Ozone, atmosphere alkene reactions

Adeniji, S.A., Kerr, J.A., Williams, M.R. (1981) Rate constants for ozone-alkene reactions under atmospheric conditions. Int. J. Chem. Kinet. 13, 209-217. 

Grosjean, D., Grosjean, E., Williams, II, E.L. (1994) Atmospheric chemistry of olefins A product study of the ozone — alkene reaction with cyclohexane added to scavenge OH. Environ. Sci. Technol. 26, 186-196. 

Grosjean, D E. Grosjean, and E. L. Williams, Atmospheric Chemistry of Olefins A Product Study of the Ozone-Alkene Reaction with Cyclohexane Added to Scavenge OH, Emiron. Sci. TechnoL, 28, 186-196 (1994c). 

Onsager inverted snowball theory (Com.) relation to Smoluchowski equation in, 35 relaxation time by, 34 rotational diffusion and, 36 Ozone in the atmosphere, 108 alkene reactions with, 108 Crigee intermediate from, 108 molozonide from, 108 ethylene reaction with, 109 acetaldehyde effect on, 113 formic anhydride from, 110 sulfur dioxide effect on, 113 sulfuric acid aerosols from, 114 infrared detection of, 108 tetramethylethylene (TME) reaction with, 117... 

Experimental studies have shown that ozone-alkene reactions in the gas phase likewise proceed via intermediate formation of 1,2,3-trioxolanes (primary ozonides) whose spontaneous decomposition then as a rule leads to a variety of subsequent products, including 1,2,4-trioxolanes (81JA3807). Because ozone is present in the atmosphere (from 0.02p.p.m. at sea level up to 0.2 p.p.m. and more in industrial and urbanized areas), reactions of... 

Channel Eq. 30b is of considerable importance as it produces OH radicals. The OH radical yield varies between 10 and 100% depending on the particular alkene [8,59]. Although it has been known for many years that OH radicals are produced in the reaction of ozone with alkenes [60] it has only recently been recognized that this could be an important nighttime source of OH radicals in the atmosphere. Channel Eq. 30a gives a stabilized biradical. The atmospheric fate of stabilized biradicals is dominated by reaction with water vapor, which proceeds predominately to give carboxylic acids, e.g.,... 

In summary, the reaction of ozone with alkenes is important in the atmospheric degradation of alkenes. In all cases the reaction leads to rupture of the > C = C < double bond. The double bond is replaced by a carbonyl group on one side and a Criegee biradical on the other. The Criegee biradical is formed energetically excited and decomposes by a variety of different routes to give a complex mixture of oxygenated products (mainly carbonyls). 

Another potential dark source of in the atmosphere, more particularly in the boundary layer, is from the reactions between ozone and alkenes. The ozonolysis of alkenes can lead to the direct production of the OH radical at varying yields (between 7 and 100%) depending on the structure of the alkene, normally accompanied by the co-production of an (organic) peroxy radical. As compared to both the reactions of OH and NO3 with alkenes the initial rate of the reaction of ozone with an alkene is relatively slow, this can be olfset under regimes where there are high concentrations of alkenes and/or ozone. For example, under typical rural conditions the atmospheric lifetimes for the reaction of ethene with OH, O3 and NO3 are 20 h, 9.7 days and 5.2 months, respectively in contrast, for the same reactants with 2-methyl-2-butene the atmospheric lifetimes are 2.0 h, 0.9 h and 0.09 h. 

In contrast to the water phase the HO radicals can have a much longer lifetime in gaseous media, i.e. up to 1 s for the OH and 60 s for the HO radical, respectively (Fabian, 1989). Despite the low concentration of OH radicals of about 10 molecules per cm in the sunlit troposphere (Ehhalt, 1999) they play an important role in controlling the removal of many organic natural and manmade compounds from the atmosphere (Eisele et al., 1997, Eisele and Bradshaw, 1993). Even in indoor environments, the formation of hydroxyl radicals is possible by ozone/alkene reactions (Atkinson et al., 1995). Steady-state indoor hydroxyl radical concentrations of about 6.7x10 ppb equivalent to 1.7x10 molecules cm were calculated at an ozone concentration of 20 ppb (Weschler and Shields, 1996). 

In an attempt to determine the atmospheric oxidation processes that would result in an arene oxide functional group in PAHs, Murray and Kong (1994) studied the reaction of particle-bound PAHs with oxidants derived from the reactions of ozone with alkenes. Phenanthrene and pyrene were converted to arene oxides under these simulated atmospheric conditions. Control experiments indicated that the oxidant responsible for the transformation was not ozone, but a product of the reaction of ozone with tetramethylethylene (TME), probably the carbonyl oxide or the dioxirane derived from TME. 

Moller, D. (1988) Production of free radicals by an ozone-alkene reaction - a possible factor in the new-type forest decline Atmospheric Environment 22, 2607-2611 Moller, D. (1989) The possible role of H2O9 in new-type forest decline. Atmospheric Environment 23, 1187-1193... 

The results of LACTOZ have provided an extended kinetic data base for the following classes of reactions reactions of OH with VOCs, reactions of NO3 with VOCs and peroxy radicals, reactions of O3 with alkenes, reactions of peroxy radicals (self reactions, reaction with HO2, other RO2, NO, NO2), reactions of alkoxy radicals (reactions with O2, decomposition, isomerisation), thermal decomposition of peroxynitrates. Photolysis parameters (absorption cross-section, quantum yields) have been refined or obtained for the first time for species which photolyse in the troposphere. Significantly new mechanistic information has also been obtained for the oxidation of aromatic compounds and biogenic compounds (especially isoprene). These different data allow the rates of the processes involved to be modelled, especially the ozone production from the oxidation of hydrocarbons. The data from LACTOZ are summarised in the tables given in this report and have been used in evaluations of chemical data for atmospheric chemistry conducted by international evaluation groups of NASA and lUPAC. 

