Evaluation of the Detailed Tropospheric Chemical Mechanism, MCM v3, Using Environmental Chamber Data: Butane and Its Degradation Products

2006 ◽  
pp. 241-252
Author(s):  
P. G. Pinho ◽  
C. A. Pio ◽  
M. E. Jenkin
Keyword(s):  
Degradation Products ◽  
Chemical Mechanism ◽  
Environmental Chamber ◽  
Environmental Chamber Data

Evaluation of two MCM v3.1 alkene mechanisms using indoor environmental chamber data

2005 ◽  
Vol 39 (38) ◽  
pp. 7251-7262 ◽  
Author(s):  
R HYNES ◽  
D ANGOVE ◽  
S SAUNDERS ◽  
V HAVERD ◽  
M AZZI
Keyword(s):  
Environmental Chamber ◽  
Environmental Chamber Data

scholarly journals Isolation and Structure Determination of Echinochrome A Oxidative Degradation Products

Molecules ◽  
2020 ◽  
Vol 25 (20) ◽  
pp. 4778
Author(s):  
Natalia P. Mishchenko ◽  
Elena A. Vasileva ◽  
Andrey V. Gerasimenko ◽  
Valeriya P. Grigorchuk ◽  
Pavel S. Dmitrenok ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
Degradation Products ◽  
Lethal Dose ◽  
Oxidative Degradation ◽  
Degradation Process ◽  
Oxidation Products ◽  
Chemical Mechanism ◽  
Ionization Mass ◽  
Echinochrome A ◽  
Esi Ms

Echinochrome A (Ech A, 1) is one of the main pigments of several sea urchin species and is registered in the Russian pharmacopeia as an active drug substance (Histochrome®), used in the fields of cardiology and ophthalmology. In this study, Ech A degradation products formed during oxidation by O2 in air-equilibrated aqueous solutions were identified, isolated, and structurally characterized. An HPLC method coupled with diode-array detection (DAD) and mass spectrometry (MS) was developed and validated to monitor the Ech A degradation process and identify the appearing compounds. Five primary oxidation products were detected and their structures were proposed on the basis of high-resolution electrospray ionization mass spectrometry (HR-ESI-MS) as 7-ethyl-2,2,3,3,5,7,8-heptahydroxy-2,3-dihydro-1,4-naphthoquinone (2), 6-ethyl-5,7,8-trihydroxy-1,2,3,4-tetrahydronaphthalene-1,2,3,4-tetraone (3), 2,3-epoxy-7-ethyl-2,3-dihydro-2,3,5,6,8-pentahydroxy-1,4-naphthoquinone (4), 2,3,4,5,7-pentahydroxy-6-ethylinden-1-one (5), and 2,2,4,5,7-pentahydroxy-6-ethylindane-1,3-dione (6). Three novel oxidation products were isolated, and NMR and HR-ESI-MS methods were used to establish their structures as 4-ethyl-3,5,6-trihydroxy-2-oxalobenzoic acid (7), 4-ethyl-2-formyl-3,5,6-trihydroxybenzoic acid (8), and 4-ethyl-2,3,5-trihydroxybenzoic acid (9). The known compound 3-ethyl-2,5-dihydroxy-1,4-benzoquinone (10) was isolated along with products 7–9. Compound 7 turned out to be unstable; its anhydro derivative 11 was obtained in two crystal forms, the structure of which was elucidated using X-ray crystallography as 7-ethyl-5,6-dihydroxy-2,3-dioxo-2,3-dihydrobenzofuran-4-carboxylic acid and named echinolactone. The chemical mechanism of Ech A oxidative degradation is proposed. The in silico toxicity of Ech A and its degradation products 2 and 7–10 were predicted using the ProTox-II webserver. The predicted median lethal dose (LD50) value for product 2 was 221 mg/kg, and, for products 7–10, it appeared to be much lower (≥2000 mg/kg). For Ech A, the predicted toxicity and mutagenicity differed from our experimental data.

