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  • 1.
    Nozière, Barbara
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM). Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Dziedzic, Pawel
    Stockholm University, Faculty of Science, Department of Organic Chemistry. Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Córdova, Armando
    Stockholm University, Faculty of Science, Department of Organic Chemistry. Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Common inorganic ions are efficient catalysts for organic reactions in atmospheric aerosols and other natural environments2009In: Atmospheric Chemistry and Physics Discussion, Vol. 9, no 1, p. 1-21Article in journal (Other (popular science, discussion, etc.))
    Abstract [en]

    In this work, inorganic ammonium ions, NH4+, and carbonate ions, CO32-, are reported for the first time as catalysts for organic reactions in atmospheric aerosols and other natural environments at the Earth’s surface. These reactions include the formation of C-C and C-O bonds by aldol condensation and acetal formation, and reveal a new aspect of the interactions between organic and inorganic materials in natural environments. The catalytic properties of inorganic ammonium ions, in particular, were not previously known in chemistry. The reactions were found to be as fast in tropospheric ammonium sulfate composition as in concentrated sulfuric acid. The ubiquitous presence and large concentrations of ammonium ions in tropospheric aerosols would make of ammonium catalysis a main consumption pathway for organic compounds in these aerosols, while acid catalysis would have a minor contribution. In particular, ammonium catalysis would account quantitatively for the aging of carbonyl compounds into secondary “fulvic” compounds in tropospheric aerosols, a transformation affecting the optical properties of these aerosols. In general, ammonium catalysis is likely to be responsible for many observations previously attributed to acid catalysis in the troposphere.

  • 2.
    Nozière, Barbara
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Dziedzic, Pawel
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Córdova, Armando
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Formation of secondary light-absorbing "fulvic-like'' oligomers: A common process in aqueous and ionic atmospheric particles?2007In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 34, no 21, p. L21812-Article in journal (Refereed)
    Abstract [en]

    Light-absorbing ''humic-like'' compounds of secondary origin have been consistently reported in partly inorganic aerosols and in fog waters but their formation could not be explained until now. In this work, we demonstrate that amino acid- and ammonium sulfate-catalyzed reactions in water and ionic solutions produce compounds of identical molecular and optical properties and account well for the quantities found in atmospheric particles. For typical aerosol concentrations of amino acids or ammonium sulfate the rate constants of reaction are found to be identical to the one in concentrated sulfuric acid (10-15 M), clearly demonstrating the efficiency of these catalysts. Our results also show that these reactions should be common in aqueous and ionic aerosols, as confirmed by the observations, and significantly impact their absorption index. In particular, previous radiative calculations indicate that they should substantially reduce current estimates of the cooling contribution of sulfate aerosols on climate.

  • 3.
    Nozière, Barbara
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Dziedzic, Pawel
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Córdova, Armando
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Inorganic ammonium salts and carbonate salts are efficient catalysts for aldol condensation in atmospheric aerosols2010In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 12, no 15, p. 3864-3872Article in journal (Refereed)
    Abstract [en]

    In natural environments such as atmospheric aerosols, organic compounds coexist with inorganic salts but, until recently, were not thought to interact chemically. We have recently shown that inorganic ammonium ions, NH4+, act as catalysts for acetal formation from glyoxal, a common atmospheric gas. In this work, we report that inorganic ammonium ions, NH4+, and carbonate ions, CO32−, are also efficient catalysts for the aldol condensation of carbonyl compounds. In the case of NH4+ this was not previously known, and was patented prior to this article. The kinetic results presented in this work show that, for the concentrations of ammonium and carbonate ions present in tropospheric aerosols, the aldol condensation of acetaldehyde and acetone could be as fast as in concentrated sulfuric acid and might compete with their reactions with OH radicals. These catalytic processes could produce significant amounts of polyconjugated, light-absorbing compounds in aerosols, and thus affect their direct forcing on climate. For organic gases with large Henry's law coefficients, these reactions could also result in a significant uptake and in the formation of secondary organic aerosols (SOA). This work reinforces the recent findings that inorganic salts are not inert towards organic compounds in aerosols and shows, in particular, that common ones, such as ammonium and carbonate salts, might even play important roles in their chemical transformations.

  • 4.
    Nozière, Barbara
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Dziedzic, Pawel
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Córdova, Armando
    Stockholm University, Faculty of Science, Department of Organic Chemistry.
    Products and Kinetics of the Liquid-Phase Reaction of Glyoxal Catalyzed by Ammonium Ions (NH4+)2009In: Journal of Physical Chemistry A, ISSN 1089-5639, Vol. 113, no 1, p. 231-237Article in journal (Refereed)
    Abstract [en]

    Glyoxal, a common atmospheric gas, has been reported to be depleted in some regions of the atmosphere. The corresponding sink could be accounted for by reactions in or at the surface of atmospheric particles, but these reactions were not identified. Recently, we showed that inorganic ammonium ions, NH4+, are efficient catalysts for reactions of carbonyl compounds, including glyoxal, in the liquid phase. To determine whether ammonium-catalyzed reactions can contribute to depletion of glyoxal in the atmosphere, the reactivity of this compound in aqueous solutions containing ammonium salts (ammonium sulfate, chloride, fluoride, and phosphate) at 298 K has been studied. The products identified by LC-HRMS and UV absorption revealed a mechanism involving two distinct pathways: a Bronsted acid pathway and an iminium pathway. The kinetics of the iminium pathway was studied by monitoring formation of a specific product. This pathway was second order in glyoxal in most of the solutions studied and should therefore be second order in most ammonium containing aerosols in the atmosphere. The corresponding rate constant, kII (M-1 s-1), increased strongly with ammonium ion activity, aNH4+, and pH:

    kII (M-1 s-1) ) (2 ( 1) × 10-10 exp(1.5 ( 0.8)aNH4+ exp(2.5 ( 0.2)pH.

    This iminium pathway is a lower limit for the ammonium-catalyzed consumption of glyoxal, but the contribution of the acid pathway is expected to be small in tropospheric aerosols. With these results the reactive uptake of glyoxal on ammonium-containing aerosols was estimated and shown to be a possible explanation for the depletion of this compound in Mexico City.

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