oxidation chain
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The article presents simple kinetic approaches to study the effect of multi-walled carbon nanotubes (MWCNTs) additives on the aerobic oxidation of hydrocarbons and to propose real acceptable mechanisms of the process. The aerobic liquid phase low-temperature oxidation of ethylbenzene conducted in the presence of multi-walled carbon nanotubes has been used as a model pattern. Kinetic analysis established the catalytic action associated with the presence of the iron compounds in inner channels of MWCNTs. These compounds are identified as ferric carbides provoking decomposition of the ethylbenzene hydroperoxide and thereby suppressing the competitive route of alky-peroxide radicals addition to the nanocarbon cage. Thus the reaction finally proceeds in the autocatalytic mode.Contradictory conclusions on the effect of CNTs on the oxidation chain processes existing in the literature are associated with the lack of control over nature and content of metal impurities in channels of nanotubes.

AbstractThe number of aroylethyl (ethyl)xanthates have been synthesized by the reaction of the exchange decomposition of β-dimethylaminopropiophenone hydrochlorides with potassium xanthate containing several functional groups (C=O, C=S, C–OH), which determine the use of these xanthates as stabilizers with internal synergy to polymeric materials. It was shown that the thermal stability of the compounds, depending on the nature of the substituent in the benzene ring of the molecule was observed in the temperature range of 149–196 °C. It was revealed that aroylethyl(ethyl)xanthates had a stabilizing effect due to the suppression of thermo-oxidative destruction of polyethylene; they increased the induction period of polyethylene oxidation by 2–6 times, and the oxidation rate was reduced by about 3–9 times. Among the studied compounds, 4-hydroxybenzoylethyl (ethyl)xanthate had the greatest stabilizing effect. The study of the mechanism of the stabilizing action of the compounds showed that xanthates react with cumene hydroperoxide (CHP), which proceeded through the stage of formation of an intermediate product that actively decomposed CHP, i.e., the oxidation chain was terminated by the decomposition of the CHP not by the initial xanthates but by their transformation products.

Abstract. After stagnating in the early 2000s, the atmospheric methane growth rate has been positive since 2007 with a significant acceleration starting in 2014. While the causes for previous growth rate variations are still not well determined, this recent increase can be studied with dense surface and satellite observations. Here, we use an ensemble of six multi-species atmospheric inversions that have the capacity to assimilate observations of the main species in the methane oxidation chain – namely, methane, formaldehyde, and carbon monoxide – to simultaneously optimize both the methane sources and sinks at each model grid. We show that the surge of the atmospheric growth rate between 2010–2013 and 2014–2017 is most likely explained by an increase of global CH4 emissions by 17.5±1.5 Tg yr−1 (mean ± 1σ), while variations in the hydroxyl radicals (OH) remained small. The inferred emission increase is consistently supported by both surface and satellite observations, with leading contributions from the tropical wetlands (∼ 35 %) and anthropogenic emissions in China (∼ 20 %). Such a high consecutive atmospheric growth rate has not been observed since the 1980s and corresponds to unprecedented global total CH4 emissions.

Abstract. After stagnating in the early 2000s, the atmospheric methane growth rate has been positive since 2007 with a significant acceleration starting in 2014. While causes for previous growth rate variations are still not well determined, this recent increase can be studied with dense surface and satellite observations. Here, we use an ensemble of six multi-tracer atmospheric inversions that have the capacity to assimilate the major tracers in the methane oxidation chain – namely methane, formaldehyde, and carbon monoxide – to simultaneously optimize both the methane sources and sinks at each model grid. We show that the recent surge of the atmospheric growth rate between 2010–2013 and 2014–2017 is most likely explained by an increase of global CH4 emissions by 17.5 ± 1.5 Tg yr−1 (mean ± 1σ), while variations in CH4 sinks remained small. The inferred emission increase is consistently supported by both surface and satellite observations, with leading contributions from the tropics wetlands (~ 35 %) and anthropogenic emissions in China (~ 20 %). Such a high consecutive atmospheric growth rate has not been observed since the 1980s and corresponds to unprecedented global total CH4 emissions.