scholarly journals Kinetic modeling of formation and evaporation of secondary organic aerosol from NO<sub>3</sub> oxidation of pure and mixed monoterpenes

2020 ◽  
Vol 20 (24) ◽  
pp. 15513-15535
Author(s):  
Thomas Berkemeier ◽  
Masayuki Takeuchi ◽  
Gamze Eris ◽  
Nga L. Ng
Keyword(s):  
Kinetic Model ◽  
Gas Phase ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Chemical Mechanism ◽  
Phase Reaction ◽  
Particle Phase ◽  
Environmental Chamber ◽  
Gas Phase Chemistry ◽  
Phase Chemistry

Abstract. Organic aerosol constitutes a major fraction of the global aerosol burden and is predominantly formed as secondary organic aerosol (SOA). Environmental chambers have been used extensively to study aerosol formation and evolution under controlled conditions similar to the atmosphere, but quantitative prediction of the outcome of these experiments is generally not achieved, which signifies our lack in understanding of these results and limits their portability to large-scale models. In general, kinetic models employing state-of-the-art explicit chemical mechanisms fail to describe the mass concentration and composition of SOA obtained from chamber experiments. Specifically, chemical reactions including the nitrate radical (NO3) are a source of major uncertainty for assessing the chemical and physical properties of oxidation products. Here, we introduce a kinetic model that treats gas-phase chemistry, gas–particle partitioning, particle-phase oligomerization, and chamber vapor wall loss and use it to describe the oxidation of the monoterpenes α-pinene and limonene with NO3. The model can reproduce aerosol mass and nitration degrees in experiments using either pure precursors or their mixtures and infers volatility distributions of products, branching ratios of reactive intermediates and particle-phase reaction rates. The gas-phase chemistry in the model is based on the Master Chemical Mechanism (MCM) but trades speciation of single compounds for the overall ability of quantitatively describing SOA formation by using a lumped chemical mechanism. The complex branching into a multitude of individual products in MCM is replaced in this model with product volatility distributions and detailed peroxy (RO2) and alkoxy (RO) radical chemistry as well as amended by a particle-phase oligomerization scheme. The kinetic parameters obtained in this study are constrained by a set of SOA formation and evaporation experiments conducted in the Georgia Tech Environmental Chamber (GTEC) facility. For both precursors, we present volatility distributions of nitrated and non-nitrated reaction products that are obtained by fitting the kinetic model systematically to the experimental data using a global optimization method, the Monte Carlo genetic algorithm (MCGA). The results presented here provide new mechanistic insight into the processes leading to formation and evaporation of SOA. Most notably, the model suggests that the observed slow evaporation of SOA could be due to reversible oligomerization reactions in the particle phase. However, the observed non-linear behavior of precursor mixtures points towards a complex interplay of reversible oligomerization and kinetic limitations of mass transport in the particle phase, which is explored in a model sensitivity study. The methodologies described in this work provide a basis for quantitative analysis of multi-source data from environmental chamber experiments but also show that a large data pool is needed to fully resolve uncertainties in model parameters.

scholarly journals Evaluation of 1,3,5 trimethylbenzene degradation in the detailed tropospheric chemistry mechanism, MCMv3.1, using environmental chamber data

2008 ◽  
Vol 8 (21) ◽  
pp. 6453-6468 ◽  
Author(s):  
A. Metzger ◽  
J. Dommen ◽  
K. Gaeggeler ◽  
J. Duplissy ◽  
A. S. H. Prevot ◽  
...  
Keyword(s):  
Degradation Mechanism ◽  
Reactive Systems ◽  
Tropospheric Chemistry ◽  
Chemical Mechanism ◽  
Oh Radicals ◽  
Environmental Chamber ◽  
Photo Oxidation ◽  
Trimethyl Benzene ◽  
Using Data ◽  
Paul Scherrer

