Gas-Phase Kinetics of a Series of cis-3-Hexenyl Esters with OH Radicals under Simulated Atmospheric Conditions.

The present relative kinetic study reports on the experimentally determined gas-phase reaction rate coefficients of OH radicals with a series of seven cis-3-hexenyl esters. The experiments were carried out in the environmental simulation chamber made of quartz from the "Alexandru Ioan Cuza" University of Iasi (ESC-Q-UAIC), Romania, at a temperature of (298 ± 2) K and a total air pressure of (1000 ± 10) mbar. In situ long-path Fourier transform infrared (FTIR) spectroscopy was used to monitor cis-3-hexenyl formate (Z3HF, (Z)-CH3CH2CH═CH(CH2)2OC(O)H), cis-3-hexenyl acetate (Z3HAc, (Z)-CH3CH2CH═CH(CH2)2OC(O)CH3), cis-3-hexenyl isobutyrate (Z3HiB, (Z)-CH3CH2CH═CH(CH2)2OC(O)CH(CH3)2), cis-3-hexenyl 3-methylbutanoate (Z3H3MeB, (Z)-CH3CH2CH═CH(CH2)2OC(O)CH2CH(CH3)2), cis-3-hexenyl hexanoate (Z3HH, (Z)-CH3CH2CH═CH(CH2)2OC(O)(CH2)4CH3), cis-3-hexenyl cis-3-hexenoate (Z3HZ3H, (Z,Z)-CH3CH2CH═CH(CH2)2OC(O)CH2CH═CHCH2CH3), cis-3-hexenyl benzoate (Z3HBz, (Z)-CH3CH2CH═CH(CH2)2OC(O)C6H5), and the reference compounds. The following reaction rate coefficients (in 10-11 cm3 molecule-1 s-1) were obtained for the OH radical-initiated gas-phase oxidation of cis-3-hexenyl esters: (4.13 ± 0.45) for Z3HF, (4.19 ± 0.38) for Z3HAc, (4.84 ± 0.39) for Z3HiB, (5.39 ± 0.61) for Z3H3MeB, (7.00 ± 0.56) for Z3HH, (10.58 ± 1.40) for Z3HZ3H, and (3.41 ± 0.28) for Z3HBz. The results are discussed in terms of hexenyl ester reactivity and compared with the available literature data and structure-activity relationship (SAR) estimates. The atmospheric implications based on the average lifetimes of the investigated cis-3-hexenyl esters are discussed in the present study. The gas-phase rate coefficients for OH radical reactions are given herein for the first time for cis-3-hexenyl isobutyrate, cis-3-hexenyl 3-methylbutanoate, cis-3-hexenyl hexanoate cis-3-hexenyl cis-3-hexenoate, and cis-3-hexenyl benzoate. The newly determined gas-phase reaction rate coefficients provide new information for existing kinetic databases and contribute to the further development of SAR methodologies useful for predicting the reactivity of oxygenated volatile organic compounds.

Gas-Phase Kinetic Investigation of the OH-Initiated Oxidation of a Series of Methyl-Butenols under Simulated Atmospheric Conditions.

Five biogenic unsaturated alcohols have been investigated under simulated atmospheric conditions regarding their gas-phase OH reactivity. The gas-phase rate coefficients of OH radicals with 2-methyl-3-buten-2-ol (k1), 3-methyl-2-buten-1-ol (k2), 3-methyl-3-buten-1-ol (k3), 2-methyl-3-buten-1-ol (k4), and 3-methyl-3-buten-2-ol (k5) at 298 ± 2 K and 1000 ± 10 mbar total pressure of synthetic air were determined under low- and high-NOx conditions using the relative kinetic technique. The present work provides for the first time the rate coefficients of gas-phase reactions of hydroxyl radicals with 2-methyl-3-buten-1-ol and 3-methyl-3-buten-2-ol. The following rate constants were measured (in 10-11 cm3 molecule-1 s-1): k1 = 6.32 ± 0.49, k2 = 14.55 ± 0.93, k3 = 10.04 ± 0.78, k4 = 5.31 ± 0.37, and k5 = 11.71 ± 1.29. No significant differences in the measured rate coefficients were obtained when either 365 nm photolysis of CH3ONO in the presence of NO or 254 nm photolysis of H2O2 was used as a source of OH radicals. Reactivity toward other classes of related compounds such as alkenes and saturated alcohols is discussed. A comparison of the structure-activity relationship (SAR) estimates derived from the available accepted methodologies with experimental data available for unsaturated alcohols is provided. Atmospheric lifetimes for the investigated series of alkenols with respect to the main atmospheric oxidants are given and discussed.

