Further studies of the temperature dependence of the rate coefficients for the reactions of OH with a series of ethers under simulated atmospheric conditions

The following temperature-dependent rate coefficients (k/cm³ molecule^–1 s^–1) of the reactions of hydroxyl radicals with aliphatic ethers have been determined over the temperature range 247–373 K by a competitive flow technique: diethyl ether,k _OH=5.2×10^–12 exp[(262±150)/T]; methyln-butyl ether,k _OH=5.4×10^–12 exp[(309±150)/T]; ethyln-butyl ether,k _OH=7.3×10^–12 exp[(335±150)/T]; di-n-butyl ether,k _OH=5.5×10^–12 exp[(502±150)/T] and di-n-pentyl ether,k _OH=8.5×10^–12 exp[(417±150)/T]. The data have been measured relative to the rate coefficientk(OH + 2,3-dimethylbutane)=6.2×10^–12 cm³ molecule^–1 s^–1 independent of temperature.Previous discrepancies in the room-temperature rate coefficients for the OH reactions with ethyln-butyl ether and di-n-butyl ether, obtained in the flow and static experiments of Bennett and Kerr (J. Atmos. Chem. 8, 87–94, 1989;10, 29–38, 1990) compared with those of Wallingtonet al. (Int. J. Chem. Kinet. 20, 541–547, 1988;21, 993–1001, 1989) and of Nelsonet al. (Int. J. Chem. Kinet. 22, 1111–1126, 1990) have been resolved. The results are considered in relation to the available literature data and evaluated rate expressions are deduced where possible. The data are also discussed in terms of structure-activity relationships.     

Kinetics of the reactions of hydroxyl radicals with alkyl nitrates and with some oxygen-containing organic compounds studied under simulated atmospheric conditions

Rate constants have been measured for the reactions of hydroxyl radicals with alkyl nitrates and with some oxygen-containing organic compounds by a competitive technique. Mixtures of synthetic air containing a few ppm of nitrous acid, ethylene and the organic substrate were photolysed in a Teflon bag smog chamber. Based on the value k _HO+C2H₄}=8.1×10^-12 cm³ molecule^-1 s^-1 the following rate constants were obtained for the hydroxyl radical reactions at 750 Torr and at 303 K in units of 10^-12 cm³ molecule^-1: CH₃ONO₂, 0.37±0.09; C₂H₅ONO₂, 0.48±0.20; n-C₃H₇ONO₂, 0.70±0.22; C₂H₅OH, 3.6±0.4; CH₃COCH₃, 0.26±0.08; CH₃CO₂ i-C₃H₇, 3.0±0.8; CH₃CO₂ n-C₃H₇, 2.4±0.2. The results are discussed in relation to the available literature data and the implications of the results are considered in terms of the smog reactivity of these molecules.     

Kinetics of the reactions of hydroxyl radicals with aliphatic ethers studied under simulated atmospheric conditions: Temperature dependences of the rate coefficients

Rate coefficients have been measured for the reactions of hydroxyl radicals with five aliphatic ethers over the temperature range 242–328 K. Competitive studies were carried out in an atmospheric flow reactor in which the hydroxyl radicals were generated by the photolysis of methyl nitrite in the presence of air containing nitric oxide. The reaction of OH with 2,3-dimethyl-butane was used as the reference reaction and the following Arrhenius parameters have been obtained for the reactions: OH+RORproducts:

Kinetic Studies of OH and O3 Reactions with Allyl and Isopropenyl Acetate

Rate coefficients have been measured for the gas phasereactions of hydroxyl (OH) radicals and ozone with twounsaturated esters, allyl acetate(CH₃C(O)OCH₂CH=CH₂) and isopropenylacetate (CH₃C(O)OC(CH₃)=CH₂). The OHexperiments were carried out using the pulsed laserphotolysis – laser induced fluorescence technique overthe temperature range 243–372 K and the kinetic dataused to derive the following Arrhenius expressions (inunits of cm³ molecule^-1 s^-1): allylacetate, k ₁ = (2.33 ± 0.27) ×10^-12 exp[(732 ± 34)/T]; and isopropenyl acetate,k ₂ = (4.52 ± 0.62) × 10^-12exp[(809 ± 39)/T]. At 298 K, the rate coefficients obtained (inunits of 10^-12 cm³ molecule^-1 s^-1)are: k ₁ = (27.1 ± 3.0) and k ₂= (69.6± 9.4). The relative rate technique has been usedto determine rate coefficients for the reaction ofozone with the acetates. Using methyl vinyl ketone asthe reference compound and a value of4.8 × 10^-18 cm³ molecule^-1s^-1 asthe rate coefficient for its reaction with O₃,the following rate coefficients were derived at 298 ± 4 K (in units of10^-18 cm³molecule^-1 s^-1): allyl acetate, (2.4 ± 0.7) andisopropenyl acetate (0.7 ± 0.2). Theresults are discussed in terms of structure-activityrelationships and used to derive atmospheric lifetimesfor the acetates.     

A Study of the Reaction of OH Radicals with N-Methyl Pyrrolidinone,N-Methyl Succinimide and N-Formyl Pyrrolidinone

A study of the oxidation mechanism of N-methyl pyrrolidinone (C₅H₉NO, NMP) initiated by hydroxyl radicals was made at EUPHORE at atmospheric pressure (1000 ± 10) mbar of air and ambient temperature (T = 300 ± 5 K). The main products were N-methyl succinimide (NMS) (52 ± 4)% and N-formyl pyrrolidinone (FP) (23 ± 9)%. The relative rate technique was used to determine the rate constants of OH with NMP, NMS and FP, the measured values were (in units of cm³ molecule ^{− 1} s^{− 1}): k_NMP = (2.2 ± 0.4) × 10^{− 11}, k_NMS = (1.4 ± 0.3) × 10^{− 12} and k_FP = (6 ± 1) × 10^{− 12}. The results are presented and discussed in terms of the atmospheric impact.     

Rate constant measurement for the reactions of OH and Cl with peroxyacetyl nitrate at 298 K

The gas phase reactions of peroxyacetyl nitrate (PAN) with OH and Cl have been studied using the discharge-flow EPR method. The rate constants are found to be k ₃=(7.5±1.4)×10^-14 and k ₄=(3.7±1.7)×10^-13 cm³ molecule^-1 s^-1 at 298 K, respectively. These results confirm that the OH+PAN reaction will be the dominant sink of PAN in the middle and upper troposphere, whereas the reaction Cl+PAN will be negligible in contrast with previous estimations.     

Kinetics of the Reactions of IO with HO2 and O(3P)

A discharge-flow tube coupled with resonance fluorescence and chemiluminescence detection has been used to investigate the reactions IO + HO₂ products (1) and IO + O(³P) I + O₂(2), at T = 296 ± 1 K and P = 1.7 - 2 Torr. The rate constants k_-1 and k₂ have been found to be (7.1 ± 1.6) × 10^-11 cm³ molecule^-1 s^-1 and (1.35 ± 0.15) × 10^-10 cm³ molecule^-1 s^-1, respectively.     

An Experimental Study on the Temperature Dependence for the Gas-Phase Reactions of NO3 Radical with a Series of Aliphatic Aldehydes

