Photo-tautomerization of acetaldehyde as a photochemical source of formic acid in the troposphere

Organic acids play a key role in the troposphere, contributing to atmospheric aqueous-phase chemistry, aerosol formation, and precipitation acidity. Atmospheric models currently account for less than half the observed, globally averaged formic acid loading. Here we report that acetaldehyde photo-tautomerizes to vinyl alcohol under atmospherically relevant pressures of nitrogen, in the actinic wavelength range, λ = 300–330 nm, with measured quantum yields of 2–25%. Recent theoretical kinetics studies show hydroxyl-initiated oxidation of vinyl alcohol produces formic acid. Adding these pathways to an atmospheric chemistry box model (Master Chemical Mechanism) demonstrates increased formic acid concentrations by a factor of ~1.7 in the polluted troposphere and a factor of ~3 under pristine conditions. Incorporating this mechanism into the GEOS-Chem 3D global chemical transport model reveals an estimated 7% contribution to worldwide formic acid production, with up to 60% of the total modeled formic acid production over oceans arising from photo-tautomerization

Application de la photolyse laser couplée à des méthodes optiques de détection pour l'étude cinétique et spectroscopique d'espèce d'intérêt atmosphérique

Les radicaux OH et HO2 jouent un rôle essentiel dans beaucoup de processus d’oxydationdans l’atmosphère. La dégradation des composés organiques volatils dans les conditionstroposphériques est généralement initiée par la réaction avec les radicaux OH, suivie par la réactiondes produits d’oxydation avec l’oxygène. Dans le cadre de cette thèse, des études ont été menéesafin de mieux comprendre les mécanismes d’oxydation d’espèces d’intérêt atmosphérique. Pour cela,un système expérimental de photolyse laser couplée à des techniques spectroscopiques de détectionrésolues dans le temps : Continuous Wave Cavity ring-down Spectroscopy (cw-CRDS) pour HO2,Laser Induced Fluorescence (LIF) pour OH et spectroscopy UV pour l’adduit Hexamethylbenzene-OH(HMB-OH) ont été utilisés. Différents systèmes chimiques ont été étudiés en utilisant ce dispositif expérimental : 1) laréaction d’HO2 avec CH2O, 2) la photolyse à 248 nm de l’acétaldéhyde et 3) la dégradation de HMBinitiée par OH. Les techniques de cw-CRDS et d’absorption UV ont été utilisées respectivement pourmesurer les sections efficaces de CH2O et de l’adduit HMB-OH.OH and HO2 radicals play a vital role in many oxidation processes in the atmosphere. Thedegradation of volatile organic compounds under tropospheric conditions is induced by reaction withhydroxyl radicals followed by the subsequent chemistry of the initial OH oxidation products with O2.This thesis deals with the kinetic study of some of these atmospherically relevant reactions to betterunderstand their oxidation mechanisms using experimental techniques such as laser photolysiscoupled to detection by Laser Induced Fluorescence (LIF, for OH), continuous wave- Cavity RingdownSpectroscopy (cw-CRDS, for HO2) and time resolved UV spectroscopy (UV, forHexamethylbenzene-OH adduct). Different chemical systems have been studied using the above techniques: 1) the reaction ofHO2 radicals with formaldehyde, 2) the 248 nm photolysis of acetaldehyde and 3) the OH initiatedoxidation of Hexamethyl benzene. In addition to this, the spectroscopic application of cw-CRDStechnique and UV spectroscopy has been used for the measurement of absorption cross section ofselected absorption lines of formaldehyde in the near infrared region and Hexamethylbenzene-OHadduct in the UV region respectively

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Not AvailableThe present investigation was undertaken to assess the hybridity of experimental F1 plants derived from the crossing of salinity and/or submergence tolerant landraces with the high-yielding popular varieties of the west coast region of India. Seven microsatellite markers were utilized for confirming the hybridity of the 16 F1 plants developed from four cross combinations, viz. Karjat-3 X KS-19-2 (Cross 1), Goa dhan-3 X Jaddubatta (Cross 2), Jaya X KS-19-2 (Cross 3) and Karjat-3 X Jaddubatta (Cross 4). Polymorphism survey using above seven markers between the parents of all the four crosses revealed that six of them were polymorphic, whereas one marker was monomorphic. The marker RM21539 was found to be polymorphic in all the four cross combinations, followed by RM493, RM3412, RM206 and RM10843 exhibiting polymorphism in three crosses, while marker RM25181 was polymorphic in two crosses. The screening of F1s with polymorphic markers revealed that the F1s from Cross 3 exhibited heterozygosity (showing alleles from both the parents) at six marker loci, whereas the F1s from Cross 1 and Cross 4 at five loci and Cross 2 at two marker loci, thereby confirming hybridity in all the 16 tested F1 plants.Not Availabl

