Review of Production of highly oxygenated organic molecules (HOMs) from trace contaminants during isoprene oxidation by Bernhammer et al.

2018 ◽  
Author(s):  
Anonymous
Author(s):  
Defeng Zhao ◽  
Iida Pullinen ◽  
Hendrik Fuchs ◽  
Stephanie Schrade ◽  
Rongrong Wu ◽  
...  

2021 ◽  
Author(s):  
Defeng Zhao ◽  
Iida Pullinen ◽  
Hendrik Fuchs ◽  
Stephanie Schrade ◽  
Rongrong Wu ◽  
...  

<p><strong>       </strong>Highly oxygenated organic molecules (HOM) are found to play an important role in the formation and growth of secondary organic aerosol (SOA). SOA is an important type of aerosol with significant impact on air quality and climate. Compared to the oxidation of volatile organic compounds by O<sub>3</sub> and OH, HOM formation in the oxidation by NO<sub>3</sub> radical, an important oxidant at night-time and dawn, has received less attention. In this study, HOM formation in the reaction of isoprene with NO<sub>3</sub> was investigated in the SAPHIR chamber (Simulation of Atmospheric PHotochemistry In a large Reaction chamber). A large number of HOM including monomers (C<sub>5</sub>), dimers (C<sub>10</sub>), and trimers (C<sub>15</sub>), both closed-shell compounds and open-shell peroxy radicals, were detected. HOM were classified into various series according to their formula, which included monomers containing one or more N atoms, dimers containing 1-4 N atoms, and trimers containing 3-5 N atoms. Tentative formation pathways of HOM were proposed reflecting known NO<sub>3</sub> and RO<sub>2</sub> chemistry in the literature under consideration of the autoxidation via peroxy pathways and peroxy-alkoxy pathways. Further mechanistic constraints were given by the time profiles of HOM after sequential isoprene addition which enabled to differentiate first- and second-generation products. Total HOM molar yield was estimated, which suggests that HOM may contribute a significant fraction to SOA yield in the reaction of isoprene with NO<sub>3</sub>.</p>


2018 ◽  
Vol 11 (8) ◽  
pp. 4763-4773 ◽  
Author(s):  
Anne-Kathrin Bernhammer ◽  
Lukas Fischer ◽  
Bernhard Mentler ◽  
Martin Heinritzi ◽  
Mario Simon ◽  
...  

Abstract. During nucleation studies from pure isoprene oxidation in the CLOUD chamber at the European Organization for Nuclear Research (CERN) we observed unexpected ion signals at m∕z = 137.133 (C10H17+) and m∕z = 81.070 (C6H9+) with the recently developed proton-transfer-reaction time-of-flight (PTR3-TOF) mass spectrometer instrument. The mass-to-charge ratios of these ion signals typically correspond to protonated monoterpenes and their main fragment. We identified two origins of these signals: first secondary association reactions of protonated isoprene with isoprene within the PTR3-TOF reaction chamber and secondly [4+2] cycloaddition (Diels–Alder) of isoprene inside the gas bottle which presumably forms the favored monoterpenes limonene and sylvestrene, as known from literature. Under our PTR3-TOF conditions used in 2016 an amount (relative to isoprene) of 2 % is formed within the PTR3-TOF reaction chamber and 1 % is already present in the gas bottle. The presence of unwanted cycloaddition products in the CLOUD chamber impacts the nucleation studies by creating ozonolysis products as the corresponding monoterpenes and is responsible for the majority of the observed highly oxygenated organic molecules (HOMs), which in turn leads to a significant overestimation of both the nucleation rate and the growth rate. In order to study new particle formation (NPF) from pure isoprene oxidation under relevant atmospheric conditions, it is important to improve and assure the quality and purity of the precursor isoprene. This was successfully achieved by cryogenically trapping lower-volatility compounds such as monoterpenes before isoprene was introduced into the CLOUD chamber.


2018 ◽  
Author(s):  
Anne-Kathrin Bernhammer ◽  
Lukas Fischer ◽  
Bernhard Mentler ◽  
Martin Heinritzi ◽  
Mario Simon ◽  
...  

Abstract. During nucleation studies from pure isoprene oxidation in the CLOUD chamber at CERN we observed unexpected ion signals at m/z = 137.133 (C10H17+) and m/z = 81.070 (C6H9+) with the recently developed proton transfer reaction time-of-flight mass spectrometer (PTR3‑TOF) instrument. The mass-to-charge ratios of these ion signals typically correspond to protonated monoterpenes and their main fragment. We identified two origins of these signals: First secondary association reactions of protonated isoprene with isoprene within the PTR3 reaction chamber and secondly [4+2] cycloaddition (Diels-Alder) of isoprene inside the gas bottle which presumably forms the favoured monoterpenes limonene and sylvestrene, as known from literature. Under our PTR3 conditions used in 2016 an amount (relative to isoprene) of 2 % is formed within the PTR3 reaction chamber and 1 % is already present in the gas bottle. The presence of unwanted cycloaddition products in the CLOUD chamber impacts the nucleation studies by creating ozonolysis products as corresponding monoterpenes, and is responsible for the majority of the observed highly oxygenated organic molecules (HOMs). In order to study NPF from pure isoprene oxidation under atmospheric relevant conditions, it is important to improve and assure the quality and purity of the precursor isoprene. This was successfully achieved by cryogenically trapping lower volatility compounds such as monoterpenes before isoprene was introduced into the CLOUD chamber.


Author(s):  
W. W. Barker ◽  
W. E. Rigsby ◽  
V. J. Hurst ◽  
W. J. Humphreys

Experimental clay mineral-organic molecule complexes long have been known and some of them have been extensively studied by X-ray diffraction methods. The organic molecules are adsorbed onto the surfaces of the clay minerals, or intercalated between the silicate layers. Natural organo-clays also are widely recognized but generally have not been well characterized. Widely used techniques for clay mineral identification involve treatment of the sample with H2 O2 or other oxidant to destroy any associated organics. This generally simplifies and intensifies the XRD pattern of the clay residue, but helps little with the characterization of the original organoclay. Adequate techniques for the direct observation of synthetic and naturally occurring organoclays are yet to be developed.


Author(s):  
Douglas L. Dorset

The quantitative use of electron diffraction intensity data for the determination of crystal structures represents the pioneering achievement in the electron crystallography of organic molecules, an effort largely begun by B. K. Vainshtein and his co-workers. However, despite numerous representative structure analyses yielding results consistent with X-ray determination, this entire effort was viewed with considerable mistrust by many crystallographers. This was no doubt due to the rather high crystallographic R-factors reported for some structures and, more importantly, the failure to convince many skeptics that the measured intensity data were adequate for ab initio structure determinations.We have recently demonstrated the utility of these data sets for structure analyses by direct phase determination based on the probabilistic estimate of three- and four-phase structure invariant sums. Examples include the structure of diketopiperazine using Vainshtein's 3D data, a similar 3D analysis of the room temperature structure of thiourea, and a zonal determination of the urea structure, the latter also based on data collected by the Moscow group.


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