Abdelwahid Mellouki

Studies on the Atmospheric Degradation of Chlorpyrifos-Methyl

The gas-phase atmospheric degradation of chlorpyrifos-methyl (a widely used organophosphate insecticide in Southern European regions) has been investigated at the large outdoor European Photoreactor (EUPHORE) in Valencia, Spain. Photolysis under sunlight conditions and reaction with ozone were shown to be unimportant. The rate constant for reaction of chlorpyrifos-methyl with OH radicals was measured using a conventional relative rate method with cyclohexane and n-octane employed as reference compounds with k = (4.1 ± 0.4) × 10(-11) cm(3) molecule(-1) s(-1) at 300 ± 5 K and atmospheric pressure. The available evidence indicates that tropospheric degradation of chlorpyrifos-methyl is mainly controlled by reaction with OH radicals and that the tropospheric lifetime is estimated to be around 3.5 h. Significant aerosol formation was observed following the reaction of chlorpyrifos-methyl with OH radicals, and the main carbon-containing products detected in the gas phase were chlorpyrifos-methyl oxone and 3,5,6-trichloro-2-pyridinol.

Rate constants for reactions of OH radicals with a series of asymmetrical ethers and tert‐Butyl alcohol

Absolute rate constants for the reactions of OH radicals with butyl ethyl ether (k1), methyl tert-butyl ether (k2), ethyl tert-butyl ether (k3) tert-amyl methyl ether (k4) and tert-butyl alcohol (k5) have been measured over the temperature range 230–372 K using a pulsed laser photolysis-laser induced fluorescence (PLP-LIF) technique. The temperature dependence of k1 − k5 when expressed in Arrhenius form gave: k1 = (6.59 ± 0.66) × 10 −12 exp|(362 ± 60)/T|, k2 = (5.03 ± 0.27) × 10−12 exp|&minus(133 ± 30)/T|, k3 = (4.40 ± 0.24) × 10−12 exp|(210 ± 37)/T|,k4 = (4.7 ± 0.7) × 10−12 exp|(82 ± 85)/T|, and k5 = (2.66 ± 0.48) × 10−12 exp| −(270 ± 130)/T|. However, the Arrhenius plots for k1–k5, were slightly curved and are best fitted by the three parameter fits which are given in the article. The room temperature values of k1, k2, k3, k4, and k5 are (2.08 ± 0.23) × 10−11, (3.13 ± 0.36) × 10−12, (8.80 ± 0.50) × 10−12, (6.28 ± 0.45) × 10−12, and (1.08 ± 0.10) × 10−12, respectively, in cm3 molecule−1 s−1.

Kinetics of the reactions of HBr with O3 and HO2: The yield of HBr from HO2 + BrO

An upper limit on the yield of HBr from reaction (R1) (HO{sub 2} + BrO {yields} products) has been determined by measuring an upper limit for the rate coefficient of the reverse reaction (R1{prime}) (HBr + O{sub 3} {yields} HO{sub 2} + BrO). The limits measured at 300 and 441 K were extrapolated to low temperatures to determine that the yield of HBr from reaction (R1) is negligible throughout the stratosphere (<0.01% of k{sub 1}). An upper limit for the rate coefficient of the reaction of HO{sub 2} with HBr was also determined to be very low {le} 3 x 10{sup {minus}17}cm{sup 3}molecule{sup {minus}1}s{sup {minus}1} at 300 K and {le} 3 x 10{sup {minus}16}cm{sup 3}molecule{sup {minus}1}s{sup {minus}1} at 400 K. The implications of these results to stratospheric chemistry are discussed. 18 refs., 1 fig., 6 tabs.

Kinetics of Cl atom reactions with butadienes including isoprene

Abstract The laser photolysis-resonance fluorescence technique was used to determine the rate constants for the reactions of Cl atoms with 1,3-butadiene, 2-methyl-1,3 butadiene (isoprene) and 2,3-dimethyl-1,3-butadiene in the pressure range 15–60 Torr and T=(298±2) K. The obtained rate constants (in units of 10−10 cm3 molecule−1 s−1) were as follows: 1,3-butadiene (3.48±0.10), isoprene (3.61±0.10) and 2,3-dimethyl-1,3-butadiene (3.63±0.14). These kinetic data are discussed.

Studies of the gas phase reactions of linalool, 6-methyl-5-hepten-2-ol and 3-methyl-1-penten-3-ol with O3 and OH radicals.