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Not AvailableSalt stress is a major abiotic stress affecting the productivity of rice crop worldwide. This study screened a set of 71 rice genotypes collected from coastal parts of Goa and Karnataka states in India for seedling stage salinity tolerance to identify genotypes alternative to standard salt-tolerant donors Pokkali, FL478, etc. Phenotyping for seedling stage tolerance was carried out under micro plots at an induced salinity of 12 dS/m. For haplotyping, 14 Saltol QTL linked simple sequence repeat (SSR) markers on chromosome 1 were utilized. On the basis of the response to salt stress, 10 genotypes were found tolerant, 16 moderately tolerant, 29 sensitive and 15 as highly sensitive. Among the SSR markers, marker RM10871 was the most polymorphic with a polymorphic information content of 0.90, exhibiting 14 different alleles followed by RM10793 (0.84) and RM3412 (0.80) with 8 and 7 alleles, respectively. These markers also exhibited high values for the effective number of alleles (Ne) and gene diversity (I). The haplotype analysis revealed that the allelic constitution of the Saltol region of 10 tolerant genotypes from our study varied in comparison to the reference tolerant check FL478. Further, the haplotype of three tolerant genotypes, namely, Goa Dhan 2, Panvel 1 and Goa wild rice (GWR) 005 appears to be completely different from the FL478 haplotype indicating tolerance in these genotypes is controlled by genomic region other than Saltol. These three genotypes with probable novel regions for seedling stage salt tolerance can be considered for enhancing salinity tolerance of rice cultivars.Not Availabl

Oxidation of n -Alkane ( n -C 8 H 18 ) under Reservoir Conditions in Response to Gas Mixture Injection (CO 2 /O 2 ): Understanding Oxygenated Compound Distribution

International audienc

Oxidation of n-Alkane (n-C8H18) under Reservoir Conditions, in Context of Gas Mixture Injection (CO2/O-2): Construction of a Kinetic Model

International audienceCO2 geosequestration or enhanced oil recovery (EOR) by CO2 injection in hydrocarbon reservoirs is suggested as a short-term solution for limiting CO2 atmospheric accumulation. In the case of oxy-combustion CO2 capture, the main annex gas associated with CO2 is O-2 in important proportion (=7%). Even if hydrocarbon oxidation processes by O-2 are well-known in high-temperaturelow-pressure (HT-LP) conditions, scarce data are available under reservoir conditions (high-pressurelow-temperature, HP-LT). To predict the hydrocarbon evolution in the presence of O-2 in an oil-depleted reservoir, it is necessary to investigate their reactivity. As a matter of fact, a double approach combining experimentation and modeling was performed in this study. Experiments were carried out on a model compound (n-octane), by injecting O-2/N-2 gas mixtures in a HP-LT titanium reactor. In parallel, a detailed kinetic model for n-octane, generated by the software EXGAS, was applied. Several reactions were added, and some rate parameters have been adjusted to adapt the model to reservoir conditions. The modified model was validated by experiments performed at different reaction temperatures and O-2 concentrations. The consistency between experimentations and modified oxidation model is promising for the development of a tool allowing the prediction of hydrocarbon reservoir stability

Oxidation of <i>n</i>‑Alkane (<i>n</i>‑C₈H₁₈) under Reservoir Conditions in Response to Gas Mixture Injection (CO₂/O₂): Understanding Oxygenated Compound Distribution

CO₂ geosequestration [carbon capture and storage (CCS)] and enhanced oil recovery (EOR) by CO₂ injection in hydrocarbon-depleted reservoirs could limit the CO₂ atmospheric accumulation. In the case of CO₂ capture by oxy-combustion, the main annex gas associated with CO₂ is O₂. O₂ that remains in the flue gas for injection can induce the oxidation of the hydrocarbons contained in the reservoirs. The effect of O₂ must be studied in terms of benefit and/or risk for CCS or EOR. To investigate the mechanism of hydrocarbon oxidation, it is essential to analyze the distributions of the formed oxygenated compounds. That is why experiments have been performed with a model compound (<i>n</i>-octane) in a closed reactor under high pressure at different temperatures and with different oxygen concentrations. The product distribution suggests two pathways of <i>n</i>-alkane oxidation, with (i) the preservation of the aliphatic chain length of the initial <i>n</i>-alkane, which generates oxygenated products with the same number of carbon, and (ii) the breakdown processes of the initial <i>n</i>-alkane, which generates low-molecular-weight oxygenated products. The new understanding of the mechanism of <i>n</i>-alkane oxidation could be incorporated into the detailed kinetic model of our previous study, which is specific to the reservoir conditions