The absolute rate constants for the gas-phasereactions of the NO₃ radical with a series ofaldehydes such as acetaldehyde, propanal, butanal,pentanal, hexanal and, heptanal were measured overthe temperature range 298–433 K, using a dischargeflow system and monitoring the NO₃ radical byLaser Induced Fluorescence (LIF).The measured rate constants at 298 K for thereaction of NO₃, in units of 10^–14 cm³molecule^–1 s^–1, were as follows:acetaldehyde 0.32 ± 0.04, propanal 0.60 ± 0.06, butanal 1.46± 0.16, pentanal 1.75 ±0.06, hexanal 1.83 ± 0.36, and heptanal 2.37 ±0.42. The proposed Arrhenius expressions arek₁ = (6.2 ± 7.5) × 10^–11 exp[–(2826 ± 866)/T] (cm³ molecule^–1s^–1),k₂ = (1.7 ± 1.0) × 10^–11 exp[–(2250 ± 192)/T] (cm³ molecule^–1s¹), k₃ =(7.6 ± 9.8) × 10¹¹ exp[–(2466 ± 505)/T] (cm³ molecule^–1s^–1),k₄ = (2.8 ± 1.4) × 10^–11 exp[–(2189 ± 156)/T] (cm³ molecule^–1s^–1), k₅ = (7.0 ± 1.8) ×10^–11 exp [–(2382 ± 998)/T](cm³ molecule^–1 s^–1), andk₆ = (7.8 ± 1.0) × 10^–11 exp[–(2406 ± 481)/T](cm³ molecule^–1 s^–1).Tropospheric lifetimes for these aldehydes werecalculated at night and during the day for typicalNO₃ and OH average concentrations and showed thatboth radicals provide an effective tropospheric sinkfor these compounds and that the night-time reactionwith the NO₃ radical can be an important, if notdominant, loss process for these emitted organics andfor NO₃ radicals.     

Solubilities of pyruvic acid and the lower (C1-C6) carboxylic acids. Experimental determination of equilibrium vapour pressures above pure aqueous and salt solutions

Henry's law constantsK _H (mol kg^–1 atm^–1) have been determined at 298.15 K for the following organic acids: formic acid (5.53±0.27×10³); acetic acid (5.50±0.29×10³); propionic acid (5.71±0.34×10³);n-butyric acid (4.73±0.18×10³); isobutyric acid (1.13±0.12×10³); isovaleric acid (1.20±0.11×10³) and neovaleric acid (0.353±0.04×10³). They have also been determined fromT=278.15 K toT=308.15 K forn-valeric acid (ln(K _H)=–14.3371+6582.96/T);n-caproic acid (ln(K _H)=–13.9424+6303.73/T) and pyruvic acid (ln(K _H)=–4.41706+5087.92/T). The influence of 9 salts on the solubility of pyruvic acid at 298.15 K has been measured. Pyruvic acid is soluble enough to partition strongly into aqueous atmospheric aerosols. Other acids require around 1 g of liquid water m^–3 (typical of clouds) to partition significantly into the aqueous phase. The degree of partitioning is sensitive to temperature. Considering solubility and dissociation (to formate) alone, the ratio of formic acid to acetic acid in liquid water in the atmosphere (at equilibrium with the gas phase acids) is expected to increase with rising pH, but show little variation with temperature.     

Fourier transform infrared kinetic studies of the reaction of HONO with HNO3, NO3 and N2O5 at 295 K

The kinetics of the reaction of nitrous acid (HONO) with nitric acid (HNO₃), nitrate radicals (NO₃) and dinitrogen pentoxide (N₂O₅) have been studied using Fourier transform infrared spectroscopy. Experiments were performed at 700 torr total pressure using synthetic air or argon as diluents. From the observed decay of HONO in the presence of HNO₃ a rate constant of k<7×10^-19 cm³ molecule^-1 s^-1 was derived for the reaction of HONO with HNO₃. From the observed decay of HONO in the presence of mixtures of N₂O₅ and NO₂ we have also derived upper limits for the rate constants of the reactions of HONO with NO₃ and N₂O₅ of 2×10^-15 and 7×10^-19 cm³ molecule^-1 s^-1, respectively. These results are discussed with respect to previous studies and to the atmospheric chemistry of HONO.     