The reaction of ozone with alkenes produces OH and other radicals. Work in LACTOZ has provided quantitative data for the yield of OH for a variety of alkenes, including biogenic hydrocarbons. Yields of around 50 % were obtained for the reaction of ozone with typical alkenes, making this a source of atmospheric free radicals, which is especially significant at night-time when photolytic sources are absent. 

Although ozone-alkene reactions were not specified in the original objectives of LACTOZ they constitute a loss process for ozone and are important for degradation of unsaturated hydrocarbons, in particular alkenes with multiple double bonds and complex structures, such as are found in the biogenic hydrocarbons. Emphasis in LACTOZ has been on the rates and mechanisms under atmospheric conditions. These studies led to downward revision of the rate constants of the O3 alkene reactions, due to complications arising in many earlier investigations from secondary reactions of radicals produced in the primary step. Some important hitherto unknown aspects of ozone reactions, such as the formation of peroxides and their dependence on the water vapour concentrations, have been discovered in LACTOZ. 

All carbonyl oxides proved to be highly photolabile, and on photolysis yield dioxiranes 3 or split off oxygen atoms to produce ketones. Oxygen atoms are also formed thermally from vibrationally excited 1. Thus, if the large exothermicity of the ozonolysis reaction is taken into account, 1 might be a source of O atoms and OH radicals in the troposphere. The role of dioxiranes has not yet been discussed in context with atmospheric chemistry, although the formation of these species in contrast to the isomeric carbonyl oxides - in ozone/alkene reactions has been unequivocally demonstrated [13]. 

Kelly, C., H. W. Sidebottom, J. Treacy, and O. J. Nielsen, Reactions of CF3O Radicals with Selected Alkenes and Aromatics under Atmospheric Conditions, Chem. Phys. Lett., 218, 29-33 (1994). Kerr, J. B Trends in Total Ozone at Toronto between 1960 and 1991, J. Geophys. Res., 96, 20703-20709 (1991). 

Photolysis of atmospheric pollutants by solar radiation results in an increase of ozone concentration in certain urban areas and is the cause of a sequence of oxidation reactions with polymers. Ozone reacts with practically all organic materials especially with alkenes. The rate of its reaction with alkene is several orders of magnitude higher than that with alkane. The ratio of the rate constants of ozone with ethene/ethane is 1.5 x 105, with propene/propane 1.6 x 106, and with butene- 1/butane 1.1 x 106, at room temperature [5],... 

Ozone is an extremely reactive chemical. Its reaction with alkenes was discussed in Section 11.11. Although it is considered a pollutant in the lower atmosphere, its presence in the upper atmosphere has beneficial health effects due to its absorption of ultraviolet light. 

In addition to OH radicals, unsaturated bonds are reactive towards O3 and NO3 radicals and reaction with these species is an important atmospheric degradation mechanism for unsaturated compounds. Table 4 lists rate constants for the reactions of 03 and NO3 radicals with selected alkenes and acetylene. To place such rate constants into perspective we need to consider the typical ambient atmospheric concentrations of O3 and NO3 radicals. Typical ozone concentrations in pristine environments are 20-40 ppb while concentrations in the range 100-200 ppb are experienced in polluted air. The ambient concentration of NO3 is limited by the availability of NO sources. In remote marine environments the NO levels are extremely low (a few ppt) and NO3 radicals do not play an important role in atmospheric chemistry. In continental and urban areas the NO levels are much higher (up to several hundred ppb in polluted urban areas) and NO3 radicals can build up to 5-100 ppt at night (N03 radicals are photolyzed rapidly and are not present in appreciable amounts during the day). For the purposes of the present discussion we have calculated the atmospheric lifetimes of selected unsaturated compounds in Table 4 in the presence of 100 ppb (2.5 x 1012 cm 3) of O3 and 10 ppt (2.5 x 108 cnr3) of NO3. Lifetimes in other environments can be evaluated by appropriate scaling of the data in Table 4. As seen from Table 4, the more reactive unsaturated compounds have lifetimes with respect to reaction with O3 and NO3 radicals of only a few minutes ... 

In summary, alkenes are reactive compounds and are removed rapidly from the atmosphere by a variety of processes. Reaction with OH radicals, ozone, and NO3 radicals all play important roles. These reactions proceed via addition to the unsaturated bond giving an adduct which decomposes and/or reacts with 02 leading to the generation of a variety of transient radical species which react to form the first generation closed-shell products (principally carbonyl compounds). 

Gasoline hydrocarbons volatilized to the atmosphere quickly undergo photochemical oxidation. The hydrocarbons are oxidized by reaction with molecular oxygen (which attacks the ring structure of aromatics), ozone (which reacts rapidly with alkenes but slowly with aromatics), and hydroxyl and nitrate radicals (which initiate side-chain oxidation reactions) (Stephens 1973). Alkanes, isoalkanes, and cycloalkanes have half-lives on the order of 1-10 days, whereas alkenes, cycloalkenes, and substituted benzenes have half- lives of less than 1 day (EPA 1979a). Photochemical oxidation products include aldehydes, hydroxy compounds, nitro compounds, and peroxyacyl nitrates (Cupitt 1980 EPA 1979a Stephens 1973). 

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