Evaluation of the Environmental Fate of a Semivolatile Transformation Product of Ibuprofen Based on a Simple Two-Media Fate Model.

Partitioning between surface waters and the atmosphere is an important process, influencing the fate and transport of semi-volatile contaminants. In this work, a simple methodology that combines experimental data and modeling was used to investigate the degradation of a semi-volatile pollutant in a two-phase system (surface water + atmosphere). 4-Isobutylacetophenone (IBAP) was chosen as a model contaminant; IBAP is a toxic transformation product of the non-steroidal, anti-inflammatory drug ibuprofen. Here, we show that the atmospheric behavior of IBAP would mainly be characterized by reaction with •OH radicals, while degradation initiated by •NO3 or direct photolysis would be negligible. The present study underlines that the gas-phase reactivity of IBAP with •OH is faster, compared to the likely kinetics of volatilization from aqueous systems. Therefore, it might prove very difficult to detect gas-phase IBAP. Nevertheless, up to 60% of IBAP occurring in a deep and dissolved organic carbon-rich water body might be eliminated via volatilization and subsequent reaction with gas-phase •OH. The present study suggests that the gas-phase chemistry of semi-volatile organic compounds which, like IBAP, initially occur in natural water bodies in contact with the atmosphere is potentially very important in some environmental conditions.

Hybrid Azine Derivatives: A Useful Approach for Antimicrobial Therapy.

Nowadays, infectious diseases caused by microorganisms are a major threat to human health, mostly because of drug resistance, multi-drug resistance and extensive-drug-resistance phenomena to microbial pathogens. During the last few years, obtaining hybrid azaheterocyclic drugs represents a powerful and attractive approach in modern antimicrobial therapy with very promising results including overcoming microbial drug resistance. The emphasis of this review is to notify the scientific community about the latest recent advances from the last five years in the field of hybrid azine derivatives with antimicrobial activity. The review is divided according to the main series of six-member ring azaheterocycles with one nitrogen atom and their fused analogs. In each case, the main essential data concerning synthesis and antimicrobial activity are presented.

Gas-Phase Ozone Reaction Kinetics of C5-C8 Unsaturated Alcohols of Biogenic Interest.

Unsaturated alcohols are volatile organic compounds (VOCs) that characterize the emissions of plants. Changes in climate together with related increases of biotic and abiotic stresses are expected to increase these emissions in the future. Ozonolysis is one of the oxidation pathways that control the fate of unsaturated alcohols in the atmosphere. The rate coefficients of the gas-phase O3 reaction with seven C5-C8 unsaturated alcohols were determined at 296 K using both absolute and relative kinetic methods. The following rate coefficients (cm3 molecule-1 s-1) were obtained using the absolute method: (1.1 ± 0.2) × 10-16 for cis-2-penten-1-ol, (1.2 ± 0.2) × 10-16 for trans-2-hexen-1-ol, (6.4 ± 1.0) × 10-17 for trans-3-hexen-1-ol, (5.8 ± 0.9) × 10-17 for cis-3-hexen-1-ol, (2.0 ± 0.3) × 10-17 for 1-octen-3-ol, and (8.4 ± 1.3) × 10-17 for trans-2-octen-1-ol. The following rate coefficients (cm3 molecule-1 s-1) were obtained using the relative method: (1.27 ± 0.11) × 10-16 for trans-2-hexen-1-ol, (5.01 ± 0.30) × 10-17 for trans-3-hexen-1-ol, (4.13 ± 0.34) × 10-17 for cis-3-hexen-1-ol, and (1.40 ± 0.12) × 10-16 for trans-4-hexen-1-ol. Alkenols display high reactivities with ozone with lifetimes in the hour range. Rate coefficients show a strong and complex dependence on the structure of the alkenol, particularly the relative position of the OH group toward the C═C double bond. The results are discussed and compared to both the available literature data and four structure-activity relationship (SAR) methods.