Abstract Background: HSP70 represents the most highly induced member of the stress protein family which is constitutively expressed in normal cell conditions as chaperon and rapidly upregulated in response to stress conditions. Vitamin E compounds are considered to be the most potent oxidation chain breaking compounds. Although α-tocopherol, has been long considered as the most potent antioxidant among the vitamin E isomers, many studies have recently suggested a higher antioxidant potency of tocotrienols compared to tocopherols. Present study was carried out to investigate the effects of tocotrienol supplementation compared to α-tocopherol on HSP70 expression.Methods: To assess whether the increase in HSP70 secondary to the stress caused by the oxidant could decrease in the presence of vitamin E; two groups of cells were incubated for 4 hours with α-tocopherol and palm tocotrienol-rich fraction respectively with concentration of 10, 20 and 30 μg/ml after the cells were pre-exposed to oxidative stress.Results: The comparison between the negative control which represents the basal expression of HSP70 and the positive control that represents the expression of HSP70 as a response to the oxidant, has clearly indicated that treatment with 100 μM copper sulphates for 24 hours resulted in a significant up-regulation of HSP70 expression. The present study has shown that the overall effect of vitamin E compounds seems to reduce the increase in HSP70 expression. α-tocopherol tended to trigger a more constant rate of response to the dose given but unable to significantly induced the decrease of the HSP70 expression as compared to tocotrienol.Conclusion: Treatment with vitamin E has conferred significant protection against stress induced cellular damage. Whether the reduction of HSP70 by vitamin E is deleterious or beneficial is still controversial and needs to be considered.

The performance degradation of rubber gaskets under vibration compression is faster than that under static load, and the degree of performance degradation will continue to increase under humidity and thermal environment. For rubber gaskets under a long-term service, the mechanical properties of rubber gaskets were measured after accelerated aging process with different temperature in the temperature box. The precipitates of rubber structures were detected by energy-dispersive spectroscopy and scanning electron microscopy. Molecular chain of silicon rubber gasket quickly breaks to form free radicals under high-frequency stress, which initiate oxidation chain reaction and mechanochemical process. Surface leakage of silicon (Si) and magnesium (Mg) indicates that a larger percent of macromolecular chains are broken and decomposed. High temperature activates the molecular chain cracking or cross-linking, while high-frequency stress leads to transport leakage on chain decomposition. The oxygen diffusion rate and activation oxidation reaction were accelerated by the residual stress to rubber oxidation reaction rate.

Abstract. The RONOCO aircraft campaign during July 2010 and January 2011 made observations of OH, HO2, NO3, N2O5 and a number of supporting measurements at night over the UK, and reflects the first simultaneous airborne measurement of these species. We compare the observed concentrations of these short-lived species with those calculated by a box model, constrained by the concentrations of the longer lived species, using a detailed chemical scheme. OH concentrations were below the limit of detection, consistent with the model predictions. The model systematically underpredicts HO2 by a factor of ~2 and overpredicts NO3 and N2O5 by factors of around 75% and 50%, respectively. Cycling between NO3 and N2O5 is fast and thus we define the NO3x (NO3x = NO3 + N2O5) family. Production of NO3x is overwhelmingly dominated by the reaction of NO2 with O3, whereas its loss is dominated by aerosol uptake of N2O5, with NO3 + VOCs and NO3 + RO2 playing smaller roles. The production of HOx and ROx radicals is mainly due to the reaction of NO3 with VOCs. The loss of these radicals occurs through a combination of HO2 + RO2 reactions, heterogeneous processes and production of HNO3 from OH + NO2, with radical propagation primarily achieved through reactions of NO3 with peroxy radicals. Thus NO3 at night plays a similar role to both OH and NO during the day in that it both initiates ROx radical production and acts to propagate the oxidation chain. Model sensitivity to the N2O5 aerosol uptake coefficient (γN2O5) is discussed, and we find that a value of γN2O5 = 0.05 improves model simulations for NO3 and N2O5, but that these improvements are at the expense of model success for HO2. Improvements to model simulations for HO2, NO3 and N2O5 can be realised simultaneously on inclusion of additional unsaturated volatile organic compounds, however the nature of these compounds is extremely uncertain.

Abstract. The space-time variations of the carbon budget at the Earth's surface are highly variable and quantifying them represents a major scientific challenge. One strategy consists in inferring the carbon surface fluxes from the atmospheric concentrations. An inversion scheme for the hydrocarbon oxidation chain, that includes CO and CH4, is presented here with a focus on the African continent. It is based on a variational principle. The multi-tracer system has been built as an extension of a system initially developed for CO2 and includes a new simplified non-linear chemistry module. Individual in situ measurements of methyl-chloroform and individual retrievals of CO concentrations from the Measurements Of Pollution In The Troposphere (MOPITT) space-born instrument have been processed by the new system for the period 2000–2006 to infer the time series of CO emissions at the resolution of 2.5°×3.75° (latitude, longitude). It is shown that the analysed concentrations improve the fit to five independent surface measurement stations located in or near Africa by up to 28% compared to standard inventories, which confirms that significant information about CO emissions can be obtained from MOPITT data. In practice, the inversion reduces the amplitude and the interannual variability of the seasonal cycle in the northern part of Africa, with a longer burning season. In the southern part, the inversion mainly shifts the emission peak by one month later in the season, consistent with previously-published inversion results.