The reactions of three unsaturated alcohols (linalool, 6-methyl-5-hepten-2-ol, and 3-methyl-1-penten-3-ol) with ozone and OH radicals have been studied using simulation chambers at T ∼ 296 K and P ∼ 760 Torr. The rate coefficient values (in cm(3) molecule(-1) s(-1)) determined for the three compounds are linalool, k(O3) = (4.1 ± 1.0) × 10(-16) and k(OH) = (1.7 ± 0.3) × 10(-10); 6-methyl-5-hepten-2-ol, k(O3) = (3.8 ± 1.2) × 10(-16) and k(OH) = (1.0 ± 0.3) × 10(-10); and 3-methyl-1-penten-3-ol, k(O3) = (5.2 ± 0.6) × 10(-18) and k(OH) = (6.2 ± 1.8) × 10(-11). From the kinetic data it is estimated that, for the reaction of O(3) with linalool, attack at the R-CH═C(CH(3))(2) group represents around (93 ± 52)% (k(6-methyl-5-hepten-2-ol)/k(linalool)) of the overall reaction, with reaction at the R-CH═CH(2) group accounting for about (1.3 ± 0.5)% (k(3-methyl-1-penten-3-ol)/k(linalool)). In a similar manner it has been calculated that for the reaction of OH radicals with linalool, attack of the OH radical at the R-CH═C(CH(3))(2) group represents around (59 ± 18)% (k(6-methyl-5-hepten-2-ol)/k(linalool)) of the total reaction, while addition of OH to the R-CH═CH(2) group is estimated to be around (36 ± 6)% (k(3-methyl-1-penten-3-ol)/k(linalool)). Analysis of the products from the reaction of O(3) with linalool confirmed that addition to the R-CH═C(CH(3))(2) group is the predominant reaction pathway. The presence of formaldehyde and hydroxyacetone in the reaction products together with compelling evidence for the generation of OH radicals in the system indicates that the hydroperoxide channel is important in the loss of the biradical [(CH(3))(2)COO]* formed in the reaction of O(3) with linalool. Studies on the reactions of O(3) with the unsaturated alcohols showed that the yields of secondary organic aerosols (SOAs) are higher in the absence of OH scavengers compared to the yields in their presence. However, even under low-NO(X) concentrations, the reactions of OH radicals with 3-methyl-1-penten-3-ol and 6-methyl-5-hepten-2-ol will make only a minor contribution to SOA formation under atmospheric conditions. Relatively high yields of SOAs were observed in the reactions of OH with linalool, although the initial concentrations of reactants were quite high. The importance of linalool in the formation of SOAs in the atmosphere requires further investigation. The impact following releases of these unsaturated alcohols into the atmosphere are discussed.

The atmospheric photolysis of o-tolualdehyde.

The photolysis of o-tolualdehyde by natural sunlight has been investigated at the large outdoor European Photoreactor (EUPHORE) in Valencia, Spain. The photolysis rate coefficient was measured directly under different solar flux levels, with values in the range j(o-tolualdehyde) = (1.62-2.15) × 10(-4) s(-1) observed, yielding an average value of j(o-tolualdehyde)/j(NO(2)) = (2.53 ± 0.25) × 10(-2). The estimated photolysis lifetime is 1-2 h, confirming that direct photolysis by sunlight is the major atmospheric degradation pathway for o-tolualdehyde. Published UV absorption cross-section data were used to derive an effective quantum yield (290-400 nm) close to unity, within experimental error. Possible reaction pathways for the formation of the major photolysis products, benzocyclobutenol (tentatively identified) and o-phthalaldehyde, are proposed. Appreciable yields (5-13%) of secondary organic aerosol (SOA) were observed at EUPHORE and also during supplementary experiments performed in an indoor chamber using an artificial light source. Off-line analysis by gas chromatography-mass spectrometry allowed identification of o-phthalaldehyde, phthalide, phthalic anhydride, o-toluic acid, and phthalaldehydic acid in the particle phase.

Rate constant for the reaction of OH radical with HFC‐365mfc (CF3CH2CF2CH3)

Rate constant for the reaction of OH with HFC-365mfc (CF3CH2CF2CH3) has been measured at a total pressure of 100 Torr, using the laser photolysis - laser induced fluorescence technique. The obtained kinetic data were used to derive the following Arrhenius expression over the temperature range 269–370 K : k = (1.68±0.21) × 10−12 exp[-(1585±80)/T] cm³ molecule−1 s−1. At 298 K, the measured rate coefficient was : k = (8.69±0.74) × 10−15 cm³ molecule−1 s−1. This study is the first investigation to be reported on this reaction. Using our kinetic data, the tropospheric lifetime of CF3CH2CF2CH3 is estimated to be 7.8 years.