Kinetics of the Gas-Phase Reactions of OH Radicals, NO3 Radicals and O3 with Three C7-Carbonyls Formed From The Atmospheric Reactions of Myrcene, Ocimene and Terpinolene

Rate constants for the gas-phase reactions of OH radicals, NO₃ radicals and O₃ with the C₇-carbonyl compounds 4-methylenehex-5-enal [CH₂=CHC(=CH₂)CH₂CH₂CHO], (3Z)- and (3E)-4-methylhexa-3,5-dienal [CH₂=CHC(CH₃)=CHCH₂CHO] and 4-methylcyclohex-3-en-1-one, which are products of the atmospheric degradations of myrcene, Z- and E-ocimene and terpinolene, respectively, have been measured at 296 ± 2 K and atmospheric pressure of air using relative rate methods. The rate constants obtained (in cm³ molecule^–1 s^–1 units) were: for 4-methylenehex-5-enal, (1.55 ± 0.15) × 10^–10, (4.75 ± 0.35) × 10^–13 and (1.46 ± 0.12) × 10^–17 for the OH radical, NO₃ radical and O₃ reactions, respectively; for (3Z)-4-methylhexa-3,5-dienal: (1.61 ± 0.35) × 10^–10, (2.17 ± 0.30) × 10^–12, and (4.13 ± 0.81) × 10^–17 for the OH radical, NO₃ radical and O₃ reactions, respectively; for (3E)-4-methylhexa-3,5-dienal: (2.52 ± 0.65) × 10^–10, (1.75 ± 0.27) × 10^–12, and (5.36 ± 0.28) × 10^–17 for the OH radical, NO₃ radical and O₃ reactions, respectively; and for 4-methylcyclohex-3-en-1-one: (1.10 ± 0.19) × 10^–10, (1.81 ± 0.35) × 10^–12, and (6.98 ± 0.40) × 10^–17 for the OH radical, NO₃ radical and O₃ reactions, respectively. These carbonyl compounds are all reactive in the troposphere, with daytime reaction with the OH radical and nighttime reaction with the NO₃ radical being predicted to dominate as loss processes and with estimated lifetimes of about an hour or less.     

Kinetic investigation of the OH + CH3Br reaction between 248 and 390 K

The rate parameters for the reaction of the OH radical with CH₃Br have been measured using the discharge flow-electron paramagnetic resonance method. The result isk ₁=(1.86±0.48)×10^–12 exp[–(1230±150)/T] cm³ molecule^–1 s^–1. This value is compared to earlier data and is found to be in excellent agreement with the most recent results, which greatly increases the accuracy of the ozone depletion potential of CH₃Br which can be derived from these kinetic data.     

Atmospheric Loss Processes of Dimethyl and Diethyl Carbonate

A combined study of the OH gas phase reaction and uptake on aqueous surfacesof two carbonates, dimethyl and diethyl carbonate has been carried out todetermine the atmospheric lifetimes of these compounds. Rate coefficients havebeen measured for gas phase reactions of OH radicals with dimethyl and diethylcarbonate. The experiments were carried out using pulsed laser photolysis– laser induced fluorescence over the temperature range 263–372K and the kinetic data were used to derive the following Arrhenius expressions(in units of cm³ molecule^–1 s^–1):for dimethyl carbonate, k₁ = (0.83±0.27)×10^–12 exp [–(247± 98)/T] and fordiethyl carbonate, k₂ = (0.46±0.15)×10^–12 exp [(503± 203)/T]. At 298 K, therate coefficients obtained (in units of 10^–12 cm³molecule^–1 s^–1) are: k₁ =(0.35± 0.04) and k₂ = (2.31± 0.29). The results arediscussed in terms of structure-activity relationships.The uptake coefficients of both carbonates on aqueous surfaces were measuredas a function of temperature and composition of the liquid phase, using thedroplet train technique coupled to a mass spectrometric detection. Dimethyland diethyl carbonate show very similar results. For both carbonates, themeasured uptake kinetics were found to be independent of the aqueous phasecomposition (pure water, NaOH solutions) but dependent on gas-liquid contacttime which characterises a surface saturation effect. The uptake coefficientvalues show a slight negative temperature dependence for both carbonates.These values vary from 1.4×10^–2 to0.6×10^–2 in the temperature range of 265–279 Kfor dimethyl carbonate, from 2.4×10^–2 to0.9×10^–2 in the temperature range of 270–279 Kfor diethyl carbonate. From the kinetic data, the following Henry's lawconstants were derived between 279 and 265 K: dimethyl carbonate,H₁ = 20–106 M atm^–1; and diethyl carbonate,H₂ = 30–98 M atm^–1. The reported data showthat the OH reaction is the major atmospheric loss process of these twocarbonates with lifetimes of 33 and 5 days, respectively, while the wetdeposition is a negligible process.     

