A. Mellouki

Kinetics of OH and Cl reactions with a series of aldehydes

The rate constants for the reactions of the OH radicals with a series of aldehydes have been measured in the temperature range 243–372 K, using the pulsed laser photolysis-pulsed laser induced fluorescence method. The obtained data for propanaldehyde, iso-butyraldehyde, tert-butyraldehyde, and n-pentaldehyde were as follows (in cm3 molecule−1 s−1): (a) in the Arrhenius form: (5.3 ± 0.5) × 10−12 exp[(405 ± 30)/T], (7.3 ± 1.9) × 10−12 exp[(390 ± 78)/T], (4.7 ± 0.8) × 10−12 exp[(564 ± 52)/T], and (9.9 ± 1.9) × 10−12 exp[(306 ± 56)/T]; (b) at 298 K: (2.0 ± 0.3) × 10−11, (2.6 ± 0.4) × 10−11, (2.7 ± 0.4) × 10−11, and (2.8 ± 0.2) × 10−11, respectively. In addition, using the relative rate method and alkanes as the reference compounds, the room-temperature rate constants have been measured for the reactions of chlorine atoms with propanaldehyde, iso-butyraldehyde, tert-butyraldehyde, n-pentaldehyde, acrolein, and crotonaldehyde. The obtained values were (in cm3 molecule−1 s−1): (1.4 ± 0.3) × 10−10, (1.7 ± 0.3)10−10, (1.6 ± 0.3) × 10−10, (2.6 ± 0.3) × 10−10, (2.2 ± 0.3) × 10−10, and (2.6 ± 0.3) × 10−10, respectively. The results are presented and discussed in terms of structure-reactivity relationships and atmospheric importance.

OH and O3-initiated oxidation of ethyl vinyl ether

The reaction rate constants of OH and O3 with ethyl vinyl ether (EVE, C2H5OCHCH2) have been measured in the temperature range 230–372 K and 298 K, respectively. The temperature dependent rate constant for the reaction with OH was found to be well represented by the expression: k1 = (1.55 ± 0.25) × 10−11 exp[(445 ± 13)/T] cm3 molecule−1 s−1, and at 298 K, k1 = (6.8 ± 0.7) × 10−11 cm3 molecule−1 s−1. The reaction rate constant of O3 with EVE was determined to be k2 = (2.0 ± 0.2) × 10−16 cm3 molecule−1 s−1 at 298 K. Using two different simulation chambers, the OH and O3-initiated oxidation of ethyl vinyl ether in air was also investigated. The main products observed from both reactions were formaldehyde and ethyl formate. The results obtained are presented and their atmospheric relevance briefly discussed.

Rate constants for the gas‐phase reactions of chlorine atoms with a series of ketones

The pulsed laser photolysis-resonance fluorescence technique has been used to determine the absolute rate coefficient for the Cl atom reaction with a series of ketones, at room temperature (298 ± 2) K and in the pressure range 15–60 Torr. The rate coefficients obtained (in units of cm3 molecule−1 s−1) are: acetone (3.06 ± 0.38) × 10−12, 2-butanone (3.24 ± 0.38) × 10−11, 3-methyl-2-butanone (7.02 ± 0.89) × 10−11, 4-methyl-2-pentanone (9.72 ± 1.2) × 10−11, 5-methyl-2-hexanone (1.06 ± 0.14) × 10−10, chloroacetone (3.50 ± 0.45) × 10−12, 1,1-dichloroacetone (4.16 ± 0.57) × 10−13, and 1,1,3-trichloroacetone (<2.4 × 10−12).

Discharge flow study of the CH3S + NO2 reaction mechanism using Cl + CH3SH as the CH3S source

Abstract The discharge flow-EPR-mass spectrometric technique has been used to determine the rate constant for the reaction Cl +CH3SH → CH3S + HCl (1). We determined k1 = (1.1 ± 0.4) × 10−10 cm3 molecule−1 s−1 at room temperature and at 0.3 Torr. This reaction was found to be a convenient source of CH3S in discharge flow systems and was used to study the mechanism of the CH3S + NO2 reaction. Rate constants were obtained for the reactions CH3SO + NO2 → CH3SO2 + NO (4) and CH3SO2 + M → CH3 + SO2 + M (5) giving k4 = (3 ± 2) × 10−11 cm3 molecule−1 s−1 and k5 ⩽ 10 s−1 from modelling the experimental profiles of the reactant and products.

Kinetics and Products of Gas-Phase Reactions of Ozone with Methyl Methacrylate, Methyl Acrylate, and Ethyl Acrylate

The kinetics and products of the gas-phase reactions of ozone with methyl methacrylate, methyl acrylate, and ethyl acrylate have been investigated at 760 Torr total pressure of air and 294 +/- 2 K. The rate coefficients obtained (in cm(3) molecule(-1) s(-1) units) were as follows: k(methyl methacrylate) = (6.7 +/- 0.9) x 10(-18), k(methyl acrylate) = (0.95 +/- 0.07) x 10(-18), and k(ethyl acrylate) = (1.3 +/- 0.1) x 10(-18). In addition to formaldehyde being observed as a product of the three reactions, the other major reaction products were methyl pyruvate from reaction of ozone with methyl methacrylate, methyl glyoxylate from reaction of ozone with methyl acrylate, and ethyl glyoxylate from reaction of ozone with ethyl acrylate. Possible reaction mechanisms leading to the observed products are presented and discussed.

Kinetics of the reactions of the OH radical with 2-methyl-1-propanol, 3-methyl-1-butanol and 3-methyl-2-butanol between 241 and 373 K

Absolute rate constants have been measured for the gas-phase reactions of hydroxyl radicals with 2-methyl-1-propanol (k1), 3-methyl-1-butanol (k2) and 3-methyl-2-butanol (k3). Experiments were carried out using two different techniques, the relative rate method and the pulsed laser photolysis-laser induced fluorescence technique. The kinetic data were used to derive the following Arrhenius expressions in the temperature range 241–373 K(in units of cm3 molecule−1 s−1):k1 = (3.1±0.9) × 10−12exp[(352±82)/T]k2 = (2.8±0.9) × 10−12exp[(503±98)/T]k3 = (2.6±0.6) × 10−12exp[(456±65)/T]At 298 K, the reaction rate constants obtained by the two methods were in very good agreement. The results are presented, discussed and used to estimate the atmospheric lifetimes for the studied alcohols.

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, k1 = (2.33 ± 0.27) ×10-12 exp[(732 ± 34)/T]; and isopropenyl acetate,k2 = (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: k1 = (27.1 ± 3.0) and k2= (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.

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 k3=(7.5±1.4)×10-14 and k4=(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.

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 Henrys 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.

Kinetics of gas phase reactions of OH and Cl with aromatic aldehydes

Rate constants for the OH and Cl reactions with four aromatic aldehydes have been determined at 298 ± 2 K and atmospheric pressure using a relative rate method. The measured rate constants are (in cm3 molecule−1 s−1): kOHkClBenzaldehyde(1.2 ± 0.2) × 10−11(10 ± 1) × 10−11o-Tolualdehyde(1.8 ± 0.2) × 10−11(19 ± 2) × 10−11m-Tolualdehyde(1.7 ± 0.2) × 10−11(17 ± 2) × 10−11p-Tolualdehyde(1.3 ± 0.2) × 10−11(14 ± 2) × 10−11 This work provides the first measurements for the OH and Cl reaction rate constants with tolualdehydes. The results obtained are presented and compared with the previous measurements only available for benzaldehyde. The atmospheric implications are also discussed.