Gas-phase IR cross-sections and single crystal structures data for atmospheric relevant nitrocatechols.

The gas-phase IR absorption cross sections for 3-nitrocatechol, 5-methyl-3-nitrocatechol, 4-nitrocatechol and 4-methyl-5-nitrocatechol were evaluated using the ESC-Q-UAIC (the environmental simulation chamber made of quartz from the "Alexandru Ioan Cuza" University of Iasi, Romania) photoreactor facilities. Specific infrared absorptions and integrated band intensities in the range of 650-4000 cm-1 were investigated by long path gas-phase FT-IR technique. Two different addition methods (solid and liquid transfer methods) of nitrocatechols into the reactor were employed in these investigations. All investigated nitrocatechols were synthesized and characterized by X-ray diffraction spectroscopy techniques beside traditional nuclear magnetic resonance (NMR) and infrared (IR) spectroscopy in order to evaluate their structure-properties relationship in gas and solid phase. This study reports for the first time the gas-phase infrared cross sections and the X-ray diffraction analysis for (methyl) nitrocatechols.

Experimental and theoretical study of the reactivity of a series of epoxides with chlorine atoms at 298 K.

Evaluating the reactivity of epoxides in the gas phase is very important due to their wide distribution in the atmosphere, potential health implications and atmospheric impact. The kinetic rate constants for the oxidation of epoxides have been very little studied until now. From the experimental data obtained in this work has been observed that there is an increase in reactivity towards chlorine atoms as a CH2 group is added to the hydrocarbon chain. The Structure Activity Relationship (SAR) method usually provides a good approximation of the rate constant for a wide series of compounds especially for those without complex structure and multiple organic functions. However, a good determination of the factors included in SAR estimations depends largely on the database of these compounds, which in the case of epoxides is very limited. The SAR estimation method also does not take into account other possible factors that could affect reactivity, such as the geometry of the molecule. The aim of this work is to further evaluate the reactivity of epoxides with chlorine atoms using experimental determinations, theoretical calculations and SAR estimations. For this, rate coefficients have been measured at 298 ± 2 K and 1000 ± 4 mbar pressure of synthetic air in a 1080 l Quartz Reactor (QUAREC) and a 480 l Duran glass reactor for the reaction of chlorine atoms with cyclohexene oxide (CHO), 1,2-epoxyhexane (12EHX), 1,2-epoxybutane (12EB), trans-2,3-epoxybutane (tEB) and cis-2,3-epoxybutane (cEB). Theoretical calculations for the reactions studied are in good agreement with our experimental findings and provide insights about the position of the H atom abstraction and reactivity trends for a series of epoxides. The importance of taking into consideration the geometrical distribution and the ring influence to improve SAR calculations is discussed.

Atmospheric Sink of (E)-3-Hexen-1-ol, (Z)-3-Hepten-1-ol, and (Z)-3-Octen-1-ol: Rate Coefficients and Mechanisms of the OH-Radical Initiated Degradation.

A kinetic study of the gas-phase reactions of OH radicals with three unsaturated biogenic alcohols, (E)-3-hexen-1-ol, (Z)-3-hepten-1-ol, and (Z)-3-octen-1-ol, has been performed. The rate coefficients obtained are (in units of 10(-10) cm(3) molecule(-1) s(-1)) k1 (OH + (E)-CH2(OH)CH2CH═CHCH2CH3) = (1.14 ± 0.14), k2 (OH + (Z)-CH2(OH)CH2CH═CHCH2CH2CH3) = (1.28 ± 0.23), and k3 (OH + (Z)-CH2(OH)CH2CH═CHCH2CH2CH2CH3) = (1.49 ± 0.35). In addition, a product study on the reactions of OH with (E)-3-hexen-1-ol and (Z)-3-hepten-1-ol is reported. All the experiments were performed at (298 ± 2) K and 1 atm of NOx-free air in a 1080 L photoreactor with in situ FTIR detection of organics. This work constitutes the first kinetic study of the reactions of OH radicals with (Z)-3-hepten-1-ol and (Z)-3-octen-1-ol as well as the first determination of the fate of the hydroxy alkoxy radicals formed in the title reactions. An analysis of the available rates of addition of OH and Cl to the double bond of different unsaturated alcohols at 298 K has shown that they can be related by the expression log kOH = (0.29 ± 0.04) log kCl - 10.8. The atmospheric lifetimes of the alcohols studies were estimated to be around 1 h for reaction with OH radicals. The products formed in the title reactions are mainly carbonylic compounds that can contribute to the formation of ozone and PANs-type compounds in the troposphere.