Rate constants for the reactions of the NO3 radical with HCOOH/HCOO− and CH3COOH/CH3COO− in aqueous solution between 278 and 328 K

The kinetics of the aqueous phase reactions of NO₃ radicals with HCOOH/HCOO^– and CH₃COOH/CH₃COO^– have been investigated using a laser photolysis/long-path laser absorption technique. NO₃ was produced via excimer laser photolysis of peroxodisulfate anions (S₂O ₈ ^2– ) at 351 nm followed by the reactions of sulfate radicals (SO ₄ ^– ) with excess nitrate. The time-resolved detection of NO₃ was achieved by long-path laser absorption at 632.8 nm. For the reactions of NO₃ with formic acid (1) and formate (2) rate coefficients ofk ₁=(3.3±1.0)×10⁵ l mol^–1 s^–1 andk ₂=(5.0±0.4)×10⁷ l mol^–1 s^–1 were found atT=298 K andI=0.19 mol/l. The following Arrhenius expressions were derived:k ₁(T)=(3.4±0.3)×10¹⁰ exp[–(3400±600)/T] l mol^–1 s^–1 andk ₂(T)=(8.2±0.8)×10¹⁰ exp[–(2200±700)/T] l mol^–1 s^–1. The rate coefficients for the reactions of NO₃ with acetic acid (3) and acetate (4) atT=298 K andI=0.19 mol/l were determined as:k ₃=(1.3±0.3)×10⁴ l mol^–1 s^–1 andk ₄=(2.3±0.4)×10⁶ l mol^–1 s^–1. The temperature dependences for these reactions are described by:k ₃(T)=(4.9±0.5)×10⁹ exp[–(3800±700)/T] l mol^–1 s^–1 andk ₄(T)=(1.0±0.2)×10¹² exp[–(3800±1200)/T] l mol^–1 s^–1. The differences in reactivity of the anions HCOO^– and CH₃COO^– compared to their corresponding acids HCOOH and CH₃COOH are explained by the higher reactivity of NO₃ in charge transfer processes compared to H atom abstraction. From a comparison of NO₃ reactions with various droplets constituents it is concluded that the reaction of NO₃ with HCOO^– may present a dominant loss reaction of NO₃ in atmospheric droplets.     

FTIR studies of reactions between the nitrate radical and haloethenes

Products and mechanisms for the gas-phase reactions of NO₃ radicals with CH₂=CHCl, CH₂=CCl₂, CHCl=CCl₂,cis-CHCl=CHCl andtrans-CHCl=CHCl in air have been studied. The experiments were carried out at 295±2 K and 740±5 Torr in a 480-L Teflon-coated reaction chamber and at 295±2 K and 760±5 Torr in a 250-L stainless steel reactor. NO₃ was generated by the thermal dissociation of N₂O₅. Experiments with¹⁵NO₃ and CD₂CDCl have also been performed. The initially formed nitrate peroxynitrates decay into carbonyl compounds, nitrates, HCl and ClNO₂. In adidtion, there are indications of nitrooxy acid chlorides being produced. The reactions with CH₂=CCl₂ and CHCl=CCl₂ are more complex due to release of chlorine atoms which eventually lead to formation of chloroacid chlorides.A general reaction mechanism is proposed and the observed concentration-time profiles of reactants and products are simulated for each compound. The rate constants for the initial step of NO₃ addition to the chloroethenes are determined as: (2.6±0.5, 9.4±0.9, 2.0±0.4 and 1.4±0.4) × 10^–16 cm³ molecule^–1 s^–1 for CH₂=CHCl, CH₂=CCl₂, CHCl=CCl₂ andcis-CHCl=CHCl, respectively.     

