Innentitelbild: Solvation-Induced Changes in the Mechanism of Alcohol Oxidation at Gold/Titania Nanocatalysts in the Aqueous Phase versus Gas Phase (Angew. Chem. 13/2018)

Abstract. The gas phase oxidation of organic species is a multigenerational process involving a large number of secondary compounds. Most secondary organic species are water-soluble multifunctional oxygenated molecules. The fully explicit chemical mechanism GECKO-A (Generator of Explicit Chemistry and Kinetics of Organics in the Atmosphere) is used to describe the oxidation of organics in the gas phase and their mass transfer to the aqueous phase. The oxidation of three hydrocarbons of atmospheric interest (isoprene, octane and α-pinene) is investigated for various NOx conditions. The simulated oxidative trajectories are examined in a new two dimensional space defined by the mean oxidation state and the solubility. The amount of dissolved organic matter was found to be very low (yield less than 2% on carbon atom basis) under a water content typical of deliquescent aerosols. For cloud water content, 50% (isoprene oxidation) to 70% (octane oxidation) of the carbon atoms are found in the aqueous phase after the removal of the parent hydrocarbons for low NOx conditions. For high NOx conditions, this ratio is only 5% in the isoprene oxidation case, but remains large for α-pinene and octane oxidation cases (40% and 60%, respectively). Although the model does not yet include chemical reactions in the aqueous phase, much of this dissolved organic matter should be processed in cloud drops and modify both oxidation rates and the speciation of organic species.

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Identifying precursors and aqueous organic aerosol formation pathways during the SOAS campaign

Atmospheric Chemistry and Physics ◽

10.5194/acp-16-14409-2016 ◽

2016 ◽

Vol 16 (22) ◽

pp. 14409-14420 ◽

Cited By ~ 19

Author(s):

Neha Sareen ◽

Annmarie G. Carlton ◽

Jason D. Surratt ◽

Avram Gold ◽

Ben Lee ◽

...

Keyword(s):

Mass Spectrometry ◽

Gas Phase ◽

Aqueous Phase ◽

Organic Aerosol ◽

Water Soluble ◽

Negative Ion ◽

Anthropogenic Sources ◽

Ionization Mass ◽

Aqueous Mixtures ◽

Aerosol Formation

Abstract. Aqueous multiphase chemistry in the atmosphere can lead to rapid transformation of organic compounds, forming highly oxidized, low-volatility organic aerosol and, in some cases, light-absorbing (brown) carbon. Because liquid water is globally abundant, this chemistry could substantially impact climate, air quality, and health. Gas-phase precursors released from biogenic and anthropogenic sources are oxidized and fragmented, forming water-soluble gases that can undergo reactions in the aqueous phase (in clouds, fogs, and wet aerosols), leading to the formation of secondary organic aerosol (SOAAQ). Recent studies have highlighted the role of certain precursors like glyoxal, methylglyoxal, glycolaldehyde, acetic acid, acetone, and epoxides in the formation of SOAAQ. The goal of this work is to identify additional precursors and products that may be atmospherically important. In this study, ambient mixtures of water-soluble gases were scrubbed from the atmosphere into water at Brent, Alabama, during the 2013 Southern Oxidant and Aerosol Study (SOAS). Hydroxyl (OH⚫) radical oxidation experiments were conducted with the aqueous mixtures collected from SOAS to better understand the formation of SOA through gas-phase followed by aqueous-phase chemistry. Total aqueous-phase organic carbon concentrations for these mixtures ranged from 92 to 179 µM-C, relevant for cloud and fog waters. Aqueous OH-reactive compounds were primarily observed as odd ions in the positive ion mode by electrospray ionization mass spectrometry (ESI-MS). Ultra high-resolution Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) spectra and tandem MS (MS–MS) fragmentation of these ions were consistent with the presence of carbonyls and tetrols. Products were observed in the negative ion mode and included pyruvate and oxalate, which were confirmed by ion chromatography. Pyruvate and oxalate have been found in the particle phase in many locations (as salts and complexes). Thus, formation of pyruvate/oxalate suggests the potential for aqueous processing of these ambient mixtures to form SOAAQ.

