,3-dimethylbutanal, and a molecular weight 112 carbonyl attributed to 4,4-dimethyl-2-pentenal [(CH(3))(3)CCH=CHCHO], with formation yields of 2.7 +/- 0.5%, 59 +/- 6%, and 3.4 +/- 0.6%, respectively. Using direct air sampling atmospheric pressure ionization mass spectrometry, additional products of molecular weight 146, 177, and 193 were observed, and on the basis of expected reaction schemes these are attributed to the dihydroxycarbonyl HOCH(2)C(CH(3))(2)CH(2)C(O)CH(2)OH, the hydroxynitrates (CH(3))(3)CCH(2)CH(OH)CH(2)ONO(2) and/or (CH(3))(3)CCH(2)CH(ONO(2))CH(2)OH, and the dihydroxynitrate O(2)NOCH(2)C(CH(3))(2)CH(2)CH(OH)CH(2)OH, respectively. The hydroxynitrates were also tentatively identified by gas chromatography, with a summed yield of approximately 15%. Acrolein and 4,4-dimethyl-2-pentenal arise from H-atom abstraction from the three equivalent CH(3) groups and the 3-position CH(2) group, and the sum of their formation yields (6.1 +/- 0.8%) is expected to be very close to the fraction of the overall reaction proceeding by H-atom abstraction.