Rate Coefficients for the Gas-Phase Reactions of Hydroxyl Radicals with a Series of Methoxylated Aromatic Compounds.

Rate coefficients for the reactions of hydroxyl radicals (OH) with a series of oxygenated aromatics (two methoxybenzene and five methoxyphenol isomers) have been obtained using the relative kinetic method in 1080 and 480 L photoreactors at the University of Wuppertal, Germany. The experiments were realized at 295 ± 2 K and 1 bar total pressure of synthetic air using in situ Fourier transform infrared spectroscopy for the chemical analysis. The following rate coefficients (in units of cm(3) molecule(-1) s(-1)) were determined: methoxybenzene (anisole), (2.08 ± 0.21) × 10(-11); 1-methoxy-2-methylbenzene, (4.56 ± 0.50) × 10(-11); 2-methoxyphenol (guaiacol), (5.40 ± 0.72) × 10(-11); 3-methoxyphenol, (6.93 ± 0.67) × 10(-11); 4-methoxyphenol, (5.66 ± 0.55) × 10(-11); 2-methoxy-4-methylphenol, (7.51 ± 0.68) × 10(-11); 2,3-dimethoxyphenol, (7.49 ± 0.81) × 10(-11); and 2,6-dimethoxyphenol (syringol), (8.10 ± 0.98) × 10(-11). The rate coefficients for the reactions of OH with 2,3-dimethoxyphenol and 1-methoxy-2-methylbenzene are first time measurements. The rate coefficients determined in this work are compared with previous determinations reported in the literature and also with the values estimated using a structure-activity relationship method. A comparison is performed between the OH rate coefficients obtained for methoxylated aromatics with those of other substituted aromatics in order to understand the influence of the type, number, and position of the different substituents on the reactivity of aromatics toward OH. In addition, a comparison is made between the OH and Cl rate coefficients for the compounds. The principal atmospheric sink of these methoxylated aromatic compounds during daytime is their reaction with OH radicals. The corresponding lifetimes for reaction with OH radicals and Cl atoms are 2-8 and 11-50 h, respectively.

Kinetic study of the gas-phase reactions of chlorine atoms with 2-chlorophenol, 2-nitrophenol, and four methyl-2-nitrophenol isomers.

Anthropogenic activities are the main source of nitrophenols and chlorophenols in the atmosphere. Nitro and chlorophenols have a high potential to form ozone and secondary organic aerosol, thus investigations on the major photo oxidation pathways of these compounds are important to assess their contribution to urban air pollution and human health. Presented here are rate coefficients determined at atmospheric pressure and (298 ± 2) K using a relative kinetic method for the reactions of chlorine atoms with 2-chlorophenol (2ClP), 2-nitrophenol (2NP) and four methyl-2-nitrophenol (2-nitrocresol, nM2NP (n = 3,4,5,6)) isomers. The following rate coefficients (in units of cm(3) molecule(-1) s(-1)) have been obtained: (5.9 ± 1.5) × 10(-12) for 2ClP, (6.8 ± 2.3) × 10(-12) for 2NP, and (14.0 ± 4.9) × 10(-11), (4.3 ± 1.5) × 10(-11), (1.94 ± 0.67) × 10(-11) and (2.68 ± 0.75) × 10(-11) for the four methyl-2-nitrophenol isomers 3M2NP, 4M2NP, 5M2NP, and 6M2NP, respectively. This study represents the first kinetic investigation for the reaction of chlorine atoms with all the nitrophenols. In addition, to assist in the interpretation of the results, rate coefficients for the reactions of Cl atoms with the cresol ortho, meta, and para isomers have been determined for the first time. The rate coefficient for the reaction with 2ClP is in good agreement with previous data and the relative reactivity of 2NP, 4M2NP, 5M2NP, and 6M2NP can be rationalized based on known substituent effects. The rate coefficient for 3M2NP is anomalously large; the observation of significant NO2 production in only this reaction suggests that an ipso substitution mechanism is the cause of the enhanced reactivity.