Abstract. The degradation mechanism of 1,3,5-trimethyl- benzene (TMB) as implemented in the Master Chemical Mechanism version 3.1 (MCM) was evaluated using data from the environmental chamber at the Paul Scherrer Institute. The results show that the MCM provides a consistent description of the photo-oxidation of TMB/NOx mixtures for a range of conditions. In all cases the agreement between the measurement and the simulation decreases with decreasing VOC-NOx ratio and in addition with increasing precursor concentration. A significant underestimation of the decay rate of TMB and thus underestimation of reactivity in the system, consistent with results from previous appraisals of the MCM, was observed. Much higher nitrous acid (HONO) concentrations compared to simulations and expected from chamber characterization experiments were measured during these smog chamber experiments. A light induced NO2 to HONO conversion at the chamber walls is suggested to occur. This photo-enhanced NO2 to HONO conversion with subsequent HONO photolysis enhances the reactivity of the system. After the implementation of this reaction in the model it describes the decay of TMB properly. Nevertheless, the model still over-predicts ozone at a later stage of the experiment. This can be attributed to a too slow removal of NO2. It is also shown that this photo-enhanced HONO formation is not restricted to TMB photo-oxidation but also occurs in other chemical systems (e.g. α-pinene). However, the influence of HONO as a source of OH radicals is less important in these more reactive systems and therefore the importance of the HONO chemistry is less obvious.

scholarly journals A comparison of chemical mechanisms using tagged ozone production potential (TOPP) analysis

2015 ◽  
Vol 15 (15) ◽  
pp. 8795-8808 ◽  
Author(s):  
J. Coates ◽  
T. M. Butler
Keyword(s):  
Degradation Products ◽  
Control Strategies ◽  
Ground Level ◽  
Chemical Mechanism ◽  
Ozone Production ◽  
Peroxy Radicals ◽  
Production Potential ◽  
Secondary Chemistry ◽  
Air Masses ◽  
Phase Chemistry

Abstract. Ground-level ozone is a secondary pollutant produced photochemically from reactions of NOx with peroxy radicals produced during volatile organic compound (VOC) degradation. Chemical transport models use simplified representations of this complex gas-phase chemistry to predict O3 levels and inform emission control strategies. Accurate representation of O3 production chemistry is vital for effective prediction. In this study, VOC degradation chemistry in simplified mechanisms is compared to that in the near-explicit Master Chemical Mechanism (MCM) using a box model and by "tagging" all organic degradation products over multi-day runs, thus calculating the tagged ozone production potential (TOPP) for a selection of VOCs representative of urban air masses. Simplified mechanisms that aggregate VOC degradation products instead of aggregating emitted VOCs produce comparable amounts of O3 from VOC degradation to the MCM. First-day TOPP values are similar across mechanisms for most VOCs, with larger discrepancies arising over the course of the model run. Aromatic and unsaturated aliphatic VOCs have the largest inter-mechanism differences on the first day, while alkanes show largest differences on the second day. Simplified mechanisms break VOCs down into smaller-sized degradation products on the first day faster than the MCM, impacting the total amount of O3 produced on subsequent days due to secondary chemistry.

scholarly journals Evaluation of detailed aromatic mechanisms (MCMv3 and MCMv3.1) against environmental chamber data

2005 ◽  
Vol 5 (3) ◽  
pp. 623-639 ◽  
Author(s):  
C. Bloss ◽  
V. Wagner ◽  
A. Bonzanini ◽  
M. E. Jenkin ◽  
K. Wirtz ◽  
...  
Keyword(s):  
Companion Paper ◽  
Reaction Chamber ◽  
No Oxidation ◽  
Chemical Mechanism ◽  
Recent Experimental Data ◽  
Benzene Toluene ◽  
Master Chemical Mechanism ◽  
Environmental Chamber Data ◽  
Model Measurement ◽  
Oxidation Of Benzene