FT-IR Study of the Kinetics and Products of the Reactions of Dimethylsulphide, Dimethylsulphoxide and Dimethylsulphone with Br and BrO

Kinetics and products of the gas-phase reactions of dimethylsulphide (DMS), dimethylsulphoxide (DMSO) and dimethylsulphone (DMSO₂) with Br atoms and BrO radicals in air have beeninvestigated using on-line Fourier Transform Infrared Spectroscopy (FT-IR) as analytical technique at 740 ± 5 Torr total pressure and at 296 ± 3 K in a480 L reaction chamber. Using a relative rate method for determining the rate constants; the following values (expressed in cm³molecule^–1 s^–1) were found: k_DMS+Br = (4.9 ±1.0) ×10^–14, k_DMSO + Br < 6 × 10^–14,k_{DMSO 2} + Br 1 × 10^–15,k_DMSO + BrO = (1.0 ± 0.3) × 10^–14 andk_{DMSO 2} + BrO 3 × 10^–15 (allvalues are given with one on the experimental data). DMSO, SO₂, COS, CH₃SBr andCH₃SO₂Br were identified as the main sulphur containing products of the oxidation of DMS by Br atoms. From the reaction between DMSO and Br atoms, DMSO₂and CH₃SO₂Br were the only sulphur containing products thatwere identified. DMSO, DMSO₂ and SO₂ were identified as themain sulphur containing products of the reaction between DMS and BrO.DMSO₂ was found to be the only product of the reaction between DMSO and BrO. For the reactions of DMSO₂ with Br and BrO no products were identified because the reactions were too slow.The implications of these results for atmospheric chemistry are discussed.     

The Reactivity of Biogenic Monoterpenes towards OH· and SO4-· Radicals in De-Oxygenated Acidic Solution

The reactivity of some selected biogenic monoterpenecompounds towards important aqueous phase free-radicaloxidants, namely OH· and SO₄ ^-·, have beeninvestigated using the complementary experimentaltechniques of pulse radiolysis and laser flashphotolysis ( = 248 nm). Rate constants forthe reactions of the OH· radical with cis-verbenol andmethacrolein have been determined to be (6.8 ± 0.5) ×10⁹ dm³ mol^-1 s^-1 and (8.0± 0.7) × 10⁹ dm³ mol^-1s^-1,respectively (T = 20 °C, pH 4.0, Ionic strength 0 mol dm^-3). Rate constants and activationenergies for the reactions of the SO₄ ^-·radical have been measured for the following compounds(T = 20 °C, pH 4.0, Ionic strength = 0.03 moldm^-3): -pinene (k = (3.1 ± 0.1) ×10⁹ dm³ mol^-1 s^-1;E _act. =(8.9 ± 1.3) kJ mol^-1), -terpineol(k = (4.1 ± 0.1) × 10⁹ dm³mol^-1s^-1; E _act. = (13.4 ± 0.6) kJmol^-1), cis-verbenol (k = (3.2 ± 0.2) ×10⁹ dm³ mol^-1 s^-1;E _act. =(10.0 ± 0.7) kJ mol^-1), verbenone (k = (1.6± 0.1) × 10⁹ dm³ mol^-1s^-1;E _act. = (6.1 ± 0.7) kJ mol^-1), myrtenal(k = (1.85 ± 0.1) × 10⁹ dm³mol^-1s^-1; E _act. = (7.5 ± 0.7) kJmol^-1)and methacrolein (k = (1.18 ± 0.1) × 10⁹dm³ mol^-1 s^-1). In most instances theabsorption spectra of the intermediate products formedby these reactions have been measured which, inconjunction with strategic conductiometric studies,have been used to suggest plausible mechanisms for theoxidation in acidic de-oxygenated solution.     