Rate coefficients for the gas-phase reaction of chlorine atoms with a series of methoxylated aromatic compounds.

The reaction of a series of oxygenated aromatics (two methoxybenzene and six methoxyphenol isomers) with chlorine atoms has been studied in two simulation chambers with volumes of 1080 and 480 L at the University of Wuppertal. Experiments were performed at 295 ± 2 K and a total pressure of synthetic air of 1 bar using the relative kinetic method with in situ Fourier transform infrared spectroscopy for chemical analysis. The following rate coefficients (in units of cubic centimeter per molecule per second) were determined: (1.07 ± 0.24) × 10(-10) for methoxybenzene, (1.20 ± 0.24) × 10(-10) for 1-methoxy-2-methylbenzene, (2.97 ± 0.66) × 10(-10) for 2-methoxyphenol (guaiacol), (2.99 ± 0.62) × 10(-10) for 3-methoxyphenol, (2.86 ± 0.58) × 10(-10) for 4-methoxyphenol, (3.35 ± 0.68) × 10(-10) for 2-methoxy-4-methylphenol, (4.73 ± 1.06) × 10(-10) for 2,3-dimethoxyphenol, and (2.71 ± 0.61) × 10(-10) for 2,6-dimethoxyphenol (syringol). To the best of our knowledge, this work represents the first determination of the rate coefficients for the gas-phase reaction of the chlorine atoms with the methoxy-aromatic compounds investigated. The reactivity of the methoxylated aromatics toward Cl is compared with that of other substituted aromatic compounds, and the differences in the rate coefficients are interpreted in terms of the type, number, and position of the different substituents on the aromatic ring. The atmospheric implications of the studied reactions are also discussed.

Products and mechanism of the reactions of OH radicals and Cl atoms with methyl methacrylate (CH2═C(CH3)C(O)OCH3) in the presence of NOx.

The OH radical and Cl atom initiated photodegradation of methyl methacrylate has been investigated in a 1080 L quartz-glass environmental chamber at 298 ± 2 K and atmospheric pressure of synthetic air using in situ FTIR spectroscopy to monitor the reactants and products. The major products observed in the OH reaction were methyl pyruvate (92 ± 16%) together with formaldehyde (87 ± 12%) as a coproduct from the C1-C2 bond cleavage channel of the intermediate 1,2-hydroxyalkoxy radical, formed by the addition of OH to the terminal carbon of the double bond which is designated C1. For the Cl atom reaction, the products identified were chloroacetone (41 ± 6%) together with its coproduct formaldehyde (35 ± 5%) and methyl pyruvate (24 ± 4%) together with its coproduct formylchloride (25 ± 4%). The results show that the fate of the intermediate 1,2-chloroalkoxy radical involves not only cleavage of the C1-C2 bond but also quite substantial cleavage of the C2-C3 bond. The present results are compared with previous studies of acrylates, showing different branching ratios for the OH and Cl addition reactions in the presence of NOx. Atmospheric implications are discussed.

Capillary atmospheric pressure electron capture ionization (cAPECI): a highly efficient ionization method for nitroaromatic compounds.

We report on a novel method for atmospheric pressure ionization of compounds with elevated electron affinity (e.g., nitroaromatic compounds) or gas phase acidity (e.g., phenols), respectively. The method is based on the generation of thermal electrons by the photo-electric effect, followed by electron capture of oxygen when air is the gas matrix yielding O2(-) or of the analyte directly with nitrogen as matrix. Charge transfer or proton abstraction by O2(-) leads to the ionization of the analytes. The interaction of UV-light with metals is a clean method for the generation of thermal electrons at atmospheric pressure. Furthermore, only negative ions are generated and neutral radical formation is minimized, in contrast to discharge- or dopant assisted methods. Ionization takes place inside the transfer capillary of the mass spectrometer leading to comparably short transfer times of ions to the high vacuum region of the mass spectrometer. This strongly reduces ion transformation processes, resulting in mass spectra that more closely relate to the neutral analyte distribution. cAPECI is thus a soft and selective ionization method with detection limits in the pptV range. In comparison to standard ionization methods (e.g., PTR), cAPECI is superior with respect to both selectivity and achievable detection limits. cAPECI demonstrates to be a promising ionization method for applications in relevant fields as, for example, explosives detection and atmospheric chemistry.