Abstract. A high quality dataset on the photo-oxidation of benzene, toluene, p-xylene and 1,3,5-trimethylbenzene has been obtained from experiments in the European Photoreactor (EUPHORE), a large outdoor environmental reaction chamber. The experiments were designed to test sensitive features of detailed aromatic mechanisms, and the dataset has been used to evaluate the performance of the Master Chemical Mechanism Version 3 (MCMv3). An updated version (MCMv3.1) was constructed based on recent experimental data, and details of its development are described in a companion paper. The MCMv3.1 aromatic mechanisms have also been evaluated using the EUPHORE dataset. Significant deficiencies have been identified in the mechanisms, in particular: 1) an over-estimation of the ozone concentration, 2) an under-estimation of the NO oxidation rate, 3) an under-estimation of OH. The use of MCMv3.1 improves the model-measurement agreement in some areas but significant discrepancies remain.

Photochemical production of sulfate from dissolved organic matter and atmospheric aqueous phases: Is there something in common?

2020 ◽  
Author(s):  
Rachele Ossola ◽  
Baptiste Clerc ◽  
Julie Tolu ◽  
Lenny H. E. Winkel ◽  
Kristopher McNeill
Keyword(s):  
Organic Matter ◽  
Dissolved Organic Matter ◽  
Aqueous Phase ◽  
Atmospheric Chemistry ◽  
Degradation Products ◽  
Chemical Mechanism ◽  
Phase Reaction ◽  
Molecular Events ◽  
Wide Range ◽  
Terrestrial Environments

&lt;p&gt;In a recent study, we showed that photodegradation of dissolved organic sulfur (DOS) from a wide range of natural terrestrial environments releases sulfate (SO&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;2&amp;#8211;&lt;/sup&gt;) and other small and highly oxidized S-containing compounds as degradation products, similar to what had already been reported for dissolved organic carbon, nitrogen and phosphorous. However, the underlying chemical mechanism of photoproduction of sulfate is still unknown.&lt;/p&gt;&lt;p&gt;To fill this knowledge gap, we selected cysteine as a DOS model compound and we investigated its photodegradation to sulfate using model sensitizers as the source of singlet oxygen (&lt;sup&gt;1&lt;/sup&gt;O&lt;sub&gt;2&lt;/sub&gt;) and triplet excited states (&lt;sup&gt;3&lt;/sup&gt;Sens*), two photochemically produced reactive species ubiquitous in sunlit surface waters. Using a combination of steady-state photochemistry experiments, kinetic modeling and mechanistic knowledge from the biochemistry literature, we reconstructed the molecular events that likely lead to the release of sulfate. We found that the release of SO&lt;sub&gt;2&lt;/sub&gt; via triplet-sensitized fragmentation of cysteine sulfinic acid, a &lt;sup&gt;1&lt;/sup&gt;O&lt;sub&gt;2&lt;/sub&gt; degradation product of cysteine, is a key step in the reaction mechanism. In the presence of oxygen and a photosensitizer, SO&lt;sub&gt;2&lt;/sub&gt; is then rapidly oxidized to SO&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;2&amp;#8211;&lt;/sup&gt;.&lt;/p&gt;&lt;p&gt;Interestingly, nowadays there is great interest in the atmospheric chemistry community on the same transformation (i.e., aqueous phase oxidation of SO&lt;sub&gt;2&lt;/sub&gt; to SO&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;2&amp;#8211;&lt;/sup&gt;) in the context of extreme haze events. Triplet-induced SO&lt;sub&gt;2&lt;/sub&gt; oxidation has already been proposed as a potential aqueous phase reaction that might explain the mismatch between measured and modelled sulfate concentrations, but the mechanism of this process is still not established. Our work provides an example of how mechanistic knowledge gained on the (photo)chemical behaviour of dissolved organic matter in aquatic systems can offer insights on processes occurring in atmospheric aqueous phases.&lt;/p&gt;

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