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Every day, large quantities of volatile organic compounds (VOCs) are emitted into the atmosphere from both anthropogenic and natural sources. The formation of gaseous and particulate secondary products caused by oxidation of VOCs is one of the largest unknowns in the quantitative prediction of the earth’s climate on a regional and global scale, and on the understanding of local air quality. To be able to model and control their impact, it is essential to understand the sources of VOCs, their distribution in the atmosphere and the chemical transformations which remove these compounds from the atmosphere. In recent years techniques for the analysis of organic compounds in the atmosphere have been developed to increase the spectrum of detectable compounds and their detection limits. New methods have been introduced to increase the time resolution of those measurements and to resolve more complex mixtures of organic compounds. Volatile Organic Compounds in the Atmosphere describes the current state of knowledge of the chemistry of VOCs as well as the methods and techniques to analyse gaseous and particulate organic compounds in the atmosphere. The aim is to provide an authoritative review to address the needs of both graduate students and active researchers in the field of atmospheric chemistry research.
The relative rate technique has been used to examine the kinetics for the reaction of the hydroxyl radical (OH) with dimethyl succinate (DMS, CH3OC(=O)CH2CH2C(=O)OCH3). The measured rate constant for OH + DMS was 1.5 +/- 0.4 x 10(exp -12) cc/molecule/s at 297 +/- 3 deg K and 1 atmosphere total pressure. This is in agreement with the predicted value of 1.15 x 10(exp -12) cc/molecule/s determined by structure activity relationships. To more clearly define DMS's atmospheric degradation mechanism, the products of the OH + DMS reaction were also investigated. The only primary product detected was mono methyl succinate (MMS, CH3OC(=O)CH2CH2C(=O)OH)) at a yield of only 2.17 +/- 0.25%. Extensive efforts were used to identify other primary products but none were measured. Formic acid (HC(=O)OH); however, was observed as a secondary product being formed at a rate of (4.6 +/- 1.3) x 10(exp 14) molecules/second, 60 minutes after initiating the OH + DMS reaction. Formic acid is believed to be a degradation product of the primary product, methyl glyoxylate (MG, CH3OC(=O)C(=O)H). Product formation pathways are discussed in light of current understanding of the atmospheric chemistry of oxygenated organic compounds.
Alkoxy radicals are key intermediates of the degradation of Volatile Organic Compounds (VOCs). Of the three major reaction pathways, reaction of alkoxy radicals with molecular oxygen is more consistently important than unimolecular decomposition and isomerization. The kinetics of alkoxy radicals reacting with oxygen has been well studied for small alkoxy radicals derived from alkanes; however, there was no data for larger alkoxy radicals derived from more complicated organic compounds, such as aromatic hydrocarbons. In this study, benzyloxy (C6H5CH2O ) has been investigated in order to understand the effect of the aromatic ring on the kinetics of alkoxy radicals reaction with oxygen. The ratio of reactions benzyloxy with oxygen and versus nitrogen dioxide has been investigated by relative rate constant method with product determination by GC-FID. Then rate constants of these two reactions have been estimated and input in kinetic model by Kintecus software. Model and experiment results have been compared and suggestions for improvement have been addressed."
To understand the reaction of OH in detail at the surface of a photocatalyst, an electrochemical analysis of the irradiated semiconductors was attempted via the fluorescence probe method. For the single crystal rutile TiO2 electrodes, the facet dependence on the OH formation could be observed along with oxygen evolution by the photooxidation of water. In the subsequent study, the authors present the kinetics and mechanism of the gas-phase reaction of CH3CH2OCH2CH2Cl (2-chloroethyl ethyl ether, 2ClEEE) with OH radical using quantum chemical methods. Optimization and frequency calculations of all the species involved in the reactions were carried out at BHandHLYP/6-311++G(2d,2p) level of theory. The closing chapter is focused on the effect of hydroxyl radical and the regulation mechanism. Host immune systems generate reactive oxygen species) in order to defend microbial pathogens. Reactive oxygen species induce oxidative stress and encompass nonradical oxidants, such as hydrogen peroxide and singlet oxygen, as well as oxygen free radicals, such as superoxide anion radical and hydroxyl radical.
The focus of this contract was to investigate selected aspects of the atmospheric chemistry of volatile organic compounds (VOCs) emitted into the atmosphere from energy-related sources as well as from biogenic sources. The classes of VOCs studied were polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs, the biogenic VOCs isoprene, 2-methyl-3-buten-2-ol and cis-3-hexen-1-ol, alkenes (including alkenes emitted from vegetation) and their oxygenated atmospheric reaction products, and a series of oxygenated carbonyl and hydroxycarbonyl compounds formed as atmospheric reaction products of aromatic hydrocarbons and other VOCs. Large volume reaction chambers were used to investigate the kinetics and/or products of photolysis and of the gas-phase reactions of these organic compounds with hydroxyl (OH) radicals, nitrate (NO3) radicals, and ozone (O3), using an array of analytical instrumentation to analyze the reactants and products (including gas chromatography, in situ Fourier transform infrared spectroscopy, and direct air sampling atmospheric pressure ionization tandem mass spectrometry). The following studies were carried out. The photolysis rates of 1- and 2-nitronaphthalene and of eleven isomeric methylnitronaphthalenes were measured indoors using blacklamp irradiation and outdoors using natural sunlight. Rate constants were measured for the gas-phase reactions of OH radicals, Cl atoms and NO3 radicals with naphthalene, 1- and 2-methylnaphthalene, 1- and 2-ethylnaphthalene and the ten dimethylnaphthalene isomers. Rate constants were measured for the gas-phase reactions of OH radicals with four unsaturated carbonyls and with a series of hydroxyaldehydes formed as atmospheric reaction products of other VOCs, and for the gas-phase reactions of O3 with a series of cycloalkenes. Products of the gas-phase reactions of OH radicals and O3 with a series of biogenically emitted VOCs were identified and quantified. Ambient atmospheric measurements of the concentrations of a number of PAHs, nitro-PAHs, nitrated polycyclic aromatic compounds and biogenic VOCs were carried out in the Los Angeles air basin. In addition to these laboratory and ambient field studies, two literature reviews of VOC atmospheric chemistry and of the kinetics of the reactions of OH radicals with alkanes were also carried out. This research has been reported in 15 peer-reviewed publications.