Atmospheric oxidation of vinyl and allyl acetate: product distribution and mechanisms of the OH-initiated degradation in the presence and absence of NO(x).

The products formed from the reactions of OH radicals with vinyl acetate and allyl acetate have been studied in a 1080 L quartz-glass chamber in the presence and absence of NO(x) using in situ FTIR spectroscopy to monitor the reactant decay and product formation. The yields of the primary products formed in the reaction of OH with vinyl acetate were: formic acetic anhydride (84 ± 11)%; acetic acid (18 ± 3)% and formaldehyde (99 ± 15)% in the presence of NO(x) and formic acetic anhydride (28 ± 5)%; acetic acid (87 ± 12)% and formaldehyde (52 ± 8)% in the absence of NO(x). For the reaction of OH with allyl acetate the yields of the identified products were: acetoxyacetaldehyde (96 ± 15)% and formaldehyde (90 ± 12)% in the presence of NO(x) and acetoxyacetaldehyde (26 ± 4)% and formaldehyde (12 ± 3)% in the absence of NO(x). The present results indicate that in the absence of NO(x) the main fate of the 1,2-hydroxyalkoxy radicals formed after addition of OH to the double bond in the compounds is, in the case of vinyl acetate, an α-ester rearrangement to produce acetic acid and CH(2)(OH)CO(•) radicals and in the case of allyl acetate reaction of the radical with O(2) to form acetic acid 3-hydroxy-2-oxo-propyl ester (CH(3)C(O)OCH(2)C(O)CH(2)OH). In contrast, in the presence of NO(x) the main reaction pathway for the 1,2-hydroxyalkoxy radicals is decomposition. The results are compared with the available literature data and implications for the atmospheric chemistry of vinyl and allyl acetate are assessed.

Kinetics and mechanisms of the tropospheric reactions of menthol, borneol, fenchol, camphor, and fenchone with hydroxyl radicals (OH) and chlorine atoms (Cl).

Relative kinetic techniques have been used to measure the rate coefficients for the reactions of oxygenated terpenes (menthol, borneol, fenchol, camphor, and fenchone) and cyclohexanol with hydroxyl radicals (OH) and chlorine atoms (Cl) at 298 ± 2 K and atmospheric pressure. The rate coefficients obtained for the reactions of the title compounds with OH are the following (in units of 10(-11) cm(3) molecule(-1) s(-1)): (1.48 ± 0.31), (2.65 ± 0.32), (2.49 ± 0.30), (0.38 ± 0.08), (0.39 ± 0.09) for menthol, borneol, fenchol, camphor, and fenchone, respectively. For the corresponding reactions with Cl atoms the rate coefficients are as follows (in units of 10(-10) cm(3) molecule(-1) s(-1)): (3.21 ± 0.26), (3.40 ± 0.28), (2.72 ± 0.13), (2.93 ± 0.17), (1.59 ± 0.10), and (1.86 ± 0.29) for cyclohexanol, menthol, borneol, fenchol, camphor, and fenchone, respectively. The reported error is twice the standard deviation. Product studies of the reactions were performed using multipass in situ FTIR (Fourier transform infrared spectroscopy) and solid-phase microextraction (SPME) with analysis by GC-MS (gas chromatography-mass spectrometry). A detailed mechanism is proposed to justify the observed reaction products.

Daytime reactions of 1,8-cineole in the troposphere.

