8 research outputs found

    The Molecular Identification of Organic Compounds in the Atmosphere: State of the Art and Challenges

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    A new source of methyl glyoxal in the aqueous phase

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    Carbonyl compounds are ubiquitous in atmospheric multiphase system participating in gas, particle, and aqueous-phase chemistry. One important compound is methyl ethyl ketone (MEK), as it is detected in significant amounts in the gas phase as well as in cloud water, ice, and rain. Consequently, it can be expected that MEK influences the liquid-phase chemistry. Therefore, the oxidation of MEK and the formation of corresponding oxidation products were investigated in the aqueous phase. Several oxidation products were identified from the oxidation with OH radicals, including 2,3-butanedione, hydroxyacetone, and methylglyoxal. The molar yields were 29.5 % for 2,3-butanedione, 3.0 % for hydroxyacetone, and 9.5 % for methylglyoxal. Since methylglyoxal is often related to the formation of organics in the aqueous phase, MEK should be considered for the formation of aqueous secondary organic aerosol (aqSOA). Based on the experimentally obtained data, a reaction mechanism for the formation of methylglyoxal has been developed and evaluated with a model study. Besides known rate constants, the model contains measured photolysis rate constants for MEK (kp  =  5  ×  10−5 s−1), 2,3-butanedione (kp  =  9  ×  10−6 s−1), methylglyoxal (kp  =  3  ×  10−5 s−1), and hydroxyacetone (kp  =  2  ×  10−5 s−1). From the model predictions, a branching ratio of 60 /40 for primary/secondary H-atom abstraction at the MEK skeleton was found. This branching ratio reproduces the experiment results very well, especially the methylglyoxal formation, which showed excellent agreement. Overall, this study demonstrates MEK as a methylglyoxal precursor compound for the first time

    Investigation of Humic Substance Photosensitized Reactions via Carbon and Hydrogen Isotope Fractionation

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    SSCI-VIDE+CARE+CGOInternational audienceHumic substances (HS) acting as photosensitizers can generate a variety of reactive species, such as OH radicals and excited triplet states ((HS)-H-3*), promoting the degradation of organic compounds. Here, we apply compound-specific stable isotope analysis (CSIA) to characterize photosensitized mechanisms employing fuel oxygenates, such as methyl tert-butyl ether (MTBE) and ethyl tert-butyl ether (ETBE), as probes. In oxygenated aqueous media, Delta (Delta delta H-2/Delta delta C-13) values of 23 +/- 3 and 21 +/- 3 for ETBE obtained by photosensitization by Pahokee Peat Humic Acid (PPHA) and Suwannee River Fulvic Acid (SRFA), respectively, were in the range typical for H-abstraction by OH radicals generated by photolysis of H2O2 (Delta = 24 +/- 2). However, (3)HS* may become a predominant reactive species upon the quenching of OH radicals (Delta = 14 +/- 1), and this process can also play a key role in the degradation of ETBE by PPHA photosensitization in deoxygenated media (Delta = 11 +/- 1). This is in agreement with a model photosensitization by rose bengal (RB2-) in deoxygenated aqueous solutions resulting in one-electron oxidation of ETBE (Delta = 14 +/- 1). Our results demonstrate that the use of CSIA could open new avenues for the assessment of photosensitization pathways

    Tropospheric Aqueous-Phase Chemistry: Kinetics, Mechanisms, and Its Coupling to a Changing Gas Phase

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    The Molecular Identification of Organic Compounds in the Atmosphere: State of the Art and Challenges

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