Atmospheric Chemistry of Benzyl Alcohol: Kinetics and Mechanism of Reaction with OH Radicals

The atmospheric oxidation of benzyl alcohol has been investigated using smog chambers at ICARE, FORD, and EUPHORE. The rate coefficient for reaction with OH radicals was measured and an upper limit for the reaction with ozone was established; kOH = (2.8 ± 0.4) × 10(-11) at 297 ± 3 K (averaged value including results from Harrison and Wells) and kO(3) < 2 × 10(-19) cm(3) molecule(-1) s(-1) at 299 K. The products of the OH radical initiated oxidation of benzyl alcohol in the presence of NOX were studied. Benzaldehyde, originating from H-abstraction from the -CH(2)OH group, was identified using in situ FTIR spectroscopy, HPLC-UV/FID, and GC-PID and quantified in a yield of (24 ± 5) %. Ring retaining products originating from OH-addition to the aromatic ring such as o-hydroxybenzylalcohol and o-dihydroxybenzene as well as ring-cleavage products such as glyoxal were also identified and quantified with molar yields of (22 ± 2)%, (10 ± 3)%, and (2.7 ± 0.7)%, respectively. Formaldehyde was observed with a molar yield of (27 ± 10)%. The results are discussed with respect to previous studies and the atmospheric oxidation mechanism of benzyl alcohol.

Reaction rate coefficients of OH radicals and Cl atoms with ethyl propanoate, n-propyl propanoate, methyl 2-methylpropanoate, and ethyl n-butanoate.

Kinetics of the reactions of OH radicals and Cl atoms with four saturated esters have been investigated. Rate coefficients for the gas-phase reactions of OH radicals with ethyl propanoate (k(1)), n-propyl propanoate (k(2)), methyl 2-methylpropanoate (k(3)), and ethyl n-butanoate (k(4)) were measured using a conventional relative rate method and the pulsed laser photolysis-laser induced fluorescence technique. At (296 +/- 2) K, the rate coefficients obtained by the two methods were in good agreement. Significant curvatures in the Arrhenius plots have been observed in the temperature range 243-372 K for k(1), k(3), and k(4). The rate coefficients for the reactions of the four esters with Cl atoms were determined using the relative rate method at (296 +/- 2) K and atmospheric pressure. The values obtained are presented, compared with the literature values when they exist, and discussed. Reactivity trends and atmospheric implications for these esters are also presented.

Photolysis of Trichloronitromethane (Chloropicrin) under Atmospheric Conditions

Abstract An experimental investigation on the photolysis of the pesticide chloropicrin, (trichloronitromethane, CCl3NO2), under atmospheric conditions was carried out at the outdoor European Photoreactor, (EUPHORE), in Valencia, Spain. The photodissociation rate coefficient, Jobs(CCl3NO2), was determined directly under sunlight conditions during spring and summer months. Values in the range Jobs(CCl3NO2) = (3.9–5.1)×10−5 s−1 were obtained, corresponding to photolysis lifetimes of 7.1–5.4 hours. Absorption cross-sections for chloropicrin were determined over the wavelength range 260–370 nm, and together with the measured solar flux intensity, were used to calculate the maximum photolysis rate for chloropicrin, Jmax. Comparison of the observed photolysis rate with the calculated maximum photolysis rate showed that the effective quantum yield of photodissociation, Φ = Jobs(CCl3NO2)/Jmax, was 0.94±0.08. Photolysis of chloropicrin in air or nitrogen gave phosgene as the major carbon-containing product with a yield close to unity based on the loss of chloropicrin. The product yield data were shown to be consistent with a mechanism in which the photolysis channel produces a CCl3 radical and NO2. Kinetic studies on the reactions of hydroxyl radicals and ozone with chloropicrin suggest that, as expected, loss of CCl3NO2 by reaction with these species will be negligible under atmospheric conditions compared to photolysis. Photolysis of chloropicrin in air in the presence of isopropanol gave significant yields of ozone and is consistent with the generation of Cl atoms and NOx following the photodissociation of CCl3NO2. The atmospheric implications of the use of chloropicrin as a pesticide are discussed.