Relative rate coefficients for the gas-phase reaction of chlorine atoms (Cl) and hydroxyl radicals (OH) with 1,8-cineole were determined by Fourier-transform infrared (FTIR) spectroscopy between 285 and 313 K at atmospheric pressure. The temperature dependence of both reactions shows simple Arrhenius behaviour which can be represented by the following expressions (in units of cm(3) molecule(-1) s(-1)): k(1,8-cineole+OH)=(6.28 ± 6.53) × 10(-8) exp[(-2549.3 ± 155.7)/T] and k(1,8-cineole+Cl)=(1.35 ± 1.07) × 10(-10) exp[(-151.6 ± 237.7)/T]. Major products of the titled reactions were identified by solid-phase microextraction (SPME) coupled to a GC-MS. Additionally, the first step of the reaction was theoretically studied by ab initio calculations and a reaction mechanism is proposed.

FTIR product distribution study of the Cl and OH initiated degradation of methyl acrylate at atmospheric pressure.

A product study is reported on the gas-phase reactions of OH radicals and Cl atoms with methyl acrylate. The experiments were performed in a 1080-L quartz-glass chamber in synthetic air at 298 ± 2 K and 760 ± 10 Torr using long-path in situ FTIR spectroscopy for the analysis of the reactants and products. In the absence of NO(x) the major product observed in the OH reaction is methyl glyoxylate, with formaldehyde as a coproduct. For the reaction with Cl only formyl chloride (HC(O)Cl), CO, and HCl could be positively identified as products, however, the concentration-time behavior of these products show that they are secondary products and originate from the further oxidation of a major primary product. From this behavior and a comparison with simulated spectra unidentified bands in the residual product spectra are tentatively attributed to a compound of structure CH(2)ClC(O)C(O)OCH(3), i.e., formation of methyl 3-chloro-2-oxopropanoate from the reaction of Cl with methyl acrylate. The present results are compared with previous results where available and simple atmospheric degradation mechanisms are postulated to explain the formation of the observed products.

OH-initiated degradation of unsaturated esters in the atmosphere: kinetics in the temperature range of 287-313 K.

The kinetics of the gas-phase reactions of hydroxyl radicals (OH) with methyl methacrylate (k(1)), butyl methacrylate (k(2)), butyl acrylate (k(3)), and vinyl acetate (k(4)) have been investigated for the first time as a function of temperature using the relative technique. The experiments were performed in a 1080 L quartz glass photoreactor over the temperature range (T = 287-313 K) at a total pressure of 760 +/- 10 Torr synthetic air using in situ FTIR absorption spectroscopy to monitor the concentration-time behaviors of reactants. OH radicals were produced by the 254 nm photolysis of hydrogen peroxide (H(2)O(2)). The following Arrhenius expressions (in units of cm(3) molecule(-1) s(-1)) adequately describe the measured rate coefficients as a function of temperature: k(1) = (1.97 +/- 0.95) x 10(-12) exp[(921 +/- 52)/T], k(2) = (1.65 +/- 1.05) x 10(-11) exp[(413 +/- 34)/T], k(3) = (4.4 +/- 2.5) x 10(-13) exp[(1117 +/- 105)/T], and k(4) = (4.06 +/- 2.02) x 10(-12) exp[(540 +/- 49)/T]. All of the rate coefficients display a negative temperature dependence and low pre-exponential factor, which supports an addition mechanism for the reactions involving reversible OH-adduct formation. The rate coefficients (in units of cm(3) molecule(-1) s(-1)) determined at room temperature (298 K) were as follows: k(1) = (4.30 +/- 0.98) x 10(-11), k(2) = (6.63 +/- 1.42) x 10(-11), k(3) = (2.17 +/- 0.48) x 10(-11), and k(4) = (2.48 +/- 0.61) x 10(-11). The results are compared with previous values of the rate coefficients reported in the literature, which were mainly measured at room temperature. The reactivity of the various unsaturated esters toward the OH radical is discussed in terms of structure activity relationships and parallels are drawn with the OH-radical activities of structurally similar compounds. Using the kinetic parameters determined in this work, residence times of the esters in the atmosphere with respect to their reaction with OH have been determined and are compared with other possible degradation pathways. Possible atmospheric implications of the various degradation pathways studied are discussed.

The Cl-initiated oxidation of CH(3)C(O)OCH=CH (2), CH (3)C(O)OCH (2)CH=CH (2), and CH (2)=CHC(O)O(CH (2)) (3)CH (3) in the troposphere.