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Influence of Water on the Dynamic Adsorption of Chlorinated VOCs on Active Carbon: Relative Humidity of the Gas Phase versus Pre-Adsorbed Water

Adsorption Science & Technology ◽

10.1260/026361706778812871 ◽

2006 ◽

Vol 24 (3) ◽

pp. 215-228 ◽

Cited By ~ 28

Author(s):

F. Cosnier ◽

A. Celzard ◽

G. Furdin ◽

D. Bégin ◽

J.F. Marêché

Keyword(s):

Gas Phase ◽

Activated Carbons ◽

Adsorbed Water ◽

Phase Versus ◽

Chlorinated Volatile Organic Compounds ◽

Adsorption Capacities ◽

Volatile Organic ◽

Influence Of Water ◽

Hindered Diffusion ◽

Induced Adsorption

The present work deals with the influence of water on the adsorption of two chlorinated volatile organic compounds (VOCs) on activated carbons (ACs) having very different pore textures and surface chemistry. Two kinds of moisture were considered, viz. pre-adsorbed on the AC or present as steam in the gaseous phase, at various relative humidities ranging from 30% to 75%. It is shown that the adsorption of the VOCs depends on the kind of moisture. If the latter is pre-adsorbed, water is just displaced by the VOCs (overshoot). The adsorption capacities of the AC remain unchanged and only some minor changes in the shape of the breakthrough front, corresponding to hindered diffusion, may sometimes occur. In contrast, the simultaneous adsorption of steam and VOC leads to competition between water and the chlorinated compound, with direct consequences on the adsorption kinetics and capacities of the AC. However, the decrease of the water-induced adsorption performances depends strongly on the AC and the VOC (through different VOC/AC and water/VOC interactions), and on the concentration of the VOC.

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Do organic surface films on sea salt aerosols influence atmospheric chemistry? – a model study

Atmospheric Chemistry and Physics ◽

10.5194/acp-7-5555-2007 ◽

2007 ◽

Vol 7 (21) ◽

pp. 5555-5567 ◽

Cited By ~ 27

Author(s):

L. Smoydzin ◽

R. von Glasow

Keyword(s):

Mass Transfer ◽

Liquid Phase ◽

Gas Phase ◽

Aqueous Phase ◽

Atmospheric Chemistry ◽

Organic Coating ◽

Sea Salt ◽

Tropospheric Chemistry ◽

Special Focus ◽

Sea Salt Aerosols

Abstract. Organic material from the ocean's surface can be incorporated into sea salt aerosol particles often producing a surface film on the aerosol. Such an organic coating can reduce the mass transfer between the gas phase and the aerosol phase influencing sea salt chemistry in the marine atmosphere. To investigate these effects and their importance for the marine boundary layer (MBL) we used the one-dimensional numerical model MISTRA. We considered the uncertainties regarding the magnitude of uptake reduction, the concentrations of organic compounds in sea salt aerosols and the oxidation rate of the organics to analyse the possible influence of organic surfactants on gas and liquid phase chemistry with a special focus on halogen chemistry. By assuming destruction rates for the organic coating based on laboratory measurements we get a rapid destruction of the organic monolayer within the first meters of the MBL. Larger organic initial concentrations lead to a longer lifetime of the coating but lead also to an unrealistically strong decrease of O3 concentrations as the organic film is destroyed by reaction with O3. The lifetime of the film is increased by assuming smaller reactive uptake coefficients for O3 or by assuming that a part of the organic surfactants react with OH. With regard to tropospheric chemistry we found that gas phase concentrations for chlorine and bromine species decreased due to the decreased mass transfer between gas phase and aerosol phase. Aqueous phase chlorine concentrations also decreased but aqueous phase bromine concentrations increased. Differences for gas phase concentrations are in general smaller than for liquid phase concentrations. The effect on gas phase NO2 or NO is very small (reduction less than 5%) whereas liquid phase NO2 concentrations increased in some cases by nearly 100%. We list suggestions for further laboratory studies which are needed for improved model studies.

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Tailoring nano-catalysts: turning gold nanoparticles on bulk metal oxides to inverse nano-metal oxides on large gold particles

Chemical Communications ◽

10.1039/c5cc00016e ◽

2015 ◽

Vol 51 (27) ◽

pp. 5975-5978 ◽

Cited By ~ 13

Author(s):

Guofeng Zhao ◽

Xin-Ping Wu ◽

Ruijuan Chai ◽

Qiaofei Zhang ◽

Xue-Qing Gong ◽

...

Keyword(s):

Gold Nanoparticles ◽

Metal Oxides ◽

High Activity ◽

Gas Phase ◽

Gold Particle ◽

Alcohol Oxidation ◽

Bulk Metal ◽

Gold Particles ◽

Nano Oxide ◽

Nano Catalysts

Inverse nano-oxide/large-gold-particle catalysts create an anti-sintering structure with a large interface thereby showing high activity/selectivity for the gas-phase alcohol oxidation with dramatic stability improvement.

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