A smog chamber for studies of the reactions of terpenes and alkanes with ozone and OH

The design and performance of a smog chamber for the study of photochemical reactions under simulated environmental conditions is described. The chamber is thermostated for aerosol experiments, and it comprises a gas chromatographic sample enrichment system suitable for monitoring hydrocarbons at the ppbv level. By irradiating NO _x /alkane-mixtures rate constants for the reaction of OH radicals with n-alkanes are determined from n-pentane to n-hexadecane to be (k±2)/10^–12 cm³ s^–1=4.29±0.16, 6.2±0.6, 7.52 (reference value), 8.8±0.3, 10.2±0.3, 11.7±0.4, 13.7±0.3, 15.1±0.5, 17.5±0.6, 19.3±0.7, 22.3±1.0, and 25.0±1.3, respectively at 312 K. Rate constants, (k±2)/10^–17 cm³ s^–1, for the reaction of ozone with trans-2-butene (21.2±1.0), cis-3-methylpentene-(2) (47.2±1.7), cyclopentene (62.4±3.5), cyclohexene (7.8±0.5), cycloheptene (28.3±1.5), -pinene (8.6±1.3), and -pinene (1.4±0.2) are determined in the dark at 297 K using cis-2-butene (13.0) as reference standard.     

Atmospheric chemistry of the monoterpene reaction products nopinone,camphenilone, and 4-acetyl-1-methylcyclohexene

Rate constants for the gas-phase reactions of OH radicals with nopinone (6,6-dimethylbicyclo[3.1.1]heptan-2-one) and camphenilone (3,3-dimethylbicyclo[2.2.1]heptan-2-one) and for the reactions of 4-acetyl-1-methylcyclohexene with OH and NO₃ radicals and O₃ have been measured at 296±2 K. The rate constants (cm³ molecule^–1 s^–1 units) obtained were, for reaction with the OH radical: nopinone, (1.43±0.37)×10^–11; camphenilone, (5.15±1.44)×10^–12; and 4-acetyl-1-methylcyclohexene, (1.29±0.33)×10^–10; for reaction with the NO₃ radical: 4-acetyl-1-methylcyclohexene, (1.05±0.38)×10^–11; and for reaction with O₃: 4-acetyl-1-methylcyclohexene, (1.50±0.53)×10^–16. These data are used to calculate the tropospheric lifetimes of these monoterpene atmospheric reaction products.     

Autoxidation of N(III), S(IV), and other Species in Frozen Solution – A Possible Pathway for Enhanced Chemical Transformation in Freezing Systems

The chemistry of glycolaldehyde (hydroxyacetaldehyde) relevant to the troposphere has been investigated using UV absorption spectrometry and FTIR absorption spectrometry in an environmental chamber. Quantitative UV absorption spectra have been obtained for the first time. The UV spectrum peaks at 277 nm with a maximum cross section of (5.5± 0.7)×10^–20 cm² molecule^–1. Studies of the ultraviolet photolysis of glycolaldehyde ( = 285 ± 25 nm) indicated that the overall quantum yield is > 0.5 in one bar of air, with the major products being CH₂OH and HCO radicals. Rate coefficients for the reactions of Cl atoms and OH radicals with glycolaldehyde have been determined to be (7.6± 1.5)×10^–11 and (1.1± 0.3)×10^–11 cm³ molecule^–1 s^–1, respectively, in good agreement with the only previous study. The lifetime of glycolaldehyde in the atmosphere is about 1.0 day for reaction with OH, and > 2.5 days for photolysis, although both wet and dry deposition should also be considered in future modeling studies.