BACKGROUND, AIM, AND SCOPE: Unsaturated esters are emitted to the atmosphere from biogenic and anthropogenic sources, including those from the polymer industry. Little information exists concerning the atmospheric degradation of unsaturated esters, which are mainly initiated by OH radicals. Limited information is available on the degradation of alkenes by Cl atoms and almost no data exists for the reactions of unsaturated esters with Cl atoms. This data is necessary to assess the impact of such reactions in maritime environments where, under circumstances, OH radical- and Cl atom-initiated oxidation of the compounds can be important. Rate coefficients for the reactions of chlorine atoms with vinyl acetate, allyl acetate, and n-butyl acrylate have been determined at 298 +/- 3 K and atmospheric pressure. The kinetic data have been used in combination with that for structurally similar compounds to infer the kinetic contributions from the possible reaction channels to the overall reaction rate. MATERIALS AND METHODS: The decay of the organics was followed using in situ Fourier transform infrared spectroscopy and the rate coefficients were determined using a relative kinetic method and different hydrocarbon reference compounds. RESULTS: The following room temperature rate coefficients (in cm(3) molecule(-1) s(-1)) were obtained: k (1) (Cl + CH(3)C(O)OCH=CH(2)) = (2.68 +/- 0.91) x 10(-10), k (2) (Cl + CH(3)C(O)OCH(2)CH=CH(2)) = (1.30 +/- 0.45) x 10(-10), and k (3) (Cl + CH(2)=CHC(O)O(CH(2))(3)CH(3)) = (2.50 +/- 0.78) x 10(-10), where the uncertainties are a combination of the 2sigma statistical errors from linear regression analyses and a contribution to cover uncertainties in the rate coefficients of the reference hydrocarbons. DISCUSSION: This is the first kinetic study of the title reactions under atmospheric conditions. The kinetic data were analyzed in terms of reactivity trends and used to estimate the atmospheric lifetimes of the esters and assess their potential importance in the marine atmosphere. CONCLUSIONS: Although reaction with OH radicals is the major atmospheric sink for the unsaturated esters studied, reaction with Cl atoms can compete in the early morning hours in coastal areas where the Cl concentration can reach peak values as high as 1 x 10(5) atoms cm(-3). The calculated residence times show that the chemistry of unsaturated esters will impact air quality locally near their emission sources. RECOMMENDATIONS AND PERSPECTIVES: The reactions need to be studied over the range of temperatures and pressures generally encountered in the marine atmosphere. In addition, product studies should also be performed as a function of temperature since this will allow degradation mechanisms to be derived, which are representative for the wide range of conditions occurring in marine environments. Inclusion of the kinetic and product data in tropospheric numerical models will allow an assessment of potential environmental impacts of the esters for different marine pollution scenarios.

Atmospheric chemistry of acetylacetone.

A kinetic study on the reactions of the OH radical and ozone with acetylacetone (AcAc) has been performed in a 1080 L quartz glass reaction chamber using in situ FTIR spectroscopy analysis. Temperature dependent rate coefficients for the reaction of AcAc with the OH radical were determined over the temperature range 285-310 K using the relative kinetic method. The following Arrhenius expression was derived: k = 3.35 x 10(-12) exp((983 +/- 130)/T) cm3 molecule(-1) s(-1), where the indicated error is the two least-squares deviation. A rate coefficient (in units of cm3 molecule(-1) s(-1)) of (1.03 +/- 0.31) x 10(-18) has been obtained at (298 +/- 3) K for the reaction of ozone with AcAc. A product investigation on the gas-phase reaction of OH radical with AcAc was conducted in a 405 L borosilicate glass chamber using in situ FTIR spectroscopy to monitor reactants and products. Methylglyoxal, acetic acid, peroxy acetic nitrate (PAN) were positively identified as products with molar yields of (20.8 +/- 4.5)%, (16.9 +/- 3.4)%, and (2.0 +/- 0.5)%, respectively. From the residual infrared spectrum the main products are attributed to 2,3,4-pentantrione (CH3-CO-CO-CO-CH3) and its hydrated analogue pentan-2,3-dione-4-diol (CH3-CO-CO-C(OH)2-CH3). Based on the observed products, a simplified mechanism for the reaction of the OH radical with AcAc is proposed.